Pyrolysis of propane for CVI of pyrocarbon. Part Ⅳ: Main pathways involved in pyrocarbon deposit

摘要

A detailed kinetic mechanism modeling both gas and surface reactions involved in chemical vapor deposition (CVD) of pyrocarbon has been developed. Simulated results have been validated by comparison with experimental data. Pyrolytic carbon deposit was realized on carbon fibers by the pyrolysis of propane at low pressure (＜3 kPa) and high temperature (≈1200K). The kinetic mechanism consists in 608 gaseous and 275 surface elementary steps, and is efficient to predict both pyrocarbon deposit rate and gas phase composition vs. temperatures, residence time ranging and fibers surface to reactant volume ratio. In this paper, the main pyrocarbon deposition pathways are proposed by using flow rate and sensitivity analyses. In our experimental conditions, pyrocarbon seems to be mainly formed by the deposition of small unsaturated species (such as acetylene and ethylene) and methyl radicals. Pyrocarbon deposition rate is controlled by the gas phase composition (H_2, CH_3, C_2H_2 and C_2H_4) and a few surface key reactions.