Discharge Air Plasma Research Articles

The pH value control in air plasma–liquid system by sodium bicarbonate

The pH value of an aqueous solution usually decreases when treated by air discharge plasma due to the formation of HNO2 and HNO3 in solution. Herein, we found that the existence of a pH-buffer material, sodium bicarbonate (NaHCO3), can maintain or even increase the solution pH value in an air plasma–liquid system depending on the discharge conditions such as the temperature and the voltage polarity of the liquid. When acidic compounds (for instance, HNO2 and HNO3) are produced by the plasma–liquid interactions, the bicarbonate ions (HCO3) existing in the solution can combine with the produced hydrogen ions (H+) to form carbonic acid molecules (H2CO3−), resulting in the maintaining of the solution pH value. However, the formed H2CO3 might be decomposed to produce water (H2O) and carbon dioxide (CO2) by the discharge plasma-induced heat, leading to a continuous consumption of H+ ions in the solution. As the quantity of H+ ions consumed by the decomposition of H2CO3 is greater than the quantity of H+ ions produced by air discharge plasma, the solution pH value will increase.

Afterglow dielectric-barrier discharge air plasma (ADDAP) for the inactivation of Escherichia coli O157:H7

The afterglow of an atmospheric pressure plasma can conveniently be used for large scale decontamination operations. In the present study, an afterglow dielectric-barrier discharge air plasma (ADDAP) was used to inactivate Escherichia coli O157:H7, which was used as a model microorganism for studying the inactivation effect of the plasma. ADDAP was generated at different input currents in the range of 0.4–0.8 A. At all tested plasma exposure times, temperatures inside sample treatment chamber remained less than 30 °C. Regarding chemical composition of ADDAP in the treatment chamber, NOx species (NO and NO2) were predominantly observed. The levels of the NOx species increased as the current intensity increases and the maximum NO and NO2 concentrations noted were 6 and 4 ppm, respectively, but that of CO was less than 1 ppm level at 0.8 A. Upon treatment using ADDAP generated at 0.4–0.8 A for 180 min, glass-bound E. coli O157:H7 counts were reduced in the range of 1.24–2.71 log CFU/mL. The inactivation patterns exhibited better fit to the Weibull tail model. The comparison of delta values indicated that superior inactivation effects were observed as current intensity increases.

Study on Generation of Glow Discharge Plasma in Air and Surface Modification of Wool Fabric

A lamellar electrode structure is proposed to achieve the generation of a large-area plasma and the effective processing of the wool fabric with the electrode on only one side of the treated material. The lamellar electrode can form the curved electric field lines passing through the discharge air gap and the wool fabric, creating the condition for the action of plasma. Meanwhile, the micron-scale discharge air gap is constructed through the direct contact between the electrode and the treated material. Specifically, it can effectively inhibit the development of the electron avalanche, thereby achieving a through-type glow discharge in air between the electrode and the wool fabric under the strong electric field. Through the scanning electron microscope and X-ray photoelectron spectroscopy tests, it can be observed that the scales on the surface of wool fiber are effectively destroyed and the polar groups are introduced to the surface of wool fiber after the plasma treatment. Obviously, the wettability of wool fiber is greatly improved, and the wetting time is reduced from more than 1800 s to less than 0.5 s.

Interaction of a plane shock wave with an area of ionization instability of discharge plasma in air

