Studies on the repassivation behavior of aluminum and aluminum alloy exposed to chromate solutions

Chidambaram, Dev; Vasquez, M. Jaime; Halada, Gary P.; Clayton, Clive R.

doi:10.1002/sia.1507

Cited by 38 publications

(32 citation statements)

References 30 publications

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“…The hexavalent chromium present in the chromate conversion coating would be able to migrate to the defects in the conversion layer where it would be reduced to Cr(III), forming a protective layer on the defect. 57,60,61 However, here, the post-treatment brings also lanthanum as a corrosion inhibitor to the TCP layer, which is present on the surface and in the coating bulk as evidenced by Tof-SIMS depth profiles (Figure 2d). Rare-earth inhibitors, particularly cerium and lanthanum, are among the most studied inhibitors for replacement of hexavalent chromium.…”

Section: Discussionmentioning

confidence: 84%

Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Ely

Światowska

Seyeux

et al. 2017

J. Electrochem. Soc.

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The effects of post-treatment applied on Trivalent Chromium Protection (TCP) coatings deposited on aluminum alloy 2024-T3 was studied by electrochemical and surface analytical techniques: X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The aim of the post-treatment was to improve the corrosion resistance of the TCP coating. To understand the influence of the post-treatment, using a bath containing H 2 O 2 and a lanthanum salt as an inhibitor, our approach was to study the effect of these two components separately. It was found that the improved corrosion protection provided by the post-treated TCP was related to a synergetic effect of the two components. XPS and ToF-SIMS analyses showed that (i) the thickness of the TCP coating is not modified by the post-treatment, (ii) lanthanum is present on the surface and in the bulk of the TCP and (iii) is found in very small amount only on the extreme surface. The total concentration of Cr(VI) (oxide/hydroxide) was estimated to be below 0.1 wt% in the post-treated TCP layer. It was concluded that lanthanum plays a significant role in improving the coating density and homogeneity and has a beneficial effect on the TCP coating cracking as observed by Scanning Electron Aluminum alloys are used for aerospace applications for their low weight and good mechanical properties.1-3 To improve the corrosion properties of aluminum alloys and to provide good paint adhesion, the first layer of coating applied on the aluminum alloy surface used to be a chromate conversion coating (CCC).4-6 However, hexavalent chromium used in the CCC coatings is highly toxic, 4,7 its use is very much restricted in Europe 8 and the United States 9 and will be forbidden by 2024 by the European Community with respect to the Registration, Evaluation, Authorization and Restriction of Chemicals (REACh).8 Therefore, new conversion coatings have been developed, and one of the most promising solutions is the Trivalent Chromium Protection coating called also as the Trivalent Chrome Process (TCP).10-14 TCP conversion coatings are formed by immersion in a solution containing Zr 4+ , Cr 3+ and F − ions, at a pH between 3.8 and 4.0. As it has already been widely discussed, the coating formation mechanism occurs by multiple chemical steps. 10,11,13,[15][16][17] The initial step involves dissolution of the aluminum oxide layer by fluorides. The removal of the oxide layer exposes the metal surface where cathodic reactions take place. Oxygen reduction reaction, and possibly hydrogen discharge, which counterbalance aluminum oxidation, consume protons and causes a pH increase at the interface between the metallic substrate and the solution, as measured by Li et al. 15 The high pH favors the precipitation of ions present in the solution, forming a hydrated layer of zirconium and chromium oxide. The thickness of the TCP layer is usually of the order of 100 nm, depending on the nature of the aluminum alloy, the concentration of the solution and the immersion time.11,12,18 ...

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Section: Discussionmentioning

confidence: 84%

Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Ely

Światowska

Seyeux

et al. 2017

J. Electrochem. Soc.

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“…The corrosion resistivity was efficiently improved due to CrO À 4 ions forming an oxide layer on the aluminum surface. Chidambaram et al [2] demonstrated reparation of scratches in chromate conversion coatings. A physical barrier was built by an Al-Cr complex and a repassivation of the flawed metal surface was observed.…”

Section: Introductionmentioning

confidence: 99%

Application of Inhibitor‐Loaded Halloysite Nanotubes in Active Anti‐Corrosive Coatings

Fix

Andreeva

Lvov

et al. 2009

Adv Funct Materials

255

138

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Halloysite particles are aluminum‐silicate hollow cylinders with a length of 0.5–1 µm, an outer diameter of ca. 50 nm and a lumen of 15 nm. These nanotubes are used for loading and sustained release of corrosion inhibitors. The inhibitor is kept inside the particles infinitely long under dry conditions. Here, halloysite nanotubes filled with anticorrosive agents are embedded into a SiOx–ZrOx hybrid film. An aluminum plate is dip‐coated and immersed into 0.1 M sodium chloride aqueous solution for corrosion tests. A defect in the sol–gel coating induces pitting corrosion on the metal accompanied by a strong anodic activity. The inhibitor is released within one hour from halloysite nanotubes at corrosion spots and suppresses the corrosion process. The anodic activity is successfully restrained and the protection remains for a long time period of immersion in NaCl water solution. The self‐healing effect of the sol–gel coating doped with inhibitor‐loaded halloysite nanotubes is demonstrated in situ via scanning vibrating electrode technique measurements.

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“…Recently, "self-repairing" coatings have been devised which can respond to such damage. For example, CCCs contain a reservoir of labile chromate species that can migrate to scratches and help re-form the protective barrier 14 (Figure 15.3).…”

Section: Tribological Damagementioning

confidence: 99%

The Intersection of Design, Manufacturing, and Surface Engineering

Halada¹,

Clayton²

2012

Handbook of Environmental Degradation of Materials

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Studies on the repassivation behavior of aluminum and aluminum alloy exposed to chromate solutions

Cited by 38 publications

References 30 publications

Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Application of Inhibitor‐Loaded Halloysite Nanotubes in Active Anti‐Corrosive Coatings

The Intersection of Design, Manufacturing, and Surface Engineering

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