Investigation on the Micro-Discharge Characteristics of Dielectric Barrier Discharge in a Needle-Plate Geometry

In this study, a dielectric barrier discharge device with needle-plate electrodes was used to investigate the characteristics of the micro-discharge in argon at one atmospheric pressure by an optical method. The results show that there are two discharge modes in the dielectric barrier discharge, namely corona mode and filamentary mode. The corona discharge only occurs in the vicinity of the needle tip when the applied voltage is very low. However, the filamentary discharge mode can occur, and micro-discharge bridges the two electrodes when the applied voltage reaches a certain value. The extended area of micro-discharge on the dielectric plate becomes larger with the increase in applied voltage or decrease in gas pressure. The variance of the light emission waveforms is studied as a function of the applied voltage. Results show that very short discharge pulse only appears at the negative half cycle of the applied voltage in the corona discharge mode. However, broad hump (about several microseconds) can be discerned at both the negative half cycle and the positive half cycle for a high voltage in the filamentary mode. Furthermore, the inception voltage decreases and the width of the discharge hump increases with the increase in applied voltage. These experimental phenomena can be explained qualitatively by analyzing the discharge mechanism.     

Preparation of Copper Nanoparticles Using Dielectric Barrier Discharge at Atmospheric Pressure and its Mechanism简

Dielectric barrier discharge （DBD） cold plasma at atmospheric pressure was used for preparation of copper nanoparticles by reduction of copper oxide （CuO）. Power X-ray diffraction （XRD） was used to characterize the structure of the copper oxide samples treated by DBD plasma. Influences of H2 content and the treating time on the reduction of copper oxide by DBD plasma were investigated. The results show that the reduction ratio of copper oxide was increased initially and then decreased with increasing H2 content, and the highest reduction ratio was achieved at 20% H2 content. Moreover, the copper oxide samples were gradually reduced by DBD plasma into copper nanoparticles with the increase in treating time. However, the average reduction rate was decreased as a result of the diffusion of the active hydrogen species. Optical emission spectra （OES） were observed during the reduction of the copper oxide samples by DBD plasma, and the reduction mechanism was explored accordingly. Instead of high-energy electrons, atomic hydrogen （H） radicals, and the heating effect, excited-state hydrogen molecules are suspected to be one kind of important reducing agents. Atmospheric-pressure DBD cold plasma is proved to be an efficient method for preparing copper nanoparticles.     

Exhaust Cleaning with Dielectric Barrier Discharge

To clean the exhaust emissions as one of the most important tasks in pollution control, a study on the treatment of engine emissions with discharge assistance was reported. A DBD plasma source shaped in grid and cylinder was examined in different engine operational modes to reduce the NOX content of diesel engine exhaust. The composition of the exhaust gases and chemical reactions initiated by the discharge were analyzed. The discharge frequency had a crucial impact on the device’s performance and gas treatment. The voltages applied to the discharge gap could alter the chemical reactions occurring in the treated gases, which were indicated by the NO to NO2 ratio. The operation of the system was studied at frequencies ranging from 400 Hz to 16 kHz.     

Growth of Fluorocarbon Films by Low-Pressure Dielectric Barrier Discharge

Plasma polymerized fluorocarbon （FC） films have been deposited on silicon substrates from dielectric barrier discharge （DBD） plasma of C4Fs at room temperature under a pressure of 25～125 Pa. The effects of the discharge pressure and frequency of power supply on the films have been systematically investigated. FC films with a less cross linked structure may be formed at a relatively high pressure. Increase in the frequency of power supply leads to a significant increase in the deposition rate. Static contact angle measurements show that deposited FC films have a stable, hydrophobic surface property. All deposited films show smooth surfaces with an atomic surface roughness. The relationship between plasma parameters and the properties of the deposited FC films are discussed.     

Filament Discharge Phenomena in Fingerprint Acquisition by Dielectric Barrier Discharge

In this paper, the dielectric barrier discharge fingerprint acquisition technique is introduced. The filament discharge phenomena were observed in the process of fingerprint acquisition. The filament discharge reduced the quality of fingerprint images. Obviously, it was necessary to eliminate streamer discharges in order to get good fingerprint images. The streamer discharge was considered to be the cause of the filament discharge in the experiment. The relationship between the critical electric field and the discharge gap was calculated with the Raether＇s model of streamer discharge. The calculated results and our experiment proved that it would be difficult for the streamer discharge to occur when the discharge gap was narrow. With a narrow discharge gap, the discharge was homogeneous, and the fingerprint images were clear and large in area. The images obtained in the experiment are very suitable for fingerprint identification as they contain more information.     

