Plasma Chemistry and Plasma Processing最新文献

A zero-dimensionl model is developed to study the chemical kinetics of a volumetric dielectric barrier discharge (DBD) reactor operating with humid air at atmospheric pressure. This work focuses on the relation between molecular vibrational excitation, the plasma reactor input power and the number densities of several species that are known to play an important role in biomedical applications (e.g. (textrm{O}_{3},textrm{NO, NO}_{2}), ...). A preliminary study is carried out to observe the influence of water molecules on the electron energy distribution function for different values of water concentration and reduced electric field. A simplified approach is then adopted to quantify the contribution of vibrationally-excited (textrm{O}_{2}) molecules to (textrm{NO}) formation. The results obtained using our detailed model suggest that for the physical conditions considered in this work (textrm{O}_{2}) vibrational kinetics can be neglected without compromising the overall accuracy of the simulation. Finally, a reaction set is coupled with an equivalent circuit model to simulate the E-I characteristic of a typical DBD reactor. Different simulations were carried out considering different values of the average plasma input power densities. A particular focus was given to the influence of the Zeldovich mechanism on (textrm{O}_{3}) and (textrm{NO}_textrm{X}) production performing simulations where this reaction is not considered. The obtained results are shown and the role of vibrationally excited (textrm{N}_{2}) molecules is discussed. The simulation results indicate also that (textrm{N}_{2}) vibrational excitation, and more precisely the Zeldovich mechanism, has a larger effect on (textrm{O}_{3}) and (textrm{NO}_textrm{X}) production at intermediate input power levels.

The paper presents a novel method for obtaining cobalt ferrites with a spinel type structure under the action of a nonequilibrium atmospheric pressure gas-discharge plasma in air on a mixture of solid iron and cobalt hydroxonitrates. The data of energy dispersive X-ray spectroscopy and X-ray phase analysis showed that the synthesized powders have a complex phase and chemical composition, which depends on the Fe:Co molar ratio in the initial salts. The best result in terms of yield of cobalt ferrite is obtained with Fe:Co = 2:1. The resulting material contains 86 wt% Fe₂CoO₄, also 13.5 wt% Fe₂O₃ and 0.5 wt% Fe₃O₄. At other ratios, Co₃O₄ is also formed. According to dynamic light scattering data, the obtained powders consist of two characteristic fractions. The main fraction (94%) is represented by particles 105 ± 4 nm in size. And the other fraction (6%) consists of particles 18 ± 4 nm in size. The resulting materials have magnetic properties. So, for powders obtained from salts with Fe:Co = 2:1 the coercive force was (sim)490 Oe. The saturation magnetization was (sim)52 emu/g, and the remnant magnetization was (sim)22 emu/g.

Cold atmospheric plasma (CAP) has been reported as a promising technique in dentistry. The biosafety and mechanisms on periodontal tissue are especially important in clinical practice. This study aims to evaluate the cytotoxicity, genotoxicity and mechanisms of human periodontal ligament fibroblasts (hPDLFs) induced by CAP. The antimicrobial effect on Porphyromonas gingivalis (P. gingivalis) was evaluated using the colony-forming unit methods (CFU). Human periodontal ligament fibroblasts were treated with CAP for variable times (1, 2, 4, 8, and 16 min). CCK-8 assays were performed to detect cell viability and flow cytometry was performed to measure the cell cycle and apoptosis. Cell migration ability was determined by scratch assays. The physicochemical properties of plasma activated medium were evaluated, including the pH values, H₂O₂ and NO levels. DCF-DA staining and analysis were performed to evaluate intracellular ROS levels inside cells using flow cytometry. Immunofluorescence of DNA double-strand breaks (DSBs) marker, phosphorylated γH2AX was used to establish the genotoxicity of plasma. The results showed that CAP has a significant inhibition effect of P. gingivalis after 6 min treatment. It has significantly dose-dependent effects that ranging from increasing cell proliferation to inducing apoptosis. A low doses (1, 2, 4, and 8 min) could enhance the cell proliferation. A high dose (16 min) resulted in the inhibition of cell proliferation (p < 0.01). It is also shown that these effects are primarily due to the formation of reactive oxygen and nitrogen species (RONS).

In this work, the successful synthesis of nanostructures based on MXenes by initiating a pulse discharge between titanium wires immersed in carbon tetrachloride is presented. By choosing carbon tetrachloride as the environment, the formation of oxide structures in the synthesized samples could be avoided. The characterization of the obtained structures was carried out using various techniques, including scanning electron microscopy, X-ray phase analysis, EDS, Raman and FTIR spectroscopy. The results confirmed the successful formation of MXenes with a Cl⁻ occupying the interlayer space. The properties of the discharge initiated in CCl₄ were also determined. The results suggest the potential of this plasma-liquid method for the synthesis of high-purity MXenes without impurities commonly found in conventionally prepared samples.

