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It is known that the reaction path for the decomposition of LiBH 4:MgH2 systems is dependent on whether decomposition is performed under vacuum or under a hydrogen pressure (typically 1-5 bar). However, the sensitivity of this multicomponent hydride system to partial pressures of H2 has not been investigated previously. A combination of in situ powder neutron and X-ray diffraction (deuterides were used for the neutron experiments) have shed light on the effect of low partial pressures of hydrogen on the decomposition of these materials. Different partial pressures have been achieved through the use of different vacuum systems. It was found that all the samples decomposed to form Li-Mg alloys regardless of the vacuum system used or sample stoichiometry of the multicomponent system. However, upon cooling the reaction products, the alloys showed phase instability in all but the highest efficiency pumps (i.e., lowest base pressures), with the alloys reacting to form LiH and Mg. This work has significant impact on the investigation of Li-containing multicomponent systems and the reproducibility of results if different dynamic vacuum conditions are used, as this affects the apparent amount of hydrogen evolved (as determined by ex situ experiments). These results have also helped to explain differences in the reported reversibility of the systems, with Li-rich samples forming a passivating hydride layer, hindering further hydrogenation.

To prepare nanosized magnesium which reversibly absorbs hydrogen with high capacity even under mild conditions, high energy ball-milling of Mg or MgH 2 with benzene or cyclohexane as additives have been studied. In ball-milling of Mg or MgH2, the use of the organic additives is very crucial in determining the characteristics of the resulting nanosized magnesium. Benzene and cyclohexane served to maintain the high-degree dispersion of nanostructured magnesium with small crystallite sizes (9-10 nm) and high surface areas (24-25 m2 g-1). The behavior of hydrogen absorption by the magnesium was extensively evaluated by differential scanning calorimetry (DSC) measurements and volumetric techniques. The nanosized magnesium prepared by ball-milling of MgH2 with benzene showed reversible DSC traces for hydriding/dehydriding under 0.1 MPa hydrogen pressure. Moreover, 1 at.% Al-doped or 2.9at.% Ni-doped nanosized samples obtained by milling of MgH2 with solutions of Al(C2H5) 3 or Ni(C5H5)2 in benzene showed satisfying hydrogen absorption rates, respectively. The reversible hydrogen absorption by the 1 at.% Al-doped sample approximately reached a maximal capacity of 7.3 wt.% even at a 0.1 MPa H2 atmosphere.

Remarkable formation of one-dimensional single crystalline MgH2 structures in the nano- and micro-meters ranges is reported. These structures have been tailored by hydrogen absorption and subsequent disproportionation of bulk Mg24Y5. The MgH2 whiskers have been structurally and morphologically characterized by X-rays diffraction, scanning and transmission electron microcopies. A growth model is proposed for the early stage of the whiskers formation by combining surface chemical and morphological investigations. The formation of MgH2 whiskers opens new engineering explorations and challenges for further experimental and theoretical studies.

Metal borohydrides are a fascinating and continuously expanding class of materials, showing promising applications within many different fields of research. This study presents 17 derivatives of the hydrogen-rich ammonium borohydride, NH4BH4, which all exhibit high gravimetric hydrogen densities (>9.2 wt % of H2). A detailed insight into the crystal structures combining X-ray diffraction and density functional theory calculations exposes an intriguing structural variety ranging from three-dimensional (3D) frameworks, 2D-layered, and 1D-chainlike structures to structures built from isolated complex anions, in all cases containing NH4+ countercations. Dihydrogen interactions between complex NH4+ and BH4- ions contribute to the structural diversity and flexibility, while inducing an inherent instability facilitating hydrogen release. The thermal stability of the ammonium metal borohydrides, as a function of a range of structural properties, is analyzed in detail. The Pauling electronegativity of the metal, the structural dimensionality, the dihydrogen bond length, the relative amount of NH4+ to BH4-, and the nearest coordination sphere of NH4+ are among the most important factors. Hydrogen release usually occurs in three steps, involving new intermediate compounds, observed as crystalline, polymeric, and amorphous materials. This research provides new opportunities for the design and tailoring of novel functional materials with interesting properties.

In a previous publication we reported the evaluation of the organometallic aluminum electrolytes for electroforming applications. The electroformed deposits were of high purity and therefore exhibited a relatively low ultimate tensile strength of 65.5 MPa

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The decomposition and oxidation behavior of magnesium diboride (MgB 2) have been studied using thermogravimetry (TG), XRD and SEM-EDS. The reactions were carried out by heating MgB2powder in a stream of argon or air at atmospheric pressure. In the temperature range explored (298-1673 K), four successive steps were observed in the decomposition process of MgB2. The rate-limiting steps of the decomposition process were found to be associated with the nucleation or formation of boron-rich phases. The oxidation process of MgB2comprised five successive phases in the temperature range explored (298-1673 K). There was close relationship between the decomposition and oxidation behavior of MgB2. Experimental results showed that the decomposition reactions occurred during the oxidation process. The acceleration shown in the weight gain curve can be ascribed to the rapid oxidation of Mg vapor released from the decomposition reactions. The microstructure and composition of the oxide scale formed in the oxidation process were investigated using XRD and SEM-EDS. The oxide layer structure was identified based on the experimental results in this study.

In situ observation on dehydrogenation of MgH2 was performed by using transmission electron microscope (TEM). The dehydrogenation of MgH 2 with 1 mol % Nb2 O5 and formation of nanosized Mg particles were observe

Mg3Sb2 has been prepared by direct reaction of the elements. Powder X-ray diffraction, thermal gravimetric, differential scanning calorimetery, and microprobe data were obtained on hot pressed samples. Single phase samples of Mg

The structure of κ-Ag2Mg5 has been refined based on X-ray powder diffraction measurements (Rwp = 0.083). The compound has been prepared by combining mechanical alloying techniques and thermal treatments. The intermetallic presents the prototypical structure of Co2Al5, an hexagonal crystal with the symmetries of space group P63/mmc, and belongs to the family of kappa-phase structure compounds. The unit cell dimensions are a=8.630(1) ? and c=8.914(1) ?. Five crystallographically independent sites are occupied, Wyckoff positions 12k, 6h and 2a are filled with Mg, another 6h site is occupied with Ag, and the 2c site presents mixed Ag/Mg occupancy. The crystal chemistry of the structure and bonding are briefly discussed in the paper.

