HYDROGEN SOLUBILITY AND THERMODYNAMICS OF HYDROGEN ABSORPTION IN PALLADIUM RICH BINARY PD1-XHOX (X=0.05 AND 0.08) SOLID-SOLUTION ALLOYS

The hydrogen solubility and the thermodynamic parameters for absorptio n of hydrogen in Pd1-xHox (x = 0.05 and 0.08) solid solution alloys ha ve been determined from the pressure-composition isotherms in the rang es 473 less than or equal to T/K less than or equal to 873 and 0 less than or equal to P/mbar less than or equal to 900 using a pressure red uction method. The results are compared with those of the previously d etermined Pd1-xREx (RE = Er, Dy, Y, Gd, Sm; x = 0.05 and 0.08) solid s olution alloys. The partial molar enthalpy of solution of hydrogen at infinite dilution (Delta H-H(o)) becomes more exothermic with increase of x(Ho) and the partial molar excess entropy of hydrogen solution at infinite dilution (Delta S-H(E,o)) decreases with increase of Ho cont ent. The relative chemical potential of dissolved hydrogen at infinite dilution (Delta mu(H)(o)) decreases with increase of x(Ho) indicating that the stability of dissolved hydrogen increases with increase of x (Ho). The Pd1-xHox-H systems fall on the correlation between the ionic diameter (d(RE)) of the substituent RE metals when in solution in Pd and Delta H-H(o) for the Pd1-xREx-H (RE = Er, Dy, Y, Gd, Sm; x = 0.05 and 0.075) systems confirming that the effective valance of Ho is 3 wh en dissolved in the host Pd lattice.