• Advances in nano research
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• 제8권2호
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• pp.135-148
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• 2020

The incorporation of carbon nanotubes in a polymer matrix makes it possible to obtain nanocomposite materials with exceptional properties. It's in this scientific background that this work was based. There are several theories that deal with the behavior of plates, in this research based on the Mindlin-Reissner theory that takes into account the transversal shear effect, for analysis of the critical buckling load of a reinforced polymer plate with parabolic distribution of carbon nanotubes. The equations of the model are derived and the critical loads of linear and parabolic distribution of carbon nanotubes are obtained. With different disposition of nanotubes of carbon in the polymer matrix, the effects of different parameters such as the volume fractions, the plate geometric ratios and the number of modes on the critical load buckling are analysed and discussed. The results show that the critical buckling load of parabolic distribution is larger than the linear distribution. This variation is attributed to the concentration of reinforcement (CNTs) at the top and bottom faces for the X-CNT type which make the plate more rigid against buckling.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.204-209
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• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, $SiC_f/SiC$ composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of $SiC_f/SiC$ composites by hot pressing method. In the present work, Monolithic LPS-SiC was fabricated by hot pressing method in Ar atmosphere at 1760 $^{\circ}C$, 1780 $^{\circ}C$, 1800 $^{\circ}C$ and 1820 $^{\circ}C$ under 20 MPa using $Al_2O_3-Y_2O_3$ system as sintering additives in order to low sintering temperature. The starting powder was high purity ${\beta}-SiC$ nano-powder with an average particle size of 30 nm. Monolithic LPS-SiC was evaluated in terms of sintering density, micro-structure, flexural strength, elastic modulus and so on. Sintered density, flexural strength and elastic modulus of fabricated LPS-SiC increased with increasing the sintering temperature. In the micro-structure of this specimen, it was found that grain of sintered body was grown from 30 nm to 200 nm.

• Elastomers and Composites
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• 제44권1호
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• pp.47-54
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• 2009

본 연구에서는 다양한 종류의 보강제를 혼합한 EPDM 컴파운드의 원적외선에 의한 가교 반응을 조사하였다. 보강제가 원적외선에 의한 가교 반응에 미치는 영향을 평가하기 위하여 컴파운드의 발열 온도 및 DSC 분석에 의한 가교도를 측정하였으며, 특히 원적외선에 의한 가교 특성을 비교하기 위하여 동일 조건에서 열풍에 의한 가교 반응을 조사하였다. 원적외선 가교 조건에서 카본블랙을 혼합한 EPDM 컴파운드는 입자크기가 증가함에 따라 열전도도가 증가하며 이에 따라 원적외선에 의한 가교도 역시 증가하였으나, 열풍에 의한 가교도의 변화에는 거의 영향을 주지 못하였다. 보강제 종류에 따른 원적외선 가교 특성 평가 결과, 열전도도가 높은 아세틸렌 블랙을 함유한 컴파운드의 가교도가 가장 높게 나타났으며, 열전도도가 유사한 카본블랙 및 침강실리카의 경우 상대적으로 원적외선 흡수 특성이 우수한 침강실리카 배합 컴파운드의 경우 원적외선에 의한 가교도가 높게 나타났다.

• 센서학회지
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• 제29권3호
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• pp.156-161
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• 2020

In this study, hierarchical mesoporous CuO spheres, ZnO flowers, and heterojunction CuO/ZnO nanostructures were fabricated via a facile hydrothermal method. The as-prepared materials were characterized in detail using various analytical methods such as powder X-ray diffraction, micro Raman spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy. The obtained results are consistent with each other. The H₂S-sensing characteristics of the sensors fabricated based on the CuO spheres, ZnO flowers, and CuO/ZnO heterojunction were investigated at different temperatures and gas concentrations. The sensor based on ZnO flowers showed a maximum response of ~141 at 225 ℃. The sensor based on CuO spheres exhibited a maximum response of 218 at 175 ℃, whereas the sensor based on the CuO/ZnO nano-heterostructure composite showed a maximum response of 344 at 150 ℃. The detection limit (DL) of the sensor based on the CuO/ZnO heterojunction was ~120 ppb at 150 ℃. The CuO/ZnO sensor showed the maximum response to H₂S compared with other interfering gases such as ethanol, methanol, and CO, indicating its high selectivity.

• 한국표면공학회지
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• 제38권3호
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• pp.100-105
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• 2005

Cr-Si-C-N coatings were deposited on steel substrate (SKD 11) by a hybrid system of arc ion plating (AIP) and sputtering techniques. From XRD, XPS, and HRTEM analyses, it was found that Cr-Si-C-N had a fine composite microstructure comprising nano-sized crystallites of Cr(C, N) well distributed in the amorphous phase of $Si_3N_4/SiC$ mixture. Microhardness of Cr(C, N) coatings and Cr-Si-N coatings were reported about $\~22 GPa$ and $\~35 GPa$, respectively. As the Si was incorporated into Cr(C, N) coatings, The Cr-Si-C-N coatings having a Si content of $9.2 at.\%$ showed the maximum hardness value. As increased beyond Si content of $9.2 at.\%$, the interaction between nanocrystallites and amorphous phase was gone, the hardness was reduced as dependent on amorphous phase of $Si_3N_4/SiC$. In addition, the average coefficient of Cr-Si-C-N coatings largely decreased compared with Cr(C, N) coatings.

