HIGH-TEMPERATURE THERMODYNAMICS OF THE SOLUTIONS OF HYDROGEN IN PALLADIUM-SILVER ALLOYS

The thermodynamic properties of solutions of hydrogen in palladium-silver alloys with silver contents ranging from 25 to 50% have been determined by a calorimetric-equilibrium method at 555 and 700 K. The results are compared with corresponding data recently reported for hydrogen in Pd and in Pd 0.9Ag0.1. (1) For the alloy Pd0.75Ag 0.25 the thermodynamic measurements give no evidence for an order-disorder transition in the considered temperature range. (2) Comparisons between the solutions of hydrogen and deuterium in the same alloy and at the same temperature allow calculations to be made of the vibrational frequencies of hydrogen. The calculated values of ṽH show a very significant increase with increasing silver content. (3) The partial excess entropies of hydrogen in dilute solutions in palladium-silver alloys are reduced significantly compared to the values in pure palladium. It is probable that these changes, in large measure, are caused by a nonrandom distribution of the hydrogen atoms among the available interstitial sites. However, other possible interpretations also are discussed. © 1979 American Institute of Physics.