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.     

Surface Modification of PBO Fibers for Composites by Coaxial Atmospheric Dielectric Barrier Discharge (PLA-PLA)

In this work, the surface modification of poly (1, 4-phenylene-cis-benzobisoxazole) (PBO) fibers by O 2 /Ar coaxial atmospheric dielectric barrier discharge was investigated, as well as the interfacial adhesion properties of modified PBO fibers/epoxy composites. The results indicated that the contact angle decreased remarkably from 84.7 to 63.5 after 3 min O 2 /Ar plasma treatment. SEM and AFM images showed that the surface of the treated PBO fibers became rather rough. In addition, XPS results suggested that the polar functional group (O=C- O) was introduced on the surface of the treated PBO fiber. The interfacial adhesion test showed that the interfacial shear strength (IFSS) and the interlaminar shear strength (ILSS) increased significantly by 63.54% and 130%, respectively. Moreover, the excellent tensile property of the PBO fibres was well preserved     

Experimental Study on Inactivation of Bacterial Endotoxin by Using Dielectric Barrier Discharge

The low-temperature plasma （LTP） generated by dielectric barrier discharge （DBD） was used to sterilize the E.coli endotoxin, which is usually difficult to kill ...     

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.     

Experimental Study on Surface Dielectric Barrier Discharge Plasma Actuator with Different Encapsulated Electrode Widths for Airflow Control at Atmospheric Pressure

The surface dielectric barrier discharge(SDBD) plasma actuator has shown great promise as an aerodynamic flow control device. In this paper, the encapsulated electrode width of a SDBD actuator is changed to study the airflow acceleration behavior. The effects of encapsulated electrode width on the actuator performance are experimentally investigated by measuring the dielectric layer surface potential, time-averaged ionic wind velocity and thrust force. Experimental results show that the airflow velocity and thrust force increase with the encapsulated electrode width. The results can be attributed to the distinct plasma distribution at different encapsulated electrode widths.     

Surface Treatment of Polyethylene Terephthalate Film Using Atmospheric Pressure Glow Discharge in Air

Non-thermal plasmas under atmospheric pressure are of great interest in polymer surface processing because of their convenience, effectiveness and low cost. In this paper, the treatment of Polyethylene terephthalate (PET) film surface for improving hydrophilicity using the non-thermal plasma generated by atmospheric pressure glow discharge (APGD) in air is conducted. The discharge characteristics of APGD are shown by measurement of their electrical discharge parameters and observation of light-emission phenomena, and the surface properties of PET before and after the APGD treatment are studied using contact angle measurement, x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It is found that the APGD is homogeneous and stable in the whole gas gap, which differs from the commonly filamentary dielectric barrier discharge (DBD). A short time (several seconds) APGD treatment can modify the surface characteristics of PET film markedly and uniformly. After 10 s APGD treatment, the     

Experimental Investigation of Flow Separation Control Using Dielectric Barrier Discharge Plasma Actuators

Influence of plasma actuators as a flow separation control device was investigated experimentally. Hump model was used to demonstrate the effect of plasma actuators on external flow separation, while for internal flow separation a set of compressor cascade was adopted. In order to investigate the modification of the flow structure by the plasma actuator, the flow field was examined non-intrusively by particle image velocimetry measurements in the hump model experiment and by a hot film probe in the compressor cascade experiment. The results showed that the plasma actuator could be effective in controlling the flow separation both over the hump and in the compressor cascade when the incoming velocity was low. As the incoming velocity increased, the plasma actuator was less effective. It is urgent to enhance the intensity of the plasma actuator for its better application. Methods to increase the intensity of plasma actuator were also studied.     

Particle Densities of the Atmospheric-Pressure Argon Plasmas Generated by the Pulsed Dielectric Barrier Discharges

Atmospheric-pressure argon plasmas have received increasing attention due to their high potential in many industrial and biomedical applications. In this paper, a 1-D fluid model is used for studying the particle density characteristics of the argon plasmas generated by the pulsed dielectric barrier discharges. The temporal evolutions of the axial particle density distributions are illustrated, and the influences of changing the main discharge conditions on the averaged particle densities are researched by independently varying the various discharge conditions. The calculation results show that the electron density and the ion density reach two peaks near the momentary cathodes during the rising and the falling edges of the pulsed voltage. Compared with the charged particle densities, the densities of the resonance state atom Ar~r and the metastable state atom Ar~mhave more uniform axial distributions, reach higher maximums and decay more slowly. During the platform of the pulsed voltage and the time interval between the pulses, the densities of the excited state atom Ar*are far lower than those of the Ar~r or the Ar~m. The averaged particle densities of the different considered particles increase with the increases of the amplitude and the frequency of the pulsed voltage. Narrowing the discharge gap and increasing the relative dielectric constant of the dielectric also contribute to the increase of the averaged particle densities. The effects of reducing the discharge gap distance on the neutral particle densities are more significant than the influences on the charged particle densities.     

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.     

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.     

