HYDROGEN STORAGE CHARACTERISTICS OF ZIRCONIUM((IRON-X)(CHROMIUM-1-X))(,2).
A literature search has revealed that AB(,2)-type intermetallic compounds exhibit desirable hydrogen storage characteristics, such as high hydrogen capacities and rapid hydriding/dehydriding kinetics. In particular, research in recent years has focussed on so-called pseudobinary alloys (A(B(,x)B(,1-w)')(,2)). The additional transition element provides a means of varying hydride enthalpies, enabling one to obtain virtually any desired stability level, while at the same time maintaining adequate sorption capacity. One group of pseudobinary compounds, ie Zr(Fe(,x)Cr(,1-m))(,2), is investigated here, over the 0.0 < x < 0.8 composition range. These intermetallics are predominantly single-phased, identified as the hexagonal, Laves phase. Hydrogen is absorbed quite readily, with no special activation treatment. Hydrogen absorption results in the formation of a distinct hydride phase, with the same crystal structure as the parent compound. The hydride formed varies in composition through the two phase region. Hydride stabilities are found to obey the rule of reversed stability, ie alloy enthalpies increase, while hydride enthalpies decrease, with increasing Fe substitution for Cr. This trend appears to be both electronic and chemical affinity dependent. Of these intermetallics, Zr (Fe(,0.75)Cr(,0.25))(,2) demonstrates the best overall energy storage characteristics, ie a relatively high sorption capacity (H/M = 1.0) and low stability ((DELTA)H = -25 kJ/mol H(,2)). This composition compares favourably to LaNi(,5), in terms of hydride stability, hydrogen capacity and reaction kinetics. In fact, kinetics are considerably better for Zr(Fe(,0.75)Cr(,0.25))(,2), both in the initial cycle and during subsequent absorption cycles. Source: Dissertation Abstracts International, Volume: 46-09, Section: B, page: 3176. Thesis (Ph.D.)--University of Windsor (Canada), 1985.
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