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The application of coatings comprising anticorrosive pigments or corrosion inhibitors has been one of the most prevalent methods of mitigating metal corrosion. Due to growing environmental concerns, efforts are focused on developing more sustainable coating formulations. This study aims to develop inhibitive pigments based on the natural biopolymer tannin through metal complexation, as an effective and eco-friendly alternative to conventional inhibitive pigments in epoxy coatings for steel protection in marine environments. Initial screening of metal cations for tannin complexation was conducted via steel immersion tests in 3.5 wt% NaCl solution. The potentiodynamic polarization tests revealed that all inhibitors including pure tannin and a combination of tannin with metal cations acted as mixed-type corrosion inhibitors. It was found that the combination of tannin with Zn2+ and Ce3+ both exhibited outstanding corrosion inhibition performance. After a 14-day immersion period, the inhibition efficiency reached 79.0% and 74.0% respectively, compared to 53.9% for pure tannin. The more uniform formation of iron-tannin complexes and the co-deposition of metal hydroxides/oxides are believed to contribute to a synergistic effect, as confirmed by ATR-FTIR and SEM-EDS analysis. Further, considering both inhibition efficiency and eco-friendliness, the cerium(III)-tannin complex (CeTA) pigment was successfully synthesized and incorporated into anticorrosive epoxy coatings. Salt spray exposure and electrochemical impedance spectroscopy (EIS) measurements consistently demonstrated improved pigment compatibility with the epoxy matrix and reinforced coating anticorrosive performance. This study suggests a strategy for developing and implementing naturally resourced green inhibitors, tannin and alike, into anticorrosive coatings, addressing issues related to solubility and compatibility.
Qi et al. (Thu,) studied this question.