Plasma Discharge Process in a Pulsed Diaphragm Discharge System

As one of the most important steps in wastewater treatment, limited study on plasma discharge process is a key challenge in the development of plasma applications. In this study, we focus on the plasma discharge process of a pulsed diaphragm discharge system. According to the analysis, the pulsed diaphragm discharge proceeds in seven stages： （1） Joule heating and heat exchange stage; （2） nucleated site formation; （3） plasma generation （initiation of the breakdown stage）; （4） avalanche growth and plasma expansion; （5） plasma contraction; （6） termination of the plasma discharge; and （7） heat exchange stage. From this analysis, a critical voltage criterion for breakdown is obtained. We anticipate this finding will provide guidance for a better application of plasma discharges, especially diaphragm plasma discharges.

Fractal microstructure of Ag film via plasma discharge as SERS substrates

According to the atmospheric pressure plasma(APP)technology,we propose a rapid synthetic approach of the substrates for enhanced Raman spectroscopy.The plasma is used to modify and etch the surface of silver film,which generates large scale hotspots'aggregation.By switching the discharge polarity and adjusting the film thickness,different surface morphologies are formed due to the oxidation,reactive etch and accumulation of the plasma product in a certain space.Especially under positive corona discharge condition,dense snake-like microstructures are formed by the gradual connection of individual nanoparticles,which are driven by the influence of the electric field on surface diffusion.In addition,the experiments verify that the corresponding enhancement factor(EF)raises at least five orders of magnitude and the treatment time is about 10 min.

Degradation of sulfamethoxazole in water by dielectric barrier discharge plasma jet:influencing parameters,degradation pathway,toxicity evaluation

Sulfamethoxazole(SMX)is an antibiotic and widely present in aquatic environments,so it presents a serious threat to human health and sustainable development.A dielectric barrier discharge(DBD)plasma jet was utilized to degrade aqueous SMX,and the effects of various operating parameters(working gas,discharge power,etc)on SMX degradation performance were studied.The experimental results showed that the DBD plasma jet can obtain a relatively high degradation efficiency for SMX when the discharge power is high with an oxygen atmosphere,the initial concentration of SMX is low,and the aqueous solution is under acidic conditions.The reactive species produced in the liquid phase were detected,and OH radicals and O3were found to play a significant role in the degradation of SMX.Moreover,the process of SMX degradation could be better fitted by the quasi-first-order reaction kinetic equation.The analysis of the SMX degradation process indicated that SMX was gradually decomposed and 4-amino benzene sulfonic acid,benzene sulfonamide,4-nitro SMX,and phenylsulfinyl acid were detected,and thus three possible degradation pathways were finally proposed.The mineralization degree of SMX reached 90.04%after plasma treatment for 20 min,and the toxicity of the solution fluctuated with the discharge time but eventually decreased.

Effect of pulse voltage rising time on discharge characteristics of a helium-air plasma at atmospheric pressure

In this paper,the influence of voltage rising time on a pulsed-dc helium-air plasma at atmospheric pressure is numerically simulated.Simulation results show that as the voltage rising time increases from 10 ns to 30 ns,there is a decrease in the discharge current,namely 0.052 A when the voltage rising time is 10 ns and 0.038 A when the voltage rising time is 30 ns.Additionally,a shorter voltage rising time results in a faster breakdown,a more rapidly rising current waveform,and a higher breakdown voltage.Furthermore,the basic parameters of the streamer discharge also increase with voltage rise rate,which is ascribed to the fact that more energetic electrons are produced in a shorter voltage rising time.Therefore,a pulsed-dc voltage with a short rising time is desirable for efficient production of nonequilibrium atmospheric pressure plasma discharge.

TREATMENT OF METALS, POLYMER FILMS, AND FABRICS WITHA ONE ATMOSPHERE UNIFORM GLOW DISCHARGE PLASMA(OAUGDP) FOR INCREASED SURFACE ENERGY AND DIRECTIONAL ETCHING

