Alumina lath-like structure-rGO–PVDF hybrid film formation with high-performance corrosion protection for 316L stainless-steel alloy

Abstract

The susceptibility of stainless steel (SS) to corrosion can necessitate the use of an effective surface coating for application in various industries. In this study, the lath-like structure of aluminium oxide (Al2O3) has been successfully synthesized via a sol–gel process using the ionic liquid, 1-hexyl-3-methylimidazolium hexafluorophosphate. The uniform alumina lath-like structures with a diameter of 105 ± 22 nm and length of 340 ± 66 nm were characterized with various techniques, including X-ray diffraction (XRD), transmission electron microscope (TEM), field emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS). Furthermore, the alumina nanoparticles were functionalized with a silane compound. Composite of reduced graphene oxide (rGO), functionalized Al2O3, and polyvinylidene fluoride (rGO/Al2O3–PVDF) with Al2O3 concentration of 1 wt.% was successfully prepared. The composites were then characterized and utilized for SS protection in a saline solution (3.5% NaCl). Excellent corrosion resistance was conferred to the SS surface using the rGO/Al2O3–PVDF coating with 1% Al2O3 (rGO/Al2O3–1.0–PVDF), which outperformed the other coatings, as indicated by electrochemical characterization using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP). The water contact angle of rGO/Al2O3–1.0–PVDF-coated SS was 142.5°, demonstrating good hydrophobicity. The protection mechanism was clarified using both electrochemical and surface characterizations. The remarkable protection performance of rGO/Al2O3–1.0–PVDF is related to the control of charge transfer at the SS/electrolyte interface, which prevents alloy dissolution. Furthermore, the presence of Al2O3 passivates any graphene defects that may be present, which further reduces the corrosion rate, thus providing enhanced protection compared to the rGO/PVDF and neat PVDF coatings.