Plasma Chemistry and Plasma Processing最新文献

Coal is an abundant natural resource and there is motivation to find new uses for it that do not intrinsically involve combustion. One approach is to explore new ways of processing coal, and in this work, we focus on the transformation of coal in a nonequilibrium plasma generated from an equimolar mixture of nitrogen and hydrogen. The outcome of the nonequilibrium plasma reaction is fundamentally different than a thermal control reaction carried out using the same gas composition, pressure, and temperature range. The nonequilibrium plasma produces a gas mixture that is enriched in acetylene and its derivatives. Furthermore, when compared to the thermal control experiment, the solid char byproduct of the nonequilibrium plasma has a very reactive surface and is spontaneously combustible at ambient temperature. Experiments performed to characterize the reaction kinetics of coal in the plasma suggest that the mechanism proceeds through a sequential process by which the coal particle temperature rises to a point where devolatilization can occur, the devolatilization reaction happens, followed by parallel reactions of released organic vapors in the plasma phase and surface activation. The reaction rate appears to be limited by the time it takes for the coal particle temperature to rise, consistent with previous results reported for reactions of coal in thermal plasma.

Hydrogen (H₂) plays an important role in meeting the demand for carbon-free steels. When reduction is done with H₂, harmless water is released as the off-gas, instead of CO₂ generated by reduction with carbon. While steel can be produced using H₂, many of its alloying elements cannot. As a result, fully carbon-free steel production necessitates a carbon-free production of its alloying elements. An important alloying element for steel, manganese (Mn), is subject to thermodynamic limitations that makes reduction with H₂ infeasible. If instead a much more reactive hydrogen plasma is used these thermodynamic limitations would disappear. The current work shows an in-depth investigation into the reduction of manganese oxide (MnO) by a thermal hydrogen plasma under various conditions. By passing H₂ through a plasma torch before it contacts an MnO-containing slag, formation of metallic Mn was achieved with a hydrogen-based reductant. Investigating the reduced samples with an electron probe micro analyser (EPMA) the amount of Mn formation in different conditions is mapped out. The reduction was found to be favoured when the torch was operated with a transferred arc mode, and for slags high in MnO, if the melting point was not too high. While the research into reduction of stable oxides with thermal hydrogen plasmas is still in an early stage and there are many unanswered questions, the work presented demonstrates the possibility of hydrogen-based manganese production.

The superiority of silicon (Si) film performance as anode material in the rechargeable battery technologies is tormented by the huge volume expansion during cycle. The combined structure of a microcrystalline Si with high porous/defect density and an isotropic amorphous Si has been proposed as a feasible solution. Our own deposition process using atmospheric-pressure (AP) plasma excited by very high-frequency (VHF) power has managed to create a non-composite Si film with gradient phase along thickness direction. It is highly indicated that a slower gas flow rate and/or a larger power input cause the nanoparticle formation in the AP-VHF plasma to occur more actively, which significantly influenced the development of a crystalline layer with a high density of grain boundaries. A good film reproducibility on Cu substrate imply an interesting possibility of heterostructured Si application for LIBs anode.

Electrified, small-scale, remote approaches are needed as an alternative to conventional centralized methods for nitrogen fixation in order to reduce our reliance on fossil fuels and ensure global food security. Plasma-based electrolytic processes offer a promising solution by directly reacting molecular nitrogen and water under mild conditions. However, the complex non-equilibrium chemistry results in a diverse range of gas-phase and liquid-phase reactions, which impacts selectivity toward desired products. In this study, we investigate the influence of feed gas composition, specifically the presence of molecular oxygen at minute quantities, on the liquid-phase nitrogen products. Specifically, oxygen gas concentrations as low as 0.1% in the gas feed are found to substantially affect the selectivity towards ammonium ions. We additionally show that the total gas flow rate has an indiscriminate effect on both ammonium and nitrate/nitrite ion yields because of the presence of water vapor. By carefully controlling these process parameters, a production rate for ammonium ions exceeding 1 mg/h with a molar selectivity of ~ 14 is achieved. Our results highlight the importance of gas-phase chemistry in plasma-based electrolytic nitrogen fixation.

A two-dimensional axisymmetric fluid model was employed to investigate the influence of varying argon volume fraction in the working gas on the propagation characteristics and reactive species generation of pulsed He + Ar + O₂ plasma jet. The results demonstrate that at an argon volume fraction of 10%, the Penning effect between He and Ar is most pronounced, and the electron temperature and electron density of the He + Ar + O₂ plasma jet reach their maxima. The electron temperature in the upstream region of the jet front dissipates more slowly due to Penning ionization between helium and argon. At the end of the pulse, higher—temperature electrons accumulate near the tube nozzle in a triangular distribution. During propagation from the tube into open air, the ionization wave of the He + Ar + O₂ plasma jet evolves from a hollow ring to a solid bullet shape, with the highest bullet velocity observed at an argon volume fraction of 10%. The densities of Ar⁺ and Ar^* reach their maxima at argon volume fractions of 10% and 30%, respectively, while the densities of He⁺ and He^* decrease monotonically as the argon volume fraction increases. Notably, the ozone generation efficiency is maximized at an argon volume fraction of 10%.

