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The effect of improved dielectric properties in the presence of an applied magnetic field is discussed in Pr doped polycrystalline Gd$_{0.55}$Pr$_{0.45}$MnO$_3$ complemented by the structural properties down to 50 K and magnetic properties. Enhanced dielectric permittivity and low dielectric loss represent the strongly field-dependent dielectric behaviour of the sample. The structural characterizations using synchrotron angle dispersive X-ray diffraction confirm the orthorhombic symmetry of the polycrystalline sample with the Pnma space group from 300 K to 50 K. There is no structural transition at lower temperatures up to 50 K; however the Mn O octahedral distortion is reduced. The investigation of dielectric properties for frequencies range 500 Hz to 1 MHz was conducted in the temperature range 8 K to 300 K with and without a magnetic field of 7 Tesla, which shows the high dielectric constant in the 500 Hz frequency region. This confirms the relaxation phenomena in polycrystalline Gd$_{0.55}$Pr$_{0.45}$MnO$_3$. ac conductivity data shows the increasing trend for frequencies along with the activation energy which increases from low frequencies to higher frequencies. Temperature-dependent dc magnetization study shows the negative magnetization in polycrystalline Gd$_{0.55}$Pr$_{0.45}$MnO$_3$ at low temperature at 100 Oe applied field, due to spin canting of Mn-Mn magnetic lattice. High coercivity due to competition in between spin ordering of Mn and Gd,Pr magnetic lattice at 5 K are also observed in the field-dependent magnetization study., Comment: 33 pages, 9 figures, 3 tables

The present investigation deals with the synthesis of ternary transition metal alloy nanoparticles of FeCoNi and graphene templated FeCoNi (FeCoNi@GS) by one-pot reflux method and there use as a catalyst for hydrogen sorption in MgH2. It has been found that the MgH2 catalyzed by FeCoNi@GS (MgH2: FeCoNi@GS) has the onset desorption temperature of ~255 °C which is 25 °C and 100 °C lower than MgH2 catalyzed by FeCoNi (MgH2: FeCoNi) (onset desorption temperature 280 °C) and the ball-milled (B.M) MgH2 (onset desorption temperature 355 °C) respectively. Also MgH2: FeCoNi@GS shows enhanced kinetics by absorbing 6.01 wt% within just 1.65 min at 290 °C under 15 atm of hydrogen pressure. This is much-improved sorption as compared to MgH2: FeCoNi and B.M MgH2 for which hydrogen absorption is 4.41 wt% and 1.45 wt% respectively, under the similar condition of temperature, pressure and time. More importantly, the formation enthalpy of MgH2: FeCoNi@GS is 58.86 kJ/mol which is 19.26 kJ/mol lower than B.M: MgH2 (78.12 kJ/mol). Excellent cyclic stability has also been found for MgH2: FeCoNi@GS even up to 24 cycles where it shows only negligible change from 6.26 wt% to 6.24 wt%. A feasible catalytic mechanism of FeCoNi@GS on MgH2 has been put forward based on X-ray diffraction (XRD), Raman spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Photoelectron Spectroscopy (XPS), and microstructural (electron microscopic) studies.

The present study is focused on the structural correlation of magneto-electric coupling that exists in polycrystalline TbMnO 3 . The X-ray diffraction patterns are collected at various conditions, which are (1) at 300 K without a magnetic field, (2) at 2 K without magnetic field and (3) at 2 K with 7 Tesla magnetic fields. The structural transition in TbMnO 3 has been observed at 2 K and some lattice modulation after applying the magnetic field at 2 K. The Rietveld refinement of TbMnO 3 confirms the orthorhombic phase with centrosymmetric space group Pnma at 300 K. We have observed that the inversion symmetry breaks at 2 K and the polycrystalline TbMnO 3 has been refined using a non-centrosymmetric orthorhombic space group which can be either Pn2 1 a or P2 1 ma. This structural transition confirms the presence of a ferroelectric phase at 2 K. After the application of 7 Tesla magnetic field, the signature of an incommensurate phase has been observed in polycrystalline TbMnO 3 at 2 K. The DC magnetization behaviour with temperature M(T) and field M(H) reveals the antiferromagnetic behaviour of polycrystalline TbMnO3 below 42 K. We have also measured magneto-dielectric property of polycrystalline TbMnO 3 at the low temperature, which confirms the strong magneto-electric coupling in polycrystalline TbMnO 3 below the transition temperature.

We describe the synthesis of MgH2 using autocatalytic effect of MgH2. The MgH2 was synthesized by ball milling Mg with 5 wt% of MgH2. The ball milling was carried out at different pressures of 15, 30 and 45 atm of H2 followed by heat treatment (heating under vacuum and annealing at 30 atm of H2 pressure (at 350 °C) for 10 h). It has been found that the MgH2 synthesized using 30 atm of H2 pressure during ball milling, followed by heat treatment and annealing (MgH230BM) is the optimum material as it has lowest desorption temperature (325 °C) faster rehydrogenation kinetic (6.60 wt% within 30 min at 300 °C and 20 atm hydrogen pressure). Also MgH230BM maintains the storage capacity of more than 6.00 wt% (loss of 0.6 wt%) after 10 cycles of de/re-hydrogenation. The as synthesized MgH2 has superior de/re-hydrogenation properties and is ∼4 times cheaper as compared to MgH2 procured from the chemical company like Alfa-Aesar. It is to be mentioned that under above mentioned temperature and pressure conditions the stand alone Mg (without having MgH2 as catalyst) doesnot at all converts to MgH2. The present study opens the gateway for economical synthesis of MgH2 at large scale.

