Study On Fabrication Of Superhydrophobic Aluminum-alloy Surface And Properties Of Corrosion Resistance And Anti-icing

Aluminum and aluminum alloy is widely used in various fields as marine industry, powerindustry, aviation, and so on, grounded on its good physical and chemical properties. However,some disadvantages exist for the aluminum and its alloy. For instance, the alunimum prones tocorrosion in sea water, and ice can easily cover onto surfaces of alunimum conductor in thecold environments. In recent years, inspired by the “lotus effect”, the superhydrophobicsurface with contact angles larger than150°has shown excellent properties as self-cleaning,corrosion resistance due to its strong water-repellence. Therefore, it is expected that theself-cleaning, corrosion resistance, and anti-icing of the aluminum and its alloy will beimproved effectively by fabricating the superhydrophobic coatings on the aluminum and itsalloy through the simple and economical preparation techniques. It has great practicalsignificance on improving the performance of aluminum and its alloys, such as corrosionresistance in seawater and anti-icing in extreme weather.In this thesis, the superhydrophobic aluminum alloy surfaces were fabricated by two facileand novel methods, and properties of corrosion resistance, anti-icing, and self-cleaning of theresulting superhydrophobic aluminum alloy surfaces were studied. The main research contentand innovation are described as follows:(1) The superhydrophobic aluminum alloy surface with water contact angle of155°and rollangle of less than5°was prepared via a facile and environment-friendly method, whichcontains roughening the aluminum alloy surface with a boiling water and modification withthe stearic acid aluminum. Effects of the treatment time in boiling water and the stearic acid,respectively, on the surface microstructure and wettability were investigated. Finally, theoptimal preparation technical parameters were determined. Thereinto, the boiling watertreatment time is5min while the stearic acid modification time is40h. Results show that thetreatment time in boiling water has much influence on the pore morphology andmicrostructure as well as the roughness of aluminum alloy surfaces, while the stearic acidimmersion time influences the grafting quantity and quality of the long hydrophobic alkylchains on the surfaces. Consequently, the formation and growth of the microstructure of theflower-like shape can be influenced.(2) The superhydrophobic aluminum alloy surface was fabricated by a step immersionmethod. The effect of the ethanol-water volume ratio on the water contact angle was studied,and the formation mechanism of the superhydrophobicity at the aluminum alloy surface wasdiscussed. Finally, the optimal process parameters were determined. Namely, the stearic acidconcentration and immersion time are10mmol/L and35h, respectively, while thealcohol-water volume ratio is1:3. As a result, the water contact angle and the roll angle at theas-prepared surface can reach156.2°and below5°. Then the microstructure and chemicalcomposition of aluminum alloy surfaces were characterized by techniques as FE-SEM, FT-IR, and XPS. Finally, the water-repellence of the aluminum alloy surface was explored byCassie-Baxter theory, and results show that a non-uniform contact forms between the waterand aluminum alloy surface. I.e, the area of the water contacts with the substrate onlyaccounts for5%while that of the water contacts with the air attains95%.(3) The corrosion resistance of the resulting superhydrophobic aluminum alloy surfaces,which were prepared by the boiling water treatment method and one-step immersion method,respectively, was investigated using the dynamic polarization curve, and results show that ascompared to the untreated aluminum alloy, the corrosion potential increases and the currentdensity decreases, respectively, of the superhydrophobic aluminum alloy, indicating that thethe corrosion course of the aluminum alloy is inhibited upon preparing the superhydrophobiccoating on the aluminum alloy. Therefore, the corrosion resistance of the aluminum alloy wasimproved. The corrosion resistance and stability were studied further by investigating thechange of the water contact angle and the morphology of the superhydrophobic aluminumalloy surfaces by soaking the superhydrophobic samples in3.5wt%of NaCl solution, and thenthe corrosion resistant mechanism of the superhydrophobic aluminum alloy surface wasdiscussed.(4) Results from the icing experiment show that as compared to the blank (namely,untreated) aluminum alloy surface, the temperature of water droplets starting to freeze on thesuperhydrophobic surface decreases about2℃, Additionally, while the time of the waterdroplets starting to freeze on the superhydrophobic aluminum alloy surface delays about8min at the same cold temperature. These indicate that the superhydrophobic surface has betteranti-icing performance. In addition, the rolling water droplets can carry off the carbon powderwhich is sprinkled onto the superhydrophobic surface as simulated contamination, while andthe superhydrophobic surface can also restrain the salt and other contaminants in thesimulated seawater adsorped onto the surface of aluminum alloy. Thus, the superhydrophobicaluminum alloy surface has outstanding self-cleaning performance as well.