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The explosion characteristics of AlH 3 dust clouds with varying micron particle sizes are investigated in this paper. The explosion mechanism of AlH 3 dust clouds is initially explored. The results indicate that the activation energy for hydrogen evolution shows an increasing trend with the AlH 3 particle size, and both of these values are comparable to the 30 kJ/mol desorption energy of hydrogen from large AlH 3 clusters. Due to the rapid dehydrogenation rate and small-size residual aluminum core, fine AlH 3 particles exhibit a continuous gas-phase flame and fast propagation velocity. With increasing particle size, the lower dehydrogenation rate, reduced specific surface area, and higher volume heat capacity contribute to a higher level of incomplete reaction. Consequently, large micro-sized AlH 3 particles display a discrete flame, slower flame velocity, and lower explosion pressure. The flame delamination phenomenon is not observed in our experiments on AlH 3 dust clouds. [Display omitted] • The explosion characteristics of AlH 3 dust with different particle sizes are studied. • The phenomenon of flame delamination is not observed in the AlH 3 dust clouds. • The activation energy for H 2 release increases with particle size, similar to large AlH 3 clusters' desorption energy. • The explosion mechanism of AlH 3 dust with different particle size is revealed. [ABSTRACT FROM AUTHOR]

Aluminum hydride (AlH 3) dust is a high-capacity hydrogen storage material but is prone to explosion. In this paper, explosion characteristics and flame propagation behavior of AlH 3 dust are investigated. The results indicate that the exposure of bare aluminum and the increase of specific surface area lead to the maximum explosion pressure of AlH 3 dust being 4 times higher than that of Al dust. The enhancement of heat transfer by hydrogen combustion causes a higher combustion rate, leading to a higher maximum explosion pressure rise rate and flame propagation velocity of AlH 3 dust. The thermo-diffusive instabilities and the evolution of hydrogen result in a pulsation flame propagation velocity of AlH 3 dust. Combining the explosion temperature calculated by NASA CEA with the explosion residues analysis, the explosion mechanism of AlH 3 dust is further revealed. The break of the oxide film and the combustion of hydrogen result in a different explosion mechanism. • The explosion characteristics and flame propagation behavior of AlH 3 dust are investigated. • The hydrogen evolution characteristic is studied by the comparison of Al dust. • The explosion mechanism of AlH 3 dust is revealed. [ABSTRACT FROM AUTHOR]

Aluminum hydride is a promising chemical hydrogen storage material that can achieve dehydrogenation under mild conditions as well as high hydrogen storage capacity. However, designing an efficient and cost-effective catalyst, especially a synergistic catalyst, for realizing low-temperature and high-efficiency hydrogen supply remains challenging. In this study, the heterojunction synergistic catalyst of Ti3C2 supported PrF3 nanosheets considerably improved the dehydrogenation kinetics of AlH3 at low temperatures and maintained a high hydrogen storage capacity. In the synergistic catalyst, Pr produced a synergistic coupling interaction through its unique electronic structure. The sandwich structure with close contact between the two phases enhanced the interaction between species and the synergistic effect. The initial dehydrogenation temperature of the composite is reduced to 70.2 °C, and the dehydrogenation capacity is 8.6 wt.% at 120 °C in 90 min under the kinetic test, which reached 93% of the theoretical hydrogen storage capacity. The catalyst considerably reduced the activation energy of the dehydrogenation reaction. Furthermore, the multielectron pairs on the surface of the catalyst promoted electron transfer and accelerated the reaction. [ABSTRACT FROM AUTHOR]

