PhD Thesis Nittaya Hansupo

Acknowledgement

First, I would like to thank Prof. Alexandre Legris, director of the UMET laboratory, and Prof. Serge Bourbigot, director of the group Ingénierie des Systèmes Polymères (ISP) and Reaction and Resistance to Fire (R2F) team for giving me the opportunity to join the laboratory and work on this project.

Gratefully, I would like to express my deepest appreciation to Prof. Serge Bourbigot, Dr.

Fabienne Samyn, Prof. Sophie Duquesne and Prof. Maude Jimenez, who gave me the chance to work with them and achieve this PhD work in the R2Fire team. Thanks a lot for their advice, encouragement and support. I really appreciate what I learnt and acquired throughout these three years.

I would like to thank Prof. Jenny Alongi, Prof. Abdelghani Laachachi, Mr. Pere Catala and Dr. Véronique Georges who accepted to be the jury, for bringing their expertise and time to assess this thesis research. I would like to acknowledge my industrial partner, 'Hempel company, Spain' for the work we achieved together and for the technical and material support throughout the project. In particular, I would like to thank Michael Hollman, Pere Catala and Joseph Palasi who started and set-up the project and placed the trust in me to lead the project; especially Michael for his kindness, help and co-operation. Then, I thank Hector Farras and Jose Fernandes for giving me a basic training about the intumescent coatings, preparation methods, analysis methods, fire tests… at the beginning of the project. That gave me an excellent experience and provided me a necessary background to conduct this project. I also appreciate the valuable discussions and suggestions that we made together during the regular meetings. Thanks also to all members of passive fire protection team for their kindness and welcoming ambience during my training in Hempel research laboratory. Oh Yep, I learnt some Spanish cultures and words... It was awesome! I would like to thank all of the technical experts for the training and instructions on how to use specific equipment. First, the NMR team, Grégory Tricot, Bertrand Revel and Bertrand Doumert for their help in designing experiments and discussing the results. I really appreciate vii PhD Thesis Nittaya HANSUPO, Univ. Lille 1 their superb expertise in NMR, availability and kindness. Thanks as well to Laurence Burylo and Pascal Roussel for the work in XRD analysis and Séverine Bellayer for the work in microscopic techniques. Moreover, I thank JoJo and Ben D. for their kindness, availability and technical support to everyday problems. Thanks especially to the big men of the lab, 'Anil' and 'Pierre' for the help, genuine suggestions and kindness from the beginning until the end.

I also sincerely thank all current and former members of the R2F team for all the moments we shared. First, thanks to all the lab's permanent members: Gaëlle, Mathilde, Séverine, Michel, Charafeddine and Fouad for a hospitality and welcoming ambience during these three years. Big thanks to 'une grande femme' of the lab 'Brigitte' for all supports and facilities. Thanks to Agnès for her kindness, friendship and all the moments (in or outside the lab) that we shared together, Ben (Mr. Toutounet) and Nicoloo for sharing 'des conneries' and teaching me the French jargons, Berthy (petit berbère) for being my universal translator, Laurie and Sarah for sharing their fascinating lifestyle. Thanks also to Chi, Hirakooo, Tatendoo, Rololo and Aditya for a friendship and their gentleness (maybe :p), Maryem for funny talks and amity, Katja (craziest labmate ) for crazy and joyous moments we made, Audrey and Gizem for joyful coffee times, candies and support during the hardest moment of this thesis. Thanks also to Renault, Mathieu, Pauline, Jonathan (Peruvian jojo), Sawsen, Elodie, Sophie K., Sayed, Charlotte, Morgan, Oscarlosss, Xiadonggg, Regis, Martin, Laura, Anne-lise, Imane and Kaiyuan for the easy-going atmosphere, friendship and many memorial events we shared. I deeply appreciate and enjoy working with them. I would like also to thank my internship students Natalia, Camille and Laura.

Finally and most importantly, I express my greatest gratitude to my lovely family, especially my dad, mom and lovely sister. I thank them so much for their support and love. I could not have reached this milestone without them. Thanks to my best friends (Vassana, Zozo, Yupin, Ying, Katja, Ting, Por, May, Jumpoon, Giftzy) for their never-ending support and encouragement during the bad and good moments during these three years. Last but not least, I really thank all of youcopainspotescolleaguesfriends for being a part of my wonderful memories in this charming city 'Lille'.

General introduction

Steel is a material used worldwide in the construction of bridges, sport arenas, buildings, offshore platforms etc. It is today the most appreciated building material all over the world because of its numerous benefits. The advantages of using steel structures are both economic (speed of construction, low project costs and ready availability) and ecologic (green construction and recycled materials) approaches. Moreover, it allows a maximum flexibility in design and better load bearing strength.

Steel is a non-combustible material. It does not contribute to a fire but its strength and stiffness are detrimentally reduced when the temperature surpasses 500 ⁰C [START_REF] Mather | Saving lives with coatings: The essentials of passive fire protection[END_REF]. The structural steel should thus be protected to maintain its integrity and to extend the evacuation time in the case of an unexpected fire. Moreover, fire safety of steel structure, especially for building regulations, is a prime requirement in many countries. An example of big disaster related to steel loss of strength is the catastrophic collapse of the World Trade Centre Twin Towers in New York City, 2001 (Figure 1). Figure 1 World Trade Center collapse, 11 September 2001 [2] Since this incident occurred, the concern about the protection of lives and assets against fire has been more and more highlighted. Two types of fire protection exist: active and passive fire protections [START_REF] Puri | Intumescent coatings: A review on recent progress[END_REF]. The active fire protections (e.g. sprinklers, alarms or gas release systems) are immediately activated in a fire. Passive fire protection systems exist in both non-reactive (e.g. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 board encasement, concrete, gypsum, mineral fiber and cementitious spray) and reactive (i.e. intumescent coating) forms [START_REF] Mariappan | Recent developments of intumescent fire protection coatings for structural steel: A review[END_REF][START_REF] Goode | Fire protection of structural steel in high-rise buildings[END_REF]. The drawback of using active fire protective systems is linked to the fact that they need time to respond (a very short delay will lead to a huge damage). Passive fire protections and in particular non-reactive systems are built as a part of the whole structures.

No requirement of operation by people or automatic controls is needed, it can be thus considered as a protector of choice with instant response to a fire. Nevertheless, non-reactive passive fire protections show some limitations. They are heavy, limited in design, hard to apply and needed plenty of space. From this point of view, reactive passive fire protection such as intumescent coatings appears as a solution of choice for fire protection since it does not only provide the efficient fire protection but can also be used as a conventional coating without affecting the aesthetic of the structural framework. Upon exposure to a fire, these intumescent coatings swell to form a multi-cellular insulative barrier which limits mass and heat transfers between the underlying materials and the flame.

Intumescent coatings are highly complex systems. The complete formulation usually contains more than ten ingredients to reach all required specifications [START_REF] Weil | Fire-Protective and Flame-Retardant Coatings -A State-of-the-Art Review[END_REF][START_REF] Gérard | New Trends in Reaction and Resistance to Fire of Fire-retardant Epoxies[END_REF]. In particular, they usually contain three major active ingredients dispersed in a binder: a carbon source (e.g. pentaerylthritol, isocyanurate or a binder itself), a blowing agent (e.g. evolving ammonia from phosphate and/or borate salts, melamine) and an acid source (e.g. borate and/or phosphate) [START_REF] Vandersall | Intumescent coating systems, their development and chemistry[END_REF].

These additives have to be chosen carefully. Indeed, the formation of an intumescent fire barrier is a dynamic process; additives should thus degrade and react at the right time and right temperature to provide an appropriate char structure.

Few recent scientific papers are devoted to the fundamental studies of intumescent coatings, but the full understanding of the mode of action of some ingredients is still lacking. In this context, this PhD thesis deals with the fundamental study of the mechanism of action of epoxy based intumescent coatings containing as main ingredients ammonium polyphosphate (APP), borates, calcium carbonate (CaCO3), silicate fibers and titanium dioxide (TiO2).

Relating to the literature, it is recognized that epoxy based intumescent coatings containing borates such as boric acid or zinc borate are highly efficient fire protective systems, PhD Thesis Nittaya HANSUPO, Univ. Lille 1 especially for hydrocarbon fire. However, REACH (European Union regulation concerning the Registration, Evaluation, Authorization and Restriction of Chemical) has reported that some borates, especially boric acid, are suspected to be CMR (Carcinogenic, Mutagenic, Reprotoxic) and should be banned in the future. On the other hand, the mode of action of boron as flame retardant is still ambiguous. Consequently, the first aim of this work is to understand the mode of action of boron and to provide some outlooks for alternative solutions.

Although boron is a critical element, the reactivity/interaction of other additives present in the formulation must be considered since the chemical reactivity in such a complex formulation can occur in various ways. The mode of action of phosphorous compounds (e.g. APP), of silicate fibers and of TiO2 in fire protective intumescent coatings have been extensively studied and reported in the literature [START_REF] Weil | Fire-Protective and Flame-Retardant Coatings -A State-of-the-Art Review[END_REF][START_REF] Duquesne | Influence of inorganic fillers on the fire protection of intumescent coatings[END_REF][START_REF] Zhou | Effect of metal oxides on fire resistance and char formation of intumescent flame retardant coating[END_REF]. CaCO3 is one of the components among all ingredients. It is generally used as a filler, its flame retardant effects have been investigated but its role in intumescent coatings is still controversy. Hence, the second objective of this project is to investigate the effect of CaCO3 on fire protective properties and its mode of action in intumescent coating.

The PhD thesis is organized in four chapters.

The first chapter gives a recent state of the art about intumescent materials emphasizing the definition of intumescence, intumescent coatings and main ingredients of intumescent coatings. Then, the fire scenarios and intumescent coating formulations are described.

Afterwards, the review specifically focuses on epoxy based intumescent coatings and on the chemical reactivity between the ingredients, which are the main interests of this project. Finally, the methods of characterization which have been used in the field of fire protective materials, are described. It focuses concisely on those implemented in this study

The second chapter presents the materials used, preparation of the coatings, fire tests as well as characterization methods for chemical, thermal and physical modifications. It describes all methods used. The aim is to describe how the research work was experimentally performed.

The third chapter details the study of the mode of action and role of borates in epoxy based intumescent coatings. First, the effects of different borates were assessed. Afterwards, PhD Thesis Nittaya HANSUPO, Univ. Lille 1 boric acid and zinc borate, which provide the most outstanding and interesting result among all, were selected to elucidate in more detail the role of borates. This chapter aims at drawing the mode of action of borates to provide some outlooks for substituting borates and to design alternative solutions.

The fourth chapter is dedicated to the investigation of the effect of carbonates on fire protection. First, the effect of calcium carbonate on fire protection was examined when it is combined with other additives (i.e. APP, borates). The mechanisms of action of the calcium carbonate were also investigated. Afterwards, the effects of various carbonates (i.e. MgCO3, ZnCO3, K2CO3, Na2CO3) on fire protective properties were examined.

At the end of the dissertation, a general conclusion is given and outlook for future works is proposed, especially the development of boron free epoxy based intumescent coatings. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Chapter I: State of the art First, a literature review regarding intumescent coatings is necessary. The aim of this chapter is to provide a background on the context and the purpose of the thesis research.

Hereafter, the concept of intumescence, intumescent coatings and its main ingredients are described. Then, the fire scenarios and conventional intumescent coating formulations are presented. Afterwards, the epoxy based intumescent coatings are detailed. In particular, the mechanism of action of intumescent coatings and the chemical reactivity of the main ingredients of the formulation are fully depicted. Lastly, the characterization methods usually used to study different aspects of intumescent coatings including char properties (e.g. thermal conductivity, viscosity, expansion & expansion rate, char strength, morphology) and chemical analyses of char (e.g. solid state NMR) are presented and fully commented. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Intumescent coatings

In this section, the definition of intumescence, intumescent coatings and ingredients of intumescent coatings are first given. The fire scenarios are then detailed. Finally, the intumescent coating formulations for specific fire scenarios are reviewed. 1.1.1 What is an intumescent material?

Definition of intumescence

The word ''intumescence'' comes from Latin, it means ''to swell up'' [START_REF] Bourbigot | Chapter 6: Intumescent based fire retardants[END_REF]. In the field of materials science, this term refers to a thermally reactive material that can swell up to several times its original thickness to form a multi-cellular insulative barrier (Figure 2). The formed structure, generally referred to as ''char'', slows down the heat and mass transfers acting as a protective layer for the underlying material.

The protection is consequently obtained mainly thanks to an action in the condensed phase. The concept of intumescence to fireproof a substrate is not a new concept. It can be traced back to 1821. Indeed, this year, Gay-Lussac reported that coating hemp and flax woven fabrics by a mixture of borate and ammonium phosphate could retard the burning of these materials thanks to the formation of a swollen char layer [START_REF] Mariappan | Recent developments of intumescent fire protection coatings for structural steel: A review[END_REF][START_REF] Wilkie | Fire Retardancy of Polymeric Materials Second Edition[END_REF]. However, the word 'intumescence' was not stated in the text.

Almost one century later, in 1938, Tramm claimed the wood protection against ignition and burning using a mixture of diammonium phosphate (or sulfate), dicyandiamide and formaldehyde via the same kind of expanded barrier. Here, the word intumescence was explicitly mentioned for the first time [START_REF] Tramm | Fireproofing of wood[END_REF]. Since that time, numerous studies have been performed on the development of intumescent formulations for both fire resistant and fire retardant applications. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Intumescent coatings

Intumescent coatings are a particularly successful application of this intumescent concept and are mainly used for the protection of steel and wood structures against fire [START_REF] Russell | Paint and coatings: A mature industry in transition[END_REF]. They preserve the functionality of substrates as long as possible in case of accidental fire. For structural steel, it means to keep the temperature below its critical temperature, usually defined as the temperature at which only 60 % of the original strength remains, point at which the failure is imminent under full design loads. Intumescent coatings are classified as 'passive reactive fireproofing materials' in opposition to active fire protections such as fire detection and fire suppression systems. Passive fireproofing materials mean insulating systems designed to decrease the heat transfers between a fire and the structure that need to be protected [START_REF] Moricone | Investigating the properties of fireproofing materials for an advanced design of equipment protection[END_REF]. It is built as a part of the buildings and acts instantaneously in case of fire. Other types of passive fireproofing materials can be used, for example board encasement, concrete, mineral fiber, cementitious spray… [START_REF] Goode | Fire protection of structural steel in high-rise buildings[END_REF][START_REF] Zuccaro | A case of choice of passive fire protection (PFP) in an Oil & Gas EPC project[END_REF].

The market share between 2001 and 2016 in Great Britain of different passive fireproofing materials is reported on Figure 3. Intumescent coating market is growing up rapidly as compared to other passive fire protection systems (i.e. broads, sprays). The significant increase over the last decade is due to the development of on-site intumescent coatings that provide better performance with cost effectiveness, the use of off-site application of intumescent coatings is slightly decreasing [START_REF]Fire protecting structural steelwork[END_REF]. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 Figure 3 Market share of passive fire protection [START_REF]Fire protecting structural steelwork[END_REF]

Main ingredients of intumescent coatings

To develop intumescence, the presence of three main ingredients namely an acid source, a carbon source and a swelling agent are required as pointed out by Vandersall [START_REF] Vandersall | Intumescent coating systems, their development and chemistry[END_REF] in the early 1970s. The intricate process that takes place upon heating and that leads to the formation of the intumescent barrier can be described as follows: the acid source (inorganic acid) is released typically between 150 ⁰C and 250 ⁰C depending on its chemistry. Then, the acid esterifies the carbon-rich components (carbon source) at temperature slightly above the acid release temperature. The mixture of the materials melts/softens prior or during esterification. The ester decomposes via dehydration resulting in the formation of a carbon-inorganic residue. The release of gases during these reactions and degradation products of blowing agent lead to the foaming of the carbonizing material. At the end, gelation and solidification result in a multicellular foam [START_REF] Bourbigot | Chapter 6: Intumescent based fire retardants[END_REF][START_REF] Alongi | Intumescence: Tradition versus novelty. A comprehensive review[END_REF]. The schematic representation of intumescent process is shown in Figure 4. The char formation is usually modelled in three zones: i) a pyrolysis zone close to the substrate, ii) a prepyrolysis zone and iii) an upper char layer close to the heat source [START_REF] Nørgaard | Investigation of char strength and expansion properties of an intumescent coating exposed to rapid heating rates[END_REF][START_REF] Duquesnea | A comparative study of the mechanism of action of ammonium polyphosphate and expandable graphite in polyurethane[END_REF]. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 Figure 4 Schematic representation of the intumescent process [START_REF] Puri | Intumescent coatings: A review on recent progress[END_REF][START_REF] Nørgaard | Investigation of char strength and expansion properties of an intumescent coating exposed to rapid heating rates[END_REF][START_REF] Duquesnea | A comparative study of the mechanism of action of ammonium polyphosphate and expandable graphite in polyurethane[END_REF] The used ingredients will only be effective if they decompose at the right temperature and in the suitable sequence. They have to be chosen and combined accordingly. Examples of main components identified in the literature are given in Table 1. However, some of them can play several roles: for example, ammonium polyphosphate (APP) can act as both acid source and blowing agent. In specific formulations, two acid sources (e.g. APP/boric acid [START_REF] Weil | Fire-Protective and Flame-Retardant Coatings -A State-of-the-Art Review[END_REF][START_REF] Hanafin | Low density, light weight intumescent coating[END_REF]) can be combined to obtain better performances. The use of two blowing agents with slightly different decomposition temperatures has also been reported to obtain greater foam heights (extend the length of gas release) [START_REF] Tesoro | Chemical modification of polymers with flame-retardant compounds[END_REF]. Concerning the carbon source, it is noticeable that the number of carbon will influence the amount of char formed whereas the number of hydroxyls will determine the rate of char formation [START_REF] Pappalardo | Intumescent flame retarded polypropylene systems containing sepiolite clays: properties and synergic effects[END_REF].

Table 1 Examples of chemicals used as acid source, blowing agent and carbon source for intumescent systems [START_REF] Alongi | Intumescence: Tradition versus novelty. A comprehensive review[END_REF][START_REF] Camino | Intumescent Fire-retardant systems[END_REF]

Inorganic acid source

Acid (e.g. boric, phosphoric, sulphuric) Ammonium salts (e.g. phosphates, polyphosphates, borates, polyborates) Amine/amide phosphate (e.g. melamine phosphate)

Blowing agent

Melamine Ammonium polyphosphate Dicyandiamide

Carbon source

Polymer (e.g. epoxy, acrylic, polypropylene) Tris (hydroxyethyl) isocyanurate (THEIC) Pentaerythritol monomer, dimer, trimer Starch, polysaccharides PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Apart from these ingredients, the use of functional additives such as inorganic fillers, synergistic agents and pigments can be pointed out. They are generally needed to improve the properties of intumescent coatings and charred layer.

Inorganic fillers such as minerals (e.g. calcium carbonate, talc, mica, kaolin, clay, silica, carbon black, titanium dioxide…) and fibers (e.g. natural fibers, glass fibers, silicate fibers…) are primarily used in intumescent coatings because of their inherent benefits concerning the mechanical properties of foamed char. They are mainly hydrophilic and immiscible with the polymer matrix leading to various morphologies [START_REF] Xanthos | Functional filler for plastics[END_REF]. They can also bring additional performances (density reduction, thermal insulation, surface properties…) and can act as a synergist. The presence of such fillers can modify the chemistry of intumescence through synergistic and/or catalytic effects as well as the physical properties of the protective char (expansion, char strength, thermal conductivity…).

For exemple, Duquesne et al. [START_REF] Duquesne | Influence of inorganic fillers on the fire protection of intumescent coatings[END_REF] studied the influences of two inorganic fillers (i.e.

titanium dioxide, mineral fibers) on the fire protection behavior of acrylic based intumescent coatings. They reported that both fillers improve the fire protective behavior of the coating.

Ahmad and Ullah research group have extensively studied the effects of fillers (i.e. wollastonite, zirconium silicate), synergists (i.e. kaolin clay) and new additives to enable to enhance fire protective properties of intumescent fire protective coatings [START_REF] Ullah | Synergistic effects of kaolin clay on intumescent fire retardant coating composition for fire protection of structural steel substrate[END_REF][START_REF] Zia-Ul-Mustafa | The effect of Wollastonite filler on thermal performance of intumescent fire retardant coating[END_REF][START_REF] Ullah | Effects of zirconium silicate reinforcement on expandable graphite based intumescent fire retardant coating[END_REF][START_REF] Amir | Study on the fibre reinforced epoxy-based intumescent coating formulations and their char characteristics[END_REF].

Depending on the fire scenarios, the formulations of the intumescent coating can be very different. The next paragraph presents the different existing fire scenarios, followed by the different types of intumescent coatings which are used in those scenarios. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Fire scenarios

Intumescent coating formulations are developed depending on the targeted applications.

Such coatings are widely used to protect substrates in three main categories of fire scenarios: cellulosic, hydrocarbon and jet fire.

Cellulosic fires correspond to a general fire scenario when the fuel sources are predominantly cellulose (e.g. wood, paper, cotton). Cellulosic fire curve (standard ISO 834) is characterized by a relatively slow temperature rise to around 927 ⁰C in 1 hour [START_REF] Gardelle | Resistance to fire of silicone-based coatings: Fire protection of steel against cellulosic fire[END_REF].

Hydrocarbon fires are mentioned when hydrocarbon fuels (e.g. oil, gas, chemical) are present in the fire situation. It is well known as hydrocarbon test curve (UL 1709) [START_REF]Rapid rise fire tests of protection materails for structural steel[END_REF][START_REF]The protection of structural steel in hydrocarbon fires[END_REF]. It corresponds to a rapid temperature rise up to 1093 ⁰C in 5 minutes. Various scenarios presenting a modified hydrocarbon fire curve and specifying a time/temperature curve have been set up by different international organizations/companies: hydrocarbon modified curve (HMC) [START_REF]Types of fire exposure[END_REF] and EN 1363-2 Hydrocarbon curve [START_REF] Beyler | Fire resistance testing for performance-based fire design of buildings[END_REF]… The examples of the standard fire curves are shown in Figure 5.

Figure 5 Standard fire test curves [START_REF]Higher Temperature applications[END_REF] PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Jet fires are a particular group of hydrocarbon-fueled fire expelled from an orifice under pressure of two bar or greater and give rise to high convective and radiative heat fluxes as well as erosive forces. It reproduces very severe fire condition combining extremely high heating and high velocity of the jet. It is the most severe fire scenario, which mimics fire risks in offshore installations [START_REF] Ciret | Investigation of intumescent coatings for fire protection application to jet fire[END_REF]. The standard condition of jet fire test is described under ISO 22899 [37,[START_REF] Standardization | Determination of the resistance to jet fires of passive fire protection materials -Part I: General requirements[END_REF].

Depending on the fire scenario, intumescent coating composition and thickness will vary.

They are usually classified either as thin or thick film coatings [START_REF] Mather | Saving lives with coatings: The essentials of passive fire protection[END_REF][START_REF] Bourbigot | Chapter 6: Intumescent based fire retardants[END_REF] and the specific formulations versus applications are described hereinafter.

Intumescent coating formulations

Thin film intumescent coatings are usually used in the case of cellulosic fires. They are generally available as waterborne or solvent-based systems. Waterborne intumescent coatings are very efficient but are more sensitive to humidity than solvent-based coatings. They can be applied by spray or brush-roller up to 3 mm thickness. Thermoplastic acrylic or poly (vinyl acetate) resins are typically used as binders. This kind of coating responds and intumesces quickly when exposed to a cellulosic fire. The advantages of these products include their low cost and relatively easy application and that is the reason why they are mostly used in buildings. However, they are unsuitable for exterior use without topcoat due to the lack of weather resistance and durability.

Intumescent thin films are often referred as 'fire retardant coatings' rather than 'fireproofing materials' due to their inferior fire resistance compared to thick film intumescent coating.

Thick film intumescent coatings are widely based on epoxy, vinyl or other elastomeric resins. They are solvent-free systems that allow application of 3 to 30 mm thickness per coat; they are particularly efficient in the case of hydrocarbon fires. They provide an excellent weather resistance, anti-corrosion, resistance to impact and vibration damage. However, they are quite expansive. In addition, these coatings have more stringent surface preparation requirements and smoke produced in fires makes them unsuitable for certain applications, such as enclosed living areas. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

To obtain a wide range of fire performances with intumescent coating formulations, complex combinations of binder, of intumescent additives as well as of co-additives are used. This explains the large number of patents on this subject. Some academic research can also be found on particular aspects, such as on the mechanisms of reaction between the ingredients and on the fire protection mechanisms involved in the intumescent coatings. The research groups of Camino [START_REF] Camino | Fire retardant polymer materials new perspectives in 8th International Symposium on Fire Safety Science[END_REF][START_REF] Camino | Mechanism of intumescence in fire retardant additives for polymers[END_REF] and Bourbigot [START_REF] Bourbigot | Applications of intumescence for reaction and resistance to fire of materials Materials China[END_REF][START_REF] Bourbigot | Fireproofing polymeric materials: problems and solutions in Organic Materials for Sustainable Construction[END_REF] have been particularly active on this research topic and have extensively studied intumescent systems.

To remain competitive and compliant with the standards in terms of performances as well as environmental and safety issues, over the last two decades extensive developments of formulations have been recorded (many patents have been granted). Evolutions have also been observed in terms of additives and of matrix used.

Interestingly, a distinctive proposition has been arisen during the last decade. A silicone based intumescent coating [START_REF] Bourbigot | Protecting substrates against damage by fire[END_REF][START_REF] Wade | Intumescent composition[END_REF] which shows advantages compared to the conventional thermoplastic acrylic or thermoset epoxy based coatings has been developed and patented. This silicone based coating releases less toxic organic gases, which makes it a noteworthy and attractive choice for the future. It was shown in some academic studies that it provides excellent fire resistance in both cellulosic and hydrocarbon fire scenarios and that reaches better performances than commercial acrylic or epoxy based coatings [START_REF] Gardelle | Resistance to fire of silicone-based coatings: Fire protection of steel against cellulosic fire[END_REF][START_REF] Gardelle | Thermal degradation and fire performance of intumescent siliconebased coatings[END_REF]. It is noticeable that silicone resins possess excellent thermal stability and better resistance to oxidation than conventional organic polymers but such kind of coatings has not yet been commercialized.

In this dissertation, the work particularly deals with the fundamental study of thick film

epoxy based intumescent coatings. This thick film epoxy based coating is a special type of such coatings that is extensively used in multi-story buildings and offshore installations to provide a protection of steelwork against hydrocarbon fire. UL1709 is used as a standard fire scenario to evaluate the fire protective properties of the coatings in this study.

