Papers by Author: Tae Whan Hong

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Authors: J.H. Choi, H.S. Yoo, K.W. Cho, N.K. Kim, S.H. Oh, E.S. Choi, S.J. Yeom, H.J. Sun, S.S. Lee, K.N. Lee, Suk Kyoung Hong, Tae Whan Hong, Il Ho Kim, Sung Lim Ryu, Soon Young Kweon
Abstract: A 16Mb 1-transistor /1-capacitor (1T1C) FeRAM device was fabricated with lead-free Bi3.25La0.75Ti3.0O12 (BLT) capacitors. The key integration processes contain a scalable MTP (Merged Top-electrode and Plate-line) cell structure and reliable BLT ferroelectric capacitors. Ferroelectric properties of BLT films were optimized on the newly developed MTP cell structure. BLT films were coated on Pt/IrOx/Ir bottom electrode using sol-gel solutions. The composition of the optimized BLT film was about Bi3.25La0.75Ti3.0O12. The switchable polarization obtained in a 100nm-thick BLT film was about 20 µC/cm2 at the 3 V applied voltage, and the optimized BLT film showed a few fatigue losses about 10% up to 1 × 1011 cycles. The imprint properties of the BLT film were also characterized at 25°C and 90°C operating temperature after 125°C data storage. The average cell signal sensing margin between data "1" and data "0" was measured to be about 900 mV, which is a sufficiently large margin for device operation.
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Authors: Y.-J. Son, Y.G. Choi, Joon Chul Kwon, K.W. Cho, Young Moon Kim, Soon Young Kweon, Tae Whan Hong, Young Geun Lee, Sung Lim Ryu, Man Soon Yoon, Soon Chul Ur
Abstract: In an approach to acclimate ourselves to the recent ecological consciousness trends, a lead free piezoelectric material, bismuth sodium barium titanate (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT), was considered as an environment-friendly alternative to the PZT system. A perovskite BNBT was synthesized by the conventional bulk ceramic processing technique.La2O3 as a dopant was incorporated into the BNBT system up to 0.025 mol, and the doping effects on subsequent piezoelectric and dielectric properties were systematically investigated. In the case of La2O3 addition, the formation of grain boundary coherency was remarkably increased, and the sintered density was increased with increasing La2O3 contents. Piezoelectric and dielectric properties were shown to have the maximum value at 0.02 mol of La2O3 addition. La3+ ions were believed to act as a softener in the BNBT system and to enhance dielectric and piezoelectric properties in this study.
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Authors: Soon Chul Ur, Y.G. Choi, Joon Chul Kwon, Sung Lim Ryu, Young Geun Lee, J.L. Lee, L.H. Kim, Tae Whan Hong, S.Y. Kwon, Man Soon Yoon
Abstract: 0.03Pb(Sb0.5Nb0.5)O3-0.03Pb(Mn1/3Nb2/3)O3-(0.94-x)PbTiO3-xPbZrO3 ceramics doped with Y2O3 were synthesized by conventional bulk ceramic processing technique. Phases analysis, microstructures and piezoelectric properties were investigated as a function of Y2O3 contents (0.03, 0.05, 0.1 0.3, 0.5 and 0.7 wt.%). Microstructures and phases information were characterized using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). Relative dielectric constant (K33 T) and coupling factor (kp) were obtained from the resonance measurement method. Both K33 T and kp were shown to reach to the maximum at 0.1wt.% Y2O3. In order to evaluate the stability of resonance frequency and effective electromechanical coupling factor (Keff) as a function of Y2O3 contents under strong electric field, the variation of resonance and anti-resonance frequency were also measured using a high voltage frequency response analyzer(FRA5096) under various alternating electric fields from 10V/mm to 80V/mm. It was shown that the effective electromechanical coupling factor was stabilized along with increasing Y2O3 contents.
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Authors: Y.G. Choi, Y.-J. Son, Joon Chul Kwon, K.W. Cho, Soon Young Kweon, Tae Whan Hong, Young Geun Lee, Sung Lim Ryu, Il Ho Kim, Man Soon Yoon, Soon Chul Ur
Abstract: To enhance high power characteristics for piezoelectric transformer, an alloy design approach in PZT base ceramic system was considered. Various Zr/Ti ratio compositions in 0.03Pb(Sb0.5Nb0.5)O3- 0.03Pb(Mn1/3Nb2/3)O3-(0.94-x)PbTiO3-xPbZrO3 (0.445x0.475 mol)[PSN - PMN - PZT] system were synthesized by the conventional bulk ceramic processing technique. To improve high power characteristics at their morphotropic phase boundary (MPB) composition of PSN-PMN-PZT system, various spectra of Zr/Ti ratio were systematically experimented, and their effects on the subsequent piezoelectric properties and dielectric properties for high power piezoelectric transformer application were investigated using an impedance analyzer and a laser vibrometer. Microstructure and phase information were characterized using X-ray diffractometer (XRD) and a scanning electron microscope (SEM). When the Zr/Ti ratios were 0.475/0.465, the mechanical quality factor and electromechanical coupling factor were shown to reach the maximum, indicating that this alloy design can be a feasible composition for high power transformer.
