Zirconia stabilized with a mixture of the rare earth oxides

A hydrothermal technique was used to prepare micropowders of ZrO₂ solid solutions stabilized by the mixture of rare earth oxides and yttria (Ln₂O₃) recovered from phosphogypsum. Phase compositions and particle sizes of the powders were measured. Zirconia solid solutions of cubic and tetragonal symmetry are the major phases. A larger Ln₂O₃ concentration promotes a greater cubic phase content. Powders having low Ln₂O₃ concentrations have small amounts of monoclinic phase present.

The phase composition, fracture toughness (K_Ic) and Vickers hardness of samples sintered at temperatures ranging from 1250 to 1350°C were measured. Tetragonal and, in some cases, monoclinic zirconia solid solutions are found in the microstructure of the sintered bodies. Two ordered phases with the formulae Ln₂Zr₂O₇ and Ce₂Zr₃O₁₀ were also detected in the system. Tetragonal zirconia polycrystals (TZP) with high (10 MPaM^0·5) fracture toughness were found.