The present study deals with the material tailoring of Mg(NH2)2–2LiH through dual borohydrides: the reactive LiBH4 and the non-reactive NaBH4. Furthermore, a pulverizer, as well as a catalyst FeTi, has been added in order to facilitate hydrogen sorption. Addition of LiBH4 to LiNH2 in a 1 : 3 molar ratio leads to the formation of Li4(BH4)(NH2)3 which also acts as a catalyst. However, the addition of NaBH4 doesn't lead to any compound formation but shows a catalytic effect. The onset dehydrogenation temperature of thermally treated Mg(NH2)2–2LiH/(Li4(BH4)(NH2)3–NaBH4) is 142 °C as against 196 °C for the basic material Mg(NH2)2–2LiH. However, with the FeTi catalyzed Mg(NH2)2–2LiH/(Li4(BH4)(NH2)3–NaBH4, it has been reduced to 120 °C. This is better than other similar amide/hydride composites where it is 149 °C (when the basic material is catalyzed with LiBH4). The FeTi catalyzed Mg(NH2)2–2LiH/(Li4(BH4)(NH2)3–NaBH4 sample shows better de/re-hydrogenation kinetics as it desorbs 3.9 ± 0.04 wt% and absorbs nearly 4.1 ± 0.04 wt% both within 30 min at 170 °C (with the H2 pressure being 0.1 MPa for desorption and 7 MPa for absorption). The eventual hydrogen storage capacity of Mg(NH2)2–2LiH/(Li4(BH4)(NH2)3–NaBH4 together with FeTi has been found to be ∼5.0 wt%. To make the effect of catalysts intelligible, we have put forward in a schematic way the role of Li and Na borohydrides with FeTi for improving the hydrogen sorption properties of Mg(NH2)2–2LiH.

We report a mechanism for how low concentrations of TiH2 can function as a dynamic additive for improving both the kinetics and the thermodynamics of the Mg/MgH2–TiH2 system. We use a combination o...

Here, we report extraordinary field emission properties from one pot synthesized aligned carbon nanotubes endowed with related Fe nanoparticles (NPs). The CNT configuration is in the form of a carbon hollow cylinder (CHC) with CNTs radially aligned towards the CHC axis. The structure generates electron field emission properties such as an ultralow turn on field (0.35 V μm−1 at 10 μA cm−2), a low threshold field (0.41 V μm−1 at 100 μA cm−2) and a high field emission current density (7.71 mA cm−2 at 0.78 V μm−1). It also exhibits multi-fold improvement in the field enhancement factor (1.34 × 104) with highly stable current emission at 100 μA measured for 14 h. No post synthesis treatment is required for enhanced field emission characteristics. The growth related Fe NPs assist in lowering the work function and hence enhancing the field emission properties. The possibility of assembling nano-structured field emitters into macroscale architectures suggests new prospects for next generation three dimensional electron sources.

The dielectric behavior and alternating current conduction mechanism of nanocrystalline (Co,Ni)Al 2 O 4 aluminate spinel have been investigated over a broad frequency range (1 kHz to 1 MHz) for different temperatures i.e. 50 °C to 90 °C. The low cost and environmental friendly method has been used to developed the nanocrystalline (Co,Ni)Al 2 O 4 spinel phase. The formation of homogeneous single phase of nanocrystalline (Co,Ni)Al 2 O 4 spinel has been confirmed by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The dielectric response and alternating current conductivity have been observed by inductance, capacitance and resistance bridge which confirms traditional dielectric behavior of (Co,Ni)Al 2 O 4 . The frequency dependent complex dielectric impedance behavior has also been explored. The activation energy of (Co,Ni)Al 2 O 4 has been found nearly 0.3–0.1 eV b/w the frequency range 1 kHz to 1 MHz. The alternating current conduction mechanism reveals the signature of correlated barrier hopping by following the power law where the maximum barrier length has been found 144 ± 0.25 MeV. This alternating current conduction also follows the Meyer-Neldel rule in the low frequency region.

The present study reports the curious catalytic action of a new class of catalyst, quasicrystal of Al65Cu20Fe15 on de/rehydrogenation properties of magnesium hydride (MgH2). Catalyzed through this catalyst, the onset desorption temperature of MgH2 gets reduced significantly from ∼345 °C (for ball-milled MgH2) to ∼215 °C. A more dramatic effect of the above catalyst has been observed on rehydrogenation. Here, 6.00 wt % of hydrogen storage capacity is observed in just 30 s at 250 °C. Improved rehydrogenation kinetics has been found even at lower temperatures of 200 and 150 °C by absorbing ∼5.50 and ∼5.40 wt % of H2, respectively, within 1 min and ∼5.00 wt % at 100 °C in 30 min. These are some of the lowest desorption temperatures and rehydrogenation kinetics obtained for MgH2 through any other known catalyst. The storage capacity of MgH2 catalyzed with the leached version of Al65Cu20Fe15 quasicrystalline alloy degrades negligibly even after 51 cycles of de/rehydrogenation. The feasible reason for catalytic ...

