Pressure Dielectric Barrier Discharge Research Articles

Statistical behavior of a single microdischarge in atmospheric-pressure air dielectric barrier discharges

This work investigates the statistical behavior including the dimensions and electrical properties of a single microdischarge (MD) generated in a planar atmospheric-pressure air dielectric barrier discharge reactor using a kHz sinusoidal power source with a gap of 1.4 mm. The MD diameters and surface wave (SW) dimensions are captured by an intensified charge-coupled device camera with currents and charge transferred being recorded. The average currents measured in positive and negative half periods (HPs) are 58.9 and 50.5 mA, respectively. The average diameters measured are 256 and 258 μm in positive and negative HPs, respectively. Therefore, the average current densities calculated in positive and negative HPs are 1.14 × 106 and 9.66 × 105 A m−2, respectively. The high current density leads to the high density of surface charge reaching up to 51.5 nC cm−2 in the positive HP at the anode, which is one order of magnitude higher than those observed in filamentary discharges using He/N2 mixtures. The gap dimension is adjusted to 2.0 mm to investigate the effect of the gap dimension on MD properties. Larger MD diameters, currents, SW dimensions, and the charge transferred are measured in the gap of 2.0 mm although the average current densities evaluated in positive and negative HPs are lower than those of gap 1.4 mm as 9.39 × 105 and 8.15 × 105 A m−2, respectively. The average density of surface charge evaluated in the positive HP at the anode of gap 2.0 mm is 51.7 nC cm−2, which is almost identical to that evaluated in the gap of 1.4 mm.

In-situ atmospheric-pressure dielectric barrier discharge plasma treated CH3NH3PbI3 for perovskite solar cells in regular architecture

The effect of atmospheric-pressure dielectric barrier discharge (DBD) treatment on the properties of methylammonium lead iodide (CH3NH3PbI3, MAPbI3) perovskite thin films is investigated. The in-situ DBD-treated MAPbI3 perovskite thin films are then used as the absorber layers for planar n-i-p perovskite solar cells (PSCs). N-O emission system is observed in the plasma during the treatment, indicating the reactions of reactive nitrogen plasma species with the organics in the precursor films. Long DBD treatment duration (60 s) leads to the phase precipitation of PbI2 and degrades the cell efficiency, whereas short DBD treatment duration (20 s) significantly improves the PSC efficiency by nearly 40%. Only slight performance enhancement is observed in the PSCs prepared by conventional thermal treatment at the same substrate temperatures as that for DBD treatment, implying that DBD provides the synergetic effect of the reactivity and plasma heating. Electrochemical impedance spectroscopy (EIS) indicates that the charge recombination impedance increases and then decreases with DBD treatment duration. The shunt resistance also shows a similar trend, and it is consistent with the PSC performance. The PSC with the 20 s DBD-treated absorber layer shows energy conversion efficiency of 14.29%, open circuit voltage of 1.022 V, short circuit current density of 19.45 mA/cm2, and fill factor of 0.72, whereas the corresponding values for the untreated counterpart are 10.32%, 0.976 V, 18.52 mA/cm2, and 0.57. The result shows that short-duration low-temperature DBD treatment effectively enhances the performance of solution-processed PSCs.

Plasmon enhanced photocatalytic and antimicrobial activities of Ag-TiO2 nanocomposites under visible light irradiation prepared by DBD cold plasma treatment

Silver nanoparticles (Ag NPs) have been deposited on powder P25 by a novel two-step method involving a precipitation reaction and atmospheric pressure dielectric barrier discharge (DBD) cold plasma treatment without the use of any environmentally and biologically hazardous reducing agents. The silver precursor is formed in the processing of precipitation reaction and then completely reduced to the metallic state by atmospheric pressure DBD cold plasma treatment as proved by X-ray photoelectron spectroscopy, UV–Visible absorption spectra and HRTEM analyses. TEM images indicate that the Ag NPs with average diameter of 3.7 nm were deposited on powder P25 with high dispersion although no reducing agents, stabilizers or surfactants were used. The prepared products show remarkable improvement for methylene blue (MB) photodegradation and effective inhibition of bacterias against Escherichia coli and Staphylococcus aureus.

