Effect of silica nanoparticles on performance of sol-gel coatings

Sol-gel coatings for corrosion protection were fabricated on high strength steel 30CrMnSiA. The effect of silica nanoparticles on performance of sol-gel coatings was studied. The morphology and chemical composition of the coatings were investigated by using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The hardness of the coatings was tested by using microscopic hardness meters. The corrosion resistance of the coatings was studied by electrochemical impedance spectroscopy (EIS) during immersion in 3.5% NaCl solution. Fourier transform infrared spectroscopy (FTIR) was used to study the chemical structure of the coatings. The results demonstrate that the optimal concentration of silica nanoparticles is 500 mg · L^-1, under which the coatings are of the best performance with uniform surface, dense structure, high hardness and excellent corrosion resistance. The doped silica nanoparticles generate active hydroxyl groups in the sol, form covalent bonds with the coating matrix, and thus strengthen the coatings.