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

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 TiO1+δ and stoichiometric TiO. Tie-lines connect CaTiO3 with TiO2–x, Magneli phases TinO2n–1 (28 ≥ n ≥ 4), Ti3O5, Ti2O3 and TiO1+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.