The present investigation describes the hydrogen storage properties of MgH2 ball milled with different additives i.e. graphene templated rare earth metal (La and Ce) fluorides, CeF4 and LaF3. MgH2 ball milled with graphene templated CeF4 (MgH2:CeF4@Gr) has onset desorption temperature of 245 °C, which is 50 °C, 52 °C and 75 °C lower than MgH2 ball milled with LaF3 templated graphene, CeF4 and LaF3 respectively. CeF4@Gr also shows the superior effect amongst all additives during rehydrogenation where MgH2:CeF4@Gr absorbs 5.50 wt% within 2.50 min at 300 °C under 15 atm H2 pressure. Dual tuning effect, i.e. lowering of thermodynamic (62.77 kJ/mol H2: lower from 74 kJ/mol for pristine MgH2) and kinetics barrier (93.01 kJ/mol) has been observed for MgH2:CeF4@Gr. Additionally, MgH2 ball milled with CeF4@Gr shows good reversibility up to 24 cycles of de/rehydrogenation. The feasible working mechanism of CeF4@Gr as additive for MgH2 has been studied in detail with the help of Transmission Electron Microscope (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction characterizations (XRD).

The present investigation describes the synergistic role of Li4(BH4)(NH2)3 and ZrFe2 in the hydrogen storage behaviour of a Li–Mg–N–H hydride system. The onset desorption temperature of ZrFe2-catalysed Mg(NH2)2–LiH–Li4(BH4)(NH2)3 is ∼122 °C, which is 83 °C, 63 °C, and 28 °C lower than that of thermally treated 2LiNH2–1MgH2, 2LiNH2–1MgH2–4 wt%ZrFe2, and 2LiNH2–1MgH2–0.1LiBH4 composites, respectively. Native Mg(NH2)2–LiH–Li4(BH4)(NH2)3 absorbed only 2.78 wt% of H2 within 30 min. On the other hand, the ZrFe2-catalysed Mg(NH2)2–LiH–Li4(BH4)(NH2)3 sample absorbed 3.70 wt% of hydrogen within 30 min and 5 wt% of H2 in 6 h at 180 °C and 7 MPa H2 pressure. Mg(NH2)2–LiH–Li4(BH4)(NH2)3 catalyzed with ZrFe2 shows negligible degradation of the storage capacity even after repeated cycles of de/rehydrogenation. The effect of ZrFe2 and Li4(BH4)(NH2)3 on a Mg(NH2)2/LiH composite has been described and discussed with the help of structural (X-ray diffraction), microstructural (electron microscopy), and vibrational modes of molecules through FTIR studies. The present results suggest that an optimum catalysis may originate from the synergistic action of an in situ formed quaternary hydride (Li4(BH4)(NH2)3) and an intermetallic-like ZrFe2, which acts as a pulverizer cum catalyst.

High-quality graphene is highly enviable material due to its seminal role amongst several areas in modern technology including its role as nanocarrier for site selective drug grafting and delivery applications. Here, we report a facile, cost-effective and single-step method to produce high-quality graphene through customised electrochemical exfoliation of graphite anode in alkaline electrolyte medium. The quality of graphene sheets (GS) were investigated by Raman, TEM/HRTEM, AFM, and FTIR techniques. The high quality as well as excellent Π-Π stacking nature of the honeycomb lattice of graphene was confirmed by measuring the quenching capability through photo-luminescence spectroscopy using organic dyes. A plausible mechanism for the graphite exfoliation has been given where evolution of high density of oxygen molecules exerts large force on the graphitic layers leads to exfoliation and consequent synthesis of graphene. Furthermore, to explore the application of the graphene sheets so synthesized, we carried out studies which may make them as suitable carriers for drug delivery. For this, graphene sheets were functionalized with L-cysteine and attached with the drugs Amphotericin-B (AmB) and Tamoxifen citrate (TMX). The conjugation of drugs with L-cysteine functionalized graphene has been confirmed through FTIR and Raman spectroscopic techniques. The drug loading efficiency of FGS for AmB and TMX was 75.00% and 94.31%, respectively. The present formulation of drugs (AmB and TMX) conjugated with graphene is suitable for the targeted drug delivery as it will enhance the efficacy and reduce cytotoxicity associated with drug.

The present study reports on the structural and magnetic phase transitions in Pr-doped polycrystalline Tb0.6Pr0.4MnO3, using high-resolution neutron powder diffraction (NPD) collected at SINQ spallation source, to emphasize the suppression of the sinusoidal magnetic structure of pure TbMnO3 and the evolution to a collinear A-type antiferromagnetic ordering. The phase purity, Jahn–Teller distortion, and one-electron bandwidth for eg orbital of Mn3+ cation have been calculated for polycrystalline Tb0.6Pr0.4MnO3, in comparison to the parent materials TbMnO3 and PrMnO3, through the Rietveld refinement study from x-ray diffraction data at room temperature, which reveals the GdFeO3 type orthorhombic structure of Tb0.6Pr0.4MnO3 having Pnma space group symmetry. The temperature-dependent zero field-cooled and field-cooled dc magnetization study at low temperature down to 5 K reveals a variation in the magnetic phase transition due to the effect of Pr3+ substitution at the Tb3+ site, which gives the signature of the antiferromagnetic nature of the sample, with a weak ferromagnetic component at low temperature-induced by an external magnetic field. The field-dependent magnetization study at low temperatures gives the weak coercivity having the order of 2 kOe, which is expected due to the canted-spin arrangement or ferromagnetic nature of Terbium ordering. The NPD data for Tb0.6Pr0.4MnO3 confirms that the nuclear structure of the synthesized sample maintains its orthorhombic symmetry down to 1.5 K. Also, the magnetic structures have been solved at 50 K, 25 K, and 1.5 K through the NPD study, which shows an A-type antiferromagnetic spin arrangement having the magnetic space group Pn′ma′.

