S. Touzain

Characterization of zinc-rich powder coatings by EIS and Raman spectroscopy

In this work, the protective mechanisms of a single coat zinc-rich powder coating are examined. Powder coating panels were applied on phosphatized steel and were studied when immersed in artificial sea water with flowing conditions. Open circuit potential and electrochemical impedance spectroscopy measurements were recorded to study changes in the coating properties with the exposure time. Moreover, Raman spectroscopy was used to analyze zinc corrosion products. This study reveals that the behavior of powder coating systems is different from solvent-based zinc-rich paints (ZRP). This is mainly attributed to the low porosity of powder coatings, due to their high wetting ability, which insulates some of the zinc particles. However, cathodic protection is active and provides the sealing of the coating pores. Finally, it is found that the barrier effect is higher than the one usually observed with solvent-based ZRP.

Zinc-rich powder coatings corrosion in sea water: influence of conductive pigments

Abstract The effect of addition of conductive pigments like carbon blacks on the corrosion behavior of zinc-rich powder paints coated steel in artificial sea water was investigated. Open circuit potential measurements were used to characterize the cathodic protection ability and duration. Micro-Raman spectroscopy analysis was performed in order to identify the corrosion products and to follow the penetration of the solution inside the coatings. Two different effects were pointed out: an increase of the porosity induced by carbon addition and a galvanic action between zinc and carbon pigments. The performance of the powder coatings, strongly improved if the carbon amount is sufficient, was compared to the one reported for solvent-based zinc-rich paints.

Characterization of deposits by direct observation and by electrochemical methods on a conductive transparent electrode. Application to biofilm and scale deposit under cathodic protection

Abstract A new device is proposed where the electrode is a transparent electrode in modified SnO 2 . With this new electrode the reduction of oxygen occurs in a way similar to a gold electrode. Simultaneously the oxygen current is recorded versus time and picture of the interface itself is taken with a digital camera through the electrode. An image analysis is performed to determine the coated area and the number of objects by surface unit. Under cathodic protection, the reduction of oxygen induces an increase of the interfacial pH and then formation of scale deposit. The usual chronoamperometric analysis was completed by an in situ observation of the scale deposit. In natural water the biofilm development was studied by electrochemical method to determine the biofilm thickness and this analysis is completed by a direct observation through the electrode. A good correlation between the two techniques was found.