• Korean Journal of Materials Research
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• v.11 no.4
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• pp.329-334
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• 2001

Microstructures of barrier-type oxide layers on aluminum was studied by XRD, TEM and RBS. Fer formation of oxide layer. aluminum was anodized in a boric acid solution. The thickness of the oxide film subjected to applied voltage increased linearly at ratio of 1.54nm/V. For oxide layer anodized at 300V, amorphous structure of oxide layer was not transformed after heat treatment at 50$0^{\circ}C$ , while for oxide layers anodized at higher voltages the amorphous structure crystallized into a ${\gamma}$-alumina without any heat treatment. It was also found that the amorphous structure of oxide layer formed at 100V transformed into crystalline structure by electron irradiation. The structure was identified as ${\gamma}$-alumina.

• Journal of Technologic Dentistry
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• v.23 no.2
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• pp.161-170
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• 2002

The Purpose of this study was to investigate the chemically improvement of metal-ceramics bond strength in the course of recasting Ni-Cr metal composite system with 10wt.%, 20wt.% and 30wt.% aluminum respectively. We have tested the bond strength, micro-structure, chemical composition of each metal composites and metal- ceramic bond interfaces by 3-point bending strength tester, SEM and EDS. We have made the conclusions through this study as follow: 1. The most suitable amount of aluminum to the Ni-Cr metal composite recasting is 20wt. % for improving metal-ceramics bond strength with debonding strength value of 49.54 kgf/mm2. 2. The aluminum must be changed to small spread alumina like phases and second aluminum-metal composites phases in the morphology of Ni-Cr metal composite system by adding during it's casting. These second phases have inclined functional oxide phases mixed with metal elements and they must take roll to improvement of metal-ceramics bond strength. 3. In the case of 30wt.% aluminum appended to Ni-Cr metal composite system, an excess of second inclined functional oxide phases produce cracks and spalling of them apart from it's base material. It must be a important factor of reduction of metal-ceramics bond strength.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.14-17
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• 2015

Cleaning effect is well known mechanism of oxide layer removal in DCEP polarity. It is also known that DCEN has higher heat input efficiency than DCEP in GTAW process. Based on these two renowned arc theories, conventional variable polarity arc for aluminum welding was set up to have minimum DCEP and maximum DCEN duty ratio to achieve the highest heat input efficiency and weldability increase. However, recent several variable polarity GTA research papers reported unexpected result of proportional relationship between DCEP duty ratio and heat input. The authors also observed the same result then suggested combination of tunneling effect and random walk of cathode spot to fill up the gap between experiment and conventional arc theory. In this research, suggested combinational work of tunneling effect and rapid cathode spot changing is applied to another unexpected phenomena of variable polarity aluminum arc welding. From previous research, it is reported that wider oxide removal range, narrower bead width and shallower penetration depth are observed in thin oxide layered aluminum compared to the case of thick oxide. This result was reported for the first time and it was hard to explain the reason at that time therefore the inference by the authors was hardly acceptable. However, the suggested combinational theory successfully explains the result of the previous report in logical way.

• Journal of Powder Materials
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• v.22 no.4
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• pp.240-246
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• 2015

Anodic aluminum oxide (AAO) has been widely used for the development and fabrication of nano-powder with various morphologies such as particle, wire, rod, and tube. So far, many researchers have reported about shape control and fabrication of AAO films. However, they have reported on the shape control with different diameter and length of anodic aluminum oxide mainly. We present a combined mild-hard (or hard-mild) anodization to prepare shape-controlled AAO films. Two main parameters which are combination mild-hard (or hard-mild) anodization and run-time of voltage control are applied in this work. The voltages of mild and hard anodization are respectively 40 and 80 V. Anodization was conducted on the aluminum sheet in 0.3 mole oxalic acid at $4^{\circ}C$. AAO films with morphologies of varying interpore distance, branch-shaped pore, diameter-modulated pore and long funnel-shaped pore were fabricated. Those shapes will be able to apply to fabricate novel nano-materials with potential application which is especially a support to prevent volume expansion of inserted active materials, such as metal silicon or tin powder, in lithium ion battery. The silicon powder electrode using an AAO as a support shows outstanding cycle performance as 1003 mAh/g up to 200 cycles.

• Applied Chemistry for Engineering
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• v.9 no.4
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• pp.463-468
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• 1998

When sulfuric acid was added in HCl etching solution, corrosion of aluminum metal was inhibited by the chemical adsorption of sulfate ions. In the presence of $SO_4^{-2}$, cyclic voltammetry showed that the protective oxide film was formed on the inner surfaces of etch pits and, pit density was increased by nucleation on both the aluminum surface and the pits inside. Structure and distribution of etch pits found in AC etching of aluminum were strongly influenced by the concentration of $SO_4^{-2}$ and the amount of cathodic pulse charging. Below $0.8mC/cm^2$ of cathodic pulse charging, oxide films formed inside actively dissolving pits indicated the higher resistance to pit nucleation as the concentration of $SO_4^{-2}$ increases. However, the structural change of oxide films occurred above the $0.8mC/cm^2$ charging and the effect of $SO_4^{-2}$ was minimized, and it resulted in the rapid formation of etch pits.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.4
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• pp.923-928
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• 2010

Anodic aluminum oxide (AAO) nanotemplates for nano electronic device applications have been attracting increasing interest because of ease of fabrication, low cost process, and possible fabrication in large area. The size and density of the nanostructured materials can be controlled by changing the pore diameter and the pole density of AAO nanotemplate. In this paper, nano porous alumina films AAO nanotemplate was fabricated by second anodization method using sputterd Al films. In addition, effects of electrolyte temperature and anodization voltate on the microstructure of porous alumina films were investigated. As the electrolyte temperature was increased from $8^{\circ}C$ to $20^{\circ}C$, the growth rate of nanoporous alumina films was increased from 86.2 nm/min to 179.5 nm/min. The AAO nanotemplate fabricated with optimal condition had the mean pore diameter of 70 nm and the pore depth of $1\;{\mu}m$.

• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.1
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• pp.69-79
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• 2013

The aim of this study was to evaluate the effect of surface conditioning on the shear bond strength of zirconium-oxide ceramic to resin cement. A total of 120 disk-shaped zirconium-oxide ceramic blocks(3-TZP, Kyoritsu, Tokyo, Japan) were treated as follows: (1) no treatment; (2) sandblasting with 110 ${\mu}m$ aluminum-oxide(Al2O3); (3) particles tribochemical silica coating(RocatecTM, 3M ESPE). Then zirconium-oxide ceramic blocks were divided into six groups(10 for each group) and bonded with resin cement(Rely X U-200, 3M ESPE). (1) No treatment / No treatment (2) No treatment / Sandblasting with 110 ${\mu}m$ aluminum-oxide particles (3) No treatment / Silica coating (4) Sandblasting with 110 ${\mu}m$ aluminum-oxide particles / Sandblasting with 110 ${\mu}m$ aluminum-oxide particles (5) Sandblasting with 110 ${\mu}m$ aluminum-oxide particles / Silica coating (6) Silica coating / Silica coating. Each group was tested in shear bond strengths by UTM. Data analysis included one-way analysis of variance(ANOVA) and the Tukey Honestly Significant Difference test (P=0.05). Group that bonded two silica coated specimen showed a highest bond strength(P<0.05). Two silica coated surface conditioning group and air-abrasion and silica coated surface conditioning group showed significantly difference with other groups(P<0.05). Other groups had no significantly difference each other. Within the limitation of this study, Surface conditioning with Rocatec treatment to each side of specimen provided the highest bond strength.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3258-3264
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• 2012

Aluminum oxide ($Al_2O_3$) nanofibers were treated thermally under an ammonia ($NH_3$) gas stream balanced by nitrogen to form a thin aluminum nitride (AlN) layer on the nanofibers, resulting in the enhancement of thermal conductivity of $Al_2O_3$/epoxy nanocomposites. The micro-structural and morphological properties of the $NH_3$-assisted thermally-treated $Al_2O_3$ nanofibers were characterized by X-ray diffraction (XRD) and atomic force microscopy (AEM), respectively. The surface characteristics and pore structures were observed by X-ray photoelectron spectroscopy (XPS), Zeta-potential and $N_2$/77 K isothermal adsorptions. From the results, the formation of AlN on $Al_2O_3$ nanofibers was confirmed by XRD and XPS. The thermal conductivity (TC) of the modified $Al_2O_3$ nanofibers/epoxy composites increased with increasing treated temperatures. On the other hand, the severely treated $Al_2O_3$/epoxy composites showed a decrease in TC, resulting from a decrease in the probability of heat-transfer networks between the filler and matrix in this system due to the aggregation of nanofiber fillers.

• Corrosion Science and Technology
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• v.18 no.6
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• pp.228-231
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• 2019

Aluminum and its alloys have been widely used in various fields because of low weight, high strength, good conductivity, and low price. It is well known that aluminum alloys that cause natural oxide film can inhibit corrosion in wet, salty environments. However, these oxides are so thin that corrosion occurs in a variety of environments. To prevent this problem, an electrochemical anodizing technique was applied to the aluminum alloy surface to form a thick layer of oxide and a unique oxide shape, such as a hierarchical pore structure simultaneously combining large and small pores. The shape of the structures was implemented using stepwise anodization voltages such as 40 V for mild anodizing and 80 V for hard anodizing, respectively. To maximize water repellency, it is crucial to the role of surface structures shape. And a hydrophobic thin film was coated by 1H, 1H, 2H, 2H-Perfluorodecyltrichlorosilane (FDTS) to minimize surface energy of the structure surface. Thus, such nanoengineered superhydrophobic surface exhibited a high water contact angle and excellent corrosion resistance such as low corrosion current density and inhibition efficiency.

• Journal of Pharmaceutical Investigation
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• v.13 no.1
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• pp.1-9
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• 1983

The effect of humidity on crystallization and polymorphic transformation of hydrous aluminum oxide under various humidity at $37^{\circ}$ was examined by means of X-ray diffraction, scanning electron micrograph, IR spectra and DTA. The humidity was an important factor influencing crystallization of hydrous aluminum oxide. The growth or crystal was strongly accelerated by humidity. The aging process is assumed that it is composed of two seperate steps, an increase of the diffraction around $36{\sim}42^{\circ}$, and an appearance and its development of the peak at $18{\sim}20^{\circ}$ of $2{\theta}$ value. The former is considered to be nucleation and the latter correspond to the growth period on crystallization. The crystalline form of aging products was various depending on the degree of humidity, directly it leads to the eventual formation of bayerite in more than 72%, $b{\"{o}}hmite$ in 50% and resembled to Nordstandite in 0% relative humidity, respectively but once formed, it was mostly stable in each surroundings and does not transform to the other more stable form in solid state even after aging for five years. The mechanism responsible for aging is further polymerization process of six-membered rings by deprotonation-dehydration reaction in which positively charged polynuclear hydroxy aluminum complexes formed in the presence of moisture are joined at their edges by double hydroxide bridges.