Anode-cathode Distance Research Articles

Electrohydrodynamic characteristics of a needle-to-ring positive corona discharges: self-consistent modeling and turbulence effects

Abstract We report on the voltage-current characteristics as well as the voltage-velocity characteristics of a needle-to-ring configuration by self-consistent, 2D-axisymmetric, multi-physics plasma-fluid simulations. Parametric studies are performed to investigate the effects of background ionization level on the plasma electrical characteristics as well as turbulence parameters on the resulting flow. Our results show that the discharge and the flow exhibit an annular structure around the needle (anode) tip, with a maximum positive ion density from 1.5×1018 - 2.7×1018 m-3 and a maximum flow velocity (ionic wind) from 10 - 15 m/s, for overvoltages between 4 - 12 kV and an anode-cathode distance of 20 mm. Good overall agreement with experimental findings is achieved, noting that background ionization level can be used as a tuning parameter to better match experimentally measured current values even with a simplified plasma-chemistry. A better agreement between simulation and experiments is achieved concerning the voltage-velocity curves. Therefore, the latter are likely to be better indicators for assessing and validating electrohydrodynamic effects of corona actuators through numerical modeling. The flow dynamics indicate that positive-corona-induced ionic winds are most likely laminar to turbulent transitional flows, with a ratio between eddy viscosity and air viscosity varying between 0 - 200.

Field enhancement induced by surface defects in two-dimensional ReSe2 field emitters.

The field emission properties of rhenium diselenide (ReSe2) nanosheets on Si/SiO2 substrates, obtained through mechanical exfoliation, have been investigated. The n-type conduction was confirmed by using nano-manipulated tungsten probes inside a scanning electrode microscope to directly contact the ReSe2 flake in back-gated field effect transistor configuration, avoiding any lithographic process. By performing a finite element electrostatic simulation of the electric field, it is demonstrated that the use of a tungsten probe as anode, at a controlled distance from the ReSe2 emitter surface, allows the collection of emitted electrons from a reduced area that furtherly decreases by reducing the tip-sample distance, i.e. allowing a local characterization of the field emission properties. Experimentally, it is shown that the turn-on voltage can be linearly reduced by reducing the cathode-anode separation distance. By comparing the measured current-voltage characteristics with the numerical simulations, it is also shown that the effective field enhancement on the emitter surface is larger than expected because of surface defects. Finally, it is confirmed that ReSe2 nanosheets are suitable field emitters with high time stability and low current fluctuations.

Effect of emitter tip spacing on Si vacuum field emitter arrays

This paper presents a qualitative and quantitative analysis of close-packed vacuum field emitter arrays. Through a combination of computational simulations and experimental verifications, the relationship between emitter spacing and electric field screening is studied. In order to obtain a uniform electron emission and large current densities from a field emitter array, it is essential to minimize the screening effect between the adjacent field emitters. As previously demonstrated, sharpening the emitter tips, reducing the background doping concentration of the emitters, and reducing the anode–cathode distance can suppress the screening effect. Field emitter arrays with different sizes and emitter spacings are fabricated and characterized. Decreasing the array size and increasing emitter spacing lead to a larger average current per emitter (19 nA/tip at an anode voltage of 250 V). However, larger current densities (up to 3.3 A/cm2) are observed in close-packed arrays. In very large arrays with a small emitter spacing, the current is scaled with the emitter area (∼4.2 nA/emitter at an anode voltage of 250 V), indicating a small current contribution from the sides of the array.

Liquid plasma discharge with low pulse voltage for efficient and ultra rapid removal of tetracycline hydrochloride and evaluation of its degradation pathway

