Marcus Campbell Bannerman

Laurent Artaud

contribution and his good mood, this trip to Scotland left me with only positive memories. I have an extremely positive thought

GENERAL INTRODUCTION

Cement has been used for thousands of years by various groups of people throughout history. In ancient times, the Egyptians already made mortars from gypsum to bind rocks together. On the other side of the earth, Mayans were building with mortars based on lime from firing limestone rocks. As time went on and knowledge improved, cement-manufacturing processes were perfected. Thus, Romans developed a process allowing constructions to be built in wet environments. The process consisted of blending lime with volcanic ash such as pozzolan. Over time, with the advent of industrialization, cement use and production increased considerably. The industrial revolution played a major role in the development of cement production technology. In 1824, the Scotsman Joseph Aspdin introduced an improved the cement manufacturing process and developed Portland cement, a reference to the limestone mined on the island of Portland, hence the common name OPC (Ordinary Portland Cement). Nevertheless, the discovery of modern cement is credited to Louis Vicat (1818). In recognition of his academic and scientific achievements, Louis Vicat (1818) refused to register a patent on the laws of hydraulicity of cements and limes. One of the advantages of cement manufacture is the fact that it is easy to obtain and the products are readily available, making it an inexpensive and widely used material in construction.

The growth of the global population in recent years required the construction of new buildings for housing, hospitals and various other constructions necessary for human life. To satisfy this demand, cement production is increasing continuously.

Since 2015, cement manufacturing has been steadily climbing at a rate of 1.5% per year [START_REF] Hodgson | Retrieved from ea[END_REF] which has a damaging impact on the environment. Indeed, cement production necessitates using limestone (CaCO3) and its calcination at high temperature contributes to the emission of greenhouse gases. Limestone constitutes about 80% of the raw materials used in the manufacture of cement and is the major source of CO2 emissions. The chemical CO2 from the CaCO3 calcination corresponds to roughly 60% of the total emissions. The other 40% are due to the use of carbon bearing fossil fuels that are used for clinkering [START_REF] Lehne | Making concrete change: Innovation in low-carbon cement and concrete[END_REF]. Cement industry pollution accounts for about 8% of the world's CO2 emissions [START_REF] Scrivener | Options for the future of cement[END_REF]. If the use of cement-based concrete were compared to a country, it would represent the third largest greenhouse gas pollutant in the world behind China and the United States. As it is currently not feasible to substitute limestone, a key issue for the cement sector is to identify alternative ways of reducing limestone input into cement production. To achieve this, the main approaches planned to reduce the carbon impact throughout the cement manufacturing process are as follows: the use of low-carbon fuels, the use of non-polluting raw materials and the development of low-emission or even near-zero emission production processes [START_REF] Hodgson | Retrieved from ea[END_REF]. To reach these targets, manufacturers are investing more and more in research and development to better understand the physiochemical processes involved in clinkerization. This is where chemical thermodynamics intervenes, which is the subject of this manuscript.

Indeed, the properties and the stability of the major phases constituting the cement clinker can be strongly affected by the insertion of minor elements and modify not only the chemistry but also the quality of the resulting clinker. However, in order to be able to model the insertion of these minor elements, high quality thermodynamic data is needed for the pure mineralogical phases of a clinker.

Clinker is the main constituent of Portland cement with a global chemical composition of 67wt.% CaO, 22wt.% SiO2, 5wt.% Al2O3, 3wt.% Fe2O3 and 3wt.% minor elements (MgO, Na2O, K2O, SO3, TiO2) (Taylor H. , 1990). Most of the raw materials in the cement clinker manufacturing process are of natural origin. The CaO source is natural limestone. Alumina, iron oxide and silica are mainly from natural clay minerals together with some of the alkalis and magnesium oxide. Iron oxide is sometimes added as hematite. A mixture of these raw materials prior to the burning is called raw mix. This raw mix is burned at temperatures close to 1450°C to transform the raw materials into the reactive phases of the clinker. The major mineralogical phases of an Ordinary Portland clinker are Alite (Ca3SiO5 with insertion of minor elements) which forms 50-70 wt% of the final clinker, Belite (Ca2SiO4 with minor elements), generally present as a β-Ca2SiO4 polymorph and an amount ranging from 15-30 wt. %, the calcium aluminate phase Ca3Al2O6 estimated to 5-10wt.% and finally the ferrite phase, the Ca2(Al,Fe)2O5 solid solution with an amount varying between 5 and 15 wt.% (Taylor H. , 1990).

In recent years, researchers in thermodynamics developed a computational procedure for studying the thermodynamic properties of multi-component systems. This approach is called CALPHAD [START_REF] Spencer | A brief history of CALPHAD[END_REF] (Calculation of Phase Diagrams) and consists of first modelling the thermodynamic properties of a unary and then binary, ternary and more complex multi-component systems in order to obtain a coherent Gibbs energy dataset which can be used for phase diagram calculations. The key to this method lies in the quality of the underlying thermodynamic data of the constituents of the system studied. As the major phases of clinker belong to the binary systems CaO-SiO2, CaO-Al2O3 and the ternary CaO-Al2O3-Fe2O3, high quality experimental data is necessary to better describe the thermodynamic reactions governing clinker formation. These data will contribute to a better simulation tools to control the manufacturing process and optimize the clinker properties. In order to build up a coherent database, the experimental contribution is therefore essential, and it is this point that motivates the work that is reported in this manuscript.

The main aim of this research is to review and to study experimentally the thermodynamic properties of the compounds and solid solutions of the main mineralogical phases of an OPC "Ordinary Portland Cement" clinker: the various polymorphs of Ca2SiO4, Rankinite (Ca3Si2O7), different Ca-aluminates (Ca5Al6O14 and CaAl12O19) and the solid solution calcium alumino-ferrite (Ca2AlxFe2-xO5). For all compounds and the solution phase, the focus lies on the indirect determination of the heat capacity at high temperature through a series of heat content measurements. In addition, the standard heats of formation were determined with a newly developed solution calorimetric method using a CaO-Al2O3 rich based solvent. All the measurements were performed on carefully synthesized and characterized samples.

The samples are produced using conventional techniques: powder mixing, grinding, pelletizing, high-temperature sintering and air-cooling. The purity of all samples was checked by X-ray diffraction. The newly generated data was used, together with the critically reviewed data from the literature, to derive new sets of Gibbs energy functions, which can be used in equilibrium calculations.

Throughout this thesis, we will study different multicomponent oxides that constitute a Portland clinker. This research work is divided into four parts, each of which constitutes a chapter:  The first chapter describes the experimental methods used in the thesis for the synthesis of the silicate, aluminates and the alumino-ferrite solid solution as well as the structural analysis techniques and the methods for the determination of the thermodynamic properties.

 The second chapter focuses on the study of the thermodynamic properties of two calcium silicates: belite (Ca2SiO4) and rankinite (Ca3Si2O7). In this chapter, we will discuss the parameters of the syntheses that allowed us to obtain these compounds; the thermodynamic properties will also be measured and discussed. We will then finish by presenting the results of a collaborative work carried out with the University of Aberdeen on the phase diagram modelling of the CaO-SiO2 binary base system for cement clinker production.

 The third chapter deals with the study of the thermodynamic properties of the Ca2(Alx,Fe1-x)2O5 solid solution as a function Al/Fe variation.

 The fourth chapter will deal with the study of the binary CaO-Al2O3 system. The solids Ca5Al6O14 and CaAl12O19 will be synthesized and their thermodynamic properties will be measured and discussed. The Gibbs energy as a function of temperature for all compounds was generated using the so-called third generation Calphad approach in which the heat capacity of a compound is described by a Plank-Einstein type function. Based on these new Gibbs energies, a full re-modelling of the quasi-binary CaO-Al2O3 was performed and will be presented.

Finally, this thesis manuscript will be terminated by a general conclusion in which I will review the important results of my work as well as possible perspectives of this study.

CHAPTER 1: EXPERIMENTAL METHODOLOGIES AND MODELLING

APPROACH.

EXPERIMENTAL METHODOLOGIES

RAW MIX PREPARATION FOR SYNTHESIS

The syntheses of all compounds performed in the laboratory during our work were done by solid state reaction. The precursor powders (CaCO3, SiO2, Al2O3, Fe2O3, MgO) with a purity ≥99.0%, are weighed by using a precision balance (±0.01g), dried for 24 hours at 500°C into a muffle furnace in air to remove any trace of moisture, then mixed by a mechanical mixer. To avoid any foreign incorporation, alumina powders are dried in alumina crucibles while calcium carbonate and silicon oxide in a platinum crucible, iron oxide and magnesium oxide in porcelain bowls. Subsequently, mixed powders are pressed into pellets to increase their reaction rate. Two alternative sets of tools were used for this task.

1. An automatic press: for sample amounts greater than 3 g, 25 tons of pressure is applied for 5 minutes.

2. A manual hydraulic press: an average pressure of 4 tons is applied to a 3g quantity of raw materials. The manual press is used by default for synthesis and for sample processing for calorimetry. The automatic press is mainly employed for high volume synthesis.

HEAT TREATMENTS OF RAW MATERIALS

Sintering of the raw mix is performed at high temperatures in various furnaces and crucibles based on the chemical elements contained in the mixed powder. Heat treatment is done in two steps:

1. The calcination of CaCO3: this step is carried out at 1000°C during 1 hour; it consists in decarbonizing the CaCO3 according to the following equation : CaCO3 (s) → CaO (s) + CO2 (g). Calcium oxide is very reactive to humidity; therefore, it is advisable to keep it as carbonate for longer storage periods to avoid any calcium hydroxide build-up.

2. The second step is the thermal reaction of CaO + additive pure raw materials (SiO2, Al2O3 and Fe2O3).

SILICATE SYNTHESIS

Calcium silicates (CaO-SiO2) are synthesized in a furnace with air atmosphere, since these oxides are stable under oxygen, no inert gas is required for proper completion of the process. Synthesis is carried out in a platinum crucible at a temperature below the melting point of the constituents and the final product. The duration of the synthesis t1, and the temperature of synthesis T1 vary with the materials being synthesized, and will be discussed in detail in each case. The heating rate of temperature ramp-up was 200K/h. Fig. 2: Silicate synthesis in a platinum crucible under air.

Each synthesis is followed by a quenching step, which can be done in air, or water. Quenching is used to cool the sample quickly to avoid any decomposition reactions on cooling. A water quench being much faster than a quench in air. Rapid cooling allows avoiding phase transformations. In Fig 3, we have an example of water quenching carried out in the laboratory; the process consists in immersing the external walls of the crucible in a container containing water until complete cooling to room temperature. For air quenching, the crucible containing the synthesized sample is taken out of the furnace at high temperature and left in the air until cooling. Throughout our work, we have attempted various methodologies for synthesis, but we will discuss only those results with positive outcome. The phase purity of the samples was checked by X-ray diffraction.

CALCIUM ALUMINATES AND FERRITES SYNTHESIS

Calcium aluminates and ferrites (CaO-Fe2O3-Al2O3) are synthesized in a muffle furnace (Fig. 4) under argon flow (30L/1h, purity: H2O (5 bar ) < 3 ppm; CnHm < 0.5 ppm; O2 < 2 ppm). Alumina crucibles are used instead of platinum ones. The heat treatment temperatures were all below 1300°C (1200°C & 1250°C), while the minimum synthesis time t1 was 12h. The temperature-heating rate in this particular case was 250K/h. The results of the synthesis are characterized by X-ray diffraction.

PHASE CHARACTERIZATION METHOD

To ensure that the previously synthesized sample contains only the expected phase, X-ray diffraction measurements were carried out. The X-ray diffraction study is performed on samples that were ground into a fine, homogeneous powder. This step enables not only the indexing of the diffraction peaks of the phase present in the sample, but also access to the crystalline structure as well as to the lattice parameters of the sought phase. The diffraction peaks of the raw diagram, obtained after acquisition, can be indexed using a database containing crystallographic information on the phase studied.

SAMPLE PREPARATION FOR CHARACTERIZATION

Samples from the syntheses are characterized by X-ray diffraction in order to identify the expected phase. The pellets are ground into a fine powder, and put into a sample holder. Powder amounts used for X-ray diffraction measurements was less than 2 g. Differential Scanning Calorimetry (DSC) measurements are performed on powders of amount ≤ 200 mg. For the drop calorimetric measurements (heat content; dissolution), pellets were produced with masses ranging from 15 mg up to 150 mg.

PRINCIPLE OF X-RAY

X-rays diffraction is a technique for characterizing solids to determine the phases present in a material. The principle is to subject the sample to a monochromatic beam of X-rays and to collect the diffraction spectrum emitted by the sample. The X-ray diffraction peaks are produced by constructive interference of the diffracted beam on condition that the difference in path travelled by the beam between two planes is δ=nλ. Bragg's law gives the conditions for diffraction:

2𝑑 ℎ𝑘𝑙 𝑠𝑖𝑛Ɵ = 𝑛.λ [1]
Where 𝑑 ℎ𝑘𝑙 corresponds to the distance between two crystallographic planes Ɵ: Bragg angle.

𝑛 :

Step.

λ: x-ray wavelength.

Fig. 5 : Principle of X-ray diffraction.

By varying the orientation of the beam with respect to crystal, several dhkl can be measured. The position of each peak and their relative intensity can be traced back to the nature of the crystal using databases. The X-rays diffraction apparatus used is a X'Pert Pro MPD from PANalytical with CuKα radiation of wavelength λ= 1.5419 Å.

The measurements are made in reflection, on a Bragg Brentano configuration. The data processing is done with the Diffract.EVA software and the database we use as a priority is PDF4+2022. This database is oriented towards inorganic materials (about 450,000 records: 90% inorganic and 10% organic or polymers).

DROP CALORIMETER

A MHTC96 calorimeter from SETARAM with two different drop measuring heads (Type S thermopile, 1300°C max, Type B thermopile, 1500°C max) equipped with thermo-cell, furnace and a multi-sample introducer that can hold up to 23 samples were used for the heat content and the drop dissolution measurements. The thermocell, composed of 16 thermocouples distributed on the bottom and on the entire lateral surface of the crucible, offers a good sensitivity. The multi-sample introducer is connected to a vertical tube, which guides the sample during the drop and acts and an exhaust for any vapours potentially given off by the sample. The furnace is connected to a closed water system, which circulates continuously and cools the external and junction of the calorimeter. An acquisition system linked to a computer enables the data collected from the measurements to be processed.

THE CRUCIBLES

The measurements are carried out in an alumina with a platinum inlay crucible (diameter 13 mm and weight 46 mm). The crucible is introduced into the measuring cell and the temperature evolution of the sample is measured by the thermocouples around. Although the regulation temperature of the furnace is taken below the measurement head, a difference exists between the furnace temperature and the sample temperature. The regulation temperature was adjusted to be as close as possible to the target temperatures of the measurements.

GAS SWEEPING

The calorimeter contains two separate gas circuits, one for the furnace and the other for the experiment chamber. The argon gas circuit protects the graphite resistance against oxidation and reduces residual traces of humidity. All measurements were performed under flowing Ar (argon gas) in the measurement cell.

CALIBRATION

Calibration process

All measurements are carried in a platinum crucible (diameter 13 mm and weight 46 mm) which is inserted in an Al2O3 crucible under flowing Ar atmosphere. The calorimeter is calibrated using pure alumina (Al2O3, 99.95%) pieces, which are dried and calcined at 1400°C for 12h. The pellets have a mass ranging from 15 to 150 mg (uncertainty ±0.02 mg). The crucible is loaded with alumina powder up to 15 mm for better reproducibility of the measurements. Three series of 6 or 7 alumina samples are dropped for each temperature from 600°C to 1480°C and the associated heat effect recorded and integrated using the Calypso software package (SETARAM). The number of drops per measurement series was limited to 6 or 7 to avoid piling up pellets in the crucible. With this number of samples, only one layer is covered in the crucible, which leads to results with better reproducibility and repeatability. The calibration constant at a given temperature is calculated using calculated heat content values for

Calibration constant

The calibrations of the calorimeters were carried out at different temperatures of measurements varying from 600°C to 1480°C. Fig. 9 shows the evolution of the calibration constant as a function of the measurement temperature. The uncertainty given is twice the standard deviation of the slope. The calibration constant values obtained as a function of temperature and the uncertainty on the data are shown in

Measurement method overview

For the heat content measurement, pellets were produced with sample weights ranging from 15 to 80 mg (uncertainty ±0.02 mg). Again, two series of 6/7 pellet dropped at each temperature of calibration. The observed integrated heat effects (surface area of peak in µV.s) were plotted as a function of the phase amount introduced into the calorimeter. A linear regression forced passing through the origin was performed to determine the slope. The uncertainty of the measurement corresponds to twice the standard deviation of the slope. The measured heat content corresponds to the slope divided by the calibration constant. The uncertainty of the heat content is the combined uncertainty of the measured surface slope and the uncertainty of the calibration constant using the following formula:

For 𝑦 = 𝑥 1 𝑥 2 ∶ 𝑢 𝑐 (𝑦) = √( 1 𝑥 2 ) 2 𝑢 2 (𝑥 1 ) + ( 𝑥 1 𝑥 2 2 ) 2 𝑢 2 (𝑥 2 ) [2]
In the above formula x1 (µV.s) is the area of the dropped sample signal x2 (µV.s.J -1 ) the calibration constant. Again, the introduction temperature was measured by thermocouple (±0.1K).

DROP SOLUTION MEASUREMENTS

The standard heat of formation of a compound can be determined using drop solution calorimetry. For any compound, at least two dissolution experiments must be performed. For a fictive compound AB with components A and B, the corresponding dissolution reactions are

 Reference drop: (A+B)(25°C) + solvent (T) = solution (T) QA+B  Compound drop: AB (25°C) + solvent (T) = solution (T) QAB
In both cases, the final state is the same, i.e. a solution at the temperature of dissolution with identical composition. The standard heat of formation becomes then:

𝛥fH = QA+B -QAB
If the concentration of A, B and AB in the solvent is small, it is possible, to separate the contribution from A and B. This means, a universal value for pure A and B are measured and can be used.

Separate reference:

 A (25°C + solvent (T) = solution (A)(T) QA  B (25°C) + solvent (T) = solution (B)(T) QB
In this case, the standard heat of formation can be determined by:

𝛥fH = QA + QB -QAB
In general, for small dilutions, the measured heat is independent of temperature. In this case, a mean value is calculated from a series of dissolution experiments. The uncertainty is then calculated from the standard deviation in a classical way. In case of an obvious composition dependence, the value at infinite dilution is calculated by linear extrapolation to zero concentration.

In the case of oxides, there are two types of solvents used in the literature:

aqueous acids or bases and salt mixtures [START_REF] Navrotsky | Progress and new directions in high temperature calorimetry[END_REF]. Typical solvents for CaO and Al2O3 based systems are hydrofluoric acid (Coughlin,1956) or Hydrochloric acid [START_REF] Koehler | Heats and free energies of foramtion of ferrites and aluminates of calcium, magnesium, and lithium[END_REF], lead borate PbO.B2O3 [START_REF] Navrotsky | Progress and new directions in high temperature calorimetry[END_REF]) [START_REF] Trofymluk | Energetics of Formation and Oxidation of Microporous Calcium Aluminates: A New Class of Electrides and Ionic Conductors[END_REF] or eutectic (Li,Na)2O.B2O3 [START_REF] Geiger | Enthalpies of formation of CaAl4O7 and CaAl12O19 (hibonite) by high temperature, alkali borate solution calorimetry[END_REF]. More recently, a pure oxide-based solvent was used by [START_REF] Koryttseva | High-temperature calorimetric study of oxide component dissolution in a CaO-MgO-Al2O3-SiO2 slag at 1450° C[END_REF]. The authors used the mixture CaO (45.9 mol%), SiO2 (35.1 mol%), Al2O3 (8.3 mol%), MgO (10.7mol%) in analogy to an Asian blast furnace slag. Due to the high SiO2 content, this solvent has an acidic nature. The evolution as a function of temperature for this composition was calculated using Factsage and the FTOxid database and is plotted in Fig. 10. The isothermal temperature of the calorimeter was set to 1450°C. Pellets of each sample (pure oxide or compound) with typical weight ranging from 5 to 15 mg were dropped into the solvent from room temperature. Again, the exact introduction temperature was recorded with a uncertainty of +/-0.1K. Dissolution time for the dissolved sample, i.e. return to the baseline, was achieved within 30min for all samples.

The measurements were performed in flowing argon atmosphere. The calibration constant at 1450°C was again determined by dropping pure Alumina pellets into a crucible filled with Al2O3 powder up to 1.5 cm. The calibration constant is 296.115 ± 5.703 µV.s/J for the drop solution measurements.

The measured heat of dissolution for the pure components are summed up in Table 2.

The heat content data for the pure compounds were calculated using Factsage and the FTOxid database.

The measurement gave reliable results for CaO, Al2O3 and Fe2O3. In the case of SiO2, an exothermic reaction takes place as shown in Fig. 12. For kinetic reasons, a solid silicate forms in the melt which is then very slow to dissolve. A reliable measurement is therefore not possible for silica.

SCANNING ELECTRON MICROSCOPY (SEM)

Scanning electron microscopy is a sample analysis technique frequently used in solid-state chemistry. This technique is mainly based on electron-matter interactions.

