Structure and Properties of Anodized Films Formed on AZ91D Magnesium Alloy

2011 ◽  
Vol 66-68 ◽  
pp. 1586-1591
Author(s):  
Jian San Li ◽  
Jun Quan Liu
Keyword(s):  
Magnesium Alloy ◽  
Current Density ◽  
Potentiodynamic Polarization ◽  
Solution Structure ◽  
Solution Temperature ◽  
Anodic Current Density ◽  
Polarization Analysis ◽  
Structure And Properties ◽  
Anodic Current ◽  
Az91d Magnesium Alloy

Anodized films on AZ91D magnesium alloy were prepared in sodium hydroxide based solution. Structure and properties of the anodized films were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical potentiodynamic polarization analysis. The results of XRD showed that the films were mainly composed of Mg(OH)2and Al(OH)3. As the solution temperature increasing, the anodized films became thicker and denser, which could cover up the substrate. The films also became thicker and denser with the increase of anodizing time. The grain in the films grew fast when anodic current density increasing and a larger grain size would be found at a higher anodic current density. The results of microscopic analysis exhibited the porous-type anodic oxide, which was similar to the films on aluminum alloy. The results of electrochemical potentiodynamic polarization analysis showed that thermodynamic stability of the alloy had a certain improvement after anodization. The anodized films also exhibited an obvious increase of polarization resistanceRPand an obvious decrease of corrosion current densityic. Discoloration time of drop test on the films lasted for 30 min, which indicated that corrosion resistance of the magnesium alloy was greatly improved by anodization.

scholarly journals Evaluation of the Synergistic Effect of Erosion-Corrosion on AISI 4330 Steel in Saline-Sand Multiphase Flow by Electrochemical and Gravimetric Techniques

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Dario Yesid Peña Ballesteros ◽  
Yelsin Enrique Mendez Camacho ◽  
Lizeth Viviana Barreto Hernandez
Keyword(s):  
Particle Size ◽  
Current Density ◽  
Electrochemical Impedance ◽  
Activation Mechanism ◽  
Anodic Current Density ◽  
Steel Alloy ◽  
Anodic Current ◽  
Steel Electrode ◽  
Potentiodynamic Curves ◽  
Erosion Corrosion

The synergistic effects of fluid flow, sand particles, and solution pH on erosion-corrosion of AISI 4330 steel alloy in saline-sand medium were studied through a rotating cylinder electrode (RCE) system by weight-loss and electrochemical measurements. The worn surface was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that, under all the test conditions assessed, the passivity of the steel alloy could not be maintained; as a result, an activation mechanism dominates the corrosion process of steel alloy. Furthermore, the potentiodynamic curves show that, with the increasing of the electrode flow rate and particle size, the anodic current density increased, which is due to deterioration of the electrode by the impacting slurry. Although the increase of particle size affects the anodic current density, the effect of particle size does not cause a significant change in the polarization behavior of the steel electrode. The electrochemical impedance and potentiodynamic curves suggest that erosion-corrosion phenomenon of the ASISI 4330 steel is under mixed control of mass transport and charge transfer. The inductive loops formed in the impedance plots are representative of an increase in roughness of the electrode caused by the particles impacting at the surface. The change in the passivity of the steel alloy as the pH is altered plays an important role in the corrosion rate.

scholarly journals Effect of Anodic Current Density on Characteristics and Low Temperature IR Emissivity of Ceramic Coating on Aluminium 6061 Alloy Prepared by Microarc Oxidation

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
Mohannad M. S. Al Bosta ◽  
Keng-Jeng Ma ◽  
Hsi-Hsin Chien
Keyword(s):  
Surface Roughness ◽  
Current Density ◽  
Ceramic Coating ◽  
Microarc Oxidation ◽  
Ceramic Coatings ◽  
Anodic Current Density ◽  
Ceramic Surface ◽  
Anodic Current ◽  
Alumina Phase ◽  
Current Densities

High emitter MAO ceramic coatings were fabricated on the Al 6061 alloy, using different bipolar anodic current densities, in an alkali silicate electrolyte. We found that, as the current density increased from 10.94 A/dm2 to 43.75 A/dm2, the layer thickness was increased from 10.9 μm to 18.5 μm, the surface roughness was increased from 0.79 μm to 1.27 μm, the area ratio of volcano-like microstructure was increased from 55.6% to 59.6%, the volcano-like density was decreased from 2620 mm−2 to 1420 mm−2, and the γ-alumina phase was decreased from 66.6 wt.% to 26.2 wt.%, while the α-alumina phase was increased from 3.9 wt.% to 27.6 wt.%. The sillimanite and cristobalite phases were around 20 wt.% and 9 wt.%, respectively, for 10.94 A/dm2 and approximately constant around 40 wt.% and less than 5 wt.%, respectively, for the anodic current densities 14.58, 21.88, and 43.75 A/dm2. The ceramic surface roughness and thickness slightly enhanced the IR emissivity in the semitransparent region (4.0–7.8 μm), while the existing phases contributed together to raise the emissivity in the opaque region (8.6–16.0 μm) to higher but approximately the same emissivities.

