• Title, Summary, Keyword: $CoAl_2O_4$

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Glycerol Steam Reforming for Hydrogen Production on Metal-ceramic Core-shell CoAl2O4@Al Composite Structures (금속-세라믹 Core-Shell CoAl2O4@Al 구조체를 적용한 불균일계 촉매의 글리세롤 수소전환 반응특성)

  • Kim, Jieun;Lee, Doohwan
    • Clean Technology
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    • v.21 no.1
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    • pp.68-75
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    • 2015
  • In this study, we investigated the structure and properties of a highly heat conductive metal-ceramic core-shell CoAl2O4@Al micro-composite for heterogeneous catalysts support. The CoAl2O4@Al was prepared by hydrothermal surface oxidation of Al metal powder, which resulted in the structure with a high heat conductive Al metal core encapsulated by a high surface area CoAl2O4 shell. For comparison, CoAl2O4 was also prepared by co-precipitation method and also utilized for a catalyst support. Rh catalysts supported on CoAl2O4@Al and CoAl2O4 were prepared by incipient wetness impregnation and characterized by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), CO chemisorption, and temperature-programmed reduction (TPR). The properties of catalysts were investigated for glycerol steam reforming reaction for hydrogen production at 550 ℃. Rh/CoAl2O4@Al exhibited about 2.8 times higher glycerol conversion turnover frequency (TOF) than Rh/CoAl2O4 due to facilitated heat transport through the core-shell structure. The CoAl2O4@Al and CoAl2O4 also showed some catalytic activities due to a partial reduction of Co on the support, and a higher catalytic activity was also found on the CoAl2O4@Al core-shell than CoAl2O4. These catalysts, however, displayed deactivation on the reaction stream due to carbon deposition on the catalysts surface.

Coloration and Chemical Stability of SiO2 and SnO2 Coated Blue CoAl2O4 Pigment (SiO2, SnO2 코팅된 청색 CoAl2O4 안료의 색상, 물성 평가 연구)

  • Yun, JiYeon;Yu, Ri;Pee, Jae-Hwan;Kim, YooJin
    • Journal of Korean Powder Metallurgy Institute
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    • v.21 no.5
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    • pp.377-381
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    • 2014
  • This work describes the coloration, chemical stability of $SiO_2$ and $SnO_2$-coated blue $CoAl_2O_4$ pigment. The $CoAl_2O_4$, raw materials, were synthesized by a co-precipitation method and coated with silica ($SiO_2$) and tin oxide ($SnO_2$) using sol-gel method, respectively. To study phase and coloration of $CoAl_2O_4$, we prepared nano sized $CoAl_2O_4$ pigments which were coated $SiO_2$ and $SnO_2$ using tetraethylorthosilicate, $Na_2SiO_3$ and $Na_2SiO_3$ as a coating material. To determine the stability of the coated samples and their colloidal solutions under acidic and basic conditions, colloidal nanoparticle solutions with various pH values were prepared and monitored over time. Blue $CoAl_2O_4$ solutions were tuned yellow color under all acidic/basic conditions. On the other hand, the chemical stability of $SiO_2$ and $SnO_2$-coated $CoAl_2O_4$ solution were improved when all samples pH values, respectively. Phase stability under acidic/basic condition of the core-shell type $CoAl_2O_4$ powders were characterized by transmission electron microscope, X-ray diffraction, CIE $L^*a^*b^*$ color parameter measurements.

Formation of $FeAl_2O_4$ in $H_2-CO_2$ and its behavior in $CO_2$(I) ($H_2-CO_2$에서 $FeAl_2O_4$의 생성기구와 $CO_2$ 중에서의 거동(I))

  • 이홍림;강명구
    • Journal of the Korean Ceramic Society
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    • v.19 no.4
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    • pp.309-315
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    • 1982
  • $FeAl_2O_4$ was formed from the starting material of $Fe_2O_3$ and $Al_2O_3$ by controlling the oxygen partial pressure using $H_2-CO_2$ gas mixture, over the temperature range of 800~120$0^{\circ}C$. The formation mechanism of $FeAl_2O_4$ was found to be a second order chemical reaction, and the activation energy of formation was observed as 39.97 kcal/mole. Vaporization behavior of $FeAl_2O_4$ under $CO_2$ atmosphere was observed over the temperature range of 800~120$0^{\circ}C$. $FeAl_2O_4$ was vaporized by a second order chemical reaction and the activation energy was found to be 21.8kcal/mole. Electrical conductivity of $FeAl_2O_4$ was also measured.

