Direct determination of the H self-diffusion constant in this H-storage alloy was studied. It was prepared in both icosahedral quasicrystalline and bulk metallic glass phases, 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 (figure 6). The H was found to obey classical Arrhenius thermally activated over-barrier hopping, whereas the significant decrease of the self-diffusion coefficient with increasing H-to-metal concentration ratio H/M was the result of 2 effects: 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 defect creation in the lattice during H loading. The actual alloy structure – the icosahedral, approximant or metallic glass – appeared to be less important for H diffusivity.

Hydrogen Diffusion in Quasicrystalline and Amorphous Zr69.5Cu12Ni11Al7.5. J.Dolinšek, T.Apih, M.Klanjšek, H.J.Kim, U.Köster: Catalysis Today, 2007, 120[3-4], 351-7