AlH 3 is a metastable hydride with a high hydrogen density of 10.1 wt% and it can release hydrogen at a low temperature of 150–200 °C. Many additives (e.g., NbF 5 , TiF 3 , etc.) introduced by ball milling can significantly reduce the decomposition temperature of AlH 3 , but often simultaneously decrease the available hydrogen capacity. In this work, TiB 2 was introduced by ball milling to improve the decomposition performance of AlH 3. AlH 3 + x wt% TiB 2 (x = 2.5, 5, 7.5, 10) composites were prepared by ball milling, and the milling conditions were optimized. It was shown that the decomposition performance of the AlH 3 + 2.5 wt% TiB 2 ball milled at 225 rpm for 108 min is the best. The onset decomposition temperature is 78 °C, which is 60 °C lower than that of pure AlH 3. The decomposition is terminated at 130 °C with 8.5 wt% of hydrogen is obtained. In addition, 5.3 wt% of hydrogen can be released within 200 min at constantly 80 °C. Under the same conditions, ball-milled AlH 3 can hardly release any hydrogen. The activation energy calculated by the Kissinger's method is 86 kJ mol−1, which was 28 kJ mol−1 lower than that of ball-milled AlH 3. Catalytic mechanism study reveals that the Al 2 O 3 layers on the surface of AlH 3 will interact with TiB 2 to form Al–Ti–B solid solution, resulting in lattice distortion. Through lattice activation, the decomposition kinetics of AlH 3 is improved. This work provides an efficient strategy to achieve both high hydrogen capacity and low decomposition temperature of metastable AlH 3 by proper ball milling with metal borides. Both high capacity and low decomposition temperature of AlH 3 were achieved by proper ball milling with TiB 2 which interacts with Al 2 O 3 surface layer to form Ti–Al–B solid solution. [Display omitted] • AlH 3 was properly milled with TiB 2. • Ball milling conditions and TiB 2 content were optimized. • Both high capacity and low decomposition temperature were achieved. • Al 2 O 3 react with TiB 2 to form Ti–Al–B solid solution. • Ti–Al–B solid solution contributes to the improvement of AlH 3 decomposition. [ABSTRACT FROM AUTHOR]

Despite the notable progress in aluminium chalcogenides, their sulfur congeners have rarely been isolated under mild conditions owing to limited synthetic precursors and methods. Herein, facile isolation of diverse molecular aluminium sulfides is achievable, by the reaction of N‐heterocyclic carbene‐stabilized terphenyl dihydridoaluminium (1) with various thiation reagents. Different to the known dihydridoaluminium 1Tipp, 1 features balanced stability and reactivity at the Al center. It is this balance that enables the first monomeric aluminium hydride hydrogensulfide 2, the six‐membered cyclic aluminium polysulfide 4 and the five‐membered cyclic aluminium polysulfide 6 to be isolated, by reaction with various equivalents of elemental sulfur. Moreover, a rare aluminium heterocyclic sulfide with Al−S−P five‐membered ring (7) was obtained in a controlled manner. All new compounds were fully characterized by multinuclear NMR spectroscopy and elemental analysis. Their structures were confirmed by single‐crystal X‐ray diffraction studies. [ABSTRACT FROM AUTHOR]

The catalytic effect of rare-earth hydrogen storage alloy is investigated for dehydrogenation of alane, which shows a significantly reduced onset dehydrogenation temperature (86 °C) with a high-purity hydrogen storage capacity of 8.6 wt% and an improved dehydrogenation kinetics property (6.3 wt% of dehydrogenation at 100 °C within 60 min). The related mechanism is that the catalytic sites on the surface of the hydrogen storage alloy and the hydrogen storage sites of the entire bulk phase of the hydrogen storage reduce the dehydrogenation temperature of AlH 3 and improve the dehydrogenation kinetic performance of AlH 3. This facile and effective method significantly improves the dehydrogenation of AlH 3 and provides a promising strategy for metal hydride modification. [Display omitted] • The dehydrogenation performance of the LaNi 5 -doped AlH 3 was investigated. • The onset dehydrogenation temperature of the composite decreased to 86 °C. • The composite released 6.3 wt% of hydrogen within 60 min at 100 °C. • The mechanism was provided according to the characterization. [ABSTRACT FROM AUTHOR]

The influence upon chemical composition and heat of combustion of composite propellant that occurs as a result of substitution of aluminium by its hydride AlH3 is investigated. Propellants based on ammonium chlorate(VII) (NH4ClO4) modified by standard HTPB binder are considered. Chemical composition and thermodynamic parameters of combustion products are evaluated by MWEQ computer program supplied with large species database. The particular attention is paid to proper choose of thermodynamic data describing temperature dependence of heat capacity, enthalpy and entropy of chemical compounds belonging to Al-Cl-O-H group. The alteration of chemical composition and temperature of combustion products that is followed by replacement of Al by AlH3 is illustrated in a quantitative mode. The prospective applicability of AlH3 as an energetic component of composites propellants is confirmed.