In the present study, the cations Co 2+ /Ni 2+ and Al 3+ distribution in nanocrystalline (Co, Ni)Al 2 O 4 spinel have been investigated using X-ray and transmission electron microscopy. The nanocrystalline (Co, Ni)Al 2 O 4 spinel has been synthesized using mechanically activated Al 70 Co 15 Ni 15 quasicrystalline precursor through annealing at 600 °C in controlled oxygen atmosphere. The mechanical activation of single phasic decagonal Al 70 Co 15 Ni 15 quasicrystal was carried out in a high energy attritor ball mill for 40 h with 40:1 ball to powder ratio using toluene as a process control agent. The high resolution x-ray diffraction data has been refined by the Rietveld method using JANA2006 and subsequently, the corresponding structure has been constructed using Diamond4.0. The structure was also confirmed by analysis of transmission electron microscopy linearized diffraction pattern profile of d -values and corresponding plane. These analyses indicate that the cations Co 2+ and Ni 2+ distributed in the tetrahedral coordinated sites are the dominant species in the normal spinel phase.

The present communication deals with the hydrogen storage performance of ambient pressure dried pristine as well as platinum doped carbon aerogel (CA-0.10 Pt). These carbon aerogels (CAs) have been prepared from resorcinol-formaldehyde (R–F) through sol–gel synthesis route with sodium carbonate as a catalyst (C). The synthesis parameters adapted led to the formation of CA having preponderance of submicropores. Structural and microstructural characteristics of these carbon aerogels have been investigated through XRD, SEM, TEM, nitrogen adsorption and Raman spectroscopic techniques. Nitrogen adsorption and TEM studies confirm the large density of micropores with the majority of pores having sizes between 0.30 and 1.46 nm (submicropores). The hydrogen storage characteristics of as synthesized carbon aerogels have been investigated by monitoring the hydrogen ad/desorption curves. At room temperature and at pressure upto 22 atm the CA and CA-0.1 Pt have hydrogen storage capacity of 0.40 wt.% and 0.33 wt.% respectively. However, under the same pressure but at liquid nitrogen temperature CA and CA-0.10 Pt have hydrogen storage capacity of 5.65 wt.% and 5.15 wt.%. Feasible reasons for the high hydrogen storage capacities at liquid nitrogen temperature for the present CAs have been put forward.

The present investigation describes the hydrogen sorption (de/absorption) behavior of MgH2 catalyzed by graphene sheet templated Fe3O4 nanoparticles (Fe3O4@GS). Hydrogen sorption studies reveal that MgH2 catalyzed by Fe3O4@GS (MgH2:Fe3O4@GS) offers improved hydrogen storage behavior as compared to stand-alone MgH2 catalyzed by graphene sheets (GS) (MgH2:GS) or Fe3O4 nanoparticles (MgH2:Fe3O4). The MgH2:Fe3O4@GS has an onset desorption temperature of ∼262 °C (∼142 °C lower than pristine MgH2), while MgH2:GS and MgH2:Fe3O4 have onset desorption temperatures of ∼275 °C and ∼298 °C respectively. In contrast to this, MgH2:GS absorbs 4.40 wt% and MgH2:Fe3O4 absorbs 5.50 wt% in 2.50 minutes at 290 °C under 15 atm hydrogen pressure. On the other hand, MgH2:Fe3O4@GS absorbs 6.20 wt% hydrogen in 2.50 minutes (which is considerably higher than recently studied catalyzed MgH2 systems) under identical temperature and pressure conditions. The MgH2 catalyzed with Fe3O4@GS shows negligible degradation of the storage capacity even after 25 cycles. Additionally, the desorption activation energy for MgH2:Fe3O4@GS has been found to be 90.53 kJ mol−1 (which is considerably lower as compared to metal/metal oxide catalyzed MgH2 and fluorographene catalyzed MgH2). The formation enthalpy for MgH2:Fe3O4@GS is 60.62 kJ per mole of H2 (13.44 kJ mol−1 lower than bulk MgH2). The catalytic effect of Fe3O4@GS has been described and discussed with the help of structural (X-ray diffraction (XRD)), micro structural (electron microscopy) and Raman spectroscopic studies.

We have investigated the structural and magnetic phase transitions in Sr doped polycrystalline Tb0.55Sr0.45MnO3, using temperature-dependent high-resolution neutron powder diffraction in the HRPT diffractometer at PSI to address the origin of magnetization reversal at low temperature. The solid solution Tb0.55Sr0.45MnO3 crystallizes in O′ type orthorhombic structure having the Pnma symmetry. The substitution of the divalent cation of Sr2+ at the site of Tb3+ dilutes the Mn–Tb interaction and affects the magnetic structure, which was observed by the field and temperature-dependent dc magnetization and neutron diffraction study. The temperature-dependent zero field-cooled and field cooled dc magnetization study reveals the indication of spin reversal phenomena, which is the nature of canted antiferromagnetic or ferrimagnetic transition at 100 Oe because of Mn–Mn sub-lattices interaction below 65 K. By increasing the applied magnetic field up to 20 kOe, a weak ferromagnetic type of behaviour is observed. The field-dependent magnetization shows weak coercivity due to the canted spin structure at low temperatures. The low-temperature neutron diffraction study of polycrystalline Tb0.55Sr0.45MnO3 reveals the non-collinear canted antiferromagnetic structure due to Tb ordering at 1.5 K, which turns into a non-collinear ferromagnetic structure along with spin canting followed by the spin reversal phenomena at 25 K.