Spectroscopic Study of a Radio-Frequency Atmospheric Pressure Dielectric Barrier Discharge with Anodic Alumina as the Dielectric

This paper presents the fabrication and a spectroscopic study of a stable radiofrequency dielectric barrier discharge(RF DBD) in Ar with a novel dielectric,anodic alumina,at atmospheric pressure.Dielectric electrodes are fabricated from commercially available low cost impure aluminum strips by a two-step anodization process in 0.3 M solution of oxalic acid.The discharge is found to be stable with excellent spatial uniformity for the RF input power range of 30~80 W.Excitation and rotational temperatures measured in the experiment range of 1472~3255 K and 434~484 K,respectively,as the input power changes from 30 W to 80 W.These temperature ranges are suitable for surface modification applications.     

Degradation of Alizarin Red by Hybrid Gas-Liquid Dielectric Barrier Discharge

A system based on dielectric barrier discharge （DBD） with improved discharge sta- bility and homogeneity was used for the degradation of Alizarin Red （AR）. This special structure of the DBD system is characterized by the high voltage electrode, which is covered with a quartz tube and partially immersed in water, and by directly using the water as the ground electrode. A transition was realized from the filamentary mode for the conventional structure of the DBD to the semi-homogeneous mode for such a configuration of the plasma discharge. The spectra of plasma are dominated by N2 molecular lines in the ultraviolet-A radiation region. Plasma degra- dation of AR in this system exhibited pseudo-first-order reaction kinetics. The degradation rate of AR reached 95% or so after 14 min treatment under favorable conditions. Alkaline conditions are favorable for the degradation of AR. The increase of conductivity of the solution, input power and usage of oxygen bubbling could enhance AR degradation.     

Atmospheric Pressure Radio Frequency Dielectric Barrier Discharges in Nitrogen/Argon

This work reports the experimental results on the characteristics of radio frequency dielectric barrier N2 /Ar discharges.Depending on the nitrogen content in the feed gas and the input power,the discharge can operate in two diferent modes: a homogeneous glow discharge and a constricted discharge.With increasing input power,the number of discharge columns increases.The discharge columns have starlike structures and exhibit symmetric self-organized arrangement.Optical emission spectroscopy was performed to estimate the plasma temperature.Spatially resolved gas temperature measurements,determined from NO emission rotational spectroscopy were taken across the 4.4 mm gap filled by the discharge.Gas temperature in the middle of the gas gap is lower than that close to the electrodes.     

Temporally-Resolved Emission Spectroscopic Diagnostics of the Atmospheric Pressure Glow Discharge in Helium

Temporally-resolved spectroscopic diagnostics of dielectric barrier discharges(DBDs) in atmospheric-pressure helium was carried out to study the discharge mechanism.Using an intensified charge-coupled device(ICCD) and a grating spectrometer,we obtained the emission spectra of homogeneous discharges and presented them in 3D graphs.We also studied the time variation of typical emissions from He,O and first negative bands of N+ 2.The results showed that the spectral lines do not develop synchronously as N+ 2(B2u+X2∑+g,0~0,λ=391.4 nm) and N∑+2(B2∑+u → X2∑+g,0~1,λ=427.8 nm) appear earlier and last for a longer time than He(33S1 → 23P1,λ=706.5 nm) and O(35P→35S,λ=777.4 nm).A certain number of He metastables produced in the initial stage of discharge.Even between adjacent pulses,the emissions from N∑+2 can still keep certain intensities while those from He and O extinguish.Since long-lifetime He metastables are produced and exist in the discharging space,it is the Penning ionization that keeps the long decay of N∑+2 emissions.     

Catalytic Decomposition of Toluene Using Various Dielectric Barrier Discharge Reactors

Decomposition of toluene was experimentally investigated with various dielectric barrier discharge （DBD） reactors, such as wire-cylinder, wire-plate and plate-to-plate, combined with multi-metal oxides catalyst （Mn-Ni-Co-Cu-Ox/Al2O3） loaded on the cordierite honeycomb and nickel foam, respectively. The effects of some factors including the residence time, reactor configuration and catalyst, upon the toluene destruction were studied. Results revealed that the use of in-plasma catalysis was more helpful to enhancing the DRE （destruction and removal efficiency） and reducing the O3 formation than that of either post-plasma catalysis or plasma alone. It was demonstrated that the wire-plate reactor was favorable for the oxidation reaction of toluene and the nickel foam-supported catalysts exhibited good activity.     

