• Polymer(Korea)
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• v.38 no.4
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• pp.502-509
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• 2014

Carbon-based nanoplatelets such as graphene oxide (GO) sheets and graphite nanoplatelets (GNPs) are frequently used as conductive nanofillers for polymer nanocomposites. In this study, polystyrene (PS)/GO and PS/GNP nanocomposites were prepared through a latex technology and investigated to compare the effect of nanofillers on rheological and electrical properties of the PS nanocomposites. PS particles were prepared by emulsifier-free emulsion polymerization and GO was synthesized by using the modified Hummers' method from graphite. Hydrophilic GO was dispersed in aqueous PS suspension, but hydrophobic GNPs were dispersed with the help of a surfactant. In comparison with PS/GO nanocomposites, the rheological properties of PS/GNP counterparts were not too high because GNP existed in aggregates of graphene layers. Conducting pathways of PS/GO and PS/GNP nanocomposites were achieved at the electrical percolation threshold of 0.50 and 5.82 wt%, respectively. The reason for enhanced electrical conductivity in PS/GO nanocomposites is that GO was thermally reduced during molding.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.35.2-35.2
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• 2009

최근 본 연구실에서 무연 솔더를 위한 새로운 Cu-Zn 합금 젖음층을 개발하였다. 전해도금을 통하여 Cu-Zn 합금층을 형성한 뒤 그 위에 Sn-4.0wt% Ag-0.5wt% Cu (SAC 405) 솔더를 리플로 솔더링을 통해 솔더접합부를 형성하였으며 계면에서 생성된 금속간 화합물의 형성 및 성장 거동을 연구하였다. SAC/Cu 시스템의 경우, $150^{\circ}C$에서 시효 처리를 실시하는 동안 솔더와 도금된 Cu 계면에서 $Cu_6Sn_5$ 상과 미세한 공공이 형성된 $Cu_3Sn$ 상이 발견되었다. 반면에 SAC/Cu-Zn 시스템에서는 계면에서 $Cu_6Sn_5$ 상만이 형성되었다. 또한 큰 판상형의 $Ag_3Sn$ 상이 SAC/Cu 시스템에 비해 현저하게 억제되었다. SAC/Cu-Zn 계면에서의 금속간 화합물의 성장 속도가 SAC/Cu 계면에서 형성된 금속간 화합물의 성장 속도보다 느리게 나타났다. Cu-Zn 젖음층의 Zn가 솔더와 Cu-Zn 층 사이에서 Cu와 Sn 원자의 상호 확산을 방해하기 때문이다. 본 연구에서는 Cu와 Cu-Zn 층을 이용한 솔더 접합부의 낙하 충격 신뢰성을 연구하였다. 낙하 충격 시험 시편은 두 개의 인쇄 회로 기판을 SAC 405 솔더볼을 이용하여 리플로를 통해 상호연결 하여 제조되었다. 이 때, 각각의 인쇄 회로 기판의 패드에는 Cu 층과 Cu-Zn층을 전해도금을 통하여 각각 $10{\mu}m$두께의 젖음층을 형성하였다. 낙하 시험 시편을 제조한 뒤, 시효 처리에 대한 낙하 저항 신뢰성의 특성을 연구하기 위해 250, 500 시간동안 시효처리를 한 후 각 조건에서 계면에 형성된 금속간 화합물의 성장 거동을 관찰하였으며, 낙하 충격 시험을 실시하였다. 낙하 시험은 daisy chain으로 연결된 시편의 저항이 100 Ohm 이상 측정되었을 때 중단되도록 하였다. Cu-Zn/SAC/Cu-Zn 시편의 경우 초기 리플로를 하였을 때 불량이 발생하는 평균 낙하 수는 350이며, Cu/SAC/Cu 시편의 평균 낙하수는 200 미만으로 나타났다. Cu/SAC/Cu 시편의 경우, 시효처리 시간이 증가함에 따라 평균 낙하수는 큰 폭으로 감소하였지만, Cu-Zn/SAC/Cu-Zn 시편은 불량이 발생하는 평균 낙하수의 감소폭이 보다 완만하게 나타났다. Cu 층에 Zn를 첨가함으로써 솔더와 젖음층 사이에서 형성된 금속간 화합물의 성장 및 미세 공공의 형성이 억제되었고, 솔더 접합부의 과냉을 감소시킴으로써 큰 판상형의 $Ag_3Sn$ 상의 형성을 억제함으로써 Cu-Zn/SAC/Cu-Zn 솔더 접합부에서 Cu/SAC/Cu 솔더 접합부보다 낙하 충격에 대한 저항성 및 신뢰성이 향상되었다. 이는 무연 솔더에 Zn를 첨가하여 낙하 충격 신뢰성을 향상시킨 것과 동일한 효과를 나타냈음을 확인하였다. 본 연구는 한국 과학 기술 재단의 전자패키지 재료 연구 센터(CEPM)와 지식 경제부의 부품 소재 기술 개발 사업의 지원을 받아 수행되었습니다.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.811-817
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• 2003

