The influence of the reverse Mossbauer effect on diffusion and desorption of hydrogen absorbed in metals

In the present work, we discuss in general the effect of the reverse Mossbauer effect (RME) on the diffusion and on the desorption of hydrogen absorbed in crystalline metals. After revising the current theoretical models proposed to describe the desorption process, we conclude that the influence of RME on this process involves essentially the diffusion of the absorbed hydrogen in bulk and adsorbed on the surface. We then derive new basic equations for the evaluation of the diffusion coefficient of a guest particle in a crystal in non equilibrium conditions, including the contribution of RME. Although the quantitative estimation of non-equilibrium diffusion coefficient is not straightforward, because it depends on a complex quantum mechanical theoretical treatment, if the diffusion coefficient of the absorbed hydrogen subject to an external agent is known, it is possible to evaluate quantitatively the contribution of the RME. The theory is applied to the anisotropic diffusion of hydrogen in Ni single crystals, and the resulting values reproduce well the experimental data. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.