Direct Current Glow Discharge Research Articles

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. This included optimizing the concentration of ReO4- in ReNPs precursor solution, solution flow rate as well as 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 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 revealed spherical and spherical-like morphologies of obtained ReNPs synthesized using FLC-dc-dc-APGD and FLA-dc-APGD modes with the actual sizes of 7.28 ± 2.90nm and 3.24 ± 0.57nm, respectively. Optimized conditions yielded ReNPs with exceptional catalytic activity, reducing 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 0.107min-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, 0.001min-1 for, 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.

Millimeter and Submillimeter Spectroscopy of the Deuterated Molecular Ion SD+

Seven rotational and fine-structure transitions of the deuterated molecular ion SD+ in the X 3Σ− ground electronic state have been measured in the 271–863 GHz region in the laboratory. This ion has been produced by direct-current glow discharge using a mixture of D2S and argon in a free space cell in a temperature range of −140°C to −160°C. The rotational, centrifugal distortion, spin–spin interaction, and hyperfine constants have been determined; the standard deviation of the residuals in the fitting is 109 kHz. The set of obtained spectroscopic parameters provides a list of accurate submillimeter rest frequencies of SD+ for astronomical detection. We have investigated lines of SD+ toward the quasar PKS 1830-211 using the Atacama Large Millimeter/submillimeter Array archive, as the z = 0.89 molecular absorber exists in front of this quasar. A data set covering the 297 GHz region includes the N J = 23–12 transition at 561 GHz due to redshift, providing an upper limit of the column density N tot = 3 × 1012 cm−2 for SD+.

DC-driven subatmospheric glow discharges in the infrared-stimulated

This paper presents a conceptual framework for experimental research combined with numerical analysis on direct current (DC) glow discharges in microscale planar gas discharge-semiconductor systems (GDSS). In the experimental section, several structural and elemental analyses, including SEM, EDAX, AFM, and near-infrared absorption spectra measurements were carried out for compound semiconductor zinc selenide (ZnSe) cathode sample. Argon (Ar) was charged into the plasma reactor cell of GDSS at pressures of 100 Torr subatmospheric and 760 Torr atmospheric, respectively, by a vacuum pump- gas filling station. Glow discharge light emissions from plasma, excited under three different intensity levels (dark, weak, strong) of infrared beam illumination on ZnSe cathode electrode, were measured by using a phomultiplier tube that is sensitive to UV–Visible wavelengths. In the numerical analysis section, simulation studies were carried out on the two-dimensional gas discharge-semiconductor microplasma system (GDSµPS) cell models using the finite-element method (FEM) solver COMSOL Multiphysics DC plasma program. Calculations and predictions were based on mixture-averaged diffusion drift theory and Maxwellian electron energy distribution function. GDSµPS cell was modeled in a square chamber with planar anode/cathode electrode pair coupled at a 50 μm discharge gap. Single side of ZnSe cathode was finely micro-digitated to increase the effective surface area for enhanced electron emission to the gas discharge cell. The electrical equivalent circuit (EEC) of the proposed model was driven by 1.0 kV DC voltage source. Binary Ar/H2 gas medium in a mixture of 3:2 molar ratio was introduced to the gas discharge chamber at constant 200 Torr subatmospheric pressure. Simulations were run for normal glow discharges to exhibit the electrical fast transient glow discharge behaviours from electron field emission state to self-sustained normal glow discharge state by numerically solving the electron density (ED), electron current density (ECD) and electric potential distribution (EPD) parameters.It is figured out that binary Ar/H2 gas discharge model can undertake a major role in shaping and controlling the spatiotemporal response to transient electro-optical behavior of microplasma-based artificial electromagnetic materials configured for high-efficiency infrared-to-visible wavelength conversion applications.

