Preparation of Ultrafine Si Powders from SiH_4 by Laser-induced Gas Phase Reaction

High quality ultrafine Si powders have been synthesized from SiH4 by laser induced gas phase reaction. The powders prduced under different synthesis conditions have mean particle size of 10-120nm in diam. with narrow particle size distribution, and free of hard agglomerates.The powders are polycrystalline with the ratio of mean grain to particle diameter being between 0.3-0.7. The size of the powder increases with increasing laser power and reaction pressure,but decreases with increasing silane gas flow rate and the addition of Ar diluent. Grain sizes drop distinctly with the rise of the addition of Ar gas and laser power, but change little with the gas flow rate and reaction temperature. The formation of Si particles under different synthesis conditions is discussed

Monte Carlo Simulation of Electron Velocity Distribution and Gas Phase Process in Electron-Assisted Chemical Vapor Deposition

The gas phase process of diamond film deposition from CH4/H2 gas mixture by electron-assisted chemical vapor deposition is simulated by the Monte-Carlo method. The electron velocity distribution under different E/P (the ratio of the electric field to gas pressure) is obtained, and the velocity profile is asymmetric. The variation of the number density of CH3 and H with different CH4 concentrations and gas pressure is investigated, and the optimal experimental parameters are obtained: the gas pressure is in the range of 2.5 kPa - 15 kPa and the CH4 concentration is in the range of 0.5% - 1%. The energy carried by the fragment CH3 as the function of the experiment parameters is investigated to explain the diamond growth at low temperature. These results will be helpful to the selection of optimum experimental conditions for high quality diamond films deposition in EACVD and the modeling of plasma chemical vapor deposition.

Effect of chloralkanes on the phenyltrichlorosilane synthesis by gas phase condensation

To enhance the process of phenyltrichlorosilane synthesis using gas phase condensation, a series of chloralkanes were introduced. The influence of temperature and chloralkane amount on the synthesis was studied based on the product distribution from a tubular reactor. The promoting effect of chloralkane addition was mainly caused by the chloralkane radicals generated by the dissociation of C–Cl bond. The promoting effect of the chloromethane with more chlorine atoms was better than those with less chlorine atoms. Intermediates detected from the reactions with isoprene and bromobenzene demonstrated that both trichlorosilyl radical and dichlorosilylene existed in the reaction system in the presence of chloralkanes. A detailed reaction scheme was proposed.

Construction of an operando dual-beam fourier transform infrared spectrometer and its application in the observation of isobutene reactions over nano-sized HZSM-5 zeolite

An operando dual‐beam Fourier transform infrared (DB‐FTIR) spectrometer was successfully developed using a facile method. The DB‐FTIR spectrometer is suitable for the real‐time study of the dynamic surface processes involved in gas/solid heterogeneous catalysis under real reaction conditionsbecause it can simultaneously collect reference and sample spectra. The influence of gas‐phasemolecular vibration and heat irradiation at real reaction temperatures can therefore be eliminated.The DB‐FTIR spectrometer was successfully used to follow the transformation of isobutene over nano‐sized HZSM‐5 zeolite under real reaction conditions.

Vibrational Nonequilibrium in the Hydrogen-Oxygen Reaction at Different Temperatures

A theoretical model of chemical and vibrational kinetics of hydrogen oxidation is suggested based on the consistent account for the vibrational nonequilibrium of HO2 radical which forms in result of bimolecular recombination H + O2 = HO2 in the vibrationally excited state. The chain branching H + O2 = O + OH and inhibiting H + O2 + M = HO2 + M formal reactions are considered (in the terms of elementary processes) as a general multi-channel process of forming, intramolecular energy redistribution between modes, relaxation, and monomolecular decay of the comparatively long-lived vibrationally excited HO2 radical which is capable to react and exchange of energy with another components of the mixture. The model takes into account the vibrational nonequilibrium for the starting (primary) H2 and O2 molecules, as well as the most important molecular intermediates HO2, OH, O2(1D), and the main reaction product H2O. The calculated results are compared with the shock tube experimental data for strongly diluted H2-O2 mixtures at 1000 T p < 4 atm. It is demonstrated that this approach is promising from the standpoint of reconciling the predictions of the theoretical model with experimental data obtained by different authors for various compositions and conditions using different methods. It is shown that the hydrogen-oxygen reaction proceeds in absence of vibrational equilibrium, and the vibrationally excited HO2 radical acts as a key intermediate in the principally important chain branching process. For T < 1500 K, the nature of hydrogen-oxygen reaction is especially nonequilibrium, and the vibrational nonequilibrium of HO2 radical is the essence of this process.

