Investigation on the synthesis, characterization and hydrogenation behaviour of new Mg-based composite materials Mg-x wt.% MmNi4.6Fe0.4 prepared through mechanical alloying

Alloys with general formula Mg-x wt.% MmNi(4.6)Fe(0.4) have been successfully synthesized through ball milling employing a high energy attritor mill. The ball milling has been done in hexane medium; various time durations and speeds (rev./min) have been employed. The hydrogenation and dehydrogenation behaviour of these new composite materials have been extensively investigated. The as-prepared (ball milled: mechanically alloyed) composite materials have been activated at 400 +/- 10 degrees C under a hydrogen pressure of similar to 40 kg cm(-2). These composite materials have been found to possess one of the highest known storage capacities. It has been found that the highest storage capacity material (similar to 5.0 wt.% at 350 degrees C) corresponds to Mg-30 wt.% MmNi(4.6)Fe(0.4). The said alloy exhibits fast absorption-desorption kinetics (about 80 cm(3) min(-1)). It is also established that the optimum mechanically alloyed samples for hydrogen storage were obtained with milling at 400 rev./min speed and time duration of similar to 5 h. The hydriding rate and the improved hydrogen storage capacity of these composite materials have been found to be strongly correlated with the structural and microstructural characteristics as brought out through XRD and SEM techniques. For example, the ball milled samples having optimum hydrogenation characteristics exhibited highly uniform particle size distribution. (C) 1999 Published by Elsevier Science S.A. All rights reserved.