Electrochemical behaviour of zinc-rich epoxy paints in 3% NaCl solution

Electrochemical impedance spectroscopy (EIS) in the 100 kHz-1 mHz frequency range was employed as the main electrochemical technique to study the corrosion protection behaviour of a zinc-rich epoxy paint in 3% NaCl solution. The EIS results obtained at the open-circuit corrosion potential have been interpreted using a model involving the impedance of particle to particle contact to account for the increasing resistance between zinc particles with immersion period, in addition to the impedance due to the zinc surface oxide layer and the electrical resistivity of the binder. Galvanic current and de potential measurements allowed us to conclude that the cathodic protection effect of the paint takes some time to be achieved. The loss of cathodic protection is due to a double effect: the decrease of the Zn/Fe area ratio due to Zn corrosion and the loss of electric contact between Zn to Zn particles. Even when the cathodic protection effect by Zn dust became weak, the substrate steel is still protected against corrosion due to the barrier nature of the ZRP film reinforced by Zn corrosion products. Copyright (C) 1996 Elsevier Science Ltd