An electron beam scans the surface of the sample and then transmits the information

MODELLING APPROACH

THE MODEL FOR THE SOLID PHASES

The Ringberg seminar [START_REF] Chase | Thermodynamic models and data for pure elements and other enmembers of solutions[END_REF], a meeting of specialist in numerical modelling of thermodynamic properties, aimed at choosing and adopting more universal models to represent and describe the heat capacity as a function of temperature of an element or compounds in its crystalline, liquid or gaseous state. The goal of this conference was to invent a mathematical model that does not necessarily have a physical significance but could be handled with more ease numerically. The heat capacity at constant pressure Cp is considered as the most important property for thermodynamic modeling, as it translates the evolution of the thermodynamic potentials (G, H and S) as a function of temperature. Thus, two models describing the heat capacity have been chosen in order to manipulate the thermodynamic properties with confidence.

Cfit,Debye=CDebye + aT + bT 2 [4]

The Debye model is given (Cfit,Debye) by the equation 4 and CDebye is described by the expression in equation 5.

C fit,Debye = 9𝑅 + ( 𝑇 Ɵ 𝐷 ) 3 ∫ 𝑒 𝑥 𝑥 4 (𝑒 𝑥 -1) 2 𝑑𝑥 Ɵ 𝐷 𝑇 0 [5] Cfit,Einstein = CEinstein + aT + bT 2 [6]
The CEinstein is described by the expression in equation 7.

CEinstein = 3𝑅 + ( Ɵ 𝐸 𝑇 ) 2 𝑒 𝑥 𝑥 4 (𝑒 Ɵ 𝐸/𝑇 -1) 2 [7]
According to the conclusions of the Ringberg seminar [START_REF] Chase | Thermodynamic models and data for pure elements and other enmembers of solutions[END_REF], the Debye model is accurate in the case of describing experimental heat capacities at low temperatures (<250K) but it is not easy to be handled to calculate G, H and S as there is no analytical solution to the function described in equation [5]. The Einstein model gives excellent results especially for T>250K and the function can easily be integrated.

Where ƟD and ƟE describe the Debye and Einstein temperatures respectively, R is the universal gas constant, aT and bT 2 are the adjustable parameters that ensure the continuity of the function describing the thermodynamic properties of the crystalline solid up to the melting point. This term of aT+bT 2 is also called anharmonic contribution. The low-order anharmonic corrections are described by the term aT, while bT 2 contains the higher-order anharmonic. Although the Debye model correctly describes the Cp at low temperature, it is advisable to use the Einstein model, which has been used recently by [START_REF] Bajenova | Implementation of the extended Einstein and two-state liquid models for thermodynamic description of pure SiO2 at 1 atm[END_REF] but also by [START_REF] Deffrennes | Thermodynamic modelling of the Ca-O system including 3rd generation description of CaO and CaO2[END_REF].

In our study, the following equation with 3 temperatures of Einstein was used to describe the heat capacity as a function of temperature of the solid phases.

Cp = 3R (∑ α i ( Ɵ E i T n i ) 2 exp( Ɵ E i T ) (exp( Ɵ E i T )-1) 2 ) + a 1 T + a 2 T 2 [8] G = E 0 + 3 2 R ∑ Ɵ i α i n i -3RT (∑ α i ln (exp ( Ɵ i T n i ) -1)) + a 1 2 T 2 - a 2 6 T 3 [9]
T(K) for the absolute temperature and α i is the weights of the input of each Einstein temperature contribution. For example, for the compounds Ca3Al2O6 the sum of α i should ideally be equal to the number of atoms in the phase stoichiometry, i.e.

11. The thermodynamic description of the heat capacities of all aluminates was performed using a 3-term Einstein function from 0K to the melting point, the anharmonic adjustment at high temperature was done with two terms a1T+a2T 2 as suggested by the Ringberg seminar. [START_REF] Bajenova | Implementation of the extended Einstein and two-state liquid models for thermodynamic description of pure SiO2 at 1 atm[END_REF] successfully used this model in the case of thermodynamic description of pure SiO2 at 1 atm and Defrennes et al (2020) for the modelling of the thermodynamic properties of pure lime CaO.

THE MODEL FOR THE LIQUID PHASES

The thermodynamic description of the liquid phase is done using the associates model . This model is particularly used when short-range order is observed in the liquid phase, which is the case in metal-oxygen systems but also in some oxide-oxide system with strong interaction. The concept is based on the one hand on the description of oxygen atoms bound to two Al (in the case of a CaO-Al2O3 binary liquid) in this case called "Bridging Oxygen" (BO) and on the other hand on an oxygen-Aluminium-calcium alternation called "Non bridging Oxygen" (NBO). Introduction of Ca + stabilizes AlO4 - [START_REF] Neuville | The structure of crystals, glasses, and melts along the CaO-Al2O3 join: Results from Raman, Al L-and K-edge X-ray absorption, and 27Al NMR spectroscopy[END_REF] and forms fictitious Q n species (where Q refers to tetrahedral site AlO4, n corresponds to the number of bridging oxygen per tetrahedron). There are different configurations Q n species of aluminium in the CaO-Al2O3 system. Q 4 for pure liquid Al2O3; Q 3 corresponds to a fictitious Ca2Al2O5 liquid species; Q 2 describes Ca3Al2O6 liquid species; Q 1 and Q 0 respectively for Ca4Al2O7 and Ca5Al2O8. Both Q 4 and Q 2 have been observed by spectroscopic measurements, Q 1 and Q 0 are associated with very high calcium compounds and are difficult to confirm experimentally due to the high melting temperature and Q 3 remains a subject of debate.

Regarding the stoichiometry of these species there is no general rule fixed on basic oxides. In the CaO-Al2O3 system, Ca3Al2O6 melt will directly describe the associate Q 2 .

Gibbs energy of the solution is therefore expressed with the Gibbs energies of the species in the solution.

G m liq = ∑ x k G k liq k + RT ∑ x k ln(x k ) + ∑ x i i x j ∑ (x i -x j ) v L i,j liq v k [10]  ∑ 𝑥 𝑘 𝐺 𝑘 𝑙𝑖𝑞 𝑘
: this term is called reference term and describes the mechanical mixture of the species without interaction. In the case for the CaO-Al2O3 system, the species are liquid CaO, Al2O3 (Q 4 ) and Ca3Al2O6 (Q 2 )  RT∑ 𝑥 𝑘 𝑙𝑛(𝑥 𝑘 ) 𝑘 : the ideal entropy with R ideal gas constant and T temperature.

 x i x j ∑ (x i -x j ) v L i,j,k liq v
: corresponds to the binary interaction terms between the different species.

𝐿 𝑖,𝑗

𝑙𝑖𝑞 are the temperature dependent binary interaction parameters, which are optimized using experimental data available such as activities as function of composition and temperature, phase diagram and heat of mixing.

L i,j liq = a i,j liq + b i,j liq

[11]

The associates model was selected for our work since it is implemented in all Gibbs energy minimization codes of various software such as Pandat, ThermoCalc, FactSage or OpenCalphad. The phase diagram modelling and calculations were performed using the Pandat software.

CHAPTER 2: THERMODYNAMIC STUDIES OF SELECTED COMPOUNDS IN THE SYSTEM C-S: BELITE & RANKINITE.

INTRODUCTION

Knowledge of the thermodynamic behaviour of the major constituents of cement is necessary to understand the factors that govern the formation and stability of Portland clinker compounds and phases. This chapter deals with the thermodynamic properties of belite (Ca2SiO4) and rankinite (Ca3Si2O7). These two compounds are important constituents of Portland type and carbonatable clinkers. The measurements carried out in this chapter are complementary to those existing in the literature. All results will constitute an important addition to a better description of the CaO-SiO2

binary system. This work will provide new data that was never measured before, especially on pure rankinte and belite. This chapter is divided into two main parts. The first part will focus on the study of belite, including a review of the literature and our experimental measurements, which will be compared with thermodynamic models.

The second part will be focused on the study of rankinite.

CA2SIO4 AND CA3SI2O7 IN CAO-SIO2 SYSTEM

The CaO-SiO2 quasi-binary phase diagram is one of the most studied in the field of oxide chemistry. Rankin and Wright (1915) carried out an early investigation on this system. Subsequently, additional experimental and assessed studies have complemented the previous cited work. Notably Philips and Muan (1959), [START_REF] Greig | Immiscibility in Silicate Melts[END_REF] and [START_REF] Roy | The system CaO-Al2O3 -SiO2-H2O. IV. Phase equilibriums in the high lime portion of the system CaO-SiO2-H2O[END_REF] for experiments contribution. Then, Pelton and Blender (1986) , [START_REF] Taylor | National Physical Laboratory[END_REF] or [START_REF] Hillert | An Assessment of CaO-SiO2 system[END_REF] for the assessed phase diagram. Four solid compounds occur in this binary system, including Ca3SiO5, Ca2SiO4, Ca3Si2O7 and CaSiO3 at atmospheric pressures. Among them, two compounds melt congruently (CaSiO3 and Ca2SiO4) while the others melt incongruently (Ca3Si2O7 and Ca3SiO5).

Building up a thermodynamically accurate database on oxides requires a consistent experimental contribution. Regarding rankinite and belite, the higher temperatures at which both oxides exist have been a limitation in the recent past. A major step in the thermodynamic study of high melting point oxides was the successful development of the calorimetric method. This method will be a starting point for the belite and rankinite research. The experiments carried out in this chapter will provide a substantial complement to the existing data and will be our experimental contribution to a joint project to reassess the CaO-SiO2 phase diagram. Fig. 21 shows the first phase diagram studied and reported by Rankin and Wright (1915). Fig. 22 is the SiO2-2CaO.SiO2 section from the experimental work of [START_REF] Greig | Immiscibility in Silicate Melts[END_REF]. In Fig. 23 and Wright (1915) and [START_REF] Greig | Immiscibility in Silicate Melts[END_REF]. Significant changes with respect to stability relations dicalcium and dicalcium silicates, based on [START_REF] Roy | The system CaO-Al2O3 -SiO2-H2O. IV. Phase equilibriums in the high lime portion of the system CaO-SiO2-H2O[END_REF].

LITERATURE REVIEW ON CA2SIO4

GENERAL ASPECT OF CA2SIO4 POLYMORPHISM

The structural properties of calcium orthosilicate were the subject of several studies due to their interest in the cement industry. Since 1915, Rankin and Wright (1915) had already reported the polymorphic character of calcium orthosilicate. [START_REF] Bredig | Polymorphism of Calcium Orthosilicate[END_REF] confirmed the results of this first study decades later. Calcium orthosilicate exists in five polymorphic forms named α, α' (α'H and α'L), β and γ. The range of existence and stability of each polymorph is temperature dependent and in some cases, the stabilization of the polymorph after quench at room temperature requires the insertion of foreign ions also known as stabilizers. The α-Ca2SiO4 polymorph is stable above 1450°C and melts at 2130°C [START_REF] Eysel | Polymorphism and solid solution of Ca2GeO4 and Ca2SiO4[END_REF]. On cooling α-Ca2SiO4 transforms into α'-Ca2SiO4, this polymorph exists in two intermediate phases α'H and α'L of close crystallographic structure, the range of existence of α'-Ca2SiO4 is between 850°C and 1400°C (Smith, 1962). The γ-Ca2SiO4 polymorph is the most stable at room temperature, its formation is the product of the transformation of the metastable β-Ca2SiO4 form upon cooling. The phase transition temperatures of calcium orthosilicate are closely related to the composition, indeed, the purity of the precursors or the presence of foreign ions can influence the transition temperature.

The insertion of iron oxide (FeO) into the calcium orthosilicate favors the increase of the β-Ca2SiO4 →γ-Ca2SiO4 transition temperature. The γ-Ca2SiO4 → α'-Ca2SiO4 transition occurs at 847°C [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF], this transformation is irreversible, similarly the β-Ca2SiO4→γ-Ca2SiO4 transition is also irreversible and occurs below 500°C [START_REF] Eysel | Polymorphism and solid solution of Ca2GeO4 and Ca2SiO4[END_REF], apart from these two mentioned transitions, the other phase transitions are reversible. It is common to find transition temperature values slightly different from those given in Fig. 24 depending on the actual composition of the polymorph: presence of impurity or stoichiometric imbalance due to an excess of one of the precursors. Influence of the composition on the transition temperatures was studied by [START_REF] Forest | Connaissance de l'orthosilicate de calcium[END_REF]. In their work, the authors showed that the composition plays a major role on the value of the transition temperature of calcium orthosilicate polymorphs. This particularity explains the differences between the transition temperature values given in the literature by different authors (Smith, 1962) [START_REF] Forest | Connaissance de l'orthosilicate de calcium[END_REF]) [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF]. Fig. 24 is a polymorphic transformation scheme for calcium orthosilicate, based on the work of [START_REF] Eysel | Polymorphism and solid solution of Ca2GeO4 and Ca2SiO4[END_REF].

Fig. 24 : Polymorphic transformation of Ca2SiO4 as a function of temperature evolution by [START_REF] Eysel | Polymorphism and solid solution of Ca2GeO4 and Ca2SiO4[END_REF].

The β-Ca2SiO4 phase is metastable and undergoes structural rearrangements on cooling and then stabilizes in the γ-Ca2SiO4 phase, this reaction is called displacive.

The β-Ca2SiO4 →γ-Ca2SiO4 transition is slow at atmospheric pressure and induces a 12% increase in crystal volume at room temperature; this phenomenon is called dusting and was observed in the laboratory during the synthesis of γ-Ca2SiO4. The γ→α'L transformation occurs only on heating, the phase transition is slow due to the low transition temperature and the large structural rearrangement. This transformation is called semi-reconstructive because it induces a change in the coordination of the Ca atoms as well as a rotation of the tetrahedron [START_REF] Forest | Connaissance de l'orthosilicate de calcium[END_REF]. It has been shown that the transformations from α'H to α'L and α'L to β are reversible (Smith, 1962) [START_REF] Eysel | Polymorphism and solid solution of Ca2GeO4 and Ca2SiO4[END_REF]) [START_REF] Saalfeld | X-Ray Investigation of Single Crystals of β-Ca2SiO4 (Larnite) at High Temperatures[END_REF]. Nevertheless, the α'H and α'L forms have similar structures and are therefore difficult to dissociate and distinguish. Since both polymorphic forms exist at probably identical free energies, transformation from α'H to α'L does not cause any consequent crystallographic cell deformation as is a continuous phase transitions.

CA2SIO4 CRYSTALLOGRAPHIC STRUCTURES

The growing interest in the crystallographic study of calcium orthosilicate polymorphs dates back to the previous century. Indeed, one of the first structural studies of the γ-Ca2SiO4 polymorph was done by analogy with the structure of the olivine Mg2SiO4 (O'Daniel and Tscheischwili, 1942) [START_REF] Smith | The Crsytal Structure of γ-Dicalcium Silicate[END_REF]

CA2SIO4 THERMODYNAMICS DATA REVIEW

One of the crucial points of this work is to fill the gap in terms of experimental thermodynamic data. The critical review of the literature has allowed us to highlight a number of gaps in the thermodynamic data for calcium orthosilicate varieties, in particular relative enthalpy. As early as 1951, the enthalpy of formation of β-Ca2SiO4

was already known thanks to the work of [START_REF] Elsner | Die Berchnung des exothermen Effekts bei der Bildung von Portlandzement aus der Zusammensetzung des gebrannten Klinkers[END_REF], [START_REF] Johannson | Studies on the Thermochemistry of the Compounds Occurring in the System CaO-Al2O3-SiO2. V. The Heats of Formation of Tricalcium Silicate and Dicalcium Silicate[END_REF], [START_REF] Ayed | Determination par calorimetrie de dissolution des enthalpies de formation de quelques silicates, aluminates et alumino-silicates de calcium[END_REF] and [START_REF] King | Heats of Formation of Crystalline Calcium Orthosilicate, Tricalcium Silicate and Zinc Orthosilicate[END_REF]. Later, [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF] measured relative enthalpy of β,α',α-Ca2SiO4 from 25°C to 1543°C and of the γ-Ca2SiO4 variety up to the inversion temperature γ-Ca2SiO4→α'-Ca2SiO4. The γ-Ca2SiO4→α'-Ca2SiO4 heat of transition was evaluated by Coughlin and later by [START_REF] Forest | Connaissance de l'orthosilicate de calcium[END_REF] but remains a subject of discussion. In this manuscript, the experimental work, especially the heat content measurements will cover a wider temperature range from the γ-Ca2SiO4 polymorph existence domain to α-Ca2SiO4. [START_REF] King | Low Temperature Heat Capacities and Entropies at 298.15 °K of Some Crystalline Silicates Containing Calcium[END_REF] and [START_REF] Todd | Low-temperature Heat Capacities and Entropies at 298.16°K of Crystalline Calcium Orthosilicate, Zinc Orthosilicate and Tricalcium Silicate[END_REF] have also measured the low temperature heat capacities of γ-Ca2SiO4 and β-Ca2SiO4 respectively and various thermodynamic databases implemented Ca2SiO4 heat of transition data by critical assessment of the available literature data [START_REF] Haas | Thermodynamic Tabulations for Selected Phases in the CaO-Al2O3-SiO2-H2O at 101.325kPa (1atm) between 273.15 and 1800[END_REF] and FactSage software).

HEAT OF TRANSITION

There are some discrepancies between the experimental values and some data calculated from FactSage software and its thermodynamic databases. Using commercial data outside of experiments induces errors in calculations of further thermodynamic properties. In fact, an excessively high heat of transition with respect to the measurements leads to an overestimation of the relative enthalpies. Although modelling is useful because it allows us to explore properties not accessed through experiments, one of the benefits of doing experiments is that it allows us to validate a model. Thus, unlike FTPS data from FactSage software, [START_REF] Haas | Thermodynamic Tabulations for Selected Phases in the CaO-Al2O3-SiO2-H2O at 101.325kPa (1atm) between 273.15 and 1800[END_REF] model provides a heat of transition more consistent with [START_REF] Coughlin | heats of formation of of crystalline CaO.Al2O3, 12CaO.7Al2O3 and 3CaO.Al2O3[END_REF][START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF][START_REF] Forest | Connaissance de l'orthosilicate de calcium[END_REF] experiment. In

HEAT OF FORMATION

Research in the literature on direct measurements of standard enthalpies of formation is gathered in Table 6. In addition, there are databases listing enthalpies of formation of Ca2SiO4 for the different polymorphs based on thermodynamic calculations or models. For example, to deduce α'-Ca2SiO4 standard enthalpy of formation, [START_REF] Haas | Thermodynamic Tabulations for Selected Phases in the CaO-Al2O3-SiO2-H2O at 101.325kPa (1atm) between 273.15 and 1800[END_REF] used the heat of decomposition of Ca3SiO5 to β-Ca2SiO4, measured by [START_REF] Benz | Thermodynamics of the solid system CaO-SiO2 from electromtive force data[END_REF]

EXPERIMENTAL STUDY OF BELITE

SYNTHESIS PROCEDURE

The previous section discussed the data available in the literature for the solid phases. There are several key measurements, which should be repeated or missing data that must be ascertained to complete a thermodynamic assessment targeted at modelling cement clinker formulation. This section details the experimental methods and preparation used to obtain these measurements. The starting materials are CaCO3 (Alpha Aesar, 99.5%) and SiO2 (Sibelco, 99%) which are dried in a muffle furnace at 500°C in air for 24h. The mixture is homogenized in a mechanical mixer for 24h and pelletized using a hydraulic workshop press (4.5 tons on 3g of powder). For Ca2SiO4, a powder mixture of CaCO3 (6.97±0.01g) and SiO2 (2.09±0.01g) is calcined at 1000°C for 1h and annealed at 1550°C for 8h followed by slow cooling to room temperature. A loss on ignition of 34.08% (in agreement with theoretical value) is recorded. Fig. 26 is the reagent mixture pelleted by press before heat treatment. After the heat treatment, the bright colour of the mix remains unchanged. Dust build-up after cooling is an indication that a γ-Ca2SiO4 phase is occurring. Structural analysis will provide a purity assessment on the phase from the reaction proceeds.

CA2SIO4 X-RAY PHASE ANALYSIS

Samples mineralogical composition identification was carried out using X-ray diffraction (X'Pert Pro MPD, PANalytical), with CuKα radiation of λ= 1.5419 Å.

Crystallographic study by X-ray diffraction confirmed a single polycrystalline phase and all peaks identified as belonging to γ-Ca2SiO4 olivine crystallizing in an orthorhombic symmetry lattice. Cell parameters adjustment was done with DIFFRAC.EVA5.2 from Brucker AXS based on PDF4+ 2022 database. X-rays recording has carried out over a period of 1h 59 min on a 2Ɵ angular range from 10° to 120°. Ca2SiO4 X-rays diffraction pattern is plotted in Fig. 27. Regarding the lattice parameters, results gathered in Table 7 agree with published literature. Discrepancies between our crystallographic data and literature are mainly related to the type and purity of starting material as well as synthesis procedure. For instance, we used 99.5% CaCO3 to produce CaO while [START_REF] Smith | The Crsytal Structure of γ-Dicalcium Silicate[END_REF] employed Ca(NO3)2 as a raw material but did not specify purity. Although [START_REF] Udagawa | Refinement of the crystal structure of γ-Ca2SiO4[END_REF] started experiment with CaCO3 as a CaO precursor; the author synthesized γ-Ca2SiO4 by flux method in presence of CaCl2 as flux in an electric furnace. 7 : γ-Ca2SiO4 crystallographic data calculated from X-ray pattern after synthesis.

