Thermodynamic optimisation of the FeO-Fe2O3-SiO2 (Fe-O-Si) system with FactSage

Phase equilibrium and thermodynamic experimental data available in the literature on the FeO-Fe2O3-SiO2 (FeO-Si) system were critically reviewed and used to obtain a self-consistent set of parameters for thermodynamic models for all oxide phases using the FactSage computer package. The present optimisation covers the range of oxygen partial pressures from equilibrium with pure oxygen to metal saturation and temperatures from 25 degrees C to above the liquidus. The present thermodynamic optimisation was performed as part of the development of a thermodynamic database for the multi-component system Al-Ca-Fe-Mg-O-Pb-Si-Zn; the thermodynamic parameters for the Fe-O-Si system therefore were chosen to be consistent not only with the experimental data in this ternary system, but also with the data in higher-order systems. The modified quasichemical model was used for the liquid slag phase. Sublattice (based upon the compound-energy formalism) and polynomial models were used for the spinel (magnetite) and monoxide (wustite) solid solutions, respectively. The use of physically reasonable models means that the models can be used to predict thermodynamic properties and phase equilibria in composition and temperature regions where experimental data are not available. From these model parameters, the optimised ternary phase diagram of the FeO-Fe2O3-SiO2 (Fe-O-Si) system was back calculated. The database of the model parameters can be used in conjunction with computer software for Gibbs-free-energy minimisation in order to calculate all thermodynamic properties and any type of phase-diagram section in the FeO-Fe2O3-SiO2 (Fe-O-Si) system.