The Influence of Dichromate Ions on Aluminum Dissolution Kinetics in Artificial Crevice Electrode Cells

Akiyama, Eiji; Frankel, G. S.

doi:10.1149/1.1392597

Cited by 43 publications

(46 citation statements)

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“…3,4 Nevertheless, the origin of this feature has not been largely discussed quantitatively, especially as the inner surface of the "IG crevice" behind the active anodic head at the point of attack 5 can also suffer dissolution at a reduced rate and at long exposures as illustrated in different works showing a blunting of the IG path. 6,7 Consequently the mass transport and/or the ohmic drop can control the intergranular penetration as it has been discussed for crevice corrosion 8 even if the geometry of the active anodic area is different.…”

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confidence: 99%

“…Nevertheless, it was impossible to validate this assumption on thin foil specimens by analysing the recorded current to find a relationship between the net current and the time of polarization which would fit with an ohmic control as suggested by results on aluminum artificial crevice electrodes. 8 This issue remains open for discussion even if recent advances in local probe techniques allows isolation of an IG path in order to record as close as possible the net current related only to the dissolving tip of the IG path. 20 Effect of potential conditions (imposed or OCP).-The same methodology was applied to determine the influence of the potential on the propagation rate.…”

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Optical and Chemical Monitoring during Foil Penetration Experiments to Study Intergranular Corrosion in AA2024

Bonzom

Oltra

2018

J. Electrochem. Soc.

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A modified version of the foil penetration technique based on an optical detection of the full penetrating intergranular defects through thin foils was applied to AA2024 samples of various thicknesses in contact with a dilute chloride solution. As the rear side of the foil was free during the experiments, it was straightforward to measure the pH of the electrolyte trapped inside the grain boundary network leaking through the emerging defects on the rear side of the foils. The penetration regime in the longitudinal direction was determined for various exposure and electrochemical conditions confirming the decrease of the propagation kinetics as function of the depth of the intergranular defects. pH measurements were used to support mass transport simulation inside a pore electrode mimicking the propagation of the anodic head of grain boundaries. After validation under potentiostatic conditions, the same modelling approach was applied under free corrosion conditions, to discuss the location of cathodic areas during immersion and droplet exposures. Frankel and coworkers 1 considered the anisotropy of the intergranular corrosion process and performed foil penetration tests using various electrochemical conditions. They proposed that the propagation rate of intergranular corrosion followed a power law of the following type:where d is either the nominal thickness of the full penetrated foil or the resulting IG path length, a and n are constants (n is between 0 and 1) and t the time for the full penetration. To discuss these results in terms of IG propagation rate the raw data can be inverted and expressed as the depth of the fastest growing site as a function of time. However the physical meaning of the exponent and its value as function the nature of the alloy have not been discussed to our knowledge. Nevertheless, interesting work described in Ref. 2 illustrated application of such a law (relation 1) deduced from laboratory experiments to operational aircraft. In these practical cases there was a large variation in corrosion growth rates from one section of a wing to the next or from an aircraft to the next. But it was demonstrated that it was possible to provide a distribution for coefficients of relation (1), especially for coefficient a, which could be deduced from documented corrosion data collected, for example, from repair data.Relation (1) which means that the intergranular (IG) propagation rate on aluminum alloys (AA2024) is decreasing as function of the IG path length has been validated under potentiostatic conditions. 1 Moreover this trend has been also frequently discussed in other studies under free corrosion conditions. 3,4 Nevertheless, the origin of this feature has not been largely discussed quantitatively, especially as the inner surface of the "IG crevice" behind the active anodic head at the point of attack 5 can also suffer dissolution at a reduced rate and at long exposures as illustrated in different works showing a blunting of the IG path.6,7 Consequently the mass transport and/or the ohmic dr...

