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Now showing items 1 - 16 of 120

  • Hydrogen storage material and manufacturing method thereof

    A hydrogen storage material includes Mg(NH2)2, LiH, and MgH2. A manufacturing method of a hydrogen storage material includes steps of manufacturing a mixture by mixing Mg(NH2)2, LiH, and MgH2, and pulverizing the mixture.
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  • Boron–nitrogen based hydrides and reactive composites for hydrogen storage

    Lars H. Jepsen   Morten B. Ley   Young-Su Lee   Young Whan Cho   Martin Dornheim   Jens Oluf Jensen   Yaroslav Filinchuk   Jens Erik Jørgensen   Flemming Besenbacher   Torben R. Jensen  

    Hydrogen forms chemical compounds with most other elements and forms a variety of different chemical bonds. This fascinating chemistry of hydrogen has continuously provided new materials and composites with new prospects for rational design and the tailoring of properties. This review highlights a range of new boron and nitrogen based hydrides and illustrates how hydrogen release and uptake properties can be improved.
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  • Highly conducting fibrous carbon-coated silicon alloy anode for lithium ion batteries

    Juyoung Jang   Inyeong Kang   Kyung-Woo Yi   Young Whan Cho  

    Graphical abstract Highlights • CVD coating reduces both the surface area and initial irreversible capacity of anode. • Carbon nanofiber grown on the surface of iron silicide improves the rate capability. • Electrical conductivities of anodes coated with different methods are compared. Abstract Carbon-coated silicon/iron silicide nanocomposite anodes developed for lithium ion rechargeable batteries present a large initial irreversible capacity owing to many pores in the carbon coating layer generated from the carbonization of polyfurfuryl alcohol (PFA) resin during the heat treatment. To overcome this issue of large initial irreversible capacity loss, we attempted to fill the pores via chemical vapor deposition (CVD) of carbon using acetylene as the source. The Brunauer-Emmett-Teller surface area is reduced from 51 to 7 m 2  g −1 and the initial irreversible capacity also decreased from 197 mA h g −1 corresponding to a simple resin-coated sample to 164 mA h g −1 after CVD of carbon on the resin-derived carbon coating. The rate capability tests show an excellent ability to maintain a capacity of 500 mA h g −1 at the rate of 7 C (10.5 A g −1 ), suggesting that the carbon nanofibers (CNFs) formed by the catalytic decomposition of acetylene on iron silicide grains aid in improving the electrical connection between the active anode particles during cycling.
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  • Porous nanocomposite anodes of silicon/iron silicide/3D carbon network for lithium-ion batteries

    Inyeong Kang   Juyoung Jang   Kyung-Woo Yi   Young Whan Cho  

    Abstract Silicon/iron silicide/three-dimensional (3D) carbon nanocomposite anodes with tunable pore structures have been prepared by a simple and environmentally benign method, which can be used to control not only the internal porosity of agglomerated anode particles, but also the density of their 3D network-like carbon coatings by varying the volume fraction of NaCl pore template. As the amount of NaCl increases, the total particle porosity and density of the carbon coating increase as well. The presence of pores in the agglomerated particles and carbon network mitigate the structural damage caused by the volume expansion during the lithiation and delithiation of active silicon inside the nanocomposite aggregates. Consequently, the electrodes fabricated from the nanocomposites with high NaCl contents exhibit enhanced electrochemical performance. After increasing the NaCl volume fraction to 46%, the capacity retention of the electrode after 100 cycles increases by more than 25% with respect to the value obtained for the composite without added NaCl. In addition, increasing the NaCl content also improves the Coulombic efficiency and rate capability of the anode. Graphical abstract Image 1 Highlights • Porous silicon/iron silicide/3D carbon composite agglomerate was synthesized. • Porosity and carbon network of agglomerate can be tuned by volume fraction of NaCl. • Electrochemical properties were improved with higher porosity and finer carbon network.
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  • Nanostructured silicon/silicide/carbon composite anodes with controllable voids for Li-ion batteries

    Inyeong Kang   Juyoung Jang   Moon-Soo Kim   Jin-Woo Park   Jae-Hun Kim   Young Whan Cho  

    Abstract Three-dimensional (3D) carbon-network-supported Si/silicide nanocomposite anodes with controllable voids are prepared using ferrosilicon, NaCl, and polyfurfuryl alcohol (PFA) resin as the starting materials. Analysis of the microstructures and the phase compositions confirms the complete removal of NaCl and the consequent formation of voids supported by a glassy carbon network, residing in between the nanostructured Si/silicide composite particles. Coin-half cell tests demonstrate the significantly improved cycling performance of the Si/silicide/carbon nanocomposites compared with that of the alloy powder without controllable voids. The electrode prepared from the coated alloy with voids maintains approximately 66% of its initial capacity after 100 cycles and its Coulombic efficiency rapidly increases to 99% after several cycles. Graphical abstract Image 2 Highlights • Si/silicide/carbon nanocomposite anode with controllable voids was synthesized by using simple method. • Voids were introduced using NaCl, which was easily removed by rinsing with water. • Si/silicide/carbon nanocomposite with voids exhibits improved cycling performance because of void spaces and carbon networks. • Size and volume fraction of voids inside anode can be controlled independently by size and proportion of NaCl.
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  • Method of fabricating ultra-fine cermet alloys with homogeneous solid grain structure

