CARBON-CARBON PROCESSING BY FORCED FLOW-THERMAL GRADIENT CHEMICAL-VAPOR INFILTRATION USING PROPYLENE

The fabrication of carbon/carbon disks using the forced flow-thermal g radient chemical vapor infiltration process was studied using a 2(3) f actorial statistical design. Propylene, diluted with hydrogen, was use d as the reagent. The independent variables were the temperature of th e bottom of the fibrous preform, concentration of the reagent, and tot al flow rate. The response variables were infiltration time, final por osity, rate of weight gain, and uniformity of densification. It was fo und that the infiltration time and rate of weight gain were affected b y each of the three independent variables. It was also observed that t he densification of the composites could be monitored by the in situ m easurement of the back pressure. The composites were cut into 12 slice s 1 cm long, 4 mm wide and 2 mm deep to measure the uniformity of dens ification. It was found that the density of the slices varied very lit tle with position within an individual composite disk. Also, coating t hickness as a function of position was measured for different composit es. In most of the runs the coating thickness increased exponentially from the cold side to the hot side of the disk. The coating thicknesse s near the cold and hot sides were used to calculate the rate constant for the pyrolysis of propylene in the preform. The activation energy was found to be similar to 21.0 kcal mol(-1) and the rate constant is given by In k(s) = 1.5 -21034/RT.