• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.710-714
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• 2006

Barium titanate nanoparticles were synthesized under N$_2$ atmosphere by the hydrolysis and condensation of barium hydroxide octahydrate and titanium (IV) isopropoxide. The synthesized particles were aggregates of nanosized primary particles. The primary particles of about 20-50 nm in diameter became building blocks of larger secondary particles, which are in most cases spherical in shape. The size and morphological evolution of secondary particles are strongly related to the precursor concentration. The observations suggest that formation and control of secondary particles is an essential step in the alkoxidehydroxide sol-precipitation process to obtain monodispersed barium titanate nanopowders.

• Korean Journal of Materials Research
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• v.12 no.12
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• pp.930-934
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• 2002

Nanosized $WO_3$ powders were synthesized by the sol-precipitation process using $WCl_{6}$ as the starting material, ethanol as a solvent and $NH_4$OH solution as a precipitant, followed by a washing-drying treatment and calcination. The effects on the powder crystallinity and microstructure of calcination temperature were investigated with XRD and FE-SEM. The $WO_3$ powders calcined at $500^{\circ}C$ and $700^{\circ}C$ showed good crystallinity and their mean particle size was 30nm and 70nm, respectively. These powders were used for the preparation of pastes which were printed as thick films on alumina substrates with comb-type Pt electrodes. The particle size strongly influenced the $NO_2$ gas sensing property of the thick films. A significant reduction in the $NO_2$ sensitivity was observed for the film prepared from larger particle size, having thus a larger grain size. For the film having a smaller grain size, on the other hand, the higher $NO_2$ sensitivity was observed and the sensitivity increased with $NO_2$ concentration.

• Korean Journal of Materials Research
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• v.23 no.8
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• pp.441-446
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• 2013

There is increasing interest in zirconia as a dental material due to its aesthetics, as well as the exceptionally high fracture toughness and high strength that are on offer when it is alloyed with certain oxides like yttria. In recent years, many solution based chemical synthesis methods have been reported for synthesis of zirconia, of which the sol-gel method is considered to be best. Here, we synthesize zirconia by a sol gel assisted precipitation method using either PEG or PVA as a stabilizing agent. Zirconia sol is first synthesized using the hydrothermal method. We used NaOH as the precipitating agent in this method because it is easy to remove from the final solution. Zirconium and yttrium salts are used as precursors and PEG or PVA are used as stabilizers to separate the metal ions. The resulting amorphous zirconia powder is calcined at $900^{\circ}C$ for 2 h to get crystallized zirconia. XRD analysis confirmed the partially stabilized zirconia synthesis in all the synthesized powders. SEM was taken to check the morphology of the powder synthesized using either PEG or PVA as a stabilizing agent and finally the transparency was calculated. The results confirmed that the powder synthesized with 10 % PVA as the stabilizing agent had highest percentage of transparency among all the synthesized powder.

• Journal of the Korean Applied Science and Technology
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• v.34 no.4
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• pp.883-891
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• 2017

For the preferential oxidation of CO contained in the fuel of polymer electrolyte membrane fuel cell (PEMFC), CuO-$CeO_2$ mixed oxide catalysts were prepared by the sol-gel and co-precipitation methods to replace noble metal catalysts. In the catalyst preparation by the sol-gel method, Cu/Ce ratio and hydrolysis ratio were changed. The catalytic activity of the prepared catalysts was compared with the catalytic activity of the noble metal catalyst($Pt/{\gamma}-Al_2O_3$). Among the catalysts prepared with different Cu/Ce ratios, the catalyst whose Cu/Ce ratio was 4:16 showed the highest CO conversion (90%) and selectivity (60%) at $150^{\circ}C$. As the hydrolysis ratio was increased in the catalyst preparation, surface area increased, and catalytic activity also increased. The highest CO conversions with the CuO-$CeO_2$ mixed oxide catalyst prepared by the co-precipitation method and the noble metal catalyst (1wt% $Pt/{\gamma}-Al_2O_3$) were 82 and 81% at $150^{\circ}C$, respectively, whereas the highest CO conversion with the CuO-$CeO_2$ mixed oxide catalyst prepared by the sol-gel method was 90% at the same temperature. This indicates that the catalyst prepared by the sol-gel method shows higher catalytic activity than the catalysts prepared by the co-precipitation method and the noble metal catalyst. From the CO-TPD experiment, it was found that the catalyst having CO desorption peak at a lower temperature ($140^{\circ}C$) revealed higher catalytic activity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.988-991
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• 2002

ITO (Indium Tin Oxide) powder was synthesized by precipitation method. ITO colloidal solutions for coating on glass were fabricated by ball milling method. ITO colloidal solution with variation of concentration from 2% to 15% were fabricated ITO thin film measured sheet resistance and transmittance. In the result, 15% sol showed the lowest value of sheet resistance, 2% sol showed the highest value of transmittance. In addition, effect of annealing temperature and $SiO_2$ film were investigated.

