scholarly journals Effect of Current Density on the Anodic Behavior of Zircaloy - 2 and Titanium-A Comparative Study

2009 ◽  
Vol 6 (s1) ◽  
pp. S12-S16
Author(s):  
N. N. S. Aparna ◽  
Ch. Anjaneyulu
Keyword(s):  
Current Density ◽  
Formation Rate ◽  
Ionic Current ◽  
Anodic Films ◽  
Differential Field ◽  
Oxide Film Thickness ◽  
Increase With Increase ◽  
Jump Distance ◽  
Current Densities ◽  
Kinetics Of

The kinetics of anodic oxidation of zircaloy-2 and titanium have been studied at current densities ranging from 2 to 12 mAcm-2at room temperature in order to investigate the dependence of ionic current density on the field across the oxide film. Thickness of the anodic films were estimated from capacitance data. The formation rate, current efficiency and differential field were found to increase with increase in the ionic current density for both zircaloy-2 and Titanium. Plots of the logarithm of formation ratevslogarithm of the current density are fairly linear. From linear plots of logarithm of ionic current densityvsdifferential field and applying the Cabrera-Mott theory, the half-jump distance and the height of the energy barrier are deduced and compared.

scholarly journals Growth Kinetics of Anodic Oxide Films Formed on Zircaloy-2 in Various Electrolytes

2009 ◽  
Vol 6 (3) ◽  
pp. 880-886
Author(s):  
V. Jeevana Jyothi ◽  
CH. Anjaneyulu
Keyword(s):  
Current Density ◽  
Formation Rate ◽  
Ionic Current ◽  
Anodic Oxide ◽  
Anodic Films ◽  
Differential Field ◽  
Increase With Increase ◽  
Jump Distance ◽  
Current Densities ◽  
Kinetics Of

The Kinetics of anodic oxidation of zircaloy-2 have been studied at current densities ranging from 4 to 12 mA cm-2at room temperature in order to investigate the dependence of ionic current density on the field across the oxide film. Thickness of the anodic films was estimated from capacitance data. The formation rate, current efficiency and differential field were found to increase with increase in the ionic current density for zircaloy-2. Plots of logarithm of formation ratevs. logarithm of current density is fairly linear. From linear plots of logarithm of ionic current densityvs. differential field and applying the Cabrera - Mott theory, the half - jump distance (a) and height of energy barrier (W) were deduced.

scholarly journals Na channel distribution in vertebrate skeletal muscle.

1986 ◽  
Vol 87 (6) ◽  
pp. 907-932 ◽  
Author(s):  
J H Caldwell ◽  
D T Campbell ◽  
K G Beam
Keyword(s):  
Skeletal Muscle ◽  
Current Density ◽  
Sharp Decrease ◽  
Na Channel ◽  
Na Current ◽  
Na Currents ◽  
Current Densities ◽  
Kinetics Of ◽  
A Current ◽  
Vertebrate Skeletal Muscle

The loose patch voltage clamp has been used to map Na current density along the length of snake and rat skeletal muscle fibers. Na currents have been recorded from (a) endplate membrane exposed by removal of the nerve terminal, (b) membrane near the endplate, (c) extrajunctional membrane far from both the endplate and the tendon, and (d) membrane near the tendon. Na current densities recorded directly on the endplate were extremely high, exceeding 400 mA/cm2 in some patches. The membrane adjacent to the endplate has a current density about fivefold lower than that of the endplate, but about fivefold higher than the membrane 100-200 micron from the endplate. Small local variations in Na current density are recorded in extrajunctional membrane. A sharp decrease in Na current density occurs over the last few hundred micrometers from the tendon. We tested the ability of tetrodotoxin to block Na current in regions close to and far from the endplate and found no evidence for toxin-resistant channels in either region. There was also no obvious difference in the kinetics of Na current in the two regions. On the basis of the Na current densities measured with the loose patch clamp, we conclude that Na channels are abundant in the endplate and near-endplate membrane and are sparse close to the tendon. The current density at the endplate is two to three orders of magnitude higher than at the tendon.

scholarly journals Temperature dependence of the kinetics of oxygen reduction on carbon-supported pt nanoparticles

