Papers by Author: Won Sik Lee

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Authors: Il Ho Kim, Won Sik Lee, Se Hyun Ko, Jin Man Jang, Ho Sung Kim
Abstract: The open cell Al (or Al foam) was employed in the alloy hydride system due to the rapid heat conductivity of Al. The hydrogen storage alloy powders were packed in this storage system made of Al open cell, and the changes of temperature and equilibrium pressure of hydrogen desorbed were measured. By applying the open cell Al in this hydrogen storage system, the reaction sensitivity of the temperature and equilibrium pressure was far rapidly increased than that without the open cell Al.
881
Authors: Il Ho Kim, Won Sik Lee, Se Hyun Ko, Jin Man Jang, Ho Sung Kim
Abstract: The effects of use of open cell Al foam and thermoelectric element in a hydrogen storage system were investigated. Extremely different heat conductivities were observed in two storage systems with or without open cell Al foam. By applying the open cell Al in this hydrogen storage system, the reaction sensitivity of the temperature and equilibrium pressure was far rapidly increased than that without the open cell Al foam. During increasing the temperature by heating element, heating rate of hydride powders was very fast in the storage system including Al foam, while temperature of powders was almost not changed in system without foam. Also, in case of using thermoelectric element, heating and cooling rate was very sensitive in the system with Al foam and heating-cooling cyclic behavior within the system controlled by thermoelectric element is seemed to be satisfied for some applications in industry.
301
Authors: Seong Ho Son, Do Won Chung, Won Sik Lee
Abstract: In the electroplating and water treatment fields, as the demand and expectation on an electrode with high productivity and high efficiency are getting increased, various electrodes(DSE) with higher reactivity and durability are being developed. This study is intended to analyze the characteristics of the produced electrodes and to establish the optimum manufacturing conditions for electrode being used that we mentioned. For improving the durability, the changes of reactivity and corrosion resistance are observed as adding Tantalum and/or another components (hereafter stated as “α”) and surface treatment of substrate(Ti). As a result, increasing the amount of Iridium, the reactivity of electrode increased, and increasing amount of Tantalum, the durability of electrode increased. And thus, it is found out that Iridium and Tantalum have the opposite role each on the electrode’s reactivity and durability. And adding α and surface treatment substrate, an electrode with excellent reactivity and durability and low oxygen evolution can be manufactured. In the water treatment field like sterilizing in a swimming pool and power-plant cooling water, the high efficiency of sodium-hypochlorite generation is surely guaranteed.
750
Authors: Won Sik Lee, Jin Man Jang, Se Hyun Ko
Abstract: In present work, manufacturing technologies of micro parts by micro forging and pressing were studied using strain softening phenomenon in nano grained Al-1.5mass%Mg alloy. During compressive test at 300, the Al alloy showed stain softening phenomenon by grain boundary sliding regardless of strain rate. Micro spur gear with ten teeth (height of 200 μm and pitch of 250 μm) was fabricated with sound shape by micro forging. During micro forging, increase of applied stress induced by friction between material and die surface was effectively compensated by decrease of stress by strain softening behavior and as a result, flow stress increased only about 50 MPa more than that in compressive test. However, in micro pressing, flow of material did not occurred sufficiently to fill die and the resultant shape of gear was very poor.
393
Authors: Jin Man Jang, Won Sik Lee, Se Hyun Ko
Abstract: In present work, manufacturing technologies of titanium hydride powder were studied for recycling of titanium tuning chip and for this, attrition ball milling was carried out under H2 pressure of 0.5 MPa. Ti chips were completely transformed into TiH2 within several hundred seconds that is very short time comparing to that in the previous report. Dehydrogenation process TiH2 powders is consist of two reactions: one is reaction of TiH2 to TiHx and the other decomposition of TiHx to Ti and H2. The former reaction shows relatively low activation energy ranged from about 100 KJ/mol to 250 KJ/mol and it is suggested that the reaction is caused by introduction of defects due to milling. In case of TiH2 powders that hardly contains defects, decomposition of TiH2 to Ti and H2 occurs directly without the reaction of TiH2 to TiHx and activation energy is very large as much as 929 KJ/mol.
