Search Results (51)

To explore the potential of plasma technology in regulating seed germination, this study compared the effects of direct treatment with needle-plate electrodes using DC and pulse power supplies, and indirect treatment with plasma-activated water on the growth characteristics of Bromus inermis seeds. By comparing different pulse power parameters, including voltage, pulse width, frequency, and duration, it was found that treatments at 15 kV, 2500 ns, 6 kHz, and 10 min significantly increased the surface hydrophilicity and germination performance of the seeds. The best conditions for DC power supply were 15 kV and 10 min. Indirect treatment with plasma-activated water (15 kV, 10 min) effectively broke the seed dormancy by regulating active nitrogen oxygen particle components, increasing the germination percentage by 50%. Analysis of antioxidant enzyme activity showed that in seedlings the activities of superoxide dismutase (SOD) and peroxidase (POD) increased by 75% and 21%, respectively, after treatment, revealing the mechanism of oxidative stress response induced by plasma. This study provides theoretical and technical references for the application of plasma technology in enhancing seed vitality and agricultural practices. Full article

This work shows an approach on the role of the gas mixture used in the pulsed DC plasma nitriding aiming to enhance the niobium cavitation erosion resistance through the formation of niobium nitride on the treated surfaces. For this purpose, nitriding was carried out at 1353 K (1080 °C) for 2 h, under a pressure of 1.2 kPa (9 Torr), and a 5 × 10⁻⁶ Nm³s⁻¹ (300 sccm) flow rate for three distinct gas mixtures, namely 30% N₂ + 50% H₂ + 20% Ar, 50% N₂ + 30% H₂ + 20% Ar, and 70% N₂ + 10% H₂ + 20% Ar. Surfaces were comparatively characterized before and after nitriding through scanning electron microscopy (SEM), X-ray diffractometry, 3D roughness, and nanoindentation hardness measurements. The cavitation erosion test was carried out in accordance with ASTM G32-09, obtaining the cumulative mass loss (CML) curve and the average (AER) and maximum (MER) erosion rate of the tested surfaces. Surfaces showed multiphase layers mainly constituted of ε-NbN and β-Nb₂N nitride phases, for the three distinct gas mixture conditions investigated. A CML of 25.0, 20.2, and 34.6 mg, and an AER of 1.56, 1.27, and 2.16 mg h⁻¹ was determined to the 960 min (16 h) cavitation erosion testing time, for NbN surfaces obtained at the 30% N₂, 50% N₂, and 70% N₂ gas mixture, respectively. In this case, the nominal incubation period (NIP) was 600, 650, 550 min, and the maximum erosion rate (MER) was 4.2, 3.4, and 5.1 mg h⁻¹, respectively. Finally, the enhancement of the cavitation erosion resistance, based on the NIP of the NbN surfaces, regarding the Nb substrates (with NIP of ≈100 min), was up ≈6 times, on average, thus significantly improving the cavitation erosion resistance of the niobium. Full article

The working conditions of tools during plastic working operations are determined by, among other things, temperature, loads, loading method, and processing speed. In sheet metal forming processes, additionally, lubricant and tool surface roughness play a key role in changing the surface topography of the drawpieces. This article presents the results of friction analysis on the edge of the punch in a deep drawing process using the bending under tension test. A DC04 steel sheet was used as the test material. The influence of various types of titanium nitride and titanium coatings applied on the surface of countersamples made of 145Cr6 cold-work tool steel was tested by means of high-intensity plasma pulses, magnetron sputtering, and electron pulse irradiation. The influence of the type of tool coating on the evolution of the coefficient of friction, the change in the sheet surface topography, and the temperature in the contact zone is presented in this paper. An increase in the coefficient of friction with sample elongation was observed. Countersamples modified with protective coatings provided a more stable coefficient value during the entire friction test compared to dry friction conditions. The electron pulse irradiated countersample provided the highest stability of the coefficient of friction in the entire range of sample elongation until fracture. The skewness Ssk of the sheet metal tested against the coated countersamples was characterized by negative value, which indicates a plateau-like shape of their surface. The highest temperature in the contact zone during friction with all types of countersamples was observed for the uncoated countersample. Full article

