Optimization of sol-gel coatings on the surface of aluminum pigments for corrosion protection

Encapsulated aluminum pigments were prepared by sol-gel method using tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) as precursors. The reaction conditions were optimized and the aluminum pigments prepared under the optimum conditions were characterized by Fourier transformation infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Subsequently the stability of the aluminum pigments in acid and alkaline aqueous media was examined. It was found that both TEOS and VTES hydrolyze and condense to form a dense netlike layer on the surface of aluminum pigments. XPS analysis shows that TEOS-VTES successfully bonded to Al surface. The 0.64 eV shift of Al 2p binding energy indicates a new Si-O-Al bond formed on Al surface. The corrosion protection efficiencies of the TEOS-VTES-coated aluminum pigments prepared under the optimum experimental conditions reach 99.8% and 99.9% in acid media of pH 1 and alkaline media of pH 11, respectively, suggesting that TEOS-VTES sol-gel coatings can protect aluminum pigments well in corrosion media.