Vol 10, No 4 (2016)

Recombination of singly charged heavy Cs⁺ and Br^– ions with stabilization with neutral Ar or Xe atoms was studied by the classic trajectory method in the range of ion collision energy and third body energy from 1 to 10 eV. The elementary reaction of recombination was studied on the potential energy surface (PES), which quantitatively reproduces the experimental results of collision-induced dissociation of CsBr molecules (the reverse of recombination). An analysis of the statistically reliable number of trajectories revealed a complex multifactor dynamics of recombination, which involves various mechanisms whose realization depends both on the mass and energy ratio of colliding particles and on the PES structure and spatial configurations of collision determined by impact parameters, orientation angles, etc. The molecules that formed as a result of recombination have nonequilibrium vibrational energy distributions and rotational energy distributions comparable to equilibrium.

Photoinduced processes in thin films of MoO₃ and mixed V₂O₅: MoO₃ oxides prepared by polycondensation of the respective oxoacids under solvothermal conditions are studied using Raman spectroscopy, ESR, and AFM. It is shown that, under UV irradiation, the photoinduced polycondensation occurs in the oxide films, leading to the formation of the oxygen bridges, an effect that opens up the possibility of developing a new photolithographic process.

The thermal decomposition of 2,4,6-triazido-1,3,5-triazine in the melt and a dinonyl phthalate solution is studied by thermogravimetry, manometry, mass spectrometry, and IR spectroscopy. The kinetic and activation parameters of the process are determined. The only gaseous product of the reaction is nitrogen. This fact, along with the structure of the condensed residue formed during the thermal decomposition of 2,4,6-triazido-1,3,5-triazine in the melt, are indicative of the abstraction of a nitrogen molecule from an azide group at the initial stage and of the subsequent reactions leading to the formation of a planar network of polyconjugated bonds between C and N atoms. For the thermal decomposition of 2,4,6-triazido-1,3,5-triazine in solution the preexponential factor and activation energy are found to be 10^12.8 s^–1 and 34100 cal/mol, respectively, which are characteristic of the thermal decomposition of most azides. To explain why these parameters are substantially higher for the reaction in the melt (10^17.4 s^–1 and 42300 cal/mol), it is assumed that, in this case, the process proceeds by the polymerization (polycondensation) mechanism to form twodimensional networks, with the apparent kinetic parameters being effective quantities. Based on these data, it is concluded that the high sensitivity of 2,4,6-triazido-1,3,5-triazine to external influences is of kinetic nature.

The effect of the ¹⁶O ↔ ¹⁸O substitution in the coordination sphere of permanganate anion MnO₄⁻ on the chemical shift of ⁵⁵Mn nuclei have been studied by ¹⁷O and ⁵⁵Mn NMR. Time constants τ_n,k of oxygen exchange in the water–permanganate anion system have been estimated. In nearly neutral solutions (pH ≈ 6.8–7.2), the oxygen exchange time is on the order of tens of hours. Bubbling gaseous HCl through this solution for a few seconds leads to the equilibrium distribution of oxygen isotopes in the manganese coordination sphere. The observed temperature dependences of isotope-induced ⁵⁵Mn NMR shifts in Mn¹⁶ O_44-n¹⁸O_n^– (n = 0–4) have been treated as a result of rovibrational averaging of Mn–O bond lengths. The change in the Mn—O bond length in caused by the ¹⁶O → ¹⁸O isotope substitution is on the order of 10^–4 Å.

The effect of process parameters on the propane conversion and the composition of oxidation products, particularly the methanol to carbon monoxide ratio, has been studied. A numerical study of the laws governing the partial oxidation of propane has been conducted in terms of a model that approximately describes the macrokinetics of the partial gas-phase oxidation of hydrocarbons in a flow tubular reactor.

The values of the ignition delay time of cyclopropane–oxygen–argon (cyclo-C₃H₆–O₂–Ar) mixtures of different compositions (φ = 0.333, 1, and 3) behind reflected shock waves at temperatures of 1200–1640 K and a pressure of (0.55 ± 0.05) MPa are measured. A kinetic mechanism of cyclopropane ignition using the known rate constants for the most important elementary reactions is developed. The mechanism closely describes both our own and published experimental data on the delay time of ignition of cyclopropane in shock waves over wide ranges of temperature (1200–2100 K), pressure (0.1–0.55 MPa), cyclopropane concentrations (0.05–11 vol %), and oxygen concentrations (0.25–21 vol %). It is shown that, with increasing fraction of diluent gas in the mixture, the dependence of the ignition delay time on the fuel-to-oxidizer equivalence ratio changes.

The kinetics of the explosive decomposition of pressed pentaerythritol tetranitrate pellets containing nickel nanoparticles with various radii has been investigated experimentally, with the explosion initiated by a neodymium laser pulse (wavelength, 1064 nm; pulse duration at half-height, 14 ns), and probability curves for this process have been recorded. The experimental values of critical initiation energy density corresponding to 50% explosion probability are 0.9, 0.7, and 1.4 J/cm² at a nickel particle radius of 67, 78, and 138 nm, respectively. The initial time interval in which the intensity of light emission accompanying the explosive decomposition increases begins during the action of the pulse and is described by a Gaussian function with an effective constant of k = (1.4 ± 0.1) × 10⁸ s^–1, which is independent of the nanoparticle radius. Experimental data of this study can be interpreted within the micro-hotspot model of thermal explosion.

