Theoretical Aspects of Hydrogen Diffusion in Metals


Relevance. The diffusion of hydrogen in metals has received a lot of attention and has been the subject of intensive training in recent decades, this is due to the practical interest in using the metal-hydrogen system for a number of technological applications, including the creation of radiation-resistant materials and filters for producing pure hydrogen, for using gas H as a secondary energy carrier, and fusion reactor technology. H diffusion in Fe alloys is very important because this leads to engineering problems associated with hydrogen embrittlement and degradation of high strength steels, reactor materials, etc.

Purpose. The aim of the present work is to study the mechanism of hydrogen atom diffusion in the crystal lattice of metals using the statistical thermodynamics method and to calculate the extended diffusion equation and the pre-exponential factor for the corresponding Arrhenius equation.

Methods. We propose to use statistical model expressions the pre-exponential factor and the jump frequency for a more accurate calculation of the hydrogen diffusion in molecular dynamics (MD) and centroid path-integral molecular dynamics (CMD).

Results. Our approach based on the first principles of a statistical model makes it possible coherently describing the temperature dependence of the diffusion coefficient H in α-Fe in a wide temperature range from 100 to 1000 K. The values of the activation energy and the pre-exponential factor of the over-barrier diffusion of hydrogen in in α- Fe, Pd, Ag, Al, Ni and γ-Fe, obtained in the present work, are good consistent with the experimental data.

Conclusions. The results show that statistical effects play a decisive role in the H migration process both at ambient temperature and at higher temperatures. The statistical model makes it possible to explain the high values of the pre-exponential diffusion factor at high temperatures due to the T2 coefficient

Keywords: statistical model, hydrogen diffusion, pre-exponential factor, molecular dynamics; activation energy, jump frequency