Dr Stéphane Mazerat

Dr Joséphine Lacroix

Dr Benoît Rufino

Dr René Pailler
email: pailler@lcts.u-bordeaux.fr

Dr Q Ma

Prof K Guerin

Prof. N Popovska-Leipertz

Prof Reinoso F Rodriguez
email: reinoso@ua.es

Prof Y Gogotsi
email: gogotsi@drexel.edu

Carbon derived from silicon carbide fibers, a comparative study

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction sentence

The paper reports a comparative study between various SiC-based fibers (11 in total) and their corresponding derived carbon, obtained by chlorination treatment at intermediate temperatures. The so obtained carbide derived carbons (CDC) are mainly microporous, but some substrates, such as high oxygen containing or third-generation SiC fibers, also show some mesoporosity. The CDC pore size distribution is found to be related to fibers chemical composition. Moreover, because the carbon free of fibers is not affected by the treatment in the selected etching condition, the percolation and amount of this former network remain intact and are correlated with CDC mechanical properties, respectively the tensile strength and the Young modulus. Hence, an analogy between SiC-based fibers derived carbon and a composite material can be proposed.

Introduction 30 words

Carbon derived from silicon carbide-based fibers is micro-mesoporous with size distribution related to the substrate chemical composition and composite-like mechanical properties: amorphous SiC/SiCO-derived carbon reinforced with sp2 carbon-free network.

Graphical abstract

Reviewers comments from Carbon:

Reviewer #1: This manuscript describes a comparative study of carbon derived from silicon carbide fibers. The authors carefully performed experiments, and the results obtained were analyzed and discussed systematically and rationally. A weak point of this manuscript is the appeal of the significance of the conclusions induced from the experiments. All the results are reasonable, but in turn they look commonplaces. I would suggest the authors to describe how the findings are valuable and can contribute to the advances of the relevant field at the introduction. Other specific comment is shown below: 1. Table 1: Please insert a footnote as for the method used for the determination of Si/C/O/X compositions as well as the ratio of SiC and SiCO. 2. In equation ( 4), the authors calculate the free carbon atomic content (%Cfree) by subtracting the amount of carbon in SiC (%Si) and SiO2 (%O/2) from the total carbon amount (%C). However in Table 1, the amount of SiCO is shown instead of SiO2. Is it possible to obtain the amount of SiO2 from SiCO? If so, please describe the method. [START_REF] Gogotsi | Carbon coating s on silicon carbide by reaction with chlorine-containing gases[END_REF]. Please clearly define the parameter Ø<beta>-SiC, in Table 1. Additionally, please describe how the authors determined it. [START_REF] Ishikawa | Carbon Materials with Nano-sized Pores Derived from Carbides[END_REF]. "Subsequently to chlorination treatment, the cross section of some fibers was observed by scanning electron microscopy (SEM Hitachi S4500) to confirm their complete transformation (no chemical contrast by SEM) (Fig. 1)." The contrast observed by SEM would be due to the difference in conductivities in C and SiC matrices, rather than chemical contrast. Charge build up is more significant on the insulative SiC surface. 5. As shown in Table 2, different chlorination temperatures are used for different samples. Please describe the reason for selecting these temperatures for each. [START_REF] Dash | Synthesis, structure and porosity analysis of microporous and mesoporous carbon derived from zirconium carbide[END_REF]. "Brunauer-Emmet-Teller" should be "Brunauer-Emmett-Teller". 7. P6: "pores sizes" should be "pore sizes". 8. As the authors are aware of the fact, use of SiC isotherm for alfa-s analysis of porous carbon is not appropriate. Instead, non-porous carbon like carbon black should be used as a standard.

Reviewer #2: The manuscript studies the preparation of porous carbons from silicon carbide fibers by the well-known method of heat treatment with chlorine. The authors prepared a variety of porous carbon fibers and have made a detailed characterization of porosity and mechanical properties, among others. The authors have demonstrated that this methodology can be successfully applied to obtain CDC fibers with different properties. Considering that the preparation method is not novel and that the main outcome is a series of porous carbon fibers derived from SiC fibers which properties are not very different to those of conventional activated carbon fibers, I cannot recommend this manuscript for publication in Carbon.

Introduction

In the last two decades, carbide-derived carbon (CDC) has gained much attention for many applications like gas storage, adsorbent, catalyst support, electrode or supercapacitor. They are produced by extraction, layer by layer, of metallic atoms from carbide leaving a carbon skeleton. This is processed by halogenation at intermediate or high temperature, resulting in the formation of volatile halides [START_REF] Yushin | Carbide-derived carbon[END_REF][START_REF] Lee | Kinetics of conversion of silicon carbide to carbide derived carbon[END_REF]. CDC has been obtained from different carbides: SiC [START_REF] Gogotsi | Carbon coating s on silicon carbide by reaction with chlorine-containing gases[END_REF], TiC, ZrC, B 4 C, Al 4 C 3 [START_REF] Ishikawa | Carbon Materials with Nano-sized Pores Derived from Carbides[END_REF][START_REF] Gogotsi | Tailoring of nanoscale porosity in carbide-derived carbons for hydrogen storage[END_REF][START_REF] Dash | Synthesis, structure and porosity analysis of microporous and mesoporous carbon derived from zirconium carbide[END_REF], Fe 3 C [START_REF] Dimovski | Synthesis of graphite by chlorination of iron[END_REF] and many others [8], silicon carbide being the most reported. CDC are porous materials with tunable pore size distribution (PSD), from micro to mesoporosity with a sub-Ångstrom accuracy, depending on the treatment temperature, the carbide precursor or its microstructure [START_REF] Dash | Synthesis, structure and porosity analysis of microporous and mesoporous carbon derived from zirconium carbide[END_REF][8][9][START_REF] Gogotsi | Nanoporous carbide-derived carbon with tunable pore size[END_REF][START_REF] Chmiola | Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer[END_REF][START_REF] Kormann | Comparative study of carbide-derived carbons obtained from biomorphic TiC and SiC structures[END_REF][START_REF] Yeon | Carbidederived-carbons with hierarchical porosity from a preceramic polymer[END_REF][START_REF] Popovska | Processing of porous carbon with tunable pore structure by the carbide-derived carbon method[END_REF][START_REF] Duan | Etching process of silicon carbide from polysiloxane by chlorine[END_REF]. Pure chlorine [START_REF] Chen | Carbide derived carbon (CDC) coatings for Tyranno ZMI SiC fibers[END_REF][START_REF] Delcamp | In-situ processing of carbon coating on the surface of SiC-based fibers[END_REF][START_REF] Brisebourg | Si-C-O fibres in gas reactive atmospheres[END_REF][START_REF] Rufino | The effect of particle size on the formation and structure of carbide-derived carbon on β-SiC nanoparticles by reaction with chlorine[END_REF], diluted in Ar or H 2 [START_REF] Gogotsi | Carbon coating s on silicon carbide by reaction with chlorine-containing gases[END_REF][START_REF] Kormann | Comparative study of carbide-derived carbons obtained from biomorphic TiC and SiC structures[END_REF] or HCl [START_REF] Cambaz | Formation of carbide-derived carbon on β-silicon carbide wiskers[END_REF], is the most reported halogen element to produce this material, even if fluorine [START_REF] Batisse | The synthesis of microporous carbon by the fluorination of titanium carbide[END_REF], bromide or iodine can be used as well. In the case of silicon carbide chlorination at intermediate temperatures and ambient pressure, carbon does not react with chlorine to form CCl 4(l or g) [START_REF] Yushin | Carbide-derived carbon[END_REF]. Process is associated with the following equation:

