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This paper presents results on the synthesis of germanium nanocrystals in electric arc discharge. During the synthesis, the surface of a germanium anode was heated to the state of surface boiling. Atoms of vaporized germanium were deposited on the surface of a copper substrate. The resulting sample was examined with an electron microscope. The deposited material was shaped as crystalline nanospheres (nanocrystals) with a size ranging from 20 to 200 nm.

A unified self-consistent model is formulated to describe a discharge gap, electrodes, and the formation of the parameters of dc microdischarges in molecular gases at atmospheric pressure. Numerical experiments performed in the current density range from 90 to 2.5 × 106 mA/cm2 have revealed the dependence of the voltage drop on a discharge on the current density, which reproduces the formation of glow, transient from glow to arc, and arc regimes. It has been shown that a transition from the glow discharge to the arc discharge with a free and unfree cathode regime can be implemented depending on boundary conditions on the outer edges of electrodes.

An extended hydrodynamic model describing the surface dielectric discharge in air is formulated in the paper. Preliminary numerical calculations have been performed demonstrating the formation of a streamer discharge structure in the case of application of a positive potential to the working electrode. The dynamics of the electron density and the electric potential for the streamer discharge are presented.

The effect of supersonic gas flow on glow discharge characteristics in interelectrode space is studied. First, gas outflow through a Laval nozzle with a central body was simulated: gas particle density distributions, gas flow velocity, Mach number, and temperature were obtained. Next, these profiles were used for numerical calculations of the parameters of a transverse glow discharge within the framework of an extended fluid description of the plasma. As a result, it was found that the cathode zones can both shrink and stretch depending on the parameters of the supersonic gas flow. The latter creates an inhomogeneous gas density in the interelectrode region and thereby affects the value of E/N, which determines the electrical characteristics of the discharge. Numerical simulation results are confirmed by experimental data.

A method for the synthesis of microdiamonds from graphite in an argon arc using germanium as a catalyst is presented. Simple microdiamonds and diamonds of complex configuration are obtained. It has been revealed that forms of synthesized nanomaterials are significantly affected by the buffer gas, the electrical and thermal parameters of the arc discharge, and the presence of germanium at the nucleation stage. Microdiamonds are formed within a few tens of seconds, which is much different from time required for their traditional production.

The paper presents methods for growing silicon nanotubes using an electric discharge with different values of the electric field strength in the interelectrode gap. It is shown that the shapes of the grown nanomaterials are significantly influenced by both the surrounding gaseous medium and the electric field strength in the interelectrode gap. The silicon nanostructures obtained have been a rather complex and, at the same time, definitely regular configuration and can be widely used in electronics, photovoltaics, batteries, and even as structural elements in composite materials.

Theoretical studies of the distribution of glow discharge parameters in a supersonic nitrogen gas flow between the central body of the nozzle and an annular electrode around the central body are carried out. Distributions of charged particle concentrations, potential, and electric field strength are obtained. The possibility of compaction or stretching of the cathode zones has been demonstrated. In the case of the organization of a supersonic gas flow near the central body-the anode, all the near-electrode zones are pressed against the anode. In this case, the cathode is located in the area of reduced pressures. Such a way of organizing the discharge can find application in the processes of applying functional coatings.

In this paper, we present the results of the synthesis of nanodiamonds from carbon nanostructures and diamondoids in an arc discharge. The electrodes used in the experiments were a molybdenum cathode and a copper anode coated with carbon nanostructures such as carbon nanotubes and diamondoids. The formation of carbon nanostructures on the surface of a copper electrode was carried out in an electric arc sunk into fuel oil. At the next stage, these carbon nanostructures served as a source of atomic carbon and diamondoids from the surface of the arc discharge anode. The use of fuel oil as a feedstock for creating the electrode material probably led to the retention of diamondoids contained in fuel oil during two vaporizations. It was found that, in addition to carbon nanotubes, nanodiamonds also formed on the cathode surface.

