Electrode Current Density Research Articles

Factors Influencing Quadriceps Femoris Muscle Torque Using Transcutaneous Neuromuscular Electrical Stimulation

Quadriceps femoris muscle torque was measured in 40 subjects during transcutaneous neuromuscular electrical stimulation (NMES). Three different electrode types (carbonized rubber, sponge, and adhesive) were used on each subject, permitting determination of the factors that influenced the magnitude of quadriceps femoris muscle torque induced by NMES. This goal was accomplished by entering the various factors into a multiple-regression model. The electrodes differed significantly in their characteristics. The carbonized-rubber electrode delivered the greatest current with the lowest impedance, resulting in the highest knee extension torque. We found that the most important factor in determining torque generation level was the quadriceps femoris muscle's intrinsic ability to be activated (as opposed to electrode size, current, current density, or skin impedance). These data suggest that NMES efficacy is primarily determined by the intrinsic tissue properties of the individual (defined in this study as "efficiency") and is not dramatically changeable by using high stimulation currents or large electrode sizes. The precise physiological basis for interindividual differences in efficiency is not known.

Electroflotation of quartz fines

Flotation of quartz fines of various size ranges has been carried out using electrolytically generated hydrogen and oxygen gas bubbles. The effect of change in diameters of hydrogen and oxygen gas bubbles on the recovery of quartz fines has been studied. A change in the electrode surface geometry and current density changes the bubble diameters as well as bubble flux thereby affecting flotation recoveries.

A Method for Measuring the Effective Conductivity of the Liquid Phase in Porous Electrodes

A technique is presented for obtaining the effective conductivity of the liquid phase in a porous electrode from the polarization response of the electrode, in the presence of a dissolved redox couple whose electrode reaction rate is controlled by convective mass transfer. An analytical solution of the polarization response shows that, for small values of the polarization parameter , a potential range exists where the square of electrode current density is linear in applied potential, with a slope that is proportional to the effective conductivity. Limits of applicability of the analytical solution and other experimental considerations are discussed.

Analysis of Convective Mass Transfer by Potential Relaxation: I . Steady‐State Copper Deposition with Laminar Natural Convection Stirring

A noncontact experimental method for determining mass‐transfer boundary layer thicknesses in electrochemical systems has been examined. The technique is based on the premise that the relaxation in concentration overpotential after current interruption is an accurate measure of liquid‐phase mass‐transfer resistance. Experimental overpotential decay data were fitted to a theoretical surface concentration decay model. Boundary layer thicknesses were determined by matching the real time scale of the experimental data and the dimensionless time scale of the theoretical analysis. Overpotential relaxation experiments were performed at a vertical flat plate copper cathode with natural convection stirring. The effects of electrode height, current density, and electrolyte composition on mass‐transfer boundary layer thicknesses were examined and correlated. The results agree well with existing Sherwood‐Schmidt‐Grashof number correlations.

Aluminum cladding of high T c superconductor by thermocompression bonding

Thermocompression bonding of aluminum to YBa2Cu3O7−x (YBCO) has been demonstrated. The superconductor is protected by a thin barrier layer of silver. The specific resistivity of the Al/Ag/YBCO interface was measured at 77 K as a function of current density and is below 3.2×10−5 Ω cm2 for electrode current densities of at least 400 A cm−2 . This technique provides a convenient means of cladding bulk superconducting ceramics with a strong, inexpensive, and highly conductive metal.

Electrochemistry of anodic F2 evolution at carbon electrodes: Bubble adherence effects in the kinetics at rotating cone electrodes

Fluorine-evolving carbon anodes exhibit unusually high overvoltages characterized also by remarkably large Tafel slopes having values 0.4–0.8 V per decade of current density change. Also, at high current densities, a so-called ‘anode effect’ associated with a type of passivation sets in. Experiments are described which aim to distinguish high polarization arising from an intrinsically large Tafel slope, generated by a non-ohmic charge transfer barrier layer effect due to ‘CF’ film formation, from effects due to difficulties of F2 bubble detechment and F2 gas film formation at the ‘CF’ film. Steady state polarization measurements have been made at a rotating carbon cone electrode from which F2 bubbles, which otherwise remain attached to the electrode and block access to the electrolyte, can be spun away. At the rotated electrode, at low and intermediate current densities, linear Tafel behaviour is still observed but with high slopes associated with the barrier layer film effect. At higher current densities an ‘anode effect’, associated with the F2 gas film, is developed, leading to a type of passivation of the electrode. The two sources of unusually high polarization in the F2 evolution reaction at carbon are not independent as it is also the formation of the ‘CF’ film that causes difficulties in gas bubble detachment owing to the lyophobic properties of the fluorinated C/F2/KF·2HF interface. Polishing effects confirm this conclusion.

Electrode breakdown potentials in MHD plasmas

Electrode breakdown potentials and current densities have been calculated for both thermionically electron emitting and non-emitting cathodes. Calculated values have been compared with the available experimental results. It is found that the cathode potential drop for the breakdown is almost unaffected by the emission. However, both the total potential difference between the anode and the cathode and the current density at the breakdown are higher for electron-emitting cathodes than for non-emitting cathodes.

