Cathode Shapes Research Articles

Cathode Shape Design for Steady-State Electrochemical Machining

The inverse or cathode shape design problem of electrochemical machining (ECM) deals with the computation of the shape of the tool cathode required for producing a workpiece anode of a desired shape. This work applied the complex variable method and the continuous adjoint-based shape optimization method to solve the steady-state cathode shape design problem with anode shapes of different smoothnesses. An exact solution to the cathode shape design problem is proven to exist only in cases when the function describing the anode shape is analytic. The solution’s physical realizability is shown to depend on the aspect ratio of features on the anode surface and the width of the standard equilibrium front gap. In cases where an exact and physically realizable cathode shape exists, the continuous adjoint-based shape optimization method is shown to produce accurate numerical solutions; otherwise, the method produces cathode shapes with singularities. For the latter cases, the work demonstrates how perimeter regularization can be applied to compute smooth approximate cathode shapes suitable for producing workpieces within the range of manufacturing tolerance.

Research on Electrochemical Controllable Machining Technology of Small-Sized Inner Intersecting Hole Rounding

Small-sized inner intersecting holes are a common structure for large engine nozzles, hydraulic valves, and other parts. In order to ensure the uniform and stable fluid state in the intersecting hole, it is necessary to process the fillet at the intersecting line and accurately control the fillet radius. Limited by the structure and size, the rounding of the small-sized inner intersecting hole is a technical problem, and the traditional machining methods have problems, in terms of efficiency and accuracy. In order to solve this problem, electrochemical machining technology was applied to the rounding of small-sized inner intersecting holes. According to the structure of inner intersecting holes, an electrochemical rounding processing scheme with built-in fixed cathode was designed. The electric field distribution of different cathode shapes was analyzed using finite element method software. The influence of processing voltage and processing time on the current density distribution was studied for different cathode shapes, to determine the most reasonable cathode shape. Taking the inner intersecting hole with a diameter of 2 mm as the research object, and according to the analysis of the influence of processing voltage on the processing effect, a suitable control factor for controlling the rounding was processing time, and the optimal processing voltage was obtained. The formulas of fillet radius and processing time were obtained by regression analysis and verified using machining examples. The results provide a feasible method for the accurate and controllable machining of small-sized inner intersecting hole rounding.

Cathode shape prediction for uniform electrochemical dissolution of array tools for ECDM applications

ABSTRACT The effect of various cathode shapes, i.e., flat-plate, conical, and spherical-shaped cathodes, on the electrochemical dissolution (ECD) behavior of the 3 × 3 area-array tool electrode is presented. The allowed variation in all tip heights is less than 30 μm. Initially, the finite element method (FEM) was used to predicts the reduction in size and heights of the 3 × 3 tips. The spherical shape cathode exhibited uniform current density distribution around the tips, resulting in the consistent dissolution for a longer time than other cathode shapes. Detailed experiments were also performed to predict the dissolution behavior. Experimental results confirmed a similar dissolution behavior. The flat-plate electrode was not suitable in the ECD of array tool electrodes as the difference between the outermost and central tip heights was more than 130 µm, while the difference was less than 30 µm with a spherical-shaped cathode. Electrochemical discharge machining (ECDM) was carried out using the area-array electrodes made by the spherical and flat plate cathodes. The energy channelized by the uniform tips during the ECDM resulted in uniform material removal beneath all the tips, resulting in consistent crater formation. In contrast, a single crater was formed when the non-uniform tips were used.

Predictive Modeling of Transport and Elastic Moduli of Porous Extreme Fast Charging Li-Ion Electrodes

Extreme-fast-charging of Li-ion batteries, where the state of charge can be increased by 80% in less than 15 minutes, is increasingly important for electric vehicles. This work demonstrates how simulation can illuminate material- and fabrication-dependent ionic and electronic transport as well as mechanical properties of advanced, fast-charging Li-ion electrodes.Developing high-power Li-ion cells without compromising energy density is a challenge because of volumetric trade-offs between electronic and ionic transport and active material energy storage. Electrode materials and manufacturing steps both affect resulting microstructure and subsequently change transport properties.A multi-phase smoothed particle model was developed within LAMMPS to simulate the drying and calendering manufacturing processes for different electrodes. Generated structures were quantitatively assessed in terms of MacMullin number, electronic conductivity, and Young’s modulus to estimate the contribution of different materials and processing factors. Active material size, shape, stiffness, and orientation were varied.Model results suggest that the size of active particles needs to be taken into careful consideration, as the interaction of active material and binder can affect electrode shrinkage and porosity, ultimately affecting the transport and mechanical properties of the electrode (Figure 1).Spherical and disk shapes (representing typical cathode and anode active material shapes) show unexpected transport properties. These results suggest that the difference between a cathode and an anode is most likely due to the active particle intrinsic conductivity and stiffness.The stiffer the particles are, the more they can handle inter-particle stresses without deformation. On the other hand, distinctive particle orientations (a particle property observed in non-spherical anode active material) are decreased after calendering when the particles seem to align more horizontally, regardless of their original alignment.Careful selection of materials and attention to fabrication process parameters can produce Li-ion electrode microstructures more conducive to extreme-fast-charging.Figure 1. Simulated microstructures after drying (left structure in each pair) and calendering (right structure in each pair) with active particle sizes of: (a) 6 µm, (b) 2-15 µm, and (c) 15 µm. Figure 1

