Compositional dependence of the oxidation behavior of SiC-ZrO2-mullite composites

Abstract

The oxidation of hot-pressed SiC-particle (SiCp)/zirconia/mullite composites with various zirconia contents, exposed in air isothermally at 1000 and 1200 degrees C respectively for up to 500 hours, was investigated. A clear critical volume fraction of zirconia existed for exposure at either 1000 or 1200 degrees C. The oxidation rate increased dramatically beyond 20 vol% ZrO2,. Additionally, oxidation modes of SiC/zirconia/mullite composites were classified on the basis of the gradient of the silica layer (formed on individual SiC particles) thickness versus depth curve. When the volume fraction of ZrO2, was below a threshold limit, the composites exhibited Mode I behavior; otherwise, Mode II was observed. For composites with zirconia content above the threshold limit, the formation of zircon, as a result of the reaction between zirconia and oxidation product (i.e. silica), might change the oxidation behavior from Mode II to Mode I.