Formation of Ultrafine Tetragonal ZrO 2 Powder Under Hydrothermal Conditions

Ultrafine tetragonal ZrO 2 powder was prepared by hydrothermal treatment at 100 MPa of amorphous hydrous zirconia with distilled water and LiCl and KBr solutions. The resulting powder consisted of well‐crystallized particles; at 200°C, the particle size was 16 nm and at 500°C, 30 nm. Under hydrothermal conditions tetragonal ZrO 2 appears to crystallize topotactically on nuclei in the amorphous hydrous zirconia.