Effect of Zirconia Content on the Oxidation Behavior of Silicon Carbide/Zirconia/Mullite Composites

Abstract

The oxidation of hot‐pressed SiC‐particle (SiC p )/zirconia (ZrO 2 )/mullite composites with various ZrO 2 contents, exposed in air isothermally at 1000° and 1200°C for up to 500 h, was investigated; an emphasis was placed on the effects of the ZrO 2 content on the oxidation behavior. A clear critical volume fraction of ZrO 2 existed for exposures at either 1000° or 1200°C: the oxidation rate increased dramatically at ZrO 2 contents of >20 vol%. The sharp transition in the oxidation rate due to the variation of ZrO 2 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 ZrO 2 contents greater than the critical value showed a large oxidation zone, whereas the composites with ZrO 2 contents less than the critical value revealed a much‐thinner oxidation zone. The results also indicated that the formation of zircon (ZrSiO 4 ) at 1200°C, through the reaction between ZrO 2 and the oxide product, could reduce the oxidation rate of the composite.