Use of pre-ionization electrodes to produce large-volume, densely distributed filamentary dielectric barrier discharges for materials surface processing

Scaling up atmospheric pressure dielectric barrier discharges is a challenging prerequisite to expanding their industrial applications. In this study, we present the results of large-volume dielectric barrier discharges (DBDs) with a parallel plate electrode configuration having an electrode surface of 50 × 200 mm2 and an interelectrode gap of 5 mm. Highly dense filamentary DBD plasma was stably generated over a large area using pre-ionization electrodes embedded in the one of electrodes. We show that the role of the pre-triggering system is crucial in producing a densely distributed filamentary discharge over the electrode surface, especially at the main discharge voltage values of 14.0–18.0 kVp-p and pre-ionization voltage of 7.0–10.0 kVp-p at the same frequency, ranging from 1 to 4 kHz. By tuning the phase difference between the pre-ionization and main discharge voltages to around 180 degrees, both discharge current amplitude and duration time per period of main DBDs are maximized. The present results indicate that such a large-volume DBD is extremely versatile and suited for a wide range of industrial applications.

Observation and Investigation of “Reverse Breakdown” in a Discharge Tube

A discharge operating in a 80-cm-long discharge tube with an inner diameter of 15 mm, filled with a 3 : 1 neon–argon mixture at a pressure of 1 Torr, was investigated experimentally. Square voltage pulses with a period of 1 s were supplied to one of the tube electrodes, the second electrode being ungrounded. The initial stage of breakdown—the primary breakdown between the high-voltage (active) electrode and the tube wall, accompanied by the propagation of the prebreakdown ionization wave—was the same as in the conventional scheme with a grounded low-voltage electrode. Since the discharge gap was not closed, the discharge was not ignited. An essentially new effect was observed after the end of the voltage pulse. After a certain time interval, voltage spikes of opposite polarity, the amplitude and shape of which were close to those observed during the primary breakdown, appeared in the voltage and current waveforms of the active electrode. Simultaneously, a radiation pulse from the region adjacent to the active electrode was observed and an ionization wave began to propagate toward the second electrode. This work is dedicated to investigating this effect (which was named “reverse breakdown”) and analyzing its mechanism. A conclusion is made on the similarity of this phenomenon to the processes occurring in atmospheric-pressure dielectric barrier discharges.

Pulsed plasma initiated chemical vapor deposition (PiCVD) of polymer layers − A kinetic model for the description of gas phase to surface interactions in pulsed plasma discharges

A new kinetic model for studying the growth mechanisms in ultra‐short square pulsed atmospheric‐pressure dielectric barrier discharges (AP‐DBD) is presented. Interpretation of the deposition rates yields information on the dominant mechanisms along each pulse cycle (i.e., initiation, propagation, chain‐transfer, and termination). Further investigations extracted important parameters for the understanding of free‐radical kinetics in the plasma deposition processes. Based on the thin films’ chemistry, topography, polymeric length and growth rates, the chemical and physical meaning of the calculated parameters and their impacts on the thin films’ polymeric structure are discussed.

Improved production of polysaccharides in Ganoderma lingzhi mycelia by plasma mutagenesis and rapid screening of mutated strains through infrared spectroscopy.

