A study was made of the temperature- and concentration-dependent H self-diffusion constant in a Zr69.5Cu12Ni11Al7.5 metallic glass, using the technique of nuclear magnetic resonance diffusion in the static fringe field of a superconducting magnet. In the investigated temperature interval, between room temperature and 420K, the diffusion constant was in the range of 10−8 to 10−9cm2/s and obeyed the Arrhenius law, indicating classical over-barrier-hopping H diffusion with an activation energy, Ea. The concentration dependence of Ea and D was studied for H/metal ratios between 0 and 1.9. At low H contents, H/M < 0.2, Ea showed no noticeable concentration dependence, whereas D exhibited a weakly pronounced maximum at H/M = 0.1 In the intermediate concentration regime, 0.2 < H/M < 0.9, Ea increased due to lattice expansion, whereas site blocking effects (increased occupancy in H sites) decreased the diffusion pre-factor D0, so that D decreased in a linear manner, from H/M = 0.2 to 0.9, by a factor 2.7. In the high concentration range, 0.9 < H/M < 1.9, D and Ea did not change any further with H/M. It was proposed that this H/M-independence originated from hydrogenation-induced microstructural changes (formation of crystalline hydride phases) of the material at high H contents; opening new paths for H diffusion that were extrinsic to the Zr69.5Cu12Ni11Al7.5 bulk metallic glass state.

Influence of the Hydrogen Content on Hydrogen Diffusion in the Zr69.5Cu12Ni11Al7.5 Metallic Glass. T.Apih, M.Bobnar, J.Dolinšek, L.Jastrow, D.Zander, U.Köster: Solid State Communications, 2005, 134[5], 337-41