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Authors: Jung Il Lee, Tae Whan Hong, Young Jig Kim, J.S. Kim, H.K. Park
Abstract: Eco-friendly development and on-going research strategy of Rotation-Cylinder Method (RCM) is given for SiCp/AZ91 Mg composites, identifying some of the key factors that need to be controlled and indicating subsequent casting processes. RCM produces U-shaped laminar melt surface with a Rankine vortex even at high rotation speed in an ambient atmosphere, which allows quick and efficient incorporation and homogeneous distribution of SiC particulates into molten Mg alloys. Therefore, sound SiCp/AZ91 Mg composites can be manufactured in conjunction with subsequent casting processes, such as investment casting and thixocasting. A transmission electron microscopy study showed that the interfacial reaction products consist of Mg2Si, MgO, Mg17Al12 and Al6Mn, which were analyzed using primitive cell volume and zero order Laue zone pattern and single convergent beam electron diffraction pattern containing higher order Laue zone ring from a nanosized region.
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Authors: Ji Hee Park, Tae Whan Hong, Mie Won Jung
Abstract: Hydrogen has attracted clean energy media as a high-quality and renewable energy source in recent years. On the one hand, a ceramic catalyst and/or catalyst support such as Al2O3 has often been a preferred choice due to their specific properties such as thermal stability and high surface area. Al2O3-CuO-ZnO was synthesized by using the sol-gel process with aluminum isopropoxide and primary distilled water as the precursor and solvent. In this synthesized process, metal oxides caused to precursors such as copper and zinc nitrate were added. To prepare membranes, cobalt metal powder was used to increase the strength and durability. The Al2O3-CuO-ZnO/Co composite membranes were produced using hot press sintering for consolidation of powders following reactively mechanical alloying process. The characterizations of membrane were measured XRD, FE-SEM and EDS. Hydrogen permeation evaluations were examined at a room temperature to 773 K under increasing pressure. Hydrogen permeation rate was obtained with 0.18 mol m-2 s-1 at 773 K result from complex diffusion mechanism such as Sievert’s type, Knudsen diffusion and/or molecular sieving.
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Authors: Kyeong Il Kim, Sang Hern Kim, Whan Gi Kim, Soon Chul Ur, Tae Whan Hong
Abstract: Nowadays, the most promising methods for high purity hydrogen production are membranes separation such as polymer, metal, ceramic and composites. It is well known that Pd and Pd-alloys membranes have excellent properties for hydrogen separation. However, it has hydrogen embrittlement and high cost for practical applications. Therefore, most scientists have studied new materials instead of Pd and Pd-alloys. On the other hand, TiN powders are great in resistance to acids and chemically stable under high operating temperature. In order to get specimens for hydrogen permeation, the TiN powders synthesized were consolidated together with pure Co powders by hot press sintering. During the consolidation of powders at HPS, heating rate was 10K/min and the pressure was 10MPa. It was characterized by XRD, SEM, and BET. Also, we estimated the hydrogen permeability by Sievert's type hydrogen permeation membrane equipment.
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Authors: Ji Hee Park, Mie Won Jung, Tae Whan Hong
Abstract: The purpose of this work was hydrogen permeation of ceramic or metal/ceramic membrane using γ-Al2O3 by synthesizing. The γ-Al2O3 was synthesized by using the sol-gel process with aluminum isopropoxide and primary distilled water as the precursor and solvent. The γ-Al2O3-based membranes were prepared using HPS. The phase transformation, thermal evolution, surface are and morphology of γ-Al2O3 and γ-Al2O3-based membranes were characterized by XRD, TG-DTA, BET and FE-SEM. The hydrogen permeation of γ-Al2O3-based membranes was examined at room temperature comparing with other paper using nickel composited membrane on alumina ceramic support.
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Authors: Kyeong Il Kim, Tae Whan Hong
Abstract: The most attractive way to storage hydrogen safely and economically is in metal hydrides. In particular, magnesium has attracted much interest since their hydrogen capacity exceeds that of known metal hydrides. One of the approaches to improve the kinetic is addition of metal oxide. In this paper, we tried to improve the hydrogen absorption properties of Mg. The effect of transition oxides, such as Nb2O5 on the kinetics of the Mg hydrogen absorption reaction was investigated. MgHx-Nb2O5 composites have been synthesized by hydrogen induced mechanical alloying. The powder synthesized was characterized by XRD, SEM, EDX, BET and simultaneous TG/DSC analysis. The hydrogenation behaviors were evaluated by using an automatic Sievert’s type PCT apparatus. Absorption/desorption kinetics and PCI of MgHx catalyzed with 5wt.%Nb2O5(as-received), 5wt.%Nb2O5(30min. milled) are determined at 423, 473, 523, 573, 623K.
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Authors: Whan Gi Kim, Soon Chul Ur, Y.G. Lee, Young Jig Kim, Tae Whan Hong
Abstract: In order to fabricate high efficiency, light-weight hydrogen storage materials in an economical way, we have been made to propose a new mechanical alloying process by high-pressure hydrogen induced planetary ball milling(HIMA) using Mg and Ni chips. Microstructural evaluations of the Mg-Ni-H systems synthesized were investigated by scanning electron microscopy and the transmission electron microscopy. X-ray diffraction analysis was also made to characterize the lattice constant, crystallite size and misfit strain. The hydrogenation properties of the particles synthesized were evaluated by automatic PCI (pressure-composition-isotherm). Adopting 66:1 BCR (ball to chips mass ratio) for HIMA process, fully hydrogenated alloys were obtained after 96 hrs of milling, resulting in total hydrogen content of 2.25 mass%.
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