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Theoretical and experimental studies of the synthesis of graphene with the introduction of nitrogen into a jet of helium plasma generated by a direct-current plasma torch with a power of to 40 kW at a pressure of 350 Torr have been performed. A propane–butane mixture was used as a source of carbon. As found by scanning microscopy, Raman scattering, and synchronous thermal analysis, the morphology of the synthesis products changed from graphene flakes to carbon nanotubes upon the addition of nitrogen in a ratio of 1 : 1.22 to the jet of helium plasma. The numerical modeling of the process showed that cyanopolyyne molecules, HC9N and HC11N, containing many carbon atoms appeared instead of C60 and C80 in the jets of helium upon the addition of nitrogen.

The results of a spectroscopic study of the conversion of acetylene and methane in a helium plasma jet produced by a direct current plasma torch are presented. The operating mode of the plasma torch corresponds to conditions that provide a high yield of carbon nanostructures. In the emission spectra recorded during the transverse observation of a 20-mm jet section following the outlet of the anode channel of the plasma torch, high-intensity Swan bands of the С2 molecule are the dominant component in the visible wavelength range. The spectra show atomic hydrogen lines of the HI Balmer series from Hα to He, numerous CI carbon lines from ultraviolet 247.9 nm to infrared 962–966 nm, and a number of HeI helium lines. The axial temperature values of the plasma jet were spectrally determined by the observed ionized carbon CII lines 283.7 nm, 392.0 and 426.7 nm. A joint analysis of the emission spectra and the mixture composition calculated in the Saha–Boltzmann approximation revealed the nature of the spatial heterogeneity of the studied He : C : H plasma jet. It is manifested by the difference in the electron temperature of the axial region of the jet, which is measured with ionized carbon lines CII (Te(0) = 12 000–14 000 K) from the vibrational and rotational temperatures of C2 molecules (TV = TR ≅ 5000 K) that emit intensely at the jet periphery. The electron density measured along the Hβ and Hγ line widths, which varies in the range of the observed jet region of ne = (4–2) × 1016 cm–3, corresponds to the ionization equilibrium in a plasma He : C : H mixture with an electron temperature close to Te measured by carbon-ion lines.

Graphene materials are synthesized in a thermal plasma jet without using size forming catalysts. The synthesis was performed on a direct current plasma torch operating at 28–30 kW with a pressure of 100–710 Torr. The synthesis products are studied by electron microscopy, X-ray diffraction, and dynamic light scattering. It is found that structures formed in the plasma jet have a flake morphology regardless of the type of the carbon bearing source. Thermodynamic calculations testify a correlation between the temperature profile in the plasma jet and the composition of condensed carbon (redistribution between C60 and C80). The application areas of flaky structures are discussed.

We studied the synthesis of composite Cu/graphene nanoparticles using the radiative characteristics of copper-containing plasma jets of a helium/hydrocarbon mixture, flowing from the nozzle of the output copper electrode of a DC plasmatron. A mixture of propane and butane was used as the hydrocarbon source. To determine the conditions for nanoparticle formation during the conversion of hydrocarbons in erosive jets, the concentration of copper was estimated by analyzing the optical emission spectra of Cu I lines observed in the spectrum. We found that the maximum saturation of graphene by copper (0.03 mass %) is reached at the copper concentration in plasma [Cu] = Nabs ≈ 3 × 1013 cm−3, which is sufficient to form a chemical bond of copper with sp2 carbon in a nanoparticle.

Conditions of substrate-free syntheses of graphene and graphene-based systems based on conversion of liquid and gaseous carbon precursors in helium, nitrogen, and argon plasma jets generated by a dc plasma torch at a reduced pressure are investigated. Using a number of physical characterization techniques, it is shown that bulk-synthesized (i.e., substrate-free) graphene has the morphology of crumpled paper. By changing the geometry of the flow-through section of the reactor, without using substrates, hydrogenated graphene structures are synthesized. Nitrogen- or copper-doped graphene can be prepared using nitrogen plasma. Thermally stable graphene oxide is obtained by introducing alcohols into argon or helium plasmas. It is concluded that graphene materials can be prepared by the plasma-assisted one-step syntheses.

