Gibbs energies of formation of intermetallic phases in the systems Pt-Mg, Pt-Ca, and Pt-Ba and some applications

Abstract

The standard Gibbs energies of formation of platinum-rich intermetallic compounds in the systems Pt-Mg, Pt-Ca, and Pt-Ba have been measured in the temperature range of 950 to 1200 K using solid-state galvanic cells based on MgF₂, CaF₂, and BaF₂ as solid electrolytes. The results are summarized by the following equations: ΔG° (MgPt₇) = -256,100 + 16.5T (±2000) J/mol ΔG° (MgPt₃) = -217,400 + 10.7T (±2000) J/mol ΔG° (CaPt5) = -297,500 + 13.0T (±5000) J/mol ΔG° (Ca₂Pt₇) = -551,800 + 22.3T (±5000) J/mol ΔG° (CaPt₂) = -245,400 + 9.3T (±5000) J/mol ΔG° (BaPt₅) = -238,700 + 8.1T (±4000) J/mol ΔG° (BaPt₂) = -197,300 + 4.0T (±4000) J/mol where solid platinum and liquid alkaline earth metals are selected as the standard states. The relatively large error estimates reflect the uncertainties in the auxiliary thermodynamic data used in the calculation. Because of the strong interaction between platinum and alkaline earth metals, it is possible to reduce oxides of Group ILA metals by hydrogen at high temperature in the presence of platinum. The alkaline earth metals can be recovered from the resulting intermetallic compounds by distillation, regenerating platinum for recycling. The platinum-slag-gas equilibration technique for the study of the activities of FeO, MnO, or Cr₂O₃ in slags containing MgO, CaO, or BaO is feasible provided oxygen partial pressure in the gas is maintained above that corresponding to the coexistence of Fe and "FeO."