• 한국세라믹학회지
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• 제45권2호
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• pp.105-111
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• 2008

Symmetric three layer composites have been prepared by freeze casting and then pressureless sintered at $l700-1800^{\circ}C$ in $N_2$ gas atmosphere. The relative sintered density of multilayer composites having microstructural characteristics of later intermediate-stage densification increased with sintering temperature and reached about 95% theoretical value at $1800^{\circ}C$. Although the indentation strength of the multilayer composites was generally reduced with increasing Vickers indentation load up to 294N, the damage resistance of multilayer composites was superior compared to monolithic layer 95AL/5SN material. The three-point bend strength of the layered materials remained at the values 266-298 MPa after indentation with a load of 49N, while that of the monolithic 95AL/5SN material was 219 MPa. The fracture toughness of the multilayer material was $5.4-6.6\;MPa\;m^{1/2}$.

• 한국분말재료학회지
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• 제16권4호
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• pp.268-274
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• 2009

For the purpose of obtaining basic information on the development of lead-free materials, a high density composites (a) W-Cu, (b) W-Sn (c)W-Cu-Sn and (d) W-Cu-Ni were fabricated by the P/M method. The particle size of used metal powders were under 325 mesh, inner size of compaction mould was $\phi8$ mm, and compaction pressure was 400 MPa. A High density composite samples were sintered at a temperature between $140^{\circ}C$ and $1050^{\circ}C$ for 1 hour under Ar atmosphere. The microstructure, phase transformation and physical properties of the sintered samples were investigated. As the results, the highest relative density of 95.86% (10.87 g/$cm^3$) was obtained particularly in the sintered W-Cu-Sn ternary system sample sintered at 450 for 1hr. And, Rockwell hardness (HRB) of 70.0 was obtained in this system.

• 한국수소및신에너지학회논문집
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• 제17권1호
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• pp.69-74
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• 2006

Thick film $H_2$ sensors were fabricated using $SnO_2$ loaded with $Ag_2O$ and $PtO_x$. The composition that gave the highest sensitivity for $H_2$ was in the weight% ratio of $SnO_2 : PtO_x : Ag_2O$ as 93 : 1 : 6. The nano-crystalline powders of $SnO_2$ synthesized by sol-gel method were screen printed with $Ag_2O$ and $PtO_x$ on alumina substrates. The fabricated sensors were tested against gases like $H_2$, $CH_4$, $C_3H_8$, $C_2H_5OH$ and $SO_2$. The composite material was found sensitive against $H_2$ at the working temperature $130^{\circ}C$, with minor interference of other gases. The $H_2$ gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on $SnO_2-Ag_2O-PtO_x$ system exhibited the high performance, high selectivity and very short response time to $H_2$ at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of $H_2$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.7-7
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• 2010

Indium tin oxide (ITO) - SWNT nano crystalline composites was synthesized at low temperature(${\sim}250^{\circ}C$)using Nano Cluster Deposition technique by Metal Orhoganic Chemical Vapor Deposition method. XRD patterns of ITO- SWNT composite shows pure cubic phases without any secondary phase. I-V measurement gives resistance of 12 ohms for Sn doped (3 wt %) indium oxide-SWNT composites. The electrical conductivity of the nano composites is significantly enhanced compared to the SWNT.

• 한국산학기술학회논문지
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• 제20권5호
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• pp.81-86
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• 2019

