Study On Structural Properties And Corrosion Resistance Of Anodized Film On Titanium Surface

The titanium surface oxide film prepared by anodic oxidation has been widely used in many fields,such as corrosion protection,biomedicine,new energy materials and hydrogen production,which thanks to its advantages of corrosion resistance,biocompatibility,photocatalysis,and the preparation process is also simple,low cost and less pollution.In this paper,the industrial pure titanium(TA2)was used as the matrix material and the anodic oxidation process was studied.The structure of the film and the phase composition were analyzed,the microstructure,the film formation process and crystallization mechanism of oxide film were studied by characterization and calculation of TA2 film surface morphology,structure,crystallization behavior and electrochemical properties.The effect of anodic oxidation potential,surface mechanical attrition treatment on the structure and properties of the oxide film was studied under the condition of 0.5 M H2SO4 electrolyte.The structure,valence state and content of titanium compounds at different depths were analyzed quantitatively by XPS sputtering method;The relationship between the content of various compounds and the depth of oxide film was established;With the theory of the influence on the anodic oxidation potential,structure characteristics,and the electrochemical properties of oxide film and defect diffusion coefficient characteristics,to construct the lattice defect model of oxide film formation and research formation mechanism and influencing factor.The results show that the thickness of the oxide film increases,the crystallization rate increases and the corrosion resistance increases with the increase of the potential.High potential promotes the formation of Ti4+ compounds and anatase core.The oxide film is composed of TiO2,Ti(OH)4,TiO2H2O,Ti2O3 and TiO,the content changes continuously with depth.The formation of oxide film is related to the diffusion of oxygen vacancy and titanium cation in the oxide film.Oxygen vacancies was formed at the interface between titanium and oxide film,and was annihilated at the interface between oxide film and the solution.The titanium cation gap was formed at the interface between the oxide film and the solution,and was annihilated at the interface between titanium and oxide film.The oxide film grows in the direction of the matrix and solution.On the basis of the above study,the TA2 was treated with two anodic oxidation in the condition of high porosity.The thickness of the oxide film can be increased and the porosity can be reduced by the two oxidation anodic oxidation treatment.The thickness of the oxide film was increased by about 17.3%,and the surface micropores disappeared at the first pressure was 30 V and the final potential was 40 V.For the first time,a dense initial oxide film was formed,the two pressure treatment reduced the density of oxygen evolution reaction,so that the porosity of the oxide film formed by the two oxidation decreased obviously.The two oxidation treatment is helpful to the growth of the oxide film to the substrate,which leads to the increase of the thickness of the oxide film.Moreover,the two oxidation treatment enhanced the corrosion resistance of TA2.Compared with the direct pressure 40 V sample,the self corrosion potential and the corrosion current density of the first time pressure of 30 V and the two times the pressure of 40 V were increased by about 0.16 VSCE,the value has decreased by about an order of magnitude.Thus,this method can reduce the corrosion tendency and reduce the corrosion rate.According to the conclusion that the surface morphology has a significant effect on the formation of oxide film,the mechanical polishing treatment of TA2 is expected to achieve the purpose of refining the surface grain,increasing residual stress,defect and surface electron density,and improving the surface activity.The mechanical grinding can increase the thickness of oxide film and improve its corrosion resistance.It is found that the surface mechanical attrition treatment can change the nucleation of oxide film.Due to the increase of the surface energy of TA2,the nucleation energy of different Ti compounds decreased,the nucleation process changed from continuous nucleation to instantaneous nucleation,and the nucleation rate increased significantly;The high surface energy can provide enough energy for the growth of oxide film,and accelerate the diffusion of vacancies and ions,This will result in the diffusion rate of oxygen vacancy and titanium cation in the oxide film,which is 2 orders of magnitude higher than that of the surface mechanical polishing process.The corrosion potential was increased by 0.462 VSCE,and the self corrosion current density decreased 0.005 A.cm-2.In the NaCl solution,the anodic oxidation of TA2 oxide film is easy to form "the oxygen concentration cell",the Cl-moves to the hole,and the inner surface of the hole forms a corrosion environment with no oxygen,low pH and high Cl-concentration,and the rupture of the oxide film in the hole causes the Ti matrix to be exposed to the corrosive medium,and the equilibrium potential decreases rapidly,thus it forms a "contact corrosion couple".The effect of corrosion acceleration is related to porosity.When the porosity is low,the corrosion rate decreases obviously.The two anodic oxidation treatment can obviously improve the surface structure,reduce the porosity of the oxide film,and reduce the influence of the hole on the corrosion resistance of the oxide film.The defect density in the oxide film is the main factor that affects the corrosion resistance of the oxide film when the surface pores almost disappear.The Cl-in the NaCl solution can be adsorbed on the point defects in the oxide film,disrupting the Mott-Schottky pair reaction,The gap between the Ti matrix and the oxide film interface leads to the separation of the oxide film and the Ti substrate,which leads to the breakdown of the oxide film.Mechanical change film nucleation mode and promote the diffusion of O vacancy and Ti cation gap etc by grinding treatment,significantly reduces the defect density of the oxide film,effectively inhibit the adsorption of Cl-on the surface of the oxide film,and ultimately improve the corrosion resistance of the film.