The influence of high-rate quenching on the cycle stability and the structure of the AB 5-type hydrogen storage alloys with different Co content

Abstract

The influence of the high-rate quenching treatment on the cycle stability and the structure of a series of hydrogen-storage alloys of compositions MLNi 4.3− x Co x Mn 0.4Al 0.3 (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 CaCu 5 structure. The high-rate 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 phase.