In Situ Plasma Studies Using a Direct Current Microplasma in a Scanning Electron Microscope

AbstractMicroplasmas can be used for a wide range of technological applications and to improve the understanding of fundamental physics. Scanning electron microscopy, on the other hand, provides insights into the sample morphology and chemistry of materials from the mm‐ down to the nm‐scale. Combining both would provide direct insight into plasma‐sample interactions in real‐time and at high spatial resolution. Up till now, very few attempts in this direction have been made, and significant challenges remain. This work presents a stable direct current glow discharge microplasma setup built inside a scanning electron microscope. The experimental setup is capable of real‐time in situ imaging of the sample evolution during plasma operation and it demonstrates localized sputtering and sample oxidation. Further, the experimental parameters such as varying gas mixtures, electrode polarity, and field strength are explored and experimental V–I curves under various conditions are provided. These results demonstrate the capabilities of this setup in potential investigations of plasma physics, plasma‐surface interactions, and materials science and its practical applications. The presented setup shows the potential to have several technological applications, for example, to locally modify the sample surface (e.g., local oxidation and ion implantation for nanotechnology applications) on the µm‐scale.

The impact of large volume atmospheric pressure air glow discharge plasma on enhancing denim fabric (textile) sewing process

A direct-current large-volume atmospheric pressure air glow discharge plasma (APAGDP) was developed to enhance the sewing process of denim fabric. The generated plasma was characterized optically, electrically, and spectroscopically. The generated plasma presents a positive electric resistance behaviour. The plasma emission spectra are dominated by the nitrogen second positive system. Its intensity increases with the applied voltage. The generated plasma was used as a pre-treatment to enhance the sewing of the denim fabric at different exposure times, from 5 to 600 s. The scanning electron microscopy images showed no damage to the surface morphology of the denim fabric after plasma treatment. The sound pressure level (SPL) was used to verify the plasma effect on the denim fabric as compared to the untreated fabric. The SPL decreases with plasma exposure time. This result indicates that the plasma improves the sewing performance of the denim fabric.

Two-dimensional numerical simulation of pre-ionized direct-current glow discharge in atmospheric helium

In this paper, the effect of pre-ionization on the small-gap and large-gap direct-current glow discharge at atmospheric pressure are investigated based on a two-dimensional self-consistent fluid model. For both the discharges, the results show that with the enhancement of pre-ionization, the charged particle distribution gradually shifts toward the cathode along the discharge direction, making the cathode fall zone shrink continuously. The width of the positive column region, negative glow space, and cathode fall zone continuously extend along the vertical discharge direction, and the distribution of electron density and ion density are more uniform. For the electric field, with the enhancement of pre-ionization, the longitudinalal component distribution of the electric field in the cathode fall zone gradually contracts toward the cathode, and the overall electric field near the cathode decreases and becomes more uniformly distributed. The transverse component distribution of the electric field gradually decreases and shrinks toward the wall. The overall electron temperature in the discharge space decreases with the enhancement of the pre-ionization level, and the electron temperature distribution in the cathode fall zone gradually shrinks toward the cathode. In addition, the overall potential of the discharge space also decreases. The introduction of pre-ionization significantly reduces the maintaining voltage and discharge power of the direct-current glow discharge. Furthermore, the potential drop in the small-gap discharge is always concentrated in the cathode fall zone as the pre-ionization increases, while the potential drop in the large-gap discharge is gradually shifted from the cathode fall zone to the positive column region. This simulation shows that the pre-ionization not only effectively enhances the discharge uniformity, but also largely reduces the maintaining voltage and energy consumption of the direct-current glow discharge. This work is an important guideline for further optimizing the electrode configuration and the operating parameters of the plasma source.

Investigation of plasma parameters, distributions, and optical emission for the anti-microbial performance of non-woven fabric under direct current glow discharge

The distribution of electron temperature Te and density Ne for direct current glow plasma discharge was investigated, using a single Langmuir probe, inserted inside the plasma cell. The radial temperature distribution has the same values, except with a small increment variation at the cathode edge, and an axial decrement for the temperature Te distribution profiles from the cathode fall region, passing the abnormal glow region, up to the faraway axial region.The radial distribution of the electron density Ne has its highest value at the cathode, with very intense plasma at the cathode fall region, and more Ne decrement in the abnormal glow region, passing the abnormal glow region up to the faraway axial region. In the axial Ne distribution, an increase in Ne from the cathode fall region reaches maximum values in the abnormal glow region and decreases in the faraway axial region.The optimal plasma surface treatment of non-woven silk fabric (n-WSF) can be achieved by utilizing a high plasma density and low energy of electrons to inactivate viable cells attached to (n-WSF) at very short application times, leading to complete inactivation, where the bacterial inactivation rate increases in the abnormal glow region. Based on analyses of the experimental data of initial and final densities of viable cells using survival curves in the abnormal glow discharge region, a dramatic inhibitory effect of plasma discharge on the residual survival microbe ratio was observed.

