Preparation Of The Porous Anodic Titania Nanotubes And Formation Mechanism

According to the theory of acidic field-assisted dissolution, Porous Anodic Titania Nanotube (PATNT) can only be prepared in containing fluorine ions electrolyte, while Barrier Anodic Titania(BAT) forms in fluorine ions free electrolyte, generation and deepening of PATNT channels are caused by acidic field-assisted dissolution. But the theory cannot give a convincing explanation for hexagonal close packed structure and hemispherical bottom structure of channels.At first, the limitations of traditional PATNT formation mechanism are discussed. We point out that the formation of PATNT channels does not result from acidic field-assisted dissolution but evolution of oxygen in nanotubes. And then we present a novel growth model and new formation mechanism based on previous studies of PATNT. The oxygen bubble mould effect can explain some problems reasonably, such as the generation and development process of nanochannels, hexagonal close packed structure and hemispherical bottom structure. Then two methods are used to prove the novel model indirectly. Secondly, in order to seek for the best pretreatment method, we study three different pretreatment processes which have different influence on the surface morphology structure of titanium and PATNT. Many kinds of the surface morphologies of titanium and PATNT can be seeen and the formation causes of them are explained. Thirdly, titanium anodic oxidation is pocessed by changing three technical conditions, the anodic oxidation voltage, time, and the electrolyte temperature included. The samples fabricated on different conditions are characterized by scanning electron microscopy emission (SEM), electrochemical test system and energy dispersive spectrometer(EDS). With the analysis of SEM images, current-time curves for anodic oxidation and EDS energy spectrum, the best technological conditions for titanium anodic oxidation method can be confirmed.Finally, in order to prepare more smooth surface morphology and highly ordered PATNT arrays, we use two post-treatment methods, which have big effects on PATNT surface morphology and nanotubes structure, and explore a post-treatment method which has the best performance.