From the crystallographic data, we have reproduced the crystallographic structure on VESTA software. The layout of the oxygen atoms around the cations can be illustrated.

DIFFERENTIAL SCANNING CALORIMETRY: CA2SIO4

We measured the transition temperature of Ca2SiO4 by DSC Labsys TM Evo. On heating, the powder in the platinum crucible sintered at high temperature, and then on cooling, the sintered powder gained volume, reflecting the transformation of α'-Ca2SiO4 to γ-Ca2SiO4 (with an intermediate metastable β-Ca2SiO4 as stated [START_REF] Eysel | Polymorphism and solid solution of Ca2GeO4 and Ca2SiO4[END_REF].

Heating

The first peak (a) on the DSC curve is the transition from γ-Ca2SiO4 to α'-Ca2SiO4, the signal is not well characterized and the temperature of this transition cannot be precisely defined. But, this signal lies between 800°C and 900°C, which is in agreement with the transition temperature of γ-Ca2SiO4 → α'-Ca2SiO4 847°C reported by [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF] and . For the second (b), the start of the curve deviates from its baseline at 1413°C forming a more defined peak than the previous one, the minimum of the peak is at 1430°C whereas the return from the baseline is at

1447°C. Although it is not clear exactly which transition temperature values should be used for the ascent, it can be seen that the interval of existence of the transition peak is in agreement with the literature value. Furthermore, it was found that the baseline increases with temperature when acquiring this particular compound.

Cooling

In crystalline materials, the exothermic transformation indicating the In Table 8, we compared the polymorphic transformation temperatures recorded during the cooling process by [START_REF] Smith | Re-Examination of the Polymorphism of Dicalcium Silicate[END_REF] with our results. As the authors have done, we have also used K2SO4 for calibration. For the α-Ca2SiO4 → β-Ca2SiO4 inversion, we agree with the value from high-temperature X-ray powder diffraction while DTA reports a higher value. For α-Ca2SiO4 → α'-Ca2SiO4, our values are lower than those in the literature. Similar to our study, [START_REF] Smith | Re-Examination of the Polymorphism of Dicalcium Silicate[END_REF] identified two unexplained peaks, but we disagree on the β-α' transition point. Raw materials purity and method of analysis influence the quality of the measurements, which partly explains discrepancies in Table 8.

CA2SIO4 RELATIVE ENTHALPY MEASUREMENT

Assessment on Ca2SiO4 thermodynamic properties reveals a lack of relevant relative enthalpy dataset and inconsistencies between the experimental information and the data stored in thermodynamic databases. Thanks to [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF] important work in providing available values on β-Ca2SiO4→α', α-Ca2SiO4. In this section new experimental measurements of relative enthalpy of Ca2SiO4 polymorphs from γ-Ca2SiO4 to α',α-Ca2SiO4 will be discussed. Relative enthalpy measurements were performed after calorimeter calibration with α-Al2O3 at Ca2SiO4 polymorph existence temperatures. As mentioned previously, starting polymorph for the drop measurements was the most stable form γ-Ca2SiO4.

RESULTS AND DISCUSSION

The results of the relative enthalpies measurements are summed up in Table 9.

There are no heat content measurements of the γ→α' Ca2SiO4 transition in the literature. [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF] Measured data are plotted in Fig. 32. Our results are compared with those in the literature. [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF] carried out thermodynamic measurements by using two distinct polymorphs as reference, namely γ-Ca2SiO4, the more stable form, and β-Ca2SiO4 containing 0.32% aluminium and iron oxide and 0.14% magnesium oxide. For α'α -Ca2SiO4, [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF] data have been adjusted with γ-Ca2SiO4→ β-Ca2SiO4 enthalpy of transition from [START_REF] Forest | Connaissance de l'orthosilicate de calcium[END_REF], in order to have the same reference state.

For γ-Ca2SiO4→ α'-Ca2SiO4, there is good agreement with [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF]. Similarly, for γ-Ca2SiO4→ α-Ca2SiO4 we agree with the corrected values from assessment.

Using [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF] data (β, α') and our experimental results (γ, α'), we calculated the average value of the γ-Ca2SiO4→ β-Ca2SiO4 transition and then deduced the β→α' transition: 1812 J.mole -1 . This result is in agreement with [START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF] finding: 1841 J.mole -1 at 697°C. We were unable to extract usable results for γ-Ca2SiO4→ α'-Ca2SiO4 transition, but by extending data to the transition temperature (847°C), we estimated the transition enthalpy to be 4722.33 J.mole -1 , which is questionable as it is much lower than the literature value: ~14 KJ.mole -1 , (

O'Brien, High temperature heat contents of calcium orthosilicate, 1957) and [START_REF] Forest | Connaissance de l'orthosilicate de calcium[END_REF]. FTPS and Haas et al (1981) data seems to be overestimated. The α'-Ca2SiO4 → α-Ca2SiO4 transition temperature is reported in the literature to be 1423°C [START_REF] Smith | Re-Examination of the Polymorphism of Dicalcium Silicate[END_REF] and 1416°C in our DSC measurements. The drop measurement was performed at 1400°C, and should correspond to α'-Ca2SiO4. However, our value anomalously high and agrees better with α-Ca2SiO4. It can be suggested that at this temperature the inversion process may have started. 2.6 LITERATURE REVIEW ON CA3SI2O7

CRYSTALLOGRAPHIC STRUCTURE AND POLYMORPHISM OF CA3SI2O7

Ca3Si2O7 is commonly found as a natural mineral in the form of two polymorphs: rankinite and kilchoanite. [START_REF] Roy | The system CaO-Al2O3 -SiO2-H2O. IV. Phase equilibriums in the high lime portion of the system CaO-SiO2-H2O[END_REF] first synthesized a Z phase with chemical formula 9CaO. 6SiO2. H2O, Kilchoanite is obtained by dihydroxylation of the hydrate without changing the symmetry. Moody first defined lattice parameters of Rankinite but did not determine crystal structure (Moody, 1952). Regarding the structure, Rankinite consists to Si2O7 structural units linked tetrahedra parallel to the c-axis and Ca atoms with seven nearest neighbours of oxygen. Kilchoanite is composed of isolated SiO4 tetrahedra and isolated Si3O10 triple-linked tetrahedra groups; the crystallographic structure is close to that of calcio-olivine (γ-Ca2SiO4). There are four types of Ca in kilchoanite; three are octahedralIy coordinated while one has eight close oxygen neighbours. Rankinite is a high temperature polymorph of kilchoanite but it is not possible to obtain kilchoanite from rankinite even with slow cooling. It consists of groups of Si2O7 tetrahedra bonded together by Ca atoms each having sevens coordinated oxygen.

CA3SI2O7 THERMODYNAMIC DATA REVIEW

The name Rankinite was used as a tribute to G. A Rankin (1915), it is a rare and natural mineral found in fused rocks and in carbonatable clinkers. Rankinite is formed from a mixture of silica and limestone in the ratio 2:3 and can be isolated and synthesized in the laboratory. However, there are very few published studies on the thermodynamics of rankinite; the main data known from the literature are low temperature heat capacities which were measured by [START_REF] King | Low Temperature Heat Capacities and Entropies at 298.15 °K of Some Crystalline Silicates Containing Calcium[END_REF], the standard enthalpy of formation by Weeks (1956) and EMF measurement by [START_REF] Benz | Thermodynamics of the solid system CaO-SiO2 from electromtive force data[END_REF] in a different temperature range. No data on relative enthalpy are known in the published papers, so it is difficult to have a precise thermodynamic description of the Gibbs energy of rankinite.

Ca2Si3O7 X-ray phase analysis

X-ray diffraction after first heat treatment reveals the secondary phases CaSiO3 and Ca2SiO4. After grinding and a second heat treatment we found a decrease in the amount of secondary phase quoted above. Intermediate grinding and mixing at each heat treatment allowed a better homogenization of the reaction products. Finally, after 4 series of thermal annealing, the minor phases (CaSiO3 and Ca2SiO4) have completely reacted according to the following equation: CaSiO3+Ca2SiO4→Ca3Si2O7.

All diffraction peaks were identified at the Ca3Si2O7 phase. The crystalline solid from the synthesis crystallizes in a monoclinic lattice; the structural parameters are gathered in Table 12. Table 12 : Ca3Si2O7 crystallographic data calculated from X-ray pattern.

DIFFERENTIAL SCANNING CALORIMETRY

The melting temperature of rankinite was determined by differential scanning calorimetry. The measurement was performed at a rate of rise of 10K per minute. The first deviation from the baseline curve is related to premelting. This effect has been observed in the past on pseudowallostonite and gehlenite and is associated with the strong dynamics of calcium atoms near the melting point. According to the studies of [START_REF] Richet | Premelting effects in minerals: an experimental study[END_REF], premelting can also be an atomic rearrangement of the solid while keeping a crystalline structural order in the proximity of the real melting point.

Premelting has for effect a notable increase of the heat capacities but also of the transport properties of some mineral (Bouhfid et al, 2002). Differential scanning calorimetry measurements indicate that the pre-melting temperature of rankinite is at 1327°C the sample increases in temperature until complete deviation from the baseline: the beginning of melting. Then, the peak decreases until the most negative value of the DSC curve: the end of the melting. The pre-melting and melting temperatures were determined through the DSC plot in Fig. 36 of the rankinite and then corrected using the calibration equation from the standard sample K2SO4 and NaCl, whose measurements were made at a rate of 10K/min. DSC first deviation from the baseline corresponds to the premelting temperature and occurs at 1328°C, the beginning of the melting starts at 1465°C that is in agreement with the temperature of the invariant given by [START_REF] Phillips | Phase Equilibria in the System CaO-Iron Oxide-SiO2 in Air[END_REF] is 1464°C, while the melting ends at 1480°C. In the case of the melting of an invariant, the temperature of the beginning of melting should be equal to the temperature of the end of melting, but in practice, the DSC curve has a slope, which approximates a vertical flow, the variation of this slope depends on the rate of temperature rise set by the experimenter. In the case of measurement on the rankinite there is a difference of 15.60°C between the beginning and the end of the melting.

In order to illustrate this effect of pre-melting on the heat capacities, we have plotted in Fig. 35 rankinite (Ca3Si2O7) relative enthalpy in the form of mean heat capacity, Cm=(HT-H298.15K) / (T-273.15). A significant increase in the mean heat capacities can be clearly observed in the area near the melting point of rankinite.

Although no particular study on rankinite in the premelting zone has been carried out, it seems that this behaviour is attributed to a cationic disorder for some oxides [START_REF] Richet | Premelting effects in minerals: an experimental study[END_REF]Bouhfid et al, 2002).

Fig. 37 : Mean heat capacity of Rankinite (Ca3Si2O7), P-Z means premelting zone.

RELATIVE ENTHALPY

The results of the heat content measurements for Rankinite are summarized in Experiments are an important step to not only provide real values but also to validate the models made accessible to customers. Many users rely on the data reported in the FTPS without checking its validity. Which, moreover, are not always describe accurately the thermodynamic and properties of the compounds studied.

ENTHALPY OF FORMATION

Although the enthalpy of dissolution of SiO2 is not measured directly, it is possible to obtain this value indirectly. By starting from the value of ΔfH fixed at -136KJ.mole -1 and the enthalpy of dissolution of Ca2SiO4, we calculated ΔdissH of SiO2 and then determined the corresponding value for the enthalpy of formation of Ca3Si2O7.

The heat of dissolution is described by linear variation. To calculate the standard heat of formation, we extrapolated the value to infinite dilution in the solvent using a linear regression. The obtained value is: We plotted in Fig. 41 experimental results and fits to these data as they were used in the collaborative project. This work has led to the writing of a collaborative paper with the University of Aberdeen [START_REF] Abdul | CaO-SiO2 Assessment: 3rd generation modelling of thermodynamic properties[END_REF].

CONCLUSION

Understanding the thermodynamic processes that govern thermal properties of of Brownmillerite is its ability to resist sulfates, which is an important property for heavy construction in water contact areas. There are also much wider applications, notably as electrodes for solid oxygen fuel cells, catalysts for hydrogen production or as gas sensors. In this chapter, the available experimental information on the structure and the thermodynamic properties will be reviewed. In addition, new experimental thermodynamic properties were measured to better describe the Gibbs energy of brownmillerite. The main thermodynamic properties studied are heat contents and the standard heat of formation as a function of composition together with the melting points. This chapter consists of a first part reviewing the existing studies on brownmillerite and a second experimental part complementing work already published.

FERRITE (C4AF) IN THE SYSTEM CAO-AL2O3-FE2O3

The ternary phase with the highest concentration of calcium occurring in the CaO-Al2O3-Fe2O3 system is brownmillerite. This compound is commonly encountered in Ordinary Portland and high alumina cements. Various studies based on methods such as X-ray and neutron diffraction, chemical and thermal analysis highlighted that this compound is in fact a solid solution Ca2Fe2-xAlxO5 is present ranging from Ca2Fe2O5 to Ca2Al2O5. Under normal atmospheric pressure conditions and in absence of other additional oxide compounds such as CaO, Al2O3 and Fe2O3, the solid solution Ca2Fe2-xAlxO5 exists in the composition range x=0 to x=1.4 [START_REF] Taylor | The crystal structure of kilchoanite, Ca6(SiO4)(Si3O10) with some comments on related phases[END_REF].

Brownmillerite is obtained when x=1 but Ca2Al2O5 (x=2) end member composition can only be synthesized at 2.5 GPa pressure [START_REF] Aggarwal | Synthesis and Properties of Dicalciumm Aluminate, 2CaO.Al2O3[END_REF]. Newkirk and Thwaite (2002) studied the ternary CaO-Al2O3-Fe2O3 phase diagrams in the composition range important to cement chemistry Fig. 42. Tie lines were determined by microscopy, X-rays diffraction and differential thermal analysis. At point E1, CaO, Ca3Al2O6 and the ferrite phase are in equilibrium at 1389°C. An Eutectic equilibrium E2 between Ca3Al2O6, Ca12Al14O33 and ferrite occurs at 1336°C while the Ca12Al14O33-CaAl2O4-ferrite invariant is present at 1335°C [START_REF] Newkirk | Pseudoternary System Calcium Oxide-Monocalcium Aluminate (CaO•Al2O3 )-Dicalcium Ferrite (2CaO• Fe2O3 )[END_REF] and melting point of Ca2FeAlO5 is reported to be 1415±5 °C [START_REF] Lea | The chemestry of Cement and Concrete[END_REF] and [START_REF] Hansen | Studies on the system calcium oxide-alumina-ferric[END_REF]).

Fig. 42: System CaO-CaO.Al2O3-2CaO.Fe2O3, pseudo-ternary [START_REF] Newkirk | Pseudoternary System Calcium Oxide-Monocalcium Aluminate (CaO•Al2O3 )-Dicalcium Ferrite (2CaO• Fe2O3 )[END_REF].

CA2FE2-XALXO5 SOLID SOLUTIONS: CRYSTAL STRUCTURE AND COMPOSITION

Since Hansen et al's work (1928), later corroborated by the investigation of Solacolu (1932), it is now known that in dicalcium ferrite (Ca2Fe2O5) part of Fe 3+ can be substituted by Al 3+ whose solid solution formula is written as Ca2Fe2-xAlxO5.

Brownmillerite consists of sheets of corner-sharing (Fe,Al)O6 octahedron connected to a single chain of (Al,Fe)O4 tetrahedron parallel to c axis, calcium (Ca 2+ ) is located in the interstitial site between alternating layer of octahedral sheet and single tetrahedral chain (Colville & Geller, 1971). Al 3+ and Fe 3+ are randomly located on both potential

MAGNETIC TRANSITION OVERVIEW

At room temperature, the Ca2Fe2-xAlxO5 solid solution is antiferromagnetically ordered when the amount of Al ions is between 0 and 1 [START_REF] Phan | Electronic structure and magnetic properties of Al-doped Ca2Fe2O5 brownmillerite compounds[END_REF]. Some studies based on Mossbauer spectra established the Neel temperature of pure Ca2Fe2O5 and Ca2FeAlO5. According to the work of [START_REF] Kim | Structural and Magentic Properties of Brownmillerite Ca2AlxFe2-xO5 System[END_REF] the magnetic transition of Ca2FeAlO5 occurs at 60±15°C while Grant et al reported 77°C. For

Ca2Fe2O5 the Neel temperature is reported to be 445°C by [START_REF] Redhammer | Structural variations in brownmillerite series Ca2(Fe2-xAlx)O5: Single-crystal X-ray diffraction at 25°C and high-temperature X-ray powder difraction (25°<T<1000°C)[END_REF] and 452°C (Zhou and Goodenough, 2005).

FERRITE HEAT OF FORMATION

The standard enthalpy of formation (ΔH°f) of brownmillerite reported in the literature was mainly measured by calorimetric methods. One of the first published data on ferrite dates from 1956. In their study, the authors, [START_REF] Newman | Heats of Formation of Hexacalcium Dialumino Ferrite and Dicalcium Ferrite[END_REF] reported Ca6Al4Fe2O15 and Ca2Fe2O5 ΔH°f at 25°C. In order to investigate the ΔH°f , [START_REF] Koehler | Heats and free energies of foramtion of ferrites and aluminates of calcium, magnesium, and lithium[END_REF] established a Hess cycle from the dissolution reactions of Ca2Fe2O5 in hydrochloric acid. Furthermore, [START_REF] Prasanna | Energetics sin the brownmillerite-perovskite pseudobinary Ca2Fe2O5-CaTiO3[END_REF] calculated ΔH°f of Ca2Fe2O3 referred to the oxides based on the enthalpies in solution of CaO, Fe2O3 and CaFeO2.5 and derived the value referred to the elements at 25°C.

Regarding Ca2FeAlO5, standard enthalpy of formation of this composition has been measured by [START_REF] Ayed | Determination par calorimetrie de dissolution des enthalpies de formation de quelques silicates, aluminates et alumino-silicates de calcium[END_REF]. The only existing data on this component is the energy of formation calculated from the elements normalized per atom in the unit cell. We have gathered in Table 15 the measured values from the constituent oxides and Table 16 calculated data from Materials Project, FactSage database, additionally we added [START_REF] Koehler | Heats and free energies of foramtion of ferrites and aluminates of calcium, magnesium, and lithium[END_REF] and [START_REF] Prasanna | Energetics sin the brownmillerite-perovskite pseudobinary Ca2Fe2O5-CaTiO3[END_REF]

EXPERIMENTAL STUDIES

To investigate thermodynamic properties, we synthesized brownmillerite with varying alumina content by solid-state reaction. In this section, the experimental study of Ca2Fe2-xAlxO5 is discussed. Raw materials are CaCO3, Fe2O3, and Al2O3, which were dried in a muffle furnace at 500°C under air for 24h. Four distinct compositions were defined (x=0, 0.5, 1 and 1.4) and the raw mix powders in appropriate amounts were mixed for 20 minutes. A first heat treatment of 1000°C was applied to calcine the CaCO3. The synthesis was carried out under argon (30L/h, 200K/h) at 1200°C. Starting composition and sintering times are listed in Table 17. X-ray sdiffraction confirmed each phase with defined compositions by comparison of the measured lattice parameters with the published data (Table 17).

crucible at a height of 15 mm in order to improve the sensitivity of the measurement and to soften dropped samples.

CA2FEALO5 MEASUREMENT RESULTS

For Ca2FeAlO5 the relative enthalpy was measured from 590 to 1096°C starting from room temperature as the starting point. Ca2FeAlO5 reaction of formation used to calculate relative enthalpies in FactSage software is given by equation [11]. The data from FTOxid are based on estimation using the Neumann-Kopp rule and the pure components. Using the FTOxid database, we calculated the relative enthalpies on FactSage by setting the same temperature range as the ones measured. In Fig. 45, we plotted our results alongside those obtained using the Gibbs energy data included in the FTOxid database. The main discrepancy between both data sets is at high temperature, where the data points at 1096°C and 985°C are respectively 13.6KJ.mole -1 and 14.5KJ.mole -1 higher than the experimental results. Below these temperatures, FTOxid data are in agreement with the measured values.

CA2FE0.6AL1.4O5 MEASUREMENT RESULTS

A similar methodology was adopted as for the previous sample (Ca2FeAlO5 A better description in the database would therefore need a remodelling. A particular issue concerning the calorimetric method applied for measuring relative enthalpy is related to the surrounding temperature control. For instance, the temperature inside the distributor above the calorimeter containing the dropped samples cannot be set. Initial temperature variation depends not only on meteorological changes, but also on furnace temperature in the calorimeter. Thus, it can be seen that in general initial temperature increases with measuring temperature (Table 18 and19). However, an increase of 3°C cannot explain the difference with the modelled value in the FTOxid database. The relative enthalpy from 24 to 27°C is estimated to be of the order of a few 100 J.mole -1 and is therefore in the reported uncertainty of the measurement. As there is no low temperature heat capacity data for the Ca2Fe2-xAlxO5 solid solution available, it is not possible to correct all experimental values to the standard reference temperature of 25°C. Furthermore, in this type of equipment the absolute uncertainty increases with temperature, this is mainly due to radiation losses at high temperatures, which are difficult to monitor.