As a traditional Chinese medicine, Ganoderma lingzhi has attracted increasing attention for both scientific research and medical application. In this work, in order to improve the production of polysaccharides from an original wide-type (WT) strain (named "RWY-0") of Ganoderma lingzhi, we applied atmospheric-pressure dielectric barrier discharge (DBD) nonthermal plasma to the protoplasts of RWY-0 for mutagenesis treatment. Through a randomly amplified polymorphic DNA (RAPD) assay, at least 10 mutagenic strains were confirmed. They also showed different mycelium characteristics in terms of shape, color, size and biomass in liquid fermentation. The mutant strains were examined by infrared spectroscopy, and based on the established near-infrared (NIR) quantification model, the polysaccharide contents in these mutants were quantitatively evaluated. As a result, we found that the Ganoderma polysaccharide contents in some of the mutant strains were significantly changed compared with that of the original WT strain. The polysaccharide content of RWY-1 G. lingzhi was considerably higher than that of the WT strain, with an increase of 25.6%. Thus, this preliminary work demonstrates the extension of the plasma mutagenesis application in acquiring polysaccharide-enhanced Ganoderma lingzhi mutants and shows the usefulness of NIR spectroscopy in the rapid screening of mutagenic strains for other important ingredients.

Experimental study on the transition between patterned and homogeneous glow in a pulse-modulated radio frequency atmospheric pressure dielectric barrier discharge in helium

In a pulse-modulated radio frequency atmospheric pressure dielectric barrier discharge in helium, the influence of the pulse width on the transition from a patterned glow discharge to a homogeneous glow discharge is experimentally investigated. The experimental results show that the discharge mode can transit from a patterned glow to a homogeneous glow at a moderate pulse width (7 μs) but only has a patterned glow at a short pulse width (4 μs) or a homogeneous glow at a long pulse width (18 μs). The characteristic regions of patterned and homogeneous glow discharges are also acquired. The results can be explained using the breakdown characteristics of the pulse-modulated radio frequency atmospheric pressure discharge.

Atmospheric pressure dielectric barrier discharge synthesis of morphology-controllable TiO2 films with enhanced photocatalytic activity

Atmospheric plasma technology is a promising next-generation alternative for replacing thermal chemical vapor deposition or wet chemical processes for the deposition of functional coatings. In this work, TiO2 films with various morphologies and thicknesses are synthesized in a controllable way by atmospheric Dielectric Barrier Discharges (DBD) under argon/oxygen ambient conditions. This method allows varying the density of the deposited coatings, from low density powders to dense compact anatase layers simple tuning of the parameters. The surface morphology and cross section of the as-synthesized films are observed by scanning electron microscopy (SEM). It is demonstrated that the total flow rate together with the absorbed power have a significant effect on the morphology of the film, which changes from granular to compact film by increasing the total flow rate or decreasing the power. In other words, changing the energy density (Ed) in the plasma allows to control the morphology of the TiO2 films. A deposition mechanism is proposed to explain the effect of the synthesis parameters on the formed films. The chemical and phase composition of these films before and after annealing for 2 h in air at 673 K are comparatively studied. The photocatalytic activities and the reusability of the TiO2 films is investigated by degrading a methylene blue (MB) solution under Ultra-Violet (UV) light. It is compared to the activity of a P25 film, deposited by drop-casting. The photocatalytic rate of the annealed TiO2 film synthesized at a total flow rate of 2.5 slm turns out to be about 2 and 15 times higher than the one of P25 and as-synthesized TiO2 films, respectively. The annealed TiO2 film were shown to be reusable for at least three cycles, without significant loss of photocatalytic activity.

Depolymerization of heparin by dielectric barrier discharge: Effect of operating modes and anticoagulant potential analysis of low-molecular-weight products

Low-molecular-weight heparin and ultra-low-molecular-weight heparin are widely used as anticoagulant and antithrombotic drugs. An atmospheric pressure dielectric-barrier discharge procedure was developed to depolymerize heparin to low- or ultra-low-molecular-weight fragments. Dielectric-barrier discharge treatment of heparin resulted in several well-separated and uniform fragments. The structural character of digested fragments below 3,000 Da was elucidated. Expected digestion products such as sulfated disaccharide, sulfated tetrasaccharide, and pentasaccharides with alternatingly-linked N-acetyl glucosamine and iduronic acid were detected. The anticoagulant potential of the digested heparin was tested. The results indicated that dielectric-barrier discharge treatment can produce various molecular weight (MW) heparin fragments and maintain anticoagulant potency.

