HYDROGEN STORAGE CHARACTERISTICS OF MECHANICALLY ALLOYED AMORPHOUS METALS

The hydrogen storage properties of a series of mechanically alloyed (MA) amorphous Ni1-xZrx alloys were studied, using both gas phase and electrochemical techniques, and are compared to H storage of rapidly quenched (RQ) amorphous Ni1-xZrx. In the MA alloys, hydrogen resides in the Ni4-nZrn (n=4, 3,2) tetrahedral interstitial sites, with a maximum hydrogen-to-metal ratio of 1.9(n4)xn(1-x)4-n. These features are identical to those of the RQ alloys and indicate that the topological and chemical order of the MA and RQ materials are essentially the same. However, the typical binding energy of hydrogen in a Ni4-nZrn site, En, is shifted in the MA alloys relative to the RQ alloys and the distribution of binding energies centered on En is broader in the MA samples. Thus, the MA and RQ alloys are not identical and annealing does not alter this distinction. The sensitivity of H storage to the presence of chemical order in binary alloys is analyzed theoretically and the data are consistent with little or no chemical order (random alloys).