The Effects Of B-side Elements And Rapid Quenching On The Microstructure And Electrochemical Properties Of AB₅ Hydrogen Storage Alloy

In this paper, the as-cast ingots and rapidly quenched thin strips of a series of hydrogen storage alloys MlNi5.xMx (M = Co, Mn, Al) were obtained by traditional arc-melting technics and rapid quenching (melt-spinning) respectively. The influence of B-side elements and the rapid quenching technics on the crystal structure, phase structure, morphology, microstructure, micro-scale element contents distribution and electrochemical properties were systematically investigated by means of X-ray diffraction analysis, metallography, SEM examination, energy dispersive spectrum analysis, TEM examination, electrochemical method and so on. The results are showed as follow:(1) The analysis of XRD indicates that after alloyed by the B side elements, the main phase of as-cast and rapid quenched hydrogen storage alloys MlNi5.xMx still maintain the CaCu5 type hexagonal structure. At the same time, the intensity of the diffraction peaks of the second phase obviously decreases for rapid quenched alloys. It is calculated that the substitution of Co, Mn, Al for Ni causes the lattic of the alloys to expand, which brings about the increase in corresponding crystal constants a, c; In comparison to those of as-cast alloys, the crystal constants of rapidly quenched alloys change slightly: the a axis contracts and the c axis extends.(2) During the solidification process of as-cast alloys nonequilibrium eutectic occurred, which led to small amount of Ni segregation at interdentritic boundary. Rapid quenching can decrease the crystal particles size and effectively suppress the element segregations and the precipitation of the second phase, so that the homogeneity of all alloy elements is improved. Rapid quenching can effectivelypromote the electrochemical cycle stability of hydrogen storage alloys, but it can also make the activation capacity deteriorated and discharge capacity decrease.(3) Co can improve the cycle stability of alloy electrode, but cause the activation capacity of alloys to decay to some degree; Mn can increase the discharge capacity, however excessive Mn may lead to segregation and deteriorate the cycle stability of alloy electrode; Al can improve the resistance corrosion in alkaline solutions, so as to increase electrode cycle stability, but with the amount of Al increasing the number of electrode activation increases and the discharge capacity decrease.(4) In the experiment the optimal range of AH?of MlNi5-xMx hydrogen storage alloys hydride is -32.0 ~ -33.3 kJ/mol.(5) In this paper the electrodes are a three-dimensional network-shape compound system made up of gas, liquid and solid phase. The intrinsic capacity of hydrogen storage alloys is influenced by the size of particles (ro), the diffusion coefficient (Da) and the capacity of hydrogen absorption of alloys. The discharge capacity of practical electrodes depends on both the activation and the decay of hydride electrodes during the charge - discharge cycles.