The mechanism of the effect of an arc discharge on heavy hydrocarbon raw materials is studied in the work. The mechanism of formation of charged particles in micro-discharges with recessed electrodes is shock ionization. As a result of the interaction of hydrocarbon raw materials with an arc discharge, long hydrocarbon molecules are broken down, light hydrocarbons such as ethylene, hydrogen, and methane are formed. In the case of the organization of a micro-arc discharge, a gentle thermal regime also provides a gentle splitting of long hydrocarbon molecules, and in this case gasoline fractions of oil are formed in greater quantities compared to the case of exposure to raw materials by a conventional arc discharge.

The paper describes a technique for the synthesis of microdiamonds, germanium nanoballs and nanotubes in an argon-germanium arc. The evaporation of germanium atoms was carried out from the surface of a graphite rod, which served as the anode of the arc discharge. The synthesis of microdiamonds was observed on graphite substrates near the anode; germanium nanotubes and germanium nanoballs were also found nearby. It has been established that germanium promotes the synthesis of nano and microdiamonds. Synthesized diamonds have a classic structure with rectangle faces and four hexagons adjacent to the edges of this rectangle. The sizes of microdiamonds reach tens of microns. The diameters of germanium nanotubes are of the order of 50-100 nm, and the length is of the order of 10 μm.

The paper proposes a method for the synthesis of silicon carbide of microscopic sizes and silicon Nano formations in the form of nanotubes and nanofilaments in an argon arc. Graphite electrodes with silicon inclusions were used as arc discharge electrodes. The electrodes were placed in a plasma reactor in an upright position at an argon pressure of 485 Torr. During the discharge, carbon and silicon atoms evaporated from the anode surface. As a result of the experiment, deposits of silicon carbide were formed on the surface of the graphite cathode, and carbon-silicon nanostructures were formed on the surface of the anode. The synthesized samples were analyzed on an electron microscope.

The paper presents the results of theoretical calculations of the gas-dynamic parameters of a supersonic flow in an axisymmetric Laval nozzle for the case when the central body removed from the nozzle serves as one of the glow discharge electrodes. It is shown that the presence of a supersonic flow makes it possible to establish a stationary inhomogeneous density of gas particles between the cathode and the anode of a glow discharge. The density of gas particles near the cathode and anode may differ by tens of times. The results of the study of the glow pattern of a discharge with a supersonic gas flow are presented. The dependence of the characteristics of the glow discharge on the distribution of inhomogeneous gas density in the interelectrode region is revealed. This effect opens up new possibilities for the use of discharges with supersonic gas flow for nanocoating and synthesis of nanostructures.

The effect of the shape of the feeding voltage on the spatiotemporal characteristics of an atmospheric- pressure barrier microdischarge in argon is demonstrated using numerical simulations based on an extended fluid model. Results of simulations performed for sinusoidal and square feeding voltages are analyzed.

A combination of an electric arc and discharge with a liquid electrolyte cathode in a single discharge gap has been created. The plasma column of discharge with liquid electrolyte cathode formed a “hollow cylinder”. The electric arc was burned in a vapor-gas environment inside the “hollow cylinder”. The gas discharge current with liquid electrolyte cathode was set in the range of 5-10 A, and the arc current varied in the range of 1-10 A. Aqueous solutions of sodium chloride with a specific electrical conductivity of 10-15 mS/cm were used as a liquid electrolyte. Spectral studies have been carried out in the visible range of radiation. In the experiments, copper and duralumin metal cathodes were used.

A dc gas discharge between copper electrodes in the current range of 5–20 А was studied experimentally. The discharge gap length was varied within 45–70 mm. The cathode was a 10-mm-diameter rod placed in the water flowing out from a dielectric tube. Three discharge configurations differing in the position of the cathode upper end with respect to the water surface were considered: (i) above water; (ii) flush with the water surface, and (iii) under water. The electric and optical characteristics of the discharge in the second configuration were studied in more detail. It is established that the discharge properties are similar to those of an electric arc. Considerable cathode erosion was observed in the third configuration. It is revealed that fine-dispersed copper grains form in the course of erosion.

