Eco-friendly and facile method of superhydrophobic surface fabricating on 304 stainless steel substrates with fluorine-free agents

A fluorine-free and time-saving process was developed to prepare superhydrophobic (SHP) surface of 304 stainless steel (SLS). Dilute aqua regia and hydrogen peroxide solution were used to construct rough micro-nanostructure on the 304 SLS surface, followed by modification with stearic acid. The effects of various etching and modification parameters on the surface wettability of SLS were examined in order to achieve high surface roughness and low surface energy. The results indicated that the molar ratio of H+/H2O2 showed the most significant influence on the water contact angle (WCA) of SLS. The optimal SHP with a maximum WCA of 158.3 degrees and a sliding angle (SA) of 2.3 degrees could be achieved at the etching time of 30 min, the molar ratio of H+/H2O2 = 1/0.4, the stearic acid concentration of 0.03 mol/L, the modification time of 3 h, and the modification temperature of 70 degree celsius. The long-term stability, wearing durability, thermal stability, and corrosion resistance of the optimal SHP sample were examined, and the results indicated that there was only a slight change in WCA and SA after exposing the sample in air for 75 days, that the sample could keep SHP property after abrasion for 300 cm under a load of 1000 g, that the sample showed good thermal stability at temperature lower than 200 degree celsius, and that the corrosion current density of the SHP SLS decreased by about 2 orders of magnitude compared to the raw SLS, with a corrosion inhibition rate of 98.6 %. The good performance of the SHP SLS in water repellency, durability, abrasion resistance, and corrosion resistance could greatly extend the application potential of SLS.