Lithium aluminium hydride

Summary

Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula or . It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids, and amides. The solid is dangerously reactive toward water, releasing gaseous hydrogen (H2). Some related derivatives have been discussed for hydrogen storage. Properties, structure, preparation LAH is a colourless solid but commercial samples are usually gray due to contamination. This material can be purified by recrystallization from diethyl ether. Large-scale purifications employ a Soxhlet extractor. Commonly, the impure gray material is used in synthesis, since the impurities are innocuous and can be easily separated from the organic products. The pure powdered material is pyrophoric, but not its large crystals. Some commercial materials contain mineral oil to inhi

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https://en.wikipedia.org/wiki/Lithium_aluminium_hydride

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L'objectif de ce cours est de fournir les connaissances et le moyen de comprendre, au niveau moléculaire, le fonctionnement des réactions chimiques organiques. Pendant le cours, l'étudiant réfléchira et résoudra de nouveaux problèmes.

Basic organometallic chemistry will be covered in this course.

Structure and bonding in organometallic compounds.
reactivity of organometallic compounds, stoichiometric reactions, catalyzed reactions and reaction mechanisms.

This course covers the metallurgy, processing and properties of modern high-performance metals and alloys (e.g. advanced steels, Ni-base, Ti-base, High Entropy Alloys etc.). In addition, the principles of computational alloy design as well as approaches for a sustainable metallurgy will be addressed

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Enhanced Electrical Conductivities of Complex Hydrides Li-2(BH4)(NH2) and Li-4(BH4)(NH2)(3) by Melting

Yu Zhou

The electrical conductivities of complex hydrides Li2(BH 4)(NH2) and Li4(BH4)(NH 2)3 consisting of (BH4)- and (NH2)- anions are investigated focusing on their low melting temperatures (365 K for Li2(BH4)(NH2) and 490K for Li4(BH4)(NH2)3). The two hydrides show lithium fast-ion conductivities of about 1 × 10 -4 S·cm-1 at room temperature. After melting, the total ion conductivities OfLi2(BH4)(NH2) and Li4 (BH 4)(NH2)3 reach 6 × 10-2 S·cm-1 (378 K) and 2 x 10-1 S·cm -1 (513 K), respectively. The crystal structure and local atomistic structures closely correlated with the lithium ion conduction before and after melting are also discussed. ©2011 The Japan Institute of Metals.

2011

Mobility and dynamics in the complex hydrides LiAlH4 and LiBH4

Pascal Martelli

The dynamics and bonding of the complex hydrides LiBH4 and LiAlH4 have been investigated by vibrational spectroscopy. The combination of infrared, Raman, and inelastic neutron scattering (INS) spectroscopies on hydrided and deuterided samples reveals a complete picture of the dynamics of the BH-4 and AlH-4 anions respectively as well as the lattice. The straightforward interpretation of isotope effects facilitates tracer diffusion experiments revealing the diffusion coefficients of hydrogen containing species in LiBH4, and LiAlH4. LiBH4 exchanges atomic hydrogen starting at 200 °C. Despite having an iso-electronic structure, the mobility of hydrogen in LiAlH4 is different from that of LiBH4. Upon ball-milling of LiAlH4 and LiAlD4, hydrogen is exchanged with deuterium even at room temperature. However, the exchange reaction competes with the decomposition of the compound. The diffusion coefficients of the alanate and borohydride have been found to be D ≃ 7 × 10-14 m2 s -1 at 473 K and D ≃ 5 × 10-16 m2 s-1 at 348 K, respectively. The BH-4 ion is easily exchanged by other ions such as I- or by NH-2. This opens the possibility of tailoring physical properties such as the temperature of the phase transition linked to the Li-ion conductivity in LiBH4 as measured by nuclear magnetic resonance and Raman spectroscopy. Temperature dependent Raman measurements on diffusion gradient samples Li(BH4)1-cIc demonstrate that increasing temperature has a similar impact to increasing the iodide concentration c: the system is driven towards the high-temperature phase of LiBH4. The influence of anion exchange on the hydrogen sorption properties is limited, though. For example, Li4(BH 4)(NH2)3 does not exchange hydrogen easily even in the melt. © The Royal Society of Chemistry 2011.

2011

Creep of aluminium-magnesium open cell foam

Frédéric Diologent, Andreas Mortensen

Aluminium-5 wt.% magnesium open cell foam produced by replication and tested in tension at 300, 350 or 450 degrees C creeps at rates between 10(-3) and 10(-8) s(-1). The behaviour of the foam matches that of the alloy from which it is made: three-power law creep with the same activation energy as for Al-Mg alloy creeping by viscous dislocation glide in the high stress regime and five-power law creep in the low stress regime. The model of Mueller et al. [Mueller R, Soubielle S, Goodall R, Diologent F. Mortensen A. Scripta Mater 2007;57:33], itself a simplified adaptation of previous variational estimates, predicts well the measured foam creep rates, in terms of both absolute value and dependence on temperature and applied stress. Agreement with the model of Andrews et al. [Andrews EW, Gibson LJ, Ashby MF. Acta Mater 1999;47:2853] is somewhat inferior, but nonetheless satisfactory. A strong dependence of creep rate on relative density is found; this feature is also captured by the variational estimate. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

2009