Arc Discharge In Gas Research Articles

Cathode erosion in a gas arc discharge at the threshold currents

The results of experimental studies of the erosion rate of high-purity tungsten cathodes after pulsed arc discharges in a pure oil-free ultrahigh vacuum and in gases of various purities are reported. The erosion rate in high-purity argon does not change compared to the rate of erosion of electrodes in a pure oil-free vacuum. The rate of erosion in "technical" argon is 10-20% less than the rate of erosion of electrodes in an oil-free vacuum. The rate of erosion in "technical" nitrogen is 15-35% less than the rate of erosion of electrodes in vacuum. Particle sizes formed in gas arcs are smaller than those formed in vacuum arcs. Keywords: arc in gas, erosion rate, ecton mechanism, particles, electron microscopy

Research of plasma radiation of low pressure dc arc gas discharge

A spectroscopic analysis of a plasma arc discharge in helium was carried out. In the obtained emission spectra in the wavelength range from 380 to 1100 nm, lines of molecular band systems, such as Swan C2 systems and C I.

Influence of the Electric Field Enhanced Thermal Electron Emission on Temperature of the Cathode with a Thin Insulating Film in the Arc Gas Discharge

A model of the electric field enhanced thermal (thermo-field) emission of electrons from the metal cathode substrate into a thin insulating film on its surface is developed. A system of equations for the cathode surface temperature in the arc discharge and the electric field strength in the film, providing the required discharge current density, is formulated. It is shown that existence of the insulating film can result in a considerable reduction of the cathode temperature in the discharge due to lower potential barrier height at the metal-insulator boundary than at the metal-discharge boundary in case of the cathode without the film. It is found that due to an enhancement of the thermal emission of electrons into the film by the electric field generated in it, an additional decrease in the cathode temperature by about 100 K takes place.

Low energy implantation of nitrogen ions by extended beam with a ballistic focusing in a stainless steel

The results of experiments on low-energy nitrogen ions implantation in stainless steel AISI 321 are presented. The treatment was carried out with a pulsed beam of nitrogen ions obtained using a ballistic system of ion focusing. The source of ions was nitrogen plasma of a non-independent gas arc discharge with a heated cathode. It was shown that the specimen surface is subjected to ion etching, which leads to the formation of a well, whose profile depends on the ionic exposure parameters. In addition, when treating specimen in such a system, the surface hardness increases up to 4 times. The increase in hardness occurs due to the formation of a modified layer in the surface, with a thickness of up to 50 microns, containing iron and chromium nitrides.

Low-energy plasma-immersion implantation of nitrogen ions in titanium by a beam with ballistic focusing

The results of experiments on low-energy implantation of nitrogen ions into VT1-0 titanium alloy are presented. Processing was performed by a nitrogen ion pulsed beam obtained using a ballistic ion focusing system. An ion source was a nitrogen plasma of the non-self-sustained gas arc discharge with a thermionic cathode. It has been shown that when the specimens are processed in such a system, hardness of the surface increases from 1.5 to 2.5 times. In addition, the surface of the specimens undergoes ion etching which causes the formation of an etching cavity whose profile depends on the ion effect parameters.

Argon gas atoms trapping by carbon dendrites

The conditions of argon gas atoms trapping by carbon dendrites, which growing in atmospheric pressure gas-discharge plasma, are considered in that paper. It’s showing that the argons atoms trapping by the carbon diamond-like cell can occur in arc gas discharge with current density more than j0 ∼ 45 mA/sm2 and provided that the eximer molecules of noble gas and carbon atoms (e.g., ArC) can be formed.

Investigation of parameters and uninterrupted service of a generator of gas-discharge plasma based on a nonsustained hot-cathode arc discharge in gas

The design of an electrode system and the characteristics of a gas-discharge plasma source (generator) based on an arc discharge in gas sustained by thermionic emission are presented. The results of an experimental investigation of the service life of a thermionic (hot) cathode of the plasma generator are reported as a function of the discharge current and voltage and the cathode filament power. It is shown that an increase in the burning voltage from 28 to 60 V considerably reduces the service life of the hot cathode, while the discharge current and the cathode filament power exert a less critical effect on its lifetime. The conditions necessary for achieving long-term service life parameters and high efficiency of plasma generation are found out.

Steam Reforming of Dimethyl Ether by Gliding Arc Gas Discharge Plasma for Hydrogen Production

Gliding arc gas discharge plasma was used for the generation of hydrogen from steam reforming of dimethyl ether (DME). A systemic procedure was employed to determine the suitable experimental conditions. It was found that DME conversion first increased up to the maximum and then decreased slightly with the increase of added water and air. The increase of total feed gas flow rate resulted in the decrease of DME conversion and hydrogen yield, but hydrogen energy consumption dropped down to the lowest as total feed gas flow rate increased to 76 ml·min−1. Larger electrode gap and higher discharge voltage were advantageous. Electrode shape had an important effect on the conversion of DME and production of H2. Among the five electrodes, electrode 2# with valid length of 55 mm and the radian of 34 degrees of the top electrode section was the best option, which enhanced obviously the conversion of DME.