금속산화물/그래핀 복합체는 고감도 가스센서 및 고용량의 이차전지와 같은 첨단 응용 분야에 활용될 수 있는 유망한 기능성 소재로 알려져 있다. 본 연구에서는 이산화주석($SnO_2$) 나노구조물을 두 영역 전기로 장치를 이용하여 화학적으로 합성된 그래핀 나노시트 위에 성장시켰다. 대면적의 그래핀 나노시트는 Cu foil 위에 열화학기상증착 장비를 이용하여 메탄가스와 수소가스로 합성하였다. 화학적으로 합성된 그래핀 나노시트는 PMMA를 이용하여 세척된 Si 기판위에 전사시켰고, $SnO_2$ 나노구조물은 그래핀 나노시트 위에 $424^{\circ}C$, 3.1 Torr 조건에서 3시간동안 성장시켰다. 합성된 그래핀의 품질과 성장된 $SnO_2$ 나노구조물의 결정학적 특성을 Raman 분광학으로 확인하였다. 그래핀 위에서 성장된 $SnO_2$ 나노구조물의 표면형상은 전계방출 주사전자현미경으로 조사하였다. 그 결과 합성된 그래핀 나노시트는 이중층 그래핀이었고, 그래핀 위에서 성장된 산화주석은 $SnO_2$ 상을 가지고 있었다. 그래핀 위에서 성장된 $SnO_2$ 나노구조물은 복잡한 표면형상을 나타내었는데, 이것은 Si 기판 위에서 성장된 $SnO_2$ 나노구조물이 nano-dots 형태인 것과 비교된다. 그래핀 위에서 성장된 $SnO_2$ 나노구조물이 복잡한 형상을 갖는 것은 그래핀 표면의 기능기의 영향인 것으로 판단된다.

• 농업과학연구
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• 제37권3호
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• pp.457-464
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• 2010

The low melting alloy impregnated wood composites with natural grain of thinned Juglans mandshurica was made and evaluated in this study. And the proper manufacturing conditions was also investigated in this study. The low melting alloy with bismuth(Bi) and tin(Sn) which are harmless to humans, was applied for this novel composites, which showed not only no defects of discoloration, delamination, swelling, and cracking, because of high dimensional stability and low thickness swelling, but also much improved performance such as high bending strength, high hardness, low abrasion, high thermal conductivity as floor materials. This study also suggested the proper impregnating condition, such as 10 minutes of the preliminary vacuum time, $187^{\circ}C$ of the heating temperature and 10 minutes of the maintaining pressure time at the pressure of 30kgf/$cm^2$. The produced composites showed 9 times higher density for small specimen, 6.6 times for actual size sample and great increase in bending strength from 102.05N/$mm^2$ to 189.47N/$mm^2$ for small size sample and to 205.4N/$mm^2$ for actual size sample, also great increase in hardness from 15.1N/$mm^2$ to 73.38N/$mm^2$ for small size sample and 64.87N/$mm^2$ for actual size sample. And the composites demonstrated great decrease in abrasion depth and in water absorption.

• Tribology and Lubricants
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• 제9권2호
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• pp.49-55
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• 1993

The dry sliding wear properties of the sintered Cu-10 wt%Sn bronze alloys reinforced with $SiC_w$ and $SiC_p$ were investigated by a pin-on-disc wear testing machine. The worn surfaces and the cross sections of the wear specimens and the wear debris were observed by SEM to study the effect of the variation of the ceramic phase contents in the composite and the wear condition on the wear behaviors. The wear of bronze matrix was dominated by the adhesive wear. The transition from mild to severe wear was found in the bronze matrix specimens at the applied load higher than 20N where the surface delamination caused the severe wear. The addition of $SiC_w$ and $SiC_p$ reinforcements in the romposites was proved to reduce the wear rate by the matrix strengthening at the applied load higher than 20N. SiC whiskers having a large length to diameter ratio which hold the deformed matrix were effective to hinder the crack propagation near the worn surface. Thus the maximum wear resistance was obtained in the composite reinforced by $SiC_w$ at the higher applied load.

