Vol 12, No 5 (2018)

Dissociative excitation of even quartet and sextet levels of the manganese atom by electron collisions with manganese diiodide molecules was studied experimentally. Twelve excitation cross-sections for transitions from quartet levels and 23 cross-sections for transitions from sextet levels were measured at an incident electron energy of 100 eV. The optical excitation function (OEF) was recorded in the range of electron energies 0‒100 eV for transitions originating at the 3d⁵4s4de⁶D_J levels. The potential channels of dissociative excitation in the range of low electron energies (E < 22 eV) were discussed.

The main stages of the nuclear fuel cycle from extraction of uranium ores to disposal of radioactive waste resulting from the processing of spent nuclear fuel were briefly analyzed. A list of the most probable radioactive substances and toxic chemicals that can be part of emergency emissions at each stage of the nuclear fuel cycle was composed. The basic physical principles of local and remote IR absorption laser technologies for detecting radioactive substances and toxic chemicals in the atmosphere for solving some unique problems of environmental monitoring were considered. The analytical potential of the currently most effective laser technologies for atmospheric monitoring at nuclear fuel cycle plants based on the achievements of diode laser spectroscopy, cavity ringdown laser spectroscopy, and optoacoustic laser spectroscopy using diode and quantum-cascade lasers was discussed. Current trends in the development of laser technologies for atmospheric monitoring in different IR spectral ranges were analyzed.

Self-oscillations of the rate of oxidation reactions of CO and CH₄ on nickel foil are compared. It has been shown that, despite significant differences in the stepwise mechanism of the two reactions, the properties of oscillation regimes are very close. In both reactions, oscillation regimes result from oxidation and reduction of nickel and are accompanied by wave processes on the catalyst surface. The similarity in the properties of rate oscillations in the reactions of CO and CH₄ oxidation shows that a change in the selectivity and the formation of carbon on the nickel surface are not key factors in the mechanism of the rate oscillations in CH₄ oxidation. An observed periodic change in the concentrations of reactants and reaction products when the reaction mixture is supplied in a pulse mode proves that, in both cases, the self-oscillations of the reaction rate are due only to the reaction mechanism and are not caused by a change in the catalyst temperature.

In this paper, we analyzed kinetic data using theoretical concepts regarding the dominant role of chain processes in gas combustion. It was concluded that water vapor and hydrogen peroxide vapor can have a promoting effect on the explosive decomposition of acetylene. This prediction contradicts earlier conclusions that were based on the thermal theory of combustion, which states that water can only exert a diluting effect on acetylene decomposition. Our statement was experimentally confirmed: at an ignition energy of 100 times lower than the initiation energy of the explosive acetylene decomposition at atmospheric pressure, it is possible to initiate it in the presence of water vapor and hydrogen peroxide. The obtained results do not contradict data in the literature and indicate that the acetylene explosiveness is largely determined by humidity.

In this work, the composition of formed products and the dynamics of decomposition related to thermal explosion and at temperatures that are stepwise increased have been experimentally studied for graphite oxide. The gaseous products formed in the explosive and stepwise thermal reduction of graphite oxide within a range from 20 to 1000°C have been determined and quantitatively characterized. The presented data have shown that the oxygen-containing groups of graphite oxide are generally decomposed in three temperature regions of 170–250, 500–600, and 750–1000°C. It has been demonstrated that the atomic ratio C: O in the end product, from around 2 in the initial graphite oxide, grows to 8 after explosion. Temperature estimates for such explosions are given for the first time. It has been revealed and substantiated that the explosive reduction of graphite oxide completely confirms the self-ignition theory of N.N. Semenov.

In this paper, the regularities of a thermal explosion of a heterogeneous system consisting of two immiscible liquids have been studied. Each phase is a solution of A and B reagents. Reagent B is extracted into a solution of reagent A, where the bimolecular exothermic reaction A + B → Products takes place. It has been shown that an exothermic reaction (combustion regime) continues to proceed in the system at high mass-exchange rates between phases after a thermal explosion. As a result, the maximal temperature may significantly exceed the temperature of the thermal explosion. The critical value of the Semenov parameter decreases with an increase in the mass-exchange rate between phases. In the limited range of values of the distribution coefficient of reagent B between phases, the increase of this coefficient is also accompanied by a decrease in the critical value of the Semenov parameter. The concentration of reagent B in the initial phase decreases monotonically due to its extraction into another phase. However, the equilibrium of the extraction of reagent B can shift, due to the temperature dependence of the distribution coefficient during the reaction. Thus, the time dependence of the concentration of reagent B on may be more complex and can pass through a minimum.

Study of the practice of using solid rocket fuels and explosives has determined the existence of an increase in the combustion rate due to turbulence. However, this rule is violated in the case of small-scale turbulence produced by the gasification zone of solid fuel. The incoming heat from the gas phase is partially consumed to maintain the chemical reaction of gasification and partially returns to the gas phase. If the return energy of turbulent motion is high, then the combustion rate decreases.

In this work, electrophilicity indices are calculated for 50 peroxyl radicals with density-functional theory (B3LYP hybrid functional and the 6-311+G(d,p) basis set). There is a relationship between general and local electrophilicity indices of peroxyl radicals and Taft inductive constants (σ*) of the substituents at the–OO^• group.

Rheological studies of solutions of amphiphilic copolymers based on hydrophilic polysaccharides chitosan (CT) and chitosan succinamide (CTS) sodium salt with methyl acrylate (MA) synthesized by radical copolymerization have been conducted. It has been found that the hydrophobic interaction of poly(methyl acrylate) blocks in solutions of CT–MA and CTS–MA copolymers leads to an increase in the degree of structuring of macromolecules; this feature leads to the formation of an elastoviscous system without introducing of an additional crosslinking agent.

Nanosized powder materials made Zn-doped titanium dioxide with concentration of 0.1, 0.5, and 1.0 mol % Zn²⁺ have been synthesized from aqueous solutions of inorganic compounds of titanium modified with zinc(II) ions. The materials obtained have been studied by electron microscopy, thermogravimetric analysis, and powder X-ray diffraction. It has been found that if zinc ions introduced in titanium dioxide the stabilization of anatase modification takes place retaining size and morphology of particles. The materials synthesized have shown photocatalytic activity under ultraviolet and visible light irradiation. The highest photocatalytic activity has been found for material containing 0.1 mol % Zn²⁺ and calcined at 600°С.

The geometric representation of the space of events is proposed, which is radically different from pseudo-Euclidian Minkowski space. In the framework of the new model, the space of events is reflected onto a four-dimensional Euclidian space in which time multiplied by the speed of light can be considered as a length of geodesic line. The existence of the limiting speed of motions appears to be the consequence of the proposed geometric interpretation of time. The possibility for the new interpretation of time is discussed in order to consider distortions of GPS signals when they pass through the Earth’s ionosphere.

Comparative characteristics of catalytic activity of electroneutral and positively charged coatings consisting of organoboron nanoparticles with a composition (C₂B₁₀H₄)_n or platinum in ammonia decomposition have been obtained for the first time. The charge on the coatings was created by the supply of a positive voltage of +6 or +10 V. It has been found that, for the same mass of the coatings at 700 K and a pressure of 5 × 10^–7 Torr, the rate of ammonia decomposition on a coating consisting of organoboron nanoparticles is 28–43% of the rate of NH₃ decomposition on the coating consisting of platinum nanoparticles depending on the voltage supplied to the coatings.