| Multi-component hydrogen-storage alloys with practical values plays a key role in the development of advanced energy materials. Alloy composition design is the key step in researching for new hydrogen storage materials. We analyzed several typical hydrogen storage alloys from the viewpiont of local cluster and found that the compositions could be described with a cluster line, i.e. cluster-plus-glue atom model, which provides a new way to design hydrogen storage alloys. The so-called cluster line is incarnated into a ternary system a composition line linking a bianry cluster with the third element, where the third element is the glue atom. We investigated hydrogen occupancies in AB5, AB2 and Laves phase-related BCC solid solution hydrogen-storage alloys. It is found that the hydrogen atoms could exist in octahedron or tetrahedron interstitials. While H occupies various interstitial sites, the enthalpy changes and lattice deformations of the crystal cells after hydrogen absorption are of much differences. The hydrogen storage properties are determined by both enthalpies and lattice deformations.A mount of tetrahedral sites are existed in icosahedral quasicrystals, which favors for hydrogen occupation. Thus this kind of quasicrystals should possess large hydrogen-storage capacity. A ternary Ti-Zr-Ni quasi crystal-forming system is selected as the basic system in this work. The quasicrystal composition Ti38Zr45Ni17 is determined by the intersection point of two cluster lines Zr8Ni3-Ti and Ti9Ni4-Zr; then a series of compositions are obtained by V alloying of this basic composition. Alloy rods with a diameter of 3 mm were prepared by copper mould suction-casting method. The experimental results indicated that the Ti38Zr45Ni17 quasicrystal can absorb 0.9 wt.%of hydrogen at the first time at 303 K, while the first-time maximum hydrogen content at 573 K reaches 2.38 wt.%. The hydrogen-absorbing process is finished in a very short time, with the release of a large amount of heat which can even sinter the powder sample into solid. The quasicrystal structure completely convert to hydrid after hydrogen absorption.5-30 at.%V alloying of the ternary quasicrystal composition enhances the first-time hydrogen absorption capacity with the maximum reaching 2.96 wt.%at 573 K. The solid solution alloy (Ti0.38Z0.45Ni0.17)40V60 absorbs hydrogen at room-temperature with a capacity of 3.2 wt.%hydrogen. Both the quasicrystalline and its V alloying quaternary alloy convert into hydrid after hydrogen absorption, which causes the hydrogen releases are difficult.A Zr-Mo-Nb alloy system is selected to interpret the application of cluster line in BCC solid solution alloys. (Mo7Zr6)100-xNbx (x=2.5,5,7.1,10,30,40 and 50 at.%) alloys are designed by cluster line Mo7Zr6-Nb, in which Mo7Zr6 icosahedral cluster derived from ZrMo2 Laves phase. The alloy ingots and rods with a diameter of 3 mm were prepared by arc-melting and copper mould suction-casting method. XRD results indicate that the alloys exhibit a monoclinic BCC structure when x=30,40,50 at.%(rod); and the BCC structure is dominant in x= 30 and 40 at.%ingot alloys. When x<=10 at.%, the main phase in alloys is ZrMo2 Laves phase. Hydrogen-storage properties change with the structures of alloys. The maximum hydrogen storage capacities increase as Nb content increases. In addition, the plateau characteristics of the alloys are improved by increasing temperature, but the maximum hydrogen capacity decreases. Compared with the typical Ti-Cr-V system, Zr-Mo-Nb alloys have inferior plateau properties but almost equal maximum hydrogen capacities (H/M). |
