• 한국초전도ㆍ저온공학회논문지
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• 제19권3호
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• pp.27-32
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• 2017

The effects of artificial holes on the trapped magnetic fields and magnetic levitation forces of very large single-grain $Y_{1.5}Ba_2Cu_3O_{7-y}$ (Y1.5) bulk superconductors were studied. Artificial holes were made for Y1.5 powder compacts by die pressing using cylindrical dies with a diameter of 30 mm or 40 m, or rectangular dies with a side length of 50 mm. The single grain Y1.5 bulk superconductors (25 mm, 33 mm in diameter and 42 mm in side length) with artificial holes were fabricated using a top-seeded melt growth (TSMG) process for the die-pressed Y1.5 powder compacts. The magnetic levitation forces at 77 K of the 25 mm single grain Y1.5 samples with one (diameters of 4.2 mm) or six artificial holes (diameters of 2.5 mm) were 10-17% higher than that of the Y1.5 sample without artificial holes. The trapped magnetic fields at 77 K of the Y1.5 samples with artificial holes were also 9.6-18% higher than that of the Y1.5 sample without artificial holes. The 33 mm and 42 mm single grain Y1.5 samples with artificial holes (2.5 mm and 4.2 mm in diameter) also showed trapped magnetic fields 10-13% higher than that of the Y1.5 samples without artificial holes in spite of the reduced superconducting volume fraction due to the presence of artificial holes. The property enhancement in the large single grain Y1.5 bulk superconductors appears to be attributed to the formation of the pore-free regions near the artificial holes and the homogeneous oxygen distribution in the large Y123 grains.

• Elastomers and Composites
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• 제37권4호
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• pp.258-264
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• 2002

본 연구에서는 열처리에 의한 실리카의 표면특성과 실리카/폴리우레탄 복합재료의 기계적 계면물성에 대하여 고찰하였다. 열처리에 의한 실리카의 표면특성은 Fourier Transform-IR(FT-IR), Solid-state 29Si NMR spectroscopy, 그리고 접촉각을 통하여 알아보았으며 실리카/폴리우레탄 복합재료의 기계적 계면물성은 인열에너지 (GIIIC)를 측정하여 관찰하였다. 본 실험결과, 열처리 온도가 증가함에 따라 실리카의 Si-OH가 축합하여 Si-O-Si를 형성하고 표면자유에너지의 비극성 요소가 증가하는 것을 확인할 수 있었다. 이러한 결과로부터, 증가된 실리카의 표면자유에너지의 비극성요소는 폴리우레탄 내에 실리카의 분산성을 향상시켜 결과적으로 실리카/폴리우레탄 복합재료의 기계적 계면물성인 인열에너지가 증가된 것으로 사료된다.

• 마이크로전자및패키징학회지
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• 제11권3호
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• pp.23-30
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• 2004

무연솔더 $Sn0.7wt{\%}Cu,\;Sn3.8wt{\%}Ag0.7wt{\%}Cu$ 솔더와 Pt층의 시효처리에 따른 계면반응에 대한 연구를 수행하였다. $250^{\circ}C$에서 30 초간 리플로한 $Sn3.8wt{\%}Ag0.7wt{\%}Cu/Pt$시편과, $260^{\circ}C$에서 30초간 리플로한 $Sn0.7wt{\%}Cu/Pt$ 시편을 이용하여 125, 150, $170^{\circ}C$에서 25-121 시간동안시효처리 하였다. 시효처리 온도와 시간에 따른 계면 금속간화합물의 두께 및 형상변화를 주사전자현미경 (scanning electron microscopy, SEM), energy dispersive x-ray spectroscopy (EDS) 및 x-ray diffractometry (XRD)를 이용하여 분석하였다. 분석 결과 계면에서 $PtSn_4,\;PtSn_2$가 발견되었고, 이런 금속간화합물 성장은 확산에 의해 지배됨을 발견하였다. 시효처리 온도와 시간에 따른 금속간화합물의 두께 변화를 이용하여 각 솔더에서의 계면 금속간화합물의 생성 활성화 에너지를 구해본 결과 $Sn3.8wt{\%}Ag0.7wt{\%}Cu/Pt$는 145.3 kJ/mol, $Sn0.7wt{\%}Cu/Pt$는 165.1 kJ/mol의 값을 가지고 있었다.

