Argon Dielectric Barrier Discharge Research Articles

Influence of surface parameters on dielectric-barrier discharges in argon at subatmospheric pressure

The influence of the secondary electron emission coefficient, γ, and the relative permittivity, ɛ r, of the dielectric layers on the characteristics of dielectric-barrier discharges (DBDs) is studied by means of numerical modelling and calculated results are compared with experimental data. The analysis has been performed for a geometrically symmetric, plane-parallel DBD in argon with copper electrodes covered by quartz dielectrics. A time-dependent, spatially one-dimensional fluid model involving the drift-diffusion approximation is applied for the numerical analysis of the DBD operating sinusoidally at a frequency of 24 kHz with applied voltages between 1.8 and 3.4 kV and pressures from 100 to 650 mbar. Main features of the model as well as the experimental setup and procedures are given. The modelling studies show especially the sensitivity of the results on the specific choice of γ and ɛ r regarding the occurrence and intensity of discharge peaks, the appearance of one or more smaller peaks after the main peak, as well the establishment of a single periodic, multiperiodic or even chaotic temporal evolution of the DBD. In particular, generally good agreement between measured and calculated discharge current signals and the power dissipated in the discharge is found for γ = 0.02 and ɛ r = 4.2.

Experimental Study of Argon and Helium Dielectric Barrier Discharge with Coplanar Electrodes at Intermediate Pressure for Reducing Radar Cross Section

Experimental Study of Argon and Helium Dielectric Barrier Discharge with Coplanar Electrodes at Intermediate Pressure for Reducing Radar Cross Section

Decolorization of indigo carmine solution by argon dielectric barrier discharge produced on liquid surface

Decolorization of indigo carmine solution was performed by excitation of argon dielectric barrier discharge (DBD) on a target solution and the effect of the gap distance on the water treatment characteristics was investigated for a gap distance between 1.0 and 2.5 mm. The argon DBD was excited by a 3 kHz sinusoidal voltage with a fixed discharge power between 1.72 and 1.76 W for each gap distance. Voltage and current waveforms and Lissajous figures were acquired to investigate the electrical characteristics of the DBD. Compared with fixing the discharge energy, a higher decolorization rate was obtained with shorter gap distance. Therefore, shortening the gap distance could lead to increased decolorization efficiency of the indigo carmine solution. The mechanism of higher efficiency with shorter gap distance is discussed on the basis of the electrical characteristics and possible plasma chemical reactions in the argon DBD on the solution surface.

Large‐area atmospheric pressure dielectric barrier discharges in Ar–HMDSO mixtures: Experiments and fluid modelling

AbstractThe electrical discharge characteristics of a large‐area experimental dielectric barrier discharge in argon–hexamethyldisiloxane mixtures containing up to about 1,600 ppm of the monomer is analysed by means of electrical measurements and numerical modelling. A time‐dependent, spatially one‐dimensional fluid model is employed, taking into account the spatial variation of the discharge plasma between the two plane‐parallel dielectrics covering the electrodes. Reasonable agreement between electrical measurements and modelling results is generally found for the gap voltages and discharge currents. Remaining differences between the measured and calculated electrical energy dissipated in the plasma per period are discussed.

Study of an argon dielectric barrier discharge reactor with atmospheric pressure for material treatment

In this study, effects of the variation in the dielectric barrier discharge’s (DBD) gap distance and the nature of dielectric layers which cover both of the reactor electrodes on the electron density, mass fraction of excited argon atoms across the discharge gap, mean electron energy, ion and electron current density, and electron temperature are investigated at atmospheric pressure. In order to find the optimal reactor gap, the DBD’s average power consumption is studied. The achievements show that when the value of dielectric constant is increased from 7.6 to 10, discharge gap of 1 mm still demonstrates the maximum power consumption, which can be considered as the optimum discharge gap. To optimize the characteristics of one-dimensional modeling of DBD system for material treatment, various types of materials with different values of the permittivity [aluminum, glass (quartz) and silicon] are embedded in the discharge gap between the two electrodes. In this case, the reactor gap is changed from 0.5 mm to 2 mm, while the dielectric constant of the dielectric layers which cover both of the metallic electrodes is assumed to be 10. Compared to the other examined materials, our numerical results illustrate that the treated material with higher value of the relative permittivity (silicon) has greater influences on the variations in the electron density, argon ion density and also total plasma current density than in the values of excited argon atom density, mass fraction of excited argon atoms and also average power consumption.

