Thermodynamic properties of Nd-Fe alloys via emf measurements in LiCl-KCl-NdCl3 electrolyte

The thermodynamic properties of Nd-Fe alloys with varying mole fractions of Nd (xNd = 0.05-0.78) were investigated via electromotive force (emf) measurements in molten chloride at 773-1073 K. The Nd-Fe alloys were heat-treated at 923 K for 7 days to stabilize equilibrium phases, and the phase transition properties were confirmed by X-ray diffraction, electron microscopy, and differential scanning calorimetry. Employing less reactive Nd-Sn alloys (xNd = 0.10, L + NdSn3) as a reference electrode, the measured emf values were consistent between alloy compositions, as shown by equivalent thermal trajectories in distinct two-phase regions of [Fe + Nd2Fe17], [Nd2Fe17 + Nd5Fe17], [Nd5Fe17 + Nd], [L + Nd2Fe17], and [L + Nd5Fe17]. The measured emf results were further validated using open-circuit potentiometry in which Nd was deposited onto an Fe electrode at 973 K, resulting in a difference of less than 18 mV for the identical two-phase alloy between the two methods.