CVD and CVI of pyrocarbon from various precursors

Vignoles, Gérard L.; Langlais, F.; Descamps, Cédric; Mouchon, Arnaud; Poche, H. Le; Reuge, Nicolas; Bertrand, Nathalie

doi:10.1016/j.surfcoat.2004.08.036

Cited by 86 publications

(45 citation statements)

References 40 publications

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“…More details on the synthesis of such pyrocarbons are given by Vignoles et al [31]. Le Poche et al [6] have shown than Regenerative laminar pyrocarbon is deposited when the maturation of the gazeous phase is high enough to produce large planar aromatic species, which are deposited by physisorption onto the substrate prior to form pyrocarbon.…”

Section: Raman Microspectroscopymentioning

confidence: 99%

Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

Vallerot¹,

Bourrat²,

Mouchon³

et al. 2006

Carbon

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152

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In pyrocarbon materials, the width of the Raman D band (FWHM D ) is very sensitive to low energy structural defects (e.g., disorientations of the graphene layers). The correlation between the two parameters, FWHM D and OA (as derived from selected area electron diffraction: SAED), has allowed to differentiate various pyrocarbons unambiguously. Furthermore, the optical properties of pyrocarbons, i.e., the extinction angle, the optical phase shift and the ordinary and extraordinary reflectance, have been accurately determined at 550 nm by means of the extinction curves method. These results are completed by in-plane and out-of-plane dielectric constant measurements by angular resolved EELS. Moreover, the hybridization degree of the carbon atoms has been assessed by the same technique. About 80% of the carbon atoms of the pyrocarbons have a sp 2 hybridization. The lack of pure sp 2 carbon atoms, as compared to graphite, might be explained by the presence of sp 3 -like line defects.

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Section: Raman Microspectroscopymentioning

confidence: 99%

Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

Vallerot¹,

Bourrat²,

Mouchon³

et al. 2006

Carbon

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152

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“…1 The process is commonly defined as CVD for chemical vapour deposition (CVI for infiltration). 2 As far as CVI is concerned, cracking reactions are conducted in order to avoid carbon black nucleation by lowering the pressure down to 1 to 10 kPa and the temperature around 1000 °C. These conditions favour mass transfer with respect to chemical deposition; consequently the homogeneity of the deposit within a preform is enhanced.…”

Section: Introductionmentioning

confidence: 99%

Low temperature pyrocarbons: a review

Bourrat¹,

Langlais²,

Chollon³

et al. 2006

J. Braz. Chem. Soc.

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Este artigo é uma síntese das pesquisas recentes na área dos pirocarbonos. Pirocarbono é uma forma de carbono preparada por deposição química em substratos quentes (acima de 900 °C) mediante pirólise de hidrocarbonetos. Aplicações se encontram nas áreas de materiais compósitos termostruturais, de reatores nucleares ou de biomateriais. Muito recentemente, um avanço importante foi obtido na compreensão dos processos de crescimento. Uma classificação dos pirocarbonos de baixa temperatura é apresentada, que se fundamenta na medição da quantia de defeitos e do grau de anisotropia, fazendo uso da espectroscopia Raman. Ela traz uma relacão bem estabelecida entre mecanismos de crescimento, estrutura e propriedades dos pirocarbonos.This article is a synthetic survey of the recent researches in the field of pyrocarbons. Pyrocarbon is the form of carbon which deposits on hot surfaces above 900°C by cracking of hydrocarbons. Applications are in the fields of composite materials, nuclear reactors or biomaterials. Very recently, an important step was reached concerning the understanding of the growth processes. A classification of the low temperature pyrocarbons is introduced. It is based on the measure of carbon defects and anisotropy, using Raman spectroscopy. It provides a comprehensive relationship between growth mechanisms, structure and properties of pyrocarbons.

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“…CH 3 attacks propene will produce CH 4 with a barrier of 80.9 kJ/ mol at 298.15 K or of 181.4 kJ/mol at 1200 K. These reactions are as follows: The reaction branching in (11)-(13) has a rate branching ratio of 1.7 3 10 40 at 298.15 K and of 4.1 3 10 10 at 1200 K. This is also large enough for the reaction to proceed in this path. The ratio for reaction (14) is 688.8 at 298.15 K and is much smaller a value of 3.2 at 1200 K. However, this does not affect the formation of CH 4 because all the next higher TSs (TS107, TS108, and TS110) are linking the same product CH 4 as shown in Figure 2c. Figure 16 shows that the reactions for the decomposition of C 2 -bearing species are H Á þ C 2 H 6 ðIM21Þ !…”

Section: Proposal Of the Most Favorable Pathsmentioning

confidence: 92%

“…2,[9][10][11][12][13] Propene (C 3 H 6 ) is extensively used as the volatile hydrocarbon (carried with H 2 gas) for preparing PyC in CVD or CVI with high-deposition rate. 14,15 This system has been investigated experimentally [16][17][18][19][20][21][22][23][24][25][26][27][28] and theoretically with numerical simulations. [29][30][31] Also as an interesting and useful reaction in dehydrogenization and cracking of hydrocarbons, the pyrolysis process has formed a topic of several investigations.…”

Section: Introductionmentioning

confidence: 99%

Reaction pathways of propene pyrolysis

Wang

et al. 2010

J Comput Chem

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The gas-phase reaction pathways in preparing pyrolytic carbon with propene pyrolysis have been investigated in detail with a total number of 110 transition states and 50 intermediates. The structure of the species was determined with density functional theory at B3PW91/6-311G(d,p) level. The transition states and their linked intermediates were confirmed with frequency and the intrinsic reaction coordinates analyses. The elementary reactions were explored in the pathways of both direct and the radical attacking decompositions. The energy barriers and the reaction energies were determined with accurate model chemistry method at G3(MP2) level after an examination of the nondynamic electronic correlations. The heat capacities and entropies were obtained with statistical thermodynamics. The Gibbs free energies at 298.15 K for all the reaction steps were reported. Those at any temperature can be developed with classical thermodynamics by using the fitted (as a function of temperature) heat capacities. It was found that the most favorable paths are mainly in the radical attacking chain reactions. The chain was proposed with 26 reaction steps including two steps of the initialization of the chain to produce H and CH(3) radicals. For a typical temperature (1200 K) adopted in the experiments, the highest energy barriers were found in the production of C(3) to be 203.4 and 193.7 kJ/mol. The highest energy barriers for the production of C(2) and C were found 174.1 and 181.4 kJ/mol, respectively. These results are comparable with the most recent experimental observation of the apparent activation energy 201.9 +/- 0.6 or 137 +/- 25 kJ/mol.

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CVD and CVI of pyrocarbon from various precursors

Cited by 86 publications

References 40 publications

Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

Low temperature pyrocarbons: a review

Reaction pathways of propene pyrolysis

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