Electrochemical Impedance Studies of Sol-Gel Based Ceramic Coatings Systems in 3.5% NaCl Solution

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Ceramic coatings based on salts like vanadia, ceria, silica and molybdate prepared by sol–gel route are proposed as alternatives to the process involving toxic hexavalent chromate. The surface of the specimens were modified under different conditions and then dipped in a corresponding salt solution prepared via sol–gel method. Electrochemical impedance spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance in 3.5% NaCl. The optimum conditions under which such treatments can provide good corrosion protection to the aluminum substrate were determined. The surface morphologies of the treated samples were investigated using SEM and EDS. Optical microscope was also used to investigate the occurrence of pitting corrosion. The surface preparation prior to sol–gel treatment was found to have a marked effect on the corrosion protection of AA6061 T6.