Electrochemical Evaluation of Corrosion Inhibiting Layers Formed in a Defect from Lithium-Leaching Organic Coatings

Visser, Peter; Meeusen, Mats; González-García, Yaiza; Terryn, Herman; Mol, J.M.C.

doi:10.1149/2.1411707jes

Cited by 55 publications

(46 citation statements)

References 35 publications

(75 reference statements)

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“…Compared with the unexposed sample and the sample without Li‐carbonate, the phase angle plot of the sample with the Li‐carbonate loaded coating showed a broadening of the time‐constant related with formation of the oxide layer and increases phase angle values at the lower frequency range which indicates improved corrosion resistance. This behaviour is characteristic for the Li‐leaching coating technology on AA2024‐T3 . A similar behaviour was observed for the samples with the Li‐carbonate loaded coatings on the AA7075W (Figure B) and the AA5083W (Figure C) after 168‐hour NSS exposure.…”

Section: Resultssupporting

confidence: 78%

“…Each graph shows a measurement of an unexposed sample to demonstrate the initial stage of the defect area with the native aluminium oxide and the measurements of the samples with and without Li‐carbonate after 168‐hour NSS exposure. Figure A shows the typical response of the impedance modulus (top) and phase angle (bottom) of a AA2024‐T3 coated with and without Li‐carbonate as leaching inhibitor . The impedance modulus (Figure A top ) of the sample with the Li‐carbonate loaded coating increased in the middle (10 1 ‐10 3 Hz) and low frequency (10 −1 ‐10 −2 Hz) ranges compared with the samples without Li‐carbonate and the unexposed sample.…”

Section: Resultsmentioning

confidence: 99%

“…Further characterisation revealed that the protective layer comprises mainly aluminium, oxygen, and lithium and features a three‐layered structure of a columnar outer layer, a porous middle layer, and a dense layer near the aluminium substrate . Electrochemical analysis demonstrated that the corrosion protective properties could be attributed to the dense inner layer …”

Section: Introductionmentioning

confidence: 99%

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Active corrosion protection of various aluminium alloys by lithium‐leaching coatings

Visser

Terryn

Mol

2019

Surface & Interface Analysis

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This study presents the active protective properties of lithium‐leaching coatings for a range of aluminium alloys. Coatings with and without lithium carbonate as leachable inhibitor were applied on the aluminium alloys, artificially damaged and exposed to the neutral salt spray. A combined approach of scanning electron microscopy and electrochemical measurements revealed that the lithium carbonate leaching coating provided effective corrosion inhibition on AA2024, AA7075, AA5083, and AA6014 by the formation of a protective layer in the defect area and preventing local corrosion processes despite the different intrinsic electrochemical activity of the alloys.

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Section: Resultssupporting

confidence: 78%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Active corrosion protection of various aluminium alloys by lithium‐leaching coatings

Visser

Terryn

Mol

2019

Surface & Interface Analysis

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“…These results are in agreement with the observations when lithium-salts are used as leachable corrosion inhibitor in organic coatings. 15 …”

Section: Mechanism Of Formation-the Results Of This Investigationmentioning

confidence: 99%

“…15 Recently, new examples of the corrosion protective properties of lithium on aluminum were published. Gharbi et al observed a protective Li/Al surface film on Al-Cu-Li 2050-T3 alloy after polarization.…”

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confidence: 99%

Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride

Visser

González-García

Mol

et al. 2018

J. Electrochem. Soc.

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This study focuses on the elucidation of the formation mechanism of passive layers on AA2024-T3 during the exposure to alkaline lithium carbonate solutions in the presence of sodium chloride. Under controlled conditions, in an electrochemical cell, a protective layer was generated comprising an amorphous inner layer and a crystalline outer-layer. In order to resolve the formation mechanism, the layers were characterized using surface analytical techniques to characterize the surface morphology, thickness and elemental composition of the layers at different stages of the formation process. In addition, electrochemical techniques were applied to link the electrochemical properties of the layers with the different stages of formation. The results demonstrate that the formation mechanism of these layers comprises three different stages: (I) oxide thinning, (II) anodic dissolution and film formation, followed by (III) film growth through a competitive growth-dissolution process. The passive properties of the layers are generated in the third stage through the densification of the amorphous layer. The combined results provide an enhanced insight in the formation mechanism and the development of the passive properties of these layers when lithium salts are used as leaching corrosion inhibitor for coated AA2024-T3. Lithium salts gained interest as corrosion inhibitor after the observations of unexpected passivity of aluminum in alkaline lithium solutions by Gui and Devine.1 Aluminum is stable in the range of pH 4 to pH 9 due to the passivity of aluminum oxide.2 However, it is known that aluminum shows a high corrosion rate at pH values higher than 10.3 The corrosion process under these alkaline conditions is dominated by two subsequent sub-processes leading to significant mass loss. First, there is the process of direct (anodic) dissolution of the aluminum metal and the formation of an amorphous aluminum hydroxide gel film on the aluminum substrate, and second, the process of chemical dissolution of the aluminum hydroxide gel film into the bulk solution.4 In contrast, aluminum shows a passive behavior by the formation of a lithium containing film when exposed to alkaline lithium salt solutions. 1,5 This passive behavior was implemented by Buchheit et al. with the development of a hexavalent chromium-free chemical conversion coating from alkaline lithium carbonate solutions (pH 11-13), generating lithium aluminum carbonate hydroxide hydrate (hydrotalcite) layers on aluminum alloys.6 They studied the composition, structure and performance of these conversion coatings in relation to processing parameters and various bath chemistries and demonstrated that these hydrotalcite coatings exhibit similar corrosion protective properties as traditional conversion coatings.7 However, application of these conversion coatings in combination with coatings did not result in an equal performance compared to hexavalent chromium-based conversion coatings. In 2010, it was discovered that lithium salts could be considered as a potential alte...

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Anticorrosive properties and rust conversion mechanism of phytic acid‐based surface tolerant coating

Shuan

et al. 2020

Asia-Pacific J Chem Eng

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A phytic acid‐based surface tolerant epoxy coating was prepared, and the effect of phytic acid on the corrosion resistance of the composite coating on rusty carbon steel substrate was investigated. The results showed that the low‐frequency impedance modulus of the composite coating on rusty carbon steel could reached 108 Ω·cm2 order of magnitude after immersing for 480 h in 3.5 wt% NaCl solution. Compared with pure epoxy coating, the phytic acid‐based surface tolerant epoxy coating on the rusty substrate exhibited better corrosion resistance even if with some artificial defects in the composite coating. The protective performance of the composite coating mainly came from the formation of a stable iron phytate chelate in the reaction of phytic acid and rust. For the rusty carbon steel, the original Fe3+ on its surface was also transformed by phytic acid penetrating to the interface between the coating and the substrate. Therefore, a dense film was formed with the reaction of phytic acid and rust on the substrates, and the dense film became a part of the whole paint film, which could improve the corrosion resistance of the surface tolerant coating.

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Electrochemical Evaluation of Corrosion Inhibiting Layers Formed in a Defect from Lithium-Leaching Organic Coatings

Cited by 55 publications

References 35 publications

Active corrosion protection of various aluminium alloys by lithium‐leaching coatings

Active corrosion protection of various aluminium alloys by lithium‐leaching coatings

Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride

Anticorrosive properties and rust conversion mechanism of phytic acid‐based surface tolerant coating

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