A direct determination was made of the H self-diffusion constant, D, in this Zr69.5Cu12Ni11Al7.5 H-storage alloy; prepared in both the icosahedral quasi-crystalline and the bulk metallic-glass phases. This was done by using the technique of nuclear magnetic resonance diffusion in the static fringe-field of a superconducting magnet. The diffusion constant exhibited a strong dependence upon temperature and H concentration. It was found that D obeyed classical Arrhenius thermally activated over-barrier hopping. A significant decrease in D, with increasing H-to-metal concentration ratio (H/M) was attributed to 2 effects. These were an increase in the activation energy for H jumps between interstitial sites, due to lattice expansion upon hydrogenation, and a decreasing number of available empty interstitials, due to site-blocking and the creation of defects in the lattice during H-loading. The actual alloy structure, icosahedral approximant or metallic glass, appeared to be less important to H diffusivity.

Hydrogen Diffusion in Quasicrystalline and Amorphous Zr-Cu-Ni-Al. J.Dolinšek, T.Apih, M.Klanjšek, H.J.Kim, U.Köster: Catalysis Today, 2007, 120[3-4], 351-7