Phase Equilibria in the CaO‐MgO‐FeO‐Fe ₂ O ₃ System: Experiments, Thermodynamic Modeling, and Its Applications

The phase equilibrium of the CaO‐MgO‐FeO‐Fe 2 O 3 system is important for the preparation of refractory materials and study of the steelmaking process. Experimental investigation was carried out using equilibrium/quenching, X‐ray diffraction (XRD), and electron probe microanalysis (EPMA) technique to measure the equilibrium compositions of liquid and solid phases at 1623 and 1673 K. The phase regions of liquid + spinel, liquid + spinel + magnesiowüstite, and liquid + magnesiowüstite + Ca 2 Fe 2 O 5 at isothermal sections of 1623 and 1673 K were determined. Based on the experiments as well as the literature data, the CaO‐MgO‐FeO‐Fe 2 O 3 system was assessed by the CALPHAD (CALculation of PHAse Diagrams) method. The ionic two‐sublattice model (Ca +2 , Fe +2 , Mg +2 ) P (O −2 , Va, FeO 1.5 ) Q was used to describe the liquid phase. A set of self‐consistent thermodynamic model parameters was obtained. The thermodynamic description obtained in this work can be used not only for the oxide system but also for the elemental system. The calculation results were in good agreement with most of experimental data. The effect of adding Fe 2 O 3 on CaO‐MgO refractories was analyzed. The present thermodynamic description of the CaO‐MgO‐FeO‐Fe 2 O 3 system contributes to compositional design in CaO‐MgO‐based refractories.