PHASE RELATION STUDIES IN THE ZrO₂–CeO₂–Yb₂O₃   SYSTEM AT 1100 °С

Abstract

Phase equilibria and structural transformations in the ternary ZrO₂−CeO₂−Yb₂O₃ system at 1100 °C were studied by X-ray diffraction in over the entire composition range. Fields of solid solutions based on monoclinic (M) and tetragonal (Т) ZrО₂ modifications, cubic (С) Yb₂O₃ modification, and cubic fluorite-type (F) СеО₂ (ZrО₂) modifications, as well as an intermediate Zr₃Yb₄O₁₂ (δ) orthorhombic phase were found to exist in the system. The boundaries of the phase field and lattice parameters of the phases were determined. The maximum solubility of cerium oxide is in the d phase is 4 mol.% at the CeO₂–(60 mol.% ZrO₂–40 mol.% Yb₂O₃) section. Solid solutions based on tetragonal ZrO₂ modification were established to form in the region with high ZrO₂ content. The solubility of Yb₂O₃ in T-ZrO₂ is low and comes to ~0.5 mol.%, which is evidenced by X-ray diffraction and microstructural analyses. The solid solutions based on the tetragonal ZrО₂ modification cannot be quenched from high temperatures in the cooling conditions. An infinite series of solid solutions of F-CeO₂(ZrO₂) type forms at 1100 ºС. The isothermal section of the ZrO₂−CeO₂−Yb₂O₃ system at 1100 °С contains one three-phase region (F + C + δ), five single-phase regions (F-CeO₂(ZrO₂), М-ZrO₂, T-ZrO₂, δ, C-Yb₂O₃), and five two-phase regions (C + F, C + δ, F + δ, F + T, Т + М). New phases were not found in the system. The nature of phase equilibria in the ternary ZrO₂−CeO₂−Yb₂O₃ system at 1100 °C is determined by the constitution of binary phase diagrams.