An electrochemical study of zinc-containing epoxy coatings on mild steel

Abstract

A comparative electrochemical study has been carried out between conventional zinc-rich and novel zinc-containing paints. To study the cathodic protection performance of these coatings an assessment method based on a galvanic couple was employed. Current and potential were monitored with immersion time in 3.5% NaCl. The zinc-rich paint offered cathodic protection for about 7 days compared with 40 days for the new paint. However, the steel coupled with the zinc-rich remained corrosion free for a further period. This was probably due to the inhibitive effect of zinc salts deposited at the cathode. Thereafter a reversal in polarity was obtained once rust formed. Thus it is concluded that established cathodic protection criteria cannot be solely used to assess the protection properties of zinc-containing paints. Electrochemical impedance spectroscopy was also used to study the state of the coating with time. Diffusion parameters indicated that the new paints were covered with a lesser amount of corrosion products.