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

The microstructure and the deposition rate of pyrocarbon deposited from pro pane 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 co nstant pressure of 2 kPa. Transitions between two different types of lamina r microstructures, smooth laminar (SL) and rough laminar (RL), have been ob served. Simultaneously, transitions between several kinetic regimes have be en seen. The kinetic results permit us to interpret changes in carbon micro structure and to develop a qualitative chemical model for the formation of laminar pyrocarbons. This model could explain both kinetic and textural tra nsitions by the occurrence of two parallel routes to carbon formation invol ving two different families of ultimate carbon precursors. (C) 1999 Elsevie r Science Ltd. All rights reserved.