Effect of Pre-treatment on Roughness and Hydrophobicity of Electro-Etched Steel with Improved Corrosion Resistance
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JMEPEG https://doi.org/10.1007/s11665-020-05074-4
Effect of Pre-treatment on Roughness and Hydrophobicity of Electro-Etched Steel with Improved Corrosion Resistance Mohammad Alinezhadfar and Mahdi Mozammel (Submitted December 18, 2019; in revised form May 23, 2020) A hydrophobic steel surface was created by a simple electro-etching technique using a cobalt sulfate bath. The effect of surface pre-treatment on the hydrophobicity and surface roughness was investigated. The wettability and roughness of the surface were determined by water contact angle (WCA) and atomic force microscopy (AFM), respectively. Accordingly, the sample abraded with 800 grit sandpaper followed by electro-etching process was selected as the optimum sample with the highest roughness and WCA (Sa = 28.4 nm, Ra = 35.4 nm, and WCA = 144 ± 1.6°, respectively). The morphology and cross-sectional images of the hydrophobic surface were investigated using field-emission scanning electron microscopy (FESEM). FESEM images showed a micro/nanostructured surface. The resulted hydrophobicity was attributed to the high roughness and overhanging structure obtained through this method. Furthermore, by using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests, the corrosion behavior of the samples was investigated. It was revealed that the surface hydrophobicity improved the corrosion resistance by increasing the polarization resistance (from 726 to 1598 X cm2) and decreasing the corrosion current density (from 0.025 to 0.012 mA cm22). The simplicity of creating a hydrophobic surface with the improved corrosion behavior, the availability, and the low cost of the materials used to develop this approach makes it a proper candidate for large-scale and industrial applications. Keywords
contact angle, corrosion, electro-etching, hydrophobic, St37, roughness
1. Introduction Hydrophobic surfaces with water contact angle (WCA) of more than 90°, due to their superlative water repellency, are the most widely studied subject in wettability (Ref 1, 2). The heated issue of hydrophobic surfaces has a wide range of applications in self-cleaning (Ref 3), antifouling (Ref 4), antifogging (Ref 5), anti-icing (Ref 6), anti-corrosion (Ref 7), microfluidics (Ref 8), lab-on-a-chip (Ref 9), oil/water separation (Ref 10) and guiding liquid sliding (Ref 11). Researchers inspired by Lotus leaf have tried to fabricate hydrophobic surfaces by either roughening the surface microstructure or lowering its surface energy. However, the rough hierarchical structure plays a more essential role than surface energy and it is claimed that increasing the roughness of a hydrophobic surface raises the WCA (Ref 12, 13). At first, YoungÕs theory described the state of water on a flat surface (Ref 14). By considering the role of surface roughness, Wenzel and Cassie–Baxter theories came up which described the state of water penetrating and suspending above the protrusions of a rough surface, respectively. The Wenzel state (penetration) and
Mohammad Alinezhadfar and Mahdi Mozam
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