Corrosion Protection of Carbon Steel by Highly Processable Conducting Polyaniline doped Phosphoric Acid and Dodecyl benzenesulfonic Acid

A processable polyaniline (PANI) was prepared via reversed microemulsion polymerization using both phosphoric acid(PA)and dodecylbenzenesulfonic acid (DBSA) as dopants. By attaching this anionic surfactant to PANI chains, solubility and hence processability of PANI in organic solvents was highly increased. Hydrophobic PANI-PADBSA also demonstrated better corrosion protection efficiency in comparison to the PANI synthesized without surface active agents. Polymerization of PANI-PA-DBSA was achieved via chemical oxidation of anilinemonomers inside micelles in the presence of ammonium persulfate (APS), phosphoric acidand dodecylbenzenesulfonic acid at room temperature within one hour. PANI-PA-DBSA was characterized using FT-IR, UV-Vis and XRD techniques before being used in a protective coating composed of xylene, as solvent, and epoxy resin, as matrix. The coating was applied, using dip coating method, on carbon steel specimens. Corrosion protection performance of different coatings was investigated by electrochemical impedance spectroscopy (EIS) and DC polarization techniques. According to DC polarization tests, corrosion potential of carbon steel was shifted about 0.2 V toward more noble potentials in case of optimized PANI-PA-DBSA. EIS data also illustrated a relatively smooth surface with very high resistance which couldserve as a good protective coating due to barrier effects of epoxy resin, reversible redox properties of PANI, and hydrophobicity of PANI-PA-DBSA. Moreover, for different samples, open circuit potential (OCP) was monitored versus time; based on the monitoring results, PANI-PA-DBSA with optimized DBSA content showed relatively little changes over time, as compared to other coatings. Further, different samples had their morphologies investigated using scanning electron microscopy (SEM).