Kinetic Model and Experiment for Self-Ignition of Triethylaluminum and Triethylborane Droplets in Air.

Triethylaluminum Al(C2H5)3, TEA, and triethylborane, B(C2H5)3, TEB, are transparent, colorless, pyrophoric liquids with boiling points of approximately 190 °C and 95 °C, respectively. Upon contact with ambient air, TEA, TEB, as well as their mixtures and solutions, in hydrocarbon solvents, ignite. They can also violently react with water. TEA and TEB can be used as hypergolic rocket propellants and incendiary compositions. In this manuscript, a novel scheme of the heterogeneous interaction of gaseous oxygen with liquid TEA/TEB microdroplets accompanied by the release of light hydrocarbon radicals into the gas phase is used for calculating the self-ignition of a spatially homogeneous mixture of fuel microdroplets in ambient air at normal pressure and temperature (NPT) conditions. In the primary initiation step, TEA and TEB react with oxygen, producing an ethyl radical, which can initiate an autoxidation chain. The ignition delay is shown to decrease with the decrease in the droplet size. Preliminary experiments on the self-ignition of pulsed and continuous TEA-TEB sprays in ambient air at NPT conditions are used for estimating the Arrhenius parameters of the rate-limiting reaction. Experiments confirm that the self-ignition delay of TEA-TEB sprays decreases with the injection pressure and provide the data for estimating the activation energy of the rate-limiting reaction, which appears to be close to 2 kcal/mol.

Correction: Borin, D., et al. Magnetorheological Effect of Magnetoactive Elastomer with a Permalloy Filler. Polymers 2020, 12, 2371.

The authors wish to make a change to the published paper [...].

Magnetorheological Effect of Magnetoactive Elastomer with a Permalloy Filler.

Within the frames of this study, the synthesis of a permalloy to be used as a filler for magnetoactive and magnetorheological elastomers (MAEs and MREs) was carried out. By means of the mechanochemical method, an alloy with the composition 75 wt.% of Fe and 25 wt.% of Ni was obtained. The powder of the product was utilized in the synthesis of MAEs. Study of the magnetorheological (MR) properties of the elastomer showed that in a ~400 mT magnetic field the shear modulus of the MAE increased by a factor of ~200, exhibiting an absolute value of ~8 MPa. Furthermore, we obtained experimentally a relative high loss factor for the studied composite; this relates to the size and morphology of the synthesized powder. The composite with such properties is a very perspective material for magnetocontrollable damping devices. Under the action of an external magnetic field, chain-like structures are formed inside the elastomeric matrix, which is the main determining factor for obtaining a high MR effect. The effect of chain-like structures formation is most pronounced in the region of small strains, since structures are partially destroyed at large strains. A proposed theoretical model based on chain formation sufficiently well describes the experimentally observed MR effect. The peculiarity of the model is that chains of aggregates of particles, instead of individual particles, are considered.

Synthesis of Siloxyalumoxanes and Alumosiloxanes Based on Organosilicon Diols.

We have drawn a few interesting conclusions while studying reaction products of Ph2Si(OH)2 with Al(iBu)3 and tetraisobutylalumoxane. In the first place, this is the production (at a Ph2Si(OH)2 and Al(iBu)3 equimolar ratio) of an oligomer siloxyalumoxane structure with alternating four- and six-member rings. In addition, it shows isobutyl and phenyl group migration between aluminum and silicon due to the formation of an intramolecular four-member cyclic complex [Ph2(OH)SiO]Al(iBu)2 → [(iBu)Ph(OH)SiO]Al(iBu)Ph. Ph2Si(OH)2 interaction with Al(iBu)3 not only starts from intramolecular complex production, but the chain is terminated for the same reason, which in the case of the Ph2Si(OH)2 reaction with tetraisobutylalumoxane results in failure of to obtain high-polymer siloxyalumoxane compounds. When Al(iBu)3 interacts with α- and γ-diols, no oligomer compounds are produced. In the Al(iBu)3 reaction with α, γ-diols are created in monomer compounds that are likely to have a cyclic structure. Notably, when Al(iBu)3 interacts with only α-diol, a double excess of Al(iBu)3 allows for full replacement of hydrogen in the α-diol hydroxyl groups by aluminum alkyl residue with 1,3-bis(diisobutylalumoxymethyl)-1,1,3,3-tetramethyldisiloxane production. At an equimolar ratio of initial reagents, the second isobutyl radical at Al does not interact with the second hydroxyl group of α-diol, apparently due to the steric hindrance, and 1-(diisobutylalumoxymethyl)-3-(hydroxymethyl)-1,1,3,3-tetramethyl-disiloxane is produced. Al(iBu)3 reactions with γ-diol also result in monomer compounds, but the presence of a chain consisting of three CH2-groups between Si and the hydroxyl group facilitates interaction between the second hydroxyl group of γ-diol and the second isobutyl radical Al(iBu)3. Tetraisobutylalumoxane reactions with α- and γ-diols result in oligomer compounds.

Structure of complexes formed by dissolution of palladium diacetate in methanol and chloroform. In situ NMR study.

The behavior of palladium diacetate cyclic trimer [Pd(OAc)(2)](3) (1) upon its dissolution in methanol and wet chloroform was studied by (1)H and (13)C NMR including 2D-HSQC and 2D-DOSY techniques. Upon dissolution, trimer 1 reacts with methanol and is completely transformed first into the methoxo complex Pd(3)(µ-OMe)(OAc)(5) (2), which already at -18 °C undergoes a slow exchange of second bridging acetate ligand between the same palladium atoms to form the symmetric dimethoxo complex Pd(3)(µ-OMe)(2)(OAc)(4), the maximum relative concentration of which reaches 20-30 mol % of initial loading trimer 1. Along with the dimethoxo complex, both soluble and insoluble polynuclear palladium clusters are gradually formed at -18 °C, and their total amount reaches up to 60% of the starting Pd(2+) loading. The increase of temperature to 27 °C results in the reduction of palladium(II) to Pd metal by methanol, which is oxidized and transformed into formaldehyde hemiacetal and methyl formate. Upon dissolution in wet chloroform, trimer 1 is reversibly hydrolyzed to the hydroxo complex Pd(3)(µ-OH)(OAc)(5) (10) in ratio 1/10 ≈ 3/1. The temperature decrease and addition of acetic acid shift the equilibrium in this system toward trimer 1, and addition of water shifts it in the opposite direction. Addition of methanol to the equilibrium mixture of 1 and 10 results in the fast exchange of bridging acetate in trimer 1 by the µ-OMe group. Substitution of the µ-OH ligand by µ-OMe in 10 occurs in parallel but more slowly. Complex 2 formed in both cases is more stable in chloroform than in methanol.