• 대한기계학회논문집
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• 제19권2호
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• pp.427-432
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• 1995

Surface heat treatment using a laser beam or an electron beam is studied through numerical analyses and experiments. For the surface heat treatment process, a theoretical model is developed to predict the effects of laser beam power, travel speed and properties of a workpiece on the depth and width of the heat affected zone(HAZ). The shape of HAZ and the hardness of heat-treated surface are experimentally obtained using an electron beam. Three materials(SS41, S45C and S55C) are selected as workpiece materials. The hardness of HAZ is increased up to 3 times for materials of a low carbon content. The results of the numerical analysis are compared with those of experiments. The comparison shows that the numerical model predicts larger depths and widths.

• Bulletin of the Korean Chemical Society
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• 제16권2호
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• pp.149-153
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• 1995

We have grown GaAs epilayers by chemical beam epitaxy(CBE) using unprecracked hydrides and metal organic compounds via a surface decomposition process. This result shows that unprecracked arsine (AsH3) or monoethylarsine (MEAs) can be used in chemical beam epitaxy(CBE) as a replacement of a precracked AsH3 source in CBE. It was also found that the uptake of carbon impurity in epilayers grown using trimethylgallium(TMG) with unprecracked AsH3 or MEAs was significantly reduced compared to that in epilayers grown by CBE process employing TMG and arsenics produced from precracked hydrides. We propose a surface structural model suggesting that the hydrogen atoms play an important role in the reduction of carbon content in GaAs epilayer. Intermediates like dihydrides from hydride sources were also considered to hinder carbon atoms from being incorporated into the epilayers or to remove other carbon containing species on the surface.

• Carbon letters
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• 제25권
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• pp.103-112
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• 2018

Hierarchically porous, chemically activated carbon materials are readily derived from biomass using hydrothermal carbonization (HTC) and chemical activation processes. In this study, empty fruit bunches (EFB) were chosen as the carbon source due to their sustainability, high lignin-content, abundance, and low cost. The lignin content in the EFB was condensed and carbonized into a bulk non-porous solid via the HTC process, and then transformed into a hierarchical porous structure consisting of macro- and micropores by chemical activation. As confirmed by various characterization results, the optimum activation temperature for supercapacitor applications was determined to be $700^{\circ}C$. The enhanced capacitive performance is attributed to the textural property of the extremely high specific surface area of $2861.4m^2\;g^{-1}$. The prepared material exhibited hierarchical porosity and surface features with oxygen functionalities, such as carboxyl and hydroxyl groups, suitable for pseudocapacitance. Finally, the as-optimized nanoporous carbons exhibited remarkable capacitive performance, with a specific capacitance of $402.3F\;g^{-1}$ at $0.5A\;g^{-1}$, a good rate capability of 79.8% at current densities from $0.5A\;g^{-1}$ to $10A\;g^{-1}$, and excellent life cycle behavior of 10,000 cycles with 96.5% capacitance retention at $20A\;g^{-1}$.

• 한국도로학회논문집
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• 제17권4호
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• pp.41-51
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• 2015

PURPOSES: This study investigates the mechanical performance of carbon-capturing concrete that mainly contains blast furnace slag. METHODS: The mixture variables were considered; these included Portland cement content, which was varied from 10% to 40% of the blast furnace slag by weight. The specimens were exposed to different conditions such as high $N_2$ and $O_2$ concentrations, laboratory conditions and high $CO_2$ conditions. Mechanical performances, including compressive and flexural strengths and carbon-capturing depth, were evaluated. RESULTS : The slump, air content and unit weight were not affected significantly by the variation in cement content. The strength development when the specimens were exposed to high purity air was slightly greater than that when exposed to high $CO_2$. As the cement content increased the compressive and flexural strength increased but not considerably. The carbon-capturing capacity decreased as the cement content increased. The specimens exposed in the field for 70 days had flexural strength greater than 3 MPa. CONCLUSIONS : The results indicate that cement content is not an important parameter in the development of compressive and flexural strengths. However, the carbon-capturing depth was higher for less cement content. Even after field exposure for 70 days, neither any significant damage on the surface nor any decrease in strength was observed.

• 한국식품저장유통학회지
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• 제17권1호
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• pp.84-90
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• 2010

본 연구에서는 국내산 사과의 주스 가공과정에서 patulin 함량 최소 방법을 모니터링 하였다. 중심합성계획법으로 ascorbic acid 첨가량(100, 200, 300 및 400 ppm)과 활성탄 사용량(50, 100, 150 및 200 ppm)을 독립변수로 설정하고 각각의 조건에서 사과주스를 제조한 결과 patulin 잔류량은 ascorbic acid 함량 237.77 ppm, 활성탄 함량 106.58 ppm에서 최소점을 나타내었다가 점차 증가하는 경향을 나타내었다. 당도는 활성탄 사용량보다는 ascorbic acid 첨가량에 영향을 더 많이 받는 것으로 나타났으며, 총 페놀성 물질 함량의 정상점은 안장점으로 나타났다. 또한, 총 플라보노이드 함량의 예측된 정상점은 최대점으로 나타나 ascorbic acid와 활성탄 함량이 증가할수록 높은 함량을 나타내었다. 이상의 결과 사과주스 가공시 patulin 잔류량은 ascorbic acid 246~274 ppm (v/v), 활성탄 93~122 ppm (v/v)에서 최소화 되는 것으로 나타났으며 사과주스 가공 품질인자의 $R^2$는 모든 구간에서 1~10% 수준에서 유의성이 인정되었다.

