Research has been carried out on the formation of tubular aluminum oxides by local electrochemical anodization in aqueous solutions of organic acids such as formic, citric, tartaric, malic and others. Self-ordered nanostructures formed this way can be used in the manufacture of various optical devices. Tubular aluminum oxides formed by local electrochemical anodization in organic acids have a high concentration of anionic complexes containing carbon atoms over 10 at.%. Studies of reflection spectra showed effective anti-reflection properties of films with a specular reflection coefficient of 0.7–1.4 %.

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.

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 temperature distribution within the anodic alumina during the anodic process has been studied. The temperature increase can reach 300 °C at high lever of Joule heat. The parameters of the heat process such as the heat temperature coefficient, the specific temperature change and the number of thermal process similarity criteria have been determined. The simulation of the temperature distribution within the test system for the given parameters of anodizing has been performed.

The surface potential of anodic alumina films and their charge properties have been studied. The surface potential of anodic alumina films after anodic process has positive values, but then this potential is decreased to zero level with subsequent transition to negative values. The negative displacement of the surface potential is associated with a negative built-in electric charge of aluminum anodic oxide. The mechanism of transition from the positive built-in electric charge to the negative one inside the anodic oxides is proposed. The highest density of the negative charge is observed in the films formed in electrolytes based on the aqueous solutions of the citric and phosphoric acids.