• 한국세라믹학회지
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• 제43권10호
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• pp.660-665
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• 2006

The mechanical properties of $Al_2O_3$-SiC composites manufactured with adding various amount and size of SiC particles have been measured and analyzed. Generally, the elastic modulus of the composites shows about 50% less than that of PL-8 (45 wt% $Al_2O_3$-51 wt% $SiO_2$-4 wt% other oxides), but the flexural strength is similar with each other. The impact resistance property of $Al_2O_3$-SiC composite against high velocity copper jet was lower than that of PL-8 when SiC particles of approximately 3 $\mu$m diameter was added to. It is caused probably due to the micro-pores made by oxidation of SiC particles. However, in the case of the less-weighted $Al_2O_3$-SiC composite adding to 10 wt% SiC with average diameter of 10 $\mu$m and sintering at 1200$^{\circ}C$, the impact resistance property was improved up to 37 percent compared with that of PL-8.

• 한국수소및신에너지학회논문집
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• 제14권1호
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• pp.24-34
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• 2003

For gaseous fuel combustion with inherent $CO_2$ capture and low NOx emission, chemical-looping combustion may yield great advantages for the savings of energy to $CO_2$ separation and suppressing the effect on environment, In chemical-looping combustor, fuel is oxidized by metal oxide medium in a reduction reactor. Reduced particles are transported to oxidation reactor and oxidized by air and recycled to reduction reactor. The fuel and the air are never mixed, and the gases from reduction reactor, $CO_2$ and $H_2O$, leave the system as separate stream. The $H_2O$ can be easily separated by condensation and pure $CO_2$ is obtained without any loss of energy for separation. In this study, five oxygen carrier particles such as NiO/bentonite, NiO/YSZ, $(NiO+Fe_2O_3)VYSZ$, $NiO/NiAl_2O_4$, and $Co_{\chi}O_y/CoAl_2O_4$ were examined &om the viewpoints of reaction kinetics, oxygen transfer capacity, and carbon deposition characteristics. Among five oxygen particles, NiO/YSZ particle is superior in reaction rate, oxygen carrier capacity, and carbon deposition to other particles. However, at high temperature ($>900^{\circ}C$), NiO/bentonite particle also shows enough reactivity and oxygen carrier capacity to be applied in a practical system.

• Composites Research
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• 제13권6호
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• pp.1-8
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• 2000

무가압함침법에 의한 $Al_2O_{3p}$/AC8A 복합재료의 제조와, 제조법과 관련하여 부가적인 Mg의 첨가와 강화상의 부피분율이 $Al_2O_{3p}$/AC8A복합재료의 기계적 성질과 마모저항에 미치는 영향을 조사하였다. 강화상 입자와 기지재료의 일부를 분말로 조합한 혼합분말 속으로 기지금속을 자발적으로 침투시켜 부피분율이 20~40%인 $Al_2O_{3p}$/AC8A 복합재료를 제조할 수 있었다. 그러나 강화상의 부피분율이 40%인 복합재료의 경우 기공율의 상승으로 복합재료의 강도는 저하하였다. Mg의 첨가량이 5~7wt% 일 때 가장 높은 강도를 나타냈으며, 경도는 Mg 첨가량의 증가에 따라 점진적으로 상승하였다. $Al_2O_{3p}$/AC8A복합재료는 저속에서 기지재료에 비해 내마모성이 저하하였으나, 고속에서는 AC8A합금에 비해 약 5.5배의 우수한 내마모성을 나타냈다. 마모기구의 관찰에 의해 부피분율 20% $Al_2O_{3p}$/AC8A복합재료의 경우 연삭마모가 주된 마모기구임을 알 수 있었으며, 부피분율 40% $Al_2O_{3p}$/AC8A복합재료는 높은 기공율로 인한 마모 가중으로 저속에서도 경미한 응착마모가 관찰됐고 마찰 속도가 증가함에 따라 격심한 마모로 진행되었다.

• 한국세라믹학회지
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• 제34권6호
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• pp.668-676
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• 1997

Al2O3/SiC nanocomposites are fabricated through intensive ball milling to mix fine SiC particles uniformly with the Al2O3 powder. Another role of milling is to reduce particle sizes by crushing particles as well as agglomerates. However, balls are worn during ball milling and the sample powder mixtures pick up to weight loss of the balls. In this study, pressureless sintering was performed to obtain Al2O3/SiC nanocomposites. It was found that the wear rate of zirconia balls during milling was considerable, and the zirconia addition after even a few hours of ball milling could increase the sintering rates of the nanocomposites significantly. Thus, addition of ZrO2 changed the sintering behaviors as well as mechanical properties of Al2O3/SiC nanocomposites.

• Journal of Electrochemical Science and Technology
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• 제9권3호
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• pp.220-228
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• 2018

This study introduced a carbon-free electrode for $Li-O_2$ cells with the aim of suppressing the side reactions activated by carbon material. Micro-particles of poly(3,4-ethylenedioxythiophene) (PEDOT), a conducting polymer, were used as the base material for the air electrode of $Li-O_2$cells. The PEDOT micro-particles were treated with $H_2SO_4$ to improve their electronic conductivity, and LiBr and CsBr were used as the redox mediators to facilitate the dissociation of there action products in the electrode and reduce the over-potential of the $Li-O_2$ cells. The capacity of the electrode employing PEDOT micro-particles was significantly enhanced via $H_2SO_4$ treatment, which is attributed to the increased electronic conductivity. The considerable capacity enhancement and relatively low over-potential of the electrode employing $H_2SO_4$-treated PEDOT micro-particles indicate that the treated PEDOT micro-particles can act as reaction sites and provide storage space for the reaction products. The cyclic performance of the electrode employing $H_2SO_4$-treated PEDOT micro-particles was superior to that of a carbon electrode. The results of the Fourier-transform infrared spectroscopic analysis showed that the accumulation of residual reaction products during cycling was significantly reduced by introducing the carbon-free electrode based on $H_2SO_4$-treated PEDOT micro-particles, compared with that of the carbon electrode. The cycle life was improved owing to the effect of the redox mediators. The refore, the use of the carbon -free electrode combined with redox mediators could realize excellent cyclic performance and low over-potential simultaneously.

