ABSTRACT
It is well known that H entry (absorption) into the bulk may lead to embrittlement of metals and alloys. This process, known as H embrittlement or H-induced cracking, often combined on non-noble metals with corrosion cracking, is particularly detrimental to the resistance of metallic materials [1]. High H concentrations may be produced in metals by thermal or electrochemical charging; H can accumulate and combine at internal defects such as microcracks or cavities present in most commercial metals or alloys; high H2 pressures can build up within these cavities, which then grow and coalesce, forming microvoids leading to loss of ductility [1]. In aqueous medium, the reaction of H absorption (HAR) into an electrode proceeds in parallel to the reaction of H2 gas evolution at the surface (HER), at cathodic overpotentials and, at the corrosion potential on non-noble metals, simultaneously with the anodic dissolution or oxidation reactions in the mixed process controlling the rate of corrosion. The H entry into transition metals increases drastically in the presence of dissolved compounds of some electronegative elements, which are known to be poisons of H adsorption. Although many explanations have been proposed to account for these effects, the detailed mechanisms of the action of these H entry promoters are not yet fully understood.
