• Journal of the Korean Ceramic Society
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• v.46 no.6
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• pp.653-656
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• 2009

Alumina bushing used for manufacturing glass fiber was fabricated by gel-casting which can fabricate complex forms. When solid loading is increased, density was increased and shrinkage and absorption were decreased. The sample loading with 57 vol% solid was optimum for alumina suspension, which showed the best physical properties. The cast sample was sintered at $1550{^{\circ}C}$ for two hours with sintering additive, $Y_2O_3$. The result showed that the alumina bushing with $Y_2O_3$ sintering additive has a density of 98%, shrinkage of 11% and bending strength of 196 kg/$cm^2$.

• Journal of the Korean Ceramic Society
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• v.45 no.2
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• pp.99-104
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• 2008

Zeta potential, sedimentation bulk density and rheology in the dispersion system have been studied in terms of solid loading (40-55 vol%), and types of additives. Ammonium polymethacrylate, glycerol, ethoxylated acetylenic diol, and polyvinyl alcohol have been used as the dispersant, cryo-protectant, surfactant, and binder, respectively. Sedimentation density greatly increased upon adding dispersant; the effect was more pronounced with ionic alumina suspension compared with covalent silicon carbide. With further addition of cryo-protectant and surfactant to dispersant, the sedimentation density increased somewhat. The suspension viscosity generally behaviored in an opposite manner to the sedimentation density, i.e., high sedimentation gave low high-shear viscosity, indicative of low order structure formation in the suspended particles. Shear rate rheology in shear rate of $2-300\;sec^{-1}$ showed a shear thinning and its onset began at similar shear rate (${\sim}100\;sce^{-1}$), regardless of solid loading.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.224-230
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• 1999

Agglomeration of colloidal alumina particles in a suspension is simulated. Particles in a suspension have potential energies between them and move to decrease the summation of all the potential energies between particles. The effects of various types of potential curves on particle agglomeration were checked. Strong short range attractive energy without repulsive energy barrier makes small strong clusters with disordered network structure but weak short-range force with big repulsive energy barrier makes big agglomerates with a close packing structure. As particles are agglomerated the potential energy with strong repulsive energy barrier between agglomerates gradually decreases the importance of the repulsive energy barrier and induces a different type of agglomeration behavior.

• Journal of the Korean Ceramic Society
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• v.42 no.1
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• pp.1-6
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• 2005

In aqueous alumina tape casting, the effects of altering the composition of the suspensions, the binders and the casting thickness were studied. The rheological behavior of the suspensions and the defects of the dried tapes were examined and the relationships between them are discussed. The changes in the defect regions reported in the previous paper were related with the rheological properties with variations of the binder, the composition and the casting thickness. The shear thinning factor increased with the organic content and the solid content (the decrease of water content). The apparent viscosity increased with the shear thinning factor. The relation between the shear thinning factor and the log apparent viscosity was similar for all binder types. In the relation between the defect free region and the rheological properties, the defect free region became narrower with increasing casting thickness. The defect free region is independent of binder type. Therefore, the thicker tape is more difficult to produce in aqueous alumina tape casting. Knowledge of the rheological properties of the suspensions could help Predict the defect type and the possibility of defect free dried tapes.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1107-1108
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• 2006

The coating of conductive polypyrrole (Ppy) on nonconductive ceramic substrates was performed by polymerization of pyrrole (Py) in an aqueous solution. The Ppy film was characterized by scanning electron microscopy and conductivity measurements. Electrophoretic deposition of bimodal alumina suspension prepared with a phosphate ester was performed using Ppy film as a cathode. Fabrication of alumina ceramics with irregular shapes or complicated patterns were also attempted by sintering the deposits together with the Ppy coated substrates in air.

• KIEE International Transactions on Electrophysics and Applications
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• v.3C no.5
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• pp.165-170
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• 2003

This paper presents development of solid core suspension disc insulators (cap and cap suspension disc insulator) for replacing cap and pin suspension disc insulators in overhead transmission and distribution lines which expose to lightning discharges. By this means the punctured problem caused by steep front surge voltage created by lightning discharge on the lines can be solved. The solid core suspension insulator was designed and constructed based on the dimensions of conventional suspension disc insulators (cap and pin insulators). The insulators are made of alumina porcelain. The electrical and mechanical characteristics of the solid core suspension insulators were carried out. The puncture test was performed in the air by applying steep front impulse voltage with amplitude about 2.5 per unit of 50% flashover (CFO) of the insulator unit at negative standard lightning impulse $1.2/50\;\mu\textrm{s}$ with steepness up to $9200\;kV/\mu\textrm{s}$. The testing results show that solid core suspension disc insulators are not punctured eventhough the steepness of the steep front impulse voltage was increased up to $9200\;kV/\mu\textrm{s}$.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.1
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• pp.8-13
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• 2005

