• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 춘계학술대회 논문집
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• pp.495-496
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• 1998

The measurement of the amplitude and phase of electric fields on high voltage transmission lines is important for several reasons including a) Metering and determination of power flow, b) protective relaying. and c) fault sensing. The work reported here is directed toward a major improvement to optically based, electric-field sensors. This is a signal processing based technique for overcoming the instabilities of conventional, optically-based, electric-field sensors to changes in optical power or temperature.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기물성,응용부문
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• pp.73-74
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• 2006

Carbon nanotubes (CNTs) have recently attracted great attention because of their excellent physical properties, such as high mechanical strength, thermal stability, and electronic properties. These useful properties of carbon nanotubes make themselves good candidates for various application field, such as a transistor, battery, field emission display, nanoscale inter-connects, and so on. Gas-phase techniques offer the unique ability to synthesize well-oriented arrays of CNTs. However, it is seldom reported that the pressure influences on the growth of CNTs under low substrate temperature. In this work, the effect of the working pressure and the influence of the catalyst preparation on the properties of CNTs grown by microwave plasma chemical vapor deposition (MPCVD) were investigated.

• 한국초전도ㆍ저온공학회논문지
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• 제13권4호
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• pp.5-9
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• 2011

We have fabricated the superconducting $MgB_2$/carbon fiber by physical vapor deposition method. Mg (Magnesium) and B (Boron) were simultaneously deposited on the carbon fiber using the RF-sputtering and thermal evaporation, respectively. To ensure the relatively high vapor pressure of Mg at the growth region and the subsequent phase stability of $MgB_2$ at the deposition temperature, inverted funnel-like guide made of Mg-foil was employed while one side of the guide were open for the sputtered B flux. Mg vapor pressure should be controlled precisely to secure the complete reaction. The $MgB_2$/carbon fiber showed a uniformly deposited thin layer with dense and well-formed grains. The $MgB_2$/carbon fibers in this study showed $T_c$~37.5K, $J_c$ ~ $2{\times}10^4\;A/cm^2$ in the 20K, 0T.

• 한국안전학회지
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• 제27권6호
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• pp.43-47
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• 2012

The unbalance currents flow the High Temperature Superconducting (HTS) power cable caused by asymmetrical fault, harmonic distortion and unbalanced load. That problem causes additional loss and leakage field in the HTS power cable, and deteriorates the electric power quality and stability. In addition, large amounts of unbalanced current can cause negative sequence and ground relays to operate. This paper presents an analysis unbalanced three-phase current distribution in HTS power cable caused by unbalanced load condition and grounding methods using PSCAD/EMTDC. The results obtained through the analysis would provide important data for the design of HTS power cables and valid information for their installation in power system.

• 열처리공학회지
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• 제21권5호
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• pp.235-243
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• 2008

Ni-C composite films were prepared using a combination of microwave plasma CVD and ion beam sputtering deposition working in a codeposition way. The structure of these films was characterized by energy-dispersive X-ray diffraction (EDXRD), transmission electron microscopy (TEM) and Raman spectroscopy. It was found that a nickel carbide phase, $Ni_3C$ (hcp), formed as very fine crystallites over a wide temperature range when Ni-C films were deposited at low $CH_4$ flow rates. The thermal stability of this nonequilibrium carbide $Ni_3C$ was also studied. As a result, the $Ni_3C$ carbide was found to decompose into nickel and graphite at around $400^{\circ}C$. With high $CH_4$ flow rates (> 0.2 sccm), the structure of the Ni-C films became amorphous. The formation behavior of the carbide and amorphous Ni-C phases are discussed in relation to the electrical resistivity of the films.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.281-281
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• 2014

The field emission properties of GaN are reported in the present study. To be a good field emitter, it requires a low work function, high aspect ratio, and strong mechanical stability. In the case of GaN, it has a quite low work function (4.1eV) and strong chemical/mechanical/thermal stabilities. However, so far, it was difficult to fabricate vertical GaN nanostructures with a high aspect ratio. In this study, we successfully achieved vertically well aligned GaN nanostructures with chemical vapor-phase etching methods [1] (Fig. 1). In this method, we chemically etched the GaN film using hydrogen chloride and ammonia gases at high temperature around $900^{\circ}C$. This process effectively forms vertical nanostructures without patterning procedure. This favorable shape of GaN nanostructures for electron emitting results in excellent field emission properties such as a low turn-on field and long term stability. In addition, we observed a uniform fluorescence image from a phosphor film attached at the anode part. The turn-on field for the GaN nanostructures is found to be about $0.8V/{\mu}m$ at current density of $20{\mu}A$/cm^2. This value is even lower than that of typical carbon nanotubes ($1V/{\mu}m$). Moreover, threshold field is $1.8V/{\mu}m$ at current density of $1mA$/cm^2. The GaN nanostructures achieved a high current density within a small applied field range. We believe that our chemically etched vertical nanostructures are the promising structures for various field emitting devices.