Numerical simulation of atmospheric-pressure 200 kHz/13.56 MHz dual-frequency dielectric barrier discharges

A 1D drift-diffusion model is used to study atmospheric-pressure dual-frequency (DF) dielectric barrier discharges in argon using the plasma modeling platform PLASIMO. The simulation exhibits an excellent agreement with the experimental results and gives insight into the DF plasma dynamics e.g. the electric field, sheath edge profiles, ionization/excitation rate and electron energy distribution function (EEDF) profiles. The results indicate that due to the radio-frequency oscillation, the electric field, sheath edge and thus the ionization/excitation are temporally modulated. As a result, the plasma conductivity is enhanced as the plasma density is higher. The discharge development is slowed down with a lower current amplitude and a longer duration. The time-averaged sheath is getting thinner with a more pronounced ionization rate and a longer contacting time near the substrate, which could help to improve the efficiency of plasma-assisted surface processing. In addition, the DF excitation exhibits a capability of modifying the EEDF profiles and controlling the plasma chemical kinetics, which can be applied to other relevant fields e.g. gas-phase chemical conversion.

Modeling of radio frequency argon dielectric barrier discharge at atmospheric pressure in argon

In this work modeling of atmospheric pressure barrier discharge in argon for rf-voltage signal applied to the electrodes was conducted. The model included balance equations for the densities of charged (electrons, ions) and the excited particles, the electron energy density, and the Poisson equation for the electric potential. The fluxes of charged and excited particles (electrons, ions) and electron energy were given in the drift-diffusion form. Distributions of spatiotemporal parameters of the discharge were obtained.

Tailored Waveform of Dielectric Barrier Discharge to Control Composite Thin Film Morphology.

Nanocomposite thin films of TiO2 in a polymer-like matrix are grown in a filamentary argon (Ar) dielectric barrier discharge (DBD) from a suspension of TiO2 nanoparticles in isopropanol (IPA). The sinusoidal voltage producing the plasma is designed to independently control the matrix growth rate and the transport of nanoparticle (NP) aggregates to the surface. The useful FSK (frequency shift keying) modulation mode is chosen to successively generate two sinusoidal voltages: a high frequency of 15 kHz and a low frequency ranging from 0.5 to 3 kHz. The coating surface coverage by the NPs and the thickness of the matrix are measured as a function of the FSK parameters. The duty cycle between these two signals is varied from 0 to 100%. It is observed that the matrix thickness is mainly controlled by the power of the discharge, which largely depends on the high-frequency value. The quantity of NPs deposited in the composite thin film is proportional to the duration of the low frequency applied. The FSK waveform has a double modulation effect, allowing us to obtain a uniform coating as the NPs are not affected by the high frequency and the matrix growth rate is limited when the low frequency is applied. When it is close to a frequency limit, the low frequency acts like a filter for the NP aggregates. The higher the frequency, the smaller the size of the aggregates transferred to the surface. By changing only the FSK modulation parameters, the thin film can be switched from superhydrophobic to superhydrophilic, and under suitable conditions, a nanocomposite thin film is obtained.

Characterization of argon dielectric barrier discharges applied to ethyl lactate plasma polymerization

The influence of the input voltage frequency (35 and 150 kHz), interelectrode gap (1 and 2 mm) and precursor concentration (250, 350, and 450 ppm) on the electron temperature (Te), number density of metastable Ar atoms (n(Arm)), and discharge current density (proportional to the electron density ne) is studied in an argon-ethyl lactate dielectric barrier discharge (DBD). An argon-ammonia Penning mixture is also considered as reference. These results are correlated to the chemistry (XPS, IR) and topography (AFM) of the ethyl-lactate-based plasma polymer coatings. Low Te values from 0.3 to 0.5 eV were obtained for all discharges. This observation, in addition to resemblances with the Ar–NH3 mixture, suggested that the ionization kinetics of ethyl lactate-based discharges is driven by Penning reactions. Among the investigated parameters, the dissipated power obtained through changes of the excitation frequency had the largest impact on both the coatings properties and the discharge behavior.

