Influence of manganese oxide on the liquid-perovskite equilibrium in the CaO–SiO₂–TiO₂ system at 1400 °C in air

In the Selective Crystallization and Phase Separation (SCPS) process, manganese oxide is used as an additive to promote the precipitation of perovskite. However, the influence of manganese oxide on the liquid domain of the perovskite primary phase field is still unclear. In the present work, the liquid-perovskite equilibrium with the addition of 0–15 wt% Mn₃O₄ was experimentally determined using a high-temperature isothermal equilibration-quenching technique, combined with X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS). It was confirmed that manganese was mainly existed as Mn²⁺ and Mn³⁺ in the molten phase, whereas titanium existed as Ti⁴⁺. Within the composition range of the present study, the 1400 °C liquid compositions varying from 0 wt% to 15 wt% Mn₃O₄ overlapped significantly, mainly located at w (CaO)/w (SiO₂) ratios between 0.9 and 1.1. The isotherms simulated by FactSage, as well as the data from the literature, generally agreed well with the present experimental results. The calculated 1400 °C isotherms at different Mn₃O₄ levels indicated that perovskite precipitation by manganese oxide was mainly promoted by increasing the Mn₃O₄ concentration to expand the primary phase field of perovskite toward both higher and lower TiO₂ content areas.