Arc Discharge Plasma Research Articles

Synthesis of Metal-Organic Framework Structures Based on Copper in a Low-Pressure Arc Discharge Plasma

Plasma-chemical synthesis of nanopowders based on copper oxide and metal-organic framework structures was carried out using low-pressure arc discharge plasma. The study of the obtained material was carried out by several methods (XRD, FTIR, TEM, TGA and EIS). TEM showed that the obtained powder is highly agglomerated particles with an average particle size of 13 nm, and the crystalline ordering of nanoparticles with a large (about 2 nm) lattice parameter is clearly visible. XRD showed the presence of four crystalline phases corresponding to [Cu3 (BTC)2], Cu, Cu2O and CuO. XRD results are in good agreement with FTIR studies. The DTA curve demonstrates a continuous exothermic process associated with a number of features of plasma-chemical synthesis and the morphology of the obtained nanoparticles. The study of the electrochemical properties of the materials obtained by the method of impedance spectroscopy revealed an anomalous accumulation of electrical charges around the electrodes due to electrochemical reactions for [Cu3 (BTC)2], which are associated with various reactions involving copper species in the organic framework.

Flow Control Effect of Spanwise Distributed Pulsed Arc Discharge Plasma Actuation on Supersonic Compressor Cascade Flow

To achieve efficient control of supersonic compressor cascade flow, a type of spanwise distributed pulsed arc discharge plasma actuation (PADPA) was designed. To simulate the influences of PADPA on the flow field, a phenomenological model was established. Then, the flow control effects of PADPA on supersonic compressor cascade flow were researched numerically. The results show that under low static pressure ratio condition, the compressive wave induced by PADPA reduced the intensity of the passage shock wave, which eventually reduced shock wave loss. It was also found that PADPA produced an adverse pressure gradient (pre-compression effect) around the actuation location, which reduced the strength of the high adverse pressure gradient induced by the passage shock wave. The airflow on both sides of the actuation location was accelerated by PADPA owing to the spanwise distributed layout. Thus, it improved the ability of the boundary layer to resist the effect of the adverse pressure gradient and reduced the separation zone. Consequently, the total pressure loss was reduced by 6.8%. Under high pressure ratio condition, the effect of PADPA on the suction side controlling the large separation of the boundary layer was insignificant. The total pressure loss also increased slightly.

The pulse vacuum-arc plasma generator for nanoengineering application

In paper described the results of work on the application of vacuum-arc machine in nanoengineering area. Researches were carried out to optimize the operation of this machine for the synthesis of nanomaterials in low-pressure arc-discharge plasma, plasma diagnosis and production of nanopowders. An electrode system based on the grounded cathode with impulse ignition has been developed. The anode current was measured and the mass output of the product was calculated. Experimental data on energy density were obtained, confirming the presence of plasma focusing on the electrode system axis due to its own magnetic field, the focus value of which reaches about 18 kJ/m2. Powder samples were also obtained in the form of clusters containing the copper particles (up to 98%) and spherical powder with size from 116 nm to 1.2 µm. Homogeneity and dispersion of powder depended on the time of the processes accompanying the deposition.

Vacuumless synthesis of tungsten carbide in a self-shielding atmospheric plasma of DC arc discharge

The goal of this paper is to simplify and reduce the cost of manufacturing tungsten carbide. The work presents the results of experimental studies that prove the possibility of synthesizing fine and ultrafine crystalline phases of tungsten carbide in the DC arc discharge plasma ignited in open air by a developed vacuumless technique. The synthesis is implemented in the process of arc discharge burning between the graphite rod (anode) placed inside the cavity of the graphite cathode in the presence of graphite and tungsten powders used as initial precursors. The cathode cavity (reaction zone) is shielded from oxygen by a stream of carbon monoxide and carbon dioxide gases, which are generated during the arc discharge burning in an open air. After studying the influence of main process parameters (parameters of the discharge circuit and graphite electrode's dimensions) and optimizing the system, the authors obtained tungsten carbide phases without impurities of oxide phases. This allows simplifying significantly the technology of tungsten carbides synthesis by excluding the stage of vacuum creation.

Strategies for Scalable Gas-Phase Preparation of Free-Standing Graphene

The preparation of graphene with high quality serves as a prerequisite for its usage. Traditional methods of graphene production, represented by liquid-phase exfoliation and chemical vapor depositi...

