ABSTRACT
The electrochemical techniques of electrochemical impedance and stepwise polarisation have been used to study the permeation of NaCl solution through thin (20–25 μm) paint films (of the acryl, alkyd, epoxy and nitro types. Coating capacitance and pore resistance were monitored with immersion time (up to 60 days) in 3% NaCl solution and their trends evaluated; the water uptake and the conductive pathways in the paint films were determined. Polarisation curves were recorded for bare and painted electrodes; the percentage decrease in the dissolution current of the steel substrate and the porosity of the protective films were calculated. The results were interpreted in terms of a model in which at first the solution rapidly penetrates the fissures and the capillaries existing as defects in the coating followed by a diffusion of solution into the polymer. All experimental results were correlated with the protective properties of paint coatings.