The effect of graphene doping with copper in a plasma jet reactor is studied. The effect is obtained during the synthesis of graphene in hydrocarbon-contating helium and nitrogen plasma jets generated by an electric arc plasma torch under reduced pressure. The graphene/copper nanocomposite synthesized has been studied by scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray microanalysis. It has been found that copper forms various bonds with carbon in graphene layers, which are due to interaction between the layers. It has been shown that the concentration of copper in the nanocomposite substantially depends on the composition of the plasma-forming gas and its flow rate.

Synthesis of graphene materials in a plasma stream from an up to 40 kW direct current (DC) plasma torch is investigated. These materials are created by means of the conversion of hydrocarbons under the pressure 350&ndash, 710 Torr without using catalysts, without additional processes of inter-substrate transfer and the elimination of impurities. Helium and argon are used as plasma-forming gas, propane, butane, methane, and acetylene are used as carbon precursors. Electron microscopy and Raman imaging show that synthesis products represent an assembly of flakes varying in the thickness and the level of deformity. An occurrence of hydrogen in the graphene flakes is discovered by X-ray photoelectron spectroscopy, thermal analysis, and express-gravimetry. Its quantity depends on the type of carrier gas. Quasi-one-dimensional approach under the local thermodynamic equilibrium was used to investigate the evolution of the composition of helium and argon plasma jets with hydrocarbon addition. Hydrogen atoms appear in the hydrogen-rich argon jet under higher temperature. This shows that solid particles live longer in the hydrogen-rich environment compared with the helium case providing some enlargement of graphene with less hydrogen in its structure. In conclusion, graphene in flakes appears because of the volumetric synthesis in the hydrogen environment. The most promising directions of the practical use of graphеne flakes are apparently related to structural ceramics.

Hydrogenated graphene has been synthesized in one step by acetylene conversion in a helium plasma jet. A dc plasma torch with a diverging anode channel and a power up to 45 kW has been used to generate plasma. The obtained graphene materials have been studied by scanning electron microscopy, Raman spectroscopy, and elemental analysis. Hydrogen desorption from the samples synthesized has been studied by thermal analysis as a function of temperature. It has been found that during annealing in vacuum, the synthesis products change their morphology because of hydrogen release.

A single-stage catalyst free synthesis of hydrogenated graphene was studied in the process of methane conversion in a helium plasma jet created by a plasma torch at the power up to 45 kW and the pressure of 710 Torr. The synthesis products were studied by the methods of scanning and transmission electron microscopy, thermal analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis.

Carbon nanostructures were synthesized without the use of catalysts by the conversion of hydrocarbons in the DC plasma jet system. The samples of carbon nanotubes, nanofibers, graphene, onion like structures have been characterized by electron microscopy, thermal analysis, Raman spectroscopy. An experimental study of the composition of the gas phase with variation of the type of the plasma-forming gas and the type of carbon source was carried out. The synthesized samples have been used in the composition of the functional ceramic and in electrochemical systems.

Carbon fibers are prepared during the conversion of acetylene and propane–butane mixture in a jet of the helium and argon plasma without using catalysts. The synthesis is carried out in a plasma jet reactor. The synthesis products are studied by electron microscopy, synchronous thermal analysis and energy dispersive X-ray spectroscopy. The effect of the synthesis parameters on the structure and properties of the carbon fibers prepared in the volume is established. When the propane–butane mixture is decomposed in an inert medium, conditions are found for the synthesis of cylindrical carbon nanofibers of a tortuous shape with a diameter of up to 20 nm and a length-to-diameter ratio of up to 1000. The decomposition of acetylene at 350 Torr produces nanofibers formed by a chain of straight cylinders with a diameter of up to 20 nm, and cylindrical fibers are synthesized in the form of spirals of up to 200 nm in diameter at 150 Torr.