The conducted study is devoted to the research area of control of high speed flows and shock-wave configurations. Experimental and numerical results on the interaction of a plane shock wave (M = 5–6) with the area formed by ionization instability in gas discharge plasma at a pressure of 3–7 Torr and gas-discharge current of 100–400 mA are presented. The region of ionization instability in plasma of high degree of ionization and non-equilibrium (gas temperature T ∼ 300–600 K, electron temperature Te∼5⋅103 K) has been obtained experimentally in air. This instability is characterized by spherical strata of changing shape. Two types of a shape of the ionization instability have been obtained: large-scale type and small-scale type. Also, the transitional type from large-scaled strata to low-scaled ones has been obtained. The influence of the ionization instability was established to cause the distortion of an initially plane shock wave up the complete disappearance of its front. Numerical modeling the interaction of the initially plane shock wave with ionization-unstable plasma using the Euler system of equations has been conducted. The area formed by ionization unstable plasma was modeled via a set of thermal layers with varying densities (and temperatures). Changing the physical–chemical properties of the gas medium was taken into account varying the ratio of specific heats. Layered structures with wavy shock-wave and contact discontinuity fronts have been observed. The multiple generations of shear layer instabilities and the Richtmyer–Meshkov instabilities have been obtained as the result of the interaction of a shock wave with thermal strata. It has confirmed that the shapes of the both discontinuities change acquiring an unstable character. Examples of the flow modes with the disappearance of the shock wave front causing by the origination of a structure with cellular order of shear layer instabilities have been presented. A good agreement at the qualitative level with the experimental Schlieren images has been demonstrated.

Microbial Decontamination of Onion by Corona Discharge Air Plasma during Cold Storage

Corona discharge air plasma (CDAP) is a nonthermal decontamination technology which is generating antimicrobial agents such as photons, electrons, positively and negatively charged ions, atoms, and free radicals. We investigated the effect of a corona discharge under atmospheric pressure on the sterilization of postharvest fungal pathogens on onion. The main antimicrobial reactive substance generated by CDAP was O3. The active species such as nitric oxide (NO) and nitric dioxide (NO2) were nearly detected in this experiment. CDAP treatment revealed different isolation frequencies depending on postharvest pathogens from diseased onions, showing less isolation frequency of Fusarium spp. and Alternaria sp. than that of Botrytis spp. when compared with untreatment onions during 10-month cold storage. CDAP treatment at 2∼2.6 ppm of O3 slightly stimulated the mycelial growth of Alternaria sp., while the treatment at 20∼24 ppm of O3 gradually inhibited mycelial growth by treatment time. However, Botrytis sp. showed different patterns of mycelial growth with CDAP treatment. Less than 4 hours’ treatment of CDAP slightly inhibited the mycelial growth of Botrytis sp., while 8 hours’ treatment of CDAP slightly stimulated the mycelial growth of Botrytis sp. not depending on the concentration of O3. The inhibitory effect of CDAP on the conidial germination of Alternaria sp. and Botrytis sp. was examined with treatment time and intensity of CDAP. The conidial germination of Alternaria sp. treated with CDAP at the concentration of 13.7∼14.4 ppm of O3 was strongly inhibited by time, showing y = 2.66x2 − 85.139x + 4.88 and R2 = 0.98. When the conidia of Alternaria sp. were exposed for 2 hours with varying plasma O3 concentration, the conidial germination was strongly inhibited as the concentration of O3 increases, showing y = −0.09x2 + 6.905x − 0.764 and R2 = 0.95. The conidia of Botrytis sp. also showed similar patterns to CDAP. The inhibitory effect of CDAP on the germination of postharvest pathogens depends on treatment time and O3 concentration.

Measurement of the flow field induced by a spark plasma using particle image velocimetry

We investigate the local flow field induced by a spark plasma discharge in quiescent air under atmospheric conditions. Particle image velocimetry (PIV) is used to quantify the induced flow field between two conical-shaped electrodes for three different electrode gaps: 8 mm, 5 mm and 2 mm. The results show the existence of three distinct stages of flow. In the first stage of flow, distinct coherent structures are observed near the tips of the electrodes. In the second stage, ambient fluid is entrained along the electrodes to produce axial jets in the electrode gap. The final flow stage is characterized by collision of the jets and decay of vorticity. The flow parameters are all scaled by the induced velocity behind the shock wave produced by the spark and the electrode gap distance. The scaling results in comparable magnitudes of velocity and vorticity induced in the 5 mm and 8 mm electrode gaps with the onset of each of the flow stages occurring at approximately the same time scale. The magnitude of axial velocity dominates the latter two stages of the flow. Significant correlation is found between circulation and entrainment calculated for the 5 mm and 8 mm electrode gaps at different time steps, where the decay rates of circulation and that of entrainment are found to be $$\sim 1/(t/{\tau )^{0.75}}$$ and $$\sim 1/(t/{\tau) ^{0.88}}$$ , respectively. The stages of flow development for different electrode gaps at times > 100 µs after the discharge are discussed comprehensively and the choice of scaling based on energy deposited in the electrode gap and gap distance is found to permit direct comparison of the two electrode gaps.

