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 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.

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.

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.

ANODIC OXIDE FILMS ON NIOBIUM: THICKNESS, DIELECTRIC CONSTANT, DISPERSION, REFLECTION MINIMA, FORMATION FIELD STRENGTH, AND SURFACE AREA

1960 ◽  
Vol 38 (7) ◽  
pp. 1141-1147 ◽  
Author(s):  
L. Young
Keyword(s):  
Dielectric Constant ◽  
Refractive Index ◽  
Field Strength ◽  
Surface Area ◽  
Current Density ◽  
Ionic Current ◽  
Anodic Oxide ◽  
Dielectric Constants ◽  
A Value ◽  
Spectrophotometric Data

The wavelengths of minimum specular reflectivity (at 11° incidence) due to interference were determined using a spectrophotometer for a series of films formed on chemically polished niobium. With a value of the refractive index n = 2.46 ± 1% at 4358 Å wavelength by the Abelès method (reported elsewhere), the spectrophotometric data give the refractive index as a function of the wavelength λ, n = 2.26 + 0.398/(λ/103 Å − 2.56)1.2. To analyze the spectrophotometric results, an auxiliary measure of thickness was required (though, with the chart given below, the thickness of a film may be determined directly from spectrophotometric measurements alone). A combination of measurements of the a-c. capacity and of the charge required to form the films gives a suitable measure of thickness (in terms of ρ/ε, where ε = dielectric constant and ρ = density) which is not dependent on a knowledge of the true surface area. The spectrophotometric data provide a calibration of this measure of thickness and thus give ε/ρ. With ρ = 4.36 g cm−3 (reported for the bulk amorphous oxide) this gives ε about 41 (compared with about 27.6 for Ta2O5). The effective surface area of the chemically polished metal was then found to be about 7% greater than the apparent area. At the ionic current density used to form the films (10 ma cm−2), the field strength in the oxide was estimated as 4.96 × 106 v cm−1 within a few per cent uncertainty. Because the field to produce a given ionic current is lower than with Ta2O5 films, the capacity of films formed to a given voltage at a given current density and temperature is not so much greater for niobium than for tantalum as the dielectric constants might lead one to expect. It is suggested that there may be a correlation between dielectric constant and ionic conductivity. The Nb2O5 films recrystallize like Ta2O5 films under an applied field but more readily, at least with the purity of metal now available.

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.

The morphology and mechanism of formation of porous anodic films on aluminium

1970 ◽  
Vol 317 (1531) ◽  
pp. 511-543 ◽  
Keyword(s):  
Steady State ◽  
Layer Thickness ◽  
Current Density ◽  
Barrier Layer ◽  
Anodic Oxide ◽  
Constant Current ◽  
Cell Diameter ◽  
Anodic Films ◽  
Constant Current Density ◽  
Barrier Layer Thickness

The morphology of porous anodic oxide films formed on aluminium in phosphoric acid electrolytes at constant current density or voltage, and under changing electrical or electrolytic conditions, has been studied quantitatively by electron microscopy. Replicas from film sections and from both film interfaces have been prepared, as well as transmission micrographs of thin films, produced under accurately defined conditions. During formation at constant current density, pore initiation occurs by the merging of locally thickening oxide regions, which seem related to the substructure of the substrate, and the consequent concentration of current into the residual thin areas. The pores grow in diameter and change in number until the steady-state morphology is established. The film barrier layer thickness has been measured directly for the first time. The steady-state barrier-layer thickness, cell diameter and pore diameter are all observed to be directly proportional to the formation voltage. It becomes evident that the barrier-layer thickness, decided largely by an equilibrium established between oxide formation in the barrier-layer and field-assisted dissolution (probably thermally enhanced) at the pore bases, determines the cell and pore sizes by a simple geometrical mechanism. Anion incorporation into the film and its hydrogen-bonded structure play secondary roles to these factors in determining the actual film morphology, although not its subsequent properties. A consequence of the mechanism is that, at constant current density, relatively non-aggressive electrolytes give thicker barrier layers, larger cells and larger pores next to the barrier layer than aggressive media, although subsequent pore widening at the outer surface of the film by simple chemical dissolution is more severe in aggressive electrolytes.

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.

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