The stepped-nozzle arc plasma torch (SNAPT) is a promising arc source due to the advantages of high stability and high energy density, but the micro-time scale discharge characteristics have not yet been adequately investigated. In this study, a SNAPT was designed and studied, in order to investigate the effects of discharge current, gas flow rate, and nozzle morphology on the discharge characteristics. The results show that the volt-ampere characteristics of the SNAPT have an increasing curve when the gas flow rate is greater than 4 Nm³/h, and a decreasing curve when the gas flow rate is 3 Nm³/h. This result is related to the position of the arc root, and an arc constriction phenomenon occurs at high current and low gas flow rate. The thermal efficiency of the SNAPT decreases with the increasing current and decreasing gas flow rate, ranging from 69.6 to 82.3% within the experimental parameters. The optical emission spectroscopy results show that there are many active particles inside the plasma. The experimental parameters of the heavy particle temperature of 4851.5 to 9189.3 K and the electron temperature of 7846.9 to 10185.6 K both correspond to the Boltzmann distribution and are close to the local thermodynamic equilibrium state. Comparative experimental results show that the cylindrical-nozzle has the decreasing volt-ampere characteristics and higher voltages, but has large voltage fluctuations and poor stability compared with the stepped-nozzle. The results of the study are of guiding significance for design, selection of operating parameters, and application scenarios for this type of plasma torch.

In this work, we investigate the effect of an external transverse weak magnetic field on the creation of metastable helium atoms and excited helium molecules in a high-voltage pulsed discharge in helium at medium pressure. A two-dimensional fluid model is used to describe a high-voltage pulsed discharge in helium in the external transverse weak magnetic field. The dynamics of discharge development in the high-voltage pulsed discharge in helium at a pressure of 30 Torr in the presence and absence of the magnetic field is studied. The effect of the external magnetic field on the behavior of the density of charged particles, metastable helium atoms, and excited helium molecules in the high-voltage pulsed helium discharge has been investigated. It is shown that in the discharge region, the density of metastable atoms decreases when a transverse magnetic field is applied, which is a consequence of an increase in the frequency of stepwise ionization.

In this study, a coaxial dielectric barrier discharge (DBD) reactor was employed using various gases: compressed air (CA), helium (He), or argon (Ar) to produce plasma-activated water (PAW) from deionized water. The influence of these gases on the generation and quantification of reactive oxygen and nitrogen species (RONS) was examined. Their impact on PAW's physicochemical properties, including pH, oxygen reduction potential (ORP), and conductivity, was also assessed. In parallel, the efficacy of produced PAW against microbial species such as Staphylococcus aureus, Escherichia coli, and Candida albicans was evaluated, in addition to their cytotoxicity to mammalian cells. Notably, after a 10-min contact, a 99.99% reduction in S. aureus and E. coli was observed when CA and Ar were used, and reductions of 99.96% and 99.95% were seen when He was employed, respectively. For C. albicans, reductions of 12.05% with CA, 22.89% with Ar, and 39.76% with He was observed. After 30 min, a reduction of up to 53.41% was achieved with Ar. Additionally, PAW generated with all the gases were classified as non-cytotoxic. These findings underscore the potential of the coaxial DBD reactor system in PAW production, emphasizing its significant antimicrobial properties and low toxicity to mammalian cells.

Over the last decade, more and more attention has been paid to applications of non-thermal plasma in agriculture, where it is used to decontaminate various microorganisms and to improve the seed germination. In this study, we present the results of a newly developed point-to-ring NTP transient spark discharge apparatus (NTP), plasma activated water (PAW) and their combined treatment on Durum wheat and Common wheat grains under laboratory conditions. Transient spark discharge treatment was used as direct treatment while indirect treatment of wheat grains was performed by PAW produced in point-to-plane NTP transient spark apparatus. We found that the degree of grain surface decontamination was in order NTP > PAW > combined treatment. In the case of Durum wheat grain germination, all treatments increased germination with increasing exposure times, while in the case of Common wheat, PAW treatment and combined treatment did not significantly increase the grain germination. In conclusion, plasma treatment has enormous potential for use in agriculture and its possibilities need to be fully explored.

The increased usage of diesel in the past 20 years, particularly in developing countries like India, has resulted in serious concerns in abating gaseous pollutants such as oxides of nitrogen (NO_X) and hydrocarbons (HC). On the other hand, the growing metallurgical processing industries leave behind tons of solid waste, making waste management a bigger issue. In the current work several industry wastes have been tested under discharge plasma environment for their catalytic properties in the removal of HCs from diesel exhaust. To explore the benefit of metal oxide components, present in industry wastes, a new approach was proposed in this work wherein two industrial wastes were blended to form a composite waste which was then powdered and bound to form pellets. Four such composite waste-based pellets, namely red mud + iron tailing, iron tailing + lignite ash, lignite ash + copper slag and red mud + oyster shells, were tested for their catalytic properties under plasma environment. Exhaust emanating from a 6 HP engine is sampled and studied for HC removal in a pulsed plasma reactor embedded with composite wastes. The pellets being porous in nature, studies were also conducted for HC adsorption by cascading composite wastes with plasma alone while treating the exhaust. All the composite wastes exhibited good plasma catalysis in HC removal (58–73%) when compared to that with plasma alone (31%). Further, there is a marked difference between plasma adsorption and plasma catalysis by a factor of 1.75–2.2 indicating synergy between plasma and metal oxides present in composite wastes while catalysing HC removal.