Thermal characteristics of a direct-current plasma torch have been studied in the framework of numerical simulations of temperature fields in a plasma channel, cathode, and anode. It is established that the temperature of the operating cathode surface exceeds the melting temperature of the cathode material.

This paper presents the results of plasma synthesis of silicon nanostructures in an air-argon medium. The synthesis of silicon nanostructures was carried out in a vacuum chamber at a gas mixture pressure of 500 Torr, with partial pressures of argon and air in the ratio of 4:1. Molybdenum and silicon embedded in a copper tube were used as electrodes. Current and voltage were maintained in the range of 8-25 A and 30-50 V, corresponding. As a result of experiments, silicon nanostructures were deposited on the surface of the electrodes. Nanostructures were studied by optical and electron microscopes. Forms of silicon nanostructures were mainly in the form of nanotubes. Their diameters range from 200 nm to 500 nm, and their length reaches 1 mm. On the surface of these nanotubes, nanovilli with a diameter of about 5 nm and a length of 100 nm are observed.

The paper describes the synthesis of germanium nanotubes in an argon microarc. The article presents the results of two experiments. The evaporation of germanium atoms was carried out from the surface of single-crystal germanium, which served as the anode of the microarc discharge. The synthesis of nanotubes was observed on the surface of a molybdenum cathode in the first experiment and on the surface of a graphite rod in the second experiment. The diameters of the obtained germanium nanotubes reach 800-900nm.

This research presents the results of the synthesis of zinc oxide nanotubes in electric arc plasma. The diameters of these nanotubes are about 120-150 nm, and the length is about several micrometers. Individual nanotubes can reach up to 1 mm. As electron microscopic studies have shown, zinc oxide nanotubes are a “matryoshka”: they are strung on a carbon nanotube. Firstly, a broken carbon nanotube with a diameter of about 30 nm is formed, and then a zinc oxide nanotube grows on it. Moreover, there is no contact between these nanotubes.

Silicon coatings consisting of micro and nanopores were obtained by plasma-arc method. An experimental setup was assembled for the synthesis of nanostructures. A number of experiments on the synthesis of silicon nanostructures with changes in parameters such as current, voltage, and pressure in a vacuum chamber were carried out. In the experiments, a molybdenum cathode was used as a substrate for the deposition of silicon nanostructures. Atomic silicon evaporated from the anode. The experiments were carried out in an argon medium at a pressure of about 500 Torus. The current in the experiments is about 8 A, and the voltage is within 80 V. The resulting coatings with silicon nanostructures will increase the active surface area by several tens of times.

In this work, an experimental physical setup is proposed and a method for the synthesis of silicon carbide in an electric arc drowned into the thickness of hydrocarbon raw materials is described. Silicon carbide and carbon nanotubes were found in the deposits at the cathode. The resulting sample was analyzed using an optical microscope. And also confirmed the hardness of silicon carbide.

The paper presents the results of the synthesis of silicon nanospheres (silicon fullerenes) in argon plasma. During the experiment, silicon atoms were evaporated from the surface of a single crystal using a plasma jet. Silicon atoms were entrained by the flow of argon plasma and, as the plasma cooled, formed in the form of spherical structures several atomic layers thick or in the form of silicon nanotubes. The diameters of silicon nanospheres range from 50 nm to 15 microns, and silicon nanotubes - from 40 to 100 nm.

In this paper, the synthesis of semiconductor spherical nanostructures is carried out by the plasma-chemical method. The sizes of the obtained nanospheres range from 100 nm to 1 mm. These structures are open on one side, have thin walls with a thickness of several nanometers, which end with “tentacles” with a diameter of several nanometers. Since the synthesis involved three elements of the fourth group of the periodic table (germanium, silicon, carbon), it has not yet been possible to determine the crystal structure of the obtained samples. All three elements are present on the surface of the sample in atomic percentages Ge-2.5%, Si-8%, C-55%. In addition to these elements, oxygen is also present in the spectrum.

