• Proceedings of the KIEE Conference
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• 2008.05a
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• pp.175-176
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• 2008

In this study, the sintering properties and structural properties of the $Mg_5Ta_4O_{15}$cation-deficient perovskite ceramics with $Li_2CO_3$ additions are investigated. The cation-deficient perovskite ceramics are prepared through the solid-state route. According to the XRD pattern, $Mg_4Ta_2O_9$, $MgTa_2O_6$ and $Mg_5Ta_4O_{15}$ phase existed in sintered pure $Mg_5Ta_4O_{15}$ ceramics. With $Li_2CO_3$, additions, the peak intensities of $Mg_4Ta_2O_9$ and $MgTa_2O_6$ phase were reduced. Also, diffraction intensity of the $Mg_5Ta_4O_{15}$ phase was increased with increments of $Li_2CO_3$ additions. The bulk densities were increased with increasing of $Li_2CO_3$ amount and approach the theoretical density of the $Mg_5Ta_4O_{15}$ ceramics, more and more. Microstructure of the $Mg_5Ta_4O_{15}$ ceramics were densified more and more by additions of $Li_2CO_3$. The bulk density of $Mg_5Ta_4O_{15}$+5wt% $Li_2CO_3$ ceramics sintered at $1500^{\circ}C$ for 10 hours was $5.88g/cm^3$.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.720-725
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• 2011

Gold catalysts supported on metal-oxides were prepared by co-precipitation using the various metal nitrates and chloroauric acid as precursors, and effect of water addition on the catalytic activity in CO oxidation was investigated. Among the various supported gold catalysts, Au/$Co_{3}O_{4}$ and Au/ZnO catalysts showed the excellent activity for CO oxidation. Water in the reactant gas had a negative effect on the oxidation activity over Au/$Co_{3}O_{4}$ catalysts and a positive effect on that over Au/ZnO, which means the activity depends strongly on the nature of support. It was also confirmed that no significant change in the particle size of gold was observed after reaction both in dry and wet conditions. This fact suggested that the deactivated catalyst due to a carbonate species could be regenerated by water addition in the reactant gas.

• 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.

• Journal of the Korean Society of Food Science and Nutrition
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• v.14 no.4
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• pp.396-400
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• 1985

For investigation of the optimum gas composition for CA storage of Shingo pear, the pears were kept at 8 different $O_2/CO_2$ concentrations for 5 months and checked in some indices related in storability and sensory quality after storage and transfer to air at $20^{\circ}C$ for 1 week. The pears kept in all the CA storage conditions in this experiment, especially in $3%\;O_2-3%,\;CO_2$, were lower in weight loss than the pears kept in cold room. Immediately after storage decay rates of the pears stored at CA storage conditions except $3%\;O_2-3%,\;CO_2$ and $3%\;O_2-4%,\;CO_2$ were more serious than that of the pears stored at cold room, and the rates of the pears, especially stored at cold room, were rapidly increased by exposure to $20^{\circ}C$ after storage. The highest soluble solid content and firmess were shown in the pears stored at the CA storage condition of $3%\;O_2-3%,\;CO_2$, and the pears stored at the conditions of $3%\;O_2$ and $4%{\sim}5%\;CO_2$ had the highest acidity. In sensory evaluation the pears kept at the conditions of $3%O_2-3%$, 4% and 5% $CO_2$ maintained a good quality after storage and after storage and transfer to air at $20^{\circ}C$ for 1 week.

• Journal of the Korean Ceramic Society
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• v.38 no.12
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• pp.1174-1179
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• 2001

Mn-Co-Ni oxide system has been used as the NTC thermistors for normal temperature applications. Mn-Co-Ni oxide-based thermistors with various compositions were sintered at 1250$^{\circ}C$ for 3 hours and then maintained at 1000$^{\circ}C$ for 3 hours. The electrical properties of the thermistors fabricated were measured. In particular the MCN622 composition (Mn$_3$O$_4$60 wt%, Co$_3$O$_4$20 wt%, NiO 20wt%) exhibited the lowest resistivity and relatively high B constant. The MCN721 composition (Mn$_3$O$_4$70wt%, Co$_3$O$_4$20wt%, NiO 10 wt%) showed the higher resistivity than any other compositions. The aging properties of each composition showed comparatively stable characteristics within ${\pm}$2%.

• Bulletin of the Korean Chemical Society
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• v.9 no.6
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• pp.333-337
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• 1988

Spinel $CoFe_2O_4$ solid solutions containing up to 50 mol% CoO were synthesized with spectroscopically pure CoO and ${\alpha}-Fe_2O_3$ polycrystalline powders. The spinel structures of the $CoFe_2O_4$ solid solutions were analyzed from XRD patterns and the Mossbauer spectra showed that the quenched $CoFe_2O_4$ had a partially inversed spinel structure ($Co_{0.23}Fe_{0.77}$) < $Co_{0.77}Fe_{1.23}$ > $O_4$, while the slowly cooled $CoFe_2O_4$ was completely inversed spinel ($Co_{0.04}Fe_{0.96}$) <$Co_{0.96}Fe_{1.04}$ > $O_4$. The $CoFe_2O_4$ specimens containing 10, 20, 30 and 40 mol% CoO turned to be a mixture of corundum and spinel structures. Electrical conductivities were measured as a function of temperature from 300 to $900^{\circ}C$ under oxygen partial pressures from $10^{-3}$ to 1 atm. The temperature dependencies of the electrical conductivity show different behaviors in the low- and high-temperature regions. The average activation energies are 0.23 eV and 0.80 eV in the low- and high-temperature regions, respectively. It is suggested that $Co^{2+} {\to} CO^{3+} + e^-$ and $Fe^{2+} {\rightleftharpoons} Fe^{3+} + e^-$ are the main conduction mechanisms responsible for the electronic conduction in the low- and high-temperature regions, respectively.

