Vol 43, No 4 (2024)

During the evaporation of magnesium and calcium in partially dissociated H₂, a glow with λ = 4571.15 Å and λ = 6572.78 Å was detected, corresponding to the transitions ³P₁⁰ → ¹S₀ in excited Mg^* and Ca^* atoms. It is assumed that this phenomenon is associated with the chemiluminescence of these atoms when they interact with H atoms.

The crystal and molecular structure of a polynuclear pivalate complex obtained by the interaction of ZrCl₄ with pivalic acid was determined by X-ray diffraction analysis. The compound C₇₁H₁₂₄O₂₈Zr₄ (compound 1) crystallizes in the monoclinic crystal system. The crystal structure was refined in the nonstandard space group I2. The asymmetric part of the structure includes three Zr atoms, six pivalate ligands, 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 ligand environment. Comparison of the results of quantum chemical calculations of the model reaction ZrCl₄ with acetic acid with the literature data on reactions of ZrCl₄ with aliphatic acids have shown 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 ZSM-5 zeolites with Si/Al ratio 50 and 80 (ZSM-5-50 и ZSM-5-80) modified by Ca-, Sr-, Cr-, Mn- и Sb-ions were synthesized and investigated in oxidation of benzene to phenol. It was shown that more active and selective in direct oxidation of benzene by nitrous oxide are catalysts containing about 0.1–0.2% of Sb. It formally corresponds to substitution of 1/12 and 1/6 ions of H-ions by Sb-ions in ratio 1 : 1 of zeolite. Yield of phenol equal to 61.2% was obtained at 450°C and contact time 1 sec. with selectivity to phenol 96% in the presence of (ZSM-5-50 + 1/12 Sb) sample. It is about twice as much than an average value of yield reported in literature for other Me-ZSM-5 catalysts. Also, (ZSM-5-50 + 1/6 Sb) sample revealed much higher stability than other catalysts based on ZSM-5 zeolites. A model of nitrous oxide activation over single active sites (located very distant from each other) of the catalyst is suggested. The suggested model of single site adsorption and catalysis allows explain more higher efficiency of nitrous oxide as oxidant than that of molecular oxygen in reaction of direct oxidation of benzene to phenol, especially over catalysts with a low concentration (less than 0.1%) of |Me-ions.

The decomposition rates of diphenylfuroxane and a number of 4-nitro-3-alkyl-furoxanes in dilute solutions were measured by manometric and calorimetric methods. In no case, an increase in the reaction rate was detected with an increase in the polarity of the solvent, which corresponds to the absence of an increase in the dipole moment of the molecule during the formation of a transition state. Based on this result, a conclusion is made about the biradical mechanism of decomposition of uncondensed disubstituted furoxanes in solutions.

Experimental studies of the combustion patterns of the ternary system (100 – x)(Ti + C) – x(Ti + 2B) of bulk density in powder and granular form used for the synthesis of composite ceramics TiC–TiB₂ were carried out. The study shows that the dependence of the powder mixture combustion rate on the Ti + 2B content has a non-monotonic character, which is associated with the influence of impurity gas release on the combustion process. By removing the influence of impurity gas by granulation, a monotonic dependence with two characteristic sections was obtained. For the granulated mixture, an increase in the Ti + 2B content > 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 the granule to the granule were determined, which allowed us to estimate the inhibitory effect of impurity gas release on the combustion rate of powder mixtures of different composition. For the convective combustion mode, it was shown that a decrease in the content of the gasifying additive in the mixture (granulation with ethyl alcohol) led to an unexpected result: an increase in the combustion rate of the mixture. For compositions with (Ti + 2B) > 60 wt. % the combustion rate with counter filtration of impurity gases was determined for the first time, which made it possible to estimate the front rate increase according to the filtration combustion theory. According to XRD results, the combustion products of all compositions contain only two main phases TiC and TiB₂.

The possibility of using radiation from a two-frequency pulsed copper vapor laser with wavelengths of 510.6 nm and 578.2 nm with an exposure of 30 to 120 s to stimulate the development of coniferous trees (spruce, pine, larch) with a single seed irradiation is shown. The stimulation effect manifests itself at various early stages of development, such as the awakening of seeds in the aquatic environment in the first hours of the experiment (according to electron absorption spectroscopy data), seed germination, and seedling growth under stressful cultivation conditions. Possible causes of light exposure to plant seeds are discussed.

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

The results of thermogravimetric and Fourier transform infrared (FTIR) analysis of polymer composite materials (PCM) based on polyethylene and polycarbonate are presented and compared to the polymers polyethylene and polycarbonate. Empirical data were obtained for mathematical modeling, including the amount of solid residue upon pyrolysis, volatile yield, and ash content of the studied PCMs and polymers. Results of the mathematical modeling of the pyrolysis process at a temperature of 600 °C are presented to quantitatively assess the composition of the pyrolysis gas.