Electrical Discharge Plasma Research Articles

Waste Foundry Sand/Bauxite Residue for Enhanced NO<italic>x</italic> Reduction in Diesel Exhaust Pretreated With Plasma/O3 Injection

The increased usage of diesel fuel of late has led the researchers to pay more attention toward abatement of increased emission of oxides of nitrogen (NOx) in the engine exhaust. The focus is, therefore, lies in providing a technique that is economical, feasible, and long lasting. The combination of electric discharge plasma with adsorbent/catalyst derived out of solid waste can be one such possible technique. In this paper, waste foundry sand from foundry industry and red mud or bauxite residue from aluminum industry have been used. Diesel engine exhaust under dry condition was exposed to an oxidizing discharge plasma environment. The plasma-treated exhaust was subjected to either adsorption over waste foundry sand or catalysis over red mud. Studies were carried out in the laboratory environment with 20% loading of diesel generator. The oxidizing plasma environment was either with direct plasma or with indirect plasma in which case ozone injection into the exhaust was accomplished. The ozone-adsorbent cascading system has resulted in about 87% NOx reduction in the dry exhaust case. The effect of O3:NO ratio was discussed from the point of NO/NO2.

Analyzing wire deflection errors of WEDM process on small arced corners

Wire electrical discharge machining (WEDM) is an advanced machining process capable of precise machining of parts with complicated shapes. Machining inaccuracy at small arced corners is a major problem of WEDM process. It is aimed to develop a novel mathematical methodology validated by experimental data for analyzing the wire deflection and evaluating total machining errors of arced corners during the WEDM process. The maximum spark gap, spark angle around the wire, spark forces applied to the wire and the resulting deflection are mathematically described based on the nature of the electrical discharge process and plasma channel properties to clarify the causes of wire deflection error in the small arced corners. The influence of the driving WEDM parameters, including discharge frequency and wire tension, are theoretically and experimentally studied in regard to the wire deflection and total machining errors for various experimental sets. Finally, the estimated wire deflection and total machining errors are compared and evaluated. The results indicate that wire deflection error is one of the major causes of machining errors in the arced corners; this error is almost 57% of the total machining error. In addition, the effect of wire vibration and excitation of discharges on the total machining errors are mentioned. According to the results, it is concluded that the proposed theoretical formulations can be used for prediction and compensation of wire deflection errors in the arced corner machining.

Electric field in Ns pulse and AC electric discharges in a hydrogen diffusion flame

Time-resolved electric field is measured in ns pulse and AC sine wave dielectric barrier discharges sustained in an atmospheric pressure hydrogen diffusion flame, using picosecond second harmonic generation. Individual electric field vector components are isolated by measuring the second harmonic signals with different polarizations. Electric field measurements in a ns pulse discharge are self-calibrating, since the field follows the applied voltage until breakdown. Electric field is measured in a ns pulse discharge sustained both in the hydrogen flow below the flame and in the reaction zone of the flame. Peak electric field in the reaction zone is lower compared to that in the near-room temperature hydrogen flow, due to a significantly lower number density. In hydrogen, most of the energy is coupled to the plasma at the reduced electric field of E/N ≈ 50–100 Td. In both cases, the electric field decreases to near zero after breakdown, due to plasma self-shielding. The time scale for the electric field reduction in the plasma is relatively long, several tens of ns, indicating that it may be controlled by a relatively slow propagation of the ionization wave over the dielectric surfaces. In the AC discharge, the electric field is put on the absolute scale by measuring a Laplacian electric field between two parallel cylinder electrodes. The measurement results demonstrate that a strong electric field in the plasma-enhanced flame is produced during the entire AC voltage period, without correlation with the random micro-discharges detected in the plasma images. The measurement results indicate consistently higher peak electric field during the negative AC half-period, as well as a significant electric field offset. Both the asymmetry and the offset of the electric field are likely responsible for the ion wind resulting in the flame distortion. The results suggest that at the present conditions the ion wind is dominated by the transport of negative ions generated in the ambient air plasma near the flame. The results demonstrate a significant potential of ps second harmonic generation diagnostics for non-intrusive measurements of the electric field in atmospheric pressure flames enhanced by electric discharge plasmas.

