The high-temperature mullite/α-alumina conversion in rapidly flowing water vapor

Mullite single crystals cut parallel to the (0 0 1) and (0 1 0) planes were exposed to rapidly streaming water vapor at 1200 °C for 3 h. This treatment decomposed mullite to α-alumina plus volatile Si(OH)4. The c-axes of the newly formed alumina crystals are oriented perpendicular to the mullite surfaces. α-Alumina crystals grown on (0 0 1)Mullite display a fiber texture while those on (0 1 0) planes show two preferential in-plane orientations: (0 0 1)Mullite∥(1 0 −1 0)α-alumina and (0 0 1)Mullite∥(1 1 −2 0)α-alumina.