Electrochemical synthesis of polyaniline on mild carbon steel as a coating material to protection of corrosion in sea water solution

Conductive polymers, especially polyaniline (PAni) have been emerged as promising alternativesas anti-corrosion pigments because of their easy preparation, low cost and chemical stability [۱].Moreover, PAni can be reversibly converted into three main oxidation states that favor the formation of passive iron oxide layer between coating and metal surface through oxy-reductionprocess, thus retarding the corrosion process even after damage in coating surface [۲, ۳]. Theemeraldine salt (ES), the conductive form of PAni, can release the anions that also delay thecorrosion reactions because they can help on the formation of oxides, hydroxides and othercomplex compounds that accumulate on the metal surface as protective layer [۲]. On the other hand, the PANI coatings appear to offer more than simple barrier effects. The protection of metalprovided by PANI has been variously ascribed to the formation of passivating metal oxide layer [۴-۶]. In this word, the Cyclic Voltammetry (CV) technique was employed for the electrosynthesis of PAni coating films. The electrosynthesis solution contained aniline (۰.۲۵ mol L−۱) and sulfuricacid (۱ mol L−۱). The potential range -۰.۲۰ to ۱.۲ V vs. Ag/AgCl for ۵th cycle by ۰.۱ mV s-۱ scan rate was applied. Emeraldine type of polymer films was electrochemically fabricated in above potential window. The corrosion process was also analyzed from Nyquist diagrams whose plotsobtained at different immersion time in NaCl ۳.۵% solution are illustrated in Fig. ۱. PAni presented larger semicircle after ۱۴ days than to ۲۵ h of immersion, indicating better anti corrosion propertiesof coating during to time line. Pani presented higher semicircle diameter after ۱۴ days, indicating higher charge transfer resistance and lower corrosion rate. This research will be extended to other conductive polymer based on due to their improved thermal stability.