Factors determining the crystal phases of zirconia powders: a new outlook

The pH of the supernatant liquid in contact with a zirconia precipitate and the time taken to effect precipitation can be used to prepare either the monoclinic or the tetragonal phase of zirconia following calcination at higher (>400[degrees]C) temperatures. Utilizing in situ X-ray diffraction, it has been observed that the precursors of either phase are first transformed to the tetragonal phase. The precursor that produces the monoclinic phase following heating to (about 450[degrees]C or higher) and then cooling in air initially forms an intermediate tetragonal phase. Mechanisms based upon solution chemistry that attempt to explain the formation of a precursor that leads directly to tetragonal zirconia or directly to monoclinic zirconia are unable to adequately account for the present results. 16 refs., 6 figs., 1 tab.