Solubility of H, D, and T in Pd at low concentrations

The solubility measurements of H, D, and T in Pd in a large temperature range are presented. Analytic expressions are given for the equilibrium constants which describe the equilibria between hydrogen isotopes in the gas phase and hydrogen isotopes dissolved in a metal at infinite dilution. These expressions are used to predict the equilibrium constant for T in Pd from H and D data in Pd, and the predictions are compared to experimental observations. The Gibbs free energies, enthalpies, and entropies of solution of H, D, and T in Pd are calculated using these expressions. Contributions to these equilibrium constants from hydrogen isotopic species in the gas phase and the hydrogen isotopic species dissolved in Pd have been separated analytically. Parameters in these expressions, which are derived from isotope effects, define the ground-state energies of the H, D, and T species in Pd relative to the energy of atomic hydrogen at rest, i.e., the dissociation limit of ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, and ${\mathrm{T}}_2$. The ground-state vibrational level for H in Pd was found to be 2322.6±1.7 meV/atom below the dissociation limit for the diatomic molecule. For D in Pd the ground state was found to be 32.6±1.1 meV/atom below that of H in Pd. The ground state for T in Pd was 46.6±2.5 meV/atom below that of H in Pd. In addition, the partition functions for H, D, and T in Pd have been determined.