Cathode Plasma Research Articles

Magnesium Oxide Powder Synthesis in Cathodic Arc Discharge Plasma in an Argon Environment at Atmospheric Pressure

Discharges with cathode spots can operate in a wide range of gas pressures. Erosion of the cathode material is an inherent property of such discharges. The erosion products are considered to be ionized atoms and electrically neutral microdroplets. In accordance with this concept, a plasma source based on a pulsed cathodic arc discharge in atmospheric-pressure argon with a current of up to 200 A, a pulse duration of 250 μs, and a pulse repetition rate of 10 Hz was implemented. Using this source, the synthesis of magnesium oxide powder was performed. The chemical composition of the erosion products was determined using the TEM/EDS method and the composition of the gas mixture in which the discharge system operated was evaluated by optical spectrometry. It was shown that particles of the synthesized powder have different morphological features, depending on the nature of the electrical erosion of the cathode material. Micron-sized particles are formed due to the removal of microdroplets from liquid–metal craters on the cathode surface at certain plasma pressures. Submicron particles are produced during the agglomeration of atoms originating from the plasma jets flowing out from cathode spots. These atoms are magnesium ions that are neutralized by collisions with gas particles. The advantages and disadvantages of this synthesis method are discussed in this paper. The reference methods for the powder synthesis of magnesium oxide are compared. The prospects of the studied method from the point of view of its application for obtaining ceramic materials are also evaluated.

The motion and distribution characteristics of cathode spot and its influence on plasma parameters

Cathode spots and plasma are the key factors affecting the breaking capacity of vacuum switches. In order to analyze the motion and distribution characteristics of cathode spot and its influence on plasmas, the experiments of cathode spot observation and plasma diagnosis were conducted in this paper. The cathode spot images were captured by ultra high-speed camera. Based on the continuous spectrum theory, the electron density was measured by the colorimetric thermometry. According to the cathode spot images and method of cathode spot recognition, the parameters of cathode spots including number, size and current were obtained. The changes of these parameters with arcing time and current amplitude were analyzed. The dependence of the cathode spots average size on spot current and spot expansion velocity was discussed. The axial and radial distributions of electron density were obtained which is related to the cathode spot distribution on the cathode surface. The significant fluctuation in the radial direction for electron density was observed.

Improving the performance of titanium bipolar plate in proton exchange membrane water electrolysis environment by nitrogen-chromium composite cathode plasma electrolytic deposition

In the proton exchange membrane water electrolysis (PEMWE), the titanium bipolar plate coated with noble metals is usually used, which puts forward higher requirements for costs. This study investigates the cathode plasma electrolytic deposition (CPED) for the titanium and obtains TiN and TiN/CrN coatings. The TiN coating exhibits the diffusion resistance in the anode PEMWE environment, resulting in an increase in the interfacial contact resistance (ICR). The denser TiN/CrN coating eliminates the diffusion resistance and increases the polarization resistance (Rp) value from 3873 Ω cm2 of TiN coating to 12,320 Ω cm2 of TiN/CrN. After long-term potentiostatic polarization, the ICR of TiN/CrN coating is 8.5 mΩ cm2, which is 3.5 times lower than that of TiN coating. Therefore, the low-cost TiN/CrN coating obtained by CPED has brought a good application prospect for bipolar plates in PEMWE.

Microstructure and Corrosion Behavior of the Modified Layers Grown In Situ by Plasma Nitriding Technology on the Surface of Zr Metal

Preparing protecting coatings on the surface of Zr claddings has been regarded as one of the accident tolerant fuel (ATF) strategies. In this study, a series of nitride-modified layers were in situ grown by hollow cathode plasma nitriding on the surface of Zr metal. The influence of nitriding currents and time on the phases, composition, microstructure and corrosion resistance of the modified layers was investigated by X-ray diffraction (XRD), X-ray Photoemission Spectroscopy (XPS), transmission electron microscope (TEM), scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) and potentiodynamic polarization curves. The ZrO2 layer with loose microstructure and cracks prefers to form under low nitriding current of 0.4 A, which also causes poor corrosion resistance. The high temperature caused by high nitriding currents (0.6 A and 0.8 A) promote the formation of compact nanocrystalline layers, made up of nitride and oxynitride. Below the nanocrystalline layer, it is Zr2N caused by N penetration. Besides this, a double-layer structure of the nanocrystalline layer, i.e., an equiaxed crystal zone with a grain size of ~10–50 nm on the surface and a long strip grain region beneath it was observed. The compact nitride/oxynitride layer with excellent interface bonding can improve the corrosion resistance effectively.

