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Ti_(12.5)Zr_(21)V_(10)Cr_(8.5)Mn_(x)Co_(1.5)Ni_(46.5-x)AB_(2)-type metal hydride alloys for electrochemical storage application: Part 1. Structural characteristics

Published

Author(s)

Leonid A. Bendersky, Ke Wang, Igor Levin, Dale E. Newbury, K. Young, B. Chao, Adam A. Creuziger

Abstract

The microstructures of a series of AB_(2)-based metal hydride alloys (Ti_(12.5)Zr_(21)V_(10)Cr_(8.5)Mn_(x)Co_(1.5)Ni_(46.5-x)) designed to have different fractions of non-Laves secondary phases were studied by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectrometry, and electron backscatter diffraction. The results indicate that the alloys contain a majority of hydrogen storage Laves phases and a minority of fine-structured non-Laves phases. Formation of the phases is accomplished by dendritic growth of a hexagonal C14 Laves phase. The C14 phase is followed by either a peritectic solidification of a cubic C15 Laves phase (low Mn containing alloys) or a C14 phase of different composition (high Mn containing alloys), and finally a B2 phase formed in the interdendritic regions (IDR). The interdendritic regions may then undergo further solid-state transformation into Zr7Ni10-type, Zr9Ni11-type and TiNi-type phases. With the Mn content in the alloy increases, the following trends were found: the abundance of the C14 phase increases, C15 and Zr_(9)Ni_(11)–type phase abundances decrease, Zr_(7)Ni_(10)–type phase abundance first increases and then decreases, TiNi-based phase abundance first increases from 0 % to 4 % and then stabilized at 2 % . The IDR compositions can be generally expressed as (Ti,Zr,V,Cr,Mn,Co)_(50)Ni_(50), which accounted for 7 % to 10 % of the overall alloy volume fraction.
Citation
Journal of Power Sources
Volume
218

Keywords

Hydrogen absorbing materials, hydrogenation, metal hydride electrode, transition metal alloys
Created August 3, 2012, Updated November 10, 2018