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Marine atmospheric corrosion initiation and corrosion products characterization

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Item Summary

Title: Marine atmospheric corrosion initiation and corrosion products characterization
Authors: Li, Shengxi
Keywords: Atmospheric corrosion
carbon steel
salt particle
Raman spectroscopy
Issue Date: Dec 2010
Publisher: [Honolulu] : [University of Hawaii at Manoa], [December 2010]
Abstract: This work focused on NaCl particle-induced marine atmospheric corrosion of carbon steel. Corrosion does not initiate under deliquescent NaCl droplets smaller than a critical size. The mechanisms of corrosion initiation and propagation were identified. The effects of diverse natural environments on the formation and aging of iron oxide products were identified.
Part I On carbon steel that were exposed to Hawaiʻi's marine test sites for 30 min, corrosion did not initiate under small seawater droplets (D < ~30 μm) but occurred under larger droplets. Similarly, laboratory study showed that corrosion did not initiate from small NaCl droplets (D < ~45 μm) formed by the deliquescence of pre-deposited NaCl particles upon exposing to high humidity (RH > 80%), while occurred under larger droplets and sometimes propagated in the form of filiform corrosion. In addition, anodic polarization showed the steel passivated under small NaCl droplets and corroded actively under larger droplets.
In situ and ex situ Raman spectra from the rust species that formed during the corrosion process showed that green rust (GR) formed close to the corrosion pit (i.e., anodic site) while lepidocrocite (γ-FeOOH) clusters precipitated in regions outside of the GR region (i.e., cathodic site). Similarly, the rust formed in Evans' droplet experiments was also indentified as GR and lepidocrocite using In situ Raman spectroscopy.
Part II The corrosion products formed on 1008 steel that were exposed to Hawaiʻi's diverse micro-climates for 1 year period were characterized using micro-Raman analysis, energy dispersive X-ray analysis (EDXA), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis.
Lepidocrocite was identified as the major rust in the surface layers on samples exposed to industrial, rainforest, dry and agricultural test sites, while goethite was detected in the inner rust layers. Akaganeite with high concentration of Cl was also found on the face-down sides of samples from dry and agricultural test sites.
In addition to the dominant rust phases--lepidocrocite in the surface rust layers and goethite in the inner rust layers--more akaganeite was detected on samples from marine test sites, both in the surface and inner rust layers, due to high airborne chlorinity.
Description: Ph.D. University of Hawaii at Manoa 2010.
Includes bibliographical references.
URI/DOI: http://hdl.handle.net/10125/101922
Appears in Collections:Ph.D. - Mechanical Engineering



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