PHASE EQUILIBRIA IN THE ZrO2 – Dy2O3 SYSTEM AT 1100°C

Abstract

Phase equilibria in the binary ZrO2– Dy2O3system at 1100°C were studied by X-ray diffraction and petrography in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcinations at 1100oC. The solid solutions based on various polymorphous forms of constituent phases were observed. The boundaries of mutual solubility and concentration dependences the lattice parameters for all phases have been determined. It was established that in the ZrO2–Dy2O3 system there exist fields of solid solutions based on cubic (C) modification of Dy2O3, tetragonal (T) crystal modifications of ZrO2, cubic modification of ZrO2 with fluorite-type structure (F). The boundaries of the homogeneity fields for F-ZrO2 and C-Dy2O3 solid solutions (were determined from samples containing 85-100 mol % Dy2O3 at heat treatment (12604 h). The lattice parameter of the unit cell decreased from а = 1.0655 nm in pure ZrO2 to а= 1.0602 nm for sample containing 20 mol % ZrO2. The solubility of Dy2O3in the T-ZrO2is low and amounts to 0.5 mol%, as evidenced by XRD analysis results. The homogeneity field of F-ZrO2in the concentration range of 90-58 mol % ZrO2at 1100 °C was established. The lattice parameters of the unit cell F-ZrO2 varies from а = 0.5161 nm for sample containing 85 mol % ZrO2 to а = 0.5235 nm for sample containing 60 mol % ZrO2