On kinetic and microstructural transitions in the CVD of pyrocarbon from propane

The microstructure and the deposition rate of pyrocarbon deposited from propane have both been studied as a function of gas phase residence time (t(r)) and reactor temperature (T) in the vicinity of 1000 degrees C and at a constant pressure of 2 kPa. Transitions between two different types of laminar microstructures, smooth laminar (SL) and rough laminar (RL), have been observed. Simultaneously, transitions between several kinetic regimes have been seen. The kinetic results permit us to interpret changes in carbon microstructure and to develop a qualitative chemical model for the formation of laminar pyrocarbons. This model could explain both kinetic and textural transitions by the occurrence of two parallel routes to carbon formation involving two different families of ultimate carbon precursors. (C) 1999 Elsevier Science Ltd. All rights reserved.