SiC (s) + 2Cl 2(g) → SiCl 4(g) + C (s) (1)
C. Vakifahmetoglu et al. used silicon oxycarbide (SiCO) materials to produce CDC [START_REF] Vakifahmetoglu | Enhanced hydrogen and methane gas storage of silicon oxycarbide derived carbon[END_REF]. The reaction involved can be written as follows:

SiC x O y + 2Cl 2 → SiCl 4 + (x-y/2)C + y/2CO 2 (2) SiC x O y + 2Cl 2 → SiCl 4 + (x-y)C + yCO (3)
The oxygen content of these materials presents a particular interest: it increases the pore size and acts as a well-controlled in-situ activation agent, which contrast with CO 2 [START_REF] Osswald | Porosity control in nanoporous carbide-derived carbon by oxidation in air and carbon dioxide[END_REF][START_REF] Kormann | Processing of carbide-derived carbons with enhanced porosity by activation with carbon dioxide[END_REF][START_REF] Schmirler | In-situ thermal activation of carbide-derived carbon[END_REF] or KOH [START_REF] Portet | Capacitance of KOH activated carbide-derived carbons[END_REF] post treatment agents. Firstly, CDC is prone to oxidation at low temperature range, down to 225 °C [START_REF] Delcamp | In-situ processing of carbon coating on the surface of SiC-based fibers[END_REF], because of its disordered microstructure [START_REF] Gogotsi | Tailoring of nanoscale porosity in carbide-derived carbons for hydrogen storage[END_REF][START_REF] Kormann | Comparative study of carbide-derived carbons obtained from biomorphic TiC and SiC structures[END_REF][START_REF] Welz | Carbon structures in silicon carbide derived carbon[END_REF]. Secondly, the mixed silicon atoms environment (SiC 3 O, SiC 2 O 2 or SiCO 3 ) destabilizes the structure and enhance its sensitivity to Cl 2 [START_REF] Brisebourg | Si-C-O fibres in gas reactive atmospheres[END_REF][START_REF] Vakifahmetoglu | Enhanced hydrogen and methane gas storage of silicon oxycarbide derived carbon[END_REF]. This later result is consistent with chlorination kinetics of first-generation SiC-based fibers. Nevertheless, only few authors studied this kind of material [START_REF] Chen | Carbide derived carbon (CDC) coatings for Tyranno ZMI SiC fibers[END_REF][START_REF] Delcamp | In-situ processing of carbon coating on the surface of SiC-based fibers[END_REF][START_REF] Brisebourg | Si-C-O fibres in gas reactive atmospheres[END_REF][START_REF] Gogotsi | Formation of carbon coating on SiC fibers by selective etching in halogens and supercritical water[END_REF][START_REF] Delcamp | Protection de fibres base SiC pour composites à matrice céramique[END_REF][START_REF] Mazerat | Fibre de renfort pour composites SiC/SiC : amélioration et corrélation de la durée de vie sous air à T<900°C avec la réactivité chimique[END_REF][START_REF] Mazerat | Composition and reactivity of various silicon carbide fibers[END_REF]. They are commercially available and display various and well documented chemical or microstructural properties, useful for fundamental research, with a flexible filament shape prone to tensile testing. The mechanical properties of CDC coatings are usually assessed, for tribological purpose [START_REF] Presser | Carbide-Derived Carbons -From Porous Networks to Nanotubes and Graphene[END_REF][START_REF] Ersoy | Tribological properties of carbon coatings produced by high temperature chlorination of silicon carbide[END_REF][START_REF] Chun | Carbide derived carbon: from growth to tribological application[END_REF][START_REF] Mcnallan | Nano-Structured Carbide Derived Carbon (CDC) Films and their Tribology[END_REF], by nanoindentation showing a Young modulus about 5 GPa [START_REF] Chen | Carbide-Derived Nanoporous Carbon and Novel Core-Shell Nanowires[END_REF]. To our knowledge, no studies deal with totally transformed SiCbased fibers characterization. The aim of this work is to produce CDC from eleven different -4-SiC-based fibers and compare some physicochemical and mechanical properties of the derived carbon (DC) with the precursor ones.

Materials and method

Materials

Silicon carbide fibers are synthesized by the conversion of polycarbosilane (PCS, commercialized by Nippon carbon Co. Ltd. under the trade name Nicalon ® ), or derivate containing small amount of organometallic (polytitanocarbosilane PTCS, polyzirconocarbosilane PZCS or polyaluminocarbosilane PACS commercialized by UBE Industries Ltd. under the trade name Tyranno ® ). The first-generation fibers are oxygen cured and thus composed of a silicon oxycarbide phase (SiCO) embedding SiC grains in nanometer range and free aromatic carbon as basic structural units (BSU) [START_REF] Laffon | Study of Nicalonbased ceramic fibres and powders by EXAFS spectrometry, X-ray diffractometry and some additional methods[END_REF]. This free carbon atomic content is approximated (considering only SiC and SiO 2 phases) from:

2 % % % % O Si C C free + - = (4)
Seven studied fibers belong to this first-generation: two without metallic element (NL101 and NL207), two doped with titanium (Grade-S and Lox-M), two other containing zirconium (ZMI and ZM) and the last one with aluminum (AM). Hi-Nicalon (referred as Hi-Ni) and ZE (containing Zr) belong to the second, whereas Hi-Nicalon type S (referred as Hi-Ni-S) and SA3 (aluminum doped) belong to the third-generation SiC-based fibers. Second-generation fibers are electron beam cured and thus show lower oxygen content, whereas the thirdgeneration underwent a high temperature treatment (CO degassing of AM or decarbonating under H 2 of Hi-Ni precursors) followed by sintering about 1800 °C [START_REF] Flores | Ceramic Fibers Based on SiC and SiCN Systems: Current Research, Development, and Commercial Status[END_REF]. The fibers from this latter generation are nearly stoichiometric with larger SiC grain sizes. A total of eleven different fibers were so investigated (Table 1).

- [START_REF] Mazerat | Fibre de renfort pour composites SiC/SiC : amélioration et corrélation de la durée de vie sous air à T<900°C avec la réactivité chimique[END_REF][START_REF] Mazerat | Composition and reactivity of various silicon carbide fibers[END_REF][START_REF] Teyssandier | Contribution to the understanding of the microstructure of first generation Si-C-O fibers[END_REF]. Chemical composition was measured at CNRS facility in Solaize by ICP-AES and oxidation [START_REF] Teyssandier | Contribution to the understanding of the microstructure of first generation Si-C-O fibers[END_REF]. The amount of crystallized β-SiC was determined by X-Ray diffraction (XRD) and the mean size (Ø β-SiC) assessed by the Scherrer formulae. The amount of SiCO infers from difference between chemical composition and quantity of β-SiC and C free .

