Atmospheric-pressure Discharge Plasma Research Articles

Removal of Cochineal Dye Color through Atmospheric Pressure Plasma Discharge Jet

The extensive utilization of dyes across diverse industries has resulted in environmental pollution, leading to the degradation of water bodies. To prevent environmental contamination, the use of eco-friendly dyes and innovative processes for dye degradation is crucial. This study aimed to investigate the color removal process of cochineal dye (Dactylopius coccus Costa) using the atmospheric pressure plasma jet (APPJ: Atmospheric Pressure Plasma Jet) technique. The dye extracted from the cochineal insect was treated with APPJ and the resulting color removal process was analyzed. Optical emission spectroscopy (OES) was used to investigate the plasma emission lines, and UV-Vis spectroscopy was used to monitor the color removal process. The results revealed that the decolorization of cochineal dye was a result of an oxidative degradation process caused by the interaction of the reactive species (NO3− and NO2−) generated by the APPJ plasma discharge with the dye molecules. This color removal process occurs in an acidic medium, leading to a pH change from 5.4 to 2.7. These pH changes can be attributed to fluctuations in the concentrations of reactive species such as nitrates and nitrites in the liquid phase. UV-Vis spectroscopy measurements showed that 90% of the cochineal color was removed within the first 10 min of treatment. This study enhances our understanding of natural color removal and provides insights into its mechanism, opening up possibilities for controlled modification and applications in various fields.

Influence of liquid conductance on the temporal evolution of self-organization patterns in atmospheric pressure DC glow discharges

Self-Organized Patterns (SOPs) at plasma-liquid interface in atmospheric pressure plasma discharges refer to the formation of intricate and puzzling structures due to the interplay of electrodynamic and hydrodynamic processes. Studies conducted to date have shown that this phenomenon results in the formation of distinctive patterns such as circular ring, star, gear, dots, spikes, etc., and primarily depends on working gas, electrolyte type, gap distance, current, conductivity, etc. However, an adequate understanding of how these patterns change from one type to another is still not available. This study aims to elucidate the influence of initial liquid conductance (σ i ) on the temporal evolution of SOPs in liquid-anode discharges. The discharge was generated in a pin-to-liquid anode configuration at a constant helium (He) flow rate of 500 sccm and DC applied voltage of 6 kV at a gap distance of 12 mm. Through the gradual increment of σ i from 1.8 μS to 4820 μS, we observe that the trend in the evolution of SOPS takes place as solid discs, spikes, dots, rings, double rings, and stars. The continuous formation of reactive species onto the liquid anode in all conductive solutions results in a decrease in pH, an increase in bulk liquid temperature, and an increase in total dissolved solutes, and these have been confirmed through experimental measurements. Observations using optical emission spectroscopy show that the electrons at the plasma-liquid interface participate in the reduction of cations followed by their excitation & ionization due to which electron density as well as emissions from excited species (mainly hydroxyl radicals & excited nitrogen) decrease with time. Our investigation provides experimental evidence on the presence of cations at the plasma-liquid interface required for SOP formation.

Using Deep Convolutional Neural Networks to Classify the Discharge Current of a Cold Atmospheric-Pressure Plasma Jet

Atmospheric-pressure plasma discharge can vary with conditions, such as working gas or discharge type, and the resulting discharge current has quite different electrical features. Hence, the provision of real-time and cost-effective monitoring of atmospheric-pressure plasma discharge is possible via current classification with a deep learning model. In addition, the current generated by an atmospheric-pressure plasma jet (APPJ) can be easily obtained, so it is suitable to use a data-driven convolutional neural network (CNN) to extract and analyze the current characteristics. This study presents two CNN classification applications of the current generated by an APPJ. First, we used the time-series classification approach known as InceptionTime to predict the APPJ working gas from helium, argon, and nitrogen. Second, InceptionTime was also used to predict the APPJ discharge type as Townsend discharge or glow discharge. InceptionTime leveraged the use of the inception module to reduce dimensions and avoid overfitting. Moreover, the use of four different sizes of filters along with the maxpooling layer provided sufficient receptive fields to analyze the entire current signal. We achieved 100% accuracy on a testing set of 1125 current signals, which did not include the training data during the working gas prediction; we also achieved 86.3% accuracy on a testing set of 750 current signals, which did not include the training data during the discharge type prediction. This study proves that the CNN can extract features from the discharge current waveforms and successfully predict the discharge type and working gas of an APPJ. The high-speed computing characteristics of deep learning may also facilitate real-time monitoring or diagnosis of APPJ.