Conclusion

Intumescent materials are not recent materials, but they still drive a lot of research and development in both universities and companies. The market share of these reactive passive fire protection materials is extending due to their noteworthy benefits over other fire protection materials. The trend is now to obtain thinner products with lower toxicity and lower smoke production. Various kinds of intumescent coatings exist (waterborne, solvent borne, solvent-free…), which have to be defined mainly depending on the fire scenario (cellulosic, hydrocarbon…)

and the application (inside, outside). Among all coatings, epoxy based intumescent coatings are of prime interest because of their efficiency against hydrocarbon fire which is the fire scenario of interest in this project. As this work deals with the fundamental study of epoxy based intumescent coatings, the next part of the state of the art especially focuses on this kind of coatings. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Epoxy based intumescent coatings

What about epoxy resins Epoxy resins are thermoset polymers obtained either through catalytic homopolymerisation of epoxy prepolymers containing epoxide rings or from the reaction between the latter and a hardener through a polyaddition mechanism. Depending on their functionality, different types of epoxy prepolymers can be distinguished. The most common one is diglycidyl ether of bisphenol A (DGEBA) obtained through the reaction between epichlorhydrin and bisphenol A in the presence of sodium hydroxide [START_REF] Boyle | Epoxy Resins[END_REF]. Apart from DGEBA, other prepolymers can be listed (Table 2) such as diglycidyl ether of bisphenol F (DGEBF), tetraglycidyl methylene dianiline (TGMDA) or triglycidyl ether of p-aminophenol (TGAP) etc. obtained. The choice of the epoxy prepolymer, of the hardener and of their ratios can lead to a large number of resin presenting various properties (stability, kinetics of polymerisation, glass transition temperature, mechanical performance, chemical resistance,…) [START_REF] Boyle | Epoxy Resins[END_REF]. Interesting properties such as high strength, excellent adhesion, chemical and heat resistance can thus be obtained [START_REF] Luo | Highly effective flame retardancy of a novel DPPA-based curing agent for DGEBA epoxy resin[END_REF]. These result in a large variety of applications of epoxy that go from coatings to adhesives as well as composite materials.

Table 2 Chemical structures of epoxy resins

Epoxy resin

In terms of fire performances, the nature of the monomers of the epoxy resin has a great impact on the performance: for example, the molecular weight of the epoxy resin can control the char expansion and formation of an uniform foamed structure. Wang and Yang [START_REF] Wang | Influences of molecular weight of epoxy binder on fire protection of waterborne intumescent fire resistive coating[END_REF] studied the influences of molecular weight of epoxy binder (Mn = 446, 568, 1025 and 1739 g/mol) on fire protection of waterborne intumescent fire resistive coating. It was found that a high molecular weight epoxy binder improves thermal stability of the coating and enhances the anti-oxidation of char at high temperature. Moreover, its melt viscosity rises with an increase of molecular weight.

Usually, a too low melt viscosity leads to an easy diffusion of gases in the melting matrix. These gases are thus not be trapped but will escape to feed the flame inhibiting char expansion and significantly decreasing the expected fire protection of the coating [START_REF] Duquesne | Thermoplastic resins for thin film intumescent coatings -towards a better understanding of their effect on intumescence efficiency[END_REF]. An increase in melt viscosity slows down the expansion speed leading to an increase of the cell size. However, a molecular weight of 1739 g/mol seems to be excessive since it leads to the formation of a loose and uneven foam structure. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Moreover, in the case of intumescent coatings, epoxy resin acts not only as a binder but also as a source of carbon, which is converted into a char in a fire. However, a major drawback of epoxy based coatings is the large emission of corrosive and toxic smokes during a fire [START_REF] Wang | Metal compound-enhanced flame retardancy of intumescent epoxy resins containing ammonium polyphosphate[END_REF][START_REF] Sorathia | Evaluation of intumescent coatings for shipboard fire protection[END_REF],

that makes them unsuitable for indoor application.

Epoxy based intumescent coating formulations

Conventional thin film epoxy based intumescent formulations use APP as acid source, pentaerythritol (PER) as char former and melamine as blowing agent, typically at a weight ratio of 3:1:1 as flame retardant package. Formulations based on these or similar components are reviewed in the paper of Vandersall [START_REF] Vandersall | Intumescent coating systems, their development and chemistry[END_REF]. However, current commercial formulations can be much more complex. In addition to these three necessary elements, functional additives such as mineral fibers, TiO2, CaCO3, carbon black, fumed silica... are also incorporated to obtain highly efficient systems.

Regarding thick film intumescent coatings based on epoxy resin used for a protection against hydrocarbon fire, up to now, the patent literature reveals that the efficiency was achieved by combining APP with another acid source in the form of borates (e.g. boric acid, zinc borate or ammonium pentaborate) [START_REF] Weil | Fire-Protective and Flame-Retardant Coatings -A State-of-the-Art Review[END_REF][START_REF] Weil | A review of current flame retardant systems for epoxy resins[END_REF]. The more recent patent from International Paints is based on alternative chemistry without boron but with modified resins or combination of resins [37].

Some examples of epoxy based intumescent coating formulations are given in Table 3. * Enhance the char strength of the intumescent coating with no diminishing of the fire performance, resulting in a surprisingly superior char foam with respect to both strength and fire performance [START_REF] Kittle | Intumescent composition comprising a silicate modified epoxy resin[END_REF] 2016 PhD Thesis Nittaya HANSUPO, Univ. Lille 1

For intumescent systems, the design of formulations is a dedicate stage. A random selection of the ingredients does not ensure an intumescent behavior. The components should degrade in an appropriate sequence to provide an effective fire protection. Thus, chemistry of the formulation plays a crucial role. Epoxy based intumescent coatings are very complex systems containing a huge number of ingredients. The patent literature for hydrocarbon fire applications have highlighted that borate and phosphate are used concurrently as acid source in these formulations and this indicates that these ingredients may play a major role resulting in an efficient intumescent behavior. Therefore, the next part of this chapter is dedicated to the review of the chemical reactivity between ingredients present in intumescent coatings such as phosphorus-based compounds, borates, carbonates, fibers and titanium dioxide. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Chemical reactivity between intumescent ingredients

As already explained in the previous sections, intumescent coating formulations are complex systems. The decomposition pathway of such system is very complicated. In addition to the reaction leading to intumescence, side reactions can occur concurrently between the three intumescent ingredients and the other components of the formulation. Yet the knowledge of the decomposition pathway and of the species formed during the development of protective layer is a key to understand how fire performances are obtained and how to design new efficient formulations. However, some parameters such as the kinetic of these reactions or the stoichiometry between additives can greatly impact the composition of an expanded char. This section thus reviews the decomposition and reactivity of typical ingredients of intumescent formulations (i.e. APP, borates, carbonates, fibers, titanium dioxide) alone or mixed together.

Phosphorus based compounds

Phosphorus based ingredients, and in particular phosphates, are essential components in classical and efficient intumescent formulations. Phosphates are indeed multifunctional; most of them can play the role of both acid source and blowing agent in the intumescent process. They are known to be involved in cross-linking of decomposition products, inducing charring and preventing char oxidation [START_REF] Herschke | Zinc phosphate as versatile material for potential biomedical applications part I[END_REF][START_REF] Sut | Interactions in multicomponent flame-retardant polymers: Solid-state NMR identifying the chemistry behind it[END_REF]. As they can also react at high temperature with numerous chemicals, their role in the formation of inorganic glassy residue is also well documented [START_REF] Naik | Outlining the mechanism of flame retardancy in polyamide 66 blended with melamine-poly(zinc phosphate)[END_REF].

Various phosphorus flame-retardants have attracted intensive interests due to their high reactivity, for example ammonium polyphosphate (APP), ammonium diphosphate (ADP), melamine phosphate, etc. Among them, APP is the most commonly used phosphorous-based compound in both fire retardant and fire resistant intumescent materials. It is also used in the studied formulation. The following section reports general information about APP.

APP is an inorganic salt of polyphosphoric acid and ammonia with the following formula:

(NH4PO3)n. It is a stable and non-volatile material. It slowly hydrolyzes in contact with water to produce monoammonium phosphate (orthophosphate). The decomposition temperature of APP is related to the length of the polymer chain. A short chain APP decomposes at about 150 ⁰C (n < 100) while a long-chain APP starts to decompose at temperature above 300⁰C [START_REF] Xanthos | Functional filler for plastics[END_REF]; APP degrades PhD Thesis Nittaya HANSUPO, Univ. Lille 1 into polyphosphoric acid and ammonia (eq.1) which act respectively as catalyst and spumific in intumescent systems. In general, only a long chain APP is used in fire protective coatings [START_REF] Camino | Study of the Mechanism of Intumescence in Fire Retardant Polymers: Part l--Thermal Degradation of Ammonium Polyphosphate-Pentaerythritol Mixtures[END_REF].

(NH4PO3)n 𝑇 ~ 280 ⁰𝐶 → (HPO3)n + nNH3 ; n ≈ 700 [START_REF] Levchik | Thermal behavior of ammonium polyphosphate-inorganic compound mixtures: Part 2 Manganese dioxide[END_REF] (eq. 1)

In presence of a carbon source, the phosphoric acid formed can react with hydroxyl or other groups of a carbon source to form an unstable phosphate ester (eq. 2) followed by its dehydration. A phospho-carbonaceous foamed structure is formed acting as an insulation layer protecting the underlying substrate [START_REF] Xanthos | Functional filler for plastics[END_REF].

(HPO3)n + carbon source → Carbon char + H3PO4 +H2O (eq. 2)

Un-reacted polyphosphoric acid (degradation product of APP) can dehydrate between 550 and 770 ⁰C to yield phosphorous oxide (P2O5), which can further sublimate (eq. 3).

2(HPO3

) n → nP2O5 (sublimate) + n H2O (eq. 3)

Thermogravimetric analyses of sole APP under air or nitrogen show that it yields a residue of about 5 -18 wt. % at 800 ⁰C [START_REF] Camino | Study of the Mechanism of Intumescence in Fire Retardant Polymers: Part l--Thermal Degradation of Ammonium Polyphosphate-Pentaerythritol Mixtures[END_REF][START_REF] Duquesne | Mechanism of fire retardancy of polyurethanes using ammonium polyphosphate[END_REF]. This high variation of residual weight is due to the sublimation of P2O5, which may be affected by the experimental conditions.

Due to its high reactivity, APP usually reacts during heating with other chemicals present in the formulation. The following part introduces these other chemicals (borates, carbonates, fibers and titanium dioxide) and their reactivity with APP. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 APP, expandable graphite and melamine Steel [START_REF] Ullah | Effect of boric acid and melemine on the intumescent fire retardant coating composition for the fire protecon of structural steel substrates[END_REF] APP and melamine Steel [START_REF] Nugent | Flexible intumescent coating composition[END_REF] Zinc borate APP, melamine and expandable graphite, ATH, alumina and talc Steel [START_REF] Ahmed | Non-toxic mineral based intumescent fire retardant coating for structural applications[END_REF] Sb2O3 Steel [START_REF] Zhang | Smoke suppression and synergistic flame retardancy properties of zinc borate and diantimony trioxide in epoxy-based intumescent fire-retardant coating[END_REF] Usually, boric acid and zinc borate exhibit the highest performance. In the following sections, their decomposition pathways are described and then, their chemical reactivity with other components of intumescent formulations and in particular with APP are reported. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Boric acid

Boric acid or orthoboric acid (H3BO3), a weak acid, is a white triclinic crystal that is soluble in water (5.64 %), alcohols, and glycerin [START_REF] Shen | Boron based flame retardants and flame retardancy[END_REF][START_REF] Smith | Kirk-Othmer Encyclopedia of Chemical Technology: Boron oxides, Boric acid, and Borates[END_REF]. Triclinic crystal of boric acid found naturally in volcanic fumaroles, hot springs, …is called Sassolite [START_REF] Rotaru | Thermal and kinetic study of hexagonal boric acid versus triclinic boric acid in air flow[END_REF][START_REF] Taguchi | Sassolite sublimated in a steam well at the Yunotani Geothermal Field, Aso Caldera[END_REF].

Decomposition of H3BO3

When heated, boric acid decomposes in two steps [START_REF] Jimenez | Kinetic analysis of the thermal degradation of an epoxy-based intumescent coating[END_REF][START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF]: a first step between 100 ⁰C and 140 ⁰C corresponding to a weight loss of about 30 wt. % and a second step in the temperature range 140 ⁰C to 200 ⁰C leading to a thermally stable material (55 wt. % of the initial mass). The first step corresponds to the dehydration of boric acid into metaboric acid (HBO2) which in the second step further dehydrates into boron oxide (B2O3) undergoing endothermic reaction (eq. 4 -5). Figure 6 shows the phase diagram of B2O3 -H2O system presenting the transformation of boric acid into boron oxide. Figure 6 Phase diagram of B2O3 -H2O system [START_REF] Kocakusak | Production of anhydrous, crystalline boron oxide in fluidized bed reactor[END_REF] PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Boron oxide is a white and hard glassy solid. It can be found in both amorphous and crystalline form. Crystalline boron oxide exists in two forms: hexagonal and monoclinic (Table 5).

The glassy and commercial form of boron oxide begins to soften at about 325 ⁰C. It is prepared in large quantity by fusing refined boric acid in a furnace followed by a rapid cooling [START_REF] Mccalla | Amorphization of crystalline orthoboric acid on a vitreous B2O3 substrate[END_REF]. The crystalline forms of B2O3 melts at about 450 ⁰C -465 ⁰C for hexagonal and 510 ⁰C for monoclinic [START_REF] Oxides | Boric Acids, and Metal Borates[END_REF][START_REF] Ferlat | Hidden polymorphs dirve vtirification in B2O3[END_REF]. A slow dehydration of boric acid followed by a slow cool down tends to yield the crystalline forms of boron oxide [START_REF] Mcculloch | A crystalline Boric Oxide[END_REF][START_REF] Berger | The crystal structure of boron xide[END_REF].

Reactivity of H3BO3 in presence of APP

The reactivity of boric acid with APP (the most commonly used phosphate) was already reported [START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF]. The mechanism of reaction was investigated on a mixture of boric acid and APP coated with THEIC. The mixtures were heated at different temperatures in a furnace to elucidate their reactions as a function of temperature. It was found that the reaction between the degradation product of H3BO3 (i.e. boron oxide) with the degradation product of coated APP (i.e.

polyphosphoric acid) occurs at about 250 ⁰C leading to the formation of borophosphate (BPO4), white infusible solid that vaporizes at 1450 ⁰C -1462 ⁰C without decomposition. It is believed that the formation of such thermally stable compound can stabilize the char and increase its mechanical resistance [START_REF] Jimenez | Characterization of the performance of an intumescent fire protective coating[END_REF][START_REF] Ullah | Effects of ammonium polyphosphate and boric acid on the thermal degradation of an intumescent fire retardant coating[END_REF]. The equations below (eq. 6 -eq. 8) described the formation of borophosphate. It was reported that the formation of borophosphate could explain the development of a hard intumescent char. When H3BO3 and coated APP are mixed together, the borates provide a hard and mechanically resistant char, while the presence of phosphorous allows promoting a good adhesion of the char to the steel plate.

2H3BO3

Ullah et al. [START_REF] Ullah | Effect of boric acid and melemine on the intumescent fire retardant coating composition for the fire protecon of structural steel substrates[END_REF] also emphasized the interests of adding boric acid in epoxy based intumescent coatings containing APP, expandable graphite and melamine. As a result, the addition of boric acid provides longer fire resistant time and a better adhesion to steel. The presence of borophosphate, boron oxide, sassolite (H3BO3) and graphite which are high thermal stability, are claimed to be partly responsible for a better fire resistance of the protective char. It was also reported that the structure of the residual char became more porous when the weight percentage of boric acid was increased with respect to that of melamine improving fire performances of the coatings.

Zinc borate

Zinc borates have found industrial, with 2ZnO.3B2O3.7H2O and 3ZnO.5B2O3.14H2O

primarily utilized in 1940s. The most important commercial zinc borate today is 2ZnO.3B2O3.3.5H2O (Firebrake ZB). It is produced by the reaction between zinc oxide and boric acid, or between zinc and borate salts, in hot water (> 65°C) [START_REF] Shen | Boron based flame retardants and flame retardancy[END_REF].

Decomposition of zinc borate

The mechanism of decomposition of Firebrake ZB was reported [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF][START_REF] Schubert | Structural characterization and chemistry of the industrially important zinc borate, Zn[B3O4(OH)[END_REF]. The first step consists in the condensation of the B-OH groups between 290 ⁰C and 420 ⁰C with release of water.

The zinc borate degrades to yield an amorphous product with corresponds to its dehydrated form (eq. 9). Then, 2ZnO.3B2O3 decomposes totally or partially to yield ZnO.2B2O3 and another nonidentified phase in the temperature range 420 ⁰C to 580 ⁰C (eq. 10 ZB decomposes by releasing water, which dilutes the gas phase, thus reducing the temperature. After decomposition, the residual borates typically form a vitreous-like layer (amorphous phase) that could improve the thermal insulation and durability of char [START_REF] Sabet | Effect of zinc borate on flammability/thermal properties of ethylene vinyl acetate filled with metal hydroxides[END_REF][START_REF] Bourbigot | Zinc borates as synergists for flame retarded polymers[END_REF].

Reactivity of zinc borate in presence of APP

The reactivity between zinc borate and APP was described in literature [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF]. It was reported that the degradation product of zinc borate (2ZnO.3B2O3, amorphous phase) reacts with the decomposition product of APP (polyphosphoric acid and/or phosphoric acid) between 300 ⁰C and 415 ⁰C, leading to the formation of BPO4 specie. Two possible reactions are proposed to explain their formation (eq. 12 and eq. 13). As a conclusion, the degradation pathway and chemical reactivity of boric acid and zinc borate are different. They decompose at different temperatures and their reactions with APP (binary mixture of APP with borates) lead to different products. In an intumescent system, which is much more complex than a binary mixture, their chemical reactivity can also be very different.

The next par detailed another types of fillers widely used in intumescent coatings: the carbonates. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 Calcium carbonate has been reported to have effects on rheology, processing and morphology depending on considered polymeric systems [START_REF] Xanthos | Functional filler for plastics[END_REF]. Its effect on flame retardant properties has also been investigated by different authors [START_REF] Tang | Investigation Into Poly(propylene)/Montmorillonite/Calcium Carbonate Nanocomposites[END_REF][START_REF] Xu | Zinc hydroxystannate-or zinc stannate-coated calcium carbonate as flame retardant for semirigid Poly(vinyl chloride)[END_REF].

For example, the flame retardant effect of CaCO3 on modified polyolefin was reported [START_REF] Hermansson | The flame retardant mechanism of polyolefins modified with chalk and silicone elastomer[END_REF]. Compared to the pure polymer, the addition of 30 % of CaCO3 in an ethylene -acrylate copolymer (EBA) leads to a dramatic decrease in the heat of combustion since the flammable polymer is diluted with an inert material that does not contribute to the fire. This effect is seen with any inorganic filler. In addition to this, CaCO3 could have a more active contribution as CO2 can be released via an endothermic reaction.

Another study showed that the complex viscosity of poly(ethylene-co-methacrylic acid)

(EMMA) modified with calcium carbonate and silicone elastomer increases above a critical temperature (250 ⁰C) due to ionomer formation between acidic groups of the polymer and calcium ions. This has a great impact on the fire performance by reducing the transportation rate of gases in and out of the material [START_REF] Karlsson | Influence of melt behaviour on the flame retardant properties of ethylene copolymers modified with calcium carbonate and silicone elastomer[END_REF].

From a general point of view, CaCO3 seems to improve the flame retardant effects of polymeric materials. However, the effect of calcium carbonate may differ when combined with flame-retardants. As an example, Almeras et al. [START_REF] Almeras | Effect of fillers on fire retardancy of intumescent polypropylene blends[END_REF] reported that the addition of CaCO3 in PhD Thesis Nittaya HANSUPO, Univ. Lille 1 intumescent polypropylene blends deteriorates its fire retardancy. Apart from that, the function of CaCO3 in passive fire protection (PFP) material was pointed out by Ciudad et al. [93] who reported the endothermic effect of CaCO3 at high temperature with a rich heat-absorbing profile.

Reactivity of CaCO3

The literature review shows that a reaction between CaCO3 with components such as APP or borates can occur as well as reaction with silicone matrix.

Relating to the article reported by Deodhar et al. [START_REF] Deodhar | Calcium carbonate and ammonium polyphosphate-based flame retardant composition for polypropylene[END_REF], the possible reactions between

CaCO3 and APP are reported in equations below (eq. 19 -20).

(NH4PO3)n Calcium carbonate, because of its basic nature, can react at low temperature (≈ 300 ⁰C)

with polyphosphoric acid (degradation product of APP) releasing carbon dioxide (CO2) and water vapor leading to the early decomposition of CaCO3. From this reaction, a thermally stable compound (β-calcium metaphosphate (Ca(PO3)2) is formed. In-situ formation of Ca(PO3)2 was reported to increase the flame retardant properties while the addition of Ca(PO3)2 as an inorganic filler does not seem to improve FR properties (e.g. in polypropylene) [START_REF] Bertelli | Intumescent Fire Retardant Systems -Effect of fillers on char structure[END_REF].

Another work by Baykal et al. [96] proposed a reaction between BPO4 and CaCO3. As mentioned in the previous part, BPO4 can be formed by the reaction between borates and phosphates contained in the formulation. In presence of CaCO3, they could react together leading to the formation of CaBPO5. The reaction can occur at around 900 ⁰C (eq. 21).

CaCO3 (s) + BPO4 (s)

𝑇 ~ 900 °𝐶 → CaBPO5 (s) + CO2 (g) (eq. 21)

In case of fire protective coatings, the interests of adding CaCO3 to a silicone based coating containing expandable graphite have also been demonstrated by Gardell et al. [START_REF] Gardelle | Resistance to fire of silicone-based coatings: Fire protection of steel against cellulosic fire[END_REF]. It was reported that the addition of CaCO3 in this coating provides a good fire protective effect resulting from the reaction between the degradation products of the silicone based compounds (i. For epoxy based intumescent coatings, a small amount of CaCO3 is usually added [START_REF] Hanafin | Low density, light weight intumescent coating[END_REF] as a filler. Nevertheless, its flame retardant effects have never been detailed in this kind of coatings.

Other types of carbonates

The effect of other carbonate species including calcium magnesium carbonate (Dolomite, CaMg(CO3)2) on a traditional intumescent flame retardant system (Epoxy-APP-H3BO3-expandable graphite-melamine) has been studied by Gillani et al. [97]. The char morphology of the coating without dolomite compared to that containing 8 % wt. of dolomite is very different. With dolomite, homogeneous with small pores, compact and uniform char structure without cracks were obtained while big holes and cracks, which can cause failure in heat shielding, were observed in the absence of dolomite. It was suggested that the incorporation of dolomite clay enhances the fire performance and significantly affects the formation of dense and continuous char. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Fibers

Fibers are mainly used as reinforcing materials. Numerous types of fibers exist, which can be classified as shown in Figure 7 [98]. Most of them (except natural fibers) are stable up to very high temperatures (T ≥ 1000 ⁰C).

Figure 7 Classification of fibers [START_REF] Claub | Fibers for ceramic matrix composites[END_REF] Fibers, such as glass, mineral and carbon fibers, are incorporated in intumescent coatings to strengthen and improve the mechanical properties of the protective char obtained in case of fire (e.g. increase char strength), which affects positively the fire protective performance of the coatings (e.g. longer fire protection time) [START_REF] Ahmad | Thermal performance of glass fiber reinforced intumescent fire retardant coating for structural applications[END_REF]. The incorporation of the fibers is very useful, especially for hydrocarbon and jet fires [100]. Another benefit of adding fibers into the intumescent coating is to adjust the viscosity of the coating as well as the melt viscosity of the intumescent matrix, which could improve the charring process and the subsequent char morphology [101].

As an example, Amir et al. [START_REF] Amir | Study on the fibre reinforced epoxy-based intumescent coating formulations and their char characteristics[END_REF] investigated the effects of fiber reinforcement on the char characteristics of epoxy based intumescent coatings. It was reported that long carbon fibers and glass fibers improve char structure, char height and char strength.

Glass and mineral fibers

Single crylstal fibers

Metal fibers organic fibers

Carbon fibers

Polymer fibers PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Another study demonstrated the benefits of adding silicate based mineral fibers (Rockforce® MS603-Roxul 1000) in an acrylic-based intumescent coating [START_REF] Duquesne | Influence of inorganic fillers on the fire protection of intumescent coatings[END_REF]. It was shown that the incorporation of either 2 % or 5% of fibers leads to a better fire resistance. These fibers improved the fire protective behavior and helped maintaining the protective performance for longer time without a collapse of charred structure The effects of different atomic ratios between titanium and phosphorous in an acrylic based intumescent coating have also been investigated [START_REF] Duquesne | Influence of inorganic fillers on the fire protection of intumescent coatings[END_REF]. Three ratios were considered: Ti/P= 0.5, 1, and 2; the best performance was obtained for the atomic ratio 0.5, corresponding to the Ti/P ratio in TiP2O7. On the contrary, Mariappan et al. [105] suggested that a slightly excess atomic ratio of Ti/P (0. The incorporation of nano-TiO2 was also reported in some intumescent coatings. For example, Aziz et al. [107] reported that the incorporation of nano-TiO2 into epoxy based intumescent coating comprising APP, melamine, boric acid and barite (BaSO4) allows increasing the residual weight of the coating and provides longer protection time compared to conventional fire retardant coatings. Another paper [108] reported synergistic effects of nano-TiO2 and eggshell micro powder on the improvement of fire protective properties of an acrylic based intumescent coating by increasing the residual weight of the chars and enhancing the anti-oxidation properties of the char at high temperature.

Conclusion

As a conclusion, the reactivity of intumescent additives in the condensed phase is a complex phenomenon. Various ingredients are present and numerous reactions can occur in many ways. Phosphorous can easily react with almost all of the elements present in the formulation such as boric acid, zinc borate, CaCO3, fibers, TiO2… The literature reports its chemical reactivity in simple systems, in flame retardant materials or outside the scope of intumescent materials. This reactivity is usually reported as an advantage. Indeed, it is widely reported that the species formed from APP or its degradation products stabilize the char, modify its sensitivity to oxidation and affect the morphology of the char which is a key aspect when dealing with heat transfer in intumescent coatings.

To investigate all those aspects, methodologies have been developed and the next part of this chapter is dedicated to the review of the characterization methodologies applied to intumescent materials. It first gives a general review and then emphasizes the ones which are implemented in the present study. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Characterization methodologies

The intumescent process is a very complicated process involving chemical, rheological, morphological, dimensional and thermo-physical modifications. To have insights of the mechanism of action, it is crucial to characterize the properties and chemical compositions of the coatings before burning, during burning and after burning (char). This section proposes a critical review of the different techniques usually used to characterize intumescent coatings. As a general comment, it can be noticed that there are different ways to characterize intumescent coatings [109,110]: (i) characterizations performed at ambient temperature on the char residue collected at characteristic time or temperature of the intumescent process namely ex-situ measurement (ii) characterizations performed during the degradation versus either time or temperature referring to in-situ measurements (iii) characterizations through numerical approach.

