• Transactions of the Korean hydrogen and new energy society
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• v.18 no.3
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• pp.317-324
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• 2007

The conversion reaction of ortho to para hydrogen was studied. The percentage of ortho and para hydrogen is mainly dependent on the equilibrium temperature. Because this reaction is known to be accelerated by the catalyst such as nickel-silicate and ruthenium on silica, we focused in the test and development of the catalysts. We studied metal-silicates because they provide high metal dispersion on support. Nickel-silicate, ruthenium-silicate and mixed-silicate were prepared by the coprecipitation method and used in the reaction at the temperature of liquid nitrogen. The conversion was measured by the difference of thermal conductivity between reference gas and sample gas. The activation condition was important and it affected the activities of the catalysts. Nickel-silicate showed high activities. Ruthenium-silicate also showed relative high activities but mixed-silicate showed poor activities.

• Journal of the Korean Electrochemical Society
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• v.17 no.4
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• pp.229-236
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• 2014

In this study, the method to improve the electrochemical performance of $LiFePO_4$ by carbon coating and morphology control into porous structure was studied. The synthesis of $LiFePO_4$ was done by coprecipitation method by two step procedure. In the first step $FePO_4$ precursor was synthesized by coprecipitation method, followed by impregnation of lithium into the precursor at $750^{\circ}C$. The carbon coating was done by both physical and chemical coating processes. Using the physical coating process, the amount of coating layer was 6% and the capacity achieved was 125 mAh/g. In case of chemical coating process, the active material delivered 130~140 mAh/g, which is about 40% improvement of delivered capacity compared to uncoated $LiFePO_4$. For the morphology control into porous structure, we added nano particles of $Al_2O_3$ or $SiO_2$ into the active materials and formed the nanocomposite of ($Al_2O_3$ or $SiO_2$)/$LiFePO_4$. Between them, $SiO_2/LiFePO_4$ porous nanocomposite showed larger capacity of 132 mAh/g.

• Journal of the Korean Chemical Society
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• v.35 no.3
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• pp.204-210
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• 1991

Multilayer adsorption isotherms of nitrogen and argon on the perovskite-type mixed oxides, synthesized by a citrate coprecipitation method, are determined at the liquid nitrogen temperature using a gravimetric adsorption apparatus. The volume of the adsorbed gas are plotted against the statistical thickness of the adsorbed layer, calculated from several universal adsorption isotherms one after another. The t-method area obtained from this plot is compared with the BET area and finally the appropriateness of universal adsorption isotherms is then discussed on the basis of the plot.

• Journal of Sensor Science and Technology
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• v.6 no.4
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• pp.316-327
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• 1997

Polycrystalline $Sr_{2}Nb_{2}O_{7}$ and $La_{2}Ti_{2}O_{7}$ ceramics with very high Curie temperatures were synthesized by the chemical coprecipitation method (CCP). The powders synthesized were identified by XRD and their sintering behavior and physical properties were studied. The grain-orientation and electrical properties of sintered ceramics were investigated as a function of firing temperature. Single phase could be obtained by CCP method at temperature lower than that of the conventional method by 100 - $150^{\circ}C$. Strontium niobate, $Sr_{2}Nb_{2}O_{7}$, powder was Prepared by CCP method at temperatures as low as $800^{\circ}C$ via intermediate phase of $Sr_{5}Nb_{4}O_{15}$ formed at $700^{\circ}C$. The resulting CCP-derived powder was observed to have finer and more uniform particle size distribution than those obtained through the conventional or the molten salt synthesis method. Sintering of CCP-derived $Sr_{2}Nb_{2}O_{7}$ powder at $1500^{\circ}C$ yielded a highly dense ceramics with 97% theoretical density. Very high grain-orientation developed along the (0k0) direction was observed by SEM, which resulted in anisotropic dielectric properties of the sintered samples, with the dielectric constant values approaching those for single crystal.

• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.2917-2921
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• 2014

Cerium-activated yttrium aluminate ($Y_3Al_5O_{12}:Ce^{3+}$) exhibiting a garnet structure has been widely utilized in the production of light emitting diodes (LEDs) as a yellow emitting phosphor. The commercialized yttrium aluminum garnet (YAG) phosphor is typically synthesized by a solid-state reaction, which produces irregular shape particles with a size of several tens of micrometers by using the top-down method. To control the shape and size of particles, which had been the primary disadvantage of top-down synthetic methods, we synthesized YAG:Ce nanoparticles with a diameter of 500 nm using a coprecipitation method under the atmospheric pressure without the use of template or special equipment. The precursor particles were formed by refluxing an aqueous solution of the nitrate salts of Y, Al, and Ce, urea, and polyvinylpyrrolidone (55 K) at $100^{\circ}C$ for 12 h. YAG:Ce nanoparticles were formed by the calcination of precursor particles at $1100^{\circ}C$ for 10 h under atmospheric conditions. The phase identification, microstructure, and photoluminescent properties of the products were evaluated by X-ray powder diffraction, scanning electron microscopy, absorption spectrum and photoluminescence analyses.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1135-1141
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• 2008

