Severe Plastic Deformation (SPD) is a very effective method to produce bulk nanostructured metals , under conditions of enhanced hydrostatic pressure and/or of a relatively low deformation temperatures. Such a heavy plastic deformation produces several crystal lattice defects like dislocations, grain boundaries, and also vacancies. In comparison with conventional cold work techniques, SPD methods achieve a much higher concentration of vacancies .
The presence of vacancies (i) significantly accelerates atomic diffusion , (ii) enables to trap up to six hydrogen atoms per vacancy, and (iii) can even create ordered vacancy sublattice [4,5]. These features can be important for a hydrogen storage technique in solid state getting more effective and safe than hydrogen storage as a gas or a liquid. One of the most attractive systems is Mg – MgH2 because of its ability to absorb hydrogen up to 7.6 wt.%, its low cost and abundance. However, sluggish desorption kinetics due to rather low hydrogen diffusion in magnesium hydride has prevented its practical use until now. The creation of additional lattice defects, particularly vacancies in the Mg structure by means of SPD methods may yield marked improvements of diffusion as well as of H2 storage capacity, although much work is still needed to fully understand processes taking place in metal-vacancy-hydrogen systems.
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