Modeling of formation of carbon cluster groups in electric arc discharge plasma

The problem of modeling complex resource-intensive processes of plasma synthesis of carbon nanostructures (CNS) on the basis of mathematical and numerical methods of solution, focused on the use of parallel and distributed computing for processing large amounts of data, allowing to investigate the relationship and characteristics of processes to obtain an effective, cost-effective method of synthesis of CNS (fullerenes, nanotubes), is an actual theoretical and practical problem. This article deals with the problem of mathematical modeling of motion and interaction of charged particles in a multicomponent plasma based on the Boltzmann equation for the synthesis of ONS by thermal sublimation of graphite. The derivation of the collision integral is presented allowing to perform a numerical solution of the Boltzmann - Maxwell equations system with respect to the arc synthesis of CNS. The high order of particles and the number of their interactions involved simultaneously in the process of synthesis of CNS requires significant costs of machine resources and time to perform numerical calculations on the constructed model. Application of the large particle method makes it possible to reduce the amount of computing and hardware requirements without affecting the accuracy of numerical calculations. The use of parallel computing technology on the CPU and GPU with the use of Nvidia CUDA technology allows you to organize all the General-purpose calculations for the developed model based on the graphics processor of the personal computer graphics card, without the use of supercomputers or computing clusters. The results of experimental studies and numerical calculations confirming the adequacy of the developed model are presented. Obtained quantitative characteristics of the total pairwise interactions between the carbon particles and interactions with the formation of clusters of carbon with various types of ties in the plasma of the interelectrode space which are the basis of the synthesized nanostructures. The formation of carbon clusters occurs in the entire interelectrode space of the plasma with different intensity and depends on the process parameters.

Electrical glow discharges and plasma parameter of planar sputtering system for silver target

DC planar sputtering system is characterized by varying discharge potential of (250-2000 volt) and Argon gas pressures of (3.5×10-2 – 1.5) mbar. The breakdown voltage for silver electrode was studied with a uniform electric field at different discharge distances, as well as plasma parameters. The breakdown voltage is a product of the Argon gas pressure inside the chamber and gab distance between the electrodes, represent as Paschen curve. The Current-voltage characteristics curves indicate that the electrical discharge plasma is working in the abnormal glow region. Plasma parameters were found from the current-voltage characteristics of a single probe positioned at the inter-cathode space. Typical values of the electron temperature and the electron density are in the range of (2.93 –5.3) eV and (10-16 -10-17) m-3 respectively.

Antimicrobial Treatment of Escherichia coli and Staphylococcus aureus in Herbal Tea Using Low-Temperature Plasma

A low-pressure capacitively coupled discharge was used to study antimicrobial treatment in herbal tea. Ambient air with a relative humidity of 40% was used as a precursor gas and fed into the chamber via a perforated power electrode. An electrical discharge plasma was produced at a radio frequency of 10 kHz and power of 80 W. The operating pressure during treatment was kept constant at 260 Pa. The target microorganisms, Escherichia coli and Staphylococcus aureus, isolated from the herbal tea were inoculated on nutrient agar petri dishes and exposed to the plasma for 0.5, 1.0, 1.5, and 2.0 min. All treatments were carried out in triplicate for different exposure times to calculate the D-value by the enumeration method. D-values of 0.73 and 0.67 min were obtained corresponding to E. coli and S. aureus reduction, respectively.

The UV-C radiation mechanism to form HO2• radicals from water

The formation of chemically active particles in distilled water via continuous and pulsed light radiation was investigated. The source of the continuous radiation was a DKB-9 UV mercury low pressure lamp (λ = 253.7 nm). Upon UV lamp irradiation of water, hydrogen peroxide was formed in a yield of (1 ± 0.2) 10−7 mol (L s)−1. The pulsed radiation source was the plasma of a spark electric discharge in air with a continuous radiation spectrum and a weak maximum at λ = 220 nm. The radiation affected the water through quartz glass. In this case, nitrous and nitric acids formed in the water, but no accumulation of hydrogen peroxide was detected. The formation of the active products can be explained by the interaction of exited water molecules that formed due to the radiation. The energy threshold for the formation of hydrogen peroxide corresponds to a radiation wavelength of less than 1220 nm. To directly identify HO2• radicals, we studied redox reactions in solutions containing Fe2+, Fe3+ and I− ions at pH values from 0.8 to 8.1. The quantum yield of HO2• radicals in an acidic medium under the action of the mercury lamp radiation was 0.015 ± 0.005.