Surface Modification of Polyethylene （PE） Films Using Dielectric Barrier Discharge Plasma at Atmospheric Pressure

Modification of the surface properties of polyethylene （PE） films is studied using air dielectric barrier discharge at atmospheric pressure. The treated samples are examined by Water contact angle measurements, Fourier transform infrared attenuated total reflection spectroscopy （FTIR-ATR）, X-ray photoelectron spectroscopy （XPS） and scanning electron microscopy （SEM）. With the increase in treating time, the water contact angle changes from 93.2° before treatment to a minimum of 53.3° after a treatment for 50 s. Both ATR and XPS results show some oxidized species are introduced into the sample surface by the plasma treatment and the tendency of the water contact angle with the treating time is the same as that of oxygen concentration on the treated sample surface. SEM result shows the surface roughness of PE samples increases with the treatment time increasing.     

Improved Ethanol Production from Xylose by Candida shehatae Induced by Dielectric Barrier Discharge Air Plasma

Xylose fermentation is essential for ethanol production from lignocellulosic biomass. Exposure of the xylose-fermenting yeast Candida shehatae （C. shehatae） CICC1766 to atmospheric pressure dielectric barrier discharge （DBD） air plasma yields a clone （designated as C81015） with stability, which exhibits a higher ethanol fermentation rate from xylose, giving a maximal enhancement in ethanol production of 36.2% compared to the control （untreated）. However, the biomass production of C81015 is lower than that of the control. Analysis of the NADH （nicotinamide adenine dinucleotide）- and NADPH （nicotinamide adenine dinucleotide phosphate）- linked xylose reductases and NAD＋-linked xylitol dehydrogenase indicates that their activities are enhanced by 34.1%, 61.5% and 66.3%, respectively, suggesting that the activities of these three enzymes are responsible for improving ethanol fermentation in C81015 with xylose as a substrate. The results of this study show that DBD air plasma could serve as a novel and effective means of generating microbial strains that can better use xylose for ethanol fermentation.     

Improving Hydrophobicity of Glass Surface Using Dielectric Barrier Discharge Treatment in Atmospheric Air

Non-thermal plasmas under atmospheric pressure are of great interest in industrial applications, especially in material surface treatment. In this paper, the treatment of a glass surface for improving hydrophobicity using the non-thermal plasma generated by dielectric barrier discharge （DBD） at atmospheric pressure in ambient air is conducted, and the surface properties of the glass before and after the DBD treatment are studied by using contact angle measurement, surface resistance measurement and wet flashover voltage tests. The effects of the applied voltage and time duration of DBD on the surface modification are studied, and the optimal conditions for the treatment are obtained. It is found that a layer of hydrophobic coating is formed on the glass surface after spraying a thin layer of silicone oil and undergoing the DBD treatment, and the improvement of hydrophobicity depends on DBD voltage and treating time. It seems that there exists an optimum treating time for a certain applied voltage of DBD during the surface treatment, The test results of thermal aging and chemical aging show that the hydrophobic layer has quite stable characteristics. The interaction mechanism between the DBD plasma and the glass surface is discussed. It is concluded that CHa and large molecule radicals can react with the radicals in the glass surface to replace OH, and the hydrophobicity of the glass surface is improved accordingly.     

Study on the Generation Characteristics of Dielectric Barrier Discharge Plasmas on Water Surface简

A new contact glow discharge electrode employed in this study. Because of the strong field the electrode and the water surface, glow discharge on the surface of water was designed and strength in the small air gap formed by plasmas were generated and used to treat waste water. The electric field distribution of the designed electrode model was simulated by MAXWELL 3D~ simulation software, and the discharge parameters were measured. Through a series of experiments, we investigated the impact of optimal designs, such as the dielectric of the electrode, immersion depths, and curvature radii of the electrode on the generation characteristics of plasmas. In addition, we designed an equipotential multi-electrode configuration to treat a Methyl Violet solution and observe the discoloration effect. The experimental and simulation results indicate that the designed electrodes can realize glow discharge with a relative low voltage, and the generated plasmas covered a large area and were in stable state. The efficiency of water treatment is improved and optimized with the designed electrodes.     

Effects of Dielectric Barrier Discharge Plasma Treatment on Pentachlorophenol Removal of Granular Activated Carbon

The pentachlorophenol(PCP)adsorbed granular activated carbon(GAC)was treated by dielectric barrier discharge(DBD)plasma.The effects of DBD plasma on the structure of GAC and PCP decomposition were analyzed by N_2 adsorption,thermogravimetric,scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS)and gas chromatographymass spectrometry(GC-MS).The experimental data of adsorption kinetics and thermodynamics of PCP on GAC were fitted with different kinetics and isotherm models,respectively.The results indicate that the types of N_2 adsorption isotherm of GAC are not changed by DBD plasma,while the specific surface area and pore volume increase after DBD plasma treatment.It is found that the weight loss of the saturated GAC is the highest,on the contrary,the weight loss of DBD treated GAC is the least because of reduced PCP residue on the GAC.The XPS spectra and SEM image suggest that some PCP on the GAC is removed by DBD plasma,and the surface of GAC treated by DBD plasma presents irregular and heterogeneous morphology.The GC-MS identification of by-products shows that two main dechlorination intermediate products,tetrachlorophenol and trichlorophenol,are distinguished.The fitting results of experimental data of adsorption kinetics and thermodynamics indicate that the pseudo-first-order and pseudo-second order models can be used for the prediction of the kinetics of virgin GAC and DBD treated GAC for PCP adsorption,and the Langmuir isotherm model fits better with the data of adsorption isotherm than the Freundlich isotherm in the adsorption of PCP on virgin GAC and DBD treated GAC.     

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.     

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.     

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.     

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.     

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.