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Lee, Byoung-Sun,Son, Seoung-Bum,Park, Kyu-Min,Lee, Geunsung,Oh, Kyu Hwan,Lee, Se-Hee,Yu, Woong-Ryeol American Chemical Society 2012 ACS APPLIED MATERIALS & INTERFACES Vol.4 No.12
<P>The effect of pores in hollow carbon nanofibers (HCNFs) on their electrochemical performance is investigated because the carbon shell itself acts as a reservoir for accommodating Li-ions through intercalation and simultaneously becomes a transport medium through which Li-ions migrate into the core materials in HCNFs. Porous HCNFs (pHCNFs) are prepared by the coaxial electrospinning of a sacrificial core solution and an emulsified shell solution containing sacrificial islands for pore generation. After a thermal treatment, a systematic study is carried out to relate the resulting pore size in pHCNFs to the sacrificial islands in the emulsified shell. As the pores are introduced in pHCNFs, their initial capacity and reversible capacity rate are proved to increase significantly to 1003 mAhg<SUP>–1</SUP> and 61.8%, respectively, compared to those (653 mAhg<SUP>–1</SUP> and 53.9%) of nonporous HCNFs. The increased pore size and expanded graphene layers are believed to facilitate lithium insertion/extraction behavior.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2012/aamick.2012.4.issue-12/am301873d/production/images/medium/am-2012-01873d_0011.gif'></P>
Improved tensile strength of carbon nanotube-grafted carbon fiber reinforced composites
Lee, Geunsung,Sung, Minchang,Youk, Ji Ho,Lee, Jinyong,Yu, Woong-Ryeol Elsevier 2019 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.220 No.-
<P><B>Abstract</B></P> <P>Increased tensile strength of carbon nanotube (CNT)-grafted carbon fiber (CF) composites has been reported, but the mechanism of this increase is not yet clear. In this study, CNT-grafted CF unidirectional (UD) and woven composites were fabricated using a low-temperature chemical vapor deposition (CVD) and resin transfer molding. Two types of CNTs (short and thin, long and thick) were successfully grown and grafted to CFs without degrading the CFs in the preforms. The CNT-grafted CFs exhibited increased interfacial shear strength (IFSS) similarly regardless of the CNT type. Interestingly, however, long and thick CNT-grafted CF UD and woven composites exhibited significant increases in tensile strength (about 20% and 30%), suggesting other mechanisms besides increased IFSS. The splitting crack initiation under the mixed mode condition was quantitatively characterized for the CNT-grafted CF UD composites, demonstrating that long and thick CNTs delayed the splitting crack initiation. Delayed fiber splitting and increased IFSS were concluded to be the main sources of increased tensile strength of CNT-grafted CF composites.</P>
Facile conductive bridges formed between silicon nanoparticles inside hollow carbon nanofibers.
Lee, Byoung-Sun,Son, Seoung-Bum,Seo, Jong-Hyun,Park, Kyu-Min,Lee, Geunsung,Lee, Se-Hee,Oh, Kyu Hwan,Ahn, Jae-Pyoung,Yu, Woong-Ryeol RSC Pub 2013 Nanoscale Vol.5 No.11
<P>This paper reports on a simple and effective method for improving the electrochemical performance of silicon nanoparticle-core/carbon-shell (Si-core/C-shell) nanofibers. Instead of increasing the encapsulation amount of Si nanoparticles, additional conductive paths between the Si nanoparticles were formed by incorporating a small percentage of multi-walled carbon nanotubes (MWNTs) (e.g., 5 wt% with respect to Si) into the Si nanoparticle core. The electrical conductivity of a single Si-core/C-shell nanofiber was measured by a four-point probe using four nano-manipulators, which showed a more than five times increase according to MWNT addition. A galvanostatic charge-discharge test demonstrated that a small amount of MWNTs greatly improved the electrochemical performance of the Si-core/C-shell nanofibers (e.g., a 25.1% increase in the Li-ion storage capability) due to the enhanced participation of Si through the additional conductive paths formed between the Si nanoparticles.</P>
Na, Wonjin,Lee, Geunsung,Sung, Minchang,Han, Heung Nam,Yu, Woong-Ryeol ELSEVIER (APPLIED SCIENCE) 2017 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.168 No.-
