TRANSFORMATIONS IN COMPOSITE POWDERS OF ALUMINUM AND ZIRCONIUM HYDROXIDES

Phase transformations in composite powders of aluminium and zirconium hydroxides were studied by heat treatment at various temperatures. Ini tially rite composite powders were found to be amorphous, with crystal lisation beginning at 900 degrees C. The sequence of phase transformat ions ill the powders was amorphorus --> delta --> theta --> alpha alum ina, and amorphous --> tetragonal zirconia. Because of the fine partic le size and the constraints imposed by the alumina matrix, zirconia wa s retained in the tetragonal form. The transformation temperature of a lpha alumina was increased by the presence of zirconia. (C) 1996 The I nstitute of Materials.