Hot-corrosion of silicon carbide in combustion gases at temperatures above the dew point of salts

To evaluate the performance of SiC to operating environments expected in future ceramic gas turbines, SiC samples were exposed in a low velocity burner rig at temperatures above the dew point of sodium sulphate (Na2SO4). Under these conditions, the corrosion behaviour should be independent of the sulphur content of the fuel, if Na2SO4(g) is not involved in the corrosion process. At 1000°C, SiC degradation was dependent on the sulphur levels in the fuel and the rates were controlled by the properties of the glassy corrosion products. Although there was an effect of PSO3 on aNa2O at 1300°C, the formation of an inner crystalline silica layer protected the material in both combustion gases so that the effect of pSO3 on corrosion was concealed. These results indicate that Na2SO4(g) is involved in the corrosion process at temperatures above the dew point, contrary to what might be predicted from thermodynamic considerations. The role of sodium on enhancing the rate of corrosion is discussed.