Plasma Chemistry and Plasma Processing最新文献

The work provides a study of the effects of an external uniform magnetic field on the underwater pulsed discharge burning process. The presence of a magnetic field affects the waveforms of current and voltage, resulting in a decrease in amplitude values and frequency of discharge pulses. The presence of an external magnetic field was found to affect processes of the synthesis of iron oxide powders. Different polymorphic modifications of Fe₂O₃ were obtained depending on the orientation of the magnetic field. The formation of larger iron oxide nanoparticles is facilitated by the magnetic field. The release of desublimation energy, accompanied by heating, encourages the increasing the degree of crystallinity of samples in the presence of a magnetic field. Shown, that the presence of an external magnetic field has significant effects on the underwater pulsed discharge process, altering the electrical properties of the discharge and influencing the synthesis of oxide nanoparticles.

Polypropylene (PP) nonwovens are used in many hygiene, healthcare and medical products due to their low cost, high chemical resistance and inertness. From an economic point of view, PP textiles would be used as an excellent support material in regenerative medicine or tissue engineering, but here surface functionalization is necessary to ensure cell adhesion and proliferation. Acrylic acid (AAc) is an excellent source of carboxylic-rich (-COOH) coatings suitable for this purpose, but their multistep preparation is time-consuming. Plasma polymerization provides an excellent solution to this demanding procedure since the process of polymerization and grafting to the substrate takes place simultaneously. Here, we propose a relatively fast and effective method for AAc plasma polymerization by using a pulsed underwater diaphragm electrical discharge operated in an aqueous solution consisting of AAc. AAc layers are successfully grafted onto PP nonwovens, which are continuously rewound through the slit where the plasma is generated. The presence of plasma polymerized AAc layer in the fibrous structure of PP nonwoven was monitored by SEM, FTIR and XPS measurements. Additionally, the improved wettability and adhesion characteristics were investigated by the critical wetting surface tension (CWST) method, the standard method of strike-through time (STT) and „tape-peel“ test. Resulting AAc modified PP nonwoven possesses hydrophilic character, enhanced adhesion and a considerable amount of -COOH groups on the surface. Although after the washing test the FTIR and XPS results indicated a lower concentration of the carboxylic groups, the CWST and STT measurements confirmed the stable hydrophilic character of the PP nonwovens surface.

Ozone production in a planar dielectric barrier discharge (DBD) in atmospheric oxygen in different discharge modes was investigated. Results show that the gas temperature in discharge channel depends strongly on discharge mode, with a value of 300–310 K in glow regime and 440–465 K in streamer regime. Ozone production yield in glow DBD is much higher than that in streamer one, with the best yield of 342.6 and 162.6 g/kWh, respectively. Gas temperature in discharge channel relates to the effective discharge area of DBD, which is a small fraction of the whole electrode surface in streamer DBD compared with nearly the whole surface in glow DBD. The gas temperature in the channel plays a decisive role in the conversion of oxygen atoms to ozone as well as the ozone equilibrium concentration. Excellent performance of glow DBD demonstrates the high energy efficiency and reliability for practical application of planar DBD-based ozone generator.

An atmospheric pressure jet that effectively prevents inner wall deposition has been developed, and its precursor distribution and thin-film deposition characteristics have been studied. The laser scattering and fluid simulation results show that the precursor (C₄H₁₀Zn) flow out of the eight holes of the central electrode and diffuse into the discharge region. Under the action of a discharge gas (Ar) of 2 slm is blown out of the plasma jet device, and will not diffuse to the inner wall of the plasma jet device. The optical photographs of the discharge show that the site of the monomer cleavage is about 1 mm closest to the inner wall of the jet device. With optical emission spectra (OES), a large number of characteristic emission peaks of Zn and CH were detected. The pattern of the deposited film closely resembles the diffusion pattern of the precursor within the plasma jet apparatus. By investigating deposited films in different regions, the influence of precursor distribution on film morphology and composition has been studied. XPS detected films near (black film) and far (white film) from the central region, and the results showed that films near the central region contained more organic components. This plasma device offers a stable plasma plume for thin film deposition and nanoparticle preparation.

In this paper, a new multiple plasma jet tangentially mixed reactor (MPJ-TMR) is proposed. The impact of varying tangent circle diameters on the mixing process is investigated through CFD simulation. The MPJ-TMR has been preliminarily applied to high-conductive carbon black (HCCB) preparation. The results show that the MPJ-TMR with a tangent circle diameter d_c/d_in = 0 is directed to form the "counter-flow recirculation zone", which impedes mixing between plasma jets and cold fluids. For the MPJ-TMR with a tangent circle diameter d_c/d_in > 0, the intensity of the "counter-flow recirculation zone" weakens and disappears as the tangent circle diameter increases. The eccentric impact flow drives the fluid to spiral around the central axis. So that a spiral vortex structure is formed to enhance the mixing. Among them, the MPJ-TMR with a tangent circle diameter d_c/d_in = 0.5 exhibits the best mixing efficiency due to its highest local circumferential velocity and axial vortex flux, resulting in good entrainment between plasma jets and cold fluids. Therefore, the MPJ-TMR with a tangent circle diameter d_c/d_in = 0.5 is applied to prepare carbon black. The resulting products show a rich branched chain structure with over 90% of the primary particle size distributed within the range of 10–20 nm. The physicochemical indices DBP Absorption, IAN and resistivity of HCCB are very close to that of acetylene carbon black. The reactor demonstrates excellent product uniformity.

