High-Temperature Phase Relations and Thermodynamics in the Iron-Titanium-Oxygen System

Phase equilibria and thermodynamics in the FeO-TiO2-Ti2O3 ternary system were studied at 1500 °C and 1600 °C. In particular, the liquid slag-phase region and its saturation boundary with respect to metallic iron, titania, and lower titanium oxides was investigated. The liquid slag-phase region extends substantially toward an anosovite (Ti3O5) composition, and considerable concentrations of divalent iron coexist with trivalent titanium in the liquid-slag phase. This seems to be a consequence of the complete solid solution between ferrous pseudobrookite (FeTi2O5) and anosovite (Ti3O5), which exists at subsolidus temperatures. The liquid-slag field is significantly enlarged toward the anosovite composition upon increasing the temperature from 1500 °C to 1600 °C. Activities of the components "FeO" and TiO2 in the liquid-slag region were determined by Gibbs-Duhem integration of the measured oxygen partial pressures at 1500 °C. The FeO shows moderate negative deviation, while titania shows a slight negative deviation in FeO-rich slags and a positive deviation in high-titania slags. The experimentally measured activity values were modeled using regular and biregular solution models, and good agreement was obtained with the biregular solution model.