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Evolution of corrosion products and metal release from Galvalume coatings on steel during short and long-term atmospheric exposures
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science.ORCID iD: 0000-0002-9453-1333
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science.ORCID iD: 0000-0003-2206-0082
2012 (English)In: Materials Chemistry and Physics, ISSN 0254-0584, Vol. 133, no 1, 419-428 p.Article in journal (Refereed) Published
Abstract [en]

Non-treated Galvalume (55% Al, 43.4% Zn and 1.6% Si by weight) coatings have been studied through a combination of surface, near surface and bulk analysis after exposure at marine conditions, and for comparison also in an urban test site and in successively more complex short-term laboratory exposures. Slightly polished Galvalume surfaces exhibit dendritic aluminum-rich areas with higher Volta potential compared with interdendritic zinc-rich areas. These effects were not observed on bare as-received surfaces due to the overall presence of aluminum oxide. As a result, preferential corrosion occurred initially in interdendritic areas. The zinc release rate followed the same time-dependence as the surface coverage of zinc-containing phases at the marine exposure condition with zinc predominantly released compared to aluminum. Short term laboratory exposures generated the same main phases as formed at marine conditions. This confirms that the evolution of corrosion products and time dependence of zinc release rates can be explained by the uniform formation of less soluble Al2O3, AlOOH and Al(OH)(3) compared to observed zinc-containing phases, e.g. ZnO, zinc hydroxycarbonate and zinc hydroxychloride. The same underlying mechanism is believed to operate also during exposure of Galvalume in the urban site studied.

Place, publisher, year, edition, pages
2012. Vol. 133, no 1, 419-428 p.
Keyword [en]
Galvalume coating, Atmospheric corrosion, Runoff, Corrosion product evolution
National Category
Materials Chemistry
URN: urn:nbn:se:kth:diva-34118DOI: 10.1016/j.matchemphys.2012.01.054ISI: 000302032300064ScopusID: 2-s2.0-84857786407OAI: diva2:419116
Knut and Alice Wallenberg Foundation
QC 20120424Available from: 2011-05-31 Created: 2011-05-25 Last updated: 2012-04-24Bibliographically approved
In thesis
1. Quantified In Situ Analysis of Initial Atmospheric Corrosion: Surface heterogeneity, galvanic effects and corrosion product distribution on zinc, brass and Galvalume
Open this publication in new window or tab >>Quantified In Situ Analysis of Initial Atmospheric Corrosion: Surface heterogeneity, galvanic effects and corrosion product distribution on zinc, brass and Galvalume
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interaction of the surface of a pure metal or an alloy with the surrounding atmosphere occurs in a highly complex interfacial regime. During atmospheric corrosion this interfacial regime involves the metal surface, often covered by a naturally formed oxide layer of a few nanometers thickness; an aqueous adlayer, typically with a thickness of a few to a few tens of nanometers, and the atmosphere from which airborne particles, oxygen, and gaseous pollutants dissolve into the adlayer and influence the atmospheric corrosion process.

This thesis work is mainly concerned with the initial atmospheric corrosion of zinc and brass induced by carboxylic acids (120 parts per billion of formic, acetic, or propionic acid) in laboratory air with 90% relative humidity. This model system has been chosen to mimic indoor corrosion with carboxylic acids as major corrosion stimulators. The study forms part of a broader research program with the ultimate goal to provide a computer model of the early stages of atmospheric corrosion of copper, zinc and copper-zinc alloys, induced by carboxylic acids. Particular emphasis has been given to identify and quantify the corrosion products formed and to determine their lateral distribution over the corroding surface. This has been accomplished through a multi-analytical approach in which two main techniques are infrared reflection absorption spectroscopy (IRAS) which can identify and quantify corrosion products with a relative accuracy of about 10%, and confocal Raman microspectroscopy (CRM) which can identify and resolve corrosion products with a surface lateral resolution of better than one micrometer.

The corrosion products identified on pure zinc are zinc oxide (ZnO) and various forms of Zn-carboxylates. On brass, the main corrosion products identified are a cuprite (Cu2O)-like phase and various forms of Zn-carboxylates. For pure zinc and brass the formation rates of corrosion products in presence of the investigated acids depend, among others, on their deposition velocity and acid strength. The interaction of pure zinc and brass with humidified air containing carboxylic acids follows two spatially separated main pathways: a proton-induced dissolution of metal ions followed by the formation of oxides, and a carboxylate-induced dissolution followed by the deposition of metal carboxylates.

When applying this multi-analytical approach, it has been possible to distinguish between anodically and cathodically active areas for brass, but not for pure zinc. Galvanic effects have been shown to play a significant role during the initial corrosion of brass. 

Further evidence of the selective formation of corrosion products has been found when exploring the more complex heterogeneous surface of Galvalume, a commercial aluminum-zinc alloy coating. This material has been exposed to humidified laboratory air with additions of carbon dioxide (CO2) and sodium chloride (NaCl) and to a marine atmospheric environment. Initiated in the interdendritic zinc-rich areas, a uniform aluminum oxide (Al2O3) layer is formed. This oxide exhibits an inhibiting effect on the subsequent formation of other corrosion products, including aluminum oxyhydroxide (AlOOH), aluminum hydroxide (Al(OH)3), ZnO, zinc hydroxycarbonate and zinc hydroxychloride.


Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 68 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2011:40
Atmospheric corrosion; Zinc; Brass; Galvalume; In Situ; Quantification.
National Category
Materials Engineering
urn:nbn:se:kth:diva-34096 (URN)978-91-7501-012-0 (ISBN)
Public defence
2011-06-14, D3, Lindstedtsvägen 5, KTH, Stockholm, 14:00 (English)
Swedish Research Council
QC 20110607Available from: 2011-06-07 Created: 2011-05-25 Last updated: 2011-06-07Bibliographically approved

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