Effect of zinc-free phosphate-based anticorrosion pigment on the cathodic disbondment of epoxy-polyamide coating

In the field of protective coatings, zinc-free pigments are proposed as promising anticorrosion compounds due to their excellent environmentally-friendly profile. In this paper, cathodic disbonding performance of a solvent-borne epoxy primer incorporating strontium aluminum polyphosphate (SAPP) as a zinc-free phosphate-based anticorrosion pigment was investigated. Regardless of the applied potential, the presence of SAPP in the coating formulation caused slower growth of the delamination area in comparison to ZP. According to the data obtained from EIS and SEM/EDX, this behavior was attributed to locally controlled pH and the precipitated film restricting active zones available for electrochemical reactions.