Effect of pressure on the properties and species production in gliding arc Ar, O2, and air discharge plasmas

A gliding arc discharge (GAD) plasma is generated inside a vacuum chamber with Ar, O2, and air at pressure 100–600 Torr driven by a 1 kHz, 3–6 kV power supply. The properties of the GAD plasma are investigated by electrical and optical emission spectroscopy methods. The power dissipation, relative intensity, jet length, rotational ( Tr) and excitational (Tex) temperatures, and electron density (ne) are studied as a function of applied voltage, pressure, and feeding gas. It is found from the electrical characteristics that the power dissipation shows decreasing trends with increasing pressure but increasing with increasing voltage. The relative population densities of the reactive species N2(C−B), O, and OH radicals produced as functions of pressure and applied voltage are investigated. It is found that the relative population densities of the species, especially N2(C−B) and O, are increased with applied voltage and pressure, while OH(A-X) is decreased. The spectroscopic diagnostics reveals that Tr≈550–850 K, Tex≈8200–10 800 K, and ne≈2.65–5.3×1014 cm−3 under different experimental conditions. Tr and ne are increased with increasing pressure, while Tex is decreased.

Study on formation mechanism of atmospheric pressure glow discharge air plasma jet

Based on the results of needle electrode discharge experiments and electric field simulations, this study proposes a tip extensional ionization theory for explaining the formation mechanism of atmospheric pressure glow discharge (APGD) plasma jets. Under the condition of DC power supply, atmospheric pressure glow discharge (APGD) air plasma jets are realized without airflow. It is found that the necessary initial electrons for discharge are derived from free electrons in space, residual electrons, or runaway electrons, and the difference of the electric field intensity between the needle electrode tip and the lateral side of the needle electrode is an essential condition for the formation of the plasma jet. It is further discovered that a space electric field with transitive change is generated in the formation process of the plasma jet, and therefore a phenomenon occurs: the plasma jet generated from the high voltage electrode exceeds the lateral ground potential electrode. This study provides a theoretical basis for the analysis of the formation mechanism of plasma jet under various discharge conditions and promotes further research such as on the formation process of the lightning leader and lightning protection.

Exploration to generate atmospheric pressure glow discharge plasma in air

Atmospheric pressure glow discharge (APGD) plasma in air has high application value. In this paper, the methods of generating APGD plasma in air are discussed, and the characteristics of dielectric barrier discharge (DBD) in non-uniform electric field are studied. It makes sure that APGD in air is formed by DBD in alternating current electric field with using the absorbing electron capacity of electret materials to provide initial electrons and to end the discharge progress. Through designing electric field to form two-dimensional space varying electric field and three-dimensional space varying electric field, the development of electron avalanches in air-gap is suppressed effectively and a large space of APGD plasma in air is generated. Further, through combining electrode structures, a large area of APGD plasma in air is generated. On the other hand, by using the method of increasing the density of initial electrons, millimeter-gap glow discharge in atmospheric pressure air is formed, and a maximum gap distance between electrodes is 8 mm. By using the APGD plasma surface treatment device composed of contact electrodes, the surface modification of high polymer materials such as aramid fiber and polyester are studied and good effect of modifications is obtained. The present paper provides references for the researchers of industrial applications of plasma.

Roles of membrane protein damage and intracellular protein damage in death of bacteria induced by atmospheric-pressure air discharge plasmas.

