Thermodynamic modeling of the CaO-CaF2-Al2O3 system aided by first-principles calculations

The CaO-CaF2, Al2O3-CaF2, and CaO-CaF2-Al2O3 systems are modeled using the CALculation of PHAse Diagram (CALPHAD) approach. The liquid phase is described by a two-sublattice ionic model (Al+3, Ca+2)p(F−, O−2, AlO3/2)q. The compounds Al2O3, CaF2, and CaO are treated as stoichiometric phases. The Gibbs energy of formation of (CaO)11(Al2O3)7(CaF2) is predicted by means of first-principles calculations. Phase diagrams of the CaO-CaF2 and Al2O3-CaF2 quasibinaries as well as the isothermal and vertical sections and the liquid surface projection of the CaO-CaF2-Al2O3 system are calculated, showing favorable accord with available experiments in the literature.