High-Temperature Thermodynamic Study of the La2O3–Fe2O3 System: Experiment and Modeling

This paper presents a high-temperature mass-spectrometric investigation of the thermodynamic properties of melts in the La2O3–Fe2O3 system at temperatures up to 1840 K. At the initial vaporization stage at temperatures from 900 to 1600 K, oxygen was the major component of the gas phase. As the temperature increased to 1650 K, Fe, O2, and FeO vapor species were identified over the studied samples. The atomic iron partial pressure determined as a function of temperature in the range 1647–1840 K both over the samples of the system under study and over pure Fe2O3 was used to determine the FeO activity and the molar enthalpy of mixing of iron oxide. The derived FeO activity versus concentration dependencies in the La2O3–FeO system were described by the Redlich–Kister and Wilson polynomials and in terms of the generalized lattice theory of associated solutions (GLTAS). The resulting thermodynamic description of the La2O3–FeO system differed from the thermodynamic values calculated using the NUCLEA database, which indicates the necessity for a new optimization of phase equilibria in the system under consideration using the CALPHAD approach.