Radio Frequency Plasma Research Articles

Effect of processing parameters on microstructure and properties of spherical WC-Co powder by plasma spheroidization

In this study, radio-frequency plasma spheroidization was used to obtain spherical WC-Co powder from granulated WC-Co powder using different parameters. The results show that the spheroidization ratio of the powder first increased and then decreased with an increase in plasma power, whereas the trend of the average particle size is the opposite. The spheroidization ratio of the powder decreased with an increase in the powder feeding rate, whereas the average particle size increased. This also indicates that cobalt loss and WC decomposition occurred during plasma spheroidization. The loss of cobalt increased continuously with increasing plasma power and decreasing powder feeding rate. Black and white particles with significantly different carbon distributions were observed in the spheroidized powder, which were mainly caused by the different degrees of WC decomposition. The flowability and apparent density of the spheroidized WC-Co powder were positively correlated with the ratio of black to white particles.

Particle simulations of ion-extraction process from a decaying plasma assisted by radio-frequency plasma heating

In this study, two-dimensional kinetic particle simulations were employed to examine the potential of radio-frequency (rf) plasma heating in enhancing ion extraction efficiency in a decaying plasma with the configuration of parallel plates. The numerical results suggest that the application of rf power based on the direct current electrostatic method leads to a remarkable increase in the ion extraction flux, thereby reducing the time required for ion extraction. The increase in the ion extraction flux is attributed to the enhancement of the penetration ability of the rf electric field into the plasma, especially in cases of high rf frequencies, which can elevate the bulk electron temperature to approach 10 eV. The propagation speed of ion rarefaction waves is enhanced by the increased electron temperature, speeding up the process of ion extraction. The study also found that an increase in rf voltage causes more intense plasma oscillations to screen out the rf disturbance, further increasing the electron temperature. Furthermore, as ion extraction continues, the heating effect of rf frequencies was found to be enhanced due to the decay of plasma density.

Similarity laws for two-dimensional simulations of low-pressure capacitively coupled radio-frequency discharges

Similarity laws (SLs) for low-pressure capacitive radio-frequency plasmas are generalized from one- to two-dimensional (2D) frameworks based on kinetic particle-in-cell simulations. Fundamental discharge parameters, such as the 2D distributions of electron densities and electric fields, are examined to assess the applicability of SLs to such discharges. The discharge characteristics are found to remain invariant when external control parameters are changed according to SLs. Even under conditions where nonlinear electron resonance heating caused by the self-excitation of the plasma series resonance due to the geometric reactor asymmetry plays an important role, the electron kinetics are shown to be invariant. Moreover, the validity of SLs for the ion dynamics is demonstrated. The results advance the applicability of SLs to a 2D cylindrical reactor geometry with azimuthal symmetry, indicating broad application prospects in practice.

Characterization of a radiofrequency linear plasma device in uniform and convergent magnetic fields

A linear radiofrequency plasma device is constructed, where a source operating at a frequency of 13.56 MHz and a maximum power of several kW is attached to a cylindrical vacuum chamber about 1 m in length. Seven solenoids are located around the source and the chamber, providing various magnetic field configurations by changing the solenoid currents. The plasma density of the radiofrequency linear plasma device is initially characterized in uniform and convergent magnetic field configurations. A blue mode argon plasma, being inherent to the helicon or high-density discharge, is observed in the chamber downstream of the source for both configurations, while the density near the antenna is lower than that in the chamber. Furthermore, the density for the convergent magnetic field configuration is found to be larger than that for the uniform case, providing a maximum density of about . Spatiotemporal measurements of the ion saturation current reveal that the density peak is formed near the rf antenna at the initial time of the discharge and the peripheral high-density region subsequently appears downstream of the antenna, implying that the rf power is efficiently coupled with the electrons downstream of the antenna once the initial plasma is created. A few ms after turning on the rf power, the density over the whole region reduces, which seems to be due to a neutral depletion.

Ion acceleration in expanding plasma in small radio frequency plasma thruster with a magnetic cusp

Ambipolar electric field is formed in the expanding plasma of the small radio frequency plasma thruster using a cusp-shaped magnetic field. A highly energized group of ion energy distribution function is observed in the z-direction, indicating the presence of axial ion acceleration downstream the magnetic nozzle owing to the electric field. The mean velocity profile of the beam ions along the z axis is evaluated using the energy distribution functions along the z axis. The high axial ion velocity profile stretches downstream, although the evaluated dimensionless velocity profile is lower than that calculated using quasi-one-dimensional models. It is suggested that ion momentum loss can result from ion-neutral collision, leading to beam divergence in the magnetic nozzle of the proposed small thruster.