• 마이크로전자및패키징학회지
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• 제9권2호
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• pp.1-9
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• 2002

실제 BGA패키지에서 Sn-Ag-(Cu) 솔더와 금속패드가 반응하여 생성된 금속간 화합물의 특성을 Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS)f) X-ray Diffractometer (XRD)를 사용하여 분석하였다. EDS로 분석한 결과를 보면 BGA 패키지에서 Sn-Ag-Cu 솔더와 Au/Ni/Cu 금속층간의 반응으로 생성된 금속간화합물은 $(Cu,Ni)_6Sn_5$로 예상되며 . Cu의 편석은 솔더와 Ni 층 사이에서 발견되었다. XRD 분석결과 Cu를 함유하고 있는 Sn-Ag-Cu 솔더와 Ni층 사이에서는 $\eta -Cu_6 Sn_5$ 타입의 금속간화합물이 분석되었으며 Sn-Ag 솔더와 Ni층 사이에서는 $Ni_3$Sn_4$가 분석되었다. 계면에 생성된 금속간화합물은 리플로 회수와솔더내의 Cu의 함량에 따라증가하였다

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.151-151
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• 2011

Large amounts of natural gas, mainly methane, in the form of hydrates are stored on continental margins. When gas hydrates are dissociated by any environmental trigger, generation of excess pore pressure due to released free gas may cause sediment deformation and weakening. Hence, damage on offshore structures or submarine landslide can occur by gas hydrate dissociation. Therefore, geotechnical stability of gas hydrate bearing sediments is in need to be securely assessed. However, geotechnical characteristics of gas hydrates bearing sediments including small-strain elastic moduli have been poorly identified. Synthesizing gas hydrate in natural seabed sediment specimen, which is mainly composed of silty-to-clayey soils, has been hardly attempted due to their low permeability. Moreover, it has been known that hydrate loci in pore spaces and heterogeneity of hydrate growth in specimen scale play a critical role in determining physical properties of hydrate bearing sediments. In the presented study, we synthesized gas hydrate containing sediments in an instrumented oedometric cell. Geotechnical and geophysical properties of gas hydrate bearing sediments including compressibility, small-strain elastic moduli, elastic wave, and electrical resistivity are determined by wave-based techniques during loading and unloading processes. Significant changes in volume change, elastic wave, and electrical resistivity have been observed during formation and dissociation of gas hydrate. Experimental results and analyses reveal that geotechnical properties of gas hydrates bearing sediments are highly governed by hydrate saturation, effective stress, void ratio, and soil types as well as morphological feature of hydrate formation in sediments.

• 대한화학회지
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• 제36권5호
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• pp.652-660
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• 1992

폴리아민 리간드인 diethylenetriamine(dien), triethylenetetramine(trien), tetraethylenepentamine(tetren), 및 pentaethylenehexamine(penten)을 Chloromethylated Polystyrene $({\circledP}-) 수지에 반응시켜 각기 {\circledP}_L-Dien, {\circledP}_L-Trien, {\circledP}_L-Tetren 및 {\circledP}_L-Penten 수지를 합성한 후 Bjerrum법으로 pH를 측정하여 산해리상수 및 금속과의 안정도상수를 결정하였으며, Van't Hoff 식에 의해 {\Delta}H와 {\Delta}G도 구하였다. 이들 수지의 안정도상수(log k1)는 금속이온의 종류에 따라 Cu(Ⅱ) > Ni(Ⅱ) > Cd(Ⅱ) > Zn(Ⅱ) > Co(Ⅱ)의 순으로 감소하였으며, 수지중 주게 원자인 질소수가 증가함에 따라 {\circledP}_L-Dien < {\circledP}_L-Trien < {\circledP}_L-Tetren < {\circledP}_L-Penten의 순으로 증가하였다. 그리고 pH 변화에 대한 금속이온의 흡착량 및 분리도를 시험해 본 결과 이들 금속이온과의 안정도 상수값의 순서와 일치하였다.

• Korean Journal of Chemical Engineering
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• 제35권11호
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• pp.2269-2282
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• 2018

Mixed micelle formation behavior of cationic surfactant-cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS) in aqueous as well as in urea medium from 303.15 K to 323.15 K at 5 K interval was carried out by conductometric method. The differences between the experimental values of critical micelle concentrations (cmc) and ideal critical micelle concentrations ($cmc^{id}$) illustrate the interaction between the amphiphiles studied. The values of micellar mole fraction ($X_1^{Rub}$ (Rubingh), $X_1^M$ (Motomura), $X_1^{Rod}$ (Rodenas) and $X_1^{id}$(ideal) of surfactant CTAB determined by different proposed models and outcome indicate high involvement of CTAB in SDS-CTAB mixed micellization, which enhance by means of the augment of mole fraction of CTAB. The negative value of interaction parameter (${\beta}$) showed an attractive interaction involving CTAB and SDS. Activity coefficients were less than unity in all case, which also reveals the presence of interaction between CTAB & SDS. The negative ${\Delta}G^0_m$ values imply the spontaneous mixed micellization phenomenon. The attained values of ${\Delta}H^0_m$ were positive at inferior temperature, while negative at superior temperature. The negative ${\Delta}H^0_m$ values in urea ($NH_2CONH_2$) medium illustrate exothermic micellization process. The magnitudes of ${\Delta}S^0_m$ were positive in almost all cases. The excess free energy of mixed micelle formation (${\Delta}G_{ex}$) was found to be negative, which indicates the stability of mixed micelle as compared to the individual's components micelles.