System-level model and experiments for irrigation water alkalinity reduction and enrichment using an atmospheric pressure dielectric barrier discharge

The treatment of distilled water with varying amounts of dissolved sodium bicarbonate (representing alkalinity) is considered using an atmospheric pressure electrical discharge. The discharge ignited between a capillary tube (used as powered electrode) and a ground electrode wrapped around the beaker holding the treated water consists of streamers propagating in ambient air and striking the water surface. The streamer interaction with water is shown to lead to a decrease in pH and an increase in nitrate concentration. The pH variation with time is shown to be similar to a titration curve for acid-base neutralization with final pH values around 3 for 22 min of treatment. The nitrate ion concentration increase with time is consistent with a two-rate system-level model that is characterized by two asymptotic rates for NO3− creation by the plasma. The two asymptotic rates are calibrated to be about 2.7 μmol/min and 22.5 μmol/min with the transition between the two rates occurring at the breakeven time that is representative of the time required for all dissolved bicarbonate to be consumed by the plasma treatment. The increase in rate of NO3− creation at the breakeven time is attributed to the increase in conductivity of the treated solution once all bicarbonate is consumed thereby modifying the plasma properties. Another system-level model that is based on the observed pH variation is also considered for comparison with measured data. While both system-level models have some discrepancies with the measurements, the two-rate model based on the nitrate ion concentration is concluded to be more useful for determining the NO3− formation rates in the context of irrigation water enrichment. The discrepancies are attributed to the simplicity of the system-level models considered here where the effect of the plasma is completely represented by the creation of just one chemical species in HNO3 thereby neglecting potentially important species such as HNO2 and H2O2. Nevertheless, the proposed system-level model could greatly assist in the design of plasma treatment systems with specified alkalinity, pH and nitrate ion levels for irrigation water.

Deposition of SiOx film on electrode surface by DBD to improve the lift-off voltage of metal particles

The free metal particles pollution has been a severe problem affecting the safety operation of gas insulated transmission lines (GIL) system and causes insulation failure. In this paper, a facile insulation film deposition method by using atmospheric pressure dielectric barrier discharge (AP-DBD) plasma was introduced. The SiO x film was deposited on copper surface to improve the lift-off voltage of metal particles. The film composition, surface morphology and film thickness based on the plasma deposition time were well studied. The results showed that deposited film was composed with Si- O-Si group, Si-OH group along with small amount of inorganic groups (CH 2 and CH 3 ). The oxidation degree and film thickness were enhanced when plasma treatment time was longer. The theoretical model of particle lift-off voltage was calculated before and after surface coating. After the electrode covered with SiO x insulation film, the lifting voltage of metal particles improved by about 38%, which agreed well with the prediction value. Our results proved that SiO x film deposited by AP-DBD was a very effective method for lift-off voltage improvement.

Degradation of norfloxacin in aqueous solution by atmospheric-pressure non-thermal plasma: Mechanism and degradation pathways

Norfloxacin is a synthetic antibiotics drug which is widely used in the treatment of infectious diseases and also often carelessly released into natural environment resulting in antibiotics-contaminated wastewater. In this work, we employed atmospheric-pressure non-thermal dielectric barrier discharge (DBD) to treat norfloxacin-contaminated water and investigated the degradation efficiency and mechanism for the plasma treatments under different conditions with varied working gas atmospheres. Our results showed that the DBD efficiency for norfloxacin degradation depended on reactive oxygen/nitrogen species (RONS) produced in the plasma treatment, while the plasma-induced hydroxyl radical played a critical role in the norfloxacin degradation. For O2-DBD, except for the contribution from reactive oxygen species (ROS), ozone could also play an important role. For N2-DBD, reactive nitrogen species (RNS) could work synergistically with H2O2 to enhance the degradation effect. We also checked the plasma activated liquid (PAL) effect and analyzed the degradation products so that the degradation mechanism and pathways could be elucidated. This work may therefore provide the guidance for effective and feasible application of low-temperature plasma technology in treatment of antibiotics-contaminated wastewater.

