| The problem of metal corrosion is urgent in many industries.In recent years,Conductive polymers especially polyaniline have been widely used in the field of metal protection due to their excellent environmental stability,ease of synthesis,reversible acid-base doping/re-doping properties,and unique doping characteristics.Unfortunately,due to the poor solubility and processability of polyaniline,its application in the field of corrosion protection is limited.At present,the more widely used method is add to polyaniline to traditional coatings,but because of its solubility and dispersion effect,this addition is often a small amount.After being doped with acid,polyaniline exhibited the ES state of emeraldine salt in the solution.It can be moved and deposited on the metal surface under the action of an external electric field.In this way,a polyaniline coating directly forms on the metal surface as an anti-corrosive primer,which can effectively avoid the problem of poor solubility of polyaniline.In this paper,the research on the preparation of polyaniline coatings was carried out.Polyaniline coatings were prepared by three methods:direct coating method,cyclic voltammetry electro polymerization method,and electrocoating method.The corrosion resistance of the coating in 0.5 mol·L-1 H2SO4 were evaluated by polarization curve and electrochemical impedance spectroscopy.Firstly,the brush coating method was used to directly obtain the hydrochloric acid and citric acid doped polyaniline coating on the surface of 304SS.The test results showed that the coating prepared by brush coating method had a certain anti-corrosion effect,but the anti-corrosion effect was poor,and the coating peeling occurred after long-term immersion.Secondly,a citric acid-doped polyaniline coating was successfully prepared on the surface of 304SS by cyclic voltammetry.The test results show that a polyaniline coating prepared by using an electropolymerized electrolytic solution of 0.7 mol·L-1 citric acid and 0.5 mol·L-1 aniline at a scan rate of 20 m V·S-1 and cycle 10,its Ecorr is 74.01 m V and icorr is 1.186?A·cm-2.After the coating was exposed to 0.5 mol·L-1 H2SO4 solution for 4 h,the coating achieved the maximum Rct value?92.05?·cm2?.However,there exist a lot of pores in the coating,which is not conducive to the long-term effectiveness of the corrosion resistance of the coating.Thirdly,hydrochloric acid-doped polyaniline slurry was synthesized in advance and then combined with electro-coating technology,a hydrochloric acid-doped polyaniline coating was successfully prepared directly on the 304SS surface.The test results indicate that the optimum conditions of the preparation with polyaniline coating were as follows:the pH of the doped acid was 2,the reaction time was 20 min,the electro-coating current was 500 m A,and the electro-coating time was 2 h.Under the optimal conditions,the prepared polyaniline coating Ecorr was 97.19 m V,icorr achieved1.492?A·cm-2.The coating was immersed in 0.5 mol·L-1 H2SO4 solution for 8 h to obtain the maximum Rct value.After 48 h of exposure,it still had a certain anti-corrosion effect.Finally,the citric acid doped polyaniline coating was successfully prepared on the surface of 304SS with the aid of electro-coating technology,which avoids the de-doping phenomenon of hydrochloric acid doping,and further improves the corrosion resistance and stability of the coating.The experiment results show that the optimal conditions for the preparation of the coating were as follows:the preparation time of the polyaniline solution should be 20 minutes,the electro-coating current should be 700 m A,and the electro-coating time should be 2 h.Under optimal conditions,icorr is 1.265?A·cm-2,and Ecorr is 386.64 m V.The maximum Rct value was obtained after the coating was soaked in 0.5 mol·L-1 H2SO4 solution for 12 h.In summary,the use of electro-coating technology can effectively avoid the problem of poor solubility of polyaniline,and the obtained polyaniline coating has excellent corrosion resistance and long-term effectiveness of corrosion resistance. |
PDF Full Text Request