• 한국과학교육학회지
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• 제15권1호
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• pp.39-53
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• 1995

The purpose of this study was development of 'Environmental Science' of high school appropriate to Sixth Natinal Education Curriculum. In view that ultimate aim of environmental education is forming responsible environmental behaviors and the goals of values and behaviors are as important as knowledges and skills, A new environmental text of high school level was developed and it was based on analysis of seven texts and environmental education in Fifth Korean Curriculum. This text have seven units, 1.Habitates : What're the Meanings?, 2.Nuclear Energy: Can't be Avoid?, 3.Acid Rain : What're the Messages", 4.Ethanol : Is this Future Fuel?, 5.Wastes : A New War!, 6.What're the National and Global Environmental Issues? and 7.Our Water: Can Drink, Really? This text was stressed equally in goals of four environmental education and avoided from the array of knowledges. Therefore included various teaching strategies and independent actions of students. 'Open-ended value learning' and 'free behavior learning' in text were special learning parts for aquisition of values and formation of behaviors. To verify the effects of new developed environmental text, the direct learning was carried out by 286 students in total. Post test scores of experimental groups per each units were significantly higher than those of control groups about four goals, respectively. The Results of questionnaires by 50 teachers from five different schools were as follows. For validity of selecting contents for units, 74% of respondents replied positively. For classification and presentation of four goal-groups, 90% replied positively in validity and 82%, in utility. For validity of various teaching strategies, 88% and for the degree of including student-centered independent actions, 86% replied positively. For importances and expected effects of 'open-ended value learning' and 'free behavior learning', showed positive responses respectively, 88%, 92%. Therefore this text is effective to acheive four goals of environmental education equally.

• Advances in materials Research
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• 제1권2호
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• pp.115-128
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• 2012

The structural and electrical properties of $(1-x)Ba(Sm_{1/2}Nb_{1/2})O_3-xBaTiO_3$; ($0{\leq}x{\leq}1$) ceramics were prepared by conventional ceramic technique at $1375^{\circ}C$/7 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were derived from the X-ray diffraction (XRD) data using FullProf software whereas crystallite size and lattice strain were estimated from Williamson-Hall approach. XRD analysis of the compound indicated the formation of a single-phase cubic structure with the space group Pm m. Dielectric study revealed that the compound $0.75Ba(Sm_{1/2}Nb_{1/2})O_3-0.25BaTiO_3$ is having low and ${\varepsilon}^{\prime}$ and ${\varepsilon}^{{\prime}{\prime}}$ a low $T_{CC}$ (< 5%) in the working temperature range (up to+$100^{\circ}C$) which makes this composition suitable for capacitor application and may be designated as 'Stable Low-K' Class I material as per the specifications of the Electronic Industries Association. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in the system. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy of the compounds.

• Bulletin of the Korean Chemical Society
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• 제33권9호
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• pp.3025-3032
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• 2012

Carbon microcapsules containing silicon nanoparticles (Si NPs)-carbon nanotubes (CNTs) nanocomposite (Si-CNT@C) have been fabricated by a two step polymerization method. Silicon nanoparticles-carbon nanotubes (Si-CNT) nanohybrids were prepared with a wet-type beadsmill method. A polymer, which is easily removable by a thermal treatment (intermediate polymer) was polymerized on the outer surfaces of Si-CNT nanocomposites. Subsequently, another polymer, which can be carbonized by thermal heating (carbon precursor polymer) was incorporated onto the surfaces of pre-existing polymer layer. In this way, polymer precursor spheres containing Si-CNT nanohybrids were produced using a two step polymerization. The intermediate polymer must disappear during carbonization resulting in the formation of an internal free space. The carbon precursor polymer should transform to carbon shell to encapsulate remaining Si-CNT nanocomposites. Therefore, hollow carbon microcapsules containing Si-CNT nanocomposites could be obtained (Si-CNT@C). The successful fabrication was confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). These final materials were employed for anode performance improvement in lithium ion battery. The cyclic performances of these Si-CNT@C microcapsules were measured with a lithium battery half cell tests.