This study presents a high-temperature mass spectrometric investigation of the thermodynamic properties of melts in the LaO–FeO system at temperatures up to 1840 K. It was shown that in the initial vaporization stage, at temperatures from 900 to 1600 K, the main component of the gaseous phase is oxygen. As the temperature increased to 1650 K, Fe, O, and FeO species were identified in the gaseous phase over the studied samples. Based on the determination of the atomic iron partial pressure as a function of temperature in the range of 1647–1840 K, both over the samples of the system under study and over pure FeO, the FeO activity and the molar enthalpy of mixing of iron oxide were found. The obtained concentration dependencies of the FeO activity in the LaO–FeO system were described using the Redlich–Kister and Wilson polynomials and based on the generalized lattice theory of associated solutions. The resulting thermodynamic description of the LaO–FeO system differed from the thermodynamic values calculated using the NUCLEA database, which indicates the necessity for a new optimization of the phase equilibria in the system under consideration using the CALPHAD approach.
V. A. Vorozhtcov (Wed,) studied this question.