• Advances in materials Research
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• 제5권2호
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• pp.93-105
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• 2016

KNN-based ceramics modified with small amounts of $Bi_4Zr_3O_{12}$ (BiZ) has been synthesized using high-throughput experimentation (HTE). The results from X-ray diffraction show that for samples with base composition $(K_{0.5}Na_{0.5})NbO_3$ (KNN), the phase present changes from orthorhombic to pseudo-cubic with more than 0.2 mol% BiZ addition; for samples with base composition $(K_{0.48}Na_{0.48}Li_{0.04})(Nb_{0.9}Ta_{0.1})O_3$ (KNNLT), the phase present changes from a mixture of orthorhombic and tetragonal symmetry to pseudo-cubic with more than 0.4 mol % while for samples with base composition $(K_{0.48}Na_{0.48}Li_{0.04})(Nb_{0.86}Ta_{0.1}Sb_{0.04})O_3$ (KNNLST), the phase present is tetragonal with <0.3 mol% BiZ addition and transforms to pseudo-cubic with more dopant addition. The microstructures of the samples show that addition of BiZ decreases the average grain size and increases the volume of pores at the grain boundaries. The values of dielectric constant for KNN and KNNLT compositions increase slightly with BiZ addition while that for KNNLST decreases gradually with BiZ addition. The dielectric loss values are between 0.02 and 0.04 for KNNLT and KNNLST compositions while they are ~ 0.05 for KNN samples. The resistivity values increases with BiZ addition and values in the range of $10^{10}{\Omega}cm$ and $10^{12}{\Omega}cm$ are obtained. The piezoelectric charge coefficient ($d{^*}_{33}$) is highest for KNNLST samples and decreases gradually from ~400 pm/V to ~100 pm/V with BiZ addition.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.200-203
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• 2003

A study on the arc resistance and light reflectance of PTFE (polytetrafluoroethylene) nozzle for circuit breaker is presented. PTFE has been used widely as a material for circuit breaker nozzle. PTFE has excellent electrical resistivity, high melt viscosity, chemical inertness, heat resistance and low loss factor. PTFE melts at $327\;^{\circ}C$ but the viscosity is very high above the melting point. In the arcing environment in a circuit breaker, the fraction of the power is emitted out of the arc and reaches the nozzle wall by radiation, causing ablation at the surface and in the depth of the wall. Some fraction of the radiation power emitted out of the arc directly break up the chemical bonds at the surface while some fraction of the radiation power penetrates into the wall, heats up the material to evaporation temperature and causes damages deeper inside the volume of the nozzle. In this paper, some fillers that have endurance in the high temperature arc environment were added into PTFE. Adding some fillers into PTFE was expected to be efficient in improving the endurability against radiation. The light reflectance and arc resistance of PTFE composites were investigated.

• 지구물리
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• 제5권1호
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• pp.29-39
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• 2002

충북 초정지역에 대하여 지하수부존과 연관된 파쇄대 분포 양상을 파악하기 위해 지리정보시스템을 이용한 각종 지국물리탐사 속성자료들을 상관해석하였다. 위성영상으로부터 얻어진 선구조밀도, 수직탐사와 검층에 의한 전기비저항, 전기비저항 표준편차분석, 방사능, 탄성파 속도, 기반암의 심도 등의 속성자료들은 복합해석을 위해 ARC/INFO를 이용한 데이터베이스로 구축하였다. 특히 전기비저항 수직탐사결과는 심도별 비저항 값들을 수평적으로 내·외삽시켜 입체적으로 재건하는 기법을 적용하였다. 전기비저항 수직탐사 자료들을 이용하여 재건한 합성결과와 GIS를 이용한 각종 물리탐사자료의 복합해석결과로 연구지역의 천부 파쇄대 분포 특성을 효과적으로 파악할 수 있었고, 특히 지하수부존과 연관된 파쇄대는 연구지역의 남동부에 발달되어 있는 것으로 확인되었다.

