Plasma Chemistry and Plasma Processing最新文献

Atmospheric-pressure plasma processing (APPP) is an important method for the fabrication of high-precision optics because it involves highly efficient and nondamaging material removal based on its pure chemical etching mechanism. However, owing to the heat accumulation phenomenon caused by the jet heat flux, the nonlinearity of the material removal rate in APPP is inevitable, making it difficult to achieve deterministic optical surfacing. To bridge this gap, this study focused on analyzing the nonlinear relationship between the material removal rate and heat accumulation. The simulation results indicated that when the sliding distance increased from 10 to 50 mm, the surface temperature of the workpiece increased from 387.3 to 419.5 K, an increase of more than 8%. When the dwell time increased from 0.33 to 2 s, the surface temperature of the workpiece increased from 348.1 to 419.5 K (including the effect of sliding distance), an increase of more than 21%. A novel algorithm that simultaneously considers dwell time and sliding distance was proposed based on the results. A threshold parameter t_q was introduced to determine whether to correct the deviation caused by the sliding distance. With the proposed algorithm, the matching residual surface root-mean-square (RMS) error decreased from 97.5 to 39.6 nm. The RMS deviation error of the matching residual surface error converged from 11.6 to 4.7% after surface-figuring experiments. The proposed algorithm is expected to provide a promising solution for future deterministic optical surfacing.

In light of the adopted green policies and strategies, thermal plasmas are gaining interest as a potential solution to electrify the industry, particularly for endothermic processes, for their tunable enthalpy and the absence of direct CO₂ emissions. However, the majority of industrial applications of thermal plasma technologies are at atmospheric or lower pressure, whether for material processing, waste treatment, gasification, assisted combustion or in electric arc furnaces. Very little information exists on thermal plasmas at pressures above 1 bar, with the majority of academic publications using either analytical or numerical methodologies. The main experimental high-pressure plasma studies conducted date back to the 1960s, the 1970s and 1980s mainly in the US and the EU for aerospace applications, in addition to gas blast circuit breaker and underwater welding applications. However, these systems operate only for a few milliseconds to a few minutes at most. The interest in operating plasma systems at high-pressure is on one hand to reduce the volume of the facilities, and therefore, global costs, and on the other hand, is of practical necessity such as the case of underwater welding and in aerospace application where plasma technology plays a role in duplicating the conditions to which a vehicle is exposed to in atmospheric entry/reentry. This paper reports a thorough literature review on all high-pressure plasma arc studies available to date, including journal articles, books, and declassified reports. The findings of the studies are classified into four categories: DC and AC technologies, electrical characteristics, thermodynamics and heat transfer, and electrode erosion. The gaps and limitations are identified, and the main hypotheses are formulated, (re)opening the way for future high-pressure thermal plasma studies. Operating thermal plasma systems at high pressure could have considerable economic benefits, and thus, leading to competitive pricing for electrified high temperature processes, but faces many challenges.

The activation of water by the atmospheric pressure air plasma is involved in the diffusion of reactive oxygen and nitrogen species (RONS) in air and water, their gas-phase and liquid-phase reactions, and their dissolution and evaporation. In this study, by generating the air spark discharge over the surface of water, we have evaluated the chemical and biological reactivities of direct–plasma treatment (DPT) and remote–plasma treatment (RPT) plasma-activated water (PAW) at different water temperatures. We have found that DPT-PAW is much more effective in increasing both the chemical and biological reactivities of PAW than RPT-PAW, and decreasing the water temperature from 40 to 6 °C leads to the rapid activation of water. Our analysis shows that when the water temperature varies from 6 to 40 °C, the activation of water by the air discharge is RONS solubility controlled, and the gas-phase and liquid-phase RONS diffusion and chemical reactions are not the controlling steps during the activation of water. The direct plasma treatment of water at a relatively low temperature contributes to an obvious increase in the RONS solubility, thus a rapid activation of DPT-PAW.

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.

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.