Influence of dopant ion and synthesis variables on mechanical properties of polypyrrole films

AbstractOxidized, conductive poly(pyrrolylium anion) films [poly(pyrrolylium) = PP+ where there exists about one cation per three pyrrole rings] have been prepared electrochemically in an effort to study the effect of counteranion structure and preparation conditions on the composition, order (crystallinity), and mechanical properties of the films. The counteranion principally employed was p‐toluene‐sulfonate (OTs−), although benzenesulfonate (BZs−), p‐ethylbenzene‐sulfonate (EBs−), and p‐dodecylbenzenesulfonate (DBs−) were incorporated in several polypyrrole films. It was found that the amount of OTs− incorporated increased with increasing potential during synthesis, suggesting a parallel increase in the extent of oxidation of the polymer. Mechanical testing of the same films demonstrated that the ultimate tensile strength decreased as the electrode potential and current density during synthesis increased. X‐ray diffraction indicated that the degree of order (reflected by the widths of the diffraction lines), albeit quite small, is dependent upon the anion species and synthesis conditions. Interestingly, samples with the highest degree of order exhibit the highest electrical conductivities.

A Study on the Anodic Oxidation of Iodide‐Mediated Sulfur Dioxide Solution

A potentiodynamic method was used to investigate the catalytic effect of potassium iodide on the anodic oxidation of sulfur dioxide solution. The catalytic depolarization effects of potassium iodide are between 0.25 and 0.5V, depending on electrode materials and current densities. The electrocatalytic oxidation behaviors are different at the platinum and graphite electrodes and are affected by the ensuing chemical reactions. At low electrode potential iodide ions are initially oxidized to iodine and this is followed by the chemical reaction of iodine with sulfur dioxide. At high electrode potential the electrochemical oxidation of iodide progresses to iodate and this is followed by the chemical reaction of iodate with sulfur dioxide. The iodide ions regenerated from the chemical reaction near the electrode surface are available again for oxidation without a supply of iodide ion from the bulk solution.

Oxygen Reduction Kinetics on a Platinum RDE Coated with a Recast Nafion Film

Measurements of currents of the oxygen reduction reaction (ORR) at a Pt RDE coated with a recast Nafion film yield the permeability of through such films. Combined with results from linear potential scanning experiments on similar electrodes, these measurements also allow the separate evaluation of the concentration of and its diffusion coefficient in such films. Similar recast Nafion films have been used successfully to promote protonic access to catalyst sites in fuel cells. Accordingly, the maximum film thickness which would allow adequate oxygen flux through such a layer is evaluated. Measurements in 85% at room temperature show that a very significant enrichment of (e.g., by a factor of 20) in a region close to the electrode can be achieved by coating the electrode with a recast Nafion film. This result is expected from the high solubility of in Nafion. However, the measured resulting enhancement of the kinetic ORR currents was found to be only a factor of two. The interpretation suggested for the lack of direct proportionality between average concentration near the electrode and ORR kinetic current density is that enhanced local ORR rates are possible only at a limited number of free Pt sites that are immediately adjacent to a surface region covered by the hydrophobic phase. Contamination by organics of lower molecular weight originating from the Nafion film may contribute to site‐blocking. With increase in temperature the enrichment effect becomes less pronounced, because the solubility of in 85% increases with temperature while in Nafion it decreases.

Method of obtaining gallium from aluminate solution by electrolysis

AbstractGallium is an increasingly important material in the fields of semiconductors and energy transfer. A prime source of gallium is the aluminate solution that remains after the purification of bauxite. The authors have sought a way of reclaiming gallium economically by electrolysis of a laboratory aluminate solution without having to use a cathode of mercury – an environmental pollutant. Cathodes of copper, indium, 70In–30Ga, Wood's alloy, and mercury (for comparison) were used with a wide range of anodes. The study accounted for the effects of electrode material, temperature, current density, and initial gallium concentration on the yield, energy consumption, and utilization of both current and electrode. The best results were obtained with indium or In–Ga cathodes and with platinum, Pt–Ti, or stainless steel anodes, at 75°C and a current density of ~100 Am−2. Electrolysis was more efficient the higher the gallium concentration, demonstrating that commercial–scale electrolysis of aluminate solution ...

Formation and Reduction of Anodic Sulfide Films on Antimony Electrodes

The growth and reduction of anodic films on antimony electrodes in alkaline sulfide solutions has been investigated using potentiodynamic, galvanostatic, and potentiostatic techniques. The sulfidation mechanism and the efficiency of charge storage in the sulfide film are dependent on the electrode potential and current density. The initial stages of film formation follow a high field growth process involving ionic transport through the sulfide film. The growth of thicker films is controlled by coupled electrochemical and chemical reactions involving mass transport and nucleation. Metal dissolution accompanies film formation under most growth conditions. The anodic and cathodic behavior of these films is consistent with their rectification or n‐type semiconductor properties.

