Pressure Glow Discharge Research Articles

Correlation between temperature distribution and changes in self-organized luminous pattern in an atmospheric pressure DC glow discharge with sheath gas flow

Abstract The self-organized luminous patterns observed above the anode surface in atmospheric-pressure DC glow discharges were changed by the composition of the gas flow. The patterns were observed not only with liquid anodes but also with metal anodes. Various pattern structures were observed by changing the helium gas flow rate in the core and the ambient oxygen gas flow rate supplied during the discharge. When the pattern formation was observed, the emission spectra and the radial spread of the positive column changed, and the voltage–current characteristic also changed. These results suggest that not only the anode surface but the entire discharge affects the pattern formation. Comparing the results for the liquid and metal anodes, the trends in the pattern formation and voltage–current characteristics were almost identical. The gas temperature in the discharge was also investigated in two different ways, by the laser-induced fluorescence spectroscopy of OH radicals and by Rayleigh scattering, showing in good agreement between both methods. Under the condition where the pattern formed, the gas temperature in the discharge was approximately 2500–3000 K and higher than that of the discharge without the pattern formation. Focusing on the gradient of the temperature distribution, the discharge with the pattern formation had a steeper gradient than that of the discharge without the pattern formation. It is suggested that not only the high temperature of the discharge but also the large gradient of the temperature change plays an important role in the pattern formation. The role of oxygen gas in the pattern formation may be the effect of increasing the temperature and altering the temperature gradient in the discharge rather than generating negative ions in the discharge.

Complex dynamics in an atmospheric pressure glow discharge in helium: transition from stationary to periodic oscillatory, and fully chaotic states

Abstract This work deals with the numerical study of spontaneous temporal oscillations in an atmospheric pressure glow discharge (APGD) in helium. The transition of helium APGD from stationary to periodic oscillatory state through the Hopf bifurcation, and further from periodic to chaotic oscillations through period-doubling bifurcations is explored. The choice of the discharge and external electric circuits parameters is guided by the relevant experiments. The ballast resistance and supply voltage of the external circuit play the role of control parameters. The method is based on the stability analysis of stationary states of the discharge. 

The stability diagram predicting parameter regimes at which stable and oscillatory states of the APGD can be expected is obtained. The effects of the discharge parameters (such as the gas gap, secondary electron emission coefficients, and capacitance in the external electric circuit) on the bifurcation curves are identified. 

The Lorenz map and corresponding period-doubling bifurcation diagram characterizing transition to chaotic oscillations in helium APGD with an increase in the control parameter are derived. The value of the capacitance in the external circuit plays a critical role in the dynamical behavior of the discharge. Decreasing its value contributes to the dissipation/damping of the system, whereas increasing it enhances the irregular behavior of the system.

Evaluation of atmospheric-plasma-source absorption mode Fourier transform Orbitrap mass spectrometry for chlorinated paraffin mixtures

Chlorinated paraffins (CP) are complex molecular mixtures occurring in a wide range of isomers and homologs of environmental hazards, whose analytical complexity demand advanced mass spectrometry (MS) methods for their characterization. The reported formation of chlorinated olefins (COs) and other transformation products during CP biotransformation and degradation can alter the MS analysis, increasing the high resolution required to distinguish CPs from their degradation products. An advanced setup hyphenating a plasma ionization source and an external high-performance data acquisition and processing system to the legacy hybrid LTQ Orbitrap XL mass spectrometer is reported. First, the study demonstrated the versatility of a liquid sampling atmospheric pressure glow discharge, as a soft ionization technique, for CP analysis. Second, enhanced resolution and sensitivity provided by the absorption mode Fourier transform spectral representation on this legacy mass spectrometer are shown. The developed Orbitrap-based platform allowed the detection of new isotopic clusters and CPs and COs to be distinguished at medium resolution (setting 30,000 at m/z 400, ~ 400 ms transients), and even chlorinated di-olefins (CdiOs) at higher resolution (setting 100,000 at m/z 400, ~ 1500 ms transients). Overall, such proof-of-principle instrumental improvements are promising for environmental and analytical research in the field of CP analysis.Graphical

