Study On Construction, Formation Mechanisum And Modification Of Titania Nanotube Arrays

In this paper, well ordered titania nanotube arrays were fabricated successfully on titanium substrate by anodic oxidation. And the morphologies, crystal forms of nanotube arrays were charactered by TEM,SEM and XRD respectively. Furthermore, the effects of anodic oxidation parameters on nanotube structure were studied. It was found that the diameters of nanotubes are controlled only by anodic oxidation potential. However, the length of nanotubes is affected by both oxidation time, temperature and pH value. As for smoothness and cleanness, they are related to the kinds of electrolyte and water contents respectively.Based on the experiments, the formation and development process of titania nanotube arrays was investigated deeply in this paper. A new mechanism named field-caused corrosion and break down was present. The main soul of this mechanism is that the occurring of tubular construction was caused by the uneven field distribution on anode surface. The lower electric field intensity leads to the chemical corrosion of titania where the nanopore forms, and the higher electric field intensity benefits happening of break down to make tube spaces. According to the field-caused mechanism, some experimental results occurring at oxidation process were explained well, for example, the proportional relation between oxide potential and tube diameter, fabrication of smooth nanotube, variation trendcy and vibration of current, the causation of lobes on nanotubes wall. Morver, the sorts of metal whose oxide can form tubular structure and nanotube arrays forming preconditions were given.According to this kind of thought, the concept of the field boundary layer was proposed. Moreover, the field distribution inside field boundary layer was obtained by means of theoretical analysis and numerical simulation, as well as the respective special behavioral feature of F-,H+ and O₂- ions inside it. In this work, the forming and growing process of nanotube arrays was divided into ten steps: 1) Formation of loose layer; 2) Formation of contact layer; 3) Occurring of microcracks; 4) developing of microcracks; 5) Formation of corrosion pits; 6) Expanding of corrosion pits; 7) Breakdown of interpores; 8) Chemical dissolution of inner pores; 9) Breakdown of interpores again; 10) Growing of nanotubesNot only that, taking thiocarbamide as additive, modified titania nanotube arrays were fabricated via anodic oxidation process. Using electrochemical workstation, the photocurrent of titania nanotube arrays made by this way were tested. The experiment results showed that whatever the samples were irradiated by visible or ultraviolet light,they had higher photocurrent density compared with unmodified samples. The photo currents of modified and unmodified samples irradiated by visible and ultraviolet light are 0.1, 0.012 and 0.7, 0.42mA/cm² respectively. At last with oxygen vacancies theory proposed by other researchers, the modified mechanism of titania nanotube arrays was explained too.