• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권11호
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• pp.505-513
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• 2006

The present study investigated the influence of the content of $Al_2O_3+Y_2O_3$ sintering additives on the microstructure, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites. Phase analysis of composites by XRD revealed mostly of ${\alpha}-SiC(4H),\;ZrB_2,\;{\beta}-SiC(15R)$ and In Situ $YAG(Al_5Y_3O_{12})$. The relative density and the flexural strength showed the highest value of 86.8[%] and 203[Mpa] for $SiC-ZrB_2$ composite with an addition of 8[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid at room temperature respectively. Owing to crack deflection and crack bridging of fracture toughness mechanism, the fracture toughness showed 3.7 and $3.6[MPa{\cdot}m^{1/2}]\;for\;SiC-ZrB_2$ composites with an addition of 8 and 12[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid at room temperature respectively. Abnormal grain growth takes place during phase transformation from ${\beta}-SiC\;into\;{\alpha}-SiC$ was correlated with In Situ YAG phase by reaction between $Al_2O_3\;and\;Y_2O_3$ additives during sintering. The electrical resistivity showed the lowest value of $6.5{\times}10^{-3}[({\Omega}{\cdot}cm]$ for the $SiC-ZrB_2$ composite with an addition of 8[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid at room temperature. The electrical resistivity of the $SiC-ZrB_2$ composites was all positive temperature coefficient(PTCR) in the temperature ranges from $25[^{\circ}C]\;to\;700[^{\circ}C]$. The resistance temperature coefficient showed the highest value of $3.53{\times}10^{-3}/[^{\circ}C]\;for\;SiC-ZrB_2$ composite with an addition of 8[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid in the temperature ranges from $25[^{\circ}C]\;to\;700[^{\circ}C]$. In this paper, it is convinced that ${\beta}-SiC$ based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.

• 한국주조공학회지
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• 제23권4호
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• pp.195-203
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• 2003

Hyper-eutectic Al-Si alloy is used much to automatic parts and material for the electronic parts because of the low coefficient of thermal expansion, superior thermal stability and superior wear resistance. In this work, A390 alloy specimens were fabricated for control of the Si particle size by various processes, such as spray-casting, permanent mold-casting and squeeze-casting. To minimize the effect of microporosity of the specimens, hot extrusion was carried out under equal condition. Each specimens were evaluated tensile properties at room temperature and thermal expansion properties in the range from room temperature to 400$^{\circ}C$. Ultimate tensile strength and elongation of the spray-cast and extruded specimens which have fine and well distributed Si particles were improved greatly compare to the permanent mold-cast and extruded ones. Specimens which have finer Si particles showed higher ultimate tensile strength and elongation than those having large Si particle size, and coefficient of thermal expansion of the specimens increased linearly with Si particle size. In case of the repeated high temperature exposures, thermal expansion properties of the spray-cast and extruded specimens were found to be more stable than those of the others due to the effect of fine and well distributed Si particles.

• Journal of Periodontal and Implant Science
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• 제30권1호
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• pp.187-203
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• 2000

The precipitation of calcium phosphate on implant surface has been known to accelerate osseointegration and to enhance osseous adaptation. The present study was performed to examine whether the precipitation of calcium phosphate on Ti-6Al-4V alloy could be affected by the immersion in NaOH solution and heat treatment. Ti-6Al-4V alloy plates of $15{\times}3.5{\times}1mm$ in dimension were polished sequentially from #240 to #2,000 emery paper and one surface of each specimen was additionally polished with $0.1{\mu}m$ alumina paste. Polished specimens were soaked in various concentrations of NaOH solution(0.1, 1.0, 3.0, 5.0, 7.0, 10.0 M) at $60^{\circ}C$ for 24 hours for alkali treatment, and 5.0 M NaOH treated specimens were heated for 1 hour at each temperature of 400, 500, 600, 700, $800^{\circ}C$. After the alkali and heat treatments, specimens were soaked in the Hank's solution with pH 7.4 at $36.5^{\circ}C$ for 30days.The surface ingredient change of Ti-6Al-4V alloy was evaluated by thin-film X-ray diffractometer(TF-XRD) and the surface microstructure was observed by scanning electron microscope(SEM), and the elements of surface were analyzed by X-ray photoelectron spectroscopy(XPS). The results were obtained as follows ; 1. The precipitation of calcium phosphate on Ti-6Al-4V alloy was accelerated by the immersion in NaOH solution and heat treatment. 2. In Alkali treatment for the precipitation of calcium phosphate on Ti-6Al-4V alloy, the optimal concentration of NaOH solution was 5.0 M. 3. In heat treatment after alkali treatment in 5.0 M NaOH solution, the crystal formation on alloy surface was enhanced by increasing temperature. In heat treated alloys at $600^{\circ}C$, latticed structure and prominences of calcium phosphate layer were most dense. On heat treated alloy surface at the higher temperature(${\geq}700^{\circ}C$), main crystal form was titanium oxide rather than apatite. The above results suggested that the precipitation of calcium phosphate on the surface of Ti-6Al-4V alloy could be induced by alkali treatment in 5.0 M-NaOH solution and by heat treatment at $600^{\circ}C$.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2008년도 추계학술발표논문집
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• pp.201-203
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• 2008

