• 한국초전도ㆍ저온공학회논문지
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• 제13권3호
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• pp.5-9
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• 2011

DC high-temperature superconducting(HTS) cable system has attracted a great deal of interest from the view point of low loss, dense structure and large capacity. A HTS cable system is made of cable and termination. The insulating materials and insulation technology must be solved for the long life, reliability and compact of cable system. In this paper, we will report on the dielectric breakdown characteristics of insulating materials for HTS cable and termination. The AC, DC and lightning impulse breakdown strength of laminated polypropylene paper(PPLP) and glass fiber reinforced plastic(GFRP) have been measured under nitrogen pressures in the range of 0.l-0.4MPa. PPLP and GFRP are found to have a significantly higher DC breakdown strength. Also, DC surface flashover voltage of negative polarity is slightly higher than that of positive polarity in GFRP.

• 대한전기학회논문지
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• 제39권9호
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• pp.956-963
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• 1990

The general shapes of prebreakdown pulses in a discharge gap were calculated and the current pulses due to avalanche were detected in SF6 by changing the polarity of the protrusion placed on an electrode at pressures up to about 400 Kpa. The mathematical model of prebreakdown pulse development with a negative protrusion shows agreement with the observed pulses. No evidence of intense bursts of field-emitted electrons was observed. Breakdown probably results from a single avalanche developing to a critical size. However the calculated shape of prebreakdown current pulse does not agree with the observed pulses with a positive protrusion. The breakdown is preceded by multiple avalanche development at pressures less than about 200 Kpa. This observation has been interpreted as due to the formation of negative ions following photoionization in the gas which drift into the critical volume near a positive protrusion.

• Bulletin of the Korean Chemical Society
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• 제13권6호
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• pp.613-620
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• 1992

The solvent-dependent photophysical properties of 2-biphenylcarboxylic acid (2BPCA) and 4-biphenylcarboxylic acid(4BPCA), which have a pre-twisted conformation in the ground state, have been investigated. The fluorescence spectra of 4BPCA show vibrational structure with a non-mirror image to the absorption spectra in nonpolar solvent while those of 2BPCA show no structure even in nonpolar solvents. As the solvent polarity increases, the fluorescence spectra become diffuse and broad with a strong red shift resulting in the large Stokes shift. The large fluorescence Stokes shift of BPCA's in polar solvent is also partially due to an intramolecular charge transfer (ICT) interaction in the excited state, as demonstrated by the large dipole moment in the excited state (7.6-10.6 D). The fluorescence decay behaviors of BPCA's (decay-times and their pre-exponential factors) also depend on solvent polarity in agreement with the solvent-dependent properties of the steady-state fluorecence. The data have been discussed in terms of change in the excited-state potential energy surface with respect to change of the dihedral angle of biphenyl moiety.

• 마이크로전자및패키징학회지
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• 제17권1호
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• pp.81-88
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• 2010

Sn-3.0Ag-0.5Cu 솔더범프의 금속간화합물 성장거동에 미치는 PCB 표면처리의 영향을 알아보기 위해서 PCB 패드 표면에 각각 OSP, immersion Sn, 그리고 ENIG를 처리하였고, 열처리는 $150^{\circ}C$ 조건에서 실험을 실시하였다. 또한, 전류인가시 Sn-3.0Ag-0.5Cu 솔더범프의 접합부 계면반응에 미치는 표면처리의 영향을 알아보기 위해서 $150^{\circ}C$, $4{\times}10^3\;A/cm^2$ 조건에서 electromigration특성을 비교 평가하였다. 열처리시 OSP와 immersion Sn의 금속간화합물 성장거동은 서로 비슷한 경향을 보인 반면, ENIG는 다른 표면처리에 비해 훨씬 느린 성장거동을 보였다. electromigration특성 평가결과 열처리에 비해 금속간화합물의 성장이 가속화되나 표면처리별 경향은 유사하였고, 전자 이동 방향에 따른 음극-양극에서 금속간화합물 형성의 차이를 보이는 극성효과(polarity effect)가 나타나는 것을 알 수 있었다.