Experiments have been carried out to study the effect of a supersonic gas flow on a transverse glow discharge in the case when the supersonic gas outflow enters the region of Faraday dark space, i.e. the positive column ends before reaching the supersonic jet. And also in the case when the supersonic outflow of gas falls into the region of the positive column. It is established that the organization of the supersonic flow changes the glow pattern of the glow discharge, creating a spatial inhomogeneity in the interelectrode space.

This paper presents the results of the synthesis of nanodiamonds and carbon nanotubes in silicon-argon plasma. At a pressure of 500 Torr in the plasma reactor, carbon atoms evaporated from the surface of the graphite anode of the electric arc. The peculiarity of the graphite anode was that small pieces of silicon were embedded on the surface of the anode. As a result of the experiment, nanodiamonds and carbon nanotubes were formed on the surface of the graphite cathode. The linear dimensions of nanodiamonds range from 10 to 50 nm. The diameters of carbon nanotubes range from 4 nm to 20 nm, and their length is from 100 to 2 microns.

According to the results of a numerical experiment, we show the possibility of control of the glow discharge parameters and structure by means of creating a supersonic gas flow in the selected section of the interelectrode spacing.

A method has been proposed for decomposition of heavy hydrocarbons into light fractions in arc plasma with rotating electrodes immersed in the hydrocarbon feedstock. Chromatographic analysis of the product gases has been performed, and the carbonaceous deposits formed on the electrodes during the experiment have been studied using electron microscopy and infrared spectroscopy.

The behavior of a glow discharge at low pressures is considered. A combined experimental and theoretical method for determining the distributions of electron and ion concentrations in the discharge chamber is proposed. It is shown that the concentrations of charged particles in the negative glow rise not due to the intense ionization by fast electrons from the cathode regions, but instead due to the slowing down of their drift motion. The use of an experimental curve of the potential distribution along a discharge chamber and account of the nonlocal dependence of the Townsend coefficient on the electric field strength have allowed obtaining the distribution of the electric field strength and determining the exact character of variation in the concentration of charged particles along the discharge axis.

A gas discharge with flowing liquid electrolyte cathode was experimentally investigated under combustion conditions inside an extended chamber with walls made of refractory material. The copper anode was located above the cathode at a distance of 20 cm. The length of the output channel was 50 cm. Heavily diluted aqueous solutions of sodium chloride were used as the electrolyte. The mass velocity of the electrolyte ranged from 8-16 g/s. A three-phase two-half-wave rectifier with voltage at the output of 2100 V served as a power source. The discharge burned stably without a ballast resistor. A plasma flow with mass velocity of 1.0-1.7 g/s in the power range of 25-30 kW was obtained. The total heat loss through electrodes did not exceed 30% of power consumption.

This paper presents a method of synthesis of silicon nanowires in microarc argon plasma. During the experiment, an adjustable direct current source with a ballast resistor was used. The cathode was a molybdenum rod, and the anode was silicon. The silicon was located in a small deepening in a graphite rod. During the experiment, synthesis of silicon nanowires was observed on the surface of molybdenum rod. The obtained silicon nanowires are straight and non-hollow inside, nanowires have a smooth surface and have a hexagonal cross-section. The resulting nanowires will be able to find further application in light emitting diodes, lithium-ion batteries, supercapacitors, photovoltaics.

This work investigates into the properties of longitudinal glowing discharge in supersonic gas stream between central body and reducer. It has been established that the properties of discharge spatial localization, intensity of radiation, formation of near-electrode areas directly depend on arrangement of supersonic stream. This work analyzes the properties of gas stream in expanding area of supersonic nozzle, pressure recovery in reducer. It has been experimentally established that gas circulation at supersonic speed in the area of glowing discharge makes it possible to control the distribution of concentration of neutral particles in interelectrode space as well as localization of near-electrode zones and positive glow.

