Effects of mechanical activation of inorganic gels on their thermal behavior. 2. Comparison of structure and thermal behavior between zirconia and titania gels
Changes in the temperature of crystallization, Tcrys, due to mechanical pretreatment were entirely opposite between titania and zirconia hydrogels. The Tcrys of the titania decreased by 18 and 44 K on rotation- and vibration-milling, respectively, while those for the zirconia increased by 14 and 18 K or 16 and 45 K, depending on the starting aqueous solutions, i.e., ZrOCl 2 or ZrO(NO 3) 2, respectively. These phenomena were discussed in terms of the microscopic phase transformation processes in noncrystalline gels during mechanical treatment. The difference between two hydrogels was concluded to be attributed to the differences in the geometry of the construction units, TiO 6 and ZrO 8, and the bond nature of metal-oxygen and metal-OH between TiO 2 and ZrO 2.