Pore resistance limitations from EIS data for the evaluation of organic DTM coatings based on a self-crosslinking acrylic resin

Abstract

Self-crosslinking Water-based acrylic resins are currently widely used in the formulation of paints for the protection of materials exposed to atmospheric corrosion. These resins, given their "self-crosslinking" designation, initiate their crosslinking process once they are applied on a previously prepared surface. It is expected that with time they will increase their protection, due to their continuing self-crosslinking mechanism.
 In this work, metallic plates coated with these resins were evaluated under simulated salt neutral spray (ASTM B117). The coating degradation processes were monitored by Electrochemical Impedance Spectroscopy (EIS) and visual inspection, according to ASTM D610 and ASTM D714, aiming to identify and quantify the appearance of blistering and corrosion products. The results revealed rapid drops in pore resistance (Rpo) for systems exposed to neutral salt spray (NSS), saline-acidic or acidified conditions, which coincided with the formation of blisters. On the contrary, the systems in the wet chamber showed an increase in the Rpo, which evidences from an electrical point of view a greater opposition to the passage of current. Notwithstanding, still the appearance of blisters on the coated surfaces was observed.