Determination of the char properties

The properties of the intumescent protective layer, a foamed residual structure widely referred as ''char'' are key parameters to understand the fire performances of the intumescent materials. Many characterization techniques exist to investigate different properties of char such as thermal conductivity, viscosity, expansion, strength, structure, etc. Next section reviews the most widely reported techniques.

Thermal conductivity

The aim of using the intumescent approach to protect substrates is to build a thermal barrier on their surfaces. Consequently, it means that the char developed during the intumescent process should exhibit the smallest conductivity value. To determine this parameter, numerical or experimental methodologies have been reported [111,112]. Staggs [113]

Viscosity, expansion and expansion rate

The viscoelastic behavior of an intumescent system during the expansion phase significantly affects the char morphology and thus the fire protection of intumescent coating [117,118]. The formation of a multicellular char layer occurs via a semi-liquid phase that coincides with gas emission and expansion. Gases released from the degradation of the intumescent material and of a blowing agent, have to be trapped and to diffuse slowly in the highly viscous melt degraded matrix to create a char layer with an appropriate morphology as shown in Figure 9. [START_REF] Alongi | Intumescence: Tradition versus novelty. A comprehensive review[END_REF] The control of the structure of the foamed residue relates not only to the gas formation process but also to the viscosity of the semi-liquid degraded matrix. Indeed, if the degraded matrix is too liquid, then the gases are not trapped but escape to feed the flame [START_REF] Duquesnea | A comparative study of the mechanism of action of ammonium polyphosphate and expandable graphite in polyurethane[END_REF]119] or dilute the gas phase. If on the contrary, the viscosity is too high, the expansion will be prevented. When the char structure is formed, if the shield becomes too hard, the creation and propagation of cracks may lead to a rapid degradation of the material [120].

Therefore, the viscoelastic properties of intumescent materials in the range of temperature corresponding to the development, stabilization and destruction of the protective char have to be investigated. Measurements of viscosity versus temperature at low heating rate (10 ⁰C/min) can be done using a Rheometer in a parallel configuration as proposed by Bugajny et PhD Thesis Nittaya HANSUPO, Univ. Lille 1 al. in 1999 [119]. Duquesne et al. [20], in early 2002, proposed to follow simultaneously the change in viscosity and expansion using the same characterization tool by introducing an autoadjustment of the gap between the plates during the measurements in order to keep the normal force at a set constant value. Jimenez et al. [81] implemented this method on epoxy based intumescent coatings and highlighted the interest of combining APP and H3BO3 in an epoxy resin both from the expansion and viscosity points of view (Figure 10).

This kind of measurements gives useful pieces of information to understand the behavior of different intumescent materials. However, this technique is not suitable for all materials, as it requires a char having a reasonable mechanical resistance when a normal force is applied.

Moreover, the normal force applied might affect the expansion and the expansion under constraint is consequently measured. However, the heating rate used for such measurement is quite low and is not representative of a real fire scenario. Another approach to follow the dynamic expansion and expansion velocity was thus developed to perform measurement during fire tests (cone calorimeter or furnace test). Gardelle et al. [121] used two methods to quantify the expansion and expansion velocity of intumescent char. For the first one called 'static state', the furnace test mimicking UL1709 was stopped at different times and the thickness of the char was measured (ex-situ measurement). In a second approach, an infrared camera monitored the development of the char during a cone calorimeter PhD Thesis Nittaya HANSUPO, Univ. Lille 1 experiment. This allowed measuring the swelling versus time during a cone calorimeter experiment (in-situ measurement). Using these two methods, swelling of silicone-based coatings containing expandable graphite versus time could be obtained (Figure 11) and the velocity of expansion was calculated from the slope of the curve during the expansion step. It reached 18%/s in static method and 19%/s using dynamic method. The same authors also used the second approach (dynamic measurement using an infrared camera) to investigate the expansion rate of silicone based coatings for the fire protection of carbon fiber reinforced composites during a jet fire bench [122].

Figure 11 Expansion of silicone-based coatings versus times in dynamic [START_REF] Mather | Saving lives with coatings: The essentials of passive fire protection[END_REF][START_REF]World trade center collapse footage[END_REF][START_REF] Puri | Intumescent coatings: A review on recent progress[END_REF][START_REF] Mariappan | Recent developments of intumescent fire protection coatings for structural steel: A review[END_REF] and static [START_REF] Goode | Fire protection of structural steel in high-rise buildings[END_REF][START_REF] Weil | Fire-Protective and Flame-Retardant Coatings -A State-of-the-Art Review[END_REF][START_REF] Gérard | New Trends in Reaction and Resistance to Fire of Fire-retardant Epoxies[END_REF][START_REF] Vandersall | Intumescent coating systems, their development and chemistry[END_REF] state Such measurements enable to follow the expansion versus time and are consequently very interesting. However, each of these tests presents different limitations. On the one hand, in the case of ex-situ measurement, each point of the curve requires the use of one sample and the repeatability of each measurement has to be checked at least by doing the experiment twice.

Therefore, to be accurate, a great number of samples is required. Moreover, sometimes for the same formulation, the intumescence process and the creation of the foamed structure vary significantly from one sample to another. Consequently, for each measurement, the uncertainty PhD Thesis Nittaya HANSUPO, Univ. Lille 1 can be relative high. The measurements done on one sample by image analysis during a fire test, on the other hand, can be difficult to applied to other fire scenario (furnace test for example).

Char strength

Another important aspect of intumescent formulations is the strength of the char. Indeed, in case of jet fire scenario for example, the intumescent char is exposed to high pressure and erosion and thus its mechanical stability is highly important. The term 'strength' associated with char is used as a general term covering resistance to external mechanical constraints such as mechanical ablation by the flame application, influence of wind,… [START_REF] Alongi | Intumescence: Tradition versus novelty. A comprehensive review[END_REF]123]. The strength of char depends on both the structure and porosity of the foamed intumescent material as well as on the chemical composition of the char. Different methodologies are mentioned in the literature to evaluate this parameter.

In early studies, Reshetnikov et al. [124,125] used various techniques to assess the mechanical strength of char of coatings designed for either buildings or space aircraft protection.

These methods are in both hot and cold states. One described method was to find the minimum force necessary to destroy the char by inserting a rod through the heated sample at a temperature up to 1200 ⁰C. Another method is used to measure the shear strength of the char at high temperature. The principle is to spin the sample at a controlled rate (1000 rounds/min), until the chars break at the weakest point. Both of these high temperature techniques are reported to perform well only in the case of low expansion factors (1.5 -2).

Afterwards, Duquesne et al. [20] developed a dynamic measurement using 'a parallel plate configuration Rheometer'. Within this technique, the mechanical strength against compression as a function of temperature is obtained. The sample is heated with a desired ramp (up to 20 ⁰C/min) to a specific temperature without any constraint. Then, maintaining the temperature at the chosen level, the upper plate is brought on the sample at a constant rate. The compression force linked to the mechanical properties of the char can then be measured as a function of the gap between lower and upper plates.

In 2013, an alternative method to investigate the mechanical stability of an intumescent char has been proposed by the Technical University of Denmark [START_REF] Nørgaard | Investigation of char strength and expansion properties of an intumescent coating exposed to rapid heating rates[END_REF]. Samples were heated in a PhD Thesis Nittaya HANSUPO, Univ. Lille 1 muffle oven in atmosphere air (1100 ⁰C) for 10 min. Char was then moved and placed on an aerated concrete stone next to the muffle oven to cool to 150 ⁰C, before placing it in a desiccator.

After cooling, the mechanical stability of the char was measured with a Texture Analyzer (Figure 12) recording the work necessary to move a cylindrical piston to a certain depth of the char. Note that an important limitation of this method is that the results are obtained at room temperature.

This investigation is important for intumescent coating applied where objects may fall down on the coating during a fire and damage the char.

Figure 12 Schematic illustration of the Texture Analyzer used to determine the strength of an intumescent char. Ls and L0 are the distance to the sample top and sample bottom from a selected initial height respectively. The height of the sample is the difference given by L0 -Ls [START_REF] Nørgaard | Investigation of char strength and expansion properties of an intumescent coating exposed to rapid heating rates[END_REF] Recently, an in-situ experimental protocol was developed by Naik et al. [123] to evaluate the char strength of intumescent coatings on steel panel during hydrocarbon fire test. In that case, an air or nitrogen jet flow was used to impact the char and evaluate its stability regarding this stress. During the test, it is thus possible to monitor at the same time the physical integrity, mechanical stability, and thermal insulation capacity of intumescent coating. The system was applied to compare silicone-based products and a commercial epoxy based coating. It was shown that silicone based char exhibits higher strength than the epoxy one. Muller et al. [126] investigated and compared several methods to demonstrate the effect of the preparation method of the char on its strength. They reported that the presence of a flame, heating type (convective or radiative heating), and quenching temperature do not modify the PhD Thesis Nittaya HANSUPO, Univ. Lille 1 mechanical properties of the resulting intumescent char. On the contrary, the critical parameters involved in the formation of a resistant char are the heating temperature and heating rate.

Moreover, they show that the modification of the temperature at which the mechanical test is performed (in-situ vs. ex-situ measurement) leads to different results.

Morphology

The morphology of a char is one of the prime factors governing the fire protective properties of intumescent char (e.g. thermal insulation, mechanical resistance of char). The chemical composition of the degrading system as well as its physical properties (i.e. viscosity, expansion) will directly influence the morphology of the resulting charred structure [109]. Wang et al. [127] demonstrated, through a numerical approach, that the pore size should be small (within 50 µm) to obtain a good insulation of charred layer. Big, open and unevenly distributed holes with low strength of charred layer could damage the fire protective properties.

Characterization of the foamed char layer (e.g. cell size, closed or open cells, number of cells) with adapted techniques appears as an indispensable way to better understand the reaction between ingredients and fire performance obtained. However, it is not an easy task.

The morphology of intumescent char can be visualized at various scales depending on the scale of interest. It includes visual observation, digital photography, optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) as well as 3D X-ray tomography.

As an exemple, Gérard et al. [128] observed the char morphology of intumescent epoxy resins using a digital photographer. In that case, it is necessary to cut off the char without damaging the sample to obtain a cross-sectional image. This can provide a visual observation on how char looks like and allows comparing the char aspects of different samples. The same researchers [129] used an optical microscope to characterize the morphology of the surface or cross-sectional cut of the charred residue after heat treatments. It also allows observing the char surface (e.g. cell size). This technique can provide a clearer view of char residues compared to a numeric photographer. It can also scale the dimension of porous structure. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

The well-known and commonly used microscopies such as SEM and TEM are also widely used in the field of research and development of flame retardant systems particularly in the case of fire protective materials [130][131][132]. They provide information on the microstructures of the studied char, dispersion of additives, crystallinity of species, dimensions of the fibers...

To study the morphology of the char, samples have to be cut off to observe the cross section of samples but the integrity of the inner structure cannot be guaranteed during the preparation of samples. To overcome this issue, X-ray computed tomography (non-destructive technique) appears as a technique of choice. Muller et al. [115] used this technique to acquire 3D images of charred structure of intumescent polyurethane containing FR additives (i.e. APP and nano-MgO). Interestingly, they correlated the obtained morphology with the thermal conductivity of the formed char. By using this technique, the intumescent process can be more precisely characterized. The application of X-ray computed tomography was also appeared in the work of Morys et al. [133] who used this technique to study the intumescent process and char properties of different intumescent coatings. This superior research tool was also combined with SEM and mechanical testing to investigate the char obtained after exposition to a standard time temperature muffle furnace. Apart from the precious information provided by X-ray computed tomography, it however has some limitations including a long scanning time and difficult treatment of data to obtain quantitative information [134]. Moreover, this technique, at the present time, does not permit to make an in-situ measurement. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Chemical analyses

In addition to the char thermo-physical properties (i.e. thermal conductivity, viscosity, expansion, expansion rate, char strength, morphology) which are described in the previous section, chemical composition of char is also an important factor among all. When intumescent coatings degrade, the carbon and organic materials originally present in the intumescent formulation react with the other ingredients of the formulation. The resulting residues generally consist in a mixture of carbonaceous char and inorganic compounds, which are formed during the intumescent process by the reactivity between ingredients. The chemical composition of the char is reported to influence significantly the fire protective performances of intumescent coatings [START_REF] Ullah | Effect of boric acid and melemine on the intumescent fire retardant coating composition for the fire protecon of structural steel substrates[END_REF]109] and thus need to be investigated. Since charred structures are poorly soluble in traditional organic solvents, most of the techniques used are solid-state analyses.

Various analytical techniques have been used for the chemical analyses of intumescent char residues. The techniques widely reported in the literature include Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope associated with Energy Dispersive X-ray Spectrometer (SEM-EDX), Electron Probe Micro-Analysis (EPMA), X-Ray Diffraction (XRD) and solid state Nuclear Magnetic Resonance (NMR).

FTIR can be a first choice for a char analysis due to its simple use [START_REF] Naik | Outlining the mechanism of flame retardancy in polyamide 66 blended with melamine-poly(zinc phosphate)[END_REF][START_REF] Duquesne | Mechanism of fire retardancy of polyurethanes using ammonium polyphosphate[END_REF]135,136], it can indicate bonding types and functional groups but it cannot provide information on the fine structures. Raman spectroscopy is also useful to investigate the ordered level of carbonaceous structure (from well-ordered graphite to a disordered carbon structure) [137]. XPS is used to elucidate the elements present in a sample in a semi-quantitative way. In addition, the XPS spectrum of specific element can be used to investigate the chemical structure [START_REF] Gardelle | Resistance to fire of silicone-based coatings: Fire protection of steel against cellulosic fire[END_REF]138]. It can be a good complement to other techniques. As an example, the 15 N solid state NMR requires a long scanning time for a measurement because of the low isotropic abundance of 15 N (0.4 %). XPS can thus be used in this case instead of solid-state NMR to investigate the structure of nitrogen.

Nevertheless, it allows analyzing only the extreme surface of the sample. EPMA allows elucidating the distribution of interesting elements on char surface or cross-section of char [138,139] PhD Thesis Nittaya HANSUPO, Univ. Lille 1 similarly to SEM-EDX [140]. XRD is a conventional technique, which allows identifying the formation of crystalline compounds. The use of XRD in this research field is extensively implemented [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF][START_REF] Deodhar | Calcium carbonate and ammonium polyphosphate-based flame retardant composition for polypropylene[END_REF]141] but is limited to crystalline compounds. Finally, solid state NMR is a technique of choice to characterize intumescent structure and this technique has been widely used [START_REF] Naik | Outlining the mechanism of flame retardancy in polyamide 66 blended with melamine-poly(zinc phosphate)[END_REF]137].

Solid state NMR is a very useful technique for char analyses. It provides not only the chemical composition but also the structures of studied materials. The measurements can be performed with elements having a non-zero spin of nuclei and can be considered as an advanced analytical tool depending on the nuclei and techniques (e.g. 2D NMR). The main advantage of NMR spectroscopy is its selectivity on specific nucleus. Furthermore, quantitative measurements can be performed, when the parameters are chosen correctly (importance of the time of spin relaxation). On the other hand, experiment can be time consuming. As an example, when dealing with 13 C NMR studies, the low natural abundance of 13 C isotope (1.1 %) [142] coupled with the weak interactions between each 13 C nucleus and important distances between isolated 13 C spins and nearest unpaired electron result in long spin relaxation time causing long time experiments.

Since two decades, our laboratory in Lille has used quite intensively 1D solid state NMR to characterize fire protected samples [START_REF] Naik | Outlining the mechanism of flame retardancy in polyamide 66 blended with melamine-poly(zinc phosphate)[END_REF]137,143]. Solid state 1D NMRs of various nuclei (e.g. 11 B, 13 C, 27 Al, 29 Si, 31 P,) were realized, which provide for example information on the evolution of carbonaceous structure of char residue ( 13 C NMR) [136], of phosphorus and of boron containing species in the condensed phase versus temperature ( 31 P and 11 B NMR) [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF] etc… Recently, with advanced tools and methods, solid state NMR has become more and more performant. Advanced NMR techniques are widely applied in various research fields such as 2D NMR sequences. In the field of flame retardancy, Karrasch et al. [144] studied flame retardant mechanisms in the condensed phase of bisphenol A polycarbonate and silicone acrylate rubber blends after pyrolysis. 31 P { 1 H} and 13 C { 31 P} Rotational Echo Double Resonance (REDOR) were used to estimate the distance between P atoms in different structural units and the surrounding protons and the distance between the various C atoms and the surrounding P atoms respectively. 2D Heteronuclear Correlation (2D HECTOR) was also used to investigate the various types of protons present. Another work by Sut et al. [58] used double resonance NMR technique including REDOR and Transfer of Population in Double Resonance (TRAPDOR) to deeply elucidate the chemistry behind the interactions in multicomponent flame-retardant polymers. Such techniques provide additional information which were not given when using 1D NMR.

Conclusion

To conclude, this section described the most common and recent characterization methods that have been used to investigate char properties; it includes the thermo-physical properties and chemical composition of char. To explore the chemical reactivity and draw the mechanism of action of intumescent systems, it is very important to use different methods and to compare the obtained results. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Conclusion

In this chapter, the basic knowledge and current state of the art on intumescence in general and on intumescent coatings in particular were reported. Concept of intumescence, intumescent process and mechanism, as well as main ingredients of intumescent coatings and associated fire tests were reviewed. A focus was made on epoxy based intumescent coatings. It was concluded that, even if some literature deal with the reactivity between two or three ingredients, the reactivity of these ingredients inside the complex intumescent formulation is rarely reported. Systematic approaches in the case of boron based flame retardant and carbonate systems are still missing.

In this context, this work focuses on the investigation of the mechanism of action of epoxy based intumescent coatings with a particular attention dedicated to boron-based compounds

and carbonates. The studied formulation contains phosphorus-based compounds (i.e. APP), borates, fibers, titanium dioxide and calcium carbonate as main ingredients. Referring to the literature, borates (and especially boric acid) are mentioned as crucial ingredients in intumescent coatings providing specific properties to a protective char to pass hydrocarbon fire test. However, no systematic approach is reported and the environmental concern related to boric acid should lead to mandatorily substitute it. The first goal of this work is thus to better understand the role of borates inside a complete intumescent formulation that can be used to protect steel against hydrocarbon fire. These results will be presented in chapter III of this dissertation. Not only borates but also other components react and play a significant role in intumescent formulations.

From this point of view, the comprehension of the reactivity between the intumescent ingredients should be taken into consideration. In this fire protective coating, the mode of action of carbonates has been reported but is still controversy. Therefore, the second objective of this work is to identify the mode of action of carbonate compounds, which are used as fillers in the coating. The results are detailed in chapter IV of this dissertation. Before going into details regarding the results, chapter II details the materials and methods which were used in this project.

It provides information on how the experimental research work was realized. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Chapter II: Materials and methods

This PhD thesis focuses on the mechanisms of action of intumescent coatings in a fire: questions remain on how the charred layer is formed, on the role and interactions of each component of the formulation. The materials and methods used in this study are detailed in this chapter. First, the preparation methods of the epoxy based intumescent coatings are described.

The sample preparation is specific for each analysis, so they are fully described. Then, the furnace test used to assess fire protective performance of the coatings and heat treatment conditions are presented. Finally, the characterization methods used to assess thermal, physical and morphological properties of the coatings and char are described. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Materials

The study was performed on an intumescent coating. The formulation hereafter called IF(BA) which is formulated by the industrial partner is used as a reference; it is a conventional and efficient intumescent formulation. The compositions as well as the commercial names and suppliers of the different ingredients are summarized in Table 6. The formulation is divided into two parts: part A based on the epoxy resin and part B based on the curing agent (aliphatic polyamide amine). Instead of molar substitution, another approach consists in weight substitution. This approach was however only performed in the formulation containing zinc borate. Boric acid was thus substituted by zinc borate in weight ratio. The formulation is named IF(ZB)wt, it is also presented in Appendix I.

Another objective of the work is to study the role of carbonates including calcium carbonate. In a first step, the formulations were simplified to be able to investigate precisely the influence of calcium carbonate (CaCO3) on fire protective performances. The compositions of the studied formulations are presented in Table 8. First, formulations containing only APP and borate were formulated and were used as reference formulations (IF-APPBA and IF-APPZB). CaCO3 was then added into these two formulations leading to IF-APPBACa and IF-APPZBCa formulation.

Another formulation without boron was also studied. It consists of a mixture between the binder, APP and CaCO3 and it is referred as IF-APPCa. For all those formulations, the ratios between the additives are similar to those of IF(BA) formulation (molar ratio). The properties of the studied carbonates are presented in Table 9. The coatings were prepared using a DISPERMAT mixer (VMA Getzman GMBH, D-51580

Reichshof). The epoxy part (part A) and curing agent part (part B) were prepared separately. First, the liquid components (e.g. epoxy resin and TCPP for part A/curing agent for part B) were stirred for about 3 -5 minutes with a low rotational speed (300 -400 rpm, Ø = 50 mm). Then, all solid ingredients (e.g. ammonium polyphosphate (APP), boric acid, zinc borate, TiO2, fumed silica) were added into the mixture. They were then mixed together for 30 -50 minutes at high rotation speed (1800 -2200 rpm) until the temperature of the mixture reached 55 -60 ⁰C. The rotation speed was then decreased before adding the mineral silicate fibers, in order to avoid shortening the fiber length. After finishing the preparation, part A and part B were stored separately and mixed together in the recommended ratio by a mixing device. The mixing ratio in weight was 3.44 of part A/1.00 of part B for all formulas.

2.2.1.2

Preparation of the coatings for fire test 100 x 100 x 3 mm 3 steel plates (S235) were blasted with steel grits of 75 -100 microns to clean the surface, increase its roughness profile and improve the adhesion of the coatings. The industrial partner prepared the steel plates. The blasted steels were kept in a tightly closed container with silica gel to avoid the rust formation during the shipment and storage. Moreover, to improve the adhesion, a primer (Epodux Zinc 57 -35, zinc epoxy primer: Maestria) was applied with a thickness of 50 -100 µm on top of the steel plate before applying the coatings.

The mixture of part A and part B with the recommended ratio was applied on the steel plate and the coating was cured at ambient temperature over a 48 hours period (Figure 13). The thickness of the coating was in the range of 4 ± 0.2 mm. To control the thickness, the cured coatings were polished with a belt sander (Scheppach bts 800) to get the required thickness. The thickness was measured using an ultrasonic thickness gauge (Elcometer 456). PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Preparation of the coatings for thermal analyses, heat treatments and chemical analyses

To perform thermal analyses, heat treatments and chemical analyses, part A and part B were mixed in the mentioned ratio. The mixture was deposited in a plastic bag and cured at ambient temperature over a 48 hours period. The cured material was then ground using an ultracentrifugal mill to produce a fine powder.

Preparation of the coatings for Rheometer test

Part A and part B were mixed in the mentioned ratio and deposited in Teflon mold to obtain disks of 25 mm of diameter and 1 mm of thickness (Figure 14). Those disks were used for rheological, expansion and mechanical measurements. The coatings were also cured for at least 48 hours before performing measurements.

Preparation of the coatings for thermal conductivity measurements

The samples prepared for Hotdisk measurements (see the section 2.2. To avoid an expensive and time-consuming experiment in a large industrial furnace test, a small-scale furnace test was developed in the laboratory to evaluate the fire performance of intumescent coatings mimicking the UL1709 hydrocarbon fire scenario.

The lab scale furnace (Figure 16) exhibits an internal volume of 26 dm

Heat treatments

Thermal treatments consist in heating a sample in a furnace (Figure 17) at a defined temperature. To perform heat treatments (HT), powder sample (≈ 2 g) was placed in a porcelain rectangular crucible (45 mm x 25 mm) and then inserted in a tubular furnace. Before heating, the sample was maintained at 30⁰C under inert atmosphere (nitrogen flow, 60ml/min) for 1 hour in order to purge air. The temperature was increased with a heating rate of 10 ⁰C/min from 30 ⁰C up to a chosen heat-treatment temperature (HTT). The sample was maintained at this temperature for 2 hours under nitrogen flow and then cooled down to ambient temperature without any defined cooling rate (still under nitrogen). Only the upper part of the sample was collected and analyzed to avoid any potential interaction between the intumescent coating and the porcelain. After heat treatments, the residue was kept in a desiccator to avoid its hydrolysis until analyzing. The samples were weighted before and after heat treatment to calculate the residual weight percentage.

Thermal characterizations

TG analyses

Thermo-Gravimetric Analyses (TGA) were carried out using TGA Discovery (TA instrument). Samples of 10 ± 0.3 mg were put in an alumina plan covered with a gold sheet to avoid the interaction between alumina pan and phosphorus-based compounds. Samples were underwent an isothermal at 30 ⁰C for 30 minutes followed by a heating ramp of 20 ⁰C/min from 30 ⁰C to 800 ⁰C or 1000 ⁰C under air or nitrogen flow to mimic thermo-oxidative or pyrolytic decomposition respectively. The balance purge flow was set to 15 ml/min whereas the sample purge flow was set to 50 ml/min.

To determine if there is or not some reactions occurring between the components, the weight difference curves between the experimental and theoretical data can be computed as follows:

 Mi (T): TG curve of the component i, The ∆(T) curve shows a potential increase or decrease in the thermal stability of a mixture.


When the experimental curve is higher than the theoretical one (or when the difference weight loss curve is positive), it indicates that the reactivity leads to a thermal stabilization of the materials. If the experimental curve is lower than the theoretical one (negative difference weight loss), the reactivity leads to a thermal destabilization of the systems.

Thermal conductivity measurements

The thermal conductivity of a material describes the transport of energy in form of heat through a material. In this work, the thermal conductivity was measured using Hot Disk thermal constant analyzer (Hot Disk TPS 2500S, Thermoconcept). The used technique is the so-called PhD Thesis Nittaya HANSUPO, Univ. Lille 1 transient plane source method equipped. The systems can be used in a furnace that has been designed for our research area, allowing measuring the thermal conductivity as a function of temperature up to 700 ⁰C. The data are acquired by using the Hot Disk Thermal Analyzer software.

The sensor, which acts as both a heater and a thermocouple, is placed in the middle of the samples (Figure 18; see section 2.2.1.5 for details concerning the preparation of the sample). The sensor typically consists in a thin layer of an electrically conducting material. During the experiment, a current passes through a nickel spiral which leads to an increase in temperature.

Then, the generated heat dissipates through the sample depending on the thermal characteristic of the tested material.

Figure 18 Experimental setup of transient plane source method

To be able to perform a measurement as a function of temperature, the furnace is directly connected to Hot Disk instrument. The furnace is purged under nitrogen flow and all experiments were carried out in an inert atmosphere to prevent the oxidation of the sensor. Mica sensor with a diameter of 3.2 mm was used for these measurements (the smallest diameter exists).

