Papers by Author: Jae Chun Lee

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Authors: Dong Bok Lee, S.J. Park, Yun Soo Lim, Jae Chun Lee
Abstract: Carbon nanofibers were reacted with SiO vapor generated from a mixture of Si and SiO2 to produce silicon carbide nanofibers at 1350oC for 2 h under vacuum. The obtained SiC nanofibers with a diameter ranging 100~200 nm had the specific surface area as high as 124 m2/g. The SiC nanofibers were not oxidation resistant, showing nearly complete oxidation at 1000 oC after about 60 h in air, though the oxidation product was amorphous silica which was generally considered to be oxidation resistant. The poor oxidation resistance was attributed to the inherent nanoporous nature of the fibers resulted from the gas-solid reaction.
Authors: Jae Chun Lee, Jin Ki Jeong, Eui-Hyuk Kwon, Sung Hwan Jang, Jeong Whan Han
Abstract: It is generally well known that PCB (Printed Circuit Board) is a complex mixture of various metals mixed with various types of plastics and ceramics. Accordingly, it is very important to extract metallic components from used PCB’s from the point of view of recycling the used resources as well as the environmental protection. In this study, a high temperature pyro-metallurgical process was investigated to extract valuable metallic components from the used PCB’s. For this purpose, used PCB’s were shredded and oxidized to remove plastic materials, and then, a high frequency induction furnace was used to melt and separate metallic components in molten state from the remaining oxides. After the oxidation of the used PCB, 30.6wt% SiO2, 19.3wt% Al2O3 and 14wt% CaO were analyzed as major oxides, and thereafter, a typical composition of 32wt%SiO2-20wt%Al2O3-38wt%CaO -10wt%MgO was chosen as a basic slag system for the separation of metallic components Moreover, in order to understand the size effect on the extraction of metallic components, oxidized PCB’s were further milled, and then, melted. As a result, it was found that the size of oxidized PCB’s was needed to be less 0.9mm to make a homogeneous liquid slag and to recycle metallic components over 95%.
Authors: Sung Hwan Jang, Jeong Whan Han, Jin Ki Jeong, Jae Chun Lee
Abstract: From materials view point, a PCB (Printed Circuit Board) is a simple mixture of various metals, plastics and oxides. Thus, it can be regarded as urbanized resources or ores. The existence of valuable metallic components in used PCB, then, becomes a major driving force for the recycling In this study, the effect of slag compositions on the extraction of valuable metallic components from the used PCB is investigated. Especially, a melting temperature of slag and slag viscosity are discussed as major operating parameters. PCB contains nearly 30wt% of SiO2 and 20wt% of Al2O3 as major oxides, and by just adding other flux components to used PCB, 20wt%Al2O3-Xwt%SiO2 - Ywt%CaO-10wt%MgO slag system with low melting point and low slag viscosity can be made to extract metallic components from used PCB by gravity separation. The slag basicity was changed under fixed compositions of Al2O3 and MgO. It was found that a proper melting temperature and slag basicity to make a homogeneous liquid slag and to extract metallic components from used PCB were 1573 K, and 0.75, respectively.
Authors: Jun Suh Yu, Sung Park, Jae Chun Lee, In Sup Hahn, Sang Kuk Woo
Abstract: Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of propane in a nitrogen atmosphere at 900°C. The amount of carbon coating was varied through adjusting deposition time to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire method, respectively. Up to 7 wt% pyrolytic carbon, the electrical conductivity σ is linearly increased to 0.02 S/cm and well fitted by the effective conductivity according to the parallel rule of a mixture σ eff = Σ Χ i ·σ i with a conductivity of pyrolytic carbon σ c= 20 S/cm .The thermal conductivity of the uncoated and coated composites is in the range 0.065-0.075 W/mK and little affected by carbon coating presumably owing to the small amount of coated carbon in this work.