Nanosizing is known to affect the hydrogenation properties of magnesium. For this reason, the long period stacking ordered (LPSO) structures, made of the stacking of nanolayers of magnesium and nanolayers of Mg-A-B (with A = rare earth and B = transition metal), were herein considered. A Mg83.3Cu7.2Y9.5 LPSO compound with 18R structure was successfully synthesized. Its hydrogenation properties were investigated at temperatures between 150 and 400 °C. The X-ray diffraction (XRD) analysis indicates that the LPSO structure decomposes into magnesium hydride, yttrium hydride, and an intermetallic compound (Mg2Cu or MgCu2). The pressure composition (PC) isotherm for Mg83.3Cu7.2Y9.5 at 400 °C combined with XRD analysis allows one to understand the three-step hydrogenation pathway, detailed in this paper. At this hydrogenation temperature, the fully hydrogenated compound contains magnesium hydride exclusively crystallized in the most stable tetragonal structure (100% of α-MgH2 was formed). When the pristine LPSO was hydrogenated at lower temperature, the amount of α-MgH2 decreased, while its polymorphic structure, γ-MgH2, appeared. Finally, hydrogenation of Mg83.3Cu7.2Y9.5 at 150 °C led to the formation of γ-MgH2 with a high phase fraction (82% of γ-MgH2/MgH2). These results suggest that the crystallographic structure of the magnesium hydride can be controlled by the hydrogenation temperature of LPSO compounds.

Mg nanocrystals of controllable sizes were prepared in gram quantities by chemical reduction of magnesocene using a reducing solution of potassium with an aromatic hydrocarbon (either biphenyl, phenanthrene, or naphthalene). The hydrogen sorption kinetics were shown to be dramatically faster for nanocrystals with smaller diameters, although the activation energies calculated for hydrogen absorption (115-122 kJ/mol) and desorption (126-160 kJ/mol) were within previously measured values for bulk Mg. This large rate enhancement cannot be explained by the decrease in particle size alone but is likely due to an increase in the defect density present in smaller nanocrystals.

Three new ternary metal hydrides of composition Eu2MgH6, Eu6Mg7H26 and Eu2Mg3H10 have been synthesised from mixtures of the binary hydrides in a multi-anvil press at quasi-hydrostatic pressures of up to 3.2 GPa and temperatures of up to 870 K. Crystal structures of the deuterides were determined by joint refinements of neutron and synchrotron powder diffraction data. All structures have alkaline earth and fluorine analogues. Eu2MgD6, K2GeF6 type structure, space group P3?m1, a=550.644(6) pm, c=410.054(6) pm; Eu6Mg7D26, Ba6Zn7F26 type structure, I2/m, a=1409.39(4) pm, b=564.55(2) pm, c=1150.90(3) pm, β=90.683(2)°; Eu2Mg3D10, Ba2Ni3F10 type structure, C2/m, a=1748.41(5) pm, b=572.31(2) pm, c=736.47(2) pm, β=111.478(2)°. The coloured compounds are saline and show volume contractions of up to 7.3% upon formation from the binary hydrides. Eu2MgH6 shows Curie-Weiss paramagnetic behaviour (μeff=7.88 μB) and orders ferromagnetic at TC=31.6 K.

Among the large variety of possible complex hydrides only few exhibit a large gravimetric hydrogen density and stability around 40 kJ mol-1H2. Mg[BH4]2 is based on theoretical approaches a complex hydride with an equilibrium hydrogen pressure of approximately 1 bar at room temperature and a hydrogen content of 14.9 mass%. The reaction of Li[BH4] with MgCl2 at elevated temperatures was investigated as a possible route to synthesize Mg[BH4]2. Li[BH4] reacts with MgCl2 at a temperature >523 K at a pressure of 10 MPa of hydrogen, where the product contains LiCl and Mg[BH4]2. The desorption pc-isotherm of the product obtained at 623 K shows two flat plateaus, which indicates that the decomposition of the product consists of a two-step reaction. The products of the first and the second decomposition reaction were analyzed by means of X-ray diffraction and found to be MgH2 and Mg, respectively. The enthalpy for the first decomposition reaction was determined to be ΔH = -39.3 kJ mol-1H2 by the Van't Hoff plot of the equilibrium measurements between 563 K and 623 K, which is significantly lower than that for pure Li[BH4] (ΔH = -74.9 kJ mol-1H2). However, only the second reaction step (MgH2 → Mg) is reversible at the condition up to 623 K at 10 MPa of hydrogen.

Nanocrystalline Mg powder without and with 2 mol% Nb2O5 catalyst was studied as an electrode material for electrochemical hydrogen charging in a 6 M KOH electrolyte. A strong influence of the compaction parameters, the current density and the catalyst on the hydrogenation behavior was observed. The addition of graphite and PTFE to the Mg/Nb2O5 electrodes improves the charging kinetics as well as the hydrogen content. The hydrogen contents achieved in Mg with Nb2O5, however, show a broad scatter. It was concluded that the catalyst distribution influences the upper limit of the storage capacity as well as the oxidation process at the surface during preparation. Since the addition of Nb2O5 was observed to reduce the hydrogen overpotential of Mg depending on the catalyst distribution, it is assumed that the catalyst influences the electrode reactions. Therefore, hydrogenation was investigated for different Nb2O5 distributions at different current densities in detail.

The hydride Mg2FeH6 was synthesized by high-energy ball milling of MgH2 and Fe under argon atmosphere without subsequent sintering. After 60 h of milling, 56% wt. of Mg2FeH6 was synthesized. This yiel

The authors propose an energy cycle based on a renewable fuel. Magnesium is chosen as an energy carrier and is combusted with water to retrieve energy using many power devices. MgO, the combustion residue, is reduced back to Mg by laser radiation generated from solar and other renewable energy sources. They have achieved an energy recovery efficiency of 42.5% for converting MgO to magnesium, using a laser. Combined with a demonstrated 38% efficiency for converting an artificial sunlight source (metal halide lamp) into laser output energy indicates that the proposed energy cycle is already in a feasible range for practical use.

Self-sintered ex-situ MgB2polycrystalline bulks have experienced a two-step sintering process, initially at 900?°C for 0–20?min and then at 650?°C for 1?h. MgB2was decomposed to MgB4and Mg at 900?°C and composed again at 650?°C from MgB4and Mg. The reversible reaction promotes the material migration, and thus eliminates pores and enhances the connectivity between the grains. The critical current density (Jc) is significantly improved due to both improved grain connectivity and the additive pinning centers such as MgB4and new-born boundaries. This two-step sintering process can be a promising method to fabricate high-performance ex-situ MgB2bulks and wires.

