• Advances in nano research
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• 제11권6호
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• pp.581-593
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• 2021

This model is proposed to describe the buckling behavior of Carbon Nanotubes (CNTs) embedded in an elastic medium taking into account the combined effects of the magnetic field, the temperature, the nonlocal parameter, the number of walls. Using Eringen's nonlocal elasticity theory, thin cylindrical shell theory and Van der Waal force (VdW) interactions, we develop a system of partial differential equations governing the buckling response of CNTs embedded on Winkler, Pasternak, and Kerr foundations in a thermal-magnetic environment. The pre-buckling stresses are obtained by applying airy's stress function and an adjacent equilibrium criterion. To estimate the nonlocal critical buckling load of CNTs under the simultaneous effects of the magnetic field, the temperature change, and the number of walls, an optimization technique is proposed. Furthermore, analytical formulas are developed to obtain the buckling behavior of SWCNTs embedded in an elastic medium without taking into account the effects of the nonlocal parameter. These formulas take into account VdW interactions between adjacent tubes and the effect of terms involving differences in tube radii generally neglected in the derived expressions of the critical buckling load published in the literature. Most scientific research on modeling the effects of magnetic fields is based on beam theories, this motivation pushes me to develop a cylindrical shell model for studying the effect of the magnetic field on the static behavior of CNTs. The results show that the magnetic field has significant effects on the static behavior of CNTs and can lead to slow buckling. On the other hand, thermal effects reduce the critical buckling load. The findings in this work can help us design of CNTs for various applications (e.g. structural, electrical, mechanical and biological applications) in a thermal and magnetic environment.

• 유기물자원화
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• 제15권1호
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• pp.143-148
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• 2007

본 연구는 대부분 매립 처분되고 있는 굴패각을 소성가공을 통한 약상 칼슘제 추출을 목적으로 굴패각의 이화화적인 특성과 열적특성 및 소성가구 후 패각의 특성 등 액상 칼슘제 추출을 위한 기초연구를 수행한 결과 굴패각 분쇄시 입자특성은 시료에 따라 입경의 차이가 큰 자이가 나타났으며, 소성온도에 따른 특성변화는 소성온도가 높을수록, 소성시산이 경과 할수록 무게감소량이 큰 것으로 나타났다. 또한 칼슘함량은 소성신간이 경과 할수록, 소성온도가 높을수록 칼슘함량이 증가하는 것으로 나타나 소성온도가 높고, 분말의 입자크기를 작게 할수록 소성가공이 가장 효율적인 것으로 나타났다. 아울러 소성가공된 패각은 식물이 이용할 수 있는 양이온치환능력(CEC) 함량이 30~60배까지 증가하는 하는 것으로 나타나 소성 가공된 굴패각을 식물에 유익한 영양소원으로 재활용 가능한 것으로 판단된다.

• 한국재료학회지
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• 제20권12호
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• pp.691-698
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• 2010

Magnesium hydroxide-melamine core-shell particles were prepared through the coating of melamine monomer on the surface of magnesium hydroxide in the presence of phosphoric acid. The melamine monomer was dissolved in hot water but recrystallized on the surface of magnesium hydroxide by quenching to room temperature in the presence of phosphoric acid. The core-shell particle was applied to low-density polyethylene/ ethylene vinyl acetate (LDPE/EVA) resin by melt-compounding at $180^{\circ}C$ as flame retardant. The effect of magnesium hydroxide and melamine content has been studied on the flame retardancy of the core-shell particles in LDPE/EVA resin according to the preparation process and purity of magnesium hydroxide. Magnesium hydroxide prepared with sodium hydroxide rather than with ammonia solution revealed higher flame retardancy in core-shell particles with LDPE/EVA resin. At 50 wt% loading of flame retardant, core-shell particles revealed higher flame retardancy compared to that of the exclusive magnesium hydroxide in LDPE/EVA composite, and it was possible to satisfy the V0 grade in the UL-94 vertical test. The synergistic flame retardant effect of magnesium hydroxide and melamine core-shell particles was explained as being due to the endothermic decomposition of magnesium hydroxide and melamine, which was followed by the evolution of water from the magnesium hydroxide and porous char formation due to reactive nitrogen compounds, and carbon dioxide generated from melamine.

• 한국결정성장학회지
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• 제16권2호
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• pp.71-75
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• 2006

소성 분위기를 변화시켜 골재를 제조할 때 골재의 중앙에 만들어지는 블랙코어(black core) 형성정도의 차이와 골재 물성의 차이점을 알아보기 위해 적점토, 탄소(carbon), 산화철($Fe_2O_3$)이 혼합된 직경 10mm 구형골재를 조성별로 산화분위기, 중성분위기, 환원분위기에서 각각 소성시키고 각각의 비중, 흡수율, 블랙코어 면적비(%)를 측정하고 비교하였다. 산화분위기에서 소성시킨 골재는 껍질(shell)과 블랙코어가 뚜렷하게 구분되는 반면 중성 및 환원분위기에서 소성한 시편에서는 시편의 단면전체에 블랙코어가 형성되었다. 산화분위기와 중성분위기와는 달리 환원분위기에서 소성된 시편에서는 탄소첨가량이 증가할수록 비중이 증가했으며, 전반적인 비중은 가장 낮았다. 흡수율은 모든 분위기에서 탄소첨가량이 증가할수록 증가하는 경향을 보였다.