Characterization of dielectric barrier discharges for analytical chemistry

Dielectric barrier discharges (DBDs) are well-established and useful tools for scientific as well as industrial applications. They have been of high interest for analytical applications due to the fact that DBDs can produce small, low temperature/power, and atmospheric plasmas. These kind of plasmas can be applied for the detection and quantification of analytes in several ways: either, DBDs can be used for example as fragmentation and excitation sources to detect elements via optical emission spectrometry (OES), or as ionization sources of molecules for the detection via mass spectrometry (MS). ISAS has developed several of these discharges and studied the impact of the DBD itself on the subsequent application. This work summarizes the development from low pressure DBD implemented in diode laser atomic absorption spectrometry to atmospheric DBDs that can be used for different ambient applications such as the trace detection of arsenic species via OES or the soft ionization of molecular compounds via MS.

Lactose powder flowability enhancement by atmospheric pressure plasma treatment

For the first time, an atmospheric‐pressure plasma process is presented that enables continuous flowability improvement of cohesive, temperature‐sensitive, and fine‐grained powder. For this, an atmospheric pressure dielectric barrier discharge operating with argon and oxygen is used to dissociate HMDSO and form nanoparticles. The nanoparticles are directly deposited on the surface of cohesive lactose powder. These nanoparticles decrease the distance‐dependent attractive van der Waals forces in between the lactose particles and therefore, improve its flowability. Flow factor and powder surface are investigated using a ring‐shear tester and scanning electron microscopy, respectively. High flow factors are found when the total flow rate and HMDSO concentration trigger the formation of large nanoparticle quantities and agglomerates. Repeating the plasma process up to three times improves flowability from the cohesive regime to the easy flowing regime.

The effect of dielectric barrier discharge plasma treatment on the air drag force of polyacrylonitrile, polyethylene, polypropylene and polyethylene terephthalate yarns

In this paper, atmospheric pressure dielectric barrier discharge (DBD) plasma was used to treat four kinds of chemical fiber yarns, namely polyacrylonitrile (PAN), polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET), for which the air drag force, moisture regain and yarn diameter were measured. Compared with untreated samples, the air drags of treated PAN, PE, PP and PET yarns increased maximally by 10.7%, 43.0%, 40.0% and 18.9%, respectively, in the present experiments. A two-way analysis of variance and correlation analysis were performed to study the effect of plasma treatment on air drag and other properties of these four chemical fiber yarns. The combination of X-ray photoelectron spectroscopy analysis and the determination of the DBD plasma component can further enhance the understanding of the difference between DBD plasma treatment processes among these four chemical fiber yarns. This study provided the experimental basis to improve the air-jet weaving efficiency of chemical fiber fabrics.

Tars removal by non-thermal plasma and plasma catalysis

The gasification of a fuel or biomass is an industrial process that is utilized for synthesis gas (syngas) production. The syngas can be used to generate electricity, but after gasification it is often polluted with tars and various other pollutants. Therefore, the syngas must be cleaned before further use. The objective of this paper was to investigate the potential of removing the tars by non-thermal plasma generated by atmospheric pressure dielectric barrier discharge in combination with various packing materials (TiO2, Pt/γ-Al2O3, γ-Al2O3, glass beads). Naphthalene was used as a model polyaromatic tar compound. The effect of discharge power, carrier gas and packing material on naphthalene removal was investigated and gaseous and solid by-products were analysed by means of FTIR spectrometry. In ambient air, a naphthalene removal efficiency of 88% and 40% was achieved for 320 J l−l with and without the catalyst, respectively. The maximum removal efficiency of almost 100% was observed with a TiO2 catalyst and oxygen carrier gas. CO, CO2, H2O and HCOOH were identified among the products, as well as more complex compounds, such as 1,4-naphthoquinone and phthalic anhydride.