Gas phase ion-molecule reactions of buckminsterfullerene C_(60) with some small organic compounds in mass spectrometer

In chemical ionization mass spectrometry (CIMS) gas phase C60+ or C60can react with fragment ions from three chloromethane and four multichloroethane molecular ions via ion-molecule reactions A dozen of gas-phase adduct ions of C60 are observed, and most of them contain chlorine atoms The results of the comparison and analysis show that the relative intensities of adduct ions are not directly proportional to the corresponding fragment ions in the MS of reagents,which implies that some fragment ions containing radicals are more reactive with C60+ or C60. This indicates that the alkene-like C60+ or C60 can act as a radical sponge in addition reactions.

MAGNETIC PROPERTIES OF R3（Fe,Mo）29Nx（R=Sm OR Y）INTERSTITIAL NITRIDES

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Jet Plasma-Chemical Reactor for the Conversion of Methane: the Use of Clustering

The research results of processes proceeding in supersonic jets of light hydrocarbons, activated by an electron beam are presented. It is shown, that condensation suppressed at activation by electrons in the initial stage of condensation. The developed condensation conditions mode leads to increasing of a part of heavy corpuscles in activated stream and not only owing to stimulation of condensation but because of formation of heavy hydrocarbonic molecules.

Ferrocene-induced switchable preparation of metal-nonmetal codoped tungsten nitride and carbide nanoarrays for electrocatalytic HER in alkaline and acid media

Transition metal nitride/carbide(TMN/C)have been actively explored as low-cost hydrogen evolution reaction(HER)electrocatalysts owing to their Pt-like physical and chemical properties.Unfortunately,pure TMN/C suffers from strong hydrogen adsorption and lacks active centers for water dissociation.Herein,we developed a switchable WO_(3)-based in situ gas–solid reaction for preparing sophisticated Fe-N doped WC and Fe-C doped WN nanoarrays.Interestingly,the switch of codoping and phase can be effectively manipulated by regulating the amount of ferrocene.Resultant Fe-C-WN and Fe-N-WC exhibit robust electrocatalytic performance for HER in alkaline and acid electrolytes,respectively.The collective collaboration of morphological,phase and electronic effects are suggested to be responsible for the superior HER activity.The smallest|ΔGH*|value of Fe-NWC indicates preferable hydrogen-evolving kinetics on the Fe-N-WC surface for HER under acid condition,while Fe-C-WN is suggested to be beneficial to the adsorption and dissociation of H_(2)O for HER in alkaline electrolyte.

A comparative study on the reactivity of cationic niobium clusters with nitrogen and oxygen

We have prepared well-resolved Nb^(+)_(n)(n=1-10)clusters and report here an in-depth study on the es-sentially different reactivity with N_(2)and O_(2),by utilizing a multiple-ion laminar flow tube reactor in tandem with a customized triple quadrupole mass spectrometer(MIFT-TQMS).As results,the Nb^(+)_(n)clus-ters are found to readily react with N_(2)and form adsorption products Nb_(n)N^(+)_(2m);in contrast,the reactions with O_(2)give rise to Nb_(n)O^(+)_(1−4)products,and the odd-oxygen products indicate O-O bond dissociation,as well as increased mass abundance of NbO^(+)pertaining to oxygen-etching reactions.We illustrate how N_(2) prefers a physical adsorption on Nb^(+)_(n)clusters with an end-on orientation for all the products,and allow for size-selective Nb^(+)_(n)clusters to act as electron donor or acceptor in forming Nb_(n)N^(+)_(2m).In contrast to these nitrides,the dioxides Nb_(n)O+2display much larger binding energies,with O_(2)always as an electron acceptor,corresponding to superoxide or peroxide states in the initial reactions.Density-of-states and orbital anal-yses show that the interactions between Nb^(+)_(n)and O_(2)are dominated by strongπ-backdonation indicative of incidental electron transfer;whereas weakπ-backdonation and simultaneousσdonation interactions exist in Nb_(n)N^(+)_(2).Further,reaction dynamics analysis illustrates the different interactions for N_(2)and O_(2) in approaching the Nb^(+)_(n)clusters,showing the energy diagrams for N_(2)adsorption and O-O bond dissoci-ation in producing odd-oxygen products.Fragment analyses with orbital correlation and donor-acceptor charge transfer are also performed,giving rise to full insights into the reactivities and interactions of such transition metal clusters with typical diatomic molecules.