The phase equilibria in the Al2O3–TiOx system were investigated in wide ranges of temperature and
oxygen partial pressure: 1300~1600°C and 10-16.6~10-8 atm, respectively. The equilibrium phases
and their compositions were identified using X-ray diffraction (XRD) and electron probe microanalysis
(EPMA), respectively. Most noticeably, a wide range of pseudobrookite solid solution was
found in equilibrium with almost pure alumina. At each temperature, the cationic ratio expressed as
RTi = nTi/(nAl + nTi)) of the pseudobrookite solid solution showed a noteworthy dependency on the
oxygen partial pressure. This resulted in the formation of a broad range of pseudobrookite solid
solutions, ranging from Al2TiO5 (RTi = 1/3) to Ti3O5 (RTi = 1.0). Complete miscibility within the
pseudobrookite solid solution was observed at 1600°C, with only a minor miscibility gap becoming
evident below 1500°C. Based on the results obtained in the present study, the behaviours of Al2TiO5
pseudobrookite have implications in two key domains: (1) understanding changes in the physical
properties of the materials, and (2) elucidating the evolution of Al–Ti complex oxide inclusions in
liquid steel which can deteriorate the steel cleanliness.