The Adsorption of Hydrogen on Tungsten Powders

Abstract

An analysis of the extensive experimental data of Frankenburg on the adsorption of hydrogen by metallic tungsten powder between −194 and 750°C has been made, using the Fowler-Guggenheim treatment of adsorption phenomena as the mode of approach. It has not been found possible to interpret the data in terms of interaction between the adsorbed species on a uniform adsorbent surface. It is shown that the experimental data can be interpreted on the basis of a non-uniform surface without interaction, the heterogeneity of the surface being specified in terms of an exponential distribution of sites given by the distribution function N=ce−χ/χm, where χ represents the energy difference between the lowest energy state of the gas and the lowest energy of the adsorption complex. Such a distribution function yields the experimentally observed relation d lnp/d lnθ=constant at constant temperature. Such a heterogeneity is especially significant in the case of tungsten metal which hitherto has been treated as an essentially uniform surface. The quantity χm has been found to vary with the temperature. The significance of this variation has been briefly explored.