• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.823-828
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• 1994

Dispersion condition of Si3N4 powder in molten wax was established by comparing relative viscosity of mixture with 20 vol% solids loading, while the evaluation of compression-molded sample was demonstrated as an effective method for developing a binder system for injection molding. The best dispersion of Si3N4 powder in molten wax was achieved when Si3N4 powder was treated with 5% stearic acid, and the critical powder volume fraction was determined to be about 0.51 from density measurement of compression-molded samples. Samples containing polar secondary binder showed markedly improved green strength, higher thermal expansion and increased wicking rate in the early stage.

• Journal of the Korean Ceramic Society
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• v.35 no.9
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• pp.911-916
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• 1998

By using {{{{ { { {Y }_{3 }Al }_{5 }O }_{12 } }} (YAG) and SiO2 as sintering additives the effect of the composition of sintering ad-ditives on microstructure and mechanical properties of the hog-pressed and subsequently annealed SiC ma-terials were investigated. Microstructures of sintered and annealed materials were strongly dependent onthe composition of sintering additives. The average diameter and volume fraction of elongated grains in an-nealed materials increased with the SiO2/YAg ratio while the fracture toughness increased with the SiO2/YAg ratio. The average MPa.{{{{ { m}^{1/2 } }} respectively. Typical strength and fracture toughness of an annealed material with SiO2/YAg ra-tionof 0.67 were 371 MPa and 5.6 MPa.{{{{ { m}^{1/2 } }} respectively.

• Journal of the Korean Ceramic Society
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• v.32 no.2
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• pp.147-154
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• 1995

Abnormal grain growth behavior of BaTiO3 ceramics with controlling of particle size distribution of calcined powder was investigated. The particle size distribution was controlled by changing the calcining temperature or by using of classification and regrinding process. With broadening of the normallized size distribution in calcined powder, it showeda normal grain growth behavior in sintered body due to an increase of volume fraction of seed grain in the calcined powder. It was supposed that the seed grains could easily contact each other for the rapid grain growth during sintering process and resulted in fast switching-over from abnormal to normal grain growth stage.

• Journal of the Korean Ceramic Society
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• v.29 no.5
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• pp.341-346
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• 1992

The effects of CaO addition on the low temperature degradation behavior of 2.5Y-TZP ceramics were investigated. Y2O3-CaO-ZrO2 ceramics were prepared from the commercial Y-TZP powder added within 1 mol% of CaO. Fully tetragonal phase could be obtained at each composition under sintering condition of 1500$^{\circ}C$ for 1 hour. As the amount of CaO increased, grain size was decreased. From the result of heat treatment at 200$^{\circ}C$, volume fraction of monoclinic phase formed on the surface of each specimen was decreased with higher CaO amount. Stability of tetragonal ZrO2 phase for low temperature heat treatment was increased by CaO addition without the degradation of mechanical properties.

• Journal of the Korean Ceramic Society
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• v.31 no.2
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• pp.227-233
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• 1994

The Bi-Sr-Ca-Cu-O thin films were deposited by RF-magnetron sputtering method on Si(P-111) wafer without a buffer layer and annealed at various temperatures in oxygen atmosphere. The temperature dependence of electrical resistance, the microstructure of intermediate phase, and the surface morphology of films were examined by four probe method, XRD, and SEM, respectively. The chemical composition and the depth profile of the films were determined by ESCA spectra. Thin films annealed at $600^{\circ}C$ and $700^{\circ}C$ in oxygen atmosphere showed onset temperatures of 90 K and 85K, and Tc(zero) of 22K and 31K, respectively. The sample annealed at $700^{\circ}C$ had the highest volume fraction of superconducting phase and showed smooth microsturcture. In ESCA spectra, the thin films were homogeneous with depth.

• Journal of the Korean Ceramic Society
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• v.47 no.1
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• pp.8-18
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• 2010

When metal oxides are exposed to chemical potential gradients, ions are driven to diffusive mass transport. During this transport process, the divergence of ionic fluxes offers the formation/annihilation of oxides. Therefore, the divergence of ionic flux may play an important role in the void formation in oxides. Kinetic equations were derived for describing chemical potential distribution, ionic fluxes and their divergence in oxides. The divergence was found to be the measure of void formation. Defect chemistry in scales is directly related to the sign of divergence and gives an indication of the void formation behavior. The quantitative estimation on the void formation was successfully applied to a growing magnetite scale in high temperature oxidation of iron at 823 K.

• Journal of the Korean Ceramic Society
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• v.32 no.10
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• pp.1131-1138
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• 1995

Variations of piezoelectric properties and compressive strength of Sr-doped PZT ceramics were investigated with poling direction. The electro-mechanical coupling constants (k31 and k33) were increased linearly with increasing poling strength. The volume fraction of intergranular fracture also increased with incresing poling strength due to weakening of grain boundaries by domain rearrangement during poling process. The internal stresses induced from the poling at 2.5 kV/mm parallel and perpendicular to the poling direction poled were 405 MPa and 89 MPa, respectively. The compressive strength of the specimen poled parallel to the poling direction was higher than that perpendicular to the poling direction.

• Journal of the Korean Ceramic Society
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• v.26 no.4
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• pp.550-558
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• 1989

Polycrystalline diamond films have been deposited on Si wafer Ly hot W filament CVD method using CH4H2 mixtures. The effects of surface pretreatment, W filament temperature, CH4 volume fraction, and addition of water vapor on the growth rate and morphology of the films were investigated. Surface pretretment was essential for depositing a continuous diamond film. Raising the filament temperature resulted in an increased growth rate and a better crystal quality of the film. As the methane content is varied from 0.5% to 5%, well-faceted crystals gradually transformed into spherical particles of non-diamond phase with a simultaneous increase in the growth rate. Addition of water vapor markedly improved the crystallinity to produce crystalline particles even with 5% methane mixture.

• Journal of the Korean Ceramic Society
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• v.32 no.5
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• pp.587-593
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• 1995

Abnomal grain growth behavior of BaTiO3 ceramics was investigated with addition of seed grains. It was foudn that the nucleation rate of abnormal grain was constant and growth of abnormal grain was linearly increased with sitnering time, regardless of amount of seed grains. These facts were also confirmed by fitting of the volume fraction of abnormal grain vs. sintering time using Avrami type equation (n=4). It was suggested that seed grains did not change the nucleation rate or growth mechanism of abnormal grain but increase the number of abnormal grains at initial stage of sintering and then it led to fine microstructure of BaTiO3 ceramics.

• Journal of the Korean Ceramic Society
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• v.50 no.4
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• pp.294-300
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• 2013

The effect of chemical treatments of porous silicon in organic solvents on its nanostructural and optical features was investigated. When the porous Si was dipped in the organic solvent with various PH values, the morphological, chemical, and structural properties of the porous silicon was sensitively affected by the chemical conditions of the solvents. The size of silicon nanocrystallites in the porous silicon decreased from 5.4 to 3.1 nm with increasing pH values from 1 to 14. After the samples were dipped in the organic solvents, the Si-O-H bonding intensity was increased while that of Si-H bonding decreased. Photoluminescence peaks shifted to a shorter wavelength region in the range of 583 to 735 nm as the pH value increased. PL intensity was affected by the size as well as the volume fraction of the nanocrystalline silicon in the porous silicon.