Hot pressing is used to prepare composite ceramic based on cubic boron nitride (CBN) reinforced with carbon nanostructures. Carbon nanostructures (CNS) are synthesized by hydrocarbon pyrolysis in a plasm-jet reactor in an argon plasma. The effect of composite material nanostructuring is obtained from results of study and specification of test composite specimens and starting materials by physicochemical methods, x-ray diffraction, and electron microscopy. This leads to a change in its functional properties.

It presented a comparative consideration of General Motors long-term activities on the current subject of fuel-cell-powered electric vehicles vs Toyota Mirai recent results, relevant to prospects on more efficient and safe technologies of the hydrogen on-board storage. It also presented a call on the project International cooperation. The main aim of this paper is to attract attention of General Motors, Toyota and/or other large car companies to a real possibility of developing and using, in the nearest future, of the break-through hydrogen on-board storage technology based on the solid H2 intercalation into graphite nanostructures.

Graphene synthesis in the helium and argon plasma jets generated by 40 kW DC plasma torch under the pressure 350 Torr is investigated experimentally and by means of the modeling. Propane-butane mixture and methane are used as the carbon feedstock. Scanning microscopy shows that in the case of helium the structure with lateral size up to 500 nm is being synthesized. In the case of argon the morphology of graphene flakes varies from rumpled to rectified sheets with lateral size up to 2 μm. Temperature and velocity profiles are determined for the helium and argon jets using the numerical simulation. Addition of hydrocarbons into the inert plasma jets creates an environments differing in the composition and the charge concentration.

We show a possibility of synthesis of graphene with the modified surface in plasma jets at atmospheric pressure and study the properties of the obtained samples by means of the electron microscopy and thermal analysis. By the XPS method, we determine the modification degree of the graphene surface by the oxygen, nitrogen, hydrogen atoms and hydroxyl groups. We show the influence of the carbon source type and the plasma-forming gas kind on the surface properties of the graphene flakes.

Porous multilayer graphenes have been synthesized by decomposition of hydrocarbons in a thermal plasma jet. Products of synthesis were characterized by electron microscopy, thermogravimetry, Raman spectroscopy, and X-ray diffraction. Possibility of producing a wide range of graphene materials with different morphology and structure has been shown. Influence of the experimental conditions on mesopores structure of the synthesis products has been investigated using the method of “limited evaporation.”

An experimental and theoretical study was performed on helium/propane-butane plasma, which enabled assembly of advanced carbon nanostructures, such as multilayer graphene flakes. A plasma jet was created at pressures ranging from 350–710 Torr, and with direct current plasma torch powers from 28–35 kW at varying mass ratios of helium to propane-butane 1:7.5 to 1:5. Graphene production was confirmed by different analytical techniques. The non-catalytic synthesis in the plasma jet volume provided the graphene purity. As a result of numerical simulation, the kinetic mechanism of the formation of carbon phase precursors in the gas phase, namely, C2 dimers, was studied. The concentration of C2 was determined, depending on the temperature and compared with the literature data on the pressure of saturated carbon vapours at temperatures ranging from 2500-5000 K. It is shown that the C2H-involving reactions provide additional C2 production, leading to the formation of supersaturated vapour from C2 molecules at temperatures of 2500-3500 K.

Results of experimental study of the one-step plasma-based process of the synthesis of unsupported graphene and hydrogenated graphene are presented. A direct current (DC) plasma torch is used, the pressure is held at 350 Тоrr, and the flow rates of plasma forming gas (helium) and carbon source (propane–butane mixture) are kept constant. An influence of reactor geometry on the properties of synthesized product is investigated. Graphene and hydrogenated graphene were synthesized in an appreciable rate in the plasma jet volume under equal conditions using cylindrical and conical reactors accordingly. Synthesized graphene materials are characterized using electron microscopy, Raman spectroscopy, x-ray, and XPS analysis, confirming the existence of graphene and of hydrogenated graphene (graphane). In order to examine an influence of input parameters on the process of the synthesis of graphene materials, the quasi-1D numerical flow model is used to calculate the distributions of temperature and velocity within the reactor channel. The key role of the temperature distribution within the reactor in the synthesis of graphene materials is established. Cylindrical flow channel provides higher temperatures compared with the conical channel. It affects the flow composition at the outlet. Under lower temperature, the flow contains in addition to condensed carbon a great amount of hydrocarbons CH, which is favorable for the production of hydrogenated graphene. Under higher temperature, the pure graphene is synthesized, since the outlet flow has the carbon mainly in the condense phase, the quantity of CH being insignificant.