During our research on alkali-fluorides, the compound NaSrMg2F7 has been prepared by a precipitation reaction of Sr2+, Mg2+ and Na+ with F- for the first time. The powder crystallizes as a single phase in the form of spherical agglomerates ～0.25 μm in diameter. The compound crystallizes in the space group Fd3m (Nr. 227) with lattice parameter a = 10.4379(4) A?. Structural analysis by the Rietveld method was done from X-ray diffraction data. In agreement with the structure analysis, spectroscopical investigations confirm the presence of two coupled fluoride ions. The crystal structure corresponds to the pyrochlore structure type A2B2X7 with 50% occupation of Sr2+ or Na+ at the A site. WILEY-VCH Verlag GmbH, 2001.

The hydrogen desorption properties of Mg-rich alloys are significantly improved by nanostructure formation. This effect is examined for a melt-spun and nanocrystallized Mg-Ni-La alloy by pressure-composition isotherm (PCT) and thermal desorption spectrum (TDS) measurements. This alloy exhibits fast desorption kinetics and favorable PCT characteristics with an H-capacity of ～4.6 wt%. TDS measurements reveal a definite peak ascribable to release of hydrogen from nanoboundaries, in addition to those associated with decompositions of hydrides such as MgH2, Mg2NiH4 and LaH3. Hydrogen transport along the nanoboundaries appears to facilitate the desorption kinetics in this alloy.

Highly reactive magnesium powder of nanometric size, which was generated by the thermal decomposition of magnesium anthracene·3THF under vacuum, can react with N2 under atmospheric pressure, even at 300°C, to form magnesium nitride. The rate and extent of the reaction can be improved effectively by doping the magnesium powder with a small amount of nickel or titanium compounds.

The hydrogenation properties of Laves phases LnMg2 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb) were investigated by thermal analysis, X-ray, synchrotron, and neutron powder diffraction. At 14.0 MPa hydrogen gas pressure and 393 K, PrMg2 and NdMg2 take up hydrogen and form the colorless, ternary hydrides PrMg2H7 (P41212, a = 632.386(6) pm, c = 945.722(11) pm) and NdMg2H7 (P41212, a = 630.354(9) pm, c = 943.018(16) pm). The crystal structures were refined by the Rietveld method from neutron powder diffraction data on the deuterides (PrMg2D7, P41212, a = 630.56(2) pm, c = 943.27(3) pm; NdMg2D7, P41212, a = 628.15(2) pm, c = 940.32(3) pm) and shown to be isotypic to LaMg2D7. The LaMg2D7 type of hydrides decompose at 695 K (La), 684 K (Ce), 684 K (Pr), 672 K (Nd), and 639 K (Sm) to lanthanide hydrides and magnesium. The Laves phase EuMg2 forms a hydride EuMg2Hx of black color. Its crystal structure (P212121, a = 664.887(4) pm, b = 1136.993(7) pm, c = 1069.887(7) pm) is closely related to the hexagonal Laves phase (MgZn2 type) of the hydrogen-free parent intermetallic. GdMg2 and TbMg2 form hydrides GdMg2Hx with orthorhombic unit cells (a = 1282.7(4) pm, b = 572.5(2) pm, c = 881.7(2) pm) and TbMg2Hx (a = 617.8(3) pm, b = 1045.8(8) pm, c = 997.1(5) pm), presumably also with a distorted MgZn2 type of structure. CeMg2H7 and NdMg2H7 are paramagnetic with effective magnetic moments of 2.49(1) μB and 3.62(1) μB, respectively, in good agreement with the calculated magnetic moments of the free trivalent rare-earth cations (μcalc(Ce3+) = 2.54 μB; μcalc(Nd3+) = 3.62 μB).

MgH2 and Ti were milled by means of ball milling and Mg-Ti-H hydride phases with a face centered cubic (FCC) structure were successfully synthesized. The Mg-Ti-H FCC hydride phases synthesized had chemical formulae of Mg40Ti60/

The reaction of hydrogen gas with magnesium metal, which is important for hydrogen storage purposes, is enhanced significantly by the addition of catalysts such as Nb and V and by using nanostructured powders. In situ neutron diffraction on MgNb0.05 and MgV0.05 powders give a detailed insight on the magnesium and catalyst phases that exist during the various stages of hydrogen cycling. During the early stage of hydriding (and deuteriding), a MgH1 phase is observed, which does not occur in bulk MgH2 and, thus, appears characteristic for the small particles. The abundant H vacancies will cause this phase to have a much larger hydrogen diffusion coefficient, partly explaining the enhanced kinetics of nanostructured magnesium. It is shown that under relevant experimental conditions, the niobium catalyst is present as NbH1. Second, a hitherto unknown Mg-Nb perovskite phase could be identified that has to result from mechanical alloying of Nb and the MgO layer of the particles. Vanadium is not visible in the diffraction patterns, but electron micrographs show that the V particle size becomes very small, 2-20 nm. Nanostructuring and catalyzing the Mg enhance the adsorption speed that much that now temperature variations effectively limit the absorption speed and not, as for bulk, the slow kinetics through bulk MgH2 layers.

To improve the hydrogen absorption properties of Mg2Ni, three kinds of specimens were prepared. They were denoted as MGNIY, DeMg-MGNIY and DeMg-MIX. The first one was a cast Mg-Ni-Y alloy, the second was prepared by vacuum heating of MGNIY to remove some part of Mg and the third was prepared by vacuum heating of a mixture of pulverized Mg-Y and Mg2Ni. The term DeMg denotes removal of Mg by vacuum heating. These samples were characterized by XRD, SEM and EPMA and found to be composed of Mg, Mg2Ni and crystallographically unknown phases. Each material was found to have its own distribution of yttrium. The composition of the crystallographically unknown phase was determined by EPMA to be MgYNi3. Yttrium-alloying and subsequent DeMg treatment caused a significant improvement in the hydrogen absorption rate. It showed hydrogen uptake amounting to about 3 mass% for DeMg-MGNIY at 473 K in 80 ks, although the improvement at room temperature could not be distinguished from that of Mg2Ni. MGNIY gave similar absorption properties with those of DeMg-MGNIY at 473 K, but showed significantly slower absorption rate than Mg2Ni at room temperature. The properties of DeMg-MIX were found to be similar to those of Mg2Ni at both temperatures. On account of the sample characterization, it was concluded that the improvement in hydrogen uptake by DeMg-MGNIY and MGNIY at 473 K was due to their specific yttrium-distribution and catalytic activity.

