Influence of the Substitution of Chromium for Manganese on the Structure and Hydrogen-Sorption Properties of Ti 47.5 Zr
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INFLUENCE OF THE SUBSTITUTION OF CHROMIUM FOR MANGANESE ON THE STRUCTURE AND HYDROGEN-SORPTION PROPERTIES OF Ti 47.5Zr30 Mn 22.5 EUTECTIC ALLOY T. V. Pryadko,1 V. A. Dekhtyarenko,1,2 K. M. Khranovs’ka,1 and H. S. Mohyl’nyi1 We study the influence of alloying with chromium on the structure and phase composition of the Ti 47.5 Zr30 Mn 22.5 eutectic alloy and its hydrogen sorption-desorption. It is shown that the addition of chromium to the alloy changes the type of crystal lattice of the Laves phase from the C14 hexagonal phase to the C15 cubic, which does not affect the hydrogen-sorption properties. It is demonstrated that hydrides obtained on the basis of the C14 and C15 Laves phases have different thermal stabilities. Keywords: eutectic, Laves phase, bcc solid solution, hydrogen capacity, sorption-desorption.
Introduction In [1, 2], it was shown that the problem of safe storage and transportation of hydrogen in the bound state can be solved with the help of a newly developed class of materials capable to play the role of hydrogen accumulators. These materials are, in fact, natural composites obtained as a result of eutectic crystallization. The application of eutectic alloys based on the Ti–Zr–Mn system and formed by the β -(Ti, Zr, Mn) bcc solid solution (high hydrogen capacity) and the (Ti, Zr)Mn 2– x Laves phase (characterized by the acceptable working temperatures, sorption capacity ∼ 1.0 H/Me [3, 4], and high rate of hydrogenation [5, 6]) makes it possible both to significantly increase sorption capacity and to improve the kinetic and thermodynamic parameters of hydrogenation and dehydrogenation due to the favorable combination of the advantages of each phase. Moreover, due to the eutectic crystallization, the β -phase of the alloys stabilizes in the initial state, the requirement of minimum content of manganese in the intermetallic compound is automatically satisfied, and an extremely branched system of phase boundaries is formed. The sorption properties of the alloys depend on numerous factors: the procedures used for the production of alloys (mechanical alloying or induction melting [7], arc melting or formation of thin strips from the melt [8]), the parameters of heat treatment [8, 9], the structural and phase compositions of the original alloys [6, 10], and the deviations of the Laves phase from stoichiometry [4, 11, 12]. As an important specific feature of the Laves phases in the Ti–Zr–Mn system, we can mention an extremely broad domain of homogeneity (∼ 10 at.%) for this class of intermetallic compounds [13]. It is characterized by a spectrum of stable nonstoichiometric compositions with significant deviations from stoichiometry (B/A = 2 ± x ) [14]. The optimal proportion of titanium and zirconium [15] makes it possible to significantly decrease the lower boundary of the domain of homogeneity of the intermetallic compound and, hence, to increase 1 2
Kurdyumov Institute for Metal Physics, National Academy of Sciences of Ukraine, Kyiv, Ukraine. Corresponding author; e-mail: [email protected].
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