• The Korean Journal of Ceramics
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• v.4 no.4
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• pp.363-367
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• 1998

Alumina/mica and spinel/mica composites were fabricated by sintering of compacts containing 20 mass% fluoromica ($KMg_3AlSi_3O-{10}F_2$) glass and alumina or spinel. In both composites, mica precipitated as plate-like crystals at temperatures lower than $1300^{\circ}C$ and melted at $1300^{\circ}C$ to $1400^{\circ}C$. In alumina/mica composites, alumina and glass reacted to produce spinel, and the densification progressed by the solution-precipitation of alumina. Consequently, the glass composition changed and the mica did not precipitate at temperatures higher than $1400^{\circ}C$. However, mica precipitated after a reheating process. In spinel/mica composites, the glass composition did not change. After the mica phase melted, it recrystallized during slow cooling. The relative density reached the maximum at $1500^{\circ}C$ for alumina/mica and at $1300^{\circ}C$ spinel/mica composites, and decreased at further high temperatures.

• Bulletin of the Korean Chemical Society
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• v.12 no.2
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• pp.153-156
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• 1991

Three humic acids, two from uranium bearing coal shale and one from the neighbouring limey shale region, are extracted from soils by dissolution in 0.1 M NaOH followed by acid precipitation. After purification cycles, they are characterized for their elemental composition, contents of inorganic impurities, molecular size distribution and proton exchange capacities. The results are compared with the data of reference and aquatic humic acids characterized under the project MIRAGE Ⅱ at TUM and also with other literature data. The proton exchange capacity determined by direct titration, is found to be 3.60 and 2.01 meq/g for coal shale and limey shale humic acids, respectively.

• Journal of Environmental Science International
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• v.21 no.9
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• pp.1115-1129
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• 2012

The objective of this study was to analyze long-term annual and seasonal trends of water chemistry on landuse patterns and seasonal precipitation using 72 sampling sites within Namhan River watershed during 2001-2010. Water quality, based on multi-parameters of water temperature(WT), dissolved oxygen(DO), biochemical oxygen demand(BOD), chemical oxygen demand(COD), suspended solids(SS), total nitrogen(TN), total phosphorus(TP), and electric conductivity(EC) varied largely depending on monsoon rain and landuse patterns such as forest, cropland, and residence. Concentrations of BOD and COD as an indicator for organic matter pollution, increased during summer monsoon season at the cropland and residential streams. Values of TN and TP were higher in residential streams than in the forest and cropland streams. In the meantime, DO values had weak relations to the landuse patterns of forest and cropland cover. Water quality was worst in cropland and residential streams, and also most degradated in 4th order streams. Overall, our results suggest that efficient water quality management is required in the cropland and residential landuse streams.

• Korean Journal of Food Science and Technology
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• v.5 no.2
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• pp.78-83
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• 1973

The naringin hydrolyzing enzyme has been purified from the culture filtrate of the mold Aspergillus S-1 which selected to remove the bitter test of the orange or citrus fruits industrily. In a view of purity naringinase was more effectively purified in order of molecular sieving on Sephadeex G-200, starach gel electrophoresis, chromatography or a DEAE-Cellulose column and fractional precipitation by ammonium sulfate. The purified enzyme is homogeneous in paper electrophoresis from a culture filtrate by treatment fractional precipitation with ammonium sulfate, DEAE-Cellulose treatment and Sephadex-200 column chromatography and it hydrolyse only naringin to purunin.

• Korean Journal of Food Science and Technology
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• v.10 no.2
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• pp.162-172
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• 1978

We have studied to develop a process for the preparation of protein isolates free of isothiocyanate and oxazolidine-thione when defatted meal was extrracted with a cold alkaline solution at pH11.0. The rapeseed protein isolates were separated at $0^{\circ}C$ using 1% sodium algiante of 500 cps as a precipitation aid, also. The proteins had original colors, namely, a grey curd at pH 6.7, a light cream at pH 5.6 and a yellow cream at pH 5.0, The purity and the color was improved by washing with water and freez-drying with acetone, not at room temperature. A countercurrent procedure was a prerequisite for a continuous large scale production of protein isolates.

