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• The oxidation area on the BPE was visualized using interference colors. • The thickness of niobium oxide films was evaluated via the electrochemical method. • The film formation behavior was consistent with that in conventional anodization. • The effective voltage contributing to film growth was lower than applied voltage. The anodic oxidation of a wireless niobium substrate serving as a bipolar electrode (BPE) in a direct or alternating current electric field was investigated in detail via spectrophotometry, electrochemical measurement, glow discharge–optical emission spectroscopy, and direct microscopic observation. Niobium oxide was a suitable material for the experiment because it is amorphous and can be evaluated through conventional electrochemical methods. It also has a clear interference color, enabling easy optical evaluation. The effect of the BPE configuration (e.g., vertical and horizontal alignments) in the cell on the anodic oxidation area was also investigated visually using the interference color. Transmission electron microscopy observation was also performed for an accurate measurement of the thickness of the anodic film formed on the niobium BPE. Although the basic film formation behavior and film composition were consistent with those in conventional anodization, even in wireless operation, the effective voltage directly contributing to film formation was found to be lower than the applied voltage (30%–70% of the applied voltage), depending on the electrolysis conditions. [ABSTRACT FROM AUTHOR]

In this study, the electrical potential distributions on aluminum bipolar electrodes (BPEs) subjected to bipolar anodization in a direct current (DC) electric field were investigated. Aluminum sheets were used as BPEs, suspended in an electrolyte solution, and positioned either vertically or horizontally at the center of a cell. The results of reflective interference measurements, depth-profiling analysis, and re-anodization clearly revealed that the thicknesses of the porous alumina films and barrier layers near the aluminum substrates can be taken to represent the potential distributions on the horizontally located BPEs; the thickest anodic alumina was formed at the edge of the anodic pole of the BPE, and its thickness continuously decreased in the direction of the cathodic pole. Furthermore, the area of the anodic reaction was much larger than expected, accounting for 90% of the BPE.

The electrical potential gradients on aluminum bipolar electrodes (BPEs) subjected to bipolar anodization in an alternating current (AC) electric field were investigated by performing scanning electron microscopy, dyeing the anodized specimens, and measuring the resistance in the alumina films after re-anodizing the samples. The thickness and morphology of each alumina film varied, which reflected the unique potential distributions on the BPEs in the AC electric field. The electrical resistance was symmetrical and increased linearly from the centers of the BPEs to their extremities. This synthetic approach should lead to the development of various functional materials using bipolar electrochemistry.

Technological features for the formation of 5-100 μm thick implanted aluminum elements and free anodic nanoporous Al2O3 structures simultaneously by a two-sided through electrochemical anodization were studied. It was proved that the thickness of the free alumina plate, the distribution and sizes of the interconnection system in its volume were varied by technological conditions.

Technological methods for the formation of 73-216 μm thick porous two-layer Al2O3 membranes with ~ 55 nm pores diameters by a two-sided through anodization in oxalic acid electrolyte and subsequent bipolar anodization were designed. High shape stability and crack resistance after high-temperature ( >500°C) treatments, ~ 20-23 W/m·K thermal conductivity, ~ 7,2 - 7,4 relative dielectric constant were obtained.

[Display omitted] • The potential gradients on bipolar electrodes were investigated. • Bipolar anodization of aluminum was conducted in a direct current electric field. • Anodic films with structural gradients were formed on the unconnected aluminum. • The area of the anodic reaction was much larger than expected. In this study, the electrical potential distributions on aluminum bipolar electrodes (BPEs) subjected to bipolar anodization in a direct current (DC) electric field were investigated. Aluminum sheets were used as BPEs, suspended in an electrolyte solution, and positioned either vertically or horizontally at the center of a cell. The results of reflective interference measurements, depth-profiling analysis, and re-anodization clearly revealed that the thicknesses of the porous alumina films and barrier layers near the aluminum substrates can be taken to represent the potential distributions on the horizontally located BPEs; the thickest anodic alumina was formed at the edge of the anodic pole of the BPE, and its thickness continuously decreased in the direction of the cathodic pole. Furthermore, the area of the anodic reaction was much larger than expected, accounting for 90% of the BPE. [ABSTRACT FROM AUTHOR]

• The potential gradients on bipolar electrodes were investigated. • Bipolar anodization of Al was conducted in an alternating current electric field. • Film thickness and electrical resistance were symmetrically distributed. • Simple visualization revealed unusual surfaces with structural gradients. The electrical potential gradients on aluminum bipolar electrodes (BPEs) subjected to bipolar anodization in an alternating current (AC) electric field were investigated by performing scanning electron microscopy, dyeing the anodized specimens, and measuring the resistance in the alumina films after re-anodizing the samples. The thickness and morphology of each alumina film varied, which reflected the unique potential distributions on the BPEs in the AC electric field. The electrical resistance was symmetrical and increased linearly from the centers of the BPEs to their extremities. This synthetic approach should lead to the development of various functional materials using bipolar electrochemistry. [ABSTRACT FROM AUTHOR]