MODELING HYDROGEN ENTRY AND EXIT IN METALS EXPOSED TO MULTIPLE CHARGING PROCESSES

A model is presented to evaluate hydrogen entry or exit in metals exposed to an aqueous environment. The model may be used to analyze data obtained from hydrogen permeation experiments through metal membranes. The model takes advantage of the ideal behavior predicted from the Nernst Equation and Sievert's Law. It provides a single parameter, kappa, to quantify the deviation from Sievert/Nernstian behavior. It is sufficiently general to allow arbitrary chemical potentials of hydrogen on both sides of a sheet, in addition to an arbitrary initial hydrogen distribution within a metal sheet. Simulated permeation curves are presented to show the influence of the model parameters upon permeation behavior. The model is applied to solution agitation during permeation of a low-carbon steel sheet as an illustration. By curve-fitting the model to experimental data, the diffusivity, surface solubilities, and kappa on both sides of a metal sheet may be obtained for a given electrochemical charging condition. When compared to other popular models, the model presented by this article fit the experimental data well. The parameters obtained by the model may be used to characterize a given charging process. As such, the effect of one or more processes may be evaluated by using the model to calculate hydrogen distributions in a metal sheet.