Improved Oxidation Resistance of 3-D Carbon/Carbon Composites

摘要

Carbon fiber reinforced silicon carbide matrix composites (C/SiC) were made by aprocess termed Supercritical Fluid Infiltration. A preceramic polymer, e.g., a polycarbosilane which can pyrolyze to form SiC, is dissolved in a supercritical fluid, the solution conveyed into a tightly woven preform of carbon fiber, and the preceramic polymer caused to deposit in the interstitial volume surrounding the fibers. Subsequent pyrolysis of the polymer forms the SiC matrix and fiber coating. Supercritical propane at conditions of 140 deg C, 4000 psi dissolves polycarbsilane to a concentration level of 30% (w/w), a level that results on substantial infiltration and deposition of the polymer. The yield of SiC from the parent polymer upon pyrolysis was determined to be about 50% (w/w); the polymer was fractionated using supercritical propane (in a process termed increasing pressure profiling), and it was found that some of the low molecular weight fractions gave extremely low yields of SiC (<25%) whereas some of the high molecular weight fractions yielded over 80% SiC. When the parent polymer was used for the infiltration studies the deposited material was modular in appearance suggesting that the liquid low molecular weight portion of the polymer was predominately and adversely influencing the uniformity.