• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.266-270
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• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine because it has excellent high temperature strength, low coefficient of thermal expansion, good resistance to oxidation and good thermal and chemical stability etc. 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/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 jiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of SiC/SiC composites by hot pressing method. In the present work, monolithic Liquid Phase Sintered SiC (LPS-SiC) was fabricated by hot pressing method in Ar atmosphere at $1800^{\circ}C$ under 20MPa using $Al_2O_3,\;Y_2O_3\;and\;SiO_2$ as sintering additives in order to low sintering temperature and sintering pressure. The starting powder was high purity $\beta-SiC$ nano-powder with all average particle size of 30mm. The characterization of LPS-SiC was investigated by means of SEM and three point bending test. Base on the composition of sintering additives-, microstructure- and mechanical property correlation, tire compositions of sintering additives are discussed.

• Composites Research
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• 제16권1호
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• pp.19-25
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• 2003

본 연구에서는 나노구조를 갖는 카본블랙이 충전된 CB/HDPE 복합재료를 용융 혼합법으로 제조한 후 온도변화에 따른 전기적 특성을 고찰하였다. 복합재료의 전기적 재현성 향상과 negative temperature coefficient (NTC) 현상의 제거를 위하여 전자선을 30-150 kGy로 조사하였으며, 조사된 복합재료의 가교함량 분석은 용매 추출법을 이용하였다. 실험결과, CB/HDPE 복합재료의 PTC 세기는 카본블랙의 함량과 입자크기에 크게 영향을 받으며. 가교함량의 급격한 증가에 따른 NTC 현상의 제거는 전자선 흡수선량이 60 kGy일 때였다. 또한 전자선 조사를 통하여 전기적 재현성이 향상되었는데, 이는 복합재료의 가교도 증가에 따른 수지의 용융온도 근처에서의 카본블랙 유동성의 감소 때문이라 사료된다.

• 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.

• 한국자기학회지
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• 제8권3호
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• pp.131-137
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• 1998

동시진공증착한 Ag-Co합금박막의 두께에 따르는 미세구조 및 거대자기저항의 거동의 변화를 연구하였다. 증착된 상태에서 40 at.%Co 합금의 200nm두께에서 최대 24%의 자기저항을 얻었다. 합금박막의 두께가 감소함에 따라, 특히 50NM 이하에서 비저항이 급격하게 증가되었고, 비저항 차 및 자기저항은 감소하였다. 비저항의 증가는 주로 표면저항의 증가가 주도하였다. 고분해능 T뜨을 사용하여 두께 감소에 따르는 합금박막의 미세구조 변화를 분석한 결과, 첫째 aG 및 cO 입자의 크기가 감소하며, 둘째 Co 및 Ag간의 상호 고용도가 증가되며, 섯째 Co입자의 형성비의 변화가 확인되었다. 이러한 미세구조적 변화는 자성체 입자의 자기모멘트, 자기이방성 등의 가지 상태의 변화를 가져오게 되어 자기저항에 영향을 끼치는 것으로 분석된다. 따라서 50nm 이하에서 거대자기저항의 감소는 표면에서의 스핀전도에 의한 형상 뿐만 아니라 미세구조의 면화도 크게 기여하는 것으로 보인다.

• Bulletin of the Korean Chemical Society
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• 제25권9호
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• pp.1371-1378
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• 2004

A porous stainless steel (SUS) as a substrate of silica composite membranes for hydrogen purification was used to improve mechanical strength of the membranes for industrial application. The SUS support was successfully modified by using submicron Ni powder, $SiO_2$ sols with particle size of 500 nm and 150 nm in turns. Silica top layer was coated on the modified supports under various preparation conditions such as calcination temperature, dipping time and repeating number of dipping-drying process. The calcination temperature for proper sintering was between H ttig temperature and Tamman temperature of the coating materials. Maximum hydrogen selectivity was investigated by changing dipping time. As repeating number of dipping-drying process increased, permeances of nitrogen and hydrogen were decreased and $H_2/N_2$ selectivity was increased due to the reduction of non-selective pinholes and mesopores. For the silica membrane prepared under optimized conditions, permeance of hydrogen was about $3\;{\times}\;10^{-5}\;cm^3{\cdot}cm^{-2}{\cdot}s^{-1}{\cdot}cmHg^{-1}$ combined with $H_2/N_2$ seletivity of about 20.

• 멤브레인
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• 제19권4호
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• pp.285-290
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• 2009

공칭 세공크기 $0.1\;{\mu}m$이고 내경이 5 mm인 정밀여과용 관형 분리막 내에 자체 설계한 배출봉을 삽입하여 막오염 감소효과에 따른 투과유속을 측정하였다. 원료용액으로는 에멀젼 상태의 dioctyl tinoxide (DOTO) 입자를 사용하였으며 0.5 wt%까지 농도를 변화시키면서 1.6 bar 이내에서 운전하였다. 배출봉의 효과는 매 실험마다 배출봉을 삽입한 경우와 사용하지 않은 경우의 투과유속을 비교하여 평가하였다. 배출봉을 사용할 경우 운전압력 1.6 bar에서 최대 20%의 투과유속이 향상되었다. 또한 DOTO 농도가 증가함에 따라서 배출봉에 의한 투과유속 향상효과는 크게 나타났으며 0.5 wt% 농도에서 43%까지 투과유속이 향상되었다.

