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Won-Wook Park 2 Articles
Effects of Porous Microstructure on the Electrochemical Properties of Si-Ge-Al Base Anode Materials for Li-ion Rechargeable Batteries
Chung Rae Cho, Myeong Geun Kim, Keun Yong Sohn, Won-Wook Park
J Powder Mater. 2017;24(1):24-28.   Published online February 1, 2017
DOI: https://doi.org/10.4150/KPMI.2017.24.1.24
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Silicon alloys are considered promising anode active materials to replace Li-ion batteries by graphite powder, because they have a relatively high capacity of up to 4200 mAh/g, and are environmentally friendly and inexpensive ECO-materials. However, its poor charge/discharge properties, induced by cracking during cycles, constitute their most serious problem as anode electrode. In order to solve these problems, Si-Ge-Al alloys with porous structure are designed as anode alloy powders, to improve cycling stability. The alloys are melt-spun to obtain the rapidly solidified ribbons, and then ball-milled to make fine powders. The powders are etched using 1 M HCl solution, which gives the powders a porous structure by removing the element Al. Subsequently, in this study, the microstructures and the characteristics of the etched powders are evaluated for application as anode materials. As a result, the etched porous powder shows better electrochemical properties than as-milled Si-Ge-Al powder.

Phase Change of Precipitates and Age Hardening in Rapidly Solidified Mg-Zn-Ca Base Alloys
Won-Wook Park, Bong-Sun You
J Korean Powder Metall Inst. 2005;12(4):303-308.
DOI: https://doi.org/10.4150/KPMI.2005.12.4.303
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Various kinds of Mg-Zn-Ca base alloys were rapidly quenched via melt spinning process. The meltspun ternary and quaternary alloy ribbons were heat-treated, and then the effects of additional elements on age hardening behavior and phase change of precipitates were investigated using Vickers hardness tester, XRD, and TEM equipped with EDS system. In ternary alloys, age hardening was mostly due to the distribution of Mg_6Ca_2Zn_3 and Mg_2Ca. The stable phases of precipitates were varied according to the aging temperature and the alloy composition. With the increase of Ca content, Mg_2Ca precipitates were detected more than Mg_6Ca_2Zn_3 precipitates. In quaternary alloys, the precipitates taken from Mg-Zn-Ca-Co were identified as new quaternary phase, whereas those taken from Mg-Zn-Ca-Zr as MgZnCa containing Zr. In general, the ternary alloy showed higher peak hardness and thermal stability than the quaternary considering the total amounts of the solutes. It implies that the structure of precipitate should be controlled to have the coherent interface with the Mg matrix.

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