Abstract
Hydride-forming alloys are used as components of the negative electrode of nickel-metal hydride (NiMH) batteries. In previous works, the study of Zr-based AB 2-type alloys indicated that the material without heat treatment (annealing) had better electrochemical characteristics than the annealed one. The effect was attributed to the presence of secondary phases Zr x Ni y formed during the solidification of the alloy button obtained by arc melting, and to the fact that these phases diminished their concentration or disappeared upon annealing. The main secondary phases formed by microsegregation are Zr 7Ni 10, Zr 9Ni 11 and Zr 8Ni 21. In order to explain the effect of each one of these micro-segregations, alloys of the above-mentioned composition were prepared by arc furnace and studied separately using powder mixtures of each Zr x Ni y phase and annealed ZrCrNi alloy. The electrochemical impedance data analysis of each Zr x Ni y alloy, using a model developed in our laboratory, allowed the identification of structural, physicochemical and kinetic parameters which determine the performance of each material. Based on this analysis it may be concluded that Zr 8Ni 21 alloy has the greatest hydrogen diffusion coefficient, being this parameter determinant of the charge/discharge performance of the alloy.
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