As a volatile organic pollutant, toluene is difficult to be activated and removed at low temperature by conventional thermal catalytic oxidation. Therefore, we reported an Ag-Co bimetallic catalyst which is supported on hydroxyapatite (HAP) and prepared by the equal-volume distribution impregnation method and investigated its performance in toluene oxidation. Enhanced toluene removal was achieved by synergizing plasma with 3Ag/15Co/HAP catalysts at low temperatures, which also improved CO₂ selectivity. Toluene conversion and CO₂ selectivity peaked at 100% and 88%, respectively, at the input power of 13 W, while the removal process demonstrated good stability during a 32 h test. The uniform dispersion of Ag NPs on the carrier facilitates the conversion of filamentary discharge into a more uniform and efficient discharge, promoting the activation of surface oxygen and thereby improving toluene removal efficiency. Additionally, the interaction between Ag and Co generated more surface-active oxygen and lattice defects on the catalyst surface, resulting in excellent low-temperature reducibility.

A reflection on the phenomenon of plasma-activated water (PAW), its brief history and properties. PAW arises from the accumulation of reactive plasma products (mainly H₂O₂, NO₂⁻, NO₃⁻, O₃ and sometimes HNO, ONOOH) in water and has many interesting and beneficial properties on both living and non-living biological objects. It has attracted considerable attention in the last 15 years and raises the question whether it might not be simpler to prepare it artificially (APAW) directly by mixing chemical compounds. There are several papers which have compared the effects of PAW with APAW and conclude that there is probably no significant difference. In this paper, we conclude that the preparation of PAW is several times more expensive than that of APAW. However, we also note that there may be specific situations in which the production of PAW could be advantageous, such as its efficient role in storing energy in the form of nitrate ions, which can serve as a nutritional source for plants.

The study investigates the potential of Plasma-Activated Water (PAW) as a nitrogen supplement in hydroponic cultivation (HS-N + PAW), specifically focusing on radish seed germination and subsequent plant growth. PAW, produced using a dielectric barrier discharge pencil plasma jet using air as plasma forming gas, is compared against conventional hydroponic solution (HS) and hydroponic solution without nitrogen (HS-N). PAW treatment completely eliminates microbial growth in seeds. Radish plants cultivated with HS-N + PAW display approximately 30% and 3% longer roots compared to those grown with HS-N and HS, respectively, with shoot length increasing by ~ 16.5% (HS-N) and < 1% (HS). Root weight sees a substantial increase of ~ 51% with HS-N + PAW compared to HS-N, while the increase with HS is not significant. Similarly, shoot fresh weight sees a notable increase of 50% (HS-N) and 10% (HS). In terms of biochemical composition, radish roots show a significant increase of approximately 15.3% in soluble sugar concentration with HS-N + PAW compared to HS-N. Protein concentration in radish leaves increases by ~ 5.1% and ~ 19.0% with HS-N + PAW compared to HS-N and HS, respectively. Heightened soluble sugar and protein concentrations in HS-N + PAW-grown plants, indicating enhanced metabolic activity and nutrient uptake. However, variations in chlorophyll and carotenoid concentrations in leaves among different growth media are statistically insignificant. The H₂O₂ concentration in both roots and shoots remains consistent across different growth media. However, variations in electrolytic leakage, phenolic leakage, and antioxidant enzyme activities reveal differential responses depending on growth conditions, highlighting how these conditions influence plant stress responses. Furthermore, sensory evaluation and physical attributes analysis underscore the negative effects of nitrogen deficiency in radish plants grown with HS-N. Conversely, HS-N + PAW cultivated plants exhibit improved visual appearance, surface texture, and overall acceptance, highlighting PAW’s potential as a nitrogen source for enhancing plant growth and quality in hydroponic systems.

Electrodes are core components in plasma discharge technology, and their material selection and structural design directly affect the performance and stability of the system. As plasma technology is widely applied in environmental treatment, materials preparation, and biomedicine, there is a growing demand for optimizing electrode materials. However, the diversity of discharge forms and application scenarios makes it difficult to draw unified conclusions about the applicability and performance of electrode materials across studies, particularly in liquid-phase discharges, where corrosion of metal electrodes becomes more prominent, posing challenges to the selection and design of electrodes. This review systematically summarizes the performance of various metal electrode materials in plasma discharge technology in different applications, particularly the generation of corrosion products in water treatment, disinfection, and sterilization, and their influence on the treatment efficacy.

Stainless steel is one of the most essential materials in daily life due to its corrosion-resistant properties. One of the vital metal components in stainless steel is chromium, which forms a protective layer on the surface of stainless steel when exposed to air. The chromium used in stainless steel production typically comes from ferrochrome, produced through chromite ore's carbothermic reduction. This production process results in CO₂ emissions of 5.4 tCO₂-eq/t ferrochrome. Hydrogen plasma smelting reduction (HPSR) has emerged as a critical area of contemporary research and development to achieve more sustainable metal production. Here, we show that HPSR can produce ferrochrome containing 50% chromium from chromite ore within 6 min. The ferrochrome produced contains no carbon, which means that no AOD (argon oxygen decarburization) converter nor VOD (vacuum oxygen decarburization) is required for stainless steel manufacturing, which leads to a shorter process route and more sustainable stainless steelmaking.