Chlorination treatment

Prior to any treatment, SiC-based fibers were desized at 650 °C for 10 min in air, followed by thin silica film removal in 10 vol.% hydrofluoric acid bath for 4 minutes. The chlorination was performed in a horizontal silica tube (Ø = 70 mm) heated by a 3-zones resistive furnace (Carbolite Ltd.) described elsewhere [START_REF] Delcamp | In-situ processing of carbon coating on the surface of SiC-based fibers[END_REF][START_REF] Brisebourg | Si-C-O fibres in gas reactive atmospheres[END_REF][START_REF] Rufino | The effect of particle size on the formation and structure of carbide-derived carbon on β-SiC nanoparticles by reaction with chlorine[END_REF][START_REF] Mazerat | Fibre de renfort pour composites SiC/SiC : amélioration et corrélation de la durée de vie sous air à T<900°C avec la réactivité chimique[END_REF][START_REF] Mazerat | Composition and reactivity of various silicon carbide fibers[END_REF]. Specimens were placed in the 250 mm hot isothermal zone. The tube tightness was checked under static vacuum, set by fore line pump, over a night. The reactor was then filled with pure chlorine and heated up with a linear ramp of 20 °C min -1 . Once atmospheric pressure reached, Cl 2 flow rate was set to 0.6 NL min -1 and outlet opened. Excess of chlorine and products of the reaction were trapped in 2 successive 1 L washing bottles of NaOH (2 mol L -1 ). The trapping system could be interchanged to a second parallel outlet. This manipulation was necessary for cleaning purpose, when the NaOH solution was saturated (Equation 5) or the output obstructed by silica gel (hydrolysis of SiCl 4 ), without disturbing the gas flow or pressure during the treatment.

Cl 2 + 4NaOH → 2NaCl + 2NaClO + 2H 2 O (5)
Two distinct treatment protocols were used to produce CDC. The first one aimed to transform 60 mm long multifilament tows, for tensile tests purpose. A two hours annealing at 850 °C -6-was selected to suit the reactivity of all fiber types. The second protocol aimed to transform larger samples to obtain 200-300 mg of CDC for further characterization. It was therefore performed on 2D woven (150 x 30 mm) or tows with adequate length. The treatment settings were selected to limit the kinetic and silica gel formation rate at the outlet, for obvious safety reasons. The treatment was hence divided in two steps: (i) etching of the firsts 3 µm in 1 hour selecting properly the temperature (T1) according to chlorination kinetics [START_REF] Brisebourg | Si-C-O fibres in gas reactive atmospheres[END_REF][START_REF] Mazerat | Fibre de renfort pour composites SiC/SiC : amélioration et corrélation de la durée de vie sous air à T<900°C avec la réactivité chimique[END_REF][START_REF] Mazerat | Composition and reactivity of various silicon carbide fibers[END_REF], (ii) followed by another hour at T2 = T1 + 25 °C (about twice the transformation kinetic observed at T1) to complete the core transformation (Table 2). This protocol assumes the etching depth is proportional to the annealing duration, confirmed elsewhere for fiber sample size [2, 16-17, 30, 40]. Subsequently to chlorination treatment, the cross section of some fibers was observed by scanning electron microscopy (SEM Hitachi S4500) to confirm their complete transformation (no difference in charge build up by SEM) (Fig. 1). The hypothesis is made that CDC remains amorphous in this temperature range (T < 900 °C) [4-5, 12, 27]. At the end of annealing time, furnace was turned-off and a nitrogen purge (1.2 NL min -1 ) initiated. Previous works performed on SiC or SiCO samples revealed that under atmospheric pressure, chlorine extraction from porosity begins at 600 °C [9-10, 12-13, 17, 19, 30]. This was found to result in effective micropore volume and equivalent specific surface area enhancement to respectively 33% and 25% [START_REF] Delcamp | Protection de fibres base SiC pour composites à matrice céramique[END_REF]. Hence, depending on chlorination temperature, a bias in CDC porosity can be anticipated. Therefore, to reliably compare the different carbons, a second annealing treatment was initiated, once the system purged, for 1 hour at 700 °C under dynamic primary vacuum.

Sample

Physico-chemical characterization

The electrical conductivity (σ, S m -1 ) of as-received fibers was measured on desized bundles comprising four or five tows (corresponding to several thousands of fibers) with a four-points testing device described elsewhere [START_REF] Chollon | Correlation between microstructure and electrical properties of SiC-based fibres derived from organosilicon precursors[END_REF]. Copper wires were connected to bundle using silver painting. The sample section (S 0 ) was calculated according to the following equation:

ρ 0 0 0 L m S = ( 6
)
Where ρ is the fiber density (Helium pycnometer, Micromeritics Co., AccuPyc II 1300), m 0 and L 0 are the bundle mass and length respectively.

Nitrogen adsorption analysis was carried out on fully transformed fibers, using a commercial

Micromeretics ASAP 2010 at 77 K with equilibration intervals of 10 s. Because of the hygroscopic nature of CDC, air contaminants, like moisture, are rapidly adsorbed in porosity and could disturb gas physisorption measurements. Hence transformed woven were directly outgassed at 300 °C under secondary vacuum for twelve hours, just after chlorination oven opening. The equivalent specific surface area (SSA in m 2 g -1 ) and the C parameter inferred from Brunauer-Emmett-Teller (BET) equation [START_REF] Brunauer | Adsorption of gases in multimolecular layers[END_REF] for P/P 0 < 0.3, with an upper partial pressure range adjusted to ensure R² > 0.999. Effective micropore volume and size distribution were calculated using the semi-empirical Horvath-Kawazoe (H-K) approach [START_REF] Horvath | Method for the calculation of effective pore size distribution in molecular sieve carbon[END_REF] with slit pore geometry. Micropores could further be subdivided into ultramicropores (pore width < 0.7 nm) and supermicropores (0.7 nm < pore width < 2 nm) [START_REF] Thommes | Physical Adsorption Characterization of Nanoporous Materials[END_REF]. These latter pore -8-sizes were characterized with alpha-s method, developed by K.S.W. Sing et al. [START_REF] Sing | Reporting physisorption data for gas/solid systems[END_REF][START_REF] Sing | Empirical method for analysis of adsorption isotherms[END_REF][START_REF] Sing | Surface Area Determination[END_REF][START_REF] Sing | The use of physisorption for the characterization of microporous carbons[END_REF][START_REF] Sing | The use of gas adsorption for the characterization of porous solids[END_REF]. For that purpose, isotherm of non-porous carbon [START_REF] Silvestre-Albero | Non-porous reference carbon for N2 (77.4 K) and Ar (87.3 K) adsorption[END_REF] (SSA = 8.70 m² g -1 ) was taken as reference and normalized by its adsorption at P/P 0 = 0.4. The mesopore size distribution (meso-PSD) was calculated by Barret-Joyner-Halenda (BJH) method [START_REF] Barrett | The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms[END_REF] based on a modified Kelvin equation. This method account for partial pressures above 0.45 and pores larger than 40 Å.

