• 전기전자학회논문지
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• 제18권4호
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• pp.620-624
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• 2014

본 연구에서는, Ni/CNT/$SiO_2$ 구조의 4H-SiC MIS 캐패시터를 제작하고 전기적 특성을 조사하였다. 이를 통하여 4H-SiC MIS 소자에서 탄소나노튜브의 역할을 분석하고자 하였다. 탄소나노튜브는 이소프로필알코올과 혼합하여 $SiO_2$ 표면에 분산하였다. 소자의 전기적 특성 분석을 위하여 300-500K의 온도 범위에서 소자의 정전용량-전압 특성을 측정하였다. 밴드 평탄화 전압은 양의 방향으로 shift되었다. 정전용량-전압 그래프로부터 계면 포획 전하 밀도 및 산화막 포획 전하 밀도가 유도되었다. 산화막의 상태는 4H-SiC MIS 구조의 계면에서 전하 반송자 또는 결함 상태와 관련된다. 온도가 증가함에 따라 밴드 평탄화 전압은 음의 방향으로 shift되는 결과를 얻었다. 실험 결과로부터, Ni과 $SiO_2$ 계면에 탄소나노튜브를 첨가함에 따라 4H-SiC MIS 캐패시터의 게이트 특성을 조절 가능할 것으로 판단된다.

• 한국지반환경공학회 논문집
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• 제25권3호
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• pp.5-11
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• 2024

이산화탄소 포집 및 지중 저장을 위해 유망한 지질학적 구조로는 대수층, 폐유전 및 가스전 등이 존재한다. 이 중 대수층은 다른 지질학적 구조에 비해 많은 양의 이산화탄소 저장이 가능한 것으로 판단됨에 따라 그 관심이 증가하고 있으며, 대수층의 특성을 반영하여 이산화탄소 저장 효율 향상을 위한 기술 개발이 필요한 실정이다. 따라서, 본 연구에서는 음이온성 계면활성제를 활용하여 공극수가 존재하는 마이크로모델 내 계면활성제 선 주입 후 초임계 이산화탄소 후속 주입에 따른 이산화탄소 저장 효율 평가를 수행하였다. 그 결과 선 주입되는 계면활성제 수용액의 농도가 증가함에 따라 이산화탄소 저장 효율이 개선되며, 농도가 낮을수록 이산화탄소 저장 효율 개선을 위한 더 많은 계면활성제의 주입이 필요한 것으로 나타난다. 또한 동일한 계면활성제 농도 조건에서 선행 연구의 계면활성제-초임계 이산화탄소 치환보다 계면활성제 선 주입 방식에서 이산화탄소 저장 효율은 약 30% 낮은 값을 나타내며, 본 연구의 최대 농도 조건에서 선행 연구와 유사한 이산화탄소 저장 효율을 나타낸다. 이러한 결과는 향후 대수층 내 이산화탄소 저장 효율 향상을 위한 계면활성제 적용 시 농도 결정에 활용될 것으로 기대된다.

• 대한기계학회논문집B
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• 제28권9호
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• pp.1081-1092
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• 2004

The synthesis of Ni-catalyzed multi-walled carbon nanotubes and nanofibers on a catalytic metal substrate, using an ethylene fueled inverse diffusion flame as a heat source, was investigated. When the gas temperature was varied from 1,400K to 900K, approximately, carbon nanotubes with diameters of 20∼60nm were formed on the substrate. In the regions where the gas temperature was higher than 1,400K or lower than 900K, iron nanorods or carbon nanofibers were synthesized, respectively. Based on the quantitative analyses of large amount of SEM and TEM images, the nanotubes formed closer to the flame had a tendency of having larger diameters. HR-TEM images and Raman spectra revealed that carbon nanotubes synthesized had multi-walled structures with some defective graphite layers at the wall. Based on the graphite mode of the Raman spectra, it was believed that the optimal synthesis could be obtained as the substrate was positioned at between 5.5mm and 5.0mm, from the flame axis.

• 한국주조공학회지
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• 제15권6호
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• pp.604-615
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• 1995

Austenitic stainless steel castings using expandable polystylene(referred to hereafter as EPS) patterns are often affected by distinctive defects associated with incomplete decomposition of the EPS as the molds are filled with metal. The quality of the castings, with particular reference to carbon pick-up in austenitic stainless steel is further influenced to a significant extent by such factors as reduced pressure, the additive by adding $Na_2CO_3$ in coating. The steel composition and microstructure were examined at the surface layer of castings, at depths of 1mm, by taking successive layers of swarf and analysis. In experiments, the carburizing atmosphere was neutralized, showing that the coating performed efficiently by decomposing almost instantly on heating and liberating $CO_2$. The upper parts of castings obtained using EPS patterns were slightly higher in carbon pick-up than other parts. Comparing the 316L and 304 stainless steel castings, qualitative and quantative differences could be found between the carbon pick-up behaviours as influence of the carbon content and alloying elements. Carbide former such as Cr makes carbon more soluble in the steel. This must make carbon pick-up in the surface layer but at the same time richer in carbon especially in the 304 stainless steel castings.

