Corrosion protection of carbon steel by special phosphonic acid nano-layers

Preparation, characterization and application of self assembled monolayers (SAM) formed by fluorophosphonic and undecenyl phosphonic acids on carbon steel surfaces as anticorrosive nanocoatings are demonstrated. The corrosion inhibiting efficiency of these layers were determined by electrochemical potentiodynamic polarization and cyclic voltammetry. Results proved that both chemicals in self assembled nanofilms presented good protection against corrosion as anodic inhibitors but the efficiency depended on the layer formation time: short time did not result in compact layers. The stability and efficiency of nanocoatings formed in longer time did not decrease significantly in time due to the proper molecular packing on the solid surface. The metal dissolution as well as the surface roughening caused by the aggressive ions were inhibited by the compact layers. There were differences in efficacy of coatings formed either by fluoro or undecenyl phosphonic acids. When the metal surfaces with and without nanolayers were visualized before and after corrosive attack, atomic force microscopic measurements confirmed the electrochemical results.