• 한국지반공학회논문집
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• 제18권5호
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• pp.195-207
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• 2002

동제련 과정에서 부산되는 동슬래그는 국내에서 연간 70여만톤에 이르나, 그 활용분야가 제한되어 사용량이 미약하여 그 처리방안이 시급히 요청되고 있는 실정이다. 이에 본 연구는 동슬래그의 입도가 0.15~5mm의 조립상태로 분포하여 환경적으로도 안정된 유리질이라는 점에 착안하여 연약지반개량공법 중의 하나인 모래다짐말뚝의 모래대체재로서의 활용방안을 모색하였다. 실내 물리.역학시험 및 모형토조시험에 의한 동슬래그의 지반공학적 재료특성을 파악하고 현장시험시공을 통해 동슬래그의 모래다짐말뚝의 모래대체재로서의 현장 적용 가능성을 일반모래와 비교.검토하였다. 그 결과 동슬래그의 재료특성이 양호하고 지지력, 침하저감효과 그리고 주변지반 개량효과면에서 동슬래그 또는 동슬래 그다짐말뚝이 우수한 것으로 나타나, 모래다짐말뚝의 모래대체재로 동슬래그를 적용할 경우 천연골재의 고갈에 따른 대체골재원으로서 산업부산물의 재활용이라는 측면에서 경제적.환경적으로 활용가치가 높으리라 판단된다.

• 한국재료학회지
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• 제22권7호
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• pp.358-361
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• 2012

Co and Ni as catalysts in $SnO_2$ sensors to improve the sensitivity for $CH_4$ gas and $CH_3CH_2CH_3$ gas were coated by a solution reduction method. $SnO_2$ thick films were prepared by a screen-printing method onto $Al_2O_3$ substrates with an electrode. The sensing characteristics were investigated by measuring the electrical resistance of each sensor in a chamber. The structural properties of $SnO_2$ with a rutile structure investigated by XRD showed a (110) dominant $SnO_2$ peak. The particle size of the $SnO_2$:Ni powders with Ni at 6 wt% was about 0.1 ${\mu}m$. The $SnO_2$ particles were found to contain many pores according to a SEM analysis. The sensitivity of $SnO_2$-based sensors was measured for 5 ppm of $CH_4$ gas and $CH_3CH_2CH_3$ gas at room temperature by comparing the resistance in air to that in the target gases. The results showed that the best sensitivity of $SnO_2$:Ni and $SnO_2$:Co sensors for $CH_4$ gas and $CH_3CH_2CH_3$ gas at room temperature was observed in $SnO_2$:Ni sensors coated with 6 wt% Ni. The $SnO_2$:Ni gas sensors showed good selectivity to $CH_4$ gas. The response time and recovery time of the $SnO_2$:Ni gas sensors for the $CH_4$ and $CH_3CH_2CH_3$ gases were 20 seconds and 9 seconds, respectively.

• 한국재료학회지
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• 제24권5호
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• pp.255-258
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• 2014

Zirconium boride is an artificial or which is rarely found in the nature. $ZrB_2$ is popular in the hard material industry because it has a high melting point, excellent mechanical properties and chemical stability. There are two known methods to synthesize $ZrB_2$. The first involves direct reaction between Zr and B, and the second is by reduction of the metal halogen. However, these two methods are known to be unsuitable for mass production. SHS(Self-propagating High-temperature Synthesis) is an efficient and economic method for synthesizing hard materials because it uses exothermic reactions. In this study, $ZrB_2$ was successfully synthesized by subjecting $ZrO_2$, Mg and $B_2O_3$ to SHS. Because of the high combustion temperature and rapid combustion, in conjunction with the stoichiometric ratio of $ZrO_2$, Mg and $B_2O_3$; single phase $ZrB_2$ was not synthesized. In order to solve the temperature problem, Mg and NaCl additives were investigated as diluents. From the experiments it was found that both diluents effectively stabilized the reaction and combustion regime. The final product, made under optimum conditions, was single-phase $ZrB_2$ of $0.1-0.9{\mu}m$ particle size.

• 대한금속재료학회지
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• 제50권3호
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• pp.201-205
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• 2012

The effects of various manganese precursors for the low-temperature selective catalytic reduction (SCR) of $NO_x$ were investigated in terms of structural, morphological, and physico-chemical analyses. $MnO_x/TiO_2$ catalysts were prepared from three different precursors, manganese nitrate, manganese acetate(II), and manganese acetate(III), by the sol-gel method. The manganese acetate(III)-$MnO_x/TiO_2$ catalyst tended to suppress the phase transition from the anatase structure to the rutile or the brookite after calcination at $500^{\circ}C$ for 2 h. It also had a high specific surface area, which was caused by a smaller particle size and more uniform distribution than the others. The change of catalytic acid sites was confirmed by Raman and FT-IR spectroscopy and the manganese acetate(III)-$MnO_x/TiO_2$ had the strongest Lewis acid sites among them. The highest de-NOx efficiency and structural stability were achieved by using the manganese cetate(III) as a precursor, because of its high specific surface area, a large amount of anatase $TiO_2$, and the strong catalytic acidity.