The influence of high-rate quenching on the cycle stability and the structure of the AB5-type hydrogen storage alloys with different Co content

The influence of the high-rate quenching treatment on the cycle stability and the structure of a series of hydrogen-storage alloys of compositions MLNi4.3-x CoxMn0.4Al0.3 (ML denotes Lanthanum-rich Mischmetal and, x =0.2, 0.4, 0.5, 0.6, 0.7 and 0.9) was investigated in detail. It was found that the quenching treatment using the melt-spinning technique could effectively improve the cycle stability of the AB(5)-type hydrogen-storage alloy, especially for the cycle stability of the alloy with low Co content. The phase structure of the investigated alloys was identified by X-ray diffraction showing that all alloys were the same AB(5) phase with CaCu5 structure. The high-rats quenching treatment led to alloys which were completely nanometer-structured and there was too much of an amorphous phase. present. This led to a decrease in capacity because amorphous AB(5)-type alloy has a much lower capacity than the crystalline. The increase of the cycle stability came from the sharp decrease in grain size and the existence of the amorphous,us phase. (C) 2001 Elsevier Science B.V. All rights reserved.