| In order to prolong the service life of galvanized sheet,it is necessary to passivate the galvanized sheet.Although the traditional chromate passivation process has a significant anti-corrosion effect,it does great harm to human body and environment due to the highly toxic hexavalent chromium.Therefore,the development of a chromium free passivation process to replace chromate passivation has become a research focus.Molybdenum disulfide is widely used in the field of anticorrosion because of its stable chemical properties.In this paper,a preparation method of two-dimensional molybdenum disulfide composite organic passivation film was studied,and its corrosion resistance mechanism was analyzed.The basic formulation of the organic passivator was studied by the experiments of copper sulfate drop and neutral salt spray.By orthogonal test,the optimum composition of the passivating agent was 400 g/L acrylic emulsion,10 g/L polyoxyethylene octyl phenol ether(OP-10),11 g/L hydroxyethylidene two phosphonic acid(HEDP),10 g/L polyoxyethylene ether(JFC)and 3 g/L tannic acid,and the optimum passivation conditions were determined as passivating agent p H value 3.5,passivation time 20 s,passivation temperature 30 degrees centigrade.Molybdenum disulfide was exfoliated and modified.The structure and chemical composition of molybdenum disulfide were analyzed by X-ray diffraction,Fourier infrared spectroscopy and X-ray photoelectron spectroscopy.The thickness and morphology of molybdenum disulfide were analyzed by atomic force microscope and transmission electron microscope.The results showed that the thickness of two-dimensional molybdenum disulfide was about 1?2.5 nm,corresponding to 2?4 layers.And dodecyl groups were connected on the surface of molybdenum disulfide.The obtained two-dimensional molybdenum disulfide was applied to the acrylic passivation film.The composite passive film was characterized by scanning microscope and X-ray photoelectron spectroscopy.The results showed that the passivation film with two-dimensional molybdenum disulfide was more smooth and compact,and there were fewer microcracks and holes on the surface.The corrosion resistance of the composite passive film was characterized by electrochemical test and neutral salt spray test.The results of potentiodynamic polarization curves showed that the corrosion voltage moved forward with the increase of molybdenum disulfide content.The corrosion current density was 9.603×10-6 A/cm2 when the addition amount was 0.2 g/L,which was about an order of magnitude smaller than that of pure acrylic acid passivation film.The results of electrochemical impedance spectroscopy showed that the pore resistance of the composite passivation film increased by about one order of magnitude after the addition of two-dimensional molybdenum disulfide,and reached the maximum value when the addition amount is 0.2 g/L.The neutral salt spray test results showed that the salt spray resistance time of the passive film increased by 25%when the amount of molybdenum disulfide was 0.2 g/L.In addition,the mechanism of corrosion resistance was discussed.Modified two-dimensional molybdenum disulfide made the surface of passivation film smoother and denser,increased the crosslinking degree of acrylic acid molecule,reduced the cracks and holes on the surface of passivation film as filler,and increased the complexity of diffusion path of corrosion factors,thus increasing the corrosion resistance of passivation film. |
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