Russian Journal of Physical Chemistry B最新文献

Advanced nanotechnologies allow synthesizing nanoparticles (NPs) with the given physical and chemical properties providing an opportunity to study the effects and mechanisms of the influence of NPs on plants in order to improve their productivity. In this study, Zn NPs introduced in the polymer coating are used as a preparation for the presowing treatment of pepper seeds. It is found that Zn NPs in concentrations of 10^–5 and 10^–6% in the composition of polymers accelerated plant growth and led to a significant increase in the number of leaves and buds, while the root mass volume increased on average by 10–30% compared to the control plants. After seed treatment with Zn NPs with a concentration of 10^–6%, the proline content in plant leaves increases by 58% (p ≤ 0.05); and the protein content, by 20% (p ≤ 0.05). The treatment of seeds with Zn NPs at a concentration of 10^–5% leads to the sugar content increasing by 36% (p ≤ 0.05), and the chlorophyll content, by 52% (p ≤ 0.05) compared with the control.

The ignition of pelletized samples of hard coals of the long-flame gas (LG), gas (G), fat (F), coke (C) grades with particle sizes ≤ 63 μm by laser pulses (λ = 532 nm, τ_i = 10 ns) is studied. When the critical radiation energy density (H_{{{text{cr}}}}^{{(1)}}), specific for each grade of coal, is exceeded, the optical breakdown occurs and a dense plasma with a continuous emission spectrum is formed. As the plasma expands and rarefies, the spectra show the emission of carbon ions CII, excited nitrogen atoms N, excited carbon molecules C₂, and carbon monoxide CO. The plasma glow’s intensity peaks at the end of the laser pulse, and the glow relaxation time is ~1 μs. The plasma glow’s amplitude increases nonlinearly with the increasing energy density of laser pulses. At a radiation energy density of H ≥ (H_{{{text{cr}}}}^{{(2)}}), specific for each grade of coal, thermochemical reactions are initiated in the volume of microparticles and coal particles are ignited in the submillisecond time interval.

Blends of polylactide and polybutylene adipate terephthalate of various compositions are obtained by mixing in the melt followed by pressing. The content of PBAT in the blends is 10, 20, and 30 wt %. The effect of water on film samples at a temperature of (22 ± 2)°C is studied for 270 days. After exposure, a change in morphology is detected: turbidity of the samples and the appearance of defects. The thermophysical characteristics before and after hydrolytic degradation are determined by differential scanning calorimetry. The decrease in the cold crystallization temperature in pure PLA and in a sample with a low content of PBAT (10%), as well as the disappearance of the cold crystallization peak at a content of 20 and 30 wt % of PBAT, is shown. The degree of crystallinity of PLA after exposure to water tends to increase from 0 to 16%. Changes in the chemical structure of the mixed samples are monitored by IR spectroscopy.

The crystal and molecular structure of a polynuclear pivalate complex obtained by the interaction of ZrCl₄ with pivalic acid is determined by X-ray diffraction analysis. The compound C₇₁H₁₂₄O₂₈Zr₄ crystallizes in a monoclinic crystal system. The crystal structure is refined in the nonstandard space group I2. The asymmetric part of the structure includes three Zr atoms, six pivalate ligands, and a bridging µ₃-O oxygen atom, as well as disordered crystallization molecules of pivalic acid with an occupancy of 50% and benzene with an occupancy of 50%. The zirconium complex molecule is a tetranuclear cluster that contains three types of Zr atoms that differ in the ligand environment. A comparison of the results of the quantum chemical calculations of the model reaction of ZrCl₄ with acetic acid with the published data on reactions of ZrCl₄ with aliphatic acids shows the possibility of the formation of both mononuclear Zr(RCO₂)₄ and polynuclear clusters in this reaction, which is a new route for obtaining polynuclear zirconium clusters. The structure of the clusters formed depends on the steric properties of carboxylate ligands.

The thermal stability of N-methyl derivatives of 7H-difurazanofuroxanoazepine and 7H-trifurazanoazepine in the nonisothermal and isothermal modes is studied. The formal-kinetic laws of the decomposition and temperature dependencies of the reaction rate constants are determined. The thermal stability of methyl, propargyl, cyanomethyl, allyl, and amine derivatives of azepines is compared.

