Studies On Preparation And Performance Of Alumina Superhydrophobic Surface

Aluminum is abundant in nature.Aluminum and its alloys are widely used in various fields due to their excellent properties,especially in aviation manufacturing,transportation and construction industries.With the development of industrialization,the application field of aluminum materials is expanding,which requires it to be able to adapt to more harsh environment,so the requirements for its anti-corrosion,anti-icing and anti-pollution performance are becoming increasingly high.At present,most of the protective measures for aluminum and its alloys are adding corrosion inhibitor and coating,but these protective measures have some shortcomings such as environmental pollution and complex process.In practical application,it is of great significance to prepare an aluminum base surface with various protective functions such as corrosion resistance,icing resistance and self-cleaning.Superhydrophobicity can avoid close contact between the liquid and the substrate,thus avoiding material failure.Therefore,the anti-corrosion,anti-fouling and anti-icing effects can be achieved by superhydrophobicizing the surface of hydrophilic aluminum and its alloys.In this paper,anodizing and hydrothermal methods were used to prepare aluminum oxide coatings with different micro-nano structures on the surface of 6061 aluminum alloy,and the superhydrophobicity was obtained after modification with lauric acid ethanol solution.The process parameters were optimized,the microstructure,crystal structure and chemical composition were characterized,and the wettability mechanism of alumina superhydrophobic coating was analyzed.The low adhesion,self-cleaning,anti-icing,stability and corrosion resistance of the superhydrophobic coating were evaluated,and the differences caused by different microstructure of the superhydrophobic surface were analyzed.The main research results are as follows:The nanowire-pore hierarchical structure was constructed on the aluminum alloy surface by anodizing method,the hexagonal prism structure almost perpendicular to the surface was constructed on the aluminum alloy surface by hydrothermal method,and the superhydrophobic surface was obtained after low-energy modification.The optimal preparation process of anodizing method is determined by single factor variable method:anodizing voltage is 60 V,oxidation time is 60 min,and H₃PO₄ electrolyte concentration is 0.3 M.The optimal preparation process of the hydrothermal reaction method is:the hydrothermal reaction temperature is160℃,the reaction time is 1 h,the concentration of Na Al O₂ is 0.15 M,and the concentration of CH₄N₂O is 0.5 M.Under the optimal parameters,the contact angle of the anodized superhydrophobic sample was 160.55°and the sliding angle was 1.91°;the contact angle of the hydrothermal superhydrophobic sample was 157.24°and the sliding angle was 5.22°.Two improved Cassie models were established based on different microstructures.The anodized coating is amorphous.After calcined at 500℃for 3 h,the crystal form of the hydrothermal coating changes from bayerite to alumina after dehydration reaction,and the microstructure of the coating remains unchanged.After low energy modification,part of lauric acid is chemically bound to the coating through dehydration reaction.Finally,the performance of the superhydrophobic surface with two different microstructures was tested.The similarities and differences of the two structures in performance were analyzed and compared.The results show that the two kinds of alumina superhydrophobic surface have some similarities:both show good low adhesion,self-cleaning,long-term stability and a certain acid resistance.The freezing time of water droplets on the two superhydrophobic surfaces is prolonged,which shows good anti-icing property.At the same time,the anodic aluminum oxide coating grows"from top to bottom"to form a nanowire-pore hierarchical structure,and the hydrothermal coating grows"from bottom to top"to form a hexagonal prism structure.The differences in the growth mode and microstructure of the coatings also lead to the differences in the properties.The anodic alumina has a closer bond with the substrate surface,so its mechanical stability is better than that of the hydrothermal superhydrophobic sample.The porous structure makes the anodized sample have a larger specific surface area and is easier to absorb C-containing impurities,so the recovery effect after high temperature treatment is better than that of the hydrothermal hexagonal prism structure.After anodic oxidation and hydrothermal treatment,the corrosion resistance of the samples is improved,and the superhydrophobic surface has the best corrosion resistance,followed by the surface without low energy modification.Since the hydrothermal coating is composed of a double composite structure of hexagonal prisms and nanosheets,the corrosion resistance of the samples after hydrothermal treatment is better than that of the samples after anodizing treatment.