Papers by Author: Sang Yeup Park

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Authors: Hee Gon Bang, Jun Ho Song, Sang Yeup Park
Abstract: During the sintering process, the onset of abnormal grain growth is depend on various factors. The abnormal grain growth behavior, however, was focused only the growth stage compared to nucleation stage. Because most of abnormal grain growth occurred to a rapid mode, the observation of abnormal grain growth was impossible. In this study, we intend to in-situ observe the nucleation stage of abnormal grain using porous alumina. As a result, the liquid phase due to unintended impurities plays a main role for the formation of abnormal nuclei by the rearrangement of small grains due to the capillary force.
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Authors: Jun Ho Song, Young Jin Jo, Hee Gon Bang, Sang Yeup Park
Abstract: Calcium-hexaluminate phase(CA6) phase is known to be effective for the crack shielding due to the spinel block crystal structure. In this study, we focused to control the CA6 morphology for the good damage tolerance behavior in alumina and zirconia/calcium-hexaluminate(CA6) composites. calcium-hexaluminate(CA6) composites were prepared from zirconia, alumina and calcium carbornate powders. Calcium-hexaluminate(CA6) phase was obtained by the solid reaction through the formation of intermediate phase(CA2). CA6 phase showed column type abnormal grain grown behavior composed of small blocks. Due to the typical microstructure of CA6, alumina and zirconia/calcium-hexaluminate composites provide well controlled crack propagation behavior.
485
Authors: Sang Yeup Park, Jun Ho Song, Young Jin Cho
Abstract: The nucleation and growth behavior of magentoplombite has been observed during the abnormal grain growth in the presence of liquid phase. Abnormal grain growth was explained in terms of grain orientation due to liquid phase. It has been observed that the nuclei formation for abnormal grain growth was driven by the capillary force due to the liquid phase. Because magnetoplumbite crystal structure has an anisotropic crystal nature, abnormal grain growth with faceted grain shape was observed depending on its chemical composition. The formation of nuclei and particle orientation was important for the occurrence of abnormal grain growth.
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Authors: Sung Hwan Kim, Hyun Chan Lee, Hee Gon Bang, Sang Yeup Park
Abstract: In this study, the effect of MgF2 additive on the mechanical properties of hydroxyapatite (HAp)/zirconia composites was investigated. As a fluoride additive, MgF2 was added to HAp/zirconia composites for the suppression of phase decomposition from HAp to tricalcium phosphate (TCP). Due to the dissolution of MgF2 at the phase decomposition temperature of HAp, the phase decomposition of non-stoichiometric HAp was suppressed. When MgF2 (5, 10 vol%) was added to HAp/zirconia composites, the decomposition of HAp was completely suppressed below 1400oC due to the ion substitution F- of for OH- in the HAp crystal structure. The flexural strength and Vickers hardness of composites was revealed more higher values compared with the MgF2-free composites.
478
Authors: Sang Yeup Park, Sung Whan Kim, Hee Gon Bang
Abstract: Mullite whiskers were synthesized by the reaction of fly-ash and alumina powder. During the reaction process, the effect of oxide additives on the formation of mullite whisker was investigated. Mullite whisker was synthesized above 1350oC with the addition of excess alumina, and the aspect ratio of mullite whisker increased with increasing sintering temperature and time. Also, the aspect ratio of mullite whisker is dependent on the liquid phase based on silicate composition. The effect of various oxide additives on the aspect ratio of mullite whisker was investigated.
538
Authors: Sang Yeup Park, Hee Gon Bang
Abstract: Alumina/Alumina: SiC laminate composites were fabricated by the pressureless sintering method. Although the laminate defect, such as channel crack, was observed under the sintering of oxidation atmosphere, laminate defects were eliminated by the sintering of non-oxidation atmospheres. Among various atmospheres, the vacuum atmosphere was effective in the elimination of laminate defects and also for homogeneous microstructure.
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Authors: Sug Woo Jung, Sung Hwan Kim, Sang Yeup Park, Suk Joong L. Kang
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Authors: Sung Jin Kim, Hee Gon Bang, Jung Wook Moon, Sang Yeup Park
Abstract: The enhancement of physical properties of porous honeycomb filter for air purification was investigated using cordierite with the addition of pore former and zirconia additive. Because cordierite honeycomb has porous body, binder formulation was varied using graphite for a pore forming agent as well as lubricating agent during the extrusion process. Also, the effect of zirconia additives on the resultant physical properties of honeycomb filter such as porosity, thermal expansion coefficient and mechanical strength was investigated.
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