Application of a pm-rf-APGD-type plasma brush for deactivation of antibiotics from liquid solutions leads to impaired development of drug resistance by bacterial pathogens

The presence of antibiotics residuals in the natural environment contributes to development and spread of drug resistance determinants among bacteria, often including clinically significant human pathogens. To tackle with this threat, we constructed a plasma brush, generating pulse-modulated radio-frequency atmospheric pressure glow discharge (pm-rf-APGD), named pm-rf-APGD-type plasma brush, intended for degradation of biologically active pharmaceuticals from both single- and five-component solutions of ciprofloxacin (CFX), enrofloxacin (EFX), ofloxacin (OFX), doxycycline (DXC), and trimethoprim (TMP). The mean antibiotics removal efficiency, achieved mainly due to the action of reactive oxygen species (ROS), was 93.3 %. This removal efficiency corresponded to a mean 62.7% decrease in the antibacterial activities. We revealed the transformation products resulting from an oxygen attack and/or internal fragmentation of the treated pharmaceuticals. Based on a laboratory evolution study, bacterial exposure to the pm-rf-APGD-treated drug lead to significantly lower rates of antibiotic resistance development in juxtaposition with a long-term exposure to the sublethal dose of the active molecules. Thus, we anticipate a great potential of high-throughput, continuous flow, eco-friendly pm-rf-APGD-type plasma brush for routine decontamination processes in the future disposal pipelines of pharmaceuticals-containing wastewaters.

Coupled multi-dimensional modelling of warm plasmas: Application and validation for an atmospheric pressure glow discharge in CO2/CH4/O2

To support experimental research into gas conversion by warm plasmas, models should be developed to explain the experimental observations. These models need to describe all physical and chemical plasma properties in a coupled way. In this paper, we present a modelling approach to solve the complete set of assumed relevant equations, including gas flow, heat balance and species transport, coupled with a rather extensive chemistry set, consisting of 21 species, obtained by reduction of a more detailed chemistry set, consisting of 41 species. We apply this model to study the combined CO2 and CH4 conversion in the presence of O2, in a direct current atmospheric pressure glow discharge. Our model can predict the experimental trends, and can explain why higher O2 fractions result in higher CH4 conversion, namely due to the higher gas temperature, rather than just by additional chemical reactions. Indeed, our model predicts that when more O2 is added, the energy required to reach any set temperature (i.e., the enthalpy) drops, allowing the system to reach higher temperatures with similar amounts of energy. This is in turn related to the higher H2O fraction and lower H2 fraction formed in the plasma, as demonstrated by our model. Altogether, our new self-consistent model can capture the main physics and chemistry occurring in this warm plasma, which is an important step towards predictive modelling for plasma-based gas conversion.

Multiparameter optimization of non-thermal plasma-driven synthesis of carbohydrate-stabilized rhenium nanoparticles towards enhancement of their catalytical activity for reduction of nitroaromatic compounds

This study aims to optimize the synthesis of carbohydrate-stabilized rhenium nanoparticles (ReNPs) utilizing cold atmospheric pressure plasma (CAPP), specifically direct current atmospheric pressure glow discharge (dc-APGD), hypothesizing that controlling synthesis parameters will enhance catalytic efficiency in the reduction of nitroaromatic compounds (NACs). The dc-APGD system operated in flowing liquid cathode (FLC-dc-APGD) and flowing liquid anode (FLA-dc-APGD) modes. Design of experiments (DOE) and response surface methodology (RSM) were employed for the first time to optimize ReNPs synthesis by adjustment of the concentration of ReO4- in ReNPs precursor solution, its flow rate, as well as the discharge current. ReNPs were characterized using high-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), and X-Ray photoelectron spectroscopy (XPS). In turn, optical emission spectroscopy (OES) was employed for the identification of reactive species generated in the plasma phase that contributed to the synthesis of ReNPs. The resultant sizes, surface charges, and phase compositions were linked with synthesis parameters and then with catalytic activities revealed by the variety of ReNPs. HRTEM photomicrographs showed spherical and spherical-like morphologies of the obtained ReNPs synthesized using FLC-dc-APGD and FLA-dc-APGD modes with the actual sizes of 7.28 ± 2.90 nm and 3.24 ± 0.57 nm, respectively. The optimized conditions yielded ReNPs of exceptional catalytic activity, that reduced 94.9 % (FLC-dc-APGD) and 90.5 % (FLA-dc-APGD) of 4-nitrophenol (4-NP) with the apparent rate constants (k1) 0.269 and 0.107 min−1, respectively. Further, the conversions of 90 % were achieved over FLC-dc-APGD-based ReNPs for nitrobenzene (NB), 2,4,6-trinitrophenol (2,4,6-TNP), 2,4-dinitrophenol (2,4-DNP), and 4-nitroaniline (4-NA). In these cases, the k1 values were 0.235, 0.174, 0.070, 0.001 min−1, respectively. The results allowed to find a correlation between ReNP size distribution, oxidation state, and catalytic activity that suggested a potential for tailored Re nanocatalysts in environmental remediation.

