• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.490-490
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• 2011

Graphene, hexagonal network of carbon atoms forming a one-atom thick planar sheet, has been emerged as a fascinating material for future nanoelectronics. Huge attention has been captured by its extraordinary electronic properties, such as bipolar conductance, half integer quantum Hall effect at room temperature, ballistic transport over ${\sim}0.4{\mu}m$ length and extremely high carrier mobility at room temperature. Several approaches have been developed to produce graphene, such as micromechanical cleavage of highly ordered pyrolytic graphite using adhesive tape, chemical reduction of exfoliated graphite oxide, epitaxial growth of graphene on SiC and single crystalline metal substrate, and chemical vapor deposition (CVD) synthesis. In particular, direct synthesis of graphene using metal catalytic substrate in CVD process provides a new way to large-scale production of graphene film for realization of graphene-based electronics. In this method, metal catalytic substrates including Ni and Cu have been used for CVD synthesis of graphene. There are two proposed mechanism of graphene synthesis: carbon diffusion and precipitation for graphene synthesized on Ni, and surface adsorption for graphene synthesized on Cu, namely, self-limiting growth mechanism, which can be divided by difference of carbon solubility of the metals. Here we present that large area, uniform, and layer controllable graphene synthesized on Cu catalytic substrate is achieved by acetylene-assisted CVD. The number of graphene layer can be simply controlled by adjusting acetylene injection time, verified by Raman spectroscopy. Structural features and full details of mechanism for the growth of layer controllable graphene on Cu were systematically explored by transmission electron microscopy, atomic force microscopy, and secondary ion mass spectroscopy.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2006년도 춘계학술발표대회
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• pp.669-672
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• 2006

고온가스냉각 원자로에서는 고온 안정성 및 핵분열생성물 차단 성능이 우수한 TRISO(tri-tsotropic) 핵연료를 사용하고 있다. TRISO 핵연료 입자는 직경이 약 1 mm인 구 형태로 입자의 중심에는 직경 $0.5{\mu}m$의 핵연료 커널(kernel)이 포함되며 커널 외곽을 코팅 층이 에워싸고 있다. 이 코팅 층은 완충(buffer) PyC(pyrolytic carbon) 층, 내부 PyC 층, SiC 층, 그리고 외부 PyC 층으로 구성되어 있다. 각 코팅 층의 두께는 수십${\sim}$백 ${\mu}m$ 범위이며, 본 연구에서는 각 코팅 층의 두께를 비파괴적으로 측정하기 위하여 마이크로포커스 X-선 발생장치와 고해상도 X-선 평판(flat panel) 검출기로 구성된 정밀한 X-선 래디오그래피 장치를 구성하고, $UO_2$ 핵물질 대신에 $ZrO_2$를 커널로 사용한 모의 TRISO 핵연료 입자에 대한 래디오그래피 영상을 획득한 후 디지털 영상처리기술을 이용하여 코팅 층 사이의 경계선이 구분 가능하도록 영상을 개선하고 디지털 영상처리 알고리즘을 개발하여 코팅 층의 두께를 측정하였다.

• 한국세라믹학회지
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• 제46권5호
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• pp.484-487
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• 2009

$SiC_f$/SiC composites with whiskers and pyrolytic carbon (PyC) coated whiskers in the matrix were fabricated for enhancement of the fracture behaviors by the whisker growing assisted chemical vapor infiltration (WA-CVI) process, respectively. $SiC_f$/SiC composites were also prepared by the conventional CVI process as reference material. The mechanical properties and fracture behaviors were analyzed by comparison of the two types of composites prepared by WA-CVI and conventional CVI. The densities of $SiC_f$/SiC composites were in the range of $2.6{\sim}2.65g/cm^3$. The flexural strengths of composite with whiskers and with those coated by PyC were 650 MPa and 600 MPa, respectively. The tensile strength of composites with whiskers was ${\sim}285$ MPa.