Surface discharge induced interactions of filaments in argon dielectric barrier discharge at atmospheric pressure

A needle-plate geometry is used to generate two barrier-discharge filaments composed of volume discharge and surface discharge in atmospheric pressure argon, interactions of which are investigated for the first time on the nanosecond timescale using an intensified charge-coupled device. The results indicate that the onset of volume discharges for the two filaments have a periodical discharge sequence, which implies interactions of the two filaments. Moreover, strong interactions of the two filaments are controlled through surface discharges, one of which is induced by that of the other filament during the positive discharge. Different from repulsive streamers, counter-propagating streamers are attractive between the two filaments.

Electron heating and mode transition in dual frequency atmospheric pressure argon dielectric barrier discharge

Plasma ionization, excitation, mode transitions and associated electron heating mechanisms in atmospheric pressure dielectric barrier discharges (DBD) driven by dual radio frequency sources are investigated in this paper. The electrons are found to be heated mainly by the high frequency component in the plasma bulk when discharged in α mode. On the contrary, the low frequency component is primarily responsible for heating in the sheath which is caused by intense motion in the sheath. It was also found that variation of the lower frequency component ratio could effectively modulate the electron energy distribution as determined from time averaged EEDF. The results above have demonstrated that the independent control of plasma parameters via non-linear synergistic effect between the dual frequency sources can be achieved through reasonable selection of processing parameters.

Functionalization of polymer surfaces by medium frequency non-thermal plasma

Abstract This work addresses the surface modification of different polymers by argon dielectric barrier discharge, using bromoform vapours. Atomic Force Microscopy and Scanning Electron Microscopy showed that plasma etching occurs in stages and may be related to the reach of the species generated and obviously the gap between the electrodes. In addition, the stages of flatten surface or homogeneity may be the result of the transient crosslinking promoted by the intense UV radiation generated by the non- thermal plasma. X-ray Photoelectron Spectroscopy analysis showed that bromine was inserted on the polymer surface as C Br bonds and as adsorbed HBr. The obtained results demonstrate that the highest degree of bromofunctionalization was achieved on polypropylene surface, which contains about 8,5% of Br. After its derivatization in ammonia, Br disappeared and about 6% of nitrogen in the form of amine group was incorporated at the surface. This result can be considered as a clear fingerprint of the Br substitution by the amine group, thus illustrating the efficiency of the proposed method for functionalization of polymer surfaces.

Control of composite thin film made in an Ar/isopropanol/TiO2 nanoparticles dielectric barrier discharge by the excitation frequency

The synthesis of composites thin films made by injecting an aerosol suspension of 20 nm‐size TiO2 nanoparticles (NPs) and isopropanol (IPA) in a filamentary argon Dielectric Barrier Discharge (DBD) is studied as a function of the DBD frequency from 1 to 50 kHz. The plasma is modulated to get homogeneous coatings. The deposition rate and morphology of the composite thin films are determined from SEM images of both surface and cross section. Their chemical composition is investigated by XPS, Raman spectroscopy and FTIR measurements. The structural composition of the NPs is examined by XRD. All the deposited composites show the chemical signature of the NPs as well as of the polymer‐like coating resulting from the plasma polymerization of IPA. No mixed phase is observed and the sizes of the NPs as well as of their aggregates are not affected by the plasma. With this method aerosol droplets are evaporated before entering the plasma and the NPs inside a same droplet are aggregated. Results show that the DBD frequency controls the composite composition by independently influencing the NPs transport and the matrix growth rate. At 1 kHz, the coating is essentially made of NPs with a low carbon coating. From 1 to 50 kHz, the Ti/C ratio is divided by two orders of magnitude. As the frequency increases the quantity of NPs decreases and since 10 kHz the matrix thickness increases. The decrease of the NPs is explained by the numerical modeling of the NPs trajectory. It is found that from 10 to 1 kHz, the lower is the frequency, the higher is the transport of the NPs to the surface due to the electrostatic force. On the other hand the matrix growth rate increases from almost zero at 10 kHz up to 19 nm · min−1 at 50 kHz because of the linear increases of the DBD power with the frequency.

