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PublicationArticle Effect of processing parameter on hydrogen storage characteristics of as quenched Ti45Zr38Ni17 quasicrystalline alloys(2011) Rohit R. Shahi; T.P. Yadav; M.A. Shaz; O.N. Srivastava; S. Van SmaalenThe present study deals with the microstructural changes with respect to the processing parameter (quenching rate) and their correlation with hydrogen storage characteristics of Ti45Zr38Ni17 quasicrystalline alloys. The ribbons of the alloy have been synthesized at different quenching rates obtained through different wheel speeds (35, 40, 45 and 50 m/s) and investigated for their hydrogen storage characteristics. The lower cooling rate obtained through low wheel speed (35 m/s) produces, i-phase grains whose size ranges from 300-350 nm, whereas higher cooling rates obtained through high wheel speed (45 and 50 m/s) promote the formation of grains with size ranges from 100-150 nm in Ti45Zr38Ni17 ribbons. It has been found that the ribbons synthesized at 35 m/s absorbed ∼2.0 wt%, whereas ribbons synthesized at 50 m/s absorbed ∼2.84 wt. % of hydrogen. Thus the hydrogen storage capacity of ribbon increases for the ribbons produced at higher quenching rate. One of the salient features of the present study is that the improvement of hydrogen storage capacity obtained through higher quenching rates (∼45 to 50 m/s wheel speed) leading to the formation of lower grain size. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.PublicationArticle Effects of mechanical milling on desorption kinetics and phase transformation of LiNH2/MgH2 mixture(Elsevier Ltd, 2008) Rohit R. Shahi; T.P. Yadav; M.A. Shaz; O.N. SrivastavaWe have investigated the ball-milling (5-45 h) followed by dehydrogenation kinetics of LiNH2-MgH2 mixture. A new result of ball-milling reveals the formation of Mg(NH2)2 for mixtures ball-milled for more than 15 h. The desorption kinetics has been found to improve appreciably by increasing the duration of milling from 5 to 45 h. This enhancement is attributed to formation of Mg(NH2)2 during this process. It was found that the Mg(NH2)2 form through the reaction 2LiNH2 + MgH2 → Mg(NH 2)2 → 2LiH. The phase and microstructural characterizations have been done through X-ray diffraction, IR-spectrometry, transmission and scanning electron microscopy. Correlation between particle size and hydrogenation behavior has also been investigated. © 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.PublicationArticle Investigations on hydrogen storage behavior of CNT doped NaAlH4(2005) D. Pukazhselvan; Bipin Kumar Gupta; Anchal Srivastava; O.N. SrivastavaIn this paper, we have carried out investigations on admixing carbon nanotubes (CNT) to increase the desorption rate of hydrogen in NaAlH 4. So far only transition metal Ti has been attempted as the suitable dopant for making NaAlH4 (purified version) a viable hydrogen storage material by increasing the hydrogen desorption rate. Out of the various materials corresponding to NaAlH4-x mol% CNT (x = 2, 4, 6, 8 and 12), we have found that the material with x = 8 mol% is the optimum material. It shows highest desorption rate leading to 3.3 wt.% of H2 at ∼160 °C within 2 h for the first dissociation reaction. The CNT admixed NaAlH4 has also been found to exhibit good rehydrogenation characteristics (reversibility on hydrogenation up to ∼4.2 wt.%). A feasible mechanism for the improvement of hydrogen desorption characteristics has been put forward. © 2005 Elsevier B.V. All rights reserved.PublicationArticle Studies on synthesis and dehydrogenation behavior of magnesium alanate and magnesium-sodium alanate mixture(2007) M. Sterlin Leo Hudson; D. Pukazhselvan; G. Irene Sheeja; O.N. SrivastavaMagnesium alanate (Mg (AlH4)2) has been synthesized by mechanochemically activated metathesis reaction involving MgCl2 and NaAlH4. Its dehydrogenation kinetics and storage capacity has been studied by using Sievert's type apparatus. We have obtained dehydrogenation capacity of 2.7 wt% H2 from Mg (AlH4)2 + 2 NaCl during the first decomposition step at 140 {ring operator} C and 1.1 wt% H2 during second step decomposition