Evolution of Mullite Texture on Firing Tape‐Cast Kaolin Bodies

Abstract

Kaolin undergoes a series of phase changes on heating to elevated temperature, proceeding through kaolin, metakaolin, γ‐Al 2 O 3 spinel, and mullite. The morphologic evolution of the kaolin–mullite reaction series was investigated in the present study. A highly textured kaolin green body was prepared by a tape‐casting technique, and the morphology evolution from kaolin flakes to mullite aciculars on firing from 450° to 1600°C was then monitored using X‐ray diffractometry and scanning electron microscopy. Equiaxed mullite nuclei first appeared at 1000°C; the aspect ratio of the mullite grains then increased with increased firing temperature. The mullite aciculars rearranged their orientation in a glassy phase until they impinged on each other. A highly textured mullite specimen was prepared by firing the kaolin tape at a temperature >1500°C.