Barrier and sacrificial protection mechanisms of zinc rich primers

Abstract

A specific type of Zinc-Rich Primer was scratched and exposed in salt fog chamber for various exposure times up to 1,000 hours. The corrosion products that developed within the scratched region were studied by optical microscopy, scanning electron microscopy, and Electrochemical Impedance Spectroscopy. Bode plots were used to obtain the total resistance of the coating by salt spray exposure time. The results suggest that the mechanism of protection of zinc rich primer may not be simply as only sacrificial action followed by only barrier action, but rather an iteration of these two mechanisms exist. Although at very short times, prior to deposition of zinc corrosion products in the scratch, sacrificial action is the only mechanism of protection, once the corrosion products start to form there is a conjunction of the two protection actions with one dominating from time to time. This dual protection mechanism continues until all the available free zinc within the throwing power distance of the scratch has been consumed, at which point only barrier protection remains in action.