A novel atmospheric pressure glow discharge system for sensitive determination of As, Sb, and Se by optical emission spectrometry following their hydride generation

Hydride generation (HG) was combined with an atmospheric pressure glow discharge (APGD), sustained in a completely novel system, to sensitively determine As, Sb, and Se by optical emission spectrometry (OES). The carrier gas with the analyte hydrides produced by chemical HG together with co-generated H2 was introduced into the APGD system, where atomization and excitation processes took place. It was revealed that the essential factors responsible for the high stability of the plasma were its operating with He discharge gas (instead of Ar), operating the gas nozzle (used to introduce carrier He) as a cathode, and forcing the cathode spot to cover most of the surface of the gas nozzle. Under optimized operating conditions, the measurement repeatability was 2–3%, proving the high stability of the HG-APGD system. The detection limits (DLs) of As, Sb, and Se were 0.6, 0.14, and 1.2 μg L−1, respectively, and compared to those previously reported for HG-APGD with liquid electrodes, the DLs were improved over 3 times. In addition to improved DLs, the novel system offered a simplified and more compact design. The accuracy of HG-APGD OES was verified using a recovery test and proved by high agreement between spiked and measured concentrations of As, Sb, and Se in mineral and tap water samples, reaching recoveries within the range of 96–103%.

Effect of the cathode surface temperature on the cathode fall layer parameters: experiment and simulation

Combined experimental and numerical studies reveal a significant effect of the cathode temperature on the basic parameters (such as the electric field profile, thickness of the cathode fall layer, current density, and gas temperature) of the cathode fall of the self-sustained normal direct current atmospheric pressure glow discharge (APGD) in helium. Numerical models are spatially one- and two-dimensional and based on drift-diffusion theory of gas discharges. It was observed that heating of the cathode, resulting from a flow of the discharge current in APGD with a constricted positive column, leads to an increase of the interelectrode voltage if the cathode is not cooled and its temperature increases. With additional heating of the cathode by an external heat source, the interelectrode voltage tends to decrease. Radially inhomogeneous profiles of the reduced electric field on the uncooled cathode surface were measured. Simulation results exhibit reasonably good agreement with experiment for APGDs with cooled and uncooled cathodes.

Ultra-sensitive determination of mercury in flue gas by atmospheric pressure glow discharge atomic emission spectrometry coupled with gold amalgam enrichment

In this work, a highly sensitive procedure for the determination of mercury in flue gas was developed, based on direct-current atmospheric pressure glow discharge in hydrogen and helium (H2-He) atomic...

