INTRODUCTION
In this study commercial epoxy resins were chemically modified with various silane monomers under the catalysis of organotin compound, aiming to enhance the corrosion resistance of epoxy coatings on 2024-T3 aluminum substrates. Immersion studies conducted in 3.5 wt.% NaCl solution showed that the coating capacitance (Cc) decreases after the silane modification, as measured by electrochemical impedance spectroscopy (EIS), indicating the higher resistance to water permeation. EIS measurements also indicated an enhancement in protectiveness of silane-modified epoxy coatings against substrate corrosion, which was characterized by higher charge transfer resistances (Rct) and lower double layer capacitance (Cdl) at substrate/electrolyte interface. The adhesion of epoxy coatings was also found to improve after the modification with silane components.
In recent years, a novel metal pre-treatment based on the formation of silane films has been developed to improve the corrosion resistance of metal substrate and the adhesion between metals and painted organic coatings [1–3]. The silane agents used have a general structure of (RO)3SiY, where RO is a hydrolysable alkoxy group, such as methoxy (OCH3), ethoxy (OC2H5) or acetoxy (OCOCH3) and Y is an organofunctional group. The formation of silane films is based on the condensation reactions between silanols (Si–OH), hydrolysis product of alkoxy group) and the metal hydroxyls (M–OH). The organofunctional silane films deposited on the metal are usually hydrophobic [4,5]. They mainly act as physical barriers against diffusion of water and corrosive ions in the initial period [6,7]. In practice, silane films were usually applied coupled with organic coatings. Another application of silanes in the field of corrosion control of metals is the usage for modification of organic coatings. Silane monomers were conventionally prehydrolyzed and condensed with the aid of water and proper catalysts to produce “stable” polysiloxanes before being mixed into polymer resins [13].
