• Carbon letters
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• 제13권2호
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• pp.99-108
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• 2012

The sol-gel technique has been studied to fabricate a homogeneous Fe-Mo/MgO catalyst. Ambient effects (air, Ar, and $H_2$) on thermal decomposition of the citrate precursor have been systematically investigated to fabricate an Fe-Mo/MgO catalyst. Severe agglomeration of metal catalyst was observed under thermal decomposition of citrate precursor in air atmosphere. Ar/$H_2$ atmosphere effectively restricted agglomeration of bimetallic catalyst and formation of highly-dispersed Fe-Mo/MgO catalyst with high specific surface-area due to the formation of Fe-Mo nanoclusters within MgO support. High-quality thin-multiwalled carbon nanotubes (t-MWCNTs) with uniform diameters were achieved on a large scale by catalytic decomposition of methane over Fe-Mo/MgO catalyst prepared under Ar-atmosphere. The produced t-MWCNTs had outer diameters in the range of 4-8 nm (average diameter ~6.6 nm) and wall numbers in the range of 4-7 graphenes. The as-synthesized t-MWCNTs showed product yields over 450% relative to the utilized Fe-Mo/MgO catalyst, and indicated a purity of about 85%.

• 한국세라믹학회지
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• 제27권8호
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• pp.956-956
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• 1990

석탄회의 탄소가 첨가된 질화반응시에 생성된 AIN, SiC 그리고 Si3N4 등의 생성물 분포를 반응온도, 시간 그리고 탄소의 첨가량에 따라 검토하였다. AIN의 조성은 시료입자가 작을수록 증가하였으며 반응온도 14500~1500℃와 약 2시간의 반응시간 그리고 약 30%의 탄소 첨가량 (시료무게 기준) 에서 최대값을 나타내었다. SiC와 Si3N4 조성변화는 서로 상반된 경향을 보였으며 반응온도가 낮고 반응시간이 작으며 그리고 탄소첨가량이 증가할 수록 SiC의 조성은 Si3N4 에 비하여 크게 나타났다.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2005년도 추계 학술대회 논문집
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• pp.32-37
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• 2005

The characteristics of the metal melting and radionuclide distribution of the radioactive has been investigated in a lab-scale arc furnace. The slag former based on the constituents of silica, calcium oxide, aluminum oxide, borate and calcium fluoride additions was used for melting of the stainless and carbon steel. In the melting of the stainless steel, the amount of slag formation increased with an increase of the concentration of the slag former. But the effects of the slag basicity on the amount of stag formation showed a local maximum value of the slag formation with an increase of the basicity index in the melting of the stainless steel as well as in the melting of the carbon steel. With an increase of the amount of slag former addition, the trends of the cobalt distribution into the ingot and the stag depended on the kind of slag former used in the melting of the stainless steel while the effect of the slag basicity on the distribution of the cobalt was not clarified in the melting of carbon steel. Tn the melting of the carbon steel, the strontium was captured at up to $50\%$ into the slag phase. Cesium was completely eliminated from the melt of the stainless steel as well as the carbon steel and distributed to the dust phase.

• 상하수도학회지
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• 제20권1호
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• pp.27-34
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• 2006

This study was conducted to evaluate the performance of a membrane bioreactor filled with high concentration of powdered activated carbon (HCPAC-MBR) to reduce DBPs at the drinking water treatment. The pilot system was installed after the rapid sand filtration process whose plant was the conventional treatment process. The removal efficiencies of DBPs were measured during pilot operation period of 2 years. HAA and THM removal rates could be maintained around 80~90% without any troubles and then tremendous reduction of HAA and THM reactivity were observed more than 52%. The average removal rate of HAA formation potential (FP) and THM formation potential (FP) were 70.5% and 67.6% respectively. It is clear that the PAC membrane bioreactor is highly applicable for advanced water treatment to control DBPs.

• Asian Journal of Atmospheric Environment
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• 제3권1호
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• pp.42-51
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• 2009

Saturated n-dicarboxylic acids ($C_2-C_7$, $C_9$), unsaturated dicarboxylic acids (maleic, fumaric, phthalic acid), ketocarboxylic acids (pyruvic, glyoxylic acid), and dicarbonyls (glyoxal, methylglyoxal) were determined in size-segregated samples with a high-volume Andersen air sampler at a suburban site in Saitama, Japan, May 12-17 and July 24-27, 2007 and January 22-31, 2008. The seasonal average concentrations of these detected organic acids were 670 $ng/m^3$, accounting for about 4.4-5.7% (C/C) of water-soluble organic carbon (WSOC) and 2.3-3.6% (C/C) of organic carbon (OC). The most abundant species of dicarboxylic acids was oxalic acid, followed by malonic, phthalic, or succinic acids. Glyoxylic acid and methyglyoxal were most abundant ketocarboxylic acid and dicarbonyl, respectively. Seasonal differences, size-segregated concentrations, and the correlations of these acids with ambient temperatures, oxidants, elemental carbon (EC), OC, WSOC, and ionic components were also discussed in terms of their corresponding sources and possible secondary formation pathways. The results suggested that photochemical reactions contributed more to the formation of particulate organic acids in Saitama suburban areas than did direct emissions from anthropogenic and natural sources. However, direct emissions of vehicles were also important sources of several organic acids in particles, such as phthalic and adipic acids, especially in winter.

