HYDROGEN SOLUBILITY AND THERMODYNAMICS OF DISSOLVED HYDROGEN IN PD1-XTBX (X = 0.05 AND 0.08) SOLID-SOLUTION ALLOYS

The hydrogen absorption and the thermodynamics of dissolved hydrogen i n Pd1-xTbx (x = 0.05 and 0.08) solid solution alloys have been determi ned from the pressure-composition temperature relation in the ranges 5 less than or equal to P/mbar less than or equal to 1000 and 473 less than or equal to T/K less than or equal to 873 using a pressure reduct ion method, The hydrogen solubility is found to increase with increase of x(Tb). The partial molar enthalpy of hydrogen solution at infinite dilution (Delta H-H(o)) and the partial molar excess entropy of disso lved hydrogen at infinite dilution (Delta S-H(E.o)) decrease with incr ease of terbium content. The chemical potential of dissolved hydrogen at infinite dilution (Delta H-H(o)) decreases with increase of X-Tb in dicating that the stability of dissolved hydrogen increases with incre ase of X-Tb. The Pd1-xTbx-H systems fall on the correlation between th e ionic diameter (d(RE)) of the substituent RE metals when in solution in Pd and the exothermicity of hydrogen absorption for the Pd1-xREx-H (RE = Er, Ho, Dy, Y, Gd and Sm; x = 0.05 and 0.075) systems.