Although plasma sterilization has attracted much attention, the underlying mechanisms and biochemical pathways are still not fully understood. In this work, we investigate the molecular mechanism pertaining to the inactivation of Escherichia coli (E. coli) by air discharge plasmas. The membrane protein YgaP and intracellular protein swc7 are over-expressed in E. coli by genetic recombination and gene inducible expression techniques and plasma exposure is demonstrated to alter the structures of YgaP and swc7 in E. coli. The plasma-induced damage of YgaP and swc7 involves changes in the secondary and tertiary structures instead of the primary structure and the modification effectiveness depends on the storage time after the plasma treatment. Owing to the unique structure of E. coli, YgaP is more susceptible to the plasma treatment than intracellular swc7. Within 1 h after plasma exposure, YgaP is modified but not swc7, but after 1 h or longer, both YgaP and swc7 proteins are indeed modified. By analyzing the plasma-induced antimicrobial efficacy and modification of YgaP and swc7, plasma-induced modification of the membrane proteins is the major cause of bacterial death but there is no identifiable relationship with modification of the intracellular protein. The new results provide insights into the mechanism of multiple plasma-induced damage to bacteria and cells as well as the disinfection mechanism.

Numerical modelling for characteristics of the meso-pressure six-phase alternative current arc discharge plasma jet

In the re-entry process of hypersonic vehicle in near space,the violent interaction between the vehicle and the surrounding air will ionize the air and leaves a complex environment in the vicinity of the vehicle surface.Both the flow field and the communication between the vehicle and the controlling center on the earth are significantly affected by the generated plasma layers.This will result in serious system operation problems such as the communication blackout or radio blackout.Numerical modelling is one of the most widely used methods to investigate such complicated physical-chemical processes involving coupled magneto-hydrodynamics,heat transfer,dissociation,ionization,excitation and their reverse processes.Due to the strong collision,non-uniform and non-equilibrium characteristics of the plasma layers formed in the vicinity of the vehicle surface,a self-consistent physical-mathematical model,as well as a database for the transport properties of non-equilibrium plasmas,describing the non-equilibrium features of plasmas is one of the pre-requisites for numerical simulations.This paper focuses on the non-equilibrium plasmas produced near the bluff body surface in the re-entry process of hypersonic vehicles in near space,and a new non-equilibrium plasma model which has been developed previously by our group is employed for conducting two-dimensional (2D) simulations on the characteristics of the non-equilibrium argon plasma jets based on the multiphase gas discharge plasma experimental platform-2015(MPX-2015) established in our laboratory.The modelling is conducted under two different flow conditions, i.e.,the sub-sonic flow condition and the super-sonic flow condition.Under the sub-sonic flow condition,the 2D nonequilibrium modeling results are consistent well with the experimental measurements which validates the reliability of the non-equilibrium physical-mathematical model,as well as the developed computer codes in this study.The modeling results under the super-sonic flow conditions show that the spatial uniformity of the plasma layer surrounding the bluff body,as well as the total heat flux to the bluff body surface from plasmas,decreases significantly with the increase of the plasma jet velocity;while the local electron number density increases in the vicinity of the head of the bluff body, the thickness of the plasma layer surrounding the bluff body first decreases,and then increases.These modelling results provide a theoretical guidance for conducting experimental studies under a super-sonic flow condition on MPX-2015. In the future research,we will extend the physical-mathematical model to investigate of the transient,non-equilibrium features of the air discharge plasmas,and the complicated interactions between the plasma jet and the surrounding air, and/or the downstream bluff body under different operating conditions.Simultaneously,we will also try to develop the in-situ experimental methods to obtain the spatiotemporal distributions of the temperature,velocity and species concentrations in the plasma layer,and conduct a comparison between modelling results and measured data.