• Metals and materials international
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• 제24권6호
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• pp.1256-1261
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• 2018

Both thermoplastic formability and electrical conductivity of Al-Ni-Y metallic glass with 12 different compositions have been investigated in the present study with an aim to apply as a functional material, i.e. as a binder of Ag powders in Ag paste for silicon solar cell. The thermoplastic formability is basically influenced by thermal stability and fragility of supercooled liquid which can be reflected by the temperature range for the supercooled liquid region (${\Delta}T_x$) and the difference in specific heat between the frozen glass state and the supercooled liquid state (${\Delta}C_p$). The measured ${\Delta}T_x$ and ${\Delta}C_p$ values show a strong composition dependence. However, the composition showing the highest ${\Delta}T_x$ and ${\Delta}C_p$ does not correspond to the composition with the highest amount of Ni and Y. It is considered that higher ${\Delta}T_x$ and ${\Delta}C_p$ may be related to enhancement of icosahedral SRO near $T_g$ during cooling. On the other hand, electrical resistivity varies with the change of Al contents as well as with the change of the volume fraction of each phase after crystallization. The composition range with the optimum combination of thermoplastic formability and electrical conductivity in Al-Ni-Y system located inside the composition triangle whose vertices compositions are $Al_{87}Ni_3Y_{10}$, $Al_{85}Ni_5Y_{10}$, and $Al_{86}Ni_5Y_9$.

• 한국전기전자재료학회논문지
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• 제36권6호
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• pp.603-608
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• 2023

Carbon black with high purity and excellent conductivity is used as a conductive filler in the semiconductive compound for EHV (Extra High Voltage) power cables of 345 kV or higher. When carbon black and CNT (carbon nanotube) are applied together as a conductive filler of a semiconductive compound, stable electrical properties of the semiconductive compound can be maintained even though the amount of conductive filler is significantly reduced. In EHV power cables, since the semi-conductive layer is close to the conductor, stable electrical characteristics are required even under high-temperature conditions caused by heat generated from the conductor. In this study, the theoretical principle that a semiconductive compound applied with carbon black and CNT can maintain excellent electrical properties even under high-temperature conditions was studied. Basically, the conductive fillers dispersed in the matrix form an electrical network. The base polymer and the matrix of the composite, expands by heat under high temperature conditions. Because of this, the electrical network connected by the conductive fillers is weakened. In particular, since the conductive filler has high thermal conductivity, the semiconductive compound causes more thermal expansion. Therefore, the effect of CNT as a conductive filler on the thermal conductivity, thermal expansion coefficient, and volume resistivity of the semiconductive compound was studied. From this result, thermal expansion and composition of the electrical network under high temperature conditions are explained.

• Advances in concrete construction
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• 제17권2호
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• pp.93-110
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• 2024

The process of concrete production consumes an immense volume of water, with approximately one billion metric tons of freshwater being utilized for tasks such as aggregate washing, fresh concrete production, and concrete curing. The accessibility of clean water for the public is hindered by the limited availability of water resources, primarily due to the rapid expansion of industries such as tanneries, stone quarries, and concrete manufacturing. These industries not only consume substantial amounts of freshwater but also generate significant volumes of various types of waste. Therefore, the use of fresh water in concrete production should be minimized. Few studies have reviewed the production of concrete using wastewater to derive practical and applicable findings for the industry. Thus, this study thoroughly explores the physical and chemical effects of wastewater on concrete, examining aspects like durability, hardened properties, and rheological characteristics. It identifies key factors that can compromise concrete properties when exposed to wastewater. The scarcity of research on integrating wastewater into concrete production underscores the urgent necessity for innovative approaches and methodologies in this field. While the inclusion of wash water typically reduces the workability of fresh concrete, it often enhances its compressive strength. Notably, significant improvements have been observed when using tertiary processed wastewater, wash water, polyvinyl alcohol-based wash water (PVAW), and reclaimed water in the concrete mixing process. The application of tertiary treatment to wastewater resulted in a notable enhancement of compressive strength, showing increases of up to 7%. In contrast, wastewater treated through secondary methods experienced a decline in strength ranging from 9% to 18% over a period of six months. However, the use of reclaimed wastewater demonstrated an improvement in strength by 8% to 17%, depending on the concentration level ranging from 25% to 100%. In contrast, the utilization of secondary processed wastewater and industrial water has a minimal impact on the concrete's strength.

