Depth profiles of akaganéite, goethite and maghemite on A1010, HPS and weathering steel panels after wet-dry corrosion tests

ABSTRACT

The panels of high chromium steel (A1010), high-performance steel (HPS 70W) and weathering steel (WS) were exposed to accelerated salt-spray corrosion test for 1 week and to less aggressive test for additional 13 weeks. After the tests, the corrosion products formed were extracted layer after layer and examined as a function of their depth with Mössbauer transmission spectroscopy. In the case of A1010 steel, the amounts of goethite (α-FeOOH) and akaganéite (β-FeOOH) were almost equal along the depth of the corroded layer up to ∼20 μm. The rust layers on HPS and WS panels were much thicker, respectively up to ∼0.6 mm and ∼1 mm, poorly adherent and contained mostly akaganéite near the metal–rust interface, α-FeOOH increasingly further away, and – after long exposure – also up to 20% Fe as maghemite (γ-Fe₂O₃). Formation of β-FeOOH near the interface was promoted by chloride concentrated by spray-dry cycles. The microstructure and depth profiles of identified species, and especially the role of β-FeOOH, are discussed.

KEYWORDS:

• Corrosion
• steels
• wet-dry test
• interfaces
• Mössbauer spectroscopy
• depth profiling
• akaganéite
• goethite
• maghemite
• chloride
• chromium

Acknowledgements

The early phase of this work was supported by Ministry of Transportation Ontario under Highway Infrastructure Innovations Funding Program, that funds research at Ontario colleges and universities to encourage basic and applied research in transportation and infrastructure engineering, and in parts by ArcelorMittal Steel and Canadian Institute for Steel Construction. The author thanks A. Coomarasamy, D. Lai, S. Ramamurthy, M. Walzak and B. Kobe for providing him the wet-dry tested steel panels and their interest in our Mössbauer analyses.

Disclosure statement

No potential conflict of interest was reported by the author.