Measurements have been carried out at the following temperatures: 25, 100, 200, 300, 400, 500, 600 and 700 ⁰C (with a precision of around ± 0.1 ⁰C). The thickness of the coating has to be adjusted depending on the temperature since the relative expansion varies. To perform a measurement in the temperature range 25 ⁰C to 300 ⁰C, the thickness was fixed at 8 mm. From 300 ⁰C, the thickness is decreased to 2.5 mm to eliminate the constraint between expanded char and sample holder due to an expansion and to avoid an overflow of char in the sample holder.

The heat pulse power and measurement time were adjusted for each sample and at each temperature to be optimized. Power varies between 10 -70 mW and measurement time is comprised between 5 and 40 s, thus insuring the reliability of the measurements. To ensure a good repeatability, each measurement was performed twice. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Physical characterizations

Rheological measurement

Rheological measurements were carried out using a Rheometric scientific ARES 20A thermal scanning rheometer (TSR) in a parallel plate configuration (Figure 19). The change of viscosity as a function of temperature was monitored up to a maximum temperature of 500 ⁰C.

Expansion measurements

To measure the expansion of char, two approaches can be followed: i) to use the Rheometer and ii) to measure the expansion of the foamed char after the furnace test. The details are described in the following part.

Rheometer test

The first method consists in the use of the Rheometer test. The expansion can be recorded at the same time as viscosity (previously described). The gap variation between the upper and lower plates was registered as a function of temperature during the test using the same experimental parameters. The relative expansion is calculated referring to the gap increase (I) versus an initial thickness (I0) of the dry coating (eq. 30).

Expansion = l/l0 x 100 (eq. 30) The relative expansion can also be calculated by comparing the thickness of the dry coating (before the furnace test) and of the foamed char (after the furnace test). The foamed char thickness was measured using a ruler and the thickness of the dry coating was measured using an ultrasonic thickness gauge (Elcometer 456). At least six measures were taken over a char surface and dry coating to determine an average of the values. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Char strength measurements

The mechanical strength of intumescent coatings was determined by measuring the char compression resistance using Rheometric scientific ARES 20A thermal scanning rheometer (TSR) in a parallel plate configuration (the same as used for the measurements of viscosity and expansion but with a different protocol). This method allows measuring online the mechanical strength of char in function of temperature. First, the sample of 25 mm of diameter and 1 mm of thickness was put into the Rheometer furnace and was heated with a heating rate of 10 ⁰C/min up to 500 ⁰C without applying any strain (the upper plate is not in contact with the sample). This allows the sample to expand without any constraint.

The temperature was then maintained at 490 ⁰C. At this temperature, the upper plate was then brought into contact with the intumescent char, and the gap between the plates was reduced at a fixed rate (0.02 mm/s). The compression force required to destroy the char was registered as a function of the distance between the two plates and corresponds to the char strength. The sample holder is the same as that used for expansion and viscosity measurements.

The upper plate used in this experiment has however a diameter of 5 mm in order to increase the pressure on the whole sample and ensure a complete destruction of the char. The experimental scheme is shown in Figure 21. The recycle delay of 10 s or 30 s (depending on the relaxation time) and a spinning speed of 20 kHz were used. All spectra were acquired as the result of 128, 64 or 32 scans. Before measuring, the calibration was done using NaBH4 (characteristic peak is -42.06 ppm). The deconvolution of the spectra has been carried out using the software DMFIT [148], assuming Gaussian/Lorentzian and Q MAS ½ (quadrupolar lineshape). The simulation allows distinguishing different boron

structures. An example of the simulated curves is shown in Figure 22a. By visual observation, it is not obvious to differentiate BO4 units whereas two types of BO4 units can be clearly differentiated by simulation as shown in Figure 22b.

Elemental analysis

Elemental analysis was performed by the external laboratory (Institut des Sciences Analytiques, Villeurbanne -France).

The determination of the amount of carbon was made by burning the sample in an excess of oxygen at 1050 ⁰C. The quantity of the evolved CO2 was then determined by carbon dioxide infrared gas detectors and was proportional to the total quantity of carbon in the sample.

For boron and phosphorous, their amount was determined by Inductively Coupled Plasma Optical Emission Spectrometry ((ICP-OES), Agilent-Varian) after dissolution of the sample in the acid mixture (HCl/HNO3).

Char morphology

A 3D optical microscope was used to investigate char morphology, which uses optic and a charge coupled device (CCD) camera to output a digital image to a monitor. In this work, Keyence VHX 1000 digital microscope was used. The lens used is 20z -200z lens. The images were captured with 3D stitching mode to increase the resolution of the images. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Conclusion

In chapter II, the studied formulations were presented in the first part. Afterwards, methods to prepare the coatings for different tests were detailed. Experimental techniques used to perform the fire test and heat-treatment were then described. Furthermore, methods to characterize the thermal, physical and chemical properties of the intumescent coatings were depicted.

The selection of the methodologies are based on our knowledge and on the literature (review detailed in chapter I). They are implemented in combination to be able to achieve the thesis objectives. The strategy used in chapter III and IV are quite similar. First, the furnace test was used to assess the fire protective properties of the formulations. The char residues collected after the furnace test were then fully characterized to investigate the chemistry in the condensed phase, char morphology, expansion rate… The thermal and physical properties were also investigated using adapted techniques in order to elucidate the intumescent behavior/process.

The heat treatments were implemented when required to investigate the chemical reactivity between the ingredients of the intumescent formulations at defined temperatures. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Chapter III: Mode of action of borates on the fire protection of epoxy based intumescent coatings

The use of different borates in intumescent coatings as well as its efficiency have been 3) were evaluated in terms of fire protective performances using a small-scale furnace test mimicking UL1709 hydrocarbon fire scenario. At the end of the tests, char expansion, adhesion, cohesion and general aspects of char were observed. The collected char residues were then analyzed to elucidate the chemical reactions taking place in the condensed phase.

Fire protective properties

Figure 23 shows the evolution of temperature as a function of time on the backside of the steel plates coated with the different intumescent formulations during hydrocarbon fire test. 500

⁰C was chosen as the failure temperature since it corresponds to the temperature at which steel begins to lose its structural properties [START_REF] Nørgaard | Investigation of char strength and expansion properties of an intumescent coating exposed to rapid heating rates[END_REF]149]. Thus, time to reach 500 ⁰C is considered as a critical point to compare the fire protective performance of the studied formulations. The longer the time to reach the failure temperature, the better the fire protection. Table 10 shows the char aspects of the four formulations after burning for 30 minutes in the furnace test. For IF(ZB)m, the char exhibits an expanded structure constituted of an homogeneous layer with small pores through its thickness. The relative expansion is of about 650%. Globally, this layer is hard, cohesive and well adhesive to the steel plate.

For IF(borax)m, there is almost no expansion (only 170 %) and the obtained char is compact, dense and hard. Several cracks can be observed on the surface of the structure.

However, the formed char presents a good adhesion to the steel plate during the test. To go further in the investigations, XRD was used to characterize the crystalline chemical species formed in these samples.

Figure 25 shows the XRD diffractograms of the char residues of the four formulations and the diffractograms of boron oxide (B2O3) and boric acid (H3BO3). The residues present various crystalline species and certain peaks are common to different residues such as B2O3 and borophosphate (BPO4).

Indeed, the XRD patterns of IF(BA) and IF(APB)m residues clearly suggest the presence of B2O3. In the case of IF(borax), only the main signal of the B2O3 specie is observed (28.1 ⁰) but the presence of this specie can be assumed nevertheless. Whereas for IF(ZB)m residue, B2O3 is not detected. The thermal decompositions of boric acid, ammonium pentaborate and borax at temperature between 100 ⁰C and 450 ⁰C, is reported to produce boron oxide as described in the eq. 31, 32 and 33 ([150-152]). In the same range of temperature on the other hand, zinc borate does not decompose into B2O3. Its decomposition yields rather to the formation of amorphous 2ZnO.3B2O3 ( [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF][START_REF] Schubert | Structural characterization and chemistry of the industrially important zinc borate, Zn[B3O4(OH)[END_REF]) as shown in eq. 34.

2H3BO3 154,155]. It was already reported to be found in the char residues of intumescent coatings when the formulations contain boric acid and APP [START_REF] Ullah | Synergistic effects of kaolin clay on intumescent fire retardant coating composition for fire protection of structural steel substrate[END_REF][START_REF] Ullah | Effect of boric acid and melemine on the intumescent fire retardant coating composition for the fire protecon of structural steel substrates[END_REF]. It is obtained by the reaction between the degradation products of these reactants (i.e. polyphosphoric acid and B2O3). Such reaction could explain the formation of BPO4 in IF(APB)m residue however it does not seem to occur for IF(Borax)m as no crystalline BPO4 is detected in this case. The reaction between PhD Thesis Nittaya HANSUPO, Univ. Lille 1

APP and zinc borate to form borophosphate, already reported in a publication [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF], could explain the formulation of BPO4 in IF(ZB)m char.

For IF(BA), IF(APB)m and IF(borax)m, the detection of B2O3 at the end of the experiment can be due to the stoichiometry of the reactants. Indeed, in the formulations, borate is in excess compared to phosphorous (P/B molar ratio = 1/3.3). There is consequently more B2O3 formed by decomposition of BA, APB and borax than APP present in the formulation. Consequently, it makes sense to get 'unreacted B2O3' in the char residue. On the other hand, when looking precisely at the peak at the 2Ѳ value of 15⁰ (split signal-like), the presence of H3BO3 in the char residue may be suspected, especially in IF(BA). Boron oxide being hygroscopic [START_REF] Mccalla | Amorphization of crystalline orthoboric acid on a vitreous B2O3 substrate[END_REF], it can absorb water under atmospheric conditions and revert back to boric acid as shown in eq. 35 [156, 157]. In our case, two assumptions can be drawn. First, during the degradation, water is released from the combustion reaction and thus the reaction can occur during the test. A second assumption consists in considering that the reaction of boron oxide with water occurs after the test (cooling phase or storage). Indeed, even if the char was conserved under dried atmosphere, this assumption cannot be dismissed.

B2O3 + 3H2O → 2H3BO3 (eq. 35)

For IF(BA), IF(APB)m and IF(borax)m, Ca3(PO4)2 is also detected. This specie was reported

[158] to be formed by reaction between calcium carbonate and phosphoric acid as shown in eq.

36 [159]. CaCO3 is one of the ingredients of the formulations and phosphoric acid comes from the degradation of the APP, Ca3(PO4)2 can thus be formed in these formulations.

3CaCO3 + 2H3PO4

950 °𝐶 < 𝑇 <1150 °𝐶 → Ca3(PO4)2 + 3H2O + 3CO2 (eq. 36)

For IF(borax)m formulation, the diffractogram shows that the residue is not highly crystalline. Apart from the peaks of B2O3 and Ca3(PO4)2, the main signal is a broad band lying between the 2Ѳ value of 18 ⁰ and 35 ⁰ indicating a disordered structure (amorphous) of the char residue. This can probably be partly attributed to the formation of pregraphitic carbon [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF] as usually observed in intumescent char. Moreover, Na/Na2O is a known fluxing agent [160], which can decrease the glass forming temperature that may consequently produce a vitrified char at lower temperature as observed in IF(borax)m formulation.

For IF(ZB)m, in addition to BPO4, other crystalline compounds are detected: zinc orthophosphate (α-Zn3(PO4)2), zinc pyrophosphate (α-and γ-Zn2P2O7), and zinc metaborate (Zn4B6O13). Zn4B6O13 is a degradation product of zinc borate, which is formed when zinc borate is heated above 800 ⁰C [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF]. Interestingly, most of the crystalline compounds formed are zinc-based compounds. It highlights the important role of zinc from zinc borate that reacts with other components (especially phosphorous-based compounds). In the opposite to other three formulations, Ca3(PO4)2 is not formed. With the presence of Zn, the formation of Zn-P compounds is probably favored rather than the one of Ca-P compounds, that is occurred in the IF(ZB)m formulation. is more intense when compared to the others but no quantification can be made because the signal was acquired using cross polarization (CP). It means that the efficiency of the magnetization transfer between 1 H and 13 C should be known precisely to make any quantification. Nevertheless, it is reasonable to explain this higher resolution of the spectra by the higher carbon content in the two formulations as already shown by elemental analysis.

Figure 26 13 C NMR spectra (9.4

T) of IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m char residues

To investigate the evolution of the phosphorus species in the char residues, 31 P solid state NMR was performed on the char samples. In 31 P solid state NMR, the Q n terminology is used to classify the structures of phosphate. Q represents a phosphorous tetrahedron and n the number of bridging oxygen atoms in this tetrahedron (Figure 27). For example, Q 2 structure contains two bridging and two non-bridging oxygen atoms and is the so-called metaphosphate [162][163][164]. In such structure, the higher the number of bridging oxygen atoms attached to a phosphorous atom, the lower the 31 P isotropic chemical shift. The peak position is an indicator of PO4 tetrehedra with varying degree of condensation/polymerization. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 In IF(ZB)m char residue, besides BPO4, additional signals appear at 3.9, -1.3, -5.3, -7.1, -10.1, -15.9, -18.8 and -21.1. The attributions can be made as follows. The sharp peak at 3.9 ppm is assigned to zinc orthophosphate (α-Zn3(PO4)2) [144,165], the triple peak appearing at -15.9,-18.8 and -21.1 is assigned to α-zinc pyrophosphate (α-Zn2P2O7) [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF]166] and the peaks at -5.3, -7.1 and -10.1 ppm can be assigned to γ-Zn2P2O7 [START_REF] Naik | Outlining the mechanism of flame retardancy in polyamide 66 blended with melamine-poly(zinc phosphate)[END_REF]167]. The identification of these species is in good agreement with XRD results. A low intensity signal appearing at -1.3 ppm is also observed.

That is assigned to Q 0 phosphate site. 172,173]. This signal at 1.9 ppm may be the characteristic signal of BO4 unit in Zn4B6O13. Unfortunately, this assumption could not be proved since this zinc borate is not commercially available.

On the other hand, the broad signal lying between 5 and 20 ppm attributed to BO3 units (typical second-order quadrupolar line shape) is observed for the four samples. At least two BO3 units are overlapping in this broad signal. Indeed, according to the XRD results (Figure 25

Conclusion

In this part, the effects of four borates namely boric acid, zinc borate, borax and APB on fire protective properties were studied. Additionally, their interactions with the other additives of the formulation in the condensed phase after testing were elucidated. As a result, it was shown that the formulation containing zinc borate exhibits the best fire protection among all (longer time to reach the failure temperature). The formation of various crystalline compounds in the formulations, which are thermally stable, are suspected to be responsible of the good fire protection. They may stabilize and strengthen the carbonaceous char. To go further in the investigation, it is of interest to investigate in more detail the decomposition pathway (as a function of temperature or exposed time in the furnace) of those formulations as well as their thermo-physical properties. For these purposes, the formulations containing either boric acid (IF(BA)) or zinc borate (IF(ZB)) were chosen. IF(ZB) was chosen because it provides promising results in the fire protection and char characteristics. IF(BA) was selected because BA is commonly used as intumescent ingredient in commercial systems [START_REF] Weil | Fire-Protective and Flame-Retardant Coatings -A State-of-the-Art Review[END_REF][START_REF] Weil | A review of current flame retardant systems for epoxy resins[END_REF][START_REF] Jimenez | Characterization of the performance of an intumescent fire protective coating[END_REF]. Moreover, as boric acid is mentioned to be CMR by REACH, the comprehension of the role of boric acid is of interest since it might give information on how to substitute it. Thus, the next part is dedicated to the investigation of the thermal decomposition and thermo-physical properties of the selected intumescent coatings during charring process. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Insight into the mechanism of action of boric acid and zinc borate in complex formulations

The previous part showed the interesting fire protective performance of the formulation containing zinc borate. The chemical species formed in the condensed phases were identified giving some clues on its mode of action. Nevertheless, the mechanism of action of intumescent material is a hugely complex and dynamic process. The characterization of the chemistry in the char residues collected at one point does not provide enough information to understand this complex process. In this part, the mechanism of action will be fully investigated. Two formulations including the formulations containing either zinc borate or boric acid were selected for a full characterization (chemical and thermo-physical modifications).

First, the thermal decompositions of the two selected coating formulations were investigated under pyrolytic condition or under a real fire test (UL 1709). The aim is to elucidate the evolution of chemical species formed in the condensed phase during the decomposition process to understand their mechanism of reaction, which occurs in the condensed phase. In the following part, the study deals with the measurements of the thermo-physical properties. It includes the investigation of the complex viscosity, relative expansion, char morphology, thermal conductivity, and char strength. Char morphology was assessed (at room temperature) as a function of the exposed times after the fire test while the thermal conductivity, complex viscosity, relative expansion and char strength were dynamically measured as a function of temperature.

Finally, the mechanisms of protection of borates, are commented. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 During the furnace test, it is admitted that most of the oxygen is consumed by the combustion leading to only 3 -4 % of oxygen left [START_REF] Jimenez | Kinetic analysis of the thermal degradation of an epoxy-based intumescent coating[END_REF]174] 11). Regarding the TG curves of the studied coatings, five temperatures were selected (blue dot lines visualized on Figure 30). The chars collected for each heat-treatment temperature were then analyzed using XRD, of 15 ⁰ and 30 ⁰ assigned to amorphous phases (e.g. disordered graphitic carbon [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF]).

Figure 31 XRD diffractograms of IF(BA) char residues versus temperatures

To investigate more precisely the evolution of phosphorous species versus temperatures, PhD Thesis Nittaya HANSUPO, Univ. Lille 1 For a HTT of 210 ⁰C (Figure 32), the spectrum is modified compared to the coating at ambient temperature. At this temperature, APP begins to degrade leading to the release of NH3 and H2O and to the formation of a highly cross-linked polyphosphoric acid (a broad band lying between -10 and -18 ppm) [161,177]. The additional broad peak centered at -7.1 ppm (observed from 210 ⁰C up to 250 ⁰C) is assigned to pyrophosphate (Q 1 ) and/or terminal phosphate groups [START_REF] Naik | Outlining the mechanism of flame retardancy in polyamide 66 blended with melamine-poly(zinc phosphate)[END_REF]143]. At 210 ⁰C and 250 ⁰C, an additional signal appearing at 1 ppm can also be detected, this can be assigned to Q 1 phosphate structure of orthophosphate [178]. Another broad band lying between -10 and -25 ppm is observed from 210 ⁰C until 550 ⁰C with very low intensity at high temperature (in rectangular dotted line). It is assigned to disordered structures of metaphosphate (Q 2 ), which is different from the degradation products of APP.

Characteristic peak of TCPP (-4.4 ppm) disappears at 250 ⁰C which is in agreement with the decomposition temperature of TCPP (244 ⁰C, product data sheet). On the other hand, at high temperatures (T ≥ 280 ⁰C), a single sharp peak is observed at -30 ppm. This band can be attributed to B-O-P bonds of borophosphate (BPO4) [START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF]179]. It is consistent with XRD results. At 250 ⁰C, the characteristic peak of BPO4 can also be observed with a very low intensity indicating that the formation of BPO4 has begun. The 31 P NMR spectra can be considered as a semi-quantitative indicator (all samples were performed with the same parameters and respecting the relaxation of the nucleus). It can be mentioned that the concentration of BPO4 increases as a function of temperature. which mainly contains trigonal boron atom (BO3) with small amount of BO4 as impurity at ambient temperature [START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF].

Figure 34 11 B NMR spectra (18.8T) of IF(BA) char residues versus temperatures

A sharp signal appearing at about -3.8 ppm, which is detected from 280 ⁰C up to 550 ⁰C, can be assigned to the characteristic signal of borophosphate (BPO4) [144,165]. This is consistent with the results shown by XRD and 31 P NMR.

In the samples heat-treated at 210 ⁰C and 250 ⁰C, a low intense peak can be distinguished at -3.4 ppm. Since the chemical shift is very close to that of BPO4, an assumption was arisen that PhD Thesis Nittaya HANSUPO, Univ. Lille 1 it may be the signal of BPO4 with less crystallinity, (e.g. initial phase of the formation of BPO4). To justify this assumption, these char residues were carried out to 1D 11 Afterwards, the evolution of boron species was taken into consideration. 11 B NMR spectra of IF(ZB)wt residues collected after different heat treatments are presented in Figure 39. The same approach was used; the spectra were simulated to quantity the BO3 and BO4 populations (Figure 40). The ratio of BO3/BO4 unit obtained by simulating the experimental spectrum of IF(ZB)wt coating at ambient temperature is 1/2.2. This is in agreement with the literature where it was reported that neat zinc borate is composed of 1 BO3 unit and 2 BO4 units [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF][START_REF] Schubert | Structural characterization and chemistry of the industrially important zinc borate, Zn[B3O4(OH)[END_REF]. At 280 ⁰C, the boron spectrum line shape is slightly modified compared to that of ambient temperature: Considering the evolution of the relative concentration of boron species versus temperature (Figure 40), it is observed that the boron species change a little bit from ambient temperature up to 280 °C. Above 280 °C, the relative concentration of BO4 units decrease whereas the amount of BO3 units and BPO4 increase. It is noteworthy that the relative concentration of borophosphate is much lower than that of BO4 unit whereas the opposite was observed in the case of IF(BA) formulation.

BO3 in zinc borate changes to BO3 in a different conformation (280 ⁰C to 380 ⁰C). This is reasonably attributed to the dehydration of zinc borate leading to the formation of 2ZnO.3B2O3

(as boron is in excess in the formulation, reactions between borates and phosphates cannot consume all boron). A broad signal of BO3 unit lying between 10 and 20 ppm might be assigned to BO3 unit in boric acid conformation (identified by XRD) and BO3 unit in 2ZnO.3B2O3

(degradation product of zinc borate). As this case, it also suggests the reversion of boron oxide to boric acid like it is observed in the case of formulation containing boric acid.

Figure 40 Relative concentrations of boron species in IF(ZB)wt char residues versus temperatures

Conclusion

The decomposition pathway of IF(ZB)wt was investigated using the same approach as in the case of IF(BA) formulation. 41. The selected times are 2, 5, 10, 12 and 15 minutes for both formulations. In addition to these, longer exposure time (20 minutes) was also used for IF(ZB)wt. This point is excluded in the case of IF(BA), since for this formulation a detachment of char at about 13 -14 minutes occurred. Note that the samples continued burning after stopping the burners since the fuel sources (e.g. polymeric contents) were not completely consumed. The burning samples were removed from the furnace and a fire was immediately extinguished.

The same approaches as done in the previous part (3.2.1.1) were used. The char residues were collected after each test to be analyzed. XRD, 11 B and 31 P NMR were used as the characterization tools for char analyses. In the following part, only the identification of chemical species formed in the condensed phase will be discussed. Meanwhile, the expansion and char morphology were also assessed and will be detailed in the section 3.2.2 (thermo-physical properties). and CaCO3. Under a fire test condition, the reversion of boron oxide to boric acid is more plausible compared to the heat treatment under pyrolytic condition. Here, boric acid was found in all samples whereas it was previously identified only in the char residue after heat-treatment of 550 ⁰C (in 3.2.1.1). The presence of CaCO3 is surprising; CaCO3 decomposes in one step in the temperature range of 680 ⁰C to 900 ⁰C [START_REF] Hermansson | The flame retardant mechanism of polyolefins modified with chalk and silicone elastomer[END_REF][START_REF] Murakami | Physicochemical study of CaCO3 from egg shells[END_REF]. With the furnace test's condition (1100 ⁰C in 5 minutes), CaCO3 was expected to decompose. The presence of large heat gradient in intumescent layers has been evidenced in the publication [185] in less severe conditions (ISO 834 vs. UL 1709).

These results showed the gradient of temperatures of about 100 to 200 ⁰C between different positions in the intumescent layer. In addition, the temperatures measured in the char are much lower than the furnace temperature. This can be the reason of the identification of CaCO3 in these char residues and it suggests that the temperature inside the charred layer stays lower than 680 ⁰C. The analyzed samples were prepared by taking all charred layers and they were ground together, it makes sense to detect CaCO3 at all characteristic times. Nevertheless, CaO (or Ca-based compounds) should be formed too but it was not detected by XRD probably because of too low concentration of these species in the residues or low crystallinity.

Figure 43 XRD diffractograms of IF(BA) char residues versus times

Afterwards, the residual samples were characterized using 31 P NMR (Figure 44). A sharp peak appearing at -30 ppm, which is a characteristic peak of BPO4, is observed in all samples (from 2 to 15 minutes). It evidences the formation of BPO4, which is in good agreement with the results obtained by XRD diffractograms. At 2 min, there is a broad peak lying between 0 and -25 ppm, which indicates the presence of amorphous phosphate. However, its intensity is very low.

The results show that the formation of BPO4 occurs immediately after starting the fire test.

This observation is consistent with the fact that the formation of BPO4 occurs at the temperature between 250 ⁰C and 280 ⁰C that is much lower than the temperature in the furnace test. Note also that APP completely decomposes to yield amorphous phosphate and reacts with boric acid. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

)) is detected. α-Zn2P2O7 is formed from about 10 minutes of the test and is still present up to 20 minutes. Note that the chemical species formed in this formulation are very complex, some crystalline species have not been attributed yet. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Figure 48 XRD diffractograms of IF(ZB)wt char residues versus times

To identify the evolution of phosphorus species, 31 P NMR was performed. Figure 49 shows 31 P NMR spectra of the char residues. It shows the formation of BPO4 (signal at -30 ppm) and α-Zn3(PO4)2 (signal at 3.9 ppm), they are formed from 2 minutes of the test. However, these two species were not identified on the XRD diffractogram at 2 minutes, probably because of their poor crystallinity and they are observed up to 20 minutes. At 2 minutes, a broad signal lying between 0 and -30 ppm is moreover observed; this indicates the disordered structure of phosphate which is then vanished (from 5 minutes). This underlines the transformation of amorphous species and/or poorly crystalline species into highly crystalline species.

In the zoom area (left hand side of Figure 49), additional peaks are observed between -5

and -20 ppm (low intense peaks). There are two sets of triple peaks, which can be assigned to the characteristic signals of α-and γ-zinc pyrophosphate (α-Zn2P2O7 → -5.2, -7.3, -10 ppm and γ-PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Zn2P2O7 → -15.9, -19, -21.1 ppm) [START_REF] Naik | Outlining the mechanism of flame retardancy in polyamide 66 blended with melamine-poly(zinc phosphate)[END_REF][START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF]167]. These are similar to what were observed in the char residues of IF(ZB)m described in 3.1.2. They are formed from 10 minutes up to 20 minutes of the test. Regarding the peak height, it suggests that these additional species are present at very low concentration. The identification of α-Zn2P2O7 is consistent with the XRD results as previously described while γ-Zn2P2O7 was not identified in XRD pattern (Figure 48). When looking at the XRD pattern of γ-Zn2P2O7 in the database or literature [186] compared to that of the char samples, it is possible to have γ-Zn2P2O7 in XRD pattern but their peaks could be hidden by other peaks.

