Phase relations and stabilities of compounds in the system CoOTiO 2

Abstract

Phase relations in the system CoOTiO 2 in the temperature range 1130–1569°C have been determined by the quenching technique. Three crystalline phases, in addition to the end members CoO and TiO 2, are stable in equilibrium with liquids, viz. Co 2TiO 4, CoTiO 3 and CoTi 2O 5. The two former melt congruently at 1562 and 1463°C, respectively, whereas the latter melts incongruently at 1482°C. The phase CoTi 2O 5 is unstable relative to the phase assemblage CoTiO 3 + TiO 2 below ≈ 1140°C. The free energies of formation of the three crystalline phases from their oxide components at 1100 and 1300°C were determined by studying equilibria between pairs of crystalline oxide phases, metallic cobalt and a gas phase of known oxygen pressures. The instability of CoTi 2O 5 relative to the phase assemblage CoTiO 3 + TiO 2 below ≈ 1140°C is confirmed by the free-energy data obtained.