Cathode liquid plasma discharge (LPD) is an efficient and ultra rapid method to degrade organic pollutants, mainly because it can produce a large number of strong oxidizing radical species during the process of plasma discharge. In this paper, the LPD process was firstly used to degrade the tetracycline hydrochloride (TCH) in water. The effects of the cathodic materials, pulse voltages, and anode-cathode distances on the degradation efficiency of the TCH were investigated, and the antibacterial activity and cytotoxicity of the degradation products were also evaluated. The results show that the degradation efficiency of the TCH can reach 98.13 % within only 1 min by the LPD process for initial concentration of 100 mg/L, and the TOC removal rate is maintained at over 81 % in 5 min. The Ti electrode performs the lowest ionic dissolution concentration and the solution near the cathode produces a plasma region for the degradation of the TCH, which contains a number of strong oxidizing radical species (such as ∙OH). The primary intermediate products (m/z = 445, 279, 149, and 123) and secondary intermediate products (m/z = 90.5, 81, and 59) are captured, and a possible degradation pathway of the TCH is also proposed. The cytotoxicity results show that the LPD degraded solutions are non-toxic effect on the NIH3T3 cells. The LPD process is a promising method to efficiently eliminate the TCH in wastewater. This work also provides a new experimental basis and reference for the ultra rapid degradation of organic pollutants in wastewater without using catalysts.

Preparation of Ti4O7 Reactive Electrochemical Membrane for Electrochemical Oxidation of Coking Wastewater

The effluent of coking wastewater comprises hundreds of refractory organics and is characterized by high toxicity and non-biodegradation. Electrochemical advanced oxidation processes (EAOPs) have been widely applied in the field of water purification. In this study, a Ti4O7 reactive electrochemical membrane (REM) was prepared using the plasma spraying method for the electro-oxidation of coking wastewater. The composition and surface morphology of the Ti4O7 REM were characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The computational fluid dynamics (CFD) simulation was used to compare the mass transfer performance of the Ti4O7 REM in traditional batch (TB) mode and flow-through (FT) mode. In the FT mode, the effects of current density and anode–cathode distance on the treatment efficiency were investigated, and the electrocatalytic performance of the anode on coking wastewater was analyzed. The results showed that the COD removal efficiency reached 76.2% with an energy consumption of 110.5 kWh kg−1 COD under the optimal condition. In addition, cathodic polarization provides an effective technique for maintaining the long-term activity of the Ti4O7 REM. The three-dimensional fluorescence results and UV-vis spectrum showed that the aromatic compounds could be effectively degraded using the Ti4O7 REM. The Ti4O7 REM demonstrated excellent performance of electrochemical oxidation and satisfactory stability, which had a strong potential for application in the field of practical wastewater and engineering practices that respond to the concept of sustainable development.

Reducing Screening Effect in Close-Packed Si Field Emitter Arrays

Electric field screening effect in close-packed semiconductor field emitter arrays (FEAs) changes the current distribution among emitter tips, such that those on the edges of the array emit much higher current than those in the middle, leading to poor reliability characteristics. Using analysis, numerical simulations, and experimental verification, three different techniques to suppress electric field screening and achieve uniform current distribution are proposed. These techniques are: 1) utilizing very sharp emitter tips; 2) reducing the anode–cathode distance (ACD) to be in the order of emitter pitch; and 3) using extremely low-doped but long field emitter tips. By adopting these techniques together, a more uniform emission from the array and a high emission current density can be achieved. FEAs with 160 K emitter tips with different ACDs and emitter sharpness were fabricated using electron beam lithography. In an array with sharp emitter tips, reliable emission with a maximum current of 0.7 mA (4.4 nA/tip) and a maximum current density of 1.75 A/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{2}}$</tex-math> </inline-formula> was achieved.

Acceleration of electrons in a combined magnetic trap in synchronous mode

The electron energy distribution function (EEDF) and the spatial profile of the electron density in the cathode–anode gap in a helium discharge are calculated within a one-dimensional model by the Monte Carlo method. Numerical studies are performed for experimental conditions known from the literature in a discharge with a hollow cathode: the cathode–anode distance of 3 cm, the helium pressure of 0.75 Torr, and the electric field strength in the discharge gap of 1.3 V/cm. The calculations are performed without and with allowance for the anode potential drop and the effect of electron reflection from the anode. The dependence of the form of EEDF on the energy spectrum of the electron source used in the calculations is also studied. In all variants of calculations, the main feature of the EEDF is retained, that is, a significant depletion of the low-energy part of the distribution function due to the effect of electron absorption by the anode. The calculated EEDF and the spatial profile of the electron density are compared with the available experimental data.

