Preparation Of Superhydrophobic Porous Titanium By Wire Electrical Discharge Machining And Its Application In Oil-water Separation

Researchers have discovered superhydrophobic phenomena and superhydrophobic surfaces with the properties of self-cleaning,anti-icing,drag reduction,and anti-corrosion,which are potentially useful in industrial fields and daily life,by studying the special wetting phenomena of animals and plants in nature.As preparing the rough structure required for superhydrophobic materials,the common method is material removal,including laser texturing,Wire-cut Electrical Discharge Machining(WEDM),electrolysis and so on.WEDM has the characteristics of high machining accuracy and low thermal influence on the machined surface,and can efficiently prepare three-dimensional rough structured surfaces.The rough structure of the super-hydrophobic surface prepared by the method of material removal is generally based on solid materials.This article research the process of the preparation of dual-scale rough structure surface by WEDM and the low surface-energy modification with 1H,1H,2H,2H-perfluorodecyltriethoxysilane(PFDTES)on porous titanium sample to prepare a superhydrophobic surface.The main results of the study are as follows:(1)The plane structure and array micro-groove structure on the surface of porous titanium substrate were processed by WEDM and low surface-energy modified with PFDTES.The wettability and surface morphology,chemical composition of the sample surface was researched.It showed that the array micro-groove structure on the porous titanium surface was initial to transform the wetting state of the surface into the Cassie-Baxter state.The influence of the electrical parameters of WEDM and the modification time on the wettability of the sample surface was studied.It was found that the preparation of superhydrophobic porous titanium surface did not have strict requirements on the electrical parameters of WEDM and modification time.As the processing voltage was 54 V-94 V,the peak current was 11 A-19 A,and the PFDTES modification time was 10 min-50 min,the as-prepared porous titanium surfaces of the sample were superhydrophobic.In order to obtain the best superhydrophobic performance one the surface,the processing voltage was set as 84 V,the peak current was set as 15 A,the PFDTES modification time was set as 30 min,and the contact angle of the asprepared porous titanium sample was 162.6°,and the rolling angle was 0.5°.(2)Through the comparison experiment of "preparation of array micro-grooves and modification" with porous titanium and pure titanium,it was turned out that the porous structure of porous titanium surface made a significant contribution to reducing surface adhesion and maintaining Cassie-Baxter state.In addition,the surface properties of superhydrophobic porous titanium were tested and studied.High-speed photography was used to observe the movement of water droplets on the superhydrophobic porous titanium surface,and it showed that the surface had a good bounce performance for water droplets.Repeated wear test showed that there was a contact angle greater than 143.9° on the superhydrophobic porous titanium surface after worn for 520 cm under a pressure of 4.355 kPa.And it showed that the surface had good chemical stability and corrosion resistance in the test.(3)The as-prepared porous titanium surfaces are superhydrophobic and superoleophilic,so the array micro-groove structure on the surface can be used for oil-water separation applications.The separation efficiency of superhydrophobic porous titanium for different oil-water mixtures was tested.And it showed that the separation efficiency of superhydrophobic porous titanium for different oil-water mixtures exceeded 98%,and it had a certain continuous water-oil separation ability.In addition,the pressure resistance of superhydrophobic porous titanium and transition process of wetting state of the surfaces in high pressure environment were studied.It was found that the critical failure pressure of the superhydrophobic porous titanium surface was inversely proportional to the depth of the micro-grooves on the surface.As the depth of the micro-grooves is 0.1 mm,the surface had the best pressure resistance with the maximum critical failure pressure of 2.009 kPa and could supported a water column with height of 20.5 cm.