N2 RF-plasma-assisted preparation of small size Ni–Ce catalysts for dry reforming of methane with high activity and great coke-resistant performance

High activity and stability are the goals sought for by industrial applications of dry reforming of methane (DRM). However, the particle size is not easy to control and carbon accumulations are key issues to be solved. Herein, a new Ce-doping Ni-based catalyst (Ni–Ce–P2h) with excellent coke resistance and eximious activity was prepared by the N2 Radio Frequency Plasma assisted impregnation method. The prepared materials were characterized by means of XRD, SEM, TEM, BET, H2-TPR, XPS and TG. The results showed that the plasma treatment time was important, and catalysts with 2 h of plasma treatment had the best catalytic performance. The initial activities of CH4 and CO2 for Ni–Ce–P2h catalyst both exceed 76% at 700 °C. Compared to the conventional catalyst Ni–C and Ni–Ce–C with high temperature calcination treatment, the initial conversion of CH4 and CO2 for Ni–Ce–P2h was improved by over 15% and 10%, respectively. Moreover, excellent stability of Ni–Ce–P2h was observed. The activity drop was no more than 3% after 10h long time reaction. And the amount of carbon accumulation was only 0.5%. The smaller grain size of active components Ni, the stronger metal-support interactions and more abundant oxygen species might be the main reasons for the better DRM performance on the Ni–Ce catalysts prepared by plasma-assisted method. The Ni particle size of the Ni–Ce–P2h catalyst was only 5.4 nm, which is much smaller than that of the Ni–C (24 nm) and Ni–Ce–C (20 nm). This study provides a new idea to explore the synergistic effect of Ce doping and the plasma treatment on Ni based catalyst with good DRM performance.

A novel endoscopic nasopharyngectomy by low-temperature plasma radiofrequency ablation in localized recurrent nasopharyngeal carcinoma.

Endoscopic nasopharyngectomy (ENPG) with en bloc resection has been well accepted in resectable localized recurrent nasopharyngeal carcinoma (rNPC), but it is a difficult technique to master for most otorhinolaryngology head and neck surgeons. Ablation surgery is a new and simplified method to remove tumors. We designed a novel method using low-temperature plasma radiofrequency ablation (LPRA) and evaluated the survival benefit. A total of 56 localized rNPC patients were explained in detail and retrospectively analyzed. The surgery method was ablated from the resection margin to the center of the tumor. The postmetastatic overall survival (OS), local relapse-free survival (LRFS) rate, progression-free survival (PFS) and distant metastasis-free survival (DMFS) were analyzed using the Kaplan-Meier method and compared by the log-rank test. All surgeries were successfully performed without any severe postoperative complications or deaths. The median operation time of ablation and harvested NSFF respectively were 29 min (range, 15-100 min) and 101 min (range, 30-180 min). The average number of hospital days postoperation was 3 days (range, 2-5 days). All cases (100.0%) had radical ablation with negative resection margins. The nasopharyngeal defects were completely re-epithelialized in 54 (96.4%) patients. As of the data cutoff (September 3, 2023), the median follow-up time was 44.3 months (range, 17.1-52.7 months, 95% CI: 40.4-48.2). The 3-year OS, LRFS, PFS and DMFS of the entire cohort were 92.9% (95% CI: 0.862-0.996), 89.3% (95% CI: 0.813-0.973), 87.5% (95% CI: 0.789-0.961), and 92.9% (95% CI: 0.862-0.996), respectively. Cycles of radiotherapy were independent risk factors for OS (p = 0.003; HR, 32.041; 95% CI: 3.365-305.064), LRFS (p = 0.002; HR, 10.762; 95% CI: 2.440-47.459), PFS (p = 0.004; HR, 7.457; 95% CI: 1.925-28.877), and DMFS (p = 0.002; HR, 34.776; 95% CI: 3.806-317.799). Radical endoscopic nasopharyngectomy by using low-temperature plasma radiofrequency ablation is a novel, safe and simplified method to master and disseminate for treating resectable rNPC. However, further data and longer follow-up time are needed to prove its efficacy.

