Plasma Chemistry and Plasma Processing最新文献

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.