• Corrosion Science and Technology
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• 제14권6호
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• pp.313-324
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• 2015

Austenitic stainless steels have been widely used in many engineering fields because of their high corrosion resistance and good mechanical properties. However, welding or aging treatment may induce intergranular corrosion, stress corrosion cracking, pitting, etc. Since these types of corrosion are closely related to the formation of chromium carbide in grain boundaries, the alloys are controlled using methods such as lowering the carbon content, solution heat treatment, alloying of stabilization elements, and grain boundary engineering. This work focused on the effects of aging and UNSM (Ultrasonic Nano-crystal Surface Modification) on the intergranular corrosion of commercial 316L stainless steel and the results are discussed on the basis of the sensitization by chromium carbide formation and carbon segregation, residual stress, grain refinement, and grain boundary engineering.

• 한국재료학회지
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• 제20권12호
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• pp.645-648
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• 2010

The structure and morphology of epitaxial layer defects in epitaxial Si wafers produced by the Czochralski method were studied using focused ion beam (FIB) milling, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Epitaxial growth was carried out in a horizontal reactor at atmospheric pressure. The p-type Si wafers were loaded into the reactor at about $800^{\circ}C$ and heated to about $1150^{\circ}C$ in $H_2$. An epitaxial layer with a thickness of $4{\mu}m$ was grown at a temperature of 1080-$1100^{\circ}C$. Octahedral void defects, the inner walls of which were covered with a 2-4 nm-thick oxide, were surrounded mainly by $\{111\}$ planes. The formation of octahedral void defects was closely related to the agglomeration of vacancies during the growth process. Cross-sectional TEM observation suggests that the carbon impurities might possibly be related to the formation of oxide defects, considering that some kinds of carbon impurities remain on the Si surface during oxidation. In addition, carbon and oxygen impurities might play a crucial role in the formation of void defects during growth of the epitaxial layer.

• 한국대기환경학회지
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• 제26권4호
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• pp.380-391
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• 2010

Airborne in-situ measurements of aerosol/cloud number concentrations were analyzed to investigate the effects of aerosols on warm cloud formation in the Pacific Dust Experiment (PACDEX) during April and May 2007. In the air masses originating from the Asian continent, high concentrations of fine particles including black carbon (BC) were observed when compared to other regions. A strong correlation (r=0.88) between condensation nuclei (CN) having sizes ranging from 0.1 to 1.0 mm ($CN_{0.1-1.0}$) and cloud condensation nuclei (CCN) at 0.4% supersaturation ($CCN_{0.4%}$) suggests that most of the $CN_{0.1-1.0}$ can contribute to cloud formation. The possibility of a cloud droplet formation by BC particles was expected at the high water vapor mixing ratio (WVMR) and the abundance of water-soluble components at the low altitude less than 3 km.

• 소성∙가공
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• 제22권8호
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• pp.456-462
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• 2013

Compression tests were conducted at the various temperatures and strain rates to investigate void formation and microstructures behavior of a 1.9wt%C ultrahigh carbon steel used in forged workrolls. The microstructure, grain size and volume fraction of cementite were determined using specimens deformed in the temperature range from 800 to $1150^{\circ}C$ and strain rates from 0.01 to 10/s. It was found from the microstructural analysis that the grain size is larger at higher temperatures and lower strain rate deformation conditions. In addition, a higher volume fraction of cementite was measured at lower temperatures. The brittle blocky cementite was fractured at $800^{\circ}C$ and $900^{\circ}C$ regardless of strain rate. As a result, numerous new micro voids were formed in the fragmented blocky cementite. It was also found that local melting can occur at temperatures of more than $1130^{\circ}C$. Therefore, the forging temperature should be controlled between $900^{\circ}C$ and $1120^{\circ}C$. The temperature rise, which depends on the anvil stroke and velocity, was estimated through cogging simulation to find the appropriate forging temperature and to prevent local melting due to plastic work.

• 반도체디스플레이기술학회지
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• 제12권2호
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• pp.1-6
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• 2013

The effects of interlayer formation and thermal treatment on the field-emission properties of carbon nanotubes (CNTs) were investigated. The CNTs were prepared on tungsten (W) micro-tip substrates using the electrophoretic deposition (EPD) method. The interlayers, such as aluminum (Al) and hafnium (Hf) were coated on the W-tips prior to CNT deposition and after the deposition of CNTs all the species were thermally treated at $700^{\circ}C$ for 30 min. The field-emission properties of CNTs were significantly improved by thermal treatment. The threshold electric field for igniting the electron emission was decreased and the emission current was increased. The Raman spectroscopy results indicated that this was attributed mainly to the enhancement of CNTs by thermal treatment. Also, the CNTs deposited on the interlayers showed the remarkably improved results in the long-term emission stability, especially when they were thermally treated. The X-ray photoelectron spectroscopy (XPS) measurement confirmed that this was resulted from the formation of the additional cohesive forces between the CNTs and the underlying interlayers.