In present investigation, the selective removal of Al from the quasi-lattice sites of quasicrystalline alloy surface was examined in order to produce the nano-particles of metal/metal oxides within the micro-porous network. Al was selectively etched from both the as-cast as well as annealed Al63Cu25Fe12 quasicrystalline alloys through the treatment with 10 mol NaOH solution at different time interval. In the as-cast sample, higher density of porosity was observed compared to that of annealed alloy. However, dealloying specifically for 4 and 8 h yielded nano-size particles on quasicrystalline surface (of both the alloys) in which very fine particles were detected at 8 h. The increase in density and decrease in size of the nano-particles was found with dealloying duration. X-ray diffraction analysis was performed to characterize the samples. Scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis were carried out to investigate the surface microstructure, internal morphology and chemical composition. The chemical dealloying treatments yielded nano-particles of Cu and Fe along with their oxides on the quasicrystalline surface. Furthermore, the catalytic activity of leached quasicrystalline materials was evaluated towards degradation of non-biodegradable and hazardous methylene blue (organic dye).

It is well-known that the evolution of society is guided by several environmental strains. One of the important strains existing at this point of time is climate change due to pollution. Other issue of paramount importance is ?energy?. One of the comparatively new energy vectors which is typically suited for India is ?hydrogen?. Hydrogen is an indigeneous fuel since it can be produced by dissociating water with a variety of input energies, out of which solar energy is of particular importance. India has both of these in plenty. Hydrogen produced from water burns back to water after use. It is thus climate-friendly, inexhaustible, clean and indigenous fuel. Hydrogen must first be produced, afterwards stored, and then

In the present investigation, the effect of Ga substitution at Al site on the phase formation and stabilization of decagonal quasicrystalline phase in the rapidly solidified Al70−xGaxPd13Mn17 alloys have been studied by employing X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive x-ray analysis. The as-cast and rapidly solidified alloys with x = 0, 2.5 and 5 have been investigated. The melt-spinning technique has been used for rapid solidification of the as-cast alloys. The alloys up to 5 at.% Ga exhibit the formation of small amount of icosahedral quasicrystalline phases along with major amount of decagonal phase in the rapidly solidied ribbons. The energy dispersive X-ray analysis investigations suggest the homogeneous presence of Ga in the quasicrystalline alloys.

The present study deals with the use of ZrFe2 for the formation of pure phase of hydrogen storage material Mg(NH2)2/LiH. Since ZrFe2 is harder than the starting material LiNH2 and MgH2, pulverization effect produced by ZrFe2 assists in the synthesis of pure phase. The formation of pure Mg(NH2)2/LiH has been examined by XRD and confirmed by FTIR. The catalytic effect of ZrFe2 has been found to improve significantly the de/rehydrogenation characteristic of Mg(NH2)2/LiH. The ZrFe2 catalyzed Mg(NH2)2/LiH shows good recyclability. The activation energy of ZrFe2 catalyzed Mg(NH2)2/LiH was found to be 74.80 kJ/mol which is better than several other reported studies using different catalysts. Based on experimental results, a viable mechanism for dehydrogenation of Mg(NH2)2 in the presence of ZrFe2 has also been proposed.

The unfavorable de/re-hydrogenation aspects of high storage capacity material, Mg can be overcome by synthesis of composites with known intermetallic hydrogen storage alloys. In this work, a new additive, ZrFe2Hx intermetallic hydride, is used to synthesize MgH2–ZrFe2Hx nanocomposite by reactive mechanical milling technique. Also this report describes the comparison of hydrogen sorption behavior of MgH2–ZrFe2 and MgH2–ZrFe2Hx nanocomposites. It is found that the composite containing ZrFe2 and ZrFe2Hx leads to decrease in desorption temperature from 410 °C (for MgH2) to 350 and 290 °C respectively. The activation energy for rehydrogenation of composite is found to be ∼61 kJ/mol. This is lowered by 30 kJ/mol compared to the pristine milled MgH2 (92 kJ/mol). Thus, the results show significant improvement of hydrogenation behavior with the addition of ZrFe2Hx. Reasons for better catalytic activity achieved by using ZrFe2Hx have been put forwarded. Based on the present studies it can be suggest that the use of hydride version instead of the parent intermetallic phase for synthesizing the composite with MgH2 has a distinct advantage in improving the hydrogenation behavior of MgH2.

Herein, we demonstrate a facile one pot synthesis of graphene nanosheets by electrochemical exfoliation of graphite. In the present study, we report a significant increase in the yield of graphene by electrolyte heating assisted electrochemical exfoliation method. The obtained results of heating assisted electrochemically exfoliated graphene (utilizing H2SO4 + KOH + DW) synthesis clearly exhibit that the yield increases ∼4.5 times i.e. from ∼17% (room temperature) to ∼77% (at 80 °C). A plausible mechanism for the enhanced yield based on lattice expansion and vibration of intercalated ions has been put forward and discussed in details. The quality of graphene was examined by Raman, XPS, FTIR, AFM, SEM, TEM/HRTEM and TGA techniques. The Raman as well as morphogenesis results confirm the quality of the graphene nanosheets. We have used this graphene as electromagnetic interference shielding material where a comparatively large quantity of graphene is required. This graphene exhibits enhanced shielding effectiveness (46 dB at 1 mm thickness of stacked graphene sheets in frequency region 12.4 to 18 GHz) as compared to conventional electromagnetic interference shielding materials, which is greater than the recommended limit (∼30 dB) for techno-commercial applications. Thus the present work is suggestive for future studies on enhancement of yield of high quality graphene by proposed method and the use of synthesized graphene in electromagnetic interference shielding and other possible applications.

