On the structure and dehydration of hydrous zirconia and hafnia xerogels

Hydrous zirconia and hafnia xerogels of compositions ZrO2 · 2.5H2O and HfO2 · 2.3H2O are dehydrated in two steps upon heating. First, molecular water is mostly removed from the structures to form phases of compositions ZrO2 · H2O and HfO2 · 0.5H2O. Second, polycondensation of OH groups occurs. Both processes are easier for ZrO2 · 2.5H 2O. Apart from these steps, the interaction of water molecules with zirconium-oxygen bridges was found to occur during dehydration of the zirconium compound. The composition of HfO2 · 0.5H2O should actually read as Hf4O7(H2O)(OH)2. © Pleiades Publishing, Ltd., 2010.