Conclusion

The decomposition pathway of IF(ZB)wt coating was investigated. The evolution of chemical species formed in the condensed phase during the furnace test (between 2 and 20 minutes) was greatly modified. The formation of BPO4 is identified from 2 to 20 minutes. While the formation of dissimilar specie to the IF(BA) formulation (i.e. Zn3(PO4)2) was also identified (2 → 20 minutes). In addition to these, the formation of zinc pyrophosphate (α-and γ-Zn2P2O7) were detected from 10 minutes of the test. This highlights the notable role of zinc borate on the formation of crystalline zinc based compounds. However, the quantity of these two latter species are very low compared to the major species such as BPO4 and Zn3(PO4)2. Whereas the reactivity of CaCO3, TiO2 or SiO2 in these char residues could not be identified. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Proposed mechanisms of decomposition

The summarization of the results are schemed in Figure 52.

Figure 52 Mechanisms of decomposition of IF(BA) and IF(ZB)wt

In the case of IF(BA), boric acid first degrades yielding boron oxide. APP then degrades at higher temperature. The reaction between boron oxide and decomposition product of APP occurs immediately after degradation. The formation of BPO4 occurs between 250 ⁰C and 280 ⁰C. B is in excess compared to P, B2O3 is thus present in the char residue. BPO4 and B2O3 are highly stable compounds, they are formed and present in the char residues up to 15 minutes of the test (B2O3: 210 → 550 ⁰C and 2 → 15 minutes and BPO4: 250 → 550 ⁰C and 2 → 15 minutes). Surprisingly, CaCO3 was found in char residues of all samples (210 → 550 ⁰C and 2 → 15 minutes), evidencing that it does not decompose nor react with any components. For TiO2 or SiO2, there is no evidence of their reaction.

In the case of IF(ZB)wt, APP first degrades. Zinc borate then degrades. The formation of PhD Thesis Nittaya HANSUPO, Univ. Lille 1 up to 20 minutes of the test (BPO4: 380 → 550 ⁰C and 2 → 20 minutes). The additional specie such as α-Zn3(PO4)2 is formed at 550 ⁰C, resulting from the contribution of zinc borate. This crystalline specie is also thermally stable compound and is found under the furnace test up to 20 minutes (α-Zn3(PO4)2: 550 ⁰C and 2 → 20 minutes). Under the furnace condition, two polymorphs of zinc pyrophosphate were found (α-Zn2P2O7: 10 → 20 minutes and y-Zn2P2O7: 10 → 20 minutes).

The formation of inorganic compounds, which are thermally stable, are supposed to be responsible for stabilizing and strengthening the carbonaceous char. BPO4 and B2O3 which were mentioned to enhance the fire protective properties and adhesion of the protective char [START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF] are found in both formulations. In the case of the formulation containing zinc borate, zinc based compounds, which are thermally stable (i.e. α-Zn3(PO4)2, α-and γ-Zn2P2O7) are additionally formed. These indicate the high reactivity of zinc from zinc borate reacting with other species in the formulation, especially phosphorous based components. It allows stabilizing phosphorus in the condensed phase, that benefits char formation and char stabilization as described in the state of the art.

Conclusion

In this part, the mechanisms of decomposition of the intumescent coatings containing either boric acid or zinc borate were investigated. The study focuses particularly on the mechanisms occurring in the condensed phase. This study highlights the important role of borate and phosphate in the complex formulations. Even if the formulations contain twelve ingredients, the reaction of borate and phosphate are predominant. In both cases, borophosphate and boron oxide are formed. Zinc from zinc borate plays a very important role in the condensed phase, zincbased compounds (e.g. Zn3(PO4)2, Zn2P2O7) are additionally formed in IF(ZB)wt char residue.

The intumescent phenomenon is a complex process. Not only chemical modifications in the condensed phase but also thermo-physical properties govern the efficiency of the intumescent char. The next part thus deals with the investigation of the thermo-physical properties of the studied intumescent coatings including IF(BA) and IF(ZB)wt. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Thermo-physical properties of the chars of IF(BA) and IF(ZB) coatings

The goal of this part is to measure the complex viscosity, dynamic expansion, char morphology, thermal conductivity, as well as the char strength of the studied intumescent coatings. The intumescent chars collected in the previous part (3.2.1.2) were analyzed ex-situ while the complex viscosity, thermal conductivity and char strength were dynamically measured as a function of temperature, namely an in-situ way. Only expansion was assessed in two aspects:

i) static (cool state after furnace test) and ii) dynamic (as a function of temperature). The results are discussed in the following.

Complex viscosity and expansion

The efficiency of the char is related to its ability to expand and form a multicellular structure. One of the main aspect is the physical structure of intumescent char (uniformity and porosity). The type of char depends on the way the intumescent develops, which is closely linked to its chemical transformation during heating [START_REF] Duquesne | Thermoplastic resins for thin film intumescent coatings -towards a better understanding of their effect on intumescence efficiency[END_REF]. The expansion of intumescent coating is due to the slow diffusion of the evolved degradation gases released into the degraded matrix. The importance of the visco-elastic properties of this layer is crucial because it directly affects the porosity of the obtained char. In the literature [119,187], good correlations between the different steps of the intumescent process and measurements of the expansion and apparent viscosity were demonstrated. It is consequently of interest to measure in-situ viscosity along with expansion of intumescent coatings and to correlate these data to their degradation behavior obtained by TG analysis.

Dynamic measurement of complex viscosity and expansion

Complex viscosity, relative expansion and TG curve of IF(BA) are presented in Figure 53.

IF(BA) exhibits a slight expansion between 150 ⁰C and 210 ⁰C, concurrently to an increase of viscosity from 1.3x10 5 Pa.s (150 ⁰C) to 4.3x10 5 Pa.s (210 ⁰C). The increase of viscosity can be attributed to the dehydration of boric acid to from B2O3. A similar result was observed by M.

Jimenez [START_REF] Jimenez | Characterization of the performance of an intumescent fire protective coating[END_REF]. The viscosity remains steady up to about 260 ⁰C while a slight expansion is still observed. The highest expansion (180 % of relative expansion) is reached when the viscosity falls PhD Thesis Nittaya HANSUPO, Univ. Lille 1 down to about 6.5x10 3 Pa.s. However, the expansion dramatically decreases when viscosity reached its lower value (5.0x10 2 Pa.s). This dramatic decrease in viscosity observed between 300 ⁰C and 460 ⁰C corresponds to the main degradation step of the coatings (see TGA), and in particular to the degradation of the epoxy resin. Indeed, epoxy resin degrades in two main steps: a first step between 220 ⁰C and 380 ⁰C, corresponding to about 84 % weight loss and a second step between 375 ⁰C and 550 ⁰C leading to the total degradation of the resin. Epoxy resin degrades by hemolytic rupture of bonds (e.g. N-C, O-CH2) producing free radicals which undergo further reactions that are expected to be of complex nature [START_REF] Jimenez | Characterization of the performance of an intumescent fire protective coating[END_REF]128]. The negative value of the relative expansion (-100 % of relative expansion) means that (i) there is no char left at this moment or (ii) char is not hard enough (upper plate easily presses the char and is totally destroyed by the upper plate pressure). The second assumption is favored in our study since weight loss is equal to around 50 wt. % at 500 ⁰C. The increase in viscosity after 370 ⁰C can be attributed to a carbonization process, the viscous phase disappears and a highly condensed char structure is produced. It can be concluded that the addition of either boric acid or zinc borate in the studied formulation shows different effects on the degradation pathway, complex viscosity and expansion of char. When boric acid is present in the formulation, the coating degrades at lower temperature to yield a structure that causes an increase in the viscosity and a slight expansion in the temperature range of 150 ⁰C to 260 ⁰C. However, the maximum value of expansion is lower than that of the formulations containing zinc borate.

Static measurement of expansion

The dynamic measurements of viscosity and expansion, as demonstrated in the previous part, provide valuable information on the mode of action of the intumescent formulations.

However, these measurements are limited by the equipment used in terms of the heating ramp (10 ⁰C/min) and maximum temperature (500 ⁰C). In parallel to the dynamic approach, static measurements of the expansion of char at characteristic times during the fire test (described in 3.2.1.2 When submitted to a fire test) were measured.

From these measurements, the expansion versus time curve can be plotted and the expansion rate (velocity of expansion) can be calculated during the expansion step. The heat conductivity is around 0.40 W/mK up to 200 ⁰C and it then drops to a minimum of 0.15 W/mK between 300 ⁰C and 400 ⁰C (related to the modification of the char structure) before increasing again at higher temperature. The increase of thermal conductivity in the temperature range of 400 ⁰C and 700 ⁰C can be due to i) the modification of char structure (e.g. bigger voids),

ii) the radiative heat transfers across the char pores [112] or the combination of these two effects.

In this studied formulation, the substitution of boric acid by zinc borate does not influence the heat conductivity of the intumescent char under these conditions.

Figure 59 Thermal conductivity (W/mK) of IF(BA) and IF(ZB)wt versus temperatures

Chapter III: Mode of action of borates 123 PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Only few papers have reported conductivity values for char materials. J.E.J. Staggs [113] calculated heat conductivity of intumescent char by numerical simulation. It was reported that heat conductivity varies from 0.1 to 0.4 W/mK from ambient temperature to 600 ⁰C. The experimental values obtained are in the range of these values mentioned by Staggs. However, his simulation does not take into account the changes induced by chemical reactions conducting to the expansion from a certain temperature. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Char strength

The mechanical resistance of char is also a key parameter, which permits to ensure the char integrity, especially under severe fire scenarios such as hydrocarbon fire [123,126].

Therefore, mechanical resistance of the coatings are examined in this section.

The curves related to the mechanical resistance of the IF(BA) and IF(ZB)wt chars are shown in Figure 60. The evolution of force is registered, in situ at 490 ⁰C versus the gap (mm) between the two plates of the rheometer. A measured strength can be related to a destructive force. When the strength is high, it means that the underlying material resists to the pressure applied on its surface. Two extreme cases can be observed… i) If a material is extremely hard, the strength recorded will immediately increase until the highest force permitted by the equipment (~1400 g) when the upper plate touches the char ii) If a material is not resistant at all, the strength recorded will be very low while the upper plate is brought down until the char is destroyed. The char strength always drastically increases at one point of the experiment, but for fragile materials, it is just the consequence of the force exerted by the broken pieces compacted at the bottom of the sample holder. When the measurement of the strength cannot be recorded anymore because of the maximum force reached, the gap is named the 'critical gap'.

The curves (Figure 60) can be divided into two parts: part I corresponds to the mechanical resistance of the structure and part II is related to the compression of the residue [189]. The char aspects at the end of the tests are shown in Table 13.

The structure formed at 490 ⁰C of IF(BA) is quite homogeneous but it shows bad cohesion as one part of the char sticks to the upper plate (similar behavior to that observed during the viscosity and expansion measurements). The force, which is applied to compress the IF(BA) char throughout it thickness, is constant (about 200 g between 13.5 and 17.5 mm of gap). In the case of IF(ZB)wt, the force increases gradually from 0 to 600 g for gap values comprised between 20 and 7.5 mm. It indicates that the char gets stronger from the top to the bottom of the samples.

Pictures taken show that IF(ZB)wt char is quite homogeneous, hard and well cohesive.

Figure 60 Mechanical resistance of IF(BA) and IF(ZB)wt char

Table 13 Residual appearances of IF(BA) and IF(ZB)wt captured after the mechanical resistance test

IF(BA) IF(ZB)wt
To conclude, the char obtained for the formulation containing zinc borate (IF(ZB)wt) exhibits a higher mechanical resistance and cohesion than that containing boric acid (IF(BA) and the char aspects after the test are different. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Mechanisms of protection of complex intumescent formulations

When crossing the data obtained relating to the thermal decomposition pathway and thermo-physical properties, the different effects provided by boric acid or zinc borate can be detected and their mechanisms of protection can be drawn.

Boric acid due to its low dehydration temperature makes the char to expand at the beginning stage of the fire test. It also leads to the huge expansion for few minutes before the detachment of char. This huge expansion could be probably due to the drastic decrease of the viscosity, which was observed by Rheometer measurement. Those phenomena lead to the higher protective performance at the beginning stage of the fire test (between 0 and 12 minutes) compared to the formulation containing zinc borate. BPO4 and B2O3 are found immediately in the beginning stage of the fire test. These species in addition to the other additives (i.e. CaCO3, TiO2, SiO2) are supposed to stabilize and reinforce the carbonaceous structure but it does not promote the char adhesion/cohesion of this formulation.

Zinc borate promotes the effective fire protection tardily compared to the formulation containing boric acid; a slow temperature increase can be obtained after 5 minutes of the fire test. It can be related to the higher dehydration temperature of zinc borate, this may delay the reactivity between the borate with other components of the formulation. Afterwards, this formulation exhibits very interesting behavior: ''a plateau region'' (very low temperature increasing rate between 7 and 18 minutes). It could be due to the formation of a very small, homogeneous and closed-cell foamed structure. A great char adhesion/cohesion could be probably due to the formation of zinc-based compounds (i.e. Zn3(PO4)2, Zn2P2O7). The char strength of the formulation containing zinc borate is obviously higher than the one containing boric acid. This high char strength can also benefit the resistance to fire of such formulation. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Conclusions

Chapter III was dedicated to the investigation of the role of different borates in epoxy based intumescent coatings. First, the effects of four borates including boric acid, zinc borate, borax and APB on fire protective properties were studied. It was shown that the formulation containing zinc borate exhibits the best fire protection among all. For these four formulations, their chemical modifications in the condensed phase were investigated.

Afterwards, the full characterization including chemical modifications and thermophysical properties of the formulations containing either boric acid or zinc borate were done.

Their mechanisms of protection are very different. When zinc borate is added into the formulation, a high fire protective performance is obtained, that is supposed to be related to the specific char morphology and the high char strength. However, boric acid also provides interesting results in terms of fire protective performance since the reactivity between the components can occur at the beginning stage of decomposition leading quickly to the formation of the protective layer. That leads to a good fire protection at the beginning stage of the fire test. The bad adhesion observed for the formulation containing boric acid may be due to the huge expansion occurring in a short time. The mechanisms of fire protection of borates (especially boric and zinc borate)

were drawn in this chapter. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Chapter IV: Influence of carbonates on the fire protection of epoxy based intumescent coatings

In chapter III, it was shown that the mechanisms of fire protection are different when incorporating boric acid (BA) or zinc borate (ZB) in the formulation. In addition to this, the coating formulation is very complex. Not only borates but also other ingredients play important roles. The mechanism of action of the components such as phosphates, silicate fibers, TiO2…have been extensively studied and they were reviewed and detailed in chapter I but the role of calcium carbonate while in a significant amount in the formulation, remains unclear. To go further in the investigation, this chapter IV intends to study the effect of carbonates (here it is not only limited to CaCO3 to get additional information on the potential role of the cation of the carbonate). First, the effect of a conventional carbonate compound (i.e. CaCO3) on fire protection was investigated.

Then, the comprehension of the mode of action of calcium carbonate was undertaken. The second part is dedicated to the assessment of the effect of various carbonates (i.e. MgCO3, ZnCO3, Na2CO3, K2CO3) on fire protective properties of intumescent coatings. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Influence of CaCO 3 on the fire protection

As detailed in chapter I, different authors studied the roles of calcium carbonate (CaCO3) as flame retardant in some polymeric systems. Negative or positive effects were obtained depending on the studied systems. Its interaction with phosphates (i.e. APP, one of the ingredients of the studied formulation), BPO4 (product formed in this system) … were also reported. For epoxy based intumescent coatings, CaCO3 was added (i.e. commercial coating [START_REF] Hanafin | Low density, light weight intumescent coating[END_REF])

but its exact role has never been investigated. In this part, the effect of CaCO3 on fire protective properties of epoxy based intumescent coatings using against hydrocarbon fire is examined. To 14.

In the case of IF-APPCa, the charred structure falls off during the test letting only a small residue at the surface of the plate. The main part of char is collected on the bottom of the furnace at the end of the test. This part of the char is multicellular, soft and easy to destroy. The fall of the char can be explained by a rapid and high expansion of char, which were observed via a quartz window during the tests. This high level of expansion could partly be due to the amount of APP added in this formulation to keep constant the ratio of APP/CaCO3. In this formulation, APP amount is thus about 3 times higher than other four formulations (in weight ratio). In addition, as described in the literature, reaction between APP and CaCO3 can occur leading to the decarbonation of CaCO3 at about 300 ⁰C [START_REF] Deodhar | Calcium carbonate and ammonium polyphosphate-based flame retardant composition for polypropylene[END_REF]. Big amount of evolved gases releasing by APP and

CaCO3 may be responsible of a high expansion observed. The expansion in the furnace test is considered as one of the key parameters in the development of fire protective coatings [117].

This parameter is necessary but a very high expansion could lead to the formation of light char with less mechanically resistance as observed in the case of IF-APPCa.

In the case of the formulations containing BA, the behavior of the coating during the test is much contrasted. Without CaCO3 in the formulation (IF-APPBA), the char falls off the plate whereas with CaCO3 (IF-APPBACa) it is maintained on the plate until the end of the experiment.

Both residues are expanded but the aspects of the chars differs greatly. The residue collected in the furnace for IF-APPBA presents non-homogeneous cell sizes on the bottom (toward the plate)

with very big holes contrary to IF-APPBACa which presents two dense layers: on the bottom layer a black and homogeneous char and on top a grey char with a bigger cell size. These differences PhD Thesis Nittaya HANSUPO, Univ. Lille 1 of structures result in different mechanical resistance of the char (evaluated roughly by hand)

with on the one hand a crumbly material without CaCO3 and a hard residue in presence of CaCO3.

With ZB, the presence of CaCO3 does not change the char aspect. In both cases, the chars are not much expanded; the relative expansion is about 120 %. Char is very hard, compact and dense.

It was noted that, at the high amount of borates (34 -37 wt. % in the formulation), zinc borate inhibits the expansion of the coatings. That is not the case for boric acid. In the particular case of boric acid, it dehydrates yielding higher amount of vapor compared to zinc borate (44 vs.

14 wt. %), that may affect the expansion of intumescent formulation. This influence might not be observed with a low amount of borates.

Table 14 Char aspects and relative expansions of IF-APPCa, IF-APPBA, IF-APPBACa, IF-APPZB and IF-APPZBCa

Conclusion

This part investigated the effect of CaCO3 on fire protective performances of intumescent coatings. At this studied ratio, it was shown that the formulation containing only APP and CaCO3 without borate does not provide a good fire protective performance. It leads to an extremely high expansion and soft char. The combination of APP and boric acid leads to a good fire protection but the char eventually falls off the plate. The addition of CaCO3 in this formulation (APPBA+CaCO3) improves a fire protective performance and promotes a good char adhesion and/or cohesion that allows keeping the intumescent structure on the steel plate. The opposite results were obtained when the formulation contains APP and zinc borate, it shows much lower fire protection than those containing boric acid. The addition of CaCO3 in this formulation (APPZB+ CaCO3) shows no positive impact on fire performance.

In this work, the contributions of CaCO3 on fire protective properties of intumescence coatings were highlighted in the formulation containing APP/BA but not for the case of APP/ZB.

To go further in the investigations, it is of interest to investigate its mechanisms of action, how it improves the fire protective performance of intumescent coatings. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Mode of action of CaCO3 in the fire protection of intumescent coatings

The furnace tests allow assessing the fire protective properties, expansion, char aspects and mechanical property of char (at room temperature after the test) and observing what is happening during the fire test, but they do not give detailed information on the effects of the additives, thermal degradation, possible interactions and rheological properties (i.e. viscosity).

In order to understand why CaCO3 works well when combined with BA/APP but not with ZB/APP, the reactivity between the additives was first investigated. The chemical interactions in binary systems containing APP with BA, ZB or CaCO3 were reported in the literature, respectively by M. Jimenez et al. [START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF], F. Samyn et al. [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF] and S. Deodhar et al. [START_REF] Deodhar | Calcium carbonate and ammonium polyphosphate-based flame retardant composition for polypropylene[END_REF] and their results were summarized in details in chapter I. In this manuscript, the work consequently focuses on the ternary systems: APP/borate/CaCO3 (the ratio between the additives is the same as in the IF(BA) coating, i.e. 23.6/69.5/6.9 % w/w). Secondly, the physical properties (i.e. viscosity and expansion) of the five formulations were measured. The results are discussed in the following part.

Reactivity of CaCO3 with APP and borates under pyrolysis condition

To study the reactivity between the three additives, the same methodologies as in 3.2.1.1 were used. TG analyses were first performed in order to predict the interaction between the additives. Heat treatments were then carried out on the mixtures of the additives. The collected residues were then characterized by XRD and solid state NMR. All experiments were performed under pyrolytic condition (i.e. under nitrogen). Note that this study was done outside the complex intumescent formulation, which allows elucidating the authentic reactions between them. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

4.1.2.1.1 APP/BA/CaCO3
Figure 62 presents the experimental TG curve of the mixture of the three components, calculated one and difference weight loss curve.

The TG curve of the mixture APP/BA/CaCO3 (black line) exhibits three steps of decomposition. The first and second steps are overlapping between 90 ⁰C and 200 ⁰C corresponding to 30 % weight loss. The third step is between 200 ⁰C and 395 ⁰C leading to a weight loss of 6 %. There is a progressive weight loss after 400 ⁰C.

According to the difference weight loss curve, a thermal destabilization can be observed from 100 ⁰C up to 600 ⁰C and then a thermal stabilization from 600 ⁰C up to 800 ⁰C. The char residue obtained experimentally is about 11 wt. % higher than expected. These results

consequently indicate that there are potential interactions between APP, BA and CaCO3. The reaction between APP and BA and reaction between APP and CaCO3 were reported to occur (refer to the literature [START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF][START_REF] Deodhar | Calcium carbonate and ammonium polyphosphate-based flame retardant composition for polypropylene[END_REF] and see chapter I). Based on this information, the assumption can be made that one part of APP can react with BA and another can react with CaCO3. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

To go further in the investigations, the mixture of APP/BA/CaCO3 was heat treated. Three characteristic temperatures including 280 ⁰C, 550 ⁰C and 800 ⁰C were performed: i) 280 ⁰C: after the massive weight loss and during the destabilization of the systems ii) 550 ⁰C: after the total degradation (the beginning of stabilization of the systems)

iii) 800 ⁰C: high thermal stabilization of the system (+11 wt. % refers to different wt. loss)

The appearance and weight of the residues after heat treatments (HT) are presented in Table 15. At 280 ⁰C, 550 ⁰C and 800 ⁰C, the residues are white powder. The aspects of the residues do not change much versus the HT temperatures. The XRD analyses were carried out on the samples and XRD diffractograms are presented in Figure 63. The diffractograms at 280 ⁰C and 550 ⁰C show identical results. Evidently, APP totally degrades after 280 ⁰C. CaCO3, BPO4 and B2O3 are identified. This result highlights the reactivity between APP and BA, which leads to the formation of BPO4, as previously described. The reaction between APP and CaCO3, which was reported to occur at the temperature about 300 ⁰C leading to the formation of calcium metaphosphate [START_REF] Deodhar | Calcium carbonate and ammonium polyphosphate-based flame retardant composition for polypropylene[END_REF], did not occur in this ternary mixture. This could be related to their kinetics of the reaction [190,191]. Obviously, it can be mentioned that CaCO3 neither degrades nor reacts up to 550 ⁰C. These results are in good agreement with the results of the complex formulation (i.e. IF(BA)) describing in 3.2.1.1. Moreover, it makes sense to get B2O3 since it results from the degradation of BA, which is in excess comparing to other additives. At PhD Thesis Nittaya HANSUPO, Univ. Lille 1 (CaBPO5) [START_REF] Baykal | X-ray powder diffraction and IR study of calcium borophosphate[END_REF]192,193] is detected, this product can be formed by the reaction between BPO4

and CaCO3 as described in chapter I. However, BPO4 is still present in the char residue at 800 ⁰C;

it makes sense since the amount of the APP and BA (precursors of the formation of BPO4) is much higher compared to CaCO3.

Figure 63 XRD diffractograms of APPBACa residues versus temperatures

To confirm these results, 31 P NMR analyses of APP/BA/CaCO3 residues heat treated at 280 ⁰C, 550 ⁰C and 800 ⁰C are performed (Figure 64). A sharp signal at -30 ppm attributed to the characteristic peak of BPO4 [START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF]165] is clearly observed from 280 ⁰C up to 800 ⁰C. These results are consistent with the results obtained by XRD. At 800 ⁰C, three additional peaks appear at 1. ,when X= Ca,Sr,Ba…) [192]. This kind of borophosphate possesses Q 2 phosphate structure (Figure 65), its chemical shift is thus different to the well-known PhD Thesis Nittaya HANSUPO, Univ. Lille 1 borophosphate (i.e. crystalline BPO4) and it swops to appear in the higher chemical shifts. This phenomenon may also involve the deshielding effect of phosphorus nucleus, in which the electron density around P nucleus decreases staggering its chemical shift to a higher ppm. This phenomenon may be occurred when P is substituted by a smaller atomic radius (e.g. boron) in the crosslinking network or it can be mentioned as the effect of the second coordination sphere of B in phosphate structures [194,195].

Conclusion

In this part, the mechanisms of interaction between the intumescent additives including APP, BA and CaCO3 (APP/BA/CaCO3 = 23.6/69.5/6.9 % w/w) were investigated. Based on the results obtained together with the literature data [START_REF] Deodhar | Calcium carbonate and ammonium polyphosphate-based flame retardant composition for polypropylene[END_REF], their mechanisms of interactions can be PhD Thesis Nittaya HANSUPO, Univ. Lille 1

proposed. It is shown that BA first degrades in the temperature range of 100 ⁰C -200 ⁰C, APP then degrades (T < 280 ⁰C). The degradation products of APP can react with the degradation products of BA (B2O3) to yield borophosphate (BPO4). BPO4 can be identified from 280 ⁰C up to 800 ⁰C. B2O3 was also found in the residues due to the excess of BA in the mixture.

The reaction between the degradation products of APP with CaCO3 due to its acidic-basic nature yielding calcium metaphosphate (Ca(PO3)2), which was described in the literature, did not occur in this ternary mixture. Instead, calcium borophosphate (CaBPO5) was identified in the char residue after the heat treatment at 800 ⁰C. This evidences the reaction between boron, The samples were heat treated at 280 ⁰C, 550 ⁰C and 800 ⁰C in a similar way as before.

iv) 280 ⁰C: beginning stage of the degradation v) 550 ⁰C: after the total degradation (destabilization of the system) vi) 800 ⁰C: high thermal stabilization of the system (+11 wt. % refers to different wt. loss) PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Residues (Table 16) do not significantly change depending on the heat treatment temperatures. It remains as a white powder for three heat treatment temperatures. At 550 ⁰C, the formation of BPO4 and of zinc orthophosphate (α-Zn3(PO4)2) are identified.

