• Title/Summary/Keyword: 세리아-지르코니아

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Microstructure of alumina-dispersed Ce-TZP ceramics (알루미나가 분산된 세리아 안정화 지르코니아 세라믹스의 미세구조)

  • 김민정;이종국
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.10 no.2
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    • pp.122-127
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    • 2000
  • Microstructural evolutions in ceria-stabilized zirconia (Ce-TZP) and alumina-dispersed Ce-TZP ceramics were investigated as functions of doping and annealing conditions. All of sintered specimens showed the relative density over 99 %. Sintered specimens had linear grain boundaries and normal grain shapes, but ceria-doped specimens had irregular grain shapes and nonlinear grain boundaries due to the diffusion-induced grain boundary migration during annealing at $1650^{\circ}C$ for 2 h. Mean grain boundary length of Ce-TZP with irregular grain shapes was higher than that of normal grain shapes, and was a value of 23pm at the maximum. Alumina particles dispersed in Ce-TZP inhibited the grain growth of zirconia particles. $Al_2O_3$Ce-TZP doped with ceria and annealed at $1650^{\circ}C$ for 2 h showed irregular grain shapes as well as small grain size. Added alumina particles showed the grain growth during sintering or annealing, and they changed the position from grain boundary to inside of the grains during the annealing. The specimens with normal grain shapes showed an intergranular fracture mode, whereas the specimens with irregular grain shapes showed a transgranular fracture mode during the crack propagation.

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Dispersion and Stability of Platinum Catalysts Supported on Titania-, Vanadia-, Zirconia- and Ceria-Incorporated Silicas (티타니아, 바나디아, 지르코니아, 세리아를 고정한 실리카에 담지된 백금 촉매의 분산성과 안정성)

  • Kim, Mi-Young;Seo, Gon;Park, Jung-Hyun;Shin, Chae-Ho;Kim, Eun-Seok
    • Korean Chemical Engineering Research
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    • v.49 no.1
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    • pp.1-9
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    • 2011
  • Platinum catalysts were prepared by impregnating platinum precursor on titania-, vanadia-, zirconia- and ceria-incorporated silicas followed by hydrogen peroxide treatment. The effects of the oxide incorporation and the hydrogen peroxide treatment in the preparation of the platinum catalysts on their platinum dispersion and catalytic activity in carbon monoxide oxidation were investigated. XRD, TEM, EXAFS, XPS and carbon monoxide chemisorption studies confirmed the high dispersion of platinum even on silica by the oxide incorporation and hydrogen peroxide treatment. However, the type of oxides incorporated on silica caused considerable variances in the adsorption and the catalytic activity in the oxidation of carbon monoxide on them. The incorporation of titania, zirconia and ceria on silica and further hydrogen peroxide treatment enhanced the platinum dispersion, resulting in the improved catalytic activities. Among the catalysts supported on the oxide-incorporated silicas, the platinum catalyst supported on zirconia-incorporated silica exhibited the highest activity because of the highest platinum dispersion due to the formation of Pt-O-Zr bonds.

Microstructure of Yttria-doped Ceria-Stabilized Zirconia Polycrystals (Yttria를 도핑한 세리아 안정화 지르코니아 세라믹스의 미세구조)

  • Lee, J.K.;Kang, H.H.;Seo, D.S.;Lee, E.G.;Kim, H.
    • Korean Journal of Materials Research
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    • v.9 no.8
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    • pp.768-774
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    • 1999
  • Yttia-doped ceria-stabilized ziconia polycrystals(Ce-TZP) was prepared by dipping method and its microstructure was investigated. By controlling doped-yttria content and annealing condition, yttria-doped Ce-TZP showed the microstructure with irregular grain shape and undulated grain boundary. Irregularity of grain shape increased with the amount of yttria doped, and severe undulated grain boundary was observed mainly at the surface region. In the case of yttria-doped Ce-TZP annealed at 1$650^{\circ}C$ for 2h after two dipping times into yttrium nitrate solution of 0.2M, it showed irregular grain shape both at the surface and at the interior region as well as the most severe irregularity. Hot pressed specimen had mean grain size of 0.3$\mu\textrm{m}$ and undulated grain boundary. All specimens with irregular grain shape were retained the tetragonal phase. The fracture toughness of yttria-doped Ce-TZP with irregular grain shape was over the value of 17.6MPa.m(sup)1/2.