• 대한화학회지
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• 제36권1호
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• pp.16-23
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• 1992

고온초전도체 $YBa_2Cu_3O_{7-{\delta}}$에서 Y를 Eu로 치환시킨 $(Y_{1-x}Eu_x)Ba_2Cu_3O_{7-{\delta}}$ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0)를 제조한 후 물성변화를 관찰하였다. X-선 회절분석결과 모든 시료가 사방정계 구조를 갖고 있었으며 x값이 증가함에 따라 격자상수 a, b 및 c도 증가하였다. 전기저항과 자화율측정으로부터 순수한 90K 이상의 고온초전도상이 생성되었음을 알았으며, x값이 커짐에 따라 임계온도가 상승하였다. 주사전자현미경을 사용하여 구한 낟알크기와 자화측정결과로부터 각각의 시료들에 대한 부피 반자성자화율을 구하였으며, x값이 커질수록 이 값은 감소하였다. Eu의 농도가 증가함에 따라 결정격자내의 Ba의 양이 감소됨을 EPMA로 확인하였으며, 이것은 부피반자성 자화율의 감소에 직접적인 영향을 주는 것으로 판단된다.

• Journal of Electrical Engineering and Technology
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• 제9권2호
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• pp.643-648
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• 2014

The accelerated thermal aging of CSPE (chlorosulfonated polyethylene) was carried out for 40.41, 121.22, and 202.04 days at $100^{\circ}C$, which are equivalent to 20, 60, and 100years of aging at $50^{\circ}C$, respectively. The volume electrical resistivities of the accelerated thermally aged CSPE samples for 0, 40.41, 121.22, and 202.04 days were $1.107{\times}10^{14}-2.097{\times}10^{14}$, $7.752{\times}10^{13}-1.556{\times}10^{14}$, $7.693{\times}10^{13}-1.521{\times}10^{14}$, and $7.380{\times}10^{13}-1.304{\times}10^{14}{\Omega}{\cdot}cm$, respectively, at room temperature. The permittivities of the accelerated thermally aged CSPE samples for 0, 40.41, 121.22, and 202.04 days were $2.89{\times}10^{-11}-3.65{\times}10^{-11}$, $3.40{\times}10^{-11}-3.70{\times}10^{-11}$, $3.50{\times}10^{-11}-3.82{\times}10^{-11}$, and $3.76{\times}10^{-11}-4.13{\times}10^{-11}$ F/m, respectively, at room temperature. The EAB (elongation at break) of the accelerated thermally aged CSPE samples for 0, 40.41, 121.22, and 202.04 days were 98.8-101.3, 59.5-60.3, 37.8-39.2, and 41.8-44.3%, respectively, at room temperature. The apparent densities of the accelerated thermally aged CSPE samples for 0, 40.41, 121.22, and 202.04 days were 1.603-1.614, 1.611-1.613, 1.622-1.628, and $1.618-1.620g/cm^3$, respectively, at room temperature. The measured currents of the accelerated thermally aged CSPE and the standard sample were almost constant after 5 min of applying a 300-V/mm electric field to the CSPE. The V-I slope of the accelerated thermally aged CSPE sample was increased if the applied electric field was increased at room temperature, and the V-I slope of the accelerated thermally aged CSPE was higher than that of standard CSPE.

