Preparation And Characterization Of TiO₂Coatings With High Wettability On The Surface Of Titanium

Using sodium tetraborate as electrolyte, a porous titania (TiO2) coating with a novel morphology of cortex-like slots was successfully prepared on the Ti surface through micro-arc oxidation (MAO). The effect of micro-arc oxidation time, electrolyte concentration, frequency and duty cycle on the TiO2coatings has been studied. Scanning electron microscopy (SEM) and X ray diffraction (XRD) were used to analyze the morphology of the oxide coating, the coating thickness and phase composition. The surface absorption behavior of the coatings was characterized by dynamic contact angle meter. Contact angle test contrasts the wettability characterization of the new coating and volcanic coating. The self-designed water absorption test device was used to study the absorption properties of the new coating and volcanic coating. Biocompatibility of the new coating and volcanic coating was studied by cultivating the MG-63cell on the surface of samples.We have studied the regularity of coating changing on the surface of Ti and the mechanism of sodium tetraborate via changing the micro-arc oxidation treating time. The results show that the growth of the oxide film is divided into three stages:the intensive oxide pore stage; the stage of the generation and growth of the worm-like deep slots; deep slots merged with each other stage. The film thickness changes in a shape of parabola during the micro-arc oxidation; and some holes in the interior of the film connect with the holes on the surface of coating. Sodium tetraborate can continuously provide plentiful hydroxyl ions through hydrolysis process during micro-arc oxidation, and then the hydroxyl ions yield oxygen through electrolysis process. Oxygen is involved in arcing reaction, and then many discharge pores form on the Ti surface. The cortex-like coatings with interconnected pores and slots have better wettability and water absorption than volcanic coatings. MG-63cell can grow in the deep slots and continued to spread out, have better biocompatibility than volcanic coatings.We have studied the change rule of coatings by changing the concentration of electrolyte. As electrolyte concentration increases, the morphology of coating was not obvious and then gradually appear, finally grow to the honeycomb morphology due to continuous discharge disappearance. With the increase of the concentration of electrolyte the film thickness changes likes a parabola; and vermiform wall gradually become loose; water absorbing ability increases gradually. The oxide film is rutile phase. The contact angle becomes zero within1min when the electrolyte concentration is greater than or equal to0.1mol/L.The change rule of coatings by changing the frequency has been studied. As the frequency increases, the cortex morphology is obvious, and then grow to honeycomb morphology due to continuous discharge made the vermiform wall peel off. The thickness of the oxide film does not change significantly with the increase of frequency and keep at about15μm; water absorbing ability of the coating increases gradually. The oxide film is rutile phase. The contact Angle becomes zero within1min when the frequency is greater than or equal to500Hz.We have studied the change rule of coatings by changing the duty cycle. The results show that with the increase of duty cycle the vermicular slot changes from the uneven distribution to uniform distribution; and cortex morphology becomes obvious gradually. When duty cycle becomes25%, the coating becomes loose honeycomb morphology. With the increase of duty cycle, the thickness of the oxide film changes likes a parabola; and water absorbing ability of the coating increases gradually. The oxide film is rutile phase. The contact angle becomes zero within1min when the frequency is greater than or equal to15%.