Characterization of water-repellent and corrosion-resistant superhydrophobic surfaces on galvanized steel

Corrosion-resistant superhydrophobic surfaces were successfully fabricated on galvanized steel through a wet oxidation treatment and stearic acid modification. In this work, the formation mechanism of superhydrophobic surfaces and structures were characterized with contact angle meter, scanning electron microscope (SEM), X-ray diffractometer (XRD), and Fourier transform infrared spectroscopy (FTIR). The surface properties of superhydrophobic and non-superhydrophobic surfaces were assessed by calculating surface free energy (γ) and work of adhesion (Wst). Moreover, the corrosion behavior and durability of superhydrophobic surfaces were examined in 3.5 wt% NaCl solution for up to 14 days. Superhydrophobic galvanized surfaces with WCAs of 168° (γ = 0.01 mN/m and 1.57 mN/m) and 162° (γ = 0.04 mN/m and Wst = 3.52 mN/m) were successfully obtained by modifying HCl etched surfaces with ethanolic stearic acid, with or without wet oxidation. According to the results, a zinc stearate layer on the surfaces effectively enhanced their corrosion resistance by numerous air pockets on the surfaces with hierarchical micro-/nanostructures that inhibited penetration by the NaCl solution. Moreover, superhydrophobic as-synthesized ZnO surface by wet oxidation had better corrosion durability than a superhydrophobic etched surface because of the strong physical and chemical bonding of stearic acid onto the as-synthesized ZnO nanorods.