• Journal of the Korean Society of Industry Convergence
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• v.25 no.6_2
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• pp.1037-1045
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• 2022

In this study, nanoscale Al₂O3 ceramic particles were used due its exceptionally high hardness characteristics, chemical stability, and wear resistance properties. These nanoparticles will be used to investigate the optimal process conditions for the electro co-deposition of the Ni-Al₂O₃ composite coatings. A Watts bath electrolytic solution of a controlled composition along with a fixed agitation speed was used for this study. Whereas the current density, the pH value, temperature and concentration of the nano Al₂O₃ particles of the electrolyte were designated as the manipulative variables. The experimental design method was based on the orthogonal array to find the optimum processing parameters for the electro co-deposition of Ni-Al₂O₃ composite coatings. The result of confirmation experimental based on the optimal processing condition through the analysis of variance ; EDX analysis found that the ratio of alumina increased to 8.65 wt.% and subsequently the overall hardness increased to 983 Hv. Specially, alumina were evenly distributed on Nickel matrix and particles were embedded more firmly and finely in Nickel matrix.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2256-2261
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• 2017

Carbon nanotube (CNT) and alumina ($Al_2O_3$) are synthesized into hybrid composites, and an advanced electrical discharge machining (EDM) system is developed for the machining of hard and conductive materials. CNT nanoparticles are mixed with $Al_2O_3$ powder and the $Al_2O_3$/CNT slurry is sintered by spark plasma. The hardness and the electrical conductivity of the $Al_2O_3$/CNT hybrid composite were investigated. The electrical discharge is controlled by a capacitive ballast circuit. The capacitive ballast circuit is applied to the tungsten carbide and the $Al_2O_3$/CNT hybrid composite. The voltage-current waveforms and scanning electron microscope (SEM) images were measured to analyze the characteristics of the boring process. The developed EDM process can manufacture the ceramic based hybrid composites, thereby expecting the variety of applications.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.165-169
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• 2008

Binary nanofluids(Binary mixture + nanoparticles) have been extensively paid attention for application in absorption system as a new working fluid. Thermal property evaluation of the new refrigerants is inevitable to apply them for actual system. The objectives of this paper are to measure the thermal conductivity of the binary nanofluids by the transient hot-wire method, and to assess the application possibility of the binary nanofluids for absorption system. It was found that the thermal conductivity of the binary nanofluids ($H_2O/LiBrAl_2O_3$) increased with increasing the concentration of the nanoparticles ($Al_2O_3$) and enhanced up to 27% at 0.1 vol % of the nanoparticles.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.140.2-140.2
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• 2013

Strong metal-support interaction effect is an important issue in determining the catalytic activity for heterogeneous catalysis. In this work, we report the catalytic activity of $Au/TiO_2$, $Au/Al_2O_3$, and $Au/Al_2O_3-CeO_2$ nanocatalysts under CO oxidation fabricated by arc plasma deposition (APD), which is a facile dry process with no organic materials involved. These catalytic materials were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and $N_2$-physisorption. Catalytic activity of the materials has measured by CO oxidation using oxygen, as a model reaction, in a micro-flow reactor at atmospheric pressure. Using APD, the catalyst nanoparticles were well dispersed on metal oxide powder with an average particle size (3~10 nm). As for catalytic reactivity, the result shows $Au/Al_2O_3-CeO_2$ nanocatalyst has the highest catalytic activity among three samples in CO oxidation, and $Au/TiO_2$, and $Au/Al_2O_3$ in sequence. We discuss the effects of structure and metal-oxide interactions of the catalysts on catalytic activity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.151-152
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• 2005

Both $Al_2O_3$ and AlN nanopowders with diameters from ${\mu}m$ to mm were bead-milled and surface-modified by stabilizing agent. The size of bead-milled nanoparticles compared with the primary powder was effectively decreased and was dependent on milling time and bead size. The results of dispersion stability analysis indicated that chemical bonding between nanoparticles and surfactant is more effective than chemical adsorption to prepare the stable transformer oils containing nanoparticles. In this study, the thermal conductivity of the transformer oils containing nanoparticles was measured by transient hot-wire and laser flash methods.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.31-32
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• 2007

Oil-based nanofluids are prepared by dispersing spherical and fiber-shaped $Al_2O_3$ and AlN nanoparticles in transformer oil. Two hydrophobic surface modification processes are compared in this investigation. It is obvious that the combination of nanoparticle, surfactant and surface modification process is very important for the dispersity of nanofluids. For ($Al_2O_3$+AIN) particles with 1% volume fraction, the enhancement of thermal conductivity and convective heat transfer coefficient is nearly 11% and 30%, respectively, compared to pure transformer oil. The cooling effect of ($Al_2O_3$+AlN)-oil nanofluids on the heating element and oil itself is confirmed by a natural convection test using a prototype transformer.