Single point total pore volume (V p,0.99 ) was assessed using the Gurvich rule, determined from the specific amount of gas adsorbed at a relative pressure close to the saturation vapor pressure (0.90 < P/P 0 < 0.99), with a density conversion factor of 1.5468 x 10 -3 cm 3 cm -3 (STP) [START_REF] Sing | Reporting physisorption data for gas/solid systems[END_REF][START_REF] Thommes | Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)[END_REF].

Thermogravimetric analysis (TAG 24, Setaram Inc.) was used to study the fiber derived carbon (fiber-DC) oxidation kinetics under pure dry oxygen flow (60 NmL min -1 ) with a linear ramp of 5 °C min -1 until 650 °C. Sample of approximately 50 mg were placed in alumina crucible and outgassed under primary vacuum at room temperature for several minutes prior to oxidation. TGA experiments were performed just after nitrogen adsorption analysis for the same contamination reasons whereas mechanical testing did not require such precautions.

Mechanical characterization

Room temperature mechanical properties were measured by tensile tests of either sized asreceived (40-50 tests) or fully transformed (20 tests) monofilaments, with a dedicated machine [START_REF] Mazerat | Improvement of silicon carbide fibers mechanical properties by Cl 2 etching[END_REF]. Samples were individually pulled out from tows and glued on a paper holder with a 25 mm window [START_REF] Lissart | Statistical analysis of failure of SiC fibres in the presence of bimodal flaw populations[END_REF]. Special care needed to be taken for manipulation of CDC specimen, because of their low density and stiffness. CDC sample kept, after treatment, the woven geometry and therefore undulated. Therefore, a slight force was applied to sample to force it to be straight and ensure axial gluing to paper holder. Fibers diameter was measured, prior to testing, using their laser diffraction pattern [START_REF] Li | Improved accuracy of the laser diffraction technique for diameter measurement of small fibres[END_REF]. Once gripped in the device, the paper holder was cut on both sides. Tensile tests were carried out at a constant elongation rate (0.5 % min -1 ). The applied load and displacement were respectively measured using load cell (0-2 N) and LVDT extensometer, mounted on the grips. The measured elongation was corrected accounting for the system compliance, ascertained with 10 extra tests at 10 and 40 mm gauge lengths.

Results and discussion

-9-

SiC-based fibers properties

Some properties of as-received fibers, such as their chemical composition, phase volume proportion, β-SiC grain size, density (ρ), mechanical properties, and electrical conductivity (σ) are reported in Tables 1 and3 The electrical conductivity of a SiC-based fiber is ascribed to the percolation state of its free carbon network. Indeed, BSU is a conductive phase embedded in a relatively insulating continuum (SiC and SiCO) [START_REF] Coustumer | Understanding Nicalon Fibre[END_REF][START_REF] Chollon | Correlation between microstructure and electrical properties of SiC-based fibres derived from organosilicon precursors[END_REF]. The family of electrically conductive fibers gathers ZMI, ZM, ZE, Hi-Ni and SA3. However, NL101, NL207, Grade-S, AM, Hi-Ni-S are electrically insulative. The Lox-M fiber is intermediate between these two families (Table 3). Except for third-generation, all fibers contain a large amount of carbon-free, exceeding 15 atomic percents. Tyranno ® fibers are C free rich in comparison to Nicalon ® ones (Table 1), but this amount does not account for its continuity. The discrepancy existing between Hi-Ni-S (insulative) and SA3 (conductive) fibers can be ascribed to the radial gradient of carbon -10-content in the latter one [START_REF] Dong | Characterization of nearly stoichiometric SiC ceramic fibres[END_REF]. As mentioned before, free carbon excess on fiber is not likely to be transformed by chlorine in the selected temperature range.

SiC-based fibers display a brittle mechanical behavior with a Young modulus dictated by the rule of mixture, knowing volume proportion (V x Table 1) of each phase:

E fiber = E SiC .V SiC + E C .V C + E SiCO .V SiCO ( 7
)
As an assumption, the SiC Young modulus (E SiC ) is set to the Hi-Ni-S fiber one (470 GPa).

Best fitting is found considering elastic moduli of 28 GPa and 175 GPa for carbon free and SiCO phases respectively, with a scattering below 17% (Table 3). The impact of manufacturing route, curing and annealing temperatures on C free and SiCO Young moduli and intrinsic β-SiC grain size partly explain this scattering. This method is naturally an approximation of the inner phase properties. It is worth to note the estimated SiCO modulus is close to oxygen rich fibers.

SiC-based fiber-DC elaboration

As mentioned in method section, CDC thickness is proportional to the etching duration (Equation 8) [16-18, 29, 31, 40, 59] in this range of sample size [START_REF] Lee | Kinetics of conversion of silicon carbide to carbide derived carbon[END_REF], revealing the etching reaction is not piloted by reactant or product transportation to or from the reaction interface.

Kinetics evolution with temperature obeys the Arrhenius law (Equation 9). e = kt (8) k = k 0 e -Ea/RT (9

)
where e is the CDC thickness (nm), k the reaction rate (nm s -1 ), t the treatment duration (s), k 0 the pre-exponential factor (nm s -1 ), E a the activation energy (J mol -1 ) (Table 4), R the universal gas constant (8.314 mol J -1 K -1 ) and T the temperature (K). As mentioned before, two experimental procedures were used. Samples for mechanical testing were treated in the same conditions whereas large samples were transformed at two successive temperatures depending on their reactivity against chlorine. The treatment temperature strongly depends on fiber type (Table 2), based on their transformation kinetics (Table 4). For instance, Grade-S was fully converted in CDC at 575 °C while Hi-Ni had to be handled at 850 °C for the same result. The oxygen amount and the nature of metallic heteroelement, when present, are found to play a critical role on the fiber reactivity (Table 4), and more likely on the SiCO phase [START_REF] Brisebourg | Si-C-O fibres in gas reactive atmospheres[END_REF][START_REF] Mazerat | Fibre de renfort pour composites SiC/SiC : amélioration et corrélation de la durée de vie sous air à T<900°C avec la réactivité chimique[END_REF][START_REF] Mazerat | Composition and reactivity of various silicon carbide fibers[END_REF]: titanium (Grade-S and Lox-M) enhanced it (lower Ea) whereas zirconium (ZMI, ZM, ZE) or aluminum (AM) reduced it (higher Ea).

The SiC-fiber-derived carbon was found to have a shape memory of the geometry during the treatment. Indeed, fibers-DC, when extracted from a treated woven, keep the geometry it had

during Si atoms extraction and undulate whereas as-received fibers are straight.

Physisorption experiments

SiC-fibers-DC display significant adsorbed volume at low relative pressure (Fig. 2) typical for type-I isotherm according to the IUPAC classification and characteristic of microporous samples (pore width < 2 nm) [START_REF] Thommes | Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)[END_REF]. Despite the same classification for all samples, adsorption isotherms can be separated into four (4) shapes:

-Shape A, nitrogen is adsorbed on a wide range of partial pressure until the mesopororosity limit (P/P 0 = 0.4) [START_REF] Gregg | Adsorption, Surface Area and Porosity[END_REF]. This indicates a broad micropore size distribution (Figs. 2.a and 3.a).

