Fabrication of carbon/carbon composites by forced flow-thermal gradient chemical vapor infiltration

摘要

The fabrication of carbon/carbon composite disks using forced flow-thermal gradient chemical vapor infiltration process using propylene diluted with hydrogen as the reagent is disclosed. The independent variables included concentration of the reagent, total flow rate and preform bottom temperature. The response variables included infiltration time, final porosity, rate of weight gain and deposition rate. The infiltration time and rate of weight gain are affected only by the three independent variables. The densification of the composites is monitored by the back pressure. The composites were cut into slices 1 cm long, 4 mm wide and 2 mm deep to measure the uniformity of densification, which varied very little within a composite. Coating thickness as a function of position increased exponentially from the cold side to the hot side of the composite. The coating thicknesses near the cold side and the hot side are used to calculate the rate constant for the pyrolysis of propylene in the preform. The activation energy is approximately 18.6 Kcal/mol and the rate constant is given by 1n k=8.2-9375.1/T (K)