• Bulletin of the Korean Chemical Society
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• 제35권10호
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• pp.2974-2978
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• 2014

$Mn_3O_4$/multi-walled carbon nanotube (MWCNT) composites are prepared by chemically synthesizing $Mn_3O_4$ nanoparticles on a MWCNT film at room temperature. Structural and morphological characterization has been carried out using X-ray diffraction (XRD) and scanning and transmission electron microscopies (SEM and TEM). These reveal that polycrystalline $Mn_3O_4$ nanoparticles, with sizes of about 10-20 nm, aggregate to form larger nanoparticles (50-200 nm), and the $Mn_3O_4$ nanoparticles are attached inhomogeneously on MWCNTs. The electrochemical behavior of the composites is analyzed by cyclic voltammetry experiment. The $Mn_3O_4$/MWCNT composite exhibits a specific capacitance of $257Fg^{-1}$ at a scan rate of $5mVs^{-1}$, which is about 3.5 times higher than that of the pure $Mn_3O_4$. Cycle-life tests show that the specific capacitance of the $Mn_3O_4$/MWCNT composite is stable up to 1000 cycles with about 85% capacitance retention, which is better than the pure $Mn_3O_4$ electrode. The improved supercapacitive performance of the $Mn_3O_4$/MWCNT composite electrode can be attributed to the synergistic effects of the $Mn_3O_4$ nanoparticles and the MWCNTs, which arises not only from the combination of pseudocapacitance from $Mn_3O_4$ nanoparticles and electric double layer capacitance from the MWCNTs but also from the increased surface area, pore volume and conducting property of the MWCNT network.

• 한국포장학회지
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• 제28권1호
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• pp.55-66
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• 2022

In this study, forty corrugated fiberboard (CF) boxes for fresh produce were collected from farms located in Gyeongsan city and evaluated its characterizations and physical properties according to Korean Standard (KS). The basis weight, flute, and paperboard combination were determined for the characterizations of CF boxes. The measured basis weights of all samples were within the tolerance limit referred to KS and the flutes were B/F, EB/F, and AB/F flute, respectively. The bursting strength (BS), edgewise crush resistance (ECR), and compression strength (CS) were tested to evaluate the physical properties. There are four single-walled (SW) CF boxes showed BS and ECR higher than 638 kPa and 3.30 kN/m, respectively. One SW CF boxes showed BS and ECR higher than 785 kPa and 3.43 kN/m, respectively. In case of double-walled (DW) CF boxes, sixteen CF boxes showed BS and ECR higher than 785 kPa, 4.96 kN/m (AB flute), or 4.90 (EB flute), respectively. The other nineteen CF boxes showed BS and ECR higher than 981 kPa, 5.29 kN/m (AB flute), or 5.20 (EB flute), respectively. All the CF boxes except two samples showed the acceptable compression strength in reference to the guideline of KS.

• Composites Research
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• 제37권1호
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• pp.32-39
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• 2024

고체수소저장은 수소 기반 경제 발전과 에너지 저장 기술 혁신의 핵심 주제로 부각되고 있다. 이러한 저장 방식은 압축 및 액화수소 저장 등 기존 방식에 비해 안전성과 저장 및 운용 효율성 측면에서 우수한 특성을 보여주고 있다. 본 연구에서는 다양한 구조적 설계 요소 별로 나노튜브 표면에서의 고체수소저장 성능을 평가하고자 한다. 본 연구는 나노튜브의 저장 메커니즘을 밝히고자 분자 역학 시뮬레이션(MD)을 도입하여 수행되었다. 본 연구의 시뮬레이션에는 다양한 직경, 다중벽 구조(MWNT), 단일벽 구조(SWNT)의 탄소나노튜브(CNT) 및 붕소-질소 나노튜브(BNNT)가 도입되어 진행되었다. 방사형 밀도 함수(RDF)를 통해 다양한 조건에서 수소의 저장 및 효과적인 방출을 분석한 결과, 반경 감소와 이중벽 구조가 고체 수소 저장을 높이는 데 기여하는 것으로 나타났다. 또한, 붕소-질소 나노튜브의 수소 저장 용량은 탄소 나노튜브에 비해 낮게 측정되었지만, 유효 수소 저장 측면에서는 탄소 나노튜브를 훨씬 능가하는 것으로 나타났다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.264-264
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• 2010

