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 CaF 2 –NdF 3 electrolyte relative to pure Nd(s). The emf values from the CaF 2 –NdF 3 electrolyte were verified in separate experiments in molten LiCl–KCl–NdCl 3 where pure Nd(s) was electrodeposited. The Nd–Bi ( x Nd = 0.20) exhibited two-phase behavior with a peritectic reaction (L + NdBi = NdBi 2 ) 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–NdCl 3 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.