Synthesis of nickel nanostructured microfibers to increase the electrochemical activity of nickel electrodes
M. Morozov, R. Mansurov, S. Drobyshev

🗏 : 260-269
DOI: https://doi.org/10.17277/jamt.2023.04.pp.260-269

At present, the investigation of the properties of nanostructured materials for electrochemical applications, in particular for the development of promising supercapacitors, is of current interest. In this regard, a special interest is directed to the study of new methods for the synthesis of nickel microfibers nanostructured materials. The research focuses on the fact that the existing synthesis methods are complicated and require either specialized equipment or a large number of chemical reagents for the synthesis of nickel nanostructured materials. The aim of this work is to determine the influence of the reagents, nickel chloride as an oxidizer and hydrazine hydrate as a reducing agent, on the parameters of nickel microfibers – length and surface development. Using this technique, nickel nanostructured microfibers were obtained depending on the oxidizer concentration. The morphology of the obtained products was characterized by optical microscopy and scanning electron microscopy. It was shown that the morphology of the microfibres changes smoothly with changes of the oxidizer concentration, which provides controllability of the product characteristics, adjustment of the required length of nickel microfibers in the range from 20 to 150 μm. The method of X-ray phase analysis confirmed that the final products of the synthesis are nickel microfibers without any side impurities. The high electrochemical activity of nickel electrodes modified by the synthesized structures in alkaline electrolyte was shown. The results obtained can be used in the electrochemical current sources, including batteries and supercapacitors, as well as in other applications where a developed surface is required, for example, in sensors and catalysis.

Promising sorbents based on compacted highly porous carbon materials
I. Shubin, E. Mkrtchyan, O. Ananyeva

🗏 : 270-278
DOI: https://doi.org/10.17277/jamt.2023.04.pp.270-278

The paper considers the stages of preparing a compacted highly porous carbon material (HPCM), which involves alkaline high-temperature activation of the initial carbonizate at a temperature of 400–7500 °C for a duration of 2 hours. As a result of activation, a material was produced with a specific surface area of 2600–2700 m2⋅g–1 and a pore volume of more than 1.3 cm3⋅g–1. The activated material was compacted using binders, which were basalt fiber (HPCM/BF), polyvinyl alcohol (HPCM/PVA) and polyvinyl acetate (HPCM/PVAC). Conditions for compacting were as follows: pressure in the range from 25 to 1600 kgf⋅cm–2, temperature 75–1900 °C and duration between 30 and 150 minutes. As a result, the compacted material had a specific surface area of 1550–2000 m2⋅g–1 and a specific pore volume of 0.693–0.849 cm3⋅g–1. For the final samples, the sorption capacity for molecules of the organic dye methylene blue (MB) was determined. The kinetic studies showed that the absorptive capacity of h the initial material HPCM was 1691 m⋅g–1, while that of compacted samples of HPCM/PVAC, HPCM/BF and HPCM/PVA was 1611, 1000, and 1270 mg⋅g–1, respectively. In this case, the time for the onset of adsorption equilibrium was 15 min. The presented results show that the compacted carbon material can be a promising sorbent of organic pollutants from aqueous solutions.

A method of obtaining aluminum tris(8-hydroxyquinoline) and its physicochemical properties
D. Belov, S. Belyaev, P. Yunin, D. Radishev

🗏 : 279-293
DOI: https://doi.org/10.17277/jamt.2023.04.pp.279-293

Obtaining high-purity single-crystalline aluminum tris(8-hydroxyquinolinate) (Alq3) in significant volumes is a topical task both for OLED technologies and for its use as a promising electron-pumped laser material. This article proposes a simple, convenient and ecologically friendly “one-pot” synthesis based on the interaction of high-purity aluminum powder and 8-hydroxyquinoline in an aqueous solvent of ammonia with high yield. The method allows for the selective synthesis of an α-polymorphic modification of the meridional isomer Alq3. An electron microscopic study of the α-phase powder mer-Alq3 was carried out. It has been determined that the substance has a uniform morphology of a treelike branching structure formed from rod-like linear crystals. The structure of the resulting compound was characterized by X-ray diffraction, Raman spectroscopy, and electron spectroscopy. Qualitative and semi-quantitative analysis of chemical elements was carried out using energy-dispersive X-ray spectroscopy (EDX method). The optical absorption spectra of Alq3 solvents in eight organic solvents were studied: DMSO, CH3CN, EtOH, i-PrOH, TEP, CHCl3, 1,4-dioxane, and toluene. The molar extinction coefficients of α-Alq3 in organic solvents were calculated in the short-wave and visible regions of the spectrum. The solvatochromic effect in the studied systems was assessed. A methodologyfor the quantitative determination of Alq3 in organic solvents and standardization of its solvents has been developed by the spectrophotometric method.

Multifunctional composite charcoal-containing microwave and X-ray radiation absorbers
O. Boiprav, V. Bogush, N. Grinchik

🗏 : 294-303
DOI: https://doi.org/10.17277/jamt.2023.04.pp.294-303

The article presents multifunctional composite absorbers of microwave and X-ray electromagnetic radiation proposed and developed by authors. Compared with the analogs, these absorbers contain powdered activated charcoal as the component absorbing microwave electromagnetic radiation energy and powdered barium sulfate as the component absorbing X-ray electromagnetic radiation energy. The absorbers are three-layer ones. It was established that microwave electromagnetic radiation absorption coefficient values of the absorbers containing the powdered activated birch charcoal vary from 0.5 rel. units up to 0.92 rel. units in the frequency bands 3.5–7.0 GHz, 10.8–14.2 GHz, and microwave electromagnetic radiation absorption coefficient values of the absorbers containing the powdered activated coconut charcoal vary within the specified limits in the frequency bands 5.0–7.5 GHz, 10.2–17.0 GHz. The values of X-ray attenuation coefficient provided by the absorbers vary from 2.0 to 8.7 rel. units. These absorbers can be used to cover the walls of rooms where X-ray machines are located. This will ensure a reduction in the degree of influence on these devices, as well as computer equipment connected to them, of microwave electromagnetic radiation from external sources, as well as a reduction in the degree of influence of X-ray radiation generated by these devices on electronic devices and on people who are outside the specified rooms.

