Abstract
Chemical vapor deposition (CVD) of carbon is applied to the manufacture of the C-SiC functionally graded material and the C/C composite. Propane is often used as carbon source. Since propane is rapidly decomposed in the gas phase, a comprehensive model of the gas-phase reactions is required for designing and controlling the CVD processes. Experiments and numerical simulation of propane pyrolysis at 1010°C, 6.7 kPa and a propane pressure of 0.1-3 kPa in helium were carried out. The carbon deposition rate and gaseous product composition were measured. Involved in propane pyrolysis, 651 elementary reactions were taken from the database. First, the number of the chemical species was limited by considering the heaviest component, butane, detected in the experiments. The number of elementary reactions was reduced by ignoring the stereoisomerism of C4 compounds. The numerical simulation was carried out for 453 reactions and 57 species. Based on the calculated results, the elementary reactions having low reaction rates under the actual reaction conditions were discarded. Then, by grouping isomers at partial equilibrium or having similar behavior and replacing consecutive reactions by the rate-determining step, a 55-reaction model was built. By examining the contribution of each reaction to the material balance of each species, important reactions were extracted. The contribution of each reaction to the deposition rate was also examined by repeating removal of one reaction and calculation of carbon deposition rate. Finally a 26-reaction model of propane pyrolysis was developed. The proposed model was able to reproduce the experimental results. The procedure of reduction of the elementary reaction model presented in this study is expected to apply to other CVD reaction systems.