<P><B>Abstract</B></P> <P>The tensile strength of unidirectional (UD) carbon fiber composites was predicted considering the interfacial shear strength (IFSS). First, the effect of the IFSS on the load transfer to the surrounding fibers when a fiber was broken was analyzed using finite element method and then the stress concentration factor (SCF) of each surrounding fiber was determined. The multiple fracture number was calculated using the SCF and a statistical approach that can calculate the probability of fiber breakage propagation due to the stress concentration when the broken fibers exist in neighbor. Finally, the tensile strength of UD carbon fiber composites was predicted using the multiple fracture number and was compared with experimental results, demonstrating the validity of the current method. An optimal IFSS that can ensure the maximum tensile strength of UD carbon fiber composites is discussed based on the calculation results.</P>
Bond strength of individual carbon nanotubes grown directly on carbon fibers
Kim, Kyoung Ju,Lee, Geunsung,Kim, Sung-Dae,Kim, Seong-Il,Youk, Ji Ho,Lee, Jinyong,Kim, Young-Woon,Yu, Woong-Ryeol IOP 2016 Nanotechnology Vol.27 No.40
<P>The performance of carbon nanotube (CNT)-based devices strongly depends on the adhesion of CNTs to the substrate on which they were directly grown. We report on the bond strength of CNTs grown on a carbon fiber (T700SC Toray), measured via <I>in situ</I> pulling of individual CNTs inside a transmission electron microscope. The bond strength of an individual CNT, obtained from the measured pulling force and CNT cross-section, was very high (∼200 MPa), 8–10 times higher than that of an adhesion model assuming only van der Waals interactions (25 MPa), presumably due to carbon–carbon interactions between the CNT (its bottom atoms) and the carbon substrate.</P>
Size estimation of nanoparticle using diffused laser scattering in Mie regime
Im Jaeseung,Kim Minwoo,Lee Geunsung,Lee Sanghyun,Choi Soobong 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.5
Inspection of the nano-sized defects on the wafer surface has become critical for the entire yield of overall semiconductor fabrication process. It requires non-destructive and rapid examination of large area to gratify the expectations. The use of laser scattering could be an easy clue because light scattering occurs beyond the difraction limit. However, the laser speckle pattern disturbs the observer. Thus, we developed difused laser scattering dark feld microscopy to take advantages of high intensity and low coherence of light to obtain better scattering response. The scattering response and its relative luminance enable us to estimate the size of nanoparticles. Our work could be utilized for in situ fabrication expecting aforementioned the requirements.
CNG용 Type 4 하이브리드 섬유 복합재 용기 개발에 대한 연구
조성민(Sung-min Cho),조민식(Min-sik Cho),정근성(Geunsung Jung),이선규(Sun-kyu Lee),이승국(Seung-kuk Lee),박기동(Ki-dong Park),류성기(Sung-Ki Lyu) 한국기계가공학회 2017 한국기계가공학회지 Vol.16 No.4
The objective of this study is to develop and commercialize an on-board fuel storage system for CNG vehicles. A type 4 vessel is made of resin-impregnated continuous filament windings on a polyamide (PA6) liner. In particular, this study localized the PA6 liner’s fabrication and development. To analyze the filament winding, a specimen test was performed, and the results were verified values obtained using finite element analysis. In this study, the filament winding and fibers were optimized for a 207 bar composite cylinder in a compressed natural gas vehicle.
브레이크 디스크 로터 표면 수직 구멍의 영향에 관한 연구
서영진(Youngjin Seo),오제하(Jeha Oh),이준상(Junsang Lee),강경수(Kyoungsoo Kang),정근성(Geunsung Jung) 한국자동차공학회 2008 한국 자동차공학회논문집 Vol.16 No.1
Cross-drilling on the brake disc is generally known as a way of improving cooling efficiency. In other theories, cross-drilled holes act like a path of gas or water and are also known that they can reduce fading and wetting of brake rotors. However, in disc rotors with cross-drilling, thermal crack phenomena have been reported more frequently and more manufacturing cost should be paid than non cross-drilled disc rotors. In this study, to examine various effects of cross-drilling on the brake disc, two kinds of brake disc rotors, cross-drilled and non cross-drilled, were used in computational fluid dynamic analyses and dynamometer tests.