Application of the Molecular Interaction Volume Model (MIVM) to Calcium-Based Liquid Alloys of Systems Forming High-Melting Intermetallics

The thermodynamic properties of multiple liquid alloys with strong negative deviation from ideality were successfully modeled by the molecular interaction volume model (MIVM). The modeled partial Gibbs free energy of calcium in Ca-Ag, Ca-In, Ca-Pb, Ca-Sn, Ca-Tl, and Ca-Zn at 800 degrees C was within 1.5 kJ/mol of the existing experimental data. The partial Gibbs free energy of calcium in Ca-Bi liquid alloys at 600 degrees C was predicted within 1.6 kJ/mol (or 1%) by the MIVM from experimental data at 800 degrees C. For the first time, the MIVM was applied to a ternary system far from ideality, Ca-Sb-Pb. The partial Gibbs free energy of Ca in six Ca-Pb-Sb alloys was determined by emf measurements in a cell configured as Ca(s)vertical bar CaF2(s)vertical bar Ca-Sb-Pb, over the temperature range of 500-830 degrees C. These values were 2% (or 5 kJ/mol) more negative than those predicted by the MIVM using experimental data for the Ca-Pb, Ca-Sb, and Pb-Sb binary alloys. This difference was attributed to the inability of the MIVM to account for interactions between the first nearest neighbors of Ca, Pb and Sb in the ternary Ca-Sb-Pb alloy.