The Research And Synthesis Of Pani Watery Anti-Corrosion Coatings

It is urgent to solve corrosion problems, as metals are easy to be corrupted in acid circumstance and sea water. In recent years, coating is the most important and economical method of all anticorrosive methods, especially the environmental friendly coating has become the research focus. The coatings including watery alkyd and doped polyaniline synthesized by emulsion copolymerization method to protect mild steel in the artificial sea water and acid circumstance was investigated in this paper. The effects of additives of Nano-SiO₂ and glass flake on the anti-corrosion property of the polyaniline-water watery alkyd coating have been studied.. Based on the experimental data of Polarization curves (Pol), Electrochemical Impendence Spectrum (EIS), Salt spray test, microstructure and element analysis, the anticorrosion mechanism of watery alkyd polyaniline coatings was summarizedDoped polyaniline was synthesized from aniline by adding (NH4)2SO4 as oxidant and DBSA as doping agent via emulsion copolymerization method. The production was blended with water alkyd in order to prepare anticorrosion coatings which were spread on the mild steel surface. Electrochemical methods and salt spray were employed to study mild steel blocks with coatings in 3.5% NaCl aqueous solution and 0.5mol·L-1H2SO4 aqueous solution respectively. The result presents the coating obtaining 5% polyaniline has excellent anticorrosion properties. Compared with coatings without polyaniline, polar resistance (Rp) of coatings with 5% polyaniline could increase three orders of magnitude and corrosion current density is lower three orders of magnitude.The nano- SiO₂ and glass flakes were blended in the coatings besides 5% polyaniline and their anticorrosion capability was better than those without nano- SiO₂ and glass flakes. The anticorrosion properties of the coatings (2#) containing 0.5% nano-SiO₂, 10% glass flakes and 5% polyaniline was more excellent than the others. Rp, Ecorro and Icorro of 2# coatings were respectively 8.67×108Ohm and 1.82×106Ohm, -0.53V and -0.56V, 1.45×10-11 A·cm-2 and 1.62×10-9A·cm-1 in 3.5% NaCl aqueous solution initially and after 800h. In the 0.5mol·L-1H2SO4 aqueous solution initially and after 1000h, the coatings′Rp, Ecorro and Icorro are 9.27×108Ohm and 2.68×106Ohm, -0.52V and -0.46V, 3.08×10-11 A·cm-2 and 2.34×10-9A·cm-1 respectively. Salt spray test of the coating was about 60 days. The properities of watery coatings were near to solvent coatings.We found that the mild steel blocks had passivation layer on surface whether samples soaked in3.5% NaCl or 0.5mol·L-1 H2SO4 aqueous solution from XPS. The main phase is properlyα-Fe2O3,γ-Fe2O3 and Fe-PANI complexes. Compared SEM photos before testing with after testing, surface of passivation layer which was soaked in 3.5% NaCl appeared lots of pinholes, but the sample soaked in H2SO4 aqueous solution has a little.The anticorrosion mechanism of polyaniline for mild steel blocks passivated in neutral and acid solution was explored in this paper. The passivation is a slow process and the formation and dissolve of the passivation competitively happened during corrosion process.