Single-walled carbon nanotubes (SWCNTs) were grown on a Si wafer by using thermal chemical vapor deposition (t-CVD). We investigated the effect of the catalyst deposition rate on the types of CNTs grown on the substrate. In general, smaller islands of catalyst occur by agglomeration of a catalyst layer upon annealing as the catalyst layer becomes thinner, which results in the growth of CNTs with smaller diameters. For the same thickness of catalyst, a slower deposition rate will cause a more uniformly thin catalyst layer, which will be agglomerated during annealing, producing smaller catalyst islands. Thus, we can expect that the smaller-diameter CNTs will grow on the catalyst deposited with a lower rate even for the same thickness of catalyst. The 0.5-nm-thick Fe served as a catalyst, underneath which Al was coated as a catalyst support as well as a diffusion barrier on the Si substrate. The catalyst layers were. coated by using thermal evaporation. The deposition rates of the Al and Fe layers varied to be 90, 180 sec/nm and 70, 140 sec/nm, respectively. We prepared the four different combinations of the deposition rates of the AI and Fe layers. CNTs were synthesized for 10 min by flowing 60 sccm of Ar and 60 sccm of $H_2$ as a carrier gas and 20 sccm of $C_2H_2$ as a feedstock at 95 torr and $810^{\circ}C$. The substrates were subject to annealing for 20 sec for every case to form small catalyst islands prior to CNT growth. As-grown CNTs were characterized by using field emission scanning electron microscopy, high resolution transmission electron microscopy, Raman spectroscopy, UV-Vis NIR spectroscopy, and atomic force microscopy. The fast deposition of both the Al and Fe layers gave rise to the growth of thin multiwalled CNTs with the height of ${\sim}680\;{\mu}m$ for 10 min while the slow deposition caused the growth of ${\sim}800\;{\mu}m$ high SWCNTs. Several radial breathing mode (RBM) peaks in the Raman spectra were observed at the Raman shifts of $113.3{\sim}281.3\;cm^{-1}$, implying the presence of SWCNTs (or double-walled CNTs) with the tube diameters 2.07~0.83 nm. The Raman spectra of the as-grown SWCNTs showed very low G/D peak intensity ratios, indicating their low defect concentrations.

• Composites Research
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• 제31권6호
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• pp.371-378
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• 2018

본 연구에서는 폴리유산 나노복합재의 열탄성 거동을 예측하기 위해 분자동역학 전산모사를 수행하고 그 결과를 열탄성 미시역학 모델 예측해와 비교하였다. 폴리유산의 두 이성질체인 D유산(Poly D-lactide)와 L유산(Poly L-lactide)을 혼합한 스테레오 콤플렉스를 모델링하였고 이들을 기지로 사용한 탄소나노튜브 나노복합재를 구성하였다. 유산의 분해 유무에 따른 유리전이온도와 탄성계수 그리고 열팽창계수를 앙상블 전산모사를 통해 예측하였다. 미시역학 모델에서는 계면의 완전 결합을 가정한 이중입자 모델을 적용하여 탄성계수와 열팽창계수를 동일한 조성에서 예측하였다. 그 결과 열적 안정성에 있어 스테레오 콤플렉스에 탄소나노튜브가 첨가될 경우 유산의 뛰어난 계면 흡착과 이에 따른 열적 안정성 향상을 보였다. 순수한 유산과 나노복합재 모두 가수 분해에 따른 열적 특성 변화는 관찰되지 않았다. 또한, 스테레오 콤플렉스와 나노튜브 간 계면은 약한 불완전 결합상태 임을 알 수 있었다.

