Plasma Chemistry and Plasma Processing最新文献

This work investigates the features of a sputtering system with an asymmetrical planar hollow cathode discharge at 10–100 Pa pressures. The asymmetrical hollow cathode discharge occurs between two planar cathodes with different negative potentials. The problem of diffusion transport of sputtered material was formulated and numerically solved. To verify the results of the numerical model, tungsten coatings were deposited at a pressure of 40 Pa. The numerical model results based on the diffusion transport were compared with experimental data. The qualitative agreement between the model and experimental results was demonstrated. For substrates with positive curvature and a size smaller than the output aperture of the sputtering system, a characteristic increase in film thickness to the edges has been experimentally and numerically shown, which is associated with the diffusive nature of the sputtered material transport.

This study presents the development of an equivalent electrical circuit model using MATLAB/Simulink to simulate the discharge behaviour of a coaxial cylindrical dielectric barrier discharge (DBD) and explores the influence of the flow regime on its electrical characteristics. Validation of the experimental findings was performed using Simulink and Chemical Workbench (CWB). The simulations provided valuable insights into the DBD behaviour, facilitating its performance optimization. The equivalent circuit model demonstrated accurate predictions of peak current amplitude ((I_{peak} )), root mean square of total current (left( { I_{rms } } right)), and microfilament discharge resistance (left( { R_{f } } right)). The study unveiled a significant impact of the flow regime on the electrical properties of the DBD. As the flow rate (Q) transitioned from the laminar flow regime (Reynolds number, Re = 300) to the turbulent flow regime (Re = 4500), the peak current ((I_{peak} )) exhibited an increase from 60 to 80 mA for Argon (Ar) and 90–140 mA for Nitrogen (N₂) gas. Simultaneously, the (R_{f }) decreased from 3.0 to 0.6 mΩ for Ar and 2.0 mΩ to 0.1 mΩ for N₂. The effect of Q on discharge mode was analyzed using image analysis. In N₂, the discharge remained more filamentary across a wider range of Q (from 5.8 to 31.5 SLPM) compared to Ar. Electron density (n_e) estimated from both experimental data and the CWB model, was found to be of the same order of magnitude. For both gases, an increase in Q led to a rise in n_e and a reduction in (R_{f}). Even at higher Q, the filamentary structure in N₂ was more persistent compared to Ar. The effect of Q on gas temperature ((T_{g })) was also studied, showing a decrease in (T_{g }) for both Ar and N₂, from 408 to 320 K for Ar and from 689 to 435 K for N₂, corresponding to increased Q under identical conditions. The impact of the flow regime on (R_{f }) was analyzed using the Peclet number (Pe) to gain a better understanding of heat/mass transport from the discharge to the surroundings. The MATLAB/Simulink and CWB models corroborated these findings, demonstrating excellent agreement with the experimental results. This validation underscores the reliability of the models in effectively characterizing the discharge parameters of the DBD.

Cold atmospheric plasma (CAP) finds numerous applications across various sectors, including industry (e.g. surface modification) and medicine (e.g. tissue regeneration, wound healing, oncology, and dentistry). However, understanding the mechanical properties of materials undergoing CAP treatment is of great importance, particularly for applications involving changes in material properties. This study aims to utilize CAP as an excitation device for assessing the mechanical properties of a polymethyl methacrylate (PMMA) sample. CAP was employed to induce vibrations on a PMMA sample around its resonance frequency, and the resulting vibrations were measured by a scanning laser doppler vibrometer. The elastic modulus of the PMMA sample was then calculated based on the stress and strain profiles obtained from the measured vibrations. The obtained elastic modulus value of 4.87 GPa showed excellent agreement with the 4.83 GPa value obtained using other excitation devices, indicating the reliability of CAP in mechanical characterization. This study is the first step toward potential applications that can break new ground in the use of CAP in monitoring and characterization of mechanical properties during CAP treatment (e.g. surface treatment), paving the way for enhanced control and optimization of CAP-based processes in various applications.

Graphical Abstract

An experimental and numerical characterization of a falling film plasma reactor for the degradation of aqueous organic pollutants in batch operation mode is reported. A pulsed corona discharge in humid air is excited by short voltage pulses (< 100 ns) generated by a capacitive-storage power source and a high-pressure gas spark-gap. Indigo carmine is chosen as the reference pollutant. A volume of 20 L of indigo carmine solution with an initial concentration of 20 mg/L are completely decolored after 11 min treatment for a reactor mean power of 33 W. The electrical-energy efficiency per order and the energy yield of the process are calculated to be 0.25 kWh/m³ and 101 g/kWh, respectively. The generation of reactive species is also assessed in both the liquid and gas phases. Very low concentrations of NO₂^– and NO₃^– ions are found, practically not causing water acidification. The main gaseous species produced by the corona discharge are O₃ and HO₂· radicals. In addition, a kinetic model of the reactor is presented and compared with measured data. The numerical results indicate that reactions in the stagnant liquid film next to the gas-liquid interface are essential to explain the measured removal rates. The rapid kinetic regime of the liquid film strongly accelerates the uptake rates of HO₂· (rapidly converted to O₂^–·) and O₃, which far exceed the uptake rates predicted by the mass transfer coefficient for a reactionless film.