Authors: Jun Suh Yu, Jae Hoon Sung, Sung Park, Jae Chun Lee
Abstract: Emissive carbon coating was prepared using a carbon black powder and a phenolic resin binder suspension. Interior of an alumina tube with an emissivity of 0.75 was coated with the emissive coating and its energy saving performance was investigated using a vacuumed alumina tube up to 1000°C. The vacuumed cavity temperature of the carbon-coated alumina tube embedded in an electrically heated furnace was always higher than that of the uncoated one for the same surface temperature of the tube. The cavity temperature difference between the carbon-coated and uncoated tube increased with the surface temperature of the alumina tube. At the surface temperature of 1000 °C, the cavity temperature difference reached about 20°C. Heating the carbon-coated alumina to raise the cavity temperature from an ambient temperature to 1000°C at a constant heating rate of 5°C/min yielded an energy consumption of 559 Wh, while the uncoated one resulted in energy consumption of 595 Wh. As the holding time to maintain the cavity temperature of 1000°C was extended to 120 min, the energy-saving increased from 6% to 11%.
Authors: Young Jae Lee, Jae Hyung Kim, Jang Soon Kim, Dong Bok Lee, Jae Chun Lee, Yun Jung Chung, Yun Soo Lim
Abstract: Activated carbon fibers were prepared from stabilized PAN-based fibers by chemical activation using potassium hydroxide at different concentration. The experimental data showed variations in specific surface area, microstructure by the activated carbon fibers. Specific surface area of about 2545 m2/g was obtained in the KOH/stabilized PAN-based fiber ratio of 1:1 at 800°. An abrupt reduction of specific surface area was observed in the experiments with the ratio of 3:1 of OH/stabilized PAN-based fiber, being dissimilar with the result of KOH/fiber ratios of 1:1 and 2:1 in the similar experiments. The high concentration of KOH led to the destruction of micropore walls instead of forming mesopores.
Authors: Moo Young Huh, J.P. Lee, Jae Chun Lee, Jong Woo Park, Young Hoon Chung
Abstract: The evolution of texture and microstructure during the equal channel angular rolling (ECAR) and subsequent annealing in aluminum alloy 3003 sheets was investigated. The tools of ECAR were designed to provide a constant shear deformation of the order of 0.5 per passage while preserving the original sheet shape. Samples of the aluminum alloy 3003 sheets were repeatedly deformed by ECAR up to twelve passages. Shear textures developed after the first passage of ECAR. However, the intensity of shear texture components decreased with increasing number of ECAR passages. After a large number of ECAR passages, a random texture developed at the expense of shear texture components. Observations by TEM and EBSD revealed that the degree of misorientations within the deformed grains increased with increasing number of ECAR passages. After recrystallization annealing, samples deformed by ECAR displayed pronounced {111}//ND fiber orientations. The annealed sheets comprising of ultra-fine grains were successfully produced in the samples deformed by a large number of ECAR passages.
Authors: Jun Suh Yu, Jae Chun Lee, Sung Park, Min Sung Hong
Authors: Jun Suh Yu, B.S. Lee, Sung Churl Choi, Ji Hun Oh, Jae Chun Lee
Abstract: Electrically conductive porous Si/SiC fiber media were prepared by infiltration of liquid silicon into porous carbon fiber preforms. The series rule of mixture for the effective electrical conductivity was applied to the disc shaped samples to estimate their silicon content, effective electrical conductivity and porosity. The electrical conductivity was estimated by assuming the disc sample as a plate of equivalent geometry, i.e., same thickness, electrode distance and volume. As the volumetric content of silicon in a sample increases from 0.026% to 0.97%, the estimated electrical conductivity increases from 0.17 S/cm to 2.09 S/cm. The porosity of the samples measured by Archimedes principle was in the range of 75~83% and 1~4% less than the one estimated by the series rule of mixture for the effective electrical conductivity.
Authors: In Sub Han, Doo Won Seo, Shi Woo Lee, Ki Seok Hong, Sang Kuk Woo, Yong Hee Chung, Jae Chun Lee
Abstract: Two different types of carbon fibre bundles were used for filament winding to obtain C/C preforms. C/C-SiC composites were produced from the C/C preforms by a silicon melt infiltration technique. The effect of the type of carbon fibre bundle on the mechanical and thermal properties of the resultant C/C-SiC composites was compared. The spun fiber preform yields C/C-SiC composites of better mechanical properties than the unidirectional continuous fiber preform. The strength of the composites from the SFP was 1.8 times higher than that from the CFP. The flexural strength and the O-ring strength of the composites from the SFP with a density of 2.35 g/cm3 were about 160 MPa and 170 MPa, respectively.
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