Cytotoxicity against cancer cells of chitosan oligosaccharides prepared from chitosan powder degraded by electrical discharge plasma

Chitosan oligosaccharides, which obtain from degradation of chitosan, possess some interesting molecular weight-dependent biological properties, especially anticancer activity. Therefore, the conversion of chitosan to chitosan oligosaccharides with specific molecular weight has been continuously investigated in order to find effective strategies that can achieve both economic feasibility and environmental concerns. In this study, a novel process was developed to heterogeneously degrade chitosan powder by highly active species generated by electrical discharge plasma in a dilute salt solution (0.02 M) without the addition of other chemicals. The degradation rate obtained from the proposed process was comparable to that obtained from some other methods with the addition of acids and oxidizing agents. Separation of the water-soluble degraded products containing chitosan oligosaccharides from the reaction solution was simply done by filtration. The obtained chitosan oligosaccharides were further evaluated for an influence of their molecular weights on cytotoxicity against cancer cells and the selectivity toward cancer and normal cells.

Quantitative microbial assessment for Escherichia coli after treatment by high voltage gas phase plasma

High voltage electrical discharge (gas and liquid) plasmas are new developing techniques used for food and water decontamination. This study investigates the influence of high voltage gas phase plasma treatment on several parameters: inactivation of Escherichia coli K12, recovery, proteomic analyses, cellular leakage and influence of pH and generated H2O2 species on inactivation of the E. coli cells. Samples were treated in a glass reactor with a point-to-plate electrode configuration. Electrical conductivity (100 and 800 μS/cm), polarity (+/−), time (5 and 10 min) and frequency (60, 90 and 120 Hz) were chosen in order to determine their influence on listed parameters. Statistical analyses were obtained to optimize conducted treatments. Treatment regime of 90 Hz, positive polarity, 100 μS/cm and 10 min resulted in the highest reduction (7.8 log10 CFU/mL) of E. coli. Recovery of cells after the treatment suggested oxidative stress overcome. Plasma processing is an energy effective process, comparing to traditional thermal processes like pasteurization and sterilization. Plasma treated liquid remains at low temperature, which lowers electrical energy consumption during industrial processes. The proposed study investigates the possible application of high voltage gas phase electrical discharge plasmas for inactivation of Escherichia coli K12 MG1655 in water. The main aim was to confirm effectiveness of plasma treatment conducted in argon (which is uninfected by plasma and can be recycled) on inactivation and cell recovery of E. coli K12. This research is a first step towards the development of the gas phase plasma technology for disinfection of liquids. However, future development, optimization and application of this technology for food sterilization will lead to acceptable ecological regulations like lowering greenhouse gas emissions.

Electrical and thermal characterization of near-surface electrical discharge plasma actuation driven by radio frequency voltage at low pressure**Project supported by the National Natural Science Foundation of China (Grant Nos. 11472306, 51407197, and 51507187).

The electrical and thermal characterization of near-surface electrical discharge plasma driven by radio frequency voltage are investigated experimentally in this paper. The influences of operating pressure, electrode distance, and duty cycle on the discharge are studied. When pressure reaches 60 Torr (1 Torr = 1.33322 × 102 Pa) the transition from diffuse glow mode to constricted mode occurs. With the operating pressure varying from 10 Torr to 60 Torr, the discharge energy calculated from the charge–voltage (Q–V) Lissajous figure decreases rapidly, while it remains unchanged between 60 Torr and 460 Torr. Under certain experimental conditions, there exists an optimized electrode distance (8 mm). As the duty cycle of applied voltage increases, the voltage–current waveforms and Q–V Lissajous figures show no distinct changes.

Generation of Craze-Formation Centers in Polymer Films under the Action of Electric Discharge Plasma

We propose a technology for generating craze-formation centers in polymers under the action of the electric discharge plasma and consider questions associated with a method for varying the geometrical sizes of crazes. The possibility of obtaining nanostructured polymers are also considered.