• Environmental Analysis Health and Toxicology
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• 제22권3호
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• pp.189-196
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• 2007

[ $TiO_2$ ] is widely used because it is non-toxic. Recently, however, nanometer size $TiO_2$ particles (P-25) have been produced and used to increase the photo catalysis efficiency. Nanometer-sized $TiO_2$ is efficient, but due to its small size ($20{\sim}30\;nm$), it can flow into ecosystems and into cells. Thus, it may affect human health. Additionally, $TiO_2$ can produce a second contaminant, OH-radical, which is a health risk for all living organisms during photo degradation reaction. Hence, when nanometer-sized $TiO_2$ flows into natural streams and attaches to living organisms, it will create health risks. We investigated the biological toxicity of this condition in zebrafish embryos. We observed abnormal morphology, hatching rate, and measured the catalase activity to determine anti-oxidation at 100 post fertilization hours. Zebrafish were somewhat affected by $TiO_2$ nanometer sized particles under UV-A (a condition similar to sunlight). Powdered $TiO_2$ is toxic to the zebrafish fly. Even without light, $TiO_2$ particles attached to embryos and flies, having an effect on both.

• 한국세라믹학회지
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• 제45권9호
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• pp.512-517
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• 2008

In this study, yttrium-doped $SiO_2$ nanoparticles are synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. Spherical Y-doped $SiO_2$ nanoparticles with a uniform size distribution are prepared using selfassembly molecules in conjunction with the hydrolysis and condensation of organometallic precursors. The water/surfactant molar ratio influenced the Y-doped $SiO_2$ particles distribution of the core-shell composite particles and the distribution of Y doped $SiO_2$ particles was broadened as the water to surfactant ratio increased. The particle size of Y increase linearly as the $Y(NO_3)_3$ solution concentration increased. The average size of the cluster was found to depend on the micelle size, the nature of the solvent, and the concentration of the reagent. The effects of synthesis parameters, such as the molar ratio of water to surfactant and the molar ratio of water to TEOS, are discussed.

• 연구논문집
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• 통권26호
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• pp.103-112
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• 1996

$Al_2O_3/SiC$ Hybrid-Composite이 일반적인 분말공정에 의하여 제조되었다. 소결시 $\gamma-Al_2O_3에서 $\alpha-Al_2O_3$로의 전이에 seed역할을 하는 $\alpha-Al_2O_3의 첨가는 균일한 미세구조를 발달시켜 강도의 증진을 가져왔다. nano size의 SiC의 첨가는 $Al_2O_3$의 소결성과 입성장에 영향을 미쳐 파괴강도의 증진을 가져왔다. $Al_2O_3/SiC$ nano-Composite에 SiC plates의 첨가는 파괴강도의 감소를 가져왔지만, 상대적으로 파괴인성은 증진되었다. SiC plates에 nitride (BN, $Si_3N_4$ 코팅을 할 경우 crack deflection을 더욱 유발하여 파괴인성이 증진되었다.

• 한국세라믹학회지
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• 제22권5호
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• pp.76-84
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• 1985

Mechanical property enhancing mechanisms of $Al_2O_3-ZrO_2$ two phase ceramic composites were studied for several compositions of different $ZrO_2$/$Al_2O_3$ ratio. Microstructural analysis of $Al_2O_3-ZrO_3$(pure) composites indicated that pre-existing microcrack due to larger $ZrO_2$ particle at grain boundary extended along alumina grain boundaries within process zone. Microcracks also nucleated when very small $ZrO_2$ particles at the grain boundaries transformed to monoclinic phase at near of main crack tip. These types of microcracks could contribute to the toughening achieved by creating additional crack surface area during crack propagation. Microstructural analyses also showed that the average grain size and abnormal grain size of $Al_2O_3$ were decreased with increasing $ZrO_2$ vol% in $Al_2O_3$ matrix. As a result it could be concluded as follows In TEX>$Al_2O_3-ZrO_3$(pure) system 1. Microcrack nucleation (stress-induced microcracking) and extension was effective mechanism for absorpiton of fracture energy 2, More narrow distribution and smaller grain size of $Al_2O_3$ due to $ZrO_2$particles mainly contributed to main-tatin the strength and hardness.

• 한국분말재료학회지
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• 제7권3호
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• pp.149-153
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• 2000

In this study, the fabrication of $Al_2O_3$/5vol.%Cu nanocomposite and its mechanical property were discussed. The nanocomposite powders were produced by high energy ball milling of $Al_2O_3$ and Cu elemental powders. The ball-milled powders were sintered with Pulse Electric Current Sintering (PECS) facility. The relative densities of specimens sintered at $1200^{\circ}C$ and $1250^{\circ}C$ after soaking process at $900^{\circ}C$ were 96% and over 97%, respectively. The sintered microstructures were composed of $Al_2O_3$ matrix and the nano-sized Cu particles distributed on grain boundaries of $Al_2O_3$ matrix. The nanocomposite exhibited the enhanced fracture toughness compared with general monolithic $Al_2O_3$. The toughness increase was explained by the crack deflection and bridging by dispersed Cu particles.