Nanocrystalline Mg powder without and with 2 mol% Nb2O 5 catalyst was studied in a 6 M KOH electrolyte as electrode material for electrochemical hydrogen charging processes. Since the hydrogen overpotential of Mg, which is a measure of the hydrogen evolution at the electrode surface, was observed to be reduced by the addition of Nb 2O5, it is assumed that the catalyst influences the electrode reactions. Considering this assumption hydrogenation was studied at different current densities. The storage capacity as well as the kinetic of Mg/Nb2O5 electrodes increased significantly up to 1 wt.% H2 at a charging time of 30 min with decreasing current density. The storage capacity of nanocrystalline Mg powder showed only minor changes to lower hydrogen contents with decreasing current density.

A fine-grained AZ91 alloy was prepared by equal channel angular pressing (ECAP). The evolution of the microstructure and the deformation behavior were investigated as a function of the number of ECAP passes. At room temperature the tensile strength of the ECA pressed specimens is higher than that of the initial state due to the grain refinement and the increase of the dislocation density during ECAP. Above 200 °C the ductility increases due to the increase of the relative fraction of c + a dislocations and also owing to the breakage of the rod-like Al12Mg17 precipitates during ECAP processing.

Reduction kinetics of magnesia with carbon and transition metal was investigated by thermogravimetry from room temperature to 1973 K. Cu, Co and Ni accelerates the reduction rate. Fe accelerates the reduction rate and decreases the initial reaction temper

The gaseous MgH2 molecule was discovered in an electrical discharge inside a furnace. The vibration-rotation emission spectrum of MgH 2 was recorded with a Fourier transform spectrometer. Three hot bands were found and rotationally analyzed. The MgH2 molecule was found to have a linear structure.

The intermetallic Mg2Sn is a promising negative electrode material for rechargeable lithium cells. Preliminary cycling tests have demonstrated stable capacities at 400 mAh/g for 20 cycles. Magnesium stannide was produced by mechanically alloying magnesium and tin powders. Mechanical alloying can convert the equilibrium Mg2Sn phase to a metastable phase by the introduction of defects with extended milling times. In situ X-ray diffraction has shown that the cubic Li2MgSn phase, which is similar in size and structure to cubic Mg2Sn, is produced by lithium insertion into the equilibrium and metastable phases. The conversion from the metastable phase is irreversible, so subsequent lithium removal from Li2MgSn produces the equilibrium Mg2Sn phase.

Destabilization of LiBH4 for reversible hydrogen storage has been studied using MgH2 as a destabilizing additive. Mechanically milled mixtures of LiBH4 + 1/2MgH2 or LiH + 1/2MgB 2 including 2-3 mol % TiCl3 are shown to reversibly store 8-10 wt % hydrogen. Variation of the equilibrium pressure obtained from isotherms measured at 315-400?°C indicate that addition of MgH2 lowers the hydrogenation/dehydrogenation enthalpy by 25 kJ/(mol of H 2) compared with pure LiBH4. Formation of MgB2 upon dehydrogenation stabilizes the dehydrogenated state and, thereby, destabilizes the LiBH4. Extrapolation of the isotherm data yields a predicted equilibrium pressure of 1 bar at approximately 225?°C. However, the kinetics were too slow for direct measurements at these temperatures. ? 2005 American Chemical Society.

Photolysis at the 3p1P 1S resonance transition of magnesium atoms isolated in hydrogen-containing rare gas matrices is found to give rise to the first observed example of a group 2 metal atom dihydride, magnesium dihydride (MgH2), with no evidence for the fragmented products, MgH + H.Isotopic substitution studies in the infrared indicate that the molecule is linear as predicted by simple Walsh type MO diagrams and ab initio calculations.This is in contrast with gas-phase studies, where only fragments are observed.Possible reasons for the differing reaction behavior (i.e. in the matrix and gas phase) are discussed in terms of the matrix cage effect and differences between the vibrational relaxation rates in the condensed phase and those in the gas phase.Similar photochemical behavior is exhibited by magnesium atoms in neat methane matrices, where the linear inserted product, methyl magnesium hydride (CH3MgH), is formed as shown by infrared isotopic substitution experiments.No electronic absorptions were observed for either products in the range 230-800 nm.Emission is observed during magnesium atom photolysis in xenon and methane matrices.The bands present in the former matrix are assigned to singlet (3p1P -> 3s1S) and triplet (3p3P -> 3s1S) atomic magnesium emission, while the possible origins of the long-lived visible emission in the latter matrix are proposed.The presence of hydrogen in a xenon matrix (1:10 H2:RG) causes a decrease in the emission intensity relative to a neat xenon matrix but adds no additional features.The observation of only linear inserted products (MgH2 and CH3MgH) is interpreted in the context of a concerted insertion mechanism with no detectable contribution from an abstraction pathway.

MgB2 can be synthesized through a new route using Mg 2Cu instead of pure Mg. When the temperature is elevated to around the melting point of Mg2Cu (568 °C), the Tc for Mg2Cu/B Fe-sheathed wires increases rapidly to about 37.5 K. Mg 2Cu with its low melting point promotes the diffusion reaction to form a high Tc MgB2 at low temperatures. A lot of second phases forms with small amounts of MgB2 in the core of the wires. However, the transport Jc value, which is greater than 105 A/cm2 at 4.2 K in ambient fields, is rather high. Since the J c value is estimated from a net-cross-sectional area of MgB 2 it is expectedly high. Moreover, Mg2 Cu/B/metal-substrate layered composites were also prepared in this study. After a heat treatment at 600 °C for 10 h in a vacuum, a 50 μm thick MgB 2 diffusion layer forms with a high-density microstructure. Cu is released from Mg2Cu, and collects on the surface of the diffusion layer. This behavior of Cu is similar to that of the bronzed process used for Nb3 Sn practical conductors.