• 한국환경과학회지
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• 제12권11호
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• pp.1145-1157
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• 2003

The surface sediments inside Hallim Harbor, one of the major harbors of Jeju Island, were sampled three times (June, September and December, 2001) and analyzed for 16 polycyclic aromatic hydrocarbons (PAHs), recommended by US-EPA as priority pollutants, to assess their distribution levels and to suggest their possible origins. The concentrations of PAHs ranged from 19 to 496 ng/g on a dry weight basis with a mean value of 245 ng/g, and the levels were low to moderate in comparison with other areas in the world. Based on comparisons of individual and total PAH concentrations with effects-based and equilibrium partitioning-based on sediment quality guidelines, the potential for the biological effects were expected to be low. The sedimentary PAHs may be correlated with organic carbon and mud contents to some extent. From the examinations of the four PAH origin indices, such as LMW/HMW (low molecular weight 2-3 ring PAHs over high molecular weight 4-6 ring PAHs), phenanthrene/anthracene ratio, fluoranthene/pyrene ratio, chrysene/benzo〔a〕anthracene ratio, it can be concluded that the sediment PAH contaminations were ascribed to both pyrolytic and petrogenic origins.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.16.2-16.2
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• 2011

Graphene has attracted significant attention due to its unique characteristics and promising nanoelectronic device applications. For practical device applications, it is essential to synthesize high-quality and large-area graphene films. Graphene has been synthesized by eloborated mechanical exfoliation of highly oriented pyrolytic graphite, chemical reduction of exfoliated grahene oxide, thermal decomposition of silicon carbide, and chemical vapor deposition (CVD) on metal substrates such as Ni, Cu, Ru etc. The CVD has advantages over some of other methods in terms of mass production on large-areas substrates and it can be easily separated from the metal substrate and transferred to other desired substrates. Especially, plasma-enhanced CVD (PECVD) can be very efficient to synthesize high-quality graphene. Little information is available on the synthesis of graphene by PECVD even though PECVD has been demonstrated to be successful in synthesizing various carbon nanostructures such as carbon nanotubes and nanosheets. In this study, we synthesized graphene on $Ni/SiO_2/Si$ and Cu plate substrates with CH4 diluted in $Ar/H_2$ (10%) by using an inductively-coupled PECVD (ICPCVD). High-quality graphene was synthesized at as low as $700^{\circ}C$ with 600 W of plasma power while graphene layer was not formed without plasma. The growth rate of graphene was so fast that graphene films fully covered on substrate surface just for few seconds $CH_4$ gas supply. The transferred graphene films on glass substrates has a transmittance at 550 nm is higher 94%, indicating 1~3 monolayers of graphene were formed. FETs based on the grapheme films transferred to $Si/SiO_2$ substrates revealed a p-type. We will further discuss the synthesis of graphene and doped graphene by ICPVCD and their characteristics.

• Journal of the Korean Wood Science and Technology
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• 제35권6호
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• pp.31-42
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• 2007

국산 침 활엽수재의 열분해 및 해부학적 특성에 관해 조사하기 위해 침엽수재 3종(소나무, 리기다소나무, 낙엽송) 및 활엽수재 3종(단풍나무, 물푸레나무, 굴참나무)의 화학적 성분분석, TG-DTA (Thermogravimetric Analysis & Differential Thermal Analysis), 메틸렌블루 흡착성능(MBA) 및 SEM 관찰을 하였다. TG-DTA에서 시료는 $1{\ell}/min$로 $N_2$ 가스가 유입되는 조건하에 $10^{\circ}C$/min의 숭온속도로 최대 $10^{\circ}C$까지 탄화되었다. 화학적 성분분석 결과 모든 시료에서 전형적인 목재 주성분의 함량을 나타냈다. TG-DTA 결과, 침엽수재의 탄화수율이 활엽수보다 높았으며 목재 주성분 중 리그닌의 탄화수율이 가장 높았다. 모든 시료가 전형적인 목재 열분해의 TGA, DTG, DTA 곡선을 나타냈지만, 침 활엽수재 간에 몇 가지 차이점이 나타났다. 리그닌의 함량이 열분해에 큰 영향을 미쳤으며, 리그닌의 분자구조에 따라 중량감소와 탄화수율이 크게 달라졌다. 메틸렌블루 흡착성능 시험 결과 침엽수재의 MBA가 활엽수재보다 높았으며 소나무의 MBA가 가장 높았지만, 활성탄이나 백탄보다는 약 23배, 4씩 낮았다. SEM 관찰 결과 탄화 과정에서 전체적인 목재의 구조와 목재 섬유의 섬유구조가 그대로 유지됨을 확인하였다.

