Determination of Pit Growth Rates on Aluminum Using a Metal Foil Technique

Hunkeler, F.; Böhni, H.

doi:10.5006/1.3577553

Cited by 91 publications

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“…These values are comparable to trends from power law fits for immersed and atmospheric conditions of Al 1100 reported elsewhere. [33][34][35] Observations of coupon-level and individual droplet experiments suggest the average corrosion rate trends may be collectively dependent on initiation, growth, and stifling of pits associated with drying of individual salt deposits. The fraction of salt deposit sites over time where corrosion is observed to occur; Fig.…”

Section: Discussionmentioning

confidence: 99%

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The controlling role of sodium and carbonate on the atmospheric corrosion rate of aluminum

et al. 2017

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Aluminum and aluminum alloys are widely used in many outdoor applications due to their inherent corrosion resistance attributed to the formation of a protective oxide layer. While corrosion rates are generally considered low for aluminum in many atmospheric environments, understanding of the corrosion performance over time is necessary to predict the cost, safety, and esthetics of these materials. The vast majority of the knowledgebase of atmospheric aluminum corrosion is built on environment-response relationships; often based on statistical correlation of corrosion rate data with atmospheric environmental conditions. However, there is still a limited mechanistic understanding of corrosion processes associated with this linkage. This lack in knowledge prevents interpretation and limits the extrapolation of these statistical datasets for prediction purposes. Here, the mechanistic dependence of aluminum corrosion rate on salt loading is explored through complimentary experimental and theoretical analysis relating corrosion rate to electrolyte chemistry, volume and corrosion products. From these results a reaction pathway is proposed for the atmospheric corrosion of aluminum that accounts for the governing effects of CO 2 and salt loading on corrosion rate. This reaction pathway provides a new perspective that highlights the importance of the formation and growth of dawsonite (NaAlCO 3 (OH) 2 ), and the subsequent gettering of sodium from the electrolyte leading to the stifling of corrosion kinetics. This study highlights the importance of accounting for the dynamic physical and chemical state of the electrolyte during corrosion in process models and measurement techniques to better understand and predict atmospheric corrosion behavior.

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Section: Discussionmentioning

confidence: 99%

“…In Fig. 4b, the estimated mass loss (Δm) is calculated assuming hemispherical pit volumes 33 with pit depths from Eq. 1, the number of corroding sites, n j,t , at t, the time of exposure from 0 to l, the total exposure time, and j, the growth time of the individual corrosion sites, from 0 to k, the total growth time of each site (from Fig.…”

Section: Discussionmentioning

confidence: 99%

The controlling role of sodium and carbonate on the atmospheric corrosion rate of aluminum

et al. 2017

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“…For pitting of aluminum in chloride solutions, the topic of this work, measurements of the potential dependence of the pit current density have been carried out by a number of investigators, who have focused on the growth of pits at potentials positive to the pitting and repassivation potentials. [1][2][3][4][5][6][7] Hunkeler and Böhni found that the pit current increases with potential and is controlled by the ohmic resistance of the pit solution. 2,3 Frankel and co-workers investigated the growth of two-dimensional pits in thin aluminum films and noted a potential region above the pitting potential in which the pit current increased with potential, and at higher potentials a current plateau which was ascribed to mass-transport limited dissolution.…”

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confidence: 99%

“…[1][2][3][4][5][6][7] Hunkeler and Böhni found that the pit current increases with potential and is controlled by the ohmic resistance of the pit solution. 2,3 Frankel and co-workers investigated the growth of two-dimensional pits in thin aluminum films and noted a potential region above the pitting potential in which the pit current increased with potential, and at higher potentials a current plateau which was ascribed to mass-transport limited dissolution. 1,4 Like Hunkeler and Böhni, they concluded that the first region was controlled by ohmic resistance.…”

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confidence: 99%

Metal Dissolution Kinetics in Aluminum Etch Tunnels

Tak

Sinha

Hebert

2000

J. Electrochem. Soc.

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The potential dependence of the metal dissolution current density of aluminum in etch tunnels was measured, using pulsed increases of current during galvanostatic etching experiments. Etching was carried out in 1 N HCl solution at 65ЊC, and was followed by analysis of the topographic development of the dissolving surfaces using scanning electron microscopy. By manipulation of the current waveform, the dissolving area and the applied current were varied independently. Parallel experiments with current interruptions were used to help identify the area of the dissolving surfaces during the anodic pulse, which were shown to be submicron size patches on the tunnel tip surfaces. After correction for solution-phase potential drops, the current was found to obey an exponential Tafel dependence on potential. Measurements of the dissolved depth vs. time show that the rate of cathodic hydrogen evolution is significantly increased during the anodic pulse, by comparison with that at the more negative potentials during constant current etching. Good agreement of the present current-potential relation was obtained with that derived from the measurements of pit currents in thin films by Frankel et al.

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“…The initial version of the foil penetration method was, in fact, based on this leaching which soaked the filter paper which was replaced in this work by a pH-indicator paper. The same approach was discussed in pioneering works of Boehni for pitting detection 15 but it was concluded that the pH information was insufficient and did not allow further conclusions concerning the chloride concentration within the pit. Experimental results.-IG propagation kinetics on AA2024 under potentiostatic conditions.-Analysis of the scattering of data.-A first set of foil penetration experiments were performed on 210-μm thick foils at different potentials above the breakdown potential (-580 mV).…”

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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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Determination of Pit Growth Rates on Aluminum Using a Metal Foil Technique

Cited by 91 publications

References 0 publications

The controlling role of sodium and carbonate on the atmospheric corrosion rate of aluminum

The controlling role of sodium and carbonate on the atmospheric corrosion rate of aluminum

Metal Dissolution Kinetics in Aluminum Etch Tunnels

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

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