Effect of zirconia content on the oxidation behavior of silicon carbide/zirconia/mullite composites

The oxidation of hot-pressed SiC-particle (SiCp)/zirconia (ZrO2)/mullite composites with various ZrO2 contents, exposed in air isothermally at 1,000 and 1,200 C for up to 500 h, was investigated; an emphasis was placed on the effects of the ZrO2 content on the oxidation behavior. A clear critical volume fraction of ZrO2 existed for exposures at either 1,000 or 1,200 C: the oxidation rate increased dramatically at ZrO2 contents of >20 vol%. The sharp transition in the oxidation rate due to the variation of ZrO2 content could be explained by the percolation theory, when applied to the oxygen diffusivity in a randomly distributed two-phase medium. Morphologically, the composites with ZrO2 contents greater than the critical value showed a large oxidation zone, whereas the composites with ZrO2 contents less than the critical value revealed a much-thinner oxidation zone. The results also indicated that the formation of zircon (ZrSiO4) at 1,200 C, through the reaction between ZrO2 and the oxide product, could reduce the oxidation rate of the composite