Thermal behavior of zirconia gel

The chemical and phase compositions, particle size, and pore structure of a hydrous zirconia xerogel were studied at temperatures up to 900 degrees C in air. The smallest particle size was observed for the sample heated to 450 degrees C, and the largest pore volume for the 900 degrees C sample. Metastable tetragonal ZrO2 forms at 320 degrees C, and monoclinic ZrO2 at higher temperatures. The minimum crystallite size is comparable to the size of primary particles of the starting sol. The forming globules are always much larger than the crystallites.