    The present invention relates to a method of fabricating ultra-fine grain cermet alloys with a homogenous solid solution grain structure. More particularly, the invention relates to a method of fabricating an ultra-fine TiC-base cermet alloy with a homogenous solid solution structure which does not comprise a core-rim structure in the carbide grain.;The object of the present invention is to provide a method of fabricating a TiC-base cermet alloy without the core-rim structure.;The above objects of the present invention could be achieved by employing a conventional sintering process (vacuum sintering) of (Ti,TM)C carbide obtained from a mechano-chemical synthesis (high energy ball-milling) from milling the powders of Ti, TM, Ni and Co metals.
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  • Thermal destabilization of binary and complex metal hydrides by chemical reaction: A thermodynamic analysis

    Young Whan Cho   Jae-Hyeok Shim and Byeong-Joo Lee  

    Some alkali and alkali-earth metal hydrides and their complex hydrides have very high hydrogen storage capacities and reversibility. Unfortunately, most of them have decomposition temperatures that are too high. This must be overcome before these hydrides can be considered seriously as practical hydrogen storage materials for on-board applications. In the present study, the CALPHAD approach has been adopted to evaluate thermodynamically the possibility of destabilizing these high temperature binary ionic hydrides and ternary complex hydrides by reacting them with light elements or other hydrides. The MgH2+Si, LiBH4+MgH2, and LiBH4+Al systems are predicted to show a significant decrease in decomposition temperature. On the other hand, the decrease in the decomposition temperatures of the MgH2+Al and NaBH4+Al systems is relatively small. The LiH+Si system also presents a considerable destabilization effect, which is consistent with experiment.
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  • Thermal destabilization of binary and complex metal hydrides by chemical reaction: A thermodynamic analysis

    Young Whan Cho   Jae-Hyeok Shim   Byeong-Joo Lee  

    Some alkali and alkali-earth metal hydrides and their complex hydrides have very high hydrogen storage capacities and reversibility. Unfortunately, most of them have decomposition temperatures that are too high. This must be overcome before these hydrides can be considered seriously as practical hydrogen storage materials for on-board applications. In the present study, the CALPHAD approach has been adopted to evaluate thermodynamically the possibility of destabilizing these high temperature binary ionic hydrides and ternary complex hydrides by reacting them with light elements or other hydrides. The MgH 2+Si, LiBH 4+MgH 2, and LiBH 4+Al systems are predicted to show a significant decrease in decomposition temperature. On the other hand, the decrease in the decomposition temperatures of the MgH 2+Al and NaBH 4+Al systems is relatively small. The LiH+Si system also presents a considerable destabilization effect, which is consistent with experiment. [All rights reserved Elsevier]
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  • Effective thermal conductivity of MgH<sub>2</sub> compacts containing expanded natural graphite under a hydrogen atmosphere

    Jae-Hyeok Shim   Mirae Park   Young Hyo Lee   Sanggon Kim   Yeon Ho Im   Jin-Yoo Suh   Young Whan Cho  

    Abstract Expanded natural graphite (ENG) was added to enhance the effective thermal conductivity of MgH 2 , which is one of the important parameters in the design of MgH 2 -based hydrogen storage tanks. Cylindrical MgH 2 compacts containing up to 20 wt% ENG flakes with various average sizes (20, 50, 200, 350 and 1200 μm) were fabricated to measure the effective thermal conductivity of MgH 2 –ENG mixtures. The radial direction effective thermal conductivity of the compacts was measured under a hydrogen atmosphere up to 70 bar. The conductivity was significantly enhanced by the addition of ENG flakes, reaching 9.3 W m −1  K −1 at 20 wt% ENG at 1 bar of hydrogen. It was observed that hydrogen pressure and the size of ENG flakes influenced the conductivity together with the amount of ENG. As hydrogen pressure increased up to 20 bar, the conductivity continued to increase. On the other hand, the conductivity very slowly increased above 20 bar, exhibiting a saturation tendency. It relatively rapidly increased with increasing average flake size up to 200 μm and then gradually decreased with further increasing size up to 1200 μm, exhibiting the maximum value at an average flake size of 200 μm. This trend might be determined by the competition between the thermal resistance at ENG/MgH 2 interfaces and the formation of conductive networks of ENG flakes. Highlights • The thermal conductivity of MgH 2 –graphite compacts is measured under H 2 pressure. • H 2 pressure up to 20 bar increases the thermal conductivity. • The thermal conductivity reaches the maximum at a graphite flake size of 200 μm.
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  • Local People's Congresses in China: Development and Transitionby Young Nam Cho

    Review by: Daniela Stockmann  

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  • Transforming Korean Politics: Democracy, Reform, and Cultureby Young Whan Kihl

    Review by: Tae Yang Kwak  

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  • Transforming Korean Politics: Democracy, Reform, and Cultureby Young Whan Kihl

    Review by: Eun Gee Yun  

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  • Transforming Korean Politics: Democracy, Reform, and Cultureby Young Whan Kihl

    Review by: Gi-Wook Shin  

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  • Pacing During a 10-km Run Time-trial in Young Boys After Diet CHO Manipulation

    Couto, Patricia G.   Kiss, Maria A. P. D.   Bertuzzi, Romulo   Lima, Hessel M.   Soares, Ruda P.   Souza, Carla C.   de-Oliveira, Fernando R.   Lima-Silva, Adriano E.  

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  • Transforming Korean Politics: Democracy, Reform, and Cultureby Young Whan Kihl

    Review by: Gi-Wook Shin  

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  • Local People\"s Congresses in China: Development and Transitionby Young Nam Cho

    Review by: Daniela Stockmann  

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