Recently, application fields of non-metallic minerals by utilizing their structure properties are broadening. Especially, layered minerals have not only excellent shielding or covering ability but also absorbing and storing characteristics of chemical elements between a layers. We considered about the above mentioned characteristics and added functional substances onto their surfaces for the preparation of new environmentally friendly functional materials. In this study, natural graphite and sericite were mainly used to produce for the new environmentally friendly functional building materials. Graphite surfaces were modified with a surfactant (Alkyl Benzyle Demethyle Ammonium Chloride) for anti-bacillus and penicillium. Surface modification mechanism are that primary adsorption by differential zeta potential between graphite and ABDM and secondary adsorption by interaction between surfactant chains take place. Surfactant layers were fully formed and it was expected up to 99.7% up the efficiency of anti-bacillus and penicillium. Also the prepared functional samples have a effect to improve a various efficiency such as electromagnetic wave shield(up to 95%), deodorization(up to 80%), heat storage(5%) etc.

• Korean Chemical Engineering Research
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• v.46 no.4
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• pp.686-691
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• 2008

There are no many research reports on the preparation of ZnO by electrochemical oxidation since the zinc oxide is very easily dissolved in an acidic or basic environment, even though zinc oxides have attracted many attentions because of their optical/electrical properties. In this paper, we describe the fabrication of self-ordered stripes of ZnO by anodization of Zn in an ethanolic sulfuric acid. The formation of stripes of ZnO originating from Zn is attributed to water-selective dissolution of ZnO during anodization. We study in detail the effects of concentration of $H_2SO_4$, applied potential, anodization time, and addition of a small amount of water on the fabrication of stripes of ZnO. Mechanisms for the fabrication of ZnO stripes are discussed in terms of the above-mentioned effects.

• Composites Research
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• v.27 no.3
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• pp.109-114
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• 2014

Manufacture of nancomposites has simple process for developing nanocomposites due to the increasing applications using nanofillers. This work studied nanofiller coated glass fiber for reinforcing material with good wetting and conductivity and the morphology of nanofiller coated glass fiber was analyzed by FE-SEM. The durability of reinforced glass fiber was investigated with different shapes of nanofillers using sonication rinsing method. Fatigue test was performed to evaluate the adhesion of reinforcing interface and stability of nanofiller coating layer for single fiber reinforced composites. Apparent modulus and conductivity of nanofiller coating layer were evaluated to realize multifunctional of nanocomposites. Fiber type of nanofiller was better than plate type due to better cohesion between fiber and nanofillers. At last, the stability of fiber type nanofiller of coating layer has better durability and conductivity than plate type case.