Transition mechanisms between selective O3 and NO x generation modes in atmospheric-pressure plasmas: decoupling specific discharge energy and gas temperature effects

Two modes of the atmospheric-pressure plasma discharge, distinguished by the dominant O3 and NO x species are studied numerically and experimentally. To investigate the mode transition mechanisms, here we develop a global chemical kinetics model for the atmospheric-pressure dielectric barrier discharge involving 63 species and 750 reactions. Validated by the experimental results, the model accurately describes the mode transition. The N, O, O2(a), and O2(b) are the essential transient intermediate species for the O3 and NO x production and loss reactions. The individual and synergistic effects of the specific discharge energy and the gas temperature on the species density and the relative contributions of the dominant reactions are quantified under the increasing discharge voltage conditions. The modeling results indicate that the gas temperature and specific discharge energy both contributed to the discharge mode transition, while the decisive factors affecting the change of the O3 and NO x density are different in the respective modes. These insights contribute to diverse plasma applications in biomedicine, agriculture, food, and other fields where selective and controlled production of O3 and NO x species is the key for the desired plasma performance.

Single Step Metal Nanoparticle Fabrication Using Atmospheric Pressure Plasma Jets

The interaction of atmospheric pressure plasma discharges with liquid or vapour phases is a hot-topic in plasma science and technology. Synthesis and processing of nanomaterials using atmospheric pressure plasma jets attracts more attention because of its simplicity and cost effectiveness. The plasma containing reactive electrons and active chemical species activates physical processes and reduction reaction of metal salts which leads to the formation of metal nanoparticles. Among the unique features of atmospheric pressure plasmas, the chemical non-equilibrium environment produces highly reactive radicals and ions from the precursors as well as inside the plasma. Thus the energy transfer could be initiated with high energy electrons and excited species from plasma and could be achieved by the reactions with reactive species of the precursors. Plasma compliments the production of nanomaterials in vapour phase or from aerosols and in solutions of the precursors. The interface between plasmas and vapors can be employed for rapid, simultaneous reduction and deposition of metal nanoparticles from metal salts, for instance gold nanoparticles from chloroauric acid (HAuCl4).We have employed an atmospheric pressure plasma jet setup operating with a mixture of He and Ar gases to produce gold nanocrystals onto a silicon wafer substrate. In this study, it reveals an easy and reliable synthesis mechanism of gold nanoparticles from chloroauric acid using atmospheric pressure plasma jet working with a high voltage source. A solution of the precursor in water acts as the feed solution for the process which is introduced to plasma in the form of microdroplets and metal nanoparticles were formed inside the plasma from the vapours containing the precursor molecules. Since the plasma-liquid/vapour chemistry allows the lead of accelerated reactions and instantly reduce the metal ions to metal atoms skipping the intermediate steps in the reduction process. The nanoparticles were collected on to a Si wafer substrate downstream of the plasma jet and characterized via scanning electron microscopy, Raman spectroscopy, transition electron microscopy etc. The polygonal nanoparticles sized 40-100 nm were obtained and they do not tend to agglomerate or fuse onto the substrate. Due to the low volatility of the precursor solution and the presence of comparatively larger microdroplets inside the plasma the nanoparticles tend to deposit in a pattern like galaxies on the silicon wafer substrate. These results would lead to the development of low cost and mobile, user-friendly atmospheric pressure plasma devices for the synthesis of nanoparticles without any toxic chemicals for the reduction of metal salt.The challenge in this process is in creating a vapour-plasma interface directly. This problem has been solved by incorporating a vaporizer directly to plasma. The vaporizer would introduce a new phase which would be a combination of gaseous plasma and plasma-liquid interface. To ease the transportation and diffusion of precursor molecules at the interface an inert gas has been introduced to the vaporizer as a carrier. At the interface, high energy electrons are introduced to the vapors containing the precursor metal ions and these wet electrons play the key role as initiators for the reduction process inside the plasma. Nanoparticles are formed inside the plasma by simple reduction mechanism carried out by short-lived reducing species formed at the interface. From the qualitative analysis carried our during the process implies the formation of short-lived reducing agents like hydrogen peroxide (H2O2) which is known as a reducing agent for chloroaurate ions in water medium. The size and shape of the nanoparticles are controlled by the residence time of the particles inside the plasma and the population density of the metal ions. Whereas the purity in turn the reduction rate of metal ions are dependent upon the feed gas flow as well as the applied voltage, i.e. plasma power.Concisely, atmospheric pressure plasma jets are outstanding choice for the synthesis of gold nanoparticles from chloroauric acid without any external reducing agents. The synthesized gold nanoparticles are promising for different applications because of its geometry and shape. Because of its polygonal geometries the particles are plasmonic active surfaces, the functional for highly specific sensing applications and nanoelectronics devices. However, the low-temperature plasma-vapour interphases containing droplets, the evaporation may add new complexities such as quantitative analysis of non-equilibrium chemistry to plasma chemistry which is yet to be understood and developed.

