The Al–Ca System, Part 2: Calorimetrie Measurements and Thermodynamic Assessment

Abstract

Abstract Drop solution calorimetry was performed to determine the enthalpies of formation of the binary Al2Ca and Al3Ca8 phases and the partial enthalpy of mixing at infinite dilution of calcium in liquid aluminum. A consistent thermodynamic model of the Al–Ca system was constructed for the four stoichiometric compounds Al4Ca, Al2Ca, AlCa and Al3Ca8 and for the liquid phase with a sub-subregular solution model. Optimization of the thermodynamic parameters using the Calphad method was done by incorporating all available experimental data on phase equilibria, enthalpies of formation and mixing and the activity coefficients in the liquid. A consistent description of the phase diagram and thermodynamic properties is presented which is well supported by the experimental data. The Ca-rich part of the phase diagram differs substantially from previous reports, mainly because of the two newly discovered phases AlCa and Al3Ca8.