Special issue: Plasma and Liquids

Special issue: Plasma and Liquids

An Experimental Investigation of the Liquid Flow Induced by a Pulsed Electrical Discharge Plasma

In this work, particle image velocimetry has been used to visualize and quantify plasma-induced flow fields in liquid water. Experiments were performed in a rod-plane plasma reactor with a thin wire electrode suspended above the surface of the liquid in argon gas and a grounded plate immersed in the liquid. The velocity field has been quantified for two types of solutions: (1) aqueous NaCl solutions of varying solution conductivities and discharge frequencies and (2) aqueous NaCl solutions containing varying concentrations of the following four organic compounds: rhodamine B dye, caffeine, fluoxetine, and perfluorooctanoic acid. Results show that in neat water and aqueous caffeine solutions, the liquid is “pulled” along by the interaction of the gas molecules with the liquid molecules at the free surface and thus the direction of the liquid flow is in the direction of the gas phase flow (i.e., away from the discharge location). However, the flow was reversed (i.e., towards the discharge) for those solutions with strong surfactants such as perfluorooctanoic acid. The magnitude of the reversal depended on the initial concentration of the compound and for some compounds as time progressed the reversed flow pattern weakened and then reverted to a normal flow pattern. To determine the most likely cause of these flow reversals, a simple numerical model of the velocity field was developed to estimate relative contributions of various flow inducing mechanisms. The model indicates that in the presence of surfactants, Marangoni stresses are responsible for inducing the flow in the liquid.

Reactive cold plasma particles generate oxidative stress in yeast but do not trigger apoptosis.

Interactions of living cells with cold plasma of electrical discharges affect cell physiology, often resulting in the loss of viability. However, the mechanisms involved in cell killing are poorly understood, and dissection of cellular pathways or structures affected by plasma using simple eukaryotic models is needed. Using selected genetic mutants of yeast (Saccharomyces cerevisiae), we investigated the role of oxidative stress and yeast apoptosis in plasma-induced cell killing. Increased sensitivity of yeast strains deficient in superoxide dismutases indicated that reactive oxygen species generated in the plasma are among the most prominent factors involved in killing of yeast cells. In mutant strains with a deletion of the key components of yeast apoptotic pathway, the sensitivity of cells towards the plasma treatment remained unaffected. Yeast apoptosis, thus, does not appear to play a significant role in plasma-induced cell killing of yeast.

Fundamental Investigation of EDM Plasmas, Part I: A Comparison between Electric Discharges in Gaseous and Liquid Dielectric Media

Electric discharge machining (EDM) in liquid dielectric media is a well-stablished manufacturing process. Dry EDM (DEDM) has been proposed as an environmentally friendlier alternative to the EDM process in oil dielectric. The working principles of EDM and DEDM are based on interactions of electric discharge plasmas with electrodes materials, which is a poorly understood phenomenon. Therefore, optimization of EDM processes is still based on empirical methods and recipes. The investigation performed in the present work uses a collisional-radiative (CR) model for advanced optical emission spectroscopy interpretation of EDM plasmas performed in oil and air as dielectric media. This analysis is additionally supported by electrical parameter and high-speed imaging measurements. These applied plasma diagnostics allow, for the first time, a detailed comparison of EDM discharge plasmas in very different dielectric media. Emission spectra simulated by the CR model give indications on several EDM discharge properties, such as density of electrons, fraction of different ionic states and plasma composition. The emission spectra simulations indicate that EDM discharges performed in oil and air have very similar electron temperatures, while the electron densities are substantially different. In addition, the fraction of EDM plasma components is estimated quantitatively, indicating that plasmas in air are mostly composed of the electrodes materials, whereas EDM plasmas in oil are dominated by species originated from the dielectric medium.

On the Electret Effect in Polymer–Ferroelectric Piezoceramic Composites with Various Values of the Electronegativity of the Polymer Matrix and Piezophase Cations

The influence of the electronegativity of phases, which is controlled by composite crystallization under the conditions of the effect of the electric discharge and covalence of piezophase cations, on the formation mechanism of the stable electret effect is determined. The specific features of the formation of the electret effect in composites based on polyolefins (HDPE, PP), fluorine-containing polymers (F42), and ferroelectric piezoelectric ceramics of the family of lead zirconate–titanate (Pb(Zr,Ti)O3) crystallized under conditions of the effect of electric discharge plasma, are revealed. A physical model of electret composites taking into account the role of homocharges and heterocharges formed in a composite by its dispersion with piezoceramic particles of various structures—rhombohedral, tetragonal, and heterogeneous—is proposed.

