Corrosion characteristics of electrochemically prepared phosphate doped polyaniline films in acidic chloride environments

We electrochemically prepared phosphate doped polyaniline films on stainless steel surface in the electrolytic solution containing various aniline concentrations and 1.0 M phosphoric acid solutions by applying a constant potential of 1.2 V (vs. SCE) for an hour at room temperature. Aniline concentrations of 0.1 M and 0.2 M were observed as optimising conditions in the phosphoric acid solution for electrodeposition. The mechanical properties of the doped polyaniline films on stainless steel revealed a strong adhesiveness and excellent uniformity. The CV diagrams of the films showed the characteristic redox couples around 0.2 V and 0.6 V. Corrosion characteristics of the coating on stainless steel (SS) 304 were investigated by polarization measurements and open-circuit potential measurements. In order to understand capability and applicability of the polyaniline coating as a protective coating against corrosion on SS 304 in acidic chloride environments, the present results were compared with the other cases. The electrolytes for corrosion test were neutral 3 wt.% NaCl, 0.5 M HCl, 0.1 M HCl + 0.4 M NaCl and 0.2 M H2SO4 + 0.2 M NaCl acidic solutions. The corrosion characteristic of the phosphate doped polyaniline films on SS resulted in not only dramatic increases in both corrosion potential and film breaking potential, but also large drop in corrosion current. The present results suggest that phosphate doped polyaniline coating on SS 304 is a strong candidate for corrosion protection of SS 304 in acidic chloride environments.