Inhibition of stainless steel corrosion by indole-carbazole copolymers

The electrodeposition of conducting polymers (CP) on active metal electrode surface as either protective coatings or film forming corrosion inhibitors has been investigated since the application of polyaniline (PAN1) by Deberry et al. PAN1 and polypyrrole (PPy) and their derivatives have been the most widely studied ones due to their environment stability and ease of synthesis. Some of the researchers were investigated in the healing effects of coating film, composite coating, the influence of substrate, the electrolyte composition. Despite the success claimed to date for CP coatings there are still along way short of replacing traditional coating system. One possible way to overcome these problem use alternative polymers that have not been used before. For this reason in this study we have first synthesized a series of new indole-carbazole (In-Cz) comonomers namely 4-[3-carbazolyl]indole (4In-3Cz), 5-[3-carbazolyl]indole (5In-3Cz), 6-[3-carbazolyl]indole (6In-3Cz), 7-[3-carbazolyl]indole (7In-3Cz) which is expected to improve the characteristic properties from its respective two components. They coated on stainless steel (SS) surface by potantiodynamic and galvanostatic methods and results were compared with polyindole (PIn) and polycarbazole(PCz). Coated electrodes were tested in 0.5 M H₂SO₄ by Tafel, Electrochemical empedance spectroscopy (EIS) and voltametric measurements at different corrosion times. Corrosion currents and potentials, polarization resistance, capacitance, porosity and redox charges were obtained from such measurements and stability of coatings was tested by comparison of these values obtained at immersion time. Tafel curves of P[6In-3Cz) coating obtained at different immersion times shows cathodic protection for longer time which indicating heealing effect (Figure 1).