The Chemical Nature of Aluminum Corrosion: III . The Dissolution Mechanism of Aluminum Oxide and Aluminum Powder in Various Electrolytes

Nguyen, T. H.; Foley, R. T.

doi:10.1149/1.2129520

Cited by 100 publications

(48 citation statements)

References 17 publications

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“…Since that time, a number of studies have been conducted on powders and oxide covered metals and in all cases the adsorption of Cl − was observed on the oxide surface. 30,35,46,53,[76][77][78] Kolics et al 78 showed, Figure 1, that Cl − adsorption was pH dependent, with the Cl − concentration on the surface decreasing with increasing pH. They associated the observed adsorption with the surface charge and the pH pzc of the oxide surface.…”

Section: Interactions At the Oxide/solution Interfacementioning

confidence: 96%

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Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

Natishan

O’Grady

2014

J. Electrochem. Soc.

231

122

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Metals and alloys such as aluminum (Al), stainless steels, and nickel-based alloys exhibit corrosion resistance in a wide range of environments due to the presence of protective, passive oxides. However, in environments that contain aggressive anions such as chloride, Cl − , the passive film becomes unstable and degrades locally causing film breakdown and pitting corrosion. A number of theories describing the initiation of pitting corrosion have been postulated and discussed but to date there is no consensus on the mechanism of breakdown. Since all current mechanisms require Cl − interactions for oxide film breakdown in Cl − containing environments, the question is what is the nature of the interaction of aggressive anions such as Cl − with the passive film, adsorption and/or absorption, leading to pitting? This communication focuses on the interaction of Cl − with the passive oxide film on pure aluminum by reviewing and summarizing the available experimental data concerning Cl − interactions. It should also be noted that the observations for Cl − interactions with Al reviewed and summarized herein might not be applicable to all metals and alloys. Technologically important metals and alloys such as aluminum (Al), stainless steels, and nickel-based alloys exhibit corrosion resistance in a wide range of environments due to the presence of protective, passive oxides.1-90 The passive oxides behave as kinetic barriers, which inhibit further oxidation of the underlying thermodynamically reactive metals. However, in environments that contain aggressive anions such as chloride, Cl − , the passive film becomes unstable and degrades locally causing film breakdown and localized corrosion, which in turn decreases the service life of the materials. The consequence of discrete oxide failure is localized corrosion, which occurs in the forms of crevice corrosion in occluded sites and metastable or stable pitting corrosion on open surfaces. It is generally agreed that localized corrosion occurs in two distinct steps: initiation and propagation.A number of theories describing the initiation of pitting corrosion have been postulated and discussed.

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Section: Interactions At the Oxide/solution Interfacementioning

confidence: 96%

“…Chloride adsorption by the oxide film has been primarily discussed in terms of surface attractive forces. 3,14,25,29,41,53,74,99 The surface composition at the oxide solution/interface is usually an oxyhydroxide type material, e.g. AlOOH.…”

Section: Interactions At the Oxide/solution Interfacementioning

confidence: 99%

Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

Natishan

O’Grady

2014

J. Electrochem. Soc.

231

122

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“…It is probable that when a sodium chloride solution is introduced into a fatigue pre-crack, the local chloride ion concentration decreases because of chloride ion uptake by the alumina film on the fatigue pre-crack's surfaces. [57][58][59][60][61][62] This is supported by experimental observations that have demonstrated that local chloride ion depletion occurs within tight crevices [63] and SCC-tip regions, [64,65] as shown in Figure 10, and chloride ion uptake by alumina Reciprocal Temperature (1/T o K) Fig. 8-SCC growth rate from the literature for low-copper [9,22,23] -and high-copper [7,31,53,55] -containing Al-Zn-Mg-Cu alloys exposed to an aqueous 0.6 M NaCl solution and for AA7079-T651(medium-copper-containing alloy) exposed to an aqueous 5 M KI solution while under anodic polarization at À700 mV (SCE).…”

Section: Local Solution Chemistry Within Pre-cracks and Propagatinmentioning

confidence: 99%

“…8-SCC growth rate from the literature for low-copper [9,22,23] -and high-copper [7,31,53,55] -containing Al-Zn-Mg-Cu alloys exposed to an aqueous 0.6 M NaCl solution and for AA7079-T651(medium-copper-containing alloy) exposed to an aqueous 5 M KI solution while under anodic polarization at À700 mV (SCE). [9,47,52] or aluminum alloy surfaces exposed to saline solutions, [57][58][59][60][61][62] as shown in Figure 11. It is also significant that the initial crack growth rates from fatigue precracked Al-Zn-Mg-Cu alloys exposed to saline solutions are the same as those reported in distilled water.…”