Nitrogen Radiofrequency Plasma Treatment of Graphene

AbstractThe incorporation of nitrogen (N) atoms into a graphitic network such as graphene (Gr) remains a major challenge. However, even if the insertion mechanisms are not yet fully understood, it is certain that the modification of the electrical properties of Gr is possible according to the configuration adopted. Several simulations work, notably using DFT, have shown that the incorporation of N in Gr can induce an increase in the electrical conductivity and N acts as an electron donor; this increase is linked to the amount of N, the sp2/sp3 carbon configuration, and the nature of C−N bonding. Nitrogen radiofrequency (RF) plasma has been used to incorporate N into Gr materials. The RF plasma method shows the possibility to incorporate N‐graphitic nitrogen into Gr after a pre‐treatment with nitric acid. X‐ray photoelectron spectroscopy and Raman spectrometry were used to quantify the functionalized groups. The modifications of the graphene surface chemistry along the amount of N inside the Gr change the chemical environment of N. This method, enabling the incorporation of N inside Gr matrix, opens up a route to a broad range of applications.

Experimental validation of particle-in-cell/Monte Carlo collisions simulations in low-pressure neon capacitively coupled plasmas

Plasma simulations are powerful tools for understanding fundamental plasma science phenomena and for process optimisation in applications. To ensure their quantitative accuracy, they must be validated against experiments. In this work, such an experimental validation is performed for a one dimensional in space and three dimensional in velocity space particle-in-cell simulation complemented with the Monte Carlo treatment of collision processes of a capacitively coupled radio frequency plasma driven at 13.56 MHz and operated in neon gas. In a geometrically symmetric reactor the electron density in the discharge centre and the spatio-temporal distribution of the electron impact excitation rate from the ground into the Ne 2p1 level are measured by a microwave cutoff probe and phase resolved optical emission spectroscopy, respectively. The measurements are conducted for electrode gaps between 50 mm and 90 mm, neutral gas pressures between 20 mTorr and 50 mTorr, and peak-to-peak values of the driving voltage waveform between 250 V and 650 V. Simulations are performed under identical discharge conditions. In the simulations, various combinations of surface coefficients characterising the interactions of electrons and heavy particles with the anodised aluminium electrode surfaces are adopted. We find, that the simulations using a constant effective heavy particle induced secondary electron (SE) emission coefficient of 0.3 and a realistic electron–surface interaction model (which considers energy-dependent and material specific elastic and inelastic electron reflection, as well as the emission of true SEs from the surface) yield results which are in good quantitative agreement with the experimental data.

Atmospheric Plasma Sources as Potential Tools for Surface and Hand Disinfection

Good hand hygiene has proven to be essential in reducing the uncontrolled spread of human pathogens. Cold atmospheric plasma (CAP) may provide an alternative to disinfecting hands with ethanol-based handrubs when handwashing facilities are unavailable. CAP can be safely applied to the skin if the energy is well controlled. In this study, radio frequency (RF) and direct current (DC) plasma sources were built with a pin-to-mesh electrodes configuration inside a fused silica tube with a 5 mm inner diameter. Microbiological assays based on EN 13697:2015+A1:2019 using Escherichia coli DSM 682 or Staphylococcus epidermidis DSM 20044 were used to examine the antimicrobial effect of various plasma conditions. Metal and silicone disks that model skin were used as inoculation matrices. The prototype air RF CAP achieved significant disinfection in the MHz range on stainless steel and silicone substrates. This is equivalent to half the performance of direct current CAP, which is only effective on conductive substrates. Using only electricity and air CAP could, with further optimization to increase its efficacy, replace or complement current hand disinfection methods, and mitigate the economic burden of public health crises in the future.

S2O82−/CeO2 Solid Superacid Catalyst Prepared by Radio-Frequency Plasma-Assisted Hydrothermal Method

CeO2 was prepared using a hydrothermal method, modified by radio-frequency plasma in the form of glow discharge, and then the solid superacid S2O82−/CeO2 was prepared by the impregnation method. A series of properties such as pore structure was characterized by N2 adsorption–desorption experiments, surface morphology was characterized by TEM, crystal phase was characterized by XRD, and surface acidity of the catalyst was characterized by Py-IR and Hammett titration. The methyl esterification reaction of tryptophan was used to evaluate the activity of the solid superacid. The results showed that the catalyst modified by radio-frequency plasma had a larger specific surface area, more surface oxygen vacancies, smaller particle size, and higher total acid content. The yield of tryptophan methyl ester reached a higher level of 94.5% (150 °C, 1 MPa, 2 h), catalyzed by the modified S2O82−/CeO2. This work verified the feasibility of plasma technology in the field of catalytic activity enhancement of solid superacid.

