Hydrogen solubility and thermodynamics of hydrogen absorption in palladium rich binary Pd 1− xHo x ( x=0.05 and 0.08) solid solution alloys

Abstract

The hydrogen solubility and the thermodynamic parameters for absorption of hydrogen in Pd 1− x Ho x ( x=0.05 and 0.08) solid solution alloys have been determined from the pressure-composition isotherms in the ranges 473≤T/K≤873 and 0≤P/mbar≤900 using a pressure reduction method. The results are compared with those of the previously determined Pd 1− x RE 4 (RE=Er, Dy, Y, Gd, Sm; x=0.05 and 0.08) solid solution alloys. The partial molar enthalpy of solution of hydrogen at infinite dilution ( ΔH H o) becomes more exothermic with increase of x Ho and the partial molar excess entropy of hydrogen solution at infinite dilution ( ΔS H E.o) decreases with increase of Ho content. The relative chemical potential of dissolved hydrogen at infinite dilution ( Δμ H o) decreases with increase of x Ho indicating that the stability of dissolved hydrogen increases with increase of x Ho. The Pd 1− x Ho x -H systems fall on the correlation between the ionic diameter ( d RE) of the substituent RE metals when in solution in Pd and ΔH H o for the Pd 1− x RE x -H (RE=Er, Dy, Y, Gd, Sm; x=0.05 and 0.075) systems confirming that the effective valance of Ho is 3 when dissolved in the host Pd lattice.