Anode Area Research Articles

Intense emission from a grid-stabilized plasma cathode

Intense emission from a grid-stabilized plasma cathode based on a glow discharge with an expanded anode area is studied. In the electrode system of the ion source, the potential difference between a large-mesh grid electrode (a hole diameter of 4–6 mm) and cathode and anode plasma reaches 200 V and the glow discharge current is up to 1 A. The current distribution over the electrodes of the plasma cathode is taken, and the dependences of the electron extraction efficiency and electron-emitting-plasma potential on the gas pressure and discharge parameters are obtained. A relationship between the geometric parameters of the grid, cathode plasma potential, and efficiency of electron extraction from the plasma is derived. It is shown that stable intense emission from the plasma cathode can be provided in wide ranges of gas pressure and discharge current by varying the geometry and mesh size of the plasma cathode grid. Discharge contraction in the grid plane at elevated gas pressures is explained. It is assumed that the emitting plasma becomes inhomogeneous due to variation in the thickness of near-electrode layers in the holes of the grid, which makes the distribution of the emission current from the plasma more nonuniform.

Theoretical investigation of sheath expansion and implant fluence uniformity in enhanced glow discharge plasma immersion ion implantation

In enhanced glow discharge plasma immersion ion implantation that involves a small-pointed anode and large area tabular cathode, the high negative substrate bias acts as the plasma producer and supplies the implantation voltage. An electric field is created to focus the electrons and the electron-focusing field in turn enhances the glow discharge process. The sheath physics is theoretically investigated using numerical simulation based on the multiple-grid particle-in-cell code. Electron focusing is corroborated and the plasma sheath has enough expansion when t=40μs so that a uniform distribution of the incident ion fluence is attained.

Crevice Corrosion of Grade-12 Titanium

Abstract The crevice corrosion of ASTM grade-12 titanium (Ti-12; 0.8 wt % Ni, 0.3 wt % Mo) has been studied in neutral 0.27 mol/L NaCl at temperatures up to 120°C using a galvanic coupling technique. The results were compared to those of similar experiments conducted on ASTM grade-2 titanium (Ti-2) specimens containing various amounts of iron impurity. The microstructural properties of the Ti-12 were determined by standard metallographic techniques and transmission electron microscopy. Penetration depth profiles were determined using metallographic and image analysis techniques. The redistribution of alloying elements (Ni, Mo) and impurities (Fe), and the location of absorbed hydrogen, were determined by secondary ion mass spectrometry (SIMS) imaging. The rate and extent of crevice propagation were significantly suppressed on Ti-12 compared to Ti-2, especially at higher temperature (120°C). Up to 97 % of the total amount of crevice propagation was driven by proton reduction inside the creviced area rather than by oxygen reduction outside the crevice. SIMS imaging shows that Ni accumulates on the corroding surface, probably in the form of residual Ti2Ni particles. Proton reduction is catalyzed on these particles, leading to their hydriding and an increase in the relative area of internal cathodes compared to available anodic surface area. This self-induced “cathodic modification” effect leads to repassivation of the corroded site before extensive damage can be sustained.

Anodic Aluminum Oxide Surface Area

not Available.

Responses from freshwater sediment during electricity generation using microbial fuel cells

In a two-electrode system, freshwater sediment was used as a fuel to examine the relationship between current generation and organic matter consumption with different types of electrode. Sediment microbial fuel cells using porous electrodes showed a superior performance in terms of generating current when compared with the use of non-porous electrodes. The maximum current densities with thicker and thin porous electrodes were 45.4 and 37.6 mA m(-2), respectively, whereas the value with non-porous electrodes was 13.9 mA m(-2). The amount of organic matter removed correlated with the current produced. The redox potential in the anode area under closed-circuit conditions was +246.3 +/- 67.7 mV, while that under open-circuit conditions only reached -143.0 +/- 7.18 mV. This suggests that an application of this system in organic-rich sediment could provide environmental benefits such as decreasing organic matter and prohibiting methane emission in conjunction with electricity production via an anaerobic oxidation process.

Experimental investigation of discharge characteristics in enhanced glow discharge plasma immersion ion implantation

In enhanced glow discharge plasma immersion ion implantation (EGD-PIII) that involves a small pointed anode and large area tabular cathode, the high negative substrate bias not only acts as the plasma producer but also supplies the implantation voltage. Consequently, an electric field is created to focus the electrons and the electron focusing field in turn enhances the glow discharge process. In this work, the discharge characteristics of EGD-PIII are investigated experimentally. The discharge initiation and extinction characteristics during pulsed biasing are discussed. The duration of the post pulse-off plasma is explained from the viewpoint of particle motion and experimentally verified by employing an auxiliary disk. Our experiments show that a dual-pulse method may be utilized to determine the remnant plasma.

