Organic-inorganic hybrid sol-gel pretreatments for corrosion protection of mild steel in neutral and acidic solutions

This work aims to develop and study sol-gel-derived anticorrosion films for mild steel. Epoxy bis-silane precursor has been prepared by reaction of liquid epoxy resin and aminopropyl triethoxysilane. A pretreatment application bath (Sol) has been prepared by dissolving epoxy-silane precursor at constant solid content and fixed water/ethanol ratio, and the solution was adjusted to acidic pH. The organic-inorganic hybrid films were deposited on mild steel by dip-coating technique, by immersion of sample panels into the sol and their withdrawal at controlled rate to facilitate the desired and uniform film. Films were subsequently cured at room temperature. The anticorrosion properties of the coatings were studied using electrochemical impedance spectroscopy, DC polarisation techniques and neutral salt spray test. This study shows that very dense and protective hybrid coatings on mild steel can be obtained by controlling the resin/silane ratio during synthesis of the precursor.