The effect of microstructural features on the ferromagnetism of nickel oxide nanoparticles synthesized in a low-pressure arc plasma

Abstract Nickel oxide nanoparticles were first synthesized by sputtering high-purity nickel in an oxygen plasma of a low-pressure arc discharge. The structure, morphology, and optical and magnetic properties of NiO nanoparticles were studied by XRD, TEM, FTIR, UV-VIS, and VSM. TEM images showed that the obtained NiO nanoparticles have a narrow particle size distribution and an average particle size of 12 nm. The XRD results and the processing of diffractograms by the Rietveld method showed that the obtained nanoparticles have a face-centered cubic lattice with an average particle size of 13 nm. With decreasing temperature, residual stresses increase and peaks corresponding to the superstructure appear. The band gap of NiO was determined from the optical absorption spectrum and amounted to 3.21 eV. Magnetic measurements showed that, at temperatures of 200 and 300 K, NiO nanoparticles, unlike bulk particles, exhibit ferromagnetic behavior, and at 5 K a magnetic hysteresis loop appears. Based on the studies, a dendritic model of the nanoparticle microstructure is proposed.

Synthesis of molybdenum carbide catalyst by DC arc plasma in ambient air for hydrogen evolution

Electrochemical water splitting is attractive for hydrogen production, however, high cost of noble metal catalysts, such as platinum, restrict its use. Herein, molybdenum carbide nanoparticles encapsulated within carbon matrices as a high-performance and low-cost electrocatalyst for hydrogen evolution reaction (HER) were prepared by DC arc discharge plasma under ambient air conditions. According to XRD patterns the synthesized product includes molybdenum carbides (β-Mo2C and Mo1.2C0.8), molybdenum and graphite crystalline phases. The resulting material shows highly active catalytic properties with very small onset potential of −63 mV, a low overpotential of −226 mV at current density of 10 mA cm−2 and Tafel slope of 66.1 mV.dec−1 in 1.0 M KOH. The long-term HER stability test for 50 h under constant current density of 10 mA cm−2 confirmed the stability of the catalytic properties of the synthesized product. Therefore, such a method for producing Mo-based material for HER electrocatalysts is promising and can have practical application.

Physicochemical Properties of Zirconium Oxide Nanopowder Synthesized in Low-Pressure Arc Discharge Plasma

The method for synthesis of zirconium oxide nanopowder in low-pressure arc plasma was developed. The physicochemical properties of the nanopowder were studied. The estimation was carried out by means of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The sequence and kinetics of structural transformations occurring in the specified time-temperature heating regimes have been examined using differential thermal analysis. It was shown that the particles have a nanometer size, a narrow particle size distribution and an amorphous-crystalline structure. The maximum specific surface area detected by the method of sorption of surfactants was 470 m2/g. The issues of crystallization were discussed. From comparison between the results of experimental studies from earlier works with the results obtained for zirconium oxide, it is concluded that the proposed method for producing NPs in a low-pressure arc discharge plasma is universal.

To the question about mechanisms for the formation of dust fractal structures from an arc plasma

The paper presents the results obtained in the study of dusty particles of an arc discharge plasma (fractal aggregates). One of the possible reasons for the formation of fractal structures is the current layers. These are ion flows between adjacent cathode spots of an arc discharge. The magnetic field of the current sheet is an energy source, the dissipation of which leads to the creation of instability of the growth front. In this area, the formation of fractal-like aggregates (drift-dissipative instability) can occur.

Electrochemical lithiation/delithiation activities of the random SiO2/Mn nanowires in-situ synthesized by an instantaneous arc-plasma