2008 ◽  
Vol 73 (6) ◽  
pp. 641-654 ◽  
Author(s):  
Nevenka Elezovic ◽  
Biljana Babic ◽  
Nedeljko Krstajic ◽  
Snezana Gojkovic ◽  
Ljiljana Vracar
Keyword(s):  
Temperature Dependence ◽  
Oxygen Reduction ◽  
Current Density ◽  
Pt Nanoparticles ◽  
Reduction Reaction ◽  
Hydrogen Electrode ◽  
Rate Determining Step ◽  
Current Densities ◽  
Kinetics Of ◽  
Mechanism Of The Reaction

The temperature dependence of oxygen reduction reaction (ORR) was studied on highly dispersed Pt nanoparticles supported on a carbon cryo-gel. The specific surface area of the support was 517 m2 g-1, the Pt particles diameter was about 2.7 nm and the loading of the catalyst was 20 wt.%. The kinetics of the ORR at the Pt/C electrode was examined in 0.50 mol dm-3 HClO4 solution in the temperature range from 274 to 318 K. At all temperatures, two distinct E-log j regions were observed; at low current densities with a slope of -2.3RT/F and at high current densities with a slope of -2.3?2RT/F. In order to confirm the mechanism of oxygen reduction previously suggested at a polycrystalline Pt and a Pt/Ebonex nanostructured electrode, the apparent enthalpies of activation at selected potentials vs. the reversible hydrogen electrode were calculated in both current density regions. Although ?H ?a,1 > ?H ?a,h , it was a,1 a, h found that the enthalpies of activation at the zero Galvani potential difference were the same and hence it could be concluded that the rate-determining step of the ORR was the same in both current density regions. The synthesized Pt/C catalyst showed a small enhancement in the catalytic activity for ORR in comparison to the polycrystalline Pt, but no change in the mechanism of the reaction.

MODELING EXCITATION AND PROPAGATION OF ACTION POTENTIALS ACROSS INHOMOGENEOUS VENTRICULAR TISSUE

2003 ◽  
Vol 13 (12) ◽  
pp. 3845-3863 ◽  
Author(s):  
Z. LI ◽  
A. V. HOLDEN ◽  
C. H. ORCHARD ◽  
H. ZHANG
Keyword(s):  
Action Potentials ◽  
Computational Models ◽  
Ionic Current ◽  
Cell Models ◽  
Intercellular Coupling ◽  
Ventricular Tissue ◽  
Current Densities ◽  
Myocardial Membrane ◽  
Transmural Heterogeneity ◽  
Kinetics Of

Heterogeneity in the electrical activity across the ventricular wall might result from transmural differences in myocardial membrane ionic current densities. Computational models of endo- and epi-cardial action potentials of guinea-pig myocytes were developed, assuming transmural differences in the ionic current densities and kinetics of i Kr and i Ks . The cell models were able to reproduce the characteristics of action potentials of endo and epi cells. One- and two-dimensional models of ventricular tissue were also developed to study the effects of transmural heterogeneity on the propagation of excitation waves across the ventricle wall. It was shown that intercellular coupling reduces the transmural heterogeneity across the ventricle wall.

Steady-state kinetics of formation of anodic oxide films on tantalum in sulphuric acid

1960 ◽  
Vol 258 (1295) ◽  
pp. 496-515 ◽  
Keyword(s):  
Steady State ◽  
Current Density ◽  
Ionic Current ◽  
Anodic Oxide ◽  
Fundamental Change ◽  
Steady State Kinetics ◽  
Kinetics Of Formation ◽  
Ionic Movement ◽  
Kinetics Of ◽  
Elementary Theories

On elementary theories, the ionic current i through the oxide is expected in the steady state to depend on the field strength E in the oxide (as measured by oxide overpotential/thickness of oxide) and the temperature T according to an equation of the form i = i 0 exp { – ( W – qaE )/ kT }, where i 0 , W and a are constants which have different significance according to the model, q is the charge on the ion, and k is Boltzmann’s constant. The relation has been investigated experimentally by a spectrophotometric method of determining the thickness of the oxide. It was found that the experimental results for dilute solutions could be represented within less than 1 % of E at 2490 Ả thickness by the above equation with qaE replaced by q (α + β E ) E where α and β are constants with i 0 = 10 8.24 A/cm 2 , W = 2.185 eV, α = 6.995Ả,β = – 3.35Ả/(10 7 V/cm) and q = 5 e . The modifications that occur as the concentration of acid is increased have been investigated. In concentrated acid, although less charge is required to form a film of given optical thickness, the films have a lower a.c. capacity, and require a higher overpotential to produce a given ionic current density. The capacity of films formed to a given overpotential at a given current density is almost independent of the concentration of the acid. The significance of the results is discussed in connexion with how far the existence of a range of site parameters (in particular, activation energy and activation distance) in an amorphous oxide tends to explain them, or whether a more fundamental change in the equations used to describe ionic movement is required.