A nanocrystalline magnesium material with a high specific surface area is expected to react rapidly and reversibly with hydrogen gas to yield magnesium hydride, a hydrogen storage medium. In this paper, the feasibility of the synthesis of magnesium materials for hydrogen storage applications by pulse electrodeposition of magnesium from ethereal electrolytes containing Grignard reagents was investigated. Deposition onto flat stainless steel electrodes established that, as in dc deposition, the morphology of the deposits varied widely with electrolyte composition and charge density. Irregular, nanocrystalline magnesium films were formed at low current density (0.4 mA cm-2) and low charge density (1 C cm-2) using butylmagnesium chloride electrolytes in dibutyl diglyme, while at a higher current density (15 mA cm-2) in tetrahydrofuran, dense films were favored.

The effect of Nb2O5 concentration on the kinetics of the magnesium hydrogen sorption reaction at 300°C and 250°C is investigated. Absorption and desorption kinetics of nanocrystalline magnesium catalyzed with 0.05, 0.1, 0.2, 0.5, and 1 mole% Nb2O5 are determined at 300 and 250°C. Fastest kinetics are obtained using 0.5 mole% Nb2O5. At 300°C, absorption and desorption of 7 wt.% of hydrogen are facilitated in 60 and 90 s, respectively. At 250°C, more than 6 wt.% are absorbed in 60 s and desorbed again in 500 s. Respective reaction rates and activation enthalpies are calculated. The activation energy for desorption varies exponentially with Nb2O5 concentration and reaches a limit of 61 kJ/mole at 1 mole%. The rate-limiting step for a particular parameter set is deduced by fitting the experimentally obtained transformed phase fraction and time data with analytical kinetics rate expressions. The results show that there is a change in the rate-limiting step with catalyst content.

Powder mixtures with a nominal composition Mg-5 wt%Ni-2 wt%Nb2O5 are used to produce ultrafine-grained bulk material by high-pressure torsion (HPT) processing. Samples subjected to 10 and 20 revolutions in torsion under a pressure of 3 GPa developed an ultrafine grain size, mainly in the 100?200 nm range. The hydrogenation properties of these HPT-processed materials have been characterized at temperatures in the interval of 373–723 K. The hydrogenation experiments clearly show faster kinetics of hydrogenation and higher storage capacities in the HPT materials compared to the initial mild-milled powder mixture. The storage capacities have been limited to about 5.5 wt% H2 by the formation of a substantial amount of MgO in the materials after several hydrogenation cycles. However, as a matter of practical relevance, the production of bulk pieces of the Mg-Ni-Nb2O5 alloy having an ultrafine grain structure allows handling of the material without special precautions against ignition, as well as its storage in contact with air for several months with no evident deterioration of its fast activation in posterior hydrogenation treatments.

Hydrogen generation via hydrolysis can provide fuel cell with the on-site and controllable supply. However, the current hydrolysis materials that exhibit poor performances at low temperatures are not suitable for portable devices and military. In this stu

Magnesium silicide (Mg2Si) is a promising eco-friendly thermoelectric material, which has been extensively studied in recent times. However, its phase behavior at high pressures and temperatures remains unclear. To this end, in this study, in situ X-ray diffraction analysis was conducted at high pressures ranging from 0 to 11.3 GPa and high temperatures ranging from 296 to 1524 K, followed by quenching. The antifluorite-phase Mg2Si decomposed to Mg9Si5 and Mg at pressures above 3 GPa and temperatures above 970 K. The antifluorite-phase Mg2Si underwent a structural phase transition to yield a high-pressure room-temperature (HPRT) phase at pressures above 10.5 GPa and at room temperature. This HPRT phase also decomposed to Mg9Si5 and Mg when heated at ～11 GPa. When 5Mg2Si decomposed to Mg9Si5 and Mg, the volume reduced by ～6%. Mg9Si5 synthesized at high pressures and high temperatures was quenchable under ambient conditions. Thermoelectric property measurements of Mg9Si5 at temperatures ranging from 10 to 390 K revealed that it was a p-type semiconductor having a dimensionless thermoelectric figure of merit (ZT) of 3.4 × 10-4 at 283 K.

A study was carried out on the synthesis of Mg-Ni compounds as well as on the extraction of pure Ni and Mg from their oxides using the method of electro-deoxidation. The oxides sintered at 1200 °C were in the form of discrete phases NiO and MgO, suitably proportioned to yield Ni, MgNi 2, Mg2Ni and Mg. The oxides were electrolyzed at 3.2 V in a eutectic mixture of CaCl2-NaCl solution maintained at a constant temperature (900-600 °C), using a graphite anode. The study has shown that NiO rich mixture, MgO:NiO = 1:2, can be reduced successfully to metallic state. Some loss of Mg was apparent in the latter, with the result that the product was far from the target composition MgNi2. The electroreduction of MgO rich mixtures was difficult to achieve. The mixture MgO:NiO = 2:1 when electrolyzed at 725 °C for 24 h, could be reduced to metallic phases only in small proportions (18 wt.%). In pure MgO, no trace of reduction was observed during the electrolysis at 600 °C. Difficulties in the electroreduction of MgO and MgO rich mixtures were partially attributed to low conductivity of MgO.

Electrodeposition of magnesium from calcium chloride-based melts was studied on metallic (tungsten and molybdenum) and glassy carbon electrodes. Pure CaCl2 melt and different alkali chloride solvents including binary CaCl2-NaCl, equimolar composition, and ternary CaCl 2-NaCl-KCl melts with compositions 35:55:10 mol %, containing different MgCl2 concentrations, were used. In the case of the binary mixture, the operating temperature was both above and below the melting point of metallic magnesium (923 K) so that solid and liquid deposits were obtained. Underpotential deposition of calcium is an important process in melts containing CaCl2 due to formation of Ca-Mg alloys, which affects the magnesium electrodeposition process. Threedimensional magnesium deposits that grow macroscopically on the studied substrates were found. This influences determination of the diffusion coefficient of Mg(II) ions. Formation of a magnesium monolayer on both electrodes, and especially on tungsten, was a stable process in the ternary mixture containing MgCl2, which was related to the presence of 10 mol % KG. Moreover, in this melt a remarkable pseudopassivation process was found at high oyerpotentials.

