Preparation Of Superhydrophobic/Superamphiphobic Titanium Alloy Surfaces And Research On Drag Reduction

Superhydrophobic surfaces have a broad application prospects in shipbuilding, water transportation and aviation, owing to the advantages in selfcleaning, anti-sticking of snow or ice, drag reduction and corrosion resistance. In general, the fabricated superhydrophobic surfaces do not have good oleophobicity, which hinder the applications of superhydrophobic surfaces in practice. Superamphiphobic surfaces repel water and oil extremely, and they could not only be used in oily circumstances, but also nearly possess all the characteristics of superhydrophobic surfaces. So superamphiphobic surfaces have broader applications than superhydrophobic surfaces, such as antifouling, water-oil repellent fabrics, crude oil transfer and especially oil pollution minimization. Titanium alloy has very important applications in military, aviation and chemical industry for its low density, high specific strength, corrosion resistance as well as good heat resistance. Therefore, preparation of superhydrophobic or superamphiphobic titanium alloy surfaces have great significances in fundamental research.According to the electrochemical anodization, this thesis proposes simple, economical and efficient methods to fabricate superhydrophobic/superamphiphobic titanium alloy surfaces. Micrometer-scale porous structures are generated on the titanium alloy substrates by one-step anodization in alkaline solution; Re-entrant micro/nano structures are generated on the titanium alloy substrates via one-step anodization in neutral solution. Both surfaces respectively show superhydrophobicity and superamphiphobicity after subsequent fluoroalkylsilane modification. Contact angle measurements, Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) are used to characterize the surface wettability, morphological features and chemical composition, respectively. The results show that the combination of suitable micro-scale rough structures and low surface energy modification plays a vital role in fabricating superhydrophobic/-superamphiphobic surfaces. Furthermore, stability tests clearly show that the created superhydrophobic/superamphiphobic surfaces possess long-term persistence and good stability under harsh conditions.In order to investigate the drag reduction of the fabricated superhydrophobic titanium alloy surfaces, the experimental installation of macro-scale channels is built on account of differential pressure method. Relation between the pressure difference with flow velocity in the common surface channel and the superhydrophobic surface channel is measured under laminar flow, respectively. The results show that superhydrophobic titanium alloy surfaces possess significant drag reduction and can reduce the flow drag by 10%-15% under laminar flow. The main reason for drag reduction of the superhydrophobic surface is analysed on the basis of surface slip-flow. Owing to the air is filled with the gap between the micro structures, water mainly flow over the air layer in the micro structures, so there is the slip flow phenomenon on the air-liquid interface. It means that the wall velocity exists when the water flow through the air-liquid interface.