| Every year economic losses due to metal corrosion in maintaining,repairing and replacing existing structures and infrastructure account for about 5%of our country’s GDP.However,traditional anticorrosive coatings,such as epoxy resin and phenolic resin,are usually hydrophilic,which makes the corrosive medium easily penetrate into the interface between coating and substrate,greatly accelerating the corrosion of metal.In addition,when the coating is mechanically scratched or impacted,the coating surface will appear microholes,cracks and other defects,seriously reducing the protection of the metal substrate.Therefore,the design and development of stable superhydrophobic anticorrosive coating is of great practical significance in the field of metal protection.In this paper,two composite coatings with superhydrophobic properties were prepared by two-step spraying method.Due to the continuous dense rough structure of the coating surface makes it easy for air to be retained in the grooves to form an air film,which well blocks the penetration of corrosive media.In addition,the addition of epoxy resin coating between the superhydrophobic layer and the substrate can,on the one hand,enhance the bonding force between the superhydrophobic layer and the substrate,and on the other hand,form a composite coating with both superhydrophobic and anticorrosive properties,thus better blocking the erosion of corrosive media on the metal surface.Firstly,inspired by the hydrophobic microstructure of worm-like expanded graphite,and a superhydrophobic composite coating of expanded graphite and zirconium dioxide modified with long-lasting anti-corrosion properties was successfully prepared.The test results showed that the water contact angle and rolling angle of the coating were 158.6±1°and 4±1°,respectively.When the addition amount of modified expanded graphite was 1 wt.%,the coating had the best anti-corrosion performance after 720 h of immersion in Na Cl solution（3.5 wt.%）,the corrosion current density was 1.1×10-10 A·cm-2,which only decreased by 2 orders of magnitude,the lowest corrosion rate was 13.613 mpy,and the low frequency impedance modulus value of 1.12×108Ω·cm2,compared with the pure epoxy resin coating increased by 4orders of magnitude,720 h of salt spray corrosion after the coating corrosion area of the smalest,the corrosion of the least spot.The coating still has excellent superhydrophobic performance after 400 cm sandpaper abrasion and 20 times tape peeling experiments;anti-icing experiments show that the superhydrophobic coating has 229 s longer icing time and 2℃lower icing temperature than the pure EP coating;in addition,the superhydrophobic layer has good self-cleaning performance and chemical stability.The hydrophobic modified silica was combined with molybdenum disulfide-modified aqueous epoxy resin to obtain a synergistic superhydrophobic coating.The test results showed that the water contact angle and rolling angle of the superhydrophobic coating were 159.2±1°and 3±1°,respectively;after 500 h of salt spray corrosion,there was no obvious corrosion extension at the scratch of the coating and less pitting appeared on the surface;after 500 h of immersion in Na Cl solution（3.5wt.%）,the low-frequency impedance modulus value of the coating specimens was4.37×108Ω·cm2 and the corrosion current density was 5.6×10-9 A·cm-2,Compared with the molybdenum disulfide-modified waterborne epoxy resin coating,the low-frequency impedance modulus was 3 orders of magnitude higher and the corrosion current density was 1 order of magnitude lower,the freezing time of water droplets was191 s longer and the freezing temperature was 5℃lower.The coating still maintains superhydrophobic properties;in addition,the superhydrophobic coating has a better self-cleaning effect on external pollutants. |
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