A numerical study of the effects of cathode geometry on tungsten inert gas type electric arcs

In this paper we address the question of the influence of cathode tip geometry on the physical quantities relevant to Tungsten Inert Gas (TIG) arc welding. Although cathode geometry is known to influence arc-plasmas, a thorough quantification of the Lorentz phenomenon, which is the dominant source of momentum in the fluid flow of TIG arcs has not been strongly investigated. Therefore, we have performed a numerical parametric study at a constant inlet electric current and arc height, for different cathode sizes and shapes (pointed, chamfered and rounded tips), parameterised by the truncation angle and tip radius. To this end, we developed a coupled steady-state magneto-hydrodynamic finite element model in a 2D axi-symmetric configuration, implemented in the [Display omitted] toolbox. The paper characterises, quantifies and analyses the influence of tip geometry on TIG arcs and the workpiece. The model reveals that tip size and truncation angle similarly influence the magnitude of the transported quantities of the arcs. We find that the imparted momentum and transferred heat flux to the workpiece vary about 4 and 2-fold between the bluntest and sharpest cathodes, respectively. This signifies the importance of the choice of cathode tips in numerical TIG welding simulations. Agreement between the literature and the current work is analysed and discussed and the importance of coupling the cathode and arc domains is highlighted.

Operational characteristics of disc and spherical cathode electrodes in dc plasma discharge

In this work, the effective of shapes for disc and spherical cathode electrodes on the operational conditions of dc discharge has been studied. Paschen curve was studied of the two cathode shapes electrodes at the discharge voltage (0- 450 V) at 38 mm distance between the electrodes. Theoretically, the distributions of equipotential line and electric field before the minimum discharge voltage between the electrodes were estimated by using SIMION software. The study showed the effect of the geometry of the cathode electrode on the operational conditions where the discharge voltages require for the spherical shape was greater than the disc at minimum values in Paschen curve. The results showed a diagnostics of plasma using a single Langmuir probe that electron temperature and ion density for spherical cathode shape was higher than the disc by, 20% and 17.9% respectively.

Design and simulation of a 1 MeV, 100 mA parallel-fed capacitive coupled cascade industrial accelerator

The construction of indigenous parallel-fed capacitive coupled cascade accelerators for industrial electron beam processing has been taken up at accelerator division of NSTRI at Iran atomic energy organization. This machine has been previously developed by Radiation Dynamics Inc. (RDI), IBA Industrial and High Voltage Engineering Europa B.V. (HVE) companies. Parallel-fed capacitive coupled cascade generators are reliable and high current sources of DC accelerators with many scientific, medical and industrial applications. We have selected this mechine because of some superiorities of that in comparison with many existing accelerators. These superiorities are as follows: compactness, simplicity, cheapness, having typically higher amount of beam current, wide range of beam energy and addressing many areas of applications. In this article, the main parts of a 1MeV, 100mA parallel-fed cascade industrial accelerator have been analyzed, designed and simulated. These parts are the electron gun, accelerating tube, voltage multiplier column (VMC) and some of the other components of the VMC. The electron gun is of a diode type with the Pierce configuration. Two electron guns with different cathode shapes have been designed and compared with each other. The intended cathode is a Dispenser type with a tungsten heater and porous tungsten matrix wich is impregnated with LaB6 and works in ambient vacuum of 10–7 Torr. The required current in our accelerator is about 100mA. For the next step, the accelerating tubes with different electrode geometries have been designed, simulated and compared with each other and the best geometry has been selected. For the VMC, we have tried to achieve a low ripple output DC voltage. The VMC has been analyzed and simulated with PSpice simulation software and optimum values of different parameters were achieved. We have tried to get the optimum values of the PSpice simulations by a mechanical design in CST Particle studio. At the end, the parameters of the mechanically designed VMC had a good accordance with the results from PSpice.