Direct exposure of samples to the active species of air generated by a One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) has been used to etch and to increase the surface energy of metallic surfaces, photoresist, polymer films, and nonwoven fab- rics. The OAUGDP is a non-thermal plasma with the classical characteristics of a DC normal glow discharge that operates in air (and other gases) at atmospheric pres- sure. Neither a vacuum system nor batch processing is necessary. A wide range of applications to metals, photoresist, films, fabrics, and polymeric webs can be accom- modated by direct exposure of the workpiece to the plasma in parallel-plate reactors. This technolopy is simple, it produces effects that can be obtained in no other way at one atmosphere; it generates minimal pollutants or unwanted by-products; and it is suitable for individual sample or online treatment of metallic surfaces, wafers, films, and fabrics. Early exposures of solid materials to the OAUGDP required minutes to produce rela- tively small increases of surface energy. These durations appeared too long for com- mercial application to fast-moving webs. Recent improvements in OAUGDP gas com- position, power density, plasma quality, recireulating gas flow, and impedance match- ing of the power supply to the parallel plate plasma reactor have made it possible to raise the surface energy of a variety of polymeric webs (PP, PET PE etc.) to levels of 60 to 70 dynes/cm with one second of exposure. In air plasmas, the high surface ener- gies are not durable, and fall to 50 dynes/cm after periods of weeks to months. Here, we report the exposure of metallic surfaces, photoresist, polymeric films, and nonwo- ven fabrics made of PP and PET to an impedance matched parallel plate OAUGDP for durations ranging from one second to several tens of seconds. Data will be re- ported on the surface energy, wettability, wickability, and aging effect of polymeric films and fabrics as functions of time of exposure, and time after exposure; the rate and uniformity of photoresist etching; and the production of sub-micron structures by OAUGDP etching at one atmosphere.

Review on reactive species in water treatment using electrical discharge plasma:formation, measurement, mechanisms and mass transfer

In the electrical discharge plasma process, various chemical and physical processes can participate in the removal of contaminants. In this paper, the chemical and physical processes that occur as a result of the electrical discharge plasma are reviewed, and their possible roles in the degradation of contaminants are discussed. Measurement methods for the quantification of important reactive species and their advantages and shortcomings are presented. Approaches on how to enhance the diffusion of the reactive species in solution are examined. In addition, the formation of typical reactive species in different electrical discharge plasma is compared.

A zirconium modified Co/SiO_2 Fischer-Tropsch catalyst prepared by dielectric-barrier discharge plasma

Co/SiO2 and zirconium promoted Co/Zr/SiO2 catalysts were prepared using dielectric-barrier discharge （DBD） plasma instead of the conventional thermal calcination method. Fischer-Tropseh Synthesis （FTS） performances of the catalyst were evaluated in a fixed bed reactor. The results indicated that the catalyst treated by DBD plasma shows the higher FTS activity and yield of heavy hydrocarbons as compared with that treated by the conventional thermal calcination method. Increase in CO conversion was unnoticeable on the Co/SiO2 catalyst, but significant on the Co/Zr/SiO2 catalyst, both prepared by DBD plasma. On the other hand, heavy hydrocarbon selectivity and chain growth probability （a value） were enhanced on all the catalysts prepared by the DBD plasma. In order to study the effect of the DBD plasma treatment on the FTS performance, the catalysts were characterized by N2-physisorption, H2-temperature programed reduction （H2-TPR）, H2-temperature- programmed desorption （H2-TPD） and oxygen titration, transmission electron microscope （TEM） and X-ray diffraction （XRD）. It was proved that, compared with the traditional calcination method, DBD plasma not only could shorten the precursor decomposition time, but also could achieve better cobalt dispersion, smaller Co304 cluster size and more uniform cobalt distribution. However, cobalt reducibility was hindered to some extent in the Co/SiO2 catalyst prepared by DBD plasma, while the zirconium additive prevented significantly the decrease in cobalt reducibility and increased cobalt dispersion as well as the FTS performance.

Treatment of Invasive Marine Species on Board by Using Micro-gap Discharge Plasma

A pilot-scale experiment of 20t/h for the treatment of ship＇s ballast water is reported in this paper. When the concentration of the dissolved OH. was 0.68 mg/L during the experiment, the rate of destroying bacteria, mono-algae, protozoan reached 100% within 2.67 s. The effect of hydroxyl radicals on biochemical processes was also studied. The attenuation rate of photosynthesis pigment was 100%. And the main reason for the cells＇ death was the strong destruction of the monose, amylose, protein, DNA and RNA in the cells. As an advanced oxidation method, the procedure can destroy invasive marine species when a ship is in the process of discharging its ballast water.

