Papers by Author: Hong Chae Park

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Authors: Jae Myung Lee, Jung Kwan Seo, Dae Suk Han, Myung Hyun Kim, Hong Chae Park
Abstract: The objective of this study is to establish a numerical technique applicable for the assessment of damage characteristics of laminate ceramic. A numerical simulator, which can be used for the optimal material design, was developed based on the damage mechanics approach. To evaluate the internal damage evolution behavior within composite material, generalized damage evolution equation was developed and implemented in way of finite element method. By virtue of an automatic data interface between the commercial FEA results and damage calculation, a simple and cost-effective damage evaluation system is constructed. It was found that the developed system can be used for the evaluation of the material performance of composite.
Authors: Hong Chae Park, Hyeong Ho Jin, Yong Taek Hyun, Won Ki Lee, Seog Young Yoon
Abstract: The β-tricalcium phosphate (β-TCP)/ poly(lactide-co-glycolide) (PLGA) composites for biodegradable scaffolds in bone tissue engineering were synthesized by in situ polymerization with microwave energy. The degradation behavior of β-TCP/PLGA composite was investigated by soaking in simulated body fluid (SBF) for 4 weeks. The molecular weight of the β-TCP/PLGA composites decreased with soaking time until week 2, whereas the loss rate of molecular weight reduced after week 2. The incubation time was needed for the degradation of the β-TCP, indicating that the β-TCP should be detached from the PLGA matrix and then degraded into SBF solution. The studies of mass loss of the composites with the soaking time revealed that the degradation behavior of PLGA would be processed with the transformation from the polymer to the oligomer followed by the degradation. Morphological changes, whisker-like, due to transformation and degradation of polymer in the composites were observed after week 2. On the basis of the results, it found that the degradation behavior of β-TCP/PLGA composites was influenced by the β-TCP content in the composite and the degradation rate of the composite could be controlled by the initial molecular weight of PLGA in the composite.
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.
Authors: Dong Hyun Kim, Seog Young Yoon, Hong Chae Park
Abstract: The sedimentation bulk density and rheology of tertiary-butyl alcohol (TBA)-based hydroxyapatite/calcium phosphate glass ceramic suspension system have been examined in terms of oxide solid loading (10, 15 vol.%), and types of additives (dispersant, dispersant/gelator, dispersant/gelator/surfactant), and calcium phosphate glass ceramic content. Sedimentation density of hydroxyapatite decreased by adding calcium phosphate glass ceramic mainly due to the coarse and hence low surface area of calcium phosphate glass ceramic powder; the decrease effect was nearly offset when the dispersant was added. The suspension viscosity generally behaved in an opposite manner to the sedimentation density. A shear thinning rheology was shown in applied shear rate, regardless of processing variables.
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
Authors: Sang Ho Min, Hyeong Ho Jin, B.S. Jun, Ik Min Park, Hong Chae Park, Seog Young Yoon
Abstract: Porous HAp scaffolds have been prepared by using the slurry including HAp and magnesia based on the replication of polymer sponge substrate. The influence of HAp and MgO content in slurry on the pore morphology and size, and density, porosity, and mechanical strength of porous HAp scaffolds was investigated. The obtained scaffolds with average pore sizes ranging 150 to 300 μm had open, relatively uniform, and interconnected porous structure regardless of HAp and MgO content. As the MgO content increased, the pore network frame of scaffolds became to be relatively stronger, even though the pore size was not much changed. The compressive strength of the scaffolds increased rapidly with the increase of MgO content at a fixed HAp content because of increasing the pore wall thickness and density of the scaffolds. As a result, the porosity, density, and compressive strength of the porous HAp scaffolds scaffolds prepared by the sponge method were significantly affected by the addition of MgO.
Authors: Dae Suk Han, Chi Seung Lee, Min Sung Chun, Myung Hyun Kim, Hong Chae Park, Jae Myung Lee
Abstract: For enhanced mechanical properties of ceramics for structural application, a great deal of attention has concentrated on preparation of layered composites. In this study, numerical simulation technique, which is applicable for the evaluation of mechanical performance for layered composite material, was developed. A generalized material constitutive equation coupled with material damage model based on the continuum damage mechanics approach was proposed and has been implemented to an in-house type finite element analysis code. The material behaviors for each component of layered composites can be simulated by the pre-defined material model on the simulation. A series of finite element analyses was carried out in order to elucidate the effect of fabrication related residual stress on the structural capacity of the layered composites.
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.
Authors: Tae Young Yang, S.Y. Yoon, Gun Dae Lee, Chang An Wang, Ron Stevens, Yong Huang, Hong Chae Park
Abstract: Freeze casting is a useful forming technique to produce complex-shaped ceramic parts. The colloidal processing stage is an essential step for preparation of freeze casting slurries. In order to optimize freeze casting slurries, several processing additives, such as dispersant, binder, surfactant, and cryo-protectant are usually employed. Dispersion and suspension rheology of aqueous alumina/ zirconia slurries with 55 and 60 vol.% solid loading have been characterized in terms of the effect of organic additives, and the resulting microstructures of the freeze cast green and sintered materials examined.
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.
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