Influence and calculation of the cathode form in the formation of uniform thickness MAO-coatings

The paper presents the results of using the methods of numerical simulation of the cathode shapes for the formation of a uniform thickness of the MAO coatings over the entire surface of the part. The data obtained by numerical simulation were tested on samples with a coating obtained according to the traditional scheme and in a scheme with a new cathode form.

Nonequilibrium simulation analysis of the power dissipation and the pressure produced by TIG welding arcs

The recently developed novel nonequilibrium model of TIG arcs is applied to study in detail the momentum balance and pressure establishment in the arc region and the power balance of the whole arc system. TIG configurations with two currents (100 and 200 A), two different cathode shapes (2-mm radius and vertex angles of 60∘ and 30∘), and an electrode distance of 5 mm are considered exemplary. The pressure analysis yields two regions of pressure in excess of atmospheric pressure below the cathode tip in front of the anode. The maximum values show weak dependence on the cathode vertex angles. The growth of the arc pressure with the arc current is predicted to be faster than quadratic. The analysis of the power budget shows the importance of the Joule heating term in the electron energy balance, which is the dominant mechanism in the vicinity of the cathode and the near surrounding while it is negative in the vicinity of the anode. The electric power deposited in the cathode space-charge sheath is a huge amount of the total power supply (40% at 200 A and 50% at 100 A) with a significant part of it being transferred to the plasma electrons.

Improvements on the stability and operation of a magnetron H− ion source

The magnetron H- ion sources developed in the 1970s currently in operation at Fermilab provide beam to the rest of the accelerator complex. A series of modifications to these sources have been tested in a dedicated offline test stand with the aim of improving different operational issues. The solenoid type gas valve was tested as an alternative to the piezoelectric gas valve in order to avoid its temperature dependence. A new cesium oven was designed and tested in order to avoid glass pieces that were present with the previous oven, improve thermal insulation and fine tune its temperature. A current-regulated arc modulator was developed to run the ion source at a constant arc current, providing very stable beam outputs during operations. In order to reduce beam noise, the addition of small amounts of N2 gas was explored, as well as testing different cathode shapes with increasing plasma volume. This paper summarizes the studies and modifications done in the source over the last three years with the aim of improving its stability, reliability and overall performance.

The Impact of Cathode Material and Shape on Current Density in an Aluminum Electrolysis Cell

A finite element model was developed to determine the impact of cathode material and shape on current density in an aluminum electrolysis cell. For the cathode material, results show that increased electrical resistivity leads to a higher cathode voltage drop; however, the horizontal current is reduced in the metal. The horizontal current magnitude for six different cathode materials in decreasing order is graphitized, semi-graphitized, full graphitic, 50% anthracite (50% artificial graphite), 70% anthracite (30% artificial graphite), 100% anthracite. The modified cathode shapes with an inclined cathode surface, higher collector bar and cylindrical protrusions are intended to improve horizontal current and flow resistance. Compared to a traditional cathode, modified collector bar sizes of 70 mm 9 230 mm and 80 mm 9 270 mm can reduce horizontal current density component Jx by 10% and 19%, respectively, due to better conductivity of the steel. The horizontal current in the metal decreases with increase of cathode inclination. The peak value of Jx can be approximately reduced by 20% for a 2 change in inclination. Cylindrical protrusions lead to local horizontal current increase on their tops, but the average current is less affected and the molten metal is effectively slowed down.

Effect of cathode shape on vertical buffered electropolishing for niobium SRF cavities

This paper reports the research results of the effect of cathode shape during vertical buffered electropolishing (BEP) by employing a demountable single cell niobium (Nb) superconducting radio frequency (SRF) cavity. Several different cathode shapes such as, for instance, bar, ball, ellipsoid, and wheels of different diameters have been tested. Detailed electropolishing parameters including I–V characteristic, removal rate, surface roughness, and polishing uniformity at different locations inside the demountable cavity are measured. Similar studies are also done on conventional electropolishing (EP) for comparison. It is revealed that cathode shape has dominant effects for BEP especially on the obtaining of a suitable polishing condition and a uniform polishing rate in an Nb SRF single cell cavity. EP appears to have the same tendency. This paper demonstrates that a more homogeneous polishing result can be obtained by optimizing the electric field distribution inside the cavity through the modification of the cathode shape given the conditions that temperature and electrolyte flow are kept constant. Electric field distribution and electrolyte flow patterns inside the cavity are simulated via Poisson–Superfish and Solidworks respectively. With the optimal cathode shape, BEP shows a much faster polishing rate of ∼2.5μm/min and is able to produce a smoother surface finish in the treatments of single cell cavities in comparison with EP.

