In this work, graphene-based ten nanofluids were synthesized, and their viscosities were determined. Also, a theoretical analysis of the molecular interactions of graphene nanoparticles is carried out in order to understand the mechanisms affecting the viscosity of nanofluids. Based on the results of experiments, an analytical function that describes the dependence of the relative viscosity on the concentration of graphene nanoparticles was obtained. It was established that the viscosity of the base fluid was affected by the graphene sheet structure. If the graphene sheet possessed an ideal surface, a decrease in the viscosity was observed, but if it contained defects, the viscosity of the nanofluid increased rapidly with increasing concentration. The reason for this behavior of graphene nanofluids was the self-assembly of graphene nanoparticles in the base fluid flow and the formation of ordered clusters from base fluid molecules. In this case, the self-assembly of the graphene nanoparticles was inextricably linked with the formation of the nanoclusters. The struggle between these two processes generated changes in the viscosity of the graphene nanofluids. In the function herein proposed, a new parameter, B/A, was introduced, which made it possible to evaluate the nature of the interactions between the graphene nanoparticles and the base fluid molecules. The reported work is highly useful to design more future graphene-based nanofluids; depending on the requirements.

The pyrolysis of acetylene was studied experimentally in a cyclic compression reactor in an atmosphere of buffer inert gases (argon, neon, helium). A significant difference in the thermodynamic conditions for the complete pyrolysis of the precursor for various buffer gases was revealed. The reaction products of acetylene in neon and helium contained up to 20% of the part soluble in organic solvents. The study of the ethanol-soluble part of the product using time-of-flight mass spectrometry with matrix-assisted laser desorption/ionization made it possible to distinguish even and odd branches in the spectrum of substances by the number of carbon atoms. A mechanism is proposed for the formation of larger particles by merging smaller ones.

Pyrolysis of a mixture of monosilane with light hydrocarbons in an argon atmosphere in a cyclic compression reactor was used to synthesize nanoparticles with a crystalline silicon core and a carbon shell. The resulting powders were tested as an anode material for lithium-ion batteries. It is shown that the maximum reversible electrochemical capacity is 603 and 242 mA h/g at current densities of 0.05 and 2 A/g, respectively.

The paper considers the history, stages of formation and development of the Department of Applied Physics of the Faculty of Physics of NSU. The structure of the department, solved and currently solved scientific tasks are described. The results of scientific, pedagogical and innovative activities of the main divisions of the department are considered.

We investigated the physicochemical aspects of the gas-phase nanopowder synthesis using a cyclic compression reactor. Compression of precursors (methane, ethylene, acetylene) under conditions close to the adiabatic ones in the atmosphere of buffer monatomic gases (argon, helium, neon) was used. The influence of pressure in the reactor and volumetric ratio of precursor/buffer gas mixture on the composition, morphology, and structure of carbon-containing particles representing the pyrolysis product was studied. Complete pyrolysis was observed for all studied precursors, but under different conditions. Thermal decomposition of methane, having the minimum enthalpy of formation, was observed in an atmosphere with argon content 97.5 % at a peak pressure more than 10 MPa. Helium showed limited possibilities for thermal relaxation under the conditions of fast reactions (< 50 ms). Only acetylene with the maximum enthalpy of formation was decomposed in the atmosphere of helium. The solid reaction products represented black colored powders with a bulk density of 20–30 mg/cm3. The powders were examined by transmission electron microscopy and scanning electron microscopy, Raman scattering and X-ray diffraction analysis. The particles represent globular bulbous structures up to 100 nm in size, either hollow or filled inside. X-ray diffraction analysis showed the presence of a graphite-like structure with crystallite sizes less than 10 nm in all samples. Raman analysis showed mainly sp2 hybridization of carbon. The cyclic compression method demonstrates wide range of opportunities for the pyrolysis of hydrocarbons aiming at the production of a variety of carbon structures, which enables for the fine tuning in terms of the yield of products of the required morphology for practical use.

The pyrolysis of acetylene was studied experimentally in a cyclic compression reactor in an atmosphere of buffer inert gases (argon, neon, helium). A significant difference in the thermodynamic conditions for the complete pyrolysis of the precursor for various buffer gases was revealed. The reaction products of acetylene in neon and helium contained up to 20% of the part soluble in organic solvents. The study of the ethanol-soluble part of the product using time-of-flight mass spectrometry with matrix-assisted laser desorption/ionization made it possible to distinguish even and odd branches in the spectrum of substances by the number of carbon atoms. A mechanism is proposed for the formation of larger particles by merging smaller ones. Keywords: cyclic compression reactor, acetylene pyrolysis, buffer inert gas, growth mechanism, carbon nanoparticles.

A cyclic adiabatic compression reactor is used for the Si powder fabrication by the monosilane decomposition in a gas mixture with argon. Along with arbitrary agglomerations of Si nanoparticles, this method allows synthesizing nanoparticle chains and nanowhiskers, as an outlet gas pressure in the reactor increases from about 2.0 to 5.0 MPa. The increase in pressure corresponds to an increase in temperature from similar to 450 to 1050 degrees C, which leads to a change in the particle structure from amorphous to crystalline and reduces the particle size distribution. The particle chain and nanowhisker formation is associated with an increase in the duration of the synthesis process. The optical properties of the synthesized Si powders were determined by Si/SiO2 interfaces appeared by the oxidation in the air. The method is characterized by a relatively high production rate of Si powders of various morphologies, which may be of interest for various applications. (C) 2021 Elsevier B.V. All rights reserved.

The paper presents the study of supramolecular structuring forming a transition region at the hydrocarbon – nanofluid interface resulting from synergistic effect by the interaction of multilayer graphene planar nanoparticles and silicon carbide nanoparticles covered with graphene layers (Core-shell). During the film formation on the interphase, filamentous formations were obtained, which resulted from interaction with thermocapillary waves. It was found that the structure of the filamentous formation was influenced by the composition and concentration of nanofluids.

