Preparation of FeSA₃/PDA composite coating on N80 steel and enhancement of corrosion resistance via surface hydrophobic modification with ODT, ODA, and DTMS-SiO₂

Subsequently, to improve the corrosion resistance of the coating, the surface of the PDA/FeSA 3 -N80 steel coating was subjected to hydrophobic functionalization by introducing octadecanethiol (ODT), octadecylamine (ODA), and n-Dodecyltrimethoxysilane-modified silica (DTMS-SiO₂). The reconstruction effect of polydopamine (PDA) on the surface of the N80 steel sheet was confirmed through scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analyses. Subsequent electrochemical experiments showed that all hydrophobic coatings significantly improved the corrosion resistance of N80 steel in a 3.5% NaCl corrosive medium. After the three types of coatings were immersed in 3.5% NaCl solution for 30 days, the corrosion current density of the hydrophobic coatings was three orders of magnitude lower than that of the pure steel sheet, and the corrosion potentials were all more positive. Specifically, the current density of the DTMS-SiO₂/PDA/FeSA 3 -N80 steel coating after 30 days of immersion was 5.6751×10⁻⁸ A/cm 2 , that of the ODT/DA/FeSA 3 -N80 steel coating was 6.3884×10⁻⁷ A/cm 2 , and that of the ODA/PDA/FeSA 3 -N80 steel coating was 6.3178×10⁻⁸ A/cm 2 . Calculations showed that the corresponding corrosion resistance rates of the three coatings were 99.99%, 99.92%, and 99.97%, respectively. It can thus be confirmed that the three coatings have efficient corrosion resistance and service stability in NaCl corrosive medium, and can effectively slow down the corrosion process.