High temperature oxidation behavior of SiC-coated C/C composites

High-temperature oxidation behavior of the SiC-coated Carbon/Carbon (C/C) composites was examined in the temperature range between 873 and 2273 It under open air environment. From the oxidation tests, three kinds of oxidation regimes were identified: i.e., oxidation reaction rate controlling regime; 873 K to 1173 K, oxygen diffusion controlling regime; 1173 K to 1973 K, and SiC sublimation regime; above 1973 It. Weight loss below 1973 K was due to the oxidation of the C/C substrate by oxygen diffusion through coating cracks. To understand the oxidation behavior, a morphological characterization of coating cracks has been done from the results of the microscopic observation of SiC coating. In particular, in the oxygen diffusion controlling temperature range, an analytical model was developed for the prediction of weight loss due to oxidation of the SiC-coated C/C composites. This model was derived from considering the oxygen diffusion in the coating cracks with the aid of statistical information on coating cracks, such as the distribution and temperature dependence of the coating crack width. Furthermore, considering the effect of silica growth at the crack walls during the oxidation, the weight loss curves were also predicted as a function of oxidation time. The oxidation rate and weight loss curves derived from this model are in fairly good agreement with the experimental results.