Catalyst (Mn)-induced growth of random SiO2 nanowires (NWs) was in-situ accomplished by direct current (DC) arc-discharge plasma. An instantaneous vapor-liquid-solid (VLS) mechanism was proposed for the formation of the SiO2/Mn NWs, evidenced by optical emission spectroscopy (OES) diagnoses on the high-temperature plasma and analyses of Gibbs free energies on the basis of Ellingham diagram. Electrochemical behaviors of SiO2/Mn NWs electrode showed a specific capacity of 1333.6 mAh⋅g−1 at the current density of 0.1 A g−1, with a Columbic efficiency of 98.1% after 100 cycles. The diffusion of Li+ ions in the SiO2/Mn NWs electrode was further promoted by consecutive cycling, which was attributed to the ionically conductive products of Li2O and lithium silicate in the SEI layer, revealed by the Li+ diffusion coefficient (2.64 × 10−17 cm2 s−1) in the initial electrode and a varied value of 8.97 × 10−17 cm2 s−1 in the subsequently cycled electrode. The excellent cycling stability of the SiO2/Mn NWs electrode was ascribed to the random SiO2 nanowires with one-dimensional structure, the uniformly embed Si species in the buffer matrix by cycling, and the positive contribution from the residual catalyst of Mn nanoparticles. The unique morphology and composition of the SiO2/Mn NWs brought in an excellent rate capability, i.e. the reversible capacity of 1076.4 mAh⋅g−1 at a current density of 0.1 A g−1 was adequately recovered after suffering from intense current impacts up to 2.0 A g−1.

Characterization of the impact of nanoparticles on micro strain in 2D graphene synthesized by arc discharge plasma

In this study, we report the impact of side growth of nanoparticles on crystalline graphene nanostructure by facile and stable arc discharge plasma method. The plasma generated between two highly purity graphite electrodes, not only exfoliate graphene layers on cathode surface, but also produces micro and nanoparticles. The characterization of microstructures produced on the graphene layers deposited under different background environments and pressures by arc discharge plasma is presented. The morphologies of graphene sheets, comprising eight to twelve layers, were confirmed using transmission electron microscopy (TEM). Furthermore, the increment of background pressure from 10−2 to 102 mbar has found to increase numbers of graphene layers resulting in a reduction in I2D/IG ratio. Tuning the background environment and pressure led to different levels of carbon nanoclusters embedment on the surface of graphene layer under the air and H2 environments. This embedment demonstrates the rise of microstrain in the form of tensile stress on graphene indicated by Williamson-Hall plot calculated at 1232 × 10−3 and 151 × 10−3 respectively under H2 and air. The redshift and splitting of G and 2D bands in Raman spectra also support the rise of strain in graphene layers. Overall, embedment of nanoparticles might be accounted by the increase in stress on graphene layers that manipulate the electronic interaction between layers, suggesting it a promising candidate for nanoelectronic and nanophotonic device applications based on graphene.

Электродуговой синтез материала на основе графита и карбида молибдена

Представлены результаты экспериментальных исследований синтеза карбида молибдена в плазме дугового разряда постоянного тока безвакуумным методом. Установлено влияние амплитуды тока разрядного контура на фазовый состав продукта синтеза. Продукт синтеза содержит микроразмерную компоненту и наноразмерную. В составе микроразмерной составляющей методами растровой электронной микроскопии и рентгеновской дифрактометрии идентифицированы углеродные волокна со структурой графита, а также модифицированные волокна, содержащие графит и карбид молибдена. Наноразмерная компонента содержит скопления частиц, представляющих собой графитовую матрицу, в которую погружены частицы карбида молибдена.

Синтез заполненных карбидом вольфрама многостенных углеродных нанотрубок в атмосферной плазме дугового разряда постоянного тока

Показана возможность синтеза многостенных углеродных нанотрубок в плазме дугового разряда постоянного тока, инициированного в открытой воздушной среде. Процесс синтеза реализован в полости графитового катода, в которой в качестве катализатора присутствует порошок вольфрама. Применяемый метод реализуется за счет генерации газообразного оксида углерода СО, экранирующего реакционную зону от кислорода воздуха, предотвращая окисление продуктов синтеза. Согласно данным рентгеновской дифрактометрии синтезированные порошковые материалы содержат более чем 85 об. % углеродных кристаллических фаз с графитоподобной структурой, а также содержат кубическую фазу вольфрама, две фазы карбида вольфрама WC и W2C. Согласно результатам просвечивающей электронной микроскопии продукт синтеза содержит углеродные нанотрубки, особенностью которых можно считать относительно большое количество слоев (до ~50 шт.) при диаметре до ~100 нм и длине до ~1.5 мкм. При этом внутри углеродных нанотрубок идентифицируются кристаллические объекты, соответствующие по структуре карбиду вольфрама WC.

