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)xOy 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.

► Nanocrystalline ZrO2 was synthesized by microwave-hydrothermal process.
► Transition of Zr(OH)xOy to t-ZrO2 increase with raising of reaction temperature.
► Formation of the m-ZrO2 at pH 7 is due to the increase of crystallite size.
► Starting crystallization temperature of t-ZrO2 vary with the Zr(OH)xOy structure.