Electron-enhanced SiO2 atomic layer deposition at 35 °C using disilane and ozone or water as reactants

Electrons can enhance SiO2 atomic layer deposition (ALD) at low temperatures using disilane (Si2H6) and either ozone (O3/O2) or water (H2O) as reactants. SiO2 electron-enhanced ALD (EE-ALD) was demonstrated at 35 °C by exposing the sample to sequential electron, oxygen reactant, and Si2H6 exposures. The reaction sequence was electron beam exposure for 3 s, purge for 5 s, O3/O2 or H2O exposure at 0.5–1.0 Torr for 3 s, purge for 10 s, Si2H6 exposure at 100 mTorr for 1 s, and purge for 15 s. The electron exposure was an electron current of ∼150 mA for 3 s. The electrons were produced by a hollow cathode plasma electron source typically operating with a grid bias of ≈−300 V. These electrons could irradiate a sample area of ∼2 × 2 cm2. In situ spectroscopic ellipsometry measurements determined that SiO2 EE-ALD films nucleated rapidly and deposited linearly versus number of EE-ALD cycles. The SiO2 EE-ALD growth rate was 0.89 Å/cycle using O3/O2 and 0.88 Å/cycle using H2O. The SiO2 growth rate was also self-limiting at higher electron and Si2H6 exposures. In addition, SiO2 EE-ALD films were grown by changing the reaction sequence or codosing the electrons with the oxygen reactant. The SiO2 EE-ALD films could be grown on conducting silicon wafers or insulating SiO2 films. SiO2 EE-ALD is believed to be possible on insulating SiO2 films because the secondary electron yield for SiO2 at electron energies of ∼100–300 eV is greater than unity. Under these conditions, the SiO2 film charges positive during electron exposure and then pulls back secondary electrons to maintain charge neutrality. The SiO2 EE-ALD films had properties that were comparable with thermal SiO2 oxides. The refractive indices of the SiO2 EE-ALD films were similar at n = 1.44 ± 0.02 for various process conditions and equivalent to the refractive index of a wet thermal SiO2 oxide film. In addition, all the SiO2 EE-ALD films yielded etch rates in dilute buffered oxide etch solution that were only slightly higher than the etch rate of a thermal SiO2 oxide film. SiO2 EE-ALD should be useful to deposit high-quality SiO2 films for various applications at low temperatures.

SERS-active substrates using DVD-R coated in silver thin films: A preliminary study for detection of commercial glyphosate

Glyphosate (GLP) is the herbicide with the highest level of global commercialization and historical use. Even though numerous studies have found this substance to be harmless, current research demonstrates that GLP might affect human health. For this reason, researcher efforts are concentrating on alternatives for analytical quantification, such as Surface Enhanced Raman Spectroscopy (SERS). In this work, a DVD-R@AgNPs SERS substrate was produced by the Cathodic Cage Plasma Deposition (CCPD) technique, which allowed a thin film layer deposition of silver nanoparticles (AgNPs) on the PC grating structure from Digital Video/Versatile Disc Recordable (DVD-R). Scanning Electron Microscopy with energy-dispersive X-ray spectroscopy was used to characterize the substrate and chemical changes on the surface after AgNPs deposition. The DVD-R@AgNPs substrate was used to detect standard crystal violet (CV), GLP, and RoundupTM GLP (GLP-RU) using Raman Spectroscopy. The CV was used as a control sample for SERS measurement, allowing the calculation of the substrate enhancement factor, which was in the order of ∼ 105. To evaluate the efficiency of the SERS substrate, the limit of detection was calculated and showed values of ∼ 10-10 mol/L for CV, 10-7 and 10-8 mol/L for GLP, and 10-6 mol/L for GLP-RU. Thus, the DVD-R@AgNPs SERS sensor is a low-cost substrate that analyzes traces of pesticides such as commercial GLP, demonstrating high SERS sensitivities and many applications.

