| It is urgent to solve corrosion problems, as metals are easy to be corrupted in acidcircumstance and sea water. In recent years, coating is the most important and economicalmethod of all anticorrosive methods, especially the environmental friendly coating hasbecome the research focus. The coatings including watery epoxy, FC emulsion and dopedpolyaniline synthesized by emulsion copolymerization method to protect mild steel in theartificial sea water and acid circumstance was investigated in this paper. The anticorrosionproperties of PANI/epoxy and PANI/FC composite emulsion coatings have been studied byelectrochemical methods.Water-based polyaniline(PANI) emulsions were prepared by emulsion polymerizationmethod used aniline (An) as monomer, ammonium persulfate(APS) as initiator, anddodecylbenzene sulfonic acid(DBSA) as emulsifier and doping agent. Transmission electronmicroscope(TEM), Fourier transform infra-red spectroscopy(FT-IR), X-ray diffraction(XRD),thermal gravimetry(Tg), four probe tester and laser particle size analyzer were used tocharacterize the properties of emulsions and latex particles. The results showed thecombination property of emulsions were best. Polyaniline latex particle distributed evenly; theaverage particle size was200nm. The result of XRD showed polyaniline had crystallineregion and amorphous region so polyaniline emulsion particles had good dispersion properties.The thermal decomposition temperature of polyaniline was273℃. The conductivity ofdoping polyaniline was good which in6.67S/cm.The composite anticorrosion coating materials of water-based polyaniline were preparedwith water-borne epoxy resin emulsion(EP) as the film-forming material and adding curingagent emulsion(HGF). The anticorrosion performance to A3steel in the presence of3.5%NaCl aqueous solution was investigated by the electrochemical methods. The results ofelectrochemical impedance spectroscopy(EIS), open circuit potential(OCP) and tafelplot(Tafel) indicated that the adding of polyaniline emulsion makes the density of corrosioncurrent decreased, the impedance and corrosion potential increased significantly, i.e. thecomposite coatings have better anticorrosion performance compared with pure epoxy resincoating. The results indicated that the anticorrosive performance of composite coatings werethe best when the mass fraction of emulsifier(DBSA) was1.0%, the mass fraction of aniline was0.6%, the molar ratio of monomer and initiator was1:1, using EP-20type epoxyemulsion and adding amount of polyaniline emulsion was50%. The composite coatings hadthe best anticorrosion performance with the way of adding polyaniline emulsion directly.The corrosion current density was1.0×10-7A/cm2, open circuit potential raised200mV, thealternating-current impedance was1.0×104·cm2. Compared SEM photos of epoxy andPANI/epoxy, surface of A3steel coated with epoxy which was soaked in3.5%NaCl appearedlots of pinholes, but the PANI/epoxy sample had no pinholes and the surface of steel wassmooth, i.e. there was no signs of any corrosion. The corrosion resistance of compositecoatings was excellent after adding the polyaniline emulsion.The composite anticorrosion coating materials of water-based polyaniline were preparedwith water-borne FC emulsion as the film-forming material in addition. The anticorrosionperformance to A3steel in the presence of3.5%NaCl aqueous solution was investigated bythe electrochemical methods. the composite coating had the best anticorrosion performance.The corrosion current density was1.0×10-7.5A/cm2, open circuit potential was-0.4V, thealternating-current impedance was1.8×104·cm2. Scanning electron microscope(SEM)showed that PANI/FC composite coatings had better anticorrosion properties to A3steelcompared with FC coatings. EDS indicated that the oxidation film formed on the metalsurface which were covered by PANI/FC composite emulsion coatings, the close oxidationfilm can prevent H2O, O2penetration and prevent corrosion effectively due to the passiveeffect of PANI pigment. |
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