Physics-informed neural networks based on source term decoupled and its application in discharge plasma simulation

In recent years, the artificial intelligence computing paradigm represented by physics-informed neural networks (PINNs) has received great attention in the field of plasma numerical simulation. However, the plasma chemical system considered in related research is relatively simplified, and the research on solving the more complex multi-particle low-temperature fluid model based on PINNs is still blank. In more complex chemical systems, the coupling relationship between particle densities and between particle densities and mean electron energy become more intricate. Therefore, the applicability of PINNs in dealing with sophisticated reaction systems needs further exploring and improving. In this work, we propose a general PINN framework (source term decoupled PINNs, Std-PINNs) for solving multi-particle low-temperature plasma fluid model. By introducing equivalent positive ions and replacing each particle transport equation with the current continuity equation as a physical constraint, Std-PINN splits the entire solution process into the training processes of two neural networks, realizing the decoupling of the source term of the heavy particle transport equation from the electron density and mean electron energy, which greatly reduces the complexity of neural network training. In this work, the application of Std-PINNs to solving multi-particle low-temperature plasma fluid models is demonstrated through two classic discharge cases with different complexity of reaction systems (low-pressure argon glow discharge and atmospheric-pressure helium glow discharge) and the performance of Std-PINN is compared with that of conventional PINN and finite element method (FEM). The results show that the training results output from the traditional PINN are completely incorrect due to the strong coupling correlation of each physical variable through the source terms of each particle transport equation, while the <i>L</i><sub>2</sub> relative error between Std-PINN and FEM results can reach up to ~10<sup>–2</sup> , thus verifying the feasibility of Std-PINN in simulating multi-particle plasma fluid model. Std-PINN expands the application of deep learning method to modeling complex physical systems and provides new ideas for conducting low-temperature plasma simulations. In addition, this study provides novel insights into the field of artificial intelligence scientific computing: the mathematical form that describes the state of a physical system is not unique. By introducing equivalent physical variables, equations suitable for neural network solutions can be derived and combined with observable data to simplify problems.

Microplasma characteristics of direct-current atmospheric pressure glow discharge in dependence of gap distance and discharge current

Microplasma at atmospheric pressure has been widely used in many fields due to the lower power consumption, higher plasma density, as well as better uniformity and stability. In this work, the microplasma characteristics of direct current atmospheric pressure glow discharge, including discharge morphology and electrical properties have been investigated with various interelectrode gaps (10–600 μm) and discharge currents (1–6 mA), and simultaneously, a finite element simulation has been conducted to obtain the distribution of the electric field and particle density. The evolution of cathode layer, anode layer and Faraday dark space at this scale was captured with a higher spatial resolution (∼1 μm) for the first time, demonstrating that the cathode layer, especially the cathode sheath rather than the positive column, plays a dominant role in the transition of the microplasma. As the gap shrinks to a size less than cathode layer (∼40 μm), the cathode sheath with a high electric field is compressed, leading to a rapid decrease of the discharge voltage. The discharge voltage remains basically unchanged regardless of the discharge current, because the electric field in the cathode sheath is limited by the accumulated space charge. The experimental results are well verified and explained by the simulation results. This study provides an in-depth understanding of the glow discharge mechanism at microscale, and of the stability of glow discharge at atmospheric pressure, and benefits to future research on the atmospheric pressure large-area microplasma and its related application.

Degradation of methylene blue through atmospheric pressure glow discharge plasma treatment

The degradation of Methylene Blue (MB) dye through treatment with an atmospheric pressure glow discharge plasma is presented in this work. The set-up used in this work has the advantage of being very simple without any gas supply. Plasma was diagnosed using optical emission spectroscopy, and rotational temperature of the hydroxyl radicals was measured. The effects of plasma current, treatment time, polarity and material of the electrodes on degradation of MB dye were studied. Experimental results showed that the degradation of dye increased with plasma current and treatment time. Polarity of the electrodes also have an effect in that the liquid cathode mode has about 14% higher degradation efficiency than liquid anode mode. Interestingly, it was found that anodic dissolution of copper electrode aids in degradation of MB dye by initiating Fenton like reactions involving copper ions, which was absent in the case of stainless steel electrode. After 40 min of treatment, the maximum degradation efficiency and COD removal rate achieved was 77% and 74% respectively, while the degradation yield obtained was 0.32 g.kW–1.h–1.

