Hydrogen solubility and thermodynamics of hydrogen absorption in palladium rich binary Pd<inf>1 - X</inf>Ho<inf>x</inf> (x=0.05 and 0.08) solid solution alloys

The hydrogen solubility and the thermodynamic parameters for absorption of hydrogen in Pd1 - xHox (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 Pd1 - xREx (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 (ΔHoH) becomes more exothermic with increase of xHo and the partial molar excess entropy of hydrogen solution at infinite dilution (ΔSE,oH) decreases with increase of Ho content. The relative chemical potential of dissolved hydrogen at infinite dilution (ΔμoH) decreases with increase of xHo indicating that the stability of dissolved hydrogen increases with increase of xHo. The Pd1 - xHox-H systems fall on the correlation between the ionic diameter (dRE) of the substituent RE metals when in solution in Pd and ΔHoH 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 when dissolved in the host Pd lattice.