Bilayer polymer coating containing a polyaniline for corrosion protection of iron

A poly(2-N-phenylamino-4,6-dimercapto-S-triazine) (PPDT) layer was first prepared electrochemically on an iron surface. The PPDT layer strongly adsorbed on the surface because of the polar triazine rings of the PPDT molecules. No electrochemical response of the PPDT layer-covered electrode to dissolved Fe(CN)63− was observed. This fact indicated that the PPDT layer is an insulating layer with low permeability to dissolved species, and thus acting as a diffusion barrier against agents causing corrosion such as H2O and O2. A polymer polyaniline (PANI) layer was electrodeposited on the PPDT layer. This system was conductive because electron transfer through the PPDT layer occurred by electrons hopping utilizing the localized electron density of the triazine ring. The obtained PANI/PPDT bilayer coating greatly lowered the anodic current peak ascribed to the anodic dissolution of iron and the corrosion current. The high anti-corrosion ability was due to a hybrid effect of the PANI layer as an in-situ oxidant and the PPDT layer as a diffusion barrier.