Thermodynamics of formation of Y-Ni alloys

The Gibbs free energies, enthalpies, and entropies of phase formation were determined for nine Y-Ni intermediate phases from electromotive force measurements. With CaF₂ solid electrolyte, emf measurements were made over the temperature range 900 to 1225 K. The Gibbs energies of formation per mole of Y reactant were found to be nearly constant for the four Y-poor phases; this is in keeping with the close structural relationship among these four phases. The Gibbs energies of formation of the Y-Ni phases at 973 K have been compared with those of the Th-Fe, Th-Co, Th-Ni, La-Co, La-Ni, Y-Fe, and Y-Co systems, and an increasing bond strength with increasing number of bonding electrons is evident. Comparison of the experimental values for the enthalpies of formation of the Y-Ni phases has been made with values predicted by the Miedema model and by the Watson-Bennett model. Both predictions yield values that are within ±50 pet of the experimental values which is the range of scatter that is normally expected from these simple models. Formerly Graduate Assistant, Department of Materials Science and Engineering, Iowa State University.