Abstract
Epoxy/polyamide coatings were loaded with different mixtures of strontium aluminum polyphosphate (SAPP) and zinc aluminum phosphate (ZPA) pigments. Moreover, a coating containing zinc phosphate (ZP) was prepared as a reference sample. The coatings were applied on St-37 steel substrates and then were exposed to 3.5wt% NaCl solution up to 35 days. The corrosion inhibition properties of the pigments extracts were studied on bare steel samples by a potentiodynamic polarization technique after 24h immersion. The morphological properties and corrosion resistance of the coatings were investigated by scanning electron microscope (SEM), optical microscope, electrochemical impedance spectroscopy (EIS) and salt spray tests.Results showed that addition of SAPP, ZPA and ZP to coatings caused a decrease in number of blisters and holes after exposure to corrosive electrolyte. The corrosion resistance of coatings was improved using certain loadings of SAPP, ZPA and ZP pigments. The greatest improvement of the corrosion resistance was observed for the coatings loaded with 100% ZPA and mixture of 20:80 of SAPP:ZPA. Results revealed that SAPP did not improve corrosion resistance of coating like ZPA. It was found that replacing ZPA with high loadings of SAPP did not cause higher coating corrosion protection properties. The results obtained in this work revealed that both pigments solubility and corrosion inhibition are important parameters affecting corrosion resistance of the coatings.
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