• 한국분말재료학회지
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• 제23권6호
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• pp.420-425
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• 2016

N-doped carbon nanofibers as catalysts for oxygen-reduction reactions are synthesized using electrospinning and carbonization. Their morphologies, structures, chemical bonding states, and electrochemical performance are characterized. The optimized N-doped carbon nanofibers exhibit graphitization of carbon nanofibers and an increased nitrogen doping as well as a uniform network structure. In particular, the optimized N-doped carbon nanofibers show outstanding catalytic activity for oxygen-reduction reactions, such as a half-wave potential ($E_{1/2}$) of 0.43 V, kinetic limiting current density of $6.2mAcm^{-2}$, electron reduction pathways (n = 3.1), and excellent long-term stability after 2000 cycles, resulting in a lower $E_{1/2}$ potential degradation of 13 mV. The improvement in the electrochemical performance results from the synergistic effect of the graphitization of carbon nanofibers and the increased amount of nitrogen doping.

• Structural Engineering and Mechanics
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• 제33권4호
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• pp.429-446
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• 2009

Three-scale homogenization procedure is proposed in this paper to provide estimates of the effective thermal conductivities of porous carbon-carbon textile composites. On each scale - the level of fiber tow (micro-scale), the level of yarns (meso-scale) and the level of laminate (macro-scale) - a two step homogenization procedure based on the Mori-Tanaka averaging scheme is adopted. This involves evaluation of the effective properties first in the absence of pores. In the next step, an ellipsoidal pore is introduced into a new, generally orthotropic, matrix to make provision for the presence of crimp voids and transverse and delamination cracks resulting from the thermal transformation of a polymeric precursor into the carbon matrix. Other sources of imperfections also attributed to the manufacturing processes, including non-uniform texture of the reinforcements, are taken into consideration through the histograms of inclination angles measured along the fiber tow path together with a particular shape of the equivalent ellipsoidal inclusion proposed already in Sko ek (1998). The analysis shows that a reasonable agreement of the numerical predictions with experimental measurements can be achieved.

• Carbon letters
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• 제27권
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• pp.98-107
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• 2018

Free-standing electrodes of CuO nanorods in carbon nanotubes (CNTs) are developed by synthesizing porous CuO nanorods throughout CNT webs. The electrochemical performance of the free-standing electrodes is evaluated for their use in flexible lithium ion batteries (LIBs). The electrodes comprising CuO@CNT nanocomposites (NCs) were characterized by charge-discharge testing, cyclic voltammetry, and impedance measurement. These structures are capable of accommodating a high number of lithium ions as well as increasing stability; thus, an increase of capacity in long-term cycling and a good rate capability is achieved. We demonstrate a simple process of fabricating free-standing electrodes of CuO@CNT NCs that can be utilized in flexible LIBs with high performance in terms of capacity and cycling stability.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.750-755
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• 1999

When the RC frame structures subjected to the seismic load, brittle shear failure of vertical members induces brittle collapse of whole structures. Failure mechanism like this is not desirable. So shear strengthening method to avoid this failure mechanism is needed. Recently, strengthening method using continuous fiber sheet is studied and used widely which have high elastic and high strength characteristics. In this study, RC columns which is strengthened by carbon fiber sheet in the form of tape or whole sheet were tested under the cyclic load. The parameter of this test is the amount of strengthening. As the amount of strengthening increase, strength, ductility and energy capacity increase. The failure mode of test results are shear and bond-split failure.

• Carbon letters
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• 제13권2호
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• pp.121-125
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• 2012

In the present work, exfoliated graphite nanoplatelets (EGN) of 1 ${\mu}m$ in average particle size, which were prepared by heating at $900^{\circ}C$ and then subjected to ultrasonic, ball-milling, and vibratory ball-milling techniques, were uniformly incorporated into phenylethynyl-terminated polyimide (PETI-5) resin. The fracture surface morphology and the electrical resistivity of the EGN/PETI-5 composites were investigated. The results showed that the fracture surfaces and the electrical resistivity strongly depended on the EGN content. The fracture surfaces became more ductile and roughened with increasing EGN and the electrical resistivity was gradually decreased with increased EGN loading, indicating the percolation threshold at 5 wt% EGN.

• 복합신소재구조학회 논문집
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• 제1권4호
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• pp.6-12
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• 2010

This study investigates how to apply composite material to the blast loading protection devices, mainly used for military purpose. Traditionally, earth-filled blast walls have been used for protecting important parts of military facilities and personnels. However these types of blast walls show difficulty in fabrication and portability because of their nature of heavy weight. Composite materials are known to have relatively higher specific stiffness and strength than any other metallic and earth-filled materials such as sand and gravels. Totally 4 times of TNT blast experiments were performed on the carbon/epoxy blast walls. After the end of each test, the improvement of blast wall was implemented to the structure. The test results show that the use of composite material in the blast protecting area is the one of very effective and reliable alternatives.