Synergy of hydrogen sorption in ball-milled hydrides of Mg and Mg2Ni

A remarkable enhancement of hydrogen desorption kinetics has been found for magnesium-based materials, ball-milled in the hydrogenated state. Ball-milling has been used to introduce both strain and structural changes in the hydrides of Mg, Mg2Ni and their mixtures, facilitating desorption of hydrogen and reducing the operational desorption temperature. Moreover, ball-milling of the mixtures of MgH2 and Mg2NiH4 results in a synergetic effect of desorption, allowing the mixture to operate at temperatures of 220 degrees C-240 degrees C, with excellent absorption/desorption kinetics and with total hydrogen capacity exceeding 5 wt.%. This behaviour has been maintained over hydrogenation cycling. It is concluded that mechanically-treated hydrides offer a new opportunity for magnesium-based materials, exploiting the high capacity of magnesium hydride while operating at much lower temperature than conventional MgH2. (C) 1999 Published by Elsevier Science S.A. All rights reserved.