Sterilization by negative and positive DC plasma with a micro discharge gap at atmospheric pressure

A new needle-to-droplet electrode structure with a micro discharge gap (2 mm) was designed to achieve direct current (DC) discharge plasma in ambient air with the aim of using the plasma to sterilize liquids. Without using noble gases or an external air flow, we succeeded in generating both a negative and positive DC plasma at atmospheric pressure. The plasma was driven by a 0 to −20,000 V, 100 W DC power supply. A stainless steel needle with a tip diameter of [Formula: see text] and a 200-[Formula: see text] droplet of bacteria-containing liquid served as the electrodes. At atmospheric pressure and room temperature (23[Formula: see text]C), utilizing the negative DC plasma, the discharge time lasted 10 s; the results showed that the higher the discharge voltage, the more efficient the sterilization effect. Conversely, when we applied a voltage of −5.5 kV, we found that the sterilization effect was more efficient for longer discharge times. Our findings demonstrate that Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) can be killed in about 30 s. Our experiments show that our sterilization method required less time and was more efficient for positive than for negative DC plasma under the same conditions.

Modification of polycarbonate surface in oxidizing plasma

The properties of the surface of the film polycarbonate Lexan 8010 were experimentally studied after treatment in a DC discharge plasma in oxygen and air at pressures of 50-300 Pa and a discharge current of 80 mA. The contact angles of wetting and surface energies are measured. The topography of the surface was investigated by atomic force microscopy. The chemical composition of the surface was determined from the FT-IR spectroscopy data in the variant of total internal reflection, as well as X-ray photoelectron spectroscopy. Treatment in the oxidizing plasma leads to a change in morphology (average roughness increases), an increase in the surface energy, and the concentration of oxygen-containing groups (hydroxyl groups, carbonyl groups in ketones or aldehydes and in oxyketones) on the surface of the polymer. Possible reasons for the difference in surface properties of polymer under the action of oxygen and air plasma on it are discussed.

Influence of gas flow velocity on the transport of chemical species in an atmospheric pressure air plasma discharge

This paper reports on a numerical study of the transport of reactive chemical species generated in an atmospheric-pressure air plasma discharge under the influence of a high velocity flowing gas. Using a 1D air plasma model, it is shown that the reactive species transported downstream of the discharge region can be categorized into three distinct groups based on their spatial distribution: (i) decaying downstream species, (ii) increasing downstream species and (iii) variable density species, where the density is a function of both spatial position and gas flow velocity. It is demonstrated that the gas flow velocity influences the dominant chemical reactions downstream of the discharge region, noticeably altering the composition of several key reactive chemical species transported to a given downstream location. As many emerging applications of atmospheric pressure plasma are driven by the flux of reactive chemical species, this study highlights the importance of gas flow velocity, not only as a means to enhance mass transport but also as a means to manipulate the very nature of the reactive plasma chemistry arriving at a given location.

Optimization of atmospheric air plasma for degradation of organic dyes in wastewater.

This study optimises the degradation of a cocktail of the dyes methyl orange and bromothymol blue by atmospheric air plasma. Response surface methodology (RSM) was employed to investigate the efficacy of the plasma process parameters on degradation efficiency. A Box-Behnken design (BBD) was employed to optimise the degradation of dyes by air plasma discharge. A second order polynomial equation was proposed to predict process efficiency. It was observed that the predicted values are significant (p < 0.001) with coefficients of determination 0.98, 0.96, 0.98 for dye degradation, pH value and ozone concentration, respectively. The analysis of variance results showed that the coefficients of the polynomials for the percentage degradation and ozone concentration responses indicated positive linear effects (p < 0.001), whereas a negative linear effect was found for pH. The positive linear effect of variable emphasises that voltage and treatment time were the most dominant factors (p < 0.001), meaning that higher degradation efficiencies are achieved with an increase in treatment duration. This study showed that a BBD model and RSM could be employed to optimize the colour degradation parameters of non-thermal plasma treated model dyes while minimising the number of experiments required.

