Ultrasound-assisted synthesis of wear-resistant Zn-Ferrocene composite coatings with high anticorrosive properties in alkaline environments

Abstract

Zn coatings are widely applied due to their low cost and negative potential in steel construction and reinforcing steel bars in concretes. However, Zn coatings have been found to perform unsatisfactorily in moist and alkaline environments. In the aqueous alkali environments that inevitably form when concretes fail, galvanized reinforcing steel bars have extremely low corrosion resistance and, consequently, are subject to corrosion. Facing these problems, various additives, including organic and inorganic compounds, have been introduced into Zn coatings to obtain enhanced corrosion resistance, with fewer experiments focusing on organometallic compound composited coatings. As a typical organometallic compound, ferrocene possesses high resistance to corrosive media, such as acids and alkalis. This makes ferrocene an extremely appropriate additive for composite Zn coatings. In this study, Zn-Ferrocene composite coatings were synthesized via electrodeposition with ultrasound assistance. Ferrocene was successfully incorporated using electrochemical control, with a maximum ferrocene content determined to be 19.4% of the C present in the composite coating. The surface morphologies and crystalline structures of the resultant coatings were significantly altered to thin, flake-like hexagonal crystals, a characteristic that was associated with the electrodepositing atomic matrix. The addition of ferrocene greatly improved the wear resistance of the composite coatings, with a 25% mass loss of pure zinc within the coating. The best properties were obtained at an ultrasound assistance level of 15 W. In addition, the corrosion mechanism of the composite coatings was studied at the molecular level. It was found that the corrosion resistance of the composite coatings in alkaline solutions was noticeably enhanced, with an Rct value doubled showing the charge transfer process was inhibited. These results indicate that ultrasound-assisted Zn-Ferrocene composite coatings hold much promise for their potential use in reinforced steel bars in concretes and other abrasive environments.