Using numerical analysis of ordinary differential equation systems to predict the chemical concentration after plasma irradiation

In this study, a zero-dimensional numerical simulation of the atmospheric pressure plasma (APP) interface with a liquid solution was performed. By assuming that the solution reaction is dependent on the injection of radicals and electrons, we were able to obtain a single short APP discharge with the liquid solution. This study can predict excitation temperature, electron temperature, and population densities of species and result in optimum conditions for a chemical reaction for the synthesis of nanoparticles or other applications of the reaction between APP and liquid surface. This work aims to explain the effect of pH values on the synthesis of gold nanoparticles compared with experimental results. We found that the effect of pH value is expected to impact the generation of gold nanoparticles. Therefore, a high pH value is suitable for generating gold atoms for nano-synthesis. The fundamental plasma properties, such as population density, electron temperature, excitation temperature, and gas temperature, and chemical reaction process were studied. The simulation results were consistent with the experimental observations.

Kinetic study of key species and reactions of atmospheric pressure pulsed corona discharge in humid air

In this study, we examined the key particles and chemical reactions that substantially influence plasma characteristics. In summarizing the chemical reaction model for the discharge process of N2–O2–H2O(g) mixed gases, 65 particle types and 673 chemical reactions were investigated. On this basis, a global model of atmospheric pressure humid air discharge plasma was developed, with a focus on the variation of charged particles densities and chemical reaction rates with time under the excitation of a 0–200 Td pulsed electric field. Particles with a density greater than 1% of the electron density were classified as key particles. For such particles, the top ranking generation or consumption reactions (i.e. where the sum of their rates was greater than 95% of the total rate of the generation or consumption reactions) were classified as key chemical reactions. On the basis of the key particles and reactions identified, a simplified global model was derived. A comparison of the global model with the simplified global model in terms of the model parameters, particle densities, reaction rates (with time), and calculation efficiencies demonstrated that both models can adequately identify the key particles and chemical reactions reflecting the chemical process of atmospheric pressure discharge plasma in humid air. Thus, by analyzing the key particles and chemical reaction pathways, the charge and substance transfer mechanism of atmospheric pressure pulse discharge plasma in humid air was revealed, and the mechanism underlying water vapor molecules’ influence on atmospheric pressure air discharge was elucidated.