Synthesis of magnesium oxide and zinc oxide powders in a glow discharge plasma at atmospheric pressure

Investigation of the processes involved in the synthesis of magnesium oxide and zinc oxide powders using the thermal effects of an atmospheric-pressure glow discharge plasma in an inert gas flow are described. The discharge operates in a repetitively pulsed mode with pulse repetition rate of several tens of kilohertz and pulse duration up to 12 μs, discharge current of 600 mA and voltage up to 300 V. These parameters lead to thermal erosion of magnesium or zinc inserts in a molybdenum crucible. The chemical and phase composition of the erosion products were determined using TEM/EDS and X-ray diffraction analysis, and the composition of the plasma was assessed by optical emission spectrometry. This experimental approach allows fabrication of powders of these metal oxides with characteristic particle size 10–50 nm, and the formation of coatings of these materials in a one-step process.

Biosafe removal of diclofenac from wastewaters by a continuous-flow mode cold atmospheric pressure plasma system

Diclofenac (DCF) is not only a versatile non-steroidal anti-inflammatory drug, but also an emerging water pollutant. There is an urgent need for innovative technology of wastewater treatment to reduce the impact of DCF on the environment. Thus, we examined the applicability of pulse-modulated radio-frequency atmospheric pressure glow discharge (pm-rf-APGD) for degradation of 1.56–50.0 mg L-1 DCF from both aqueous solutions and synthetic wastewaters. The removal rates varied from 84.0 ± 3.8% to 100.0 ± 0.1% for the aqueous solution and increased together with the decreasing concentration of DCF. For synthetic wastewaters, the DCF removal was enclosed in the range from 21.0 ± 1.0% to 74.8 ± 0.1%. The energy efficiencies varied from 0.0116 to 0.312 g kW-1h-1 for aqueous solutions and from 0.00779 to 0.0087 g kW-1h-1 for synthetic wastewaters, respectively. By application of ultraperformance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) and gas chromatography-mass spectrometry (GC-MS), the pm-rf-APGD-driven DCF degradation pathways were revealed to involve decomposition, nitration, and dehalogenation reactions yielding dichloroaniline, nitro-diclofenac and 8-chlorocarbazole-1-acetic acid, respectively, before achieving the total decomposition of DCF to carbon dioxide, water, chlorides, nitrates and amines. Notable increases in the contents of the radicals, i.e., H2O2 in addition to NO2- and NO3-, were observed in the plasma-treated DCF solutions in contrast to the controls. Finally, no cytotoxic activity of the pm-rf-APGD-treated DCF solutions was demonstrated on model non-malignant human endothelial cells (HUVEC) and human immortalized keratinocytes (HaCaT). We anticipate that the described continuous-flow pm-rf-APGD-based reaction discharge system might be applied for biosafe removal of DCF from the effluents originating from wastewater treatment plants.

Investigation of potential polyatomic interferences on uranium isotope ratio measurements for the LS-APGD-Orbitrap MS system

The determination of actinide (e.g., U and Pu) content and isotopics is of importance to the nuclear forensics and safeguards communities. However, in the analysis of environmental samples, such as those collected by the International Atomic Energy Agency, uranium measurements can be complicated by isobaric interferences from polyatomic variants of heavy elements (e.g., Pb). This leads to complex, time-consuming sample manipulations (i.e., separations) before determining isotope ratios. An alternative strategy to sample pretreatment is to use high-resolution mass spectrometric platforms during the analysis to fully resolve the uranium isotopes from potential polyatomic interferences, negating the need for prior chemical separation. The liquid sampling - atmospheric pressure glow discharge (LS-APGD) coupled with an Orbitrap mass spectrometer provides a high-resolution (>70,000 m/Δm at m/z 200) inorganic mass spectrometry platform. As a demonstration of the power of this instrumental platform, and indeed, the high-resolution approach in general, uranium isotope ratios were determined in the presence of elemental impurities (e.g., Pb, Pt, Ta, W) commonly encountered with environmental sample swipe analysis, without any prior treatment. Even at elemental impurity concentrations of 1000–5000× relative to uranium, no interference was observed with the 235U or 238U signal. In addition, the 235U/238U isotope ratio for the samples with the concomitants present are within 2 standard deviations of the values obtained without their addition, indicating that these impurities do not impact the determined uranium isotope ratio. These findings represent a significant first step in leveraging the high resolution of the LS-APGD-Orbitrap-MS to overcome isobaric and molecular interferences instead of relying on chemical separations.

