Necessity of 3D modeling for simulation of impact of skin effect of hydrogen charging on the binding energy of traps determined from the thermal desorption spectra

Influence of the skin effect caused by the hydrogen charging of the samples on the thermal desorption spectra and the values of the hydrogen binding energy are critically analyzed. For the study, the experimental data and the McNab–Foster model are used. It is shown that an artificially formed specific inhomogeneity in the distribution of hydrogen concentrations significantly affects the shape of thermal desorption spectra and in turn the results of their interpretation based on the Choo–Lee plot and the Kissinger formula. Large errors are possible in the binding energies determined by means of the thermal desorption spectra, provided that the skin layer is formed artificially when the samples are charged with hydrogen. It is shown that the standard description of thermal desorption of hydrogen based upon the one-dimensional model leads to errors. The three-dimensional formulation of problem of hydrogen diffusion in cylindrical sample results in a broken line in the Choo–Lee plot rather than a straight line obtained in the framework of one-dimensional formulation. Comparison of experimental data with the 3D simulation data convinces that effect of the skin layer on the thermal desorption spectra is associated only with the diffusion of hydrogen at the sites of the crystal lattice in the McNab–Foster model.