MELTING POINT

The melting point determinations were performed by differential scanning calorimetry Labsys TM Evo (DSC). The scanning rates were 5K/min and 10K/min and the maximum temperature was set at 1508°C. In this study, we measured melting point of Ca2Fe2-xAlxO5 for the compositions x=0.5, x= 1 and x=1.4, the results are listed in The melting point of the solid solution depends on the Al content in the solid solution. It is observed that the insertion of Al ions leads to a reduction of the melting temperature, for the Ca2FeAlO5 composition the melting point we measured is 13°C higher than reported in the literature (1415°C±5). Pure Ca2Fe2O5 melts at 1450°C [START_REF] Lea | The chemestry of Cement and Concrete[END_REF], this value is close to that of the composition at x=0.5 but is still 4K higher. For this composition, a lower value than pure Ca2Fe2O5 should be expected, as the insertion of Al influences the melting point in the solid solution.

STANDARD HEAT OF FORMATION OF CA2ALFEO5

The standard heat of formation was measured using dissolution calorimetry.

Two series of Ca2AlFeO5 samples were dissolved in the basic slag solvent described in Chapter 1. The obtained results are presented in Fig. 47. The heat of dissolution varies linearly with composition. Again, to calculate the standard heat of formation, we extrapolated the value to infinite dilution in the solvent using a linear regression. The obtained value is given by: Qdiss (25°C) = 452618.7 ± 44015.3 J.mole -1 .

Similarly, using the dissolution data for pure CaO, Al2O3 and Fe2O3 from chapter 1, the standard heat of formation can be calculated and the value is:

ΔfH(25°C) = -46844.5 ± 44512.5 J.mole -1 .

Our new value agrees with the one reported by [START_REF] Ayed | Determination par calorimetrie de dissolution des enthalpies de formation de quelques silicates, aluminates et alumino-silicates de calcium[END_REF] considering the uncertainty of our measurement.

CONCLUSION

The Ca2Fe2-xAlxO5 solid solution was studied experimentally and the results reported in this chapter; solid-solid synthesis under inert atmosphere is a necessary parameter to avoid any side reaction such as the formation of Ca12Al14O33 stabilized by water vapour. The heat contents as a function of temperature were measured for two compositions relevant to cement systems x=1 and x=1.4. The calculated data from

FTOxid agrees with the experimental data for the first composition while the second was overestimated. As far as the transition temperature measurements are concerned, the addition of aluminium reduces the melting point of the solid solution. The measured enthalpy of formation still has a considerable uncertainty but experimental value is in reasonable agreement with the only experimental data point available in the literature.

INTRODUCTION

The knowledge of thermodynamic properties of CaO-Al2O3 is a major issue in different fields such as the cement industry, metallurgy, geology, ceramic materials A review of available literature information on the CaO-Al2O3 system was carried out in this chapter in order to determine the various missing additional data. Starting from the literature, a new method of thermodynamic description based on the third generation Einstein model was used to describe the thermodynamic properties of the heat capacities of all calcium aluminates from 0K to the melting point. In addition, thermodynamic properties such as relative enthalpies and heat of formations were measured in particular for the compound CaAl12O19 as well as Ca5Al6O14 for which no relevant thermodynamic data is reported in the literature up to now. Finally, a new version of the CaO-Al2O3 system was modelled and calculated. This chapter is divided into three parts: first, we will review the available literature, then we will present the additional experimental results obtained in the laboratory and finally we will finish with the modelling of the thermodynamic properties of calcium aluminates.

CRYSTALLOGRAPHIC DATA OF SOLID COMPOUNDS IN THE CAO-AL2O3

SYSTEM

There are five compounds and one solid solution in the CaO-Al2O3 pseudobinary system. These phases are commonly noted according to the cement nomenclature as: CA (CaAl2O4), CA2 (CaAl4O7), C3A (Ca3Al2O6), CA6 (CaAl12O19), C5A3 (Ca5Al6O14), the high pressure phase C2A (Ca2Al2O5 ) and the solid solution C12A7 (Ca12Al14O32+x) with x ranging from 0 to roughly 1.5. The stability range of C5A3

phase is not clear. The compound is said to be metastable because it can be destabilized in the presence of excess oxygen. Rankin and Wright (1915) first identified this phase but its crystallographic structure was studied years later. The structure of C5A3 consists of alternating twisted sheets of deformed AlO4 tetrahedra connected at the corners to form a network of five-membered rings and layers of Ca atoms. Two main, separate and concordant studies have shown that C5A3 crystallizes in an orthorhombic lattice of the Cmc21 space group [START_REF] Aruja | The Unit Cell of Orthorhombic Pentacalcium Trialuminate 5CaO.3Al2O3[END_REF] and Vincent ( 1978)). CA exists as two polymorphs. The first polymorph consists of an AlO6-octahedral double layer structure; the Ca atoms are located in the interstitial sites and form a bridge between two layers of AlO6-octahedral. While the second polymorph has a tunnel structure [START_REF] Horkner | Zur Kristallstruktur von CaAl2O4[END_REF] . The structure of C3A consists of rings of six AlO4 tetrahedra surrounding holes and Ca 2+ ions holding the rings together [START_REF] Jeffery | The Crystal Structure of Tricalium Aluminate[END_REF]. C3A crystallizes in a cubic lattice of space groups Pm3m

or Pa3 according to the most recent study [START_REF] Jeffery | The Crystal Structure of Tricalium Aluminate[END_REF]. The assessment of the crystal structure of CA2 has been the subject of various contradictory discussions; however, the most recent works agree that CA2 phase crystallizes in a monoclinic lattice (Table 21). C12A7 is a solid solution variable in oxygen Ca12Al14O32+x, stable in air (P(O2) =0.21 atm, x>0), in the presence of H2O (Ca12Al14O33 (OH)2, it can therefore stabilized by traces of moisture. C12A7 has a capacity to absorb up to 1.3% H2O from the furnace atmosphere at 950°-1350°C [START_REF] Aggarwal | Synthesis and Properties of Dicalciumm Aluminate, 2CaO.Al2O3[END_REF]).

The formation of C12A7 occurs by the reaction of non-stoichiometric calcium aluminate (e.g. 5Ca3Al2O6 + 9CaAl2O4 ↔ 2[Ca12Al14O32] 2+ : O 2-) [START_REF] Boysen | Structure and oxygen mobility in mayenite (Ca12Al14O33): a high-temperature neutron powder diffraction study[END_REF]. The cubic crystal structure reported to belong to space group I4-3d according to different sources.

Obtaining C12A7 crystals from the melt can also be done by the incorporation of various "modifiers" that can initiate the development of the nuclei of the structure. The C12A7 crystal is stabilized by the surrounding atmosphere (O2, H2O, CO2, CO, SO3)

or by the addition to the melt of CaF2, CaCl2, CaS, CaSO4 or CaCO3. Previous work by [START_REF] Jeevaratman | Anion Substitution and Structure of 12CaO7A12O3[END_REF] on the structural stability of C12A7 by anion substitution in the cell led to three conclusions; firstly, C12A7 contains two reactive O -2 , which can be replaced totally or partially by four univalent ions, which will induce a probable modification.

PHASE DIAGRAM REVIEW

INVARIANTS REACTIONS

Upon cooling along the liquidus curve, compositions between C3A and CA form a eutectic liquid. Samples in this composition range were investigated by hightemperature microscopy by Nurse et al (1965) and the nature of the invariant reaction was confirmed by DTA under argon atmosphere by [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF]. The C3A solid compound dissociates incongruently into a mixture of liquid and CaO by a peritectic reaction. The incongruent melting point slightly differ according to the works published in the literature (Nurse (1965) and [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF], but both values are in reasonable agreement when taking into account the uncertainties. Indeed, Rankin et al's (1915) preliminary work concluded on a temperature of 1808K while Nurse et al (1965) measured a temperature of 1539°C, which is in agreement with [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF] recent work whose incongruent melting point value was 1540°C.

For CA, the melting type has been the object of contradictory discussion. In some works, it was reported that CA melts congruently. While, Nurse et al (1965) and later [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF] measured an incongruent melting point. According to them, CA melts peritectically into CA2 and liquid with a composition close to CA. However, all authors agree on the melting temperature. Table 21 gathers the phase diagram data measured and modelled from the published papers. The equilibrium equations are for peritectic and eutectic mixtures but the melting type is specified.

C12A7 was first defined as being in reversible equilibrium with water molecules in the atmosphere in the form of Ca12Al14O32(OH) . According to Nurse et al, it is not certain that the hydroxide group shown in the structure will be completely removed before the compound melts. The existence of C12A7 in the presence of moisture has been confirmed and its melting point measured. The stability of C12A7 in water free environments has been debated, it is now established that this compound is able to incorporate an excess of oxygen in its framework.

There are different evaluations of the melting relations of CA2 in the literature. Rankin (1915) firstly identified this compound as C3A5. According to the author, C3A5 crystallizes in two forms, (I) stable and (II) unstable. The stable phase (I) melts congruently at 1720°C and forms a eutectic with CA and liquid. The melting point of the unstable phase (II) has not been determined and there is apparently no stability region for this phase according to Rankin and Wright (1915). Nevertheless, the congruent nature of the melting type was contradicted by the subsequent hightemperature microscope from Nurse et al (1965) and D.T.A from [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF] measurements, which concluded that CA2 melts incongruently. There are few studies on phase diagram data of CA6; the known peritectic melting point measured is 1830±5°C (Nurse et al 1965) and 1852±7°C [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF].

One issue concerning C12A7 is its stability in the C-A quasi-binary section.

Preliminary work by Nurse indicated that this phase was stabilized by oxygen hydroxide (OH) molecules in air and in moisture nitrogen. In the same paper, Nurse measured the melting temperature of C12A7 and stated that the phase lost OH molecules before melting. Jerbestov's work also reported the presence of traces of water in the C12A7 phase. Recent work by Trofymluk indicates that C12A7 exists as a [Ca12Al12O32-δ] +2δ (2δe-), 0<δ≤1, solid solution from which Ca12Al12O33 crystals can be obtained by the floating zone method. This oxygen variation thus suggests that it would be interesting to describe C12A7 in a ternary Ca-Al-O section rather than in the CaO-Al2O3 section. However, if one is interested in the CaO-Al2O3 quasi-binary system, the compound Ca12Al14O33 must be considered. Regarding C5A3, it would appear that this phase is screened by C12A7 in an oxidizing environment and its synthesis therefore requires a neutral atmosphere. This phase exists in the C-A section but there are no relevant thermodynamic data in the literature that can be used in a phase diagram Table 23 : Invariants reactions in the CaAl4O7-CaAl12O19 composition range

LIQUIDUS

One of the first studies providing the phase diagram of the CaO-Al2O3 system was carried out in 1915 (Rankin and Wright, 1915). In this system, four distinct intermediate compounds were identified in the binary section, namely Ca3Al10O18, CaAl2O4, Ca5Al6O14 and Ca3Al2O6. Further research on this system has been conducted. Thus [START_REF] Filonenko | Equilibrium Conditions in the Al2O3 angle of the Ternary System CaO-Al2O3-SiO2[END_REF] identified by microscopic study the CA6 phase which was previously reported as Ca3Al32O51 (Rankin and Wright, 1915). Later X-ray diffraction developments showed that Ca5Al6O14 corresponds to C12A7, Ca3Al10O18 to CaAl4O7.

Various authors also published studies on the alumina-rich portions (references), but

Nurse et al published the first complete experimental diagram in 1965 under controlled atmosphere. Subsequently, [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF] works carried out under argon confirmed the previous results of Nurse et al (1965).

Fig. 48 : First CaO-Al2O3 phase diagram reported by Rankin and Wright (1915).

STABILITY OF C12A7 IN THE CAO-AL2O3 SECTION

Since the early works by Rankin and Wright (1915) on the CaO-Al2O3 system, it is now certain that C12A7 is not a polymorph of C5A3 but a distinct and isolated phase.

Nevertheless, in the past, the focus of discussion around C12A7 has been on the stability of this phase in an dry environment of the CaO-Al2O3 condensed section. The results published on C12A7 by Nurse et al (1965) concluded that C12A7 is not completely anhydrous. Indeed, in that paper, C12A7 was synthesised by melting at

PHASE DIAGRAM MODELLING IN THE LITERATURE

Thermodynamic modelling is a technique for calculating phase diagrams from optimized Gibbs energy datasets using the available experimental data. The general method consists of simultaneously evaluating all the experimental & theoretical information available for the system under study by simultaneous numerical modelling of the Gibbs energy of all the phases of the system. Using these Gibbs energy expressions as a function of temperature and composition, a phase diagram can be calculated. The particularity of this method is that it describes the thermodynamic properties from a mathematical model containing adjustable parameters and thus allows the prediction of properties in areas of the phase diagram where no experimental thermodynamic data are available. We reviewed the entire literature on optimized phase diagrams of the CaO-Al2O3 system. In this part, we will discuss the individual modelled results from the literature.

Calculated phase diagram based on the quasi-chemical model for the liquid phase

The phase diagram calculated and optimized by [START_REF] Eriksson | Critical Evaluation and Optimization of the Thermodynamic Properties and Phase Diagrams of the CaO-Al2O3, Al2O3-SiO2, and CaO-Al2O3-SiO2 Systems[END_REF] [START_REF] Eriksson | Critical Evaluation and Optimization of the Thermodynamic Properties and Phase Diagrams of the CaO-Al2O3, Al2O3-SiO2, and CaO-Al2O3-SiO2 Systems[END_REF]. [START_REF] Hallstedt | Assessment of the CaO-Al2O3 System[END_REF] performed the modelling of CaO-Al2O3 phase diagram presented in Fig. 54. A two-sublattice subregular solution model was used to describe the liquid phase. In this model, the liquid consists of two sub-lattices, one for cations:

Calculated phase diagram based on two-sublattice model for the liquid phase

(Al 3+ , Ca 2+ )P and the other for anions and neutral species: (Al 3+ , Ca 2+ )P, where P and Q are the number of sites on each sublattice. The Gibbs energy of the liquid derived from [START_REF] Hillert | A two-Sublattice Model for Molten Solutions with Different Tendency for Ionization[END_REF] model.

G m = y Al 3+ + °GAl 2 3+ O 3 2-+ y Ca 2+ °GCa 2 3+ O 2 2-+ 2RT(y Al 3+ lny Al 3+ + y Ca 2+ lny Ca 2+ ) + G m E [12]
There, P=2 and 𝑄 = 𝑦 𝐶𝑎 2+ + 𝑦 𝐴𝑙 3+ where y is the mole fraction of each sublattice. 𝐺 𝑚 𝐸 is the excess Gibbs energy depending on interaction between Al 3+ and Ca 2+ on the cation sublattice. These interactions are more precisely defined by a Redlich-Kister polynomial [13]:

G m E = y Ca 2+ y Al 3+ [°L + L 1 (y Ca 2+ -y Al 3+ )] [13]
The L parameters are set to account for the temperature dependence. °L for the regular temperature dependent and L 1 for the temperature independent subregular. Pure solid phases stated by equation [14] °G -H SER = A + BT + CTlnT + DT 2 + ET 3 + FT -1 [14]

Equation [15] applied to the solid intermediate constituents of the CaO-Al2O3 section.

All aluminates are dealt with as stoichiometric compounds and their Gibbs energy is calculated in relation with pure oxides.

°GC X A Y =X°G CaO + Y°G Al 2 O 3 + A + BT + CT lnT [15]
The phase diagram computed in Fig. 54 is based on the two-subregular model for the liquid phase. The data on the invariant equilibria and the liquid are taken from the experimental work from (Nurse et al 1965). No constraints were set on the melting type of CA2 and CA, all compounds are stoichiometric and C12A7 is considered unstable as reported by Nurse et al (1965) . Temperatures in brackets are from Nurse et al (1965) DTA measurement while [START_REF] Hallstedt | Assessment of the CaO-Al2O3 System[END_REF] The diagram including the experimental liquidus data is reproduced in Fig. 55.

The agreement of the calculated Al2O3-rich liquidus with the experimental data is correct, but the CaO-rich part of the liquidus is not in agreement with the data of Nurse et al (1965). According to [START_REF] Hallstedt | Assessment of the CaO-Al2O3 System[END_REF], it was not possible to obtain a reliable CA6 Gibbs energy of formation by fitting CA6-Al2O3-liquid simultaneously. Nevertheless, the Gibbs energy curve seemed reasonable only when the temperature of the three equilibrium phases CA6-Al2O3-liquid was above the value of Nurse et al (1965). The lack of sufficient thermodynamic data on CA6 is clearly the reason of these discrepancies.

G m = y Al 3+ y AlO 2 -1 °GAl +3 :AlO 2 -1 + y Al +3 y O -2 °GAl +3 :O -2 + y Ca 2+ y AlO 2 -1 °GCa +2 :AlO 2 -1 + y Ca +2 y O -2 °GCa +2 :O -2 + P′RT(y Al 3+ lny Al 3+ + y Ca +2 lny Ca +2 ) + Q′RT(y AlO 2 -1 lny AlO 2 -1 + y O -2 lny O -2 ) + G m E [16]
As in the two-sublattice subregular description, y is the site fraction; P' and Q' are adjustable parameters that ensure the electroneutrality condition. °𝐺𝐴𝑙 +3 :𝐴𝑙𝑂 2 -1 and °𝐺𝐶𝑎 +2 :𝑂 -2 are respectively similar to the Gibbs energy of two moles of pure G(Al2O3) and G(CaO). The description of the solid phases is similar to those given in the twosublattice subregular. The Gibbs energies of the pure liquid phases Al2O3 and CaO came from [START_REF] Hallstedt | Assessment of the CaO-Al2O3 System[END_REF] assessment.

The calculated phase diagram as modelled by [START_REF] Mao | A re-evaluation of the liquid phases in the CaO-Al2O3 and MgO-Al2O3 systems[END_REF] is given in Fig.

56

C12A7 IN SECTION CAO-AL2O3

Oxygen concentration is an important parameter in C12A7 formation, stabilization at high temperature occurs by absorption of excess oxygen from any oxidizing atmosphere even when PO2 pressure is as low as 10 -8 atm (Zhmoidin and Chatterjee, 1985). Regarding the phase diagram, there are few modelling works in literature including this phase in an anhydrous section. In the Fig. 57, [START_REF] Li | Phase diagram assessment of CaO-Al2O3-La2O3 system[END_REF] added C12A7 in CaO-Al2O3 section and calculated the interactions parameters in the liquid phase between CaO and Al2O3 by using a sub-regular Redlich-Kister equation.

At the same time, the liquidus was also computed using the commercial software FactSage. Moreover, the authors synthesized C12A7 also. The synthesis consisted in mixing Al2O3 and CaO powders, pre-treated in a furnace at 1000°C for 2h and then transferred to a Mo crucible for heat treatment at 1500°C during 2h in open atmosphere (Air). Finally, XRD analysis confirmed the obtaining of C12A7 phase but the authors did not measure the oxygen content. [START_REF] Hallstedt | Assessment of the CaO-Al2O3 System[END_REF]. The experimental data are from the congruent melting reported by Rankin and Wright (1915) and Nurse et al (1965).

Ball et al (1993) used a non-ideal interacting associated species to describe thermodynamics properties of oxides melts in the CaO-Al2O3 system and recalculated another phase diagram. In this model, the thermodynamic data comes from Scientific Group Thermodata Europe (SGTE) substance database while for the stoichiometric solids come from CaO-Al2O3 assessed by [START_REF] Hallstedt | Assessment of the CaO-Al2O3 System[END_REF]. The calculated phase diagram is computed by using experiment liquids data from Nurse et al (1965).

HIGH ALUMINA PORTION IN CAO-AL2O3

One of the most frequently encountered contradictions concerns the melting type of intermediate compounds in the CaO-Al2O3 section. Although the most consistent studies by Nurse et al (1965), Jerebtsov, and[START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF] conclude that, with the exception of C12A7, all other aluminates in the binary section melt incongruently, CA and CA2 compounds are often represented as congruently melting in some calculated phase diagrams. On the one hand, the lack of experimental data of liquidus and solidus explains discrepancies between some phase diagrams reported in the past Fig. 60. On the other hand, the difficulty to reproduce the new thermodynamic values can also explain some differences between the experimental data and the calculated. Moreover, the temperatures of the invariants CA6-Al2O3-Liquid and CA2-CA6-Liquid are in agreement with the work of [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF], i.e. 8°C above the experimental measurements. Similarly, the peritectic melting temperature of CA is in agreement with those reported by Nurse et al (1965) and then [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF] some years later.

