Phase diagram of the system Ca-Ti-O at 1200 K

Abstract

Phase relations in the system Ca-Ti-O have been established by equilibration of several samples at 1200 K for prolonged periods and identification of phases in quenched samples by optical and scanning electron microscopy, XRD and EDS. Samples representing 20 compositions in the ternary system were analyzed. There was negligible solid solubility of Ca in the phases along the binary Ti-O, and of Ti in CaO. Four ternary oxides were identified: CaTiO₃, Ca₄Ti₃O₁₀ and Ca₃Ti₂O₇ containing tetravalent titanium, and CaTi₂O₄ containing trivalent titanium. Tie-lines link calcium titanite (CaTi₂O₄) with the three calcium titanates (CaTiO₃, Ca₄Ti₃O₁₀ and Ca₃Ti₂O₇), CaO, oxygen excess TiO_1+δ and stoichiometric TiO. Tie-lines connect CaTiO₃ with TiO_2−x , Magneli phases Ti _n O_2n−1 (28 ≥ n ≥ 4), Ti₃O₅, Ti₂O₃ and TiO_1+δ . CaO was found to coexist with TiO, and Ti-O solid solutions α and β. The phase diagram is useful for understanding the mechanisms and kinetics of direct calciothermic reduction of TiO₂ to metal and electrochemical reduction of TiO₂ using graphite anode and molten CaCl₂ electrolyte.