Effect of reaction temperature on crystallization of nanocrystalline zirconia synthesized by microwave-hydrothermal process

Nanocrystalline zirconia (ZrO₂) was synthesized by hydrothermal assisted with the microwave heating. The effect of reaction temperatures on crystallization of ZrO₂ powders was discussed. The phase and microstructure of ZrO₂ powders was investigated. Results show that the starting crystallization temperature of t-ZrO₂ is 150, 160, and 180 °C at the pH value of 2, 7, and 13 respectively. This results from the various structure of amorphous Zr(OH)_xO_y at different pH values. The t-ZrO₂ content increases with the increase of temperature when the pH value is 2 and 13. At the pH value of 7, pure t-ZrO₂ can get at the temperature between 180 to 200 °C. When the temperature is greater than 200 °C, m-ZrO₂ can be found in the prepared powder. The critical crystallite size for the tetragonal-monoclinic transition is about 20 nm.