• 대한기계학회논문집A
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• 제35권9호
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• pp.999-1005
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• 2011

고무복합재료에 대해 변형에 의한 결정화(SIC)가 기계적 특성에 미치는 영향을 연신율(${\lambda}$) 및 다중벽 탄소나노튜브(CNT)와 카본블랙(CB)의 함유량을 함수로 하여 연구하였다. 시차 주사 열량(DSC) 분석을 통해 CB 및 CNT의 함유량에 따라 결정화 정도가 증가함을 확인 하였다. 또한 연신율이 증가함에 따라 복합재료의 유리전이온도(Tg)는 증가하였고, 결정화 잠열 값(LHc)은 ${\lambda}$=1.5에서 최대값을 보였다. CNT의 함유량 증가에 따라 기계적 특성과 LHc는 비례관계임을 확인하였다. 열 중량 분석(TGA)을 통해 기지의 소실율은 94.3%였고, 복합재료의 소실율은 보강재의 함유량 증가에 따라 감소하였다. 인장탄성율 비는 고무 내의 CNT 배향으로 인장강도 비보다 높게 나타났다.

• Elastomers and Composites
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• 제43권1호
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• pp.1-7
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• 2008

DSC 및 컴파운드 온도 측정을 통해 원적외선에 의한 EPDM의 가교 반응을 연구하였으며, 특히 동일 조건에서의 열풍에 의한 가교 시험을 통해 원적외선 가교시의 효율성을 평가하였다. 원적외선 및 열풍에 의한 EPDM 컴파운드의 가교도를 분석한 결과, 동일 조건에서 원적외선가교 시료의 가교도가 열풍가교에 비해 높게 나타남을 확인할 수 있었으며, 특히 3 mm 두께 시편의 경우 약 2배가량 높은 가교도를 나타내었다. EPDM 컴파운드의 열전도도의 증가는 원적외선에 의한 가교도를 크게 증가시켰으나, 열풍에 의한 가교도의 변화에는 거의 영향을 주지 못하였다.

• 한국자기학회지
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• 제21권6호
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• pp.225-230
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• 2011

자성 재료는 전기적 에너지와 기계적 에너지간 상호 전환 가능한 특성을 가지고 있기 때문에 발전 및 모터 분야 등에 널리 적용되고 있다. 그 중에서도 모터 분야의 효율성 향상을 위해서 외부의 자장 없이도 지속적으로 자성 특성을 나타내는 영구 자석은 그 활용도가 매우 높다. 특히, 영구 자석은 최대 자기적이 높은 희토류 자석이 개발된 후 이를 중심으로 개발 및 응용분야가 지속적으로 확대되었다. 그러나, 최근 모터의 용도가 확대되는 추이에 따라서 회토류 자석의 사용이 증대됨에 따라서 희토류 원자재 수급 문제에 봉착하여 이를 해결하기 위해 희토류 저감 및 대체 자석에 대한 연구 분야가 중요한 이슈가 되고 있다. 본 보고서에서는 현재 사용 되고 있는 영구 자석에 대해 설명하고 이를 대체할 수 있는 기술 중 가능성이 높은 방법으로써 exchange-coupling 현상을 이용한 영구 자석 개발 기술에 대해 기술하고자 한다.

• Macromolecular Research
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• 제16권3호
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• pp.204-211
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• 2008

A platinum-catalyzed polyelectrolyte porous membrane was prepared by solid-state compression of electrospun polystyrene (PS) fibers and in-situ metallization of counter-balanced ionic metal sources on the polymer surface. Using this ion-exchange metal-polymer composite system, fiber entangled pores were formed in the interstitial space of the fibers, which were surrounded by sulfonic acid sites ($SO_3^-$) to give a cation-selective polyelectrolyte porous bed with an ion exchange capacity ($I_{EC}$) of 3.0 meq/g and an ionic conductivity of 0.09 S/cm. The Pt loading was estimated to be 16.32 wt% from the $SO_3^-$ ions on the surface of the sulfonated PS fibers, which interact with the cationic platinum complex, $Pt(NH_3)_4^{2+}$, at a ratio of 3:1 based on steric hindrance and the arrangement of interacting ions. This is in good agreement with the Pt loading of 15.82 wt% measured by inductively coupled plasma-optical emission spectroscopy (ICP-OES). The Pt-loaded sulfonated PS media showed an ionic conductivity of 0.32 S/cm. The in-situ metallized platinum provided a nano-sized and strongly-bound catalyst in robust porous media, which highlights its potential use in various electrochemical and catalytic systems.

• 한국표면공학회지
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• 제54권5호
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• pp.230-237
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• 2021

In this study, the influence of silicon contents on the microstructure, mechanical and tribological properties of Ti-Al-Si-N coatings were systematically investigated for application of cutting tools. The composition of the Ti-Al-Si-N coatings were controlled by different combinations of TiAl₂ and Ti₄Si composite target powers using an arc ion plating technique in a reactive gas mixture of high purity Ar and N₂ during depositions. Ti-Al-Si-N films were nanocomposite consisting of nanosized (Ti,Al,Si)N crystallites embedded in an amorphous Si₃N₄/SiO₂ matrix. The instrumental analyses revealed that the synthesized Ti-Al-Si-N film with Si content of 5.63 at.% was a nanocomposites consisting of nano-sized crystallites (5-7 nm in dia.) and a three dimensional thin layer of amorphous Si₃N₄ phase. The hardness of the Ti-Al-Si-N coatings also exhibited the maximum hardness value of about 47 GPa at a silicon content of ~5.63 at.% due to the microstructural change to a nanocomposite as well as the solid-solution hardening. The coating has a low friction coefficient of 0.55 at room temperature against an Inconel alloy ball. These excellent mechanical and tribological properties of the Ti-Al-Si-N coatings could help to improve the performance of machining and cutting tool applications.