This shape gathers carbons derived from all first-generation fibers (oxygen cured) excepting NL101-DC.

-Shape A*, nitrogen adsorption isotherm curve is shape A-like below 0.4 P/P 0 but displays an H2a-like [START_REF] Thommes | Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)[END_REF] single steeped hysteresis loop (0.4 < P/P 0 < 0.55). This behavior is typical for mesoporous materials (type IV isotherm according to IUPAC classification) exhibiting pore sizes between 2 and 50 nm (Fig. 3.b). The partial pressure for which loop is closed (0.45 P/P 0 )

indicates a cavitation controlled evaporation of the capillary condensate from mesopores, that -12-is obstructed by the pore constriction (ink bottle-like with neck size < 4 nm) [START_REF] Thommes | Physical Adsorption Characterization of Nanoporous Materials[END_REF][START_REF] Sing | Reporting physisorption data for gas/solid systems[END_REF][START_REF] Thommes | Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)[END_REF]. This phenomenon can be related to the adsorbate nature (carbon wall), temperature and cavities linked to micropores. The first generation NL101-DC displays this isotherm shape (Fig. 2.a).

-Shape B, nitrogen is adsorbed on a sharp partial pressure domain, showing narrow micropore size distribution (Figs. -Shape B*, nitrogen adsorption isotherm curve is shape B-like below 0.4 partial pressure. It is characterized by a single steeped hysteresis loop between adsorption and desorption branches, H2a-like (0.4 < P/P 0 < 0.9) closing at 0.4-0.5 P/P 0 (Fig. Table 5 summarizes pore structure properties for all here studied CDC. Excepting for Grade-S-DC, equivalent specific surface area (SSA) ranges from 1100 to 1800 m 2 g -1 , associated with effective micropore volume (H-K method) from 0.5 to 0.8 cm 3 g -1 . Some mesopority is also identified with limited volume according to BJH method (taking account for pore larger than 40 Å from adsorption branch). CDC can thus be considered as mostly microporous.

These properties agree with previous works performed on SiC-based fibers chlorination etching [START_REF] Delcamp | In-situ processing of carbon coating on the surface of SiC-based fibers[END_REF][START_REF] Delcamp | Protection de fibres base SiC pour composites à matrice céramique[END_REF] but do not reach values calculated on SiCO-DC ( > 2000 m² g -1 ) [START_REF] Vakifahmetoglu | Enhanced hydrogen and methane gas storage of silicon oxycarbide derived carbon[END_REF]. A higher temperature for carbide halogenation has often been reported to increase the SSA, the effective micropore volume and PSD, until 800 °C on SiC-DC for instance [START_REF] Ishikawa | Carbon Materials with Nano-sized Pores Derived from Carbides[END_REF][START_REF] Gogotsi | Tailoring of nanoscale porosity in carbide-derived carbons for hydrogen storage[END_REF][START_REF] Gogotsi | Nanoporous carbide-derived carbon with tunable pore size[END_REF][START_REF] Chmiola | Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer[END_REF][START_REF] Kormann | Comparative study of carbide-derived carbons obtained from biomorphic TiC and SiC structures[END_REF]. In the present work, this has not been observed because of the substrate chemical composition and microstructure predominant impact. The highest SSA (Table 5) are indeed obtained with oxygen rich fibers (Table 1), etched at lower temperatures (Table 2).

Fiber SSA (m 2 g -1 )

Vol µp (cm 3 g -1 ) µp size (Å)

Vol meso (cm 3 g -1 )

V p,0.99 (cm 3 BET equation [START_REF] Brunauer | Adsorption of gases in multimolecular layers[END_REF] can be used to ascertain the degree of interaction between N 2 molecules and sample (adsorbent/adsorbable) via the C parameter [START_REF] Sing | Reporting physisorption data for gas/solid systems[END_REF]. This value is related to the energy of adsorption of the first monolayer: higher C is, more energetically carbon sites are [START_REF] Thommes | Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)[END_REF][START_REF] Sing | The use of nitrogen adsorption for the characterisation of porous materials[END_REF]. These values are found to extend from 420 to 14500 (Table 5). CDC obtained by chlorine etching of first-generation fibers show a C parameter ranging from 420 to 970. With a second-generation substrate, this value lies about 3500, whereas highest values are calculated with third-generation derived carbon. This parameter hence falls when the oxygen content increases. Such phenomenon may infer from energetically carbon sites depletion, caused by partial CDC oxidation by in-situ oxygen. The Grade-S-DC does not follow this trend with a C parameter intermediate between second and third generation fiber-derived carbons, showing the singularity of this microporous carbon compared to others.

The narrowest micropores measurable with nitrogen are about 4.5 Å width [START_REF] Thommes | Physical Adsorption Characterization of Nanoporous Materials[END_REF]. For pore width below 7 Å (named ultramicropores), the adsorption is limited to a single step pore filling by a molecular volume of adsorbable (for P/P 0 ≤ 10 -6 ). However, for larger partial pressure, cooperative and multistep molecular filling of adsorbable volume occurs (for 10 -6 < P/P 0 ≤ 10 -1 ) in supermicropores. Their respective volumes are revealed by alpha-s method [START_REF] Sing | Empirical method for analysis of adsorption isotherms[END_REF][START_REF] Sing | Surface Area Determination[END_REF][START_REF] Sing | The use of physisorption for the characterization of microporous carbons[END_REF][START_REF] Sing | The use of gas adsorption for the characterization of porous solids[END_REF]. Second and third generation fibers (Hi-Ni, ZE, Hi-Ni-S and SA3) derived carbons exhibit a larger ultramicropores effective volume fraction than supermicropores. Such distinction in micropore sizes is not evidenced on first-generation SiCO fibers derived.

c). Even if the

PSD derived from adsorption branch is questionable because not in thermodynamic equilibrium and that BJH method is not adapted for pores smaller than 40 Å, this similarity indicates no pore blocking effect drives the desorption of these small mesopores. However, desorption-derived PSD shows a shoulder of artificial pores around 37 Å diameters. This peak is attributed to cavitation phenomenon: the capillary condensate of all coarser pores suddenly and spontaneously evaporates at a given pressure, not dictated by neck size, rather the adsorbate or temperature [START_REF] Groen | Pore size determination in modified micro-and mesoporous materials. Pitfalls and limitations in gas adsorption data analysis[END_REF][START_REF] Bertier | On the use and abuse of N 2 physisorption for the characterization of the pore structure of shales[END_REF]. Therefore, peak at 37 Å observed on shape B* desorptionderived PSD does not correspond to a given size, rather larger mesopores extending to 80 Å or above. The mesoporous volume given in table 5 (accounting for pores larger than 40 Å) is derived from adsorption branch, despite not in thermodynamic equilibrium, for that reason: pore volume ascertained from desorption branch is underestimated. It is generally admitted that BJH method can underestimate the pore size by up to 20-30% for mesorpores smaller than 100 Å [START_REF] Thommes | Physical Adsorption Characterization of Nanoporous Materials[END_REF][START_REF] Barrett | The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms[END_REF].