PLASMA-ELECTROLYTIC MODIFICATION OF STEEL AND TITANIUM SURFACES BY COMBINING CATHODIC NI-TRIDING AND ANODIC POLISHING

The possibility of increasing the wear resistance of steel 45 surfaces by 19.9 times and titanium alloy VT6 by 3.6 times after cathodic electrolytic plasma nitriding in a solution of ammonium chloride and ammonia and subsequent anodic electrolyte-plasma polishing in a solution of ammonium sulfate. A positive effect on wear resistance was revealed reducing surface roughness and removing the outer part of the oxide layer using anodic electrolytic plasma polishing and increasing the hardness of the surface layer as a result of cathodic nitriding. The wear mechanism is defined as fatigue upon plastic contact and boundary friction.

Electrochemical Corrosion Behavior of Ti-N-O Modified Layer on the TC4 Titanium Alloy Prepared by Hollow Cathodic Plasma Source Oxynitriding

TC4 alloy is widely used in dental implantation due to its excellent biocompatibility and low density. However, it is necessary to further improve the corrosion resistance and surface hardness of the titanium alloy to prevent surface damage that could result in the release of metal ions into the oral cavity, potentially affecting oral health. In this study, Ti-N-O layers were fabricated on the surface of TC4 alloy using a two-step hollow cathode plasma source oxynitriding technique. This resulted in the formation of TiN, Ti2N, TiO2, and nitrogen-stabilized α(N)-Ti phases on the TC4 alloy, forming a Ti-N-O modified layer. The microhardness of the samples treated with plasma oxynitriding (PNO) was found to be 300–400% higher than that of untreated (UN) samples. The experimental conditions were set at 520 °C, and the corrosion current density of the PNO sample was measured to be 7.65 × 10−8 A/cm2, which is two orders of magnitude lower than that of the UN sample. This indicates that the PNO-treated TC4 alloy exhibited significantly improved corrosion resistance in the artificial saliva solutions.

Effects of anode material on the evolution of anode plasma and characteristics of intense electron beam diode

In this paper, three kinds of materials including graphite, titanium (Ti) and molybdenum (Mo) are used as anodes to figure out the influence factors of anode material on the characteristics of the intense electron beam diode. The results show that the characteristics of diode are mainly determined by the cathode plasma motion under a 15 mm diode gap, in which the typical electron beam parameters are 280 kV, 3.5 kA. When the diode gap is reduced to 5 mm, the voltage of the electron beam reduces to about 200 kV, and its current increases to more than 8.2 kA. It is calculated that the surface temperatures of Ti and Mo anodes are higher than their melting points. The diode plasma luminescence images show that Ti and Mo anodes produce plasmas soon after the bombardment of electron beams. Ti and Mo lines are respectively found in the plasma composition of Ti and Mo anode diodes. Surface melting traces are also observed on Ti and Mo anodes by comparing the micromorphologies before and after bombardment of the electron beam. These results suggest that the time of anode plasma generation is closely related to the anode material. Compared with graphite, metal Ti and Mo anodes are more likely to produce large amounts of plasma due to their more significant temperature rise effect. According to the moment that anode plasma begins to generate, the average expansion velocities of cathode and anode plasma are estimated by fitting the improved space-charge limited flow model. This reveals that generation and motion of the anode plasma significantly affect the characteristics of intense electron beam diode.

