Investigation On Novel Anti-corrosive Coatings Based On Nanopolyaniline Additives

Polyaniline （PANI） has attracted much attention due to their advantages of electrochemicalperformance, reversible redox properties and environment-friendly. Because of its specialproperties, PANI has shown enormous prospect in applications of anticorrosion. However, theapplication of polyaniline （PANI） is restricted by its poor solubility, infusible and almostnon-processable properties. Traditionally, PANI is commonly prepared by polymerization ofthe aniline monomer using （NH4）2S2O8as oxidant. Though with high conductivity, itsapplication is restricted by its poor solubility. This paper is focused on the polymerizationmethod of polyaniline and its application in the anticorrosion coatings. The main results are asfollows:Polyaniline nanoparticles with good dispersibility are synthesized by chemical oxidativepolymerization of aniline using H₂O/FeCl₂/H₂O₂as a novel, mild oxidizing system. Thestructure and morphology of the polyaniline was characterized by IR spectra and SEM.Different kinds of nano-polyanilines are prepared by using （NH4）2S2O8as oxidant and fourkinds of inorganic acids （hydrochloride, sulfuric acid, nitric acid, phosphoric acid）, three kindsof organic acids （dodecylbenzenesulfonic acid, benzenesulfonic acid, camphosulfonic acid） andperchloric acid as doped acid. Select as oxidant, nano-polyanilines are respectively prepared inphosphomolybdic acid and sulfuric acid solution, and undoped polyanilines are synthesizedwithout any acid. The dispersibility experiment indicates that nano-polyanilines prepared inFeCl₂/H₂O₂system is much better than that of traditional polyaniline.The synthesized nano-polyaniline was dispersed in epoxy resin and composite coatings wereprepared by the simple mechanical polishing. Then the surface morphology of compositecoatings was studied and the adhesion strength was tested by scratching method. The corrosionprevention of composite coatings was investigated through the salt spray test, seawaterimmersion test and electrochemical method （Electrochemical impendance spectroscopy （EIS）technique and Tafel polarization test）. The results showed that the epoxy composite coatingmixed with nano-polyaniline prepared in FeCl₂/H₂O₂system was provided with excellentprotective function and best adhesion strength for carbon steel, the anticorrosion performance of perchloric acid doped-polyaniline composite coating was worse than before, however, theepoxy composite coating mixed with inorganic acid, organic acid, doped-polyaniline displayedthe worst protective effect. Therefore, the polyaniline with good dispersibility usually had thebest anticorrosion performance.The anticorrosion performance of inorganic doped nano-polyaniline, nano-polyanilineprepared in FeCl₂/H₂O₂system composite coatings and pure epoxy coating were comparedrespectively. Coating deterioration processes were researched by EIS method. EIS parametersin different immersing time were attained by using impedance models. The results obtainedshowed that nano-polyaniline can improve the anticorrosion performance of compositecoatings due to the effect of pinhole passivation. We supposed that once the better dispersibilityof nano-polyaniline, the pore of composite coating was much smaller, the passivation effectwas much better and the protect performance of composite coating was much excellent.