Influence of ethanol vapor addition on the surface modification of polyethylene in a dielectric barrier discharge

In this paper, ethanol vapor up to 50% is added to an argon, air or nitrogen dielectric barrier discharge at medium pressure to profoundly investigate the effect of ethanol addition on the surface modification of low density polyethylene (LDPE). Water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS) measurements show that the ethanol vapor addition effect on the LDPE surface depends on the used carrier gas. Adding ethanol to an argon plasma has no significant effect on the wettability nor on the chemical composition of LDPE compared to a pure argon plasma treatment. Ethanol addition does however slightly increase the LDPE surface roughness. Addition of small amounts of ethanol vapor to an air plasma makes it possible to incorporate additional nitrogen and oxygen groups on the LDPE surface, resulting in an extra decrease of 11% in WCA value. Moreover, the LDPE surface roughness is slightly increased due to the ethanol vapor addition. The most significant effect of ethanol addition is however observed when nitrogen is used as carrier gas. After an N2/2% ethanol plasma treatment, an 85% reduction in WCA value to 8.5° is found compared to a pure N2 plasma treatment. This very hydrophilic LDPE surface is obtained due to a significantly high incorporation of oxygen and nitrogen groups on the surface with an O/C and N/C ratio reaching 32% and 53% respectively. FTIR measurements also reveal that the observed extremely high wettability of LDPE is not the result of plasma activation but is due to plasma polymerization effects occurring on the surface resulting into the deposition of a plasma polymer containing ketones, amides as well as CN groups. In addition, ageing studies have also been conducted and these studies reveal that for all carrier gases, ethanol addition to the discharge gas significantly suppresses the ageing effect. All the above mentioned conclusions therefore indicate that ethanol vapor based plasmas can be an excellent tool to increase the surface energy of polymers.

Two-dimensional simulation of argon dielectric barrier discharge excited by a Gaussian voltage at atmospheric pressure

A two-dimensional self-consistent fluid model was employed to investigate the spatiotemporal characteristics of discharges in atmospheric pressure argon (Ar) dielectric barrier discharge driven by a Gaussian voltage. The simulation results show that a discharge with multiple current pulses occurs each half-cycle in the gas gap. A transition from the Townsend mode to the glow mode is observed with the increasing applied voltage each half-cycle at a lower driving frequency (7.5 kHz). It is also found that the glow mode survives all the discharge phases at a higher driving frequency (12.5 kHz and 40 kHz). The change in the discharge mode with the driving frequency mainly lies in the fact that a lot of charged particles created in the discharge gap have no enough time to drift and diffuse around, and then these particles are assembled in the discharge space at higher frequency. Additionally, the spatial distributions of the electron density indicate that a center-advantage discharge is ignited at the driving frequencies of interest, resulting in the radial non-uniformity of discharge because of the edge effects. However, this overall non-uniformity is weakened with the driving frequency increased to 40 kHz, at which concentric ring patterns are observed. These distinct behaviors are mainly attributed to the fact that many charged particles generated are trapped in the gas gap and then accumulated to make the extension along the radial direction due to the charged particles transport and diffusion, and that the effective overlapping of a large number of avalanches induced by the increased “seed” electron density with the driving frequency. Meanwhile, the surface charged particles accumulated on the dielectric barriers are also shown to play a role in the formation of the discharge structure.

Influence of Driving Frequency on the Argon Dielectric Barrier Discharge Excited by Gaussian Voltage at Atmospheric Pressure

A 1-D self-consistent fluid model was employed to investigate the effect of driving frequency on the discharge characters of a dielectric barrier discharge at atmospheric pressure in argon excited by a periodic Gaussian voltage. The simulation results indicate that there are two discharge modes: 1) Townsend and 2) glow modes in the multipulse discharge and different transitions between them during the discharge take place with the increase in driving frequency. When the driving frequency is 1 kHz, there is a tendency of transition from the Townsend mode through glow and finally back to the Townsend one during the positive half-circle of applied Gaussian voltage. However, the discharge in the half-circle can all along operate in the glow mode with the higher driving frequency. Moreover, when the driving frequency is sufficiently high, there are also distinct fluctuations of spatial performance of the charge densities in the positive column during the glow discharge. This is caused by the fact that a lot of charged particles created in the gas gap have not enough time to drift and diffuse to the dielectric barriers, and then these particles are preserved in the local discharge gap at such a high frequency. A comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increase in the driving frequency can enhance the plasma chemistry and also expand its volume.