Shape A* shows, like shape B*, a progressive decrease of differential pore volume for smallest mesopores (between 20 and 30 Å) found on adsorption and desorption-derived PSD.

A shoulder about 34 Å is observed on PSD calculated from desorption branch. This shoulder is observed on NL101-DC (Fig. 3.b), but also on NL207-DC, Grade-S-DC and Lox-M-DC (Fig. 3.d), even if less obvious on shape A isotherms (Fig. 2.a). The 34 Å mesopores size is not observed on zirconium and aluminum doped fibers (ZMI-DC, ZM-DC and AM-DC) despite similar oxygen content. This peak is, again, purely artificial [START_REF] Groen | Pore size determination in modified micro-and mesoporous materials. Pitfalls and limitations in gas adsorption data analysis[END_REF][START_REF] Bertier | On the use and abuse of N 2 physisorption for the characterization of the pore structure of shales[END_REF] and should not be interpreted as actual mesopore family. Indeed, it results from cavitation effect, independent to neck size, and corresponds to simultaneous evaporation of all larger mesopores capillary condensate [START_REF] Thommes | Physical Adsorption Characterization of Nanoporous Materials[END_REF].

C. Vakifahmetoglu et al. observed micro-mesoporous carbon formed by SiCO chlorination

and attributed mesoporosity to domain sizes where silicon has a mixed carbon-oxygen environment [START_REF] Vakifahmetoglu | Enhanced hydrogen and methane gas storage of silicon oxycarbide derived carbon[END_REF]. Another origin for these mesopores would be an in-situ oxidation of carbon walls separating pores (Equations. 2 and 3), resulting in their fusion. This controlled oxidation can explain the absence of ultramicroporisty on first-generation derived carbon, transformed in supermicropores (between 0.7 and 2 nm pore width) or mesopores ( > 2 nm). This -16-hypothesis meets the following observation: micropore size increases with oxygen content (Tables 1 and5). These two parameters are otherwise correlated by a logarithmic law (Fig. 4).

Indeed, low oxygen content fibers (second and third-generation) show 6-7 Å micropore median width range, whereas first-generation SiCO show it above 7.5 Å. Grade-S-DC does not follow the same tendency. The particular case of Grade-S-DC shall now be discussed. This CDC shows an original behavior compared to others. Indeed, despite an oxygen content above the NL101 (Table 1), its equivalent SSA, total pore volume, microporous effective volume and median micropore width are low and its C parameter high. No relevant volume of ultramicroporosity could be highlighted by alphas-s method that could have explained the C value. This fiber derived carbon displays, by far, the highest reactivity among the considered samples for this work [START_REF] Mazerat | Composition and reactivity of various silicon carbide fibers[END_REF]. A hypothesis infers from the low transformation temperatures (550 °-575 °C Table 2) used for its transformation: as mentioned, chlorine is thermally desorbed from micropores above 600 °C and ambient pressure, even during the chlorination treatment. Grade-S fiber is the only sample transformed below this temperature threshold. Therefore, chlorine is likely to be partly trapped in CDC while forming, and would avoid, in some way, amorphous carbon organization or rearrangement. This may explain the high C value calculated. During the desorption post treatment, all chlorine species are extracted which could lead to a micro or mesoporosity collapsing, explaining the low effective microporous volume measured (Fig. 4).

-17-

SiC-fiber-DC oxidation kinetics

The oxidation behavior of CDC has been investigated by thermogravimetric analysis (TGA) under pure and dry oxygen. In figure 5, records show the mass loss as a function of temperature for seven [START_REF] Dimovski | Synthesis of graphite by chlorination of iron[END_REF] fibers derived carbon belonging to all generations. CDC burn-off is observed since 400 °C [START_REF] Kormann | Comparative study of carbide-derived carbons obtained from biomorphic TiC and SiC structures[END_REF] or even below [START_REF] Delcamp | Protection de fibres base SiC pour composites à matrice céramique[END_REF]. Grade-S-DC is clearly the most sensitive to oxidation, behavior consistent with its low synthesis temperature [START_REF] Kormann | Comparative study of carbide-derived carbons obtained from biomorphic TiC and SiC structures[END_REF] and, as mentioned before, its presumed structural instability. As far as other samples are concerned, results are in accordance with pore structure: the larger the pore size, the higher the accessibility of oxygen is, and thus the faster the burn-off proceeds. Indeed, Hi-Ni-DC (shape B isotherm with narrow The apparent activation energy of CDC oxidation is calculated from the Arrhenius equation (Equation 9) with k the kinetic constant (s -1 ), ascertained with the first derivation of the curves in 300 °-500 °C temperature range (Fig. 5). Apparent activation energies are summarized in table 6 for all studied SiC-fiber-derived carbons. Small differences in reactivity are highlighted between samples. CDC with broadly distributed micropore size (shape A or A* isotherms) show activation energies in the 95-100 kJ mol -1 range, excepting when derived from zirconium-doped fibers (no mesoporosity detected on desorption-derived meso-PSD).

Carbon derived from second or third-generation fibers show higher activation energies, even when mesoporosity is detected, which is consistent with the free carbon network organization (high temperature pyrolysis process) and, in less extend, with the chlorination temperature. A. 6: Data extracted from burn-off TGA experiments under pure dry oxygen on SiC-fiberderived-carbon.

SiC-fiber-DC mechanical properties

Mechanical properties of CDC were measured by tensile testing 20 fully transformed SiC monofilaments of each type, extracted from tows chlorinated in the same conditions: 850 °C for 120 min. The CDC displays a brittle behavior (Fig. 6), with average elastic moduli between 7 GPa and 19 GPa and elongation between 0.9% and 4% (Table 7). This former property is larger than the 5 GPa elastic modulus reported and extracted from nanoindentation experiments on β-SiC whiskers derived carbon [START_REF] Chen | Carbide derived carbon (CDC) coatings for Tyranno ZMI SiC fibers[END_REF]. The tensile strength is found to drastically drop compared to the as-received fibers. None of these properties seem to be correlated with the porosity structure (Table 5), the initial microstructure or oxygen content (Table 1). Therefore, the differences between CDC mechanical properties found a different origin. The CDC tensile strength seems however correlated to the electrical conductivity of asreceived fibers (Fig. 7). Hi-Ni-S-DC is found to slightly differ from this behavior. As mentioned before, electrical conductivity characterizes the percolation state of the BSU. This correlation means the tensile strength of CDC reflects the continuity of former carbon free network, as it is the only phase remaining intact after the chlorination treatment [START_REF] Yeon | Carbidederived-carbons with hierarchical porosity from a preceramic polymer[END_REF]. This CDC Young modulus is likely to follow the mixture rule. As an assumption, Young moduli of carbon free network, amorphous carbon-derived from SiC and from SiCO, are respectively considered to be 28 GPa, 5 GPa [START_REF] Chen | Carbide derived carbon (CDC) coatings for Tyranno ZMI SiC fibers[END_REF] and negligible (E SiCO = 0 GPa). Considering the volume proportions given in table 1, third-generation fibers (Hi-Ni-S-DC and SA3-DC), and in a lower extend the Hi-Ni-DC, show a lower calculated modulus (Table 7). This observation is consistent with as-received fibers results presented in table 3 and attributed to the underestimation of the C free modulus after higher temperature pyrolysis. The Young modulus extracted from tensile tests on all other fibers derived carbons, is close but lower than the ones calculated by the mixture rule (Table 7). An overestimation of the C free modulus could here be pointed out.

