| In this dissertation, the polyurethane powder coating is selected and produced on Q235 steel by electrostatic powder spray, added with nano-kaolin and hydrophobic agents. The failure process of PU coating with artificial defect immersed in natural seawater is investigated using EIS, AFM and FT-IR. The effect of the addition of nano-kaolin and hydrophobic agents on the anti-corrosion performance of PU is researched. The best added amount is got according to the experiment results. What's more, the failure process of PU composite coating immersed in seawater is further investigated. The main contents are listed as follows:(1) The deterioration process of Polyurethane coating immersed in natural seawater is investigated by EIS technique, complemented by AFM. The results indicate that Polyurethane powder coating has a pretty flat and uniform surface and an excellent adhesion strength, which indicates a good barrier property of the coating. The electrochemical corrosion process can be primarily divided into six stages in terms of immersion time and EIS characteristics..(2) The anti-corrosion performance of composite coating is investigated using EIS. The results indicate that the addition of appropriate amount of nano-kaolin or hydrophobic agents contributes to the compactness and penetration resistance of the coating and prolongs the diffusion path of electrolyte solution, O2 and corrosive medium, thus considerably improve the anti-corrosion performance of the composite coating. The best added amounts of nano-kaolin and hydrophobic agents are 3% and 5‰, respectively.(3) The failure process of both PU coating and PU composite coating immersed in natural seawater is investigated using EIS and FT-IR. Results indicate that the failure process can be mainly divided into three stages. The main reason for composite coating failure is the fracture of polymer chains in PU coating and hydrophobic agents after a long immersion time. |
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