The Coloration And Properties Of Titanium Oxide Films By Anodization

Titanium and titanium alloys are widely used as medical materials because of their good biocompatibility and corrosion resistance.The surface modification can improve the biocompatibility,and different types of implants can be color-coded as well.Among the many surface modification methods for titanium and titanium alloys,anodization has attracted attention because of its simple controllability,low cost with simple equipment.The purpose of this study is to study the growth mechanism of the oxide film during the anodization of titanium and the relationship between the oxide film thickness and its color.In previous work,a pure titanium film was deposited on a silicon plate by magnetron sputtering and then anodized in an acidic electrolyte.The thickness of the titanium oxide film was adjusted by parameters such as applied voltage and time.The thickness of the oxide film was analyzed by an ellipsometry to obtain the relationship between the thickness of the oxide film and the applied voltage.The effect of the applied potentials and the thickness of the oxide film on color was studied by transferring reflection spectrum to the CIE chromaticity coordinate system and shown in CIE coordinate directly.The effect of anodizing potentials on the composition,structure and morphology of the anodic oxide films was also analyzed by XPS,XRD and SEM techniques.This work also studied the growth process of anodic oxide film through anodizing.The growth model of anodic oxide films was established by studying of the anodizing current,dissolution of oxide film and the distribution of each element in anodic oxide films with depth,combining with the theory of ion migration,showing a good coincidence with the measured growth process of anodic oxide films.Compared with the oxide film anodized directly on the titanium plate in previous studies,the preparation method can obtain an oxide film with a smooth surface,so when the color and optical properties of the oxide film are studied,more accurate results can be obtained.In previous works,the color and optical properties of anodic oxide films were studied on metallic Ti.However,regular pretreatment pickling and high applied potentials cause the increasing of roughness of anodic oxide films surfaces,resulting diffused reflection and effects optical analysis such as ellipsometry and reflection,which is sensitive to the sample surface.In this work,the fabricated method is able to obtain oxide films with smooth surface and oxide/substrate interface.Therefore,accurate results of the color and optical properties were obtained for the oxide films.According to the study,the growth thickness of the oxide film has a good linear relationship with the increasing voltage.The growth of the oxide film is the result of the directional migration of ions under the electric field,of which the growth rate decreases along time exponentially.The color of the oxide film changes with the voltage and film thickness continuously and periodically,excluding the hypothesis that color was influenced by composition,indicating that the color of the anodic oxide film was mainly due to interference.