The high-pressure synthesis of new hydrides of Mg-RE-H systems, where RE = Y, La, Ce, Pr, Sm, Gd, Tb and Dy, were conducted by using a cubic-anvil-type apparatus, and their crystal structure, thermal stabilities and hydrogen contents were investigated. In Mg-Y-H system, newly found MgY2H y with a FCC-type structure has been prepared. In MgH2-x mol% REH (REH = LaH3, CeH2.5 and PrH3), new hydrides with primitive tetragonal structure were synthesized around x = 25-33 under GPa-order high pressures. The lattice constants were a = 0.8193 nm, c = 0.5028 nm, a = 0.8118 nm, c = 0.4979 nm and a = 0.8058 nm, c = 0.4970 nm at x = 25 in Mg-La, Ce and Pr systems, respectively. The hydrogen contents of the novel compounds were 4.1, 3.7 and 3.9 mass% in Mg-La, Ce and Pr systems, respectively, and the chemical formulae were found to correspond to Mg 3LaH9, Mg3CeH8.1 and Mg 3PrH9. The new hydrides decomposed into Mg and rare-earth hydride at about 600 K (Mg3LaH9: 614 K, Mg 3CeH8.1: 609 K, Mg3PrH9: 630 K) with an endothermic reaction. In MgH2-x mol% hREH (hREH = GdH 3, TbH3 and DyH3), new hydrides with FCC-type structure were synthesized around x = 67.

Abstract: The kinetics of the hydrogenation of magnesium composites with graphene-like material (GLM) on which nickel particles are deposited (Ni/GLM) and dehydrogenation of MgH2+Ni/GLM composites is studied. The mechanism of the reactions is revealed using the obtained results and the mathematical processing of curves with the Avrami–Erofeev equation. It is found that Ni/GLM considerably accelerates the hydrogenation of Mg and the decomposition of MgH2 in the composite. The hydrogen-accumulating Mg+Ni/GLM composite is shown to have cyclic stability with rapid and virtually complete reversible hydrogenation.

Magnesium hydride and its complex variants, i.e. Mg(AlH4)2 and Mg(BH4)2 are known for their high hydrogen capacity. The theoretical capacities of these three are 7.6 wt%, 9.3 wt% and 14.4 wt%, respectively. In spite of having very attractive H2 capacities, their high operating temperature, i.e. more than 300 °C and sluggish kinetics are big issues to be solved before these can be realized for a practical hydrogen storage system. There are several efforts devoted to reduce the working temperature and enhance the sorption kinetics using various additives. Ti-based additives have always been interesting contenders in enhancing the kinetics as well as altering thermodynamics thus reducing the working temperature for various hydrides. Recently, TiF4 has shown superior catalytic activity on the decomposition of Mg(AlH4)2. This motivates us to study its effect on the decomposition of all the above-mentioned Mg-based hydrides. It is observed that the addition of 10 wt% TiF4 to the above materials greatly influences the decomposition temperature. The decomposition temperature for all three reactions is shifted to the lower temperature side. The oxidation state of the catalyst surface has been investigated using the XPS technique and then the detailed mechanism associated with this improvement is proposed herein.

The hydrogen storage and hydrogen generation of CaMg2and CaMg1.9Ni0.1alloys were investigated by X-ray diffraction (XRD) and pressure-composition-isotherm (PCI) measurements. The results confirmed that the CaMg2alloy cannot absorb hydrogen at room temperature. While the addition of Ni to the CaMg2-based alloys resulted in room-temperature hydrogen absorption without an activation process, and a maximum hydrogen-absorption capacity of 5.65?wt%. The hydrolysis performance of hydrogenated CaMg2and hydrogenated CaMg1.9Ni0.1(abbreviated as H-CaMg2and H-CaMg1.9Ni0.1hereafter) was also evaluated. The hydrolysis reaction of H-CaMg2occurred rapidly in water and resulted in a hydrogen yield of 800?mL/g. Furthermore, the hydrolysis properties of H-CaMg1.9Ni0.1were significantly enhanced with the addition of Ni, as evidenced by a hydrogen yield of 1053?mL/g in 12?min, this yield is 94.7% of the theoretical hydrogen yield of H-CaMg1.9Ni0.1.

The hydrogen storage performance of a 4MgH2-LiAlH4 composite system was greatly improved by adding TiH2. The temperature-programmed release curve of the 4MgH2-LiAlH4-TiH2 composite reflecte

In this study, the effects of different amounts (5, 10, 15, 20 and 50 wt%) of an SrFe12O19 nanopowder, doped into MgH2 and prepared by the ball milling method, were investigated with the aim of improving hydrogen storage p

NaMgH3 hydride with perovskite structure has been synthesized by high-energy ball milling, the maximum hydrogen-desorbed amount of which is 3.42 wt.% at 638 K. Two decomposition steps have been detected for perovskite-type NaMgH3 hydride, calculated values of activation energy for the two steps are 180.25 ± 8.25 kJ/mol and 156.23 ± 18.54 kJ/mol by Kissinger method. In comparison with NaMgH3 hydride, Li0.5Na0.5MgH3 hydride has better dehydriding kinetic properties and higher hydrogen-desorbed amount (4.11 wt.%) due to partial replacement of Na by Li. LiMgH3 hydride with perovskite structure cannot be synthesized by milling of the mixture of LiH and MgH2 hydrides. However, the maximum hydrogen-desorbed amount of this milled mixture is 5.54 wt.% at 638 K, this may suggest that LiH is a good catalyst for dehydrogenation of MgH2, but further research is needed.

We have studied the effect of additions of Ca compounds, CaC2 and CaH2, to the filling powder on the transport critical current density (Jc) properties of ex situ processed MgB2 tapes. These additives are expected to reduce MgO present in as-received commercial MgB2 powder and improve the grain coupling of MgB2 in the tapes. Heat treatment of the hand mixed powders, MgB2 and the Ca compounds, brings about both disappearance of MgB4 and formation of CaB6 and Mg, compared with heat treated MgB2 powder. They are observed much more clearly for the mixtures with CaH2 addition. The MgO content decreases by the additions of those compounds. Neither of the a-axis and the c-axis parameters of MgB2 are changed by the additions, suggesting no reactions of substitutions of Ca for Mg and C for B in MgB2. The Jc properties of the tape samples using the hand mixed filling powder with CaC2 addition degrade, whereas those with CaH2 addition are slightly improved. When using the ball milled mixtures, slight contraction of the a-axis parameter occurs only by CaC2 addition. Although the additions cause the reactions similar to those observed for the hand mixed powders, the MgO content reduces more clearly, compared with the MgB2 content. The Jc properties of the tapes are enhanced in the high-field and low-field regions by the additions of CaC2 and CaH2, respectively. These enhancements are attributed to the carbon substitution, the improved grain coupling and the increased content of MgB2.