The present investigation describes the hydrogen storage properties of 2:1 molar ratio of MgH 2 –NaAlH 4 composite. De/rehydrogenation study reveals that MgH 2 –NaAlH 4 composite offers beneficial hydrogen storage characteristics as compared to pristine NaAlH 4 and MgH 2 . To investigate the effect of carbon nanostructures (CNS) on the de/rehydrogenation behavior of MgH 2 –NaAlH 4 composite, we have employed 2 wt.% CNS namely, single wall carbon nanotubes (SWCNT) and graphene nano sheets (GNS). It is found that the hydrogen storage behavior of composite gets improved by the addition of 2 wt.% CNS. In particular, catalytic effect of GNS + SWCNT improves the hydrogen storage behavior and cyclability of the composite. De/rehydrogenation experiments performed up to six cycles show loss of 1.50 wt.% and 0.84 wt.% hydrogen capacity in MgH 2 –NaAlH 4 catalyzed with 2 wt.% SWCNT and 2 wt.% GNS respectively. On the other hand, the loss of hydrogen capacity after six rehydrogenation cycles in GNS + SWCNT (1.5 + 0.5) wt.% catalyzed MgH 2 –NaAlH 4 is diminished to 0.45 wt.%.

The aim of the present investigation is to synthesize mixed sodium potassium alanate (K2NaAlH6) and to explore its hydrogen sorption characteristics. K2NaAlH6 is synthesized through ball milling of KH and NaAlH4 in the molar ratio 2:1 under hydrogen pressure of 10 bar. The temperature programmed desorption experiment shows that the synthesized K2NaAlH6 has peak desorption temperature of ∼352°C and reveals appreciable rehydrogenation kinetics under 6 bar hydrogen pressure at 300°C. The investigations are also focused on the catalytic effect of carbon nanostructures (CNS) namely, the graphene sheet (GS) and single wall carbon nanotube (SWCNT) and titanium halides (TiCl3 and TiF3) on K2NaAlH6. In the case of graphene and SWCNT catalyzed K2NaAlH6, the peak desorption temperature gets reduced to ∼347°C and ∼341°C respectively. The catalytic effects of CNS and titanium halide on K2NaAlH6 are also compared in the investigation. Between the two types of catalysts, halides are found to be better than CNS and out of the two halides, TiF3 is found to be the best catalyst for hydrogen sorption in K2NaAlH6. The peak desorption temperature decreases significantly from 352°C to ∼324°C for TiF3 catalyzed K2NaAlH6. Thus, the desorption activation energy reduces drastically from 124.43 kJ/mol (synthesized K2NaAlH6) to 88.05 kJ/mol for TiF3 catalyzed K2NaAlH6.

The effect of different carbon nanostructures specifically carbon nanotubes (CNTs) and carbon nanofibers (CNFs) on the improvement of the de/re-hydrogenation characteristics of a Mg(NH2)2/LiH mixture have been studied. Amongst CNTs and CNFs, the improvement in the hydrogenation properties for the Mg(NH2)2/LiH mixture is higher when CNFs are used as a catalyst. Investigations are also focused on the deployment of two different types of CNF (a) CNF1 (synthesized using a ZrFe2 catalyst) and (b) CNF2 (synthesized using a LaNi5 catalyst). The results show that CNF2 is better. The maximum decomposition temperature for the pristine Mg(NH2)2/LiH mixture is found to be ∼250 °C, which is reduced to ∼180 and ∼150 °C for the sample mixed with 4 wt% of multi-walled carbon nanotubes (MWCNTs) and CNF2 respectively. The activation energy for the dehydrogenation reaction is found to be 74 and 68 kJ mol−1 for the samples mixed with MWCNT and CNF2 respectively, whereas the activation energy for the dehydrogenation reaction of the pristine Mg(NH2)2/LiH mixture is 97 kJ mol−1. The catalytic activity and the de/re-hydrogenation characteristics of the Mg(NH2)2/LiH mixture mixed with different carbon nanostructures are described and discussed.

Present work describes the synthesis of Al (Ga)–Pd–Mn quasicrystalline films via flash evaporation followed by annealing. The icosahedral quasicrystal of Al65Ga5Pd17Mn13 alloy has been used as a precursor material. An amorphous phase with very fine icosahedral grain was found in the as-deposited films of ~ 1.5 μm thickness. After annealing at 300 °C for 120 h, the film completely transformed into an icosahedral phase showing micron size islands, these are precipitated on the surface of film. The X-ray diffraction and transmission electron microscopy confirms the formation of icosahedral phase. The energy dispersive X-ray analysis reveals that the final stoichiometry is maintained in the film. The formation of icosahedral Al–Ga–Pd–Mn film provides opportunities to investigate the useful properties of quasicrystals including the surface characteristics, which may well enhance the scientific interest in applied aspect of quasicrystals.

In the present study, we have investigated the combined effect of different transition metals such as Ti, Fe and Ni on the de/rehydrogenation characteristics of nano MgH 2 . Mechanical milling of MgH 2 with 5 wt% each of Ti, Fe and Ni for 24 h at 12 atm of H 2 pressure lead to the formation of nano MgH 2 -Ti5Fe5Ni5. The decomposition temperature of nano MgH 2 -Ti5Fe5Ni5 is lowered by 90 °C as compared to nano MgH 2 alone. It is also found that the nano MgH 2 -Ti5Fe5Ni5 absorbs 5.3 wt% within 15 min at 270 °C and 12 atm hydrogen pressures. However, nano MgH 2 reabsorbs only 4.2 wt% under identical condition. An interesting result of the present study is that mechanical milling of MgH 2 separately with Fe and Ni besides refinement in particle size also leads to the formation of alloys Mg 2 NiH 4 and Mg 2 FeH 6 respectively. On the other hand, when MgH 2 is mechanically milled together with Ti, Fe and Ni, the dominant result is the formation of nano particles of MgH 2 . Moreover the activation energy for dehydrogenation of nano MgH 2 co-catalyzed with Ti, Fe and Ni is 45.67 kJ/mol which is 35.71 kJ/mol lower as compared to activation energy of nano MgH 2 (81.34 kJ/mol). These results are one of the most significant in regard to improvement in de/rehydrogenation characteristics of known MgH 2 catalyzed through transition metal elements.