Aluminium hydride (AlH 3 ) is a promising hydrogen storage material because it possesses a high theoretical hydrogen capacity of 10.01 wt%. However, the stability and decomposition mechanism of some AlH 3 polymorphs ( e.g. , γ-AlH 3 ) still remain unclear. In this work, the hydrogen desorption behaviours of γ-AlH 3 with or without TiF 3 addition were investigated by hydrogen desorption measurement and thermal analysis. It was revealed that the decompositions of the outer layer and the inner part of γ-AlH 3 particle follow diverse decomposition mechanisms. The outer layer of γ-AlH 3 particle tends to decompose directly, while the inner part of γ-AlH 3 particle prefers to first transform to more stable α-AlH 3 and then decompose. TiF 3 addition significantly lowers the temperature for the direct decomposition of outer layer γ-AlH 3 by about 30 °C but scarcely impacts the decomposition of inner part γ-AlH 3 , which further confirms the decomposition mechanism of γ-AlH 3 . It was suggested that the particle size plays an important role in the thermal stability of γ-AlH 3 . The results of this work will help understanding the decomposition mechanisms of other AlH 3 polymorphs for hydrogen storage. [ABSTRACT FROM AUTHOR]

LiBH 4 can be destabilized by AlH 3 addition. In this work, the hydrogen desorption kinetics of the destabilized LiBH 4 AlH 3 composites were investigated. Isothermal hydrogen desorption studies show that the LiBH 4 + 0.5AlH 3 composite releases about 11.0 wt% of hydrogen at 450 °C for 6 h and behaves better kinetic properties than either the pure LiBH 4 or the LiBH 4 + 0.5Al composite. The apparent activation energy for the LiBH 4 decomposition in the LiBH 4 + 0.5AlH 3 composite estimated by Kissinger's method is remarkably lowered to 122.0 kJ mol −1 compared with the pure LiBH 4 (169.8 kJ mol −1 ). Besides, AlH 3 also improves the reversibility of LiBH 4 in the LiBH 4 + 0.5AlH 3 composite. For the LiBH 4 + x AlH 3 ( x = 0.5, 1.0, 2.0) composites, the decomposition kinetics of LiBH 4 are enhanced as the AlH 3 content increases. The sample LiBH 4 + 2.0AlH 3 can release 82% of the hydrogen capacity of LiBH 4 in 29 min at 450 °C, while only 67% is obtained for the LiBH 4 + 0.5AlH 3 composite in 110 min. Johnson−Mehl−Avrami (JMA) kinetic studies indicate that the reaction LiBH 4 + Al → ‘Li Al B’ + AlB 2 + H 2 is controlled by the precipitation and subsequently growth of AlB 2 and Li Al B compounds with an increasing nucleation rate. [ABSTRACT FROM AUTHOR]

Lithium borohydride (LiBH 4 ) possesses a very high hydrogen capacity (18.5 wt%) but suffers from high thermal stability. In this work, the as-prepared aluminium hydride (AlH 3 ) was ball milled with LiBH 4 forming 2LiBH 4 + AlH 3 composite to improve the hydrogen desorption properties of LiBH 4 . Hydrogen desorption measurements showed that a hydrogen capacity of 11.2 wt% is obtained from the 2LiBH 4 + AlH 3 composite and the desorption temperature of LiBH 4 with AlH 3 addition is reduced by more than 30 °C. AlH 3 is better as an Al source than the as-received Al in that the hydrogen desorption extent of AlH 3 -doped LiBH 4 reaches 70%, while it is 54% and 61% for the pure LiBH 4 and the Al-doped LiBH 4 . This is due to the brittle and oxide-free nature of AlH 3 . Microstructure investigations showed that during heating process, the 2LiBH 4 + AlH 3 composite undergoes AlH 3 decomposition forming Al* and releasing hydrogen, followed by the decomposition of LiBH 4 . LiBH 4 will react with Al* forming AlB 2 and Li Al B compounds during its decomposition, which contributes to the improved hydrogen desorption properties of LiBH 4 . [ABSTRACT FROM AUTHOR]