Abstract

A hollow cathode discharge with a CuNi (Cu50Ni50) cathode was operated in an Ar/N(_2)/O(_2) gas mixture. The energy distribution of plasma ions is investigated with the help of energy-resolved mass spectrometry. Formation of singly ionised Ar(^+) and of Cu(^+) and Ni(^+) ions is observed in pure argon. With the addition of N(_2) or O(_2) gas the additional formation of molecular N(_2^ +) or O(_2^+) ions is observed. The intensity of these ions is reduced in the Ar+N(_2)+O(_2) gas mixture and molecular NO(^+) ions become the most abundant ionic species. The formation of neutral NO molecules is confirmed by optical emission spectroscopy. Gas samples collected at the exhaust of the vacuum chamber confirm the formation of NO and, additionally, of NO(_2) molecules.

Graphic Abstract

Sample taken from the exhaust of the plasma chamber with a liquid-nitrogen-cooled glass container showing solid nitrogen oxide (blue).

An experimental and numerical study was conducted on the polymer ablated arc with an electrode configuration of a one-side gas flow outlet model. The polymers used for molded case circuit breaker and gas circuit breaker, such as PA6, POM, and PTFE, were compared. In the experiment, the polymer ablated arc characteristics of arc voltage, arc energy, and mass loss of polymer by ablation were measured. In the numerical calculation, an electromagnetic thermofluid simulation for polymer ablated arc was conducted using a calculation model of similar structure but without using empirical values. In the model used, the polymer ablation was treated as the pyrolytic ablation rather the photodegraded ablation because the arc plasma was definitely in contact with the polymer. The comparison of both experiment and numerical simulation results revealed the relationship between arc energy and mass loss of polymer by ablation, and these values agreed well. Therefore, the numerical simulation model with pyrolytic ablation developed was indicated to be valid for predicting the polymer ablated arc with plasma-polymer contact.

The rising demand for precision optics widely employed in ground and space-based astronomical instruments and other scientific instrumentation requires highly efficient advanced fabrication methods. Due to complex-shaped fused silica substrate surfaces like freeform or aspheres with strong curvatures or very small-sized components, a novel non-contact medium-pressure plasma-based method is developed to finish optical components. The present study critically compares the polished optical surfaces of a prism with a medium-pressure plasma process and wet chemical etching to provide insight into their smoothing. The results show that surface roughness (R_a) increases from 0.54 to 2.61 nm and 0.53 to 0.57 nm at 5 and 20 mbar total pressures, respectively, using a plasma process without surface contamination. However, wet chemical etching increases surface roughness (R_a) from 0.52 to 15.9 nm. The substrates' surface morphology, elemental composition, and surface topography are analyzed using FESEM, EDX, and AFM. Moreover, subsurface improvements are analyzed using Raman spectroscopy analysis.

Cold atmospheric plasma (CAP) has gaining potential, and very effective to curb or deactivate the various microorganisms such as bacteria and virus. Lately, the major outbreak SARS-CoV-2 infection has affected humanity largely with added complexity of its ability to mutate to variants such as Omicron. We have earlier shown the effectiveness of CAP on SARS-CoV-2 spike protein and, in this study, we have evaluated the effectiveness of CAP to deactivate Omicron. We studied the ability of the binding of Angiotensin converting Enzyme Protein (ACE2) protein to the plasma treated spike S1-S2 protein and spike Receptor binding domain (RBD) using Cold atmospheric plasma direct treatment as well as Plasma activated water (PAW). Results have shown the binding efficiency of Omicron spike protein to ACE2 decrease with increase in treatment time with both direct treatment and PAW as evidenced using spectroscopic techniques. The reactive species (RONS) play a major role in the efficient deactivation of the binding of ACE2 to the Omicron spike protein. Correspondingly, the comparison between the efficiency between direct treatment and PAW has also been discussed.

Oxygenates production from the partial oxidation of liquid fuel is required for a cleaner combustion. The effect of Mn/Fe ratio was investigated to improve the oxygenates formation via plasma catalytic n-C₅H₁₂ partial oxidation over FeMn/Al₂O₃ catalyst. The oxygenates selectivities exhibited a volcano shape with the Mn/Fe ratio and the highest value of 69% was obtained at Mn/Fe ratio of 7/3. The oxygenates selectivities were dominated by both the acidity and active oxygen species of catalyst, which could be tuned by Mn/Fe ratio. A close relationship between oxygenates selectivities, acidity, and active oxygen species of catalyst was established. The higher the active oxygen species content and the lower the acidity, the higher the oxygenates selectivities.