In the present investigation, we have synthesized different morphologies of carbon nanofibres (CNFs) to investigate their catalytic effect on the hydrogenation characteristics of 25 h ball-milled MgH2 (nano MgH2). The TEM analysis reveals that 25 h of ball-milling leads to the formation of nanocrystalline particles with size ranging between 10 and 20 nm. Different morphologies of CNFs were synthesized by catalytic thermal decomposition of acetylene (C2H2) gas over LaNi5 alloy. Helical carbon nanofibers (HCNFs) were formed at a temperature 650 °C. By increasing the synthesis temperature to 750 °C, planar carbon nanofibres were formed. In order to explore the effectiveness of CNFs towards lowering the decomposition temperature, TPD experiments (at heating rate 5 °C/min) were performed for nano MgH2 with and without CNFs. It was found that the decomposition temperature is reduced to ~334 and ~300 °C from 367 °C for the PCNF and HCNF catalysed nano MgH2. It is also found that HCNF admixed nano MgH2 absorbs ~5.25 wt% within 10 min as compared with pristine nano MgH2, which absorbs only ~4.2 % within the same time and same condition of temperature and pressure. Thus the HCNF possesses better catalytic activity than PCNF. These different levels of improvement in hydrogenation properties of HCNF catalysed nano MgH2 is attributed to the morphology of the CNFs.

The effect of carbon nanofibres (CNFs) on the de/re-hydrogenation characteristics of 1:2 magnesium amide (Mg(NH2)2) and lithium hydride (LiH) mixture is investigated. It is found that the desorption as well as absorption characteristic of the 1:2 Mg(NH2)2/LiH mixture is improved with admixing of different shaped (planar and helical) CNFs separately. The different shaped CNFs were synthesized through catalytic decomposition of acetylene gas over LaNi5 alloy. The synthesized CNFs contain Ni-metal nano particles. Among two different types of nanofibres namely planar carbon nanofibres (PCNFs) and helical carbon nanofibres (HCNFs), the later was found to act as a better catalyst. The decomposition temperature of the pristine Mg(NH2)2/LiH mixture is ∼250 °C, reduced to 150 and 140 °C for the PCNF and HCNF admixed Mg(NH2)2/LiH mixture respectively. The activation energy for dehydrogenation reaction was found to ∼97.2 kJ/mol, which is further reduced to ∼67 and ∼65 kJ/mol for the PCNF and HCNF admixed Mg(NH2)2/LiH mixture respectively. The lowering of decomposition temperature and enhancement in desorption kinetics, with admixing of different shaped CNFs are described and discussed.

In the present investigation, ( Cu, Cr, Fe ) Al 2O4 spinel was synthesized from decagonal quasicrystalline precursor using mechanical milling followed by air annealing. The optimum annealing temperature and time were found to be 600°C and 60 h respectively. The evolution of the spinel structure started upon air annealing at 600°C from the B2 phase formed due to milling of quasicrystalline phase for 40 h. The relevant optical property of mechanically milled and air annealed samples prepared at different temperatures (400°C, 500°C and 600°C) were evaluated by photoluminescence technique. These studies suggested the presence of emission characteristics in blue region i.e. at 430 nm.

In the present investigation, the formation and stability of icosahedral phase in Al70− x Ga x Pd17Mn13 alloys has been explored using X-ray diffraction, scanning, transmission electron microscopy and energy dispersive X-ray analysis. Cast alloys and melt-spun ribbons with x = 2.5, 5, 7.5, 10, 12.5, 15 and 20 have been investigated. In both cases, the alloys up to 5 at% Ga exhibit the formation of pure icosahedral phase. However, for x ≥5 at% Ga content, the cast alloy exhibits the formation of multiphase material, consisting of an icosahedral phase along with AlPd-type B2 and ξ′ crystalline (orthorhombic structure with unit cell a = 23.5 A, b = 16.6 A and c = 12.4 A) phases. In the case of the melt spun ribbon for x = 5 at% Ga, only an icosahedral phase has been found, but for 15 > x > 5 at% Ga, an icosahedral phase is the majority phase with AlPd-type B2 phase being the minority component. For x = 15 at% Ga, a Al3Pd2-type hexagonal phase together with a small amount of quasicrystalline phase is formed. ...

The present study deals with the microstructural changes with respect to the processing parameter (quenching rate) and their correlation with hydrogen storage characteristics of Ti 45 Zr 38 Ni 17 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 Ti 45 Zr 38 Ni 17 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.

In the present study, we have investigated the effect of vanadium and its compounds (V, V 2 O 5 and VCl 3 ) on desorption characteristics of 1:2 magnesium amide (Mg(NH 2 ) 2 ) and lithium hydride (LiH) mixture. The hydrogen storage characteristics of 1:2 Mg(NH 2 ) 2 /LiH mixture gets enhanced with admixing of V, V 2 O 5 and VCl 3 separately. The VCl 3 has been found to be the most effective followed by V and V 2 O 5 . The activation energy for dehydrogenation process of 1:2 Mg(NH 2 ) 2 /LiH mixture with and without catalyst has been evaluated using a method suggested by Ozawa et al. [25] . Based on the experimental results, schematic reaction scheme for decomposition of Mg(NH 2 ) 2 in the presence of VCl 3 has also been proposed.