Investigation of plasma distribution in electron-focused electric field enhanced glow discharge plasma immersion ion implantation

In enhanced glow discharge plasma immersion ion implantation (EGDPIII) that involves a small pointed anode and large area tabular cathode, the high negative substrate bias not only acts as the plasma producer but also supplies the implantation voltage. Consequently, an electric field is created to focus the electrons and the electron-focusing field enhances the glow discharge process. In this work, the plasma distribution is measured using a Langmuir probe to obtain the plasma density. Numerical interpolation is performed to obtain the plasma density distribution throughout the entire discharge region. The effects of different distances between the anode and cathode on the glow discharge characteristics and the influence of the plasma electron density are also evaluated. Our results experimentally verify the electron-focusing phenomenon and suggest optimal processing windows for enhanced ionization rates and efficiency in EGDPIII.

Galvanic currents and corrosion rates of reinforcements measured in cells simulating different pitting areas caused by chloride attack in sodium hydroxide

Chlorides induce localized corrosion in the reinforcement. The pits formed a substantial reduction in the cross-sectional area. The smaller is the ratio between the size of the corrosion spot and the surrounding passive metal area acting as cathode, the higher is the corrosion rate or the progression in the pit depth. This, however, is not always the case. To understand well the macro or microcell behavior of the corrosion of reinforcements, this paper reports a study on the effect of decreasing sizes of anodic zones until relatively small, maintaining the size of the cathode constant. In addition, to enhance the pure anodic behavior of the corroding zone, an acidic solution was used as an anolyte. Measuring the galvanic current ( I g ) and the corrosion rate ( I corr ) by using zero resistance ammeter (ZRA) and polarization resistance ( R p ) techniques, respectively, was crucial to differentiate the microcell contribution from that of the macrocell. The results indicate that while I g increased as the anodic area decreased, I corr presented a maximum for the area ratios, S A / S C = 1/3.

Effects of unipolar stimulation on voltage and calcium distributions in the isolated rabbit heart

The effect of electric stimulation on the polarization of cardiac tissue (virtual electrode effect) is well known; the corresponding response of intracellular calcium concentration ([Ca(2+)](i)) and its dependence on coupling interval between conditioning stimulus (S1) and test stimulus (S2) has yet to be elucidated. Because uncovering the transmembrane potential (V(m))-[Ca(2+)](i) relationship during an electric shock is imperative for understanding arrhythmia induction and defibrillation, we aimed to study simultaneous V(m) and [Ca(2+)](i) responses to strong unipolar stimulation. We used a dual-camera optical system to image concurrently V (m) and [Ca(2+)](i) responses to unipolar stimulation (20 ms +/- 20 mA) in Langendorff-perfused rabbit hearts. RH-237 and Rhod-2 fluorescent dyes were used to measure V(m) and [Ca(2+)](i), respectively. The S1-S2 interval ranged from 10 to 170 ms to examine stimulation during the action potential. The [Ca(2+)](i) deflections were less pronounced than changes in V(m) for all S1-S2 intervals. For cathodal stimulation, [Ca(2+)](i) at the central virtual cathode region increased with prolongation of S1-S2 interval. For anodal stimulation, [Ca(2+)](i) at the central virtual anode area decreased with shortening of the S1-S2 interval. At very short S1-S2 intervals (10-20 ms), when S2 polarization was superimposed on the S1 action potential upstroke, the [Ca(2+)](i) distribution did not follow V(m) and produced a more complex pattern. After S2 termination [Ca(2+)](i) exhibited three outcomes in a manner similar to V(m): non-propagating response, break stimulation, and make stimulation. Changes in the [Ca(2+)](i) distribution correlate with the behavior of the V (m) distribution for S1-S2 coupling intervals longer than 20 ms; at shorter intervals S2 creates more heterogeneous [Ca(2+)](i) distribution in comparison with V(m). Stimulation in diastole and at very short coupling intervals caused V(m)-[Ca(2+)](i) uncoupling at the regions of positive polarization (virtual cathode).

Study of electroplated silver–palladium biofouling inhibiting coating

Biofouling can cause many undesirable effects in industrial and medical settings. In this study, a new biofouling inhibiting Ag–Pd surface was designed to form an inhibiting effect by itself. This design was based on silver combined with nobler palladium, both with catalytic properties. Owing to the potential difference between silver and palladium while contacting with an electrolyte, the surface can form numerous discrete anodic and cathodic areas, so that an inhibiting reaction can occur. In this paper, a series of electrochemical and biological investigations were conducted to study the properties and biofouling inhibiting mechanism of these surfaces. In this study, the evidence is presented that the inhibiting effect can be caused by the electrochemical interactions and/or electric field between Pd and Ag/AgCl combined with an organic environment.