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.

Kinetics of Ibuprofen Degradation in Aqueous Solution by the Action of Direct-Current Glow Discharge in Air

Kinetics of Ibuprofen Degradation in Aqueous Solution by the Action of Direct-Current Glow Discharge in Air

Nitrogen fixation as NOx using air plasma coupled with heterogeneous catalysis at atmospheric pressure

AbstractThis study presents insights into the use of activated catalysts to improve the energy efficiency of production in atmospheric pressure air plasma. The introduction of catalysts in the direct current glow discharge system reduces the energy cost of production by up to 45% at low gas flow rates. Notably, even when positioned away from the plasma zone, the catalyst enhanced production, suggesting a significant role for the catalytic activation of downstream neutral species. The study also introduced a novel approach involving an air plasma jet infused with floating catalyst powder. This method significantly increased energy efficiency at higher discharge currents, with an associated energy cost of 2.9 MJ/mol for production.

PROBE AND SPECTRAL DIAGNOSTICS OF PLASMA GAS ENVIRONMENT: BCl3-Cl2

Probe and spectral measurements of the plasma of the gaseous medium BCl3-Cl2 were carried out. Data were obtained on the influence of the initial composition of the gaseous medium on the electric field strength, gas temperature, particle concentration, reduced electric field strength under conditions of a direct current glow discharge. The emission spectra of the plasma of the gaseous medium BCl3-Cl2 were analyzed, the main emitting components were identified, and the relationships between radiation intensities and particle concentrations were established.

Kinetics of Ibuprofen Degradation in Aqueous Solution by the Action of Direct-Current Glow Discharge in Air

Kinetics of Ibuprofen Degradation in Aqueous Solution by the Action of Direct-Current Glow Discharge in Air

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.

Assessing apparent secondary electron yield from current–voltage characteristics of abnormal DC glow discharges

The problem of assessing apparent secondary emission coefficient based on electrical properties of direct-current (DC) glow discharges using numerical modeling is revisited. An analysis of potential sources of uncertainties resulting from errors in experimental data as well as from model assumptions and approximations is presented. An estimation method based on a previously developed analytical model of a DC glow discharge is suggested. Application of the method is demonstrated in the example available in the literature of current–voltage characteristics of DC glow discharges in argon with copper electrodes. Values obtained for the considered data fall into two distinguishable groups, closely corresponding to those for clean and dirty copper cathode surfaces. The obtained preliminary results suggest the feasibility of estimating apparent secondary emission coefficients in DC discharges using numerical modeling.

Interaction of a precursor soliton with wake structure in a flowing dusty plasma

We report experimental observations on the interaction of a precursor soliton with a wake structure in a flowing dusty plasma system. The experiments are carried out in an inverted ∏-shaped experimental device in which a dusty plasma is created in a direct current glow discharge Ar plasma using micrometer sized Kaolin particles. Two copper wires installed radially on the cathode serve as charged objects in the plasma environment. Precursor solitons and wake structures are excited by each of the charged objects when the dust fluid flows supersonically over both the objects. In the frame of the fluid, the solitons propagate in the upstream direction, whereas the smaller amplitude wake structures propagate in the downstream direction. A soliton, excited by one of the objects, interacts with the wake structure generated by the other object in the region between the two charged objects. After the interaction, the amplitude and velocity of the soliton increase whereas its width decreases. The results are explained theoretically using numerical solutions of a model forced Korteweg-de Vries equation driven by two source terms.

