SYNTHESIS, CHARACTERIZATION AND HYDROGENATION BEHAVIOR OF MG-XWT-PERCENT-FETI(MN) AND LA2MG17-XWT-PERCENT-LANI5-NEW HYDROGEN STORAGE COMPOSITE ALLOYS

New hydrogen storage materials with higher capacity and better suited for applications have been successfully synthesized. The hydriding behaviour of the new composite materials, Mg-xwt.%FeTi(Mn) and La2Mg17-xwt.%LaNi5, were studied for various values of x (x = 10, 20, 30, 40 and 50). The Mg-x%FeTi(Mn) materials were activated under a hydrogen atmosphere (about 33 kgf cm-2) and an optimum storage capacity of about 3.5 wt.% corresponding to room temperature hydrogenation was established for x = 40. This high storage capacity-almost double the storage capacity of the well-known FeTi(Mn)-has been observed under ambient conditions. The La2Mg17-x%LaNi5 materials were activated at higher temperatures (about 360-degrees-C) in a hydrogen atmosphere. An optimum storage capacity of 4 wt.% in terms of pressure and composition was observed for La2Mg17-20%LaNi5 at 350-degrees-C. In comparison with the native ingredient La2Mg17, much faster (nearly three times) kinetics were found. In order to understand the hydrogenation behaviour and the high storage capacity, structural-microstructural and chemical analyses of these composite materials were carried out. From the structural investigations it has been found that all the synthesized materials are multiphase. The composite material Mg-FeTi(Mn) was found to contain FeTi1-x, magnesium, titanium and Ti-Mg phases. The higher storage capacity (about 3.5 wt.%) in the case of Mg-40%FeTi(Mn) is probably due to FeTi-Mg complexes. The hydrogen molecule is split at the FeTi surface and diffuses into the magnesium matrix via FeTi. In the case of La2Mg17-x%LaNi5, the composite material consists of La2Mg17, MgNi2, nickel and LaNi3 phases. Because of the presence of nickel and nickel-containing phases (e.g. Mg-Ni), it is assumed that the dissociation of hydrogen is easier and hence the system La2Mg17-x%LaNi5 has better kinetics than its counterpart La2Mg17 alone.