Corrosion Protection of Mild Steel in Acidic Environments by Cetrimonium Cinnamates in Solution and Added to a Low Volatile Organic Compound Coating.

Protection of mild steel from acidic solutions used in the industry by environmentally friendly methods is an area of need. This work explores the anticorrosive properties of cetrimonium cinnamate compounds for mild steel in acid solutions as an additive in solution and as a pigment in a low-volatility organic compound (VOC) coating. Immersion tests show that protection is considerably enhanced after 24 h, at pH 1 for the control being 330 μA/cm compared to 4.3 μA/cm for CTA-MeOcinn, suggesting synergy between the cetrimonium cation and cinnamate anion systems. NMR and cryo-transmission electron microscopy (cryo-TEM) suggested entrapment of the cinnamate within the cetrimonium micelles. This is further supported by molecular dynamics (MD) simulations, which also show that the carboxylate groups on the cinnamate protrude from the cetrimonium micelles, enhancing the attachment to the surface. The inhibitors are incorporated into waterborne polymeric coatings and tested in solutions at pH 1. Electrochemical impedance spectroscopy (EIS) data show that the inhibitors form a protective barrier, significantly increasing pore and charge transfer resistances for the coating, thus demonstrating the use of safe methods to protect mild steel in acidic conditions.