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Preparation of Ceria-stabilized Zirconia Ceramics with Irregular Grain Shape (불규칙 입자형상을 갖는 세리아 안정화 지르코니아 세라믹스의 제조)

  • 강현희;이종국
    • Journal of the Korean Ceramic Society
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    • v.36 no.4
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    • pp.372-379
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    • 1999
  • Hihg-toughened ceria-stabilized tetragonal zirconia ceramics with irregular grain shape and undulated grain boundary was prepared by ceria doping. Irregularity of grain shapes was increased with the amount of doped ceria. But in case of the large amount of doped ceria grain boundary was migrated to the reverse direction of DIGM. Ceria-stabilized zirconia ceramics annealed at 1650$^{\circ}C$ for 2h after twice dippings into cerium nitrate solu-tion of 0.2M and sintering at 1500$^{\circ}C$ for 2h showed the highest grain boundary length with a value of 23.6$\mu\textrm{m}$ Ceria concentration difference between convex and concave sides in irregular grains was observed over 1 mol% but not observed in normal grains, Specimens with normal grain shape showed intergranular fracture mode whereas the specimens with irregular grain shape showed transgranular fracture mode.

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Syngas and Hydrogen Production from $CeO_2/ZrO_2$ coated Foam Devices under Simulated Solar Radiation (다공성 폼에 코팅된 $CeO_2/ZrO_2$ 를 이용한 고온 태양열 합성가스 및 수소 생산 연구)

  • Jang, Jong-Tak;Yoon, Ki-June;Han, Gui-Young
    • 한국태양에너지학회:학술대회논문집
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    • 2012.03a
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    • pp.260-266
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    • 2012
  • Syngas and hydrogen from the $CeO_2/ZrO_2$ coated foam devices were investigated under simulated solar radiation. The $CeO_2/ZrO_2$ coated SiC, Ni and Cu foam device were prepared using drop-coating method. Syngas production step was performed at $900^{\circ}C$, and hydrogen production process was performed for ten repeated cycles to compare the CeO2 conversion in syngas production step, $H_2$ yield in hydrogen production step and cycle reproducibility. The produced syngas had the $H_2$/CO ratio of 2, which was suitable for methanol synthesis or Fischer-Tropsch synthesis process. In addition, syngas and hydrogen production process is one of the promising chemical pathway for storage and transportation of solar heat by converting solar energy to chemical energy. After ten cycles of redox reaction, the $CeO_2/ZrO_2$ was analyzed using XRD pattern and SEM image in order to characterize the physical and chemical change of metal oxide at the high temperature.

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Syngas and Hydrogen Production under concentrated solar radiation : Redox system of $ZrO_2$ nano-structure (고온 태양열을 이용한 합성가스 및 수소 생산 : $ZrO_2$ 나노 구조화에 따른 산화/환원 특성)

  • Jang, Jong-Tak;Lee, Jong-Min;Cho, Eun-Su;Yang, Seung-Chan;Yoon, Ki-June;Han, Gui-Young
    • 한국태양에너지학회:학술대회논문집
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    • 2012.03a
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    • pp.463-469
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    • 2012
  • Solar thermochemical syngas and hydrogen production process bv redox system of metal oxide was performed under direct irradiation of the metal oxide on the SiC ceramic foam device using solar simulator. $CeO_2/ZrO_2$ nanotube has been synthesized by anodic oxidation method. Syngas and hydrogen production process is one of the promising chemical pathway for storage and transportation of solar heat by converting solar energy to chemical energy. The produced syngas had the $H_2/CO$ ratio of 2, which was suitable for methanol synthesis or Fischer-Tropsch synthesis process. After ten cycles of redox reaction, $CeO_2$ was analyzed using XRD pattern and SEM image in order to characterize the physical and chemical change of metal oxide at the high temperature.

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Mechanical Properties Observation of Ce-TZP Ceramics by Quantity Change of CeO2 (CeO2의 첨가량 변화에 따른 세리아 안정화 지르코니아 세라믹스의 기계적 특성 관찰)

  • Kang, Jong-Bong
    • Journal of the Korean Ceramic Society
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    • v.47 no.5
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    • pp.439-444
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    • 2010
  • The usual ceramic process of mixing and milling in state of oxide of $ZrO_2$ and $CeO_2$ was adopted in wet process to manufacture Ce-TZP in this study. The maximum dispersion point of every slurry manufactured with mixture of $ZrO_2$ and $CeO_2$ was neat at pH10. The stable slurry in average particle size of 90 nm can be manufactured when it is dispersed with use of ammonia water and polycarboxylic acid ammonium. The sintered Ce-TZP ceramics manufactured with addition of $CeO_2$ less than 10 mol% was progressed to the fracture of specimen due to the monoclinic phase existence more than 30% at the room temperature. More than 99% of tetragonal phase was created for the sintered body with addition of $CeO_2$ beyond 18 mol%, but the mechanical property degrade on the entire specimen was brought due to the $CeO_2$ existing above 3%. Consequently, the optimal Ce-TZP combined in oxide state was identified in 16 mol% of $CeO_2$ contents.

