Anode Geometries Research Articles

Electrolytical Coating of Inhomogeneous Structures Distributed on Metallic Surfaces

In modern electrochemical coating technology, it is common practice to create uniform layers. However, this study focuses on the deposition of non-uniform layers achieved through a deliberate arrangement of micro structured electrodes on the anode side. The "dog bone effect” was employed as the primary approach [1]. When electroplating on an otherwise uniform surface, this effect selectively processes an area influenced by the geometric edge effect (figure 1 left). The coating within this area is intended to be (i) unevenly distributed and (ii) non-reproducible. Process data was obtained through electrochemical simulations and subsequently applied to a specially designed micro-galvanic setup. This enabled the production of suitable micro structured anodes, validation of coating parameters, and the deposition of visually imperceptible structured areas with inhomogeneous properties using "adhesive gold" on appropriate substrates such as silver and nickel. The layers and their local topography were characterized and analyzed using confocal laser microscopy, X-Ray fluorescence analysis (XRF), as well as a self-designed and constructed laser interference device. As a result, this specific galvanic process technology successfully produced metallic layers that (i) cannot be visually confirmed by the naked eye, (ii) exhibit varied microstructural anode geometries, (iii) display unique differences in layer thickness, (iv) possess non-reproducible and chaotic topographies, and (v) can be detected and identified using conventional analysis techniques or a simple interference setup.

New evidence about the nature of plasma filaments in plasma accelerators of type plasma-focus

In this work, new evidence and information about both the origin and evolution of filamentary structures observed in the current sheath of a small plasma focus (PF) discharge are reported. The experiments were carried out in a small generator of low energy (multipurpose generator) at the PF configuration, under different operating conditions. These include different anode and insulator geometries, without return bars and in a high-performance regime of the generator at high pressures (10 mbar). The evolution of the plasma structures is characterized by means of refractive optical techniques. The electrical behavior of the discharge, as well as its performance, are monitored with conventional electrical diagnostics and neutron and x-ray detectors, respectively. Plasma filaments of the same species are present in all tested configurations, however, in experiments with larger effective anode length (and smaller anode radii), the plasma region containing the filaments moves away from the anode surface and remains confined in a region of the plasma sheath, such as a toroidal plasma belt, without reaching the top of the anode nor participating in the radial compression phase. According to images of the plasma sheath in its early phase, the filaments originate and evolve from a precursor annular plasma formed in the lower part of the anode next to the insulator, during the process of electrical breakdown. The local character that these dense-filamentary structures acquire in the evolution of the plasma sheath would discard the current-filament hypothesis. On the other hand, experiments performed in deuterium gas with anodes of larger effective lengths and without filaments in the radial compression phase allowed the production of neutrons and x-rays at a high performance.

Investigation of Subsonic to Supersonic Transition of a Low-Pressure Plasma Torch Jet

The plasma jet emanating out of a thermal plasma torch operating at low pressure ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 30$ </tex-math></inline-formula> mbar) has been investigated experimentally. Different anode exit diameters are chosen, and the torch is operated at various gas flows and discharge current and their thermodynamic outputs have been calculated. Current–voltage characteristics (CVC) of plasma torch with different anode geometries are explored highlighting their differences. Interesting correlations are found between the anode exit diameter and the threshold limit for subsonic to supersonic transition of the jet. The spectral analysis of the voltage fluctuations reveals the presence of different frequencies and also yields the threshold. The kinetic energy (KE) component of the plasma jet has a direct correlation with the oscillations in the arc voltage. In addition to restrike mode and Helmholtz mode, an acoustic mode of oscillations is also investigated. A new resonator model explaining the different oscillations occurring in the low-pressure operation is also presented. The Helmholtz mode oscillations are validated by comparing the experimental values with the theoretical calculations. The power associated with the Helmholtz mode and acoustic mode has direct correlation with the plasma velocity and acts as a signature of the transition from subsonic to supersonic regime.

