Preparation And Properties Study Of Super-hydrophobic TiO₂ Films By Micro-arc Oxidation

Surface wettability, which refers to the spreading capability of liquid at the surface of solid, is one of the important characteristics of the material surface. People’s daily life is closely related to the surface wettability. Due to its advantages in self-cleaning, anti-fouling and anti-friction, the superhydrophobic material surface has received general attention. Titanium surface with super hydrophobic properties is widely used in the field of aviation and navigation industry.Based on the point of bionics, superhydrophobic surface needs to have a micro-nano composite structures and low surface energy. It has been proved that a surface with micro-nano double-scale structures can be formed on titanium substrate in the electrolyte of sodium tetraborate by micro-arc oxidation (MAO). In this paper, to get a hydrophobic layer on titanium, the method depositing a layer of low surface energy materials to this hierarchical structure was adopted. The influences of MAO parameters, the varieties of electrolyte and the depositing parameters on surface morphology were analyzed. The morphology and binding degree were charactered by SEM. The roughness of the surface was charactered by surface profiler. The phase composition was charactered by XRD. The contact angle before and after depositing the hydrophobic film were measured. The elemental composition of the surface was charactered by EDS. The bond composition was charactered by XPS.The research showed that the power parameters of micro-arc oxidation affected the final appearance of the surface directly. At a constant voltage, micropores were formed after nanopores with the increasing of oxidation time. Then micropores grew up and formed microgrooves, meanwhile the number of micropores decreased. Since the microgrooves and nanopores existed on the surface, the final appearance became to the micro-nano double structures. With the increasing of voltage, the passive film of the surface was easy to be broke down. The diameter of nanopores decreased with the increasing of frequency, that is why the surface was smoother and the roughness of the film was gradually decreased. The effect of pulse width and frequency to the film was quite similar with each other. At high pulse width, the chemical reaction was strong and nanopores were easy to grow up. If pulse width was too high, the film had a loose structure and was easy to shed. During deposition of the material with low surface energy, ultrasonic cleaning, ultraviolet, dipping time and solution concentration directly affected the hydrophobicity of the surface. Hydrophobic layer on titanium oxide surface by self-assembly technique had strong time effectiveness. According to the analysis of different MAO substrates which were prepared by four electrolytes and have different surface morphologies, the hydrophobic properties were different with each other, although the components of MAO coatings were basically the same. Using the electrolyte of sodium tetraborate, the surface had micro-nano double-scale structures, which was more suitable for preparing the super-hydrophobic surface compared to the other three electrolytes. The contact angle of the film was 159.6°, so the surface was super-hydrophobic.