• 한국전기화학회:학술대회논문집
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• 2004.06a
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• pp.115-118
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• 2004

• Korean Journal of Materials Research
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• v.26 no.3
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• pp.136-142
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• 2016

To study the dispersion factors of silica sol prepared from fumed silica powder, we prepared silica sol under an aqueous system using a batch type bead mill. The dispersion properties of silica sol have a close relationship to dispersion factors such as pH, milling time and speed, the size and amount of zirconia beads, the solid content of fumed silica, and the shape and diameter of the milling impellers. Especially, the silica particles in silica sol were found to show dispersion stability on a pH value above 7, due to the electrostatic repulsion between the particles having a high zeta potential value. The shape and diameter of the impellers installed in the bead mill for the dispersion of fumed silica was very important in reducing the particle size of the aggregated silica. The median particle size ($D_{50}$) of silica sol obtained after milling was also optimized according to the variation of the size and amount of the zirconia beads that were used as the grinding medium, and according to the solid content of fumed silica. The dispersion properties of silica sol were investigated using zeta potential, turbiscan, particle size analyzer, and transmission electron microscopy.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 2000.06a
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• pp.143-150
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• 2000

Wet-chemical process using ammonia to precipitate aluminum ion dissolved in a zirconia sol solution is examined. Formation of crystalline bayerite is unfavorable for fine dispersion of zirconia nanoparticles in alumina matrix after heat treatment. To avoid the bayerite formation, it was preferred to make a precipitation with a diluted ammonia or with an ammonia gas flow at high temperature. By optimizing the precipitation process and the calcination temperature, we successfully prepared the uniform microstructure in which tetragonal zirconia particles of ∼30nm is finely dispersed within the alumina grains.

• 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.29 no.1
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• pp.35-40
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• 1992

Porous glass in the ZrO2-SiO2 system containing up to 30 mol% zirconia were prepared from the mixed solutions of Zr(O.nC3H7)4 and partially prehydrolyzed TEOS by the sol-gel method. Pore characteristics, physical properties and alkali resistance were investigated. The gels converted into the porous glass by heating at $700^{\circ}C$, it was found that the glass like skeleton was already made up in lower temperature regions. The specific surface area of the porous glass was 227 $m^2$/g, average mean pore size was about 19$\AA$ and porosity was 19.2%, pore characteristics and physical properties depended on heating temperature. Alkali resistance of the porous glass increased as the zirconia content increased, because of the appearance of Zr-enriched layer at glass surface.

• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1475-1482
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• 1994

Compositionally triphasic boehmite-silica-zirconia composite gels were prepared by a multiphasic sol-gel route. Phase-formation characteristics and densification behavior of the gel compacts were examined with and without $\alpha$-Al2O3 seeding. In the unseeded triphasic gels, both $\alpha$-Al2O3 and mullite crystallize simultaneously at 130$0^{\circ}C$. On the other hand, the $\alpha$-Al2O3 seeding selectively induces the formation of corundum phase ($\alpha$-Al2O3) at a significantly lower temperature (~110$0^{\circ}C$) and facilitates an epitaxial growth of $\alpha$-Al2O3 between 1100~130$0^{\circ}C$. The densification of alumina-mullite-zirconia composite (derived from the triphasic gels) was also enhanced by the $\alpha$-Al2O3 seeding, and this was attributed to the delayed crystallization of mullite in the $\alpha$-Al2O3 seeded gel.

• Proceedings of the Korea Crystallographic Association Conference
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• 2003.05a
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• pp.20-20
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• 2003

A new and simple method has been developed to synthesize highly crystalline and monodisperse maghemite (γ-Fe₂O₃) and zirconia (ZrO₂) nanocristallites. High temperature aging of metal-surfactant complex was founded to generate monodisperse nanoparticles, wherein the nuclei were prepared by the thermal decomposition of iron-oleate complex in case of iron oxide and nonhydrolytic sol-gel reaction in case of zirconia respectively. By varying the experimental conditions, in other words concentration of surfactants, kind of metal precursor, reaction temperature and so on, the diameter of spherical nanoparticles could be controlled at various size. The synthesized nanoparticles were characterized by electron diffraction, X-ray diffraction, and low- and high-resolution transmission electron microscope.

• Journal of the Korean Applied Science and Technology
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• v.20 no.4
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• pp.358-365
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• 2003

Zirconium nitride powders were synthesized at a relatively lower temperature using methane as a reducing agent in the nitridation of zircoia. $ZrO_2$ powder was prepared by a sol-gel technique. The resulting sol-gel was centrifuged, and the gel was washed with deionized water. Anhydrous ammonia was used as the nitrogen source and methane was used as the reducing agent. Conversion diagrams show the equilibrium solid phase as a function of reagent concentrations for a specific temperature and gas pressure for the reagent system $NH_3-ZrO_2-CH_4$. The reagent concentration ranges within which pure ZrN is formed increase with increasing reaction temperature. Low pressure with an excess of hydrogen decreases the reaction temperature at which pure ZrN is formed. Low pressure together with the introduction of excess hydrogen into the reaction system increases Zr and N conversion efficiency and retards C deposition.

• The Korean Journal of Ceramics
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• v.1 no.3
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• pp.160-164
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• 1995

Mechanical and chemical tests were performed on $Zro_2 \cdot SiO_2$ glass fibers manufactured by the sol-gel method and E-glass fibers-reinforced cement composites in order to investigate the interactions between glass fibers and cement matrices. Chemical attack leads to corrosion of the glass fiber surfaces. In the corrosion reactions, the surface of $30ZrO_2 \cdot 70 SiO_2$ glass fibers developed a densified concentric layer, which consists of glass corrosion products with much higher Zr and lower Si than the fresh glass fiber. The layer of reaction product is regarded to stiffen the cement matrices and provide a useful improvement to the mechanical properties. The addition of $ZrO_2$ content increases the corrosion resistance of glass fibers in cement by forming a passivating layer on the surface of glass fibers.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.824-828
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• 1990

Zirconia gel fibers were fabricated by sol-gel processing using zirconium alkoxides and 2, 4-pentanedione. Their phase transformation and microstructural evolution were studied after heat treatments up to 150$0^{\circ}C$. Tetragonal ZrO2 began to form at 50$0^{\circ}C$ and followed by monoclinic, tetragonal phase during subsequent heat treatments at 1000, 150$0^{\circ}C$ for 1hour respectively. During cooling from 150$0^{\circ}C$, cracks were created, propagated along grain boundaries due to the volume change from tetragonal to monoclinic transformation.