Corrosion behaviour of nano structured sol-gel alumina coated 9Cr-1Mo ferritic steel in chloride bearing environments

摘要

A stable boehmite sol was synthesized using Al-isopropoxide as a precursor in an appropriate ratio with water. Afterwards, the 9Cr-1Mo steel specimens were coated with prepared boehmite sot by dip coating technique. AFM analysis of the coated specimens confirmed the presence of nano sized particles (8-12 nm) in the coating. Electrochemical measurements like potentiodynamic and potentiostatic polarisations, electrochemical impedance spectroscopy (EIS) in different concentrations of Cl- ions indicated that the sol-gel alumina coating is able to make an appreciable improvement in the corrosion resistance of the base alloy. It was also observed that the sol-get coatings can control the pitting attack up to a certain extent in 100 ppm Cl- containing solution. However, the coatings become susceptible towards pitting attack in 200 ppm Cl- bearing solution. The SEM micrographs of the corroded surfaces revealed the occurrence of severe pitting on the uncoated specimens in 100 ppm Cl- solution and also on the coated specimen in 200 ppm Cl- solution.