• 대한금속재료학회지
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• 제48권2호
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• pp.122-132
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• 2010

Higher strength and fracture toughness of reactor pressure vessel steels can be obtained by changing the material specification from that of Mn-Mo-Ni low alloy steel (SA508 Gr.3) to Ni-Mo-Cr low alloy steel (SA508 Gr.4N). However, the operation temperature of the reactor pressure vessel is more than $300^{\circ}C$ and the reactor operates for over 40 years. Therefore, we need to have phase stability in the high temperature range in order to apply the SA508 Gr.4N low alloy steel for a reactor pressure vessel. It is very important to evaluate the temper embrittlement phenomena of SA508 Gr.4N for an RPV application. In this study, we have performed a Charpy impact test and tensile test of SA508 Gr.4N low alloy steel with changing impurity element contents such as Mn and P. And also, the mechanical properties of these low alloy steels after longterm heat treatment ($450^{\circ}C$, 2000hr) are evaluated. Further, evaluation of the temper embrittlement by fracture analysis was carried out. Temper embrittlement occurs in KL4-Ref and KL4-P, which show a decrease of the elongation and a shifting of the transition curve toward high temperature. The reason for the temper embrittlement is the grain boundary segregation of the impurity element P and the alloying element Ni. However, KL4-Ref shows temper embrittlement phenomena despite the same contents of P and Ni compared with SC-KL4. This result may be caused by the Mn contents. In addition, the behavior of embrittlement is not largely affected by the formation of $M_3P$ phosphide or the coarsening of Cr carbides.

• Transactions on Electrical and Electronic Materials
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• 제13권4호
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• pp.171-176
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• 2012

As langasite $A_3BC_3D_2O_{14}$ compounds with piezoelectric properties exhibit no phase transition up to the melting point of 1,400-$1,500^{\circ}C$, many high temperature applications are expected for the SAW filter, temperature sensor, pressure sensor, and so on, based on the digital transformation of wider bandwidth and higher-bit rates. It has a larger electromechanical coupling factor compared to quartz and also nearly the same temperature stability as quartz. The $La_3Ga_5SiO_{14}$ (LGS) crystal with the $Ca_3Ga_2Ge_4O_{14}$-type crystal structure was synthesized and the crystal structure was analyzed by Mill et al. It is also an important feature that the growth of the single crystal is easy. In the case of three-element compounds such as $[R_3]_A[Ga]_B[Ga_3]_C[GaSi]_DO_{14}$ (R=La, Pr and Nd), the piezoelectric constant increases with the ionic radius of R. In this study, crystal structures of four-element compounds such as $[A_3]_A[B]_B[Ga_3]_C[Si_2]_DO_{14}$ (A = Ca or Sr, B = Ta or Nb) are analyzed by a single crystal X-ray diffraction, and the mechanism and properties of the piezoelectricity depending on the species of cation was clarified based on the crystal structure.

• 대한화장품학회지
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• 제48권1호
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• pp.55-64
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• 2022

Cleansing foam이라 불리는 지방산 칼륨 cream soap은 crystal gel 구조로 이루어져 있어 유화계와는 달리 전단응력에 약하며 고온의 보관조건에서 쉽게 분리되는 특성을 보여준다. Crystal gel 구조는 지방산의 종류 및 비율, 중화도, polyol의 종류와 사용량에 따라 크게 영향을 받는다. Crystal gel 구조에 미치는 이들의 영향을 조사하기 위해 water/potassium hydroxide (KOH)/fatty acid ternary system에서 실험을 실시하였다. Differential scanning calorimeter (DSC) 측정 결과 myristic acid (MA) : stearic acid (SA) = 3 : 1 비율에서 공융점(eutectic point)를 갖고 이 혼합비가 가장 안전한 삼성분계(ternary system)를 만든다는 것을 발견했다. 점도 측정과 편광현미경 (POM) 관찰 결과 중화도는 75% 부근이 최적이라고 판단된다. 삼성분계의 melting point (T_m)이 보관온도보다 높을 때, 그리고 crystal phase가 lamellar gel phase로 상 전이가 일어날 때 안정하나 지방산 함량의 증가는 안정성에 거의 영향을 미치지 않는다. 삼성분계에 polyol의 첨가는 T_m을 변화시키고 상전이를 일으키는데 중요한 역할을 한다. 클렌징폼의 구조는 저온 주사전자현미경 (Cryo-SEM), 소각 및 광각 X-선 산란 (SAXS, WAXS) 분석으로 규명하였다. Butylene glycol (BG), propylene glycol (PG), dipropylene glycol (DPG)은 T_m을 낮추어주며 lamellar gel phase 형성을 어렵게 하는 반면 glycerin, PEG-400, sorbitol은 T_m을 상승시키고 lamellar gel phase 형성을 용이하게 하며 안정한 삼성분계를 만든다.

• Composites Research
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• 제35권3호
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• pp.201-215
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• 2022

본 연구에서는 초고온 환경에서 내화학성 및 열적 안정성이 우수한 지오폴리머 기반의 알루미노실리케이트 레진과 세라믹 섬유를 활용한, 목표주파수 X-band(8.2 GHz to 12.4 GHz)에서 전자파를 흡수하는 세라믹 복합재(Radar-absorbing ceramic composite, RACC)를 구현하였다. 주 성분이 FeSi인 판형 구조의 샌더스트 자성 입자를 분산시킨 알루미노실리케이트 레진은 목표 주파수 대역에서 자성 및 유전손실 특성을 발휘하였고, 입도와 무게분율별 유전특성을 Cole-Cole Plot으로 표현하였다. 샌더스트가 분산된 알루미노실리케이트 레진의 미세구조, 화학적 성분 및 결정, 자기 및 열적 특성 등을 분석하기 위해 SEM, EDS, VSM 및 TGA를 측정하였다. 샌더스트의 입도 크기 35 ㎛, 무게분율 40 wt.%를 분산시킨 레진의 유전손실 특성을 활용하여, X-band에서 약 1.51 GHz 대역폭에 대해 -10 dB 이하의 반사손실 성능을 발휘하는 단층형(t = 1.585 mm) RACC를 설계 및 제작하였다. 제작된 RACC의 초고온(25℃ to 1,000℃)에서 전자파 흡수 거동을 살피기 위해 개발된 초고온 환경 자유공간측정 장비를 활용하여 X-band 대역에서 그 성능을 검증하였다.