Biofunctional coating of stainless steel surfaces with carvacrol- and eugenol-derived film using atmospheric dielectric barrier discharge plasma: aiming for suppression of biofilm formation and corrosion protection

Metallic biomaterials are the most used materials as orthopedic and dental implants due to their excellent mechanical properties. However, attention must be paid when choosing the materials to be used in the implant medical device to assure their best performance in the biological environment. In addition to good biocompatibility and chemical stability, in several situations, the ideal material must also be able to inhibit implant bacterial colonization. In this context, we have investigated a biofunctional coating of the carvacrol-derived film (CDF) and eugenol-derived film (EDF) on stainless steel surfaces using atmospheric pressure plasma discharge to improve their electrochemical and biological properties. Atomic force microscopy results showed that both CDF and EDF coatings disappeared all the irregularities of the pristine substrate and acquired a uniform surface, free of defects and scratches. Infrared spectra results showed the deposited films largely maintained the mimicking group of the monomer, such as hydroxyl and aromatic, which is a key feature of the film for the antibacterial and electrochemical activity. CDF exhibited a reduction in biofilm growth rate up to 44% for Pseudomonas aeruginosa and 60% for Candida albicans. Similarly, EDF exhibited up to 36% suppression for P. aeruginosa and 52% for C. albicans. These film coatings also decrease the corrosion current density and corrosion rate up to 35% in comparison with the uncoated substrate in 3.5% (w/v) NaCl. Therefore, surface treatment with the present methods is a promising alternative for steel substrate since it improves the electrochemical behavior and suppression tendencies against these microbial biofilms.

Single Step Synthesis and Deposition of Gold Nanoparticles Using Atmospheric Pressure Plasma Jet

The interaction of atmospheric pressure plasma discharges with liquid or vapor phase is a hot topic in plasma nanoscience and technology. Synthesis and processing of nanomaterials using atmospheric pressure plasma jets attract wide attention because of its simplicity and cost-effectiveness. The plasma containing reactive electrons and active chemical species activates physical processes and reduction of metal salts, leading to the formation of metal nanoparticles. Among the unique features of atmospheric pressure plasma, the chemical non-equilibrium environment produces highly reactive radicals and ions from the precursors, as well as inside the plasma. Thus the energy transfer could be initiated with high energy electrons and excited species from plasma and by the reactions with reactive species of the precursors. Plasma compliments the production of nanomaterials in the vapor phase or from aerosols and in solutions of the precursors. The interface between plasma and vapors can be employed for rapid, simultaneous reduction and deposition of metal nanoparticles from metal salts, for instance gold nanoparticles from chloroauric acid (HAuCl4).We have demonstrated an atmospheric pressure plasma jet (APPJ) setup operating with a mixture of He and Ar gases to deposit gold nanocrystals on a silicon substrate. In this study, we revealed an easy and reliable synthesis mechanism of gold nanoparticles from chloroauric acid using an APPJ working with a high voltage source and He gas. Chloroauric acid in water is used as the precursor for the process which is introduced to plasma in the form of micro droplets produced by the insertion of Ar gas to the precursor solution. The metal nanoparticles are formed inside the plasma by the plasma-assisted reduction of precursor molecules. Since the plasma-liquid/vapor chemistry allows the lead of accelerated reactions and instantly reduce the metal ions to metal atoms skipping the intermediate steps in the reduction process. The nanoparticles were deposited on a Si wafer substrate downstream of the plasma jet, and characterized via scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. The polygonal nanoparticles sized 40-100 nm were obtained and they do not tend to agglomerate or fuse onto the substrate. Due to the low volatility of the precursor solution and the presence of comparatively larger micro droplets inside the plasma the nanoparticles tend to deposit in a pattern like galaxies of gold nanocrystals on the silicon. These results would lead to the development of low cost and mobile, eco-friendly atmospheric pressure plasma devices to synthesis the nanoparticles without any hazardous chemical reducing agents.To create a plasma-vapor interaction, a vaporizer has been employed and the new interaction phase would be a combination of gaseous plasma and plasma-liquid interface. To ease the transportation and diffusion of precursor molecules at the interface Ar gas has been used to as a carrier. At the interface, high energy electrons play the key role as initiators for the reduction of metal ions inside the plasma. Nanoparticles were formed by a simple reduction mechanism carried out by short-lived reducing species formed at the interface. From the optical emission spectra taken during the process implies the formation OH radicals which may form short-lived reducing agents like hydrogen peroxide (H2O2) which is known as a reducing agent for chloroaurate ions in water medium. The size and shape of the nanoparticles are controlled by the plasma parameters by controlling the population density of the metal ions. Whereas the purity, in turn, the reduction rate of metal ions, is dependent upon the feed gas flow as well as the applied voltage, i.e. plasma power.The application of gold nanoparticles are promising for different applications depends on its geometry and shape. Therefore, the synthesized gold nanoparticles in this work with polygonal geometries can be potential candidates for plasmonic active surfaces for highly specific sensing applications and nanoelectronics devices. However, the low-temperature plasma-vapor interphases containing droplets, the evaporation may add new complexities such as quantitative analysis of non-equilibrium chemistry to plasma chemistry which is yet to be understood and developed, which will open a new era of plasma-surface interaction.

