Russian Journal of Physical Chemistry B最新文献

A thermogravimetric analysis of the thermal decomposition of polymethylmethacrylate (PMMA) in a carbon dioxide flow is carried out. The kinetic constants of the process are determined. The heating rate of the sample varies over in wide range and amounts to 2, 5, 8, 20, 35, and 50 K/min. The values of the kinetic constants of PMMA decomposition are determined using the isoconversional method. For the degree of conversion of the substance ranging from 10 to 90%, the values of activation energy for the thermal decomposition of PMMA vary in the range from 213.5 to 194.3 kJ/mol, and the values of the preexponential coefficient change in the range from 1.62 × 10¹⁶ to 6.85 × 10¹² 1/s. The average activation energy for the thermal decomposition of PMMA in a carbon dioxide flow is 206 kJ/mol.

To verify the hypothesis of electrical hot spots (HSs)—channels of local electrical breakdowns—the analysis of the electrical properties of condensed explosives and the evaluation of the electric field strength in shock-loaded dielectrics are carried out. It is established that conditions for electrical breakdowns can be created in the compressed zone of explosives due to polarization phenomena (electric field) and shock-induced electrical conductivity (free electrons). The position of the electric model of detonation kinetics are formulated. The results of the experiments with liquid nitromethane (NM) and monocrystalline PENT are explained.

The neutralization of sulfur compounds during the filtration combustion of model mixture compositions containing iron sulfide or copper sulfate by adding marble (CaCO₃) is studied. It has been experimentally shown that during burning model charge compositions with additions of both iron sulfide and copper sulfate, replacing chemically inert sapphire with marble leads to a decrease in the combustion temperature by approximately 150–200°C. At the same time, the content of CO₂ in gaseous products increases, and the concentrations of CO and H₂ decrease. The greatest effect on the absorption of sulfur-containing substances when adding marble is shown in experiments where sulfur is present in the fuel in sulfide form: the addition of 50% marble makes it possible to capture 72% of the initial sulfur content, and for compositions with 90% marble in the charge, 85%. The absorption of the sulfur compounds formed during the combustion of model mixture compositions with copper sulfate is much worse. When the charge contains 50 and 85% marble, sulfur-containing compounds were absorbed by only 19 and 24%, respectively.

The uptake of O₃ on a salt film coating of MgCl₂·6H₂O at T = 254 and 295 K is studied in the range ([O₃] = 2.5 × 10¹³–1.6 × 10¹⁴ cm^–3) using a flow reactor with a movable insert and mass spectrometric recording. The time dependence of the uptake coefficient of the ozone at different O₃ concentrations is obtained in the relative humidity range from zero to 24%. Using the method of mathematical modeling, based on the shape of the dependence of the uptake coefficient and its time decay on the ozone concentration, the uptake mechanism is established and the elementary kinetic parameters are assessed, based on which it is possible to extrapolate the time behavior of the uptake coefficient to tropospheric conditions at arbitrary ozone concentrations. The ozone uptake at room temperature occurs through the reaction mechanism of an adsorbed molecule on the surface of the substrate. The mechanism includes the stage of reversible adsorption, formation of an adsorbed complex, and its unimolecular decomposition with the release of molecular chlorine into the gas phase. At low temperatures, the uptake proceeds through recombination via the Eley-Rideal reaction mechanism: it includes reversible adsorption, formation of a surface complex, its reaction with an ozone molecule from the gas phase, and the release of an oxygen molecule into the gas phase. In this case, no chlorine is formed. The dependence of the uptake coefficient on relative humidity in the range of values from 0 to 24% at T = 254 K is not detected.

The influence of atmospheric waves generated by a tropospheric convective source on the state of the upper atmosphere and ionosphere during the recovery phase of the geomagnetic storm on May 27–28, 2017 is studied. A new approach to accounting for atmospheric waves generated by tropospheric convective sources in large-scale atmospheric models without using wave parameterization is proposed and implemented. The developed approach makes it possible to comprehensively study the effects generated by atmospheric waves against the background of various geophysical events, including geomagnetic storms. The multimodel study shows that the proposed approach allows us to reproduce perturbations of the critical frequency of the ionosphere’s ionospheric F2 layer caused by the propagation of atmospheric waves generated by a tropospheric meteorological source. It is shown that the inclusion of a heat inflow source simulating the propagation of atmospheric waves from the lower atmosphere in the global model enhances the effects of a geomagnetic storm, which manifests itself as an additional decrease in the critical frequency of the F2 layer, which can reach 7% of the absolute values.