• Korean Chemical Engineering Research
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• 제56권6호
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• pp.901-908
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• 2018

흑연은 리튬이온전지에 사용 되는 대표적인 음극활물질이다. 그러나 최대 이론 용량이 $372mA\;h\;g^{-1}$으로 제한되기 때문에 고용량의 리튬이온전지 개발을 위해서는 새로운 음극 소재 활물질이 필요하다. 실리콘의 최대 이론 용량은 $4200mA\;h\;g^{-1}$으로 흑연보다 높은 값을 나타내지만 부피 팽창이 400%로 크기 때문에 음극 소재 활물질로 바로 적용하기에는 적합하지 않다. 따라서 부피 팽창으로 인한 방전 용량의 감소를 최소화하기 위해 건식 방법으로 실리콘을 분쇄 하여 기계적 응력 및 반응상의 체적 변화를 감소시키고 입도 제어 된 실리콘 입자에 탄소를 코팅하여 체적의 변화를 억제하였다. 그리고 탄소 섬유를 입자 표면에 실타래처럼 성장시켜 2차적으로 부피 팽창을 제어하고 전기전도성을 개선하였다. 실험 변수에 따른 재료들의 물리화학적 특성을 XRD, SEM 및 TEM을 사용하여 측정하였고 전기화학적 특성을 평가 하였다. 본 연구에서는 실리콘의 수명 특성을 향상시켜 음극 소재 활물질로 사용 할 수 있는 합성 방법에 대하여 알아보았다.

• 청정기술
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• 제16권3호
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• pp.198-205
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• 2010

염화탄화수소 열분해와 생성물분포 특성을 고찰하기 위해 등온 관형 반응기를 이용해 두 가지 실험을 수행하였다. 첫 번째는 반응분위기에 따른 열분해 특성을 파악하기 위해 $H_2$ 또는 Ar 반응분위기에서 dichloromethane ($CH_2Cl_2$) 분해율과 생성물분포 특성을 고찰하였다. Ar 반응분위기($CH_2Cl_2$/Ar 반응계)에서 보다 $H_2$ 반응분위기($CH_2Cl_2/H_2$ 반응계)에서 $CH_2Cl_2$ 분해율이 더 높았다. 이는 반응성 기체인 $H_2$ 분위기에서 $CH_2Cl_2$ 분해를 촉진시키며 수소 첨가 탈염소반응을 통해 탈염소화된 탄화수소화합물을 생성시키며, 다환방향족탄화수소 (polycyclic aromatic hydrocarbon: PAH)와 soot 생성을 억제하기 때문이다. $CH_2Cl_2/H_2$ 반응계에서 주요생성물로 탈염소화합물인 $CH_3Cl,\;CH_4,\;C_2H_6,\;C_2H_4,\;HCl$ 등이 생성되었으며, 미량 생성물로 chloroethylene이 검출되었다. $CH_2Cl_2$/Ar 반응계에서는 탄소물질수지가 낮았으며 특히 반응온도 $750^{\circ}C$ 이상에서 탄소물질 수지가 더 낮게 나타났다. 주요 생성물로는 chloroethylene과 HCl이 검출되었으며, 미량 생성물로는 $CH_3Cl$과 $C_2H_2$이 검출되었다. 고온 Ar 반응분위기에서 $CH_4$ 주입에 따른 chloroform($CHCl_3$) 분해와 생성물분포 특성을 비교 고찰하였다. $CHCl_3$ 분해율을 비교해 보면 $CH_4$을 주입할 경우($CHCl_3/CH_4/Ar$ 반응계)가 $CH_4$을 주입하지 않았을 경우($CHCl_3$/Ar 반응계)보다 분해율이 낮았다. 이는 $CHCl_3$가 분해되면서 생성되는 활성도가 큰 이중라디칼(diradical)인 :$CCl_2$가 첨가물로 주입된 $CH_4$와 반응하여 소모됨으로써 $CHCl_3$ 분해율이 상대적으로 감소되기 때문이다. Ar 반응분위기에서 $CH_4$ 첨가 여부에 따라 $CHCl_3$이 분해되면서 생성되는 생성물 분포는 큰 차이를 나타내고 있었다. 앞에서 고찰된 각 반응계에서 분해율 비교와 생성물 분포특성을 고려하고 열화학이론 및 반응속도론을 기초로 주요 반응경로를 제시하였다.

