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

• Proper alternative for zinc phosphate revealing undesirable performance was proposed.
• Cathodic disbonding of epoxy with strontium aluminum polyphosphate (SAPP) was studied.
• EIS and electrochemical noise were used to assess behavior of SAPP in solution phase.
• EIS was used to study the efficiency of SAPP on the resistance to cathodic disbonding.
• The mechanism by which SAPP improves resistance to cathodic disbonding was studied.

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.