Anticorrosive behavior of epoxy coating modified with hydrophobic nano-silica on phosphatized carbon steel

Corrosion existing in many fields brings lots of troubles to our life. In this work, epoxy coatings modified by hydrophobic nano-silica and hydrophilic nano-silica were fabricated to provide corrosion protection for phosphatized Q235 carbon steel. The traditional epoxy coating was prepared by the polymerization of trimethylolpropane triglycidyl ether and diethylenetriamine. The modified epoxy coating was fabricated by the polymerization and mixing of trimethylolpropane triglycidyl ether, diethylenetriamine and nano-silica. The microscopic morphologies of various epoxy coatings were investigated by SEM. Wettability of epoxy coatings was measured by static contact angle measurement instrument. Thermal stability was tested by thermo gravimetric analyzer. Corrosion behaviors was investigated by electrochemical workstation. Adhesion was reflected by cross-cut test and pull-off test. Equivalent circuits were used to fit the electrochemical impedance spectrum (EIS). According to experimental results, modified epoxy coatings present good hydrophobicity, good thermal stability at 250 °C with only about 3 % weight loss and the ca. 10 μm modified epoxy coating added with the most hydrophobic nano-silica shows the best anticorrosive performance with impedance of 5.25 × 105 Ω•cm2 (0.01 Hz) at 0 h immersion. The anticorrosive performance of epoxy coating is significantly improved when hydrophobic nano-silica is added into epoxy matrix. Adding hydrophobic nano-silica can effectively prolong the diffusion path of water-soluble corrosive medium and the hydrophobicity is able to retard the diffusion of water.