• 한국세라믹학회지
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• 제40권1호
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• pp.37-45
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• 2003

$BaTiO_3$의 Ba 자리에 Ca, Ti 자리에 Zr을 첨가한 $(B a_{1-x}Ca_x)(Ti_{0.96-y}Zr_{y}Sn_{0.04})O_3$ $(0.15 {\leq} x{\leq}0.20,\; 0.09{\leq}y{\leq}$0.14) 조성에 2차상 형성을 유도하여 복합체를 만든 후 유전 및 소결 특성을 조사하였다. Ca량이 15mol% 이상 첨가됨에 따라 $CaTiO_3$를 주성분으로 하는 2차상이 석출하여 복합체가 형성되었으며, Ca량의 증가에 따라 2차상 분율이 증가하였다. Ca량의 증가는 큐리 온도를 mol%당 $1.7^{\circ}C$ 감소시키며, 저유전율 2차상의 영향으로 Ca량 증가에 따라 최대 유전율은 mol%당 200 감소하였다. Zr 첨가는 큐리온도를 mol%당 $10^{\circ}C$ 감소시키며, 확산형 상전이 현상을 증가시켜 최대 유전율을 217 감소시켰다. 2차상의 증가에 의하여 비정상 입성장이 억제되어 소결밀도, 내전압 특성이 향상되었으며, Zr 첨가에 의하여 커패시턴스의 온도 안정성을 제어하여 EIA 규격을 만족하는 고압, 고유전율 Y5U 콘덴서 조성을 개발하였다.

• 한국재료학회지
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• 제20권11호
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• pp.611-616
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• 2010

A cobalt oxide - tin oxide nanocomposite based gas sensor on an $SiO_2$ substrate was fabricated. Granular thin film of tin oxide was formed by a rheotaxial growth and thermal oxidation method using dc magnetron sputtering of Sn. Nano particles of cobalt oxide were spin-coated on the tin oxide. The cobalt oxide nanoparticles were synthesized by polymer-assisted deposition method, which is a simple cost-effective versatile synthesis method for various metal oxides. The thickness of the film can be controlled over a wide range of thicknesses. The composite structures thus formed were characterized in terms of morphology and gas sensing properties for reduction gas of $H_2$. The composites showed a highest response of 240% at $250^{\circ}C$ upon exposure to 4% $H_2$. This response is higher than those observed in pure $SnO_2$ (90%) and $Co_3O_4$ (70%) thin films. The improved response with the composite structure may be related to the additional formation of electrically active defects at the interfaces. The composite sensor shows a very fast response and good reproducibility.

• Elastomers and Composites
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• 제49권2호
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• pp.110-116
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• 2014

디에틸렌글리콜(DEG, 분자량 106.1)과 폴리에틸렌글리콜600(PEG600, 분자량 603.3)을 아디프산(AA)과 반응시켜 폴리(옥시에텔렌-아디페이트)-디올 공중합체를 합성하는 에스테르 반응에서, stannous 2-ethylhexanoate 촉매의 농도가 반응속도에 주는 영향을 연구하였다. 반응에 사용되는 AA의 카르복실기 당량 대비 폴리올의 히드록실기의 당량비를 2로 맞추어서 합성된 폴리(에테르-에스테르)의 양말단이 OH기로 결합되도록 유도하였다. 반응은 $170^{\circ}C$에서 촉매농도 0.15 ~ 2.0 wt.%로 수행하였다. 합성된 폴리(옥시에텔렌-아디페이트)-디올의 수평균 중합도는 약 3 이었다. DEG와 AA로부터 폴리(옥시에텔렌-아디페이트)-디올이 합성되는 반응의 겉보기속도상수($k_{app}$) 값은 촉매의 농도가 커짐에 따라 $k_{app}=0.88[C_{cat}]$의 관계를 가지며 선형적으로 증가한 반면에, PEG600과 AA의 에스테르 반응의 $k_{app}$ 값은 촉매농도와 $k_{app}=0.123[C_{cat}]^{0.55}$의 관계로 증가하며 포화되는 경향을 나타내었다. DEG와 AA사이의 합성반응에서도 반응속도의 촉매농도에 대한 의존성이 비선형 관계로 바뀌는 것이 예상되며, 이때의 촉매농도는 [$Sn(C_8H_{15}O_2)_2$ mole/mole of AA mole] 값이 0.066([$C_{cat}$]=0.22M)에 가까운 영역에 있을 것으로 추정된다.