Study of the Ion Composition of the Diffuse Vacuum Arc on a Hot Cathode by the Time-of-Flight Method

The study of a diffuse vacuum arc (DVA) is of interest in connection with the developing methods of plasma processing of the spent nuclear fuel (SNF). This type of discharge can provide a high degree of ionization of the vapors of the cathode material in the absence of droplets and multiply charged ions. This work is devoted to the study of the ion composition of the arc discharge plasma at a consumable hot gadolinium cathode by analyzing the optical and mass spectra of ions. The plasma ion composition is determined at a discharge current of 50 A, arc voltage ranging from 4 to 14 V, and cathode temperature ranging from 1.9 to 1.95 kK. The obtained data, together with the data recorded using the condensation probe method, showed that at an arc voltage of 5 to 6 V a plasma is generated with an ionization degree close to 100%, which contains more than 95% of singly charged ions among all the charged states.

Effect of Gas Dynamics on Discharge Modes and Plasma Chemistry in Rotating Gliding Arc Reactor

This article investigates the effect of gas flow rate on arc discharge mode and plasma chemistry in a nonmagnetic rotating gliding arc reactor. This article is conducted using oxygen as a plasma forming gas under transient (5 LPM), turbulent (25 LPM), and highly turbulent (50 LPM) flow conditions. The voltage-current (V-I) characteristics reveal discharge modes, such as glow mode under transient flow (I <; 1 A), glow-spark transition mode under turbulent flow (I <; 1 A & I ≫ 1 A), and spark mode under highly turbulent flow (I ≫ 1 A). Arc completes full rotation under transient flow, whereas it is blown off before completing full rotation under turbulent flows. The captured optical emission lines of the discharge indicate domination of excitation reactions under glow and glow-spark transition modes and domination of both the excitation and electron impact ionization reactions under spark mode. These observations reveal that the gas dynamics changes the discharge mode of the rotating arc that in turn alters the plasma chemistry, which is a positive feature to promote specific reaction pathways.

Plasma-enhanced catalytic activation of CO2 in a modified gliding arc reactor

For the first time, this paper demonstrates a synergistic effect from the combination of a gliding arc discharge plasma with a photocatalyst TiO2 for CO2 dissociation. The effects of adding a tray downstream the discharge and the combination of the catalyst with plasma have been investigated. Two different combination modes of plasma catalysis, i.e., in-plasma catalysis and post-plasma catalysis, have been evaluated with the emphasis on the analysis of potential mechanisms. The results show that modifying the gliding arc reactor by the addition of a tray can enhance the fraction of gas treated by plasma, thus improving the reaction performance. An exceptional synergistic effect of combining the gliding arc discharge with TiO2 for CO2 activation forms in the in-plasma catalysis mode. The presence of TiO2 significantly enhances the CO2 conversion by 138% and the energy efficiency by 133% at a flow rate of 2 L/min. The plasma activation effect, which produces energetic electrons that can create the electron–hole pairs on the catalyst surface, is believed to be the major contributor to the generation of the plasma catalysis synergy. This mechanism has been further evidenced by the negligible influence of the post-plasma catalysis on the reaction performance.

Obtaining Titanium Carbide in an Atmospheric Electric Discharge Plasma

The results of experimental studies on the development of scientific and technical foundations of a method to obtain cubic titanium carbide in plasma of a DC arc discharge initiated in air have been presented. According to X-ray diffractometry of powder materials obtained in a series of experiments, the dependences of phase composition of the product on the duration of synthesis have been determined. Using the results of scanning electron microscopy and energy dispersion analysis, several morphological types of titanium carbide particles, which are formed as a result of uneven energy distribution in the reaction volume, have been revealed.