Ternary hydride of LiBH 4 –MgH 2 –NaAlH 4 confined into carbo n aerogel scaffold (CAS) via melt infiltration for reversible hydrogen storage is proposed. Nanoconfinement of hydrides into CAS is obtained together with surface occupation of some phases, such as Al and/or LiH. Regarding nanoconfinement, not only multiple-step decomposition of LiBH 4 –MgH 2 –NaAlH 4 hydride reduces to about single step, but also reduction of dehydrogenation temperature is significantly observed, for example, ∆ T up to 70 °C regarding last dehydrogenation step. Moreover, decomposition of NaBH 4 in nanoconfined sample can be done at 360 °C (dehydrogenation temperature in this study), which is 115 and 180 °C lower than that of NaBH 4 in milled LiBH 4 –MgH 2 –NaAlH 4 and bulk NaBH 4 , respectively. The reaction of LiBH 4 +NaAlH 4 →LiAlH 4 +NaBH 4 takes place during nanoconfinement and the decomposition of LiAlH 4 is observed, resulting deficient hydrogen content liberated. However, hydrogen content released (1st cycle) and reproduced (2nd–4th cycles) from this ternary hydride enhances up to 11% and 22% of full hydrogen storage capacity due to nanoconfinement. After rehydrogenation ( T =360 °C and P (H 2 )=50 bar H 2 for 12 h), NaBH 4 , MgH 2 , and Li 3 AlH 6 are reversible, whereas Li 3 AlH 6 and NaBH 4 in milled sample cannot be recovered due to deficient hydrogen pressure ( T =360 °C and P (H 2 )=80 bar) and probably evaporation of molten sodium during dehydrogenation, respectively. The latter results in inferior hydrogen content reproduced from milled sample to nanoconfined sample. [ABSTRACT FROM AUTHOR]

Abstract: Recently, interest in aluminium hydride (alane) as a rocket propulsion ingredient has been renewed due to improvements in its manufacturing process and an increase in thermal stability. When alane is added to solid propellant formulations, rocket performance is enhanced and the specific impulse increases. Preliminary work was performed at AFRL on the characterization and evaluation of two alane samples. Decomposition kinetics were determined from gravimetric TGA data and volumetric vacuum thermal stability (VTS) results. Chemical analysis showed the samples had 88.30% (by weight) aluminium and 9.96% hydrogen. The average density, as measured by helium pycnometery, was 1.486g/cc. Scanning electron microscopy showed that the particles were mostly composed of sharp edged crystallographic polyhedral such as simple cubes, cubic octahedrons and hexagonal prisms. Thermogravimetric analysis was utilized to investigate the decomposition kinetics of alane in argon atmosphere and to shed light on the mechanism of alane decomposition. Two kinetic models were successfully developed and used to propose a mechanism for the complete decomposition of alane and to predict its shelf-life during storage. Alane decomposes in two steps. The slowest (rate-determining) step is solely controlled by solid state nucleation of aluminium crystals; the fastest step is due to growth of the crystals. Thus, during decomposition, hydrogen gas is liberated and the initial polyhedral AlH3 crystals yield a final mix of amorphous aluminium and aluminium crystals. After establishing the kinetic model, prediction calculations indicated that alane can be stored in inert atmosphere at temperatures below 10°C for long periods of time (e.g., 15 years) without significant decomposition. After 15 years of storage, the kinetic model predicts ∼0.1% decomposition, but storage at higher temperatures (e.g. 30°C) is not recommended. [Copyright &y& Elsevier]

The syntheses of two Group 13 complexes of the sterically demanding carbene, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, (IPr), are reported, vis. [MX3(IPr)] M=Al, X=H; M=In, X=Br; both of which have been structurally characterised. Also reported is the crystal structure of the imidazolium salt [IPrH][InBr4], formed by the presence of adventitious water in the preparation of the [InBr3(IPr)] adduct. The preparation of the complex [InBr3(IMes)], IMes=1,3-bis(2,4,6-trimethylpheny)imidazol-2-ylidene, is described as are details of its crystal structure analysis. In addition, two indium tribromide adducts of nitrogen donor ligands, namely a bulky diazabutadiene and quinuclidine have been investigated. The crystal structures of N,N′-1,4-bis(2,6-diisopropylphenyl)diazabutadiene indium tribromide and bis(quinuclidine)indium tribromide are reported. [Copyright &y& Elsevier]