EFFECTS OF THE SUBSTRATE ON DEPOSIT STRUCTURE AND REACTIVITY IN THE CHEMICAL-VAPOR-DEPOSITION OF CARBON

The objective of this work was to determine the effects of the carbon substrate on matrix structure and composite reactivity upon infiltrati on of carbon cloths with pyrolytic carbon. Pyrolysis of propylene at 7 50 degrees C was used to produce carbon fiber/carbon matrix composites . Carbon (and ceramic) substrates of differing crystalline order and s urface 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 mat rices. Under the conditions examined, the kinetics of pyrolytic carbon formation were controlled by the surface area of the substrate. It wa s 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 com posites prepared by infiltration of low-temperature (ungraphitized) su bstrates were greater than those of composites produced by infiltratio n of high-temperature substrates. This was attributed to stress-enhanc ed graphitization of the matrix due to pore shrinkage. (C) 1998 Elsevi er Science Ltd. All rights reserved.