Effects of plasma treatments on the surface wettability properties of PTFE polymeric films

A cold cathode plasma source is constructed for modifying PTFE surface characteristics. The source was easily built, had a consistent plasma discharge medium and acceleration system. A cylindrical Langmuir probe is also used to evaluate plasma parameters like density, temperature or even plasma potential. This probe is designed to be moveable so that it may approach any desired position in the plasma volume. The influences of nitrogen pressure and probe-cathode gap on plasma parameters were investigated. The electron temperature [Formula: see text] fluctuated from [Formula: see text] to [Formula: see text][Formula: see text]eV as the pressure rises from 0.2 to 0.4[Formula: see text]mbar. Further, by increasing the cathode-probe gap from 0.4 to 2[Formula: see text]cm, the electron densities increased from [Formula: see text][Formula: see text]cm[Formula: see text] to [Formula: see text][Formula: see text]cm[Formula: see text]. Furthermore, the contact angles, work of adhesion and surface free-energy of pristine as well as irradiated PTFE films, were estimated. The results demonstrated that by extending the plasma exposure duration from 0 to 12[Formula: see text]min, the water contact angle is lowered from 82.2∘ to 30.5∘. At these conditions, the work of adhesion is raised from 81.9 to 134.1[Formula: see text]mJ/m2, as the surface free energy is increased from 29.8 to 71.8[Formula: see text]mJ/m2.

High-efficiency degradation of norfloxacin by cathodic micro-arc plasma electrolysis:Optimization of operation parameters and investigation on kinetics

In this work, the norfloxacin antibiotic (NOR) in simulated wastewater solution was rapidly degraded by a novel cathodic micro-arc plasma electrolysis (CMPE) treatment within 20 min. The effects and kinetics of initial pH value of solution, supporting electrolyte, and applied voltage on this NOR degradation process were systematically investigated. The intermediate products are analyzed by a Liquid Chromatograph-Mass Spectrometer (LC-MS), and the possible degradation pathways in the NOR degradation process were proposed. The results obtained showed that the NOR removal efficiency increased with the increase of the initial pH value of the solution. When KCl was employed as the supporting electrolyte instead of KNO3 and K2SO4, the removal efficiency of NOR is the highest. In addition, the removal efficiency is not significantly different at 340 V, 380 V, and 420 V, but it is more beneficial to the removal of chemical oxygen demand (COD) and the increase of average current efficiency (ACE) at 380 V. Furthermore, under the optimized operating parameters for the initial pH value of 9, supporting electrolyte of KCl, and applied voltage of 380 V, the 100 mg/L NOR solution can be completely removed within 10 min, and the energy yield and average current efficiency were 0.385 g (kW⋅h)-1 and 0.118. Further, it is found that the degradation pathways of NOR mainly include the piperazine ring opening, hydroxylation, defluorination, and quinoline ring transformation. Overall, this study provides a high-efficiency and novel technique for the NOR degradation treatment.

Time-resolved plasma diagnostics of cathodic cage plasma nitriding system with variable pulsed duty cycle and surface modification of plain carbon steel

Cathodic cage plasma nitriding (CCPN) is an efficient technique to improve the surface properties of metallic and non-metallic materials, including steels. Usually, CCPN is powered by pulsed voltage sources due to additional control of the nitrided layer's thickness and composition as well as the discharge transition to the arc region can be controlled by varying the pulsed duty cycle. As the behavior of pulsed plasma varies with time, it is important to monitor variation in plasma parameters by using time-resolved plasma diagnostics. Unfortunately, the fundamental time-resolved diagnostics of such discharges are still very limited. Here, we report time-resolved measurements of current, voltage, plasma emission, space, and time-resolved emission from a single hole in the cathode as a function of pulsed duty cycle (15–75 %) at constant total current. The results show that the electron temperature is higher if a higher peak current and the shortest 15 % pulsed duty cycle are used. The results obtained from plasma diagnostics are confirmed by treatment of plain carbon steel samples in identical conditions and found that the best hardness, wear, and corrosion resistance is obtained at the lowest pulsed duty cycle. The study suggests that plasma generated at a low pulsed duty cycle and a higher peak discharge current exhibits higher electron temperature and less fluctuations in plasma emission which are more efficient in attaining high surface hardness, better wear, and corrosion resistance to nitride plain carbon steel.

