The anodic growth conditions of titania with a tubular structure are investigated. We propose a mechanism of anodic growth of tubular titania, which presupposes that electrochemical oxidation of titanium is predominantly confined to the bottom of pores in a barrier layer, i.e., where the anodic current density is higher, which causes a temperature rise in these regions. As the barrier layer temperature exceeds a certain threshold, the structure of growing oxide changes from the commonly obtained porous honeycomb-like structure to a tubular one. The proposed mechanism is supported by experimental results.

The conditions for the formation of anodic titanium oxide with a tubular structure were studied. The mechanism for the formation of tubular titanium oxide based on the localization of the electrochemical oxidation of titanium in the places of the barrier layer at the bottom of the pore, where the density of the flowing anodic current is increased, as a result of which the temperature of these regions increases. With an increase in the temperature of the barrier layer above the threshold value, a transition from the traditional «honeycomb-like» porous structure to the tubular structure takes place. The proposed mechanism is confirmed by the results of experimental research.

Local porous aluminum anodizing with a photolithography mask has been carried out at anodic voltages varying from 15 to 200 V in sulfuric acid electrolytes. Record anodic voltages at room temperature have been achieved leading to new parameters of porous alumina such as interpore distance up to 320 nm, forming cell factor up to 1.2 nm/V, thickness expansion factor up to 3.5, porosity up to 1%, sulfur concentration up to 7.7 at.%. A central angle of porous alumina cells has been measured in concave points as well as in peak points of porous alumina cells at the border with aluminum. The measurements have shown that central angles can reach 90 degrees at anodic voltages larger than 100 V. The electric field distribution in porous alumina cells has been simulated for different central angles. It is found that the electric field reaches 2.7x10(10) V/m in the layers with a porosity of 1% in growing alumina.

We have shown that the surface potential of anodic alumina films changes in time: immediately after the anodization process it was positively followed by the substantial decrease to negative values. Such variations of the surface potential can be associated with the negative built-in electric charge in alumina. The highest negative charge density occurs in the films formed in citric and phosphoric electrolytes.

The formation conditions of anodic alumina with a tubular structure have been investigated. It is shown that alumina has the self-ordered tubular structure at temperature of barrier oxide layer to be several tens of degrees more than electrolyte temperature in cases of viscous electrolytes (viscosity more than 10-2 Pa·s at 20 °C) and hundred degrees more in cases of low viscous electrolytes (viscosity less than 10-2 Pa·s at 20°C). It is assumed that temperature of the barrier layer during the formation of the self-ordered tubular alumina can reach several hundred degrees because of the presence of spherical structures in the pores mouths. These spheres are expected to be formed due to the melting of an aluminum substrate during the anodizing process.