Preparation and Characterization of Ceria Stabilized Tetragonal Zirconia Polycrystals(I) : Effect of CeO2 Contents on the Mechanical Properties of Ce-TZP (세리아 안정화 지르코니아의 제조 및 특성(I) : CeO2첨가량 변화에 따른 Ce-TZP의 기계적 특성)

  • Jung, Seung-Hwa;Kang, Jong-Bong
    • Korean Journal of Materials Research
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    • v.20 no.7
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    • pp.379-384
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    • 2010
  • The usual ceramic process of mixing and milling in state of oxides $ZrO_2$ and $CeO_2$ was adopted in this study in a wet process to manufacture Ce-TZP. $CeO_2$-$ZrO_2$ ceramics containing 8~20 mol% $CeO_2$ were made by heat treatment at $1250\sim1500^{\circ}C$ for 5hr. The maximum dispersion point of every slurry manufactured with a mixture of $ZrO_2$ and $CeO_2$ was neat at pH10. A stable slurry with average particle size of 90 nm can be manufactured when it is dispersed with the use of ammonia water and polycarboxylic acid ammonium. The sintered Ce-TZP ceramics manufactured with the addition of $CeO_2$ in a concentration of less than 10 mol% progressed to the fracture of the specimen due to the existence of a monoclinic phase of more than 30% at room temperature. More than 99% of the tetragonal phase was created for the sintered body with the addition of $CeO_2$ beyond 18 mol%, but the degradation of the mechanical properties on the entire specimen was brought about due to the $CeO_2$ existing in a percentage above 3%. Consequently, the optimal Ce-TZP level combined in the oxide state was identified to be 16 mol% of $CeO_2$ contents.

Low Temperature Selective Catalytic Reduction of NO with $NH_3$ over Mn/$CeO_2$ and Mn/$ZrO_2$ (Mn/$CeO_2$와 Mn/$ZrO_2$ 촉매 상에서 $NH_3$를 사용한 NO의 선택적 촉매 산화 반응)

  • Ko, Jeong Huy;Park, Sung Hoon;Jeon, Jong-Ki;Sohn, Jung Min;Lee, See-Hoon;Park, Young-Kwon
    • Applied Chemistry for Engineering
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    • v.23 no.1
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    • pp.105-111
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    • 2012
  • Manganese (Mn) catalysts were generated using $CeO_2$ and $ZrO_2$supports synthesized by the supercritical hydrothermal method and two different Mn precursors, aimed at an application for a low-temperature selective catalytic reduction process. Manganese acetate (MA) and manganese nitrate (MA) were used as Mn precursors. Effects of the kind and the concentration of the Mn precursor used for catalyst generation on the NOx removal efficiency were investigated. The characteristics of the generated catalysts were analyzed using $N_2$ adsorption-desorption, thermo-gravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. De-NOx experiments were carried out to measure NOx removal efficiencies of the catalysts. NOx removal efficiencies of the catalysts generated using MA were superior to those of the catalysts generated using MN at every temperature tested. Analyses of the catalyst characteristics indicated that the higher NOx removal efficiencies of the MA-derived catalysts stemmed from the higher oxygen mobility and the stronger interaction with support material of $Mn_2O_3$ produced from MA than those of $MnO_2$ produced from MN.

The Effect of Calcination Temperature on the Performance of Ni-Ce0.8Zr0.2O2 Catalysts for Steam Reforming of Methane under Severe Conditions (가혹한 조건의 SRM 반응에서 Ni-Ce0.8Zr0.2O2 촉매의 소성온도에 따른 영향)

  • Jang, Won-Jun;Jeong, Dae-Woon;Shim, Jae-Oh;Roh, Hyun-Seog
    • Journal of Hydrogen and New Energy
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    • v.23 no.3
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    • pp.213-218
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    • 2012
  • Steam reforming of methane (SRM) is the primary method to produce hydrogen. Commercial Ni-based catalysts have been optimized for SRM with excess steam ($H_2O/CH_4$ > 2.5) at high temperatures (> $700^{\circ}C$). However, commercial catalysts are not suitable under severe conditions such as stoichiometric steam over methane ratio ($H_2O/CH_4$ = 1.0) and low temperature ($600^{\circ}C$). In this study, 15wt.% Ni catalysts supported on $Ce_{0.8}Zr_{0.2}O_2$ were prepared at various calcination temperatures for SRM at a very high gas hourly space velocity (GHSV) of $621,704h^{-1}$. The calcination temperature was systematically varied to optimize 15wt.% $Ni-Ce_{0.8}Zr_{0.2}O_2$ catalyst at a $H_2O/CH_4$ ratio of 1.0 and at $600^{\circ}C$. 15wt.% $Ni-Ce_{0.8}Zr_{0.2}O_2$ catalyst calcined at $500^{\circ}C$ exhibited the highest $CH_4$ conversion as well as stability with time on stream. Also, 15wt.% $Ni-Ce_{0.8}Zr_{0.2}O_2$ catalyst calcined at $500^{\circ}C$ showed the highest $H_2$ yield (58%) and CO yield (21%) among the catalysts. This is due to complex NiO species, which have relatively strong metal to support interaction (SMSI).