Bronze corrosion protection by bilayer systems: Self-assembled monolayers of phosphonic acid/waterborne acrylic coating

The self-assembled monolayers of three long-chain phosphonic acids were investigated as possible adhesion promoters and corrosion inhibitors that could improve the corrosion protection of bronze by an acrylic waterborne coating. Corrosion behaviour was investigated by polarization measurements and electrochemical impedance spectroscopy (EIS) under continuous exposure to simulated acid rain and accelerated aging in a corrosion chamber with NO2. The obtained results showed that all the studied phosphonic acids can improve the protective properties of waterborne coating, but their effect depended on the application method. For adsorption carried out by immersion in an acid solution, the 12-aminododecyl phosphonic acid/coating system showed the best corrosion protection while for the brush application that was 12-phosphonododecylphosphonic acid/coating system. Adhesion measurements showed significant improvement of coating adhesion for 12-aminododecyl phosphonic acid immersion application. The surface wettability investigated by contact angle measurements turned to be a good indicator of the effectiveness of the surface pretreatment.