Section: Local Solution Chemistry Within Pre-cracks and Propagatinmentioning

confidence: 99%

“…The predicted lengths for total chloride ion depletion behind the crack-tip of a 2-mm fatigue pre-crack in a conventional DCB specimens, [5,66] exposed to sodium chloride solutions and loaded to various stress intensity factors are shown in Figure 12, using the chloride surface uptake data for alumina from Figure 11 and assuming that the pre-crack geometry may be represented by a trapezoidal region [67,68] with its dimensional dependency upon the applied stress intensity factor described by a relationship developed by Mostovoy et al [69] The chloride ion uptake by the alumina surfaces covering a 2-mm fatigue pre-crack may be estimated using, the measured chloride ion concentration obtained from 5 lL samples taken from the crack-tip region [64,65] ( Figure 10) and published chloride ion-alumina adsorption data [57][58][59][60][61][62] combined with estimated local solution volumes, again assuming a trapezoidal crack geometry [67,68] with a dimensional dependency upon the applied stress intensity factor as described by the relationship provided by Smith and Piper. [70] The estimated solution volume within a 2-mm precrack loaded to K = 20 MNm À3/2 is 1.65 lL and the measured chloride ion concentration of 0.2 M from 5 lL test samples taken during the initial stages of testing ( Figure 10) suggest that 0.33 M had been depleted from the crack-tip region.…”

Section: Local Solution Chemistry Within Pre-cracks and Propagatinmentioning

confidence: 99%

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Stress Corrosion Cracking in Al-Zn-Mg-Cu Aluminum Alloys in Saline Environments

Holroyd

Scamans

2012

Metall Mater Trans A

108

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Stress corrosion cracking of Al-Zn-Mg-Cu (AA7xxx) aluminum alloys exposed to saline environments at temperatures ranging from 293 K to 353 K (20°C to 80°C) has been reviewed with particular attention to the influences of alloy composition and temper, and bulk and local environmental conditions. Stress corrosion crack (SCC) growth rates at room temperature for peak-and over-aged tempers in saline environments are minimized for Al-Zn-Mg-Cu alloys containing less than~8 wt pct Zn when Zn/Mg ratios are ranging from 2 to 3, excess magnesium levels are less than 1 wt pct, and copper content is either less than~0.2 wt pct or ranging from 1.3 to 2 wt pct. A minimum chloride ion concentration of~0.01 M is required for crack growth rates to exceed those in distilled water, which insures that the local solution pH in crack-tip regions can be maintained at less than 4. Crack growth rates in saline solution without other additions gradually increase with bulk chloride ion concentrations up to around 0.6 M NaCl, whereas in solutions with sufficiently low dichromate (or chromate), inhibitor additions are insensitive to the bulk chloride concentration and are typically at least double those observed without the additions. DCB specimens, fatigue pre-cracked in air before immersion in a saline environment, show an initial period with no detectible crack growth, followed by crack growth at the distilled water rate, and then transition to a higher crack growth rate typical of region 2 crack growth in the saline environment. Time spent in each stage depends on the type of precrack (''pop-in'' vs fatigue), applied stress intensity factor, alloy chemistry, bulk environment, and, if applied, the external polarization. Apparent activation energies (E a ) for SCC growth in Al-Zn-Mg-Cu alloys exposed to 0.6 M NaCl over the temperatures ranging from 293 K to 353 K (20°C to 80°C) for under-, peak-, and over-aged low-copper-containing alloys (<0.2 wt pct) are typically ranging from 80 to 85 kJ/mol, whereas for high-copper-containing alloys (>~0.8 wt pct), they are typically ranging from 20 to 40 kJ/mol for under-and peak-aged alloys, and based on limited data, around 85 kJ/mol for over-aged tempers. This means that crack propagation in saline environments is most likely to occur by a hydrogen-related process for low-copper-containing Al-Zn-Mg-Cu alloys in under-, peak-and over-aged tempers, and for high-copper alloys in under-and peak-aged tempers. For over-aged high-copper-containing alloys, cracking is most probably under anodic dissolution control. Future stress corrosion studies should focus on understanding the factors that control crack initiation, and insuring that the next generation of higher performance Al-Zn-Mg-Cu alloys has similar longer crack initiation times and crack propagation rates to those of the incumbent alloys in an over-aged condition where crack rates are less than 1 mm/month at a high stress intensity factor.

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Basics of Corrosion

2017

Cyclodextrins

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The Chemical Nature of Aluminum Corrosion: III . The Dissolution Mechanism of Aluminum Oxide and Aluminum Powder in Various Electrolytes

Cited by 100 publications

References 17 publications

Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

Stress Corrosion Cracking in Al-Zn-Mg-Cu Aluminum Alloys in Saline Environments

Basics of Corrosion

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