Facet Topography and Dislocation Structure as a Possible Source for Electrical Heterogeneity in [001] TILT Bicrystals of YBa2Cu3O7-δ

1996 ◽  
Vol 54 ◽  
pp. 338-339
Author(s):  
I-Fei Tsu ◽  
D.L. Kaiser ◽  
S.E. Babcock
Keyword(s):  
Grain Boundary ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Electromagnetic Properties ◽  
Length Scale ◽  
Density Values ◽  
Current Densities ◽  
Applied Fields ◽  
A Current

A current theme in the study of the critical current density behavior of YBa2Cu3O7-δ (YBCO) grain boundaries is that their electromagnetic properties are heterogeneous on various length scales ranging from 10s of microns to ˜ 1 Å. Recently, combined electromagnetic and TEM studies on four flux-grown bicrystals have demonstrated a direct correlation between the length scale of the boundaries’ saw-tooth facet configurations and the apparent length scale of the electrical heterogeneity. In that work, enhanced critical current densities are observed at applied fields where the facet period is commensurate with the spacing of the Abrikosov flux vortices which must be pinned if higher critical current density values are recorded. To understand the microstructural origin of the flux pinning, the grain boundary topography and grain boundary dislocation (GBD) network structure of [001] tilt YBCO bicrystals were studied by TEM and HRTEM.

Electron-beam damage of oxides at high current densities

1989 ◽  
Vol 47 ◽  
pp. 634-635
Author(s):  
M. R. McCartney ◽  
J. K. Weiss ◽  
David J. Smith
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Current Density ◽  
Transition Metal Oxides ◽  
Time Resolved ◽  
Rapid Acquisition ◽  
Resolution Electron ◽  
Current Densities ◽  
Electron Stimulated Desorption ◽  
Channel Analyzer

It is well-known that electron-beam irradiation within the electron microscope can induce a variety of surface reactions. In the particular case of maximally-valent transition-metal oxides (TMO), which are susceptible to electron-stimulated desorption (ESD) of oxygen, it is apparent that the final reduced product depends, amongst other things, upon the ionicity of the original oxide, the energy and current density of the incident electrons, and the residual microscope vacuum. For example, when TMO are irradiated in a high-resolution electron microscope (HREM) at current densities of 5-50 A/cm2, epitaxial layers of the monoxide phase are found. In contrast, when these oxides are exposed to the extreme current density probe of an EM equipped with a field emission gun (FEG), the irradiated area has been reported to develop either holes or regions almost completely depleted of oxygen. ’ In this paper, we describe the responses of three TMO (WO3, V2O5 and TiO2) when irradiated by the focussed probe of a Philips 400ST FEG TEM, also equipped with a Gatan 666 Parallel Electron Energy Loss Spectrometer (P-EELS). The multi-channel analyzer of the spectrometer was modified to take advantage of the extremely rapid acquisition capabilities of the P-EELS to obtain time-resolved spectra of the oxides during the irradiation period. After irradiation, the specimens were immediately removed to a JEM-4000EX HREM for imaging of the damaged regions.

Comparative investigation on the removal of methyl orange from aqueous solution using three different advanced oxidation processes

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Zahia Benredjem ◽  
Karima Barbari ◽  
Imene Chaabna ◽  
Samia Saaidia ◽  
Abdelhak Djemel ◽  
...  
Keyword(s):  
Methyl Orange ◽  
Current Density ◽  
Advanced Oxidation Processes ◽  
Degradation Rate ◽  
Supporting Electrolyte ◽  
Advanced Oxidation ◽  
Comparative Investigation ◽  
Oxidation Processes ◽  
The Comparative Study ◽  
Kinetics Of