THERMODYNAMIC PROPERTIES

HEAT CAPACITY AND RELATIVE ENTHALPY

In our work, we measured the heat content values of CA6 and C5A3 by drop calorimetry. The lack of studies on heat contents and Cp measurements for these compounds does not allow us to compare the various data in the literature. However, the measurement techniques used by the authors, in particular calorimetry; make it possible to obtain precise and relevant values. The ΔH and Cp values reported in the literature for calcium aluminates are provided in

HEAT OF FORMATION

Enthalpy of formation is a characteristic thermodynamic value determined experimentally for a wide range of chemical compounds. The calorimetric method is the most commonly used to determine these thermodynamic data. Two types of calorimeters are commonly used, namely isothermal, in which the temperature surrounding the calorimeter is kept constant. Various authors using the calorimetric method have measured the standard enthalpy of formation of aluminates experimentally. The study of the literature has enabled us to collect existing data (Table 25 & 26). [START_REF] Coughlin | heats of formation of of crystalline CaO.Al2O3, 12CaO.7Al2O3 and 3CaO.Al2O3[END_REF] measured the heat of formation of C3A, C12A7 and CA by calorimetric method in hydrochloric acid solution as solvent. For C3A and C12A7, [START_REF] Koehler | Heats and free energies of foramtion of ferrites and aluminates of calcium, magnesium, and lithium[END_REF] found a more exothermic value than those of Coughlin (Coughlin, heats of formation of of crystalline CaO.Al2O3, 12CaO.7Al2O3 and 3CaO.Al2O3, 1956). This difference is mainly due to the standard heat of formation values of Al2O3 used by the authors. C3A calculated from experimental values by [START_REF] Eliezer | Thermodynamic properties of calcium aluminates[END_REF] and corrected by heat capacity [START_REF] Bonnickson | High temperature heat contents of aluminates of calcium and magnesium[END_REF]) is in agreement with [START_REF] Koehler | Heats and free energies of foramtion of ferrites and aluminates of calcium, magnesium, and lithium[END_REF] while the Materials Project database (using DFT calculations) reports more negative heat of formation (C3A and C12A7) than [START_REF] Coughlin | heats of formation of of crystalline CaO.Al2O3, 12CaO.7Al2O3 and 3CaO.Al2O3[END_REF]. For CA the literature data globally agree, but there is -18.3kJ.mole -1 difference between [START_REF] Coughlin | heats of formation of of crystalline CaO.Al2O3, 12CaO.7Al2O3 and 3CaO.Al2O3[END_REF] and the Materials Project database. Discrepancies between CA2 heats of formations in Table 25 are mainly due to disagreement on the relevance of the reported experimental values. Indeed, [START_REF] Hemingway | Comment on "Thermodynamlc Properties of Calcium[END_REF] rejected the heat of formation reported by [START_REF] Eliezer | Thermodynamic properties of calcium aluminates[END_REF] and argued there was an error in Hess cycle applied by [START_REF] Koehler | Heats and free energies of foramtion of ferrites and aluminates of calcium, magnesium, and lithium[END_REF], whereas [START_REF] Eliezer | Thermodynamic properties of calcium aluminates[END_REF] assumed that the error lies in original experiment. The other data in Table 25 were estimated [START_REF] Eysel | Polymorphism and solid solution of Ca2GeO4 and Ca2SiO4[END_REF] or calculated (MaterialsProject, s.d.). Regarding C5A3 the only value is reported by Materials project. (1956) previous result. Similarly, the experimental heat of formation data for CA from literature agrees [START_REF] Coughlin | heats of formation of of crystalline CaO.Al2O3, 12CaO.7Al2O3 and 3CaO.Al2O3[END_REF]. [START_REF] Koehler | Heats and free energies of foramtion of ferrites and aluminates of calcium, magnesium, and lithium[END_REF] determined the enthalpy of formation of CA2 from the heat of formation of gibbsite from α-Al2O3 and liquid water (ΔH°f = 30.8±2.6KJ.mole -1 unpublished work of R. Barany one of the author) combined to overall calorimetric reaction. The result is 9.0 and 14.5kJ.mole -1 smaller than [START_REF] Coughlin | heats of formation of of crystalline CaO.Al2O3, 12CaO.7Al2O3 and 3CaO.Al2O3[END_REF] and [START_REF] Geiger | Enthalpies of formation of CaAl4O7 and CaAl12O19 (hibonite) by high temperature, alkali borate solution calorimetry[END_REF], respectively. In addition, the error bar is quite large. As suggested by Eliezer (1970), this gap may be related to the original experiment. For CA6 the only experimental data is that measured at 1060K i.e. ΔH°f = -33±9.7 KJ.mole Results from both works are given in the 1981) and 1500.16K [START_REF] Sharma | Activities in lime-alumina melts[END_REF].

ΔfH° Referred to the elements

ΔfH° Referred to the oxides

COMPONENT ACTIVITIES IN THE

STANDARD MOLAR GIBBS FREE ENERGIES OF FORMATION

Standard free energies of formation of the CaO-Al2O3 system were studied in the literature for the compositions CA3, C12A7, CA, CA2 and CA6; Gibbs free energy data are not available for C5A3. We have gathered various data for each composition in Tables (28-31). In order to compare the different data collected we have plotted the evolution of Gibbs energy as a function of temperature for each composition (Fig. 62-65). For C12A7 the Gibbs free energies were only measured by [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF], thus it is not possible to compare the data for this compound from other sources.

TRICALCIUM ALUMINATE: C3A

Table 28 gathers the Gibbs free energy of formation data of C3A. As the results plotted in Fig. 62 indicate, the data from [START_REF] Kumar | The Utilization of Galvanic Cells Using Caβ"-Alumina Solid Electrolytes in Thermodynamic Investigation of CaO-Al2O3 System[END_REF] are in agreement with [START_REF] Rog | Determination of standard Gibbs free energies of formation of calcium aluminates from the oxydes by e.m.f measurements[END_REF]. The data from [START_REF] Nagata | Standard Free Energies of Formation of CaO-Al2O3 Intermediate Compounds by Means of EMF Measurement of Galvanic Cells[END_REF] are more negative than those from [START_REF] Popov | Thermodynamic stabibility of calcium hexaaluminate CaO.6Al2O3 and its reaction with oxides[END_REF] and [START_REF] Rog | Determination of standard Gibbs free energies of formation of calcium aluminates from the oxydes by e.m.f measurements[END_REF]. When extrapolated to the temperature range of the other two authors we find a mean deviation of 2.51KJ. mole -1 . Although [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF] could not quantify the C3A data by EMF, the authors suggested the following equation: ΔG°=-1700-32.0T (±1500) J.mole -1 . This equation is based on Gibbs energies calculated from the properties of the liquid phase with an entropy compatible with the heat capacity data. The plot of the data from this equation reveals significant discrepancies with others experimental data.

MAYENITE: C12A7

For C12A7, [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF] measured the Gibbs free energy of formation by the EMF method. According to them, the results are probably not relevant due to the dissolution of the solvent CaF2 in C12A7. Equation [17] was established based on thermochemical data [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF].

12/7CaO(s) + Al2O3(s) → 12/7 CaO.Al2O3 (s) [17] ΔG°= -12300-29.3T (±2500) J. mole -1 Dissolution of CaF2 in C12A7 leads to the formation of a highly stabilised solid solution. As stated by [START_REF] Jeevaratman | Anion Substitution and Structure of 12CaO7A12O3[END_REF], the O -2 ions are partially or totally replaced by univalent ions. The attractive inductive effect of fluorine enhances the stability of C12A7, probably forming the compound Ca12Al14O32F2 [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF].

This stabilization effect results in very negative Gibbs energies.

MONOCALCIUM ALUMINATE: CA

Table 29 provides the Gibbs free energies of formation as a function of temperature. In Fig. 63, the data of Kumar et al are also in agreement with those of Rog et al. The data of both Allibert et al and [START_REF] Nagata | Standard Free Energies of Formation of CaO-Al2O3 Intermediate Compounds by Means of EMF Measurement of Galvanic Cells[END_REF] are more negative than [START_REF] Kumar | The Utilization of Galvanic Cells Using Caβ"-Alumina Solid Electrolytes in Thermodynamic Investigation of CaO-Al2O3 System[END_REF] in the same temperature range. The mean differences between Allibert and Kumar then Nagata and Kumar are respectively 3.4KJ and 1.62KJ.mole -1 . In contrast to CA6 and CA2, the extrapolated data of [START_REF] Nagata | Standard Free Energies of Formation of CaO-Al2O3 Intermediate Compounds by Means of EMF Measurement of Galvanic Cells[END_REF] are less negative than [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF]. The CaF2 solvent used by the authors can explain this discrepancy in values. Indeed, [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF] indicate the possibility of the formation of a ternary compound 3CaO.3Al2O3.CaF2, which can affect the EMF measurement results.

GROSSITE CA

CA2 Gibbs free energies of formation are given in Table 30 and plotted in Fig.

64

. As in the case of CA6, the experiments of [START_REF] Kumar | The Utilization of Galvanic Cells Using Caβ"-Alumina Solid Electrolytes in Thermodynamic Investigation of CaO-Al2O3 System[END_REF] and [START_REF] Rog | Determination of standard Gibbs free energies of formation of calcium aluminates from the oxydes by e.m.f measurements[END_REF] agree. The data from [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF] are more negative than Kumar and Rog et al (1993)by ~2 and ~2.3KJ.mole -1 respectively. Similarly, evolution of the Gibbs free energies of formation as a function of temperature reported by [START_REF] Nagata | Standard Free Energies of Formation of CaO-Al2O3 Intermediate Compounds by Means of EMF Measurement of Galvanic Cells[END_REF] have an average deviation of 1.4kJ.mole -1 from those of [START_REF] Kumar | The Utilization of Galvanic Cells Using Caβ"-Alumina Solid Electrolytes in Thermodynamic Investigation of CaO-Al2O3 System[END_REF].

However, extrapolating these data to low temperature shows a similarity with reported Gibbs free energy by [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF].

HIBONITE: CA6

The comparison of experimental Gibbs free energy data of CA6 formation shows some disagreement between the different authors. [START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF]and [START_REF] Popov | Thermodynamic stabibility of calcium hexaaluminate CaO.6Al2O3 and its reaction with oxides[END_REF] both used an EMF technique with CAF2 as electrolyte; the difference between their experiments is mainly the nature of the reference electrodes used in the measurements. Indeed, [START_REF] Popov | Thermodynamic stabibility of calcium hexaaluminate CaO.6Al2O3 and its reaction with oxides[END_REF] used a mixture of Ca0.17Zr0.83O1.83 and CaZrO3 under oxidising atmosphere as reference electrode while Allibert et al had CaO under air as reference electrode. Despite the experimental similarities, the temperature dependence of the Gibbs energy of the two studies are very different. The Gibbs energies reported by [START_REF] Popov | Thermodynamic stabibility of calcium hexaaluminate CaO.6Al2O3 and its reaction with oxides[END_REF] are more negative. The galvanic cell method in the presence of Ca Caβ"-alumina solid electrolytes was used by [START_REF] Kumar | The Utilization of Galvanic Cells Using Caβ"-Alumina Solid Electrolytes in Thermodynamic Investigation of CaO-Al2O3 System[END_REF] and [START_REF] Rog | Determination of standard Gibbs free energies of formation of calcium aluminates from the oxydes by e.m.f measurements[END_REF], in both studies the reference electrodes were CaO/air and O2 respectively. The Gibbs energy curves of the two studies overlap over the common temperature range of 827°C to 927°C. [START_REF] Kumar | The Utilization of Galvanic Cells Using Caβ"-Alumina Solid Electrolytes in Thermodynamic Investigation of CaO-Al2O3 System[END_REF] are ~0.37KJ.mole -1 more negative than [START_REF] Rog | Determination of standard Gibbs free energies of formation of calcium aluminates from the oxydes by e.m.f measurements[END_REF], and extrapolating data to higher temperatures, both studies remain in agreement. [START_REF] Nagata | Standard Free Energies of Formation of CaO-Al2O3 Intermediate Compounds by Means of EMF Measurement of Galvanic Cells[END_REF] used 4CaO.P2O5 as a solvent in the galvanic cells, the Gibbs energy found to be less negative ~4KJ.mole -1 than [START_REF] Kumar | The Utilization of Galvanic Cells Using Caβ"-Alumina Solid Electrolytes in Thermodynamic Investigation of CaO-Al2O3 System[END_REF]. Additionally, extrapolating [START_REF] Nagata | Standard Free Energies of Formation of CaO-Al2O3 Intermediate Compounds by Means of EMF Measurement of Galvanic Cells[END_REF]

SYNTHESIS AND CHARACTERISATION OF C5A3 AND CA6

The synthesis of C5A3 was done under argon in order to avoid the formation of C12A7, which is more stable in an oxidizing environment. A first synthesis with a heat treatment duration of 6h showed the formation of the first diffraction peaks attributed to a minority phase C5A3, two other phases corresponding to CA and C3A were also identified. During the synthesis of C5A3, the intermediate phases CA and C3A are formed first for kinetic reasons and then react according to the following equation:

2CaAlO4 + Ca3Al2O6 →Ca5Al6O14. This synthesis is slow most likely due to a small difference in the enthalpy of reaction and a low driving force. After 48 H of reaction, a second X-ray analysis showed an increase in the diffraction peaks of the C5A3 phase.

This confirms the slow nature of the reaction but also the thermodynamic stability of this compound. Finally, after 18 days of reaction combined with intermediate grinding every 24 to 48h of reaction, X-ray analysis allowed us to identify C5A3 as the major phase. However, two minor phases remain CA and C3A. The amounts of these two phases are too small to react to completion, and the distribution of these two phases seems to be inhomogeneous, which prevents the synthesis of a 100% pure sample. We did not obtain a pure CA6 phase either. There was additional CA2 phase and Al2O3 coexisting with the major phase. After a second thermal annealing, the CA2 phase totally reacted but there was still some Al2O3 which remained stable, knowing that the formation of CA6 is done according to the equation CaAl4O7 + 4Al2O3→CaAl12O19, it is thus admitted that the quantity of CaAl4O7 formed was not sufficient to react with the remaining Al2O3. We were able to quantify the percentage of Al2O3 by quantitative analysis on HighScore Fig. 68 and we obtained 12.2% Al2O3 as impurity.

CRYSTALLOGRAPHIC DATA OF THE SYNTHESISED PHASE

The lattice parameters from the crystallographic analysis are given in Table 32.

C5A3 crystallises in an orthorhombic lattice of space group Cmc21. The values of the crystallographic parameters of the major phase are in agreement with the literature [START_REF] Aruja | The Unit Cell of Orthorhombic Pentacalcium Trialuminate 5CaO.3Al2O3[END_REF]) (Vincent & Jeffery, 1978). The CA phase present in the material has similar structural characteristics to that of [START_REF] Horkner | Zur Kristallstruktur von CaAl2O4[END_REF].

Despite the presence of the minor phase Al2O3, the lattice parameters of the synthesised CA6 are in agreement with the literature [START_REF] Utsunomiya | Structure Refinement of CaO.6Al2O3[END_REF]).

Ca5Al6O14 CaAl12O19

Space

RELATIVE ENTHALPY MEASUREMENTS RESULTS

HEAT OF FORMATIONS MEASUREMENT

The standard heat of formation was measured using dissolution calorimetry by dissolving Ca5Al6O14 and CaAl12O19 samples in the basic slag solvent used for Ca3Si2O7 and Ca2AlFeO5. The obtained results are respectively presented in Fig. 73 and Fig. 74.

Qdiss (25°C) = 957461.7 ± 71451.2 J.mole -1 heat of dissolution for Ca5Al6O14 .

Qdiss (25°C) = 984697.7 ± 34196.2 J.mole -1 heat of dissolution for CaAl12O19.

To calculate the enthalpy of formation we proceeded as follows: using the dissolution data for pure CaO and Al2O3 measured in chapter 1, the standard heat of formation can be calculated and the value is given by: ΔfH(25°C) = -123559.2 ± 73126.1 J.mole -1 for Ca5Al6O14.

ΔfH(25°C) = -15513.3 ± 37847.3 J.mole -1 for CaAl12O19.

THERMODYNAMIC MODELLING

HEAT CAPACITY MODELLED

The heat contents of the aluminates (C12A7, C3A, CA2 and CA) were measured over a temperature range of 53.50 to 298. 16K (1955); no other values above these temperatures are reported in the literature. However, [START_REF] Bonnickson | High temperature heat contents of aluminates of calcium and magnesium[END_REF] measured heat contents above 298.16K on the above-mentioned aluminates, over a temperature range of 373.6 to 1807.9K. The modelling of heat capacities and the parameter optimization of the multiple Einstein model was carried out using the PARROT module of ThermoCalc. The experimental data used combined the low temperature heat capacity (1955) and the high temperature heat contents [START_REF] Bonnickson | High temperature heat contents of aluminates of calcium and magnesium[END_REF]. For this work 3 Einstein temperatures were used for the description of the heat capacities and we added a polynomial function to take into account the anharmonic contributions at high temperature. The thermodynamic description of aluminates is valid from 0K by extrapolation to the melting temperature of each modelled solid. Fig. 76 : Modelled heat content of calcium aluminates compared with the literature data [START_REF] Bonnickson | High temperature heat contents of aluminates of calcium and magnesium[END_REF] normalized to 1 mole of oxide. of formation, relative enthalpy and melting point of these oxides provide new data that can be used to predict the formation and properties of clinkers.

For Belite, the relative enthalpy data of the γ, α' α,-Ca2SiO4 polymorphs complement those of β-Ca2SiO4 measured by Coughlin (reference). Similarly, the transition temperatures are consistent with data reported in the literature. By studying Rankinite, we were able to measure relative enthalpies not reported in the literature and to confirm the melting point of this compound. For C4AF, the enthalpies of formation and relative enthalpies of the solid solution were measured for the first time and will be the subject of a future article. The synthesis of C5A3 resulted in a 93.9% pure compound, it is difficult to go beyond this percentage given the slow kinetics linked to the low enthalpy of reaction, moreover the conditions of synthesis require an inert gas environment to avoid any formation of C12A7. Nevertheless, we were able to measure the first relative enthalpies on this compound. The study of CA6 allowed us to measure the relative enthalpies mainly, which also contributes to enrich the database of the oxides of the C-A system. We were also able to model the heat capacities of the aluminates CA, CA2, C3A and C12A7 from the low-temperature Cp and then to compute the Gibbs energy dependence as a function of temperature.

One of the major challenges encountered during this thesis was the time constraint. Indeed, the Covid-19 confinement has affected the progress of the work, from an experiment point of view, some experiments have been rescheduled. Practical training on the use of the SEM, for example, was cancelled. We also started the study of the solubility limits of minor elements such as MgO in C3A but due to time constraints, these results could not be fully exploited. Similarly, it was planned to measure the heat capacities of C5A3 and CA6, but unfortunately, this could not be done due to delays in the delivery of the equipment planned for this experiment. As a continuation of this work, it would be interesting to complete the missing thermodynamic data and to produce a complementary phase diagram of the C-A system including these missing data. The introduction of C5A3 in the quasi-binary C-A section would be a first, as in all the phase diagram models reported in the literature this phase has always been excluded. It would also be interesting to study the premelting effects of C3S2 on the heat capacities and to measure the enthalpy.

Concerning the Ca12Al14O32+x solid solution, the stability of this phase could have been studied as a function of the quantity of oxygen and the quantity of OH -measured in case of synthesis in a free-moisture environment and the melting point of this phase could have been re-evaluated. The work presented in this manuscript nevertheless brings new data of primary importance in the study of the major constituents of Portland clinker. However, it is planned to write articles on the results obtained on C4AF solid solution and the C-A system. In spite of these undesirable points outside of our control, through these three years of work, we were able to contribute in a non-negligible way to the conception of a solid database and open new perspectives on future work that will be carried out in the laboratories in order to complete this preliminary work.

LIST OF FIGURES

Mesures des propriétés thermodynamiques Calorimétrie de chute

La calorimétrie de chute directe est une méthode de mesure de variation de l'enthalpie des phases condensées avec la température. Un échantillon de masse connue à une température T0 est chuté dans un calorimètre maintenu à une température de mesure T. A pression constante la variation de l'enthalpie ΔH est égale à la variation de chaleur ΔQ. Cette relation (ΔH= ΔQ) permet de déterminer l'enthalpie d'échauffement entre T0 et T et d'en dériver par intégration la capacité thermique (Cp).

Cette méthode a été appliquée afin de déterminer les enthalpies relatives des oxydes étudiées. Nous avons également mesuré les enthalpies de formation des oxydes par calorimétrie dans un solvant solide type CAS (CaO-Al2O3-SiO2).

Calorimétrie différentielle à balayage

La calorimétrie différentielle à balayage est une technique d'analyse thermique qui permet de caractériser la température et l'enthalpie des transitions de phase dans le matériau étudié. Cette technique peut être utilisée pour mesurer la température de transition, les enthalpies des réactions de transition et la capacité thermique (Cp).

Dans ce manuscrit, nous avons mesuré les enthalpies de transition de phase des polymorphes du C2S et de la solution solide C4AF. Dans ce chapitre, nous nous sommes focalisé sur l'étude expérimentale de la belite (C2S) et de la rankinite (C3S2). La revue de la littérature a mis en évidence un manque de donnée thermodynamique à haute température de ces deux phases solides. Après avoir synthétisé puis identifier les phases par diffractions de rayons X, les températures de transitions polymorphiques de C2S ont été mesuré et sont en accord avec la littérature. Par la suite, les enthalpies relatives ont été mesurées puis comparer aux valeurs fournies par la base de données commerciale FTPs ainsi que les résultats issus des calculs de Haas et al (1981)

MODELISATION

CHAPITRE 3 : ETUDE DE LA PHASE C4AF

La solution solide de C4AF a été étudiée expérimentalement dans ce chapitre.

De même comme dans le chapitre précèdent, les températures de transition (fusion) ont été mesuré pour chaque composition, tandis que les enthalpies relatives à haute température ont été mesuré sur deux compositions distinctes : x=1 et x=1.4. En ce qui concerne la première composition, les valeurs expérimentales valident les données calculées de la base FTOxid tandis que celle de la seconde composition, la base donnée rapporte des valeurs plus exothermiques. L'enthalpie de formation de C4AF (x=1) a également été mesurée par calorimétrie de dissolution.