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Optical and Chemical Monitoring during Foil Penetration Experiments to Study Intergranular Corrosion in AA2024

Bonzom

Oltra

2018

J. Electrochem. Soc.

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“…Lead-in-pencil or artificial pit electrodes, [22][23][24][25][26][27] Normansky interference contrast microscopy, 5 artificial crevices techniques, 28 X-ray micro-tomography, 29 synchrotron based micro-tomography, 30 as well as electrode arrays 31 have all been used to study crevice corrosion under various conditions. However, to our knowledge, an Ångstrom resolved real-time visualization of the initiation of crevice corrosion inside a confined environment has not been experimentally demonstrated.…”

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Real-Time Monitoring of Aluminum Crevice Corrosion and Its Inhibition by Vanadates with Multiple Beam Interferometry in a Surface Forces Apparatus

Shrestha

Baimpos

et al. 2015

J. Electrochem. Soc.

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Crevice corrosion (CC) of metals remains a serious concern for structural materials. Yet a real-time in situ visualization of corrosion, and its inhibition within a confined geometry, remains challenging. Here, we present how multiple-beam interferometry in a Surface Forces Apparatus can be utilized to directly visualize corrosion processes in real-time and with Ångstrom resolution within welldefined confinement geometries. We use atomically smooth muscovite mica surfaces to form round-shaped ∼1000 μm 2 crevices on aluminum. After exposure to NaCl solutions we can detect and track active sites of aluminum corrosion within this confined geometry. CC of aluminum randomly initiates in the confined crevice mouth, where the distance between apposing surfaces is between 20-300 nm. We can directly track oxide dissolution/formation, and corrosion-rates as well as their retardation due to sodium vanadate inhibitors present in solution. Formation of a compacted oxide layer effectively inhibits CC in 5 mM NaCl solutions with 2.5 mM of added NaVO 3 , while inhibition rapidly breaks down at chloride concentrations above 50 mM. Breakdown of the inhibition-layers is initiated by rapid dissolution of the protective oxide within the confined zone. Our technique may be adapted for monitoring CC, corrosion inside of crack-tips, and evaluation of inhibitor efficiencies in a variety of metals.

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“…3 Artificial pit or ''lead in pencil'' electrodes have been used by researchers previously to study pit growth kinetics. [4][5][6][7][8][9][10][11] The artificial pit electrode geometry forms a single pit in which the whole electrode area is active, generates a natural pit environment, and provides an ideal onedimensional transport condition. The artificial crevice electrode is similar to the artificial pit electrode, except that a metal foil instead of a wire is used to create a recessed band instead of a recessed disk.…”

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“…The artificial crevice electrode is similar to the artificial pit electrode, except that a metal foil instead of a wire is used to create a recessed band instead of a recessed disk. 10,11 Hydrogen bubbles can escape easier from this geometry, so artificial electrodes are useful for studying the localized corrosion kinetics of Al or Mg, in which copious hydrogen is evolved.…”

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The Influence of Inhibitor Ions on Dissolution Kinetics of Al and Mg Using the Artificial Crevice Technique

Meng

Thodla

Frankel

2002

Electrochem. Solid-State Lett.

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The effect of four anions on dissolution kinetics of Al and Mg in chloride-containing solution was investigated using the artificial crevice technique. Polarization curves for Al and Mg artificial crevice electrodes were obtained by first dissolving the artificial crevice electrode to a fixed depth at a high potential and then scanning the potential downward to the repassivation potential. Potential components were obtained by fitting the polarization curve to an equation describing activation overpotential and ohmic potential drops. Of chromate, dichromate, molybdate, and nitrate, only nitrate was found to inhibit the dissolution kinetics of Al artificial crevice electrodes. In contrast, all anions inhibited the dissolution kinetics of Mg artificial crevice electrodes. The results indicate that the mechanism of localized corrosion inhibition of Al alloys by chromate must be something other than inhibition of anodic dissolution in an active pit or crevice.High strength Al alloys such as AA2024-T3 are widely used in aircraft applications, but are extremely susceptible to localized corrosion. In order to protect them from localized corrosion, protective coatings containing inhibitors, typically chromates, must be used. Chromates (or dichromates) dissolved in solution are also extremely effective in inhibiting corrosion, even at dilute concentrations.

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The Influence of Dichromate Ions on Aluminum Dissolution Kinetics in Artificial Crevice Electrode Cells

Cited by 43 publications

References 17 publications

Optical and Chemical Monitoring during Foil Penetration Experiments to Study Intergranular Corrosion in AA2024

Optical and Chemical Monitoring during Foil Penetration Experiments to Study Intergranular Corrosion in AA2024

Real-Time Monitoring of Aluminum Crevice Corrosion and Its Inhibition by Vanadates with Multiple Beam Interferometry in a Surface Forces Apparatus

The Influence of Inhibitor Ions on Dissolution Kinetics of Al and Mg Using the Artificial Crevice Technique

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