It is shown that the front of the flame of a thoroughly mixed diluted methane-oxygen mixture at 298 K and 100–300 Torr propagating to the ends of hollow cylindrical and conical obstacles does not form a von Kármán path (vortex shedding) behind them; however, this instability occurs under the same conditions in the flow of hot products after obstacles. The reason that vortex shedding is not observed behind an obstacle during flame propagation but appears in the course of propagation of a reflected stream of hot products is that thermal conductivity reduces the curvature of the flame and leads to its stabilization. Indeed, the convex areas of the chemical reaction zone in a combustible mixture give off more heat in relation to cold ones than in a flat flame: the heat from them is not only transmitted forward in the direction of flame propagation but also in the lateral directions. The resulting cooling of the reaction zone causes the flame regions that burst forward to lag behind. The opposite situation is observed in concave areas, where the temperature rises for the same reasons. The rate of reactions increases and they spread forward faster as the flame spreads. Thus, the surface of the curved front of the flame is evened out. In other words, thermal conductivity has a stabilizing effect on a curved flame. This effect is missing in non-reactive gas. This effect is absent in a nonreacting gas. Calculations based on the acoustic approximation of the Navier–Stokes equations for a compressible reacting medium make it possible to take into account the main observed feature of the flame front approaching an obstacle in the form of a cylinder: vortex shedding is not observed behind the obstacle during flame propagation. Thus, a qualitative model allows obtaining both the mode of the emergence of a von Kármán instability in a chemically inert gas and its absence during flame propagation.

It follows from the observational data that variations of the atmospheric electric field occur during geomagnetic storms. In this paper, we present the simulation results of ionospheric electric fields during the main phase of the geomagnetic storm on March 17, 2015, within the framework of a quasi-stationary model of a conductor consisting of the atmosphere and the ionosphere. For this purpose, the satellite data on the global distribution of currents between the magnetosphere and the ionosphere are used to describe the magnetospheric source of the electric field. A variation of the electric potential in the ionosphere leads to a variation of the electric field in the entire atmosphere, including its surface layer. It is important that during a geomagnetic storm, the observatory in which the atmospheric electric field is measured significantly changes its position relative to the direction of the Sun. This leads to significant changes in the ionospheric conductivity above the observatory, which affects both the ionospheric electric field and the atmospheric part of the global electrical circuit (GEC). Therefore, when assessing the effect of a geomagnetic storm on the atmospheric electric field in a particular observatory, it is necessary to take into account the local time when comparing the measurement data with the geomagnetic activity indices. For the storm on March 17–18, 2015, we found that taking into account the variations of the ionospheric electric field when calculating the atmospheric electric field allowed us to reproduce the disturbances of the fair weather electric field observed at the Borok Geophysical Observatory. Based on the simulation results, it is shown that during extremely strong magnetic storms, additional atmospheric electric field variations in some places on the Earth have the same scale as the fair-weather field itself.

The effect of a moderate magnetic field (MF, 600 mT) of a permanent magnet on the generation of radicals (W_i) in mixed micellar systems of quaternary ammonium compounds (QACs) with hydroperoxides (QAC–ROOH) is studied and measured by the inhibitor method. The effect of an MF on the rate of radical polymerization initiated by radicals generated from a surface chemisorbed on a solid QAC carrier during the interaction with the hydroperoxide dissolved in the monomer is evaluated. It is established that in micellar solutions the MF reduces W_i and the magnetic effect (ME) ≈ –0.45. In the case of the radical polymerization of styrene containing cumyl hydroperoxide on the surface of mica plates with a chemisorbed monolayer of QAC (CTAB or ACh), the rate of polymerization and, consequently, W_i increase in the MF, i.e., ME > 0.

This paper presents the results of calculations of the length of ozone destruction chains in the lower stratosphere in HO_x-, NO_x-, and ClO_x-catalytic cycles, taking into account heterogeneous chemical reactions (HCRs) involving particles of the Junge layer. Taking into account these reactions leads to a change in the type of high-altitude profiles of the length of the chains in these cycles, calculated in the approximation of the absence of HCRs. At the lower boundary of the Junge layer, a degeneration of the chain destruction of ozone in the NO_x cycle is observed, caused by a sharp decline in the concentrations of components of this family due to the capture of N₂O₅ gas molecules. At the same time, there is an increase in the chain length in the HO_x cycle by more than an order of magnitude due to the decrease in the concentrations of OH and HO₂ radicals and, as a result, a decrease in the rate of chain breakage with their participation. At high altitudes, the length of the ozone destruction chains, taking into account HCRs, on the contrary, are higher; this is due to the acceleration of the destruction of O₃ by chain carriers in HO_x- and ClO_x-cycles. The increase in their concentrations is due to the reduced content of NO and NO₂ in the air. The considered effect of HCR practically disappears at the upper boundary of the Young layer due to the evaporation of particles.

A series of probe measurements to determine the electron concentration in the gas ahead of a strong shock wave (SW) front are carried out using a modified double-diaphragm shock tube (DDST-M) of the Institute of Mechanics, Moscow State University. At the same time, the light flux from the region of the shock-heated gas is recorded, which makes it possible to calculate the electron concentration behind the SW using the spectroscopic method. The experiments are carried out in air, oxygen, and nitrogen at SW velocities ranging from 8.3 to 11.3 km/s and an initial pressure of 0.25 Torr in the low-pressure chamber (LPC). The dependencies of the electron concentration on the SW velocity and the distance from the observation point to the SW are obtained. The spectroscopic measurements make it possible to determine the dependence of the electron concentration on the composition of the gaseous medium. The obtained data are compared with the experimental data of other authors.