2000 Volume 73 Issue 6 Pages 282-289
The corrosion protection ability and degradation behavior of various organic coatings in aqueous solutions were investigated by electrochemical parameters, specifically coating film resistance (Rf) determined by electrochemical impedance spectroscopy (EIS) and current density (i) determined by scanning vibrating electrode technique (SVET). Clear paints of epoxy (EP) and polyester (PES) were used in this study. These paints were applied on mild steel substrates at different coating film thicknesses, as follows : 20, 60,100 and 150 μm. Paint coated steel samples were immersed in aqueous 3% sodium chloride (NaC1) and 100 ppm NaC1 solutions for EIS and SVET measurements, respectively. Results of experiments showed that Rfgenerally decreases with increasing immersion time for all coating thicknesses. The upper limits of Rf were increased higher with increasing coating thickness for both EP and PES coated steels. Moreover, the rate of deterioration of Rf of coating decreased with increasing coating film thickness. EP-based clear coating was observed to have the superior protection ability in both immersing solutions. A good correlation between coating film thickness and protection ability of coatings to steel substrate was practically observed by EIS and SVET measurements.
