Effect of gas phase conditions on resultant matrix pyrocarbons in carbon/carbon composites

Abstract

The various microstructures obtained by the low temperature (< 1500°C) chemical vapor deposition (CVD) of carbon in carbon fiber substrates fall into three major types identified as rough laminar, smooth laminar, and isotropic. It is shown that the type of microstructure is a function of the temperature of deposition, the total gas pressure, and the carbon to hydrogen ratio of the source gas. These experimental results are found to be in good agreement with a previously reported carbon CVD model which relates the microstructure to a single parameter, the equilibrium gas phase C 2H 2 C 6H 6 molar ratio. The densities and crystallographic parameters of the heat-treated composites are significantly affected by the type of microstructure. The rough laminar material has by far the most graphitic characteristics and is followed by the smooth laminar and isotropic materials, in that order.