Generation and properties of hydrogenation catalysts based on palladium bisacetylacetonate and lithium alkoxyhydroaluminates

Generation and properties of a catalytic system for hydrogenation, based on Pd(acac)₂ and LiAlH₄ and modified with n-BuOH and t-BuOH, were studied. The promoting and inhibiting effects of the alcohols were revealed, and their causes were discussed.     

Kinetic analysis of n-decane–hydrogen blend combustion in premixed and non-premixed supersonic flows

Numerical analysis of ignition and combustion of an n-decane–hydrogen fuel blend in a premixed supersonic flow and in a model scramjet duct is performed using a reduced reaction mechanism built especially to describe the oxidation of blended n-C₁₀H₂₂–H₂ fuel in air at the temperature T₀ > 900–1000 K in the pressure range P₀ = 0.1–13 atm. The developed kinetic mechanism involves the principal reactions responsible for chain mechanism development both for n-decane and for hydrogen oxidation. It has been shown that using blended n-C₁₀H₂₂–H₂ fuel makes it possible to enhance the ignition and combustion both in premixed and in non-premixed supersonic fuel–air flows compared to burning pure hydrogen–air and n-decane–air mixtures. This allows high combustion completeness in the scramjet duct at the distance of ～1 m even at extremely low air temperature T₀ = 1000 K and pressure P₀ = 0.3 atm. This is due to the interaction of kinetics of the formation of highly reactive atoms and radicals, carriers of chain mechanism, in H₂–air and n-C₁₀H₂₂–air mixtures.     

Magnetic and Magnetoelectric Properties of Scandoborate NdSc3(BO3)4

Physics of the Solid State - Trigonal neodymium scandoborate NdSc3(BO3)4 single crystals have been grown by the batch flux method using bismuth trimolybdate and their magnetic and magnetoelectric...     

Hydrogen bonds,coordination isomerism,and catalytic dehydrogenation of alcohols with the bifunctional iridium pincer complex $$^{{{\left( {HOC{H_2}} \right)}_2}}\left( {P{C_{s{p^3}}}P} \right)$$IrHCl

The reaction of iridium(iii) hydride complex 1 based on the pincer dibenzobarrelene ligand \(^{{{\left( {HOC{H_2}} \right)}_2}}\left( {P{C_{s{p^3}}}P} \right)\) with pyridine proceeds stepwise to show different reactivities of the starting fac-isomers 1A and 1B. The kinetic product of the reaction is mer-complex 2 with a trans disposition of the pyridine and hydride ligands. Isomerization into the thermodynamic product 2′ containing pyridine in the cis-position with regard to hydride proceeds slowly. The estimation of activation parameters (ΔH ^≠ and ΔS ^≠) shows that the change in the geometry of fac-complexes upon coordination of pyridine occurs through an associative transition state, while isomerization of the mer-complexes is a dissociative process. The isomers of complex 1 and its pyridine-containing derivatives 2 and 2′ are shown to exhibit different reactivities in the formation of dihydrogen bond and the catalytic dehydrogenation of PrⁱOH under model conditions.     

Intensification of shock-induced combustion by electric-discharge-excited oxygen molecules: numerical study

Mechanisms of combustion enhancement in a supersonic H₂–O₂ reactive flow behind an oblique shock wave front are investigated when vibrational and electronic states of O₂ molecule are excited by an electric discharge. The analysis is carried out on the base of updated thermally nonequilibrium kinetic model for the H₂–O₂ mixture combustion. The presence of vibrationally and electronically excited O₂ molecules in the discharge-activated oxygen flow allows to intensify the chain mechanism and to shorten significantly the induction zone length at shock-induced combustion. It makes possible, for example, to ignite the atmospheric pressure H₂–O₂ mixture at the distance shorter than 1 m behind the weak oblique shock wave at a small energy E_s = 1.2 × 10^–2 J · cm^–3 input to O₂ molecules. At higher pressure it is needed to put greater specific energy into the gas in order to ignite the mixture at appropriate distances. It is shown that excitation of O₂ molecules by electric discharge is much more effective for accelerating the hydrogen–oxygen mixture combustion than mere heating the gas.     

Thermal stability of YBa2Cu3O7−δ films deposited on Ni-W textured substrates by laser ablation

The degradation processes of YBa₂Cu₃O_6.77(3) films 600 nm thick deposited on substrates from a textured (100) foil of the Ni-W alloy with the YSZ (Y₂O₃ + ZrO₂) (100 nm) and CeO₂ (50 nm) buffer layers at 200°C in air have been investigated. It has been shown that the degradation proceeds in the same manner as in the bulk ceramic materials with the same oxygen content, namely, initially the single-phase material with the orthorhombic structure laminates into the fractions depleted (the main fraction) and enriched with oxygen. After holding for more than 20 h, the oxygen-depleted fraction is first subjected to the structural phase transformation with the transition of the orthorhombic structure into the cubic one, which is associated with the redistribution of barium and yttrium atoms over their sites in the presence of water vapors.     

Problem of the conservation of the fissile-nucleus-spin projection onto the fissile-nucleus symmetry axis and quantum dynamics of the low-energy fission process

Within quantum-mechanical fission theory, it is shown that, in the low-energy fission of actinide nuclei, the projection K of the spin of a fissile nucleus onto its symmetry axis is conserved as this nucleus traverses the second well of the deformation potential and the region of descent from the external fission barrier to the scission point, this spin projection being an integral of motion despite the effect of Coriolis interaction. This leads to the conclusion that the fission probability is determined by the concerted effect of the internal- and external-fission-barrier penetration factors. A global analysis of information that can be extracted from experimental investigations of (n, f) and (γ, f) reactions and which can be employed in theoretically describing fission mechanisms is performed.     

Laser-initiated ignition of hydrogen-air mixtures

The subject of investigation is the kinetic mechanisms intensifying chain reactions that proceed in a hydrogen-air mixture when O₂ molecules dissociate under the action of laser radiation with wavelength λ _I = 193.3 nm and are excited into the b ¹Σ _g ⁺ electron state by radiation with λ _I = 762.346 nm. The efficiencies of both methods to initiate ignition are compared. Numerical simulation shows that the ignition temperature for the laser-induced excitation of O₂ molecules into theb ¹Σ _g ⁺ state is lower than for the dissociation of O₂ molecules by UV laser radiation, with the energy supplied to the mixture being the same. However, both photochemical methods are much more efficient than mere heating of the mixture by laser radiation or another source of heat.