Comparative SEM and Cathodoluminescence Microanalysis of Porous GaP Structures

2000 ◽  
Vol 638 ◽  
Author(s):  
M.A. Stevens-Kalceff ◽  
S. Langa ◽  
I.M. Tiginyanu ◽  
J. Carstensen ◽  
M. Christophersen ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Current Density ◽  
Electrochemical Etching ◽  
High Current Density ◽  
Anodic Current Density ◽  
High Current ◽  
Induced Voltage ◽  
Current Line ◽  
Anodic Current ◽  
Porous Layers

AbstractElectron microscopy and cathodoluminescence (CL) microanalysis were used for a comparative study of porous layers fabricated by electrochemical etching of n-GaP substrates in a sulfuric acid solution. Both the CL and morphology of porous layers were found to depend upon the anodic current density. At high current density (100 mA/cm2) anodization leads to the formation of so-called current-line oriented pores and an increase in the CL intensity. We observed self-induced voltage oscillations giving rise to a synchronous modulation of the diameter of pores and CL intensity. When the current density decreased to values as low as 1 mA/cm2 the pores began to grow along <111> crystallographic directions and the CL intensity was observed to be lower than that of bulk GaP.

Origin of Mosaic Structure Obtained During the Production of Porous Silicon with Electrochemical Etching

2019 ◽  
Vol 11 (12) ◽  
pp. 1218-1224
Author(s):  
Dao Tran Cao ◽  
Cao Tuan Anh ◽  
Luong Truc Quynh Ngan
Keyword(s):  
Porous Silicon ◽  
Oxide Layer ◽  
Current Density ◽  
Silicon Oxide ◽  
Electrochemical Etching ◽  
Silicon Layer ◽  
Mosaic Structure ◽  
Anodic Current Density ◽  
Anodic Current ◽  
Silicon Oxide Layer

So far, while producing porous silicon (PSi) with anodic etching of silicon in an aqueous solution of hydrofluoric acid, many researchers (including us) have obtained the crack-into-pieces (or mosaic) structure. Most of the authors believed that the cause of this structure is the collapse and the cracking of the porous, especially highly porous, silicon layer which took place during the drying of PSi after fabrication. However, our study showed that the mosaic structure was formed right during the course of silicon anodization at high anodic current density. Furthermore, our study also showed that at high anodic current density the real silicon etching has been replaced by the growth of a silicon oxide layer. This is a layer of another substance that grows on silicon, so when the layer is too thick (which is obtained when the anodic current density is too high and/or the anodization time is too long) it will crack, creating mosaic pieces. When the silicon oxide layer is cracked, the locations around the cracks will be etched more violently than elsewhere, creating trenches. Thus, the mosaic structure with mosaic pieces emerged between the trenches has formed.

Comportement photoélectrochimique de ZnIn2S4(n) dans l'obscurité et sous éclairement en solution électrolytique aqueuse

1992 ◽  
Vol 70 (4) ◽  
pp. 1098-1104 ◽  
Author(s):  
O. Savadogo
Keyword(s):  
Electron Transfer ◽  
Redox Potential ◽  
Current Density ◽  
Flat Band ◽  
Tunnel Effect ◽  
Anodic Current Density ◽  
Flat Band Potential ◽  
Anodic Current ◽  
Species Concentration ◽  
Diffusion Controlled

Photoelectrochemical characteristics of ZnIn2S4(n) have been studied by potentiodynamic methods and capacity measurements. The variation of the anodic current density (ia) as a function of [OH−] and [H3O+] has been studied under darkness. This darkness current is small (~1 μA cm−2) and it has been attributed to the anodic dissolution of the material. This process is not diffusion controlled. This behaviour was attributed to electron transfer by tunnel effect via localized interface states. The dissolution of the material under illumination has been determined. Its dissolution requires eight holes. The variation of the stabilisation coefficient S (iox/it) with the redox potential (Vredox) and the S2− species concentration (Cr) has been studied. The effects of [S2−] and illumination on the flat band potential of the electrode have been determined.

Anodic Oxidation Parameters on Al-Cu Alloy Anodizing Film's Electrochemical Ability by EIS

2006 ◽  
Vol 11-12 ◽  
pp. 665-668
Author(s):  
Chao Guo ◽  
Yu Zuo ◽  
Jing Mao Zhao ◽  
Xu Hui Zhao ◽  
Jin Ping Xiong
Keyword(s):  
Anodic Oxidation ◽  
Porous Layer ◽  
Current Density ◽  
Barrier Layer ◽  
Oxidation Time ◽  
Equivalent Circuits ◽  
Anodic Current Density ◽  
Anodic Current ◽  
Cu Alloy ◽  
Oxidation Parameters

EIS is used in this paper to study the effects of anodic oxidation parameters on the film’s ability, and multi-layer equivalent circuits are proposed. The oxidation time has great effect on porous layer, the porous layer’s impedance increases as the anodic oxidation time prolong; anodic current density has effect on both barrier layer and porous layer, higher current density gets higher impedance values in both barrier layer and porous layer; anodic oxidation temperature has great effect on barrier layer, when the temperature decreases, the barrier layer’s impedance increases.

