Effect of CeO2 on reaction-sintered mullite-ZrO2 ceramics

The effect of ceria on mullite formation and the sintering of zircon and alumina powders was investigated. Quantitative X-ray powder analysis was used to determine the formation of mullite and zirconia of both monoclinic and tetragonal forms. Scanning electron microscopy and electron-probe microanalysis were used for microstructural analysis. It was found that the addition of CeO₂ enhanced the formation of mullite and increased the fraction of tetragonal zirconia. The addition of CeO₂ caused the formation of mullite directly from reaction of zircon with alumina without decomposition of zircon into zirconia and silica. In addition to forming a liquid phase, the ceria essentially formed a solid solution with zirconia. The fracture toughness of the mullite-zirconia composites was about 5.5–6.0 MPa m^1/2.