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Now showing items 1 - 9 of 9

  • Morphology Controlled Co-precipitation Method for Nano Structured Transparent MgAl 2 O 4

    Nam, Sangwoo   Lee, Munkeun   Kim, Byung-Nam   Lee, Younghwan   Kang, Shinhoo  

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  • Carbide/binder interfaces in Ti(CN)-(Ti, W)C/(Ti, W)(CN)-based cermets

    Park, Choongkwon   Nam, Sangwoo   Kang, Shinhoo  

    Partially solutionized carbide cermets (PSCs) were prepared for cutting tool applications by replacing a portion of Ti(CN) with (Ti0.88W0.12) C or (Ti0.88W0.12)(C0.7N0.3) in a conventional Ti(CN)-based cermet. The PSC containing (Ti0.88W0.12) C exhibited high fracture toughness with no loss of hardness. The elimination of Ti(C0.7N0.3) cores in the microstructure reduced the strain at the core/rim interfaces, leading to the increase in fracture toughness. The PSC containing (Ti0.88W0.12) C showed coherent relationships at the core/rim and rim/binder interfaces, contributing to the improved mechanical properties. In contrast, nitrogen in (Ti0.88W0.12)(C0.7N0.3) resulted in a different microstructure and properties. The major factors determining the mechanical properties of the cermets are discussed in terms of the carbide/binder interfaces and the thermal stability of the added carbides. (C) 2015 Elsevier B.V. All rights reserved.
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  • Characterization of Alginate/Silver Nanobiocomposites Synthesized by Solution Plasma Process and Their Antimicrobial Properties

    Nam, Sangwoo   MubarakAli, D.   Kim, Jungwan  

    Solution plasma process (SPP) was adopted to prepare alginate/silver nanoparticle (AL/AgNP) biocomposites. The biocomposites were synthesized in solutions of varying concentrations of AgNO3 (1-5mM) and alginate (0.1-0.3%, w/w) by discharging plasma for 7 min at 800 V with 30 kHz frequency using a pulsed unipolar power supply. The AL/AgNP emulsion was fabricated into 3D scaffolds by freeze drying and lyophilization and then stabilized by cross-linking via UV irradiation. UV-Vis spectroscopy of the biocomposites showed a characteristic absorbance at the maximum of 415-440 nm with increase in the intensity of the peaks as the concentration of AgNO3 increased. FE-SEM analysis showed that the 3D scaffolds had microporous structures with fine and uniform pores of 3-9 +/- 2.0 mu m in diameter. TEM analysis revealed that AgNPs in the biocomposites were in spherical shape with size range of 5-40 +/- 2.0 nm (AL0.3/Ag5) and well distributed in the matrix. The AL/AgNP biocomposites showed microbicidal activity against 9 human pathogens with MIC of 9.6-21 mu g/mL for bacteria and 85-425 mu g/mL for fungi. Almost all of the E. coli cells (99.8%) were killed by the treatment with 42.5 mu g/mL of AgNPs at room temperature for 1 h.
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  • Enhanced toughness of titanium carbonitride-based cermets by addition of (Ti,W)C carbides

    Park, Choongkwon   Nam, Sangwoo   Kang, Shinhoo  

    Ti(CN)-based cermet is a potential alternative to WC-Co for cutting applications. We attempted to improve the mechanical properties of Ti(CN)-based cermets by adding (Ti0.88W0.12)C and (Ti0.88W0.12)(C0.7N0.3). The (Ti0.88W0.12)C phase decreased the number of Ti(CN) cores more effectively than (Ti0.88W0.12)(C0.7N0.3) and thus improved toughness was obtained. The binder phase fractions were altered substantially by the kind of carbides. In particular, the presence of N in (Ti0.88W0.12)(C0.7N0.3) increased the binder fractions and refined the microstructure of Ti(CN) cermets significantly. However, the increase in the binder faction provided a limited improvement in toughness in the systems of study. (C) 2015 Elsevier B.V. All rights reserved.
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  • Neutralization of Acidic Intracellular Vesicles by Niclosamide Inhibits Multiple Steps of the Dengue Virus Life Cycle In Vitro

