Changes of Microstructure and High-Temperature Strength of Ceramic Composite in the Mullite-ZrO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub> System Using an In-Situ Reaction between Synthetic Zircon and

Abstract

Ceramic composite was synthesized using an in-situ reaction between synthetic zircon and Al2O3. High-temperature strength did not decrease up to 1500°C for the sample having only mullite for matrix. While, the strength decreased above 1300°C for others. With increase of the Al2O3 precipitated in the mullite matrix phase, the mullite grains became isotropic and small, which may occur the creep deformation. On the contrary, the ceramic composite used in the in-situ reaction revealed excellent high-temperature strength. It was found that ZrO2 and Al2O3 particles dispersed in the grains of mullite matrix, contributed to increase the room temperature strength, and to improve effectively the high-temperature strength. Remarkable difference of the microstructure was not observed in the composite obtained from the natural zircon instead of the synthetic zircon at same composition. However, high-temperature strength decreased markedly due to the increase of impurity content in the natural zircon. High-temperature strength of the ceramic composite obtained from synthetic mullite, ZrO2 and Al2O3 powders by the mixing method, decreased significantly at 1300°C. This behavior can be explained by the shape and size of the mullite in matrix, or the quantities of ZrO2 and Al2O3 precipitated at the grain boundary.