| In order to improve the corrosion resistance of the hot-dip galvanized steel sheet,the surface of the hot-dip galvanized layer needs to be passivated in the production of hot-dip galvanized steel to extend its service life.At present,chromate passivation is still the main passivation process of zinc coating,but chromate is harmful to the environment and human body,so it is very meaningful to find an efficient passivation process without chromium.In this paper,boron nitride nanosheets were obtained by chemical stripping,and then the boron nitride nanosheets were modified.The modified boron nitride nanosheets were applied to water-based acrylic acid to passivate the surface of hot-dip galvanized steel sheet.The influence of modified boron nitride nanosheets on the structure and properties of passivation films was studied,and the corrosion resistance mechanism of boron nitride composite passivation films was investigated.The main research contents of this article are as follows:In this experiment,boron nitride nanosheets were obtained by chemical stripping method.The boron nitride nanosheets were characterized by XPS,XRD,SEM,AFM,etc.The experimental measurement showed that the size of the boron nitride nanosheets was3-5?m,and the thickness of the layer was 1.5-2.6nm nanosheets.The boron nitride nanosheets were modified with dopamine and silane coupling agent to characterize the chemical composition,the experimental results show that the surface of the boron nitride nanosheets was successfully grafted with a silane coupling agent.The optimal amount of modified boron nitride nanosheets in the composite passivation agent was 0.1 g/L.Compared with the acrylic passivation film,the corrosion current density of the composite passivation film was 2.325×10-7A/cm2,which is two times lower than that of the acrylic passivation film(corrosion current density 2.279×10-5A/cm2).Simultaneously,the surface morphology of the composite passivation film was dense,without obvious cracks,and the porosity of the passivation film is also reduced.The reason why the composite passivation film improves the corrosion resistance was that the modified boron nitride nanosheets promoted cross-linking of acrylic molecules and the dehydration condensation of silane made the surface of the passivation film flat and dense,and the modified boron nitride nanosheets were extended.The diffusion channel of the corrosive medium in the passivation film increased the time for the corrosive medium to reach the metal substrate,so improving the corrosion resistance of the passivation film. |
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