Plasma Chemistry and Plasma Processing最新文献

This study investigates the electrical and chemical characteristics of a non-thermal atmospheric pressure DC plasma discharge in a needle-to-liquid configuration. A high-voltage (HV) needle is placed at 2 mm above the liquid surface, while the ground electrode is submerged in a potassium halide solution (potassium iodide (KI) or potassium chloride (KCl)). The reactive species in the liquid are estimated based on their reaction with KI, producing iodine (I₂), either through direct titration of the plasma-treated KI or back titration of the plasma-treated KCl. Different discharge regimes are identified for each polarity: Trichel corona, unstable glow, and stable glow for negative polarity, and onset streamer, Hermstein glow corona, unstable glow, and stable glow for positive polarity. The presence of a liquid surface allows for higher voltage and current ranges without sparking and facilitates the establishment of a stable glow discharge, which is challenging in the case of a needle-to-plate configuration. The concentration of reactive species in the liquid is significantly lower in corona regimes compared to glow regimes, due to their lower power consumption, and the absence of direct contact between the plasma and the liquid. Moreover, the positive unstable glow is three times more efficient than the negative stable glow. One explanation is that the flow induced within the liquid during the positive unstable glow discharge enhances mixing of reactive species, preventing their saturation at the gas-liquid interface and improving their penetration into the liquid phase.

Hydrocarbon chains produced as byproduct of natural gas extraction and petrochemical processing can be valorised into syngas/H₂ and oxygenated fuels in a modular fashion through electrified modular plasma reactors. A plethora of configurations is available for light hydrocarbons reforming, with cold plasma assemblies emerging as the favourite option for both gas-phase and biphasic gas/liquid set-ups. Accurate control of dehydrogenation or partial oxidation reactions is provided by the implementation of a catalyst or through microreactor technology. On the contrary, warm plasma reactors are more suitable for reforming of gasoline/diesel chains, promoting higher throughput of H₂ per energy input. This reaction route does not necessarily require the deployment of a catalyst, hence making these systems more suitable for modular, decentralized processes. Online diagnostic techniques shed light on the reaction mechanism, where solid carbon deposits embody a low-value byproduct.

The reactive oxygen and nitrogen species generated by plasma have demonstrated consequential effects on diverse commercial applications. Hence, studying the chemistry and spatial distribution of reactive species in plasma is imperative for understanding the influence of plasma in various applications. This study aims to systematically explore the plasma chemistry of a pin-to-plate negative direct current (DC) corona discharge in dry air, using simulations based on a two dimensional (2D) axisymmetric fluid model. The model encompasses a comprehensive set of chemical reactions involving 33 biomedically active species (ROS and RNS). This study entails a rigorous evaluation of the 2D spatial distribution of all chemical species, detailing their minimum and maximum values, at a needle voltage of −10 kV. To enhance visualization and enable comparisons, we integrate contour lines into the density distributions to indicate the average density of each species. ({text{N}}_{2}left({text{A}}^{3}sumright)) among nitrogen species, O₃ and ({text{O}}_{2}left({text{a}}^{1}Deltaright)) among oxygen species, and N₂O among NOx species exhibit the highest average density in the simulation domain. Furthermore, key reactions involved in the production and consumption of each species are thoroughly discussed. Additionally, the research examines the influence of needle voltage, ranging from −5 to −12.5 kV, on the peak and average densities of all species investigated. Lastly, to validate the simulation model, an experimental study of the pin-to-plate negative DC corona discharge is conducted, during which the voltage-current characteristics and optical emission spectrometry (OES) profiles are measured. The simulation results are in good agreement with the experimental data.

This study focuses on tuning the metal content in a polymer/metal composite produced by a low-pressure cold plasma process using an organometallic precursor. Firstly, the evolution of the metal content is studied according to the experimental parameters. Monomer fragmentation and the balance between ablation and polymerization influence the metal content in the composite. In addition, physical sputtering through argon plasma treatment of the composite can be used to significantly increase its metal content. Finally, the ageing of the composite is studied. Both the inorganic and organic parts of the material are affected by oxidation. A comparison of the composite ageing with a purely organic polymer highlights the effect of copper on oxidation.

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.