ITO 투명전극을 양극으로 사용하고 PEDOT:PSS 고분자 물질위에 PVK와 Ir(ppy)3를 각각 host와 dopant로 사용하여 고분자 발광다이오드를 제작하였다. 전자 수송층의 역할로 TPBI, 음극으로 Al을 증착하여 최종적으로 ITO/PEDOT:PSS/PVK:Ir(ppy)3/TPBI/LiF/Al 구조를 갖는 녹색 인광 고분자 유기발광소자(PhPLED)를 제작하였다. 제작 된 소자의 발광부 dopant인 Ir(ppy)3도핑 농도에 따른 전기적 광학적 특성을 평가하였다. PVK:Ir(ppy)3를 host와 dopant system으로 dopant Ir(ppy)3의 도핑 양을 0.5 wt%에서2.5 wt%까지 씩 변화시키면서 최적의 농도를 찾고자 하였다. TPBI를 전자 수송층으로 사용 하였을 경우 최대 휘도는 약 8600 cd/$m^2$ (at 8V)이고, 전류밀도는 337mA/$cm^2$ 를 나타내었다.

• 한국군사과학기술학회지
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• 제23권3호
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• pp.195-203
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• 2020

Selective laser melting(SLM) is one of the powder bed fusion(PBF) processes, which enables quicker production of nearly fully dense metal parts with a complex geometry at a moderate cost. However, the process still lacks knowledge and the experimental evaluation of possible process parameter sets is costly. Thus, this study presents a finite element analysis model of the SLM process to predict the melt pool characteristics. The physical phenomena including the phase transformation and the degree of consolidation are considered in the model with the effective method to model the volume shrinkage and the evaporated material removal. The proposed model is used to predict the melt pool dimensions and validated with the experimental results from single track scanning process of Ti-6Al-4V. The analysis result agrees with the measured data with a reasonable accuracy and the result is then used to evaluated each of the process parameter set.

• Bulletin of the Korean Chemical Society
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• 제19권7호
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• pp.733-737
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• 1998

Using an atom superposition and electron delocalization molecular orbital (ASED-MO) method, we have compared adsorption properties of adsorbates on the Pt(Ill) surface with the Pt(lll)/γ-Al203 surface in the ethylene hydrogenation reaction. In two-layer thick model systems, the calculated activation energy of the hydrogenation by the surface platinum hydride is equal to the energy by the hydride over supported platinum/γ-alumina. The transition structure on platinum is very close to the structure on the supported platinum/γ-alumina surface. Hydrogenation by the surface hydride on platinum can take place easily because the activation energy is about 0.5 eV less than hydrogenation by ethylidene. On supported platinum/,y-alumina the activation energy of the hydride mechanism is about 0.61 eV less than that of ethylidene mechanism. In one-layer thick model systems, the activation energy of hydrogenation by ethylidene is about 0.13 eV less than the activation energy of hydride reaction. The calculated activation energy by the hydride over the supported platinum y-alumina is 0. 24 eV higher than the platinum surface. We have found from this result that the catalytic properties of one-layer thick model systems have been influenced by the support but the two-layer thick model systems have not been influenced by the support.

