• Korean Journal of Materials Research
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• v.16 no.7
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• pp.416-421
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• 2006

The varistor properties of ZPCCL-based ceramics were investigated at different $La_2O_3$ contents in the range of $0{\sim}2.0$ mol%. As $La_2O_3$ content increased, the ceramic density greatly increased in the range of $4.71{\sim}5.77\;g/cm^3$ and the varistor voltage greatly decreased in the range of $503.5{\sim}9.4$ V. The varistor with 0.5 mol% $La_2O_3$ exhibited good nonlinearity, in which the nonlinear exponent is 81.6 and the leakage current is 0.2 ${\mu}A$. Furthermore, the varistors exhibited the high electrical stability, with $%{\Delta}V_{1mA}=-1.1%,%{\Delta}{\alpha}=-3.7%$, and $%{\Delta}I_L=+100%$ for DC accelerated aging stress condition of 0.95 $V_{1mA}/150^{\circ}C/24$ h.

• Journal of the Korean Ceramic Society
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• v.36 no.9
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• pp.893-900
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• 1999

Silica films were prepared on Si single crystal substrates by sol-gel process using TEOS as starting materials. Films were fabricated by a spin coating technique. Sol solutions were prepared by varying the compositions of CH3OH, H2O and DMF with fixed molar ratio of TEOS=1, HCl=0.05(mol). Wetting behavior viscosity of solutions gelation time thickness of films and cracking behavior were investigated with the various solution compositions. Wetting behaviors of solutions depended on the solution compositions mixing method and mixing rate. The optimum composition of sol was TEOS : DMF ; CH3OH: H2O :HCl=1:2:4:4:0.05(mol) and the mixing rate of solution was optimized at 1 ml/min. Viscosity of solutions were controlled by choosing a reaction time(elapsed time after mixing) at a room temperature so that we could get up to 800nm thick film The surface roughness was getting poor when thickness of films was thicker than 500nm. Thickness of coated films were increased with decreasing amount of CH3OH. The best surface roughness was obtained at the content of CH3OH 4 mol. The shortest gelation time was obtained with the content of CH3OH 8 mol. Crack-free filkms were fabricated when sintered at 500$^{\circ}C$ for 1 hr with heating rate of 0.6$^{\circ}C$/min.

• Korean Journal of Plant Resources
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• v.34 no.6
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• pp.566-574
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• 2021

This research was carried out to investigate the correlation between soil chemical properties and bioactive compounds of Acer tegmentosum Maxim. The methods of determining bioactive compounds were determined by high performance liquid chromatography, that contained (-)-gallocatechin (0.04±0.01 ~ 0.43±0.28%), salidroside (0.90±0.06 ~ 3.86±0.59%), tyrosol (0.03±0.00 ~ 0.43±0.00%), (-)-catechin (0.05±0.01 ~ 0.37±0.14%), 6'-O-galloylsalidroside (0.02± 0.01 ~ 0.31±0.06%), (-)-epicatechin-gallate (0.01±0.00 ~ 0.04±0.01%). The soil chemical properties analysis such as soil pH, electric conductivity (EC), organic matter (OM), total nitrogen (TN), available phosphate (Avail. P₂O₅), exchangeable cation and cation exchange capacity (CEC) were performed following the standard manual. The correlation analysis between soil chemical properties and bioactive compounds of A. tegmentosum, soil pH, available phosphate and exchangeable cation (Ca²⁺ and Mg²⁺) were negatively correlated with content of salidroside. On the other hand, soil exchangeable cation (Na⁺) showed positive correlation with content of salidroside. The results of this study was able to investigate the correlation between soil chemical properties and bioactive compounds of A. tegmentosum.

• Resources Recycling
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• v.16 no.2 s.76
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• pp.32-39
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• 2007

The measurement of physicochemical properties of ASR incineration ash has been carried dot and the preparation of light-weight material has also been performed using ASR ash for recycling point of view as building or construction materials. For this aim, chemical composition, particle size distribution, and heavy metal leachability were examined for 2 bottom ashes and 4 fly ashes obtained from the domestic ASR incinerator. In the present work, attempt has been made to prepare the lightweight material using boiler ash as a raw material, which is prepared by forming the mixture of boiler ash, lightweisht filler and inorganic binder and followed by calcination at elevated temperature. As a result, the content of Cu in bottom ash was as high as about 3wt% so that the recovery of Cu from ash was required. The major compound of SDR #5 and Bag filter #6 was found to be $CaCl_2{\cdot}Ca(OH)_2{\cdot}H_2O\;and\;CaCl_2{\cdot}4H_2O$, respectively. It is thought that heavy metal teachability of lightweight material prepared with boiler ash was significantly decreased due to the encapsulation or stabilization of heavy metal compounds.

