Synthesis of hybrid organosilicon materials of various chemistries as efficient protective coatings for mild steels in NaCl media

Abstract

This study focuses on optimizing the thermal, morphological, scratch resistance, and anti-barrier characteristics of newly developed hybrid sol-gel coatings. The coatings were formulated by varying the synthetic precursors and incorporating a clay additive. The hybrid coatings were prepared using a mixture of organosilane and zirconium propoxide precursors, and further modified with polydimethylsiloxane (PDMS) and Cloisite 20 A (C20A) clay additives. The coatings were applied onto mild steel substrates and their corrosion protection in 3.5 wt% NaCl solutions were evaluated through electrochemical and visual observation testing. Contact angle measurements revealed a hydrophobic nature of the developed coatings on the steel surfaces, primarily attributed to the presence of an organosilane precursor with a long C18-alkyl chain functionality in all formulations. Electrochemical testing data demonstrated that the coating formulation containing the polydimethylsiloxane precursor exhibited good corrosion protection. After 14 days of immersion in a saline medium, this sample exhibited impedance values higher than 106 Ω.cm2 and a low corrosion rate of 3.5 × 10−3 mpy, as determined by electrochemical impedance spectroscopy (EIS) and polarization testing, respectively. Morphological analyzes confirmed the homogeneous and integrated coating layer of this sample, which contributed to its enhanced corrosion protection. Furthermore, the inclusion of the Zr-propoxide precursor in a formulation containing only silane precursors demonstrated favorable effects on the desired coating properties. The hybrid sol-gel coatings exhibited excellent anti-barrier characteristics, which can be attributed to the formation of highly cross-linked Si-O-Si networks. Overall, the reported hybrid coating formulations offer promising alternatives to commercially available toxic conversion coatings, as they exhibit excellent anti-barrier properties and can be considered environmentally friendly.