Mechanism study of self-organized TiO2 nanotube arrays by anodization

Abstract

Based on analysis of the current-time curve and observation of surface morphology including top, cross-section, bottom and substrate views by scanning electron microscopy (SEM), a new growth, dissolution-breakdown model, of self-organized titania nanotube arrays is presented. By this model, many phenomena raised during anodization are explained, such as the sharp decrease of current in initial period, current transient, occurring of ridges on tube walls, and formation of not pores but tubes etc. Furthermore, the reason for the occurrence of a porous structure, the balance between internal energy and surface energy, was proposed too. This study may also shed light on the formation of porous oxide films on other valve metals.

Formation of Hydroxyapatite Coating on Anodic Titanium Dioxide Nanotubes via an Efficient Dipping Treatment

“…It is well accepted that the formation of TiO 2 nanotubes in F -containing solution relies on three spontaneous processes: field-assisted oxidation of titanium to form titanium dioxide, fieldassisted dissolution of titanium dioxide, and chemical dissolution of the TiO 2 by etching with fluoride ions. [29,32,33] It is believed that the final thickness of nanotube array is dominated by the dynamic equilibrium between the oxidation and the dissolution processes. As shown in Figure 3(d), the diffusion of fluoride anions through the short nanotubes to etch the titanium substrate to develop the TiO 2 nanotubes is relatively facile, as demonstrated in the first 60 minutes of anodization.…”

“…During the last decade, there have been numerous studies on the formation of TiO 2 nanotubes by anodization. [26][27][28][29][30] It was reported that the tubes with lengths ranging from 15 to 500 nm with about several micron thickness could be grown under anodic potentials ranging from 1 to 20 V in F -containing acidic electrolyte, [26,27] resulting in TiO 2 nanotubes possessing a hollow structure for filling with bioactivating species and providing an interface suitable for anchoring connective tissue. It was reported that the TiO 2 nanotubes have many potential biomedical applications, for example, use as a bond scale and supporting platform for bone and stem cells, local delivery of antibiotics off-implant at the site of implantation, and the control of hemorrhaging by forming significantly stronger clots with reduced clotting times.…”

Anodic formation of aligned and bamboo-type TiO2 nanotubes at constant low voltages

“…(b) Localized dissolution and breakdown of barrier occurs due to the presence of F À ions under electric field, and some small pits originate on the Ti surface which, in turn increase the electric field intensity across the remaining barrier layer resulting in further pore growth. (c) At the steady growing stage, as there are periodical current oscillations occurring during the anodization process that can be very regular [29], when meeting with a current spike, the oxygenation of Ti is faster and deeper than usual. (d) Gradually, tensile stress starts to occur between the two neighboring tubes as a result of volume expansion.…”

“…One of the main factors for generating gaps is the mechanical stress in the oxide tubes coming from the electrostriction and the volume expansion between the metal and oxides [23]. It is known that the bond lengths of Ti-Ti and Ti-O are 0.189 nm and 0.185 nm, respectively [29]. So obviously with the generation of TiO 2 , the volume expands in some degree due to the participation of O atoms.…”

Photovoltaic Behavior of Dye-sensitized Long TiO2Nanotube Arrays

“…For example, there are several reports on the correlation of NT length to the photovoltaic properties of NT-based DSCs. [26][27][28][29][30][31] In early studies, short NTs of less than a few microns in length were applied, with an observed η of 1.1-3.3%. [21][22][23][24][25][26][27][28][29][30][31][32] Recently, Diau et al controlled the NT lengths to 6-30 μm 17 and 15-57 μm, 18 and in these ranges η was monotonously increased up to 5.2% and 6.1%, respectively, reporting that the η enhancements were caused by the increases in the overall surface area of the NT arrays.…”