NUMERICAL analysis of the effects of current collector plate geometry on performance in a cylindrical PEM fuel cell

In this study, a numerical analysis was conducted to investigate the effects of current collector plate geometry on performance in a cylindrical PEM (Proton Exchange Membrane) fuel cell. For this purpose, 2 anode and cathode current collector plate geometries for each helix channel and straight channel were designed. Current collector plates with different geometries were combined with different sequences, and four different main model fuel cell geometries were created. Accordingly, anode and cathode current collector plates for Model-1, Model-2, Model-3, and Model-4 geometries were determined as straight-straight, helix-helix, straight-helix, and helix-straight, respectively. Using these model geometries, simulations were conducted for three different operating pressures, four different operating flow rates, and ten different operating voltages. It was observed that when helix flow channels were used instead of straight flow channels in current collection plate geometries, the flow density increased by approximately 63.18%. The results also revealed that the current density increased by approximately 206.9% when the fuel cell operating pressure increased. In addition, the power density increased as the operating pressure increased. As the gas flow to anode and cathode increased, a 19.05% increase in the current increase in the pressure difference was observed. As a result, the helix flow channel usage performed better than the straight flow channel for the parameters adopted in this study.

Interfacial studies on the effects of patterned anodes for guided lithium deposition in lithium metal batteries

The lifetime and health of lithium metal batteries are greatly hindered by nonuniform deposition and growth of lithium at the anode-electrolyte interface, which leads to dendrite formation, efficiency loss, and short circuiting. Lithium deposition is influenced by several factors including local current densities, overpotentials, surface heterogeneity, and lithium-ion concentrations. However, due to the embedded, dynamic nature of this interface, it is difficult to observe the complex physics operando. Here, we present a detailed model of the interface that implements Butler-Volmer kinetics to investigate the effects of overpotential and surface heterogeneities on dendrite growth. A high overpotential has been proposed as a contributing factor in increased nucleation and growth of dendrites. Using computational methods, we can isolate the aspects of the complex physics at the interface to gain better insight into how each component affects the overall system. In addition, studies have shown that mechanical modifications to the anode surface, such as micropatterning, are a potential way of controlling deposition and increasing Coulombic efficiency. Micropatterns on the anode surface are explored along with deformations in the solid-electrolyte interface layer to understand their effects on the dendritic growth rates and morphology. The study results show that at higher overpotentials, more dendritic growth and a more branched morphology are present in comparison to low overpotentials, where more uniform and denser growth is observed. In addition, the results suggest that there is a relationship between surface chemistries and anode geometries.

Design of 3D microbial anodes for microbial electrolysis cells (MEC) fuelled by domestic wastewater. Part I: Multiphysics modelling

The performance of a microbial electrolysis cell (MEC) supplied with domestic wastewater (dWW) is essentially limited by the kinetics of the anodic bioelectrochemical reactions and the low ionic conductivity of the electrolyte. A strategy to boost-up the anodic bioelectrochemical kinetics is to use three-dimensional (3D) microbial anodes that offer a high total anodic surface area and volume density of electroactive biofilm. In this work, a 3D multiphysics model was designed to simulate the current generation and resulting hydrogen production in double and triple-compartment MECs fed continuously with dWW. Simulations indicated that optimised 3D microbial anode geometries could simultaneously increase current and chemical oxygen demand (COD) removal by 86% compared to a 2D planar graphite electrode. At a constant CEM voltage, the current produced increased with the thickness of the 3D microbial anode up to a limiting thickness of 20 mm. Beyond this value, the current was stagnant due to the predominant ohmic drop. Current generation and COD removal could be further increased by designing 3D anode geometrical arrangements that force the dWWs to flow through the porosity of the 3D microbial anode. A gain of 20% was calculated by substituting a monolithic 3D graphite anode with a 3D anode of the same thickness (20 mm) but constructed of plates stacked on top of each other and spaced 2.5 mm apart. Finally, hydrogen production performance was additionally optimised by a further + 20% by switching from a two-compartment MEC design (anode-cathode) to a three-compartment MEC design (cathode-anode-cathode).

A First Molecular Dynamics Study for Modeling the Microstructure and Mechanical Behavior of Si Nanopillars during Lithiation.

This is the first study that employs large-scale atomistic simulations to examine the stress generation and deformation mechanisms of various Si nanopillars (SiNPs) during Li-ion insertion. First, a new robust and effective minimization approach is proposed to relax a lithiated amorphous SiNP (a-SiNP), which outperforms the known methods. Using this new method, our simulations are able to successfully capture the experimental morphological changes and volume expansions that SiNPs, hollow a-SiNPs, and solid crystalline SiNPs (c-SiNPs) experience upon maximum lithiation. These simulations enable us to selectively track the displacement of Si atoms and their atomic shear strain in the Li3.75Si alloy region, allowing us to observe the plastic flow and illustrate the atomistic mechanism of lithiation-induced deformation for various SiNPs for the first time. Based on the simulation results, a simple fracture mechanistic model is used to determine the fracture resistance of SiNPs, showing that the hollow a-SiNP is the optimal form of Si as an anode because it has the highest fracture resistance. The crack propagation simulation suggests that the preexisting dislocations in pristine c-Si can contribute toward the fracture of c-SiNPs during lithiation. These findings can guide the design of new Si-based anode geometries for the next-generation Li-ion batteries.

