Plasma Chemistry and Plasma Processing最新文献

Fluorinated gases, e.g., CF₃I, C₃F₈, C₄F₈, C₄F₇N, and C₅F₁₀O, show potential to replace SF₆ in power industry due to their high dielectric strength and low global warming potential . However, particle condensation from arc plasmas of these compounds may reduce dielectric performance. We perform a systematic investigation of particle condensation in two-temperature (2T) arc plasmas of various SF₆ replacements mixed with CO₂, N₂, and O₂, by the Gibbs free energy minimization and entropy maximization methods. The influences of buffer gases, non-equilibrium degree, and gas pressure on particle condensation are discussed in various cases. The results indicate that O₂ is necessary to prevent graphite formation in carbon–fluorine gaseous arcs, and specific mixing ratios of CO₂ and N₂ are required to avoid graphite and iodine crystals in CF₃I arc plasmas. The relationship between condensation temperature and non-equilibrium degree is complex, with peaks and valleys observed for graphite and iodine crystal condensation temperatures. Moreover, different calculation methods (Gibbs free energy minimization versus entropy maximization) show varying sensitivity of condensation temperatures to pressure changes. All the above findings highlight the importance of considering non-equilibrium effects and multiple condensed species in evaluating arc plasma compositions of SF₆ replacements.

C₅F₁₀O-Air mixtures have a great potential to replace SF₆ in medium-voltage power equipment. However, during the partial overheating or arc discharge, C₅F₁₀O-Air mixtures are inevitably to decompose to form various byproducts. The local chemical non-equilibrium and local thermal non-equilibrium appears due to the finite reaction rates and insufficient energy change between species. This paper establishes a chemical kinetic model to calculate the decomposition byproducts of C₅F₁₀O-Air mixtures from 500 K to 3500 K by taking into account the local thermal non-equilibrium and local chemical non-equilibrium simultaneously. The chemical kinetic model contains 50 species and 249 reactions. All the reactions are assumed to be reversible except the reactions producing photos. The local thermal non-equilibrium is characterized by the difference of the electron temperature (T_e) and the temperature of heavy species (T_h). In this work, the ratio of T_e to T_h is determined to be a function of the electron number density. Therefore, the value varies with electron number density. The temperature dependent decomposition composition of C₅F₁₀O-Air mixtures with C₅F₁₀O content to be 5%, 10% and 15% are obtained. In order to investigate the effects of Air on the decomposition of C₅F₁₀O, the decomposition products of pure C₅F₁₀O from 500 K to 3500 K are also investigated. In addition, the main chemical processes in 0.1C₅F₁₀O-0.9Air mixture are investigated by capturing the main reaction pathways. The main reaction pathways can help interpret the formation mechanism of the decomposition products.

Applications of plasmas in agriculture are fascinating researchers because of its potentiality. Plasmas are applied either for seed treatment or as foliar application of plasma-activated water (PAW) for studying agricultural yield. No work has been done so far to study the effects on growth parameters, enzymatic activities, nutritional parameters, and yield of potato (Solanum tubersum L.) grown from the second-generation seeds (G2) (seeds collected from the potato plants where foliar spray of PAW was applied). Two-fold plasma treatments were applied in this experiment: (a) potato seeds were treated in water with plasma and (b) foliar spray of PAW was applied to potato plants. Effects of plasma treatments were characterized by enzymatic activities, sugar and protein concentrations, potato plant growth and yield characters. The findings show that the plant length, stem diameter, fresh weight, and the concentrations of total chlorophyll and carotene are increased in the plants where G2 treated seeds along with foliar spray of PAWs were provided. Further, the concentrations of total soluble sugar, protein and minerals were increased. Besides, the yield of potato was enhanced by (23.95%), and (23.21%), respectively, in the plants where combined plasma treatments were used compared to controls of first-generation (G1) plasma treated and untreated seeds along with PAW foliar spray.

The aim of this article is to improve the performance of DBD excimer lamps systems for UV production. Within this framework, our approach considers two distinct directions: the geometric dimensions of the double-barrier lamp bulb and the characteristics of the power supply. To explore these directions, a sampling of 19 bulbs of different geometries is considered, and a specially designed power supply is used, capable of controlling the shape (duration and magnitude) and frequency of current pulses injected into the plasma. A dedicated test bench, including a supervisory program that drives the power supply and collects system performance data, is used to perform parametric sweeps and guarantee measurement repeatability: the set of electrical parameters is fully explored for each lamp, and each experiment is characterized by UV emission performance and electrical generator operating conditions. Multiquadric response surfaces, used to format the results of this multi-variable exploration, reveal the most efficient directions for system optimization: increasing gas volume and, at a given operating frequency, providing the shortest possible current pulses with high amplitude can increase both UV emission and conversion efficiency.

