Phase equilibria of Al2O3–TiOx system under various oxygen partial pressure: Emphasis on stability of Al2TiO5–Ti3O5 pseudobrookite solid solution

Abstract

Phase equilibria of Al2O3–TiOx system were experimentally determined in a wide range of T and PO2: 1300 °C ≤T≤ 1600 °C and −16.6≤logPO2≤−8.0 (in atm). X-Ray diffraction and electron probe micro-analysis were employed to obtain equilibrium phases and compositions. Corundum (Al2O3 with limited Ti2O3), rutile (TiO2 with limited Al2O3), and pseudobrookite (Al2TiO5–Ti3O5) solid solutions were found. The liquid oxide phase was not found up to 1650 °C. At each temperature, the cationic ratio of the pseudobrookite solid solution (RTi = nTi/(nAl + Ti)) increased as PO2, thereby forming a wide range of solid solution from Al2TiO5 (RTi = 1/3) to Ti3O5 (RTi = 1.0). The pseudobrookite solid solution was a complete miscible solution at 1600 °C, while it exhibited a small miscibility gap at 1500 °C. Based on the results obtained in the present study, the behavior of Al2TiO5 was discussed in two aspects: (1) changes in physical properties and (2) evolution of Al–Ti complex oxide inclusions in liquid steel.