engleski

Modified Polyaniline Coatings in Stainless Steel Corrosion Protection

Polyaniline (PANI) has been proven as suitable coating in corrosion protection. In most of the applications chemically synthesised PANI in appropriate solutions was applied as primer coating. Some of the work is published also on the electrochemical synthesised coatings of stainless steel by PANI. The results show good protection of stainless steel in acidic solutions, but the protection fails in presence of chloride anion. In this work PANI coatings have been modified by the addition of ortho-phenylenediamine monomer (OPDA) in the 0.5 M solution of aniline in 3M phosphoric acid, and the synthesis was carried out by means of cyclic voltammetry. All the experiments were carried out at open air atmosphere and at room temperature (22&plusmn ; ; ; 2 C). A stainless steel disk (13% Cr) served as the working electrode. The additions of OPDA monomer to the stock solution were 5, 10, and 50 mM. The synthesis of the corresponding coating has been carried out by applying 3 voltammetric cycles after the initiation of the synthesis, or as thicker layers corresponding to the thickness examined in an earlier work. The obtained coatings were examined by electrochemical impedance spectroscopy (EIS) and corresponding electrical circuits, describing the electrical elements of the coating are presented. The testing of the coatings on stainless steel were carried out at the open circuit potential (Eo.c.) in different media: 3 M H3PO4, 3 M H3PO4 + 0.1 M NaCl and in 0.1 M HCl. The time of retaining Eo.c. in the passive region of stainless steel is shown to depend on the composition of the testing solution. The examined layer prove to protect stainless steel in phosphoric acid solution over the time (t) of the test (t > 100 hours of testing), but the time of protection decreased in solutions with Cl- present. However, the time of retaining the Eo.c. in passive region is increasing with the increased content of OPDA. The operating mechanism in stainless steel corrosion protection is discussed, which includes the role of ˝chemical potentiostat˝ function of PANI, as well as the role anion exchange property of the conducting form of PANI. The influence of OPDA addition is discussed in view of altered morphology of the layer under the influence of increased ratio of OPDA in resulting modified polyaniline coatings.

electrosynthesis; modified PANI; corrosion protection; elctrochemical impedance spectroscopy

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