at 280 {ring operator} C. Efforts were carried out to reduce NaCl content from the product using Soxhlet extraction technique. The Soxhlet extracted product gives the total dehydrogenation capacity of 4.7 wt% H2. To enhance the storage capacity, we have synthesized a complex hydride consisting of mixture: x Mg (AlH4)2 + y NaAlH4(0 < x < 1, y ≥ 1) . In the alanate mixture 0.5 Mg (AlH4)2 + NaAlH4, the dehydriding temperature of NaAlH4 gets lowered by ∼ 50 {ring operator} C (from 190 {ring operator} C to 140 {ring operator} C) with 4 times faster desorption kinetics. The total hydrogen liberated in 180 min from NaAlH4 + 0.5 Mg (AlH4)2 (+ NaCl) mixture at 140 {ring operator} C has been observed to be 3.7 wt% H2. © 2007 International Association for Hydrogen Energy.PublicationArticle Thermodynamical, structural, hydrogen storage properties and simulation studies of P-C isotherms of (La, Mm) Ni5 - y Fey(2007) Rajesh Kumar Singh; M.V. Lototsky; O.N. SrivastavaThe present work is focussed on the synthesis, structural/microstructural characterization, hydrogenation behaviour and computer simulation studies of P-C isotherms of a new series of alloys represented by Lax Mm1 - x Ni5 - y Fey (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 and y = 0.1), where Mm denotes Ce-rich mischmetal. The alloys have been analysed using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The alloy corresponding to LaNi4.9 Fe0.1 has been found to have high storage capacity of ∼ 1.68 wt % which is one of the highest reported capacity for AB5 type storage systems. A feasible mathematical model has been developed to simulate the P-C isotherms. The model describes the asymmetry of the 'pressure-composition' isotherms, temperature-dependent plateau slopes and smooth transitions between α, α + β and β-regions. P-C isotherms, enthalpy and entropy changes (Δ H and Δ S) have been evaluated experimentally for the alloys Lax Mm1 - x Ni4.9 Fe0.1 in order to have input data for the simulation. Special software was developed to simulate the P-C isotherms using the said model. The simulated and experimental curves have been found to match closely. © 2007 International Association for Hydrogen Energy.PublicationArticle Studies on synthesis and hydrogenation behaviour of graphitic nanofibres prepared through palladium catalyst assisted thermal cracking of acetylene(2004) Bipin Kumar Gupta; R.S. Tiwari; O.N. SrivastavaThe nano-variants of carbon including graphitic nanofibres (GNF) have recently been considered to be exotic (light weight, high storage capacity) hydrogen storage materials. In the present paper, we report growth of aligned bundles of GNF. The length and width of cross-section of the bundles is ~50 and ~25μm, respectively. The length of individual GNF is ~50μm and diameter ~0.25μm. The GNFs have been synthesized through thermal decomposition of acetylene using palladium (Pd) sheets as catalyst. This represents a new form of catalyst. The GNFs bundles grown by the present method are easier to hydrogenate. They adsorb hydrogen at a lower pressure of ~80atm as against ~120atm for the GNF grown in the earlier studies. The storage capacity obtained in the present investigation is ~17wt.%. Electron microscopic investigations reveal that as against the as grown GNF, the hydrogenated version embodies microstructures exhibiting fragmentation of graphitic layer bundles. The reasons for the growth of GNF in the form of aligned bundles, the ease of hydrogenation and relevance of GNF fragmentation after hydrogenation have been outlined. © 2004 Elsevier B.V. All rights reserved.PublicationConference Paper Effect of different sized CeO2 nano particles on decomposition and hydrogen absorption kinetics of magnesium hydride(2013) Rajesh Kumar Singh; T. Sadhasivam; G.I. Sheeja; P. Singh; O.N. SrivastavaIn present paper, different sizes of CeO2 nanoparticles were synthesized by ball milling and their effect on the absorption kinetics and decomposition temperature of MgH2 was studied. It was found that a small amount of admixing of the above said catalysts with MgH2 exhibits improved hydrogen storage properties. Among these different sizes of CeO2 nanoparticles, 2 weight % admixed CeO2 with a particle size of ∼10-15 nm led to decrease in desorption temperature by ∼50 K. Moreover, it also shows 1.5 times better absorption kinetics with respect to pure MgH2. The samples were characterized using SEM, TEM and XRD techniques. The hydrogenation/dehydrogenation properties were measured by gas reaction controller. