Aluminum Monohydride Research Articles

Effects of Size and Prestressing of Aluminum Particles on the Oxidation of Levitated exo-Tetrahydrodicyclopentadiene Droplets.

Addition of high-energy-density materials such as aluminum (Al) microparticles or nanoparticles to liquid propellants potentially improves performance of the fuel. We report on the effects of untreated, prestressed, and superquenched aluminum particles with diameters of 100 nm, 250 nm, 500 nm, 1.6 μm, and 8.8 μm on the combustion of JP-10 droplets acoustically levitated in an oxygen-argon atmosphere. Ignition was initiated by a carbon dioxide laser, and the resulting oxidation processes were traced by Raman, Fourier-transform infrared (FTIR), and ultraviolet-visible (UV-vis) spectroscopies together with high-speed optical and IR thermal-imaging cameras. The UV-vis emission spectra reveal that the key reactive radical intermediates hydroxyl (OH), methylidyne (CH), dicarbon (C2), aluminum monoxide (AlO), and aluminum monohydride (AlH) were formed in addition to atomic aluminum (Al) and the final oxidation products of JP-10, namely, water (H2O) and carbon dioxide (CO2). The Al particles facilitated ignition of the JP-10 droplets and produced higher temperatures in the combustion process of up to typically 2600 K. The effect of the Al particles on the ignition and maximum flame temperatures increased as the diameters reduced. The different stress treatments did not produce observable changes for the ignition or combustion of the droplets, which indicates that the liquid propellant was not significantly affected by manipulating the mechanical properties of the fuel particle additive. The initiation and enhancement of the combustion were a consequence of forming highly reactive atomic oxygen (O) and aluminum monoxide (AlO) radicals in the reaction of aluminum atoms with molecular oxygen in the gas phase. These radicals initiate the degradation of JP-10 via atomic hydrogen abstraction forming the hydroxyl (OH) and aluminum hydroxide (AlOH) radicals in reactions which are mainly exothermic by up to 68 kJ mol-1. In contrast, hydrogen abstractions from JP-10 by molecular oxygen or atomic aluminum are strongly endothermic by up to 236 kJ mol-1, thus making these reactions less competitive. The generation of C10H15 hydrocarbon radicals from the JP-10 initiates successive oxidations and chain reactions with molecular oxygen leading eventually to carbon dioxide and water. These combined experimental results provide insight into how aluminum particles facilitate the oxidation and reaction mechanisms of JP-10 droplets.

Ab Initio Ground-State Potential Energy Function and Vibration-Rotation Energy Levels of Aluminum Monohydride.

The accurate ground-state potential energy function of aluminum monohydride (AlH) has been determined from ab initio calculations using the multireference averaged coupled-pair functional (MR-ACPF) method in conjunction with the correlation-consistent core-valence basis sets up to septuple-zeta quality. The vibration-rotation energy levels of the two isotopologues, AlH and AlD, were predicted to near the "spectroscopic" accuracy. The importance of electron correlation beyond the MR-ACPF level of approximation, the scalar relativistic, spin-orbit, adiabatic, and nonadiabatic effects was discussed. © 2019 Wiley Periodicals, Inc.

Aluminum Monohydride Catalyzed Selective Hydroboration of Carbonyl Compounds.

The well-defined aluminum monohydride compound [{(2,4,6-Me3-C6H2)NC(Me)}2(Me)(H)]AlH·(NMe2Et) (1) catalyzes hydroboration of a wide range of aldehydes and ketones under mild reaction conditions. Moreover, compound 1 displayed chemoselective hydroboration of aldehydes over ketones at rt.

Simple and compact nozzle design for laser vaporization sources

We have developed and implemented a compact transparent nozzle for use in laser vaporization sources. This nozzle eliminates the need for an ablation aperture, allowing for a more intense molecular beam. We use this nozzle to prepare a molecular beam of aluminum monohydride (AlH) suitable for ion trap loading of AlH+ via photoionization in ultra-high vacuum. We demonstrate stable AlH production over hour time scales using a liquid ablation target. The long-term stability, low heat load and fast ion production rate of this source are well-suited to molecular ion experiments employing destructive state readout schemes requiring frequent trap reloading.

