Transformations in composite powders of aluminium and zirconium hydroxides

Phase transformations in composite powders of aluminium and zirconium hydroxides were studied by heat treatment at various temperatures. Initially rite composite powders were found to be amorphous, with crystallisation beginning at 900 degrees C. The sequence of phase transformations ill the powders was amorphorus --> delta --> theta --> alpha alumina, and amorphous --> tetragonal zirconia. Because of the fine particle size and the constraints imposed by the alumina matrix, zirconia was retained in the tetragonal form. The transformation temperature of alpha alumina was increased by the presence of zirconia. (C) 1996 The Institute of Materials.