Research of Bearing Crown Roller-Raceway by Non-Uniform Interelectrode Gap Electrochemical Mechanical Machining

Electrochemical mechanical machining (ECMM) is introduced to the manufacture of bearing crown roller-raceway in consideration of the very problems appearing in traditional machining methods. Firstly, numerical model on the non-uniform interelectrode gap ECMM is established and anode crown shapes under different cathode shapes are analyzed. Afterwards, according to the requirement of anode crown related cathode shape is formed through numerical simulation. In the end, the crown of bearing roller-raceway is machined by practical concave cathode with improved surface quality and certain crown face.

Ion energy distributions measured inside a high-voltage cathode in a BF3 pulsed dc plasma used for plasma doping: experiments and ab initio calculations

The purpose of this paper is the characterization of a plasma-doping system in BF3. Energy distributions (IEDs) of boron ions crossing a high-voltage sheath (up to 1 kV) are measured in a BF3 plasma under different experimental conditions. It is demonstrated that relative percentages of boron ions reaching the cathode and IED shapes are governed by the number of collisions inside the sheath. Heavy molecular ions , are dissociated inside the sheath and light boron ions (B+, BF+) are created. Based on experimental results and ab initio calculations of boron ion structures, the mechanisms occurring in the sheath are discussed. Furthermore, the charge exchange cross-section between and BF3 is estimated to be 8.8 × 10−19 m2.

Electricity generation from wastewaters with starch as carbon source using a mediatorless microbial fuel cell

Microbial fuel cells represent a new method for producing electricity from the oxidation of organic matter. A mediatorless microbial fuel cell was developed using Escherichia coli as the active bacterial component with synthetic wastewater of potato extract as the energy source. The two-chamber fuel cell, with a relation of volume between anode and cathode chamber of 8:1, was operated in batch mode. The response was similar to that obtained when glucose was used as the carbon source. The performance characteristics of the fuel cell were evaluated with two different anode and cathode shapes, platinised titanium strip or mesh; the highest maximum power density (502mWm−2) was achieved in the microbial fuel cell with mesh electrodes. In addition to electricity generation, the MFC exhibited efficient treatment of wastewater so that significant reduction of initial oxygen demand of wastewater by 61% was observed. These results demonstrate that potato starch can be used for power generation in a mediatorless microbial fuel cell with high removal efficiency of chemical oxygen demand.

Characteristics of miniature electronic brachytherapy x‐ray sources based on TG‐43U1 formalism using Monte Carlo simulation techniques

The goal of this study is to determine a method for Monte Carlo (MC) characterization of the miniature electronic brachytherapy x-ray sources (MEBXS) and to set dosimetric parameters according to TG-43U1 formalism. TG-43U1 parameters were used to get optimal designs of MEBXS. Parameters that affect the dose distribution such as anode shapes, target thickness, target angles, and electron beam source characteristics were evaluated. Optimized MEBXS designs were obtained and used to determine radial dose functions and 2D anisotropy functions in the electron energy range of 25-80 keV. Tungsten anode material was considered in two different geometries, hemispherical and conical-hemisphere. These configurations were analyzed by the 4C MC code with several different optimization techniques. The first optimization compared target thickness layers versus electron energy. These optimized thicknesses were compared with published results by Ihsan et al. [Nucl. Instrum. Methods Phys. Res. B 264, 371-377 (2007)]. The second optimization evaluated electron source characteristics by changing the cathode shapes and electron energies. Electron sources studied included; (1) point sources, (2) uniform cylinders, and (3) nonuniform cylindrical shell geometries. The third optimization was used to assess the apex angle of the conical-hemisphere target. The goal of these optimizations was to produce 2D-dose anisotropy functions closer to unity. An overall optimized MEBXS was developed from this analysis. The results obtained from this model were compared to known characteristics of HDR (125)I, LDR (103)Pd, and Xoft Axxent™ electronic brachytherapy source (XAEBS) [Med. Phys. 33, 4020-4032 (2006)]. The optimized anode thicknesses as a function of electron energy is fitted by the linear equation Y (μm) = 0.0459X (keV)-0.7342. The optimized electron source geometry is obtained for a disk-shaped parallel beam (uniform cylinder) with 0.9 mm radius. The TG-43 distribution is less sensitive to the shape of the conical-hemisphere anode than the hemispherical anode. However, the optimized apex angle of conical-hemisphere anode was determined to be 60°. For the hemispherical targets, calculated radial dose function values at a distance of 5 cm were 0.137, 0.191, 0.247, and 0.331 for 40, 50, 60, and 80 keV electrons, respectively. These values for the conical-hemisphere targets are 0.165, 0.239, 0.305, and 0.412, respectively. Calculated 2D anisotropy functions values for the hemispherical target shape were F(1 cm, 0°) = 1.438 and F(1 cm, 0°) = 1.465 for 30 and 80 keV electrons, respectively. The corresponding values for conical-hemisphere targets are 1.091 and 1.241, respectively. A method for the characterizations of MEBXS using TG-43U1 dosimetric data using the MC MCNP4C has been presented. The effects of target geometry, thicknesses, and electron source geometry have been investigated. The final choices of MEBXS design are conical-hemisphere target shapes having an apex angle of 60°. Tungsten material having an optimized thickness versus electron energy and a 0.9 mm radius of uniform cylinder as a cathode produces optimal electron source characteristics.

