Effect of hydrophobicity in hybrid sol-gel coating for enhanced barrier property on mild steel

Hydrophobic coatings have generated growing interest in mitigating the deterioration of metals against corrosion due to their water-repellency properties. For organic-inorganic hybrid (OIH) coatings derived from Sol-Gel, enhancing their hydrophobicity is an efficient way to limit the diffusion of corrosive species to the substrate through the mesopores and low-density zone. This research successfully applied crack-free multicomponent Sol-Gel coating based on zirconium oxide and silicate on mild steel. By doping Octadecyltriethoxysilane (ODTES) with an alkyl group (C18), the coating's hydrophobicity was tailored either on its surface or within the mesopore structure. It was proved in the first place that the enhancement of corrosion resistance is mainly due to the microcapillary effect rather than the surface wettability. Moreover, the effect of the alkyl group addition depends strongly on the coating's microstructure, which is determined by the Sol composition. The most promising composition arose from balancing the coating's density and hydrophobicity. So-prepared samples showed a low current density with increasing potential, which is four orders of magnitude lower than that of the bare substrate. Until a critical potential, denoted Ec, the corrosion species were driven by the electrostatic force to the underlying metal.