• Applied Chemistry for Engineering
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• v.34 no.6
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• pp.613-618
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• 2023

Modern society spends more than 80% of its daily life indoors, emphasizing the need for attention to indoor air pollution due to the improvement in living standards. In this study, the performance and reaction characteristics of the Pt/TiO₂ catalysts prepared by liquid-phase reduction for the removal of formaldehyde (HCHO), one of the indoor air pollutants, at room temperature without the need for additional light or heat were investigated. As a result, it showed that catalysts prepared by the same method showed approximately 40~80% various activities depending on the type of TiO₂. XRD, BET, and XPS analyses were performed to investigate the particle size, crystal structure, specific surface area, and O/Ti molar ratio of the support material, and it revealed that the correlation between the properties and performance was insignificant. To explore the oxidation reaction pathway of formaldehyde (HCHO), in situ DRIFT analysis using carbon monoxide and H₂-TPR was perfomed. The results revealed that the performance was demonstrated by the oxidation state of the active metal and the adsorption-desorption characteristics of the adsorbate species.

• Korean Chemical Engineering Research
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• v.56 no.4
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• pp.561-567
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• 2018

In this study, the electrochemical characteristics of Silicon/Carbon anode materials were analyzed to improve the cycle stability of silicon as an anode materials of lithium ion battery. Porous silicon was prepared from TEOS by the $st{\ddot{o}}ber$ method and the magnesiothermic reduction method. Silicon/Carbon anode materials were synthesized by varying the mass ratio between porous silicon and pitch. Physical properties of the prepared Silicon/Carbon anode materials were analyzed by XRD and TGA. Also the electrochemical performances of Silicon/Carbon anode materials were investigated by constant current charge/discharge, rate performance, cyclic voltammetry and electrochemical impedance tests in the electrolyte of $LiPF_6$ dissolved in organic solvents (EC : DEC = 1 : 1 vol%). The Silicon/Carbon anode composite (silicon : carbon = 5 : 95 in weight) has better capacity (453 mAh/g) than those of other composition cells. The cycle performance has an excellent capacity retention from 2nd cycle to 30th cycle.

• Journal of the Korean Vacuum Society
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• v.22 no.3
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• pp.138-143
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• 2013

Recently, ZnO nanoparticles have been studied in various application fields due to their physico-chemical properties. In this study, we have researched on the ZnO photocatalytic activity by redox reaction. ZnO nanoparticles have low photocatalytic activity in comparison with $TiO_2$ nanoparticles because it has the disadvantage that the formation of $Zn(OH)_2$ in water solvent. Therefore, we were synthesized ZnO nanoparticles by spray-pyrolysis method, and then studied on stability in water solvent. At the results, the water treated-ZnO nanoparticles showed higher photocatalytic activity than non-treated ZnO nanoparticles because molecular $H_2O$ was increased onto the ZnO surface under the water treatment. Also, we confirmed that the ZnO nanoparticles synthesized by spray-pyrolysis method is very stable in the water solvent.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.3
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• pp.50-61
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• 1995

In recent years, many ceramic researchers have discoved various methods of joining ceramic to metal. However, most of these joining methods are perfomed under vacuum and pressured circumstances. So, when we join ceramic to metal,the proceedings are very complicated and require a very high cost. The purpose of this study is to develop a new joining method of an alumina ceramic to an aluminum metal in air atmosphere. The joining condition, such as copper metallizing, nickel plating, brazing, etc. was investigated through the shear strength test of the trial joint. The results obtained from the above experimenta are summarized as follows : 1) In the case of the $Al_2O_3$/$Al_2O_3$joint, the shear strength of the joint was affected by the various foctor such as kaolin content, copper metallizing thickness, firing temperature, firing time. 2) The better shear strength of the $Al_2O_3$/Al joint was obtained when Ni plating was conducted under higher current density than existing plating condition. 3) The shear strength of the $Al_2O_3$/Al joint increases with the Ni plating thickness is confined to the range of this paper. 4) The shear strength of the thermal-shocked specimen($Al_2O_3$/Al joint) was far more deteriorated than that of the as-bonded specimen.

