Corrosion Study of Zinc-Rich Epoxy Ester Paints for Cold Galvanizing of Mild Steel

Abstract

This study aims at producing zinc (Zn)-rich epoxy ester (EE) paints for cold galvanizing of mild steel. Zn particles with a narrow particle size distribution of 1μm to 5μm were dispersed in EE resin by vacuum centrifuge mixer. The effect of Zn concentration in EE resin on cathodic protection ability of resulting paints was studied. Galvanic corrosion protection ability of the paints was studied in 3.5% (mass ratio) NaCl solution using electrochemical characterization techniques such as open circuit potential (OCP), Tafel analysis and electrochemical impedance spectroscopy (EIS). The results showed that cathodic protection ability depends on the loading of Zn particles in the EE and it is effective when the mass fraction of Zn was equal to or exceeded 90%. At this concentration, Zn particles developed interconnecting conducting networks as determined by scanning electron microscopy (SEM) which were responsible for the galvanic effect of the coating. The EE paints developed at mass ratio below 90% behaved as a conventional organic barrier coating and did not show any cathodic protection effect due to the lack of contact between Zn particles. The EE paint showed good resistance to abrasion and wear. The electrochemical behavior of Zn-rich EE paint (with cathodic protection ability) developed in this study was compared with commercial acrylic-based "cold galvanized paint"(Roval). EE-based "cold galvanized paints"were found to be more protective and long lasting compared to commercial "cold galvanized paints".