The effect of 15 wt%Al₂O₃ addition on the equilibrium phase relations of CaO–SiO₂–TiO₂ system at 1400 °C in air

The combined processing of industrial wastes of titania-bearing slags with coal fly ash is an important part of the circular economy. In the present work, the effect of Al₂O₃ on the 1400 °C liquidus isotherms of the perovskite, rutile and tridymite primary phase fields in the CaO–SiO₂–TiO₂–Al₂O₃ system has been determined by employing a high-temperature equilibration-quenching technique, followed by X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-ray Spectrometry. Titanium was confirmed to be stable as TiO₂ in the present equilibria. The equilibrium solid phases of perovskite CaO·TiO₂, rutile TiO₂ and tridymite SiO₂ were confirmed to be coexisting with the liquid oxide phase. The comparison of the addition of 0–15 wt% Al₂O₃ was beneficial for expanding the primary phase field of perovskite to lower TiO₂ concentrations. Comparisons of the experimental 1400 °C isotherm with the predictions using FactSage and MTDATA databases confirmed some differences to the present experimental data, thus demonstrating the direction for updating the present thermodynamic titania-bearing oxide databases.