Activity Measurements in Nickel−Platinum Alloys

Abstract

The thermodynamic properties of Ni−Pt metallic alloys, in the temperature range 500−720 °C, are measured from energy dispersive analysis of the X-ray of alloys prepared by fused salt electrolysis at constant potentials in the cell: Ni−Pt alloy|fused electrolyte + NiCl 2 |Ni. For nickel-rich alloys, the partial entropy of nickel exhibits a nearly ideal behavior. For a molar fraction of nickel between 0.4 and 0.6, a rapid change in the thermodynamic properties occurs. A minimum in the entropy of mixing is found at x Ni ≃ 0.5. The departure from ideality of the Gibbs energy is mainly due to the negative value of the molar enthalpy of mixing; Δ H 0.5 = −10.5 kJ mol -1 . This behavior, which results from the preferential interaction Pt−Ni, is linked to an order−disorder transformation around the equiatomic composition.