Synthesis of polypyrrole-magnetite/silane coatings on steel and assessment of anticorrosive properties

This work presents a detailed study of the synthesis of polypyrrole-magnetite/silane coatings (PPy-Fe3O4/GPTMS-TEOS-γ-APS) and their anticorrosion properties. The use of a bilayer system is proposed consisting of a PPy-Fe3O4 internal conductive coating (active coating), obtained electrochemically, and an outer coating or insulating barrier consisting of silanes (passive coating). This latter is composed by Tetraethoxysilane (TEOS), glycidoxypropyltrimethoxysilane (GPTMS) and γ-aminopropyl-silane (γ-APS). The GPTMS-TEOS-γ-APS hybrid was obtained by the sol-gel method and applied by the dip coating technique. The anticorrosive properties of the PPy-Fe3O4/GPTMS-TEOS-γ-APS bilayer coating applied on carbon and stainless steel substrate were assessed by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and Raman spectroscopy. The electrochemical characterization has shown that the anodic polarization of the substrate by the conductive polymer was beneficial for the carbon steel substrate whereas it induced pitting corrosion to stainless steel. It was also demonstrated that the addition of Fe3O4 to the PPy matrix slows down its reduction rate increasing its stability and that the presence of a barrier top-coat (like a silane film) is fundamental to preserve the effective anticorrosion performance of the PPy-Fe3O4 composite coating for long term exposure.