The formation of zinc boron oxide (ZnB4O7) is also found at this temperature. While CaCO3 is still present in the residue, it can be mentioned that the degradation product of APP does not react with CaCO3, being opposite to what was observed in the case of the APP/CaCO3 mixture [START_REF] Deodhar | Calcium carbonate and ammonium polyphosphate-based flame retardant composition for polypropylene[END_REF]. This event is similar in both systems (APP/BA/CaCO3 and APP/ZB/CaCO3); there is no reaction between CaCO3 and borates or phosphates up to 550 ⁰C.

BPO4 is not detected at 800 ⁰C whereas α-Zn3(PO4)2 and ZnB4O7 are still present in the residue. Additionally, the XRD pattern of α-Zn2P2O7 and α-CaZn2(PO4)2 are detected. When looking precisely on the XRD diffractograms, there is no evidence of the formation of CaBPO5, which was found in APP/BA/CaCO3 mixture. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 At 550 ⁰C, two sharp signals appear at -30 ppm and 3.9 ppm, which are assigned to the characteristic signal of BPO4 and of α-Zn3(PO4)2) [165]. There is a huge evolution of phosphorus species between 550 ⁰C and 800 ⁰C. At 800 ⁰C, the signal of BPO4 at -30 ppm disappears. The results obtained by NMR are in good agreement with XRD results. The disappearance of BPO4 at high temperature in similar system was suggested by F. Samyn [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF]. It was proposed that Zn3(PO4)2 reacts with BPO4 to form zinc pyrophosphate (Zn2P2O7) and B2O3 as described in the eq.

42.

PhD Thesis Nittaya HANSUPO, Univ. Lille 1 2Zn3(PO4)2 + 2BPO4 → B2O3 + 3Zn2P2O7 (eq. 42)

The signal of α-Zn3(PO4)2 can still be observed at 800 ⁰C. In addition to this, other sharp signals are observed at 9.9, 2.2, -1.3, -9.3, -14.8, -15.8, -18.8, -21 ppm. Sharp peaks suggest a high crystallinity of the formed products. The triple signals at -15.8, -18.8 and -21 ppm can be attributed to the characteristic signal of α-Zn2P2O7 [START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF]. Additional peaks at 9.9 and 2.2 ppm correspond to the characteristic signals of calcium zinc orthophosphate (α-CaZn2(PO4)2) [142,166,197]. These are consistent with XRD results. Interestingly, the characteristic peak of CaBPO5 at -9.3 ppm can also be observed but the peak intensity is extremely low (it is almost invisible) and this specie is not detected in XRD pattern.

The peaks at -1.3 and -14.8 ppm can be attributed to Q 0 phosphate structure (orthophosphate) and Q 1 phosphate structure (pyrophosphate) respectively. It is very interesting that the presence of zinc borate can change phosphorus species to many crystalline phases compared to the system containing BA. probably starts to degrade. At 550 ⁰C, the formation of BPO4 is also observed (a sharp signal at -3.8 ppm). At 800 ⁰C, the characteristic signal of BPO4 still appears with very low intensity but the presence of BPO4 at this temperature was not identified in neither XRD nor 31 P NMR. This can be due to the higher sensitivity of 11 B NMR experiment comparing to other techniques.

BO3 unit of zinc borate lying between 10 and 16 ppm (at ambient temperature) changes to BO3 in a different conformation at 550 ⁰C to 800 ⁰C, broad and poorly defined line shape suggests the presence of amorphous species. This could be reasonably attributed to the dehydration of ZB leading to the formation of 2ZnO.3B2O3. At 550 ⁰C and 800 ⁰C, there is a sharp signal of BO4 unit appearing at 1 ppm, this signal is supposed to belong to BO4 unit in ZnB4O7 which was identified by XRD. It is consistent with the network structure of ZnB4O7 reported, it is exclusively composed of tetrahedral boron units (BO4) [198,199].

Conclusion

In this part, the mechanisms of interaction between the intumescent additives including APP, ZB and CaCO3 (APP/ZB/CaCO3 = 23.6/69.5/6.9 % w/w) were investigated. As a result, borophosphate is formed similar as the system containing BA but its quantity decreases at high temperature (small quantity is left detecting in In this part, the mechanisms of interaction of the ternary mixture of additives (i.e.

APP/BA/CaCO3, APP/ZB/CaCO3) were studied under pyrolytic condition. The results showed that the mechanisms of interactions are different between the systems containing BA or ZB.

For APP/BA/CaCO3 mixture, it was shown that BPO4 is formed at temperature below 280 ⁰C. B2O3 (degradation product of boric acid) is present in all heat-treatment temperatures. While

CaCO3 does not react with any species up to 550 ⁰C, the reactivity of CaCO3 leading to the formation of CaBPO5 was remarked between 550 ⁰C and 800 ⁰C. The formation of CaBPO5 is supposed to occur by the reaction between CaCO3 and BPO4 or between CaCO3, B2O3 and P2O5.

These reactions, especially the second possibility are supposed to be highly beneficial to the intumescent phenomenon since phosphorous species can be more stabilized in the condensed phase.

For APP/ZB/CaCO3 mixture, the formation of BPO4 was found at higher temperature (between 280 ⁰C and 550 ⁰C) and it then decreases at 800 ⁰C. Other species, especially zinc and calcium based compounds (i.e. Zn3(PO4)2, Zn2P2O7, ZnB4O7, CaZn2(PO4)2, CaBPO5) were found in this system. Interestingly, in this system, calcium based compound tends to react with both Zn-P compounds and B-P based compounds. However, it is more favorable to react with Zn-P rather than B-P based compounds.

As previously described, not only chemical but also physical properties are also important parameters to understand the mechanisms of action of intumescent system. The fire test results present in 4.1.1 showed the huge difference in char aspect and char expansion between the five formulations: i) promising expansion (IF-APPBA and IF-APPBACa), ii) high expansion (IF-APPCa), and iii) very low expansion (IF-APPZB and IF-APPZBCa). Relating to the fact that the viscosity is a key parameter governing the char aspect and char expansion. This arises an interest in investigating the viscosity of the five formulations. Moreover, the expansion of the five studied formulations cannot be compared after the furnace test due to a detachment of some formulations. Thus, the measurements of expansion using a lab scale test (i.e. Rheometer) were also taken into account. The results will be discussed in the following part. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Complex viscosity and expansion

The aim of this part is to investigate the complex viscosity and expansion of the five studied formulations to be able to understand their behaviors in a fire, which were reported in the previous part (4.1.1).

Figure 71 shows the complex viscosity, relative expansion and TG curve of IF-APPCa measured as a function of temperature. The viscosity is steady up to 300 ⁰C. It is consistent with TG curve of this formulation. This formulation shows no decomposition up to 300 ⁰C. Afterwards, the viscosity decreases drastically to the lowest value of about 2 x 10 2 Pa.s (340 ⁰C), this is called the critical point, which corresponds to the decomposition of epoxy matrix [200]. Then, the viscosity increases slightly until 400 ⁰C before a drastic increase up to the end of the test, that can be attributed to a carbonization process of the intumescent char [START_REF] Duquesnea | A comparative study of the mechanism of action of ammonium polyphosphate and expandable graphite in polyurethane[END_REF]. The viscous phase disappears and a highly condensed char structure is produced. It was stated [127] that a low viscosity of melted coating results in the formation of many open holes in charred layer deteriorating fire protective performance of the charred layer. This is consistent with that occurred in this case. It can be mentioned that the formulation containing only APP and CaCO3 leads to a very low viscosity at the critical point (degradation of the epoxy resin), which causes a huge expansion, which was observed during the furnace test.

When looking at the relative expansion, it has no expansion up to 300 ⁰C, which is well consistent with TG curve (no degradation before 300 ⁰C). An expansion occurs when the viscosity decreases promptly (at about 305 ⁰C). Then, the expansion drops to a minus value (-80 % of expansion). At the end of the test, the char aspect was observed, it was found (Table 17) that IF-APPCa coating has a huge expansion and the lower plate is overflowing with the char. This is well consistent with what observed during the furnace test (very high expansion). When taking out the upper plate, it was remarked that char was very fragile and was totally ruined. The minus value was recorded because all material blew up and no char remained in the lower plate. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 To do so, the viscosity and expansion of IF-APPZB and IF-APPZBCa were also measured.

The similar results were obtained. The addition of CaCO3 has no significant effect on the viscosity and expansion of the coatings (up to 500 ⁰C). The results are presented in Appendix IV.

The decarbonation of CaCO3 as a blowing agent is not effective in the case of IF-APPBACa and IF-APPZBCa since the decarbonation occurs outside the region of the significant modification of the viscosity (300 ⁰C -400 ⁰C). Since CaCO3 takes place in the reaction between 550 ⁰C and 800 ⁰C as shown in the previous part. This is opposite to the case of IF-APPCa, in which the decarbonation occurs at lower temperature (≈ 300 ⁰C) by the interaction between APP and CaCO3, that enhances the expansion of intumescent coating. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 No beneficial effect of CaCO3 in the mixture of APP/ZB is supposed to be due to the additive ratio, high amount of zinc borate exhibits the expansion and changes the properties of the molten matrix (e.g. too high viscosity). This may be the reason why the incorporation of CaCO3 into APP+ZB does not improve/change any intumescent properties. However, the benefits of CaCO3 in the fire protection of epoxy based intumescent coatings were highlighted (i.e.

improvement of fire protection and adhesion, stabilization of B and P in the condensed phase).

Consequently, CaCO3 plays an important role in the condensed phase by reacting with other components to form the thermally stable compounds (i.e. CaZn2(PO4)2, CaBPO5) stabilizing the PhD Thesis Nittaya HANSUPO, Univ. Lille 1 other components of the formulation but the decarbonation of CaCO3 in the case of IF-APPBACa and IF-APPZBCa does not benefit the expansion of the intumescent char. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Conclusion

In this part, the effects of CaCO3 on fire protective properties of intumescent coatings and its mode of action were investigated. The graphic conclusion of this part is shown in Figure 73.

Figure 73 Graphic conclusion of the study of the effect of CaCO3 on intumescent coatings

The addition of CaCO3 into the formulation containing APP and borate was proven to be beneficial for the epoxy based intumescent coatings enhancing the fire protective properties and char adhesion/cohesion of intumescent coatings (when the additive ratio between APP and borate is optimized). CaCO3 or its degradation products react with other components of the formulation (e.g. P, B, Zn based compounds), that forms inorganic species which are thermally stable enhancing the stabilization of the char residues. The combination of CaCO3 and high amount of APP was not recommended since this combination exhibits a too low viscosity and extremely high expansion, which lead to a detachment of charred layer deteriorating fire protective properties of intumescent coatings. Based on these results, the effect of other carbonates on fire protection of intumescent coatings is also of interest. To follow this purpose, IF-APPBACa formulation was chosen to study the effects of carbonates in the next part since it exhibits promising results. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Influence of different carbonates on fire protection

In the previous part, it was demonstrated that the addition of CaCO3 in the formulation containing APP and BA improves the fire protective performance and adhesion/cohesion of intumescent char. For this reason, other carbonates as ingredient of intumescent formulation were examined.

To study the effects of different carbonates, the IF-APPBACa formulation was chosen. Four IF-APPBAMgCO3 char is hard and compact. A grey char was formed on the surface. The char is quite homogeneous, holes between the char can also be observed but they are smaller than those of IF-APPBACa. For IF-APPBAZnCO3, the char is brittle and crumbly. Then, there are big boles between the char structure. For IF-APPBANa2CO3, the char is compact and dense with a medium size pores. Glassy and hard char is found on the surface. For IF-APPBAK2CO3, the char is fragile, it is not possible to cut at the middle since it splits and breaks into small pieces.

Conclusion

In this part, the effects of five carbonates on fire protective properties, char aspects and char expansion were investigated. It was shown that the incorporation of carbonates into epoxy based intumescent coatings improves the fire protective performances compared to the reference without carbonates, except the formulation containing zinc carbonate which possesses a bad adhesion leading to a shorter time to reach the failure temperature. Among all, the addition of calcium or magnesium carbonates exhibits the best results. For the char aspects, the formulation containing magnesium carbonate forms a dense and homogeneous char without big holes between the charred layers while the one containing calcium carbonate has similar char aspect but some big holes are produced. Char aspects of zinc, potassium and sodium carbonates are different from the two mentioned above. To try to understand the different fire protective behaviors obtained, the char residues collected after the furnace test were characterized and the results will be discussed in the next part. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Chemical composition analyses

This part aims at analyzing the chemical compositions formed in the condensed phase influenced by the different carbonates. It is expected to understand the mechanisms of protection, in particular in the condensed phase. The char residues of the five formulations collected after 18 minutes of the tests were characterized using XRD and solid state NMR. In addition to this, the char residues of IF-APPBACa and IF-APPBAMgCO3 collected after 30 minutes were also analyzed since these two latter formulations do not have a detachment problem.

XRD is used to characterize the presence of crystalline phases in the char residues. Figure 75 To complete the results obtained by XRD, 31 P and 11 B solid state NMRs were used to characterize precisely the effects of carbonates on the modifications of phosphorous and boron structures/species in the condensed phase.

Figure 77 shows the 31 P NMR spectra of the five formulations. A sharp peak at -30 ppm, which is a characteristic peak of borophosphate (BPO4) [START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF]165], is found for all formulations.

Regarding the peak height, BPO4 is the main product compared to the other chemical species. It means that the formation of BPO4 by the reaction between the degradation products of APP and of BA takes place predominantly in all cases.

For IF-APPBACa, in addition to a characteristic peak of BPO4, there are signals appearing at -7.5, -7.9, -9.3 and -10.3 ppm (very low intensity). In this range of chemical shift, these signals can be attributed to Q 1 phosphate structure (or pyrophosphate). Calcium pyrophosphate (Ca2P2O7), which possesses quadruple peaks can be suspected. If it is formed, it is supposed to be poorly crystalline (not identified in XRD). Additionally, a broad signal (very low density) centered at 1 ppm is also detected; it is assigned to Q 0 structure in phosphate [161,178].

For IF-APPBAMgCO3, four additional peaks are detected at 0, -13.2, -18.6 and -19.5 ppm.

The signal at 0 ppm can be attributed to the signal of Q 0 phosphate (e.g. phosphoric acid (H3PO4) [START_REF] Jimenez | Intumescent fire protective coating: Toward a better understanding of their mechanism of action[END_REF]161]). The signals at -13.2 and -19.5 ppm are assigned to α-Mg2P2O7 while the signal at -18.6 is assigned to β-Mg2P2O7 [162,207]. Nevertheless, the species identified in 31 P NMR (i.e. α-Mg2P2O7, β-Mg2P2O7) are not detected in XRD diffractograms, it could be due to the poor crystallinity or low amount of these species. Regarding the literature [184], it was mentioned that crystalline Mg2P2O7 has a typical line width at half maximum (LW1/2) of about 243 Hz (1.5 ppm) , whereas their amorphous counterparts normally exhibit the LW1/2 about ten times greater. In 31 P NMR of IF-APPBAMgCO3, the LW1/2 of the signal at - 13.2, -18.6 and -19.5 ppm are of 112, 194 and 154 Hz respectively. This evidences the high crystallinity of the magnesium phosphate species formed. Therefore, its low quantity is the reason why they were not identified in XRD pattern. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

For IF-APPBAZnCO3, apart from BPO4 there is an additional sharp peak at 3.9 ppm, which is assigned to zinc orthophosphate (α-Zn3(PO4)2) [START_REF] Sut | Interactions in multicomponent flame-retardant polymers: Solid-state NMR identifying the chemistry behind it[END_REF][START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF]. Triple peaks at -16.4, -19 and -21.2 also appear with very low intensity (zoom in the red dotted line), they are assigned to zinc pyrophosphate (α-Zn2P2O7) [START_REF] Sut | Interactions in multicomponent flame-retardant polymers: Solid-state NMR identifying the chemistry behind it[END_REF][START_REF] Samyn | Effect of zinc borate on the thermal degradation of ammonium polyphosphate[END_REF].

IF-APPBANa2CO3 and IF-APPBAK2CO3 exhibit different results from the others. There is no crystalline species formed, except BPO4. In the opposite, there is a broad signal lying between -10 and -25 ppm. The band is centered at about -20 ppm representing the Q 2 tetrahedral sites of metaphosphate chains. This broad signal can be assigned to amorphous forms of phosphates.

Regarding the raw material of the formulations, the amorphous phosphates could be XPO3 [208,209] or amorphous phosphate containing X2O (when X = Na or K). residues, the signal of BO4 is also observed but the chemical shift is different (appear at 0 ppm).

A broad peak indicates the low crystallinity of this BO4 unit.

For all formulations, additional signal lying between 20 and 5 ppm (broad signal) is observed: it is attributed to trigonal boron (BO3) units. XRD results (Figure 75) suggested the presence of B2O3, which should be observed in 11 B NMR spectra of the samples. When compared the 11 B NMR spectra of the five formulations to the spectrum of B2O3 (green line in Figure 79), they are quite different to the one of B2O3. An assumption can be made that there is at least another BO3 unit apart from the one of B2O3 superimposing in this signal.

Conclusion

The effects of carbonates on the fire protective properties and on the modifications of chemical species formed in the condensed phase were studied. The graphic conclusion is shown in Figure 81. The results showed that the addition of MgCO3 in the epoxy based intumescent coating containing APP and BA shows the good fire protective properties as well as that containing

CaCO3. Nevertheless, the char aspects and expansion of these two formulations are a bit different.

The formulation with CaCO3 exhibits more expansion with the presence of big holes between charred layers whereas the addition of MgCO3 produces less expansion (half of what obtained in the case of CaCO3) with more dense and compact char structure. ZnCO3 would provide a better fire protection if the char adhesion would have been improved. Na2CO3 and K2CO3 improve the fire protective properties when compared to the reference formulation (APP+BA). The homogeneous and dense intumescent char performed when incorporated CaCO3 and MgCO3 are probably responsible for a good fire protection obtained. In addition to these, the incorporation of these two carbonates is supposed to stabilize more phosphorus in the condensed phase compared to the others; these could be the reason of the good fire protective performances obtained.

Figure 81 Graphic conclusion of the study of the effects of carbonates on intumescent behaviors

PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Conclusion

Chapter IV deals with the investigation of the effects of carbonates. The results showed that the addition of low amount of CaCO3 into epoxy based intumescent coating, which contains phosphate and borate (e.g. APP+BA), improves the fire protective properties and adhesion/cohesion of the intumescent coating. These benefits are due to the reactivity of CaCO3 19. The char aspects and relative % of expansion of four formulations are shown in Table 20.

For IFZnB, char possesses three layers: i) top layer -char is yellow and fibrous, which is quite brittle, ii) medium layer -char is grey with big size cells, they are quite homogeneous and iii) bottom layer -char is black, dense, compact and hard.

For IFZnS and IFZnO, both chars are quite similar. Three layers of char are observed. The yellow fibrous char on top layer, which is similar to IFZnB is observed. Char in medium layer builds like a multi-sheet. In the black part, there is a black sheet on the top, which is very hard and a crumbly char is found underneath.

For IFZnSO4, expanded char can also be distinguished into three layers. The yellow fibrous char is still observed on the top. Differently, many small holes appear on the surface. It could be due to the dehydration of zinc sulfate occurring during the intumescent process. The grey layer in the middle possesses the big holes like IFZnB. Black char on the bottom is different from others (less hard than LF1-ZnO and LF1-ZnS, it is not layered but it is homogenous and crumbly). Additionally, another prospect of interest is the elucidation of the mechanisms of action of MgCO3 which also exhibits promising results in fire protection. The formulation containing

MgCO3 provides a similar level of fire protection to CaCO3 with lower expansion (-40 % of expansion). This behavior is very interesting for the fire protection against more aggressive fire such as jet fire. The incorporation of MgCO3 in intumescent coating using against jet fire could be a subject of interest for future work. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

List of figures

  Preface ............................................................................................................................................... v 1 PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Figure 2

 2 Figure 2 Intumescent material (before and after heating)

  used curing agents for epoxy resins are amines, amine derivatives, anhydrides, phenols, alcohols, and thiols. The polymerization process, referred as crosslinking or curing of the resin, is exothermic and irreversible. An infusible three-dimensional network is

H3BO3𝑇

  Si-C-O, Si-C-N-O, Si-B-C-N...)

Figure 8

 8 Figure 8 Evolution of heat conductivity as a function of temperature for intumescent polyurethane systems (PU30%APP and PU28%APP2%nano MgO) [115]

Figure 9

 9 Figure 9 Schematic view of an intumescent coating with different zones (a) and intumescent development as a function of the conversion degree α (b)[START_REF] Alongi | Intumescence: Tradition versus novelty. A comprehensive review[END_REF]

Figure 10 (

 10 Figure 10 (a) Relative expansion (b) complex viscosity [81] of intumescent epoxy-based coatings (A: epoxy resin, B: epoxy resin+APP, C: epoxy resin+H3BO3, D: epoxy resin+APP+H3BO3)

  step, the influence of various carbonates (including magnesium, zinc, sodium and potassium carbonates) on the fire protective performances of the intumescent coatings was also investigated. The formulations were made by substituting CaCO3 in IF-APPBACa by another carbonate compound, the substitution is made by maintaining the weight ratio. The formulations were named IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBANa2CO3, and IF-APPBAK2CO3 respectively. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Figure 13

 13 Figure 13 Photos of 100 x 100 x 3 mm 3 steel plate coated with 4 mm of intumescent coating

Figure 14

 14 Figure 14 Sample of 25 mm of diameter and 1 mm of thickness for Rheometer test

  3.2) correspond to a disk of 25 mm of diameter. A mixture of part A and part B in the previously defined ratio was put into two Teflon mold having a diameter of 25 mm. A mica sensor was then placed between two disks and the coatings were cured at ambient temperature for at least 48 hours. This ensures a good contact between the sample and the sensor during the measurement. The thickness of the sample was adjusted to have enough material to give the heat impulsion during the test and to avoid an overflow of the char formed in the sample holder. The setup of the sample in the specific device to perform measurements at high temperature is presented in Figure15.

Figure 15

 15 Figure 15 Sample installation for thermal conductivity measurement

  Figure 16 Small-scale furnace test

Figure 17

 17 Figure 17 Schematic representation of heat-treatment

  xi is the content of component I in the formulation  Mexp (T): TG curve of the intumescent coating  Mcal (T): calculated TG curve computed by linear combination between the values of weight given by TG curves of the component i, ii,…, n: Mcal (T) = ∑ 𝑥𝑖 𝑀𝑖(𝑇) 𝑛 𝑖  Weight difference curve: ∆(T) = Mexp (T) -Mcal (T)

Figure 19

 19 Figure 19 Rheometer in a parallel plate configuration

Figure 20

 20 Figure 20 Measurement of viscosity 2.2.4.2 Expansion measurements

Figure 21

 21 Figure 21 Protocol to measure mechanical resistance of char

Figure 22

 22 Figure 22 Example of simulated 11 B NMR spectrum (18.8 T) using the software DMFIT (i.e. neat IF(ZB)wt coating) (a) (b)

  recognized in the literature and described in chapter I. Boric acid and zinc borate are the most commonly used borates. Borax and APB were also claimed to be used in some intumescent formulations. However, comprehensive work detailing the exact roles of borates in intumescent coatings has never been done so far. This chapter deals with the investigation of the role of borates in epoxy based intumescent coating used as a protection against hydrocarbon fire. It aims at systematically examining the effects of different borates including boric acid (BA), zinc borate (ZB), borax and ammonium pentaborate (APB) on fire protective properties of complex intumescent formulations. Other goals are to characterize the evolution of chemical species formed in the condensed phase under different conditions (under pyrolytic condition at defined temperature or when submitted to a fire test) and to examine the thermo-physical properties of the intumescent char. It is then expected to determine the mode of action of borates in intumescent formulations. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 3.1 Influence of borates on the fire protection In this section, intumescent coatings containing different borates namely BA, ZB, borax and APB (respectively called IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m) with constant P/B molar ratio (1/3.

Figure 23

 23 Figure 23 Time -temperature curves of IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m

  IF(BA) and IF(APB)m have similar chars which differ greatly from the one of IF(ZB)m. At the point of collection, only a small part of char still sticks to the steel plate whereas the majority of the char falls off. For IF(BA), char falls two times: the biggest part (1) first falls at 14 minutes and another part[START_REF]World trade center collapse footage[END_REF], which is about half of the steel plate, falls off at the end of the test when the sample was removed. Both IF(BA) and IF(APB)m chars are light and brittle, and some shrinkage has occurred. The observation of the fallen part of the char indicates that during the test the decomposition gasses should accumulate to form big holes in the middle of the structure resulting in their detachments. For IF(BA) and IF(APB)m, the expansion has not been measured due to a detachment of char residues. PhD Thesis Nittaya HANSUPO, Univ. Lille 1Table 10 Char aspects and relative expansions of IF(ZB)m, IF(borax)m, IF(BA) and IF(APB)mformulations, the formulation containing zinc borate leads to a good adhesion and good char characteristics resulting in the best fire resistance. The formulations containing boric acid or ammonium pentaborate exhibit similar fire protective behaviors and char aspects. A different result is obtained when borax is incorporated; a low expansion is obtained while fire protective performance is intermediate between the formulation containing zinc borate and these containing boric acid or ammonium pentaborate. To try to understand the fire protective behaviors obtained when different borates were incorporated, further investigations have to be made. It is of interest to investigate the chemical species formed in the condensed phase that relates to its mechanism of action/protection. The next part thus aims at understanding the fire protective behavior and char aspects obtained when the different borates were incorporated. For all formulations, the tests were stopped at 30 minutes and the char residues were collected and characterized. Elemental analysis, XRD, solid state13 C, 31 P and 11 B NMR have been used as characterization tools. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 3.1.2 Characterization of the char residues of complex formulations collected after a furnace test First, elemental analysis has been carried out to determine the phosphorus (P), boron (B) and carbon (C) contents remaining in the char residues. The quantities of P, B and C in the nondegraded coatings were also calculated from the composition of the formulation. P/C and B/C ratios of the non-degraded coatings and char residues of IF(BA), IF(ZB)m, IF(APB)m and IF(borax)m are shown in Figure 24. The P/C and B/C ratios of the non-degraded coatings of four formulations are the same (P/C = 0.07 and B/C = 0.08) since these formulations were formulated by keeping constant the molar ratio of the additives. P/C ratios of the char residues for all formulations increase when compared to these of the non-degraded coatings. This means that the stabilization of the phosphorous species is favored compared to the carbonaceous species. When looking at the B/C ratio, the similar tendency was obtained suggesting the stabilization of the boron species as well. Between the four formulations, the carbon species in the formulation containing zinc borate are more stabilized compared to the others. The formulations containing boric acid or APB contain less carbon content than the previous one and the formulation containing borax has the value between them.