Atmospheric pressure plasma deposition of eugenol-derived film on metallic biomaterial for suppression of Escherichia coli and Staphylococcus aureus bacterial biofilm

Eugenol (4-Allyl-2‑methoxy phenol) is widely used as a condiment and bactericidal coatings for food packing and biomaterials. We have investigated the deposition and characterization of eugenol-derived films (EDF) on stainless steel surfaces deposited using atmospheric pressure plasma discharge for suppression of Escherichia coli and Staphylococcus aureus bacterial adhesion and proliferation. The thickness of the deposited films was in the range of 1,000 to 2,500 nm with a roughness up to 800 nm. Infrared spectra showed that the EDF preserves the hydroxyl and aromatic groups found in liquid eugenol, which is a key feature for the antibacterial activity of the film. X-ray photoelectron spectroscopy analysis has revealed increased oxygen content with the deposition time. Scanning electron microscopy has shown that the entire surface of the substrate is covered by a circular structure approximately 10 to 20 µm in diameter. Wettability analysis revealed an increase in the hydrophilicity of the surface after the deposition. Microbiological evaluation of bacterial growth, revealed that the surfaces inhibited the adhesion and proliferation of E. coli and S. aureus by more than 78 and 65%, respectively, while in the untreated samples the growth was greater than 90% for both microbes in comparison with polystyrene plates used as a positive control. Therefore the eugenol thin film deposited by this method was effective for biofilm suppression with a potential application for biocompatible material coating processes.

Delivery and expression of plasmid DNA into cells by a novel non-thermal plasma source

Medical applications such as plasma assisted gene transfer is a minimally invasive approach that can substantially reduce potential discomfort of treated area. Atmospheric pressure plasma discharge is an effective approach to deliver plasmid DNA for in vitro and in vivo applications. We investigated plasma assisted delivery in vitro in mouse melanoma cells (B16F10) using a novel surface plasma device, which is operated in air. We evaluated the influence of applied voltage and distance between the surface device and cell monolayer. We found no significant effect on the viability of cells. Highest expression following delivery of a plasmid encoding green fluorescent protein was achieved with an applied voltage of 11.25 kV at a 2 mm distance and 5 s exposure time. To better understand the influence of oxidative damages and stress on cells after plasma delivery, a mRNA expression study was performed. Our results indicated that TNFα mRNA was significantly upregulated. The mRNA response may be attributed to the RONS generated by plasma; however, this mRNA upregulation was not adequate to be reflected in a coordinate protein upregulation. From the results reported here, it is clear that this novel plasma device could be used for plasmid delivery.

Assessment of the potential of non-thermal atmospheric pressure plasma discharge and microwave energy against Tribolium castaneum and Trogoderma granarium.

