Anodic Behavior of Aluminum Straining and a Mechanism for Pitting

Wexler, S.; Galvele, J.R.

doi:10.1149/1.2401665

Cited by 63 publications

(33 citation statements)

References 17 publications

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“…Polynuclear complexes could be formed, or further degrees of hydrolysis could occur. Nevertheless, reaction [2] will give the minimum degree of acidification expected inside a pit. On the other hand, either no polynuclear complexes are reported for the metals used in the present work, or their formation rate is very slow (18,19).…”

Section: Pit Modelmentioning

confidence: 99%

“…The pH of the bulk solution could have any value, and is given as a boundary condition. (iii) It is assumed that reaction [1] is followed by a hydrolysis equilibrium of the type Me n+ -t-H20~ Me(OH) ('~-1)+ -t-H + [2] and that this equilibrium is very quickly reached (18). Reaction [2] is a simplified description of the processes taking place inside a pit.…”

Section: Pit Modelmentioning

confidence: 99%

“…(iii) It is assumed that reaction [1] is followed by a hydrolysis equilibrium of the type Me n+ -t-H20~ Me(OH) ('~-1)+ -t-H + [2] and that this equilibrium is very quickly reached (18). Reaction [2] is a simplified description of the processes taking place inside a pit. Polynuclear complexes could be formed, or further degrees of hydrolysis could occur.…”

Section: Pit Modelmentioning

confidence: 99%

“…Nevertheless, none of these mechanisms could account for the way in which variables such as pH, ionic concentration, and inhibitor concentration affect the pitting potential. In recent publications, Wexler and Galvele (2) and Alvarez and GaIvele (3) reported that the pitting potential was the minimum potential at which localized acidity could be maintained inside a pit. The present paper, based on simple transport equations shows that such acidification can be obtained even at the very early stages of pitting, and that, as was recently reported (4), transport calculations inside the pit explain why variables such as an aggressive anion concentration, nonaggressive anion concentration, external pH, presence of weak acid salts, and alloying elements modify the pitting potential o'f a metal.…”

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confidence: 99%

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Transport Processes and the Mechanism of Pitting of Metals

Galvele

1976

J. Electrochem. Soc.

782

467

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A pit model was developed on the assumption that the metal ions hydrolyze inside the pits and that the corrosion products are transported by diffusion. Concentrations of Me e+, Me(OH)+, and H + ions, as a function of pit depth and current density, for Zn, Fe, Ni, Co, AI, and Cr were calculated. The main reason for passivity breakdown at the initial stages of pit growth, was found to be the localized acidification due to metal ions hydrolysis. Assuming a critical pH value for pit initiation, the following experimental facts could be explained: (i) the effect of the external pH on the pitting potential of Fe and stainless steel; (it) the effect of sodium borate concentration on the pitting potential of Zn; (it{) the effect of weak acid salts on the pitting potential of AI; (iv) the oscillations of the electrode potential of stainless steel and nickel in solutions of Cl-+ SO4 = ions; (v) the existence of a pitting inhibition potential; and (vi) the existence of a pitting protection potential. Through analysis of the transport processes inside a pit it was also concluded that the pitting potential of a metal should change with the CI-ion concentration according to the equation E~ = E/ --B 9 log [CI-] B = 0.059V being the slope of the curve at room temperature.

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Section: Pit Modelmentioning

confidence: 99%

Section: Pit Modelmentioning

confidence: 99%

Section: Pit Modelmentioning

confidence: 99%

mentioning

confidence: 99%

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Transport Processes and the Mechanism of Pitting of Metals

Galvele

1976

J. Electrochem. Soc.

782

467

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“…11 Nitrate was found to have only a minor influence at a concentration of 0.05, but a much larger effect at 0.5 M. The influence of nitrate in solution might be related to an increase in the crevice pH associated with nitrate reduction. 12 The fact that nitrate has a significant inhibiting effect on the dissolution of an Al artificial crevice indicates that this technique is suitable for the determination of Al anodic inhibition.…”

mentioning

confidence: 99%

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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