• Journal of Radiation Protection and Research
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• 제24권2호
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• pp.73-86
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• 1999

현재 경수로형 원자력발전소의 일차계통 냉각수 정화를 위해 사용되는 이온교환방법은 제염효과가 우수하고 공정이 단순하며 조작이 간편하기 때문에 광범위하게 활용되고 있으나 비금속성분도 함께 제거하여 수지의 수명이 단축되고 폐이온교환수지가 발생되는 단점이 있다. 본 연구에서는 일차계통 냉각수 정화를 위해 사용되는 이온교환수지의 대체공정으로서 전기투석과 이온교환이 결합된 전기탈이온법의 사용가능성을 조사하기 위해 모의 용액을 이용하여 다양한 실험조건하에서 수행하였다. 실험결과 유입유량이 증가할수록 제거율은 증가하고 전력소모는 감소하였다. 금속성분 제거율에서 제염계수 1000으로 일정한 경향을 나타내었으며 전력소모 면에서는 TDS 3 ppm이하를 기준으로 유입유량이 $2.0{\ell}/min$일 때 $40.3mWh/{\ell}$ 이었다. 유입유속이 동일한 조건에서는 희석실에 채운 이온 교환수지의 함량이 증가할수록 금속성분 제거율과 전력소모에서 효과적인 것으로 평가되었다. 이온 교환수지를 채운 전기탈이온 공정은 이온교환수지 자체에 의한 수리적 저항과 현탁질에 의한 수지의 오염으로 인해 운전이 계속될수록 유량이 감소하게 된다. 이러한 단점을 극복하기 위해 이온교환수지 대신 이온전도성 스페이서를 설치하여 실험한 결과 유입유량 문제는 해결할 수 있었으나 전력소모와 금속성분 제거율 및 전류효율 면에서 비효율적인 것으로 평가되었다. 전기탈이온 공정의 연속운전에서도 금속성분 제거율에서 제염계수가 1000으로 안정적인 수준을 유지하였다.

• 폴리머
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• 제28권2호
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• pp.143-148
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• 2004

옥타메틸싸이클로테트라실록산과 1,3,5-트리메틸싸이클로트리실록산 및 1,3,5,7-테트라비닐-1,3,5,7-테트라메틸싸이클로테트라실록산을 테트라메틸암모늄 실록산올레이트 촉매 하에서 1,1,3,3-테트라메틸디실록산과 평형중합으로 이들을 공중합시켜 $\alpha$,$\omega$-하이드로겐 폴리(메틸-디메틸-메틸비닐)실록산 전구체를 제조하였다. 제조된 $\alpha$,$\omega$-하이드로겐 폴리(메틸-디메틸-메틸비닐)실록산 전구체에 디메틸아크릴아마이드를 백금촉매 작용 하에서 반응시켜 아크릴아마이드 변성 $\alpha$,$\omega$-하이드로겐 폴리(메틸-디메틸-메틸비닐)실록산 전구체 (APMDMS)를 제조하였으며 여기에 금속산화물인 NiO, FeO를 배위결합시켜 금속산화물이 2차 결합으로 부가된 APMDMS-MO를 제조하였다. 제조된 화합물의 구조를 FT-IR과 $^1$H-NMR로 분석하여 확인하였다. $\alpha$,$\omega$-비닐 폴리디메틸실록산과 APMDMS-MO를 백금촉매 존재 하에서 컴파운딩시켜 금속산화물 함유 액상 실리콘 고무 복합체를 제조하였으며 이 화합물을 이용하여 제조된 쉬이트의 열 전도도는 0.29 W/mW로 액상 실리콘 고무 복합체의 0.215 W/mK 보다 우수하였고 체적 저항은 1.64${\times}$$10^{5}$$\Omega$ㆍcm로 낮은 값을 나타내었다. 또한 디메틸아크릴아마이드 변성 액상 실리콘 고무 복합체의 기계적 및 열적특성은 UTM과 TGA로 측정하였다.다.