Influence of PANI Layer Protonation Degree on Corrosion Protection of Steel

M. Kraljić Roković, M. Kalić and L. Duić

Abstract
The aim of this work was to study the protective properties of polyaniline (PANI) layers of different degrees of protonation on stainless steel immersed in c = 0.1 mol dm–3 NaCl solution. Methods of testing were open circuit potential monitoring, and electrochemical impedance spectroscopy. Different degrees of PANI protonation were obtained by keeping stainless steel covered with PANI layer during one day time in solutions of different pH values. The testing solutions were c = 3 mol dm–3 phosphoric acid solution (pH 0.4), and buffer solutions of pH 4.3 and pH 7.8. Although all PANI layers were tested in the same solution of c = 0.1 mol dm–3 NaCl, depending on a degree of previously achieved protonation, different protection time of steel samples was obtained. The best protective properties were obtained for steel covered with the PANI layer kept one day in the buffer solution of pH 7.8, before testing, where a complete deprotonation was achieved. The results obtained point out that PANI, under those conditions, presents a physical barrier to the ingress of chloride ions into the passive film, and the electrochemical mechanism of protection is not significantly involved.

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Keywords
Polyaniline, electrochemical synthesis, stainless steel, chlorides, corrosion protection