    Jung, Eunhye   Nam, Sangwoo   Oh, Hyeryeon   Jun, Sangmi   Ro, Hyun-Joo   Kim, Baek   Kim, Meehyein   Go, Yun Young  

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  • Morphology controlled Co-precipitation method for nano structured transparent MgAl2O4

    Nam, Sangwoo   Lee, Munkeun   Kim, Byung-Nam   Lee, Younghwan   Kang, Shinhoo  

    MgAl2O4 spinel nano powders with various morphologies were synthesized with ammonium aluminum carbonate hydroxide by carbonate precipitation. The powders with rod, corn, and spherical morphologies were synthesized, varying the concentration of ammonium ions, by growth and aggregation of nano precipitates. The powders with spherical morphology formed spinel phase at a lower calcination temperature than those with other shapes. The morphology provided a superb sinterability due to improved particle packing. Although the synthetic conditions resulted in a composition slightly off the stoichiometric composition with Mg loss, this provided a proper condition for inhibiting grain growth. Finally, Mg-spinel which was obtained from spherical particles and fabricated by spark plasma sintering (SPS) showed much improved transparency with an average grain size of 200 nm (MT and TFT are 55.92% and 63.75% at 550 nm 75.35% and 78.91% at 1500 nm, respectively) than those from other shaped particles.
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  • Post-annealing effect on transparent Mg-Zn aluminate solid solutions fabricated by spark plasma sintering

    Nam, Sangwoo   Kang, Shinhoo   Kim, Byung-Nam   Jung, In-Ho   Kim, Young-Min  

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  • Effect of Process Parameters on Deposition Properties of Functionally Graded STS 316/Fe Manufactured by Laser Direct Metal Deposition

    Nam, Sangwoo   Cho, Heewon   Kim, Cheolhee   Kim, Young-Min  

    Stainless steel 316 (STS316)/Fe functionally graded materials were fabricated by direct energy deposition (DED) method using laser as a heat source. The feeding amount of the mixed powder was evaluated and the powder feeding condition was optimized through the section evaluation. The reliability of the powder feed was evaluated by regression analysis, and it was confirmed through the energy dispersive spectrometer (EDS) analysis and X-ray diffractometer (XRD) that the graded functional material of the designed composition was manufactured. Defects and microstructures were analyzed by scanning electron microscope (SEM).
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  • Microstructure evolution of in-situ (Ti,W)C-Al2O3 particle-reinforced alloy fabricated by gas tungsten arc cladding

    Nam, Sangwoo   Kim, Cheolhee   Kim, Young -Min  

    This paper reports the fabrication of TiC-Al2O3 or (Ti,W)C-Al2O3 ceramic reinforced metal matrix composites (MMC) using gas tungsten arc cladding. For fabrication of the MMC, an in-situ reaction was used to reduce oxides by employing C and Al as reducing materials during the cladding process, and the strengthened particles formed on the surface by solid state reaction were then grown through interaction in the metal matrix. The reactions forming phases in this system were subsequently examined through thermodynamic calculations. Results showed that TiC and Al2O3 peaks were observed in XRD for the reduction of TiO2 and WO3 by Al and C. The cladded hardfacings were covered by a composite slag zone, which consisted of Al2O3 particles embedded in Al and Ti based ceramic matrix, and that carbide particles such as TiC and (Ti,W)C were distributed intensively inside the MMC zone. Most of the TiC particles in the MMC zone had a slow growth rate because the interface controlled the growth; however, some particles that highly interacted with metals exhibited a dendrite structure. (Ti,W)C particles without dendrite growth formed a spherical shape, and the size of the particles was controlled by diffusion of the solute. Following the dissolution and precipitation process, (Ti,W)C-strengthened particles were found to have a sintering-like core/rim structure. Furthermore, the microhardness of the clad obtained was 600-900 HV0.2, which is significantly better than that obtained with commercial TiC powder.
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