Interaction of hydrogen with dislocations in palladium—II. Interpretation of activity results by a fermi-dirac distribution

Abstract

Measurements of the activity of hydrogen in deformed palladium have revealed a strong interaction with dislocations. Therefore, a Fermi-Dirac distribution was applied and the distribution function could be replaced by a step function similar to the electrons in metals. The “Fermi energy of hydrogen” is equal to the interaction energy and contains a contribution of −18kJ/mole H which was attributed to the formation of a hydride close to the dislocation core. The elastic contribution was calculated from the stress field of an edge dislocation and its dependence on the reciprocal distance from the dislocation core corresponds to a dependence on the reciprocal square root of concentration in agreement with experimental findings. Deviations from this behavior at small distances were explained by a failure of the continuum mechanical calculations of the stress field yielding a cut-off radius of one Burgers vector. The application of a step function is not allowed for high concentrations and numerical calculations were made showing that the hydride phase grows to a diameter of about 25 Å at concentrations of some thousand at.ppm H. Consistent results were evaluated at high and low concentrations for different degrees of deformation and for two temperatures.