Study of the Corrosion Resistance of Benchmark Coatings Using Electrochemical Impedance Spectroscopy
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The corrosion resistance of polymer-coated carbon steel exposed to corrosive environment of 3.5% NaCl solution (weight fraction) at ambient conditions was evaluated using electrochemical impedance spectroscopy (EIS) technique. The analysis of impedance models involved using suitable electrical equivalent circuit that consists of passive electrical components. The impedance results suggested that there were two types of impedance models are applicable to the tested samples, one for intact coating and the other one for damaged or non-existent coating. Results of laboratory experiments indicated that water uptake for the intact coating was negligible and that polarization resistance was very high of orders higher than 10^11 Ω cm^2 which indicates excellent corrosion protection. The obtained values also indicated that the corrosion resistance depends on the coating thickness. On the other hand, for the damaged coatings and non-coated metal, impedance models suggested the existence of a Warburg element referring to the metal diffusion and lower polarization resistance of orders lower than 10^7 Ω cm^2 which indicates that corrosion reactions took place. This conclusion was confirmed using microscopic observation of corrosion products and change in defect depth using 3D profile surface analysis. Experimental results for damaged coating indicated that the depth of the defect influences the corrosion rate but all damaged coatings follow the same impedance model.
Ghannam, Safwan (2015). Study of the Corrosion Resistance of Benchmark Coatings Using Electrochemical Impedance Spectroscopy. Master's thesis, Texas A & M University. Available electronically from