• Bulletin of the Korean Chemical Society
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• 제32권5호
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• pp.1534-1538
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• 2011

Uniform, hollow nanosilica spheres were prepared by the chemical coating of cationic polystyrene (cPS) with tetraethylorthosilicate (TEOS), followed by calcination at 600 $^{\circ}C$ under air. cPS was synthesized by surfactant-free emulsion polymerization using 2,2'-azobis (2-methyl propionamidine) dihydrochloride as the cationic initiator, and poly(vinyl pyrrolidone) as a stabilizer. The resulting cPS spheres were 280 nm in diameter, and showed monodispersion. After coating, the hollow silica product was spherically shaped, and 330 nm in diameter, with a narrow distribution of sizes. Dispersion was uniform. Wall thickness was 25 nm, and surface area was 96.4 $m^2/g$, as determined by BET. The uniformity of the wall thickness was strongly dependent upon the cPS surface charge. The effects of TEOS and ammonia concentrations on shape, size, wall thickness, and surface roughness of hollow $SiO_2$ spheres were investigated. We observed that the wall thicknesses of hollow $SiO_2$ spheres increased and that silica size was simultaneously enhanced with increases in TEOS concentrations. When ammonia concentrations were increased, the irregularity of rough surfaces and aggregation of spherical particles were more severe because higher concentrations of ammonia result in faster hydrolysis and condensation of TEOS. These changes caused the silica to grow faster, resulting in hollow $SiO_2$ spheres with irregular, rough surfaces.

• Structural Engineering and Mechanics
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• 제57권5호
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• pp.823-835
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• 2016

Using the Complementary Functions Method (CFM), a general solution for the one-dimensional steady-state thermal and mechanical stresses in a hollow thick sphere made of functionally graded material (FGM) is presented. The mechanical properties are assumed to obey the exponential variations in the radial direction, and the Poisson's ratio is assumed to be constant, with general thermal and mechanical boundary conditions on the inside and outside surfaces of the sphere. In the present paper, a semi-analytical iterative technique, one of the most efficient unified method, is employed to solve the heat conduction equation and the Navier equation. For different values of inhomogeneity constant, distributions of radial displacement, radial stress, circumferential stress, and effective stress, as a function of radial direction, are obtained. Various material models from the literature are used and corresponding temperature distributions and stress distributions are computed. Verification of the proposed method is done using benchmark solutions available in the literature for some special cases and virtually exact results are obtained.

• Bulletin of the Korean Chemical Society
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• 제35권12호
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• pp.3583-3589
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• 2014

This study evaluated a simple and useful route to the synthesis of mesoporous $TiO_2$ microcapsules with a hollow macro-core structure. A hydrophilic precursor sol containing the surfactants in the hydrophobic solvents was deposited on PMMA polymer surfaces modified by non-thermal plasma to produce mesoporous shells after calcination. The surface of the PMMA polymer spheres was coated with $NH_4F$ and CTAB to control the interfacial properties and promote the subsequent deposition of inorganic sols. These hollow type mesoporous $TiO_2$ microcapsules could be applied as an efficient substrate for the immobilization of DNA oligonucleotides.

• Bulletin of the Korean Chemical Society
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• 제30권5호
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• pp.1118-1120
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• 2009

Micro-size CdS spheres of hollow shape were fabricated through the self-assembly of high density arrow-like nanorods. The synthesis of the CdS hollow spheres were accomplished in an aqueous solution of cadmium nitrate and triblock copolymer (Pluronic P123) at low temperature (80 ${^{\circ}C}$) through the slow release of S2- ions from thioacetamide. Morphology of the fabricated CdS hollow spheres was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The results indicate that the arrow-like CdS nanorods are simultaneously grown and attached each other to form the building units that become the spheres with hollow inside as a self-assembled process. The CdS spheres have a diameter of $2{\sim}3 {\mu}m$ and consist of the nanorods with a length of$\sim$800 nm. The nanocrystal building blocks have a hexagonal CdS structure.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.33.1-33.1
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• 2009

To date, nanostructured tungsten oxides with a variety of stoichiometries, such as WO3, WO2.9, W18O49, and WO2, have been prepared, because they are promising candidates for applications such as gas sensors, photocatalysts, electrochromic devices, and field emission devices. Among them, W18O49 and WO2 have been widely studied due to their outstanding chemical sensing, catalytic, and electron emissive properties. Here we report, for the first time, a one-pot solution-phase route to synthesizing a novel composite hierarchical hollow structure without adding catalysts, surfactants, or templates. The products, consisting of a WO2 hollow core sphere surrounded by a W18O49 nanorod shell (yielding a sea urchin-like structure), were generated as discrete structures via Ostwald ripening. To our knowledge, this type of composite hierarchical core/shell structure has not been reported previously. The morphological evolution and the detailed growth mechanism were carefully studied. We also demonstrate that the size of the hollow urchins is readily tunable by controlling the reactant concentrations.Interestingly, although bulk tungsten oxides are weakly paramagnetic or diamagnetic, the as-prepared products show unusual ferromagnetic behavior atroom temperature. The urchin structures also show a very high Brunauer-Emmet-Teller (BET) surface area, suggesting that they may potentially be applied to chemical sensor or effective catalyst technologies.

