A Review of the Mechanism and Kinetics of Electrochemical Hydrogen Entry and Degradation of Metallic Systems

Abstract : A review of the mechanism and kinetics electrochemical hydrogen entry and degradation of metallic systems is presented. The partitioning of the discharged hydrogen into molecular hydrogen evolving on the metallic surface and atomic hydrogen entering into a metallic material is considered. A rigorous model has been developed that yields the surface hydrogen coverage, the surface coverage-dependent transfer coefficient of the hydrogen evolution reaction (h.e. r.), and other parameters under a variety of experimental conditions from the permeation data. Further, the catalytic behavior which is quantified by the adsorption rate constant, are for the first time determinable by applying the model to the permeation data for various membrane thicknesses. Use of these parameters for analyzing the vulnerability of a solid metallic material to hydrogen entry and subsequent embrittlement is discussed. The model can also successfully analyze the effects of poisons, such as Hydrogen sulfide, on hydrogen entry, and the more complex case of hydrogen entry when the metal is covered with a film on its surface. Keywords: Hydrogen charging; Hydrogen embrittlement.