Thermodynamic properties of rare-earth alloys by electrochemical emf measurements

Thermodynamic properties of Nd-Bi and Nd-Sn alloys were determined via electromotive force (emf) measurements at 725-1075 K. The emf measurements of an Nd-Bi alloy at mole fraction x_Nd= 0.20 were conducted using a solid CaF₂-NdF₃electrolyte relative to pure Nd(s). The emf values from the CaF₂-NdF₃electrolyte were verified in separate experiments in molten LiCl-KCl-NdCl₃where pure Nd(s) was electrodeposited. The Nd-Bi (x_Nd= 0.20) exhibited two-phase behavior with a peritectic reaction (L + NdBi = NdBi₂) at 926 K from differential scanning calorimetry. The two-phase Nd-Bi (x_Nd= 0.20) was employed as a stable reference electrode in molten LiCl-KCl-NdCl₃for emf measurements of Nd-Bi (x_Nd= 0.15-0.40) and Nd-Sn (x_Nd= 0.10) alloys. The emf measurements of these alloys were reproducible during thermal cycles over 50 h and were used to calculate thermodynamic properties, including the partial molar Gibbs energy, entropy, and enthalpy.