New Formulation of Anticorrosive Waterborne Epoxy Coatings for SAE 1010 Steel Protection

This work presents the formulation and characterization of waterborne epoxy paints designed for SAE 1010 steel protection with three commercial phosphate-based anticorrosive pigments: zinc molybdophosphate (ZMP), zinc aluminum polyphosphate hydrate (ZAPP) and zinc calcium aluminum strontium orthophosphate polyphosphate silicate hydrate (ZCPP). The anticorrosive efficacy of these pigments was evaluated by electrochemical tests in 0.1 M NaCl. Corrosion potential measurements revealed that ZCPP and ZMP shifted the corrosion potential of steel toward more positive values, while ZAPP shifted it to more negative values. Linear polarization curves showed that all three pigments exhibit a good anticorrosive performance, with inhibition efficiency higher than 90%. SEM-EDX analysis of the samples exposed to pigment dispersions in the corrosive medium supported these electrochemical findings. All pigments resulted in a Fe/O ratio higher than the obtained for the reference steel sample exposed to the 0.1 M NaCl solution without pigment addition, indicating a reduction in corrosion products formation. The epoxy paints were formulated as a typical two-pack system, and each part was prepared separately in a high-speed disperser. The paints were assessed through accelerated tests (salt spray and humidity chambers), electrochemical tests (ionic resistance and electrochemical impedance spectroscopy) and service tests. The results suggest that the three waterborne epoxy paints performed really well, maintaining their protective qualities after 700 days of exposure in service conditions.