• 한국군사과학기술학회지
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• 제24권1호
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• pp.1-11
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• 2021

Thermal protection system structures such as double-panel structures are used on the skin of the fuselage and wings to prevent the transfer of high heat into the interior of an high supersonic/hypersonic aircraft. The thin-walled double-panel skin can be exposed to acoustic loads by high power engine noise and jet flow noise, which can cause sonic fatigue damage. In order to predict the fatigue life of the skin, the octave bandwidth SPL should be calculated as narrow bandwidth PSD or acoustic load history using interpolation method. In this paper, a method of converting the octave bandwidth SPL acoustic load into a narrow bandwidth PSD and reconstructed acoustic load history was investigated. The octave bandwidth SPL was converted to the narrow bandwidth PSD using various interpolation methods such as flat, log and linear scale, and the probabilistic characteristics and fatigue damage results were compared. It was found that average error of fatigue damage index by the log scale interpolation method was relatively small among three methods.

• 한국표면공학회지
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• 제41권5호
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• pp.194-198
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• 2008

Several methods for improving dispersion of carbon nanotubes (CNTs) have been investigated. CNTs modified by acids and hydrogen peroxide ($H_2O_2$) showed improved dispersion. From SEM micrographs and photos of dispersion, CNTs modified with nitric acid and $H_2O_2$, showed no agglomeration in solution even standing for 4 months, which means successfully improved dispersion property. TEM micrographs of surface modified single CNT treated with 69% $HNO_3$ in boiling acid solution as the optimum method were obtained. For confirmation of CNTs' application to EDLC electrode materials, characteristics of EDLC have been analyzed by cyclic voltammetry curve, specific capacitance of unit cell, electrode discharge curves and AC impedance curve. From the results, it could be confirmed that electrochemical properties of CNTs were enhanced after surface modification with 69% $HNO_3$ acid treatment.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 춘계학술대회
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• pp.668-671
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• 2007

A numerical study was conducted on a simplified model of a high-temperature solar receiver which incorporates liquid-metal heat pipe. The objective of this paper is to compare the isothermal characteristics of the heat pipe receiver with the conventional receiver utilizing convection of molten salt as heat carrier. The solar receiver was assumed to be subject to a concentration ratio between 50 and 1,000 to supply high-temperature heat to a stirling engine for electric power generation. For simplicity of the analysis, a cylindrical geometry was assumed and typical dimensions were used based on available literature. The heat pipe had a shape of double-walled cavity and the working fluid was a sodium. The analysis was performed assuming that the radiation heat flux on the inner walls of the receiver was uniform, since the focus of this study was laid on the comparison of the conventional type and heat pipe type receiver. The results showed that the heat pipe type exhibited superior performance when the operating temperature becomes higher. In addition, to explore the advantage of the heat pipe receiver, the channel shape and dimensions should be adjusted to increase the heat transfer area between the wall and the heat trnasfer medium.

• 에너지공학
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• 제26권2호
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• pp.73-79
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• 2017

In nucleation assisted crystallization process formed $CO_2$ leaves as colloid gas and is used as the template by the rapidly growing crystals in the nucleation site. This emulsion of $CaCO_3$ micro-crystals & $CO_2$ micro-bubbles forms hollow particles. Formed hollow particles are double walled, both internal and external faces belonging to the cleavage aragonites which separate the surrounding water from the enclosed gas cavity. Hence, the reverse reaction of $CO_2$ with water forming Carbonic Acid is not possible and the pH stability is maintained. In fact every excess $CaCO_3$ crystals are buffering any carbonic acid left over. This $CO_2$ based nucleation technology prevents scale formation in water channels, but it also helps to reduce the previously formed scales. This process takes out water dissolved $CO_2$ in almost-visible micro-bubbles forms that helps reducing previously formed scale over a period of time (depends on the usage period). The aragonite crystals can't form scale because of its stable molecular structure and neutral surface electro potentiality.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.525-528
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• 2006

Transparent conducting films were fabricated on polyethylene terephthalate substrate by a spray method using double-walled carbon nanotubes dispersed in organic solvent and water-based solution. We analyzed the films by absorption spectra, sheet resistance, and scanning electron microscopy. Transparent conducting films with high uniformity and high transparency were fabricated by the spray method. We found that the dispersion particularly nanodispersion of CNTs was of crucial importance to improve the film performance.