This study was carried out to investigate the efficacy of the non-thermal atmospheric pressure plasma produced with dielectric barrier discharge (APPD) using air as a processing gas and microwave energy to control Tribolium castaneum and Trogoderma granarium adults and larvae in wheat grains. Insects' mortality was found to be power and time-dependent. The results indicated that non-thermal APPD and the microwave have enough insecticidal effect on the target pests. From the bioassay, LT50's and LT90's levels were estimated, T. granarium larvae appeared more tolerant to non-thermal APPD and the microwave energy than adults 7 days post-exposure. The germination percentage of wheat grains increased as the time of exposure to the non-thermal APPD increased. On the contrary, the germination percentage of wheat grains decreased as the time of exposure to the microwave increased. In addition, changes in antioxidant enzyme activities, catalase (CAT), glutathione S-transferase (GST) and peroxidase, in adults and larvae were examined after 24 h post-treatment to non-thermal APPD at 15.9 W power level, which caused 50% mortality. The activity of CAT, GST and lipid peroxide in the treated larvae showed a significant increase post-exposure to the non-thermal APPD at 15.9 W power level. On the other hand, no significant change in GSH-Px activity was observed. Reductions in the level of glutathione (GSH) and protein content occurred in treated larvae in comparison with the control.

Optimization of accurate controlled formation of Au MNPs via non-thermal microplasma continuous glow discharge within aqueous electrochemical (GDE) method

In this work, micro plasma-induced non-equilibrium liquid chemistry was utilized to synthesize and controlled formation of gold metallic nanoparticles (Au MNPs) by governing the concentration of (HAuCl4). These new approaches based on both plasma and liquid electrolytes contain charged species, and the interactions between the two phases represent a unique combination of physics, chemistry, and materials science. Continuous and stable DC glow discharge was done in home–made cavity to synthesize the definite sizes of (Au MNPs) by means of (3 kV) discharge voltage and (2 mA) discharge current for a period of (7 min) in aqueous solution of HAuCl4 with four different concentrations of about 1 mM, 5 mM, 10 mM and 20 mM at room temperature. The atmospheric pressure plasma discharge between stainless steel capillary tube cathode electrode over the (HAuCl4) solution and platinum plate as an anode dipped in solution for rapid formation of colloidal Au MNPs. Morphology aspects of the synthesized Au MNPs layer were studied by examining the (FE-SEM), HR-TEM images and X-ray difraction (XRD) pattern. Optical features of (Au MNPs) were considered via a UV–Vis beam spectrophotometer. These measurements showed that Au MNPs were organized by governing the concentration of HAuCl4, and uniform Au MNPs with specific exclusive sizes were acquired. Grain size, specific surface area and optical stability of Au MNPs strongly be affected by the HAuCl4 concentrations.

Gas Discharge Atmospheric Pressure Systems for the Biomedical Use

The analysis of world literature is carried out, which indicates the intensive development of the scientific and technical field “Plasma in Medicine” based on the use of different gas-discharges for biomedical purposes. The atmospheric pressure plasma discharge systems have the favorite features and are very suitable for medical physiotherapy, bactericide treating and even for sterilization. The systems with non-thermal plasma are in the most use and one of their applications is generation of gas ozone. The given paper is devoted to looking for atmospheric pressure discharge modes, which are more suitable for ozone therapy equipment taking into account the peculiarities of such type of electronic apparatus. As practice shows, for the generation of ozone, discharges with a secondary-emission cathode and non-thermal plasma are most preferable, and of these two types of discharges are discharges with a dielectric barrier and corona discharges with uncoated metal electrodes. The article focuses on the appropriateness of the use of a corona discharge for ozone therapy equipment. This is justified by the fact that the corona discharge ozonizers have certain design advantages over the ozonizers on the discharge with dielectric barriers, namely that the advantages of the ozonizers on the corona discharge are the absence of a expensive barrier and low resistance to the gas flow, so there is no need to significantly increase the pressure at the ozonizer oxygen inlet, and possibility of power supplying the ozonizer with DC voltage. Also, ozonizers on the corona discharge have a lower cost. From the literature and the authors' own practice, there is a wide variety of configurations of electrode systems for creating the corona discharge, but they always have electrodes with a small radius of curvature of the surface: threads, wires, nets, various pointed needles, serrated electrodes. The article considers the physical mechanism of maintaining the corona discharge of a unipolar or bipolar type and notes the role of secondary electron emission of the cathode. All types of corona discharge are capable of generating ozone because discharge electrons have the energy required to dissociate oxygen molecules in a non-thermal gas environment. Then a free oxygen atom attaches to an oxygen molecule to form a metastable ozone molecule. It is noted that the corona discharge and ozone generation were studied in detail mainly in unipolar point-of-plane or wire-in-pipe systems. The data on ozone generation in bipolar discharge is not enough to develop an ozone therapy apparatus, although this form of discharge is interesting because it requires relatively small values of the supply voltage and operates at a direct current. Based on the review of the prospects for the use of bipolar corona discharge in biomedical apparatus and practical considerations of the realistic and expanded future usage of bipolar corona equipment in the ozone therapy, the tasks have been formulated to be solved. It is necessary to thoroughly study the characteristics of the developed equipment and the influence of various external operational factors and physico-chemical processes in the ozonizer electrode system on them. It is necessary to ensure that the parameters of the equipment are maintained during operation, which means that during the eight-hour working day and with the total time between failures of at least 1000 hours. Also, it is necessary to take into account the effect of the decomposition of ozone molecules at elevated temperatures and not to allow excessive heating of the ozonizer. These requirements must be met by choice of the configuration and materials of the electrode system and must be experimentally verified. It is proposed to ensure the linearity of the calibration characteristics of the ozonizer and to formalize it mathematically to simplify the setting and maintenance of stable operating modes of ozone equipment. It is necessary to prove its therapeutic efficacy, including for sterilization treatment, with the participation of medical specialists.