• 한국공간구조학회논문집
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• 제15권4호
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• pp.65-72
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• 2015

To overcome the weakness of spread foundation in large space structure, the research of precast pile for replace spread foundation have been conducted. The new type of joint between PHC pile and steel column is named HAT Joint(Hollow hAlf-sphere cast-sTeel Joint). It connected PHC Pile by bolt that verification of bolt connection should be accomplished. In this paper, pull-out test and flexural performance for HAT Joint to verifying the bolt connection is explained. As a result, the pull-out and flexural capacities of bolt were checked to use in real structure. Furthermore, the equation of pull-out strength was proposed.

• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2003년도 춘계총회 및 연구발표회 초록집
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• pp.91.1-91
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• 2003

• 한국재료학회지
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• 제22권10호
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• pp.531-538
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• 2012

Hollow silica spheres were prepared by spray drying of precursor solution of colloidal silica. The precursor solution is composed of 10-20 nm colloidal silica dispersed in a water or ethanol-water mixture solvent with additives of tris hydroxymethyl aminomethane. The effect of pH and concentrations of the precursor and additives on the formation of hollow sphere particles was studied. The spray drying process parameters of the precursor feeding rate, inlet temperature, and gas flow rate are controlled to produce the hollow spherical silica. The mixed solvent of ethanol and water was preferred because it improved the hollowness of the spheres better than plain water did. It was possible to obtain hollow silica from high concentration of 14.3 wt% silica precursor with pH 3. The thermal conductivity and total solar reflectivity of the hollow silica sample was measured and compared with those values of other commercial insulating fillers of glass beads and $TiO_2$ for applications of insulating paint, in which the glass beads are representative of the low thermal conductive fillers and the $TiO_2$ is representative of infrared reflective fillers. The thermal conductivity of hollow silica was comparable to that of the glass beads and the total solar reflectivity was higher than that of $TiO_2$.

• Korean Chemical Engineering Research
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• 제50권4호
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• pp.621-626
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• 2012

본 연구에서는 마이크로 기공의 중공구를 유기 고분자 수지와 복합화한 유/무기 하이브리드 물질을 제조하여 우수한 단열 성능을 갖는 코팅유리를 개발하고자 하였다. 유기 고분자 물질로는 투명성과 접착성이 우수한 6관능기의 우레탄 아크릴레이트(UP118), 3관능기의 trimethylolpropane triacrylate (TMPTA), 2관능기의 1,6-hexanediol diacrylate (HDDA), 광 개시제(Irgacure184) 등으로 구성된 자외선 경화형 수지를 사용하였다. 유리 및 실리카 중공구를 고분자 수지에 각각 10~40 vol%까지 첨가하여 얻어진 코팅 졸을 투명유리에 바(bar)코팅 방식으로 박막을 형성시킨 후 자외선 경화를 통해 최종 코팅유리를 제조하였다. 마이크로 중공구의 종류 및 함량이 제조된 코팅유리의 광 투과율, 열전도도, 접착성 및 표면 경도에 미치는 영향을 조사하였다. 복합물 코팅유리는 중공구가 과량 첨가되어도 우수한 접착성(5B)을 유지하였으며, 단열 성능은 각 중공구가 20 vol%만 함유되어도 뚜렷하게 향상된 결과를 나타냈다. 또한 실리카 중공구(SP)를 단열 재료로 사용하였을 경우 광 투과율 80 %의 투명 코팅유리를 얻을 수 있었다.

• 공업화학
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• 제10권8호
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• pp.1186-1191
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• 1999

고분자 화합물의 첨가제로서 개질제, 물성 향상제, 충진제, 강화제 등의 용도로 사용되고 있는 유리 중공구체를 혼합액상 전구체를 사용하여 제조하였다. 혼합액상 전구체는 40% 규산나트륨($Na_2O:SiO_2$= 1:2) 수용액에 불용제인 붕산과 팽창제인 요소를 혼합한 용액이며, 이 용액을 오븐에 건조시킨 후, 볼밀로 분쇄시켜 기체 화염로에 투입될 원료 입자를 제조하였다. 유리 중공구체의 물성에 영향을 미치는 인자로서는 로에 투입될 원료 입자의 크기($53{\sim}63{\mu}m$, $63{\sim}180{\mu}m$)와 로 내부의 온도($800{\sim}1200^{\circ}C$), 그리고 요소의 변화량(0~30 g)을 택하여 실험하였으며, 실험 결과 유리 중공구체의 평균 입경은 원료 입자의 크기가 작을수록, 로 내부의 온도가 클수록, 그리고 요소의 조성이 증가할수록 증가하는 결과를 보여 주었다. 또한, 유리 중공구체의 파쇄 강도는 요소의 양이 증가할수록 감소하는 경향을 나타내었다.