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

ИССЛЕДОВАНИЕ ДЖОУЛЕВА РАЗОГРЕВА ОКСИДА АЛЮМИНИЯ В ПРОЦЕССЕ ЭЛЕКТРОХИМИЧЕСКОГО АНОДИРОВАНИЯ

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.Проведено исследование распределения температуры внутри оксида алюминия вследствие выделения джоулева тепла во время электрохимического анодирования. Обнаружено, что температура растущего оксида может достигать 300 °С в зависимости от мощности выделяемого джоулева тепла. Определен ряд параметров (коэффициент теплопередачи, удельное изменение температуры) и значения критериев подобия процесса теплопередачи. Проведено численное моделирование распределения температуры внутри исследуемых систем при заданной потребляемой мощности электрохимического анодирования

Computational fluid dynamics / Monte Carlo simulation of dusty gas flow in a “rotor-stator” set of airfoil cascades

A dusty gas flow through two, moving and immovable, cascades of airfoils (blades) is studied numerically. In the mathematical model of two-phase gas-particle flow, the carrier gas is treated as a continuum and it is described by the Navier-Stokes equations (pseudo-DNS (direct numerical simulation) approach) or the Reynolds averaged Navier-Stokes (RANS) equations (unsteady RANS approach) with the Menter k-ω shear stress transport (SST) turbulence model. The governing equations in both cases are solved by computational fluid dynamics (CFD) methods. The dispersed phase is treated as a discrete set of solid particles, the behavior of which is described by the generalized kinetic Boltzmann equation. The effects of gas-particle interaction, interparticle collisions, and particle scattering in particle-blade collisions are taken into account. The direct simulation Monte Carlo (DSMC) method is used for computational simulation of the dispersed phase flow. The effects of interparticle collisions and particle scattering are discussed

Effects of particle mixing and scattering in the dusty gas flow through moving and stationary cascades of airfoils

Time-dependent two-dimensional (2D) flow of dusty gas through a set of two cascades of airfoils (blades) has been studied numerically. The first cascade was assumed to move (rotor) and the second one to be immovable (stator). Such a flow can be considered, in some sense, as a flow in the inlet stage of a turbomachine, for example, in the inlet compressor of an aircraft turbojet engine. Dust particle concentration was assumed to be very low, so that the interparticle collisions and the effect of the dispersed phase on the carrier gas were negligible. Flow of the carrier gas was described by full Navier-Stokes equations. In calculations of particle motion, the particles were considered as solid spheres. The particle drag force, transverse Magnus force, and damping torque were taken into account in the model of gas-particle interaction. The impact interaction of particles with blades was considered as frictional and partly elastic. The effects of particle size distribution and particle scattering in the course of particle-blade collisions were investigated. Flow fields of the carrier gas and flow patterns of the particle phase were obtained and discussed

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

Strong green erbium-related luminescence from a xerogel-porous anodic alumina structure

Room temperature, green photoluminescence from erbium-doped titania and indium-tin oxide xerogel films confined in porous anodic alumina has been examined. The dependence of the photoluminescence intensity and the shape of the spectra on xerogel composition, erbium concentration and degree of pore filling is shown.</p

INVESTIGATION OF ALUMINA JOULE HEATING AT ELECTROCHEMICAL ANODIZATION

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

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