Wasserstoff und Deuterium in Vanadium als wechselwirkende Gittergase

Abstract

Pressure-composition isotherms at temperatures between 150 and 550 °C for solutions of hydrogen and deuterium in vanadium and the temperature dependence of the heat capacity in a series of V_D alloys habe been determined in the single phase regions ($\alpha$-phase) of the V_H(D) phase diagrams. The concentration dependences of the partial molar enthalpies $\Delta$H$_{H(D)}$ and entropies $\Delta \overline{H}_{H(D)}$ of hydrogen and deuterium have been derived from the solubility data. For both isotopes $\Delta \overline{H}_{H(D)}$ decreases with incresing H of D concentration x = [H(D)]/[V] at low x and increases a higher H or D content, having a munimum near x $\approx$ 0.4. The concentration dependence of $\Delta \overline{S}_{H(D)D}$ shows a large negative deviation from the ideal configurational entropy for random occupation of tetrahedral interstitial sites. The heat capacity of V-D$_{x}$ contains a substantial excess contribution, which remains when estimated electronic and vibrational contributions are substracted from the experimental data. The experimental results are analyzed by means of Monte Carlo simulations of a lattice gas with repulsive short range interactions between hydrogen (deuterium) atoms. The essential features of the experimental results are described by a lattice gas model which includes hard core interactions (blocking effect) and finite repulsive interactions outside the hard core