Архив

The objective of this paper is to study the process of free SHS compression of composite materials in the ZrO2-Y2O3-SiO2-TiB2 system. The content of Y2O3 stabilizing additive varied in the ratio (x–1)ZrO2-xY2O3 from 0 to 9 mol %. The influence of such technological parameters as the delay time, the strain rate, the pressing pressure, on the process of molding the selected materials, as well as the processes of phase and structure formation were studied. To establish the influence of the specified technological parameters on the process of selected materials molding, their formability was assessed. It was found that the nature of the dependences of the combustion characteristics of the studied materials on the content of the stabilizing additive correlates with the nature of the curves of the dependences of the degree of deformation on the delay time and the rate of deformation. It was shown that on the curve of the dependence of the degree of deformation on the pressing pressure, there is a limiting value, above which an increase in pressure does not affect the formability of the materials. It was shown that at a Y2O3 content of 0 to 4 mol %, the monoclinic and cubic modification of ZrO2 is predominantly observed. A further increase in the Y2O3 content leads to the formation of a tetragonal modification of ZrO2 in the obtained compact blanks. It was also found that in the studied materials the texture formation was observed in the direction perpendicular to the direction of pressure application.

The paper studies the influence of the ratio of components in the TiO2-KOH-KNO3 reaction mixture on the structural properties of the quasi-amorphous particles of the product obtained (potassium polytitanate, PPT) which has the chemical composition of K2O·(4.18 ± 0.16)TiO2·(2.2 ± 0.1)H2O. It is shown that by decreasing the KOH content in the melt used during heat treatment of TiO2 powders (500 °C, 2 h), a degree of crystallinity of the PPT particles increases, while the proportion of the titanium in the valence state Ti3+ and the amount of chemically adsorbed water decrease. The mechanism of the processes occurring during the synthesis of potassium polytitanate in nitrate- hydroxide melts is analyzed and an explanation for the patterns of change in the structure of the PPT particles observed with a change in the oxidizing properties of the meltis given. On the basis of the data obtained, some recommendations are given in order to use different variants of nitrate- hydroxide melts for the synthesis of PPT powders, depending on their further application.

The paper considers the kinetics of lead ions (Pb2+) sorption from model aqueous solutions using underoxidized and overoxidized graphene oxide samples obtained from synthetic and natural (taken as comparison material) graphite. It was experimentally found that the contaminant is sorbed in the first 5 min (for the underoxidized samples) and 30 min (for the overoxidized samples), achieving a sorption capacity of 105–138 mg g–1. Moreover, the capacity of the material increases with an increase in its oxidation state. The capacity of the synthetic material is slightly higher than that of the natural one. To study the removal mechanisms and determine the process parameters, the experimental data were fitted to kinetic (pseudo-first and pseudo-second order, as well as Elovich) and diffusion (internal diffusion – Morris-Weber and external diffusion – Boyd) models. It was found that the metal sorption is controlled by mixed diffusion of the sorbate into the bulk of the sorbent. It was also determined that this process is limited by the chemical interaction between the sorbent and the sorbate and depends on the sorbate concentration and the ambient temperature. Besides, the surface morphology of the samples was studied using scanning electron microscopy, and information on their elemental composition before and after the sorption was obtained using energy dispersive spectrometry, which confirmed the mechanism of the sorption processes occurring in the systems.

The article presents the results of a study of the structure of the friction surface formed when using modified detonation synthesis nanodiamonds with sizes up to 200 and 600 nm in the oil composition. During friction, a layer is formed on the steel friction surface, consisting mainly of wear products of friction bodies and fragments of nanodiamond and oil destruction. The thickness of the layer does not usually exceed 10 ?m, but in some cases, an additional layer can completely compensate for wear. The layer is porous and, with simple technology, can always be impregnated with oil, which eliminates dry friction at the start of movement. The diameter of the pores does not exceed 100 nm. The composition of the layer has been studied through atomic force microscopy, X-ray photoelectron spectroscopy, as well as X-ray absorption spectroscopy (XANES) and diffraction using synchrotron radiation, including after etching with Ar+ ions. The resulting layer, separating the friction bodies, minimizes contact wear occurring at the beginning of movement, during overloads and micro-impacts, and partially or completely restores the geometry of the friction surfaces. Using modified nanodiamonds in the oil composition, it is possible to significantly increase the service life of mechanisms, which is determined by the contact wear of friction pairs.