Treatment of Dye Wastewater by Using a Hybrid Gas/Liquid Pulsed Discharge Plasma Reactor

A hybrid gas/liquid pulsed discharge plasma reactor using a porous ceramic tube is proposed for dye wastewater treatment. High voltage pulsed discharge plasma was generated in the gas phase and simultaneously the plasma channel was permeated through the tiny holes of the ceramic tube into the water phase accompanied by gas bubbles. The porous ceramic tube not only separated the gas phase and liquid phase but also offered an effective plasma spreading channel. The effects of the peak pulse voltage, additive gas varieties, gas bubbling rate, solution conductivity and TiO2 addition were investigated. The results showed that this reactor was effective for dye wastewater treatment. The decoloration efficiency of Acid Orange II was enhanced with an increase in the power supplied. Under the studied conditions, 97% of Acid Orange II in aqueous solution was effectively decolored with additive oxygen gas, which was 51% higher than that with argon gas, and the increasing 02 bubbling rate also benefited the decoloration of dye wastewater. Water conductivity had a small effect on the level of decoloration. Catalysis of TiO2 could be induced by the pulsed discharge plasma and addition of TiO2 aided the decoloration of Acid Orange II.

Atmospheric pressure gliding arc discharge plasma treatments for improving germination, growth and yield of wheat

Wheat （Triticum aestivum） seeds were treated with atmospheric pressure gliding arc discharge plasmas to investigate the effects on water absorption, seed germination rate, seedling growth and yield in wheat. The surface architectures and functionalities of the seeds were found to modify due to plasma treatments. 6 rain treatment was provided 95%-100% germination rate. For the treatment duration of 3 and 9 rain the growth activity, dry matter accumulation, leaves chlorophyll contents, longest spikes, number of spikes/spikelet and total soluble protein content in shoots were improved. The grain yield of wheat was increased ,--20% by 6 min treatment with H2O/O2 plasma with respect to control.

Application of the Multi-Electrode in the Degradation of Alizarin Red Induced by Glow Discharge Plasma

This paper presents a novel set-up to be used in the degradation of dye, Various influencing factors, such as the voltage, the number of the anodes, and the catalytic action of Fe^2＋, were examined. Chemical oxygen demand （COD）, ultraviolet （UV）, FTIR absorption spectra, and atomic force microscopy （AFM） were used to monitor the degradation process. The results showed that the efficiency of degradation is raised by increasing the applied voltage, and is further improved when two or three anodes are used. Moreover, the use of Fe^2＋ ion can promote the degradation reaction and shorten the degradation time. So the multi-electrode instrument is more efficient in degrading the dye and should be further studied.

A Cascaded Discharge plasma—Adsorbent Technique for Engine Exhaust Treatment

A cascaded system of electrical discharges (non-thermal plasma) andadsorption process was investigated for the removal of oxides of Nitrogen (NO_x) and totalhydrocarbons (THC) from an actual diesel engine exhaust. The non-thermal plasma and adsorptionprocesses were separately studied first and then the cascaded process was studied. In this study,different types of adsorbents were used. The NO_x removal efficiency was higher withplasma-associated adsorption (cascaded) process compared to the individual processes and the removalefficiency was found almost invariant in time. When associated by plasma, among the adsorbentsstudied, activated charcoal and MS-13X were more effective for NO_x and THC removal respectively.The experiments were conducted at no load and at 50 % load conditions. The plasma reactor was keptat room temperature throughout the experiment, while the temperature of the adsorbent reactor wasvaried. A relative comparison of adsorbents was discussed at the end.

Discharge Plasma Assisted Adsorbents for Exhaust Treatment: A Comparative Analysis on Enhancing NO_x Removal

An analysis has been made on the discharge plasma coupled with an adsorbent system for NOx removal. The cascaded plasma-adsorbent system may be perceived as a better alternative for the existing adsorbent-based abatement system in the industry. In this study the exhaust is sourced from a diesel generator set. It was observed that better NO removal in a plasma reactor can be made possible by achieving higher average fields and subsequent NO2 removal can be improved using an adsorbent system connected in cascade with the plasma system. The paper describes various findings pertaining to these comparative analyses.

Characterization and Properties of Electroless Nickel Plated Poly (ethylene terephthalate) Nonwoven Fabric Enhanced by Dielectric Barrier Discharge Plasma Pretreatment

In order to develop a more economical pretreatment method for electroless nickel plating, a dielectric barrier discharge （DBD） plasma at atmospheric pressure was used to improve the hydrophilicity and adhesion of poly （ethylene terephthalate） （PET） nonwoven fabric. The properties of the PET nonwoven fabric including its liquid absorptive capacity （WA）, aging behavior, surface chemical composition, morphology of the surface, adhesion strength, surface electrical resistivity and electromagnetic interference （EMI）- shielding effectiveness （SE） were studied. The liquid absorptive capacity （WA） increased due to the incorporation of oxygen-containing and nitrogen-containing functional groups on the surface of PET nonwoven fabric after DBD airplasma treatment. The surface morphology of the nonwoven fibers became rougher after plasma treatment. Therefore, the surface was more prone to absorb tin sensitizer and palladium catalyst to form an active layer for the deposition of electroless nickel. SEM and X-ray diffraction （XRD） measurements indicated that a uniform coating of nickel was formed on the PET nonwoven fabric. The average EMI-SE of Ni-plating of PET nonwoven fabric maintained a relatively stable value （38.2 dB to 37.3 dB） in a frequency range of 50 MHz to 1500 MHz. It is concluded that DBD is feasible for pretreatment of nonwoven fabric for electroless nickel plating to prepare functional material with good EMI-SE properties.