Effect of a near-cathode sheath on heat transfer in high-pressure arc plasmas

Numerical simulation of a high-pressure arc discharge has been performed with a self-consistent modelling of most of the components, including the electrodes, and the interactions between them. In particular, the arc column and the cathodic part of the discharge are simulated by means of a two-temperature hydrodynamic model and of a model of nonlinear surface heating, respectively. Simulation results are given for a free-burning arc in atmospheric-pressure argon in the range of arc currents from 10 to 200 A. It is found that the electric power deposited into the near-cathode layer is transported not only to the cathode but also to the arc column, an effect that cannot be described by the local thermodynamic equilibrium (LTE) model. The electron enthalpy transport substantially exceeds the net contribution of thermal conduction by the electrons and heavy particles and is thus the dominating mechanism of energy transfer from the near-cathode layer to the arc column. The predicted gas temperatures along the arc axis in the arc column using the LTE model are much higher than the calculated electron and heavy-particle temperatures (∼1000–2000 K or higher) under the same operation conditions using the non-equilibrium model with the consideration of the near-cathode sheath for the cases studied in the present paper. Studies on the influences of the cathode shapes and metal vapour contaminations on the arc characteristics will be conducted in future work.

Dependence of Energy Source Properties of Tube Cathode Arc on Cathode Shape

A plasma torch can stabilize high temperature arc plasma by employing shielding gas and has high heating efficiency and highly controllable characteristics. Therefore, it is widely utilized as a heat source device, for example, for production of nano-particles, material processing, or treatment of toxic waste and so on. Tube Cathode Arc (TCA) is a kind of plasma torch which produces the arc plasma by introducing the shielding gas from the hole of the tube cathode. It has been studied as a heat source especially in lower pressure environment, for example, for space welding or plasma CVD. For an application in atmospheric pressure, it enables heating of materials uniformly and, therefore, to be suitable for processes such as thermal spraying, brazing or buildup. In this paper, as basic energy source properties of argon TCA, dependence of the arc plasma property on cathode shapes such as diameter and conical angle of the cathode are numerically analyzed.

Modeling ion extraction from a free-plasma surface with a flexible conformal mesh

This paper describes a new method for numerical modeling of extraction of high-current ion beams from a plasma source. The challenge in the application is to satisfy simultaneously requirements for space-charge-limited flow and uniform ion flux. The plasma surface must assume a special shape that is not known in advance. The method involves the use of finite-element techniques coupled with a dynamic conformal mesh. Starting from an initial estimate, the flexible mesh is shifted to achieve uniform flux over the emission surface. The approach achieves high accuracy and has the versatility to handle complex emission surfaces in gridded guns. In contrast to trial-and-error approaches, the method proceeds directly to the optimum solution. The technique can also be applied to determine cathode shapes for uniform-flux electron guns. Benchmark calculations using the Trak two-dimensional ray-tracing code are described. The program automatically carries out the surface search.

Modeling of Glow Discharge Sources with Flat and Pin Cathodes and Implications for Mass Spectrometric Analysis

A set of three-dimensional models for a direct current glow discharge in argon, developed previously in our group, is applied to analytical glow discharge cells with either flat or pin-type cathodes. Among other quantities, the densities of the plasma species are calculated and compared for these two cathode shapes. A comparison is also made for the computed argon and sputtered cathode (copper) ion currents leaving the glow discharge cell and entering the mass spectrometer, because this is of major interest from the analytical point of view. Finally, for the pin cell, the influence of sampling distance (i.e., distance between cathode pin and exit slit to the mass spectrometer) on the calculated plasma quantities is investigated.