• Journal of Sensor Science and Technology
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• v.23 no.3
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• pp.207-210
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• 2014

$TiO_2$ oxide semiconductor is being widely studied in various applications such as photocatalyst and photosensor. Pd/$TiO_2$ gas sensor is mainly used to detect $H_2$, CO and ethanol. This study focus on increasing hydrogen detection ability of Pd/$TiO_2$ in room temperature through Al-doping. Pd/$TiO_2$ was fabricated by the hydrothermal method. Contacting to Aluminum (Al) foil led to Al doping effect in Pd/$TiO_2$ by thermal diffusion and enhanced hydrogen sensing response. $TiO_2$ nanoparticles were sized at ~30 nm of diameter from scanning electron microscope (SEM) and maintained anatase crystal structure after Al doping from X-ray diffraction analysis. Presence of Al in $TiO_2$ was confirmed by X-ray photoelectron spectroscopy at 73 eV. SEM-energy dispersive spectroscopy measurement also confirmed 2 wt% Al in Pd/$TiO_2$ bulk. The gas sensing test was performed with $O_2$, $N_2$ and $H_2$ gas ambient. Pd/Al-doped $TiO_2$ did not response $O_2$ and $N_2$ gas in vacuum except $H_2$. Finally, the normalized resistance ratio ($R_{H2on}/R_{H2off}$) of Pd/Al-doped $TiO_2$ increases about 80% compared to Pd/$TiO_2$.

• Toxicological Research
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• v.34 no.4
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• pp.343-354
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• 2018

Aluminum oxide nanoparticles ($Al_2O_3$ NPs) are among the most widely used nanomaterials; however, relatively little information about their risk identification and assessment is available. In the present study, we aimed to investigate the potential toxicity of $Al_2O_3$ NPs following repeated inhalation exposure in male Sprague-Dawley rats. Rats were exposed to $Al_2O_3$ NPs for 28 days (5 days/week) at doses of 0, 0.2, 1, and $5mg/m^3$ using a nose-only inhalation system. During the experimental period, we evaluated the clinical signs, body weight change, hematological and serum biochemical parameters, necropsy findings, organ weight, and histopathology findings. Additionally, we analyzed the bronchoalveolar lavage fluid (BALF), including differential leukocyte counts, and aluminum contents in the major organs and blood. Aluminum contents were the highest in lung tissues and showed a dose-dependent relationship in the exposure group. Histopathology showed alveolar macrophage accumulation in the lungs of rats in the $5mg/m^3$ group during exposure and recovery. These changes tended to increase at the end of the recovery period. In the BALF analysis, total cell and neutrophil counts and lactate dehydrogenase, tumor necrosis factor-${\alpha}$, and interleukin-6 levels significantly increased in the 1 and $5mg/m^3$ groups during exposure. Under the present experimental conditions, we suggested that the no-observed-adverse-effect level of $Al_2O_3$ NPs in male rats was $1mg/m^3$, and the target organ was the lung.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.3
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• pp.233-239
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• 2006

Two different nanofluids were prepared by dispersing $Al_{2}O_3$ nanoparticles in transformer oil after hydrophobic surface modification. The agglomerated alumina nanoparticles with diameters from ${\mu}m$ to mm were ball-milled and then treated with surfactants such as lauric acid, stearic acid and oleic acid. The surface characteristics of modified nanoparticles were examined by FTIR spectroscopy. It showed that the hydrophobicity of nanoparticles was caused by esterification between hydroxyl groups on the particle surface and functional groups of surfactant. The shape and size distribution of ball-milled particles were analyzed by TEM and PSA. The results compared with the primary particles indicated that the size distributions of nanoparticles were dependant on milling times. The dispersion stability of modified nanoparticles dispersed in oil was highly dependent on the composition and amounts of surfactants.

• Journal of Sensor Science and Technology
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• v.17 no.4
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• pp.281-288
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• 2008

Polyacrylonitrile(PAN)/metal oxide(MO) nanocomposite mats with a thickness of 0.12 mm were electrospun by adding 0 to 10 wt% of MO nanoparticles ($Fe_2O_3$, ZnO, $SnO_2$, $Sb_2O_3-SnO_2$) into PAN. Pt electrode was patterned on $Al_2O_3$ substrate by DC sputtering and then the PAN(/MO) mats on the Pt patterned $Al_2O_3$ were electrically wired to investigate the $CO_2$ gas sensing properties. As the MO content rose, the fiber diameter decreased due to the presence of lumps caused by the presence of MOs in the fiber. The PAN/2% ZnO mat revealed a faster response time of 93 s and a relatively short recovery of 54 s with a ${\Delta}R$ of 0.031 M${\Omega}$ at a $CO_2$ concentration of 200 ppm. The difference in sensitivity was not observed significantly for the PAN/MO fiber mats in the $CO_2$ concentration range of 100 to 500 ppm. It can be concluded that an appropriate amount of MO nanoparticles in the PAN backbone leads to improvement of the $CO_2$ gas sensing properties.