Measurement and calculation of the ZrO 2-CeO 2-LaO 1.5 phase diagram

Abstract

A thermodynamic assessment of the CeO 2-LaO 1.5 system has been conducted and combined with recently evaluated thermodynamic parameters for the ZrO 2-CeO 2 and ZrO 2-LaO 1.5 systems to predict the ZrO 2-CeO 2-LaO 1.5 ternary phase diagram. Based on the predicted 1400 °C isothermal section, twenty-five decisive samples, which were prepared by co-precipitation method and arc melting of melts, were annealed at this temperature for 848 h. The annealed samples were analyzed by using X-ray diffraction method and precise lattice parameter measurement. It was found that the phase assemblages resulting from eighteen of the twenty-five samples can be described by the predicted isothermal section. The agreement between the measured and calculated 1400 °C isothermal sections is improved by introducing ternary interaction parameters to the Gibbs energies of Css (cubic solid solution) and Tss (terminal solid solution based on tetragonal ZrO 2). The same samples as above were annealed at 1550 °C for 100 h, and the resultant phase assemblages were compared with the 1550 °C isothermal section calculated by using the above assessed ternary parameters. The comparison shows that twenty-three of the twenty-five samples can be reproduced by the calculation. A few isothermal and vertical sections as well as the reaction scheme are calculated for practical use. The combined use of the CALPHAD technique and experimental methods to establish multicomponent ZrO 2 phase diagrams is stressed.