The present invention relates to materials for hydrogen storage which are characterized by C14 hexagonal crystal structure and ZrCr.sub.2 stoichiometry.
It is well-known that the AB.sub.2 Laves phase alloys (A:Zr, B:V, Cr,Mn) show considerable promise as a hydrogen storage material because of its large hydrogen absorption capacity and rapid reaction rate with hydrogen. An article entitled "Storing Hydrogen in AB.sub.2 Laves-Type Compounds" by D.O. Northwood et al. (Z. Phys Chem. N.F., 147, 191-209, 1986) discloses that ZrV.sub.2, ZrCr.sub.2 and ZrMn.sub.2 alloy systems are capable of absorbing large quantities of hydrogen but its hydrides are too stable to be of practical significance. Therefore, many studies performed so far have paid attention to increase the vapor pressure of the alloy without markedly reducing the hydrogen storage capacity by partial substitution of the A or B elements by other elements (Ti,Cr, Mn,Fe etc.). In many cases, titanium and iron have been used for A and B element substitution, respectively. In search of improved ZrCr.sub.2 type systems for hydrogen storage, ternary or quarternary alloys with ZrCr.sub.2 stoichiometry have been developed. For example, in Shaltiel et al., J.Less-Comm.Metals, 73,369-376 (1980), there are described new alloys with the empirical formula Zr.sub. 1-x Ti.sub.x B.sub.2 wherein B=Cr,Mn and in Northwood et al., J.Less-Comm.Metals, 147, 149-159 (1989), compounds with the formula Zr(Fe.sub.x Cr.sub.1-x).sub.2. Quarternary allows consisting of zirconium, titanium, chromium and iron, represented by the empirical formula Zr.sub.1-x Ti.sub.x Cr.sub.2-y Fe.sub.y are provided by Wallace et al., U.S. Pat. No. 4,556,551, wherein "x" has a value in a range from 0.0 to 0.9 and "y" has a value of 0.1 to 1.5. Wallace et al. also provided alloys of particular interest for hydrogen storage within the above scope as ZrCr.sub.0.6 Fe.sub.1.4,Zr.sub.0.8 Ti.sub.0.2 Cr.sub.0.6 Fe.sub.1.4,Zr.sub.0.7 Ti.sub.0.3 Cr.sub.0.6 Fe.sub.1.4 and Zr.sub.0.8 Ti.sub.0.2 Cr.sub.0.7 Fe.sub.1.3 by showing desorption pressure-composition-isotherm curves of these alloys.
However, in Suda et al., J.Less-Comm. Metals, 89,269-274 (1983), the use of cyclic hydroding-dehydriding reactions for various applications, e.g. in heat pump systems as well as hydrogen storage, requires accurate control of P-C-T relations, hysteresis and plateau slopes. It is thus important to find to Laves phase alloys with such low hysteresis and flat plateaux.