Preparation and process optimization of randomly oriented C/C composites by a novel method

Conventional ways of fabricating C/C composites are unable to achieve wetting in the core of the carbon fiber tow by molten pitch because a single tow has thousands of fibers. Pitch stabilization after infiltration into the carbon fiber preform results in local oozing of the pitch and a non-uniform microstructure due to non-uniform pitch stabilization in the preform. The objective of this research was to devise a method by which complete wetting of fibers in the tow with mesophase pitch is attained by mixing stabilized pitch and chopped and scattered carbon fibers, followed by hot-pressing and carbonization. The influence of process parameters on the carbon yield of the stabilized mesophase pitch is evaluated. The carbon yield divided by processing time and the carbon yield multiplied by the ratio of the apparent density to real density of the C/C composites are used to optimize process parameters. Results show that complete wetting of fibers with mesophase pitch is attained by this method. The carbon yield of the stabilized mesophase pitch decreases with heating rate and the mass ratio of stabilized pitch to carbon fibers, and increases with hot-pressing pressure. At high pressures and high mass ratios, local oozing of the stabilized pitch occurs. The optimum C/C composite was prepared under a hot-pressing pressure of 15 MPa, a heating rate of 0.2 °C/min and a mass ratio of stabilized pitch to carbon fibers of 1:1.