ELift, Helium Plasma Radiofrequency (Renuvion) Subdermal Treatment and Minimal Access Face and Neck Lift, is an Effective Facial Rejuvenation Technique with Minimal Downtime

eLift, Helium Plasma Radiofrequency (Renuvion) Subdermal Treatment and Minimal Access Face and Neck Lift, is an Effective Facial Rejuvenation Technique with Minimal Downtime

Permeation of low-pressure deuterium through niobium under radio-frequency plasma condition

The behavior of permeation of deuterium through niobium under the condition of radio-frequency plasma has been investigated in this paper. The external solenoid coupled plasma was applied as plasma source. The dependences of stable permeation flux on mode of discharge, membrane temperature, input power, gas pressure, surface oxidation layer and impurity concentration have been studied. The bulk diffusion was one of the controlling steps with 0.5 mm membrane and the substantially increase was due to plasma assisted dissociation. The mixtures with large amount of argon or nitrogen had finite influence on stable permeation flux which was attributed to the ion energy driven dissociation at surface. These results imply the inductively coupled plasma driven permeation is beneficial to rapid separation and purification of hydrogen isotopes for low surface sputtering rate of membrane surface and gases with hydrogen-containing compounds.

Impacts of Postoperative Enteral Nutrition and Rosiglitazone on Quality of Life Together with Prognosis of Patients with Early-Stage Glottic Laryngeal Carcinoma

We aimed to clarify the influence of postoperative enteral nutrition and rosiglitazone on the quality of life and prognosis of patients with early stage glottic laryngeal carcinoma. Low-temperature plasma radiofrequency ablation was performed in the control group, while the observation group additionally received rosiglitazone and postoperative enteral nutrition. After therapy, the observation group had lower fundamental frequency perturbation and amplitude perturbation and higher harmonic-to-noise ratio and effective rate than the control group. One month after treatment, the serum levels of albumin, prealbumin, and hemoglobin in the observation group were higher than those in the control group. Moreover, peripheral blood immune markers, CD3+, CD4+, and CD4+/CD8+ levels were higher in the observation group, while CD8+ levels were lower. The incidence rate of adverse reactions was lower in the observation group than in the control group. The five-year survival rates were 77.14% (27/35) and 54.29 % (19/35) in the observation and control groups, respectively. Postoperative enteral nutrition and rosiglitazone can prolong survival, improve immune function and quality of life in patients with early-stage glottic laryngeal carcinoma, and reduce adverse reactions during treatment, which is an ideal treatment plan.

Recent applications in dielectric barrier discharge and radio frequency plasmas‐engineered transition metal electrocatalysts for water splitting

AbstractHydrogen generated by water electrolysis is considered as one of the most promising protocols to partly replace the roles of traditional fossil fuels. However, high‐performance electrocatalyst satisfied with the industrial requirement still faces significant challenges. Low‐temperature plasma contains numerous high‐energy ions, electrons and other reactive species, which can provide a highly reactive environment for tuning the physio‐chemical structures of catalysts through plasma milling, etching, doping and/or deposition. It is well‐known that high‐temperature micro‐filaments contained in plasmas can cause some special modifications of the catalyst surface, thus effectively adjusting the physio‐chemical structure of latterly engineered compounds. Therefore, low‐temperature plasma technologies, especially the dielectric barrier discharge (DBD) and radio frequency (RF) plasmas, can be considered as a green and sustainable strategy for engineering high‐performance electrocatalysts for water splitting (hydrogen evolution reaction [HER]; oxygen evolution reaction [OER]). Herein, recent progress of DBD and RF plasmas for fabricating and modifying transition metal‐based electrocatalysts (e.g. sulphide, phosphide, selenide, oxide, hydroxide) for hydrogen evolution reaction or OER is comprehensively reviewed, and the role of plasma is also discussed.

Case Reports of Low-Temperature Plasma Radiofrequency Treatment for Congenital Epiglottic Cysts in Neonates and Infants.

