Thermodynamics of dilute solutions of hydrogen in PdNi, PdCo, and PdFe alloys

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Abstract
We report the results of a calorimetric-equilibrium investigation of the dilute solutions of hydrogen and deuterium in the solid solutions Pd0.9Ni0.1, Pd0.75Ni0.25, Pd0.9Co0.1, and Pd0.9Fe0.1 at 555 and 700 K. The results are compared with corresponding data for hydrogen and deuterium in pure palladium and in the alloys of palladium with silver, gold, copper, and manganese. Alloying palladium with nickel, cobalt, and iron gives rise to more positive enthalpies of solution and more negative entropies of solution than in pure palladium. The reductions in entropy probably are largely caused by a highly nonrandom distribution of the hydrogen atoms among the available interstitial sites. Among the palladium solid solutions studied so far this effect is most pronounced for the palladium–iron alloys.