Electrochemical methods for studying diffusion, permeation and solubility of hydrogen in metals

Abstract

Electrochemical methods for the investigation of metal-hydro gen systems are superior to other techniques, e.g., gas-volumetric, because of their simple procedure and their flexibility towards variation of experimental conditions. Moreover, these techniques allow measurements at very low hydrogen equilibrium pressures which occur, for instance, in the V(a)-metal-hydrogen systems in the concentration range of ideal dilute solutions at normal temperatures.The removal of surface layers, which retard the hydrogen passage from the electrolyte into the metal and vice versa, is a necessary condition for electrochemical methods to be applicable. Using ultra-high-vacuum techniques, surface hindrances on base metals like V, Nb, Ta, Ti, and others, can be eliminated. Thus, it is possible to study diffusion, permeation, and solubility of hydrogen (isotopes), in these metals as well as in precious metals such as palladium and its alloys.Various electrochemical hydrogen-diffusion and permeation methods are presented and compared. Their applicability and the limits of application are demonstrated for pre-selected systems.A recently developed electrochemical technique for measuring hydrogen (isotope) solubility in transition metals is described. By means of this method, pressure-concentration equilibrium isotherms of V, Nb, and TaH systems have been obtained recently, at ordinary temperatures, from vanishingly low hydrogen concentrations, corresponding to extremely low equilibrium pressures, up to atomic ratios H/Me of 0.5.