• Carbon letters
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• 제12권2호
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• pp.70-80
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• 2011

Two pitches with different average molecular structures were electrospun and compared in terms of the properties of their fibers after oxidative stabilization, carbonization, and activation. The precursor with a higher molecular weight and greater content of aliphatic groups (Pitch A) resulted in better solubility and spinnability compared to that with a lower molecular weight and lower aliphatic group content (Pitch B). The electrical conductivity of the carbon fiber web from Pitch A of 67 S/cm was higher than that from Pitch B of 52 S/cm. The carbon fiber web based on Pitch A was activated more readily with lower activation energy, resulting in a higher specific surface area compared to the carbon fiber based on Pitch B (Pitch A, 2053 $m^2/g$; Pitch B, 1374 $m^2/g$).

• 대한화학회지
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• 제15권6호
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• pp.370-377
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• 1971

The Carbon-14 content in surface air at Seoul, Korea, was measured from February 1970 to August 1971 and a Larix Leptolepis, Gordon tree (Ip-Gal Namu) grown at Kwang-Nung, Kyunggi-Do, Korea, having 37 growth rings, was assayde for $^{14}C$. From the results of the surface air study, it was calculated that during the above period the inventory of excess $^{14}C$ in the atmosphere decreased with a half-time of 4.6 years. The overall yearly decrease was also checked. The tree-ring study showed that the tree's atmosphere was affected by $^{14}C$ from nuclear tests after 1956. In one study, atmospheric $CO^2$ samples were collected bi-monthly by the absorption of $CO^2$ in alkaline hydroxide solution. In the other, 5 year annual growth rings were assayed for radiocarbon. For the radioactivity measurement, carbon atoms in samples were converted to carbon atoms of benzene. The resulting benzene was taken as primary solvent for liquid scintillation counting.

• 한국표면공학회지
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• 제27권5호
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• pp.303-311
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• 1994

In this study, the factors, such as coating temperature T(K), reaction time t(sec) and mobile carbon content $C^*$ (wt%) of steels affecting, the growth rate of carbide layer were investigated in the reactive deposition and diffusion coating using the fluidized bed. From the results, the coating thickness d(cm) can be expressed by an equation. d=$C^*$$(KT)^{1/2}$, where K=K$\circ$exp(~Q/RT), KTEX>$\circ$ = 1.4$\times$$10^{-2}cm^{-2}$/sec, and Q=46Kcal/ mol. It was in a good aggrement with the experimental results, reguardless of the diffusion coating method and the carbide layer. Therefore, if the mobile carbon content of carbon steels and alloyed steels is known, the thickness under coating conditions can be predicted from the previous equation.

• 한국연초학회지
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• 제18권1호
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• pp.85-91
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• 1996

Commercially available activated carbon was treated with 0.2N NaOH/0.1N HCl to decrease the ash contents and to analyze the effect of demineralization. We have studied their properties and adsorptivity to solvents such as benzene, acetone, toluene and carbon tetrachloride, ammonia and also aldehydes of cigarette smoke. By demineralization with NaOH/HCl, surface area and pore volume were increased up to 10 - 20% according to developement of micro-pore and pH of activated carbon was also changed from 10.2 to 6.3. Surface acidity of the activated carbon treated with chemicals increased slightly. The chemical treatment led to small increase in adsorptioil properties of solvents, ammonia and aldehydes of cigarette smoke, but content of chlorine and sulfur in activated carbon were reduced. As the results of smoking test, charcoal taste caused by the activated carbon was reduced significantly by the treatment with NaOH/HCl.

• Carbon letters
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• 제28권
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• pp.47-54
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• 2018

High surface carbon aerogels with hierarchical and tunable pore structure were prepared using ionic liquid as carbon precursor via a simple salt templating method. The as-prepared carbon aerogels were characterized by nitrogen sorption measurement and scanning electron microscopy. Through instant visual observation experiments, it was found that salt eutectics not only serve as solvents, porogens, and templates, but also play an important role of foaming agents in the preparation of carbon aerogels. When the pyrolyzing temperature rises from 800 to $1000^{\circ}C$, the higher temperature deepens the carbonization reaction further to form a nanoporous interconnected fractal structure and increase the contribution of super-micropores and small mesopores and improve the specific surface area and pore volume, while having few effects on the macropores. As the mass ratio of ionic liquid to salt eutectics drops from 55% to 15%, that is, the content of salt eutectics increases, the salt eutectics gradually aggregate from ion pairs, to clusters with minimal free energy, and finally to a continuous salt phase, leading to the formation of micropores, uniform mesopores, and macropores, respectively; these processes cause BET specific surface area initially to increase but subsequently to decrease. With the mass ratio of ionic liquids to salts at 35% and carbonization temperature at $900^{\circ}C$, the specific surface area of the resultant carbon aerogels reached $2309m^2g^{-1}$. By controlling the carbonization temperature and mass ratio of the raw materials, the hierarchically porous architecture of carbon aerogels can be tuned; this advantage will promote their use in the fields of electrodes and adsorption.