Abstract
Electrochemical impedance spectroscopy (EIS) in the l00 kHz-10 mHz frequency range was employed as the main electrochemical technique to study the corrosion protection behaviour of 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 dc 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 become weak, the substrate steel is still protected against corrosion due to the barrier nature of the ZRP film reinforced by Zn.
Highlights
The application of zinc-rich primers on ferrous substrates is a very efficient method of anticorrosion protection
Electrochemical impedance spectroscopy (EIS) in the l00 kHz - 10 mHz frequency range was employed as the main electrochemical technique to study the corrosion protection behaviour of zinc rich epoxy paint in 3% NaCl solution
Even when the cathodic protection effect by Zn dust become weak, the substrate steel is still protected against corrosion due to the barrier nature of the zinc-rich paints (ZRPs) film reinforced by Zn
Summary
The application of zinc-rich primers on ferrous substrates is a very efficient method of anticorrosion protection. For solvent-based zinc-rich paints (ZRPs), it seems to be established that, at least at the beginning of immersion, zinc particles provide a cathodic protection of the steel substrate [1,2]. The zinc dust (spherical or lamellar shape, or a combination of both) is dispersed in an inorganic (usually orthosilicates) or organic binder (usually epoxies) [8] These particles must be in electrical contact between themselves and the metallic substrate in order to ensure a well-established electrical conduction within the coating. The aim of this work was to study the protective mechanisms of a single coat solvent-based zinc-rich paints ZRPs. Primer coating panels were applied on sandblasting steel and were studied when immersed in artificial 3% NaCl solution. The main objective is to propose a model of EIS results accounting for the zinc particles distribution and mechanisms of water entrance within the coating
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