• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2367-2370
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• 2014

"Cat's eye"-shaped $[^{57}Co]CoO@SiO_2$ core-shell nanostructure was prepared by the reverse microemulsion method combined with radioisotope technique to investigate a potential imaging agent for a single photon emission computed tomography (SPECT) in nuclear medicine. The core cobalt oxide nanorods were obtained by thermal decomposition of $Co-(oleate)_2$ precursor from radio isotope Co-57 containing cobalt chloride and sodium oleate. The $SiO_2$ coating on the surface of the core cobalt oxide nanorods was produced by hydrolysis and a condensation reaction of tetraethylorthosilicate (TEOS) in the water phase of the reverse microemulsion system. In vivo test, micro SPECT image was acquired with nude mice after 30 min of intravenous injection of $[^{57}Co]CoO@SiO_2$ core-shell nanostructure.

• Analytical Science and Technology
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• v.6 no.2
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• pp.207-215
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• 1993

$Si_3N_4$ powders were mixed with sintering additives($3Y_2O_3{\cdot}5Al_2O_3$, YAG) by coprecipitation method. Mixing homogeneity, sintered and mechanical properties of coprecipitation-mixed powder compacts were compared with those of mechanically-mixed ones. SIMS-analysis for composition on the surface and in the matrix of prepared powder mixtures showed that the added YAG exists mainly on the $Si_3N_4$ powder surfaces in a form of coating. From this result it could be concluded that coprecipitation method is superior to mechanical mixing in the mixing homogeneity. This mixing homogeneity can accompany an improvement in sintered density, microstructure and consequently the mechanical properties of sintered bodys.

• Journal of Magnetics
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• v.2 no.1
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• pp.16-21
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• 1997

Those were investigated, the crystallographic, morphological, and magnetic properties of barium ferrite film (SiO2/Si substrate) prepared by sol-gel dip coating. Appropriate sol was prepared by dissolvin barium and iron nitrate in ethylene glycol at 80$^{\circ}C$. To obtain the films, thermally oxidized p-type silicon substrate with (111) of crystallographic orientation were dipped into the sol, dried at 250$^{\circ}C$ to remove organic material, and heated at 800$^{\circ}C$ for 3 hours in air for the crystallization of barium ferrite. It was found that the particles of barium ferrite formed on the substrate exhibited needle-like shape placing parallel to the substrate and its c-axis is long axis direction. There was tendency that the coercive force in horizontal direction to the substrate was higher than that in vertical direction to it. This tendency was profound in large thickness.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.335-338
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• 1998

Ferroelectric Sr$_2$(Nb,Ta)$_2$O$_{7}$ (SNTO) thin films were prepared by chemical solution deposition processes. SNTO thin films were spin-coated on Pt/Ti/SiO$_2$/(100)Si substrates. After multiple coating, dried thin films were heat-treated for decomposition of residual organics and crystallization. B site-rich impurity phase, i.e. [Sr(Nb,Ta)$_2$O$_{6}$], was found after annealing, where its appearance was dependent on process temperature indicating the possible reaction with substrate. Dielectric and other relevant electrical properties were measured and the results showed a little possibility in ferroelectric gate random access memory devices.s.s.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1746-1751
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• 2015

In this study low voltage Plasma Electrolytic Oxidation (PEO) was utilized to eliminate high voltage PEO drawbacks such as high cost, dimensional deformation and porosity. Low voltage PEO produces a thin coating which causes low corrosion resistance. In order to solve such problem, 0.1~0.6M pyrophosphates were added in a bath containing 1.4M NaOH, and 0.35M Na₂SiO₃. 70 V PEO was conducted at 25℃ for 3 minutes. Chemical composition, morphology and corrosion resistance of the anodized coating were analyzed. The anodized film was composed of MgO, Mg₂SiO₄, and Mg₂O₇P₂. The morphology of film showed appropriately dense structure and low porosity in the anodized layers. It is found that low voltage Plasma Electrolytic Oxidation in cooperation with phosphating treatment can provide a good corrosion protection for the AZ31B magnesium alloy.

• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1521-1528
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• 1994

To improve mechanical strength of bioglass, it is considered to use the glass as a coating material to alumina, but the difference in thermal expansion coefficient between two materials is too high to make a good coating. The aim of the present study, therefore, is to find out proper glass composition matching its thermal expansion coefficient to that of alumina without losing biocompatibility. In the present work, various glasses were prepared by substituting B2O3 and CaO for Na2O in the glass system of 55.1%SiO2-2.6%P2O5-20.1%Na2O-13.3%CaO-8.9%CaF2 (in mole%), and the thermal expansion property and reaction property in tris-buffer solution for the resulting glasses were measured. The thermal expansion coefficient of the glass was decreased with the substitution of B2O3 for Na2O, and it became close to that of alumina in the glass in which 8 mole% of CaO was substituted for Na2O. Hydroxyapatite formation was enhanced and silica rich layer thickness was decreased with B2O3 substitution for Na2O. CaO substitution for Na2O didn't deteriorated the hydroxyapatite development.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.281-281
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• 2010