Nuclear Waste Glass Melter Design Including the Power and Control Systems

An energy balance of a joule-heated nuclear waste glass melter is used to discuss the problems in the design of the melter geometry and in the specifications of the power and control systems. The relationships between geometry, electrode current density, production rate, load voltage, and load power are presented graphically. The influence of liquid feeding on the surface of the glass and the variability of nuclear waste glass on the design and control during operation is discussed.

Failure modes of Na-beta alumina

Degradation of sodium-beta aluminas can take two forms: Mode I and Mode II. Mode I is the well-documented electro-mechanical propagation of a pre-existing microcrack in the surface of the elevtrolyte. The critical electrode current densities, jcrit, were determined below 100°C using acoustic emission detection during electrolysis. The temperature dependence and magnitudes of j indicate that the applied voltage is an important factor. Mode II, a degradation involving internal sodium formation is briefly reviewed.

Determining the Volume of Sampled Soil When Using the Four‐Electrode Technique

AbstractA theoretical discussion of the ratio between apparent resistivity and real resistivity of a soil layer as a function of (i) layer thickness/electrode spacing ratio; (ii) the soil layer thickness and resistivity of an underlying layer; and (iii) horizontal distance of a different medium from the current electrode is presented. Laboratory experimental work was carried out in order to study the effects the electrode spacing and current density have on the determination of the electrical conductivity of soil solution. It was found out that the depth sensed by a Wenner Configuration would be deeper than the inner electrode spacing for most field situations and especially where there are large variations in conductivity (due to salinity or water content) with depth. The laboratory calibration of the salinity probe should be done in a volume of about 2.5 liters or greater. The volume sensed by this method is greater the lower is the water content. The implications in laboratory calibration‐field measurements relationships are discussed.

Local electrode current density and flaw decoration of sodium-beta″ alumina

Simple decoration methods are described that can qualitatively reveal local electrode current densities and permit decoration of fine, sodium filled cracks in sodium beta″ alumina solid electrolytes.

Investigation of copolymer formation on the electrode surface during electrochemical initiation of the polymerization of monomers

A study has been made of copolymer formation on the electrode surface as a result of electrochemical initiation of polymerization of monomers and equations have been derived for dependences of the electrode potential and current density on the polarization time and monomers concentration under galvanostatic and potential-static conditions. An analysis of theoretical equations leads to conclusions on the type of electrochemical initiation (direct or indirect) and on the copolymerization mechanism (radical or ionic). The theoretical relations obtained were conformed experimentally by a study of the electrochemical initiation of polymerization of styrene and methyl methacrylate mixtures.

The recharging characteristics of miniature sulphur electrodes with unidirectional current flow

Miniature sulphur electrodes have been used to study the rechargeability of sodium-sulphur cells in the two liquid phase region of the operating cycle. With increasing current density electrodes normally exhibit an abrupt transition from full rechargeability to non-rechargeability. The influence of the carbon matrix is also quite pronounced, and it has been found that electrodes capable of recharging at 150 mA cm −2 can be produced by the simple expedient of varying the matrix orientation.

On the Electrode Damage and Current Densities of Carbon Arcs

Arc damage on carbon electrodes has been examined as a function of the charge passing through each arc in the range from 10-6 to 10-1 coloumb. Two forms of arcing damage were observed: that due to the so-called vapor arc, which has a very high current density (~6 × 107 A/cm2) and low erosion rate, and that due to the so-called thermionic arc with a lower current density (~2 × 103 A/cm2) and higher erosion rate. Unlike damage observed on metallic electrodes raised rims were not formed around the carbon craters. The vapor mode damage is compared with two known models of cathode erosion. Differences between the vapor and thermionic modes and the transition between them are discussed. A whitish-gray deposit observed on the arced electrodes appears to be a form of graphite.

Analysis of the seeded combustion gas boundary layer near a cold electrode

The boundary layer of potassium-see ded combustion gas over a cold electrode under the condition of diffusive current mode without arcs is studied theoretically and experimentally. The theoretical analysis features the introduction of charge separation between electrons and ions, electron thermal nonequilibrium, finite ionization rate, and no assumption of thin sheath layer adjoining the electrode surface. To simplify the problem, the case when the current is produced by an applied external electric field without a magnetic field is studied. In this paper, because of the reliability and suitability of the electric boundary condition adopted in the analysis, the boundary layer around the anode is specifically taken up. For the laminar boundary layer, numerical results for the colder electrode and smaller seed fraction show that the region of the electron-ion charge separation extends much wider than the Debye length from the surface and that both electron thermal and ionizational nonequilibria are considerably remarkable near the electrode even in the seeded combustion gas, and the calculated performance of the electrode voltage drop and current density agrees fairly well with experimental results. On the other hand, for the turbulent boundary layer under the condition of practical MHD generator operation, it is shown from numerical calculations that the charge separation region is limited to the extent of several Debye lengths from the surface and that the electron number density is very close to that obtained by Saha equation for the electron temperature.