• Clean Technology
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• v.21 no.1
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• pp.39-44
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• 2015

This study investigated the effects of six metal oxide nanoparticles (NPs: CuO, NiO, TiO₂, Fe₂O₃, Co₃O₄, ZnO) on seed germination and germination index (G.I) for five types of seeds: Brassica napus L., Malva verticillata L., Brassica olercea L., Brassica campestris L., Daucus carota L. NPs of CuO, ZnO, NiO show significant toxicity impacts on seed activities [CuO (6-27 mg/L), ZnO (16-86 mg/L), NiO (48-112 mg/L)], while no significant effects were observed at > 1000 mg/L of TiO₂, Fe₂O₃, Co₃O₄. Tested five types of seed showed different sensitivities on seed germination and root activity, especially on NPs of CuO, ZnO, NiO. Malva verticillata L. seed was highly sensitive to toxic metal oxide NPs and showed following EC₅₀s : CuO 5.5 mg/L, ZnO 16.4 mg/L, NiO 53.4 mg/L. Mostly following order of toxicity was observed, CuO > ZnO > NiO > Fe₂O₃ ≈ Co₃O₄ ≈ TiO₂, where slightly different toxicity order was observed for carrot, showing CuO > NiO ≈ ZnO > Fe₂O₃ ≈ Co₃O₄ ≈ TiO₂.

• Journal of Powder Materials
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• v.22 no.5
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• pp.350-355
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• 2015

Perforated polygonal cobalt oxide ($Co_3O_4$) is synthesized using electrospinning and a hydrothermal method followed by the removal of a carbon nanofiber (CNF) template. To investigate their formation mechanism, thermogravimetric analysis, field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy are examined. To obtain the optimum condition of perforated polygonal $Co_3O_4$, we prepare three different weight ratios of the Co precursor and the CNF template: sample A (Co precursor:CNF template- 10:1), sample B (Co precursor:CNF template-3.2:1), and sample C (Co precursor:CNF template-2:1). Among them, sample A exhibits the perforated polygonal $Co_3O_4$ with a thin carbon layer (5.7-6.2 nm) owing to the removal of CNF template. However, sample B and sample C synthesized perforated round $Co_3O_4$ and destroyed $Co_3O_4$ powders, respectively, due to a decreased amount of Co precursor. The increased amount of the CNF template prevents the formation of polygonal $Co_3O_4$. For sample A, the optimized weight ratio of the Co precursor and CNF template may be related to the successful formation of perforated polygonal $Co_3O_4$. Thus, perforated polygonal $Co_3O_4$ can be applied to electrode materials of energy storage devices such as lithium ion batteries, supercapacitors, and fuel cells.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.6
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• pp.396-401
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• 2014

Nanomaterials have been widely used in many fields. This study investigates the effects of metal oxide nanoparticles (CuO, NiO, $TiO_2$, $Fe_2O_3$, $Co_3O_4$, ZnO) on germination and germination index (G.I.) of seeds, Lactuca and Raphanus. Under aqueous exposure, CuO on Lactuca shows the most significant impacts on activities compared to others, showing $EC_{50s}$ for germination and G.I. as 0.46 mg/L and 0.37%, respectively. The effects of nanoparticle phytotoxicity on seed Lactuca was much higher than that of Raphanus. In general, the toxicities on seed germination and germination index were as following orders : CuO > ZnO > NiO ${\gg}$ $TiO_2$, $Fe_2O_3$, $Co_3O_4$. No measurable inhibition was observed at 1,000 mg/L (maximum exposure concentration) of $TiO_2$, $Fe_2O_3$, $Co_3O_4$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.6
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• pp.270-275
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• 2021

ZnO was synthesized according to the transformation behavior and crystallization conditions of Zn-intermediate obtained by zinc sulfate as a precursor and NaOH, Na₂CO₃ as a alkali agents. For ZnO crystallization, Zn₄(OH)₆SO₄·H₂O and Zn₅(OH)₆(CO₃)₂·H₂O as a Zn-intermediate were calcined at 400℃ and 800℃ for 1 h, respectively, based on decomposition temperature from TGA. Zn₄(OH)₆SO₄·H₂O was confirmed to have mixed Zn₄(OH)₆SO₄·H₂O and ZnO at 400℃, and was completely thermally decomposed at 800℃ to form ZnO phase. The prepared Zn₅(OH)₆(CO₃)₂·H₂O as a Zn-intermediate by the reaction with Na₂CO₃ was transformed to a complete ZnO crystallization over 400℃. Nano-sized ZnO can be synthesized at a relatively lower calcination temperature through the reaction with Na₂CO₃.