The Experimental Investigations of Dielectric Barrier Discharge and Pulse Corona Discharge in Air Cleaning

The dielectric barrier discharge (DBD) and pulse corona discharge(POD) plasmagenerator was used to remove NHa, H2S, C7H8 etc. from atmosphere. The principle and charac-teristic of the two ways was discussed in the article. The test shows the result of PCD is betterthan that of DBD.     

Direct and Indirect Applications of Dielectric Barrier Discharge Plasma to Catalytic Reduction of Nitrogen Oxides from Exhaust Gas

Dielectric barrier discharge （DBD） plasma was utilized to oxidize NO contained in the exhaust gas to NO2, ultimately improve the selective catalytic reduction of nitrogen oxides （NOx）. In the one case, DBD was created directly in the exhaust gas （direct application）, and in the an other case, ozone produced by DBD was injected into the exhaust gas （indirect application）. A comparative study between such direct and indirect applications of DBD plasma was made in terms of the NOx removal efficiency and the energy consumption. The NO2 content in the exhaust gas was changed by the voltage applied to the DBD device （for direct application） or by the amount of ozone added to the exhaust gas （for indirect application）. In both cases, NO was easily oxidized to NO2, and the change in NO2 content largely affected the NOx removal performance of the catalytic reactor placed downstream, where both NO and NO2 were reduced to N2 in the presence of ammonia as the reducing agent. The experiments were primarily concerned with the effect of reaction temperature on the catalytic NOx reduction at various NO2 contents. The direct and indirect applications of DBD were found to remarkably improve the catalytic NOx reduction, especially at low temperatures.     

Deposition of Thin Titania Films by Dielectric Barrier Discharge at Atmospheric Pressure

A homogeneous atmospheric pressure dielectric barrier discharge is studied. It is in argon with small admixtures of titanium tetrachloride vapour and oxygen for the deposition of thin titania films on glass substrates. A special electrode configuration was applied in order to deposit the titania film uniformly. The sustaining voltage （6 kV to 12 kV）, current density （about 3 mA/cm^2） and total optical emission spectroscopy were monitored to characterize the discharge in the gap of 2 mm. Typical deposition rates ranged from approximately 30 nm/min to 120 nm/min. The film morphology was investigated by using scanning electron microscopy （SEM） and the composition was determined with an energy dispersive x-ray spectroscopy （EDS） analysis tool attached to the SEM. The crystal structure and phase composition of the films were studied by x-ray diffraction （XRD）. Several parameters such as the discharge power, the ratio of carrier gas to the precursor gas, the deposition time on the crystallization behavior, the deposition rate and the surface morphology of the titania film were extensively studied.     

Miniaturized Argon Plasma: Neutral Gas Characteristics in Dielectric Barrier Discharge

Plasma-neutral gas dynamics is computationally investigated in a miniaturized microthruster that encloses Ar and contains dielectric material sandwiched between two metal plates using a two-dimensional plasma mode. Spatial and temporal plasma properties are investigated by solving the Poisson equation with the conservation equations of charged and excited neutral plasma species using the COMSOL Multiphysics 4.2b. The microthruster property is found to depend on the secondary electron emission coefficient. The electrohydrodynamic force(EHD) is calculated and found to be significant in the sheath area near the dielectric layer and is found to affect gas flow dynamics including the Ar excimer formation and density. The effects of pressure and secondary emission coefficient are discussed. The plasma characteristics are affected by small changes in the secondary electron emission coefficient, which could result from the dielectric erosion and aging, and is found to affect the electrohydrodynamic force produced when the microthruster is used to produce thrust for a small spacecraft.     

Excited Electron Temperature and Molecular Vibration Temperature During Transition from Filamentary Discharge to Glow Discharge in Surface Discharge in Air

A dielectric barrier surface discharge device was used to investigate the transition from a filamentary discharge to a glow discharge in air at different gas pressures. Discharge images and waveforms of the applied voltage and discharge current were recorded simultaneously, and it was found that the discharge could transit from filamentary to glow with the decrease in pressure. Optical emission spectra during the transition from a filamentary discharge to a glow one were recorded. Excited electron temperature can be determined from the ratios of the relative intensities of spectral lines while molecular vibration temperature can be measured by analysing spectral lines of the N2 second positive band system. The results show that both the excited temperature and molecular vibration temperature increase with the decrease in the gas pressure. Qualitative explanations are given.     

