Plasma Chemistry and Plasma Processing最新文献

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.

Atmospheric pressure low power plasma jets operating in noble gases are a widespread tool in plasma medicine studies. We present experimental results obtained in one such device, which combine physical, chemical and biological measurements to assess the effectiveness in production of reactive oxygen and nitrogen species and in inactivation of Escherichia coli, a model microorganism. We proved that it exists a threshold effect on the source control parameters, defining a voltage level which has to be exceeded in order to obtain effective bacteria inactivation. This result is discussed in terms of the reactive species produced within the plasma and in treated water.

Surface dielectric barrier discharges (sDBD) are efficient and scalable plasma sources for plasma-based gas conversion. One prominent feature of an sDBD is the generation of an ion wind, which exerts a force on the neutrals, thus leading to an efficient mixing of plasma and a passing gas stream. This becomes apparent by the creation of upstream and downstream vortices in the vicinity of the plasma. In this study, these vortices are generated by high voltage burst pulses consisting of two half cycles of an almost sinusoidal voltage shape. The vortices are monitored by Schlieren imaging diagnostic to benchmark and connect two simulations of the sDBD: a plasma model simulating a streamer for 25 ns starting from the electrode and propagating along a dielectric surface followed by a decay. The streamer is the source of electrical charges accelerated as ion wind by the applied electric field from the sDBD power supply. A second flow simulation models this ion wind as a time-averaged thrust acting on the passing gas stream. The conversion of the time-resolved forces from the nanosecond plasma simulation into the steady state thrust in the flow simulation indicates that the force from the plasma lasts much longer than the actual streamer propagation phase. This is explained by the fact that the charges in the streamer channel remain present for almost 100 ns, and the voltage from the power supply lasts for a few microseconds being applied to the electrode so that ions in the streamer channel are still accelerated even after a streamer stops to propagate after a few ns. The thrust generated during the streamer phase, including the relaxation phase, agrees well with predictions from flow simulation. Additionally, properly converting the time-resolved forces from the plasma simulation into a time-averaged thrust for the flow simulation yields exactly the synthetic Schlieren images as measured in the experiments.

In negative hydrogen ion sources in situ adsorption of Cs is typically used to generate low work function converter surfaces. The achievement of a temporally stable low work function coating is, however, challenging due to the hydrogen plasma interaction with the surface. Particularly in ion sources for neutral beam injection systems for fusion with pulse durations of minutes to hours temporal instabilities are a major issue and limit the source performance. To clarify the influence of the hydrogen plasma on the converter surface, investigations are performed at an experiment equipped with an absolute work function diagnostic based on the photoelectric effect. Caesiated surfaces are exposed to the full plasma impact by the generation of plasmas in front of the surface as well as to selected plasma species (H atoms, positive ions and VUV/UV photons) from an external plasma source to identify driving mechanisms that lead to surface changes. Depending on the exposure time and initial surface condition, the plasma strongly affects the surface in terms of work function and quantum efficiency (QE). For degraded Cs layers (work function (ge 3) eV) a favorable increase in QE and reduction in work function can be achieved, while for Cs layers with an ultra-low work function of (1.2-1.3) eV the opposite is true. It is found that each plasma species can influence the Cs layers and that VUV photons lead to a work function increase of ultra-low work function layers. For sufficiently high VUV fluences a severe work function increase by 0.5 eV is given, highlighting the relevance of photochemical processes in the plasma-surface interaction and demonstrating that ultra-low work function layers are not stable in a hydrogen plasma environment.

Cold plasmas have been considered an effective method in numerous scientific fields. One excellent target for plasma treatment is amino acids. Transient spark plasma discharge (TSP) is very useful in changing the chemical structures of biological systems due to its high electron density. TSP discharges as DC-driven self-pulsing discharges allow ionization and effective chemical processes to be performed easily. This type of plasma discharge consists of numerous streamers with a high electric field that can be transferred into short spark current pulses. In this study, we utilized a pin-to-ring TSP with a fixed voltage and frequency of ~ 5 kV and 220 Hz, respectively. The present study was conducted to estimate the synergetic effect of a TSP device and cysteine (Cys) in stopping hepatotoxicity. The interaction of Ar plasma with Cys solution was investigated by LCMS/MS, revealing that many new biochemical products with different molecular weights were produced under plasma treatment. Glutathione (GSH) level and DPPH scavenging activity were performed. Biochemical markers and histopathological analysis were also evaluated. Results revealed that by increased levels of GSH and anti-oxidant activity, PTC solution can preserve as opposed to injuries caused by CCl₄ injection to a greater extent than untreated Cys even at a low dose of amino acid. The ALP, ALT, and AST activity levels were closer to the normal level when PTC was received than Cys. After receiving PTC, more positive liver and kidney tissue changes were observed in the CCl₄ group. It also had a great impact on oxidative antioxidant parameters. Therefore, PTC as an effective drug has shown a positive effect in inhibiting hepatotoxicity because it contains various biomolecules under the influence of the plasma-produced reactive species.

The large natural metabolic diversity of microorganisms has allowed them to survive in very harsh conditions of high temperature, high ionizing radiation, and high concentrations of reactive chemical species. The environment of low temperature plasma generated with liquids is comparable to many natural conditions (high temperature, highly oxidative, presence of various types of radiation) and thus suggests microbes can evolve or be engineered to not only survive but thrive in such extreme conditions. The evidence from the literature and previous work suggests that the in-situ coupling of engineered and evolved strains of bacteria with low temperature plasma generated with liquid water may provide enhanced functionality with respect to organic chemical reactions.

High-energy chemistry is a method of accelerating chemical reactions by transferring copious amounts of energy to individual molecules. The synthesis of acetylene and benzene is a valuable chemical process used in many organic products. The article proposes an original scheme of experimental setup and technology for plasma-activated methane conversion into acetylene and benzene. The system enables the creation of two distinct active zones within the reactor: the “hot zone,” where plasma and active elements are generated, and the “relaxation zone,” where the synthesis of organic products occurs. The optimal temperature of the blowing gas, i.e., the gas that propels the plasma reactor walls, has been found to be a crucial factor in heat removal from reaction zones. This temperature has been observed to vary within an interval of 290–310°K, while the reactor gas pressure has been identified as a significant variable within a range of 10–40 mbar. These two factors have been identified as the primary determinants of the yield of products, with acetylene yields reaching approximately 70–80% and maximal benzene yields reaching 40%. Furthermore, the duration of plasma exposure is a critical variable in methane conversion. The optimal acetylene yield of 80% was achieved when the reactor was operated in stationary mode for 15 s. A variation of the input gas flow in flow mode within an interval of 5–15 m³/h resulted in a decrease in the yield of acetylene to 60 percent, while an increase in the benzene yield up to 50 percent was observed. This was accompanied by an overall increase in the total volume of products produced per time unit. A general qualitative model of methane reforming is proposed, combining methane dehydration in the plasma flame with direct synthesis of acetylene from carbon and hydrogen atoms in the relaxation zone. Benzene formation occurs through the trimerization of acetylene molecules under heat dissipation near the reactor walls.