Currently, metal ferrites are promising yet under-researched narrow band gap semiconductors for preventing biofouling. In the present study, nanoparticles with copper ferrites content of 55, 85 and 95 % were synthesized by electrical explosion of iron and copper wires in mixed oxygen and argon atmosphere. CuFe2O4 content was ranged by the wires diameter. According to the X-ray diffraction analysis, an increase of iron content in the twist led to an increase of copper ferrite phase up to 95 %. Copper oxide (I, II) and copper phases also were found in nanoparticles. The XRD data showed a uniform distribution of Cu and Fe in nanoparticles. Nanoparticles with CuFe2O4 content of 85 wt. % showed the highest efficiency in Congo red degradation reaction under visible light irradiation (decolorisation efficiency of 72 %). Nanoparticles (85 wt. % CuFe2O4) showed a high antibacterial activity against antibiotic resistant MRSA ATCC 43300 (bacteria growth reduction by 98.7 %). Moreover, NPs were active against P. aeruginosa biofilm, thus making them potential antibiofouling agents for water-contact items.

This study investigated the antibacterial properties of the biologically active exo- and endometabolites of the microalgae Chlorella sorokiniana Shihira & R.W. Krauss IPPAS C-1 and the cyanobacteria Anabaena sphaerica Born. et Flah. IPPAS B-404, under photosynthetically active radiation of 100 ?moL photons?(m2*s)–1 and in darkness. The dependence of the quantitative composition of intracellular metabolites (water-soluble proteins and non-polar lipids) of Chlorella sorokiniana and Anabaena sphaerica IPPAS B-404 on the cultivation conditions, namely the level of photosynthetically active radiation and temperature, was determined. The results revealed that the cultivation conditions influence the antibacterial efficiency of these metabolites. The values of minimum inhibitory concentrations of non-polar substances of lipid nature and water-soluble peptide fractions against Gram-positive bacterial culture isolated from air were determined experimentally. The antibacterial activity of non-polar lipids extracted from the culture fluid of the cyanobacterium Anabaena sphaerica IPPAS B-404 was demonstrated against the test bacterial cultures used: Bacillus subtilis B-3395, Enterobacter asburiae B-1048, Enterococcus durans B-603, both in darkness and under 100 µmoL photons?(m2*s)–1 of photosynthetically active radiation.

The urgent task is to develop models for the effects of classifier operating modes on the granulometric composition of fine powder fractions separated by the air-centrifugal method, because the use of sieve classification is not effective for the dust fraction of powders with a size of less than 40 µm, which has great potential for use outside of classical additive technologies. In this study, a small amount of Kovar precision alloy powder was classified using aircentrifugal technology for powder injection molding (PIM) applications. The aim of the research was to develop a model that would allow us to select the optimal conditions for air-centrifugal classification in order to obtain a powder with a specific grain size distribution. The methods of laser diffraction and scanning electron microscopy were used to determine the granulometric composition and morphology of the powder. A method of isoconversion analysis of granulometric composition is described, which allows one to obtain model-free (i.e. without hypotheses about the type of kinetic model) single-factor dependencies of the influence of the frequency of air-centrifugal classification on the granulometric composition of the final fraction of the obtained powder. The practical significance of this research lies in the potential for producing powder fractions with a specific average particle size using any combination of a powder with an initial granulometric composition and an air-centrifugal classifier.

Demand for affordable devices that can quantify blood glucose levels continues to rise, prompting a search for reliable low cost solutions. Electrochemical biosensors based on modified graphite and other carbon nanomaterials have shown promise. Carbon materials offer a wide electrochemical stability window, chemical inertness, and low cost, making them attractive for electrode fabrication - the core of such biosensors. Screen printing is widely used for producing carbon electrodes because it is simple and scalable. However, electrode performance depends heavily on the formulation of the conductive carbon paste, typically a mixture of carbon particles, a polymeric binder, and solvents. Common carbon fillers include graphite, graphene, carbon nanotubes, and carbon black; binders may be polystyrene, polyaniline, polystyrene sulfonate, polyvinyl chloride, or ethylcellulose. This review summarizes the status of conductive carbon pastes for electrochemical glucose biosensors and outlines development prospects in Russia.