Permeation and thermal desorption model of hydrogen in steel: a sensitivity analysis

This work presents a fully physical model of the hydrogen diffusion and trapping kinetics in metals, integrating permeation and thermal desorption within a unified framework. Based on the McNabb and Foster approach, it requires only binding energy and number density of trap sites. It correctly reproduces the physics of the system and the results of the analytical solutions of the permeation kinetics. It is also capable of reproducing thermal desorption spectra with considerable accuracy. The sensitivity analysis has elucidated the relationships among the processing conditions and the parameters commonly used to characterize permeation and thermal desorption experiments. An equation empirically derived from the simulation results, expressing the dependence of time lag in desorption on specimen thickness, number density of occupied trap sites, and cathodic concentration, is proposed. In summary, the model represents a valuable tool in supporting the interpretation and rationalization of experiments also from a quantitative viewpoint.