The Influence of Anode Trench Geometries on Electrical Properties of AlGaN/GaN Schottky Barrier Diodes

AlGaN/GaN lateral Schottky barrier diodes (SBDs) with three different anode geometries (stripe, circular, and the conventional plane one) and different rows of anode trenches are fabricated and electrically characterized to study the influence of anode trench geometries. The SBDs with anode trenches exhibit the lower on-state resistance (RON) than that with the conventional plane one. It can be explained that the anode trenches made the Schottky metal directly contact to the 2DEG at the sidewall of the AlGaN/GaN interface, removing the AlGaN barrier layer in the conventional plane anode. In addition, the RON of the SBDs with circular trenches is smaller than that of the SBDs with stripe ones. Furthermore, the RON decreases with the increasing rows of anode trenches, which can be attributed to the increased contact area between the Schottky metal and the 2DEG. For the reverse characteristics, the anode trenches do not lead to performance degradation. The fabricated devices exhibit the low reverse current (IR, IR &lt; 1 μA/mm), and the breakdown voltage (VBK) remains unchanged with different anode geometries.

Shifts in average energy of deposited atoms by magnetron sputtering through modifications in anode geometry: a simulation study

The deposition of titanium and gadolinium films by magnetron sputtering was simulated by using software SiMTra. The main goal is to analyze the average energy of deposited atoms as a function of argon pressure at different anode geometries. Two different anode configurations were used: a grid inserted between the target and the substrate, in the so-called grid-assisted magnetron sputtering, and a disk with different apertures. In the case of grid anode, simulations were also performed with a shutter in front of the substrate. The presence of the grid increases the average energy of atoms arriving at the substrate for pressures in the range between 1.0 and 8.0 Pa. The disk anode also changes the average energy, but such effect depends on the size of aperture.

Modeling spectral properties of X-ray sources for dosimetric Monte Carlo simulations of computed tomography: Influence on total energy deposition and spatial distribution of deposited energy

Purpose:X-ray spectra emitted by computed tomography (CT) sources differ in shape and mean spectral energy (Emean) due to different anode geometries, materials and filtration. Nonetheless, a variety of spectra and monoenergetic photons are employed in Monte Carlo (MC) simulations, despite possible differences in total energy deposition (Etotal) and its spatial distribution (Espatial). This study aims at assessing resulting differences and implications. Methods:The effect of different measured and generated 120 kVp-equivalent CT X-ray spectra on Etotal and Espatial in a water phantom (Ø = 32 cm, d=16 cm) was determined with MC simulations. Spectra were either measured in-house (reference: Emean,ref=57.7keV@0° fan angle; and fan-angle dependent spectra (FADS)) or generated (online tool) without and with 3.3 mm aluminum filtration, the latter matching Emean,ref. Additionally, monoenergetic photons matching Emean,ref were applied. Simulations were performed with (FM) and without (NM) beam-shaping. Results:Compared to simulations employing the reference spectrum and using beam-shaping, relative differences in Etotal are: +2.2% (FADS), −5.4% (online tool, unfiltered), +0.1% (online tool, filtered) and −1.0% (57.7 keV). Maximum relative differences in Espatial are larger: −10% (FADS), −20% (online tool, unfiltered), −3% (online tool, filtered) and −20% (57.7 keV). Ignoring fan-angle dependent fluence modulation causes up to +50% difference in Espatial. Conclusion:For the use of different X-ray spectra, Etotal and Espatial are comparable for matching peak tube potential and Emean. Additionally, simulations of accurate Espatial require modeling of beam-shaping. Monoenergetic photons matching Emean,ref should not be employed for X-ray source emission modeling due to large inaccuracies in Espatial.