Therefore, mechanical properties of CDC can be used to estimate the free carbon amount using the mixture rule, as well as its percolation, linked to the electrical conductivity of former SiC-based fibers. Hence, tensile test of SiC-fibers-DC could be simplified to the characterization of the carbon free network, embedded into amorphous carbon with poor mechanical properties. The similarity with composite materials, here carbide or oxycarbidederived carbon reinforced with sp2 carbon network, can thus be proposed. It is worth noting -21-the considered modulus and the volume fraction in the mixture rule are indirectly assessed and do not account for the synthesis temperature. This calculation can therefore be misleading, whereas the electrical conductivity is a direct measurement. Such result could be used to target some mechanical properties of CDC for the desired application. The carbon free amount can for example be adjusted in SiCO glasses by process settings [START_REF] Yeon | Carbidederived-carbons with hierarchical porosity from a preceramic polymer[END_REF].

Conclusion

A large number of silicon carbide fibers, covering a wide range of chemical compositions and microstructures, were fully converted into porous carbon by selective etching of silicon atoms with chlorine in the temperature range 550 °-850 °C. These materials were mostly microporous with high equivalent specific surface area ( > 1000 m² g -1 ). Carbon derived from third-generation fibers highlighted some mesoporosity, likely formed during fibers sintering process. The pore size was found to be correlated to the oxygen content of as-received fibers: second and third generation fibers gave carbon revealing ultramicroporosity (width < 7 Å) whereas carbon derived from first-generation fibers showed pore enlargement, up to mesopores. This was attributed to nano-domains of mixed silicon environment or to the in- situ oxidation of carbon walls, decreasing in the mean while the C parameter. The PSD difference (mesoporosity detection) between titanium or aluminum and zirconium doped fibers-CD did not found clear explanation and would need further dedicated investigations.

Grade-S-DC did not follow the trend with limited mesoporosity, low SSA and high value of C, despite its former high oxygen content. This could be ascribed to its high chemical reactivity and associated low transformation temperature, limiting chlorine desorption during the treatment and, presumably, preventing carbon organization. The oxidation of CDC was observed since 400 °C but all samples did not follow the same kinetic; behavior correlated with the accessibility of oxygen to the carbon and thus to the PSD. The oxidation apparent activation energy was found to range from 95 to 180 kJ mol -1 . This property could be linked to free carbon BSU organization in as-received fibers and thus their manufacturing process.

Mechanical properties of CDC were tuned by free carbon excess in the former materials: the tensile strength was linked to its percolation state whereas the Young modulus was attributed to its amount and organization. This former statement was deduced from the relationship existing between electrical conductivity and tensile strength of respectively as-received and transformed fibers. The later statement, concerning the relationship between carbon free amount and CDC elastic modulus, resulted from the relevancy of the mixture rule considering -22-a 28 GPa modulus for carbon free, 5 GPa for SiC-DC and neglecting the SiCO-DC one. These materials can be associated to amorphous carbon matrix composites reinforced by aromatic carbon.

As known, CDC are unique materials offering the possibility to fine tune the pore size distribution, from micro to mesopores, by proper substrate selection or treatment condition adjustment. The oxidation sensitivity of such materials makes them inappropriate for application in oxidizing environment at temperatures exceeding 400 °C, even 300 °C for long duration. Their shape memory, offered by small diameter fibers, and their mechanical properties however did not retained attention of previous studies. The latter can be adjusted using a sub-network of etching-inert materials (for instance, carbon, silica, alumina can be selected against chlorine) embedded in the carbide matrix. This opens a new investigation field for CDC future development in mechanically stressed applications.

2 :

 2 Chlorination treatment temperatures (first hour at T1, 3µm etching, and second hour at T2=T1+25 °C) used to fully transform tow/woven of SiC fibers for subsequent physisorption and oxidation analysis.

Fig. 1 :

 1 Fig. 1: SEM observation of fiber section after chlorination treatment showing its progressive transformation into CDC as the treatment duration increases. Fully transformed fibers were considered for this work (arrow show the untransformed fiber core).

  2.b and 3.a). Isotherms of the second-generation fibers-DC belong to this shape (Hi-Ni-DC, ZE-DC).

Fig. 2 :

 2 Fig. 2: Nitrogen physisorption isotherms for SiC-based fibers fully transformed in CDC after chlorine etching treatment displaying (a), broad micropore size without (shape A) or with

Fig. 3 :

 3 Fig.3: Pore size distribution of carbon derived from silicon carbide fiber calculated from nitrogen physisorption experiments: (a) micro-PSD using H-K approach with slit pores geometry (b-c), comparison of meso-PSD calculated from adsorption (∆) and desorption (□) branches of isotherm using BJH method and (e) meso-PSD (calculated from desorption branch of isotherm) of different first-generation fibers.

Fig. 4 :

 4 Fig. 4: Relationship between the oxygen content of the as-received SiC fibers and the median micropore size (H-K method) once fully transformed in CDC by chlorination treatment.

  PSD) shows the lowest oxidation kinetics whereas SA3-DC and Hi-Ni-S-DC (shape B* isotherm micro-mesoporosity) display a sharp mass loss from 500 °C. CDC with a broad micropore size distribution (shapes A and A*) are intermediate. The effect of heteroelements on oxidation sensitivity could be pointed out but questioned by the different temperatures used for etching treatment. Therefore, the oxidation sensitivity of CDC obtained with different SiC fibers precursors correlates with the porosity structure, mainly the PSD, characterized by N 2 physisorption experiments.

Fig. 5 :

 5 Fig. 5: TGA burn-off curves of silicon carbide based fiber derived carbon, obtained under pure and dry oxygen with a 5 °C min -1 heating ramp.

Fig. 6 :

 6 Fig. 6: Tensile strain-stress curves of different SiC-based monofilaments, fully transformed in CDC by chlorination treatment at 850 °C for 120 min.

- 20 -Fig. 7 :

 207 Fig. 7: Relationship between the electrical conductivity (σ) of as-received SiC-fibers and the tensile strength (σ f ) of corresponding CDC after 120 min chlorination at 850 °C.