• Journal of the Korean Chemical Society
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• v.65 no.2
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• pp.125-132
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• 2021

An electrochromic nickel oxide thin film was fabricated on a flexible PET/ITO substrate using a nanocrystallite- dispersed coating sol and bar coater. Nanocrystalline NiOx of 3-4 nm crystallite size was first synthesized by base precipitation and thermal conversion. This NiOx nanocrystallite powder was mechanically dispersed in an alcoholic solvent mixed with a silane binder to prepare a coating sol for thin film. This sol method is different from the normal sol-gel method in that it does not require the conversion of precursor by heat treatment. Therefore, this method provides a very facile method to prepare NiOx thin films on any kind of substrate and it can be easily applied to mass production. The electrochromic performance of this NiOx thin film on PET/ITO electrode with a thickness of about 400 nm was investigated in a nonaqueous LiClO4 electrolyte solution by cyclic voltammetric and repeated chronoamperometric measurements in conjunction with spectrophotometry. The visible light modulation of 44% and the colorization efficiency of 41 ㎠/C at 550 nm were obtained at the step potentials of -0.8/+1.2 V vs Ag and a duration of 30 s.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.183-190
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• 2022

Diopside (CaMgSi₂O₆) is known to have high bioactivity as well as excellent mechanical properties. In this study, we tried to improve the bioactivity of zirconia ceramics by surface coating of diopside and its bioactivity was investigated through an in vitro test. Surface coating on zirconia substrate was prepared by sol-gel method using a diopside sol which was prepared by dissolving Ca(NO₃)₂·4H₂O, MgCl₂·6H₂O and Si(OC₂H₅)₄ in ethanol with a fixed molar ratio and then hydrolysis. To examine the bioactivity of diopside coating, we examined the surface dissolution and the precipitation of new hydroxyapatite particles through in vitro test in SBF (Simulated Body Fluid) solution. Dense and thick diopside coating layers could be fabricated on zirconia substrate by sol-gel method. Also, we confirmed that they contained high bioactivity from the in vitro test, indicated the precipitation of hydroxyapatite particles after the 14 days immersion in SBF solution. In addition, we checked that the bioactivity of diopside coated layers was dependent on the repeated coating cycle and coating thickness.

• Journal of the Korean Ceramic Society
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• v.34 no.9
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• pp.941-948
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• 1997

CuCl nanocrystallites dispersed nonlinear optical silica and borosilicate glasses were fabricated by sol-gel process. CuCl powder was dissolved in TEOS(Si(OC2H5)4) and TMB((CH3O)3B), precursors of silica and borosilicate glasses, with ethanol, water and HCl, and precipitated through the heat treatment in the matrix glass. The optical properties of CuCl doped glasses were measured using the spectrophotometer at room temperature and low temperature(77K); Z1, 2 and Z3 exciton peaks from the absorption spectra, were observed at about 370 nm and 380 nm, respectively. The average radius of nanocrystallites, calculated from the blue shift of Z3 excitons, was measured according to annealing temperature and time. The precipitation temperature of CuCl nanocrystallites was decreased when boron was added to silica glass. Increase of annealing temperature and time made average radius of nanocrystallites saturated about 2 nm.

• Journal of Powder Materials
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• v.10 no.5
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• pp.310-317
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• 2003

Two-component ceramic (alumina-zirconia) composites were fabricated by a soft-solution process in which polyethylene glycol (PEG) was used as a polymeric carrier. Metal salts and PEG were dissolved in ethyl alcohol without any precipitation in 1:1 volume ratio of alumina and zirconia. In the non-aqueous system, the flammable solvent made explosive, exothermic reaction during drying process. The reaction resulted in formation of volume expanded, porous precursor powders by a vigorous decomposition of organic components in the precursor sol. The PEG content affected the grain size of sintered composites as well as the morphology of precursor powders. The difference of microstructure in sintered composite was attribute to the solubility and homogeneity of metal cations in precursor sol. At the optimum amount of the PEG polymer, the metal ions were dispersed effectively in solution and a homogeneous polymeric network was formed. It made less agglomerated particles in the precursor sol and affected on uniform grain size in sintered composite.

• Journal of the Korean Ceramic Society
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• v.31 no.5
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• pp.499-504
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• 1994

PbTiO3 thin films were prepared by sol-gel spin coating method using metal alkoxide and diethanolamine (DEA). The precipitation of the PbTiO3 sol occurred at pH 7.3 with HNO3 addition, regardless of the amount of DEA. The gelation time of the PbTiO3 sol was reduced with increasing amount of HNO3 and/or water. When the PbTiO3 films prepared by 0.2 molar coating solution were annealed at $650^{\circ}C$ for 30 min, dense and single phase perovskite films were obtained. Dielectric constant and loss tangent of the film were 239 and 0.01 at 1 kHz, respectively.