Experimental investigation and mathematical modeling of triode PEM fuel cells

The triode operation of humidified PEM fuel cells has been investigated both with pure H2 and with CO poisoned H2 feed over commercial Vulcan supported Pt(30%)-Ru(15%) anodes. It was found that triode operation, which involves the use of a third, auxiliary, electrode, leads to up to 400% power output increase with the same CO poisoned H2 gas feed. At low current densities, the power increase is accompanied by an increase in overall thermodynamic efficiency. A mathematical model, based on Kirchhoff’s laws, has been developed which is in reasonably good agreement with the experimental results. In order to gain some additional insight into the mechanism of triode operation, the model has been also extended to describe the potential distribution inside the Nafion membrane via the numerical solution of the Nernst-Planck equation. Both model and experiment have shown the critical role of minimizing the auxiliary-anode or auxiliary-cathode resistance, and this has led to improved comb-shaped anode or cathode electrode geometries.

Development of miniaturized, spectroscopically assisted Penning gauges for fractional helium and hydrogen neutral pressure measurements

Direct measurements of the helium (He) fractional neutral pressure in the neutral gas around fusion devices is challenging because of the small mass difference between the abundant D2 molecules and the He ash which will be produced by deuterium-tritium fusion. To study He exhaust, an in situ Penning gauge system is being developed at UW-Madison that is optimized for good pressure and high spectroscopic sensitivity. Three different anode geometries have been studied regarding their vacuum electrostatic fields, light output, and ion current. The light output of the two new anode configurations are at least one order of magnitude above the currently available designs, hence improving the spectroscopic sensitivity at similar total neutral pressure resolution.

Resolution changes of MCP-PMTs in magnetic fields

Micro-channel plate photomultiplier tubes (MCP-PMTs) are chosen in many applications that have to cope with strong magnetic fields. The DIRC detectors of the PANDA experiment plan to employ them as they show excellent timing characteristics, radiation hardness, relatively low dark count rates and sufficient lifetime. This article mainly focuses on the performance of the position reconstruction of detected photons. Two different MCP-PMTs with segmented anode geometries have been tested in magnetic fields of different strengths. The variation of their performance has been studied. The measurements show improved position resolution and image shifts with increasing magnetic field strength.

Anode Geometry Effects on Ion Beam Energy Performance in Helicon Electrostatic Thruster

The ion beam energy performance in a helicon electrostatic thruster with various anode geometries was investigated. For discharge voltages from 100 to 300 V, the ion beam energy increased almost linearly with the discharge voltage. The rate of increase strongly depended on the anode inner diameter (ID). However, the ion beam energy was fit to a single linear function of the total input power irrespective of the anode ID. The effect of an insulation cover set on the side wall of the anode depended on the anode ID; while with the anode ID being equaled to that of the helicon source tube, i.e., 27 mm, the ion beam energy was decreased by about 30%, with the anode ID of 40 mm the electrostatic acceleration became negligible. Under typical operation conditions, the ion beam energy had a flat-hat profile with a diverging angle of 47°; the specific impulse, thrust efficiency, and propellant utilization efficiency evaluated from probe survey measurements were 2000 s, 9.7%, and 98%, respectively.

Removal of polyaromatic hydrocarbons from waste water by electrocoagulation

In the present study, two important groups of factors were studied; the first one corresponds to the Electrocoagulation (EC) process parameters such as current density, pH, electrolysis time and electrolyte concentration that were investigated in terms of their effects on the removal efficiencies of polyaromatic hydrocarbons, specially β-naphthols. The second group of factors analyses the effect of three different anode geometries on the percentage removal of β-naphthols. The present study achieved the following results: The optimum conditions for the removal of β-naphthols for cell No. 1 and 2 were achieved at current density 20 mA/cm2, initial pH 7 treated volumes 1.5 L, NaCl concentration 1 g/L and temperature 25°C. Meanwhile, the optimum conditions for cell No. 3 achieved at 106 mA/cm2, initial pH = 7, NaCl concentration = 1 g/L and temperature 25°C, treated volume = 0.5 L. The maximum separation efficiency was achieved for cell No. 1 and the lowest for cell No. 2. Key words: PolyaromaticHydrocarbons, β-naphthols, electrocoagulation, waste water treatment.

Theoretical calculation of the p-emitter length for snapback-free reverse-conducting IGBT

A physically based equation for predicting required p-emitter length of a snapback-free reverse-conducting insulated gate bipolar transistor (RC-IGBT) with field-stop structure is proposed. The n-buffer resistances above the p-emitter region with anode geometries of linear strip, circular and annular type are calculated, and based on this, the minimum p-emitter lengths of those three geometries are given and verified by simulation. It is found that good agreement was achieved between the numerical calculation and simulation results. Moreover, the calculation results show that the annular case needs the shortest p-emitter length for RC-IGBT to be snapback-free.

