Corrosion protection of AISI 1018 steel using Co-doped TiO₂/polypyrrole nanocomposites in 3.5% NaCl solution

A polypyrrole nanocomposites (PPy NTCs) have been effectively synthesized in the presence of TiO₂ and Co-doped TiO₂ nanoparticles (NPs) by an in situ chemical oxidative polymerization. Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy revealed a tube shape structure of the PPy. The TEM results confirmed that the nanocomposite size of Co-doped TiO₂/PPy NTCs was smaller than TiO₂/PPy NTCs thereby increasing the interaction between the PPy nanotube and the AISI steel surface. The corrosion performance of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements in 3.5% NaCl solution. The EIS results show that the log |Z| of AISI 1018 coated with Co-doped TiO₂/PPy NTCs and TiO₂/PPy NTCs reached about 8.2 and 6.0 respectively after 30 days of exposure in 3.5% NaCl solution. This is likely due to the increased surface area of the PPy synthesized in the presence of Co-doped TiO₂ NPs. The EIS results are confirmed by the potentiodynamic polarization and open circuit potential values of the Co-doped TiO₂/PPy which indicated little changes between 1 and 30 days of exposure which confirms the protection ability of this coating. . It is evident that the presence of Co-doped TiO₂ NPs can enhance the resistance against corrosion at the steel/electrolyte interface. - Highlights: • Polymerization of pyrrole monomer in the presence of Co-doped TiO₂ decreases the size of the polypyrrole nanotube (PPy NT). • The corrosion protection increases with the increase in PPy NT dispersion. • The corrosion resistance of steel coated with Co-doped TiO₂/PPy NTCs is considerably higher. • TiO₂/PPy with Co doping reduces the charge transfer across the electrolyte/AISI 1018 steel interface.