Study of the Effect of the Anode on EEDF and the Spatial Profile of the Electron Density in a Discharge with a Hollow Cathode in Helium

The electron energy distribution function (EEDF) and the spatial profile of the electron density in the cathode–anode gap in a helium discharge are calculated within a one-dimensional model by the Monte Carlo method. Numerical studies are performed for experimental conditions known from the literature in a discharge with a hollow cathode: the cathode–anode distance of 3 cm, the helium pressure of 0.75 Torr, and the electric field strength in the discharge gap of 1.3 V/cm. The calculations are performed without and with allowance for the anode potential drop and the effect of electron reflection from the anode. The dependence of the form of EEDF on the energy spectrum of the electron source used in the calculations is also studied. In all variants of calculations, the main feature of the EEDF is retained, that is, a significant depletion of the low-energy part of the distribution function due to the effect of electron absorption by the anode. The calculated EEDF and the spatial profile of the electron density are compared with the available experimental data.

Response surface analysis of Zn–Ni coating parameters for corrosion resistance applications: a Plackett–Burman and Box–Behnken design of experiments approach

AbstractThe development of cost-effective coatings with exceptional corrosion resistance is an ongoing challenge in the field of materials science. Among the promising coatings, zinc–nickel (Zn–Ni) coatings have shown great potential, especially when produced using economical electroplating technology. However, achieving optimal performance while minimizing coating thickness remains a complex task. In this study, the behavior of the responses was investigated according to the coating standards and levels, focusing on eight variables including temperature, time, cathodic current density, nickel concentration, substrate hardness, roughness, cathode–anode distance, and magnetic stirring speed. Four responses were investigated: coating thickness, roughness, microhardness, and corrosion rate with potentiodynamic polarization, using two design of experiments (DOE) methods: Plackett–Burman design (12 runs) and response surface methodology with Box–Behnken design (15 runs). The results show the degree of influence of each variable on the responses and their contribution to changing the responses. Additionally, response surfaces have been determined and it is shown that large response values can be achieved with small thicknesses. The morphological study using SEM, EDX, and XRD techniques revealed that the deposition conditions play an important role in the surface morphology. Some samples showed microcracks, while others had small grain size and were free of cracks and pores. Overall, this study provides new insights into the improvement of Zn–Ni coatings with exceptional corrosion resistance and cost-effectiveness.

ВІДНОВЛЕННЯ ШТОКІВ СИЛОВИХ ГІДРОЦИЛІНДРІВ АВТОМОБІЛІВ ЛЕКТРОЛІТИЧНИМ ХРОМУВАННЯМ

The quality of the repair of parts of military equipment and the increase of their service life largely depends on how it is organized and in what ways the restoration of malfunctioning or damaged parts is carried out. To restore the full functionality of the damaged parts, it is necessary to return them to their initial dimensions, geometric shape, hardness, corrosion resistance and other properties. One of the progressive methods of restoring the working rods of hydraulic cylinders is the application of electrolytic coatings on their working surface. The purpose of the study is to improve the method of restoration of hydraulic cylinder rods by electrolytic chroming with the aim of intensifying the process, improving operational properties and obtaining electrolytic chromium deposits of uniform thickness on the restored rods. The scientific and practical direction of the work consists in the fact that for the first time the technology of process intensification, improvement of the quality of coatings and obtaining of electrolytic chromium deposits uniform in length with the use of an ejector anode design has been considered. The research methodology is to identify the influence of the chrome plating process parameters on the uniformity, microhardness and microcracking of chrome coatings made of universal (250 г/л – СrO3; 2,5 г/л – H2SO4) та кріолітового (10 г/л – Na3AlF6; 250 г/л – СrO3; 2,5 г/л – H2SO4) of electrolytes by the ejector method. The results of the study are the establishment of the dependence of uniformity, microhardness and microcracking on the parameters of the ejector chromium plating process in standard and cryolite electrolytes and the determination of the optimal temperature and current density for use in restoring the rods of hydraulic cylinders of military equipment. The value of the conducted research is that for the first time an ejector anode is used as a positive electrode, which ensures obtaining high-quality and uniform electrolytic coatings directly in the chrome plating bath. Anode-ejector provides height-adjustable suspension suction of gaseous products of electrolysis and renewal of electrolyte in the interelectrode space due to the ejector effect in the anode tubes when the electrolyte is passed under pressure in the jet tubes. Keywords: stom density, anode-cathode distance, uniformity, cracking, microhardness, electrolyte temperature, anode-ejector.

