• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.583-590
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• 1997

The effects of Mn2O3 and Y2O3 additives on the microstructure and dielectric properties of Sr(Zr, Ti)O3 have been investigated. Powders with Sr(Zr1-xTix)O3(0$\leq$x$\leq$0.1) composition were prepared by the conventional solid state processing from commercial TiO2 and precipitation-processed ZrO2. The powders containing sintering additives of Mn2O3 and Y2O3 were compacted and then sintered at 1,55$0^{\circ}C$ for 4 h to get>97% relative density. Mn2O3 suppressed the grain growth and Y2O3 enhanced the density of sintered body. The oxidation state of Mn ions were determined by a chemical wet method and EPR spectroscopy. Mn ions were present as Mn2+ and Mn4+ in SrZrO3, while as Mn3+ and Mn4+ in Ti-substituted Sr(Zr, Ti)O3. With the substitution of Ti, the lattice parameters of SrZrO3 decreased and its dielectric constant increased with remarkable decrease in Q value. The dielectric constant of Sr(Zr, Ti)O3 was in the range of 30 to 40, Q values 1,200~5,400 at 6 GHz and temperature coefficient of resonant frequency -67~100 ppm/K.

• Advances in materials Research
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• v.4 no.4
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• pp.193-205
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• 2015

Contamination by bacterial strands is a major problem after bone replacement surgeries, so there is a great need to develop low cost biocompatible antibacterial bioactive scaffolds to be used in bone tissue engineering. For this purpose, nano-zinc doped hydroxyapatite with different zinc-concentrations (5, 10 and 15 mol%) was successfully prepared by the wet chemical precipitation method. The prepared powders were used to form porous scaffolds containing biodegradable Ca-cross-linked alginate (5%) in order to enhance the properties of alginate scaffolds. The scaffolds were prepared using the freeze-gelation method. The prepared powders were tested by X-ray diffraction; transmission electron microscope and Fourier transform infrared analyses, while the prepared scaffolds were investigated by Fourier transform infrared analyses, thermogravimetric analyses and measurement of the antibacterial properties. Best results were obtained from scaffold containing 15% mol zinc-doped hydroxyapatite powders and 5% alginate concentration with ratio of 70:30.

• Transactions of the Korean hydrogen and new energy society
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• v.11 no.3
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• pp.119-125
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• 2000

To improve the photochemical energy conversion efficiency and the stability of CdS particulate film electrode which is used to produce hydrogen from the aqueous $H_2S$ solution photoelectrochemically, surface treatment of this film was carried out using $TiCl_4$ solution. CdS particles for preparation of the films were synthesized by precipitation reaction of $Cd({NO_3})_2{\cdot}9H_2O$ and $Na_2S{\cdot}4H_2O$. Then, the CdS sol was hydrothermally treated for 12hr in an autoclave with the variation of treatment temperature to control the crystalline phase of particles. CdS film electrode was thus prepared by annealing at $400^{\circ}C$ for 12hr of the wet-film cast at room temperature, and subsequently surface treated with $TiCl_4$ solution. The electrodes were characterized using XRD, SEM, and the photocurrent meter. The photocurrents of Cds film electrodes prepared with surface treatment were up to two times higher than the electrodes without surface treatment, indicating about $4.0mA/cm^2$. Hydrogen production rate in a continuous flow system using photoelectrochemical or photochemical cells prepared with surface treatment also increased in proportion to the increase of photocurrents.

• Journal of the Mineralogical Society of Korea
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• v.5 no.1
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• pp.22-31
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• 1992

The Sancheong kaolin was fractionated into 9 size fractions by wet sieving, sedimentation, and centrifugation. The systematic X-ray diffraction combined with electron microscopy shows that the clay mineral composition of each size fraction is related to the original fabric of kaolin. Minerals such as halloysite (10${\AA}$), kaolinite, illite, and goethite which were formed by procipitation from solution are generally concentrated in the finer fractions, whereas verniculite which was formed by pseudomorphic transformation from other primary minerals are concentrated in the coarser factions. Kaolinits of various types which were formed by precipitation or transformation show a wide size range but they are generally concentrated in the coarser fractions. Halloysite or halloysite-kaolinite clusters in coarse fractions are the fragmentation products of the walls of original boxwork clusters in coarse fractions are the fragmentation products of the walls of original boxwork kaolin which escaped the complete dispersion even through the grinding, ultrasonic agitation, and chemical treatment. Separation of fully hydrated halloysite and kaolinite was possible by systematic wet size fractionation. The coarse-grained minerals such as vermiculite and kaolinite are usually removed during the preparation of clay fraction smaller than 2${\mu}m$, whereas the fine-grained minerals such as illite and goethite are overlooked in X-ray diffraction of the bulk samples because of their minor contents. The systematic wet size fractionation is needed for understanding of the exact mineralogy of kaolin of weathering origin.