Preparation of Aluminum Hydrides with Chelating Anilido‐Imine Ligands by Addition of an Al–H Bond to a C=N Bond

AbstractReacting o‐C6H4F(CH = NC6H3iPr2‐2,6) (L) with H3Al·NMe3 resulted in the aluminum dihydride with coordinated NMe3 of composition [o‐C6H4F(CH2NC6H3iPr2‐2,6)]AlH2(NMe3)(1). Furthermore, the aluminum monohydride [o‐C6H4N(C6H3iPr2‐2,6)(CH2NC6H3iPr2‐2,6)]AlH(NMe3) (2) was prepared by treatment of the anilido‐imine ligand o‐C6H4N(C6H3iPr2‐2,6)(CH = NC6H3iPr2‐2,6) (L*) with H3Al·NMe3 in high yield. The formations of the two complexes both involve aluminum hydride addition to the C=N double bond. Compounds 1 and 2 were characterized by 1H NMR and IR spectroscopic, elementary analysis, and single‐crystal X‐ray diffraction studies.

Synthesis of 1, 6‐Bis(trimethylsilylamino)benzene‐Substituted Aluminum Hydrides: The Characterization of a Product from Ring‐Opening Reaction of Tetrahydrofuran

AbstractThe reaction of 1, 6‐bis(trimethylsilylamino)benzene (LH2) (1) in toluene with H3Al·NMe3 yielded the aluminum monohydride with coordinate NMe3 of composition [1, 6‐(Me3SiN)2C6H4]AlH(NMe3) (2). However, the same reaction in THF resulted in the ring opening of THF with formation of {[1, 6‐(Me3SiN)2C6H4]AlH}2O(CH2)4NMe3 (3) in good yield. Both the spectroscopic data in solution as well as the X‐ray crystallographic data confirmed that a THF molecule underwent a ring‐opening reaction. Compound 2 is the first monomeric aluminum hydride compound containing the 1, 6‐bis(trimethylsilylamino)benzene. Compound 3 exhibits an intermolecular zwitterion of composition –O(CH2)4NMe3+ between two aluminum atoms. Complexes 2 and 3 were characterized by 1H NMR spectroscopy, elementary analysis, and single‐crystal X‐ray diffraction studies.

Reactions of the Aluminum(I) Monomer LAl [L = HC{(CMe)(NAr)}2; Ar = 2,6‐iPr2C6H3] with Imidazol‐2‐ylidene and Diphenyldiazomethane. A Hydrogen Transfer from the L Ligand to the Central Aluminum Atom and Formation of the Diiminylaluminum Compound LAl(N=CPh2)2

AbstractThe solid‐state reaction of LAl and imidazol‐2‐ylidene at elevated temperature (120 °C) yielded the aluminum monohydride N‐heterocyclic carbene adduct [{HC[C(CH2)NAr] (CMeNAr)}AlH‐{CN(R)C2Me2N(R)}] [R = iPr (1), Me (2)]. Compounds 1 and 2 have been characterized by spectroscopic (IR, and 1H and 13C NMR), mass spectrometric, and elemental analyses, and 1 was further characterized by X‐ray structural analysis. These experimental data indicate that the Al−H bond is formed by hydrogen migration from one of the methyl groups of the β‐diketiminato ligand backbone. The reaction of LAl with two equivalents of diphenyldiazomethane afforded the diiminylaluminum compound LAl(N=CPh2)2 (3), while an excess of diphenyldiazomethane resulted in the formation of Ph2C=N−N=CPh2. This suggests that Ph2C=N−N=CPh2 is initially generated and then reacts further by oxidative addition to yield 3. The X‐ray structural analysis reveals that compound 3 contains the shortest Al−Niminyl bond among those with a four‐coordinate aluminum center. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

High resolution infrared emission spectra of AlH and AlD

High resolution infrared emission spectra of aluminum monohydride and monodeuteride have been recorded. Gaseous AlH and AlD were generated by reacting molten aluminum metal with hydrogen and deuterium gas. Approximately 265 AlH lines with v=1→0 to v=5→4 and 470 AlD lines with v=1→0 to v=7→6 are reported. Dunham Yij constants were obtained by fitting the data of each isotopomer separately to the Dunham energy level expression while mass-reduced Dunham Uij constants were obtained from a combined fit of all isotopomer data. A second set of Dunham Uij constants was obtained from a fit where Uij’s with j<2 were treated as adjustable parameters and all remaining Uij’s fixed to values that satisfy the constraints imposed by the Dunham model. Finally, an effective Born–Oppenheimer potential was determined by fitting all the data directly to the eigenvalues of the radial Schrödinger equation containing a parametrized potential function.

Infrared diode laser spectroscopy of aluminum monohydride. The determination of mass scaling coefficients

The vibration—rotation transitions of aluminum monohydride were observed using an infrared diode laser spectrometer. Aluminum monohydride was generated by the reaction of heated aluminum metal with hydrogen gas. The observed spectra were combined with those for aluminum monodeuteride to determine mass-independent parameters and mass scaling coefficients.