CHAPITRE 4 : ETUDE THERMODYNAMIQUE DU SYSTEME C-A

Une revue de la littérature complète a été effectuée sur les phases solides du système C-A (CaO-Al2O3). Les composées solides C5A3 et CA6 ont été synthétisés ainsi que des diagrammes de phase de la section quasi-binaire. Il semblerait qu'une atmosphère inerte nécessaire pour l'obtention de C5A3. Due à la faible enthalpie de réaction, la synthèse de ce dernier est thermodynamiquement lente. Néanmoins, 93.9 % de pureté a été obtenue. Ce travail s'est conclu par la réévaluation du diagramme de phase basé sur les fonctions d'Einstein de 3 e génération.

CONCLUSION

Fig. 1 :

 1 Fig. 1 : Automatic hydraulic work press on the left (1). Manual press on the right (2).

Fig. 3 :

 3 Fig. 3 : Example of quenching the samples in water.

Fig. 4 :

 4 Fig. 4 : Heat treatment in muffle furnace under argon gas.

Fig. 6 :

 6 Fig. 6 : PANalytical's X'Pert Pro MPD for X-ray diffraction measurements.

Fig. 7 :

 7 Fig. 7 : Drop Calorimeter MHTC96 from SETARAM used for heat content measurements.

  Al2O3 using the FTOxid database. The measured surface (in µV.s) for each sample is plotted as a function of heat content of Al2O3 (in J). The calibration constant (in µV.s/J) was calculated by performing a linear regression passing through origin. The uncertainty of the calibration constant corresponds to twice the standard variation of the slope. The temperature of the introduction into the calorimeter was measured with a calibrated thermocouple (uncertainty ±0.1K). The variation of the high temperature calorimeter is ±0.4K and a return to the baseline is observed within 25 min.

Fig. 8 :

 8 Fig. 8 : Signal obtained after dropping a pellet between the ambient temperature and the measurement temperature.

Fig. 10 :

 10 Fig. 10 : Phase evolution as a function of temperature for the Asian slag solvent used by[START_REF] Koryttseva | High-temperature calorimetric study of oxide component dissolution in a CaO-MgO-Al2O3-SiO2 slag at 1450° C[END_REF]

Fig. 11 :

 11 Fig. 11 : Phase evolution as a function of temperature for the novel basic solvent used in this work.

Fig. 12 :

 12 Fig. 12 : Dissolution of SiO2 with an exothermic reaction overlapping the dissolution.

Fig. 16 :

 16 Fig. 16 : Labsys TM Evo used in the laboratory for sample measurements.The apparatus used in the laboratory for DSC is the Labsys TM Evo designed by SETERAM. It is composed of a TG balance connected to the DSC sensors, a metal resistor furnace with a maximum temperature of 1600°C, a gas circuit (Ar: H2O (5 bar ) < 3 ppm; CnHm < 0.5 ppm; O2 < 2 ppm) and a cooling water circuit. Gas circuit protects the crucible and sample from oxidation and the sensors when working temperature is above 500°C. Pure platinum crucibles are used for all measurements in this work.

  Melting temperature from reference compound. In order to establish the calibration equation, we have plotted in Fig. 19 the mean values of the melting temperatures measured at 5K/min and 10K/min as a function of the literature data. The linear regression described by equation [3] is used to correct the experimental values. 𝑇 𝑟𝑒𝑎𝑙 = 𝑎𝑇 𝑚𝑒𝑎𝑠 + 𝑏 [3] Tmeas and Treal are respectively the measured and corrected values, the coefficient a and constant b come from the linear regression given in Fig. 19.

Fig. 19 :

 19 Fig. 19 : Temperature calibration curve.

  Fig. 20 : Representation of the different interactions between the material and the electron beam during a SEM measurement.

  , we have shown the diagram currently used by ceramists and drew by Philips and Muan (1959),whose research is based on data fromRankin and Wright, Greig (1927) and Roy(1958).

Fig. 21 :

 21 Fig. 21 : CaO-SiO2 first phase diagram from Rankin and Wright (1915).

Fig. 22 :

 22 Fig. 22 : Lime-silica (SiO2-2CaO.SiO2) phase diagram reported by[START_REF] Greig | Immiscibility in Silicate Melts[END_REF].

Fig. 23 :

 23 Fig. 23 : Phillips and Muan (1959) CaO-SiO2 phase diagram based on data of Rankin

Fig. 26 :

 26 Fig. 26 : Sample in a platinum crucible for heat treatment. For Ca2SiO4, heat treatment in pellet form is not required as the pellets change to powder at low temperatures. Nevertheless, the specific reaction area is greater and heat transfer is more homogeneous.

Fig. 27 :

 27 Fig. 27 : X-ray diffraction pattern over an angular range from 10 to 120°. pace group Pbnm Lattice parameter a 5.078 Å Lattice parameter b 6.760 Å Lattice parameter c 11.225 Å α=β=ϒ 90.000° Unit cell Volume 385.324 Å 3 Table7: γ-Ca2SiO4 crystallographic data calculated from X-ray pattern after synthesis.

Fig. 28 :

 28 Fig. 28 : Crystallographic structure of Ca2SiO4 obtained after X-rays measurement on the synthesized sample.

Fig. 29 :

 29 Fig. 29 : Ca2SiO4 dusting after DSC measurement.

Fig. 30 :

 30 Fig. 30 : DSC Labsys TM Evo signal of the Ca2SiO4 variety obtained after two runs at 5°C and 10°C on heating.

  Fig. 31 : DSC Labsys TM Evo signal of the Ca2SiO4 variety obtained after two runs at 5°C and 10°C on cooling.

Fig. 32 :Fig. 33 :

 3233 Fig.32: Comparison between Coughlin's experimental data and our measurements.[START_REF] Coughlin | High temperature heat contents of calcium orthosilicate[END_REF] data for α'-Ca2SiO4 have been corrected with enthalpy of transition γ-Ca2SiO4→ β-Ca2SiO4 from[START_REF] Forest | Connaissance de l'orthosilicate de calcium[END_REF] to have the same reference state.

Fig. 34 :

 34 Fig. 34 : Crystallographic representation of the two polymorphs of Ca3Si2O7.

Fig. 35 :

 35 Fig. 35 : Ca3Si2O7 X-ray diffraction pattern over an angular range from 10 to 120°.

Fig. 36 :

 36 Fig. 36 : DSC Labsys TM Evo signal of the Ca3Si2O7 variety obtained after two runs at 5 and 10K/min on heating.

Fig. 38 :

 38 Fig. 38 : Comparison of experimental data and theoretical thermodynamic models.

  Fig. 39 : Heat of dissolution of Ca3Si2O7.

Fig. 40 :

 40 Fig. 40 : New phase diagram assessed including experimental data obtained in this chapter (Abdul, Mawalala, Pisch, & Bannerman, 2022).

Fig. 41 :

 41 Fig. 41 : Experimental relative enthalpy of Ca3Si2O7 and γ,α'-Ca2SiO4 and fitting at high temperature.

  Rankinite and Belite is important in Portland cement clinkers. This chapter highlighted a lack of available data for Ca3Si2O7 and the Ca2SiO4 polymorphs. Rankinite and belite were synthesized by the solid-solid method, the pure phases were identified by X-rays and the relative enthalpies of γ-Ca2SiO4→α'-Ca2SiO4, γ-Ca2SiO4→α-Ca2SiO4 and Ca3Si2O7 were measured by drop calorimetry. Regarding the temperature transition, for γ, β, α', α-Ca2SiO4, inversion was identified in the temperature range in agreement with the value reported in the literature but some discrepancies are reported. Our study of Rankinite has provided new relative enthalpy values never before measured; the peritectic melting point obtained experimentally also corresponds to that quoted in the literature. Additionally, a premelting effect on Ca3Si2O7 could be an interesting prospect for further investigation. This work contributed to the re-assessment of the CaO-SiO2 phase diagram through collaborative work with the University of Aberdeen. known as C4AF in cement chemistry nomenclature, is one of the four constituents commonly found in Portland cement. It is known since 1897 through the work of Tornebohm who originally named it celite. An interesting feature

  Fig. 43 : Unit cell volume variations in the solid solution Ca2Fe2-xAlxO5 at 25°C.

  Substitution of Fe 3+ ions by Al 3+ induces a decrease of the lattice parameters and therefore the volume of the crystal. Aluminium atoms are smaller (50pm) than iron atoms (64pm) and take up less cell space. Evolution of the volume as a function of the Al 3+ ions composition Fig.40is characterized by a slope shift between 0≤x≤0.6[START_REF] Redhammer | Structural variations in brownmillerite series Ca2(Fe2-xAlx)O5: Single-crystal X-ray diffraction at 25°C and high-temperature X-ray powder difraction (25°<T<1000°C)[END_REF] corresponding to the Pcmn→Ibm2 transition zone. In addition, Al 3+ insertion in crystal cell affects the mean metal-oxygen bond length[START_REF] Redhammer | Structural variations in brownmillerite series Ca2(Fe2-xAlx)O5: Single-crystal X-ray diffraction at 25°C and high-temperature X-ray powder difraction (25°<T<1000°C)[END_REF]. For the structural parameters, we have gathered data from two main compositions (x= 0 and x=1) in

Fig. 45 :

 45 Fig. 45 : Ca2FeAlO5.relative enthalpy plotted with FTOxid data from FactSage Software.

Fig. 46 :

 46 Fig. 46 : Relative enthalpy of Ca2Fe0.6Al1.4O5. plotted with FTOxid data from FactSage Software.

Fig. 47 :

 47 Fig. 47 : Experimental heat of dissolution of Ca2AlFeO5 in a basic slag solvent.

  and cosmology. Due to these numerous applications, the experimentally observed compounds present in cement have been the subject of various structural and thermodynamic investigations over the past century. Various authors studied the phase diagram containing aluminates component. The high melting point of the intermediate compounds in this system is one of the reasons. As early as 1909, Rankin and Wright (1915) reported a first version of the quasi-binary CaO-Al2O3 phase diagram. Later, investigations of portions of the diagram as well as thermodynamic and crystallographic properties of the intermediary compounds of this system completed this upstream work. The pioneering research work is probably the study of the moisture-free CaO-Al2O3 system (Nurse et al (1965)) by high temperature microscopy.From this study, many different versions of thermodynamic modelling and calculated phase diagrams were derived. Thanks to the development of time-temperature analysis methods otherwise differential thermal analysis,[START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF] re-investigated this binary diagram and confirmed the general trend of the preliminary diagram. However, there are still important thermodynamic data missing.

  Fig. 51 : Portion of phase diagram: liquidus data near the C12A7 composition by very high-temperature microscopy, reported by Nurse et al(Nurse, Welch, & Majumdar, 1965).

  is shown in Fig. 53. The modified quasi-chemical model was used to describe the thermodynamic properties of the liquid phase. This model describes a binary system in which the particles of two compounds mix by substitution in a quasi-lattice [reference Pelton]. The evaluations are valid from room temperature to above liquid temperatures.As for the experimental phase diagram(Nurse et al, 1965), C12A7 has been excluded from the modelled CaO-Al2O3 section. This phase considered unstable in anhydrous surroundings. C3A and CA6 phases melt incongruently at temperatures close to the DTA measurements ofNurse et al, i.e. 1541°C (1539±5°C, Nurse et al, 1965 and 1833°C (1830±15°C Jerebtsov 2000). However, the CA and CA2 phases melt congruently, which is in contradiction withNurse et al (1965) report. Although the melting point are in agreement with the experimental data. The nature of the melting of CA and CA2 was a subject of conflicting discussion. Authors have tended to prioritise the data concluding on congruent melting.

Fig. 53 :

 53 Fig. 53 : Liquidus CaO-Al2O3 optimized phase diagram. The authors defined the composition is in function of components CaO-AlO1.5[START_REF] Eriksson | Critical Evaluation and Optimization of the Thermodynamic Properties and Phase Diagrams of the CaO-Al2O3, Al2O3-SiO2, and CaO-Al2O3-SiO2 Systems[END_REF].

  Fig. 54 : Phase diagram from Hallstedt (1990) optimization with three phase equilibrium data and invariant temperature from Nurse et al (1965) and calculated temperature.

Fig. 55 :

 55 Fig. 55 : Hallstedt (1990) part of phase diagram from 20 to 100% alumina. Invariant three phase equilibria and liquidus are including. The experimental data come from various sources. Mao et al (2004) also used the ionic two-sublattice model to describe the thermodynamic properties for the liquid phase of the CaO-Al2O3 system. A new 𝐴𝑙𝑂 2 -1 species was introduced to describe the tetrahedral network. Hence, the model is described by the following formulas: (Al +3 , Ca 2+ )P (AlO 2 -1 , O -2 )Q and Gibbs energy by equation [16].

  Fig. 56 : Phase diagram including calculated liquid of CaO-Al2O3 (Mao et al, 2004) system with experimental data from various authors.

Fig. 57 :

 57 Fig. 57 : Li et al (2017) Computed phase diagram of CaO-Al2O3 including C12A7 in the section.

Fig. 59 :

 59 Fig. 59 : Calculated binary phase diagram from Ball et al (1993), based on Associate model. Experimental data come from Nurse et al (1965).

Fig. 60 :

 60 Fig. 60 : High Alumina portion in CaO-Al2O3. Comparison between various studies by L. G. Wisnyi, Doctor's thesis, Rutgers University, State University of New Jersey, New Brunswick, New Jersey, January 1955.

Fig. 61 :

 61 Fig. 61 : Part of the system CaO-Al2O3 from Phase diagrams for Ceramists: A. Auriol, G. Hauser, and J. G. Wurm, private communication, Nov. 19, 1961.

  LIQUID PHASESharman and Richardson (1961) measured the capacities of sulphides in a solution containing a mixture of CaO and Al2O3. From the data collected, the activities of CaO and Al2O3 were established at 1500°C. Work by Allibert et al also yielded compositiondependent activities of CaO and Al2O3 by mass spectroscopy at 1787°C[START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF]. The experiment was first carried out in an induction furnace containing a block of Mo in which CaO and Al2O3 were placed. The mixture under He (gas) was heated above the melting point of Al2O3. The block was then heated in a vacuum spectrometer.

Fig. 62 :

 62 Fig. 62 : C3A Gibbs energy plotted in function of temperature.

Fig. 64 :

 64 Fig. 64 : CA2 Gibbs energy plotted in function of temperature.

Fig. 65 :

 65 Fig. 65 : CA6 Gibbs energy plotted in function of temperature.

Fig. 66 :

 66 Fig. 66 : Quantitative estimation of phases obtained after Ca5Al6O14 synthesis.

Fig. 67

 67 Fig.67shows the evolution of the major phase C5A3 as a function of reaction time.The quantification of the phase amounts was done using a Rietveld analysis and the HighScore software as shown in Fig.66. The quantitative analysis of the constitutive phases of the synthesized material showed that we had reached 93.9% of C5A3, 1.3% C3A and 4.9% CA.

Fig. 68 :

 68 Fig. 68 : Quantitative estimation of phases obtained after CaAl12O19.

Fig. 69 :

 69 Fig. 69 : Crystallographic representation of Ca5Al6O14.

Fig. 70 :

 70 Fig. 70 : Crystallographic representation of CaAl12O19..

Fig. 72 :

 72 Fig. 72 : Comparison between measurement and FTPs database.

Fig. 73 :

 73 Fig. 73 : Heat of dissolution of C5A3.

Fig. 75 :

 75 Fig. 75 : Calcium Aluminates modelled heat capacity compared with literature (1955) normalized to 1 mole of oxide.

Fig. 77 :

 77 Fig. 77 : Calculated CaO-Al2O3 phase diagram computed with experiments data from Nurse et al (1965),[START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF],Wisnyi (1955) and[START_REF] Rolin | Phase Diagrams of Mixtures not Reacting with Molybdenum[END_REF].

Fig. 1 :Fig. 2 :Fig. 3 :Fig. 4 :Fig. 5 :Fig. 9 :

 123459 Fig. 1 : Automatic hydraulic work press on the left (1). Manual press on the right (2). ................................................................................................................................. Fig. 2: Silicate synthesis in a platinum crucible under air. ........................................ Fig. 3 : Example of quenching the samples in water. ...............................................Fig. 4 : Heat treatment in muffle furnace under argon gas. ...................................... Fig. 5 : Principle of X-ray diffraction. ......................................................................... Fig. 6 : PANalytical's X'Pert Pro MPD for X-ray diffraction measurements. .............. Fig. 7 : Drop Calorimeter MHTC96 from SETARAM used for heat content measurements. ......................................................................................................... Fig. 8 : Signal obtained after dropping a pellet between the ambient temperature and the measurement temperature. ................................................................................ Fig. 9 : Evolution of the calibration constant as a function of the temperature. ......... Fig. 10 : Phase evolution as a function of temperature for the Asian slag solvent used by (Koryttseva & Navrotsky, 2017) ...........................................................................Fig. 11 : Phase evolution as a function of temperature for the novel basic solvent used in this work. ...................................................................................................... Fig. 12 : Dissolution of SiO2 with an exothermic reaction overlapping the dissolution. .................................................................................................................................Fig. 13 : Heat of dissolution as a function of CaO content. .......................................

Fig. 14 :

 14 Fig. 14 : Heat of dissolution as a function of Al2O3 content. ...................................... Fig. 15 : Heat of dissolution as a function of Fe2O3 content. ..................................... Fig. 16 : Labsys TM Evo used in the laboratory for sample measurements. ............... Fig. 17 : DSC signal for NaCl reference sample. ...................................................... Fig. 18 : DSC signal for K2SO4 reference sample. .................................................... Fig. 19 : Temperature calibration curve. ...................................................................Fig. 20 : Representation of the different interactions between the material and the electron beam during a SEM measurement. ............................................................ Fig. 21 : CaO-SiO2 first phase diagram from Rankin and Wright (1915)................... Fig. 22 : Lime-silica (SiO2-2CaO.SiO2) phase diagram reported by Greig (1927)..... Fig. 23 : Phillips and Muan (1959) CaO-SiO2 phase diagram based on data of Rankin and Wright (1915) and Greig (1927). Significant changes with respect to stability relations dicalcium and dicalcium silicates, based on Roy (1958). ........................... Fig. 24 : Polymorphic transformation of Ca2SiO4 as a function of temperature evolution by Eysel and Hahn (1970). ........................................................................ Fig. 25 : Crystallographic representation of Ca2SiO4 polymorphs............................. Fig. 26 : Sample in a platinum crucible for heat treatment. For Ca2SiO4, heat treatment in pellet form is not required as the pellets change to powder at low temperatures. Nevertheless, the specific reaction area is greater and heat transfer is more homogeneous. ................................................................................................. Fig. 27 : X-ray diffraction pattern over an angular range from 10 to 120°. ............... Fig. 28 : Crystallographic structure of Ca2SiO4 obtained after XRD measurement on the synthesized sample. ........................................................................................... Fig. 29 : Ca2SiO4 dusting after DSC measurement. ................................................. Fig. 30 : DSC Labsys TM Evo signal of the Ca2SiO4 variety obtained after two runs at 5°C and 10°C on heating. .........................................................................................Fig. 31 : DSC Labsys TM Evo signal of the Ca2SiO4 variety obtained after two runs at 5°C and 10°C on cooling. .........................................................................................Fig. 32 : Comparison between Coughlin's experimental data and our measurements. Coughlin (1957) data for α'-Ca2SiO4 have been corrected with enthalpy of transition γ-Ca2SiO4→ β-Ca2SiO4 from Forest (1971) to have the same reference state....... Fig. 33 : Comparison between experimental data and data from theoretical models. .................................................................................................................................Fig. 34 : Crystallographic representation of the two polymorphs of Ca3Si2O7. ..........

Fig. 35 :

 35 Fig. 35 : Ca3Si2O7 X-ray diffraction pattern over an angular range from 10 to 120°. .Fig. 36 : DSC Labsys TM Evo signal of the Ca3Si2O7 variety obtained after two runs at 5 and 10K/min on heating. ........................................................................................ Fig. 37 : Mean heat capacity of Rankinite (Ca3Si2O7), P-Z means premelting zone. Fig. 38 : Comparison of experimental data and theoretical thermodynamic models.70 Fig. 39 : Heat of dissolution of Ca3Si2O7. ..................................................................Fig. 40 : New phase diagram assessed by using the experimental data obtained in this chapter (Abdul, Mawalala, Pisch, & Bannerman, 2022). ....................................Fig. 41 : Experimental relative enthalpy of Ca3Si2O7 and γ,α'-Ca2SiO4 and fitting at high temperature. ..................................................................................................... Fig. 39: System CaO-CaO.Al2O3-2CaO.Fe2O3, pseudo-ternary (Newkirk & Thwaite, 1958). ....................................................................................................................... Fig. 43 : Unit cell volume variations in the solid solution Ca2Fe2-xAlxO5 at 25°C. ..... Fig. 44 : Synthesis step followed for each composition. ........................................... Fig. 45 : Ca2FeAlO5.relative enthalpy plotted with FTOxid data from FactSage Software. ..................................................................................................................Fig. 46 : Relative enthalpy of Ca2Fe0.6Al1.4O5. plotted with FTOxid data from FactSage Software. .................................................................................................. Fig. 47 : Experimental heat of dissolution of Ca2AlFeO5 in a basic slag solvent. ...... Fig. 45 : First CaO-Al2O3 phase diagram reported by Rankin and Wright (1915). .... Fig. 46 : CaO-Al2O3 experiment phase diagram in moisture-free atmosphere without C12A7 (Nurse, Welch, & Majumdar, 1965)............................................................... Fig. 50 : Experimental phase diagram by differential thermal analysis DTA method under argon atmosphere. Study conducted by Jerebtsov and Mikhailov (Jerebtsov & Mikhailov, 2000). ...................................................................................................... Fig. 51 : Portion of phase diagram: liquidus data near the C12A7 composition by very high-temperature microscopy, reported by Nurse et al (Nurse, Welch, & Majumdar, 1965). .....................................................................................................................Fig. 52 : Currently accepted liquidus data near the C12A7 al (Nurse, Welch, & Majumdar, 1965). ...................................................................................................Fig. 53 : Liquidus CaO-Al2O3 optimized phase diagram. The authors defined the composition is in function of components CaO-AlO1.5[START_REF] Eriksson | Critical Evaluation and Optimization of the Thermodynamic Properties and Phase Diagrams of the CaO-Al2O3, Al2O3-SiO2, and CaO-Al2O3-SiO2 Systems[END_REF]. ..

