Methane Pyrolysis Stimulated by Admixture of Atomic Hydrogen: 2. Mechanism Analysis and Kinetics Calculation

The kinetics of methane pyrolysis stimulated by the introduction of atomic hydrogen into the reaction medium from an arcjet plasma source was analyzed. Numerical simulation of the reaction kinetics demonstrated that the thermal pyrolysis at lower temperatures (1800 K or lower) followed the radical chain mechanism with short chains (a chain length of 2 or 3), and the addition of atomic hydrogen considerably increased the rate of the process. An analysis of the kinetics of pyrolysis in a stirred reactor showed that acetylene was formed immediately after methane degradation without the buildup of by-products in the reaction medium.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 4, 2005, pp. 312–316.Original Russian Text Copyright © 2005 by Baranov, Demkin, Zhivotov, Nikolaev, Rusanov, Fedotov.     

From disjoining pressure to line tension

The thermodynamic line tension of rectangular edge for amorphous or crystalline bodies with dispersion forces is calculated. The dependence of the local surface tension of the face adjacent to the edge on the distance to the edge is calculated preliminarily and it is shown that the linear tension is practically formed at three intermolecular distances to the edge. The order of magnitude of line tension is determined by the product of surface tension and intermolecular (interplanar for crystals) distance.     

Enhanced production of fast multi-charged ions from plasmas formed at cleaned surface by femtosecond laser pulse

We present atomic, energy, and charge spectra of ions accelerated at the front surface of a silicon target irradiated by a high-contrast femtosecond laser pulse with an intensity of 3×10¹⁶ W/cm², which is delayed with respect to a cleaning nanosecond laser pulse of 3-J/cm² energy density. A tremendous increase in the number of fast silicon ions and a significant growth of their maximum charge in the case of the cleaned target from 5+ to 12+ have been observed. The main specific features of the atomic, energy, and charge spectra have been analyzed by means of one-dimensional hydrodynamic transient-ionization modeling. It is shown that fast highly charged silicon ions emerge from the hot plasma layer with a density a few times less than the solid one, and their charge distribution is not deteriorated during plasma expansion.This revised version was published online in August 2005 with a corrected cover date.     

Solubilization of Nile Red in Micelles and Protomicelles of Sodium Dodecyl Sulfate

A spectrophotometric study of the solubilization and aggregation of the Nile red dye (NR) in premicellar and micellar aqueous solutions of sodium dodecyl sulfate (SDS) was carried out. The experiments were conducted both with saturated solutions of NR under conditions of thermodynamic equilibrium of the solution with a dye precipitate, and at a constant concentration of NR in a homogeneous solution. In the first case, it was proved theoretically and verified experimentally that with an increase in the SDS concentration, the NR concentration always increases, and at the limit of low concentrations, the dependence is linear. In both cases, the concentration of NR dimers as a function passes through a maximum in the premicellar region. There are no dimers in the micellar region. The extinction coefficients of NR monomers in SDS solutions were determined both below and above the critical micelle concentration (CMC) of SDS. A solubilization curve with branches for the premicellar and micellar regions was constructed, the intersection of which was used to find the CMC value in the system under study. The state of deep supersaturation of the NR solution in the metastable state upon dilution of the micellar system with water was studied. It was found that, in addition to dimers, molecular aggregates of higher orders were also formed.     

Diastereoselective cycloaddition of (S)-N-(1-phenylethylimino)trifluoropropionate and trifluoroethylphosphonate with diazomethane

The cycloaddition reaction of (S)-(α-phenylethylimino)trifluoropropionate with diazomethane leads to a diastereomeric mixture (4.5:1) of 5-trifluoromethyl-1,2,3-triazoline-5-carboxylates. Enantiopure diastereomers were isolated by column chromatography and converted into their respective non-racemic 2-trifluoromethyl-aziridine-2-carboxylates and carboxylic acids. The absolute configuration of newly formed stereogenic centers was determined by XRD analysis. The stereoselective reaction between (S)-N-(α-phenylethyl)trifluoroacetimidoylphosphonate and diazomethane produces a diastereomeric mixture (2.5:1) of 5-trifluoromethyltriazoline-5-phosphonates readily separated by column chromatography in diastereomerically pure forms.     

Mechanochemical Effects in Processes of Corrosion of Metals

Mechanochemical effects have been investigated in the processes of corrosion of bent plates of unalloyed and high-alloy steel in aqueous solutions of sulfuric and hydrochloric acids. Special attention was paid to the strain sign effect discovered recently and caused by the existence of a surface stress in solids. The use of the weight method and the hydrogen method of corrosion control has yield well consistent results confirming the existence of the mechanochemical effect of the strain sign even under condition of the starting corrosion cracking. The domination of corrosion on the concave side gives evidence of the negative sign of surface stress at the steel/solution boundary, which can be explained by the formation of the electrical double layer.