In order to analyze the properties of domestically produced 36,000lb porcelain insulators by change of the alumina addition to raw materials, 36000lb ball socket type suspension insulators that were manufactured in 1989, 1995 and 2001 were removed from transmission lines and an experiment was performed. The results indicated that 8 [wt.%] alumina, which influences the mechanical properties and arc resistance properties in the case of insulators that were manufactured in 1989 was contained, and the relative density and the fracture toughness of insulators appeared by 94.2% and 1.4 [MpaㆍM/sup 1/2/], respectively. However, 12 [wt.%] alumina was contained in the case of insulators that were manufactured in 1995, and the relative density and the fracture toughness of insulators appeared preferably lower by 92% and 1.3 [MpaㆍM/sup 1/2/], respectively. The greatest amount of alumina was contained by 17 [wt.%] in the case of insulators that were manufactured in 2001. It was confirmed that the electrical and mechanical characteristics such as the relative density and the fracture toughness appeared remarkably by 96% and 1.7 [Mpaㆍm/sup 1/2/], respectively.

• Journal of the Korean Ceramic Society
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• v.40 no.3
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• pp.293-300
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• 2003

It was investigated that effect of suspension and electrolyte concentrations on zeta potential of alumini suspension and Iso-Electric Point(I.E.P.). The alumina powders in 0.1∼l $\mu\textrm{m}$ particle size distribution, and the electrolyte NH$_4$NO$_3$ were used for preparing the suspension and electrophoresis method was used for measuring zeta potential in this work. As the concentration of suspension was increased, zeta potential and the I.E.P. were increased, respectively. On the other hand, as the electrolyte concentration was increased, the I.E.P. was decreased. As a result of this work, the best condition for measuring zeta potential was the 0.01 wt% and 10 mM of the suspension and the electrolyte concentration, respectively.

• Membrane Journal
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• v.25 no.1
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• pp.15-26
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• 2015

In this study, porous metal (O.D. = 10 mm, length = 10 mm, 316 L SUS, Mott Corp.) and ${\alpha}$-alumina tube (O.D. = 10 mm, length = 50 mm, Pall, German) support was modified with suspension sols, which were consisted of $3{\sim}4{\mu}m$ and 150 nm size of ${\alpha}$-alumina particle in the water or silica-zirconia colloidal sol. The porous support was fabricated by dip coating method for 5 seconds with suspension of alumina particles. After drying at $100^{\circ}C$ for 1 h, it was calcined at $550^{\circ}C$ for 30 min. It was repeated several times in order to decrease big pore on support. The surface roughness and largest pore size on the porous support was decreased by increasing coating times with $3{\sim}4{\mu}m$ size of ${\alpha}$-alumina particle and alumina coating with 150 nm size of ${\alpha}$-alumina particle served as further smoothening the surface and decreasing the pore size of the substrate. And the silica-zirconia membranes were successfully prepared on the modified porous metal and ${\alpha}$-alumina supports, and showed hydrogen permeance in the range of $1.8-8.4{\times}10^{-4}mol{\cdot}m^{-2}{\cdot}s^{-1}{\cdot}Pa^{-1}$ and $3.3-5.0{\times}10^{-5}mol{\cdot}m^{-2}{\cdot}s^{-1}{\cdot}Pa^{-1}$, respectively.

• Korea-Australia Rheology Journal
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• v.20 no.2
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• pp.65-71
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• 2008

Pressure filtration technique was used to obtain defect-free microstructure of green cast ceramic bodies. Stable alumina suspensions of desired rheology (<5 Pa s at $1\;s^{-1}$) containing 60-80 mass. % solid loading were prepared in the alkaline region (at $pH{\approx}9$) with an optimum amount of 0.5 dmb % of Tiron added. Acidic region (at $pH{\approx}4$) enabled the preparation of 60 mass. % suspensions with addition of 1.5 dmb % of Tiron. The best quality slip was processed from an 80 mass.% suspension with 63% of theoretical density. The homogeneity of particle packing and the absence of defects in microstructure were proven by narrow pore size distribution (ranging from 32 to 64 nm, with up to 85% abundance), confirming advantages of the wet consolidation route.