Influence of the Gas Mixture Ratio on the Correlations Between the Excimer XeCl Emission and the Sealed Gas Temperature in DIelectric Barrier Discharge Lamps

For dielectric barrier discharge lamps filled with various gas mixture ratios,the correlations between the excimer XeCl emission and the sealed gas temperature have been founded,and a qualitative explication is presented.For gas mixture with chlorine larger than 3%,the emission intensity increases with the sealed gas temperature,while with chlorine about 2%,the emission intensity decreases with the increase in the gas temperature,and could be improved by cooling water .However,if chlorine is less than 1.5% ,the discharge appears to be a mixture mode with filaments distributed in a diffused glow-like discharge,and the UV emission is independent on the gas temperature.     

Wire-to-Plate Surface Dielectric Barrier Discharge and Induced Ionic Wind

The electrical and mechanical characteristics of the wire-to-plate surface dielectric barrier discharge and the induced ionic wind are investigated experimentally.The different temporal behaviors in positive and negative half-cycles are studied by time-resolved images.It is shown that the discharge and the light emission are generally stronger in the positive half cycle.The discharge is inhomogeneous and propagates in streamer mode;however,in the negative half-cycle,the discharge appears visually uniformly and operates in the diffuse mode.The surface discharge can produce ionic wind about several m/s above the dielectric surface.There exists an optimal width of the grounded electrode to produce a larger plasma area or active wind region.Increasing of the applied voltage or normalized dielectric constant leads to a larger wind velocity.The performance of ionic wind on flow control is visualized by employing a smoke stream.     

Study of Humidity Effect on Benzene Decomposition by the Dielectric Barrier Discharge Nonthermal Plasma Reactor

The humidity effects on the benzene decomposition process were investigated by the dielectric barrier discharge(DBD) plasma reactor.The results showed that the water vapor played an important role in the benzene oxidation process.It was found that there was an optimum humidity value for the benzene removal efficiency,and at around 60% relative humidity(RH),the optimum benzene removal efficiency was achieved.At a SIE of 378 J/L,the removal efficiency was 66% at 0% RH,while the removal efficiency reached 75.3% at 60% RH and dropped to 69% at 80% RH.Furthermore,the addition of water inhibited the formation of ozone and NO_2 remarkably.Both of the concentrations of ozone and NO_2 decreased with increasing of the RH at the same specific input energy.At a SIE of 256 J/L,the concentrations of ozone and NO_2 were 5.4 mg/L and 1791 ppm under dry conditions,whereas they were only 3.4 mg/L and 1119 ppm at 63.5%RH,respectively.Finally,the outlet gas after benzene degradation was qualitatively analyzed by FT-IR and GC-MS to determine possible intermediate byproducts.The results suggested that the byproducts in decomposition of benzene primarily consisted of phenol and substitutions of phenol.Based on these byproducts a benzene degradation mechanism was proposed.     

Dielectric Barrier Discharge Plasma-Induced Photocatalysis and Ozonation for the Treatment of Wastewater

The physicochemical processes of dielectric barrier discharge （DBD） such as insitu formation of chemically active species and emission of ultraviolet （UV）/visible light were utilized for the treatment of a simulated wastewater formed with Acid Red 4 as the model organic contaminant. The chemically active species （mostly ozone） produced in the DBD reactor were well distributed in the wastewater using a porous gas diffuser, thereby increasing the gas-liquid contact area. For the purpose of making the best use of the light emission, a titanium oxide-based photocatalyst was incorporated in the wastewater treating system. The experimental parameters chosen were the voltage applied to the DBD reactor, the initial pH of the wastewater, and the concentration of hydrogen peroxide added to the wastewater. The results have clearly shown that the present system capable of degrading organic contaminants in two ways （photocatalysis and ozonation） may be a promising wastewater treatment technology.     

Discoloration of Congo Red by Rod-Plate Dielectric Barrier Discharge Processes at Atmospheric Pressure

A dielectric barrier discharge (DBD) reactor with a rod-plate electrode configuration was used for the oxidative decomposition of Congo red dye in an aqueous solution.Plasma was generated in the gas space above the water interface under atmospheric pressure.Discharge characteristics were analyzed by voltage-current waveforms.Effects of applied voltage,initial conductivity,and initial concentration were also analyzed.Congo red discoloration increased with increased applied voltage and decreased conductivity.The initial conductivity significantly influenced the Congo red discoloration.Under the same conditions,the highest discoloration rate was obtained at 25 mg/L.The presence of ferrous ions in the solutions had a substantial positive effect on Fenton dye degradation and flocculation.At an applied voltage of 20 kV,about 100％of dye was degraded after 4 min of Fe2+/DBD treatment.Results showed that adding a certain dosage of hydrogen peroxide to the wastewater could enhance the discoloration rate.Possible pathways of Congo red discoloration by DBD plasma were proposed based on GC/MS,FTIR,and UV-vis spectroscopy analyses.