• Journal of the Korean Chemical Society
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• v.56 no.4
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• pp.431-439
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• 2012

Dissipative particle dynamics (DPD) was carried out to study the nucleation and crystal growth process of $CeO_2$ nanoparticles in different alcohol aqueous solutions. The results showed that the nucleation and crystal growth process of $CeO_2$ can be classified into three stages: nuclei growth, crystal stabilization and crystal aggregation except the initial induction stage, which could be reproduced by collecting simulation results after different simulation time. Properly selecting the sizes of $CeO_2$ and water bead was crucial in the simulation system. The influence of alcohol type and content in solutions, and precipitation temperature on the particle dimension were investigated in detail and compared with the experimental results. The consistency between simulation results and experimental data verify that the simulation can reproduce the macroscopic particle aggregation process. The effect of solvent on the nucleation and crystal growth of $CeO_2$ nanoparticles are different at three stages and can not be simply described by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory or nucleation thermodynamics theory. Our work demonstrated that DPD methods can be applied to study nanoparticle forming process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.2049-2054
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• 2013

Recently, magnesium hydroxide ($Mg(OH)_2$) has many applications in various field, due to its outstanding characteristics such as a nontoxic, noncorrosive and thermal stable properties. In this study, different shapes of flower and flake type magnesium hydroxide were synthesized by precipitation method at room temperature using $MgSO_4$, $MgCl_2$ and $Mg(NO_3)_2$ as magnesium sources, NaOH and $NH_3$ as alkaline sources. Influence of synthesis on the morphological characteristics, sizes and shapes of magnesium hydroxide particles, was investigated, such as different precursors and parameters. The shape of magnesium hydroxide depend on magnesium and alkali sources. Average size of flower particle had about $1{\mu}m$, and flake had about 20 ~ 50 nm. The synthesised magnesium hydroxide groups were characterized by XRD, FE-SEM, FT-IR, EDS, PSA and TG.

• Applied Chemistry for Engineering
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• v.27 no.6
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• pp.555-564
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• 2016

In recent years, methanol has attracted much attention since it can be cleanly manufactured by the combined use of atmospheric $CO_2$ recycling and water splitting via renewable energy. For the concept of "methanol economy", an active methanol synthesis catalyst should be prepared in a sophisticated manner rather than by empirical optimization approach. Even though Cu/ZnO-based catalysts prepared by coprecipitation are well known and have been extensively investigated even for a century, fundamental understanding on the precipitation chemistry and catalyst nanostructure has recently been achieved due to complexity of the necessary preparation steps such as precipitation, ageing, filtering, washing, drying, calcination and reduction. Herein we review the recent reports regarding the effects of various synthesis variables in each step on the physicochemical properties of materials in precursor, calcined and reduced states. The relationship between these characteristics and the catalytic performance will also be discussed because many variables in each step strongly influence the final catalytic activity, called "chemical memory". All discussion focuses on how to prepare a highly active Cu/ZnO-based catalyst for methanol synthesis. Furthermore, the preparation strategy we deliver here would be utilized for designing other coprecipitation-derived supported metal or metal oxide catalysts.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.498-503
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• 1999

La-doped $BaTiO_3$ ceramics were prepared from BaTiO(C_2O_4)_2\;{\cdot}\;XH_2O(BTO)$, which was synthesized by homogeneous precipitation using dimethyl oxalate. The electrical properties of La-doped $BaTiO_3$ were investigated with variation of La-contents and particle size. It was found that a large PTCR (positive temperature coefficient of resistivity) effect was appeared in the conditions at the 0.6 mol% of La-content and at small particle size of BTO as 1.0$\mu\textrm{m}$. The plot of temperature vs. 1/$\varepsilon_m$(T) above Curie temperature $(T_c)$ was agreed with Curie-Weiss law. The potential barrier calculated from measured resistance and capacitance of specimen, also gave higher value at small particle size of BTO as 1.0 $\mu\textrm{m}$ and at La-content of 0.6 mol%.

• Analytical Science and Technology
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• v.32 no.5
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• pp.173-184
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• 2019

As the size of semiconductors becomes smaller, it is necessary to perform high precision polishing of nanoscale. Ceria, which is generally used as an abrasive, is widely used because of its uniform quality, but its stability is not high because it has a high molecular weight and causes agglomeration and rapid precipitation. Such agglomeration and precipitation causes scratches in the polishing process. Therefore, it is important to accurately analyze the size distribution of ceria particles. In this study, a study was conducted to select dispersants useful for preventing coagulation and sedimentation of ceria. First, a dispersant was synthesized and a ceria slurry was prepared. The defoamer selection experiment was performed in order to remove the air bubbles which may occur in the production of ceria slurry. Dynamic light scattering (DLS) and asymmetrical flow field-flow fractionation (AsFlFFF) were used to determine the size distribution of ceria particles in the slurry. AsFlFFF is a technique for separating nanoparticles based on sequential elution of samples as in chromatography, and is a useful technique for determining the particle size distribution of nanoparticle samples. AsFlFFF was able to confirm the presence of a little quantities of large particles in the vicinity of 300 nm, which DLS can not detect, besides the main distribution in the range of 60-80 nm. AsFlFFF showed better accuracy and precision than DLS for particle size analysis of a little quantities of large particles such as ceria slurry treated in this study.