Depth-profiling analysis of ZnO layers with three morphologies by direct-current glow discharge mass spectrometry

In the fabrication of high-quality materials, information regarding the element concentration and distribution in the depth direction is particularly important. In this study, the potential applicability of direct-current glow discharge mass spectrometry (dc-GD-MS) was explored for depth-profiling analysis of zinc oxide (ZnO) layers on steel substrates. The ZnO layers on steel substrates presented three morphologies of thin films, network textures and nanorods fabricated by magnetron sputtering (ZnO-1/steel), sol–gel method (ZnO-2/steel) and hydrothermal synthesis (ZnO-3/steel), respectively. The discharge conditions were optimized based on dc-GD-MS to obtain the ideal depth resolutions. The results revealed that compared with ZnO layers of ZnO-2/steel and ZnO-3/steel, the dc-GD-MS depth-profiling analysis of ZnO-1/steel presented superior performance with depth resolution of 0.22 μm and a clear interface between ZnO layer and steel substrate. dc-GD-MS depth-profiling analysis suggested that the ZnO layer morphology, thickness and sputtering rate could affect the depth resolution. Furthermore, the fuzzy synthetic evaluation method (FSEM) suggested that the layer morphology had a greater impact on the depth resolutions than thickness and sputtering rate under the optimized discharge conditions. The study presented an efficient and sensitive approach for determining the elemental concentrations and distributions of semi-conducting materials, offering novel insights into material fabrication.

Non-contact gaseous microplasma electrode as anode for electrodeposition of metal and metal alloy in molten salt

Microplasma based on glow discharge could act as a non-contact gaseous electrode and has attracted much attention in both fundamental research and application. Herein, with microplasma as the anode, the electrodeposition process of a series of metal and metal alloys in molten salt has been systemically studied. Four metal cations with different valence states, silver (Ag+), nickel (Ni2+), copper (Cu2+), and iron (Fe3+), could all be reduced on the solid cathode with high current efficiency and the corresponding metal products were of high purity. The electrodeposition of aluminum-lanthanum (Al-Ln) alloy on the aluminum cathode was also successfully carried out with microplasma as the anode, and the same alloy was obtained by using the conventional anode electrode. These results indicated that microplasma anode based on non-contact direct-current (DC) glow discharge is a promising electrode to be applied in molten salt electrolysis.

Numerical simulation of the large-gap and small-gap pre-ionized direct-current glow discharges in atmospheric helium

A one-dimensional self-consistent fluid model was employed to comparatively investigate the influence of pre-ionization on the helium direct-current glow discharge in the large gap and the small gap at atmospheric pressure. For the large-gap and small-gap discharges, the negative glow space and the cathode fall layer are both offset to the cathode with the increase in pre-ionization, which is mainly ascribed to the decrease in charged particle density in the original negative glow space as a result of the increased probability of collision and recombination between ions and electrons, and the new balance between the positive and negative charges established at the distance closer to the cathode. The electron density tends to grow in the negative glow space due to the elevated pre-ionization, while the ion density exhibits an overall downward tendency in the cathode fall layer because the increase in secondary electrons produces more newly born electrons that neutralize more ions via the recombination reaction. Thanks to the pre-ionization, a significant reduction of sustaining voltage and discharge power is obtained in both the large-gap and small-gap discharges. A remarkable characteristic is that the absent positive column in the small-gap discharge comes into being again due to the pre-ionization. Moreover, with the increase in the pre-ionization level, the potential fall shifts from the cathode fall layer to the positive column in the large-gap discharge, while it is always concentrated in the cathode fall layer in the small-gap discharge.

Deposition and morphology of direct current plasma-polymerized aniline

Plasma polymerization is a simple, solvent-free, dry process that involves vaporizing a monomer and ionizing them to the plasma state. This study reports the plasma polymerization of aniline in a direct current glow discharge. Aniline was introduced into a vacuum chamber and plasma-polymerized onto an indium-doped tin oxide/glass substrate at varying discharge potentials and deposition times. The resulting plasma-polymerized aniline films were in the leucoemeraldine form, as evidenced by UV-Vis and infrared spectral analyses. Monocarbon species that are products of the aromatic ring rupture were observed from the optical emission spectra of the discharge. The films reveal a smooth, pinhole-free surface across different process parameters. The film thickness from the 200 to 600 nm range presents a linear relationship with respect to the duration of deposition. The deposition rate also increased and has a good linear relationship when the discharge potential was varied.