The gas discharge between liquid electrolyte cathode and metal anode was experimentally investigated. Aqueous solutions of sodium chloride, potassium chloride, sodium sulfate, sodium hydroxide, and potassium hydroxide were used as the electrolyte cathode. Decrease aqueous solution was compensated by adding distilled water (solvent) in a continuous mode in the discharge burning process. It was found that, despite the significant dilution with a solvent, the specific electrical conductivity of aqueous solutions of alkali metal salts and alkalis varies slightly.

A low-pressure glow discharge in a transverse supersonic gas flow was experimentally studied for the case where the flow only partially fills the interelectrode gap. It is shown that the space region with supersonic gas flow has a higher concentration of gas particles and, therefore, works as a charged particle generator. The near-electrode regions of glow discharge are concentrated specifically in this region. This structure of glow discharge is promising for plasma deposition of coatings under ultralow pressures.

An original method of decomposition of heavy hydrocarbons into light fractions in the plasma of a microarc discharge initiated between electrodes submerged in a liquid is proposed. The characteristics of the microarc discharges between electrodes submerged in different liquids were investigated. A chromatographic analysis of the gases formed in this case has been performed.

In the presented research the experimental setup is proposed and the new method for the multilayer carbon nanotubes synthesis from liquid hydrocarbons is described. The systematic studies of the drowned electric arc interaction in the hydrocarbon feedstock with hydrocarbon molecules were carried out to obtain atomic carbon. The resultant product in the carbon black form was analysed through the electron microscope. It is shown that much carbonaceous deposits on the cathode are contained in carbon nanotubes.

A discharge device providing the ability to create an area in the interelectrode space with a controlled concentration of neutral particles due to the supersonic flow arrangement has been developed and implemented. The possibility to control the internal discharge parameters distribution by supersonic gas flow arrangement in a limited area of the glow discharge is shown experimentally.

An electrical discharge between a flowing electrolyte and a metal electrode was experimentally investigated in modes in which an intense transfer of a liquid electrolyte substance into the plasma column occurs. The cathode area of the discharge was investigated by the method of high-speed visualisation. A mathematical model for describing the processes of transfer of matter and charges from a liquid electrolyte cathode into a plasma was proposed.

This paper describes the experimental setup and outlines the original methodology for conducting an experiment on growing germanium nanostructures. The obtained samples were examined with an electron microscope. It is shown that this technique allows one to grow both germanium nanotubes and germanium.

Preliminary numerical calculations have been carried out, demonstrating the formation of a streamer structure of the surface dielectric barrier discharge in the case of the application of a positive potential to the working electrode. The dynamics of electron density and electric potential for a streamer form of discharge is presented.

A synthesis method of carbon nanomaterials in an argon arc is described in this paper. The two separate cases have been considered. In the first case it is carried out by evaporation of a graphite anode followed by deposition of carbon vapor on a tungsten cathode. In the second case the anode material was specially synthesized in the electric arc recessed into liquid hydrocarbon raw material. The fuel oil was used as a hydrocarbon raw material. During that decomposition of this material took place and as a result carbon deposits were formed on the electrodes. Then these carbon deposits were used as the arc discharge anode at the next stage of the process. In both cases the carbon synthesis of nanotubes was carried out on the tungsten cathode surface. There was the intensive growth of carbon nanotubes during the experiments.

This paper proposes a method for creating silicon nanotubes in electric arc plasma, by evaporating the anode material and collection it on the cathode. During the experiments, various types of power sources were tested. Silicon nanotubes of complex configuration in the form of a straight stem with cylindrical branch and single-wall curved nanotubes were obtained. The obtained nanotubes will be able to find further application in light-emittingdiodes, lithium-ion batteries, and photovoltaics.

A drift model of a glow discharge is proposed, which takes account of the nonlocal dependence of the ionization source on the electric field strength. The problem is reduced to solving a nonlinear differential equation of second order for the strength squared using the Newton–Kantorovich quasilinearization method.