• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.140.2-140.2
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• 2013

Strong metal-support interaction effect is an important issue in determining the catalytic activity for heterogeneous catalysis. In this work, we report the catalytic activity of $Au/TiO_2$, $Au/Al_2O_3$, and $Au/Al_2O_3-CeO_2$ nanocatalysts under CO oxidation fabricated by arc plasma deposition (APD), which is a facile dry process with no organic materials involved. These catalytic materials were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and $N_2$-physisorption. Catalytic activity of the materials has measured by CO oxidation using oxygen, as a model reaction, in a micro-flow reactor at atmospheric pressure. Using APD, the catalyst nanoparticles were well dispersed on metal oxide powder with an average particle size (3~10 nm). As for catalytic reactivity, the result shows $Au/Al_2O_3-CeO_2$ nanocatalyst has the highest catalytic activity among three samples in CO oxidation, and $Au/TiO_2$, and $Au/Al_2O_3$ in sequence. We discuss the effects of structure and metal-oxide interactions of the catalysts on catalytic activity.

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3609-3614
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• 2013

Orthorhombic and hexagonal lanthanum(III) hydroxycarbonate ($LaCO_3OH$) and $Ln^{3+}$-doped $LaCO_3OH$ ($LaCO_3OH:Ln^{3+}$, where Ln = Ce, Eu, Tb, and Ho) powders were prepared by a hydrothermal reaction under ambient pressure and characterized by thermogravimetry, powder X-ray diffraction, infrared and luminescence spectroscopy, and field-emission scanning electron microscopy. The polymorph of $LaCO_3OH$ depended on the reaction temperature, inorganic salt additive, species of $Ln^{3+}$ dopant, and solvent. The calcination of orthorhombic $LaCO_3OH:Ln^{3+}$ (2 mol %) powers at $600^{\circ}C$ yielded a mixture of hexagonal and monoclinic $La_2O_2CO_3:Ln^{3+}$ powders. The relative quantity of the latter increased with decreasing ionic radius of the $Ln^{3+}$ dopant ion and increasing doping concentrations. On the other hand, the calcination of hexagonal $LaCO_3OH:Ln^{3+}$ (2 mol %) powders at $600^{\circ}C$ resulted in a pure hexagonal $La_2O_2CO_3:Ln^{3+}$ powder, regardless of the species of $Ln^{3+}$ ions (Ln = Ce, Eu, and Tb). The luminescence spectra of $LaCO_3OH:Ln^{3+}$ and $La_2O_2CO_3:Ln^{3+}$ were measured to examine the effect of their polymorph on the spectra.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.416-417
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• 2006

Nanostructured ceria powder was synthesized by a thermochemical process and investigated its applicability for an oxygen gas sensor. An amorphous precursor powders prepared by spray drying a cerium-nitrate solution were transformed successfully into nanostructured ceria by heat-treatment in air atmosphere. The powders were a loose agglomerated structure with extremely fine $CeO_2$ particles about 15 nm in size, resulting in a very high specific surface area $(110\;m^2/g)$. The oxygen sensitivity and the response time $t_{90}$ measured at sintered sample at $1000^{\circ}C$ was about -0.25 and very short, i.e., $3{\sim}5$ seconds, respectively.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2004년도 International Symposium on Powder Materials and Processing
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• pp.3-4
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• 2004

• 한국분말재료학회지
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• 제9권6호
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• pp.394-408
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• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• 한국물환경학회지
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• 제31권6호
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• pp.632-636
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• 2015

This study aims to evaluate arsenic adsorption efficiencies over various metal oxides (CeO₂, TiO₂, Fe₃O₄, ZrO₂, AlOOH, SiO₂, α-Al₂O₃, and γ-Al₂O₃) and investigate the correlation between physico-chemical characteristics of metal oxides and their efficiencies. From XPS, XRD BET analysis and isotherm adsorption test, TiO₂ powder showed that the best adsorption efficiency, and it's mechanism was highly depended on the chemical adsorption.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.386-386
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• 2012

For white light emitting diode (LED) applications, it has been reported that Y3Al5O12:Ce3+ (YAG:Ce) in nano-sized phosphor performs better than it does in micro-sized particles. This is because nano-sized YAG:Ce can reduce internal light scattering when coated onto a blue LED surface. Recently, there have been many reports on the synthesis of nano-sized YAG particles using bottom-up method, such as co-precipitation method, sol-gel process, hydrothermal method, solvothermal method, and glycothermal method. However, there has been no report using top-down method. Top-down method has advantages than bottom-up method, such as large scale production and easy control of doping concentration and particle size. Therefore, in this study, nano-sized YAG:Ce phosphors were synthesized by a high energy beads milling process with varying beads size, milling time and milling steps. The beads milling process was performed by Laboratory Mill MINICER with ZrO2 beads. The phase identity and morphology of nano-sized YAG:Ce were characterized by X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FESEM), respectively. By controlling beads size, milling time and milling steps, we synthesized a size-tunable and uniform nano-sized YAG:Ce phosphors which average diameters were 100, 85 and 40 nm, respectively. After milling, there was no impurity and all of the peaks were in good agreement with YAG (JCPDS No. 33-0040). Luminescence and quantum efficiency (QE) of nano-sized YAG:Ce phosphors were measured by fluorescence spectrometer and QE measuring instrument, respectively. The synthesized YAG:Ce absorbed light efficiently in the visible region of 400-500 nm, and showed single broadband emission peaked at 550 nm with 50% of QE. As a result, by considering above results, high energy beads milling process could be a facile and reproducible synthesis method for nano-sized YAG:Ce phosphors.

