Choong-Soo Chi

Formation behavior of anodic TiO2 nanotubes in fluoride containing electrolytes

TiO2 nanotube 层能在由电气化学的方法包含氟化物的电解质与钛被形成。氟化物离子，阳极的氧化物的 crystallinity，和化学状态的角色被调查。结果证明阳极的电影由氧化物和氢氧化物的小数量组成。F 的存在？离子导致 Ti 氧化物层的化学溶解并且阻止氢氧化物降水。因而，有增加氟化物的化学溶解率增加在 02% 的范围满足(在集体部分) 因为 F 吗？在电解质的离子攻击接口并且允许电解质的离子容易渗透进接口。同样阳极化的 TiO2 nanotubes 展览非结晶的结构。热地对待的 nanotubes 由锐钛矿和金红石阶段的混合物组成。

Electrochemical characteristics of alumina dielectric layers

Abstract The electrochemical characteristics of alumina dielectric layers were studied using a surface roughness factor and an impedance spectroscopy. From the limiting diffusion current method, the surface area factor of the dielectric anodic layer with low electrical conductivity was estimated to be 1.03. As alumina dielectric films on Al have a variable stoichiometry, the electrochemical behavior of Al 2 O 3 layer can be monitored by evaluating an equivalent circuit with Young impedance of dielectric constant with a vertical decay of conductivity.

Stress corrosion cracking properties of environmentally friendly unleaded brasses containing bismuth in Mattsson's solution

The purpose of the present investigation was to study the stress corrosion cracking (SCC) properties of environmentally friendly Bi-brasses in Mattssons solution (0.05 M copper sulfate and 0.5 M ammonium sulfate, pH 7.4) at room temperature. Three unleaded brasses with Bi content ranging from 1 to 3 wt.% and a conventional leaded brass for comparison were investigated. The effect of Bi on SCC of unleaded brasses was studied through polarization test, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and slow strain rate tests (SSRT). Potentiodynamic polarization studies indicated that the corrosion resistance of Bi-containing brasses was improved as the content of Bi, which shown passivating characteristic in Mattssons solution, increased. The Pb- and Bi-containing brasses presented an inductive behavior on impedance data in low frequency region at the open-circuit potential (OCP). Such behavior could be attributed to the adsorption process on the alloy surface. The observed dezincified layers after SSRT should be particularly good initiators of SCC as they could induce tensile stress. As the content of Bi increased, the thickness of dezincified layer and the volume fraction of preferentially attacked phase decreased, therefore, SCC resistance of the Bi-containing brasses was improved.

Surface roughness factor of anodic oxide layer for electrolytic capacitors

Abstract The roughness factor of barrier-type anodic oxide layer with low electrical conductivity was evaluated using electrochemical measurement in electrolyte with redox couple. To evaluate the surface roughness factor, the surface of barrier-type oxide layer was covered with thin layer of platinum by sputtering. From the limiting diffusion current method the surface roughness factor of barrier-type Al 2 O 3 estimated to be 1.03. This factor is in good agreement with the results of the cross-sectional characteristics by using transmission electron microscope.

A Control of the Nanopore Regularity in Alumina Layer

This study placed a focus on fabrication factors and surface morphology characteristics to obtain anodic alumina layers with ordered nanopore arrays using two-step anodization process. The regularity of nanopore arrangement in anodic alumina was prepared in oxalic acid at 40 V. The regular array was shown to be more strongly dependent on the time of first anodization than that of second anodization. The widening process of oxide surface in H3PO4 solution clearly exhibits that the nanopore diameter of the alumina layer subjected to widening time increased linearly at a rate of 0.6 nm/min at 30°C, and 0.8 nm/min at 40°C. The pore arrays in anodic alumina were analyzed by SEM.

Purifying behavior of photocatalytic TiO2 anodized in nitrate ion containing solution

Abstract Mesoporous titanium dioxide films were fabricated on titanium plates by micro-arc oxidation method. To increase the photocatalytic activity of the films, NH4NO3 was added to the H2SO4 solution, and anodizing was carried out at high voltages using a DC power supply. The crystal structure, chemical composition, surface morphology and the optical property of the films were investigated by XPS, XRD, UV-VIS spectroscopy and SEM. The photocatalytic activity of the films was evaluated by the decomposition of aniline blue, and the activity of the films for the degradation turned out to be improved by the additives to the electrolyte solution. The enhanced photocatalytic activity might result from the increased porosity and nitrate ion incorporation into the anodic films by micro arcing, and thereby the TiO2 layer might exhibit an improved absorption property for the visible light.

Impedance of Barrier-Type Oxide Layer on Aluminum

The impedance characteristics of barrier-type oxide layers on aluminum was studied using impedance spectroscopy. Since anodic films on Al have a variable stoichiometry with a gradual reduction of oxygen deficiency towards the oxide-electrolyte interface, the interpretation of impedance spectra for oxide layers is complex and the impedance of surface layers differs from those of ideal capacitors. This frequency response of the layer with conductance gradients cannot be described by a single resistance–capacitance (RC) element. The oxide layers of Al are properly described by the Young model of dielectric constant with a vertical decay of conductivity.

Characteristics of Photocatalytic Titania Fabricated by Anodization

The anodic titanium dioxide (TiO2) films for photocatalyst were prepared by anodization in acid solution. The characteristics of surface layer and the photocatalytic efficiency of the anodic film have been investigated. The chemical states of anodic film were analyzed using XPS, and the photocatalytic efficiency was evaluated by the degradation rate of aniline blue. From XPS results the component elements of the electrolyte, P and S, were observed in the anodic film, which were incorporated from the electrolyte into the oxide layer during anodization. The porous TiO2 film exhibited high photocatalytic efficiency for degradation of aniline blue.

Fabrication Parameters for Highly Ordered Nano-Pore Arrays in Alumina Template

The fabrication parameters for highly ordered nanopore arrays formed by self-organized anodization on aluminum have been investigated. To fabricate ordered nanopore arrays in alumina layer a two-step anodization process was used in oxalic acid solution. The regular nanopore arrangement, interpore distance and pore diameter in alumina surface were strongly dependent on the applied potential at anodization. The interpore distance and pore diameter increased with anodic applied potential, and hexagonally ordered pore arrangements in alumina were obtained by anodization at 40V. For the effects of the heat treatment of aluminum substrate on size of domains with same pore orientation, the domain size increased with increasing annealing time.

Effects of Hydration Treatments on the Phase Transition of Anodic Aluminum Oxide Layers

Hydration treatments were performed on the pure aluminum substrate at followed by anodizing and heat treatments on the layers. The transformation behaviors of the oxide layers according to the hydration treatment were studied using TEM, XRD, RBS etc. Above the hydrous oxide film could be formed, which were turned out to be hydrous oxides(AlOOH O). The anodization on the hydrous oxide film was more effective for the transition of amorphous anodic oxides to the crystalline comparing with the case for anodizing on the aluminum substrate without hydration treatment And additional heat treatments were also helpful for the acceleration of the transformation of the hydrous oxide to . During the heat treatment the interface between and the hydrous oxide layers migrated to the outer side of hydrous layer.