Enhanced accumulation of U(VI) by Aspergillus oryzae mutant generated by dielectric barrier discharge air plasma

Aspergillus oryzae was isolated from radionuclides’ contaminated soils, and dielectric barrier discharge plasma was used to mutate A. oryzae to improve bioremediation capability of U(VI) pollution. The maximum accumulation capacities of U(VI) on mutated A.oryzae was 627.4 mg/g at T = 298 K and pH = 5.5, which was approximately twice than that of raw A.oryzae. XPS analysis indicated that U(VI) accumulation on mutated A. oryzae was largely attributable to nitrogen- and oxygen-containing functional groups on fungal mycelia. The mutated A. oryzae can be harnessed as bioremediation agents for radionuclides pollution.

Modeling of the chemical composition of DC atmospheric pressure air discharge plasma in contact with aqueous solutions of sodium dodecylbenzenesulfonate

The results of calculation of the chemical composition of plasma of the DC atmospheric pressure discharge in air in contact with aqueous solutions of sulfonol (C12H25C6H4SO3Na) in the concentration range of 0–10 g/L at a discharge current of 40 mA are presented. At modeling, the combined solution of Boltzmann equation for the electron gas, equations of vibrational kinetics for ground states of N2, O2, H2O, and NO molecules, equations of chemical kinetics and plasma conductivity equation were used. It was shown that sodium atoms appearing as a result of transfer processes from the liquid cathode affect the chemical composition of the plasma and the characteristics of the electron gas.

The effect of humidity on hydroxyl and ozone production by nanosecond discharges

The interplay of humidity and non-equilibrium, transient plasma was studied via ignition experiments in a C2H4–air mixture, concentration measurements in humid air, and detailed simulations. Hydroxyl (OH) and ozone (O3) produced via non-equilibrium plasma were characterized in a flowing H2O–air mixture at atmospheric pressure with varying the levels of humidity using planar laser-induced fluorescence (PLIF) and UV absorption, respectively. The OH, which was created in the discharge streamers, peaked at a concentration of ∼5×1014/cm3 and then decayed below 1×1014/cm3 after ∼100µs. O3, which is long lived, peaked at a concentration of 1.4×1015/cm3. An increase in humidity from XH2O≈0.2% to 1% resulted in a monotonic increase in the concentration of OH and a 67% decrease in that of O3. Zero-dimensional Boltzmann modeling of non-equilibrium plasma discharges in humid air showed qualitative agreement with these results and points to the decrease in O concentration (with increasing humidity) as the reason for the decreased O3 concentration. In spite the dramatic decline in XO3 with increased humidity, there was no strong commensurate effect on ignition and flame propagation in C2H4–air mixtures: Peak pressure rise rate was at its maximum value at XH2O=1% but was only 25% less at XH2O=5%.

Long-Time Stability of Catalytic Coatings on the Basis of Nanoporous TiO2 under the Influence of Corona Discharge Plasma in Air

ABSTRACTThe present paper contains results of the experimental researches of structure properties of the catalytic coating based on the nanoporous TiO2 film affected by corona-discharge plasma in air atmosphere under atmospheric pressure in the test system of needle-plane electrodes. Coating of the plate electrode was found to influence insignificantly on the discharge current-voltage characteristic, however if there is a coating on the plane electrode surface, an offset is observed towards lower currents under constant voltage at the gap. Obtained data on the surface morphology change shows that under negative corona erosion of the nanoporous TiO2 coating surface is practically absent and under positive corona, decrease of the coating thickness is observed.

Redox processes induced in methemoglobin solution by mercury lamp UV light and spark-discharge plasma radiation

The buildup of–SH groups in methemoglobin by irradiation with emission of spark discharge plasma in air and UV light from a low-pressure mercury lamp (λ = 253.7 nm) has been studied. The concentration of–SH groups increases the during spark discharge treatment, with the methionine amino acid residue in the methemoglobin molecule being reduced by nitrous and peroxynitrous acids; the bonds in the methemoglobin molecule are destroyed within 20 minutes of the spark treatment. By the action of UV radiation, methionine is reduced through chromophores (tryptophan, tyrosine) and methemoglobin is reduced by O2.- radical ions to oxy- and deoxyhemoglobin.