Passivation of Crevices During Anodic Protection

CORROSION ◽  
1968 ◽  
Vol 24 (8) ◽  
pp. 247-251 ◽  
Author(s):  
W. D. FRANCE ◽  
N. D. GREENE
Keyword(s):  
Current Density ◽  
Electrochemical Behavior ◽  
Experimental Studies ◽  
Industrial Applications ◽  
Anodic Current Density ◽  
Rapid Rate ◽  
Anodic Current ◽  
Anodic Protection ◽  
Theoretical Analyses ◽  
Electrolyte Characteristics

Abstract The protection of crevices poses an important problem in industrial applications of anodic protection. Experimental studies with a special crevice assembly have shown that the interiors of crevices often remain active and corrode at a rapid rate. These experiments, together with theoretical analyses, demonstrate that the ability to passivate crevices during anodic protection is controlled by electrolyte characteristics, crevice geometry, and the electrochemical behavior of the protected metal. Of these, critical anodic current density, ic, is the most important parameter.

scholarly journals Computational modeling of anodic current distribution and anode shape change in aluminium reduction cells

2015 ◽  
Vol 51 (1) ◽  
pp. 7-15 ◽  
Author(s):  
Y. Xu ◽  
J. Li ◽  
H. Zhang ◽  
Y. Lai
Keyword(s):  
Current Distribution ◽  
Current Density ◽  
Shape Change ◽  
Bottom Surface ◽  
Carbon Anode ◽  
Anodic Current Density ◽  
Arbitrary Lagrangian Eulerian ◽  
Anodic Current ◽  
Secondary Current ◽  
Aluminium Reduction

In aluminium reduction cells, the profile of a new carbon anode changes with time before reaching a steady state shape, since the anode consumption rate, depending on the current density normal to anode surfaces, varies from one region to another. In this paper, a two-dimension model based on Laplace equation and Tafel equation was built up to calculate the secondary current distribution, and the shift of anode shape with time was simulated with arbitrary Lagrangian-Eulerian method. The time it takes to reach the steady shape for the anode increases with the enlargement of the width of the channels between the anodes or between the anode and the sidewall. This time can be shortened by making a sloped bottom or cutting off the lower corners of the new anode. Forming two slots in the bottom surface increases the anodic current density at the underside of the anode, but leads to the enlargement of the current at the side of the anode.

scholarly journals Definition of the transfer coefficient in electrochemistry (IUPAC Recommendations 2014)

2014 ◽  
Vol 86 (2) ◽  
pp. 259-262 ◽  
Author(s):  
Rolando Guidelli ◽  
Richard G. Compton ◽  
Juan M. Feliu ◽  
Eliezer Gileadi ◽  
Jacek Lipkowski ◽  
...  
Keyword(s):  
Transfer Coefficient ◽  
Current Density ◽  
Cathodic Current Density ◽  
Anodic Current Density ◽  
Anodic Current ◽  
Cathodic Current ◽  
Electrode Processes ◽  
Green Book ◽  
Definition Of ◽  
Applied Electric Potential

Abstract The transfer coefficient α is a quantity that is commonly employed in the kinetic investigation of electrode processes. An unambiguous definition of the transfer coefficient, independent of any mechanistic consideration and exclusively based on experimental data, is proposed. The cathodic transfer coefficient αc is defined as –(RT/F)(dln|jc|/dE), where jc is the cathodic current density corrected for any changes in the reactant concentration on the electrode surface with respect to its bulk value, E is the applied electric potential, and R, T, and F have their usual significance. The anodic transfer coefficient αa is defined similarly, by simply replacing jc with the anodic current density and the minus sign with the plus sign. This recommendation aims at clarifying and improving the definition of the transfer coefficient reported in the 3rd edition of the IUPAC Green Book.

Poly(SNS) Electrochemical Synthesis and Processability

1999 ◽  
Vol 600 ◽  
Author(s):  
T. F. Otero ◽  
S. Villanueva ◽  
E. Brillas ◽  
J. Carrasco
Keyword(s):  
Current Density ◽  
Polymer Films ◽  
Electrochemical Synthesis ◽  
Platinum Electrode ◽  
Anodic Current Density ◽  
Anodic Current ◽  
Dark Violet

AbstractThe flow of an anodic current density of 0.5 mA. cm−2 through a 5 mmol/l solution of 2,5-di-(2-thienyl)pyrrole (SNS), in acetonitrile, gives dark-violet and uniform polymer films coating the platinum electrode in presence of different electrolytes. The process is named either electropolymerization or electrogeneration.

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