Reaction–diffusion simulations of hydrogen isotope trapping and release from cavities in tungsten, II: Array of cavities

We present a reaction–diffusion model of hydrogen (H) trapping and release from a metal containing an array of cavities. The model is based on a kinetic description of H trapping in chemisorption sites at the cavity surface and H2 gas precipitation in the cavity volume. Significant differences compared to the case of a single cavity (Zibrov and Schmid, 2022) are observed at high cavity number densities due to retrapping effects. They affect the shape of thermal desorption spectroscopy (TDS) curves, the variation of the TDS peak position with the heating rate, and the desorption at a fixed temperature. The TDS spectra from cavities exhibit features that are very difficult to describe with conventional models but are readily observed in experiments: Sharp rising edges of desorption peaks and constant desorption at a fixed temperature. Also the dynamics of H transport and trapping in the material containing cavities differs from that for point defects, especially at low temperatures. The non-equilibrium effects in the interaction of H with cavities are particularly important for metals with low H solubility, such as tungsten and beryllium.