Электретный эффект в композитах полимер-сегнетопьезокерамика с различной электроотрицательностью полимерной матрицы и катионов пьезофазы

AbstractThe influence of the electronegativity of phases, which is controlled by composite crystallization under the conditions of the effect of the electric discharge and covalence of piezophase cations, on the formation mechanism of the stable electret effect is determined. The specific features of the formation of the electret effect in composites based on polyolefins (HDPE, PP), fluorine-containing polymers (F42), and ferroelectric piezoelectric ceramics of the family of lead zirconate–titanate (Pb(Zr,Ti)O_3) crystallized under conditions of the effect of electric discharge plasma, are revealed. A physical model of electret composites taking into account the role of homocharges and heterocharges formed in a composite by its dispersion with piezoceramic particles of various structures—rhombohedral, tetragonal, and heterogeneous—is proposed.

Application of high voltage electrical discharge plasma for the inactivation of Escherichia coli ATCC 700891 in tangerine juice

A tangerine juice inoculated with Escherichia coli ATCC 700891 was treated using direct-in-liquid electrical discharge plasma. The reactor system used a point-plane electrode configuration with both a high voltage electrode and a grounded electrode submerged in the juice. The effectiveness of the treatment was assessed at different applied voltages (17–30 kV), discharge frequencies (20–80 Hz) and temperatures (15–35 °C). At optimum operational parameters (30 kV, 40 Hz, and 25 °C), E. coli was reduced by 4.8 Log10 CFU/mL after a plasma exposure of 2 min and below the detection limit of >1 Log10 CFU/mL within 3 min. Scanning electron microscopy (SEM) revealed changes in cell morphology following the treatment suggesting that E. coli might be inactivated by cell wall damage caused by shock waves produced by the plasma. Physicochemical characteristics of the tangerine juice were not altered by the plasma treatment when compared to the untreated tangerine juice. In contrast, there were significant changes observed in total acidity, ascorbic acid and total phenol content in pasteurized tangerine juice. The results obtained in this study promote the further development of this technology for the inactivation of foodborne pathogens and extended shelf-life of fruit-based beverages.

The impact of high voltage electrical discharge plasma on the chromatic characteristics and phenolic composition of red and white wines

Abstract The cold plasma is an emerging electrotechnology for the improvement of food safety without loss of physicochemical or sensory properties. The purpose of this study was to evaluate the effects of plasma treatments on the chromatic characteristics and phenolic composition of red and white wines. The red wine Cabernet Sauvignon and white wine Grasevina were treated with high voltage electrical discharge plasma considering the variations in frequency (60, 90 and 120 Hz) and processing time (3, 5 and 10 min). Total phenolics, total anthocyanins, total tannins and chromatic characteristics were analyzed by spectrophotometry while free anthocyanins, phenolic acids and flavan-3-ols by the HPLC-UV/Vis. Obtained results illustrated that plasma treatments have influenced the stability of phenolic compounds in wines without major changes in color parameters. Also, among two different processing parameters, the duration time was the most significant factor inducing changes on wines. Industrial relevance High voltage electrical discharge plasma has been shown to affect the stability of wine phenols without any significant change in the color. An increase in the concentration of certain phenolic compounds in white wine suggest that this technique could be used in the wine industry as an alternative technique for enhancing the oxidative stability of wine and consequently the wine quality during the aging process.

Detailed Investigation of the Electric Discharge Plasma between Copper Electrodes Immersed into Water

A phenomenological picture of pulsed electrical discharge in water is produced by combining electrical, spectroscopic, and imaging methods. The discharge is generated by applying ~350 μs long 100 to 220 V pulses (values of current from 400 to 1000 A, respectively) between the point-to-point copper electrodes submerged into the non-purified tap water. Plasma channel and gas bubble occur between the tips of the electrodes, which are initially in contact with each other. The study includes detailed experimental investigation of plasma parameters of such discharge using the correlation between time-resolved high-speed imaging, electrical characteristics, and optical emission spectroscopic data. Radial distributions of the electron density of plasma is estimated from the analysis of profiles and widths of registered Hα and Hβ hydrogen lines, and Cu I 515.3 nm line, exposed to the Stark mechanism of spectral lines’ broadening. Estimations of the electrodes’ erosion rate and bubbles’ size depending on the electrical input parameters of the circuit are presented. Experimental results of this work may be valuable for the advancement of modeling and the theoretical understanding of the pulse electric discharges in water.