Studying various mixtures of 3-aminopropyltriethoxysilane (APS) and tetraethylorthosilicate (TEOS) silanes on the corrosion resistance of mild steel and adhesion properties of epoxy coating

Different mixtures of tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APS), i.e. 100/0, 70/30, 50/50, 30/70 and 0/100, were applied on mild steel samples. The morphology and composition of the silane coatings were investigated by field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS) and contact angle analysis. Open circuit potential (OCP) and electrochemical impedance measurements were performed on the bare steel and silane coated samples by electrochemical impedance spectroscopy (EIS). Results showed that a mixture of 70/30 of TEOS/APS resulted in a more consecutive and compact film formation on the steel surface. It was shown that the mixture of TEOS/APS provided better corrosion protection properties than the single ones. The film composed of APS decreased the contact angle more than TEOS. An epoxy coating was applied on the surface of steel samples treated by various mixtures of silanes. Pull-off and salt spray tests were performed on these samples to investigate the effects of surface treatment on the adhesion and corrosion protection properties of the epoxy coating. It was found that the mixture of silanes significantly enhanced the adhesion and corrosion protection properties of the epoxy coating.