Electrical Properties of Reversed-Polarity Ball Plasmoid Discharges

Ball plasmoid discharges are a unique type of atmospheric-pressure plasma discharge with a lifetime on the order of a hundred milliseconds without attachment to a power source. These discharges are generated by a moderate current pulse over the surface of an aqueous electrolyte, and some consider the spherical plasmoid that results to bear some resemblance to ball lightning. This article presents the first analysis of the electrical properties of ball plasmoid discharges in a reversed-polarity configuration, i.e., with the central electrode serving as the anode rather than as the cathode. These experiments demonstrate that ball plasmoids can indeed be generated with either electrode polarity with similar observable properties. These results are contrary to what has previously been discussed in the literature and raise additional questions regarding formation mechanisms of ball plasmoids. Analysis of images and electrical measurements collected at various discharge energies show that two distinct processes occur during discharges with our circuitry and in this reversed-polarity configuration: the formation of spark channels between the anode and electrolyte, and the generation of streamers and a jet from the surface of the anode.

Synthesis OF AG/TIO2 nanocomposite via plasma liquid interactions and degradation methylene blue

A novel method employing atmospheric pressure discharge plasma has been developed to reduce supported Ag nanoparticles (Ag NPs) and deposited on TiO2 powder without the use of any environmentally and biologically hazardous reducing chemicals. Ag/TiO2 nanocomposite was prepared by the atmospheric direct current plasma in water solution. Trisodium citrate and CMC was used as a capping agent for Ag nanoparticles. The nanocomposites were characterized using UV–Vis spectroscopy, X-ray diffraction, scanning electron microscopy. The results showed that Ag NPs with an average diameter of 20–35.5 nm were uniformly distributed on the powders surface. The presence of nanosilver particles in TiO2 matrix is clearly visible. The bandgap of TiO2/Ag was confirmed (2.65–2.85 eV) through UV–vis DRS, which was lower than TiO2 (3.8 eV). The photocatalytic effect was conducted by methylene blue degradation test. The photocatalytic activity of a series of 2 wt. % Ag/TiO2 composites was evaluated in the degradation of MB (used as a model pollutant) in aqueous solution under solar light. The 2.0 mol % of Ag-doped TiO2 shows 96% degradation of methylene blue (MB) within 50 min under visible light irradiation and exhibit highest photocatalytic performance.

