Issue

Co-Mn-containing composites based on diatomite as a carrier (matrix) were prepared using the energy-efficient low-temperature combustion method using natural and activated diatomite from the Utesai deposit (Republic of Kazakhstan) as a support (matrix). Activation included the stages of washing with water, calcination at 500 град.C, and treatment with an HCl solution in various combinations. The phase containing 5 wt. % of Co + 5 wt. % of Mn (calculated as metals) was applied to diatomite by low-temperature combustion of a mixture of Co and Mn nitrates (oxidizers) with urea (reducing agent, fuel) applied to diatomite. The maximum temperature in the combustion wave reached 337 град.C. The physicochemical properties of the composites were studied using X-ray diffraction, SEM/EDS, and the specific surface area was measured according to BET on nitrogen. The main phases in the composites, according to XRD data, were modifications of SiO2 (quartz, tridymite, and cristobalite). According to the SEM/EDS results, there is an uneven distribution of the Co-Mn-containing phase components over the surface of the catalyst granules, due to the heterogeneity of the surface morphology and internal pores of natural diatomite. Impurity elements (Mg, Al, Na, K, Ca, Fe) were also detected in the composition of the supports and catalysts. The specific surface area of the support samples ranged from 56.0 to 83.5 m2g-1, and that of the composites - from 46.4 to 78.5 m2g-1. The resulting composites are expectedto be used as catalysts for deep oxidation of CO and hydrocarbons for environmentally important technologies for the neutralization of man-made exhaust and waste gases.

The paper provides the phenomenological description of the effects of cluster formation and separation of cohesionless spherical particles by size and density in a bed of a rarefied granular medium under the action of vibrations in microgravity conditions. Mathematical modeling of the structural and kinematic parameters of the granular medium is performed based on its equation of state as a "gas of solid particles". It is established that the condition for particle cluster formation is sufficiently high values of the solid phase fraction and the thickness of the vibrating bed, at which the quasithermal vibration flux has a limited area of active penetration into the bed volume. The separation process is a consequence of the quasi-diffusion interaction of particles with different fluctuation velocity in the presence of a gradient in the fraction of voids in the granular medium. The distribution of particles of a binary mixture of varying sizes was simulated using the separation dynamics equation, which describes the transport of non-uniform particles as a result of the coupling of quasi-diffusion separation and mixing fluxes. The simulation results are compared with experimental data obtained with support from the European Space Agency (Parabolic Flight Campaign PFC64) using the VIP-Gran instrument.

This paper summarizes the results of structural investigations of carbon nanomaterials using Raman spectroscopy. The conducted research revealed that the distances between defects are 26-43 nm in graphites, 12-16 nm in multi-walled carbon nanotubes (MWCNTs) and 11-15 nm in carbon black. It is shown that the Raman spectra of highquality graphites and graphenes are characterized by a narrow G band (width less than 35 cm-1), intensity ratio I(D)/I(G) < 0.3. The Raman spectra of carbon nanotubes are characterized by wide G bands (width > 50 cm-1), high I(D)/I(G) ratio (> 0.5) and the presence of 2D bands with a maximum position of about 2670 cm-1. The Raman spectra of carbon blacks are characterized by a strongly broadened G band (width > 70 cm-1), the I(D)/I(G) ratio is close to 1 and more. The presence, position and width of 2D bands are sensitive to the structures of carbon materials. For ordered graphites, the position of the 2D band maximum is about 2680 cm–1, and their width is < 85 cm-1. For MWCNTs, the 2D band maximum is in the range of 2670–2690 cm-1, and the band width is about 90–100 cm–1. In the Raman spectra of carbon blacks, the 2D band may be absent; the position of the maximum may be shifted to the long-wave or short-wave regions, the 2D band is strongly broadened (width > 150 cm-1).

The paper presents new methods for eliminating random and systematic errors that occur when registering the current-voltage characteristics of field cathodes in the high-voltage fast scanning mode. The methods are implemented in the LabVIEW graphical programming environment and integrated into the experimental installation software, which registers and processes field emission data in real time. The developed program consists of three modules. The first one eliminates the effect of constant interference on current and voltage signals. The second module eliminates the systematic sinusoidal error associated with the presence of capacitance in the measuring circuit. The third module reduces the effect on the signal of noise associated with measuring equipment, as well as fluctuations in the emission activity of the cathode. The resulting current-voltage characteristic is processed in semi-logarithmic coordinates using the Murphy-Good equation. As a result of the processing, the values of the effective parameters are obtained. A test experiment was conducted with a field cathode based on multi-walled carbon nanotubes grown by the plasma-assisted chemical vapor deposition (PECVD-method). The technique was also used to accurately evaluate the emission properties of various types of cathodes: those based on carbon nanoparticles, regular matrix tips, and single-pointed cathodes.