Figure 24 P

 24 Figure 24 P/C ratio and B/C ratio in non-degraded coatings (by calculation) vs. in char residues (by elemental analysis)Based on these results, it can be mentioned that the addition of zinc borate stabilizes the carbonaceous char (increasing the remaining carbon in the residue) when compared to the other borates.

Figure 25 XRD

 25 Figure 25 XRD diffractograms of IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m char residues (30 minutes) and of H3BO3 and B2O3

Figure 27 Q

 27 Figure27Q structure of phosphate: Q 0 isolated units (ortho-P), Q 1 end units (pyro-P), Q 2 middle units (meta-P) and Q 3 crosslinking units (ultra-P)

31 P

 31 NMR spectra of IF(borax)m char residue exhibits a broad signal lying between 10 and -30 ppm, which can be assigned to amorphous phosphates. In this range of 31 P chemical shift, these phosphate structures could be composed of Q 2 , Q 1 and Q 0 phosphate structures. Additional peaks are observed at 10.2 and 11.4 ppm, these sharp peaks suggest the formation of crystalline species. They can be attributed to (RO)2PO-H, i.e. phosphonate structures[168, 169] and could be formed through the reduction of phosphate (+V) in phosphonates (+III). PhD Thesis Nittaya HANSUPO, Univ. Lille 1 Ca3(PO4)2 which is suggested by XRD exhibits a signal lying between 5 and -2 ppm [170]. This signal does not appear in the 31 P NMR spectrum of IF(BA), IF(APB)m and IF(Borax)m. Its absence may be explained by its low quantity in the char sample (there is only 1.91 wt. % of CaCO3 in the initial formulation).

Figure 28 31 P

 2831 Figure 28 31 P NMR spectra (9.4T) of the IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m char residues

1 Figure 29 11 B

 12911 Figure 29 11 B NMR spectra (18.8T) of the IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m char residues and of B2O3

  . The decompositions were thus examined under pyrolysis conditions (i.e. under nitrogen) by TGA. TG curves of IF(BA) and IF(ZB)wt coatings are presented in Figure 30. In the following part, the characterizations were made on the IF(ZB)wt formulation due to the practical reason since IF(ZB)m and IF(ZB)wt exhibit the similar results in fire protective properties and thermal degradation pathway (superimposed TGA curves).IF(BA) exhibits four successive degradation steps. The first step (between 90 ⁰C and 140 ⁰C) corresponds to a weight loss of about 6 % and the second one(between 140 ⁰C and 198 ⁰C) corresponds to a weight loss of 3 %. These two steps can be attributed to the dehydration of boric acid, which is one of the ingredients in IF(BA) coating. This attribution can be confirmed by a theoretical calculation. In IF(BA) formulation, there is 19.3 wt.% of boric acid which degrades in two steps between 100 ⁰C and 250 ⁰C leading to a total weight loss of 44 %[START_REF] Jimenez | Kinetic analysis of the thermal degradation of an epoxy-based intumescent coating[END_REF] 141]. This should lead to 8.5 % of total weight loss of the coating formulation. Theoretical and experimental results are thus well correlated (8.5 vs. 9 wt. %). The third step of degradation (between 198 ⁰C and 280 ⁰C) corresponds to a weight loss of about 8 % and the fourth one (main degradation step) leads to a total weight loss of 46 %. The third and fourth steps are assigned to the degradation of the epoxy resin and of the other components in the formulation. From 600 ⁰C, there is a slight weight loss of 2 % until 800 ⁰C. The residue at 800 ⁰C is about 35 wt. %. IF(ZB)wt degrades into two steps. The first one (between 200 ⁰C and 275 ⁰C) corresponds to 10 wt. %. The second one (between 275 ⁰C and 550 ⁰C) is the main degradation step corresponding to 48 wt. %. There is a slight weight loss of 2 % from 600 ⁰C similar to that occurring for IF(BA). The degradation pathway of IF(ZB)wt is different from the one of IF(BA). It has a slightly higher residual weight than IF(BA)(40 vs. 35 %); this difference could be due to the nature of PhD Thesis Nittaya HANSUPO, Univ. Lille 1 borates (i.e. residual weight at 800 ⁰C of zinc borate and of boric acid are 88 and 56 wt. % respectively).

Figure 30 TG

 30 Figure 30 TG curves of IF(BA) and of IF(ZB)wt Consequently, both IF(BA) and IF(ZB)wt decompose in multi-steps. The formulation containing zinc borate possesses higher char residue at high temperature and the decomposition pathways between the two formulations are different. To study the decomposition pathway and mechanism of reaction occurring in the condensed phase, the coatings were heat treated at different characteristic temperatures (Table11). Regarding the TG curves of the studied coatings,

Figure 31

 31 Figure 31 shows the diffractograms of IF(BA) coating at ambient temperature in comparison with the residues after heat-treatment at different characteristic temperatures. XRD pattern of the coating at ambient temperature shows the presence of ammonium polyphosphate (APP), boric acid, CaCO3 and TiO2. It is consistent with the composition of the coating. The signals of Si based compounds (from fumed silica, expanded silicate or silicate fibers) were also expected but they are not identified in XRD. It is probably due to their low crystallinity.

Figure 32 31 P 1 TCPPFigure 33

 3231133 Figure 32 31 P NMR (9.4T) of IF(BA) char residues versus temperatures and the zoom out of the spectra at 210 ⁰C and 250 ⁰C (in the blue dotted line)

  (BA) at ambient temperature exhibits BO3 and BO4 units. Their relative concentrations are equal to 92 % and 8 % for the BO3 and BO4 units respectively. These signals correspond to the characteristic line shape of boric acid (only one boron source in the formulation). The spectrum of boric acid at ambient temperature shows a second-order quadrupolar line shape, that is typical boron atom in a trigonal bonding configuration[180, 181],

  B( 31 P) D-HMQC experiment [182] to filter the 11 B signal which possesses the spatial proximity with P nucleus. This allows identifying the presence of B-O-P linkage (e.g. B-O-P in BPO4). The char residues of HT at 250 ⁰C and 280 ⁰C were measured by D-HMQC experiment. As a result (Figure 35), for char residue at 250 ⁰C, no signal in 11 B( 31 P) D-HMQC NMR spectrum is observed but the one at 280 ⁰C exhibits a signal at -3.8 ppm confirming the presence of B-O-P linking of BPO4 as expected. Consequently, the signal at -3.4 ppm which appears at the temperature of 210 ⁰C and 250 ⁰C, is assigned to BO4 unit in another conformation (not BPO4) and the formation of BPO4 at 280 ⁰C (sharp peak at -3.8 ppm) is moreover confirmed by 1D 11 B( 31 P) D-HMQC NMR.

Figure 35 1D

 35 Figure 35 1D 11 B( 31 P) D-HMQC NMR (B connected to P nucleus, 18.8T) vs. 1D 11B NMR signal of IF(BA) char residues at 250 ⁰C (left) and 280 ⁰C (right)The evolution of BO3, BO4 and BO4 (in BPO4) conformations (Figure36) can be estimated (semi-quantitative). It is observed that when the temperature increases from ambient temperature up to 280 ⁰C, the BO3 units of boric acid turn into BO3 units in different configurations (e.g. B2O3) and BPO4 (formed by the reaction between B2O3 and phosphate). In contrast, at high temperature the relative concentration of BO4 units obviously decreases when the relative concentration of BPO4 increases and the relative concentration of BO3 units remains constant. The formation of borophosphate occurs by the reaction of one mole of boron and one mole of phosphorous. The molar ratio of phosphorous to boron in IF(BA) is 1/3.3, boron is thus in excess. The presence of BO3 units at high temperature could thus be attributed to BO3 units of B2O3; this attribution is further supported by XRD results.

Figure 36

 36 Figure 36 Evolution of the relative concentration of boron species in IF(BA) versus temperatures

Figure 38 31 P

 3831 Figure 38 31 P NMR spectra (9.4 T) of IF(ZB)wt char residues versus temperatures

a

  BO3 band lying between 16 and 20 ppm and a broad BO4 signal lying between -2 and -6 ppm appear. Indeed, zinc borate starts to degrade at the temperature of 290 ⁰C. Under heat treatment condition, the samples were heat-treated at 280 ± 5 ⁰C for 2 hours, zinc borate could partially degrade or modify at this temperature. The characteristic peak of borophosphate at -3.8 ppm are observed from 380 ⁰C up to 550 ⁰C. These are in good agreement with the results obtained from XRD and 31 P NMR.

Figure 39 11 B

 3911 Figure 3911 B NMR spectra(18.8 T) of IF(ZB)wt char residues versus temperatures

Figure 41

 41 Figure 41 Time-temperature curves of IF(BA) and IF(ZB)wt pointing out the characterisric times a) IF(BA) formulation

Figure 42

 42 Figure 42 Photos of IF(BA) residual aspects collected after the furnace test (2 and 5 minutes)

Figure 44 31 P

 4431 Figure 44 31 P NMR spectra (9.4 T) of IF(BA) char residues versus times

Figure 45 11 B 1 Conclusion

 45111 Figure 45 11 B NMR spectra (18.8 T) of IF(BA) char residues versus times

Figure 47

 47 Figure 47 Photos of IF(ZB)wt residual aspects after the furnace test (2 and 5 minutes)

Figure 49 31 P

 4931 Figure 49 31 P NMR spectra (9.4 T) of IF(ZB)wt char residues versus times

Figure 50 11 B

 5011 Figure 50 11 B NMR spectra (18.8 T) of IF(ZB)wt char residues versus times

Figure 53

 53 Figure 53 Complex viscosity, relative expansion and TG curve of IF(BA)

Figure 54

 54 Figure 54 Complex viscosity, relative expansion and TG curve of IF(ZB)wt

Figure 55 shows

 55 Figure55shows the relative expansion (%) and expansion rate (%/s) of IF(BA) and IF(ZB)wt. Between 5 and 10 minutes, the two formulations exhibit similar behavior; their relative expansions increases about 100 %. Nevertheless, IF(BA) has a higher expansion compared to

Figure 55

 55 Figure 55 Relatvie expansion (%, left) and expansion rate (%/s, right) of IF(BA )and of IF(ZB)wt 3.2.2.2 Char morphology

Figure 56

 56 Figure 56 Char appearances of IF(BA) versus times captured by numeric camera

Figure 57 1 Figure 58 3

 57158 Figure 57 Char appearances of IF(ZB)wt versus times captured by numeric camera

4 . 1 . 1

 411 investigate the intrinsic effect of CaCO3, the formulation was simplified. It was done by adding CaCO3 into the formulation containing APP and borate since these two latter additives are the main components of the intumescent formulation as shown in chapter III and reviewed in chapter I: state of the art. The studied borates are either boric acid or zinc borate using the same considerations to what were argued in chapter III. Then, the mode of action of CaCO3 in presence of different borates (i.e. APPBACaCO3 and APPZBCaCO3) was investigated to explain the results obtained. Fire protective properties This part aims at investigating the effect of CaCO3 on fire protective properties of the intumescent coatings. Comparison between the performances of the five formulations evaluated using the small-scale furnace test (UL 1709) is made. These formulations are based on IF(BA) in terms of ratios between additives (see details in chapter II) but the number of components is reduced to a minimum to be able to evidence the potential interactions between the APP, BA or ZB and CaCO3. Three formulations are used as references. They contain two additives; i.e. APP with either borate or CaCO3. They are named IF-APPBA, IF-APPZB and IF-APPCa. The last two formulations called IF-APPBACa and IF-APPZBCa are the formulations of interest as they contain APP/borate/CaCO3. The formulation containing only borate and CaCO3 was not taken into account since its calculated difference weight loss curve based on TG data (mixture ratio refers to IF(BA)) shows no significant thermal stabilization or PhD Thesis Nittaya HANSUPO, Univ. Lille 1 destabilization indicating that the reaction between borates and CaCO3 does not occur up to 800 ⁰C. The details are shown in Appendix III. Time-temperature curves of IF-APPCa, IF-APPBA, IF-APPZB, IF-APPBACa and IF-APPZBCa are shown in Figure 61; it presents the evolution of temperature as a function of time at the backside of the coated steel plates. The failure temperature of 500 ⁰C is considered as the critical point as mentioned in chapter III.

Figure 61

 61 Figure 61 Time-temperature curves of IF-APPCa, IF-APPBA, IF-APPZB, IF-APPBACa and IF-APPZBCa

  % PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Figure 62

 62 Figure 62 Experimental, calculated TG curves and different weight loss of the mixture of APP/BA/CaCO3

Figure 64 Figure 65

 6465 Figure 64 31 P NMR spectra (9.4T) of APPBACa residues versus temperatures

Figure 66 11 B

 6611 Figure 66 11 B NMR spectra (18.8T) of APPBACa residues versus temperatures

  phosphorous and calcium based compounds. Two possible ways of formation of CaBPO5 can be suggested: i) CaCO3 reacts with BPO4 (formed in the early stage) releasing CO2 and ii) it may be occurred by the reaction between P2O5, B2O3 and CaCO3 yielding the same products as the first reaction (CaBPO5 and releasing CO2). P2O5 comes from the degradation of APP and it general sublimates in the temperature range of 550 ⁰C and 770 ⁰C[START_REF] Camino | Study of the Mechanism of Intumescence in Fire Retardant Polymers: Part l--Thermal Degradation of Ammonium Polyphosphate-Pentaerythritol Mixtures[END_REF] 135]. If the formation of CaBPO5 is occurred by the latter possibility, this can prevent the sublimation of P2O5 and stick phosphorus into the condensed phase favoring the char formation and char stabilization as described in the state of the art. According to this study, the mechanisms of reaction of CaCO3 in condensed phase, when APP and BA are present, can be proposed in the following equations (eq. 37-41compounds (i.e. CaBPO5), which are formed in the char residues, are supposed to be involved to improve fire protective properties and adhesion of intumescent coatings, that was shown in the previous part. PhD Thesis Nittaya HANSUPO, Univ. Lille 14.1.2.1.2 APP/ZB/CaCO3Hereafter, the interactions between APP/ZB/CaCO3 are investigated. The same approaches as previously were followed (TGA, HT, XRD and solid state NMR). The experimental and calculated TG curves as well as the difference weight loss curve of APP/ZB/CaCO3 are shown in Figure67. The experimental TG curve of the mixture APP/ZB/CaCO3 (black line) exhibits two steps of decomposition between 295 ⁰C and 470 ⁰C corresponding to 18 % weight loss. A progressive weight loss after 470 ⁰C is observed (2 % wt. loss up to 800 ⁰C). The difference weight loss curve shows that the interactions between the three additives lead to a thermal destabilization in the temperature range 300 ⁰C to 600 ⁰C. A thermal stabilization appears from 600 ⁰C up to the end of the experiment (+11 wt. % at 800 ⁰C). This suggests the interactions between APP, ZB and CaCO3.

Figure 67

 67 Figure 67 Experimental, calculated TG curves and different weight loss of the mixture of APP/ZB/CaCO3

  : 91 wt. %) (Residual weight: 83 wt. %) (Residual weight: 81 wt. %) XRD diffractograms of the APP/ZB/CaCO3 char residues at different heat treatment temperatures are shown in Figure 68. At 280 ⁰C, it is clearly showed that the diffractogram of the mixture looks similar to the superimposition of those of zinc borate and CaCO3. It evidences that ZB and CaCO3 do not degrade at this temperature. It makes sense considering the degradation temperature of those additives (TDecomposition of ZB ≈ 290 ⁰C and of CaCO3 ≈ 680 ⁰C). APP is not identified but at this temperature, APP totally degrades, as similar to what was demonstrated in 3.2.1.1.

Figure 68 XRD

 68 Figure 68 XRD diffractograms of APPZBCa residues versus temperatures

Figure 69 31 P

 6931 Figure 69 31 P NMR spectra (9.4 T) of APPZBCa residues versus temperatures

Figure 70 11 B

 7011 Figure 70 11 B NMR spectra (18.8 T) of APPZBCa residues versus temperatures

Figure 71

 71 Figure 71 Complex viscosity, relative expansion and TG curve of IF-APPCa Table 17 Char aspect of IF-APPCa after the rheological measurement

Figure 72 

 72 Figure 72 Complex viscosity, relative expansion and TG curves of IF-APPBA and IF-APPBACa

  carbonate compounds including MgCO3, ZnCO3, K2CO3 and Na2CO3 were considered in this part.MgCO3 was reported to use as a flame retardant additive in poly(vinyl chloride)[201] and in polypropylene[202]. ZnCO3 was mentioned to improve the flame retardant properties of polymeric materials forming protective inorganic glasses and limiting the release of combustible gases[203, 204]. K2CO3 was used as a flame retardant additive in polymeric materials (e.g. polymethylmethacrylate, polypropylene, nylon) and it was reported to reduce the heat release rate without significantly increasing smoke or carbon monoxide during the combustion[205]. And Na2CO3 was used as an ingredient of coating formulation for fire retardancy of cotton textile[206].However, the use of these four carbonates as intumescent ingredients in epoxy based intumescent coating has never been investigated. Four carbonate compounds were added into IF-APPBACa formulation instead of CaCO3 with the same weight ratio (3.45 % w/w of carbonate in the formulation). The formulations are named IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBANa2CO3, and IF-APPBAK2CO3. The coatings were carried out to the small-scale furnace test to assess its fire protective properties and the char collected after the furnace test were characterized to investigate the chemistry in the condensed phase and so, to determine the influence of each carbonate. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 4.2.1 Fire protective properties Time -temperature curves of the studied formulations are shown in Figure 74. The results showed that the addition of MgCO3 exhibits good fire protective properties as similar to those of CaCO3. Their time -temperature curves are almost superimposed. For IF-APPBACa and IF-APPBAMgCO3, times to reach the failure temperature are 24.6 and 25.3 minutes respectively. The addition of ZnCO3 exhibits an interesting result from the beginning of the fire test up to about 14 minutes but after this time, the intumescent falls off leading to a sharp increase of temperature. IF-APPBAZnCO3 takes 16.6 minutes to reach the failure temperature. For IF-APPBANa2CO3 and IF-APPBAK2CO3, the fire protective behaviors are quite similar, times to reach the failure temperature are of 20.3 and 19.3 minutes respectively. Afterwards, for both Na2CO3 and K2CO3, a sharp temperature increase which corresponds to a detachment of char, was observed after passing the failure temperature (≈ 22 -23 minutes of the test). When compared to the reference formulation IF-APPBA, which takes 18.1 minutes to reach the failure temperature, it was found that the formulations containing Na2CO3 or K2CO3 exhibit a better fire protective performance than the reference one (IF-APPBA).

Figure 74

 74 Figure 74 Time-temperature curves of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBAK2CO3 and IF-APPBANa2CO3

  shows the XRD diffractograms of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBANa2CO3 and IF-APPBAK2CO3 char residues collected after 18 minutes of the tests. The XRD diffractograms of the char residues of the five formulations are identical. It demonstrates the presence of crystalline BPO4 and B2O3. In addition to these, there is a convex signal lying between the 2Ѳ value between 20 and 33 ⁰ indicating the presence of amorphous phase. XRD patterns show no effect of cations (e.g. Ca 2+ , Mg 2+ , Zn 2+ ) on the formation of crystalline species. However, the influence of cation on the formation of amorphous species may be occurred; this cannot be distinguished by XRD. When looking at the XRD diffractograms of the char residues of IF-APPBACa and IF-APPBAMgCO3 (Figure 76) collected for a longer time after the furnace test (30 minutes), additional crystalline phases in addition to BPO4 and B2O3 are identified. It shows the presence of calcium borophosphate (CaBPO5) in IF-APPBACa char residue and magnesium pyrophosphate (α-Mg2P2O7) in IF-APPBAMgCO3 char residue. PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Figure 75 XRD

 75 Figure 75 XRD diffractograms of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBAK2CO3and IF-APPBANa2CO3 char residues(18 minutes)

Figure 77 31 P

 7731 Figure 77 31 P NMR spectra (9.4 T) of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBAK2CO3 and IF-APPBANa2CO3 char residues (18 minutes)

Figure 78

 78 Figure78shows the31 P NMR spectra of IF-APPBACa (a) and IF-APPBAMgCO3 (b) comparing the spectra of char residues collected after 18 minutes and 30 minutes. For both cases, it demonstrated that the phosphorous species are not modified between these two points. The quantities of CaBPO5 and Mg2P2O7 (α-and β-) are supposed to increase at 30 minutes (regarding the peak intensity). This is probably the reason why these species were detected in XRD patterns at 30 minutes but not at 18 minutes.

Figure 79 11 B

 7911 Figure 79 11 B NMR spectra (18.8T) of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBANa2CO3 and IF-APPBAK2CO3 char residues (18 minutes)

Figure 80

 80 Figure 80 Relative concentration of BO3, BO4 and BPO4 in the IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBANa2CO3 and IF-APPBAK2CO3 char residues

1 Outlook

 1 in the condensed phase. It reacts with B-and P-based compounds forming various inorganic species, that could stabilize the charred structure. The decarbonation of CaCO3 may enhance the expansion of intumescent char, if it occurs in the temperature range of the significant modification of viscosity (between 300 -400 ⁰C). When it occurs outside this temperature range, the role of CaCO3 as a blowing agent by releasing CO2 is not effective. The decarbonation of CaCO3 can occur at different temperatures depending on its reactivity with other components of the studied systems. In this study, the lack of benefit of CaCO3 in the formulation containing APP+ZB is supposed to be due to the formula itself (i.e. high weight percent of zinc borate). Consequently, this work highlights the positive effects of conventional filler CaCO3 on the fire protective properties of intumescent coatings. Moreover, it was demonstrated that not only CaCO3 but also MgCO3 can be a favorable candidate as an ingredient of intumescent coating with improving the fire protective properties of intumescent coatings. The chemistry in the condensed phase (e.g. chemical reaction, chemical species formed) is different when different carbonate is added into the formulation; these influence the char formation, char aspect, cohesion/adhesion, expansion and fire protection obtained. PhD Thesis Nittaya HANSUPO, Univ. Lille 1General conclusionPlaying with the chemistry of the formulation is a challenging work since it can be finetuned in a thousand ways. To develop the competitive and initiative formulations, a fundamental comprehension of the formulation is mandatory. This dissertation was devoted to the fundamental study of epoxy based intumescent coatings for fire protection of steel structures. It aims at providing the comprehension on the mechanisms of action of an epoxy based intumescent coating. The first goal of this work is to draw the mode of action of borates. The second goals are to examine the effects of carbonates on the fire protective properties and to elucidate its mode of action.Four borates including boric acid, zinc borate, borax and APB were studied to have global information of borates. The incorporation of zinc borate exhibits the best fire protection among all. To get an insight of its mode of action, the formulation containing either zinc borate or boric acid were characterized in more detail examining both chemical and thermo-physical modifications during the intumescent process. It was found that the formation of homogeneous, dense and compact charred structure with high mechanical properties are responsible for a good fire protection as obtained in the case of the formulation containing zinc borate. The formation of the expanded structure occurs lately in presence of zinc borate compared to the one containing boric acid because of its relatively high dehydration temperature. These make zinc borate less competitive against boric acid at the beginning of fire test. In the case of boric acid, the potential reaction and formation of expanded char occur quickly. This provides the potential fire protection at the beginning but a fast development of expanded char in a short time (high expansion) harms the fire protective properties since the charred structure afterwards falls off form the steel.Apart from the identification of the role of borates, the benefits of adding calcium carbonate into epoxy based intumescent coating were emphasized. It improves the fire protective properties and adhesion/cohesion of intumescent coating when it is added into the formulation containing APP and borate (work for APPBA but not for APPZB). It is opposite to what occurred in the previous part (chapter III: performance of zinc borate is better than boric acid). Note that the PhD Thesis Nittaya HANSUPO, Univ. Lille 1 formulation was simplified to examine the effects of carbonates. The additive ratio was kept to the model formulation but their percent weight in the formulation was changed. The mode of action of CaCO3 was studied in detail. It was showed that CaCO3 reacts with other components of the formulation forming different inorganic species, which are thermally stable compounds.These reactions favor stabilizing B and P based compounds in the condensed phase. The decarbonation of CaCO3 as a blowing factor of intumescent systems can be effective in some cases: it depends on the chemical reaction of CaCO3 with the components of the studied system, that makes the decarbonation occur at different temperature range. Additionally, various carbonates as an intumescent ingredient were examined. The results showed that not only CaCO3 but also MgCO3 provide benefits to the fire protective properties of the coating. The incorporation of other carbonates (i.e. Na2CO3, K2CO3) exhibits less protective performance compared to the two mentioned above, they however improve the fire protective performances compared to the reference formulation without carbonate.In summary, this work provides the fundamental comprehension of epoxy based intumescent coatings. Based on these results, the possibilities to substitute borates can be pointed out. The reactivity of zinc (i.e. from zinc borate) is outstanding as shown in chapter III, it reacts with P, B and Ca based compounds playing an important role in the condensed phase. An extension of this work is the development of boron free intumescent system. In this context, some works were thus performed and the results will be discussed in the outlook. PhD Thesis Nittaya HANSUPO, Univ. LilleBased on what we learnt in this work, it suggested the important role of zinc (e.g. synergistic effect) conducting an efficient fire protection. It was observed, for example, in the formulation containing zine borate (in chapter III). From this point of view, the interest is in incorporating zinc-based compounds instead of zinc borate. Three zinc-based compounds were selected including ZnO, ZnS and ZnSO4.7H2O. ZnO and ZnS because they showed synergistic effect as a flame retardant in silicone rubber composites[210]. It was also reported that ZnSO4.7H2O enhances the flame retardancy of polypropylene by balancing the molten viscosity and the intumescent process and strengthening the char layer[211]. The study has been applied on another formulation called IFZnB. This formulation is one of the formulations of interest formulated by the industrial partner. The composition of the formulation is presented in Table

  To realize the study, zinc borate in the studied formulation(IFZnB) was substituted by another zinc-based compound with constant zinc molar ratio. The formulations are named IFZnO, IFZnS and IFZnSO4 respectively. Their compositions are shown in Appendix II. Four formulations with different zinc source were carried out to the furnace test to assess their fire protective performances against hydrocarbon fire. Time -temperature curves of four formulations are presented in Figure 82. The formulation containing zinc borate leads to the longest time to reach the failure temperature; it takes 24 minutes while IFZnS, IFZnO and IFZnSO4 take 22, 21 and 18 minutes respectively. The incorporation of ZnO and ZnS exhibits interesting results because their times to failures are close to that of the reference formulation containing zinc borate. If the formulations containing ZnO and ZnS were fine-tuned and optimized, it could be expected to get the fire protective properties of the reference formulation.

