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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, ZrFe 2 H x intermetallic hydride, is used to synthesize MgH 2 –ZrFe 2 H x nanocomposite by reactive mechanical milling technique. Also this report describes the comparison of hydrogen sorption behavior of MgH 2 –ZrFe 2 and MgH 2 –ZrFe 2 H x nanocomposites. It is found that the composite containing ZrFe 2 and ZrFe 2 H x leads to decrease in desorption temperature from 410 °C (for MgH 2 ) 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 MgH 2 (92 kJ/mol). Thus, the results show significant improvement of hydrogenation behavior with the addition of ZrFe 2 H x . Reasons for better catalytic activity achieved by using ZrFe 2 H x 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 MgH 2 has a distinct advantage in improving the hydrogenation behavior of MgH 2 . [ABSTRACT FROM AUTHOR]

Abstract: The present study deals with the microstructural changes with respect to the addition of Ti and their correlation with hydrogen storage characteristics of (Zr69.5Al7.5Cu12Ni11)100− x Ti x (x =0, 4 and 12) quasicrystalline alloys. The grain size of quasicrystals decreases with addition of Ti. It has been found that the alloy with x =0 absorbed 1.20 wt. %, whereas the alloys with x =4 and 12 absorbed 1.38 wt. % and 1.56 wt. % of hydrogen respectively. Hydrogenation was found to exhibit a significant effect on the structure/microstructure and microhardness behavior of (Zr69.5Al7.5Cu12Ni11)100− x Ti x quasicrystalline alloys. Variation in the microhardness behavior has been discussed based on a structure–property correlation. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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 MgH2. Mechanical milling of MgH2 with 5 wt% each of Ti, Fe and Ni for 24 h at 12 atm of H2 pressure lead to the formation of nano MgH2-Ti5Fe5Ni5. The decomposition temperature of nano MgH2-Ti5Fe5Ni5 is lowered by 90 °C as compared to nano MgH2 alone. It is also found that the nano MgH2-Ti5Fe5Ni5 absorbs 5.3 wt% within 15 min at 270 °C and 12 atm hydrogen pressures. However, nano MgH2 reabsorbs only 4.2 wt% under identical condition. An interesting result of the present study is that mechanical milling of MgH2 separately with Fe and Ni besides refinement in particle size also leads to the formation of alloys Mg2NiH4 and Mg2FeH6 respectively. On the other hand, when MgH2 is mechanically milled together with Ti, Fe and Ni, the dominant result is the formation of nano particles of MgH2. Moreover the activation energy for dehydrogenation of nano MgH2 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 MgH2 (81.34 kJ/mol). These results are one of the most significant in regard to improvement in de/rehydrogenation characteristics of known MgH2 catalyzed through transition metal elements. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: In this paper, we describe and discuss the synthesis, structural-microstructural and hydrogen storage behaviour of three AB2 type storage materials namely (a) ZrFe2, (b) Zr(Fe0.75V0.25)2 and (c) Zr(Fe0.5V0.5)2. These alloys were synthesied by radio frequency induction melting in argon atmosphere. X-ray diffraction and transmission electron microscope have been employed for structural and microstructural characterizations. The XRD study reveals that the lattice constants and the unit cell volume of ZrFe2, Zr (Fe0.75V0.25)2, Zr(Fe0.5V0.5)2 alloys, which has C14 type hexagonal Laves phase. The Surface morphology and elemental composition of these alloys were investigated by scanning electron microscope and energy dispersive X-ray analysis. The pressure composition isotherms of these alloys were investigated at room temperature and pressure ranges of 0–100 atm respectively, measured through a fully computerized PCI apparatus. As we increase the concentration of V (substituted for Fe), the total hydrogen storage capacities increased up to 1.45 wt%. This capacity is achieved in Zr(Fe0.5V0.5)2 alloy, while the reversible hydrogen storage capacity decreases due to the formation of a stable hydride phase. It has been found that the lattice constants increase with higher vanadium concentration. This is indicating that the majority of vanadium atoms reside in the B-site. The broader X-ray diffraction peaks observed in Zr(Fe0.5V0.5)2 alloy indicates a higher degree of disorder for alloys with the higher V-content. The yet another interesting feature observed in our present study is that the plateau pressure remains well below 1 atm for all the compositions. [Copyright &y& Elsevier]

In the present investigation, the formation and stability of icosahedral phase in Al70-xGaxPd17Mn13 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 Å, b = 16.6 Å and c = 12.4 Å) 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. However, for x = 20, only a hexagonal Al3Pd2 phase results. [ABSTRACT FROM AUTHOR]

Abstract: The 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. [Copyright &y& Elsevier]

Abstract: In the present study, we have investigated the effect of vanadium and its compounds (V, V2O5 and VCl3) on desorption characteristics of 1:2 magnesium amide (Mg(NH2)2) and lithium hydride (LiH) mixture. The hydrogen storage characteristics of 1:2 Mg(NH2)2/LiH mixture gets enhanced with admixing of V, V2O5 and VCl3 separately. The VCl3 has been found to be the most effective followed by V and V2O5. The activation energy for dehydrogenation process of 1:2 Mg(NH2)2/LiH mixture with and without catalyst has been evaluated using a method suggested by Ozawa et al. . Based on the experimental results, schematic reaction scheme for decomposition of Mg(NH2)2 in the presence of VCl3 has also been proposed. [Copyright &y& Elsevier]

Abstract: We have investigated the ball-milling (5–45h) 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 15h. The desorption kinetics has been found to improve appreciably by increasing the duration of milling from 5 to 45h. 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. [Copyright &y& Elsevier]