Abstract The Advanced Oxidation Processes (AOPs) are promising environmentally friendly technologies for the treatment of wastewater containing organic pollutants in general and particularly dyes. The aim of this work is to determine which of the AOP processes based on the Fenton reaction is more effective in degrading the methyl orange (MO) dye. The comparative study of the Fenton, photo-Fenton (PF) and electro-Fenton (EF) processes has shown that electro-Fenton is the most efficient method for oxidizing Methyl Orange. The evolution of organic matter degradation was followed by absorbance (discoloration) and COD (mineralization) measurements. The kinetics of the MO degradation by the electro-Fenton process is very rapid and the OM degradation rate reached 90.87% after 5 min. The influence of some parameters such as the concentration of the catalyst (Fe (II)), the concentration of MO, the current density, the nature and the concentration of supporting electrolyte was investigated. The results showed that the degradation rate increases with the increase in the applied current density and the concentration of the supporting electrolyte. The study of the concentration effect on the rate degradation revealed optimal values for the concentrations 2.10−5 M and 75 mg L−1 of Fe (II) and MO respectively.

scholarly journals Effect of Plating Current Density on the Ball-On-Disc Wear of Sn-Plated Ni Coatings on Cu Foils

Coatings ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 56
Author(s):  
Ashutosh Sharma ◽  
Byungmin Ahn
Keyword(s):  
Current Density ◽  
Wear Loss ◽  
Wear Properties ◽  
Friction Behavior ◽  
Track Geometry ◽  
Cu Substrates ◽  
Current Densities ◽  
The Impact ◽  
Sliding Distance ◽  
Ball On Disc

Metallic and alloyed coatings are used widely in several decorative and technology-based applications. In this work, we selected Sn coatings plated on Cu substrates for joining applications. We employed two different plating baths for the fabrication of Sn and Ni coatings: acidic stannous sulfate for Sn and Watts bath for Ni layer. The plating current densities were varied from 100–500 mA/cm2. Further, the wear and friction behavior of the coatings were studied using a ball-on-disc apparatus under dry sliding conditions. The impact of current density was studied on the morphology, wear, and coefficient of friction (COF) of the resultant coatings. The wear experiments were done at various loads from 2–10 N. The sliding distance was fixed to 7 m. The wear loss was quantified in terms of the volume of the track geometry (width and depth of the tracks). The results indicate that current density has an important role in tailoring the composition and morphology of coatings, which affects the wear properties. At higher loads (8–10 N), Sn coatings on Ni/Cu had higher volume loss with a stable COF due to a mixed adhesive and oxidative type of wear mechanism.

scholarly journals Fundamental Mechanisms of Copper CMP – Passivation Kinetics of Copper in CMP Slurry Constituents

2009 ◽  
Vol 1157 ◽  
Author(s):  
Shantanu Tripathi ◽  
Fiona M. Doyle ◽  
David A. Dornfeld
Keyword(s):  
Electrochemical Impedance ◽  
Protective Film ◽  
Current Decay ◽  
Glycine Solution ◽  
Current Densities ◽  
Circuit Elements ◽  
Copper Cmp ◽  
Cu Cmp ◽  
Kinetics Of ◽  
Capacitive Charging

AbstractDuring copper CMP, abrasives and asperities interact with the copper at the nano-scale, partially removing protective films. The local Cu oxidation rate increases, then decays with time as the protective film reforms. In order to estimate the copper removal rate and other Cu-CMP output parameters with a mechanistic model, the passivation kinetics of Cu, i.e. the decay of the oxidation current with time after an abrasive/copper interaction, are needed. For the first time in studying Cu-CMP, microelectrodes were used to reduce interference from capacitive charging, IR drops and low diffusion limited currents, problems typical with traditional macroelectrodes. Electrochemical impedance spectroscopy (EIS) was used to obtain the equivalent circuit elements associated with different electrochemical phenomena (capacitive, kinetics, diffusion etc.) at different polarization potentials. These circuit elements were used to interpret potential-step chronoamperometry results in inhibiting and passivating solutions, notably to distinguish between capacitive charging and Faradaic currents.Chronoamperometry of Cu in acidic aqueous glycine solution containing the corrosion inhibitor benzotriazole (BTA) displayed a very consistent current decay behavior at all potentials, indicating that the rate of current decay was controlled by diffusion of BTA to the surface. In basic aqueous glycine solution, Cu (which undergoes passivation by a mechanism similar to that operating in weakly acidic hydrogen peroxide slurries) displayed similar chronoamperometric behavior for the first second or so at all anodic potentials. Thereafter, the current densities at active potentials settled to values around those expected from polarization curves, whereas the current densities at passive potentials continued to decline. Oxidized Cu species typically formed at ‘active’ potentials were found to cause significant current decay at active potentials and at passive potentials before more protective passive films form. This was established from galvanostatic experiments.

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