Nanotubular anodic TiO2 initial layer morphology evolution under controlled hydrodynamic and temperature conditions

Self-organized anodic TiO2 nanotubular (TNT) layers are highly interesting materials among valve metal oxides, because of the combination of a regular and controllable nanoscale geometry with the various functional properties... [ view full abstract ]

Self-organized anodic TiO2 nanotubular (TNT) layers are highly interesting materials among valve metal oxides, because of the combination of a regular and controllable nanoscale geometry with the various functional properties of titania, which make the material suitable for applications in electro- and photocatalysis, solar energy conversion, sensing, biomedical devices and Li-ion batteries [1]. Over the past few years, various research groups have published a number of works devoted to the study of morphology, chemical, electrical and optical properties of the TNT layers. However, until now some TNT morphology evolution aspects during the electrochemical oxidation were not studied well. In particular the formation, evolution and properties of TNT initial layer, formed at the beginning of anodization process on titanium surface [2], from various anodizing process conditions, which is an important factor for design, manufacture and efficiency increasing of TNT based devices.
In this paper, the origin nature concept and geometric parameters evolution studies are presented as well as the chemical and structural properties of initial TNT layer which is formed during the anodizing process of titanium substrates in non-aqueous fluorinated electrolytes under controlled hydrodynamic conditions and electrolyte temperature. During the research it was found that the thickness of the initial layer is almost independent from titanium anode rotation speed and electrolyte temperature, however with increasing of electrode rotation speed and the temperature thinning of the initial porous layer cell walls was observed. Further increase of temperature and anodization process duration leads to the main nanotubular titanium oxide layer etching that eventually leads to detachment of the upper layer from the rest of the oxide layer. X-ray diffraction and XPS analysis showed the presence of crystalline phases in the initial layer and amorphous phase of nanotubular layer underneath it, which may serve as an explanation of such behavior of TNT initial layer.

The work was supported by RFBR grant for young scientists № 31 16-33-60217 «mol_a_dk».