High-power pulse magnetron sputtering is a new type of magnetron sputtering technology that has advantages such as high peak power density and a high ionization rate compared to DC magnetron sputtering. In this paper, we report the effects of different pulse widths on the current waveform and plasma spectrum of target material sputtering, as well as the structure and properties of Cu films prepared under the same sputtering voltage and duty cycle. Extending the pulse width can make the sputtering enter the self-sputtering (SS) stage and improve the ion quantity of sputtered particles. The Cu film prepared by HiPIMS with long pulse width has higher bond strength and lower electrical resistivity compared to the Cu film prepared by short pulse width. In terms of microstructure, the Cu film prepared by HiPIMS with the long pulse width has a larger grain size and lower micro-surface roughness. When the pulse width is bigger than 200 μs, the microstructure of the Cu film changes from granular to branched. This transformation reduces the interface on the Cu film, further reducing the resistivity of the Cu film. Compared to short pulses, long pulse width HiPIMS can obtain higher quality Cu films. This result provides a new process approach for preparing high-quality Cu films using HiPIMS technology. Full article

The paper presents the results of preliminary research on the possibility of synthesizing ZnO-TiO₂ mixed coatings by plasma electrochemical oxidation (PEO). The aim of the work was to synthesize TiO₂-ZnO mixed coatings on a titanium substrate from an electrolyte containing ZnO nanoparticles (NPs) and to assess the parameters of PEO on the structure, chemical composition, and properties of the obtained oxide coatings. The PEO process was carried out under various current–voltage conditions using different signals: DC, DC pulse, and AC. In this work, optimal conditions for the PEO process were determined to obtain well-adhering oxide coatings with the highest possible content of ZnO. The structure and morphology of the resulting oxide coatings were investigated, and their chemical and phase composition was comprehensively examined (EDX, XRD, XPS, and GD-OES). In addition, their basic optical properties were assessed. It has been shown that in the PEO DC pulse process, it is possible to obtain oxide coatings characterized by a high degree of structure order, high ZnO content in the oxide coating (3.6 at.%, XPS), and prospective applications for photocatalytic purposes (3.12 eV). Full article

This manuscript presents the results of our recent work focused on the plasma electrolytic oxidation of aluminum in a sodium tungstate solution using a microsecond-range pulsed DC signal. DC pulses of 50, 300 and 900 μs were followed by 5- and 25-times longer pauses between the pulses, showing the effect of the pulse duration and duty cycle on the morphological, phase and chemical properties of formed oxide coatings. It is shown that all coatings are partially crystalline with gamma-alumina, WO₃ and metallic W phases present in formed PEO coatings. A higher duty cycle value results in the higher crystallization of the obtained PEO coatings. Although the chemical composition of the obtained coatings is not very sensitive to processing parameters, their roughness and porosity change significantly, as well as their thickness. The photocatalytic activity and photoluminescence properties of the obtained coatings are dependent on their morphology and chemical composition, i.e., on the processing time. The highest photoactivity and photoluminescence intensity is observed for the coating formed with t_on = 300 μs and t_off = 25 t_on. A comparable application potential is found for the sample processed with t_on = 50 μs and t_off = 25 t_on, which requires considerably less energy for PEO processing. Full article

The DC negative corona of needle-plate electrodes can generate atmospheric pressure low-temperature plasma active particles, which have important effects on biological mutagenesis. The DC negative corona discharge of an air needle-plate electrode with effective consideration of NO_x particles was simulated and the Trichel pulse current was obtained, focusing on the development of particles and the distribution of active nitrogen oxides (RONS) at four moments in the pulse process. The simulation results indicate that the positive ions (N₂⁺ and O₂⁺) and negative ions (O⁻ and O₂⁻) were closely related to the current changes, and the negative ions (O⁻ and O₂⁻) presented a typical stratification phenomenon. RONS (H₂O₂, O₃, and NO) were approximately uniformly distributed above the level of the plate electrode at the same instant, with H₂O₂ and O₃ except for the area below the needle tip. They trended to a cumulative increase in concentration with time. This study provides a theoretical basis for corona discharge plasma seed treatment technology. Full article

The recent energy crisis revealed that there is a strong need to replace hydrocarbon-fueled industrial nitrogen fixation processes by alternative, more sustainable methods. In light of this, plasma-based nitrogen fixation remains one of the most promising options, considering both theoretical and experimental aspects. Lately, plasma interacting with water has received considerable attention in nitrogen fixation applications as it can trigger a unique gas- and liquid-phase chemistry. Within this context, a critical exploration of plasma-assisted nitrogen fixation with or without water presence is of great interest with an emphasis on energy costs, particularly in plasma reactors which have potential for large-scale industrial application. In this work, the presence of water in a multi-pin plasma system on nitrogen oxidation is experimentally investigated by comparing two pulsed negative DC voltage plasmas in metal–metal and metal–liquid electrode configurations. The plasma setups are designed to create similar plasma properties, including plasma power and discharge regime in both configurations. The system energy cost is calculated, considering nitrogen-containing species generated in gas and liquid phases as measured by a gas analyzer, nitrate sensor, and a colorimetry method. The energy cost profile as a function of specific energy input showed a strong dependency on the plasma operational frequency and the gas flow rate, as a result of different plasma operation regimes and initiated reverse processes. More importantly, the presence of the plasma/liquid interface increased the energy cost up to 14 ± 8%. Overall, the results showed that the presence of water in the reaction zone has a negative impact on the nitrogen fixation process. Full article

