Thermodynamics of solutions of hydrogen and deuterium in palladium–gold alloys at 555 and 700 K

The thermodynamic properties of solutions of hydrogen and deuterium in palladium–gold alloys with gold contents of 10, 25, and 40 at.% have been determined by a calorimetric–equilibrium method at 555 K (H2 and D2) and 700 K (H2). The results are compared with corresponding data recently reported from this laboratory for hydrogen and deuterium in palladium–silver and palladium–copper, and with earlier equilibrium data for hydrogen in palladium–gold measured at room temperature. (1) 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 ?H increase significantly with increasing gold content. In this respect these alloys are similar to palladium–silver but differ from palladium–copper. (2) The partial excess entropies of hydrogen in dilute solutions in palladium–gold alloys are reduced very significantly compared to the values in pure palladium. These reductions, in large measure, are caused by a nonrandom distribution of the hydrogen atoms among the available interstitial sites.