Hybrid model of hydrogen thermal desorption from structural materials

Abstract

To solve problems of hydrogen power engineering, there is an intensive search for materials for hydrogen storage. Thermal desorption spectrometry (TDS) is one of the effective experimental methods for studying the interaction of structural materials with hydrogen isotopes. A sample (we consider a thin plate made of a material with metallic properties) pre-saturated with dissolved atomic hydrogen is heated relatively slow in a vacuum chamber. The degassing flux is registered using a mass spectrometer. The spectrum is the dependence of the desorption flux density from a two-sided surface of the sample on the current temperature. Quite often, several local peaks are registered on the spectrum. Traditionally, this is associated with the reversible capture of various kinds of traps (inhomogeneities of the material) with different binding energies. However, numerical experiments on models with dynamic boundary conditions describing the dynamics of surface concentrations show the possibility of a different scenario. The following scheme is possible: The first peak occurs when hydrogen leaves the surface and the subsurface volume. Then, a large concentration gradient is formed at the surface. For this reason, and during continued heating, diffusion influx from the volume is significantly activated, which leads to the next peak of desorption. Recommendations on how to distinguish degassing scenarios corresponding to these essentially different physicochemical reasons are given. This is fundamentally important for the correct recalculation of modeling results from laboratory samples to real constructions. The hybrid thermal desorption model can be considered as a computational algorithm for solving a partial differential system using an approximation by an ODE system (but this is not a straight-line method).