Effect of cosintering of anode–electrolyte bilayer on the fabrication of anode-supported solid oxide fuel cells

A comparative study is carried out on the effect of cosintering temperature of anode–electrolyte bilayer on the fabrication and cell performance of anode-supported solid oxide fuel cells from commercially available tape casting materials. It was found that the sintering conditions have profound effects on the anode characteristic and cell performance. For low cosintering temperature as low as 1,250 °C, the electrolyte is unable to sinter fully and forms a porous structure which leads to a reduced open-circuit potential and poor cell performance especially under low current output. For further increasing cosintering temperature to 1,350 °C, the cell performance was lower under low current operation. However, the cell performance turns out to be better than that of high-temperature cosintering under high current output. Although at temperature as high as 1,500 °C the cell performs better than that of low temperature cosintering, the trend turn out to be reverse for high current operating due to less anode surface area resulting from overagglomeration of anode layer. An optimal cosintering temperature of 1,350–1,450 °C is recommended for commercially available anode–electrolyte bilayer of anode-supported solid oxide fuel cells.

A critical crevice solution and IR drop crevice corrosion model

This paper presents a mechanistic model describing the dynamic concentration profiles and corrosion currents within a corroding crevice. The model couples anodic areas within the crevice with cathodic areas on the bold surface. It also incorporates the combined effects of the chemical attack of the crevice solution along with the electric potential changes in the crevice and over the bold surface. The mathematical model is used to predict the dynamic crevice pH profile and remarkable agreement with experimental data is evident. Three crevice corrosion phases were determined that correspond to the evolution of the electric potential drop within the crevice.

Application of EIS and SEM to Study the Corrosion Behaviors of Organic Coatings/Substrate System

Electrochemical corrosion behaviors of two common-used ship coatings——epoxy aluminum coating, chloride rubber iron red coating and their composite coatings immersed in 3.5%NaCl solution were investigated using electrochemical impedance spectroscopy combined with open circuit potential measurements and SEM micrograph analysis. Potential-time result indicates that the free corrosion potential of these three coatings with immersion time are more positive than that of metal substrate, which can serve as barrier layer to protect metal substrate from corrosion. During the course of immersion, increasingly negative shift potentials with time reveal the growth of electrochemical area of anode and corrosion takes place continuously. EIS shows that corrosive species can penetrate into coatings and reach the coating/substrate interface promptly, causing the decrease of its shielding role and the beginning of electrochemical corrosion. SEM micrographs suggest that coatings were compact and continuous compared with obviously coarse and loose after corrosion, indicating the penetration of corrosive species destroys cross linkage of coatings. Composite coatings present better protection performance, displaying the effect of “1+1>2” remarkably.

Effect of Anode Area on the Cell Performance in a Molten Carbonate Fuel Cell

The effect of the geometrical anode area of a molten carbonate fuel cell on the cell performance was investigated with class single cells. A cell with a area anode (cell I) and another cell with a area anode (cell II) were used. The cathode area of the cells was . The cell with anode area was prepared by filling the edge area of the class cell with 100 meshes of Ni, which was wrapped by thick Al foil. Other conditions for the preparation of the cells were identical. Cell performance was analyzed with steady-state polarization, inert gas step addition, and reactant gas addition methods. The analyses revealed that cell II showed an larger anodic overpotential than cell I. This implies that the anode performance is less dependent on its geometrical area. Cathodic overpotential was also larger for cell II than for cell I, likely due to higher electrolyte contents at the cathode in cell II.

Initial NaCl-particle induced atmospheric corrosion of zinc—Effect of CO 2 and SO 2

Initial corrosion and secondary spreading effects during NaCl particle induced corrosion on zinc was explored using in situ and ex situ FTIR microspectroscopy, optical microscopy, and SEM/EDAX. The secondary spreading effect which occurs upon introduction of humid air on NaCl deposited zinc surfaces was strongly dependent on the CO 2 and SO 2 content of the introduced air. Ambient level of CO 2 (350 ppm) resulted in a relatively low spreading effect, whereas the lower level of CO 2 (<5 ppm) caused a much faster spreading over a larger area. In the presence of SO 2, the secondary spreading effect was absent which could limit the cathodic process in this case. At <5 ppm CO 2, the corrosion is more localized, with the formation of simonkolleite (Zn 5(OH) 8Cl 2 · H 2O), zincite (ZnO) and sodium carbonate (Na 2CO 3), and a larger effective cathodic area. At 350 ppm CO 2, the corrosion is more general and formation of simonkolleite, hydrozincite (Zn 5(OH) 6(CO 3) 2) and sodium carbonate was observed. Sodium carbonate was mainly formed in more alkaline areas, in the inner edge of the electrolyte droplet and in the secondary spreading area. Oxidation of sulphur and concomitant sulphate formation was enhanced in the presence of NaCl particles, due to the formation of a droplet, the separation of the anodic and cathodic areas and the accompanying differences in chemical composition and pH in the surface electrolyte.

