Research On Fabrication Of Superhydrophobic Surface On Aluminum Substrat

Superhydrophobic surface, with a water contact angle greater than 150°and tilt angle less than 10°, is of great prospect applied in the fields of construction, textile, communication, military and aviation for its particular characteristics such as self-cleaning, anti-icing, anti-attrition, drag reduction and corrosion resistance. However, the development of superhydrophobic surface is restricted for the reason that either expensive equipment or complex process are usually required in the fabrication of superhydrophobic surface by the main technologies, which are also difficult to fabricate large area of superhydrophobic surface. Aluminum and its alloy are widely used in various industrial products for their physical and chemical properties. Therefore, it's of great significant to develop a simple and inexpensive method to fabricate superhydrophobic surface, especially the large area of superhydrophobic surface on aluminum substrate.In this thesis, electrochemical anode etching method is developed to fabricate the superhydrophobic surface on the aluminum substrate. Furthermore, the method is carried out to prepare the large area of superhydrophobic surface successfully.By applying the neutral electrolyte (NaCl) and the applied field, the micro/nano-structure of the aluminum substrate is generated with applied electric field, which can induce the grain-boundaries/dislocations to dissolve prior to the grain itself. After modification with fluoroalkylsilane on the micro/nano-structure, superhydrophobic surface was obtained with water contact angle of 167°and tilt angle of 3°.Processing conditions such as electrolyte type, processing voltage, current, time were investigated to get their influence upon the superhydrophobicity of the surface, and the optimum processing condition was found. The scanning electronic microscope was used to investigate the micro-structure of the aluminum surface and showed that many pits of approximately 2-5μm in width and 2-5μm in depth are distributed on the aluminum surface. In addition, smaller step-like structures are evenly distributed on the whole surface, constituting the dual-scale micro/nano-structure, which is necessary to superhydrophobic surface.The influence of the surface morphologies with different removal weight on the superhydrophobicity of the surface is studied both macroscopically and microscopically, moreover, the influence of different removal speed under same removal weight on the superhydrophobicity of the surface is studied. Results shows that:for the aluminum plate of 9cm2, original surface is evenly and completely removed and superhydrophobicity of surface is obtained when removal weight reaches 0.20g; the superhydrophobicity of surface keeps excellent when the current density is smaller or equal to 25mA/cm2, but decreases when the current density exceeds 35mA/cm2.Electrochemical machining using a moving cathode is proposed to fabricate the large area of superhydrophobic surface. Experimental facility is established and the experiment is carried out. Results indicate that electrochemical machining is feasible to fabricate the large area of superhydrophobic surface by using the moving cathode, which solves the problem that the large area of superhydrophobic surface is difficult to prepare. Under optimum machining conditions, large area of superhydrophobic surface is achieved with water contact angle of 167°and tilt angle of 3°on average.