Experimental studies of the combustion patterns of the ternary system (100 – x)(Ti + C) – x(Ti + 2B) of bulk density in the powder and granular form used for the synthesis of TiC–TiB₂ composite ceramics are carried out. The study shows that the dependence of the powder mixture’s combustion rate on the Ti + 2B content has a non-monotonic character, which is associated with the influence of the impurity gas (IG) release on the combustion process. By removing the influence of the IG by granulation, a monotonic dependence with two characteristic sections is obtained. For the granulated mixture, an increase in the Ti + 2B content to >60 wt % leads to a change from the conductive combustion mode to the convective one, accompanied by a sharp increase in the combustion rate. For the conductive combustion mode, the combustion rate of the substance inside the granule and the combustion transfer time from granule-to-granule are determined, which allows us to estimate the inhibitory effect of the IG release on the combustion rate of powder mixtures of different compositions. For the convective combustion mode, it is shown that a decrease in the content of the gasifying additive in the mixture (granulation with ethyl alcohol) leads to an unexpected result: an increase in the combustion rate of the mixture. For compositions with (Ti + 2B) > 60 wt %, the combustion rate with the counterfiltration of IGs is determined for the first time, which makes it possible to estimate the front rate increase according to the filtration combustion theory. According to the X-ray phase analysis (XPA), the combustion products of all compositions contain only two main phases: TiC and TiB₂

This paper studies the influence of the conditions for obtaining materials based on the synthetic polymer polylactide on their physical-mechanical and rheological characteristics. These materials are promising for creating temporary biodegradable polymer implants to maintain the mechanical properties of broken bones during the healing period. They are designed to replace the titanium fixators currently used for these purposes, which is due not only to the need for repeated surgery to extract them but also to the fact that the strength and modulus of elasticity of titanium fixators exceed the values of bone strength indicators by an order of magnitude, which can cause the phenomenon of bone resorption and a decrease in its strength. It is established that with an increase in temperature in the plasticization and pressing zone, as well as with an increase in pressure in the press, there is a natural decrease in the viscosity of the polylactide melt, as well as the values of the elastic modulus and breaking stress of solid samples. Varying the cooling rate of the material during the pressing process affects the degree of its crystallinity. At the same time, the lower the cooling rate the greater the degree of crystallinity of the polylactide and the greater the values of the elastic modulus and breaking stress.

The effect of ultraviolet radiation of various wavelengths (254 and 365 nm) on compositions based on polylactide with the addition of natural rubber was studied. It was found that the effect of the UV wavelength of 254 nm on the studied samples was much more active than that of UV 365 nm, which was characterized by a decrease in the melting temperature and the degree of crystallinity of polylactide in the compositions, as well as a deterioration in the physical and mechanical properties. The FTIR-ATR spectroscopy method confirmed the photodegradation process by the change in the intensities of structurally sensitive polylactide and natural rubber bands.

The decomposition rates of diphenylfuroxane and a number of 4-nitro-3-alkyl-furoxanes in dilute solutions are measured by the manometric and calorimetric methods. An increase in the reaction rate with an increase in the polarity of the solvent is not detected in any instance, which corresponds to the absence of an increase in the dipole moment of the molecule during the formation of a transition state (TS). Based on this result, a conclusion is made about the biradical (BR) mechanism of the decomposition of uncondensed disubstituted furoxanes (FOs) in solutions.

The energy pathways of possible decomposition and isomerization reactions of iso-propyl (i-C₃H₇) and n-propyl (n-C₃H₇) radicals are studied by computational methods of quantum chemistry. The B3LYP, M062X, MP2, and CBS-QB3 methods are used to localize stationary points on the potential energy surface of a system containing propyl radicals. A number of intermediate compounds formed during the isomerization and decomposition of propyl radicals are identified and information is obtained on their structure and thermochemical parameters. Based on the results of the research, a diagram of the energy levels of the system under consideration is constructed.