A Comparison of the Corrosion Response of Zinc-Rich Coatings with and Without Presence of Carbon Nanotubes Under Erosion and Corrosion Conditions

Electrochemical impedance spectroscopy tests were conducted on carbon nanotubes (CNTs) enriched zinc-rich epoxy coating and a commercial zinc-rich coating. Coating performances were examined after exposure to a corrosive environment (a CO₂ saturated aqueous electrolyte with 2,000 ppm chloride concentration and pH 3.5 to 5.3) at an elevated temperature of 60°C. The coatings’ response after solid particle impingement erosion was also studied. Equivalent circuit models were proposed to elucidate the degradation mechanisms of the zinc-rich coatings under the synergic effect of corrosion and erosion. Results showed that the addition of CNTs into zinc-rich coatings provided better barrier protection for the steel substrate than traditional zinc-rich coatings in the noneroding environment. However, the CNT-filled zinc-rich epoxy coatings did not provide adequate protection when the coated specimens were exposed to an erosive and corrosive environment. CNTs could help with maintaining continuous electrical paths within zinc-rich coatings; however, the conductivity of the coating decreased significantly when zinc particles were partially oxidized. When defects caused by erosion are present in the coatings, CNTs may form galvanic couples with the steel and thus increase the corrosion rate of steel substrate.