Investigation of Anticorrosion Coatings for Iron Using Polyaniline By Electrochemical Impedance Method

Abstract

<Introduction>The most efficient corrosion inhibitors are based on heavy metal such as Cr. However, the use of them has now been widely restricted by law due to environmental and toxicological issues. So recently, anticorrosion method with conducting polymer has attracted attention because of free heavy metal. The conducting polymer, polyaniline is known to have a number of molecular configurations by redox status and pH. Two half oxidized forms, protonated emerardine salt(ES) and deprotonated emerardine base(EB) change reversibly by acid-base processing. In order to investigate the anticorrosion mechanism of the iron plate coated by deprotonated polyaniline film, we investigate electrochemical characteristics by AC impedance technique in the different anion solutions. Moreover, native oxidation layer of bare iron is also investigated. The three models of the equivalent circuits are proposed to explain the anticorrosion mechanism of the iron plate coated by deprotonated polyaniline film. <Experiment>The metallic samples used in this study were bare iron JISG3141, rolled steel plate. All metallic samples were degreasing with acetone. EB was dissolved in N-methyl-2-pyrrolidinone and that 5.0 mg/mL polyaniline(EB) solution was prepared. This solution was casted to iron plate on the hot plate at 60 ° C. This state was maintaining for 6 hours to get EB coating plate. All AC impedance measurements were conducted using three-electrode system. Working electrode is iron electrode, reference electrode is saturated calomel electrode and counter electrode is Pt coil electrode. Also, two electrolysis solutions, 1.0 M NaCl solution and 0.1 M Na2B4O7 solution were used to compare corrosion behavior by anion species. [1] D. W. DeBerry, J.Electrochem.Soc., 132, 1022-1026(1985).