Morphology and Composition of Corrosion Products Formed on Painted Mild Steel in Marine Atmosphere after 4, 8 and 12 Months Exposure

Corrosion is one of the few chronic issues pertaining to marine structures. It is significant to characterize the corrosion products formed on the metal surface in the order to establish the nature of corrosive attack and for the development and improvement of the material’s corrosion resistance. In this study, characterization of the corrosion products formed on painted mild steel was carried out. Painted mild steel test panels were exposed to marine atmosphere in Karachi, Pakistan according to ISO 8565 norm for a period of 12 months. Morphology and composition of the corrosion products formed after four, eight and twelve months of exposure were studied by scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) analysis. Lepidocrocite (?-FeOOH) was found as major component of corrosion products formed after 4 and 8 months of exposure. After 12 months of exposure corrosion product obtained was composed of lepidocrocite (?-FeOOH), goethite (?-FeOOH) and magnetite (Fe3O4). Changes in the morphology and size of lepidocrocite (?-FeOOH) formed after 4, 8 and 12 months of exposure were noticed. Presence of very harmful form of rust that is lepidocrocite could be realted to very high corrosivity of the marine atmosphere of Karachi, Pakistan. The conversion of lepidocrocite to goethite (?-FeOOH) was also noticed.