The method of producing of nano-dimensional silicon carbide by compressing in a cyclic chemical reactor is proposed. Pyrolysis is initiated in mixtures of monosilane and hydrocarbon with argon. The resulting product is examined by X-ray diffraction and electron microscopy. It is established that the powder contains crystallites of silicon carbide with an average size of 5-12 nm. It is shown that at certain ratios of precursor concentrations in argon, the formation of carbon nanoparticles and/or graphene coating on the surface of SiC particles is also possible. The method is technological and efficient, it can be used in the production of high purity silicon carbide nanopowders and other compounds.

The formation of supramolecular structures forming a transition region at the oil-nanofluid interface with a low surface tension is studied as a result of a synergistic effect in the interaction of planar graphene nanoparticles and silicon carbide nanoparticles coated with graphene layers (Core-shell). In model experiments on a Hele-Shaw cell, it was shown that in a porous medium such hybrid nanofluids have a high displacing ability of residual oil. At the same time, the oil – nanofluid interface remains stable, without the formation of sticky fingers. In the process of research using power electron microscopy, a transition region was observed, in the structuring of which nanoparticles were directly involved. The efficiency of displacement by hybrid nanofluid depends on the concentration of nanoparticles and their interaction.

The method of producing nanopowders of Si and SiC by pyrolysis of a silicon-hydrocarbon mixture by compression in a cyclic process in a flow reactor is proposed and implemented. The obtained powders are characterized by X-ray diffraction and transmission electron microscopy. The new design solutions and use of ceramic coatings obtained by applying microarc oxidation for the piston-cylinder assembly – a compression unit of the reactor - allowed avoiding the use of compression rings and lubricants, achieving a high compression ratio and pressure and temperature in the reactor needed for monosilane pyrolysis. Pyrolysis in the flow reactor is convenient, technological and efficient in terms of its use in the production of high purity nanopowders.

The method of producing of nano-dimensional silicon carbide and experimental results of pyrolysis of a mixture of a silicon-hydrocarbon composition by compressing in a cyclic chemical reactor has been proposed. New structural design solutions and ceramic coatings obtained by applying the technology of microarc oxidation were used in the compression unit of the chemical compression reactor. This allowed us to forego the traditional schemes, to achieve a high compression ratio, and to obtain the pressure and temperature required in the reaction zone for silicon-hydrocarbon composition pyrolysis. The flow-through pyrolysis method in chemical compression reactor is convenient, technological and efficient to be used in the production of high purity silicon carbide nanopowders.

The method of producing nano-dimensional silicon powders from monosilane pyrolysis by compressing in a cyclic process in the flow reactor has been proposed and implemented. The resulting powder has been examined by X-ray diffraction and electron microscopy. The new design solutions and ceramic coatings obtained by using microarc oxidation for the piston-cylinder assembly – a compression unit of the reactor, allowed avoiding the use of compression rings and lubricants and achieving high compression ratio, pressure and temperature in the reactor needed for monosilane pyrolysis. Pyrolysis in the flow reactor is convenient, technological and efficient to be used in the production of high purity silicon nanopowders.

An experimental plasmochemical apparatus is described to study physical and chemical processes in gas flows with a wide range of physical states and parameters; knowledge about this is necessary when developing promising vacuum technologies. The equipment allows investigation of supersonic improperlyexpanded jets, interaction of jets with barriers, kinetics of discharge-initiated plasmochemical reactions, an ionic or electron beam in condensing flows of gases and gas mixtures, relaxation, cluster formation and condensation processes, as well as modeling a nozzle flow in a wide range of gas-dynamics parameters. The apparatus is equipped with modern measuring instrumentation and a set of optical, electronic, ionic, chromatographic, and mass-spectrometric systems.

A description of the installation for adiabatic compression in a cyclic process is presented here. Experimental results of conversion of light hydrocarbons by this process are given. New structural design solutions and ceramic coatings obtained by applying the technology of microarc oxidation were used in the compression unit of the chemical compression reactor (the piston–cylinder assembly). This allowed us to forego the use of compression rings and lubricant, to achieve a high compression ratio, and to obtain the pressure and temperature required in the reaction zone for oxidative conversion.

The method of flow visualization by electron-beam-induced radiation emission has been used to study the shape and structure of supersonic gas jets emitted into rarefied submerged space via sonic and supersonic nozzles from a forechamber at high pressure (stagnation pressure P (0)). It is established that the longitudinal size of a traditional primary supersonic jet increases with the stagnation pressure at fixed ratio P (0)/P (h), where P (h) is the surrounding background gas pressure. This character of jet expansion via both sonic and supersonic nozzles is related to variation of the condensate fraction and average cluster size in the jet. Under the conditions of formation of large-size clusters in the supersonic jet of argon, a nontraditional gas jet shape with a long "wake" has been observed. No such secondary structure has been observed during the expansion of noncondensing helium and weakly condensing nitrogen. It is suggested that the formation of wake under conditions of developed condensation and significant rarefaction is related to the formation of a secondary clustered jet.

In most cases, the initiation of oxidation and synthesis of methane-air mixtures is carried out by increasing the temperature to above the limit ignition. The possibility of using of a pair of compression piston cylinder with the unique performance features for the conversion of hydrocarbons are discusses. The experimental facility enables working in the pressure range that would be unattainable in diesel engines.

The possibility of using of a pair of compression piston - cylinder with the unique performance features for the conversion of hydrocarbons are discusses. The experimental facility enables working in the pressure range that would be unattainable in diesel engines. The necessary degree of compression is managed and maintained by the computer system with a feedback.