AN ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY STUDY OF ZINC RICH PAINTS ON STEELS IN ARTIFICIAL SEA-WATER BY A TRANSMISSION-LINE MODEL

Electrochemical impedance spectroscopy (EIS) in the 50 kHz-1 mHz frequency range was applied to characterize the corrosion protection behaviour of zinc rich ethyl silicate paints (ZRP) on steel in artificial sea water. The most accurate description of the experimental impedance spectra at the open circuit potential as a function of exposure time for different coating thicknesses, was obtained by introducing a dynamic system analysis based on the transmission line model and assuming cylindrical pores in the coating structure for the corresponding transfer function. Characteristic coating parameters of this type of ZRP during the galvanic protection period derived from nonlinear fit routines at different immersion times correlate well with the gradual coating deterioration. Results can be interpreted in terms of corrosion processes going on extensively through pores and cracks in the relatively thick ZRP coatings.