Investigation of the physical process inside the crater during the ablation of the cathode material of a micro-cathode arc thruster

In this paper, the relationship between the morphology of the cathode crater and plasma ionization between thrusters is studied by adjusting the input energy of the micro-cathode arc thruster (μCAT). We monitor the morphology of the cathode crater of the μCAT using scanning electron microscopy and explore the relationship between the crater morphology and the internal energy loss of the cathode crater. This relationship, combined with the numerical simulation results, is used to monitor the ionization between the electrodes of the μCAT using an enhanced intensified charge coupled device spectrum detector. The effect of cathode crater morphology on the ionization of the propellant during the operation of the μCAT is determined. The results show that with a change in the input power processing unit voltage, the external profile and depth-to-diameter ratio of the cathode crater change, resulting in a change in the internal energy loss of the thruster cathode crater and then affecting the ionization efficiency of the cathode working fluid in the μCAT. Under the condition of basically unchanged cathode feed energy flow density, reasonable adjustment of the depth-to-diameter ratio of the cathode crater can effectively improve the ionization efficiency of the cathode working fluid in the μCAT.

Synthesis of biocompatible coating on Ni-Cr alloy by cathodic cage plasma processing technique as anti-pathogenic bacteria for medicinal applications

The current research work reports the deposition of titanium-based multilayer coating (TiO/TiN) on Ni-Cr metallic alloy by a cathodic cage plasma processing technique using a titanium cage along with various combinations of gas mixtures i.e., N2-H2-Ar-O2 at 400 °C. The samples were characterized using x-ray photoelectron spectroscopy (XPS), which revealed the surface coating of TiO/TiN with Ti 2p at 462 eV, N 1s at 406 eV and O 1s at 530.09 eV. The x-ray diffraction (XRD) analysis confirmed the polycrystalline structure in the titanium-based coating with (111) for TiO/TiN and a crystallite size of 32 nm. Scanning electron microscopy (SEM) and x-ray dispersive spectroscopy (EDX) analysis of titanium-based TiO/TiN coatings was well correlated with the above mentioned findings. Corrosion analysis using polarization potentio-dynamic plots (PDP) and electrochemical impedance spectroscopy (EIS) revealed a significant improvement in various corrosion parameters like corrosion resistance, corrosion rate, surface porosity, corrosion protection efficiency, impedance, and charge transfer resistance. A spectrophotometer was used to measure the leaching of toxic ions (Ni, Cr) from untreated and treated specimens in NaCl electrolyte. Findings revealed efficient antibacterial activity of TiO/TiN-coated specimens against E. coli and S. aureus as compared to untreated samples. This work will be helpful for understanding the biological features of metallic materials for medicinal applications.

Corrosion Behavior of Nitrided Layer of Ti6Al4V Titanium Alloy by Hollow Cathodic Plasma Source Nitriding.

Ti6Al4V titanium alloys, with high specific strength and good biological compatibility with the human body, are ideal materials for medical surgical implants. However, Ti6Al4V titanium alloys are prone to corrosion in the human environment, which affects the service life of implants and harms human health. In this work, hollow cathode plasm source nitriding (HCPSN) was used to generate nitrided layers on the surfaces of Ti6Al4V titanium alloys to improve their corrosion resistance. Ti6Al4V titanium alloys were nitrided in NH3 at 510 °C for 0, 1, 2, and 4 h. The microstructure and phase composition of the Ti-N nitriding layer was characterized by high-resolution transmission electron microscopy, atomic force microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. This modified layer was identified to be composed of TiN, Ti2N, and α-Ti (N) phase. To study the corrosion properties of different phases, the nitriding 4 h samples were mechanically ground and polished to obtain the various surfaces of Ti2N and α-Ti (N) phases. The potentiodynamic polarization and electrochemical impedance measurements were conducted in Hank's solution to characterize the corrosion resistance of Ti-N nitriding layers in the human environment. The relationship between corrosion resistance and the microstructure of the Ti-N nitriding layer was discussed. The new Ti-N nitriding layer that can improve corrosion resistance provides a broader prospect for applying Ti6Al4V titanium alloy in the medical field.