• Clean Technology
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• v.17 no.2
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• pp.166-174
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• 2011

The xAl-yCe oxide catalysts with different mol ratios of Al/(Al+Ce) were prepared by a co-precipitation method and Pt supported on xAl-yCe oxide catalysts were synthesized by an incipient wetness impregnation method. The catalysts were characterized by X-ray Diffraction (XRD), $N_2$ sorption, and $H_2$/CO-temperature programmed reduction ($H_2$/CO-TPR) to correlate with catalytic activities in co oxidation. Among the catalysts studied here, Pt/1Al-9Ce oxide catalyst showed the highest activity in dry and wet reaction conditions and the catalytic activity showed a typical volcano-shape curve with respect to Al/(Al+Ce) mol ratio. When the presence of 5% water vapor in the feed, the temperature of $T_{50%}$ was shifted ca. $30^{\circ}C$ to lower temperature region than that in dry condition. From CO-TPR, the desorption peak of $CO_2$ on Pt/1Al-9Ce oxide catalyst showed the highest value and well correlated the catalytic performance. It indicates that the Pt/1Al-9Ce oxide catalyst has a large amount of active sites which can be adsorbed by co and easy to supplies the needed oxygen. In addition, the amount of pentacoordinated $Al^{3+}$ sites obtained through $^{27}Al$ NMR analysis is well correlated the catalytic performance.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.3
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• pp.83-89
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• 2004

In this work, HA/$TiO_2$ biocomposite to get high mechanical properties with biocompatibility were prepared. HA/$TiO_2$ biocomposite powders were prepared by mixing $TiO_2$ and HA powders which were synthesized through sol-gel, precipitation and hydrothermal methods. The mixing ratio was fixed at 1:1 ratio (HA/$TiO_2$, wt%). HA/$TiO_2$ biocomposite powders showed different microstructures depending on their particle size and shape. The smaller particles were coated on the surface of larger particles, whereas they were well mixed and dispersed when both $TiO_2$ and HA were nanocrystallites. HA/$TiO_2$ biocomposite powders with homogeneous microstructure showed high sintered density and good mechanical properties.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.3
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• pp.239-244
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• 2000

Synthesis and high temperature phase stability of $_{1+x}$ Co$_{y}$ Mn$_{2-y}$ $O_4$(0$\leq$x$\leq$0.2,y=0,1/9,1/6) spinel, both the excess lithium and cobalt added, have been studied. The spinel was prepared by oxalate precipitation method as the wet chemical process. Oxalate derived spinel was synthesized by heating of precipitates at temperature lower than $600^{\circ}C$. As a result of the TG-DTA and XRD analysis of prepared and quenched powders, it was found that reversible phase transitions started at temperatures $T_1$, $T_2$및 $T_{2'}$. The transitions involved weight (oxygen) loss and gain during heating and cooling. The effects of Li excess and Co doping on the spinel lattice constant, phase stability and transition temperatures of the prepared powders are investigated. This study would provide important data for determining the spinel preparation process such as synthesis temperature and cooling speed.

• Journal of Korean Society for Atmospheric Environment
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• v.15 no.2
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• pp.89-100
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• 1999

The rain water samples were collected at Chunchon and Seoul by using wet only automatic sampler from January 1996 through 1997. The daily base rain water samples collected over than 95% rainy events components, $SO_4^{-2}$, $NO_3^-$, $CI^-$, NH_4^+$, $Ca^{2+}$, $Mg^{2+}$, $Na^+$, and $K^+$, by ion chromatography. In 1996, about 77% of sampled rain water showed below pH 5.6 and the 60% of rain water was lower than pH 5.0. The volume weighted average pH was 4.7 at all sites. In 1997, the volume weighted average pH was 4.6 and 4.9 at Seoul and Chunchon, respectively. Among the rain water samples,, 87% and 55% fo samples showed below than pH 5.6 and 5.0, respectively. The pH value of Chunchon was significantly (p＜0.05) lower than Seoul at the rain samples for less than 20mm rainfall. However conductivity of the rain samples were 20.9$\mu$S/cm for 1996 and 27.7$\mu$S/cm for 1997 at Seoul, and 19.1$\mu$S/cm for 1996 and 14.1$\mu$S/cm for 1997 at Chunchon. $H_2SO_4$ and $HNO_3$ contributed 65.9% and 29.6% of free acidity at Seoul, respectively. The ratio of [$NO_3^-$]/[nss-$SO_4^{-2}$] were 0.43 at Seoul and 0.51 at Chunchon for rain samples for less than 20mm rainfall. The annual wet deposition of $CI^-$, $NO_3^-$, $SO_4^{-2}$, $H^+$M, $Na^+$, NH_4^+$, $K^+$, $Mg^{2+}$, and $Ca^{2+}$, respectively, 568.8kg/$ extrm{km}^2$, 1489.3kg/$\textrm{km}^2$, 3184.8kg/$\textrm{km}^2$, 20.9kg/$\textrm{km}^2$, 249.4kg/$\textrm{km}^2$, 1091.2kg/$\textrm{km}^2$, 189.8kg/ $\textrm{km}^2$, 90.2kg/$\textrm{km}^2$ and 702.4kg/$\textrm{km}^2$ at Seoul for 1996; 656.4kg/$\textrm{km}^2$, 2029.7kg/$\textrm{km}^2$, 3280.7kg/$\textrm{km}^2$, 27.2kg /$\textrm{km}^2$, 229.4kg/$\textrm{km}^2$, 1063.9kg/$\textrm{km}^2$, 106.9kg/$\textrm{km}^2$, 78.2kg/$\textrm{km}^2$, 645.3kg/$\textrm{km}^2$ at Seoul for 1997; 116.9kg/ $\textrm{km}^2$, 983.3kg/$\textrm{km}^2$, 1797.0kg/$\textrm{km}^2$, 21.4kg/$\textrm{km}^2$, 83.2kg/$\textrm{km}^2$, 648.1kg/$\textrm{km}^2$, 78.0kg/$\textrm{km}^2$, 22.2kg/$\textrm{km}^2$, 368.8kg/$\textrm{km}^2$ at chunchon for 1996; 100.2kg/$\textrm{km}^2$, 1077.6kg/$\textrm{km}^2$, 1754.0kg/$\textrm{km}^2$, 13.4kg/$\textrm{km}^2$, 146.0kg/$\textrm{km}^2$, 602.3kg/$\textrm{km}^2$, 88.8kg/$\textrm{km}^2$, 16.2kg/$\textrm{km}^2$ and 206.8kg/$\textrm{km}^2$ at chunchon for 1997.

