FINE ZIRCONIA POWDERS BY HYDROTHERMAL PROCESSING.

Fine zirconia powders were prepared by hydrothermal crystallization of amorphous zirconia and hydrothermal oxidation of Zr metal, both recently developed in our laboratory. In hydrothermal crystallization, metastable tetragonal ZrO//2 was formed only from the amorphous phase. Hydrothermal oxidation of Zr metal by pure water yielded monoclinic ZrO//2. When Ca solutions were used, fine cubic zirconia grains were partially formed in addition to monoclinic zirconia, particularly in the case of Ca(NO//3)//2 solutions with excess Zr metal at 700 degree C. This cubic zirconia was stabilized by calcium and nitrogen. Y(NO//3)//3 or NH//4NO//3 solutions also yielded a small amount of cubic zirconia phase.