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 P-O2:1300 degrees C <= T <= 1600 degrees C and -16.6 <= logP(O2) <= -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 degrees C. At each temperature, the cationic ratio of the pseudobrookite solid solution (R-Ti = n(Ti)/(n(Al) + (Ti))) increased as P-O2, thereby forming a wide range of solid solution from Al2TiO5 (R-Ti = 1/3) to Ti3O5 (R-Ti = 1.0). The pseudobrookite solid solution was a complete miscible solution at 1600 degrees C, while it exhibited a small miscibility gap at 1500 degrees 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.