Glow discharge characteristics of non-thermal microplasmas at above atmospheric pressure

Normal glow discharges in micrometer scales are being widely studied for a variety of ultrafine processing technologies. DC glow discharge characteristics were investigated at an atmospheric pressure in the range of 0.1–1.65 MPa. The operational discharge characteristics such as voltage–current (V–I) measurement, discharge size, gas temperature, vibrational, and rotational temperatures were obtained for helium (He) and nitrogen (N2) gases. Optical emission spectroscopy studies were carried out to measure rotational and vibrational temperatures using the nitrogen second positive system. Discharge above atmospheric pressure was characterized for the current range of 0.1–1.2 mA and an electrode gap of 5–250 μm. This paper presents evidence for a discharge size as small as 7 μm in N2 and 16.7 μm in He, while operating at a low current of 0.5 mA and at high pressures of 1.65 and 0.34 MPa, respectively. To the best of our knowledge, this is the first time an experimentally obtained normalized current density corrected with effective pressure has been estimated to be close to an analytical value (400 μA cm−2 Torr−2) for N2 using a stainless-steel cathode at above atmospheric pressure. The observation of the breakdown of two different gases (N2 and He), the V–I characteristics, and high current densities indicate that microplasma exhibits a stable glow discharge when a low capacitance external circuit is used. Rotational and vibrational temperatures are obtained in the ranges of 1186–2894 K and 4208–3608 K, respectively, for the pressure range of 0.10–1.65 MPa in N2 gas for a constant discharge current of 0.5 mA and an electrode gap of 150 μm. It is also notable that the transition from non-equilibrium to equilibrium discharge in both rotational and vibrational temperatures was observed in N2 at 0.86 MPa, without the transition to thermal plasma (arc discharge).

Increased arc length and stability in a magnetic gliding arc discharge using a cylindrical notched cathode

Intermediate arc discharge plasmas allow for working with ions at lower temperatures than thermal plasmas and can generate greater selectivity in certain chemical reactions due to the high vibrational and electron temperature. In this paper, a magnetic gliding arc discharge (MGA), which is an intermediate plasma, was developed and is described. The reactor is operated with CO2 as the working gas, but open to atmosphere. It presents increased arc length and stability by using a cylindrical notched cathode (CNC). The constructed rectangular section of the notch channel on the cylindrical cathode surface allowed the arc to be confined within the channel with enhanced stability. The changes in the cathode geometry allowed the system to reach radial arc length of 40 mm, plasma disc diameter of 102 mm, and from 300 to 400 mA of current. A low cost electro-optical device was set up to determine the arc rotation frequency and is described in detail. Measurements of frequency (f) as a function of current (I) indicates that the developed MGA-CNC follows the relation f∝ I0.5, which agrees with the theoretical prediction. In order to compare the MGA-CNC data acquired with other reported MGAs, an analysis considering the distinct magnetic field intensities (Br) and different cathode diameters (D) was performed. Thus, a linear relationship was observed for f D/(Br=D/2)1/2 as a function of I1/2, which may represent the general experimental behavior of different MGA operated in air at atmospheric pressure. The arc diameter (d) in the region near the cathode (at r = D/2) can be determined from the slope α of the plot (α = 6.03 m kg−1/2); the obtained value (d = 3.2 ± 0.7 mm) is coherent with measured values elsewhere.

Plasma mediated disinfection of rice seeds in water and air

The efficacy of seed disinfection utilizing atmospheric pressure non-thermal plasma is still a subject of intensive research. Previously, we found that rice seeds infected by Fusarium fujikuroi (fungus causing bakanae disease) could be disinfected via underwater arc discharge plasma. In this study, we further investigated the mechanism of disinfection and the effect on disease severity. In addition, we evaluated disinfection of rice seeds in air by surface DBD plasma. Disease severity was significantly reduced in seedlings germinated from rice seeds treated with underwater arc plasma, compared to non-treated seeds (44%–62% plasma treated compared to 92% non-treated). A shockwave of 11 atm pressure was generated during arc discharge, which likely caused fungal detachment from the seed surface. Moreover, reactive oxygen species such as atomic oxygen (O) was emitted from the underwater arc discharge plasma and could have contributed to the degeneration of the chemical composition on the seed surface and the inactivation of the fungal spores. Rice seeds treated with surface DBD plasma in the presence of H2O2 at a lower pressure (0.6 atm) for 30 min showed the highest seed disinfection efficiency (about 93% seed disinfection) and a significant reduction in disease severity in the germinated seedlings (23% plasma-treated compared to 100% non-treated). Taken together, our results suggested that underwater arc discharge and surface DBD plasma could be usefully applied to develop control strategies for seed-borne fungal diseases via seed decontamination during dry storage or water imbibition before sowing.