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Influence of different pH values on PANI layer properties and on its application in corrosion protection

The aim of this work was to study protecting properties of PANI layers of different degrees of protonation in 0.1 mol dm-3 NaCl solution. Methods of testing, used in this work, were open circuit potential monitoring and Electrochemical impedance spectroscopy. Different degrees of PANI protonation were obtained by keeping the layer during one day in different solutions, like 3 mol dm-3 phosphoric acid solution (pH=0.4), or in buffer solutions (pH=4.3, pH=7.8). Although all the layers were tested in the same solution, depending on a degree of previously achieved protonation, different protecting properties were obtained. The best protecting properties, in solution containing Cl-, were obtained with the polymer layer kept before testing during one day in buffer solution of pH=7.8 where a complete deprotonation was achieved. It points out that PANI presents physical barrier to the ingress of chloride ions to the passive film and no additional electrochemical mechanism is present.

polyaniline ; electrochemical synthesis ; electrochemical impedance spectroscopy ; chlorides ; corrosion protection

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