• 한국생산제조학회지
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• 제7권1호
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• pp.34-40
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• 1998

Conductive metal matrix composite(MMC) material of 30% silicon carbide particulated based on aluminum matrix was machined by die sinking electrical discharge machining(EDM) process according to different current and duty factor for reverse polarity of electrode. Material removal rate(MRR) was examined by process under various operation conditions. The surface morphology was evaluated by surface roughness parameter and scanning electron microscopy(SEM) research. The MRR was suddenly increased over 11 ampere of current, and it was slightly changed over 0.3 of duty factor. The maximum surface roughness of EDMed surface was affected by the duty factor. The SEM photograghs of EDMed surface showed wide recast distribution region of melting materials as increased of current and duty factor.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.827-831
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• 1997

Conductive veramic matrix composite(CMC) workpiece of TiC 33%/Al /sab 2/O /sab 3/ 66% Y /sab 2/ O /sab 3/ was machined by die sinking electrical discharge machining(EDM) according to different pulse duration and suty factor for reverse polarity of electrode. Material removal rate(MRR) was examined by process under various operating conditions. The surface morphology was evaluated by surface roughness values and scanning electron microscopy(SEM) research. The more MRR was obtained according to increase pulse duration and duty factor. Also the maximum surface roughness(Rmax) of EDMed surface was slightly changed with increased pulse duration and duty factor. The SEM photographs of EDMed surface showed wide recast wide recast distribution region of melting materials in purse duration 0.130(ms) than 0.048(ms).

• Fibers and Polymers
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• 제2권2호
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• pp.71-74
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• 2001

Surface characterization of materials has been considered critical in the development of biomaterials, as many unfavorable responses from the body occur at the interface between a material and the body component. The contact angle measurement is one means to characterize the surface properties and to correlate them to the biocompatibility of materials. In this paper, surface characteristics of silk fibroin/S-carboxymethyl kerateine, representative fibrous proteins, were investigated by contact angle measurements of ESCA. The biocompatibility of the blends was evaluated based on minimal interfacial free energy concept, and compared with other potential biomaterials. It was also hypothesized that the enhanced surface polarity of the blends was generated from the conformational transition of proteins. This approach to evaluate the biocompatibility of materials based on surface characteristics may find wide utility in many biomedical applications.

• 한국의류학회지
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• 제36권10호
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• pp.1117-1124
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• 2012

This study was a preliminary study to investigate the influence of surface morphology and characteristics on the self-cleaning of substrates. PI film was treated by $O_2$ plasma to modify the surface; in addition, AFM and Fe-SEM were employed to examine the morphological changes induced on a PI film treated by $O_2$ plasma and surface energies calculated from measured contact angles between several solutions and PI film based on the geometric mean and a Lewis acid base method. The surface roughness of PI film treated by $O_2$ plasma increased with the duration of the $O_2$ plasma on PI film due to the increased surface etching. The contact angle of film treated by $O_2$ plasma decreased with the increased treatment time in water and surfactant solution; in addition, the surface energy increased with the increased treatment times largely attributed to the increased portion on the polar surface energy of PI film. The coefficient of the correlation between surface roughness and surface polarity such as contact angle and surface energy was below 0.35; however, it was over 0.99 for the contact angle and surface energy.

• Elastomers and Composites
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• 제39권1호
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• pp.12-22
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• 2004

라디오 주파수(13.56 MHz) 무전극 종형 플라즈마 반응기를 이용하여 천연고무 가교체의 표면을 클로로디플루오로메탄으로 처리하였다. FT-적외선 분광분석으로 표면개질 정도를 정성적으로 조사하였다. 플라즈마 처리표면의 마찰힘은 플라즈마 처리시간 증가에 따라 감소하였다. 고무표면에 에틸렌글리콜과 물을 떨어뜨려 접촉각을 측정한 결과 플라즈마 처리에 따라 감소하는 것으로 미루어 플라즈마 개질에 따라 표면극성이 증가하는 것을 확인하였다. 유리판 표면을 동일조건으로 플라즈마 처리한 경우는 극성의 감소만이 확인되었다. 표면자유에너지의 London 비극성 및 극성요소를 계산하는데 있어서 기하평균법과 조화평균법이 유용한 것으로 확인되었다. 평균방법에 관계없이 플라즈마 처리시간이 증가함에 따라 표면자유에너지는 증가하였다 그러나 조화평균법으로 계산된 자유에너지가 기하평균법으로 계산된 값에 비해 상대적으로 높았다. 플라즈마 표면개질은 마찰의 계면, 히스테리시스, 점성요소들에 영향을 미침으로써 마찰계수를 변화시키는 것으로 나타났다.

• 한국표면공학회지
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• 제26권6호
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• pp.285-290
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• 1993

A series of samples were prepared by treating natural zeolite from Kampo area with HCl and NaOH. And, the adsorption characteristics of some liquid samples were investigated by the Diamond-Kinter method. The adsorption amount of all liquid investigated was more effective in acid treatment than in alkali treatment. In the case of n-, iso-C3H7OH, thed adsorption amount of n-form which has smaller molecular size was larger. Similar tenedncy was observed in n-, iso-C4H9OH, but the amount was lower than n-, iso-C3H7OH. In CHCl3 and CCl4, that of CHCl, which is smaller molecular size and has polarity, was far lager. From the view of the molecular size, adsorption amount of C6H5CH3 and p-C6H4(CH3)2 showed the characteristics of surface activity rather than chemical treatment.