Browsing by Author "K. Dutta"

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Investigation on synthesis, characterization and hydrogenation behaviour of the La2Mg17 intermetallic
(1990) K. Dutta; O.N. Srivastava
Synthesis, structural characterization and hydrogenation behaviour of the La2Mg17 system have been investigated. One of the interesting results obtained is the hydrogen desorption at room temperature. For the first hydrogenation cycle, the as-synthesised intermetallic. La2Mg17, is activated up to 150 ± 10°C under hydrogen pressure, but no activation through heat treatment is needed for absorption-desorption for the second and subsequent cycles. The hydrogen desorption capacity of La2Mg17 is calculated by weight percentage and hydrogen capacity per mole of La2Mg17. The maximum value corresponds to 6.63% which represents one of the highest hydrogen capacities exhibited by a reversible intermetallic hydride system. © 1990.
Synthesis and hydrogen storage characteristics of the composite alloy La2Mg17-x wt% MmNi4.5Al0.5
(1993) K. Dutta; O.N. Srivastava
Recently, composite type materials consisting of known hydrogen storage systems e.g. Mg-LaNi5, ZrFeCr-Mg, etc. 1, H. Nagai et al., J. Less-Common Metals 157, 15 (1990); [2], H. Fujii et al., J. Less-Common Metals 175, 243 (1991) have been shown to have better hydrogen absorbing/desorbing properties. The present paper reports the synthesis and hydrogenation/dehydrogenation behaviour of the composite alloy La2Mg17-x wt% MmNi4.5Al0.5. It has been shown that the optimum hydrogen storage characteristics are possessed by the material with x = 10% i.e. La2Mg17-10% MmNi4.5Al0.5. The hydrogen storage capacity for this material, where effective dehydrogenation occurs at 400°C, is 4.85%. Also, the kinetics for the said composite material are much better than La2Mg17 alone. The x = 10 wt% material also has a faster kinetics-about 3 times faster than that of La2Mg17 alone. Evidence and arguments have been advanced to show that the improved hydrogenation-storage capacity and better kinetics of the composite material arise due to the multiphase nature of the material (besides the majority phase La2Mg17, other minority phases exist, e.g. MgNi2, Mm2Ni7 and Ni are present). © 1993.
Synthesis, characterization and hydrogenation behaviour of Mg-ξwt.%FeTi(Mn) and La2Mg17-ξwt.%LaNi5-new hydrogen storage composite alloys
(1992) P. Mandal; K. Dutta; K. Ramakrishna; K. Sapru; O.N. Srivastava
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-ξwt.%FeTi(Mn) and La2Mg17-ξwt.%LaNi5, were studied for various values of ξ (ξ = 10, 20, 30, 40 and 50). The Mg-ξ-%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 ξ=40. This high storage capacity-almost double the storage capacity of the well-known FeTi(Mn)-has been observed under ambient conditions. The La2Mg17-ξ-%LaNi6 materials were activated at higher temperatures (about 360 °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 °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-ξ1 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-ξ%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-ξ%LaNi5 has better kinetics than its counterpart La2Mg17 alone. © 1992.
Synthesis, structural characterization and hydrogenation behaviour of the new hydrogen storage composite alloy La2Mg17-x wt% LaNi5
(Kluwer Academic Publishers, 1993) K. Dutta; O.N. Srivastava
Alloys with the general formula La2Mg17-xwt % LaNi5 (x=10, 20, 30 and 40) have been synthesized and the hydrogen storage capacity of these new composite materials investigated. The materials were activated at temperatures of ∼ 360 °C under a hydrogen pressure of ∼ 33 kg cm-2. Optimum storage capacity of 5.24% in terms of pressure and composition was observed for La2Mg17-10 wt% LaNi5 at ∼ 400°C. This is one of the very highest hydrogen storage capacities known so far. The hydriding rate of La2Mg17 in the presence of LaNi5 is about 3-4 times that of La2Mg17 alone. In order to elucidate the role of LaNi5 in accelerating the hydrogen desorption rate of La2Mg17, the structural and microstructural characteristics of the composite material were carried out employing the XRD, SEM and EDAX techniques. The hydriding rate and hydrogen storage capacity are closely related to the microstructure and the types of phase present in the alloys. © 1993 Chapman & Hall.
The synthesis and hydrogenation behaviour of some new composite storage materials: Mg-xwt% FeTi(Mn) and La2Mg17-xwt% LaNi5
(1994) K. Dutta; P. Mandal; K. Ramakrishna; O.N. Srivastava
The composite alloys La2Mg17-xwt% LaNi5 and Mg-xwt% FeTi(Mn) have been successfully synthesized and the hydriding behaviours of these materials were studied for various values of x. Both these systems have been found to possess characteristics which are superior to the individual storage systems alone. In contrast to La2Mg17, hydrogen storage capacities of 5.24wt% with 3-4 times faster kinetics have been obtained for La2Mg17-xwt% LaNi5. For Mg-40wt% FeTi(Mn), the optimum storage capacity in relation to their reversible characteristic has been found to be about 3.5wt% even at ambient conditions, which is almost double the storage capacity of well-known FeTi(Mn) (∼ 1.9). In order to understand the hydrogenation behaviour and high storage capacity, structural/microstructural characteristics and chemical analyses of these composite materials were carried out employing the XRD, SEM and EDAX techniques. © 1994.