Corrosion resistance of tannic acid, d-limonene and nano-ZrO2 modified epoxy coatings in acid corrosion environments

The protection of rusted carbon steel in acid corrosion environments is of great significance for equipment to keep safe operation. In this work, we presented a method to protect the rusted steel by rust conversion treatment and epoxy coating. Tannic acid was selected as rust conversion agent. Tannic acid, d-limonene and nano-ZrO2 were used to improve the corrosion resistance of epoxy coatings. The Raman spectra, X-ray diffraction and 3D confocal images were used to characterize the rust conversion reaction. Adhesion test showed that the loss of wet adhesion of the optimal coating was relatively low due to the addition of tannic acid, limonene and nano-ZrO2. The corrosion resistance of five different coatings was investigated by scanning electron microscopy (SEM) and electrochemical analysis. Results show that after 264 h acid immersion, the low frequency resistance of the optimal coating consisting of rust conversion treatment and additives is 107 Ω cm2, three orders magnitude higher than that of the pristine coating. Moreover, SEM indicates that the optimal coating possesses a smooth surface and an unbroken interface between substrate and coating. Accordingly, the corrosion-resistant mechanism of the hybrid coating is proposed.