Ceramics-Silikáty 21, (2) 147 - 150 (1977)

The sillimanite-mullite transformation has been investigated by means of X-ray single-crystal methods. A single crystal of sillimanite Al[SiAlO5] was successively heated to temperatures up to 1650 °C. It turned out that sillimanite-like structure was preserved in the specimen until 1600 °C, accompanied from 1500 °C by polycrystalline corundum. Only the latter phase, together with glass, was observed in the specimen after heating to 1650 °C. The surprising occurrence of corundum after heat treatment of sillimanite suggests that the thermal decomposition of sillimanite to mullite might proceed through intermediate steps.