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.PublicationArticle On the synthesis and hydrogenation behaviour of MmNi5-xFe x alloys and computer simulation of their P-C-T curves(2004) Rajesh Kumar Singh; Bipin Kumar Gupta; M.V. Lototsky; O.N. SrivastavaThe present paper deals with the synthesis of MmNi5-xFe x alloys (x = 0.05, 0.1, 0.3, 0.5). It has been found that Fe substitution, because of the higher electron attractive power of the Fe when substituted, leads to enhancement of the hydrogen storage capacity. Thus, the material MmNi4.9Fe0.1 shows a storage capacity of ∼1.66wt.%, which is one of the highest capacities for any as synthesised AB5 type alloy. The P-C isotherms at various temperatures have been simulated by a suitable mathematical model. For this, the randomised variables ΔH and ΔS have been evaluated experimentally. These have been used as input parameters in the modelling. The simulated and experimental curves have been found to match closely. It is suggested that mathematical modelling is useful for predicting P-C-T behaviours when the hydride is used at different temperatures. © 2003 Elsevier B.V. All rights reserved.PublicationArticle High-yield production of graphitic nanofibers(2008) Bipin Kumar Gupta; O.N. SrivastavaThe primary aim of the present paper is focused on the gram-scale (>1 g) synthesis and characterization of graphitic/carbon nanofibers (GNF). The GNFs were grown by spray pyrolysis of benzene. The optimum growth conditions for the high-yield GNFs are as follows: spray nozzle diameter (inner diameter) ∼0.52 mm, flow rate of benzene solution ∼5 ml/min with reaction temperature ∼750 °C and flow rate of hydrogen as carrier gas ∼1500 cc/min. The structural and microstructural characterizations have been evaluated by X-ray diffraction and transmission as well as by Scanning electron microscopy. The typical length and diameter are ∼60 μm and ∼250 nm, respectively. Most of the GNF samples exhibit coiled/helical-like fibers. The yield of GNF in the spray pyrolysis growth mode has been found to be of the order of gram-scale (1.45 g) per run. The details of the experimental parameters for optimum growth conditions have been studied and will be described. © 2008 International Association for Hydrogen Energy.PublicationConference Paper Improvement of hydrogen storage characteristics of carbon nanostructural variants admixed nano MgH2(Committee of WHEC2014, 2014) Rajesh Kumar Singh; Rajesh Kumar; Himanshu Raghubanshi; O.N. SrivastavaIn the present work, we have synthesized and studied the catalytic effect of different carbon nanostructures (CNSs) on the absorption kinetics, decomposition temperature of MgH2. Ball-milling was used to reduce the particle size of MgH2 and CNS catalysts were used to enhance the hydrogen storage properties at lower temperatures. In particular, 2wt% twisted carbon nanofibres (TCNF) admixed ball-milled MgH2 (MgH2-2TCNF) corresponds to better hydrogenation/ dehydrogenation behaviour. The commencement of H-desorption temperature is ∼420 ?C for pure MgH2, ∼ 330 °C for TCNF admixed MgH2, which is further lowered to 297 °C for TCNF admixed ball-milled MgH2. Thus, desorption temperature gets more than 125 °C lower compared to commercial MgH2. After the desorption, Mg- 2TCNF (ballmilled) shows 5.03 wt% absorption as compared to 3.05 wt% for the ball milled MgH2 in the first 10 minutes even at 180 °C and an applied pressure of 2MPa. Whereas in the case of 2TCNF admixed MgH2 it shows absorption of 4.28 wt% at a higher temperature 300 °C and an applied pressure of 2 MPa. The improved properties originate due to the CNSs catalyst and nanostructure of MgH2 introduced during ball milling in hydrogen pressure. Copyright © (2014) by the Committee of WHEC2014 All rights reserved.