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-NdF3 electrolyte relative to pure Nd(s). The emf values from the CaF2-NdF3 electrolyte were verified in separate experiments in molten LiCl-KCl-NdCl3 where 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-NdCl3 for 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.