Transformation of ZrO2 crystal structure under hydrothermal conditions

The preparation of ZrO2 powders under hydrothermal conditions has been extensively studied, but the details of the transformation in crystal structure associated with hydrothermal treatment, which will be discussed in the present paper, are unclear. The present results indicate that the t-ZrO2 phase formed from the precursor in the early stages of hydrothermal treatment is converted to m-ZrO2 as hydrothermal treatment proceeds. The pure m-ZrO2 phase was formed after 18 h at 180°C. These results differ from those reported by Stefanic et al., which probably refer to an intermediate stage in the transformation during hydrothermal treatment at 95°C, reflecting the kinetics of the crystallisation process. The present results indicate that the kinetics of crystallisation is significantly delayed at this relatively low temperature when compared with the transformation at the relatively high temperature of 180°C.