The present Full Paper article discloses a survey of our recent results obtained in the context of the enantioselective halogenation-initiated semi-pinacol rearrangement. Commencing with the fluorination/semi-pinacol reaction first and moving to the heavier halogens (bromine and iodine) second, the scope and limitations of the halogenative phase-transfer methodology will be discussed and compared. An extension of the fluorination/semi-pinacol reaction to the ring-expansion of five-membered allylic cyclopentanols will be also described, as well as some preliminary results on substrates prone to desymmetrization will be given. Finally, the present manuscript will culminate with a detailed mechanistic investigation of the canonical fluorination/semi-pinacol reaction. Our mechanistic discussion will be based on in situ reaction progress monitoring, complemented with substituent effect, kinetic isotopic effect and non-linear behaviour studies.

Metal dodecaborates M2/nB12H12 are among the dehydrogenation intermediates of metal borohydrides M(BH4)n with a high hydrogen density of approximately 10 mass%, the latter is a potential hydrogen storage material. There is therefore a great need to synthesize anhydrous M2/nB12H12 in order to investigate the thermal decomposition of M2/nB12H12 and to understand its role in the dehydrogenation and rehydrogenation of M(BH4)n. In this work, anhydrous alkaline earth metal dodecaborates MB12H12 (M = Mg, Ca) have been successfully synthesized by sintering M(BH4)2 (M = Mg, Ca) and B10H14 in a stoichiometric molar ratio of 1 : 1. Thermal decomposition of MB12H12 shows multistep pathways with the formation of H-deficient monomers MB12H12-x containing icosahedral B12 skeletons and is followed by the formation of (MByHz)n polymers. Comparison of the thermal decomposition of MB12H12 and M(BH4)2 suggests different behaviours of the anhydrous MB12H12 and those formed from the decomposition of M(BH4)n.

The hydrogen storage system [MgH2-2LiBH4] shows attractive properties such as favorable thermodynamics, high hydrogen capacity and reversibility. However, there exists an incubation period that amounts up to 10 hours in the dehydrogenation steps, which restricts this system as a practical material. In this study, the influences of stoichiometry and the nanoscale MgH2 were investigated for the system. Considerably shortened incubation times were achieved with deficit amounts of LiBH 4 or by using nanoscale MgH2. In addition, the application of nanoscale MgH2 prevented or suppressed the formation of [B 12H12]2- in the dehydrogenation, which is otherwise an issue concerning the re-cyclability. The Royal Society of Chemistry.

Cracked under strain: Strained allylic cyclobutanols and cyclopropanols readily undergo a ring expansion described by the title rearrangement. This reaction is promoted by catalytic amounts of 1 and displays high tolerance with respect to the substrate scope. The corresponding β-fluoro spiroketone products are isolated in high yields and with excellent stereoselectivities. EDG=electron-donating group, EWG=electron-withdrawing group. Copyright

This paper reports the synthesis of Mg3La alloys with different hydrogenation degree through controlling the hydrogen amount introduced and reveals the hydrogenation mechanism. The hydrolysis rate and hydrogen yield of Mg3La hydride

Improvement of the reversibility of metal borohydrides is a key issue for hydrogen storage applications. In this study, we carefully investigated the first rehydrogenation of pure Mg(BH4)2 and Ca(BH 4)2 under a hydrogen pressure of 40.0 MPa. Mg(BH 4)2 is produced even at a relatively low temperature of 473 K, and its amount increases with the temperature up to 673 K, leading to the increased rehydrogenation content and a maximum (7.6 mass%, equivalent to 51% of Mg(BH4)2) at 673 K. Under the same condition, more than 90% of rehydrogenation is confirmed through the formation of α-Ca(BH 4)2 as clearly observed by XRD and NMR measurements. Comparison of the rehydrogenation properties of Mg(BH4)2 and Ca(BH4)2 suggests that control of dehydrogenation products would be an important approach to improve the reversibility of metal borohydrides.

Various metal nanoparticles including base metal were produced by a brief accelerated electron beam irradiation of 1-alkyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide room-temperature ionic liquid without a stabilizing agent, which is usually employed so as to prevent aggregation.

This paper describes the kinetic study of a number of gas-phase reactions involving neutral Mg-containing species, which are important for the chemistry of meteor-ablated magnesium in the upper mesosphere/lower thermosphere region. The study is motivated by the very recent observation of the global atomic Mg layer around 90 km, using satellite-born UV-visible spectroscopy. In the laboratory, Mg atoms were produced thermally in the upstream section of a fast flow tube and then converted to the molecular species MgO, MgO2, OMgO2, and MgCO3 by the addition of appropriate reagents. Atomic O was added further downstream, and Mg was detected at the downstream end of the flow tube by laser-induced fluorescence. The following rate coefficients were determined at 300 K: k(MgO + O → Mg + O2) = (6.2 ± 1.1) × 10-10; k(MgO2 + O → MgO + O2) = (8.4 ± 2.8) × 10-11; k(MgCO3 + O → MgO2 + CO2) ≥ 4.9 × 10-12; and k(MgO + CO → Mg + CO2) = (1.1 ± 0.3) × 10-11 cm3 molecule-1 s-1. Electronic structure calculations of the relevant potential energy surfaces combined with RRKM theory were performed to interpret the experimental results and also to explore the likely reaction pathways that convert MgCO3 and OMgO2 into long-lived reservoir species such as Mg(OH)2. Although no reaction was observed in the laboratory between OMgO2 and O, this is most likely due to the rapid recombination of O2 with the product MgO 2 to form the relatively stable O2MgO2. Indeed, one significant finding is the role of O2 in the mesosphere, where it initiates holding cycles by recombining with radical species such as MgO 2 and MgOH. A new atmospheric model was then constructed which combines these results together with recent work on magnesium ion-molecule chemistry. The model is able to reproduce satisfactorily some of the key features of the Mg and Mg+ layers, including the heights of the layers, the seasonal variations of their column abundances, and the unusually large Mg+/Mg ratio.