In the present study, the surface of non-woven polypropylene (NW-PP) fabric was modified to form CN layers using a modified DC-pulsed (frequency: 60 kHz, pulse shape: square) sputtering with a roll-to-roll system. After plasma modification, structural damage in the NW-PP fabric was not observed, and the C–C/C–H bonds on the surface of the NW-PP fabric converted into C–C/C–H, C–N(CN), and C=O bonds. The CN-formed NW-PP fabrics showed strong hydrophobicity for H₂O (polar liquid) and full-wetting characteristics for CH₂I₂ (non-polar liquid). In addition, the CN-formed NW-PP exhibited an enhanced antibacterial characteristic compared to NW-PP fabric. The reduction rate of the CN-formed NW-PP fabric was 89.0% and 91.6% for Staphylococcus aureus (ATCC 6538, Gram-positive) and Klebsiella pneumoniae (ATCC4352, Gram-negative), respectively. It was confirmed that the CN layer showed antibacterial characteristics against both Gram-positive and Gram-negative bacteria. The reason for the antibacterial effect of CN-formed NW-PP fabrics can be explained as the strong hydrophobicity due to the CH₃ bond of the fabric, enhanced wetting property due to CN bonds, and antibacterial activity due to C=O bonds. Our study presents a one-step, damage-free, mass-productive, and eco-friendly method that can be applied to most weak substrates, allowing the mass production of antibacterial fabrics. Full article

Pulsed plasma thrusters (PPT) have demonstrated enormous potential since the 1960s. One major shortcoming is their low thrust efficiency, typically <30%. Most of these losses are due to joule heating, while some can be attributed to poor efficiency of the power processing units (PPUs). We model PPTs to improve their efficiency, by exploring the use of power electronic topologies to enhance the power conversion efficiency from the DC source to the thruster head. Different control approaches are considered, starting off with the basic approach of a fixed frequency flyback converter. Then, the more advanced critical conduction mode (CrCM) flyback, as well as other optimized solutions using commercial off-the-shelf (COTS) components, are presented. Variations of these flyback converters are studied under different control regimes, such as zero voltage switching (ZVS), valley voltage switching (VVS), and hard switched, to enhance the performance and efficiency of the PPU. We compare the max voltage, charge time, and the overall power conversion efficiency for different operating regimes. Our analytical results show that a more dynamic control regime can result in fewer losses and enhanced performance, offering an improved power conversion efficiency for PPUs used with PPTs. An efficiency of 86% was achieved using the variable frequency approach. This work has narrowed the possible PPU options through analytical analysis and has therefore identified a strategic approach for future investigations. In addition, a new low-power coaxial micro-thruster model using equivalent circuit model elements is developed.This is referred to as the Carlow–Stuttgart model and has been validated against experimental data from vacuum chamber tests in Stuttgart’s Pulsed Plasma Laboratory. This work serves as a valuable precursor towards the implementation of highly optimized PPU designs for efficient PPT thrusters for the next PETRUS (pulsed electrothermal thruster for the University of Stuttgart) missions. Full article

A pulsed plasma pyrolysis reactor with an efficient control system was designed for fuel oil processing. Non-thermal plasma pyrolysis was carried out in the liquid phase at low temperatures (not higher than 100 °C) in a 300 cm³ reactor without additional reagents or catalysts. The main process parameters and characteristics of non-thermal plasma fuel oil products were investigated within the DC source voltage range of 300–700 V. An increase in the energy of pulsed discharges led to an increase in the productivity of the plasma pyrolysis process and the yield of hydrogen but reduced the yield of acetylene and ethylene. The resulting gas consisted predominantly of hydrogen (46.5–50.0 mol%), acetylene (28.8–34.3 mol%), ethylene (7.6–8.6 mol%), methane (4.2–6.2 mol%), and C3–C5 hydrocarbons. The solid-phase products were in the form of disordered graphite and multilayer nanotubes. Full article