This study investigates the effectiveness of plasma treatment in degrading organic contaminants from denim industry wastewater using a dielectric barrier discharge (DBD) plasma jet. A 3-way full factorial design was applied to evaluate the influence of treatment time, power, and airflow rate on degradation efficiency. Initial tests on dyes such as crystal violet, congo red, methylene blue, and indigo confirmed the efficacy of the plasma jet, with degradation efficiencies of 96.3%, 86.3%, 93.4%, and 97.8%, respectively, within treatment times ranging from 8 to 60 min. For denim industry wastewater, plasma treatment resulted in notable reductions in chemical oxygen demand (COD), with 35.0% removal for virgin wastewater and 15.9% for industry-treated wastewater. Total organic carbon removal increased by 42.6% for virgin wastewater and 18.2% for industry-treated wastewater, indicating substantial mineralization. Toxicity analysis showed that plasma-treated wastewater supported freshwater algae growth, suggesting a non-toxic nature and enrichment with nitrogen-based nutrients. Regression analysis and optimization identified plasma treatment time and power as the key factors in maximizing COD removal. Under optimal conditions, COD removal reached 97.65% for virgin wastewater and 98.1% for industry-treated wastewater. In conclusion, plasma treatment offers an effective and sustainable method for wastewater management in the textile industry, ensuring significant pollutant degradation, improved water quality, and a non-toxic, nutrient-rich effluent suitable for environmental applications.

The presented study shows experimental results with literature comparison for understanding of the oxygen removal in coke oven gas (COG) with plasma. The reaction of oxygen with the main COG components H₂, CH₄, and CO are investigated as well as the occurrence of potential side reactions as the splitting of CO₂ and CH₄. Further potential side reactions in the COG mixture known from literature as hydrogenation reactions are discussed in contrast to the observations of the experiments.

Conventional chemical processing methods, employed for transforming hydrocarbon mixtures into more valuable forms, are known to consume high amounts of energy and produce a substantial amount of greenhouse gas emissions. This paper investigates an alternative approach employing non-thermal plasma, in a controlled temperature environment, to synthesize higher-order hydrocarbons. The method examined in this paper, has the potential to reduce energy requirements. Effects of temperature and hydrocarbon chain length on liquid and gas production efficiency are studied. A comparative analysis of the different hydrocarbons as reactants underscores the promising attributes of n-octane in this application. With the proposed reactor configuration, the highest average liquid production efficiency was found in n-octane at 20 °C. Organic compounds with carbon chain lengths as large as 20 carbons where successfully synthesized in the reactor configuration when using decane as the reactant. The observed trends alluded to different chemical reaction pathways being prevalent in different temperature conditions.

In this study, we present a novel pulsed microwave-induced plasma (MIP) source coupled with a glow discharge for optical emission spectrometry (MIP-OES), operating at 1000 W power and a frequency of 2.45 GHz. The MIP cavity consists of a stainless steel cylindrical waveguide connected to a circular resonator made of the same material, joined through a dielectric quartz disc. The output of the MIP cavity is linked to a closed glow discharge quartz tube and a mechanical pump. Numerical simulations were employed to optimize the structure and dimensions of the MIP cavity. The nozzle position of the cylindrical resonator's output was precisely adjusted to align with the maximum magnetic field, achieving the TM₀₁₁ mode, which results in a point plasma with high density. This configuration enables the cavity to produce a dense, warm plasma emission zone with a consistent emission rate around the circumference of the emitting source. The results demonstrate that the designed MIP source exhibits a significantly higher density and temperature compared to other sources with similar microwave parameters.

We establish an excilamp model of the Kr/Cl₂ Dielectric Barrier Discharge (DBD) and prove the rationality of the model by the experiment. It includes forward reactions of higher excited KrCl, such as the harpooning reaction, quenching reaction, and discharge radiation. Based on the forward reaction system, we present an energy level diagram of the reaction path, which serves as a foundation for deeper comprehension of the impact of the activated KrCl and Kr₂Cl chemical processes on the production and intensification of radiation at 222 nm. The microdischarge amplitude appears to be reduced due to the quenching equilibrium effect which is enhanced when the KrCl excited state converts to Kr₂Cl and the discharge current appears to lag due to the figinternal field resistance. The density of excited KrCl particles decreases by 7.6% and power efficiency rises by 1.7% lift with every 20 mbar increment for a higher probability of inelastic collision. A greater proportion of chlorine increases the probability of a reaction with chlorine, inhibiting the creation of radiation particles and enhancing the quenching of radiation reactions. The action balances the numerical concentrations of Kr and Cl and strongly suppresses the excited Kr₂Cl particles. The simulation demonstrates that there are negligible disturbance on power supply efficiency as the proportion of 325 nm radiation in the spectrum decreases from 6 to 1%. The change of discharge gap will cause the change of discharge mode, and higher discharge gap will cause more intense glow discharge.

Non-thermal plasma (NTP) is explored as a sustainable technology to treat and enhance seed germination and growth of major food crops to address food security issues worldwide. This review would provide an overview on the latest advancement of NTP applications for food crop seeds, considering the different food crop groups, and summarizes the mechanism of how NTP improves germination and growth. Results vary based on seed type, plasma setup, and source, such as direct glow plasma or plasma-activated water (PAW). In direct glow plasma, reactive species induce morphological changes by bombarding seed surfaces with ions and radicals. PAW, on the other hand, promotes seed germination through reactive oxygen and nitrogen species (RONS) present in the water. Regardless of treatment sources, RONS ions also play a crucial role in modifying seed morphology, activating antioxidant enzymes, and influencing hormonal pathways to stimulate growth processes while suppressing inhibitory signals. NTP treatment shows promising potential in plasma agriculture, but excessive exposure may adversely affect plant growth. Additionally, NTP induces epigenetic changes, such as DNA methylation, which regulates stress-related genes, further supporting seed performance. Despite these advancements, critical knowledge gaps remain, including the need for standardized plasma energy evaluations, long-term yield impact, and safety validations for food produced from plasma-treated seeds. Future research must address these aspects to ensure the widespread, sustainable application of NTP technology in agriculture.