Corrosion performance of superhydrophobic nickel stearate/nickel hydroxide thin films on aluminum alloy by a simple one-step electrodeposition process

Abstract

Superhydrophobic thin films are fabricated on chemically cleaned aluminum alloy substrates by a one-step electrodeposition process in the ethanolic solution containing Ni2 + ions and stearic acid (SA) under applied DC voltage. Morphological features observed by scanning electron microscopy (SEM), indicate that the thin films are composed of cauliflower-like structures with micro-nano scale particles. The chemical compositions of these films are characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), which indicate that these films consist of low energy nickel stearate (Ni(SA)2). A schematic model of the electrodeposition process of Ni(SA)2 is also presented. Wetting analysis demonstrates that the surface of the film is superhydrophobic with a water contact angle (CA) of 160 ± 1° with contact angle hysteresis (CAH) of 2.1 ± 1°, which is obtained under optimum electrodeposition conditions based on a 0.4 molar ratio of Ni2 +/SA solution. The corrosion resistance properties calculated from the Tafel curve of superhydrophobic surfaces prepared in this solution are 280 times larger than the chemically cleaned aluminum alloy substrate. Furthermore, electrochemical impedance spectroscopy (EIS) analysis demonstrates that the charge transfer resistance is 1.63 × 107 Ω·cm2 for superhydrophobic films (Ni2 +/SA = 0.4) compared to that of chemically cleaned aluminum alloy substrates (1.56 × 103 Ω·cm2). Therefore, the superhydrophobic film of Ni(SA)2 on the chemically cleaned aluminum alloy substrate improves the corrosion resistance performance of aluminum substrates in corrosive environments.