Abstract
In order to study the effects of mechanical milling on the properties of metal hydrides, we have measured the proton nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates in two classes of nanostructured ball-milled systems: Laves-phase hydrides ZrCr 2H 3 and MgH 2-based hydrides with some additives (V 2O 5, Al). The proton NMR measurements have been performed at the resonance frequencies of 14, 23.8 and 90 MHz over the temperature range 11–420 K. Hydrogen mobility in the ball-milled ZrCr 2H 3 is found to decrease strongly with increasing milling time. The experimental data suggest that this effect is related to the growth of the fraction of highly distorted intergrain regions where H mobility is much lower than in the crystalline grains. For the MgH 2-based systems we have not found any effects of H jump motion at the NMR frequency scale up to 420 K. However, the measured proton spin-lattice relaxation rates for the nanostructured MgH 2-based samples appear to be several orders of magnitude higher than for the coarse-grained MgH 2. This relaxation rate enhancement can be attributed to the interaction between proton spins and intrinsic paramagnetic centers appearing in the process of ball milling.
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