Phase relations in the ZrO₂–Nd₂O₃–Y₂O₃ system: experimental study and CALPHAD assessment

Abstract

The thermodynamic parameters of the Nd2O3–Y2O3 system were re-assessed for better reproduction of experimental data. The thermodynamic parameters were combined from binary descriptions to calculate phase diagrams for the ternary system ZrO2–Nd2O3–Y2O3. The calculated phase diagrams were used to select compositions for the experimental studies at 1 250, 1400 and 1 600°C. The samples were synthesised by co-precipitation and heat treated at 1 250–1 600 °C, investigated by X-ray diffraction and scanning electron microscopy combined with energy dispersive Xray spectroscopy. It was found that solubility of the Y2O3 in the pyrochlore phase exceeds 10 mol.%. The experimental data obtained for phase equilibra were used to derive thermodynamic parameters for fluorite, Y2O3 cubic phase C, monoclinic B and Nd2O3 hexagonal A phases by CALPHAD method. The isothermal sections and liquidus surface were calculated for the ZrO2–Nd2O3–Y2O3 system.

Phase Relations in the ZrO2-Nd2O3-Y2O3 System: Experimental Study and Advanced Thermodynamic Modeling

“…Additionally it should be mentioned that in that work, samples with maximal concentration of Nd 2 O 3 of 77 mol% were studied, but formation of Nd 2 O 3 _A phase stability was not clearly indicated. Few contradictions between experimental results and preliminary calculations [9] can be resolved by re-optimization of the ZrO 2 -Nd 2 O 3 binary system.…”

“…The thermodynamic descriptions of the ZrO 2 -Y 2 O 3 and Nd 2 O 3 -Y 2 O 3 system were accepted from works of Fabrichnaya et al, [14,15] and [9] respectively. At the first stage thermodynamic description of the phases in the ZrO 2 -Nd 2 O 3 system were accepted the same as in work of Fabrichnaya et al [12] except for enthalpy and entropy terms of Nd 2 Zr 2 O 7 , pyrochlore.…”

“…Samples were synthesized from precursor solution in a similar way to that described by Fabrichnaya et al [9] The starting chemicals were zirconium acetate solution in acetic acid, Zr(CH 3 COO) 4 (99.99%, Sigma-Aldrich), Nd(NO 3 ) 3 AE 6H 2 O (99.99%, Alfa Aesar) and Y(NO 3 ) 3 AE6H 2 O (99.9%, Alfa Aesar). In the first step, the Nd(NO 3 ) 3 AE6H 2 O and Y(NO 3 ) 3 AE6H 2 O were dissolved in distilled water and the initial zirconium acetate solution was diluted.…”

“…Particularly, the solubility of Y 2 O 3 in pyrochlore phase was not investigated. Phase equilibria in the ZrO 2 rich corner at Y 2 O 3 content 0.5-1.5 mol% and Nd 2 O 3 content 0.5-2 mol% at 1723 K were investigated by Xu et al [4,6] In our previous work by Fabrichnaya et al [9] experimental phase equilibria data at 1523, 1673 and 1873 K were combined with preliminary thermodynamic calculations without taking into account solubility of Y 2 O 3 in Nd 2 Zr 2 O 7 pyrochlore phase, though it was indicated experimentally in our work and in work of Mandal et al [10] It should be mentioned that in work of Mandal et al [10] phase relations in the Nd 2 Zr 2 O 7 -Y 2 O 3 section were investigated for samples synthesised by solid state reactions and the obtained results on Pyr/Pyr + F/F phase boundaries are not consistent with results of Fabrichnaya et al, [9] obtained for co-precipitated samples. Additionally it should be mentioned that in that work, samples with maximal concentration of Nd 2 O 3 of 77 mol% were studied, but formation of Nd 2 O 3 _A phase stability was not clearly indicated.…”

“…The Calphad method will be used to reproduce experimental data at 1523, 1673 and 1873 K. Solubility of Y 2 O 3 in pyrochlore phase found in our previous study [9] will be taken into account by advanced thermodynamic modeling.…”