Table 1 :

 1 Chemical composition, phase volume proportion and microstructure of the selected silicon carbide fibers

	5-

Table 3 :

 3 [START_REF] Mazerat | Fibre de renfort pour composites SiC/SiC : amélioration et corrélation de la durée de vie sous air à T<900°C avec la réactivité chimique[END_REF][START_REF] Mazerat | Composition and reactivity of various silicon carbide fibers[END_REF][START_REF] Teyssandier | Contribution to the understanding of the microstructure of first generation Si-C-O fibers[END_REF]. These fibers display a wide range of Details of mechanical and physical properties of the as-received SiC-based fibers.

	composition, from first-generation with high oxygen content (NL101 or Grade-S with
	respectively 16.7 and 19.4 at.% O) to the near stoichiometric third-generation (Hi-Ni-S and
	SA3), through intermediate fibers with oxygen content around 10 at.% (Lox-M and ZMI) or
	lower like ZM (8.6 at.% O) and ZE (1.7 at.% O). The β-SiC mean grain size is otherwise
	correlated to the oxygen content: higher the oxygen content is, lower SiC crystallite sizes are
	[38, 56]. This latter comment need to account for manufacturing pyrolysis temperature, excess
	of carbon and heteroelement nature. For example, titanium is used to inhibit SiC grains
	growth.
			Mechanical properties ± std. dev.		Physical properties
	Fiber	Tensile strength (GPa)	Elongation (%)	Young modulus (GPa)	E (mixture rule) (GPa)	σ (S m -1 )	ρ (g cm -3 )
	NL101	2.2 ± 0.6	1.2 ± 0.3	180 ± 13	190	0.02	2.57
	NL207	2.8 ± 0.7	1.3 ± 0.3	210 ± 20	220	0.006	2.58
	Grade-S	2.8 ± 0.6	1.5 ± 0.3	180 ± 10	150	0.09	2.35
	Lox-M	3.0 ± 0.7	1.5 ± 0.3	200 ± 10	220	2.6	2.37
	ZMI	3.1 ± 0.7	1.5 ± 0.3	210 ± 20	220	16	2.48
	ZM	3.4 ± 0.7	1.6 ± 0.3	220 ± 10	220	47	2.48
	AM	3.0 ± 0.5	1.6 ± 0.2	180 ± 12	180	0.15	2.42
	Hi-Ni	3.0 ±0.4	1.0 ± 0.1	300 ± 20	300	32	2.74
	ZE	3.3 ± 0.7	1.5 ± 0.3	230 ± 18	230	380	2.55
	Hi-Ni-S	2.9 ± 0.4	0.6 ± 0.1	470 ± 45	400	0.14	3.05
	SA3	2.8 ± 0.5	0.7 ± 0.3	420 ± 20	400	80	3.00

Table 4 :

 4 It is worthwhile noting transformation kinetics of SA3 fibers is not reported because of etching depth inconsistency, presumed to occur preferentially at grain boundaries[START_REF] Mazerat | Fibre de renfort pour composites SiC/SiC : amélioration et corrélation de la durée de vie sous air à T<900°C avec la réactivité chimique[END_REF][START_REF] Mazerat | Composition and reactivity of various silicon carbide fibers[END_REF][START_REF] Mazerat | Improvement of silicon carbide fibers mechanical properties by Cl 2 etching[END_REF]. Arrhenius parameters describing the kinetics of SiC-based fibers etching by pure chlorine at intermediate temperatures (550 °-850 °C).

		Fiber	Ea ± std. dev. (kJ mol -1 )	k 0 (nm s -1 )
		NL101 128 ± 8	1.3 x 10 7
	Nicalon ®	NL207 132 ± 4 Hi-Ni 280 ± 10 Hi-Ni-S 322 ± 50	9.0 x 10 6 8.8 x 10 12 3.1 x 10 14
	Tyra	rade-S 106 ± 7 Lox-M 152 ± 10 nnoG	2.2 x 10 6 2.8 x 10 8

Table 5 :

 5 Data extracted from N 2 physisorption isotherms at 77 K using BET equation, H-K and BJH (from adsorption branch of isotherm) methods, on SiC-based fibers derived carbon.

		C parameter
	g -1 )	a.u.

  Delcamp et al. give apparent activation energy of 120 kJ mol -1 for ZMI-DC[START_REF] Delcamp | In-situ processing of carbon coating on the surface of SiC-based fibers[END_REF][START_REF] Delcamp | Protection de fibres base SiC pour composites à matrice céramique[END_REF] in accordance with the present work but lower than the ones reported for activated carbon oxidation, more likely about 150-180 kJ mol -1[START_REF] Smith | The intrinsic reactivity of carbons to oxygen[END_REF]. This parameter seems more likely governed by the fiber synthesis route rather than the PSD.

	Shape	Sample	Ea (kJ mol -1 )	k 0 (s -1 )
	A*	NL101-DC	100	240
	A	NL207-DC	100	220
	A	Grade-S-DC	98	16
	A	Lox-M-DC	96	210
	A	ZMI-DC	110	660
	A	ZM-DC	160	5.2 x 10 6
	A	AM-DC	100	420
	B	Hi-Ni-DC	120	4300
	B	ZE-DC	150	2.6 x 10 5
	B*	Hi-Ni-S-DC	180	6.5 x 10 7
	B*	SA3-DC	140	6.0 x 10 5
	Table

Table 7 :

 7 Mechanical properties of carbon-derived from SiC fibers measured by tensile tests.

		Experimental properties ± std. dev.	Calculated
	Samples	Tensile strength	Elongation	Young modulus	E (mixture rule)
		(MPa)	(%)	(GPa)	(GPa)
	NL101-DC	168 ± 45	1.5 ± 0.8	11 ± 2.3	13.6
	NL207-DC	130 ± 50	2.1 ± 0.8	7.0 ± 2	12.7
	Grade-S-DC	130 ± 45	0.9 ± 0.3	14 ± 2.9	16.1
	Lox-M-DC	310 ± 75	2.1 ± 0.8	13 ± 1.0	16.3
	ZMI-DC	330 ± 45	2.8 ± 0.4	12 ± 1.5	16.7
	ZM-DC	480 ± 130	3.0 ± 0.7	16 ± 2.2	17.5
	AM-DC	240 ± 60	2.1 ± 0.9	11 ± 1.5	16.8
	Hi-Ni-DC	510 ± 75	2.8 ± 0.4	19 ± 1.5	14.0
	ZE-DC	670 ± 150	4.0 ± 0.8	16 ± 1.9	17.7
	Hi-Ni-S-DC	370 ± 75	2.5 ± 0.6	16 ± 2.0	8.5
	SA3-DC	420 ± 140	2.4 ± 0.9	16 ± 2.6	8.5

Acknowledgment

The authors acknowledge R. Denoyel for editorial advices and the financial support of the Snecma Propulsion Solide (now Safran Ceramics) for this work. carbide at moderate temperatures. J Mater Chem 2004; 14:238-43. doi: 10.1039/b311938f [8] Kukushkina YA, Sokolov VV, Tomkovich MV. Nanoporous carbon prepared by thermochemical treatment of carbide with chlorine. Russ J Appl Chem 2014; 87(10):1517-23. doi: 10.1134/S107042721410019X -24-[9] Urbonaite S, Juarez-Galan JM, Leis J, Rodriguez-Reinoso F, Svensson G. Porosity development along the synthesis of carbons from metal carbides. Microp Mesop Mater 2008;

Data availability

The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.