Phase equilibria investigations and thermodynamic modeling of the system Bi₂O₃-Al₂O₃

The system Bi₂O₃-Al₂O₃ has been experimentally investigated above 600 °C by DTA, XRD and EPMA under air and low oxygen pressure. Only two compounds were found to exist in equilibrium, which are Bi₂Al₄O₉(1Bi₂O₃:2Al₂O₃) and Bi₂₅AlO₃₉(25:1). The latter exhibits a sillenite structure and does not contain pentavalent bismuth. A peritectoid decomposition of (25:1) and a peritectic melting of (1:2) occur at 775 °C and 1075 °C respectively, while an eutectic transformation was observed at 815 °C for 97 mol% Bi₂O₃. On the basis of the results obtained within the present work as well as experimental data provided from literature, a thermodynamic modeling where the liquid phase is described by the two-sublattice ionic liquid model was performed according to the Calphad approach. The resulting thermodynamic optimization yielded good agreement with experimental results in the investigated region.