Phase equilibria and stability of Ca3Fe2TiO8 in the CaO-Fe2O3-TiO2 system: Implications for vanadium-titanium magnetite sintering

The CaO-Fe 2 O 3 -TiO 2 system governs the formation and structural evolution of Ti-bearing phases during vanadium-titanium magnetite sintering. Phase equilibria at 1523 and 1623 K in air were investigated by equilibrium quenching, X-ray diffraction, and electron probe microanalysis, and the corresponding isothermal sections were constructed. The phase assemblages involve perovskite (CaTiO 3 ), dicalcium ferrite (Ca 2 Fe 2 O 5 ), calcium ferrotitanate (Ca 3 Fe 2 TiO 8 ), hematite (Fe 2 O 3 ), pseudobrookite (Fe 2 TiO 5 ), rutile (TiO 2 ) solid solutions, and liquid. Ca 3 Fe 2 TiO 8 was experimentally confirmed as a stable solid-solution phase at both temperatures. Its presence reconstructs the conventional CaTiO 3 -Ca 2 Fe 2 O 5 relationship by separating their stability fields and introducing additional phase boundaries in the ternary system. The critical TiO 2 contents for CaTiO 3 precipitation were further determined at different CaO/Fe 2 O 3 ratios. Increasing the CaO/Fe 2 O 3 ratio enlarges the CaTiO 3 -free region and improves TiO 2 tolerance. These results clarify the structural phase relationships and provide experimental constraints for thermodynamic modeling and phase-control strategies in Ti-bearing ceramic and metallurgical systems.