The parameters of a non-catalytic process for synthesizing carbon nanostructures during the conversion of methane / helium and propane-butane / helium jets have been studied. The spectral features of the radiation of mixed systems have been investigated. Analysis of the spectra showed that the main part of carbon dimers is withdrawn from the hot region of the plasma in the outlet plasma stream. Synthesized products were been characterized by scanning electron microscopy, Raman spectroscopy, thermal analysis and X-ray photoelectron spectroscopy. It is shown that carbon nanostructures have a bamboo-like morphology and similar properties when using both methane and propane-butane mixture as a carbon source. It has been established that the morphology of synthesized carbon nanofibers is not affected by the pressure of the medium.

Thermal plasma processing of carbon sources using a plasma jet with high heat capacity is one of the most promising methods for the synthesis of new materials. This paper describes the low-temperature deposition of carbon nanomaterials by remote plasma-enhanced chemical vapor deposition (PECVD) in the absence of catalysts. The remote PECVD process differs from conventional and direct PECVD process in two ways: (a) only a subset of the process reactants and/or diluents are directly plasma excited; and (b) thin film deposition takes place on a substrate that is outside of the plasma glow region. In conventional CVD methods, carbon is produced from the decomposition of carbon sources such as hydrocarbons, carbon monoxide, alcohols, and so on, over a metal catalyst. The unavoidable metal species remaining in carbon nanomaterials would lead to obvious disadvantages for property characterization and application exploration. Despite sustained efforts, it is still an intractable problem to remove metal catalysts completely from carbon nanomaterials samples without introducing defects and contaminations. Good reactor design allowed to overcome problems of chemical and structural purity, and poor process robustness in terms of phase composition of product from run to run. For the synthesis of graphene materials, carbon black, carbon nanotubes, nanowires we used the thermal plasma generator which is a high current divergent anode-channel DC plasma torch. The experiment involved a simultaneous input of hydrocarbons (methane, propane, butane, acetylene) with the plasma forming gas (helium, argon, nitrogen) into the plasma torch, wherein heating and decompositions occurred in the plasma jet and in the region of the arc discharge, followed by condensation of the synthesis product on metallic surfaces. The deposition rate was varied with distance from the plasma. Consumption of carbon source, plasma forming gas and plasma torch power were changed independently from each other. For the experimental conditions the electric power of plasma torch was set up to 40 kW. Regularities of formation of carbon thread-like nanostructures and graphene in the course of hydrocarbons pyrolysis in thermal plasma without participation of catalytic particles were studied by means of electron microscopy, X-ray diffraction, IR-spectrometry and thermogravimetry. Depending on the pyrolytic synthesis parameters, different proportions of crystal carbon and soot may be obtained. It has been demonstrated that the phase composition is varied by hydrocarbons flow rate, plasma forming gas pressure and dc plasma torch power. It has been established through the experiments that carbon nucleation is volumetric and proceeds according to the model of explosive soot formation.

An experimental and numerical study of plasma-assisted synthesis of graphene and carbon nanotubes is presented. Experiments were carried out using methane/nitrogen plasma generated by a DC plasma torch with pressure variation in the 100–710 Torr range. The synthesis products were studied by synchronous thermal analysis and scanning electron microscopy. The results of these experiments are shown in thermogravimetry graphs and snapshots of the synthesized structure morphology. It is shown that structures in the form of graphene 'flakes' are thermally stable. Carbon nanotubes synthesized at different pressures show different morphologies. Using express gravimetric analysis, the maximum nitrogen content in nanostructures was determined to be 8 at.%. Spectral investigation of a jet of nitrogen plasma with the addition of methane and pure nitrogen under atmospheric pressure was performed. The results of the emission spectra analysis agree with the gas phase composition obtained by kinetic modelling. It is shown that the conversion products consist of the following components: H, H2, C2, CN, HCN, C2H2, C4H4, and C6H6, the ratio of which varies with decreasing temperature. Our calculations show that the gas phase composition remains practically unchanged at different pressures.

