THE CORROSION PROTECTION OF STEEL IN SEA-WATER USING ZINC-RICH ALKYD PAINTS - AN ASSESSMENT OF THE PIGMENT-CONTENT EFFECT BY EIS

The effect of pigment volume concentration (c(v,p)) on the corrosion resistance properties of zinc-rich paints (ZRP) has been investigated using electrochemical impedance spectroscopy (EIS) combined with cathodic protective potential measurements. Painted naval steel samples were studied during the exposure to artificial sea water for up to 45 days. ZRP coatings were prepared employing zinc pigment content in the 77-88% concentration range. Results show clearly that samples prepared with c(v,p), values >86% deteriorated more rapidly than panels painted using a relatively lower pigment content. The corrosion behaviour of painted steel samples was found to be practically independent of c(v,p), within the 78-86% range. The cathodic protection effect in action during 45 days' immersion time arises because these alkyd resin paint coatings behave like a porous active surface layer. Under aggressive conditions similar to those afforded by the artificial sea water, zinc-rich alkyd coatings containing c(v,p) values within the 78-86% range seem to provide longer corrosion protection to steel substrates than other types of ZRP commonly used.