Development of dual functional: anticorrosive and hydrophobic sol-gel coatings on stainless steel

Date

2025-7-25

Author

Yardımcı, Ecem

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Sol-gel coatings have been developed to enhance the corrosion resistance and control surface function of ferritic AISI 430 stainless steel (SS). SS has an intrinsic protective Cr₂O₃ layer on the surface, but corrosion can occur due to compositional deficiencies and when this layer is damaged. The objective was to develop a dualfunctional glassy coating, to improve both the corrosion resistance and hydrophobic properties of SS. Silica-based coating sols have been formulized for this purpose. Coating sols were either pure glassy silica prepared using tetraethyl orthosilicate (TEOS)- or organically modified silica-Ormosils, where inorganic SiO-Si network was modified with different organic functions. These include hybrid binary coating sols with TEOS, associated with methyltriethoxysilane (MTES), trimethoxysilane(TMSM), (3-glycidyloxypropyl)trimethoxysilane (GPTMS), and aminopropyltriethoxysilane (APTES). Assessment of coating formulation and defining processing parameters; such as number of coating layers, post deposition treatments (drying/calcination), coating sol aging have been performed. The coatings were deposited by dip-coating, and further processed by various post treatments. The characterization methods employed included optical microscopy for surface morphology analysis, scanning electron microscopy for more detailed and in-depth microstructural examination, contact angle tests for assessing surface hydrophobicity, and high-temperature oxidation tests (800 °C, 10 days) to evaluate oxidation resistance and corrosion behavior in a modelling aggressive environment. Pure glassy (TEOS-derived) sols resulted in micro-cracked coatings, with poor coverage. Ormosils (TEOS: organosilane) coatings exhibited improved surface homogeneity and crack-free coating formation, especially when the TEOS amount in the Ormosil formulation was relatively low. Crack formation was found to be not only related with chemistry of the sol, but also affected by post deposition operations. Extensive hairline cracks and even lift-off of the coating was observed, in the case of multilayered Ormosil coatings subjected to intermediate natural drying. The number coating layers does not directly affect the microstructural and functional characteristics (hydrophobicity and high temperature oxidation resistance) of the Ormosil coatings. Among the all studied TEOS: Ormosil combinations MTES: TEOS formulation at a specific 3:1 molar ratio exhibited the best dual-functional performance, with the highest hydrophobicity (a contact angle higher than 100°) and best oxidation/corrosion protection (only 0.02 mg/cm² weight gain), demonstrating its effectiveness as a dual-functional protective coating. These values were, (65° ± 2°) and bigger than 0.40 mg/cm², respectively for bare SS. The high hydrophobicity of the coating is attributed to the defect free and unique textured microstructure, provided by controlling aging state of the coating sol prior to deposition.

Subject Keywords

Stainless steel, Sol-gel, Corrosion, Coating, Ormosil

URI

https://hdl.handle.net/11511/115487

Collections

Graduate School of Natural and Applied Sciences, Thesis