Surface functionalization of automated fiber placement manufactured composites by atmospheric pressure plasma jet

This work is part of the National Aeronautics and Space Administration's (NASA) Advanced Composite Project (ACP) focused on reducing the timeline to certification and directly follows guidelines provided by the Federal Aviation Administration (FAA, Advisory Circular 20-107B, 2010) on improved process controls for adhesively bonded airframe structures. High performance airframe composite structures require reliable fabrication and high fidelity bonding for assembled components. However, a low inherent surface energy and happenstance of surface contamination in multiple manufacturing steps, both contribute to poor adhesive properties in composite materials. Proper surface preparation of pre-bond composite surfaces is, therefore, an active research topic focused on improving fidelity of adhesive bonding. This work discusses application of air driven atmospheric pressure plasma discharge device to mitigate detrimental effects of contaminants on adhesive bonds between carbon fiber composite surfaces. The experimental results indicate that contaminated surfaces treated with Atmospheric Pressure Plasma Jet (APPJ) exhibited higher adhesive retention, resulting in higher fracture toughness in double cantilever beam tests.

Application of atmospheric pressure discharges with a liquid cathode for determination of alkaline-earth metal ions in aqueous solutions

The concentrations alkaline-earth metal ions in water solutions were determined by the method of emission actinometry of atmospheric pressure discharge plasma with a liquid cathode. The rubidium atoms were the actinometer component in plasma, whose cations with a known concentration were added to the analyzed solution. The solutions of magnesium, calcium, barium with concentrations of 10−6-10−4 gl−1 were analyzed. It is established that the addition of electrolytes in the solution influence on the emission intensity of the metal atom lines. However, the use of the ratio of the intensities of the radiation of the analyzed components and the component-actinometer can improve the accuracy of the analysis. The water hardness factor of the tap water was determined using this method.

Multi-mode ionization instability induced striations in RF driven He/H2O atmospheric pressure plasma (APP) discharges

Previously [E. Kawamura et al., Plasma Sources Sci. Technol. 25, 054009 (2016) and E. Kawamura et al., J. Phys. D: Appl. Phys. 50, 145204 (2017)], one dimensional (1D) particle-in-cell (PIC) simulations of 1 to 4 mm gap, He/2%H2O atmospheric pressure plasma discharges showed an ionization instability resulting in bulk striations. Assuming that the ionization rate coefficient Kiz is related to the root mean square electric field E by Kiz ∝ Eq, a striation theory showed that q < 0 is a necessary condition for the instability. A local calculation yielded q > 0, implying that nonlocal electron kinetics are required for the instability. Wider gaps can fit in a wider range of wavelengths, resulting in multi-mode striations. Previously, we assumed a single mean q value for each discharge, and did not calculate q for each mode separately. Here, we develop a wavelength resolved global striation model and apply it to 1D PIC simulations of 4 mm gap discharges with input currents Jrf = 0.04 to 0.30 A/cm2. We first examine a base case at 0.23 A/cm2 and observe a mixture of unstable modes within a window of wavelengths λ. At shorter λ, the modes are suppressed by diffusion. At longer λ, we observe a transition to locality in which q becomes less negative with increasing λ, approaching its local positive value and stabilizing the modes. The window of unstable modes shifts to shorter λ with increasing Jrf, causing the modes to be suppressed by diffusion at higher Jrf. At lower Jrf, the decrease in bulk plasma density with decreasing Jrf suppresses the striations.

Chemical Composition and Processes in the DC Discharge Plasma of Atmospheric Pressure with a Liquid Electrolyte Cathode

In this study, the concentrations of sodium, copper, and oxygen atoms in the ground state were obtained on the basis of spectral measurements. The values of concentrations agree with the results of kinetic studies of condensate accumulation. The modeling of the formation processes and further transformations of active particles in atmospheric pressure discharge plasma with a sodium chloride solution used as a cathode was performed. Experimental data on the composition of the gas phase and the physical parameters of plasma were used in the numerical simulation. The calculations were carried out using experimental values of E/N and gas temperatures for the discharge currents range of 10–70 mA. The concentrations of many active particles (O2(a1Δg), O2(b1Σg+), O(3P), NO, H2O2, OH, HO2) in the gas phase were determined. The channels of influence of the transfer processes on the properties of the discharge were established.