In situ Raman Spectroscopic Study of NaCl Particle-Induced Marine Atmospheric Corrosion of Carbon Steel

Abstract

The study of NaCl particle-induced atmospheric corrosion is facilitated by in situ Raman spectroscopic analysis through real time identification of corrosion products. Droplet formation on carbon steel by the deliquescence of pre-deposited NaCl particles that were exposed to high relative humidity (RH) (>80%), and corrosion initiation under the droplets were observed using an optical microscope. Pitting initiated within several minutes under the NaCl droplets. In situ and ex situ Raman spectra from the various rust species that formed during the corrosion process show that green rust (GR) formed close to the corrosion pit (i.e., anodic site) while lepidocrocite (γ-FeOOH) clusters precipitated outside of the GR region. A small amount of magnetite (Fe3O4) was also detected, mostly in the transitional region from GR to lepidocrocite. Upon exposure to an ambient atmosphere, GR transformed to lepidocrocite. This study confirms that the initial rust formed in NaCl particle-induced marine atmospheric corrosion of carbon steel is GR and lepidocrocite. While revealing the initiation mechanisms of NaCl particle-induced marine atmospheric corrosion of carbon steel, this study also provides insights for future studies involving wet-dry cycle exposures, which are more akin to the real atmospheric corrosion process.

A Micro-Raman Spectroscopic Study of Marine Atmospheric Corrosion of Carbon Steel: The Effect of Akaganeite

“…1a) indicates the presence of lepidocrocite. 9,10,21 Band decomposition enabled the separation of contributions from goethite which are at 241, 297, 391, 415 (shoulder (sh)), 478, 546 and 682 cm −1 , those from lepidocrocite which are at 248, 335 (sh), 375, 515 and 641 cm −1 and those from akaganeite which are at 311 and 720 cm −1 . [18][19][20]28 The Raman spectrum ( Additional Raman spectra from more exfoliated regions on the face-up side of the sample S1 show similar results as shown in Fig.…”

“…The major constituents of the corrosion products that form during atmospheric corrosion on steel are lepidocrocite (γ-FeOOH), goethite (α-FeOOH), akaganeite (β-FeOOH) and feroxyhite (δ-FeOOH), 6,7 among which goethite is the most stable phase. 8 Lepidocrocite is believed to form in the initial stages of atmospheric corrosion [9][10][11] and transform to goethite in certain conditions. Akaganeite is formed only in the presence of salinity 7 and was widely found in marine environments 12,13 and in chloride-rich solutions [14][15][16] and soils.…”

“…[17][18][19][20] Raman spectroscopy, as a powerful non-destructive spectroscopic technique, has been successfully used for the identification of pure iron oxides [21][22][23][24] and steel corrosion products. [8][9][10]12,[14][15][16][17][18][19][20][24][25][26][27][28][29][30] Its ability to distinguish between the various phases of iron oxides and oxyhydroxides, which are normally found in atmospheric corrosion products, is extremely helpful in the identification of corrosion products.…”

Aerosol Salt Particle Deposition on Metals Exposed to Marine Environments: A Study Related to Marine Atmospheric Corrosion

“…The Fe(OH) 2 is not stable in oxygenated aqueous media and will further react to form other iron oxides or oxyhydroxides. [42][43][44] Fe → Fe 2+ + 2e Coconut Island moderate marine test site.-In contrast to the KI test site, less salt particles and corroded areas were found on 1018 steel samples that were exposed to the CI test site. Possible reasons were the absence of shore-breaking waves, and the relatively low wind velocity which was approximately only 2.2 m/s (during sample exposure) that is below the critical value for salt-particle generation from ocean waves.…”

In situ pH responsive fluorescent probing of localized iron corrosion

“…12c). This suggests that these brown rust is cFeOOH [41,42], which is a stable reaction product in this condition.…”