Solubility and kinetic properties of deuterium in single crystal Pd

The pressure-composition (PC) behavior of deuterium in single crystal Pd has been measured over a temperature range extending from room temperature to 393 K. These data allow the determination of (i) relative partial molar enthalpy and entropy, without the contribution of the configuration entropy, for the dilute solid solution phase, (ii) enthalpy and entropy change characterizing the alpha-->alpha' phase transformation, and (iii) Gibbs free energy loss associated with the PC thermodynamic hysteresis. Comparison of these quantities with published data for polycrystal Pd and with our own polycrystal Pd measurements show good agreement, indicating grain boundary interfaces and second phase inclusions known to exist in polycrystalline Pd do not influence these thermodynamic properties. The time dependence of deuterium absorption and desorption from the gas phase has been measured in both single and polycrystal Pd as well. The activation energy and diffusion constant of deuterium in the solid solution phase of Pd agree with published values. The time dependence of deuterium absorption and desorption within the miscibility gap are reduced by approximately two orders of magnitude compared to solid solution behavior. The two-phase kinetic data exhibit an Arrhenius behavior with a factor of two increase in the activation energy compared to diffusion. This is attributed to the phase transformation process controlling the deuterium absorption/desorption kinetic behavior when the Pd-D system is within the miscibility gap. (C) 2000 Elsevier Science B.V. All rights reserved.