• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.37-40
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• 2003

Amorphous $Al_2O_3$ nanotubes have been fabricated by utilizing the ZnO nanowires as template with wet etching method. ZnO nanowires synthesized by thermal evaporation are conformally coated with $Al_2O_3$ by atomic-layer deposition(ALD) method. The $Al_2O_3$-coated ZnO nanowires are of core-shell structure; ZnO core nanowires and $Al_2O_3$ shells. When the $ZnO/Al_2O_3$ core-shell structure is dipped in $H_3PO_4$ solution at $25^{\circ}C$ for a 6 min, the core ZnO materials are completely etched, and only $Al_2O_3$ nanotubes are remained. This nanotube fabrication is technically easier than others, and simply approachable. Transmission electron microscopy shows that the $Al_2O_3$ nanotubes have various thicknesses that can be controlled.

• 한국응용과학기술학회지
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• 제22권2호
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• pp.96-105
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• 2005

Core-shell polymers of methyl methacrylate-styrene system were prepared by sequential emulsion polymerization in the presence of sodium dodecyl benzene sulfonate(SDBS) as an emulsifier using ammonium persulfate(APS) in an initiator and the characteristics of these core-shell polymers were evaluated. Core-shell composite latex has the both properties of core and shell components in a particle, whereas polymer blends or copolymers show a combined physical properties of two homopolymers. This unique behavior of core-shell composite latex can be used in various industrial fields. However, in preparation of core-shell composite latex, several unexpected matters are observed, for examples, particle coagulation, low degree of polymerization, and formation of new particles during shell polymerization. To solve this matters, we study the effects of surfactant concentrations, initiator concentrations, and reaction temperature on the core-shell structure of PMMA-PSt and PSt-PMMA. Particle size and particles distribution were measured by using particle size analyzer, and the morphology of the core-shell composite latex was observed by using transmission electron microscope. Glass temperature was also measured by using differential scanning calorimeter. To identify the core-shell structure, pH of the composite latex solutions was measured.

• 한국세라믹학회지
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• 제46권2호
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• pp.131-136
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• 2009

Radio frequency (RF) plasma treatment is studied for the size reduction and the spheroidization of coarse particles to change them into nano-sized powders of spherical shape in MLCC fields. The uni-nanoadditives manufactured by RF plasma processing for high dispersion have been investigated for the effect on core-shell structure in dielectrics of MLCC. Microstructures have been characterized using scanning electron microscope (SEM), transmission electron microscope (TEM) and Electron Probe Micro Analyzer (EPMA). We compared the distribution of core-shell grains between specimens manufactured using uni-nanoadditive and using mixed additive. In addition, the uniformity of rare earth elements in the core-shell structured grains was analyzed. It was shown, from TEM observations, that the sintered specimen manufactured using uni-nanoadditives had more dense small grains with well-developed core-shell structure than the specimen using mixed additives, which had a homogeneous microstructure without abnormal grain growth and shows broad temperature coefficient of capacitance (TCC) curves in all temperature ranges because of well dispersed additives.

• Macromolecular Research
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• 제17권5호
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• pp.339-345
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• 2009

The core/shell type structure of the highly crosslinked poly(glycidylmetharylate-co-divinylbenzene) microspheres prepared in the precipitation polymerization in acetonitrile was thoroughly verified by means of swelling, $^1H$ NMR, XPS, TEM and TGA measurements. In the XPS measurement, the higher the GMA content, the higher the oxygen content was observed, implying that the higher content of GMA is observed in the particle surface. The further verification of the core/shell structure of the poly(GMA-co-DVB) particles was carried out using $^1H$ NMR and TEM techniques, resulting in the poly(GMA-co-DVB) particles with the GMA rich-phase and DVB rich-phase. In overall, the poly(GMA-co-DVB) microspheres consist of a highly crosslinked DVB rich-phase in the core and slightly or non-crosslinked GMA rich-phase in the shell part due to the different reaction ratios between two monomers and self-crosslinking density of DVB.

• 한국가구학회지
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• 제24권4호
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• pp.379-388
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• 2013

In this study, the effect of various glass fiber (GF) contents in a shell layer and shell thickness changes on the flexural property of coextruded wood plastic composites (WPCs) in combination with three core systems (weak, moderate, and strong) was investigated. GF behaved as an effective reinforcement for the whole coextruded WPCs and GF alignments in the shell layer played an important role in determining the flexural property of the coextruded WPCs. At a given shell thickness, the flexural property of the whole coextruded WPCs was improved with the increase of GF content in shell. For core quality, when the core is weak, increase of GF content in shell led to improved flexural property of the whole composites and increase of shell thickness helped it. On the other hand, when the core is strong, the flexural property of the whole composites showed reduced features at low GF content in shell and increase of shell thickness aggravated it. This approach provides a method for optimizing performance of the coextruded WPCs with various combinations of core-shell structure and properties.

• Corrosion Science and Technology
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• 제21권5호
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• pp.412-417
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• 2022

Proton exchange membrane fuel cells (PEMFCs) provide zero emission power sources for electric vehicles and portable electronic devices. Although significant progresses for the widespread application of electrochemical energy technology have been achieved, some drawbacks such as catalytic activity, durability, and high cost of catalysts still remain. Pt-based catalysts are regarded as the most efficient catalysts for sluggish kinetics of oxygen reduction reaction (ORR). However, their prohibitive cost limits the commercialization of PEMFCs. Therefore, we proposed a NiCo@Au core shell structure as Pt-free ORR electrocatalyst in PEMFCs. NiCo alloy was synthesized as core to introduce ionization tendency and autoxidation reaction. Au as a shell was synthesized to prevent oxidation of core NiCo and increase catalytic activity for ORR. Herein, we report the synthesis, characterization, electrochemical properties, and PEMFCs performance of the novel NiCo@Au core-shell as a catalyst for ORR in PEMFCs application. Based on results of this study, possible mechanism for catalytic of autoxidation core@anti-oxidation shell in PEMFCs is suggested.