Fig. 54 :

 54 Fig. 54 : Phase diagram from Hallstedt (1990) optimization with three phase equilibrium data and invariant temperature from Nurse et al (1965) and calculated temperature. ........................................................................................................... Fig. 55 : Hallstedt (1990) part of phase diagram from 20 to 100% alumina. Invariant three phase equilibria and liquidus are including. The experimental data come from various sources. ..................................................................................................... Fig. 56 : Phase diagram including calculated liquid of CaO-Al2O3 (Mao, Selleby, & Sundman, 2004) system with experimental data from various authors. ................. Fig. 57 : Li et al (2017) Computed phase diagram of CaO-Al2O3 including C12A7 in the section. ............................................................................................................. Fig. 58 : Part of the phase diagram including C12A7 calculated in isolation[START_REF] Hallstedt | Assessment of the CaO-Al2O3 System[END_REF]. The experimental data are from the congruent melting reported byRankin and Wright (1915) andNurse et al (1965). ................................................. Fig. 59 : Calculated binary phase diagram from Ball et al (1993), based on Associate model. Experimental data come from Nurse et al (1965). ......................................Fig. 60 : High Alumina portion in CaO-Al2O3. Comparison between various studies by L. G. Wisnyi, Doctor's thesis, Rutgers University, State University of New Jersey, New Brunswick, New Jersey, January 1955. .......................................................... Fig. 61 : Part of the system CaO-Al2O3 from Phase diagrams for Ceramists: A. Auriol, G. Hauser, and J. G. Wurm, private communication, Nov. 19, 1961. ..................... Fig. 62 : C3A Gibbs energy plotted in function of temperature. .............................. Fig. 63 : CA Gibbs energy plotted in function of temperature. ................................ Fig. 64 : CA2 Gibbs energy plotted in function of temperature. .............................. Fig. 65 : CA6 Gibbs energy plotted in function of temperature. .............................. Fig. 66 : Quantitative estimation of phases obtained after Ca5Al6O14 synthesis. .... Fig. 67 : Evolution of Ca5Al6O14 as main phase in function of time of sintering. .....Fig. 68 : Quantitative estimation of phases obtained after CaAl12O19. ....................

Fig. 69 :

 69 Fig. 69 : Crystallographic representation of Ca5Al6O14. ..........................................

Fig. 70 :

 70 Fig. 70 : Crystallographic representation of CaAl12O19.. ..........................................

Fig. 71 :

 71 Fig. 71 : Ca5Al6O14 Heat contents evolution in function of temperature. .................

Fig. 72 :

 72 Fig. 72 : Comparison between measurement and FTPs database. ........................ Fig. 73 : Heat of dissolution of C5A3. ..................................................................... Fig. 74 : Heat of dissolution of CA6. .......................................................................

Fig. 75 :

 75 Fig. 75 : Calcium Aluminates modelled heat capacity compared with literature (1955) normalized to 1 mole of oxide. ................................................................................ Fig. 76 : Modelled heat content of calcium aluminates compared with the literature data (Bonnickson, 1955) normalized to 1 mole of oxide. ........................................ Fig. 77 : Calculated CaO-Al2O3 phase diagram computed with experiments data fromNurse et al (1965),[START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF],Wisnyi (1955) and[START_REF] Rolin | Phase Diagrams of Mixtures not Reacting with Molybdenum[END_REF]. .......................................................................................................... Fig. 78 : Activity at 1000°C in relation to the composition. ......................................

  . Nous avons ainsi confirmé la validité du modèle de Haas d'une part pour les polymorphes γ, α'-C2S et d'autre part la validité des valeurs provenant de FTPs pour γ-C2S. Toutefois, les enthalpies relatives des polymorphes α', α-C2S ont été surévalué. Ces données ont été utilisées dans le cadre d'un travail collaboratif avec l'université d'Aberdeen pour la réévaluation du diagramme de phase du système C-S (CaO-SiO2).

L

  'étude thermodynamique des oxydes contenue dans le clinker de Portland permet de mieux comprendre les processus physico-chimiques des constituants majeurs du ciment de Portland. L'approche CALPHAD permet de modéliser le processus complexe de formation des clinkers et d'optimiser le procédé. Pour ce faire, il est nécessaire de constituer une base de donnée solide basée sur des mesures expérimentales des différents oxydes constituant du clinker (matière brute utilisée pour la fabrication de ciment). Dans cette thèse, nous nous sommes concentré sur l'étude thermodynamique de la Belite (C2S), Rankinite (C3S2), des Alumino-ferrite (C4AF) et des aluminates (CA6, C5A3). Les mesures d'enthalpie de formation, d'enthalpie relative et de point de fusion de ces oxydes apportent des données nouvelles qui pourront être utilisées afin de prédire les formations et les propriétés des clinkers. Concernant la Belite, les données d'enthalpies relatives des variétés γ, α' α, -Ca2SiO4 viennent compléter celles de β-Ca2SiO4 mesuré par Coughlin. De même que les températures de transitions constituent des données consistant en accord avec reporté dans la littérature. Par l'étude de la Rankinite, on a pu d'une part mesurer les enthalpies relatives non reportées dans la littérature et d'autre part confirmer le point de fusion de ce composé. Pour le CAF, les enthalpies de formation et enthalpies relatives de la solution solide ont été mesurées pour la première fois et feront l'objet d'un prochain article. La synthèse de C5A3 a abouti à un composé pur à 93.9 %, il est difficile d'aller au-delà de ce pourcentage étant donné la cinétique lente liée à la faible enthalpie de réaction, de plus les conditions de synthèse exige un milieu sous gaz inerte pour éviter toute formation de C12A7. Néanmoins, nous avons pu mesurer les premières enthalpies relatives sur ce composé. À travers l'étude de CA6, nous avons mesuré les enthalpies relatives à haute température, ce qui contribue également à enrichir la base de données des oxydes du système C-A. Nous avons pu également modéliser les capacités calorifiques des aluminates CA, CA2, C3A et C12A7 à partir des Cp basses températures ainsi que la dépendance d'énergie de Gibbs en fonction de la température. L'une de problématique majeurs rencontré lors de cette thèse a été la contrainte liée au temps. En effet, le confinement lié au Covid-19 a impacté l'avancement des travaux. Des formations pratiques sur l'utilisation du MEB par exemple ont été annulé. Nous avons également commencé l'étude des limites de solubilités d'élément, mineurs tels que le MgO dans C3A, mais par contrainte de temps ces résultats n'ont pas pu être exploité totalement. De même, il était prévu de mesurer les capacités calorifiques de C5A3 et CA6, mais cela n'a pas pu également pu être réalisé suite à des délais de livraison de l'appareillage prévu pour cette expérimentation. Dans la continuité de ces travaux, il serait intéressant de compléter les données thermodynamiques manquantes et de réaliser un diagramme de phase complémentaire du système C-A. L'introduction de C5A3 dans la section quasi-binaire C-A serait une première, car dans tous les modèles de diagramme de phase reporté dans la littérature, cette phase a toujours été exclue. Il serait également intéressant d'étudier les effets de pré-fusion de C3S2 sur les capacités calorifiques et d'en mesurer l'enthalpie. Concernant la phase C12A7, on aurait pu étudier la stabilité de cette phase en fonction de la quantité d'oxygène et d'en mesurer la quantité d'OH -en cas de synthèse dans un milieu humide puis de réévaluer la température de fusion de ce composé. Les travaux présentés dans ce manuscrit apportent néanmoins des données nouvelles primordiale dans l'étude des constituants majeur de Clinker de Portland. Il est toutefois prévu de rédiger des articles notamment sur les résultats obtenus sur C4AF et le système C-A. Malgré ces contraintes indépendantes de notre volonté, à travers ces trois années de travail, nous avons su contribuer de manière non-négligeable à la conception d'une base de données solide et aussi ouvert des perspectives nouvelles sur des futurs travaux qui seront menés au laboratoire afin de compléter ce travail préliminaire.

Table 1 .

 1

	T (°C)	Calibration	u(constant)
		( µV.s/J)	(2 )
	600	485.63	5.79
	800	483.6	5.58
	900	467.3	5.26
	1000	443.8	5.38
	1100	433	5.86
	1200	411.15	6.3
	1300	339.37	5.34
	1400	307.03	2.82
	1450	288.18	4.31
	1480	287.55	5.49

Fig. 9 : Evolution of the calibration constant as a function of the temperature.

Table 1 :

 1 Calibration constant at different selected temperatures.

		600.00
	(µV.s/J)	500.00 550.00				Head S	Head B
	constant	400.00 450.00
	Calibration	250.00 300.00 350.00
		200.00
		500	700	900	1100	1300	1500	1700
					T (°C)

Table 2 :

 2 The heat of solution of CaO and Al2O3 at 1450°C in the basic solvent is

		Hdiss	H(1450°C) -H(25°C)	Hsol (1450°C)
	Oxide	(kJ/mol)	(kJ/mol)	(kJ/mol)
	CaO	77.6 ± 2.7 74.7	-3.1± 2.7
	Al2O3 148.6± 2.7 173.3	-24.7± 2.7
	Fe2O3 352.5± 7.4 202.0	149.5± 7.4

exothermic. For Fe2O3, the heat value is endothermic.

Table 4 :

 4 [START_REF] Ghosh | Review The chemestry of dicalcium silicate mineral[END_REF]. The crystallographic parameters of the calcium orthosilicate polymorphs are summarized in Table4. The α,α',β-Ca2SiO4 polymorphs are shown in Fig.25, the γ-Ca2SiO4 variety will be synthesized and represented in the experimental part of our investigation.

	. The γ-Ca2SiO4

Crystallographic data of Ca2SiO4 polymorphs according to different studies from the literature.

Table 5

 5

	, we gathered polymorph Ca2SiO4 heat of transition data
	from various sources.

Table 5 :

 5 Enthalpy and temperature of polymorphic transition of Ca2SiO4.

Table 6 :

 6 via E.M.F. Similarly, for β-Ca2SiO4 value was derived from the enthalpy of reaction Ca3SiO5 ↔ β-Ca2SiO4 + CaO reported by[START_REF] Brunauer | The heat of decomposition of tricalcium silicate into β-dicalcium silicate and calcium oxide[END_REF] in solution calorimetry in HNO3 acid. Methods used to obtain these values do not imply the validity of data; we aimed to report only experimental values whose measurement methods are explicitly described in the papers. Heat of formation reported in various published paper.

	Chemistry	ΔH°f(KJ/mole)		Method of	Sources
		from oxides	from elements	investigation
	β-Ca2SiO4	-126.31 ±0.96 -2256.85	Hydrofluoric Acid	King (1951)
				solution calorimeter.
		-139	-	Calorimeter Richards	Johannson and
				adiabatic type: heat	Thorvaldson
				of solution in HCl-	(1934)
				200H2O at 20°C
		-116.36	-	Reported by	(MaterialsProject,
				Materials Project	s.d.)
		-125.	-	Dissolution	Eitel and Richter
				calorimetry in	(1942)
				HCl+20H2O and
				HCl+200 H2O
		-123.2	-	Dissolution	Elsner et al
				calorimetry in	(1935)
				HNO3+HF acid bath
		-	-2306.77±4.44	High-temperature	Grevel (2022)
	γ-Ca2SiO4	-	-2315.98±4.47	drop-solution
				calorimetry at 700°C
				using a custom-built
				Tian-Calvet-type
				twin-

Table 9 :

 9 measured the β, α'-Ca2SiO4 relative enthalpy by an inversed drop calorimetric technique. The temperature of transition γ→α' is situated near 847°C. Therefore, in this present work the measured values include the γ-Ca2SiO4 Relative enthalpies data from drop calorimetry for Ca2SiO4.

		Relative enthalpy
	T	T	HT-H298K	u(∆H)
	°C	K	J/ mol	J/mol	%
		Ca2SiO4 (mol. wt. 172.24)
	25	298.15	-	-	-
	699.7	972.86 108430.8 3617.9	3.3
	798.9 1072.09 123306.7 3251.5	2.6
	898.2 1171.39 148801.8 3879.2	2.6
	998.5 1271.67 171305.2 4185.5	2.4
	1097.9 1371.05 187889.9 4479.1	2.4
	1197.9 1471.05 212360.1 6444.6	3
	1399.6 1672.77 263620.1 7455.5	2.8
	1451.1 1724.25 277736.3 9601.6	3.5
	1482.1 1755.25 281175.5 11658.3	4.1

to α'-Ca2SiO4 in the temperature range 699.7-1482.1°C.

When the temperature is above 847°C, pellets turned into powder after cooling step at low temperature due to the dusting effect to γ-Ca2SiO4 on cooling. In contrast to γ-Ca2SiO4→α'-Ca2SiO4 transition, the α'→γ inversion is not a direct reaction, a metastable intermediate form β-Ca2SiO4 bridges α'-Ca2SiO4 and γ-Ca2SiO4. As a result, a volume expansion occurs in the material due to structural rearrangements, which leads to a pellet dusting. It indicates compound revert to a γ-Ca2SiO4 state.

Table 10 :

 10 Structural data of the polymorph of Ca3Si2O7.

	Compound	Structure	Symmetry &	Cell content Lattice	Sources
		type	Space group		parameter (Å)
	Ca3Si2O7	Kilchoanite	Orthorhombic	Z=8	a=11.42	Taylor
			I2cm		b=5.09	(1971)
					c=21.95

Table 11 :

 11 Table 11 summarizes various data from the literature. This work will provide additional experimental data on rankinite. Thermodynamic data of Rankinite polymorph.

	Chemistry Transition type	Transition	Method of	Sources
			temperature	investigation
			(°C)
	Ca3Si2O7 Kilchoanite→Rankinite 954-1090	-	Hanic
					(1987)
			1150	DTA	Mistuda and
					Fukuo
					(1969)
		Heat of formation referred to oxides component
	Chemistry Heat of formation	Uncertainty	Method of	Sources
		(KJ.mole-1)	(±)	investigation
	Ca3Si2O7	-229.137	2.092	Solution	Weeks
	(rankinite			Calorimetry	(1953)
	form)			with solvent
				composition
				5%HF and
				20%HCl
				acid at 81°C
		-206	2	Calorimeter	Ayed et al
				of	(1993)
				dissolution
				in PbO-
				B2O3 at
				900°C

Ca3Si2O7. As in the case of Ca2SiO4, a mineralogical composition was carried out by X-ray diffraction (X'Pert Pro MPD, PANalytical), with CuKα radiation of λ= 1.5419 Å.

Additionally, Ca3Si2O7 Melting point was measured by differential scanning calorimetry with apparatus Labsys TM Evo designed by SETERAM. We carried out calibration with NaCl and K2SO4 as reference sample at 5K and 10K ramp rates.

Table 13

 13

		290
		285						T Pre-Melting →
		280
		275
	C m (J/mol.K)	260 265 270									P-Z
		255
		250								T Melting →
		245
		240
		800	900	1000	1100	1200	1300	1400	1500	1600	1700	1800
							T (K)

. No experimental data exists in the literature on the heat capacity or heat content of Rankinite at these high temperatures.

Table 13 :

 13 Experimental results of heat content measurements on rankinite.

[START_REF] Haas | Thermodynamic Tabulations for Selected Phases in the CaO-Al2O3-SiO2-H2O at 101.325kPa (1atm) between 273.15 and 1800[END_REF]

suggested a thermodynamic model describing the evolution of relative enthalpy over the temperature range from room to the melting point. This model is based on Neumann Kopp's additive rule and the authors used the heat capacities measured by

[START_REF] King | Low Temperature Heat Capacities and Entropies at 298.15 °K of Some Crystalline Silicates Containing Calcium[END_REF]

for the low temperature boundary and estimated high temperature values from CaO and SiO2 constituents summation. Haas claims that his model applied to Ca3Si2O7 is valid over a temperature range from room temperature to 1127°C at a reference pressure of 101.325 kPa. To assess the accuracy of

[START_REF] Haas | Thermodynamic Tabulations for Selected Phases in the CaO-Al2O3-SiO2-H2O at 101.325kPa (1atm) between 273.15 and 1800[END_REF]

and FTPS models with respect to the experimental results, we plotted data in the same Fig.

38

.

Table 14 .

 14 This shows that, the lattice parameter values from the various studies are in the same order of magnitude.

	Chemistry	Structure	Symmetry &	Cell content	Lattice	Sources
		type	Space group		parameter
					(Å)
	Ca2Fe2O5	Perovskite	Pseudo-	Z=4	a=5.64	Bertaut,
			quadratic		b=14.68	Blum, &
			Pcmn		c=5.39	Sagnières,
					α=β=γ=90°	(1959)
					=5.596	Redhammer
					b=14.76	et al (2004)
					c=5.427
					α=β=γ=90°
	Ca2FeAlO5	Perovskite	Orthorhombi	Z=2	a=5.58	Bertaut et al,
			c		b=14.50	(1959)
			Ibm2		c=5.34
					α=β=γ=90°
				Z=4	a=5.584	Colville and
					b=14.60	Geller (1971)
					c=5.374
					α=β=γ=90°
					a=5.52	Solacolu
					b=14.44	(1932)
					c=5.34
					α=β=γ=90°

Table 14 :

 14 Crystallographic data of Ca2Fe2-xAlxO5 solid solution as a function of composition from various sources for two selected compositions.

Table 15 :

 15 results. Although this chapter is particularly focused on the study of Ca2FeAlO5, it is important to highlight the work that has been done on the other ferrites coexisting around C4AF according to the ternary phase diagram. Standard enthalpy of formation referred to the oxides component, experimental data. a This value corresponds to the enthalpy of formation at 800°C.

	Chemistry	ΔH°f(kJ/	Uncerta	Method of investigation		Sources
		mole)	inty (±)
	Ca2Fe2O5	-31.13	0.42	Isothermal-jacket calorimeter: heat of solution	Newman and
				in HCl, 26.61 H2O (2.00 N at 25±0.8°C), 1g	Hoffman (1956
				dissolved in 600g of solvent. Heat of dilution of	)
				aqueous CaCl2, AlCl3 and FeCl3 in the same
				acid.
		-44.18	3.01	Hydrochloric acid calorimetry at 30.00°C,	Koehler et al
				4.0779g of dicalcium ferrite with 1.936.2g of	(1961)
				4.360 molal hydrochloric acid.
		-45.00 a 3.80	High temperature Calvet twin Calorimeter at	Prasanna and
				800°C with 2PbO.B2O3 as solvent (20 mg in	Navrotsky
				30g of glass-solvent under Ar flow)	(1994)
	Ca2FeAlO5	-47	2	Dissolution calorimetry in High Temperature	Ayed et al
				Calvet Calorimeter, wih 2PbO-B2O3 at 1173K	(1993)
	Ca6Al4Fe2O15 -76.53	2.51	Isothermal-jacket calorimeter: heat of solution
				in HCl, 26.61 H2O (2.00 N at 25±0.8°C), 1g dissolved in 600g of solvent. Heat of dilution of aqueous CaCl2, AlCl3 and FeCl3 in the same	Newman and Hoffman (1956)
				acid.
	Chemistry	ΔH°f(KJ/mole) Uncertainty (±) Method of	Sources
					investigation
	Ca2Fe2O5	-2139.80	4.40	Same method	Prasanna &
					as in Table 2.	Navrotsky,
						(1994)
			-2139.03	2.80	Same method	Koehler et al
					as in Table 2.	(1961)
			-2131.14	-	Calculated	FactSage
					values	database
			-2443.38	-

Table 16 :

 16 Standard enthalpy of formation referred to the elements, calculated data from Materials Project database online and FactSage software.The enthalpy of formation referred to the elements reported by[START_REF] Prasanna | Energetics sin the brownmillerite-perovskite pseudobinary Ca2Fe2O5-CaTiO3[END_REF] were derived without heat content correction since Ca2Fe2O5 heat capacities are not available. If we assume that formation reaction between 800°C and 25°C takes place with a ΔCp(T,P)~0, ΔH°f from elements can be calculated but in a less accurate way. Although this last result is in agreement with[START_REF] Koehler | Heats and free energies of foramtion of ferrites and aluminates of calcium, magnesium, and lithium[END_REF], we can wonder about ΔH°f referred to oxide used by the latter. According to Koehler et al, -44.18 KJ.mole -1 corresponds to the standard enthalpy of formation at 25°C. This

value is more exothermic than

[START_REF] Newman | Heats of Formation of Hexacalcium Dialumino Ferrite and Dicalcium Ferrite[END_REF]

: -31.13 KJ.mole -1 , but closer to that reported by

[START_REF] Prasanna | Energetics sin the brownmillerite-perovskite pseudobinary Ca2Fe2O5-CaTiO3[END_REF]

at 800°C: ΔH°f (800°C, oxides) =-45.00 KJ.mole -1 . Regarding the values stored in the thermodynamic databases, FactSage gave a ΔH°f close to the published values while Materials Project calculated a more exothermic ΔH°f.