Data available from the literature are used to calculate the enthalpic contribution from the trinitromethyl group for a number of C-trinitromethyl derivatives of aromatic and heteroaromatic compounds and to recalculate the enthalpies of formation of these compounds in the condensed phase. The calculated data are used to estimate the efficiencies of these compounds as oxidizers in energetic compositions.

The thermal reaction characterization of micron-sized aluminium powder in carbon dioxide were investigated by simultaneous thermal analysis technology (TG/DSC), using a series of heating rates (5, 10, 15, 20°C/min). The results showed that the reaction process of micron-sized aluminium powder in carbon dioxide was divided into three stages: the initial slow oxidation stage, the sharp oxidation stage and the last oxidation stage. The thermal performance was increased with the increase in the heating rates. Evolution of the samples was determined by collecting the products at the initial, sharp, and last oxidation stages of the process. The reaction products morphology was examined using scanning electron microscopy (SEM). The corresponding chemical changes were analysed by X-ray diffraction spectrometry (XRD). The effects of heating rate on the thermal reaction characteristics were discussed. A new reaction mechanism of micron-sized Al particle in CO₂ with gradually increased temperature was proposed.

The optical and photovoltaic properties of two-component TPP–Yt_0.95Er_0.05VO₄ films prepared by the spincoating method are for the first time studied. A 30% increase in the photovoltage (PV) of TPP: Yt_0.95Er_0.05VO₄ = 3: 2 films on silicon carbide (SiC) supports as compared to TPP one-component films is observed. In contrast, for films on tin dioxide (SnO₂) supports, the PV drops by 35–96% as the TPP content in the film decreases from 80 to 20%. The properties of the films are monitored by atomic force microscopy. The highest roughness of the films corresponds to a 40–60% TPP content.

The process of comminution of EPDM vulcanizates with different content of plasticizer (paraffin oil) is studied. A sol–gel analysis is performed, and the crosslink density in the rubber powders obtained is determined. The surface morphology of these rubber powders is examined by scanning electron microscope. The surface of the particles shows characteristic regions of plastic and brittle fracture. A model of the structure of particles of rubber powders is proposed.

The limiting polymerization temperatures of PFPVE at pressures 5.28–10.56 kbar (T_c = 200°C at 7.04 kbar and T_c = 240°C at 10.56 kbar) are measured. The volume of reaction ΔV and enthalpy of polymerization ΔH are determined.

The structural dynamic parameters of ultrafine fibrous matrices of poly-3-hydroxybutyrate (PHB) and composite mixtures of PHB with chitosan were studied by differential scanning calorimetry, EPR spectroscopy, and scanning electron microscopy. The melting enthalpy of PHB fibers considerably increased when a small amount of chitosan was added. Amorphous regions with diverse morphology were found in the fibers under study. The dynamics of the TEMPO spin probe in these regions and its change in the fibers under the action of temperature, aqueous medium, and ozone was determined. The mechanism responsible for the effect of chitosan, temperature, and aggressive oxidating medium on the structure of ultrafine PHB fibers was suggested.

X-ray diffraction and thermal analyses, microscopy, and specific surface area measurements are used to study the formation, structure, and reactivity of mechanoactivated Mg/MoO₃ and Al/MoO₃ nanocomposites during slow heating (10°C/min). The optimal mechanoactivation dose is determined. The mechanoactivated Mg/MoO₃ composite is a dense mixture of two nanosized components with a contact surface of ~8 m²/g (upper estimate). The area of the contact surface between the components of the Al/MoO₃ composite is less than 2 m²/g, with the sample consisting of micron-sized aluminum flakes coated with nanoparticles oxide nanoparticles. When heated, the Mg/MoO₃ system explodes, with the temperature of explosion being determined by the heating conditions. The minimum temperature of conversion is ~250°C, close to the temperature of autoignition of fuel–air mixtures promoted by these additives. The Al/MoO₃ system is characterized by a phased progress of the reaction in the temperature range of 200 to 1000°C. The reasons for the differences in the reactivity of the mixtures are discussed.

An experimental and theoretical justification of the efficiency of a highly porous basalt-fiber-based heat insulation capable of providing geophysical equilibrium conditions for the existence of permafrost during the operation of steam-heated oil wells in the Far North is given. A mathematical model of heat transfer in highly porous fibrous materials is proposed to describe the steady-state mode of the process, with consideration given to Stefan–Boltzmann radiation into the pores of the highly porous material, thickness of the heat insulation layer, and temperature of the hot wall. The temperature dependence of the thermal conductivity of a highly porous heat-insulating material is obtained. It is shown that the thermal conductivity of a basaltbased fibrous heat-insulating material decreases by two orders of magnitude as its temperature rises to 930°C. The analysis performed provided new information of the parameters of the pore space of fibrous material in the processes of conductive heat transfer. The proposed solution makes it possible to calculate the thickness of a heat-insulating layer and concurrently optimize the porosity of the material. The results provide a basis for selecting suitable technological solutions.