Manganese-catalyzed homo-coupling of aryl magnesium chlorides to give biphenyls was successfully achieved using manganese chloride as catalyst. A variety of aryl magnesium chlorides were efficiently converted into the corresponding symmetrical biaryls using 10 mol% MnCl2 as catalyst in the presence of a stoichiometric amount of 1,2-dichloroethane. Since the aryl chlorides, from which the Grignard reagents were prepared, are cheaper and more readily available that the corresponding bromides and iodides this procedure should become the method of choice for preparing symmetrical biaryls.

The formation of the nanostructured orthorhombic LaMg2Ni phase using the melt-spinning and the intensive ball milling routes has been studied for the La25Mg50Ni25 and La20Mg50Ni30/sub

Samples with MgmAlNin composition (m, n ≤ 3) were synthesized by ball milling in form of crystalline nanoparticles, and were found to be a single phase with partially disordered CsCl-type cubic structure. For compositions with large

Nanoclusters of 25 nm sized Mg-THF have been prepared by the solvated metal atom dispersion method. Roomtemperature digestive ripening of these nanoclusters in the presence of hexadecylamine (HDA) resulted in highly monodisperse colloidal Mg-HDA nanoparti

Nanocrystalline Mg powders of different particle size were obtained by inert gas evaporation and studied during electrochemical and gas-phase hydrogen cycling processes. The samples were compared to dehydrided samples obtained by mechanical milling of MgH2 with and without 2 mol% Nb2O5 as catalyst. The hydrogen overpotential of the pure Mg, which is a measure of the hydrogen evolution at the electrode surface, was observed to be reduced with smaller particle sizes reaching values comparable to samples with Nb2O5 additive. On the other hand gas-phase charging experiments showed the capacity loss with smaller particle sizes due to oxidation effects. These oxidation effects are different depending on the synthesis method used and showed a major influence on the hydrogen sorption kinetics.

The sorption capacity and kinetics of mechanically activated binary mixtures of Mg with nine different metals (Al, Cu, Fe, Mn, Mo, Sn, Ti, Zn, Zr) have been studied to determine whether these metals act as catalyzing/destabilizing agents in formation/decomposition of Mg hydrides. Identification of crystalline phases before and after the absorption/desorption processes assists our understanding of the different behaviors displayed by the studied compounds. Cu, Al and Zn take active part in Mg hydrogenation/dehydrogenation, but only the addition of Cu is actually effective in MgH2 destabilization, leading to a substantial decrease of the desorption temperature of this phase (down to 270 °C), and to an improved desorption kinetics. With the other metals, the hydrogen release usually occurs at a significant rate only above 320 °C and the kinetics of the absorption/desorption processes are slower than in the Mg/MgH2 system.

A successful synthesis of the Mg(AlH4)2 + 2NaCl mixture by the mechano-chemical activation synthesis (MCAS) for 5 and 10 h has been achieved. The nanocrystalline Mg(AlH4)2 hydride in the mixture has the grain size on the order of 18 nm. Even relatively short milling for just 10 h seems to result in a partial decomposition of the initially formed Mg(AlH4)2 into the nanocrystalline β-MgH2, elemental Al (grain size ～26 nm) and hydrogen gas. A number of DSC tests at the scan rate of 4 °C/min of the Mg(AlH4)2 + 2NaCl mixture synthesized for 5 and 10 h show either endothermic or exothermic heat flow changes at the ～125-180 °C range due to the decomposition of Mg(AlH4)2. Endothermic peaks with the maxima at ～271 and 316 °C due to the decomposition of β-MgH2 and the formation of Al3Mg2 intermetallic as well as Al(Mg) solid solution are present. The peak at ～452 °C is due to the eutectic melting of the Al3Mg2 and Al(Mg) mixture. Prolonged milling for 40 h results in a complete decomposition of the Mg(AlH4)2 into two nanocrystalline solid phases such as β-MgH2 (grain size ～11 nm) and the elemental Al (grain size ～20 nm), and hydrogen gas. DSC tests at the scan rate of 4 °C/min up to 500 °C of the 40 h milled powder, which contains β-MgH2, results in two endothermic peaks with the maxima at ～292 °C due to the decomposition of β-MgH2 and ～452 °C due to the eutectic melting. TGA tests for the 5 and 10 h milled sample give the total weight loss of ～2.45 and 2.16 wt.%, respectively. The hydrogen desorption kinetics of the as-synthesized powders directly after milling were also evaluated using a Sieverts-type apparatus.

Thermal analyses of the mixture of MgH2 and LiBH4 doped with TiCl3, and each element MgH2 or LiBH4 doped with TiCl3 were performed under an inert gas flow and 0.5 MPa H2-gas conditions. It was indicated that the hydrogen desorption reaction of MgH2 + 2LiBH4 to MgB2 + 2LiH + 4H2 phases proceeded at temperature above 400 °C under 0.5 MPa hydrogen, whereas, under an inert gas atmosphere, the reaction of the same mixture was transformed into Mg + 2B + 2LiH + 4H2 phases in a temperature range from 350 to 430 °C. Before these reactions, the dehydrogenation of MgH2 and the melting of LiBH4 took place under both hydrogen and the inert gas atmospheres with increasing temperature. In addition, the molten LiBH4 did not decompose into LiH, B and H2 below 450 °C under 1 MPa H2, while the LiBH4 decomposed even below 450 °C under an inert gas atmosphere. From these results, it is deduced that the reaction producing MgB2 is a solid-liquid reaction between solid Mg and liquid LiBH4 above 400 °C without decomposition of molten LiBH4 under a hydrogen atmosphere, while MgH2 dehydrogenate. A characteristic solid-liquid reaction is realized under a hydrogen atmosphere for proceeding of the MgB2 producing reaction in this system.

In one embodiment of the present disclosure, a process for cyclic dehydrogenation and rehydrogenation of hydrogen storage materials is provided. The process includes liberating hydrogen from a hydrogen storage material comprising hydrogen atoms chemically bonded to one or more elements to form a dehydrogenated material and contacting the dehydrogenated material with a solvent in the presence of hydrogen gas such that the solvent forms a reversible complex with rehydrogenated product of the dehydrogenated material wherein the dehydrogenated material is rehydrogenated to form a solid material containing hydrogen atoms chemically bonded to one or more elements.

A new dehydrogenation mechanism for LiBH4-MgH2 mixtures revealed that magnesium destabilised the LiBH4 resulting in complete dehydrogenation of the borohydride phase and the formation of a Li-Mg alloy. The Royal Society of Chemistry 2006.