Formation enthalpy of intermetallic phases from Ag–Ca system. Experiment vs. modeling

Highlights: • The enthalpy of solution of Ag in liquid Sn. • Preparation and identification of the Ag–Ca intermetallic phases. • Enthalpy of formation of Ag₇Ca₂, Ag₂Ca, AgCa and Ag₃Ca₅ phases. • Comparison with Miedema model. - Abstract: The enthalpy of solution of Ag in liquid Sn and the standard formation enthalpy of the Ag₇Ca₂, Ag₂Ca, AgCa and Ag₃Ca₅ intermetallic phases were measured with the use of the solution calorimetric method. These phases were prepared of Ag and Ca, which were melted in a glove-box filled with high purity argon with a very low concentration of impurities. X-ray diffraction investigations were conducted to confirm the structure of the prepared phases. A Setaram MHTC 96 Line evo calorimeter was used for the determination of both the heat of solution of Ag in Sn and the formation enthalpies of the above-cited intermetallic phases. The enthalpies of solution of Ag in liquid Sn were measured at 723 K, 824 K, 925 K, 1247 K and they equalled: 3.5 ± 0.7 kJ/mol at., 3.8 ± 0.2 kJ/mol at., 3.3 ± 0.3 kJ/mol at., 3.6 ± 0.5 kJ/mol at., respectively. The obtained experimental values of the standard formation enthalpy were: −18.8 ± 0.5 kJ/mol at., −24.1 ± 0.4 kJ/mol at., −28±0.8 kJ/mol at. and −26.7 ± 0.5 kJ/mol at. for Ag₇Ca₂, Ag₂Ca, AgCa, and Ag₃Ca₅, respectively. All the measured values of the standard formation enthalpy of the Ag–Ca intermetallic phases were compared with the data calculated with the use of the Miedema model (this model has been added as an extension to the Entall database, available at entall.imim.pl)