Enhanced Performance of Discharge Plasma in Raw Engine Exhaust Treatment-Operation under Different Temperatures and Loads

This paper reports improved performance of discharge plasma in raw engine exhaust treatment. For the purpose of investigation, both filtered and raw diesel engine exhaust were separately treated by the discharge plasma. In raw exhaust environment, the discharge plasma exhibits a superior performance with regard to NOx removal, energy consmnption and formation of by-products. In this study, experiments were conducted at conditions of different temperatures and loads.

Unfiltered Diesel Engine Exhaust Treatment by Discharge Plasma: Effect of Soot Oxidation

A cascaded system of electrical discharges (Non-thermal plasma), catalyst andadsorption process was investigated for the removal of oxides of nitrogen (NO_x) and carbonmonoxide (CO) from a Diesel engine raw exhaust. The three processes were separately studied first,and then the cascaded processes, namely plasma-catalyst and plasma-adsorbent, were investigated. Inthis paper main emphasis was laid on the effect of carbonaceous soot oxidation on the plasmatreatment process. While the cascaded plasma-catalyst process exhibits a higher CO removal, thecascaded plasma-adsorbent process exhibits a higher NO_x removal. The experiments were conductedunder no-load. The plasma and adsorbent reactors were kept at room temperature throughout theexperiment while the catalyst reactor was kept at 200℃ / 300℃.

Fischer-Tropsch Performance of an SiO2-Supported Co-Based Catalyst Prepared by Hydrogen Dielectric-Barrier Discharge Plasma

A silica-supported cobalt catalyst was prepared by hydrogen dielectric-barrier dis- charge （H2-DBD） plasma. Compared to thermal hydrogen reduction, H2-DBD plasma treatment can not only fully decompose the cobalt precursor but also partially reduce the cobalt oxides at lower temperature and with less time. The effect of the discharge atmosphere on the property of the plasma-prepared catalyst and the Fischer-Tropsch synthesis activity was studied. The re- sults indicate that H2-DBD plasma treatment is a promising alternative for preparing Co/SiO2 catalysts from the viewpoint of energy savings and efficiency.

Low Pressure DC Glow Discharge Air Plasma Surface Treatment of Polyethylene (PE) Film for Improvement of Adhesive Properties

The present work deals with the change in surface properties of polyethylene （PE） film using DC low pressure glow discharge air plasma and makes it useful for technical applications. The change in hydrophilicity of the modified PE film surface was investigated by measuring contact angle and surface energy as a function of exposure time. Changes in the morphological and chemical composition of PE films were analyzed by atomic force microscopy （AFM） and X-ray photoelectron spectroscopy （XPS）. The improvement in adhesion was studied by measuring T-peel and lap-shear strength. The results show that the wettability and surface energy of the PE film has been improved due to the introduction of oxygen-containing polar groups and an increase in surface roughness. The XPS result clearly shows the increase in concentration of oxygen content and the formation of polar groups on the polymer surface. The AFM observation on PE film shows that the roughness of the surface increased due to plasma treatment. The above morphological and chemical changes enhanced the adhesive properties of the PE＇film surfaces, which was confirmed by T-peel and lap-shear tests.

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.

Ni/MgO catalyst prepared using atmospheric high-frequency discharge plasma for CO_2 reforming of methane

A new type of Ni/MgO catalyst was prepared using atmospheric high-frequency discharge cold plasma. The influences of conventional method, plasma method, and plasma plus calcination method on the catalytic activity were studied and the CO2 reforming of methane was chosen as the probe reaction. The catalysts were characterized by X-ray diffraction （XRD）, transmission electron microscope （TEM）, X-ray photoelectron spectroscopy, and CO2 temperature-programmed surface reaction techniques. The results suggested that the nickel-based catalyst prepared by plasma plus calcination method possessed a smaller particle size and a higher dispersion of active component, better low-temperature activity and enhanced anti-coking ability. The conversion of CO2 and CH4 was 90.70% and 89.37%, respectively, and the reaction lasted for 36 h without obvious deactivation under 101.325 kPa and 750°C with CO2/CH4 = 1/1.