The objective of this work was to determine the effects of the carbon substrate on matrix structure and composite reactivity upon infiltration of carbon cloths with pyrolytic carbon. Pyrolysis of propylene at 750 degrees C was used to produce carbon fiber/carbon matrix composites. Carbon (and ceramic) substrates of differing crystalline order and surface area were infiltrated with pyrolytic carbon at various partial and total propylene pressures. The infiltrated substrates (composites) were heat-treated to 2900 degrees C in order to determine the effect of porosity on the graphitization behavior of the pyrolytic carbon matrices. Under the conditions examined, the kinetics of pyrolytic carbon formation were controlled by the surface area of the substrate. It was found that the mesoporous surface was entirely covered by pyrolytic carbon, but only the larger micropores were accessible to the products of propylene pyrolysis. The oxidation resistances of heat-treated composites prepared by infiltration of low-temperature (ungraphitized) substrates were greater than those of composites produced by infiltration of high-temperature substrates. This was attributed to stress-enhanced graphitization of the matrix due to pore shrinkage. (C) 1998 Elsevier Science Ltd. All rights reserved. References: 22
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