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P123-Templated Co3O4/Al2O3 Mesoporous Mixed Oxides for Epoxidation of Styrene

  • Jung, Mie-Won;Kim, Young-Sil
    • Korean Journal of Materials Research
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    • v.22 no.6
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    • pp.316-320
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    • 2012
  • $Co_3O_4$, $Al_2O_3$ and $Co_3O_4$/$Al_2O_3$ mesoporous powders were prepared by a sol-gel method with starting matierals of aluminum isopropoxide and cobalt (II) nitrate. A P123 template is employed as an active organic additive for improving the specific surface area of the mixed oxide by forming surfactant micelles. A transition metal cobalt oxide supported on alumina with and without P123 was tested to find the most active and selective conditions as a heterogeneous catalyst in the reaction of styrene epoxidation. A bBlock copolymer-P123 template was added to the staring materials to control physical and chemical properties. The properties of $Co_3O_4$/$Al_2O_3$ powder with and without P123 were characterized using an X-ray diffractometer (XRD), a Field-Emission Scanning Electron Microscope (FE-SEM), a Bruner-Emmertt-Teller (BET) surface analyzer, and $^{27}Al$ MAS NMR spectroscopy. Powders with and without P123 were compared in catalytic tests. The catalytic activity and selectivity were monitored by GC/MS, $^1H$, and $^{13}C$-NMR spectroscopy. The performance for the reaction of epoxidation of styrene was observed to be in the following order: [$Co_3O_4$/$Al_2O_3$ with P123-1173 K > $Co_3O_4$/$Al_2O_3$ with P123-973 K > $Co_3O_4$-973 K>$Co_3O_4$/$Al_2O_3$-973 K > $Co_3O_4$/$Al_2O_3$ with P123-1473 K > $Al_2O_3$-973 K]. The existence of ${\gamma}$-alumina and the nature of the surface morphology are related to catalytic activity.

Hydrothermal synthesis of $(Li,Al)MnO_2(OH)_2$:Co compound (수열법에 의한 $(Li,Al)MnO_{2}(OH)_{2}$:Co 화합물의 합성)

  • 최종건;황완인;김판채
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.11 no.4
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    • pp.154-159
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    • 2001
  • (Li,Al)$MnO_2(OH)_2$:Co compound was synthesized by hydrothermal method. $MnO_2$, LiOH.$H_2$O, $Co_3O_4$ and $Al(OH)_3$ were used as starting materials and the optimum conditions for synthesis of monolithic (Li,Al)$MnO_2(OH)_2$:Co compound were as follows : reaction temperature; $200^{\circ}C$, reaction time; 3 days, hydrothermal solvent; 3M-KOH solution, reaction apparatus; seesaw type, atomic ratio of Li:Al:Mn;Co = 1:2.1:2.5~2:0.5~1. Monolithic(Li,Al)$MnO_2(HO)_2$:Co compound synthesized in this work had a god crystallinity and excellent color forming effect as a blue pigment compatible with natural mineral. The particles of the synthesized (Li,Al)$MnO_2(OH)_2$:Co compound have hexagonal plate shape with the size of 0.5~1 $\mu\textrm{m}$.

