Thermodynamic modeling of phase diagrams in La2O3-SiO2, Dy2O3-SiO2 and Er2O3-SiO2 systems

Abstract

Thermodynamic modeling of the La₂O₃-SiO₂, Dy₂O₃-SiO₂ and Er₂O₃-SiO₂ systems is part of a broader effort to obtain thermodynamic databases of the rare earth silicates that can help offer insight on designing the environmental barrier coatings in gas turbine engines. The main aim of the present work is to focus on obtaining a set of self-consistent thermodynamic parameters of La₂O₃-SiO₂, Dy₂O₃-SiO₂ and Er₂O₃-SiO₂ systems. The ionic two-sublattice model was accepted to express the liquid phase, and all the binary phases were described as stoichiometric compounds due to the negligible solubility. After a critical literature review on the experimental phase diagrams data and thermodynamic properties for the La₂O₃-SiO₂, Dy₂O₃-SiO₂ and Er₂O₃-SiO₂ systems, thermodynamic optimizations were performed by means of the CALPHAD (CALculation of PHAse Diagram) method. The modeling was done using Thermo-Calc software with PARROT module. The comprehensive comparison between the experimental results and our calculations exhibits that the calculated phase diagrams and thermodynamic properties were in good agreement with the available experimental data, except for experimental data with doubtful quality. This means that our thermodynamic descriptions were reasonable and could provide a reliable basis for thermodynamic calculations in RE₂O₃-SiO₂-based higher-order systems.