This study utilized a direct current-needle system for plasma generation and liquid flow inducement. The liquid flow was visualized and analyzed by particle image velocimetry. Electrolyte solutions of potassium chloride, potassium bromide, potassium iodide, calcium chloride and chromium(III) nitrate with concentrations ranging from 0.1 to 1.0 mM were studied. The results indicate that the plasma induces an upward liquid flow with an area mean velocity of up to 3.0 mm/s. The flow speed decreases with increasing electrolyte concentration and shows a strong dependence on the solution’s conductivity. This study proposed a physical model based on these findings. The plasma generates short-lived ions and electrons, which shift the hydrogen bonds among the water molecules through their electrical effect. This process creates an intermolecular force gradient and induces liquid flow on the water surface. The distance that electrostatic effect of a charged particle can persist in an electrolyte solution is defined as Debye length. This physical quantity decreases with increasing ionic strength or electrical conductivity. Thus, the plasma induces slower liquid flow in solutions with higher electrolyte concentration. Based on the regression analysis, the characteristic flow velocity is significantly proportional to the square of the solution’s Debye length, with a coefficient of determination of 0.9365.

In this work, the productions of reactive oxygen and nitrogen species (RONS) with duty ratio in atmospheric pressure plasma jet was studied. This study uses the duty ratio comprising an on-time duration with a sinusoidal voltage bunch and an off-time duration without any voltage bunch for the plasma jet operation. The reactive species NO, NO₂, N₂O, and O₃ were measured in the plasma jet in accordance with the duty ratio by gas-FTIR and ozone meter. The NO_x are the mainly produced in the plasma jet due to the high temperature, and all reactive species exhibited increased production when increasing the duty ratio. But, under the fixed duty-ratio of 10%, reactive species were different trends by the on-time duration. Although there was no additional dissipated power at a given duty ratio, NO production enhanced by 1.5 times, whereas the production of the other species decreased with increasing on-time duration. These phenomena were explained by measured rotational temperature with on-time in this experiment.

Plasma dose quantification is one of the core problems in clinical of plasma medicine. The spatial-temporal distribution and the total dose of the reactive species from plasma into the processed object are especially important in clinic. In this study, we developed a measurement scheme based on image processing technology for quantifying the penetration dose of reactive oxygen species (ROS) into model tissues, and analyzed the effects of treatment conditions on the concentration distribution and the total amount. First, by establishing a numerical relationship between the color index and ROS concentration through image processing and titration experiment, the spatial concentration distribution of ROS on each sliced layer of the treated sample was calculated. Then, the ROS penetration depth was obtained through image segmentation of longitudinal sliced tissue image. Finally, by integrating the concentration of each layer and the depth, the absolute amount of ROS was obtained. Both the penetration depth and absolute amount exhibit a positive correlation with treatment time and a negative correlation with treatment distance under an Ar plasma jet treatment. A range of penetration depth of 0.5–3 mm and total dose of 0.05–0.47 µmol was obtained under the setting conditions. The effectiveness of the proposed method was confirmed by comparing with the total ROS amount measured by UV-Vis method dissolved in liquid, providing a new solution for the issue in plasma dose quantification, and is also benefit for the understanding of plasma-tissue interaction.

This article presents a comprehensive investigation of the impact of cathode and anticathode geometries on the performance of a cold cathode Penning ion source. Both experimental and simulation-based approaches were employed to optimize plasma production and ion extraction. Specifically, the effects of cathode geometry on breakdown voltage and extraction current, as well as the effects of anticathode geometry on extraction current under different voltage and hydrogen gas pressure conditions, were studied for two cathode models and three anticathode models. The study also reported on the effects of setup conditions, including ignition and working pressure range, on the ion source performance during the experiment, which lasted for the first, third, and seventh days. The experimental results revealed that changes in cathode geometry under the same conditions led to a 160 V reduction in breakdown voltage and a four-fold increase in extraction current in the proposed design. Furthermore, altering the geometry of the anticathode resulted in an increase in extraction current of the ion source with the conical aperture anticathode, which exhibited greater efficiency compared to the cylindrical aperture anticathode. Overall, this study contributes to a deeper understanding of the relationship between electrode design and plasma properties in cold cathode Penning ion sources, and offers important insights for optimizing their performance and efficiency.

Graphical Abstract

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.