185
Authors: Jin Man Jang, Won Sik Lee, Se Hyun Ko, Il Ho Kim, Seong Ho Son, Do Won Jung
Abstract: Using commercial Ti powders and recycled TiH2 powders made from titanium turning chips, the effects of hydrogen on microstructures and oxygen reduction were investigated. Each powder was hot-pressed at 750oC and 1100oC, which are below and above β-transition temperature (880oC), respectively. The TiH2 and Ti samples of sintered at 1100oC showed equiaxed α phase. However, TiH2 sample sintered at 750oC consist of primary α phase, secondary α phase and titanium hydride (TiH2), though Ti sample represented single α phase. The formation of complex microstructure in TiH2 sample sintered at 750oC is due to hydrogen remained after sintering. The oxygen contents after sintering in TiH2 samples were relatively lower than Ti samples, although those before sintering were higher than Ti. This result can be explained that hydrogen gas generated from dehydrogenation of TiH2 leads to the reduction of oxygen contents and protection of re-oxidation during sintering.
995
Authors: Gue Serb Cho, Jung Kyu Lim, Kyeong Hwan Choe, Won Sik Lee
Abstract: CNTs were decorated with Ni nanoparticles to decrease floatation of CNTs and improve the wettability between CNT and Al melt by electroless plating method. The as-received size of multi-wall CNTs with 99.5% purity was 10~20nm in diameter and 20um in length. Before Ni deposition, the wet ball milling was tried to improve the dispersion of CNTs in the Ni sulfate solution for several hours. After wet ball milling, the Ni electroless platings have been performed for 1hours at electroless deposition temperature. The Ni deposited CNTs have been characterized in respect of dispersion and size changes of CNTs and Ni particles with field emission scanning electron microscopy(FESEM). The deposited Ni nanoparticles onto the CNTs were 50nm in diameter without ball milling, but they increased in size with increasing milling times up to 120nm. Also, the milled CNTs were damaged and changed from its original morphology due to the high ball milling energy. The addition of surfactant improved the distribution and spheroidization of precipitated Ni nanoparticles. From this study, the multi-wall CNTs have been deposited and decorated with spherical Ni nanoparticles by electroless deposition at a proper milling time and surfactant addition.
360
Authors: Se Hyun Ko, Jin Man Jang, Won Sik Lee
Abstract: Al-Mg and Al-Mg-Cu alloys are known well to reveal superplasticity in tension at high temperatures. In this study, deformation behaviors of those alloys nanograined were investigated under compression test at room temperature. During plastic deformation softening phenomena occurred obviously in nanograined Al-1.5wt%Mg and Al-0.7wt%Mg-1.0wt%Cu alloys while slight strain hardening appeared in nanograined pure Al. These results suggest that the softening strongly depends on composition of alloys. The softening takes place over strain rate range from 10-4 up to 10-1.
3489
Authors: Jin Man Jang, Won Sik Lee, Se Hyun Ko, Il Ho Kim
Abstract: Manufacturing technology of bulk titanium by milling and sintering was studied for recycling of pure titanium tuning chip. Ti chips were milled at RT under H2 pressure of 0.5MPa. All titanium chips were pulverized and hydrided within several minutes, which is very short time comparing to other thermal processes. The hydrided powders were hot pressed at 750°C. After hot pressing, bulk sample was identified to α-phase Ti by XRD measurement and measured density(4.509g/cm3) was very close to theoretical density(4.512g/cm3) of pure Ti. Consequently, it is carefully suggested that hydriding and sintering process is efficient and practicable solution for recycling of pure titanium tuning chip.
171
Authors: Gue Serb Cho, Won Sik Lee, Se Hyun Ko, Seong Ho Son, Chang Woo Lee, Jun Ki Kim
Abstract: Vibration characteristics of 5μm- thick Ni film were investigated with applying acoustic wave to the Ni diaphragm of 2mm x 2mm unit size. In the modal analysis, the first resonance mode of the diaphragm showed an out-of-plane piston-like movement and the first natural frequency was 1,643 Hz, whereas in this experiment, the first natural frequency appears at about 1,300 Hz under sound pressure of 0.2 Pa. The amplitudes of diaphragm increase with increase of sound pressure level in the applied frequency range from 300 Hz to 1,000 Hz, indicating that area of diaphragm influences directly the amplitude.
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