The $La_{1-x}(Ca\;or\;Sr)xCrO_3$(x=0 and 0.25) interconnect materials for high temperature electrolysis of steam were investigated in views of sinterability and electrical conductivity. $LaCrO_3$, $La_{0.75}Ca_{0.25}CrO_3$ (LCC), and $La_{0.75}Sr_{0.25}CrO_3$ (LSC) powders were synthesized by coprecipitation method. Crystal structure was confirmed by X-ray diffraction (XRD). The sintering characteristics were analyzed by relative density and scanning electron microscopy. The electrical conductivity was measured by a DC four probe method. From the analyses of relative densities, it was found that the doped $LaCrO_3$ showed better sinterability than $LaCrO_3$ and the those sinterability increased with decrease of those particle sizes. The XRD results at different sintering temperatures for LCC and LSC revealed that the sinterability is closely related to the second phase transformation, that is, the second phase melting above $1,300^{\circ}C$ for LCC and $1,400^{\circ}C$ for LSC significantly promotes the sinterability. In case of electrical conductivities of LCC and LSC, which had a similar relative density, LCC showed better electrical conductivity than LSC.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.5
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• pp.237-242
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• 2010

Magnesium-substituted BCP (biphasic calcium phosphate) powders were prepared by incorporating small amounts of magnesium into the structure of different hydroxyapatite (HAp)/${\beta}$-tricalcium phosphate (${\beta}$-TCP) ratios through coprecipitation method. A series of magnesium substitutions ranging from 0, 0.5, and 1.0 wt%, which are comparable to the measured magnesium contents, were performed. The obtained powders were characterized by the following analytical techniques: X-ray diffraction analysis (XRD), Thermo Gravimetric Analyzer (TGA) and Fourier transform infrared spectroscopy (FT-IR). The results have shown that substitution of magnesium in the calcium-deficient apatites resulted in the formation of biphasic mixtures of different HAP/${\beta}$-TCP ratios after heating above $1000^{\circ}C$. The 1.0 wt% magnesiumsubstituted-BCP were soaked in Hank's solutions after 2 weeks to observe the morphology of the biocement, especially needle-like hydroxyapatite crystals and to estimate the length and diameter of nanoneedle crystals.

• Carbon letters
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• v.13 no.3
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• pp.157-160
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• 2012

In this work, iron oxide ($Fe_3O_4$) nanoparticles were deposited on multi-walled carbon nanotubes (MWNTs) by a simple chemical coprecipitation method and $Fe_3O_4$-decorated MWNTs (Fe-MWNTs)/polypyrrole (PPy) nanocomposites (Fe-MWNTs/PPy) were prepared by oxidation polymerization. The effect of the PPy on the electrochemical properties of the Fe-MWNTs was investigated. The structures characteristics and surface properties of MWNTs, Fe-MWNTs, and Fe-MWNTs/PPy were characterized by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The electrochemical performances of MWNTs, Fe-MWNTs, and Fe-MWNTs/PPy were determined by cyclic voltammetry and galvanostatic charge/discharge characteristics in a 1.0 M sodium sulfite electrolyte. The results showed that the Fe-MWNTs/PPy electrode had typical pseudo-capacitive behavior and a specific capacitance significantly greater than that of the Fe-MWNT electrode, indicating an enhanced electrochemical performance of the Fe-MWNTs/PPy due to their high electrical properties.

• Applied Chemistry for Engineering
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• v.10 no.7
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• pp.1003-1007
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• 1999

The activity and products distribution for the hydrogenation of butadiene and pentadiene over the gold and cobalt catalysts prepared by coprecipitation and impregnation method was investigated with using a flow reactor under atmospheric pressure. The reaction characteristics of the highly dispersed gold particles and its role were studied. The activity of the gold catalyst by coprecipitation was much higher than that by impregnation. The selectivity of butene on all gold particles was always 100% even in the absence of butadiene in the stream, but butadiene on cobalt supported catalyst was easily hydrogenated to butane. It was therefore considered that the active sites at circumferences of the gold particles possessed an unique property which took a proper affinity to hydrogen. In the hydrogenation of butadiene and pentadiene, the percentages of 1-butene and 2-pentene were 60%~70% and about 62%, respectively. The results could be simply explained by a statistical concepts of hydrogen addition.

• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2217-2221
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• 2011

We investigated the selective deoxyribonucleic acid (DNA) adsorption on layered double hydroxide (LDH) nanoparticles via studying the interaction between positively charged LDH nanoparticle as adsorbent and negatively charged adsorbates such as methyl orange (MO), fluorescein (FL), and DNA strands. The size controlled LDH $(Mg_{0.78}Al_{0.22}(OH)_2(CO_3)_{0.11}{\cdot}mH_2O)$ was prepared by conventional coprecipitation method, followed by the hydrothermal treatment. According to the adsorption isotherms, the adsorbed amounts of MO and FL were similar, however, that of DNA were much larger. The adsorption behaviors were well fitted to Freundlich adsorption model. The concentration dependent adsorption behavior on LDH surface was described in order to verify the selective DNA separation ability. The result showed that the LDH has advantages in selective adsorption of DNA competing with single molecular anions.