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Crystallographic and Magnetic Properties of the Hyperthermia Material CoFe2O4@AlFe2O4

  • Choi, Hyunkyung;An, Mijeong;Eom, Wonyoung;Lim, Sae Wool;Shim, In-Bo;Kim, Chul Sung;Kim, Sam Jin
    • Journal of the Korean Physical Society
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    • v.70 no.2
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    • pp.173-176
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    • 2017
  • Hard/soft $CoFe_2O_4@AlFe_2O_4$ core/shell nanoparticles were prepared by using a high temperature thermal decomposition method with seed-mediated growth. The structural, magnetic and thermal properties of the nanoparticles were investigated by using X-ray diffraction, vibrating sample magnetometer, MagneTherm, and $M{\ddot{o}}ssbauer$ spectroscopy. The crystal structure of nanoparticles was determined to be cubic spinel ferrite with space group Fd-3m. The $CoFe_2O_4$ nanoparticles were found to show high magnetization and coercivity while $AlFe_2O_4$ nanoparticles were found to show low magnetization and coercivity. The $CoFe_2O_4@AlFe_2O_4$ core/shell nanoparticles showed intermediate values of magnetization and the coercivity between those of $CoFe_2O_4$ and $AlFe_2O_4$. Also, the blocking temperature ($T_B$) of the nanoparticles (NPs) was observed to be 280, 50, and 225 K for $CoFe_2O_4$, $AlFe_2O_4$ and $CoFe_2O_4@AlFe_2O_4$, respectively. The core/shell ferrite shows a $T_B$ near 225 K, associated with the harder $CoFe_2O_4$ NPs. Temperatures below 225 K, the zero-field-cooled curves show changes in their slopes at a temperature near 50 K, corresponding to the second blocking temperature associated with the softer $AlFe_2O_4$ NPs.

Synthesis of (Co,Mg)Al2O4 and (Ni,Mg)Al2O4 Blue Ceramic Nano Pigment by Polymerized Complex Method (착체중합법을 이용한 (Co,Mg)Al2O4 및 (Ni,Mg)Al2O4 청색 나노 무기안료 합성)

  • Son, Bo-Ram;Yoon, Dea-Ho;Kim, Jin-Ho;Han, Kyu-Sung;Cho, Woo-Suk;Hwang, Kwang-Taek
    • Journal of the Korean Ceramic Society
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    • v.50 no.6
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    • pp.510-517
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    • 2013
  • In this study, the properties of blue inorganic nano-pigments with a spinel structure were systematically investigated. We report the preparation of a blue ceramic nano-pigment and the Co and Ni substitutional effects on the blue color. $MgAl_2O_4$ was selected as the crystalline host network for the synthesis of cobalt and nickel-based blue ceramic nano-pigments. Various compositions of $Co_xMg_{1-x}Al_2O_4$ and $Ni_xMg_{1-x}Al_2O_4$ ($0{\leq}x{\leq}1$) powders were prepared using apolymerized complex method. The obtained powder was preheated at $400^{\circ}C$ for 5 h and then calcined at $1000^{\circ}C$ for 5 h. XRD patterns of the (Co,Mg)$Al_2O_4$ and (Ni,Mg)$Al_2O_4$ samples showed a single phase of the spinel structure in all compositions. TEM results indicated nano-sized pigments for (Co,Mg)$Al_2O_4$ and (Ni,Mg)$Al_2O_4$ with a particle size ranging from 20 to 50 nm. The characteristics of the color tones of (Co,Mg)$Al_2O_4$ and (Ni,Mg)$Al_2O_4$ were analyzed by CIE $L^*a^*b^*$ measurements. In addition, the thermal stability and the binding characteristics of (Co,Mg)$Al_2O_4$, (Ni,Mg)$Al_2O_4$ are discussed in terms of the TG-DSC and FT-IR results, respectively.

1-Butyl-3-methylimidazolium tetrafluoroborate/Al2O3 Composite Membrane for CO2 Separation (이산화탄소 분리를 위한 이온성 액체 1-butyl-3-methylimidazolium tetrafluoroborate/Al2O3 복합체 분리막)

  • Yoon, Ki Wan;Kang, Sang Wook
    • Membrane Journal
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    • v.27 no.3
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    • pp.226-231
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    • 2017
  • 1-Butyl-3-methylimidazolium tetrafluoroborate ($BMIM^+BF_4{^-}$) and $Al_2O_3$ as metal oxide for preparation of composite membrane were utilized for the $CO_2$ separation. When 13 nm $Al_2O_3$ nanoparticles were incorporated into ionic liquid $BMIM^+BF_4{^-}$, the separation performance for composite membrane showed the selectivity ($CO_2/N_2$) of 30.5 and $CO_2$ permeance of 45.7 GPU. The enhanced separation performance was attributable to the increased $CO_2$ solubility by both oxide layer of $Al_2O_3$ and abundant free ions of ionic liquid. In particular, $Al_2O_3$ nanoparticles acted as obstacles to nitrogen gas, resulting in the decrease of permeability of nitrogen gas. As a result, the carbon dioxide separation performance could be enhanced.

