Heat-treatment induced evolution of the morphology and microstructure of zirconia prepared from chloride solutions during

The properties of hydrous zirconia prepared from ZrOCl2 solutions were studied as functions of precipitation pH and subsequent heat treatment. Precipitation at pH <= 6 yields hydrous zirconia containing excess sorbate anions (Cl-), and at pH >= 7, ammonium ions. This difference considerably affects the thermolysis and morphology of the resulting samples. The samples prepared at pH >= 7 have far better developed surfaces. The morphological and structural evolution of hydrous zirconia samples during heat treatment is described. The involved processes are interpreted. At initial stages, the major process is the formation of metastable tetragonal ZrO2, which transforms to the monoclinic phase during subsequent heating.