• 기계와재료
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• v.24 no.2
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• pp.38-46
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• 2012

인구의 증가와 급속한 산업화 그리고 편안함을 추구하고자 하는 문명의 이기로 인한 에너지 사용량 증가는 환경오염을 가속화시키는 문제를 유발하고 있어 전 세계적으로 심각한 사회문제로 대두되고 있다. 이에 반해 삶의 질의 향상에 따라 보다 쾌적한 환경에 대한 욕구와 인식의 변화로 환경보호에 대한 관심이 증가하는 추세이며, 이에 따라 각 국의 환경규제는 날로 강화되고 있다. 이러한 환경문제를 해결하기 위한 국제협력이 활발해지면서 무역과 연계된 국제 환경규제가 가속화되고 있으며, 환경선진국은 이러한 환경규제를 무역장벽으로 이용하고 있어 국가의 대외경쟁력에도 직 간접적으로 영향을 미치고 있다. 환경오염물질 중 질소산화물(NOx), 황산화물(SOx), 일산화탄소(CO), 이산화탄소($CO_2$) 및 휘발성유기화합물(VOCs), 다이옥신 그리고 입자상물질(PM)과 같은 대기오염물질은 대기 중으로 쉽게 확산되는 특성에 의해 인접한 지역까지 영향을 미치기 때문에 국제적인 규제대상의 초점이 되고 있으며, 경제협력개발기구(OECD, Organization for Economic Cooperation and Development), 유엔산하 국제해사기구(IMO, International Maritime Organization) 및 국제연소기구협회(CIMAC, International Council on Combustion engines)등 여러 국제기구를 중심으로 각종 규제수단을 개발하여 적용하고 있다. 특히, 국제해사기구(IMO)에서는 선박에서 발생되는 오염물질 등에 대한 규제강화를 위하여 새로운 국제해양오염방지협약(MARPOL)을 채택, 발효하여 그 규제 범위를 넓혀감에 따라 선박에 대한 각종 환경규제가 대폭 강화되고 있어 친환경 선박 및 관련 기술 개발이 활발히 진행 중에 있다. 이 글에서는 선박에서 배출되는 대기오염물질 중 그 자체로도 인체에 유해하며, 산성비, 광화학스모그 등 다양한 환경문제를 유발시키는 대표적인 물질인 질소산화물(NOx)과 질소산화물 배출규제에 대한 대응기술인 선택적촉매환원법(SCR, Selective Catalytic Reduction)과 SCR 탈질시스템에 사용되는 SCR 촉매에 대해 소개하고자 한다.

• Applied Chemistry for Engineering
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• v.1 no.2
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• pp.207-214
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• 1990

The catalytic reaction between CO and NO on polycrystalline Pt surface, which is very important in the development of catalyst for automobile exhaust gas control, has been studied using thermal desorption spectrometry(TDS) and steady-state experiment under ultra-high vacuum(UHV) conditions. With the pressures of CO and NO of each $1{\times}10^{-7}Torr$, the $CO_2$ formation rate showed a maximum at 560K. At the reaction temperature of 560K and the NO pressure of $1{\times}10^{-7}Torr$, the production of $CO_2$ was first order in $CO_2$ was first order in CO pressure below $1.35{\times}10^{-7}Torr$ of CO pressure whereas at higher CO pressures the rate became minus 0.3 order in CO. But the efforts of reactant pressure on the reaction was understood in consideration of the surface concentrations of adsorbates. With the results, we proposed a new reaction mechanism for this reaction.