Metal-insulator-semiconductor type diode based on implanted β-Ga2O3 epilayers grown on sapphire substrate by metalorganic chemical vapor deposition

Conductive β-Ga2O3 epilayers grown on the sapphire substrate using metalorganic chemical vapor deposition (MOCVD) were studied by Si-ion implanted. A metal-insulator-semiconductor diode (MISD) was fabricated using undoped and Si implanted β-Ga2O3 epitaxial layer. The electrical and carrier transport properties of the different MISD with different distance between cathode and anode contact ranging from 10 to 200 μm is studied. The various parameters such as forward current density, reverse breakdown voltage and ideality factor of the diodes has been calculated from the current-voltage curve. A reverse breakdown voltage of about 1.1 kV was observed in case of anode-cathode distance of 200 μm.

Effect of Cathode Distance, Anode and Electroplating Time on Aluminum Alloy Corrosion Rate

Aluminum foil is used more often than actual aluminum in everyday life because aluminum is actually quite unstable and is not suitable for securing heavy containing objects. For car wheels, aluminum is mixed with manganese and then hardened to withstand the load. Using aluminum alloys requires an electroplating process to increase corrosion resistance, decorative value and friction resistance. The purpose of this study was to determine the properties of anodized cathode aluminum alloy and the required coating time. In this study, a quantitative experiment used 20 samples. The results showed that there were defects in the aluminum alloy lattice, but not too significant. Different corrosion rate values were shown using electrolysis periods of 30 minutes and 60 minutes combined with anode-cathode distances of 5 cm, 10 cm and 15 cm. The group with 30 minutes of coating time and 5 cm anode-cathode distance had the highest corrosion rate (0.853 mm/year), while the group with 30 minutes of coating time and 10 cm anode-cathode distance had the lowest corrosion rate (0.610). The group with 60 minutes of coating time and 10 cm distance between the anode and cathode had the highest corrosion rate of 1,564 mm/year, while the group with 60 minutes of coating time and 15 cm distance had the lowest corrosion rate. The anode-cathode distance partially affects the corrosion rate of aluminum alloy electroplating. The smaller the distance between the anode and cathode, the higher the corrosion rate of the aluminum alloy. The longer the coating lasts, the higher the corrosive rate of the Al alloy.

Physical Factors Governing the Shape of the Miram Curve Knee in Thermionic Emission

In a current density versus temperature (J-T) (Miram) curve in thermionic electron emission, experimental measurements demonstrate there is a smooth transition between the exponential region and the saturated emission regions, which is sometimes referred to as the "roll-off" or "Miram curve knee". The shape of the Miram curve knee is an important figure of merit for thermionic vacuum cathodes. Specifically, cathodes with a sharp Miram curve knee at low temperature with a flat saturated emission current are typically preferred. Our previous work on modeling nonuniform thermionic emission revealed that the space charge effect and patch field effect are key pieces of physics which impact the shape of the Miram curve knee. This work provides a more complete understanding of the physical factors connecting these physical effects and their relative impact on the shape of the knee, including the smoothness, the temperature, and the flatness of the saturated emission current density. For our analyses, we use a periodic, equal-width striped ("zebra crossing") work function distribution as a model system and illustrate how the space charge and patch field effects restrict the emission current density near the Miram curve knee. The results indicate there are three main physical parameters which significantly impact the shape of the Miram curve. Such physical knowledge directly connects the patch size, work function values, anode-cathode voltage, and anode-cathode gap distance to the shape of the Miram curve, providing new understanding and a guide to the design of thermionic cathodes used as electron sources in vacuum electronic devices (VEDs).