• 한국응용과학기술학회지
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• 제26권2호
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• pp.199-204
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• 2009

Silicone dioxide absorbed polyoxyethylene alkylether sulfate (EU-S133D) surfactant was prepared. Core-shell polymers of inorganic/organic pair, which have both core and shell component, were synthesized by sequential emulsion polymerization using Acrylate as a shell monomer and potassium persulfate (KPS) as an initiator. We found that when Acrylate core prepared by adding 2.0 wt% EU-S133D, silicone dioxide/Acrylate core-shell polymerization was carried out on the surface of silicone dioxide particle without forming the new silicone dioxide particle during acrylate shell polymerization in the inorganic/organic core-shell polymer preparation. The structure of core-shell polymer were investigated by measuring to the thermal decomposition of polymer composite using thermogravimetric analyzer and morphology of latex by scanning electron microscope(SEM).

• 한국응용과학기술학회지
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• 제27권1호
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• pp.56-60
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• 2010

Titanium dioxide particles are used as photocatalysts, sensors, adsorbents and catalyst. Core-shell polymers of inorganic/organic pair, which have both core and shell component, were synthesized by sequential emulsion polymerization using Acrylate as a shell monomer and potassium persulfate (KPS) as an initiator. We found that when Acrylate core prepared by adding 0.5~2.0 wt% EU-S133D, Titanium dioxide / Acrylate core-shell polymerization was carried out on the surface of Titanium dioxide particle without forming the new Titanium dioxide particle during acrylate shell polymerized in the inorganic/organic core-shell polymer preparation. The structure of core-shell polymer were investigated by measuring to the thermal decomposition of polymer composite using thermogravimetric analyzer(TGA) and morphology of latex by scanning electron microscope(SEM).

• 한국재료학회지
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• 제16권8호
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• pp.524-528
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• 2006

On the synthesis of Au/$TiO_2$ core-shell structure nanoparticle, the effect of concentration of $Ti^{4+}$ and reaction temperature on the morphology and optical property of Au/$TiO_2$ core-shell nanoparticles is examined. A gold colloid was prepared by $HAuCl_4{\cdot}4H_2O\;and\;C_6H_5Na_3{\cdot}2H_2O$. Titanium stock solution was prepared by mixing solution of titanium(IV) isopropoxide (TTIP) and triethanolamine (TEOA). The concentrations of $Ti^{4+}$ stock solution were adjusted to $10.01{\sim}0.3$ mM, and then the gold colloid is added to the $Ti^{4+}$ stock solution. Au/$TiO_2$ core-shell structure nanoparticles could be prepared by the hydrolysis of the $Ti^{4+}$ stock solution at $80^{\circ}C$. The size of synthesized Au nanoparticles was 15 nm. The thickness of $TiO_2$ shell on the surface of gold particles was about 10 nm. The absorption peak of synthesized Au/$TiO_2$ core-shell nanoparticles shifted towards the red end of the spectrum by about 3 nm because of the formation of $TiO_2$ shell on the surface of gold particles. The good $TiO_2$ shell is produced when $Ti^{4+}$ concentration is varied between 0.01 and 0.05 mM, and reaction temperature is maintained at $80^{\circ}C$. The crystal structure of $TiO_2$ shell was amorphous.

• Elastomers and Composites
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• 제37권1호
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• pp.21-30
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• 2002

개시제 ammonium persulfate(APS)와 유화제 sodium dodecyl benzene sulfonate(SDBS)를 이용하여 methyl methacrylate(MMA), styrene(St), ethyl acrylate(EA)등의 단량체를 core(내부)와 shell(외부)의 폴리머성분이 다른 core-shell 폴리머를 합성하고 각 core-shell 폴리머에 대한 구조를 연구하였다. 한 입자의 내부와 외부의 고분자 조성이 다른 composite 라텍스는 고분자 블렌딩과 공중합의 물성과는 달리 한 입자 내에서도 상반된 두 가지 물성을 동시에 나타내는 특성으로 인하여 여러 산업 분야에 응용이 가능하다. 그러나, core-shell 라텍스를 제조할 때 반응중입자가 성장하는 과정에서 입자의 응집과 중합율이 떨어지고, 라텍스의 응용시 기계적 안정성이 문제점으로 되고 있다. 따라서 shell 중합시에 새로운 입자의 생성이 적고 중합중 안정성이 우수한 라텍스를 제조하기 위해 유화제농도, 개시제농도, 중합온도가 PMMA/PSt과 PSt/PMMA의 core-shell 구조에 미치는 영향과 중합 후 입도분석기(particle size analyzer; PSA) 및 투과전자현미경(transmission electron microscope; TEM)을 이용하여 실제 입자측정과 입자형태 특성을 확인하였으며 시차주사열량계(differential scanning calorimeter, DSC)를 이용하여 유리전이온도($T_g$)의 측정, 최저성막온도(minimum film formation temperature; MFFT), NaOH 첨가에 의한 가수 분해에 따르는 pH를 측정하여 core-shell의 새로운 특성을 확인하였다.