Chemistry and kinetics of chemical vapor deposition of pyrocarbon -: VI.: influence of temperature using methane as a carbon source

The chemical vapor deposition of carbon from methane was investigated at an ambient pressure of about 100 kPa, a methane partial pressure of 10 kPa and temperatures ranging from 1050-1125 degrees C. Carbon deposition rates and compositions of the gas phase as a function of residence time have been determined using a substrate with a surface area/reactor volume ratio of 40 cm(-1). Increasing temperatures lead to strongly increasing deposition rates, decreasing partial pressures of ethane and increasing partial pressures of ethene, ethine and benzene. The overall activation energy of carbon deposition, determined from the initial deposition rates at a residence time versus zero amounts to 446 kJ/mol as compared to 431.5, 448 and 452.5 kJ/mol reported in earlier papers. Two possible rate-limiting steps are discussed, namely dissociation of methane, which is favored in the earlier papers, and dissociation of carbon-hydrogen surface complexes. (C) 1999 Elsevier Science Ltd. All rights reserved.