Effective Processes for Arc-Plasma Treatment in Large Vacuum Chambers of Technological Facilities

Characteristics and design features of electrode systems for sources of gas-discharge plasmas produced in an arc discharge in gas sustained by electron emission from a hot cathode and advanced vacuum-plasma facilities relying on them are presented. High values of the parameters and advantageous properties of the plasmas generated by the proposed sources in large vacuum volumes are obtained. Effective techniques and technological processes designed for surface modification of metal parts by the methods of cleaning, alloying (doping), and forming multicomponent composite coatings using low-pressure arc discharges are demonstrated.

Hydrogen production by methanol decomposition using gliding arc gas discharge

AbstractDirect decomposition of methanol has been investigated using gliding arc gas discharge (GRD) at atmospheric pressure. Depending on the experimental conditions of Ar flow rate, methanol concentration, the electrode gap, input voltage and vaporization room temperature (VRT), different conversions are achieved ranging from 51.0% to 81.7%. Interestingly, the selectivity to the production of hydrogen and carbon monoxide is kept almost constant under all the experimental conditions. The formation of little methane and C2Hx as a byproduct, and trace quantity of carbon dioxide are detected. The reaction channels of methanol decomposition induced by GRD plasma is proposed in detail.

Decomposition of Naphthalene by dc Gliding Arc Gas Discharge

Gliding arc discharge has been proved to be effective in treatment of gas and liquid contaminants. In this study, physical characteristics of dc gliding arc discharge and its application to naphthalene destruction are investigated with different external resistances and carrier gases. The decomposition rate increases with increasing of oxygen concentration and decreases with external resistance. This value can be achieved up to 92.3% at the external resistance of 50 kOmega in the oxygen discharge, while the highest destruction energy efficiency reaches 3.6 g (kW h)(-1) with the external resistance of 93 kOmega. Possible reaction pathways and degradation mechanisms in the plasma with different gases are proposed by qualitative analysis of postdestructed products. In the air and oxygen gliding arc discharges, the naphthalene degradation is mainly governed by reactions with oxygen-derived radicals.

Plasma assisted dry methane reforming using gliding arc gas discharge: Effect of feed gases proportion

The influence of feed gases proportion on the performance of gliding arc discharge (GAD) plasma assisted methane reforming with carbon dioxide process (DMR) is investigated, especially focused on the reagents conversion, the main by-product distribution and the energy consumption. An additional analysis of the theoretical conditions of equilibrium and its comparison with the experimental results are also included. The GAD assisted DMR process is effective in converting CH 4/CO 2 into synthesis gas with C 2H 2 and C 2H 4 detected as the main hydrocarbon compounds. Strong dehydrogenation in the GAD assisted DMR process is suggested with no obvious C 2H 6 observed in the effluent and serious coke formation and deposition detected in the relative high CH 4/CO 2 feed ration and supply voltage condition. Compared to other plasma systems reported before, the GAD reactor used in current work shows lower energy consumption for methane conversion but higher energy consumption for C 2H 2 formation. The increase of CH 4/CO 2 molar ratio in the feed gases favors the reagents conversion and consequently promotes the formation of each by-product. Meanwhile, the by-product selectivities, the value of H 2/CO ratio in the effluent, the coke formation, and the special energy consumption for reagents conversion and synthesis gas formation are shifted. It is clearly demonstrated that under some certain circumstances, the GAD plasma reactor assisted reaction can be totally out of thermodynamic equilibrium.

Simultaneous removal of ethyl acetate, benzene and toluene with gliding arc gas discharge

The simultaneous removal of ethyl acetate, benzene and toluene with relatively low or high initial concentration is studied using a laboratory scale gliding arc gas discharge (GA) reactor. Good decomposition efficiencies are obtained which proves that the GA is effective for the treatment of volatile organic compounds (VOCs) with either low or high concentration. A theoretical decomposition mechanism is proposed based on detection of the species in the plasma region and analysis of the decomposition by-products. This preliminary investigation reveals that the GA has potential to be applied to the treatment of exhaust air during color printing and coating works, by either direct removal or combination with activated carbon adsorption/desorption process.

