Sintering of ZrO₂ Toughened Mullite Ceramics and Its Microstructure

Abstract

Mullite/ZrO₂ composite ceramics were fabricated from sol-gel derived powders. The effects of ZrO₂ content and firing temperature on the densification and microstructure development have been investigated by means of SEM, TEM and XRD. It was clarified that the 5 to 25vol% addition of ZrO₂ to mullite improved the sinter-ability. The effect is more striking in the composites containing 10 or 15vol% ZrO₂. The growth of mullite grains was inhibited by dispersing ZrO₂ particles. The effects were, especially, most predominant in the composite containing 15vol% ZrO₂. However, in composites fired at 1650°C and above, remarkable grain growth was observed, and needle-like mullite grains having Al-rich composition appeared. These results may be ascribed to the coalescence of fine ZrO₂ crystals.