• Journal of Chest Surgery
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• 제24권2호
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• pp.161-170
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• 1991

Clinical results with the Mechanical cardiac valves were reviewed for 261 patients who underwent cardiac valve replacement from September, 1985 to July, 1990. of the Mechanical valves used, 156 were Carbomedics, 109 Duromedics, 52 St. Jude and 11 Bjork-Shiley. Overall hospital mortality was 14 out of 261[5,36%]: 9 out of 159[5.66%] for MVR, 1 out of 35[2.86%] for AVR and 4 out of 67[5.96%] for DVR[AVR+MVR]. Two hundred and forty seven operative survivors were followed up for a total 466.8 patient-years, ranged from 1 month to 4.9 years [a mean 1.8 years] and the follow up was 96.0%. There were 12 valve-related complications: three from thromboembolism, three from valve thrombosis, three from prosthetic valve endocarditis, two from paravalvular leak and the other one from hemorrhage. Actuarial rate free from all valve-related complication at 4.9 years was 96$\pm$1.3%. There were 11 late deaths: two from thromboembolism, one from valve thrombosis, one from prosthetic valve endocarditis, one from hemorrhage and the others 6 from non-valve-related complications. Actuarial survival rate at 4.9 years was 94$\pm$2.0%. 96$\pm$3.0% for MVR, 94$\pm$4.2% for AVR and 91$\pm$3.7% for DVR[AVR+MVR]. And there are 7 reoperations: three from paraprosthetic leak, two from prosthetic valve endocarditis and two from valve thrombosis. Actuarial rate free from reoperation at 9 years was 96$\pm$2.9%. On the basis of this 4.9 years of experience, the pyrolytic carbon mechanical valves appears to be an excellent mechanical prosthesis for cardiac valve replacement, in terms of hemodynamic performance, low mortality and low thrombogenecity.

• 한국환경과학회지
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• 제14권2호
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• pp.105-119
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• 2005

The surface sediments inside Songsanpo and Seogwipo Harbors, major harbors of Jeju Island, were collected three times (June, September and December, 2001) and analyzed for 16 polycyclic aromatic hydrocarbons (PAHs) recommended by US-EPA as priority pollutants to assess their distribution levels and their biological effects on the marine organisms, and to suggest their possible origins. The concentrations of total PAHs inside Songsanpo and Seogwipo Harbors ranged from 41 to 288 ng/g on a dry weight basis with a mean value of 121 ng/g and from 14 to 268 ng/g with a mean value of 119 ng/g, respectively, and the levels were low as compared with those in other areas of the world. The sedimentary PAHs may be correlated with organic carbon and mud content to some extent. Based on comparisons of individual and total concentrations with effects-based sediment quality guidelines, the potential for the biological effects on the marine organisms were expected to be very low. From the examinations of the four PAH origin indices, such as LMW /HMW (low molecular weight 2-3 ring PAHs over high molecular weight 4-6 ring PAHs), phenanthrene/anthracene ratio, fluoranthene/pyrene ratio, chrysene/benzo[a]anthracene ratio, it can be concluded that the sediment PAH contaminations were ascribed to both of pyrolytic and petrogenic origins.