Simulation assisted design and manufacturing of anode for the hard chrome plating of components with complex geometry

Hard chrome plating is a widespread coating technique for applying a protective coating layer to the surface of components. Due to the simplicity of industry-applied lead anodes, components with complex geometry are often plated with a non-uniform layer of chrome. In this work, a cost-effective process based on thermal arc spraying and additive manufacturing for fabricating anode with complex geometry is presented. A simulation-based approach was employed to design the anode geometry. The influence of anode-cathode distance and shielding on coating thickness was examined using a developed simulation model. The designed anode structure was additively manufactured using Multi-Jet-Fusion (MJF) process and subsequently arc sprayed with an electrically conductive coating system. The test samples were both plated with conventional lead anodes and the developed anode under the same industrial conditions to validate the simulation model. The coating thickness of the plated samples was characterized using an optical microscope. The results concluded that the developed simulation model can give a precise prediction of the thickness of the deposited coating. The strategy of varying anode-cathode distance is able to optimize small thickness inhomogeneity. To eliminate the edge effect, the shielding strategy is more effective. Chrome-plated samples using the developed anode show more homogenous coating distribution compared to those chrome-plated samples using conventional lead anodes.

Primary Production of Aluminium and Its Alloys in Molten Salts with Oxygen Evolving Anodes: Overview

Carbon dioxide and other greenhouse gases are emitted during the production of primary aluminium through the Hall-Heroult process. Moreover, the process requires specific energy consumption of as high as 14.685 kWh/tonne of Al. There is an urgency to replace the existing process with a more environmentally and economically friendly process. One such process involves the use of inert anodes instead of traditional carbon anodes, where Al2O3 → 2Al + 1.5O2 occurs instead of 1.5C + Al2O3 → 2Al + 1.5CO2. The life span of inert anodes can be improved by using them at low operating temperatures, however, alumina solubility and dissolution rate decrease at low operating temperatures. Instead of using a traditional NaF-AlF3 molten solution, NaF-KF-AlF3 or KF-AlF3 could be used as low-temperature electrolytes. Introducing KF salt into the NaF-AlF3 mixture increases the alumina solubility and reduces the liquidus temperature of the molten salt. Another factor that affects the liquidus temperature of the mixture and alumina solubility in the electrolyte is the cryolite ratio , where M = Na or K (or both). It should be noted that the cells with AlF3-rich NaF electrolytes suffer with problems such as high cell voltage, low aluminium purity and unstable frozen side ledges. The addition of CaF2, MgF or LiF to the electrolyte mixture could improve the physical-chemical properties of the electrolyte. For instance, the addition of CaF2 to KF-AlF3 molten salts improves the electrical conductivity of the electrolyte. Specific energy consumption of the cell can be significantly reduced by using a vertical electrode cell with reduced anode-cathode distance (ACD). However, the major problem with low ACD is the contamination of reduced aluminium at cathode by anode products. This problem can be solved by using suspension electrolytes where the electrolyte contains excess about of Al2O3 in the electrolyte which obstructs the transportation of anode products into the aluminium diffusion layer on the cathode, thus maintaining high aluminium purity. In this paper, we summarise the developments obtained in designing the inert anode cells. We mainly focus on three main components: Inert anodes, wettable cathodes, and low-temperature electrolytes. The influence of additives on the properties of electrolytes will be discussed in detail. We also discuss the energy consumption, environmental impact and economic aspects of producing aluminium using vertical electrode cells.

Mechanistic investigation into flow-through electrochemical oxidation of sulfanilamide for groundwater using a graphite anode

The technical effectiveness/merit of electrochemical oxidation (EO) has been recognized. Nonetheless, its practical application to groundwater remediation has not been fully implemented due to several technical challenges. To overcome the technical incompleteness, this study adopted a graphite anode in the flow-through system and studied the mechanistic roles of a graphite anode. To this end, groundwater contaminated with sulfanilamide was remediated by means of EO, and sulfanilamide oxidation was quantitatively determined in this study. Approximately 60% of sulfanilamide was degraded at the anode zone, and such observation offered that the removal of sulfanilamide was not closely related with current variations (10–100 mA). However, this study delineated that sulfanilamide removal is contingent on the flow speed. For example, the removal of sulfanilamide was lowered from 59 to 25% owing to a short contact time when the flow velocity was increased from 0.14 to 0.55 cm/min. This study also delineated that a shorter anode-cathode distance could offer a favorable chance to enhance the removal of sulfanilamide even under an identical current. A shorter distance could offer a chance to save energy due to the lower voltage operation. This study also offered that chloride (Cl−) and sulfate (SO42−) electrolytes served a crucial role in the generation of active species. In contrast, bicarbonate (HCO3−) and synthetic groundwater electrolytes impeded the oxidation rate because HCO3− scavenged the other active species. In an effort to seek the oxidation mechanisms of a graphite anode, scavenger, cyclic voltammetry test, and electron https://en.wikipedia.org/wiki/Electron_paramagnetic_resonanceparamagnetic resonance (EPR) analysis were done. From a series of the tests, it was inferred that a graphite anode did not directly affect the generation of the active species. Thus, the prevalence of the oxygenated functional groups on an anode surface could be the main mechanism in sulfanilamide removal due to the enhanced electron transfer.