AlMg6–AlMg6 weld interface: microstructure and mechanical properties after explosive welding
A. Malakhov, I. Saikov, I. Denisov, A. Berdychenko, S. Ivanov, N. Niyozbekov

🗏 : 304-315
DOI: https://doi.org/10.17277/jamt.2023.04.pp.304-315

Due to their low density, high strength, and resistance to corrosion, Al-Mg alloys are widely used in the railcar construction and shipbuilding, and other industries. The aim of this study was to carry out a detailed analysis of the microstructure of the AlMg6-AlMg6 weld interface after explosive welding (EW). The results of this study are important for a better understanding of the joint formation process in EW of AlMg6 with other metals and alloys. The study included optical and electron microscopy of metallographic specimens with etched surfaces. Vickers hardness tests and tear strength tests were carried out to determine the mechanical properties of the joint. Optical and electron microscopy revealed a large number of adiabatic shear bands (ASBs) formed during EW and dark-etching structures formed after etching. An increase in explosive welding parameters leads to an increase in ASBs in the flyer plate and parent plate. The dark-etching structures are most likely the accumulations of structural defects and intermetallic compound fragments. The tear testing of the weld joint showed that higher EW parameters lead to much higher tear strength with a non-uniform distribution along the length of the plates. It was concluded that in order to achieve a joint between AlMg6 and other alloys and metals with the highest strength, plastic deformation in the weld interface must be sufficiently high, while heating must be minimal. The maximum joint strength was 150 MPa in mode 2 and 242 MPa in mode 3, respectively.

Evaluation of the effect of a complex nanomodifying additive “lignosulfonate / graphene oxide” on the non-autoclaved aerated concrete hydration process
D. Aljaboobi, I. Burakova, A. Burakov, V. Yarkin

🗏 : 316-323
DOI: https://doi.org/10.17277/jamt.2023.04.pp.316-323

The article evaluates the influence of various plasticizing and structure-forming additives on the hydration process of non-autoclaved aerated concrete (NAC). The authors have developed a method for the NAC formation with the introduction of the following modifiers: lignosulfonate (LS), graphene oxide (GO) (1 % aqueous suspension) and a complex additive – GO/LS. The formation of the structure and the study of new mineral formations in cement stone as a result of hydration were carried out by X-ray diffraction and differential thermal analysis. According to XRD-analysis, gas blocks of all compositions contain quartz, tobermorite, calcium hydrogarnets, xonotlite, C–S–H(I), and calcite. The diffraction pattern of the sample with the addition of GO/LS shows that NAC contains, first of all, high-intensity reflections of tobermorite, xonotlite, as well as C–S–H and calcite. All other NAC samples are characterized by a lower intensity of reflections of the indicated calcium hydrosilicates. TG- and DSC-curves for all studied gas blocks have a similar character – 3 stages of weight loss, except for the control sample. Aerated concrete without additives at temperatures up to 100 °С loses 0.96 % of its weight, with the addition of LS – 1.20 %, GO – 1.35 %, and complex additive – 1.72 %. In the temperature range of 400–500 °С, an endothermic effect appears, which indicates the dehydration of weakly crystallized gel-like hydrosilicates and calcium hydrogarnets. It is this peak that is absent in the control sample. Thus, based on the diagnostic results, it was established that the complex modifying additive allow to increase of the hydration product crystallinity of the hardened NAC. The results suggest that the modified NAC containing a complex additive is more stable and functional during operation than comparative samples of concrete of a traditional composition without this additive.

Synthesis of the TiC + 20 % NiCr composite from a granular mixture
N. Abzalov, B. Seplyarskii, R. Kochetkov, T. Lisina, M. Alymov

🗏 : 324-332
DOI: https://doi.org/10.17277/jamt.2023.04.pp.324-332

For the first time, the synthesis of the TiC + 20 % NiCr composite from a granular mixture with titanium of different dispersion, containing different amounts of impurity gases, was carried out. The features of the combustion process of a granular charge are explained by its structure – the presence of physically separated cells (granules) with a powder mixture, which can ignite because of conductive heat transfer from granule to granule or convective heating by gas released from the charge. The combustion front in the powder and granular charge based on titanium with a smaller characteristic size of titanium particles propagated at a higher rate, despite the higher content of impurity gases in it. The effect of impurity gas release on the combustion rate of powder mixtures is explained using a convective-conductive combustion model. It is shown that the combustion of the studied mixtures with granules 0.6 and 1.7 mm in size took place in a safe conductive mode, making it possible to scale the process. X-ray phase analysis of the combustion products showed that the phase composition of the synthesis products did not depend on the size of the granules. When using a granular mixture containing finely dispersed titanium powder, synthesis products were obtained without side phases of intermetallic compounds, which were easily crushed to micron sizes and could be used for plasma spraying of wearresistant coatings.