Dy co-doping effect on photo-induced current properties of Eu-doped SrAl2O4 phosphor (Eu 도핑 SrAl2O4 형광체의 광 여기 전류 특성에 대한 Dy 코-도핑 효과)

  • Kim, Sei-Ki
    • Journal of Sensor Science and Technology
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    • v.18 no.1
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    • pp.48-53
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    • 2009
  • $Eu^{2+}$-doped ${SrAl_2}{O_4}$ and $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors have been synthesized by conventional solid state method. Photocurrent properties of $Eu^{2+}$ doped ${SrAl_2}{O_4}$ and $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors, in order to elucidate $Dy^{3+}$ co-doping effect, during and after ceasing ultraviolet-ray (UV) irradiation have been investigated. The photocurrent of $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors during UV irradiation was 4-times lower than that of $Eu^{2+}$-doped ${SrAl_2}{O_4}$ during UV irradiation, and 7-times higher than that of $Eu^{2+}$-doped ${SrAl_2}{O_4}$ after ceasing UV irradiation. The photocurrent results indicated that holes of charge carriers captured in hole trapping center during the UV irradiation and liberated after-glow process, and made clear that $Dy^{3+}$ of co-dopant acted as a hole trap. The photocurrent of ${SrAl_2}{O_4}$ showed a good proportional relationship to UV intensity in the range of $1{\sim}5mW/cm^2$, and $Eu^{2+}$-doped ${SrAl_2}{O_4}$ was confirmed to be a possible UV sensor.

Low Temperature Sintering and Dielectric Properties of Ceramic/glass Composites with CAS-Based glass (CAS계 유리가 첨가된 ceramic/glass 복합체의 소결 및 마이크로파 유전 특성)

  • Kim, Kwan-Soo;Kim, Myung-Soo;Kim, Yun-Han;Kim, Kyung-Joo;Kim, Shin;Yoon, Sang-Ok
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.195-195
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    • 2008
  • CAS계 유리에 $CaCO_3-Al_2O_3$ 혼합물 및 화합물을 10, 30 wt% 첨가하여 저온 소걸 및 마이크로파 유전 특성을 고찰하였다. CAS계 유리의 연화온도는 $841^{\circ}C$ 이며, CAS계 유리에 $CaCO_3$ 와 30 wt%의 $CaCO_3-Al_2O_3$ 혼합물을 melting되며, 10 wt%의 $CaCO_3$, $Al_2O_3$, $1CaCO_3-1Al_2O_3$ 혼합물 및 $CaAl_2O_4$ 화합물를 10 wt% 첨가하였을 때 $900^{\circ}C$ 이하에서 소걸이 가능하였다. 복합체의 XRD 상 분석 결과, CaCO3를 첨가하였을 때에는 모든 조성이 비정질을 나타내었고, $Al_2O_3$$1CaCO_3-1Al_2O_3$ 혼합물은 $Al_2O_3$ 결정상이 생성되었고, $CaAl_2O_4$ 화합물은 $CaAl_2Si_2O_8$의 hexagonal와 anorthite 결정상이 생성되었다. 따라서 CAS-10 (A, C-A, CA) 복합체는 $900^{\circ}C$에서 각각 유전율 ($\varepsilon_r$) 6.4, 6.9, 5.15 와 품질계수 ($Q^*f$) 2,400, 1,500, 3,000의 마이크로파 유전 특성을 나타내어 LTCC 기판 재료로 사용이 가능하며, 특히 $CaAl_2O_4$ 화합물을 사용하였을 때 가장 우수한 유전 특성을 나타내는 것을 확인하였다.

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