• Korean Journal of Environmental Agriculture
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• v.26 no.2
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• pp.116-123
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• 2007

This experiment was conducted to investigate the distribution and burden characteristics of heavy metals in the rainwater sampled at Suwon area, in the middle part of Korea, from April 2002 to October 2003. The relationship between concentration of heavy metal and other chemical properties in the rainwater was also evaluated. Chemical properties in the rainwater were various differences with raining periods and years. It appeared that a weighted average pH of rainwater was ranged from 4.7 to 5.5. Heavy metal concentrations in the rainwater were ranked as Zn>Pb>Cu>Ni>Cr>As>Cd. As compared with heavy metal concentrations of rainwater in 2002, Cd, Cu and As were higher than other element in 2003. There were positive correlation between major ionic components, such as Ca, Mg, and K, and heavy metal concentrations of rainwater, and As, CU, Cu, Zn and Ni were relatively higher relationship than Pb and Cr in respective to correlation coefficient. For heavy metal distribution of rainwater, the order of average enrichment factors was Cd>Pb>AS>Cu>Zn>Ni>Cr, and these were relatively higher than the natural component such as Fe, Mg and Ca. The monthly enrichment factors were relatively high in the spring (from April to May) at Suwon. The monthly amount of heavy metal precipitation was high in the rainy season from June to August because of great influence of rainfall.

• Korean Journal of Environment and Ecology
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• v.33 no.5
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• pp.605-619
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• 2019

The objective of this study was to analyze eutrophication characteristics, empirical model analysis, and variation of water quality according to monsoon intensity in Hapcheon Reservoir for 16 years from 2002 to 2017. Long-term annual water quality analysis showed that Hapcheon Reservoir was in a meso-nutrition to eutrophic condition, and the eutrophic state intensified after the summer monsoon. Annual rainfall volume (high vs. low rainfall) and the seasonal intensity in each year were the key factors that regulate the long-term water quality variation provided that there is no significant change of the point- and non-point source in the watershed. Dry years and wet years showed significant differences in the concentrations of TP, TN, BOD, and conductivity, indicating that precipitation had the most direct influence on nutrients and organic matter dynamics. Nutrient indicators (TP, TN), organic pollution indicators (BOD, COD), total suspended solids, and chlorophyll-a (Chl-a), which was an estimator of primary productivity, had significant positive relations (p<0.05) with precipitation. The Chl-a concentration, which is an indicator of green algae, was highly correlated with TP, TN, and BOD, which differed from other lakes that showed the lower Chl-a concentration when nutrients increased excessively. Empirical model analysis of log-transformed TN, TP, and Chl-a indicated that the Chl-a concentration was linearly regulated by phosphorus concentration, but not by nitrogen concentration. Spatial regression analysis of the riverine, transition, and lacustrine zones of $log_{10}TN$, $log_{10}TP$, and $log_{10}CHL$ showed that TN and Chl-a had significant relations (p<0.005) while TN and Chl-a had p > 0.05, indicating that phosphorus had a key role in the algal growth. Moreover, the higher correlation of both $log_{10}TP$ and $log_{10}TN$ to $log_{10}CHL$ in the riverine zone than the lacustrine zone indicated that there was little impact of inorganic suspended solids on the light limitation in the riverine zone.