A calorimetric-equilibrium study of dilute solutions of hydrogen and deuterium in palladium at 555 to 909 K

The thermodynamic properties of dilute solutions of hydrogen and deuterium in palladium have been studied by a calorimetric-equilibrium method in the temperature range 555-909 K. The new enthalpy data are compared with data for lower temperatures reported in the literature, and are used to obtain analytical expressions for the relative partial enthalpies and heat capacities of hydrogen and deuterium. The derived partial heat capacities are larger than values calculated from the harmonic oscillator model and show distinct maxima in the temperature range 500-600 K. It is possible that this may reflect a localized-mobile transition of the hydrogen atoms.