Papers by Author: Young Min Park

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Authors: Tae Young Yang, Young Min Park, Gun Dae Lee, Seog Young Yoon, Ron Stevens, Hong Chae Park
Abstract: The sedimentation density significantly decreased after addition of dispersant; the effect was more pronounced with pure alumina, as compared with SiC-containing slurry. With further addition of surfactant, the sedimentation density increased somewhat, but decreased with binderadditions. The suspension viscosity generally behaved in an opposite manner to the sedimentation density, i.e., low sedimentation density gave high low-shear viscosity, indicative of high structure formation in the suspended particles. Shear rate rheological measurements showed continuous shear thinning behavior.
1035
Authors: Yong Yee Kim, Young Min Park, Hoy Yul Park, Hong Chae Park, Seog Young Yoon
Abstract: Monodispersed Cu powders were prepared in aqueous solution through a wet-reduction process with hydrazine hydrate (N2H4·H2O). In particular, the effect of the dispersant such as sodium pyrophosphate decahydrate (Na4O7P2·10H2O), carboxymethyl cellulose sodium salt (CMC) in water solvent on the particle size for the prepared Cu powders was investigated. The Cu powders essentially were monodispersed and irregular in shape regardless of reaction temperature and dispersant. In the case of adding the Na4O7P2·10H2O, the particle size of Cu powders increased with the increase of reaction temperature, which the particles were agglomerated in irregular shape and became to be large. The particle size distributions was asymmetry and to be broad regardless of reaction temperature. On the other hand, when the CMC was added, the particle size of Cu powders, which were much finer compared with adding the Na4O7P2·10H2O as a dispersant, was not much changed with reaction temperature. The particle size distribution of Cu powder was much narrow regardless of reaction temperature. As a result, it would be suggested that the CMC was more effective dispersant reagent to produce the monodispersed and fine Cu powders with narrow size distribution using the wet chemical reduction process
2118
Authors: Seung Woo Lyu, Dae Seok Han, Young Min Park, Tae Young Yang, Jae Myung Lee, Hong Chae Park
Abstract: Symmetric three-layer Al2O3/ZrO2 composites have been prepared by freeze casting and pressureless sintering at 1400-1600o C in air. The layered composite with Al2O3 containing 15 vol.% ZrO2 as an outer layer and containing 20 vol.% ZrO2 as an inner layer, sintered at 1600o C showed the maximum bend strength (300 MPa). Contact damage resistance was superior in layered composites compared with monolithic materials, possibly due to the development of compressive stress in the outer layer.
351
Authors: Young Min Park, Tae Young Yang, Seog Young Yoon, Ron Stevens, Hong Chae Park
Abstract: Calcium deficient (Ca/P = 1.53-1.61, molar ratio) whisker shaped hydroxyapatite (HAp) with a high aspect ratio ~26 (diameter: 0.2-0.3 µm) has been prepared by the hydrolysis of a-Ca3(PO4)2 (a-TCP) in an aqueous solvent system under controlled conditions. The influence of processing variables on the conversion of a-TCP to HAp, and the microstructure and composition of the HAp was characterized by means of XRD, SEM, TEM and ICP instruments.
1511
Authors: Tae Young Yang, Seung Woo Lyu, Young Min Park, Seog Young Yoon, Ron Stevens, Hong Chae Park
Abstract: Symmetric three-layer composites prepared by sintering freeze cast compacts of alumina with additions of nanoparticle/whisker SiC, in 1-atm nitrogen at 1700-1800oC have been characterized in terms of microstructure and mechanical properties. Additions of SiC to Al2O3 result in improvement in toughness. In such cases, however, the reduction in strength at small flaw sizes must be overcome. Contact damage resistance is greatly increased in layered composites compared with monolithic composites, possibly due to redirection of indentation flaws along the layer interface.
2583
Authors: Young Min Park, Tae Young Yang, Seog Young Yoon, Hong Chae Park
Abstract: Tetragonal zirconia polycrystal ceramics prepared by sintering compacts of 3 mol.% Y2O3- and 12 mol.% CeO2-doped ZrO2 powders, in air at 1400o and 1500o C have been characterized in terms of microstructure and mechanical properties. With increasing 12 mol.% CeO2-doped ZrO2 content, the average grain size of sintered materials increased in the range 0.27-1.93 μm. The bend strength and indentation fracture toughness were 374-962 MPa and 6-10 MPa.m1/2 respectively, dependent on batch composition.
355
Authors: Seung Woo Lyu, Young Min Park, Tae Young Yang, S.C. Ryu, Ron Stevens, Hong Chae Park
Abstract: The dispersion and rheological behavior of aqueous alumina, zirconia, and mixed alumina/ zirconia slurries have been studied in terms of solid loading and the incorporated multiple processing additives. Darvan-C, Dynol 604, Glycerol, and PVA were used as the dispersant, surfactant, cryoprotectant, and binder, respectively. Sedimentation density increased significantly on adding the dispersant; its effectiveness was similar for both the alumina and zirconia suspensions. With further addition of binder, the sedimentation density decreased. The suspension viscosity generally behaved in an opposite manner to the sedimentation density, i.e., low sedimentation density gave high low-shear viscosity, indicative of high order structure formation in the suspended particles. Shear rate rheology of suspensions with high dispersant content showed a shear thinning but with low dispersant content (≤2 wt.%), however, it showed a shear thickening at high shear rate (>600 s-1).
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