Oxidation behavior of non-oxide ceramics in a high-pressure, high-temperature steam environment

This paper provides a review of two recent studies undertaken to examine the oxidation behavior of monolithic SiC and SiC-SiC composites in simulated and actual gas turbine environments. In the first study, a high-pressure and high-temperature test facility was used to expose a variety of structural ceramics and ceramic matrix composites to 15% water vapor carried in an air environment at 10 atm of total pressure and 1204°C. The second study involved the exposure of a SiC-SiC combustor liner in an industrial gas turbine for approximately 2300 h at a total pressure of 10 atm and peak liner temperature of 1150°C. In the two studies microstructural analyses were used to measure the rates of both silica scale formation and SiC recession. These experimentally determined rates were then compared with values predicted from established oxidation/volatilization models. The estimates of the temperature and pressure sensitivities of the oxidation and volatilization rate constants, required for this comparison, were obtained from the literature. For the case of the combustor liner, the recession rate of SiC was well described by the model. However, the predicted rates of scale formation in both studies were significantly lower that the corresponding experimental values. Possible reasons for this discrepancy are addressed.