Effects of Cell Design Parameters on Zinc-Air Battery Performance

Zn-air batteries have attracted considerable attention from researchers owing to their high theoretical energy density and the abundance of zinc on Earth. The modification of battery component materials represent a common approach to improve battery performance. The effects of cell design on cell performance are seldom investigated. In this study, we designed four battery structures as follows. Cell 1: close-proximity electrode, Cell 2: equal-area electrode, Cell 3: large zinc electrode, and Cell 4: air channel flow. The effects of four factors: (1) carbon paste, (2) natural and forced air convection, (3) anode/cathode area ratio, and (4) anode–cathode distance were also investigated. Results showed that the addition of carbon paste on the air side of 25BC increased cell power density under forced air convection. Moreover, cell performance also improved by increasing the anode/cathode ratio and by decreasing the anode–cathode distance. These four types of cells were compared based on the oxygen reduction reaction electrode area. Cell 3 displayed the highest power density. In terms of volumetric power density, the proximity cell (Cell 1) exhibited the highest power density among the cells. Therefore, this cell configuration may be suitable for portable applications.

Study the Optimal Operative Conditions of New Glow Discharge Ion Source for Polymeric Treatment

The design, manufacturing, and systematic parametric evaluation of a modified glow discharge ion source (with a pear-shaped anode and a plane cathode) are detailed to extract low-power, high plasma density, and high-intensity ion beam current for material processing. The study includes determining the optimal operative conditions for ion source performance and optimizing its properties. The ion beam current was measured at various argon gas pressures and anode-cathode distances as well as its measurements at various ion source - collector plate distances. At the optimum settings, the influence of discharge pressure on the output current was evaluated using various gases (argon, oxygen, nitrogen and hydrogen). In addition, the influence of applied negative voltages on the extractor electrode (different hole diameters) on the generated ion beam current is being explored. Finally, SIMION computer program evaluated and studied ion beam optics. The simulation and experimental results for a highly efficient ion beam derived from the planned ion source agreed well.

An Electrochemical Tilt Sensor with Double-Band Electrodes Fabricated by Wire Winding.

This paper presents the principle, design, fabrication, and characterization of Molecular Electronic Transducer (MET) dual-axis tilt sensors. The proposed sensor has a 3D-printed cylindrical channel inserted with four double-band electrodes and partially filled with a liquid electrolyte. The double-band electrodes were fabricated by wire winding with a ~0.1 mm anode-cathode distance under controlled tension. It allows the electrode to become any 3D coil rather than a 2D structure by microfabrication and exhibits good repeatability (). The tilting changes the electrolyte level and electrode-electrolyte contact area, resulting in Faradaic current changes. The x-axis and the y-axis sensitivity reach 0.121 V/° and 0.154 V/°, respectively.

How the Number and Distance of Electrodes Change the Induced Electric Field in the Cortex during Multichannel tDCS.

Multichannel transcranial direct current stimulation (tDCS) is a promising approach to target neuromodulation of neural networks by making use of variable number of electrodes and distances to facilitate/inhibit specific connectivity patterns. Optimization of the electric field (EF) spatial distribution through computational models can provide a more accurate definition of the stimulation settings that are more effective. In this study, we investigate the effect of increasing the number of cathodes around a central anode placed over the target. We demonstrate that anode-cathode distance has the largest influence in the EF and using more than 3 cathodes did not result in considerable changes in the EF magnitude and direction. This could be relevant for simultaneous tDCS-electroencephalography (EEG) applications, by saving electrode positions for EEG acquisition. Clinical Relevance- This study demonstrates that distance between electrodes is more relevant than electrode number in determining the electric field distribution, and that a highly-focused stimulation can be equally effective with fewer electrodes.