Very low refractive index (<1.4) materials have been proved to be the key factor improving the performance of various optical components, such as reflectors, filters, photonic crystals, LEDs, and solar cell. Highly porous SiO2 are logically designed for ultralow refractive index materials because of the direct relation between porosity and index of refraction. Among them, ordered macroporous SiO2 is of potential material since their theoretically low refractive index ~1.10. However, in the conventional synthesis of ordered macroporous SiO2, the time required for the crystallization of organic nanoparticles, such as polystyrene (PS), from colloidal solution into well ordered template is typical long (several days for 1 cm substrate) due to the low interaction between particles and particle - substrate. In this study, polystyrene - polyacrylic acid (PS-AA) nanoparticles synthesized by miniemulsion polymerization method have hydrophilic polyacrylic acid tails on the surface of particles which increase the interaction between particle and with substrate giving rise to the formation of PS-AA film by simply spin - coating method. Less ordered with controlled thickness films of PS-AA on silicon wafer were successfully fabricated by changing the spinning speed or concentration of colloidal solution, as confirmed by FE-SEM. Based on these template films, a series of macroporous SiO2 films whose thicknesses varied from 300nm to ~1000nm were fabricated either by conventional sol - gel infiltration or gas phase deposition followed by thermal removal of organic template. Formations of SiO2 films consist of interconnected air balls with size ~100 nm were confirmed by FE-SEM and TEM. These highly porous SiO2 show very low refractive indices (<1.18) over a wide range of wavelength (from 200 to 1000nm) as shown by SE measurement. Refraction indices of SiO2 films at 633nm reported here are of ~1.10 which, to our best knowledge, are among the lowest values having been announced.

• Proceedings of the Membrane Society of Korea Conference
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• 1994.04a
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• pp.58-58
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• 1994

슬립캐스팅법으로 제조한 튜브형 $\alpha$-알루미나 담체 (평균기공크기 = $0.1 \mum$)에 졸-겔 침지코팅(dipcoating) 또는 가압코팅 (pressurized coating) 법에 의하여 극미세입자 $\gamma$-AlOOH, $TiO_2, SiO_2$, 및 aluminosilicate diphasic 졸을 코팅한 후 300 ~ 500$\circ$C 에서 열처리하여 세라믹 복합막을 제조하였다. 복합막 전체에 대한 균열유무는 $N_2$ 기체투과율의 평균압력에 대한 의존성으로부터 평가하였으며, 한외여과 (ultrafiltration)에의 응용성을 규명하기 위하여 막의 재질 및 제조조건에 따른 polyethylene glycol (PEG) 수용액의 분획분자량 변화를 측정하였다. 합성 세라믹 복합막의 분획분자량 측정 결과 $SiO_2$의 경우 2,000 정도로 매우 우수하였으며 $\gamma-Al_2O_3, TiO_2$, 그리고 aluminosilcate 막들은 6,000 ~ 10,000 범위 값을 갖고 있었다. 또한 막의 기공크기 및 분획분자량을 제어하기 위한 방법으로서 $TiO_2$ 복합막을 300 ~ 700$\circ$C 에서 열처리하였으며 이들에 대한 분획분자량 변화를 비교 분석하였다.

• Journal of Powder Materials
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• v.20 no.3
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• pp.210-214
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• 2013

This manuscript reports on compared color evolution about phase transformation of ${\alpha}-FeOOH@SiO_2$ and ${\beta}-FeOOH@SiO_2$ pigments. Prepared ${\alpha}$-FeOOH and ${\beta}$-FeOOH were coated with silica for enhancing thermal properties and coloration of both samples. To study phase and color of ${\alpha}$-FeOOH and ${\beta}$-FeOOH, we prepared nano sized iron oxide hydroxide pigments which were coated with $SiO_2$ using tetraethylorthosilicate and cetyltrimethyl-ammonium bromide as a surface modifier. The silica-coated both samples were calcined at high temperatures (300, 700 and $1000^{\circ}C$) and characterized by scanning electron microscopy, CIE $L^*a^*b^*$ color parameter measurements, transmission electron microscopy and UV-vis spectroscopy. The yellow ${\alpha}$-FeOOH and ${\beta}$-FeOOH was transformed to ${\alpha}-Fe_2O_3$ with red, brown at 300, $700^{\circ}C$, respectively.

• Journal of the Korean Electrochemical Society
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• v.18 no.4
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• pp.143-149
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• 2015

Carbon-coated $Li_2MnSiO_4$ powders as the active materials for the cathode were synthesized by planetary ball milling and solid-state reaction, and their phase formation behavior and charge-discharge properties were investigated. Calcination temperature and atmosphere were controlled in order to obtain the ${\beta}-Li_2MnSiO_4$ phase, which was active electrochemically, and the carbon-coated $Li_2MnSiO_4$ active material powders with near single phase ${\beta}-Li_2MnSiO_4$ could be fabricated. The particles of the synthesized powders were secondary particles composed of primary ones of about 100 nm size. The carbon incorporation was essential to enable the Li ions to be inserted and extracted from $Li_2MnSiO_4$ active materials, and the initial capacity of 192 mAh/g could be obtained in the $Li_2MnSiO_4$ active materials with 4.8 wt% of carbon.