Chemistry and kinetics of chemical vapor deposition of pyrocarbon - V - Influence of reactor volume/deposition surface area ratio

Pyrocarbon deposition from methane was studied at ambient pressure and a temperature of 1100 degrees C using a vertical hot-wall reactor with a honeycomb structure as substrate. Compared to the deposition tube used in previous studies this substrate exhibits a 15-fold increase in surface area. The methane initial partial pressure was varied up to 75 kPa, and the residence time up to 1 second. The results are compared with those obtained with the tube. The surface area is shown to decisively influence the chemistry and kinetics of deposition reactions and thus also the major growth species of pyrocarbon. With residence time increasing from zero to one second the ratio of surface-related pyrocarbon deposition rates obtained with tube and honeycomb structure vary by a factor of about 18. With increasing initial partial pressure, deposition rates tend to approach a limiting value indicating saturation adsorption. Pyrocarbon deposition rates as a function of residence time and initial partial pressure have been simulated considering complex homogeneous and heterogeneous reactions. (C) 1998 Elsevier Science Ltd. All rights reserved.