The main objective of the proposed work is to investigate the formation of nanoquasicrystalline and related nanocrystalline phases in Al—Cu—Fe system during mechanical milling at the initial stage of milling. The mechanical milling of a quasicrystalline Al65Cu20Fe15 alloy was performed in a high-energy ball mill (Szegvari attritor) by varying milling time from 2.5 min to 60 min under liquid hexane medium at the speed of 400 rpm with a ball to powder ratio of 40 : 1. X-ray diffraction was carried out for evaluating the lattice strain, lattice parameters and crystallite sizes of the milled sample. It was found that the evolution of monoclinic Al13Fe4 phase from Al65Cu20Fe15 quasicrystalline phase occurred after 2.5 min of milling, which was further confirmed by transmission electron microscopy. After 5 min of ball milling nano size disordered B2 phase (bcc, a = 0.29 nm) was also found. The systematic analysis of the XRD patterns for evolving lattice parameter, sequential strain suggests that the lattice strain during milling has been quite considerable.

We 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(NH2)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.

This paper reports mischmetal (Mm) as an effective catalyst for fast desorption kinetics (3.7 wt% in 60 min in which ∼3.3 wt% observed in 30 min and ∼5 wt% in 180 min at the desorption temperature of 150 °C for the 2 mol% Mm-doped material) and rehydrogenation (up to 35 cycles) of the light weight hydrogen storage material NaAlH 4 . In fact this catalyst Mm has been shown to be better than the presently known catalyst Ti. For Mm, its presence when admixed in NaAlH 4 is discernible. Also the higher reversible hydrogen storage capacity (4.77 wt% which is 86% of the total reversible storage capacity) of the total is achievable in the 12th cycle. The possible modes of catalyst Mm for fast desorption kinetics has been outlined and the most feasible mechanism in terms of weakening of Na and AlH 4 bonding has been put forward.

In the present investigation, the decagonal phase in Al70Ni24Fe6 alloy was used for studying the structural and microstructural stability during ball milling in an attritor mill for 1, 2, 4, 8, and 12 h under hexane medium with a powder to ball ratio of 1:100. The milled powder was annealed in an argon atmosphere for durations ranging from 1 to 40 h at 500°C. The as-cast alloy was found to consist of micron size decagonal phase as a major one along with minor amount of Al3Ni and Al13(Fe,Ni)4 crystalline phases. Powders milled for more than 8h contained predominantly the B2 phase. The crystallite size of the B2 phase was estimated to be around 17 nm after 12 h of milling. A lamellar like microstructure exhibiting the presence of nano-phase embedded in the grain of B2 phase has been found to evolve after 8 h of ball milling. Subsequent annealing treatment at 500°C for 10, 20 and 40 h of mechanically milled powder for 12 h has led to the transformation of B2 phase to the τ3 type vacancy ordered phase. The im...

The alloy with composition Al70Co15Ni15 forms one of the important quasicrystalline phase exhibiting formation of decagonal variants [1, 2]. In the present investigation, copper has been substituted in place of cobalt i.e. the phases corresponding to Al70Co15– x Cu x Ni15, have been investigated. It is found that when copper concentration reaches to a value of 10 atomic percent with the composition corresponding to Al70Co5Cu10Ni15, the decagonal phase starts yielding to give rise to vacancy ordered phase. When all cobalt is replaced by copper i.e. when the composition corresponds to Al70Cu15Ni15, the decagonal phase disappears and the only phase observed is the vacancy ordered phase. It can thus be said that copper substitution brings in decagonal to vacancy ordered (VOP) phase transition. It has also been observed that gradual increase in concentration of Cu in Al70Co15– x Cu x Ni15 leads to cellular to dendritic transition in morphology.

The Ti–Zr–Ni forms one of the interesting systems of quasicrystals and related structures. It is the only system in Ti-based quasicrystalline phases which belongs to Bergman class and at the same time gives rise to a stable quasicrystalline structure. We report the formation of nanoquasicrystalline phase directly from melt spinning of molten Ti 53 Zr 27 Ni 20 alloy. Such a phase has been obtained at an optimum copper wheel speed (40 m/s) and jet pressure of 90 atm. We have also measured the mechanical response of this material by the microhardness technique. It shows much better ductility, strength and fracture toughness than the usual alloy having micron-sized quasicrystalline phase. Even at higher load (200 g) no crack seems to appear. We do observe shear bands suggesting the better toughness of bulk material containing nanoquasicrystalline/nanocrystalline phase.

Hydrogen is a promising alternative energy vector, but its use at an appropriate site requires storage, which is a crucial aspect. Hydrogen storage (HS) in the form of metal hydrides represents an attractive possibility, and is being investigated worldwide. La(Ni0.95Fe0.05)5 (LNF) has achieved significant attention as a HS media due to its suitable thermodynamics. However, its use as an effective storage material is hindered due to burning of hydrogenated LNF (LNFH) on exposure to air. The pristine LNFH catches fire rapidly on exposure to atmosphere. Here, a breakthrough strategy is demonstrated for design of hydrogenated air-stabilized hybrid material by encapsulating LNF inside reduced graphene oxide-ethyl cellulose. This novel hybrid material does not ignite upon exposure to air. This proposed hybrid material could be the ultimate choice for air-stable and safe storage for fuel cell/internal combustion engine-based vehicles. Further, the effectiveness of this hydrogen storage material is demonstrated for fuel cells.