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

The system Bi2O3-Al2O3 has been experimentally investigated above 600 degrees C by DTA, XRD and EPMA under air and low oxygen pressure. Only two compounds were found to exist in equilibrium, which are Bi2Al4O9(1Bi(2)O(3): 2Al(2)O(3)) 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 degrees C and 1075 degrees C respectively, while an eutectic transformation was observed at 815 degrees 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.