In the present study, the sputtered aluminum nitride (AlN) films were processed in a reactive pulsed DC magnetron system. We applied a total of 15 different design of experiments (DOEs) on DC pulsed parameters (reverse voltage, pulse frequency, and duty cycle) with Box–Behnken experimental method and response surface method (RSM) to establish a mathematical model by experimental data for interpreting the relationship between independent and response variables. For the characterization of AlN films on the crystal quality, microstructure, thickness, and surface roughness, X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission-scanning electron microscopy (FE-SEM) were utilized. AlN films have different microstructures and surface roughness under different pulse parameters. In addition, in-situ optical emission spectroscopy (OES) was employed to monitor the plasma in real-time, and its data were analyzed by principal component analysis (PCA) for dimensionality reduction and data preprocessing. Through the CatBoost modeling and analysis, we predicted results from XRD in full width at half maximum (FWHM) and SEM in grain size. This investigation identified the optimal pulse parameters for producing high-quality AlN films as a reverse voltage of 50 V, a pulse frequency of 250 kHz, and a duty cycle of 80.6061%. Additionally, a predictive CatBoost model for obtaining film FWHM and grain size was successfully trained. Full article

Traditional dc magnetron sputtering has a low ionization rate when preparing metallic thin films. With the development of thin film science and the market demand for thin film material applications, it is necessary to improve the density of magnetron-sputtered films. High-power pulsed magnetron sputtering (HiPIMS) technology is a physical vapor deposition technology with a high ionization rate and high energy. Therefore, in this work, HiPIMS was applied to prepare metallic tungsten films and compare the surface morphology and microstructure of metallic tungsten films deposited using HiPIMS and dc magnetron sputtering (dcMS) technology under different pulse lengths, as well as related thermal resistance performance, followed by annealing treatment for comparative analysis. We used AFM, SEM, XRD, and plasma characterization testing to comprehensively analyze the changes in the TCR value, stability, repeatability and other related performance of the metallic tungsten thin-film sensor deposited by the HiPIMS technology. It was determined that the thin film prepared by the HiPIMS method is denser, with fewer defects, and the film sensor was stable. The 400 °C annealed sample prepared using HiPIMS with a 100 μs pulse length reaches the largest recorded TCR values of 1.05 × 10⁻³ K⁻¹. In addition, it shows better stability in repeated tests. Full article

The solid-state Marx pulse generator is widely used in various fields such as biomedical electroporation, food processing, and plasma material modification. In this paper, an inductor is chosen as an isolation device and by adding a switch to the circuit, a solid-state boost-Marx pulse generator (BMPG) is formed. On the one hand, the inductor forms a boost circuit to multiply the output voltage gain, and on the other hand, it solves the shortcomings of conventional Marx pulse generators where the charging speed and total efficiency during high-frequency pulse generation are drastically affected by the isolation resistor. The selection criteria for inductors is well derived. Based on the PSpice simulation verification, a 12-module prototype of BMPG is built. The test results show that the circuit can achieve 10 kV high-voltage pulse output with a pulse width of 200–1000 ns and an adjustable repetition frequency of 0–10 kHz. While the input DC voltage requirement is only 235 V, the pulse voltage boost multiple is up to 42.5 times. Additionally, with the different switching sequences, the proposed BMPG can realize the adjustable change of pulse rising time and falling time. Full article

This paper aims to perform experimental validation of RF–plasma interaction behaviors for the purposes of wave transmission and reflection. Wave reflection from plasma is of interest as it finds applications in pulse compression and RF polarizer-based systems. Simulations are performed using a combination of Magic3D and COMSOL multiphysics to characterize the plasma–wave interaction and discharge tube properties. The goal is to generate plasma with characteristics that wholly reflect the incident electromagnetic wave. A glass tube of inner diameter 22 mm and length 100 mm, with 12 mm brass electrodes, is fabricated for plasma generation. Argon-based DC glow discharge is sustained at 500 volts at a pressure of 3.8 Torr. Plasma density is calculated to be $2.529\times {10}^{19}$ m${}^{-3}$, with a corresponding plasma frequency of 7.18 GHz. Due to this higher frequency, a 3 GHz incident RF wave is reflected, as measured through S-parameter measurements using a network analyzer. Off and on states of the tube correspond to $S_{11}=-40$ dB and $S_{11}=-13$ dB, which show wave transmission and reflection, respectively. When the plasma column is ignited, the reflected wave has a phase difference of ${180}^{\circ }$. Full article