Crystallization of monoclinic zirconia from metastable phases

Zirconia gel has been hydrothermally treated at 110°C for 7 days in the presence of increasing concentrations of MOH basic mineralizers (M=Li, Na, K and (CH3)4N). The formation of crystalline products characterized by the presence of single or mixed phases of zirconia either as stable (monoclinic) or metastable forms (tetragonal or cubic) has been detected. At increasing temperatures of calcination, the structure of metastable cubic changes from cubic to tetragonal, then to stable monoclinic; while the structure of metastable tetragonal changes directly into monoclinic. The rate of crystallization and crystal growth of monoclinic zirconia, as well as the incorporation of M+ in the hydrothermally synthesized products are discussed in terms of nature and concentrations of mineralizers.