Thermodynamic Properties of Pd‐Nd Alloys

Abstract

AbstractA complete set of thermodynamic functions was determined for the palladium‐rich solid solution and for the intermetallic compounds Pd5Nd, Pd3Nd, Pd2Nd, Pd4Nd3, and PdNd from electromotive force measurements between 700 and 800°C. A CaF2 single crystal was employed as the solid electrolyte. The activity of Nd in Pd‐rich alloys shows pronounced negative deviations from Raoult's law with a relative partial excess Gibbs energy of Nd at infinite dilution of −305 kJ/mol. Two effects are discussed to account for the non‐ideal properties of the solid solution: the transfer of the valence electrons of Nd to the electron gas of the alloy and the lattice distortion brought about by the size difference of the components. Remarkably exothermic values were obtained for the heats of formation of the intermetallic compounds. The results are compared with predictions of the Miedema model.