Issue

Efficient heat transfer is essential in many industrial sectors to ensure safe and efficient operation of equipment. Thermal pastes are materials used to improve heat transfer between different surfaces. In this study, the influence of carbon nanotubes on the heat-conducting properties of thermal pastes was studied in order to create a new, more efficient and economical composite. The study included an experiment consisting in selecting the optimal type of thermal paste, as well as determining the most effective amount of carbon nanomaterial, in order to assess the thermal stability and improve the characteristics of thermal pastes when adding carbon nanotubes. The results of the study showed that the addition of carbon nanotubes makes it possible to improve the distribution and transfer of heat, namely, when carbon nanotubes were introduced at a concentration of 0.01 %, the processor temperature remained lower by 15 °C with preliminary exposure to nanotubes with ultrasound, and by 10 °C without pretreatment in an ultrasonic stirrer. The results highlight the potential of carbon nanotubes as a promising additive for improving the thermal conductivity properties of thermal pastes in various applications.

A method for manufacturing broadband radioabsorbing coatings based on a polymer matrix modified with multi-walled carbon nanotube “Taunit-MD” for radio-frequency anechoic chamber application has been developed. It is shown that a high aspect ratio (> 1000) of carbon nanomaterials provides the formation of a developed three-dimensional conductive net in the structure of the polymer matrix at a low additive concentration, which has a positive effect on the electromagnetic energy absorption properties and ensures that the filler does not pour out. Using a 250 mm high pyramid array absorber provides more than –40 dB of reflectance attenuation in the frequency range from 1 GHz, while using a 100 mm high pyramid array absorber provides more than –30 dB of reflectance attenuation in the frequency range from 10 GHz. The full retention of the electromagnetic radiation absorption properties of the developed pyramidal absorbers was demonstrated in the wear resistance test, while the industrial sample with carbon black filler showed a decrease in the absorption of electromagnetic radiation by –20 dB.

Modifying additives are introduced into the composition of modern bituminous binders to meet the high modern requirements for the performance of road surfaces. The use of carbon nanomaterials as modifiers imparts antistatic properties to bituminous binders and opens up the possibility of applying an innovative approach to healing cracks in the asphalt pavement under the action of microwave radiation with its subsequent regeneration. A series of samples of nanocomposite materials based on BND 60/90 bitumen and hybrid filler containing graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWСNTs) were prepared using a simple mixing technique. The use of hybrid with a ratio of MWCNTs to GNP equal to 4:0.1 made it possible to achieve the maximum electrical conductivity of bitumen nanocompositions, the value of which was 4.82⋅10–3 S⋅cm–1 at a filler concentration of 8 wt. %. The optimal ratio of MWCNTs to GNP components equal to 4:1 was experimentally found, at which the percolation threshold decreased by 50 and 100 % compared with nanocomposites having a MWCNT to GNP ratio of 4 : 0.1 and 1 : 1, respectively. A mechanism for the formation of a double percolation contour in a bitumen-based nanocomposite system containing GNP and MWCNTs in a ratio of 4 : 1 is proposed.

The article investigates and evaluates the adsorption properties of a new highly porous carbon material in a wide range of pressures at temperatures above the critical level. It has been shown that the activated carbon material obtained from coffee waste is an effective adsorbent for CH4. So, in this study, carbonized coffee grounds were used as a precursor to obtain a highly porous carbon material (HPCM5), by chemical activation at 750 °C for efficient CH4 adsorption. Porometry shows that the obtained adsorbent is micromesoporous with a narrow pore size distribution, having a BET specific surface area of 3456 m2⋅g–1 and a pore volume of 1.604 cm3⋅g–1. The adsorption of CH4 on the resulting carbon material was studied at temperatures of 298.15–323.15 K and pressures up to 100 bar. HPCM5 demonstrates a high CH4 adsorption capacity of 19 mmol⋅g–1 at 10 MPa and 298.15 K. Experimental data on CH4 adsorption on HPCM5 were analyzed using typical Langmuir and Freundlich adsorption models in the temperature range 298.15–323.13 K. The results show that CH4 adsorption on HPCM5 in the range of temperatures and pressures considered in this study correspond to the Langmuir adsorption; this is confirmed by the obtained values of the correlation coefficients equal to 0.99 and the average relative deviations between the experimental results and the results obtained with the Langmuir model, which are less than 3 %. The values of isosteric heats were calculated for different absolute amounts of CH4 adsorption on the resulting HPCM5, which are in the range from ~10.0 to 17.0 kJ⋅mol–1. This characterizes the process as a physical adsorption, and the bond strength between the CH4 molecule and adsorbent surface refers to the van der Waals force. The adsorption isotherm data and thermodynamic parameters evaluated in this study are useful for designing adsorption-based gas storage systems.

The possibility of cobalt sorption of by anion exchangers from hydrochloric acid solutions in the presence of nickel was evaluated in the paper. The highest value of sorption capacity was observed in the gel anion exchange resin with pyridinium functional groups (Axionit VPA G.2.4) and the macroporous anion exchange resin with functional groups of secondary and tertiary amine (Indion 850). Processing of cobalt sorption isotherms with Indion 850 and Lewatit MP 800 anion exchangers was carried out using the Langmuir equation with constant values of (7⋅10–2 ± 0.03) and (0.2 ± 0.02) L⋅mg–1, the values of the maximum sorption capacity were (109 ± 5) and (74 ± 3) mg⋅g–1, respectively. The value of the Freundlich constant during the treatment of the sorption isotherm of cobalt with anionite Axionit VPA G.2.4 was (9.6 ± 0.3) mg⋅g–1. The kinetics of cobalt sorption by Axionit VPA G.2.4 and Indion 850 anionites was studied; the kinetic data of cobalt sorption with the highest value of the coefficient of determination R2 are described using the pseudo-second order equation. Using mathematical processing of the kinetic data of cobalt sorption according to the Weber-Morris equation, the intradiffusion nature of sorption was determined. The analysis of the results of the influence of elements accompanying the complex processing of waste rhenium-containing superalloys – iron, aluminum and chromium – suggests that iron and chromium have a competitive effect on the sorption of cobalt due to the possibility of the formation of their anionic forms in hydrochloric acid solutions for processing secondary rhenium-containing raw materials.

Models for the formation of nanocluster fractal structures of various configurations are considered within the framework of a number of approaches in the aspect of controlling their electrophysical characteristics, and the results of some experiments in this direction by laser experiment are presented. Emphasis is placed on the discussion and analysis of the following issues: physical principles and models for the electrical conductivity in topological nanostructures; local fields in nanoscale and their contribution to the gain coefficient for electrical conductivity in aspect of parameters of the medium and the geometry factors for roughness; experimental technique; current-voltage characteristics and mechanisms of electrical conduction for topological nanostructures under different conditions. At the same time, occurrence of conduction electropaths, and also the algorithms and models considered for calculating of electrical conductivity for nanostructures of different configuration are analyzed, experimental results and their interpretation are presented, and the role of photoconductivity were studied in such nanostructures. The results obtained can be useful in the development of certain elements and systems of nanotopological electrophysics and nanophotonics based on new physical principles.