| In this thesis,a cationic silicone modified acrylic emulsion was prepared by soap-free emulsion polymerization using a polymerizable aminosiloxane oligomer as a functional monomer.Composite passivation solution were prepared by physical mixing with the self-made modified cationic emulsion as a film-forming substance,phosphoric acid?H3PO4?as pH conditioning agent the nano-silica dispersion?S01A?as a blocking agent,and sodium metavanadate?NaVO3?or ammonium fluorotitanate??NH4?2TiF6?as corrosion inhibitors.The hot-dip galvanized sheets produced by Maanshan Iron and Steel Co.,Ltd.were used as a metal substrate to prepare a composite coating.The corrosion resistance of the coating was investigated by electrochemical test,neutral salt spray test and lead acetate dripping method and the optimal solution formula were determined.The laboratory-made polymerizable amino siloxane oligomer was used as the functional monomer to modify the acrylate latex.The cationic emulsion was prepared by soap-free emulsion polymerization.The effects of the polymerization temperature,the amount of initiator,the amount of monomer and the silicon oxide on the acrylate emulsion were investigated.The results showed that when the polymerization temperature was 75?,the initiator dosage was 0.6%,and the first addition ratio of the siloxane oligomer was 30%,the obtained acrylate emulsion have no coagulation and the performance of the latex all reached the industry standard.At the same time,the properties of different proportions of silicone modified acrylic latex were investigated.The results showed that the heat resistance and corrosion resistance were the best when the ratio of silicone to acrylate was 1:4.The self-made modified cationic emulsion was used as the film-forming material.The different chromium-free composite passivation coating was prepared by changing the content of the assistant phosphoric acid,the blocking agent nano-silica and the corrosion inhibitor sodium metavanadate.The corrosion resistance of the coating was examined by electrochemical test,72 h and 96 h neutral salt spray test.The results showed that the optimum formula of the composite passivation solution of sodium metavanadate/siloxane oligomer modified acrylic latex was H3PO4?0.3%?,S01A?0.8%?and NaVO3?0.2%?.The coatingon the surface of the hot-dip galvanized sheet has the best corrosion resistance.The impedance modulus of the coating is 49765?,the corrosion potential is-1.066V,and the corrosion current density is 5.09×10-8A·cm-2.The 96 h neutral salt spray results showed the coating is basically non-corrosive.Through the performance test of the optimal coating,the coating has good electrical conductivity,heat resistance,solvent resistance and fingerprint resistance,and the passivation solution can be stable and long-term in the natural environment.The chromium-free composite passivation coating was prepared by designing orthogonal test with ammonium fluorotitanate as corrosion inhibitor.The corrosion resistance of the coating was examined by electrochemical test,72 h and 96 h neutral salt spray test.The results show that the best formula for the composite passivation solution of ammonium fluorotitanate/siloxane oligomer modified acrylic latex is H3PO4?0.2%?,S01A?0.8%?,?NH4?2TiF6?0.1%?.The coatingon the surface of the hot-dip galvanized sheet has the best corrosion resistance.Its impedance modulus is42500.3?,the corrosion potential is-1.047V,and the Corrosion current density is8.555×10-88 A·cm-2.The results of 96 h neutral salt spray test showed that the metal surface is non-corrosive and the performance of all aspects of the coating meet industry standards. |
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