Preparation And Study Of Titanium Dioxide Nanotubes And Hydroxyapatite On The Surface Of Titanium

Among metal materials,titanium and titanium alloys are considered to be the most suitable bone graft materials because of their high mechanical strength,excellent corrosion resistance and good biocompatibility.Research has shown that surface modification of titanium and titanium alloys can make them have bone binding activity and even promote bone growth.Hydroxyapatite,as the component of human bone,has good biocompatibility.It can promote bone growth and attach bone to the implant surface.The chemical and biological properties of hydroxyapatite can be combined with the mechanical properties of titanium matrix,and the hydroxyapatite coating of bioinert metal implant can be studied.In this paper,the surface of pure titanium was modified by anodic oxidation and The preparation technology of titanium dioxide nanotube on titanium surface was studied.On this basis,hydroxyapatite coating was prepared by electrodeposition and the effect of current density on the coating was studied.The effect of current density on the coating was studied,and optimize the electrochemical deposition condition.The main contents are as follows:1.Titanium matrix was anodized in an organic electrolyte of 30-75V,0.25-0.3wt.%NH4F,water and ethylene glycol at 25?stirring at constant temperature for 2-5h.The effects of different process conditions on the morphology of nanotubes were studied and characterized by SEM and XRD.The experimental results show that the oxidation voltage has a great influence on the diameter of titanium dioxide nanotubes.When the voltage reaches 60 V,the diameter of nanotubes reaches 101.4 nm.When the voltage increases further,the nanotubes are damaged.The oxidation time mainly affects the length of nanotubes.When the oxidation time reaches 2 hours,titanium dioxide nanotubes begin to form.When the oxidation time reaches 5 hours,the length of nanotubes increases from 1.94 to 2.82 microns.When the content of NH₄F in electrolyte is 0.3wt.%,the nanotubes grown on the surface of titanium matrix are most uniform and compact.When the content of NH₄F is too high,the corrosion of nanotubes is serious.The water content in the electrolyte affects the formation of nanotubes and the smoothness of the tube wall.When the water content is 10%,the separation degree of the nanotubes is good and the tube wall is corrugated.After annealing at 450 C,the nanotubes were transformed from amorphous structure to anatase structure,and the morphology remained unchanged.By constant current oxidation before constant voltage anodic oxidation,the titanium dioxide nanotubes are more uniform and uniform,and the morphology is improved.2.Hydroxyapatite coatings were prepared by electrochemical deposition on the surface of titanium dioxide nanotubes formed after oxidation of titanium matrix.The effect of current density on the hydroxyapatite coatings during deposition was studied.The experimental results show that the current density affects the local pH value and hydrogen evolution reaction of the cathode.With the increase of current density,the local pH value of the cathode increases,which promotes the nucleation of hydroxyapatite.The hydroxyapatite shows more compact,thicker and have higher bonding strength.When the current is further increased,the hydrogen evolution reaction of the cathode is intense,and the large amount of hydrogen escaping leads to the hydroxyapatite coating composition.Solution and fracture make the coating show porous structure,reduce thickness and easy to fall off from the matrix.The results show that the surface of the hydroxyapatite coating is dense,the thickness is 14.3 um,and the bonding strength is 18.5 MPa at the current density of 2 mA/cm²..