Fundamental characteristics of degradation of carbon/carbon composite material in reduction atmosphere made by fuel-rich combustion of methane-air

The fundamental characteristics of degradation of carbon fiber-reinforced/carbon composite materials (C/C composites) in reducing and high-temperature gas streams were experimentally studied. Test samples of C/C composite and reference samples of graphite were exposed to a reducing atmosphere generated by a fuel-rich premixed combustion of methane-air in which little oxygen was believed to exist for 30 minutes. The weight loss fractions of the samples were measured under the equivalence ratios of 0.93, 1.3 and 1.4. After cooling the samples, the features of the surface were observed by a scanning electron microscope. The results of the experimental observation revealed that the C/C composite lost weight more readily than the graphite under the same experimental conditions. The degradation of the matrix of the C/C composite took place prior to that of the carbon fibers, and the chemical degradation became more remarkable by raising of the temperature. The fabric of the carbon fibers additionally peeled off beyond about 1330 K thus increasing the weight loss fractions in a step-wise manners. Moreover, the degradation was restrained by the coexistence of carbon monoxide or hydrogen, and the effect was promoted with increasing equivalence ratio of methane-air. The reason may be that the equilibrium of the reaction; C + H2O = CO + H-2 was shifted to the left side.