Analysis of different modeling approaches for simulation of glow discharge in helium at atmospheric pressure

One-dimensional numerical models of a direct current atmospheric pressure glow discharge in helium are developed and examined. The models use a fluid description of charged and neutral particles and a drift-diffusion approximation for particle fluxes. The effects of plasma-chemical models, the form of the electron energy distribution function (Maxwellian vs non-Maxwellian), the energy loss due to gas heating and the width of the gas gap on the discharge characteristics are analyzed. The performance of different modeling approaches is examined by superimposing computed current–voltage characteristic (CVC) curves with each other and with measured and computed CVCs available in the literature.

An impact of the material and diameter of tubes in the flowing liquid cathode atmospheric pressure glow discharge system on its analytical performance – Preliminary study

Tubes of different diameters and materials were tested as solution (tungsten, molybdenum, titanium, corundum, quartz, and graphite) and gas (tungsten, molybdenum, and titanium) delivery tubes for the flowing liquid cathode atmospheric pressure glow discharge (FLC-APGD) microplasma system. For work purposes, FLC solutions both with and without the addition of formic acid were tested and the results were compared. Additionally, to elucidate the impact of various combinations of tubes on the excitation conditions in the discharge, the excitation (Texc(H)), rotational (Trot(OH)), and vibrational (Tvib(OH)) temperatures, as well as the electron number density were all determined. It was found that certain combinations of the tubes affected the discharge stability, therefore, either the precision was poor or the discharge could not be maintained at all. As a result, detection limits (DLs) of the studied elements were assessed for some combinations of tubes in order to establish the impact of the discharge stability on the background fluctuations. It was noticed that certain materials of the tubes, namely tungsten and corundum, were superior in terms of their resistance to the conditions under which the discharge was sustained. The analytes signals were found to be slightly affected by changing tubes, however, it was shown that the tungsten and corundum tubes provided better results in terms of signals intensity, than the other ones. Additionally, the commonly used combination of glass and graphite tubes turned out to give the lowest analytes signals and relatively high DLs.

Electrical and optical characteristics of radio-frequency atmospheric dielectric barrier discharge using anodic alumina barriers

It is widely accepted that dielectrically insulated electrodes can control plasma contraction in radio frequency atmospheric pressure glow discharge at very large currents. It is also known that thin dielectric barriers maximize the permissible discharge current, thus boosting the reactive plasma species and enhancing the application efficacy. An experimental investigation of radio-frequency atmospheric pressure dielectric barrier discharge (rf APDBD) using a thin layer of a novel dielectric, anodic alumina grown by a wet electrochemical process to insulate electrodes is presented in this paper to demonstrate that rf APDBD with anodic alumina barriers remains stable and retains volume without contraction over a wide current range in the γ-mode. The electrical characterization of the rf APDBD is performed using an equivalent electric circuit model based on the measured electrical parameters. In normal glow discharge, the measured impedance data closely matched the simulated data. Optical emission spectroscopy demonstrated that a higher discharge current facilitated active plasma chemistry. The estimated excitation, vibrational, and gas temperatures indicate that rf APDBD with anodized electrodes is well suited for surface treatment and decontamination applications in open air.

Effect of Cold Plasma Treatment on Surface Modification of Rice Grains

The influence of cold plasma of atmospheric-pressure glow discharge on the surface properties of rice grains has been studied. It has been established that as a result of the impact of nonthermal atmosphericpressure glow-discharge plasma on the seed surface, the surface becomes hydrophilic and is characterized by a decrease in the contact angle, an increase in surface energy, and enhancement of surface roughness, indicating the effective formation of polar groups on the surface of rice grains.

Preliminary investigation of an uncertainty budget for uranium isotope ratio analysis using a liquid sampling—atmospheric pressure glow discharge—orbitrap mass spectrometer system

Preliminary investigation of an uncertainty budget for uranium isotope ratio analysis using a liquid sampling—atmospheric pressure glow discharge—orbitrap mass spectrometer system