CRYSTAL STRUCTURE AND MICROSTRUCTURE OF RAPIDLY SOLIDIFIED La(Ni, Sn)5+x(x=0.1-0.4) HYDROGEN STORAGE ALLOYS
CRYSTAL STRUCTURE AND MICROSTRUCTURE OF RAPIDLY SOLIDIFIED La(Ni, Sn)（5+x）(x=0.1---0.4) HYDROGEN STORAGE ALLOYS

Hydrogen storage alloys La(Ni, Sn)5+x(x=0.1-0.4) with CaCu5-type structure were prepared by are melting and melt-spinning. Morphologies, crystallites and crystal structures of these alloys were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD Rietveld refinement results indicate that there are lots of Ni-Ni " dumbbells " distributed along c-axis in the crystal structure of the alloy prepared by casting. The nanometer scale crystallites in the as-cast alloy are flat, while the grains observed by SEM take on the form of dendrite. Besides the La-Ni-Sn ternary phase, some LaNi5 and metallic Sn were also found for the as-cast alloy. As increasing cooling rate, the size of crystallites of rapidly solidified alloys along (001) is enlarged obviously in comparison with that along (100). SEM results indicate that the grains of the alloys prepared at higher cooling rates (10, 15, 20 m/s),are small dendrite and columnar.