Table 18 :

 18 Table 18 reports raw experimental results obtained on the investigated compound. The measurements are carried out on six pellets for each temperature and the uncertainty on the results is less than 4%. In the case of Ca2FeAlO5 the initial uncorrected temperatures ranged from 22.5 to 25.9°C. Relative enthalpies measured in function of temperature from 584.87°C to 1092.59°C.

		1 2	𝐶𝑎 2 𝐹𝑒 2 𝑂 5 +	1 2	𝐶𝑎 2 𝐴𝑙 2 𝑂 5 → 𝐶𝑎 2 𝐹𝑒𝐴𝑙𝑂 5 [11]
					Heat Contents
	T(°C)			T (K)	HT-H298K	u(∆H)
	Initial		Final			J.mol -1	J.mol -1	%
			Ca2FeAlO5 (mol. wt. 243)
	22.52	590.15	863.30 118119.42 4560.51	3.85
	24.57	689.39	962.54 141167.68 4723.04	3.35
	25.11	793.90	1067.05 163214.35 4723.32	2.88
	25.63	894.45	1167.60 186393.16 4349.50	2.31
	25.56	984.95	1258.10 200484.90 7525.71	3.75
	25.90	1096.07	1369.22 227991.51 8603.93	3.72

Table 19 :

 19 ). Ca2Fe0.6Al1.4O5 relative enthalpy plotted with FTOxid data from FactSage Software.

		300000
		250000	This work
	H(T)-H(298.15)[J/mol]	100000 150000 200000	FTOxid data
		50000
		0
		0	200	400		600	800	1000	1200	1400	1600
							T(K)
	Ca2Fe0.6Al1.4O5, solid solution composition was measured from 584.87 to 1092.59°C,
	sample distributor temperature ranged from 24.4 to 27.78°C and peak error on the data
	was 5.04%. Results are reported in Table 19. Equation [12] was applied on FactSage
	to calculate the relative enthalpies for each implemented temperature and plotted with
	measured data in the Fig. 46.
		3 10	𝐶𝑎 2 𝐹𝑒 2 𝑂 5 +	7 10	𝐶𝑎 2 𝐴𝑙 2 𝑂 5 → 𝐶𝑎 2 𝐹𝑒 0.6 𝐴𝑙 1.4 𝑂 5 [12]

Lack of experimental data in the literature is a constraint to the establishment of relevant and predictive models of the thermodynamic properties of Ca2Fe2-xAlxO5 solid solution as a function of aluminium composition and temperature. In fact, comparison of both datasets, experiment and theoretical, reveals that FTOxid overestimated the relative enthalpies of Ca2Fe0.6Al1.4O5; the closest point to the experimental one is 584.9°C. Analysis of laboratories data of both compositions Ca2Fe0.6Al1.4O5 and Ca2FeAlO5 highlights that increasing Al ions in the solid solution leads to a lowering in relative enthalpy with respect to the modelled data in the FTOxid database in Factsage.

Table 20 .

 20

	Chemistry	Mass (mg)	Molar mass	Alx contents	Tfusion liquidus	Scan rate
			g.mol -1		(°C)	(K/min)
	Ca2Fe2-xAlxO5 103.1	254.4	0.5	1454±5	5
		55.7	242.9	1	1428±5	5 and 10
		66.94	231.4	1.4	1400±5	5 and 10

Table 20 :

 20

Melting proprieties of solid solution Ca2Fe2-xAlxO5 in function of Al ions contents.

Table 24 .

 24

	Chemistry	Measurement	Temperature range	Method of	Sources
			(K)	investigation
	Ca3Al2O6	Heat capacity	53.86→298.16	Calorimeter referred to	King (1955)
	Ca12Al14O33 Heat capacity	53.89→298.16	Nernst Method.
	CaAl4O7	Heat capacity	53.50→298.16
	CaAl2O4	Heat capacity	53.52 →298.16
	Ca3Al2O6	Relative	373.6→1807.9	High temperature drop	Bonnickson
		enthalpy		Calorimeter: platinum-	(1955)
	Ca12Al14O33 Relative	394.4→1672.6	rhodium capsules.
		enthalpy
	CaAl2O4	Relative	402.6→1800.2
		enthalpy
	CaAl4O7	Relative	403.7→1801.5
		enthalpy

Table 24 :

 24 Thermodynamic data for aluminates in the CaO-Al2O3 pseudo-binary.

Table 25 :

 25 -1 (Geiger et al 1988). Recalculated value from Koehler et al experiment data. The value is revised because the authors advanced that there are errors on the Hess cycle used by Koehler et al. Enthalpy of formation of calcium aluminates referred to the elements (298.15K).

	Phase	ΔH°f(kJ/mole) Uncertaint	Method of investigation
		y (±)

Table 26 :

 26 Enthalpy of formation of calcium aluminates referred to oxides (298.15K).

Table 27 :

 27 Table27. We have gathered all the data from the available literature: calculated and measured. Component activities at 1787°C(Allibert, Chatillon, Jacob, & Lourtau,

	Sources	Temperature	Method of investigation xCaO	a(CaO) a(Al2O3)
		(°C)		(mole)
	Alibert et al	1787	Mass spectrometer	0.645	0.42	0.02
	(1981)		equipped with multi	0.578	0.2	0.05
			effusion cell containing	0.548	0.14	0.06
			homogenous melt of	0.495	0.082	0.2
			different composition.	0.438	0.048	0.41
			CaO satured melt and	0.414	0.04	0.25
			pure Al2O3 used as	0.352	0.025	0.5
			reference.
	Sharma and	1500.16	Gas & slag equilibrium	0.58	0.21	0.15
	Richardson,		technique: activities	0.6	0.25	0.115
	(1961)		obtained from Sulphide	0.62	0.3	0.085
			capacities	0.64	0.38	0.06
			measurement	0.66	0.5	0.04
			containing CaO and	0.68	0.67	0.025
			Al2O3.	0.71	1	0.007

Table 28 :

 28 curve, we find the result is in agreement with[START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF]. Standard Gibbs free energy of C3A.

	Reactions	Temperature	dG(J)=A-BT(K)	Estimated	Method	Sources
		(K)	[J.mol -1 ]		error
			A(J)	B(J/K)
	3CaO+Al2O3→C3A 1050-1320	-	-29.4972 ±836.8	Galvanic Cells	Kumar and
			7818.6408				using Caβ"-	Kay (1985)
							alumina solid
							electrolytes
		1000-1200	-6530	-30.6		-	Galvanic Cells	Rog et al
							using Caβ"-	(1993)
							alumina-CaF2
							solid electrolytes
		1373-1635	-11790	-28.27	±1190	Galvanic Cells	Nagata et
							using 4CaO.P2O5	al (1989)
	Reactions	Temperature	dG(J)=A-BT(K) [J.mol -	Estimated	Method	Sources
		(K)	1 ]			error (J)
			A(J)	B(J/K)
	CaO+Al2O3→CA 1050-1500	-	-18.2004		±836.8	Galvanic Cells using	Kumar
			15113.026				Caβ"-alumina solid	and Kay
							electrolytes	(1985)

Table 29 :

 29 Standard Gibbs free energy of CA.

	Reaction	Temperature	dG(J)=A-BT(K)	Estimated	Method	Sources
		(K)	[J.mol -1 ]		error (J)
			A(J)	B(J/K)
	CaO+2Al2O3→CA2 1100-1500	-	-26.74 ±1255.2	Galvanic Cells	Kumar & Kay
			12916.426			using Caβ"-	(1985)
						alumina solid
						electrolytes
		1373-1873	-15650	-25.82 ±900	Galvanic Cells	Nagata et al
						using	(1989)
						4CaO.P2O5
		1000-1200	-11870	-27.5	-	Galvanic Cells	Rog et al
						using Caβ"-	(1993)
						alumina-CaF2
						solid
						electrolytes
		923-1223	-16070	-25.7	±800	EMF with CaF2	Allibert et al
						electrolyte	(1981)
		1260-1400	-18409.6	-18.78		EMF method	Popov et al
						with CaF2 as	(1979)
						electrolyte

Table 30 :

 30 Standard Gibbs free energy of CA2.

	Reaction	Temperatur	dG(J)=A-BT(K)	Estimated	Method	Sources
		e (K)	[J.mol -1 ]		error (J)
			A(J)	B(J/K)
	CaO(s)+6Al2O3(s)	1100-1500 -17869.45 -39.3296 ±836.8	Galvanic Cells	(Kumar & Kay,
	→CA6(s)					using Caβ"-	1985)
						alumina solid
						electrolytes
		1373-1873	-16380	-37.58 ±1730	Galvanic Cells	Nagata et al
						using	(1989)
						4CaO.P2O5
		1000-1200	-15460	-41.1		Galvanic Cells	Rog et al
						using Caβ"-	(1993)
						alumina-CaF2
						solid
						electrolytes
		923-1223	-17430	-37.2 ±1500	EMF with	Allibert et al
						CaF2	(1981)
						electrolyte
		1260-1400	-31380	-		EMF method	Popov et al
				28.3675		with CaF2 as	(1979)
				2		electrolyte

Table 31 :

 31 Standard Gibbs free energy of CA6.

Table 32 :

 32 Lattice parameters of Ca5Al6O14 and CaAl12O19 synthesis compounds.

	group	Cmc21	P63/mmc
	Lattice parameter a (Å)	11.281	5.559
	Lattice parameter b (Å)	10.994	5.559
	Lattice parameter c (Å)	10.306	21.902

Table 33 :

 33 Table33summarises the results of measuring heat contents of C5A3. The values obtained are corrected using the enthalpies of CA and C3A as the compound has a purity of 93.9%. The measurements were carried out at five different temperatures from room temperature to the high temperature of measurement; the error on the values did not exceed 3%, Measurements on C5A3 are made with a 95% confidence interval. Lack of thermodynamic description in the literature does not allow for comparisons between experimental and modelled values. Relative enthalpy data from Drop calorimetry for Ca5Al6O14. the model described in the FTPs database. The measurements are done under the same experimental conditions as for C5A3. The experimental results confirm the estimated data as recorded in the FTPs database.

		Relative enthalpy
	T	T	HT-H298K	u(∆H)
	°C	K	J.mol -1	J.mol -1	%
		Ca5Al6O14 (mol. wt. 586.28)
	799.66	1072.81 434459.97 13076.42	3.01
	898.51	1171.66 489697.91 10738.37	2.19
	998.72	1271.87 559500.72	8864.55	1.58
	1099.26	1372.41 602791.62 11466.47	1.90
	1198.03	1471.18 628306.37 13984.21	2.23

Table 34 :

 34 Relative enthalpy data from Drop calorimetry for CaAl12O19.

Table 35 :

 35 Einstein and polynomial parameters from room temperature to melting point.

	Chemistr	Ɵ1	Ɵ2	Ɵ3	α1	α2	α3	a1	a2
	y
	C12A7	1156.49 502.74 206.2	15.80 27.05 16.15 1.15E-01	-
				0
	C3A	1020.13	480.05	195.4	2.74	5.31	2.96	1.16E-02	-
		1	0	4
	CA2	1109.65 508.76 209.9	4.69	4.65	2.66	1.03E-02	-
				7
	CA	1047.39 458.84 178.7	2.75	2.73	1.52	1.32E-03 4.24E-06
				0

Table 36 :

 36 Invariant melting point from this study and assessment.

	T(°C)

Table 8 :

 8 Transition temperature during cooling compared to those reported by Smith et al (1961). ..............................................................................................................

Table 9 :

 9 Relative enthalpies data from drop calorimetry for Ca2SiO4. .....................

Table 10 :

 10 Structural data of the polymorph of Ca3Si2O7. .........................................

Table 11 :

 11 Thermodynamic data of Rankinite polymorph. .......................................

Table 12 :

 12 Ca3Si2O7 crystallographic data calculated from X-ray pattern. ................

Table 13 :

 13 Experimental results of heat content measurements on rankinite............

Table 14 :

 14 Crystallographic data of Ca2Fe2-xAlxO5 solid solution as a function of composition from various sources for two selected compositions. ...........................

Table 15 :

 15 Standard enthalpy of formation referred to the oxides component, experimental data. a This value corresponds to the enthalpy of formation at 800°C.

Table 16 :

 16 Standard enthalpy of formation referred to the elements, calculated data from Materials Project database online and FactSage software. ..............................

Table 17 :

 17 Composition table for Ca2Fe2-xAlxO5 synthesis. ........................................

Table 18: Relative enthalpies measured in function of temperature from 584.87°C to 1092.59°C. ............................................................................................................... Table 19 : Ca2Fe0.6Al1.4O5 relative enthalpy plotted with FTOxid data from FactSage

Software. .................................................................................................................. Table 20 : Melting proprieties of solid solution Ca2Fe2-xAlxO5 in function of Al ions contents. ................................................................................................................... Table 21 : Invariants reactions in the Ca3Al2O6 -CaAl2O4 composition range without C12A7. .....................................................................................................................

Table 22 :

 22 Data on C12A7 invariant and melting point. ............................................

Table 23 :

 23 Invariants reactions in the CaAl4O7-CaAl12O19 composition range ...........

Table 24 :

 24 Thermodynamic data for aluminates in the CaO-Al2O3 pseudo-binary. .

Table 25 :

 25 Enthalpy of formation of calcium aluminates referred to the elements (298.15K). ...............................................................................................................

Table 26 :

 26 Enthalpy of formation of calcium aluminates referred to oxides (298.15K). ...............................................................................................................................

Table 27 :

 27 Component activities at 1787°C[START_REF] Allibert | Mass-Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO-Al2O3[END_REF] and 1500.16K[START_REF] Sharma | Activities in lime-alumina melts[END_REF]. ..............................................

Table 28 : Standard Gibbs free energy of C3A. ...................................................... Table 29 : Standard Gibbs free energy of CA. ........................................................ Table 30 : Standard Gibbs free energy of CA2. ......................................................

Table 31 :

 31 Standard Gibbs free energy of CA6. ......................................................

Table 32 :

 32 Lattice parameters of Ca5Al6O14 and CaAl12O19 synthesis compounds.

Table 33 :

 33 Relative enthalpy data from Drop calorimetry for Ca5Al6O14. .................

Table 34 :

 34 Relative enthalpy data from Drop calorimetry for CaAl12O19. ..................

Table 35 :

 35 Einstein and polynomial parameters from room temperature to melting point. .......................................................................................................................

Table 36 :

 36 Invariant melting point from this study and assessment. .......................

Table 37 :

 37 Standard entropy for the calcium aluminates as compared to values from King (1955). ............................................................................................................

CHAPITRE 2 : ETUDE THERMODYNAMIQUE DE LA BELITE ET DE LA RANKINITE.

  La modélisation des phases solides réalisées sur C3A, C12A7, CA et CA2 est basé sur la fonction d'Einstein à trois températures pour les capacités calorifiques basse température. Afin d'éviter les divergences du modèle à haute température, nous avons ajouté une fonction polynomiale pour une description plus ajuster comme décrit dans l'équation ci-dessous.La description thermodynamique de la phase liquide se fait à l'aide du modèle associé.Ce modèle est particulièrement utilisé lorsqu'un ordre à courte portée est observé dans la phase liquide, ce qui est le cas dans le système métal-oxygène mais aussi dans certains systèmes oxyde-oxyde à forte interaction. 𝑥 𝑘 𝑙𝑛(𝑥 𝑘 ) + ∑ 𝑥 𝑖 𝑖 𝑥 𝑗 ∑ (𝑥 𝑖 -𝑥 𝑗 ) 𝑣 𝐿 𝑖,𝑗

	𝐺 𝑚 𝑙𝑖𝑞 = ∑ 𝑥 𝑘 𝐺 𝑘 𝑙𝑖𝑞 𝑘	+ 𝑅𝑇 ∑ 𝑙𝑖𝑞 𝑣 𝑘
	8.3
	𝐶𝑝 = 3𝑅	(	∑ 𝛼 𝑖 ( Ɵ 𝐸 𝑖 𝑇 𝑛 𝑖	) 2	exp ( (𝑒𝑥𝑝 ( Ɵ 𝐸 Ɵ 𝐸 𝑖 𝑇 ) 𝑇 ) -1) 2 𝑖	)	+ 𝑎 1 𝑇 + 𝑎 2 𝑇 2

CHAPTER 3: THE FERRITE PHASE.

CHAPTER 4: THERMODYNAMIC STUDY OF THE C-A SYSTEM

RESUME DE LA THESE EN FRANCAIS

ACKNOWLEDGMENTS

Synthesis monitoring was done by X-ray diffraction after 12 hours of processing.

Multiphase compounds are ground again and annealed until the pure intended phase is achieved. Fig. 44 illustrates each synthesis step including mechanical mixing (1), pellet de-carbonization (2) and heat treatment.

RELATIVE ENTHALPIES MEASUREMENT

Relative enthalpy values of the solid solution were measured for two distinct compositions by drop calorimeter MHTC96 (Type S thermophile, 1300°C max).

Ca2FeAlO5 and the more alumina-rich compound Ca2Fe0.6Al1.4O5 were studied.

Powders of identical composition to the samples studied were put at the bottom of the Table 22 : Data on C12A7 invariant and melting point. Nurse et al (1965) and [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF] reported that the C12A7 phase contained ~1 mass% water evaporated near to the melting point.

Only C3A melts incongruently in the Fig. 45 and forms a C3A-CaO-Liquid invariant. C3A is stable along the liquidus joining points E (eutectic) and P (peritectic) and then destabilizes above 1531°C into CaO and liquid. CA melts congruently and forms a first eutectic mixture with C5A3 and a second with C3A5. There is no CA6 phase reported by the authors in the CaO-Al2O3 section. All phases melt incongruently. C12A7 is assumed to be non-anhydrous, which means that it is not stable in the absence of air humidity. [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF] conducted recently an additional study of the CaO-Al2O3 system by the differential thermal analysis DTA method. As reported by Nurse et al (1965), no C12A7 was detected by the authors in an dry atmosphere and all aluminates melt incongruently. Nevertheless, the existence of C12A7 in the presence of traces of moisture was confirmed through the eutectic at 1403°C. [START_REF] Jerebtsov | Phase diagram of CaO-Al2O3 system[END_REF].

CaO-Al2O3 in argon atmosphere

PHASE DIAGRAM COMPUTED

A new phase diagram based on the 3rd generation CALPHAD functions combined with the associate model to describe the liquid phase was computed. The pure CaO description is based on the evaluation of [START_REF] Deffrennes | Thermodynamic modelling of the Ca-O system including 3rd generation description of CaO and CaO2[END_REF]. The alumina-rich liquid data are in agreement with the model; the shape of the CaO-rich liquid is related to the effects of the associate and shows a discrepancy with the experimental data. Nevertheless, this simple description is sufficient. For CA6, the heat capacities used for the modelling are the ones derived from [START_REF] Haas | Thermodynamic Tabulations for Selected Phases in the CaO-Al2O3-SiO2-H2O at 101.325kPa (1atm) between 273.15 and 1800[END_REF] as they agree well with our measurements. We have measured the relative enthalpies but low temperature Cp experimental data is missing. For C5A3 the experimental data are not enough for a complete thermodynamic description of this phase.

G Liquid (C, C3A, A): [START_REF] Deffrennes | Thermodynamic modelling of the Ca-O system including 3rd generation description of CaO and CaO2[END_REF]. [START_REF] King | Heat capacities at low temperatures and entropies at 298.16°K of crystalline calcium and magnesium aluminates[END_REF].

We

CONCLUSION

In this section, we have critically evaluated the literature and highlighted a certain lack of thermodynamic data, especially on CA6, but also an absence of experimental data on C5A3. The formation of C5A3 requires a neutral gas atmosphere to avoid the formation of C12A7. The reaction is slow due to the small enthalpy of reaction difference with respect to CA and C3A and the compound obtained contains these two secondary phases. Both aluminates were synthesized and the relative enthalpies

GENERAL CONCLUSION

Increasing greenhouse gas pollution is a global concern. The Kyoto Protocol of 1997, which entered into effect in 2005, aims to reduce emissions of the six greenhouse gases CH4, N2O, HFCs, PFCs, SF6 and CO2. The latter is particularly produced by the cement industries, whose overall pollution of the sector accounts for 8% of emissions into the air. Since the implementation of the near zero emission policy by the year 2050, the cement industries are investing in research and development to reduce the carbon footprint effects of cement production. As limestone (CaCO3) is the major CO2-producing element in the cement industry, one of the solutions is to find an alternative to produce cements with low limestone content. A thorough knowledge of the thermodynamic properties of the key oxides contained in Portland clinkers allows a better understanding of the physico-chemical processes and stability of the major constituents of Portland cement. Reliable experimental data and modelling using the CALPHAD approach allows the complex clinker formation process to be modelled and the process to be optimised. For this purpose, it is necessary to build up a high quality database based on experimental measurements of the various oxides constituting clinker (raw material used for cement manufacture). In this thesis, we focused on the thermodynamic properties study of Belite (C2S), Rankinite (C3S2), Alumino-ferrite (C4AF) and selected calcium aluminates (CA6, C5A3

LIST OF TABLES