Electricity generation with simultaneous wastewater treatment by a microbial fuel cell (MFC) with Cu and Cu–Au electrodes

AbstractBackground: A microbial fuel cell (MFC) consisting of anaerobic and aerobic chambers separated by a salt‐agar slab was used for electricity generation with simultaneous wastewater treatment where copper and gold covered copper wires were used as anode and cathode, respectively. The electrons produced from degradation of carbohydrates in anaerobic chamber traveled through the copper wire generating electricity and the protons were transferred from cathode to anode through the salt‐agar slab. Variation of the current intensity (mA) and the electrical power (mW) were investigated as function of the surface area of anode and also the chemical oxygen demand (COD) content of the synthetic wastewater.Results: The generated power density (mW m−2) increased with increasing surface area of the electrodes and also with the COD content of the wastewater. Both the current intensity (mA) and the power generated (mW) increased with time and reached maximum levels at the end of batch operation. More than 80% COD removal was achieved in the aerobic chamber with an electricity generation of 2.9 mW m−2 when the initial COD content was 6000 mg l−1.Conclusion: The MFC configuration and the use of Cu and Cu‐Au electrodes instead of graphite were proven to be effective for electricity generation with simultaneous wastewater treatment. The electrical current (0.24 mA) and power (2.9 mW m−2) obtained in our microbial fuel cell are comparable with the literature studies utilizing salt bridge. The microbial fuel cell developed in this study can be improved further to yield higher power generations by modifications. Copyright © 2007 Society of Chemical Industry

Electricity Production from Cellulose in a Microbial Fuel Cell Using a Defined Binary Culture

Microbial fuel cells (MFCs) convert biodegradable materials into electricity, potentially contributing to an array of renewable energy production strategies tailored for specific applications. Since there are no known microorganisms that can both metabolize cellulose and transfer electrons to solid extracellular substrates, the conversion of cellulosic biomass to electricity requires a syntrophic microbial community that uses an insoluble electron donor (cellulose) and electron acceptor (anode). Electricity was generated from cellulose in an MFC using a defined coculture of the cellulolytic fermenter Clostridium cellulolyticum and the electrochemically active Geobacter sulfurreducens. In fed-batch tests using two-chamber MFCs with ferricyanide as the catholyte, the coculture achieved maximum power densities of 143 mW/ m2 (anode area) and 59.2 mW/m2 from 1 g/L carboxymethyl cellulose (CMC) and MN301 cellulose, respectively. Neither pure culture alone produced electricity from these substrates. The coculture increased CMC degradation from 42% to 64% compared to a pure C. cellulolyticum culture. COD removal using CMC and MN301 was 38 and 27%, respectively, with corresponding Coulombic efficiencies of 47 and 39%. Hydrogen, acetate, and ethanol were the main residual metabolites of the binary culture. Cellulose conversion to electricity was also demonstrated using an uncharacterized mixed culture from activated sludge with an aerobic aqueous cathode.

Effect of Graded Porous Structure on Ni-YSZ Anode Performance

SOFC anode requires long three phase boundaries (TPBs) and appropriate gas diffusion passes for the fast transport of both fuel and exhaust gases, but the area where gas diffusion passes are especially required would be different from the area suitable for electrochemical reaction in the anode. Then gradient porous structures of SOFC anodes have been proposed to fulfill the anodic functions in adequate anodic areas. Ni- YSZ anodes with various gradient pore-distributions were then prepared using pore-formers by screen-printing method. The relationship between maximum power densities and the pore size and porosity distributions was investigated to identify an effective gradient porous structure that can improve anode performance. The gradient porous structure improved anodic polarization. Pore structure contains two factors of pore size and porosity but the gradient in pore size was more effective in improving anode performance.

Effect of Wall Charge on Striation in Plasma Display Cells

Different configurations and driving voltages have been employed toinvestigate the effect of the wall charge on the striations inmacroscopic plasma display panel (PDP) cells. The experimentalresults show that a discharge channel near the dielectric layer isindispensable to striation occurring in the anode area during adischarge, while the pre-accumulated charge on the dielectric layerand the surface state are not important. The origin of the striationis related only to the physical process in the cell. The dielectriclayer acts as a charge collector during a PDP discharge.

Effect of Anode Area on the Cell Performance in a Molten Carbonate Fuel Cell

not Available.