Effect of mineralizers on the crystallization of the solid solutions in the system ZrO2-CeO2 under hydrothermal conditions

The process of the crystallization of the solid solutions in the system ZrO2-CeO2 were studied under hydrothermal conditions. Samples prepared by coprecipitation method were treated under 100 MPa at 6000C for 2 -- 72 h using distilled water or the solution of alkaline metal (Li, Na, K) fluorides, chlorides, bromides, carbonates, nitrates, sulfates, or hydroxides as mineralizers. Monoclinic zirconia (m-ZrO2 s.s.), ceria (CeO2 s.s.), and/or ZrO2-rich solid solution (C1 s.s.) phases were produced by the hydrothermal treatments of coprecipitated samples. The crystallite size of these phases and the production of C1 s.s. depended on the species of anions used as the mineralizer. The crystallite of m-ZrO2 s.s. was grown larger than that of CeO2 s.s. in the solution of fluorides, carbonates, or hydroxides. The crystallite of CeO2 s.s. was grown larger than that of m-ZrO2 s.s. in the solution of chlorides, bromides, or sulfates. The crystallite of m-ZrO2 s.s. and CeO2 s.s. did not increase significantly in the solution of nitrates or distilled water. In the solution of chlorides and bromides, C1 s.s. was produced in addition to m-ZrO2s.s. and CeO2 s.s.. The effect of each mineralizer might be different in the crystallization process which consists of the dissolution/precipitation and the structural rearrangement. The fluorides, carbonates, and hydroxides enhanced the dissolution/precipitation process, while the chlorides and bromides enhanced the structural rearrangement process in the crystallization of the solid solutions in the system ZrO2-CeO2. (author)