Corrosion of SiC/SiC composite in Na2SO4 vapor environments from 1000 to 1500 °C

Corrosion of a three-dimensional SiC/SiC composite with a CVD SiC coating was investigated in environments containing Na2SO4 vapor, oxygen and water vapor at temperatures from 1000 to 1500 °C. The corrosion behavior was greatly related to temperature. Below 1200 °C, the composite exhibited excellent resistance to corrosion, and then the residual flexural strength nearly kept the same value as the as-received strength. From 1200 to 1300 °C, the interaction of oxidation and corrosion led to a rapid weight gain. Above 1300 °C, weight loss due to volatilization and sublimation of Si(OH)4 and Na2O · xSiO2 on the surface increased continuously. At the same time, the gas release resulted in the formation of bubbles/corrosion pits and the maximum diameters of them increased with an increasing temperature. Additionally, above 1200 °C, with an increasing temperature, the residual flexural strength of the composite decreased greatly.