Experimental determination and numerical evaluation under simplifying assumptions of the ozone concentration in an atmospheric-pressure air DBD plasma

In this work ozone concentration in a plane-to-plane Dielectric Barrier Discharge (DBD) reactor has been evaluated both experimentally and numerically. The reactor geometry has been chosen to generate a homogenous discharge. Therefore, simplified approaches for both experiments and numerical simulations have been utilized. The discharge was excited for 20 s in atmospheric-pressure quiescent air by means of a sinusoidal voltage of 15 kV peak at a frequency of 5 kHz in continuous operation. Electrical and optical measurements have been done to estimate the input parameters for the kinetics model. The ozone density within the discharge gap was measured by using the UV absorption method. The optical path travelled by the UV beam inside the reactor gap was estimated by means of Schlieren imaging. Within the time intervals and the dimensions considered, plasma was assumed to be uniform. This assumption was confirmed experimentally by iCCD images of the discharge. Numerical simulations have been performed by means of the zero-dimensional open-source code ZDPlasKin. A set of 622 reactions among 62 chemical species has been implemented, accounting for a 1% water vapour fraction. Reduced electric field, electron density and gas temperature were the input parameters of the code. Ozone density presented a production peak of about 1.3 ⋅ 1017 cm−3 half a second after discharge ignition. A steady state value of 6 ⋅ 1016 cm−3 was reached after a transient of about 12 s. Numerical simulation delivered ozone concentrations in good agreement with experimental data.

Escherichia coli cellular responses to exposure to atmospheric-pressure dielectric barrier discharge plasma-treated N-acetylcysteine solution.

To understand the underlying cellular mechanisms during inactivation of Escherichia coli in response to antimicrobial solution of nonthermal plasma-activated N-acetylcysteine (NAC). The recommended techniques were used to demonstrate E.coli cellular and transcriptomic changes caused associated with peroxynitrite and compared with plasma-treated NAC solution. The findings demonstrate that E.coli cells respond to plasma-treated NAC and undergo severe oxidative and nitrosative stress, and leading to stress-induced damages to different components of bacterial cells, which includes loss of membrane potential, formation of oxidized glutathione (GSSG), formation of nitrotyrosine (a known marker of nitrosative stress), DNA damage, and generated a prominent pool of peroxynitrite. Reverse-transcriptase (RT)-polymerase chain reaction analysis of reactive nitrogen species (RNS) responsive genes indicated their differential expressions. For the first time, we report that the plasma-treated NAC solution activates predominantly nitrosative stress-responsive genes in E.coli and is responsible for cell death. The reactive species generated in solutions by nonthermal plasma treatment depends on the type of solution or solvent used. The plasma-treated NAC solution rapidly inactivates E.coli, mostly involving highly RNS generated in NAC solution, and has high potential as disinfectant.

Investigation of airflow effects on the dielectric barrier discharge with single/double discharge channel arrangement

Atmospheric-pressure dielectric barrier discharge (DBD) with airflow participation has been widely used in recent years. In this paper, effects of airflow on DBD characteristics are experimentally investigated by single/double pin-to-plate DBD arrangements with an AC exciting source. The discharge electrical characteristics and the movements of discharge channels in airflow are investigated with a single pin electrode arrangement. The current intensities increase in positive cycles and decrease in negative cycles with the increase in airflow velocity. The transition from a filamentary discharge to a diffuse discharge is observed under certain airflow conditions, and the discharge channels move with the airflow with a movement velocity less than the corresponding airflow velocity. In the cases of double pin electrode arrangements, the repulsion between double pin discharge channels is apparent at a 10 mm distance but is not obvious at a 20 mm distance. When the airflow is introduced into the discharge gap, not as in the case of single pin electrode arrangement, the movements of discharge channels in airflow are affected by adjacent discharge channels. The corresponding reasons are analyzed in the paper.