• 한국농림기상학회지
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• 제19권4호
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• pp.203-214
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• 2017

본 연구에서는 진주, 수원, 춘천의 정보로만 추정한 유전 모수(New1~New3)와 지역 조합으로 추정한 유전 모수(New4~New7), NICS (2010)와 Kim et al. (2004)의 유전 모수의 개화시기 및 잠재수량의 예측력을 평가하여 기존의 유전 정보와 새로운 유전 정보에 대한 불확실 정도를 알고 다음 후속 연구에 활용 가능성을 알아보고자 수행했다. 결과적으로, 개별 및 지역조합 유전 모수에서 모수 추정 지점 혹은 참여한 지점의 유전 모수의 평가 지표들은 비교적 좋은 결과를 보여 주었지만 뚜렷하게 나타나지 않았다. 대구, 밀양, 전주에서 New7 유전 모수의 개화시기의 예측력은 NICS (2010)나 Kim et al. (2004)의 유전 모수의 개화 시기 예측력보다 개선되지 않았다. 그러나 New7 유전 모수의 잠재수량의 예측력은 큰 차이는 아니지만 NICS (2010)나 Kim et al. (2004)의 유전 모수의 잠재 수량 예측력보다 개선되는 현상을 보였다. 예를 들면, 밀양에서 NICS (2010)와 Kim et al. (2004)의 유전 모수의 잠재수량 결정계수가 0.00과 0.01로 전혀 예측력이 없는 것으로 평가하였지만 New7 유전 모수의 잠재수량 결정계수는 0.31로 나타났다. 반면, 전주에서 NICS (2010)과 Kim et al. (2004)의 유전 모수의 잠재수량 결정계수는 0.66과 0.41로 평가되었는데, New7 유전 모수의 잠재수량 결정계수는 0.00으로 예측력이 없는 것으로 평가되었다. 새로운 유전 모수의 예측력(New1~New7)이 기존의 유전 모수(NICS (2010)과 Kim et al. (2004))의 예측력보다 크게 개선되지는 않았지만, 평가 결과가 좋은 지역 조합 유전 모수를 지역별 개화시기 및 잠재수량을 예측하는 데에는 활용할 수 있을 것으로 판단된다.

• 한국전자통신학회논문지
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• 제4권3호
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• pp.197-203
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• 2009

부호이론이나 암호학의 응용분야에 유한체는 매우 중요한 내용이고, 컴퓨터에서의 구현시에는 종규기저를 사용하는 것이 효과적이다. 본 논문에서는 유한체 타입 I 최적정규기저를 가지는 $GF(2^{mk})$는 $GF(2^m)$의 확대체가 된다는 사실을 이용하여 지금까지 알려진 가장 효율적인 Reyhani-Masoleh and Hasan의 곱셈기보다 25%정도 빠른 곱셈기를 소개하려고 한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 하계학술대회 논문집
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• pp.201-203
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• 1991

T. Kanal et al, were studied the superconducting properties in Bi system by mechanical grinding, in which the authors found that the samples ground degraded from the superconducting phases to nonsuperconducting phases. To obtain more information of the practical application in Bi system with high-Tc phase in this paper, these samples mechanically ground and the high-Tc phase properties of grinding powder samples were investigated.

• Asian Journal of Atmospheric Environment
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• 제5권3호
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• pp.196-203
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• 2011

The main aim of this study is to establish methods of morphological preservation and elemental quantification for individual snow crystals. Individual snow crystals were collected at a height of 20 m above ground level. To stabilize and preserve the original morphologies of the snow crystals, cyanoacrylate, which has been used to fix liquid droplets, was applied (Kasahara et al., 2000). Several different kinds of snow crystals (dendrite, sectored plate, quasi-sectored plate, and hexagonal plate) were successively stabilized using this method. The stabilized snow crystals were pretreated with acetone, and then the elemental components contained in a whole snow crystal were quantified with the Particle Induced X-ray Emission (PIXE) analytical technique. The snow crystal residual composition determined in the present study was dominated by sulfur and mineral components, and the elemental mass showed an apparent crystal size dependence, where the elemental mass gradually decreased as the crystal size increased.