Scale-up analysis and development of gliding arc discharge facility for volatile organic compounds decomposition

The influences of inlet gas flow rate and reactor configuration on volatile organic compounds (VOCs) decomposition efficiency in a traditional gliding arc (T-GA) facility are studied based on laboratory experiments and numerical simulation. The ratio of the nozzle diameter and the shortest distance of two electrodes should be maintained in a suitable value range to guarantee the decomposition efficiency, which indicates simply enlarging the nozzle inner diameter is not a proper way to raise the T-GA treatment capacity in a fixed supply voltage condition. A developed gliding arc gas discharge (D-GA) reactor based on a modified gas feed system is proposed: small flow rate air goes through the bottom nozzle to process the GA evolution, and high flow rate contaminated gas goes frontal through the plasma region and decomposes. The performances of D-GA reactor in the decomposition of VOCs with relative high gas flow rate, including decomposition efficiency and specific energy consumption, are better than T-GA reactor. D-GA reactor also avoids the drawbacks of the increases of power system amount and electric power consumption in multi-electrode GA system.

The Dependence of Gliding Arc Gas Discharge Characteristics on Reactor Geometrical Configuration

The dependence of gliding arc gas discharge characteristics, including gas flow field, arc column motion and volatile organic compounds (VOCs) decomposition performance, on reactor configuration parameters was investigated based on numerical simulation and laboratory experimental findings. For a given supply voltage (10 kV) and a certain nozzle outlet diameter (1.5 mm), increasing the electrodes gap (1–4 mm) or decreasing vertical distance between electrode throat and nozzle outlet (25–10 mm) will increase the gas flow rate through the electrode throat, the gas velocity in the plasma region, the arc column velocity, the maximum attainable position of the arc column and the electrical power consumption, also, higher VOCs decomposition rate and lower specific energy requirement are observed according to the n-butane and toluene decomposition experiments.

Effects of Oxygen and Water Vapor on Volatile Organic Compounds Decomposition Using Gliding Arc Gas Discharge

The combined effects of oxygen and water vapor on three typical volatile organic compounds, i.e. tetrachloromethane, n-butane and toluene, decomposition efficiency under gliding arc gas discharge conditions are studied. The electron density and the density of the reactive radicals such as O and OH are modified by addition of oxygen and water vapor. Consequently, the decomposition process can be enhanced or suppressed, depending on the involved chemical structures and reaction channels. The addition of oxygen and water vapor suppresses the tetrachloromethane decomposition which indicates that this process is mainly controlled by the electron dissociation reactions. By contrast, the n-butane and toluene decompositions are enhanced, which shows that they can be mainly ascribed to the radical induced reactions. Especially, in a moist atmosphere the OH radicals are supposed to play the most important role in the n-butane decomposition process.

Study of Mechanism for Hexane Decomposition with Gliding Arc Gas Discharge

The mechanism of hexane decomposition under gliding arc gas discharge conditions is studied from both qualitative and quantitative analyses of its products for various hexane initial concentrations and different background atmospheres : nitrogen, argon, air (O2 21% N2 79% vol.) and N2–O2 mixtures. The decomposition rate, which decreases with increasing hexane initial concentration, can reach 94% when the carrier gas is air. Due to the electron energy consumed by the dissociation of nitrogen, the decomposition rate of hexane in nitrogen is lower than in argon. The radical channel plays a predominant role in the hexane decomposition process. With increasing oxygen concentration in the carrier gas, the hexane decomposition rate increases and promotes the conversion of CO– CO2, but it also leads to the formation of NO2.

Effect of a protective layer on the lifetime and output radiation intensity decay rate of quartz low-pressure gas discharge lamps

A protective layer of rare earth metal oxides deposited onto the inner surface of a quartz bulb increases the lifetime of low-pressure inert gas arc discharge lamps and decreases the output UV radiation intensity decay rate in low-pressure amalgam lamps.

Synthesis of B–C–N nanotubes by means of gas arc discharge with a rotating anode

B–C–N nanotubes were synthesized by plasma rotating electrode process (PREP) and examined by scanning electron microscope (SEM) and X-ray diffraction (XRD). Compared with results at 0 rpm of the anode, the number of B–C–N nanotubes was increased by rotating the anode. In addition, peak intensity ratio of h-(BN) 0.26C 0.74 to graphite was increased with rotation of the anode and/or the increase of metal concentration. That indicates the yield of B–C–N nanotubes was increased. These results could be explained by an increase of plasma temperature and a swirl in the plasma by rotation of the anode that promote the mixing to aid chemical reactions between evaporated species and atomic nitrogen.

Characteristics of the gravity-free gas-arc discharge and its application to fullerene production

A gas-arc discharge is strongly influenced by the force of gravity. In this study, endohedral metallo-fullerenes and single-wall carbon nanotubes are produced by means of a gravity-free gas-arc discharge and their production efficiencies are compared with those produced by the conventional gravity method. As a result, their production rates are found to dramatically increase. The reason is conjectured to be stabilization of the arc and the longer reaction time of the cluster production under the gravity-free and convection-free conditions.This article was due to appear in issue 5 of Plasma Physics and Controlled Fusion. To access this special issue please follow this link: http://www.iop.org/EJ/toc/0741-3335/45/5.