• 대한화학회지
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• 제55권3호
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• pp.436-443
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• 2011

o-phenylenediamine, 3-acetyl-6-methyl-(2H)pyran,2,4(3H)-dione (dehydroacetic acid 또는 DHA) 및 2, 4-dihydroxy benzaldehyde에서 비롯된 4-hydroxy-3-(1-{2-(2,4-dihydroxy-benzylidene)-amino phenylimino}-ethyl)-6-methyl-pyran-2-one ($H_2$L)의 La(III), Ce(III), Pr(III), Nd(III), Sm(III) 및 Gd(III) 고체착물을 합성하여 원소분석, 전도도법, 자기수자율, UV-vis, FT-IR, 1H-NMR, X-선 회절, 열분석으로 특성을 규명하였으며, 항미생물 활성도를 조사하였다. FT-IR 스펙트럼 결과에 의하면 이 리간드는 중심금속에 대해 ONNO 주개원자를 통해 이염기성 사배위 리간드로 행동함을 알 수 있다. 원소분석 결과로부터 이들 착물의 화학량론비는 1:1 (금속: 리간드)임을 알 수 있다. 물리 및 화학적 실험결과로부터 La(III), Ce(III), Pr(III), Nd(III), Sm(III) 및 Gd(III) 착물은 일그러진 팔면체의 기하구조를 가짐을 알 수 있다. X-선 회절 데이터로부터 La(III) 및 Ce(III) 착물은 단사정계, 그리고 Pr(III) 및 Nd(III) 착물은 사방정계를 가짐을 알 수 있다. 이들 착물의 열적 행동(TG/DTA)을 연구하였으며, 속도론적 파라메타를 Horowitz-Metzger 및 Coats-Redfern 방법으로 결정하였다. 리간드와 그 착물의 항박테리아 활성도를 Staphylococcus aureus, Escherichia coli 및 Bacillus Sp.에 대해, 그리고 살균활성도를 Aspergillus Niger, Trichoderma 및 Fusarium oxysporum에 대해 각각 조사하였다.

• 한국분말재료학회지
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• 제20권2호
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• pp.142-147
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• 2013

$YBa_2Cu_3O_{7-y}$ (Y123) powders for the fabrication of bulk superconductors were synthesized by the powder reaction method using $Y_2O_3$ (99.9% purity), $BaCO_3$ (99.75%) and CuO (99.9%) powders. The raw powders were weighed to the cation ratio of Y:Ba:Cu=1:2:3, mixed and calcined at $880^{\circ}C-930^{\circ}C$ in air with intermediate repeated crushing steps. It was found that the formation of Y123 powder was more sensitive to reaction temperature than reaction time. The calcined Y123 powder and a mixture of (Y123 + 0.25 mole $Y_2O_3$ + 1 wt.% $CeO_2$, $Y_{1.5}Ba_2Cu_3O_x$ (Y1.5)) were used as raw powders for the fabrication of poly-grain or single grain superconductors. The superconducting transition temperature ($T_{c,onset}$) of the sintered Y123 sample was 91 K and the transition width was as large as 11 K, whereas the $T_{c,onset}$ of the melt-grown Y1.5 sample was 90.5 K and the transition width was 3.5 K. The critical current density ($J_c$) at 77 K and 0 T of the sintered Y123 was 700 $A/cm^2$, whereas the $J_c$ of the top-seeded melt growth (TSMG) processed Y1.5 sample was $3.2{\times}10^4\;A/cm^2$. The magnetic flux density (H) at 77 K of the TSMG-processed Y123 and Y1.5 sample showed the 0.53 kG and 2.45 kG, respectively, which are 15% and 71% of the applied magnetic field of 3.5 kG. The high H value of the TSMG-processed Y1.5 sample is attributed to the formation of the larger superconducting grain with fine Y211 dispersion.

• 한국재료학회지
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• 제24권1호
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• pp.33-36
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• 2014

This study was aimed at synthesizing and characterizing cerium-doped titania. Cerium-doped anatase titania powders were prepared by sol-gel process, with ammonium (IV) nitrate and titanium (IV) butoxide as the raw materials. The characteristics of pure $TiO_2$ and cerium-doped $TiO_2$ were investigated by XRD, TG/DTA, FE-SEM, and UV-vis spectroscopy. The results of this study show that anatase type of $TiO_2$ was obtained in as-prepared and calcined $TiO_2$ and Ce-$TiO_2$ powder. A DTA curve was also observed as the crystallization temperature decreased with increasing cerium contents. We found that the crystallite size of the obtained anatase particles decreased from 55 nm to 25 nm and the particle size decreased with increasing cerium contents. Moreover, UV-vis spectra showed that anatase titania powders with various cerium contents effectively extend the light absorption properties to the visible region.