Figure 82

 82 Figure 82 Time -temperature curves of IFZnB, IFZnO, IFZnS and IFZnSO4

Table 20

 20 Char aspects and relative expansions of IFZnB, IFZnO, IFZnS and IFZnSO4 out that the development of boron free intumescent coatings is possible with zinc-based compounds. Nevertheless, the formulation should be optimized to attain a longer protection time. It is also of high interest to investigate the mechanisms of action of zinc (e.g. synergistic, catalytic).

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1 Figure 28 31 P

 12345678912831 Figure 1 World Trade Center collapse, 11 September 2001 [2] ...................................................... Figure 2 Intumescent material (before and after heating) .............................................................. Figure 3 Market share of passive fire protection [17] ..................................................................... Figure 4 Schematic representation of the intumescent process [3, 19, 20] .................................... Figure 5 Standard fire test curves [35] ........................................................................................... Figure 6 Phase diagram of B2O3 -H2O system [75] ........................................................................Figure 7 Classification of fibers [98] ............................................................................................... Figure 8 Evolution of heat conductivity as a function of temperature for intumescent polyurethane systems (PU30%APP and PU28%APP2%nano MgO) [115] ..................................... Figure 9 Schematic view of an intumescent coating with different zones (a) and intumescent development as a function of the conversion degree α (b) [18] ................................................... Figure 10 (a) Relative expansion (b) complex viscosity [81] of intumescent epoxy-based coatings (A: epoxy resin, B: epoxy resin+APP, C: epoxy resin+H3BO3, D: epoxy resin+APP+H3BO3) ........... Figure 11 Expansion of silicone-based coatings versus times in dynamic (1-4) and static (5-8) state ................................................................................................................................................ Figure 12 Schematic illustration of the Texture Analyzer used to determine the strength of an intumescent char. Ls and L0 are the distance to the sample top and sample bottom from a selected initial height respectively. The height of the sample is the difference given by L0 -Ls [19] ........................................................................................................................................................ Figure 13 Photos of 100 x 100 x 3 mm 3 steel plate coated with 4 mm of intumescent coating ... Figure 14 Sample of 25 mm of diameter and 1 mm of thickness for Rheometer test .................. Figure 15 Sample installation for thermal conductivity measurement ......................................... Figure 16 Small-scale furnace test ................................................................................................. Figure 17 Schematic representation of heat-treatment ................................................................ Figure 18 Experimental setup of transient plane source method ................................................. Figure 19 Rheometer in a parallel plate configuration .................................................................. Figure 20 Measurement of viscosity .............................................................................................. Figure 21 Protocol to measure mechanical resistance of char ...................................................... Figure 22 Example of simulated 11 B NMR spectrum (18.8 T) using the software DMFIT (i.e. neat IF(ZB)wt coating) ............................................................................................................................ Figure 23 Time -temperature curves of IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m .................... Figure 24 P/C ratio and B/C ratio in non-degraded coatings (by calculation) vs. in char residues (by elemental analysis) ................................................................................................................... Figure 25 XRD diffractograms of IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m char residues (30 minutes) and of H3BO3 and B2O3 ....................................................................................................Figure 26 13 C NMR spectra (9.4 T) of IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m char residues ... Figure 27 Q structure of phosphate: Q 0 isolated units (ortho-P), Q 1 end units (pyro-P), Q 2 middle units (meta-P) and Q 3 crosslinking units (ultra-P) ..........................................................................

Figure 55

 55 Figure 28 31 P NMR spectra (9.4T) of the IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m char residues ........................................................................................................................................................ Figure 29 11 B NMR spectra (18.8T) of the IF(BA), IF(ZB)m, IF(borax)m and IF(APB)m char residues and of B2O3 ..................................................................................................................................... Figure 30 TG curves of IF(BA) and of IF(ZB)wt ............................................................................... Figure 31 XRD diffractograms of IF(BA) char residues versus temperatures ................................ Figure 32 31 P NMR (9.4T) of IF(BA) char residues versus temperatures and the zoom out of the spectra at 210 ⁰C and 250 ⁰C (in the blue dotted line) .................................................................. Figure 33 Chemical structure of TCPP (a) and 31 P NMR spectra (9.4T) of TCPP and of neat IF(BA) coating (b)....................................................................................................................................... Figure 34 11 B NMR spectra (18.8T) of IF(BA) char residues versus temperatures ........................ Figure 35 1D 11 B( 31 P) D-HMQC NMR (B connected to P nucleus, 18.8T) vs. 1D 11B NMR signal of IF(BA) char residues at 250 ⁰C (left) and 280 ⁰C (right).................................................................. Figure 36 Evolution of the relative concentration of boron species in IF(BA) versus temperatures ........................................................................................................................................................ Figure 37 XRD diffractograms of IF(ZB)wt char residues versus temperatures ............................. Figure 38 31 P NMR spectra (9.4 T) of IF(ZB)wt char residues versus temperatures ...................... Figure 39 11 B NMR spectra (18.8 T) of IF(ZB)wt char residues versus temperatures .................... Figure 40 Relative concentrations of boron species in IF(ZB)wt char residues versus temperatures .................................................................................................................................. Figure 41 Time-temperature curves of IF(BA) and IF(ZB)wt pointing out the characterisric times ...................................................................................................................................................... Figure 42 Photos of IF(BA) residual aspects collected after the furnace test (2 and 5 minutes) Figure 43 XRD diffractograms of IF(BA) char residues versus times ............................................ Figure 44 31 P NMR spectra (9.4 T) of IF(BA) char residues versus times ..................................... Figure 45 11 B NMR spectra (18.8 T) of IF(BA) char residues versus times ................................... Figure 46 Relative concentration of boron species in IF(BA) char residues versus times ........... Figure 47 Photos of IF(ZB)wt residual aspects after the furnace test (2 and 5 minutes) ............ Figure 48 XRD diffractograms of IF(ZB)wt char residues versus times ........................................ Figure 49 31 P NMR spectra (9.4 T) of IF(ZB)wt char residues versus times ................................. Figure 50 11 B NMR spectra (18.8 T) of IF(ZB)wt char residues versus times ............................... Figure 51 Relative concentration of boron species in IF(ZB)wt char residues versus times ....... Figure 52 Mechanisms of decomposition of IF(BA) and IF(ZB)wt ................................................Figure 53 Complex viscosity, relative expansion and TG curve of IF(BA) ...................................Figure 54 Complex viscosity, relative expansion and TG curve of IF(ZB)wt ................................Figure 55 Relatvie expansion (%, left) and expansion rate (%/s, right) of IF(BA )and of IF(ZB)wt ...................................................................................................................................................... Figure 56 Char appearances of IF(BA) versus times captured by numeric camera ..................... Figure 57 Char appearances of IF(ZB)wt versus times captured by numeric camera ................. Figure 58 Char morphology of IF(BA) and IF(ZB)wt versus times observed by microscope optic ......................................................................................................................................................

Figure 59

 59 Figure 59 Thermal conductivity (W/mK) of IF(BA) and IF(ZB)wt versus temperatures ............... Figure 60 Mechanical resistance of IF(BA) and IF(ZB)wt char ..................................................... Figure 61 Time-temperature curves of IF-APPCa, IF-APPBA, IF-APPZB, IF-APPBACa and IF-APPZBCa ....................................................................................................................................... Figure 62 Experimental, calculated TG curves and different weight loss of the mixture of APP/BA/CaCO3 .............................................................................................................................. Figure 63 XRD diffractograms of APPBACa residues versus temperatures ................................ Figure 64 31 P NMR spectra (9.4T) of APPBACa residues versus temperatures ............................ Figure 65 Chemical structures of crystalline BPO4 and (BPO5) 2-anion ........................................ Figure 66 11 B NMR spectra (18.8T) of APPBACa residues versus temperatures ......................... Figure 67 Experimental, calculated TG curves and different weight loss of the mixture of APP/ZB/CaCO3 .............................................................................................................................. Figure 68 XRD diffractograms of APPZBCa residues versus temperatures .................................. Figure 69 31 P NMR spectra (9.4 T) of APPZBCa residues versus temperatures .......................... Figure 70 11 B NMR spectra (18.8 T) of APPZBCa residues versus temperatures ......................... Figure 71 Complex viscosity, relative expansion and TG curve of IF-APPCa................................ Figure 72 Complex viscosity, relative expansion and TG curves of IF-APPBA and IF-APPBACa... Figure 73 Graphic conclusion of the study of the effect of CaCO3 on intumescent coatings ...... Figure 74 Time-temperature curves of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBAK2CO3 and IF-APPBANa2CO3 .............................................................................................. Figure 75 XRD diffractograms of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBAK2CO3 and IF-APPBANa2CO3 char residues (18 minutes) ........................................................................ Figure 76 XRD diffractograms of IF-APPBACa and IF-APPBAMgCO3 char residues (18 vs. 30 minutes) ....................................................................................................................................... Figure 77 31 P NMR spectra (9.4 T) of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBAK2CO3 and IF-APPBANa2CO3 char residues (18 minutes) ................................................... Figure 78 31 P NMR spectra (9.4T) of IF-APPBACa and IF-APPBAMgCO3 char residues (18 vs. 30 minutes) ....................................................................................................................................... Figure 79 11 B NMR spectra (18.8T) of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBANa2CO3 and IF-APPBAK2CO3 char residues (18 minutes) ................................................... Figure 80 Relative concentration of BO3, BO4 and BPO4 in the IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBANa2CO3 and IF-APPBAK2CO3 char residues ............................................. Figure 81 Graphic conclusion of the study of the effects of carbonates on intumescent behaviors ...................................................................................................................................................... Figure 82 Time -temperature curves of IFZnB, IFZnO, IFZnS and IFZnSO4 .................................. Figure 83 Experimental, calculated residual weight and difference weight loss of BA/CaCO3 (91/9 % w/w) ..........................................................................................................................................Figure 84 Complex viscosity, relative expansion and TG curves of IF-APPZB and IF-APPZBCa ...

Table of

 of

contents viii PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Table of contents

 of

Table 3

 3 Examples of intumescent coating formulations

	Name	Formulation	Ref. Year
	PPG	Epoxy-based mastic/ Versamid 150 (curing agent)	[53] 1985
	(PITTCHAR)	Additives: boric acid, zinc borate, APP, wollastonite, tris(2-
		chloroethyl) phosphate, tall oil fatty acid, melamine and
		attapulgite gallant, aerosol, silica, talc

PPG

Flexible epoxy resin (polyester chain-extended epoxy)

Additives: APB, APP, zinc borate, silica, talc….

[54] 1991 PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Table 4

 4 Uses of borates in intumescent coatings

	Borates	Co-additives	Substrates	Ref.
	Melamine borate	Melamine phosphate	Wood and Steel	[63]
	Borax	A water-soluble sodium silicate,	Steel	[64]
		aluminum trihydroxide (ATH) and kaolin
	Ammonium	Zinc, boron and phosphorus containing	Steel	[65]
	pentaborate	compounds
	Boric acid	perlite and ceramic fibers APP, triaryl phosphate, THEIC, silica,	Steel	[21]

Table 5

 5 Physical properties of boron oxides[START_REF] Oxides | Boric Acids, and Metal Borates[END_REF][START_REF] Ferlat | Hidden polymorphs dirve vtirification in B2O3[END_REF]

	Properties	Vitreous form	Crystalline forms
			α -form or B2O3 (I)	β -form or B2O3 (II)
	Mp (°C)	Softens 325	450 -465	510
	Density (g/ml)	1.84	2.46	2.95
	Crystal form	-	Hexagonal	Monoclinic

Table 6

 6 Compositions of IF(BA) formulation

	Description	Commercial name (supplier)	Part B (%w/w)	Part A (%w/w)
	Aliphatic polyamide amine	Ancamide 903 MAV (Air Products)	17.59
	Calcium Carbonate or Dolomite	Micral 5 (Reverté)	1.91
	Based on ammonium polyphosphate	Exolit AP 755 (Clariant)	2.20	8.54
	Titanium dioxide, rutile	Tronox CR-826 (Huntsman)	0.37
	Natural, expanded silicate	Rotocell 0,5 mm (Rotec)	1.07	0.57
	Composite reinforcement, Man-made vitreous (silicate) fibers	Rockforce MS603-Roxul1000 (Lapinus)	2.64	1.28
	Composite reinforcement, Man-made vitreous (silicate) fibers	Rockforce MS605-Roxul1000 (Lapinus)	3.16	1.28
	Bisphenol A diglycidylether epoxy	Epikote 828 (Momentive)		31.20
	Tris(2-chloroisopropyl)phosphate (TCPP)	Fyrol PCF (ICL)		8.03
	Carbon black	Lamp Black 101 (Orion engineered carbons)		0.06
	Fumed silica	AEROSIL R 8200 (Evonik)		0.85
	Boric acid	Optibor (20 Mules team)		19.25
	Total (% w/w)	28.94	71.06

One objective of this work is to compare systematically the effects of different borates (i.e. boric acid, zinc borate, borax and Ammonium pentaborate (APB)). To follow this purpose, boric acid in the reference formulation was substituted by another borate (i.e. zinc borate, borax or APB). It was made by maintaining the molar content of boron (B) constant. The corresponding formulations are called IF(ZB)m, IF(borax)m and IF(APB)m respectively. The formulation details are presented in Appendix I.

Table 7

 7 describes the properties, chemical structures and suppliers of the different borates used in this study.

Table 7

 7 Suppliers, properties and chemical structures of boric acid, zinc borate, borax and APB

	Properties	Boric acid	Zinc borate	Borax	APB
	Formula	H3BO3	2ZnO.3B2O3.3.5H2O Na2B4O7•10H2O NH4B5O8.4H2O
	Commercial name	Optibor	Firebrake ZB	Borax decahydrate	Ammonium pentaborate
	Supplier	20 Mule team	20 Mule team	20 Mule team	20 Mule team
	Molecular weight (g/mol)	61.8	434.5	381.4	272.2
	Density (g/cm 3 )	1.51	2.60	1.73	1.58
	Decomposition
	(Dehydration	100 ⁰C	290 ⁰C	75 ⁰C	110 ⁰C
	Temp)
	Wt. % of boron (B)	17.5	14.9	11.3	19.9
	Water release (wt. %)	44	14	46	37

Chemical structure PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Table 8

 8

		IF-APPCa	IF-APPBA	IF-APPBACa	IF-APPZB	IF-APPZBCa
	Epoxy	31.97	31.97	31.97	31.97	31.97
	Curing agent	18.03	18.03	18.03	18.03	18.03
	APP	38.7	12.68	11.8	12.68	11.8
	H3BO3 or BA		37.32	34.75
	ZB				37.32	34.75

Compositions of IF-APPCa, IF-APPBA, IF-APPBACa, IF-APPZB and IF-APPZBCa

Table 9

 9 Suppliers and properties of CaCO3, MgCO3, ZnCO3, Na2CO3 and K2CO3

	Properties	CaCO3	MgCO3	ZnCO3	Na2CO3	K2CO3
	Commercial name	Micral 5	Magnesium carbonate	Zinc carbonate	Sodium carbonate	Potassium carbonate
	Suppliers	Reverté	Acros	Prolabo	Carbo Erba	Sigma Aldrich
	Molecular weight (g/mole)	100	84.3	125.4	106	138.2
	Density (g/cm 3 )	2.71	2.96	4.44	2.54	2.43
	Decomposition	680-900	620-650	300-452	850	890
	temperature (⁰C)	[87, 88]	[145]	[146, 147]	(SDS)	(SDS)
	CO2 release (% wt.) by calculation	44	52	35	41.5	31.8

31 P solid-state NMR measurements were

  Solid state NMR is a powerful technique for structural analyses. The conditions used for the analyses are detailed hereafter. All NMR data were obtained at room temperature. performed on a Bruker Avance 400 at 162 MHz (9.4 T) with MAS (magic angle spinning) and high power 1 H decoupling (DD) using 4 mm standard probe. For all samples, a recycle delay is set at 120 s ( 31 P has a long relaxation time, T1)

	and a spinning speed at 12.5 kHz. All spectra were acquired as the result of 8 or 16 scans. H3PO4
	in aqueous solution (85%) was used for the calibration.
	1D 11 B solid-state NMR measurements were performed on Bruker Avance III 800 at 256.6
	MHz (18.8 T) with MAS (magic angle spinning) using 3.2 mm probe. In this study, MAS 11 B NMR
	2.2.5.2 at high magnetic field (18.8 T) was used in order to eliminate the quadrupolar interaction and Solid state NMR
	separate the peaks of BO3 and BO4 units. 11 B spectra were obtained through direct observation.
	1D 13 C solid-state NMR measurements were performed on a Bruker Avance 400 at 100.8
	MHz (9.4 T) with MAS (magic angle spinning), high power 1H decoupling (DD) and 1 H -13 C cross
	polarization (CP) using 4 mm standard probe. For all samples, a recycle delay (d1) is set at 3 s, a
	contact time at 1 ms and a spinning speed at 12.5 kHz. All spectra were acquired as the result of
	2048 scans. Tetramethylsilane (TMS) was used for the calibration.

When performing solid-state NMR measurements, the large number of protons in the sample interferes with decay of the isolated nucleus due to weak interactions of the spins. The dampening of the signal can be removed by a strong radio frequency signal, which holds the protons in a highly resonating state so that they are not capable of absorbing resonance from the nuclei. This is called 1 H dipolar decoupling (DD). On the other hand, in a solid state, the chemical shift anisotropy (CSA) has a severe effect on the spectra resulting in broadened peaks. This effect is worsened when the mobility of the chains or molecules decreases. Through a tensoral analysis of the magnetic moments in a molecule, it is possible to demonstrate that a ''Magic Angle'' exists with respect to the applied magnetic field at which rapid spinning of the solid sample minimizes an absorption line broadening due to chemical shift anisotropy. This angle is called 'magic angle spinning or MAS'. PhD Thesis Nittaya HANSUPO, Univ. Lille 1 1D

Table 11

 11

	Selected heat treatment temperatures of IF(BA) and of IF(ZB)wt
	HTT (⁰C)	IF(BA)	IF(ZB)wt
	210	After the first and second step of	-
		degradation
	250	Maximum weight loss of the third step	Maximum weight loss of the first step
	280	After the third step of degradation	End of the first step of degradation
	380	Maximum weight loss of the main step	Maximum weight loss of the main step

550

After the total degradation and stabilization of the residue PhD Thesis Nittaya HANSUPO, Univ. Lille 1

  31 P and11 B solid state NMR. Hereafter, it is of interest to identify the chemical species formed at defined temperature under pyrolytic conditions, which can suggest what could occur in a real fire test. The results are presented in the following section.

	3.2.1.1.2	Identification of the chemical species formed
	In this part, the decomposition pathway of IF(BA) is first discussed and that of IF(ZB)wt is
	examined afterwards.

a) IF(BA) formulation

  The decomposition pathway of IF(ZB) is different to IF(BA) due to

	3.2.1.2	When submitted to a fire test
		In the previous part, the chemical species formed in the condensed phase after heat-
	treatment (at defined temperatures under pyrolytic condition) were identified. It can give
	the different dehydration temperature of borates. The obtained results can be summarized as information on the decomposition pathway and on how the additives react together. However,
	follows: it should be noticed that the heating ramp and the studied temperatures are hugely different
	from real fire test: low temperature with a long heating time (HT) vs. high temperature with a
	i) BPO4 is formed but it is found at higher temperature (380 ⁰C vs. 250 ⁰C) when ZB is short exposed time (under fire test). Hence, this part investigates the transformation of species
	used instead of boric acid formed in the condensed phase when the coatings are exposed to a fire test.
		ii) Formed BPO4 has a lower crystallinity than that found in IF(BA)
		iii) Formation of boric acid (H3BO3) by the hydration of boron oxide (B2O3) can be found
		in both cases
		iv) Additional compound because of zinc borate (i.e. α-Zn3(PO4)2) is found at 550 ⁰C

v) CaCO3 and TiO2 do not decompose nor react with other components in the formulation up to 550 ⁰C as similar to IF(BA) vi) No sign of reactions between Si based compounds (from fumed silica, expanded silicate, silicate fibers) with any components is observed PhD Thesis Nittaya HANSUPO, Univ. Lille 1 The coated steels were submitted to the furnace test (UL1709) and stopped at different characteristic times. The time-temperature curves of IF(BA) and IF(ZB)wt pointing out the characteristic times are shown in Figure

Table 12 Residual

 12

appearances of IF(BA) and IF(ZB)wt captured after the rheological measurements IF(BA) IF(ZB)wt

Table 15

 15 APPBACa residues at different heat treatment temperatures

	HT of 280 ⁰C	HT of 550 ⁰C	HT of 800 ⁰C
	(Residual weight: 65 wt. %)	(Residual weight: 62 wt. %)	(Residual weight: 59 wt. %)

Table 16

 16 APPZBCa residues at different heat treatment temperatures

  11 B NMR spectrum). It is supposed that borophosphate reacts with zinc orthophosphate to yield boron oxide and zinc pyrophosphate, this phenomenon is similar to what was observed in the binary system (mixture APPZB) reported in the literature. CaCO3 remains in the char residue and it does not take part in the reaction up to 550 ⁰C. Between 550 ⁰C and 800 ⁰C, calcium based compound (e.g. CaO, degradation product of

	4.1.2.1.3 Conclusion
	CaCO3) reacts with zinc and phosphorus based compounds forming calcium zinc orthophosphate
	(CaZn2(PO4)2). This is different to what occurred in the system containing BA. The formation of
	CaBPO5 is also evidenced in 31 P NMR spectrum but its concentration seems to be very low
	(regarding the peak intensity). In addition to BPO4, CaZn2(PO4)2 and CaBPO5, other crystalline
	species are formed including zinc orthophosphate (Zn3(PO4)2), zinc pyrophosphate (Zn2P2O7) and
	zinc boron oxide (ZnB4O7). The mechanisms of reaction occurred in this system is much more
	complex than the one containing BA.
	PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Table 18

 18 shows the char aspects and expansions of IF-APPBACa, IF-APPBAMgCO3, IF-APPBAZnCO3, IF-APPBANa2CO3, and APPBAK2CO3. At first, the tests were stopped at 30 minutes.It evidenced that three formulations including IF-APPBAZnCO3, IF-APPBANa2CO3, and APPBAK2CO3 have no char left on the steel plate due to a detachment of char as previously described. Thus, it is not evident to compare the char aspects of the five formulations at this point.Therefore, 18 minutes after exposing in the furnace test was chosen to be able to compare the char aspects and to elucidate the chemical modifications in the condensed phase affecting by different carbonates.The char aspects(18 minutes) are obviously different between the five formulations. IF-APPBACa has a hard and compact char structure, some big holes are found between the char layers. The char aspect shown in this part is a bit different to that shown in 4.1 Influence of CaCO3 on the fire protection because the exposed times in the furnace are different(18 vs. 24 minutes).

  Three distinct layers are observed. It includes the dark grey char on top, light grey char in the middle and black char underneath.

	IF-
	APPBANa2CO3 610 ± 20 %
	When looking at the relative % of expansion after cooling down the samples, IF-APPBACa
	exhibits the highest expansion. It expands to 898 %, while IF-APPBAMgCO3 has 484 % of
	expansion, which is the lowest expansion among all. Low expansion but high fire protective
	performance in the case of IF-APPBAMgCO3 is probably due to its charred structure (dense and
	compact). IF-APPBANa2CO3 and IF-APPBAK2CO3 expand to 508 and 610 % of relative expansion
	respectively; they provide an intermediate expansion between the highest and lowest ones.
	PhD Thesis Nittaya HANSUPO, Univ. Lille 1

Table 19

 19 Compositions of IFZnB

	Product name	Commercial name (supplier)	Part B (% w/w)	Part A (% w/w)
	Aliphatic polyamide amine	Ancamide 903 MAV (Air Products)	8.95
	2.4.6-tris(dimethylaminomethyl)phenol	Acamine K54 (Air Products)	1.77
	Melamine	Melafine (OCI Nitrogen)	15.66
	Titanium dioxide, rutile	Tronox CR-826 (Huntsman)	4.27	2.01
	Modified derivative of castor oil	Thixatrol ST (Elementis Specialties)	0.27	0.61
	Composite reinforcement, Man-made vitreous (silicate) fibres	Rockforce MS605-Roxul1000 (Lapinus)	2.41	9.89
	Bisphenol A diglycidylether epoxy binder	Epikote 828 (Momentive)		20.97
	Tris(2-chloroisopropyl)phosphate	Fyrol PCF (ICL)		6.44
	Ammonium polyphosphate	Exolit AP 422 (Clariant)		18.96
	zinc borate, flame retardant	Firebrake ZB (20 Mule team)		6.01
	Calcium Carbonate or Dolomite	Micral 5 (Reverté)		1.72
	Carbon black	Lamp Black 101 (Orion engineered carbons)		0.05
	Total (% w/w)	33.33	66.

[START_REF] Ahmed | Non-toxic mineral based intumescent fire retardant coating for structural applications[END_REF]

PhD Thesis Nittaya HANSUPO, Univ. Lille 1

PhD Thesis Nittaya HANSUPO, Univ. Lille 1

PhD Thesis Nittaya HANSUPO, Univ. Lille 1[START_REF] Bourbigot | Chapter 6: Intumescent based fire retardants[END_REF] B solid state NMR spectra of IF(BA) residues are presented inFigure 34, 11 B NMR

PhD Thesis Nittaya HANSUPO, Univ. Lille 1[START_REF] Bourbigot | Chapter 6: Intumescent based fire retardants[END_REF] B NMR spectra of APP/BA/CaCO3 residues heat treated at 280 ⁰C, 550 ⁰C and 800 ⁰C

PhD Thesis Nittaya HANSUPO, Univ. Lille 1[START_REF] Bourbigot | Chapter 6: Intumescent based fire retardants[END_REF] B NMR spectra of APP/ZB/CaCO3 residues heat treated at 280 ⁰C, 550 ⁰C and 800 ⁰C are

List of tables and figures

List of tables

Table Examples of chemicals used as acid source, blowing agent and carbon source for intumescent systems [START_REF] Alongi | Intumescence: Tradition versus novelty. A comprehensive review[END_REF][START_REF] Camino | Intumescent Fire-retardant systems[END_REF] Appendix III: Potential interactions between CaCO3 and BA

Figure 83 shows the experimental, calculated and difference weight loss curves of BA/CaCO3. The mixture ratio of BA and CaCO3 is 91/9 % w/w, which is respected to that present in IF(BA) formulation. The difference weight loss gives an evidence on the interactions between the additives (the details were described in chapter II).

The stabilization and destabilization are a bit remarkable in two points: i) between 100 ⁰C and 200 ⁰C and ii) after 700 ⁰C. It was found that the difference weight loss is between 0 and -2.

The difference weight loss approaches zero (non-significant value) pointing out the absence of reaction between the two additives. It can be concluded that there is no reaction between BA and CaCO3 up to 800 ⁰C.