The changes of surface potential and built-in charge in alumina films after the anodization process

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

Effect of anodic voltage on parameters of porous alumina formed in sulfuric acid electrolytes

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° 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 2.7×1010 V/m in the layers with a porosity of 1% in growing alumina

ОСОБЕННОСТИ ФОРМИРОВАНИЯ АНОДНОГО ОКСИДА АЛЮМИНИЯ С ТРУБЧАТОЙ СТРУКТУРОЙ

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.Проведено исследование условий формирования пористого анодного оксида алюминия с трубчатой структурой. Показано, что самоупорядоченная трубчатая структура оксида алюминия формируется в том случае, если температура барьерного слоя превышает температуру электролита на несколько десятков градусов для вязких электролитов (вязкость более 10-2 Па·с при 20 °С) и на сто градусов и более для водных электролитов с низкой вязкостью (вязкость менее 10-2 Па·с при 20 °С). Сделано предположение, что температура барьерного слоя в процессе формирования самоупорядоченного трубчатого оксида алюминия может достигать нескольких сот градусов, что объясняет возникновение шарообразных структур в устьях пор, формируемых в результате оплавления алюминия в процессе анодирования

Pecularities of tubular anodic alumina formation

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

Extreme Heating of Alumina Barrier Layer During High Electric Field Anodization of Aluminum

The temperature of alumina barrier layer during a high electric field anodization of aluminum (the current density more than 50mA/cm2)2) has been studied by analyzing the aluminum film resistance. In the case of Joule heat power density to be larger than 20W/cm2, the temperature inside the barrier layer can exceed 660∘660∘C, which leads to the local melting of aluminum. Scanning electron microscopy has shown the location of molten aluminum droplets and their movement during the anodization process

Anodic titanium oxide with controllable optical properties for biomedical applications

Titanium oxide films have been intensively studied in recent years due to application of this material in medicine as coating for titanium implants [1-3]. The investigations of anodic titanium oxide fabrication and titanium oxide optical properties are presented in this work. In addition we have reviewed the possibilities of utilization of these oxide films in maxillofacial surgery for visualization and masking of titanium implants

Mechanism of Anodic Growth of Tubular Titania

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

Pecularities of tubular anodic alumina formation

Проведено исследование условий формирования пористого анодного оксида алюминия с трубчатой структурой. Показано, что самоупорядоченная трубчатая структура оксида алюминия формируется в том случае, если температура барьерного слоя превышает температуру электролита на несколько десятков градусов для вязких электролитов (вязкость более 10-2 Па·с при 20 °С) и на сто градусов и более для водных электролитов с низкой вязкостью (вязкость менее 10-2 Па·с при 20 °С). Сделано предположение, что температура барьерного слоя в процессе формирования самоупорядоченного трубчатого оксида алюминия может достигать нескольких сот градусов, что объясняет возникновение шарообразных структур в устьях пор, формируемых в результате оплавления алюминия в процессе анодирования. 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