The Effect of the Dry Film Thickness, Temperature, and Electrolyte on the Cathodic Current of Painted Steel

Abstract

The properties of cathodically polarized painted steel specimens have been examined by determining the change in the net cathodic current and the paint film resistivity as a function of temperature, dry film thickness, and electrolyte. The net (external) cathodic current is found to increase strongly with increasing temperature. This is most probably due to a decrease in resistivity. The activation energy of charge transport through the paint films has been determined and was found to vary between 51 and 227 kJ/mol. The resistivity of paint films seems to increase with increasing thickness. The change in resistivity was found to take place mainly below a “critical thickness” of about 100 μm. For short times of exposure,i.e., 10–20 days, the net cathodic current and the paint film resistance are found to be independent of the type of electrolyte for paint films with a dry film thickness above or equal to 100 μm.