Isolation and characterization of astaxanthin-hyperproducing mutants of Haematococcus pluvialis (Chlorophyceae) produced by dielectric barrier discharge plasma

:Haematococcus pluvialis has potential commercial application for its ability to accumulate astaxanthin under stress conditions. To improve astaxanthin productivity, nonthermal plasma can be used to produce mutant algal strains with enhanced production of astaxanthin. In this work, atmospheric pressure argon dielectric barrier discharge (DBD) was used for mutation induction. Several new algal strains with increased growth rate and higher astaxanthin accumulation were obtained. For analysis of the DBD-treated algal mutants, genetic variation was examined by random amplification of polymorphic DNA, and the pigment pattern in response to inhibitors (diphenylamine and nicotine) of carotenoid biosynthetic pathway was characterized by high-performance liquid chromatography. Furthermore, photosynthetic activity and gene expression were also examined by pulse amplitude-modulated fluorometry and quantitative real-time polymerase chain reaction, respectively. Our results confirmed that the enhanced astaxanthin accumulation in the mutants was associated with increased expression levels of lycopene cyclase, which is involved in the conversion of lycopene to β-carotene. As such, this work demonstrates a successful example for the effective application of DBD in the mutation breeding of astaxanthin-hyperproducing algal strains.

Characterization and mechanism studies of argon dielectric barrier discharge excited by a Gaussian voltage at atmospheric pressure

A one-dimensional self-consistent fluid model is employed to investigate the atmospheric-pressure argon dielectric-barrier discharge (DBD) excited by periodic Gaussian voltage. With the driving frequency, voltage amplitude, and gas gap set at certain values, the temporal evolutions of discharge current density and gas voltage are obtained, together with the spatial distributions of electron and ion densities and electric field. Simulation results indicate that there are two discharge modes: Townsend and glow modes in the multi-current pulse discharge. A mutual transition between the Townsend mode and glow one occurs during each half cycle of the applied Gaussian voltage. The space charges in the gas gap and the surface charges on the dielectrics play a key role in the transition between the two discharge modes. Additionally, a residual current peak is observed during the falling phase of each half cycle. This is resulted from the fact that amounts of space charges are trapped in the gas gap during the rising phase of the applied Gaussian voltage. These findings contribute much to the design of plasma excitation source in applications, such as materials processing, pollution control, and biomedical sterilization.

Surface modification of polyvinyl alcohol/malonic acid nanofibers by gaseous dielectric barrier discharge plasma for glucose oxidase immobilization

Polymeric nanofiber prepares a suitable situation for enzyme immobilization for variety of applications. In this research, we have fabricated polyvinyl alcohol (PVA)/malonic acid nanofibers using electrospinning. After fabrication of nanofibers, the effect of air, nitrogen, CO2, and argon DBD (dielectric barrier discharge) plasmas on PVA/malonic acid nanofibers were analysed. Among them, air plasma had the most significant effect on glucose oxidase (GOx) immobilization. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrum analysis and X-ray photoelectron spectroscopy (XPS) results revealed that in case of air plasma modified nanofibers, the carboxyl groups on the surface are increased. The scanning electron microscopy (SEM) images showed that, after GOx immobilization, the modified nanofibers with plasma has retained its nanofiber structure. Finally, we analysed reusability and storage stability of GOx immobilized on plasma modified and unmodified nanofibers. The results were more satisfactory for modified nanofibers with respect to unmodified ones.

Electron temperature and density measurement of a dielectric barrier discharge argon plasma generated with tube-to-plate electrodes in water

A dielectric barrier discharge argon plasma was generated with tube–to-plate electrodes in the water by a sinusoidal excitation voltage at atmospheric pressure. Time-averaged optical emission spectroscopy was used to measure the plasma parameters, of which the rotational temperature of OH was obtained by comparing the simulated spectrum with the measured spectrum at the A2Σ+→X2Π band transition and the electronic excitation temperature was determined by Boltzmann’s plot method. Furthermore, the emission intensity ratio of atomic argon lines λ = 811.5 nm to λ = 750.4 nm was used to determine the electron temperature and the Stark broadening of the hydrogen Balmer Hα line was applied to measure the electron density. It has been found that the electron temperature and density in this argon plasma were in the range of 1.02–1.43 eV and on the order of 1014 cm−3, respectively, and the excitation temperature, rotational temperature, and electron density increase with the increase of applied voltage. Besides, the properties of the argon dielectric barrier discharge were also studied by electrical diagnosis.