• Polymer(Korea)
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• v.29 no.4
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• pp.375-379
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• 2005

The morphology and therma]/viscoelastic characteristics were investigated for PLLA/MMT nanocomposite manufactured by incorporating inorganic nanosized silicate nanoplatelets into biodeuadable poly(l-lactic acid) (PLLA). The XRD difiactogram and TEM image may be regarded as a formation of homogeneously dispersed nanocomposites. The melting energy(${\Delta}H_m$) was increased during hydrolysis process because of increase of crystallinity. As MMT played a role of reinforcing agent, the storage modulus was increase in case of PLLA/MMT nanocomposite, it was well coincided with our previous results. From SEM image, many tiny pinholes formed by spinodal decomposition were observed on the surface, and the shape of nanocomposite was maintained during hydrolysis process. In this study, it was shown that the control of biodegradation rate, thermal/mechnical property was possibile by incorporating MMT.

• Korean Journal of Materials Research
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• v.10 no.8
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• pp.532-539
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• 2000

Co-0.5C-(15~20)Cr-20Ni-8W-(2~7)Fe alloy bond in diamond-impregnated abrasive tool was synthesized by ball-milling and mechanical alloying process. When the powders were mechanical alloyed for 6h, micro-welding in most metal powders was observed irrespective of addition of stearic acid. Without stearic acid in metal powders, partial-ly coarse powders were obtained, which could be unfaverable to the densification of composite of composite powders. The hot-pressed compacts showed rupture strength of 1100MPa and hardness of about $46H_{RC}$, respectively.

• Korean Journal of Materials Research
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• v.8 no.2
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• pp.126-130
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• 1998

Aluminum sulfate, $AI_{2}(SO_4)_3\cdot18H_2O$ was prepared by adding of kaolin-dissolved sulphuric acid into ethanol and its thermal decomposition behavior was discussed. As-synthesized high purity precipitate particles were platelike shapes of $2\mu\textrm{m}$ size. With increasing drop rate of leach liquor into ethanol, the crystallite sizes of the precipitate decreased. The apparent activation energies for dehydration and sulfate decomposition of the precipitate were $11.9Kcal mol^{-1}$ and $48.2kcal mol^{-1}$ respectively.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1084-1089
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• 2010

This study elucidates the formation mechanism of SnO plate observed during the precipitation reaction of a $SnCl_2$ aqueous solution. $Sn_{21}Cl_{16}(OH)_{14}O_6$ and $Sn_6O_4(OH)_4$ precipitates was formed at pH=3~5 and at pH=11, respectively. When the pH was in the range of 11.5~12.5, the $Sn_6O_4(OH)_4$ precipitates dissolved into $HSnO_2{^-}[Sn_6O_4(OH)_4+4OH^-={6HSnO_2{^-}+2H^+]$ and dissolved $HSnO_2{^-}$ ions reprecipitated to SnO plate $[HSnO_2{^-}+H^+=SnO+H_2O]$. The $Sn_6O_4(OH)_4$ precipitates completely transformed into SnO plate through a repeated process of dissolution-precipitation in the range of pH=11.5~12.5.

• Electrical & Electronic Materials
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• v.6 no.5
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• pp.446-453
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• 1993

초기충진압력이 서로 다른 시편에 가한 가압횟수와 열처리시간의 혼합공정이 임계전류밀도 특성에 미치는 영향을 관찰하기 위하여 power-in-tube방법으로 초전도 선재를 제조하였다. 일정 초기충진압력에서 테이프화를 위한 열처리 및 가압이 혼합공정횟수가 증가할수록 임계전류밀도가 증가하였다. 초기충진압력이 1000kg/$cm^{2}$에서 Bi-2223 고온상 체적비가 가장 높게 나타났고 결정립이 판상으로 성장되었을 뿐만 아니라 C축과 직각방향으로 잘 배양되어 있음을 관찰할 수 있었다. 특히 초기충진압력 1000kg/$cm^{2}$의 시편을 두께를 줄이기 위하여 3회 가압하고 450시간 열처리하였을때 임계전류밀도가 5800A/$cm^{2}$를 나타내었으며 이를 중심으로 500, 2500kg/$cm^{2}$이 양측단으로 가우시안분포를 보였다. 결론적으로 시편의 임계특성은 적정 초기충진압력, Bi-2223 고온상 체적비, 테이프화를 위한 가압횟수, 결정의 일방향배열, 결정립의 성장등에 강하게 의존함을 알 수 있었다.