This paper examines the laser thermodynamics of topological structures - dendrites - obtained by laser ablation of several high-entropy alloys using laser pulses. Laser experimental synthesis schemes and parameters for producing dendritic structures in various high-entropy alloys are discussed. For various configurations of such structures, the possibilities for controlling the functional characteristics of dendritic samples (electrophysics and optics) for potential technological applications are analyzed within nanocluster/island topological models. Thermodynamic conditions for targeted dendritic synthesis are modeled and evaluated under various experimental conditions with laser irradiation from a Gaussian radiation source using the Matlab Laser Toolbox approximation. The thermodynamic conditions for the synthesis of dendritic systems formed from high-entropy alloys are studied using analytical estimates of the temperature field. The procedure performed allowed us to estimate the actual melting temperatures for the components of the nanostructured high-entropy alloy. Models of dendritic structures in the diffusion approximation under diffusion-limited aggregation were proposed. Their electrical conductivity was estimated using simulations of the current-voltage characteristics within the tunneling and hopping approximations, as well as the enhancement of the electric field on fractal structures at their inhomogeneous boundaries. The developed models were implemented in MATLAB and were directly related to the parameters of the actual synthesis scheme, and the estimates obtained using them were consistent with the actual values.

Samples of commercial adsorbents - activated carbon (AC), zeolite (ZS), and silica gel (SG) - were studied in the adsorption processes of hydrogen, methane, nitrogen, carbon dioxide, and carbon monoxide in order to assess their efficiency for hydrogen purification from gas impurities. The composition and morphology of the materials were characterized using scanning electron microscopy and energy-dispersive X-ray microanalysis. Textural properties (specific surface area and pore structure) were determined from nitrogen cryosorption data using the BET, Gurvich, and BJH models. Adsorption isotherms were obtained for all studied gases at pressures up to 25 atm and temperatures ranging from 0 to 50 град.C. Isosteric heats of adsorption and ideal selectivities for the "impurity gas – hydrogen" pairs were calculated. To evaluate the behavior of the studied adsorbents toward multicomponent gas mixtures, simulations were performed using the Ideal Adsorbed Solution Theory (IAST). This approach revealed that in real mixtures, the selectivity SIAST(CO2/H2) increases by a factor of 1.5–3 compared to the values estimated from single-gas data.

In light of the findings from experimental studies, adsorption isotherms were obtained for carbon dioxide, carbon monoxide, methane, and hydrogen gases on industrial adsorbents. A methodology has been put forth for calculating the coefficients of the Dubinin-Astakhov equation based on experimental isotherms. This approach enables the determination of the equilibrium adsorption of components of a hydrogen-containing gas mixture with a high degree of accuracy. The approach includes: calculating the limiting adsorption volume of a given adsorbent and the characteristic adsorption energy of a standard gas (nitrogen) for the specified adsorbent using experimental nitrogen adsorption isotherms obtained at a temperature of 77.3 K in the relative pressure range from 0 to 1 for each of the studied adsorbents, namely: NaX, CaA, SKT-4; determining the calculated values of the affinity coefficients, the exponent, and the thermal coefficient of limiting adsorption in the Dubinin–Astakhov equation (for the temperatures and pressures at which the experimental sorption isotherms of the studied gases were obtained), which minimize the residual between the calculated and experimental isotherms; averaging the obtained values of the affinity coefficients and the exponent. The efficacy of the proposed approach is substantiated by the calculation of the parameters of the Dubinin–Astakhov equation for CO2, CO, and CH4 using NaX and CaA zeolites and SKT-4 activated carbon. The root mean square deviation between the calculated and experimental data does not exceed 6.6 % over a wide range of pressures (up to 3.0 MPa) and temperatures (293–353 K) for the studied sorbents (zeolites NaX, CaA, and activated carbon SKT-4).

The development of new electrolyte solutions with improved characteristics is a key challenge for creating highperformance batteries, fuel cells, supercapacitors, and other electrochemical devices. The study of the potential energy landscape (PEL) plays an important role in this process, providing information about the interactions between solution components at the molecular level. In this work, we review the practice of applying PEL research methods based on classical and quantum-chemical algorithms to analyze the structure, dynamics, and thermodynamic properties of electrolyte solutions. Intermolecular and ion-molecular interactions at the microscopic level, which determine the macroscopic properties of the electrolyte solution, are considered in detail. The importance of identifying stable configurations of ions and their solvates is emphasized. PEL analysis allows for the systematic determination of the most probable structures and complexes formed in solution, which is important for understanding ion transport mechanisms. The study of the PEL allows for the determination of the energy barriers that must be overcome for ion migration, which is related to the conductivity of the electrolyte. The application of PEL research methods in combination with experimental data opens up new possibilities for the rational design of electrolyte solutions with desired physicochemical properties.