The Effect of Prior Cathodic Polarization on the Initiation of Pitting on Aluminum

Lin, Ching-Feng; Hebert, Kurt R.

doi:10.1149/1.2086293

Cited by 30 publications

(22 citation statements)

References 20 publications

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“…This is immediately evident for the dc process from the tunnel structures that result. 8,11,13 The growth rates we calculate are much greater than the ones reported for those investigations. For both processes, the steady-state dissolution potential is the repassivation potential, because this is the only potential at which both passivation and dissolution can occur.…”

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confidence: 65%

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Crystallographic Pit Growth on Aluminum (100)

Ôno¹,

Makino²,

Alwitt³

2005

J. Electrochem. Soc.

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Crystallographic pits were grown on Al͑100͒ at temperatures from 30 to 90°C, in solutions of HCl ϩ H 2 SO 4 . Pits grew during a galvanostatic anodic pulse for 5-100 ms that was preceded by a galvanostatic cathodic pulse of 50 ms. The anodic potential has a small peak for 1-2 ms and then remains constant. The cathodic pulse causes rapid pit nucleation so most pits nucleate within 5 ms, and pit passivation and pit growth are the dominant processes at longer times. It was determined that a substantial fraction of pits passivates during the pulse, so growth rates were calculated from the increase in largest pit size with pulse duration. The growth rate is constant at each temperature and follows an Arrhenius temperature dependence with an activation energy of 7.2 kcal mol Ϫ1 . There are significant differences between the growth of pits and the growth of etch tunnels. The activation energy for pit growth is one-half that for tunnel growth, and pit growth rates are greater than tunnel growth rates. It is proposed that the chemisorbed chloride complex postulated to be an intermediary for Al dissolution changes from one structure during pit growth to another, more stable, structure during tunnel growth.

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confidence: 65%

“…The ac etch process operates near room temperature, whereas the dc process is run at temperatures above 65°C. Hebert and Lin 11 found that prior cathodic polarization enhances early pit nucleation and reduces the size of the potential transient. This is immediately evident for the dc process from the tunnel structures that result.…”

mentioning

confidence: 99%

Crystallographic Pit Growth on Aluminum (100)

Ôno¹,

Makino²,

Alwitt³

2005

J. Electrochem. Soc.

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“…2, the stationary anodic currents are plotted on a logarithmic scale vs. the corrected potential, which was obtained by subtracting lo and iR3 from the applied potential. In terms of the electrical model, the corrected potential here is 4)2 + Vr -0.27 V. The linear relation between log i and the corrected potential in the figure ( aF c= exP_-__1oJ-exPI--i-iioJj [5] [6]…”

Section: Resultsmentioning

confidence: 99%

An Electrical Model for the Cathodically Charged Aluminum Electrode

Wang

Hebert

1996

J. Electrochem. Soc.

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A mathematical model was formulated for the surface film on aluminum which considered the film to consist of an inner barrier high-field conducting layer and an outer, porous, ohmically conducting layer. It included all relevant capacitive and faradaic processes, and incorporated the nonlinearity of conduction and reaction rate expressions. The model was used to investigate structural changes produced by cathodic polarization in acid solutions, which has been found to promote anodic pitting strongly in ac etching processes. The film's structural parameters were fit to experimental current transients following anodic potential steps after cathodic charging. The model was found to represent experimental current decays realistically over several orders of magnitude variation of current density (factor of 103) and time (factor of 105). To a first approximation, cathodic activation could be described in terms of a decrease of the inner layer thickness (δ) from about 30 to 15 or 20 Å and an increase of the porosity (p) to 0.02. These changes were interpreted as being due to the rapid penetration of pores into the outer portion of the initial film. The pores may have been produced by electrochemical dissolution of the oxide during cathodic current flow through the film. The promotion of pitting by cathodic charging in chloride solutions suggests that some fraction of the pores may penetrate to the metal. A mathematical model was formulated for the surface film on aluminum which considered the film to consist of an inner barrier high-field conducting layer and an outer, porous, ohmically conducting layer. It included all relevant capacitive and faradaic processes, and incorporated the nonlinearity of conduction and reaction rate expressions. The model was used to investigate structural changes produced by cathodic polarization in acid solutions, which has been found to promote anodic pitting strongly in ac etching processes. The film's structural parameters were fit to experimental current transients following anodic potential steps after cathodic charging. The model was found to represent experimental current decays realistically over several orders of magnitude variation of current density (factor of 10) and time (factor of 10). To a first approximation,, cathodic activation could be described in terms of a decrease of the inner layer thickness (8) from about 30 to 15 or 20 A and an increase of the porosity (p) to 0.02. These changes were interpreted as being dueto the rapid penetration of pores into the outer portion of the initial film. The pores may have been produced by electrochemical dissolution of the oxide during cathodic current flow through the film. The promotion of pitting by cathodic charging in chloride solutions suggests that some fraction of the pores may penetrate to the metal. IntroductionSurface films on structural metals generally have a high electrical resistance which protects them from corrosion. However, the film resistance presents an obstacle to their use in applications where reactiv...

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“…The electrograining procedure involves cycling of the potential of the alloy, such that anodic film formation followed by pitting occurs under anodic potentials and hydrogen evolution, with associated deposition of hydrated alumina, under cathodic potentials . The cathodic polarization has an important role in ensuring uniformity of pitting during the anodic part of the cycle . The resultant plate has a convoluted surface that is desired for its water retentive property and the adhesion of a photosensitive coating .…”

Section: Introductionmentioning

confidence: 99%

Effect of magnesium and titanium on the cathodic behaviour of aluminium in nitric acid

García‐García

Chiu

Skeldon

et al. 2014

Surf. Interface Anal.

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Cathodic polarization of aluminium and Al-0.18 wt.% Mg and Al-0.08 wt.% Ti alloys in 0.24 mol dm À3 nitric acid solution at 38°C has been employed to assist understanding of the roles of alloying elements in electrograining. The findings indicate that additions of magnesium and titanium to aluminium accelerate the corrosion of the substrate under the alkalization caused by the cathodic reactions. The accelerated dissolution and the consequent formation of hydrated alumina result in a decreased net cathodic current density in potentiostatic and potentiodynamic polarization conditions relative to the behaviour of aluminium.

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The Effect of Prior Cathodic Polarization on the Initiation of Pitting on Aluminum

Cited by 30 publications

References 20 publications

Crystallographic Pit Growth on Aluminum (100)

Crystallographic Pit Growth on Aluminum (100)

An Electrical Model for the Cathodically Charged Aluminum Electrode

Effect of magnesium and titanium on the cathodic behaviour of aluminium in nitric acid

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