Progress in the Development of CdZnTe Unipolar Detectors for Different Anode Geometries and Data Corrections

CdZnTe detectors have been under development for the past two decades, providing good stopping power for gamma rays, lightweight camera heads and improved energy resolution. However, the performance of this type of detector is limited primarily by incomplete charge collection problems resulting from charge carriers trapping. This paper is a review of the progress in the development of CdZnTe unipolar detectors with some data correction techniques for improving performance of the detectors. We will first briefly review the relevant theories. Thereafter, two aspects of the techniques for overcoming the hole trapping issue are summarized, including irradiation direction configuration and pulse shape correction methods. CdZnTe detectors of different geometries are discussed in detail, covering the principal of the electrode geometry design, the design and performance characteristics, some detector prototypes development and special correction techniques to improve the energy resolution. Finally, the state of art development of 3-D position sensing and Compton imaging technique are also discussed. Spectroscopic performance of CdZnTe semiconductor detector will be greatly improved even to approach the statistical limit on energy resolution with the combination of some of these techniques.

Fourier transform infrared matrix‐isolation analysis of acetaldehyde fragmentation products after charge exchange with Ar•+ under varied ionization density conditions

The products of the Ar(•+) charge exchange ionization of acetaldehyde have been isolated and compared with related photoionization results and computational work. Acetaldehyde has been used to assess the effect of varied ion density in the ionization region of the electron bombardment matrix isolation apparatus. The amount of acetaldehyde destruction has been measured for constant gas-sample composition and constant ionization current for two anode geometries: a pin anode and a plate anode. For the same ionization current, a pin-shaped anode demonstrates higher precursor molecule destruction efficiency (85%) than the plate-shaped anode (30%), resulting in substantial effect on the yield and quantity of isolated products. When the plate anode is used, the observed infrared products correspond to matrix-isolated carbon monoxide (CO), methane (CH(4)), ketene (CH(2)CO), ethynyloxy radical (HCCO), formyl radical (HCO(•)), acetyl radical (CH(3)CO(•)), vinyl alcohol (H(2)C = CH-OH), and cationic proton-bound dimer, Ar(2)H(+). When the pin anode is used, the same products are observed with different relative proportions and new absorption features corresponding to dicarbon monoxide (CCO) and methyl radical (CH(3)(•)) are observed. The surprising observation of infrared absorptions corresponding to vinyl alcohol along with low yield of products anticipated through the analysis of photoelectron-photoionization coincidence measurements suggests that the initially formed fragmentation products are able to further react within the matrix-isolation environment to influence observed product yields. Related experiments, using the isotopomer CD(3)CHO, suggest that the observed products are formed via radical-radical reactions that occur under the high pressure conditions of the matrix isolation environment.

Study on the Anode-to-Cathode Distance in an Aluminum Reduction Cell

A two-dimensional (2D) finite element model (FEM) of an anode immersed in an aluminum reduction cell was developed to study the initial current distribution in the anode as a function of anode geometry and electrical anode conductivity gradients. The numerical results of the initial state of the anode electrical current were used to describe analytically how this will affect the variation in the anode-to-cathode distance (ACD) in a steady-state scenario after several hours in the electrolysis bath. The electrical power loss in the anode has also been studied at different anode geometries and material properties. The slot positioning, slot depths, and stub hole dimensions have been considered in the FEM. The anode is implemented as an inhomogeneous orthotropic material with a defined six-parameter equation. The degree of initial inhomogeneous anode current density, which is expressed with a defined parameter k 0, can reach values to cause variations in the ACD typically measured in the aluminum industry. To avoid a variation in the ACD for this case, the defined bath conductivity relation n should be within certain limits for the analyzed industrial reduction cell. The lowest degree of initial inhomogeneous current in the anode is achieved with deeper slots closer to each other and with an electrical current entering the anode in the bottom of the anode stub hole.

Experimental Determination of Galvanic Anode Current Output for Common Geometries Used in Civil Works Applications

Abstract The current output from various common galvanic (sacrificial) anode geometries used in immersion service was experimentally determined. The results showed a specific functional dependence on exposed surface area and a scalable inverse relationship to the resistivity of the surrounding electrolyte medium. The use of this information as applied to cathodic protection design is also presented using three of the most readily available freshwater sacrificial anode metal alloys.