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1336-1336
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• 1998

A twt -step carbothermal reduction scheme has been employed for the synthesis of SiC whiskers in an Ar or a H2 atmosphere via vapor-solid two-stage and vapor-liquid-solid growth mechanism respectively. It has been shown that the whisker growth proceed through the following reaction mechanism in an Ar at-mosphere : SiO2(S)+C(s)-SiO(v)+CO(v) SiO(v)3CO(v)=SiC(s)whisker+2CO2(v) 2C(s)+2CO2(v)=4CO(v) the third reaction appears to be the rate-controlling reaction since the overall reaction rates are dominated by the carbon which is participated in this reaction. The whisker growth proceeded through the following reaction mechaism in a H2 atmosphere : SiO2(s)+C(s)=SiO(v)+CO(v) 2C(s)+4H2(v)=2CH4(v) SiO(v)+2CH4(v)=SiC(s)whisker+CO(v)+4H2(v) The first reaction appears to be the rate-controlling reaction since the overall reaction rates are enhanced byincreasing the SiO vapor generation rate.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.402-409
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• 2013

The objective of this study was to develop a synthesis process for ${\beta}$-SiC powders to reduce the synthesis temperature and to control the particle size and to prevent particle agglomeration of the synthesized ${\beta}$-SiC powders. A phenol resin and TEOS were used as the starting materials for the carbon and Si sources, respectively. $SiO_2$-C hybrid precursors with various C/Si mole ratios were fabricated using a conventional sol-gel process. ${\beta}$-SiC powders were synthesized by a carbothermal reduction process using $SiO_2$-C hybrid precursors with various C/Si mole ratios (1.6 ~ 2.5) fabricated using a sol-gel process. In this study, the effects of excess carbon and the addition of Si powders to the $SiO_2$-C hybrid precursor on the synthesis temperature and particle size of ${\beta}$-SiC were examined. It was found that the addition of metallic Si powders to the $SiO_2$/C hybrid precursor with excess carbon reduced the synthesis temperature of the ${\beta}$-SiC powders to as low as $1300^{\circ}C$. The synthesis temperature for ${\beta}$-SiC appeared to be reduced with an increase of the C/Si mole ratio in the $SiO_2$-C hybrid precursor by a direct carburization reaction between Si and excess carbon.

• Korean Journal of Materials Research
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• v.24 no.5
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• pp.243-248
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• 2014

Silicon-carbon composite was prepared by the magnesiothermic reduction of mesoporous silica and subsequent impregnation with a carbon precursor. This was applied for use as an anode material for high-performance lithium-ion batteries. Well-ordered mesoporous silica(SBA-15) was employed as a starting material for the mesoporous silicon, and sucrose was used as a carbon source. It was found that complete removal of by-products ($Mg_2Si$ and $Mg_2SiO_4$) formed by side reactions of silica and magnesium during the magnesiothermic reduction, was a crucial factor for successful formation of mesoporous silicon. Successful formation of the silicon-carbon composite was well confirmed by appropriate characterization tools (e.g., $N_2$ adsorption-desorption, small-angle X-ray scattering, X-ray diffraction, and thermogravimetric analyses). A lithium-ion battery was fabricated using the prepared silicon-carbon composite as the anode, and lithium foil as the counter-electrode. Electrochemical analysis revealed that the silicon-carbon composite showed better cycling stability than graphite, when used as the anode in the lithium-ion battery. This improvement could be due to the fact that carbon efficiently suppressed the change in volume of the silicon material caused by the charge-discharge cycle. This indicates that silicon-carbon composite, prepared via the magnesiothermic reduction and impregnation methods, could be an efficient anode material for lithium ion batteries.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.4
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• pp.160-166
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• 2019

Cerium oxide ($CeO_2$, often called as Ceria) is one of the valuable rare earth oxide materials, which has been widely used for high temperature applications such as solid oxide fuel cells, automotive three-way catalysts and oxygen storage capacity. Considering those application, it is important to improve high redox and thermal stability with high surface morphology because the high surface area of $CeO_2$ could improve the catalytic reactivity at high temperature conditions. Herein we successfully fabricated hierarchical flower-like $CeO_2$ deposited via controlling pathway of precipitation reaction to supply carbonate ion lead to the flower-like morphology. The hexagonal lattice system of precipitated precursor shows better thermal stability then orthorhombic one during thermal cycling condition.