An uncommon benign condition in neonates, known as congenital epiglottic cyst, can lead to symptoms such as neonatal dyspnea, laryngeal stridor, and, in severe cases, even pose a potential threat of asphyxia-related mortality. A congenital epiglottic cyst is one of the neonatal emergencies. Fibrolaryngoscopy is the predominant method of diagnosis, and early identification, diagnosis, as well as treatment are the key points. Successful endoscopic ablation of congenital epiglottic cysts in 3 newborns was achieved through the utilization of a low-temperature plasma radiofrequency ablation system. Consequently, the purpose of this case report is to assist pediatric emergency physicians in the timely identification of congenital epiglottic cysts with the potential risk of mortality and to provide additional experience in clinical management.

Deep understanding the formation of hollow ZnO@ZnS core-sheath heterojunction towards efficient CO2 photoreduction

The utilization of solar energy to convert CO2 into small energy molecules is a potential “carbon neutral” technology for CO2 emission reduction. However, the industrial application is significantly constrained due to the low reduction efficiency, complexity of the synthesis methods, and limitations in scaling up the catalyst materials. In this work, we have successfully designed and synthesized a series of hollow tubular ZnO@ZnS core-sheath heterostructured materials, by combining radio-frequency thermal plasma and hydrothermal treatment technologies. The S:Zn molar ratio, reaction time, and temperature were systematically investigated, and the morphology of intermediate products was successfully captured, which provided conclusive evidence for the proposed formation mechanism. Notably, the photocatalytic CO yield of the ZS0.5O hollow nanotube core-sheath composite is not only 3.20 or 4.03 times higher than that of the pure ZnO or ZnS, respectively, but also possesses excellent stability. By in-depth characterization, we found that the hollow core-sheath heterostructure enhances light capture and absorption, exposes more effective active sites, and builds a type-II heterojunction between ZnO and ZnS to enhance the separation efficiency of charge carriers. The synergy of these factors significantly improves the catalytic performance, offering new insights for photocatalytic, electrocatalytic, and photoelectrocatalytic CO2 reduction.

Clinical manifestation and treatment strategy of intervertebral space infection after radiofrequency ablation of lumbar nucleus pulposus

To study the clinical manifestations and treatment of intervertebral space infection after percutaneous lumbar radiofrequency ablation of nucleus pulposus. A retrospective analysis was performed of 496 patients who underwent percutaneous lumbar disc decompression using low-temperature plasma radiofrequency ablation nucleus pulposus from June 2009 to June 2019. Six patients had lumbar infection, and the infection rate was 1.21%. All patients were male, ranging in age from 20 to 61 years old. Three patients underwent single segment radiofrequency ablation, two patients underwent dual segments ablation;and one patient underwent three segment ablation, totaling 10 intervertebral discs. One patient was complicated with type 2 diabetes before operation. The interval between infection occurrence ranged from 21 to 65 days. All 6 patients were followed up, and the duration ranged from 18 to 40 months, with an average of 24 months. Among them, 2 patients presented with symptoms of low back pain accompanied by fever, and imaging examination showed intervertebral space infection accompanied by abscess. In addition, 4 patients experienced low back pain but no fever, and MRI showed abnormal signals of the infected intervertebral endplate or vertebral body. One patient showed staphylococcus aureus in blood culture, while the remaining 5 patients showed negative bacterial culture. All the patients were treated with antibiotics after diagnosis. Four patients were treated with conservative management to control infection;1 patient was treated with debridement of posterior lumbar infection focus, and 1 patient was treated with debridement of posterior lumbar infection focus combined with interbody fusion and internal fixation. The occurrence of intervertebral space infection during lumbar radiofrequency ablation nucleoplasty should be given sufficient attention. Strict aseptic technique, avoiding repeated multi segment puncture, realizing early detection and treatment, and selecting appropriate treatment methods according to the severity of infection is the guarantee of achieving curative effect.

Direct bonding of stainless steel and PEEK using non-thermal atmospheric pressure plasma-assisted joining technology

This work demonstrates the direct bonding of stainless steel (SUS304) to poly(ether ether ketone) (PEEK) using non-thermal atmospheric pressure plasma-assisted joining technology in association with thermal press fitting. The tensile shear stress values of specimens bonded after plasma treatment of both the SUS304 and PEEK surfaces were higher than those of untreated samples and samples for which only one of the two surfaces was exposed to the plasma. These results indicate that the surface physical and chemical changes induced by exposure to the radio frequency plasma jet significantly increased the bonding strength.

Model of the Interaction of Reactive Gases with Polymer Materials in Low-Pressure Radio-Frequency Plasma

Model of the Interaction of Reactive Gases with Polymer Materials in Low-Pressure Radio-Frequency Plasma