• 한국재료학회지
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• 제31권9호
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• pp.525-531
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• 2021

Carbon-encapsulated Ni catalysts are synthesized by an electrical explosion of wires (EEW) method and applied for CO₂ methanation. We find that the presence of carbon shell on Ni nanoparticles as catalyst can positively affect CO₂ methanation reaction. Ni@5C that is produced under 5 % CH₄ partial pressure in Ar gas has highest conversions of 68 % at 350 ℃ and 70 % at 400 ℃, which are 73 and 75 % of the thermodynamic equilibrium conversion, respectively. The catalyst of Ni@10C with thicker carbon layer shows much reduced activity. The EEW-produced Ni catalysts with low specific surface area outperform Ni catalysts with high surface area synthesized by solution-based precipitation methods. Our finding in this study shows the possibility of utilizing carbon-encapsulated metal catalysts for heterogeneous catalysis reaction including CO₂ methanation. Furthermore, EEW, which is a highly promising method for massive production of metal nanoparticles, can be applied for various catalysis system, requiring scaled-up synthesis of catalysts.

• 한국분말재료학회지
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• 제11권6호
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• pp.510-514
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• 2004

Iron-carbon nanocapsules were synthesized by plasma arc discharge (PAD) process under various atmosphere of methane, argon and hydrogen gas. Characterization and surface properties were investigated by means of HRTEM, XRD, XPS and Mossbauer spectroscopy. Fe nanocapsules synthesized were composed of three phases $({\alpha}-Fe,\;Y-Fe\;and\;Fe_{3}C)$ with core/shell structures. The surface of nanocapsules was covered by the shell of graphite phase in the thickness of $4{\~}5$nm.

• 한국주조공학회지
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• 제7권3호
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• pp.184-191
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• 1987

In this study the principles of melting phenomena of compacted vermicular graphite cast iron are discussed by considering the effects of the variation of phosphorus content and heating rate on the quenched microstructure of the specimens. In compacted vermicular graphite cast iron containing little phosphorus, the melting phenomena are found initially at the outer region of austenite shell and subsequently progressed with the diffusion of carbon through the austenite shell without regard to heating rate. But as the phosphorus content was increased over than 0.12wt.%, the melting phenomena initiated at the boundary of eutectic shell and progressed along the contact area between the melt and graphite tips at higher heating rate. At lower heating rate, the melt of steadite dissolved at the lower temperature than that of eutectic was moved toward the graphite through the austenite grain-boundary and promoted melting of graphite and matrix.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.284-284
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• 2013

중 에너지 이온 산란 분석법(Medium Energy Ion Scattering Spectrometer, MEIS)은 50~500 keV로 이온을 가속 후 시료에 입사시켜 시료의 원자와 핵간 충돌로 산란되는 일차이온의 에너지를 측정하여 시료를 분석하는 기법으로, 원자층의 깊이 분해능으로 초박막의 표면 계면의 조성과 구조를 분석 할수 있는 유용한 미세 분석기술이다. 본 실험에서 에너지 70~100 keV의 He+ 이온을 사용하여 Pulse Width 1 ns의 Pulsed ion beam을 만들어 Start 신호로 사용하고 Delay-line-detector에 검출된 신호를 End 신호를 이용한 TOF-MEIS System을 개발하였다. 활용 가능한 분석시편으로 Ultra thin film 시편으로 1, 1.5, 2, 2.5, 3, 4 nm의 HfO2, 1.8, 4nm의 SiO2 시편을 분석 하였으며 Ultra Shallow Junction 시편으로 As Doped Si, Cs Doped Si 시편 및 Composition, Core/shell 구조의 Q-dot 시편으로 CdSe, CdSe/ZnS등 다양한 분석 실험을 진행 하였다. Composition, Core/shell 구조의 Q-dot 시편은 Diamond Like Carbon(DLC)의 Substrate에 Mono-layer로 형성하여 분석하였다.

• Computers and Concrete
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• 제30권4호
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• pp.269-276
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• 2022

In this paper, frequency vibrations of double-walled carbon nanotubes (CNTs) has been investigated based upon nonlocal elastic theory. The inference of small scale is being perceived by establishing nonlocal Love shell model. The wave propagation approach has been operated to frame the governing equations as eigen value system. An innovational nonlocal model to examine the scale effect on vibrational behavior of armchair, zigzag and chiral of double-walled CNTs. An appropriate selection of material properties and nonlocal parameter has been considered. The influence of dimensionless nonlocal parameter has been studied in detail. The dominance of end condition via nonlocal parameter is explained graphically. The results generated furnish the evidence regarding applicability of nonlocal shell model and also verified by earlier published literature.

• Carbon letters
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• 제10권3호
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• pp.198-201
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• 2009

Among other filters such as light filter, wave filter, air filter, ultra filter and filter paper, a novel adsorption filter from thermostable polyester nonwoven fabrics immobilized with functional super activated carbon by means of quinoline soluble, activateable isotropic pitch binder were developed in this study. The activated carbon precursor is available in the market branded as coconut shell based activated carbon(CCS-AC) produced by Dongyang Carbon Co. Ltd. BET-surface area of this precursor was $1,355\;m^2/g$, after KOH-activation it increased over $2,970\;m^2/g$ and was named as super activated carbon. In the preliminary research, this precursor was impregnated with $PdCl_2$(0.188 wt%) $KMnO_4$(3 wt%) and redox-agent(CuCl2, 0.577 wt%) in order to promote TOF up to 100/h and Selectivity up 99% and patented as a functional AC for the ethylene adsorption. The enhancement of the isotropic pitch binder to the AC-immobilized adsorption filter was BET-surface area upgraded by $266\;m^2/g$ and promoted the Iodine- and MB-adsorption by 1.4 times, respectively and also micro pore wide ranges < $5{\AA}{\sim}30\;{\AA}$ >.