A method to synthesize graphene materials using a DC high current divergent plasma torch has been developed. Carbon atoms were generated by the decomposition of propane-butane, methane and acetylene in a thermal plasma jet. The graphene materials were characterized by electron microscopy, thermogravimetry, Raman spectroscopy. The influence of the experimental conditions on the morphology and phase composition of the synthesis products was investigated. The optimal conditions for the synthesis of high-purity graphene flakes have been found.

The possibility of doping graphene during its synthesis in a plasma jet of nitrogen has been studied. Direct current plasma torch with power of up to 40 kW was used as plasma jet generator. The source of carbon was propane-butane mixture, acetylene or methane. Synthesized materials are characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. It has been shown that XPS spectra of graphene flakes produced in nitrogen plasma differ in atomic nitrogen content. The maximum degree of nitrogen doping of graphene was obtained at decomposition of acetylene at 77 Torr.

By means of DC plasma torch of up to 45 kW power, few-layered graphene sheets were obtained. Their properties and structure were characterized by using electron microscopy, thermal analysis, Raman and infrared (IR) spectroscopy. Boundary surface of samples have been investigated using the method of "limited evaporation" and BET method. Electrochemical examination of their properties was conducted. Due to the activity and stability of synthesized materials the conclusion was made regarding the possibility of the use of them as catalysts carriers for fuel cells electrodes, electric current sources, conducting additives for electrodes in non-aqueous electrolytes.

Ceramic composite reinforced with plaits of carbon nanotubes have been fabricated by the reaction bonded silicon carbide method. Carbon nanotubes (CNTs) are produced using a 35 kW dc plasma torch and C2H2 as carbon precursor. Effective methods of CNTs adding and dispersing in the preform volume have been found. The optimal content and operational technological parameters have been determined for ceramic matrix. Physico-mechanical properties of the reinforcing ceramic matrices with nanomaterials have been investigated.

The results of the synthesis of carbon nanostructures at high temperatures using a DC plasma torch are presented. Plasma was generated by introduction of argon, nitrogen and helium into the plasma torch with an anode in the form of an expanding channel. Sustainable modes of the plasma torch operation have been achieved by simultaneous tangential input of a plasma gas with a carbon source. Obtained solid products were studied using electron microscopy, thermogravimetry, Raman spectroscopy and X-ray diffraction to characterize their properties and morphological structures.

A method to synthesize graphene-like materials using dc high current divergent anode-channel plasma torch has been developed. Carbon atoms are generated by decomposition of propane-butane and methane in a thermal plasma jet. Products of synthesis are characterized by electron microscopy, thermogravimetry, Raman spectroscopy and porosimetry. Effect of experimental conditions on the morphology, phase composition and porosity of the products of synthesis are investigated. The optimal conditions have been found.

In this study we propose the high-performance technology to produce carbon nanotubes (CNT) in plasma jet reactor by means of a direct current plasma torch. This technology provides excellent opportunities to investigate a direct evaporation of materials and their subsequent condensation on the carbon surface. Experiments were carried out at the electric power of a plasma torch up to 30 kW. Helium and argon served as plasma gases. CNT synthesis at pyrolysis of soot was catalyzed by the metal disperse powders of Ni, Co, Y2O3. We applied x-ray diffraction and electronic microscopy to investigate the structure of obtained products. Also we utilize the thermogravimetric analysis to determine the phase structure of carbon nanomaterials. Using available experimental data we were able to sequentially scale the production process of CNT of desirable space structure. Finally we established that structural and morphological properties of CNT produced at evaporation of soot in the presence of high- percentage combined catalysts depend upon the catalyst structure.