Improved Wear Resistance of Low Carbon Steel by Duplex Surface Treatment Combining Cathodic Plasma Electrolytic Nitrocarburising and Anodic Plasma Electrolytic Polishing

Improved Wear Resistance of Low Carbon Steel by Duplex Surface Treatment Combining Cathodic Plasma Electrolytic Nitrocarburising and Anodic Plasma Electrolytic Polishing

Synthesis of Ti–Nb–C–N based composite coating on AISI-4340 steel by modified cathodic cage plasma deposition

Synthesis of Ti–Nb–C–N based composite coating on AISI-4340 steel by modified cathodic cage plasma deposition

Corrosion resistance of austenitic stainless steel using cathodic plasma electrolytic oxidation

Substantial improvement of corrosion resistance of austenitic stainless steel (SS) has been demonstrated with a protective oxide layer formed by the cathodic plasma electrolytic oxidation (CPEO) process. Two distinct layers, a porous-structured outer layer comprising Fe oxides and a compact inner layer comprising Cr oxides, were created on the SS surface after the CPEO process. The thicknesses of the outer and inner layers were approximately 7 μm and 12 μm, respectively, and the oxide layers were fabricated in an exceptionally short time of <30 s. A potentiodynamic polarization analysis exhibited a 65 % decrease in the corrosion current after the formation of the protective oxide layer, verifying the effectiveness of the CPEO treatment on the corrosion resistance of SS. An electrochemical impedance spectroscopy study revealed that the outer layer captured corrosive species due to its porous structure, while the inner layer had high resistance to reactions with corrosive species due to the compact structure of Cr oxides. Additionally, a Rockwell C indentation test demonstrated the robust mechanical property of the protective oxide layer with a strong bonding strength to the substrate.

Tribological Behavior of SINTER30 Steel Subjected to Duplex Treatment

Plasma nitriding has been extensively used to improve materials’ surface and mechanical properties using conventional plasma techniques. However, this process generally results in a nonuniformity of the properties. In the cathodic cage plasma nitriding (CCPN), the plasma is active only on the surface of the cathodic cage, eliminating inherent defects of conventional plasma nitriding. Herein, a duplex treatment, CCPN and TiN deposition, is used on SINTER30 tool steel for the first time. Vickers microhardness tests, X‐ray diffractometry, Raman scattering spectroscopy, and scratching tests characterize the samples. The results show that TiN post‐coating attains higher surface hardness. All the groups increase their microhardness properties when compared with nontreated substrates. The prior treatment of plasma nitriding assists hardening of the substrate surface. The best condition is obtained when the sample is placed inside the titanium cage and positions directly on the sample port, with simultaneous duplex treatment. When the substrate passes through this simultaneous duplex process, peaks corresponding to Fe3N and TiN are observed at Raman spectra. Suitable TiN layers improve the film adhesion, which is correlated to the system's load‐bearing capacity.

On the mechanism of anomalous phenomena in current-carrying magnetized plasma

The explanation of the mechanisms of anomalous resistance and diffusion of plasma, as well as the generation of fast particles, is given from a unified position on the basis of experimental results obtained in plasma in a magnetically isolated diode of an electron accelerator with a microsecond pulse duration. It is shown that oscillations of the potential and current in plasma with current occur by charge separation and the formation of electric domains with a strong field. Electric domains are generated by means of runaway electrons resulting from the redistribution of the current density and its channelling in the current-carrying plasma. An increase in plasma resistance occurs due to a decrease in the number of electrons in the current-conducting state, since some of the plasma electrons pass into layers of excess negative charge of electric domains. The speed of movement of electrons in the composition of the electric domain is much lower than the velocity of electrons in the conducting state. The nucleation of domains is accompanied by microwave emission. Quasi-neutrals in whole electrical domains are injected into the region of the anode wall. The destruction of domains leads to the appearance of plasma channels between the anode and cathode plasma. The transverse electromagnetic waves generated during the nucleation of domains capture charged particles and inject them in a direction that is perpendicular to the insulating longitudinal magnetic field. Plasma turbulence occurs due to charge separation and the generation of electrical domains that create channels between the plasma and the chamber wall, as well as generating fluxes of fast particles.