• Journal of Ginseng Research
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• v.37 no.4
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• pp.442-450
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• 2013

The aim of this study was to determine and compare the preventive effect of Korean White Ginseng and Red Ginseng on oxidative stress in $H_2O_2$-treated HepG2 cells. The roots of ginseng were extracted with 70% methanol and partitioned with butanol to obtain saponin fractions, which have been known as bioactive constituents of ginseng. 2',7'-Dichlorofluorescein diacetate (DCF-DA) assay and malondialdehyde (MDA) content were measured for evaluating intracellular reactive oxygen species (ROS) generation. Also, mRNA expressions and activities of antioxidant enzymes were analyzed to determine the antioxidant activity of saponin or non-saponin fractions of ginsengs. According to DCF-DA assay, $H_2O_2$-induced MDA release and ROS generation were significantly reduced by treatment with saponin fractions of white and red ginseng roots. Also, saponin fractions increased effectively intracellular antioxidant enzyme activities including catalase, glutathione peroxidase and superoxide dismutase in $H_2O_2$-treated HepG2 hepatoma cells. In general, red ginseng was more effective than white ginseng for reducing oxidative stress. These results indicate that administration of red ginseng may certainly contribute relatively stronger than white ginseng to prevent from damaging liver function by oxidative stress.

• Journal of the Korean Society of Food Science and Nutrition
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• v.42 no.5
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• pp.792-799
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• 2013

This study was designed to develop natural browning inhibitors. The anti-browning effects of distilled water (SBD) and 80% ethanol extracts (SBE) of Scutellaria baicalensis Georgi in apple slices were investigated by L and ${\Delta}E$ values. Both SBD and SBE were effective in reducing the browning of apple slices and were successively fractionated into chloroform ($CHCl_3$), ethyl acetate (EtOAc), and water ($H_2O$) fractions. These extracts were measured for total phenolic content, flavonoid content, anti-oxidative activity (through free radical scavenging activity and the FRAP assay), ferrous ion chelation, and the inhibition of PPO (polyphenol oxidase) activity. Overall, fractions of SBE were better than fractions of SBD in all measurements. The highest total phenolic and flavonoid content were measured in the EtOAc and $CHCl_3$ fractions of SBE. EtOAc and $CHCl_3$ fractions also exhibited the highest anti-oxidative activities (in DPPH and ABTS free radical scavenging and the FRAP assay). Unusually, the highest ferrous ion chelating capacity was found in the $H_2O$ fraction of SBD, but the other fractions showed more than triple the ascorbic acid already in use. Also, $CHCl_3$ fractions showed a stronger inhibition of PPO activity than ascorbic acid. All of these results suggest that EtOAc and $CHCl_3$ fractions from Scutellaria baicalensis can be used as natural anti-browning agents.

• Korean Chemical Engineering Research
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• v.40 no.6
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• pp.741-745
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• 2002

Yttria-stabilized zirconia(YSZ) nanopowders were prepared by sol-gel method using zirconium-n-butoxide(ZNB) and yttrium nitrate as precursors. In addition, the effect of water content added during the hydrolysis reaction of ZNB was investigated on the phase composition and pore structure of the product powders. The phase composition of YSZ nanopowders with calcination temperatures showed the same trend, irrespective of $H_2O$ amounts added during the hydrolysis reaction of ZNB. All powders dried at $100^{\circ}C$ were amorphous and transformed to cubic phase at $400^{\circ}C$, which converted to tetragonal phase at $1,000^{\circ}C$. Monoclinic phase also appeared at $1,000^{\circ}C$. The powders showed the mixture of tetragonal and monoclinic phases from $1,000^{\circ}C$ to $1,400^{\circ}C$. The pore size distributions of the dried powders prepared with small amounts of water(less than or equal to $H_2O/ZNB=20$) showed mesopores, while those prepared with large amounts of water(greater than or equal to $H_2O/ZNB=50$) exhibited micropores.

• The Journal of Engineering Research
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• v.2 no.1
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• pp.139-145
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• 1997

The effect of Ba addition on the thermal stabilization of $\gamma$-$Al_2O_3$ powders were studied. Ba additive was introduced into $\gamma$-$Al_2O_3$ powders by wet impregnation of $Ba(No_3)_3$.$6H_2O$. Ba additive was proved to be effective on the thermal stabilization of $\gamma$-$Al_2O_3$ powders by suppression of sintering. The optimum content of Ba was determined by 5 mol%, through the calcinations temperature range. It is suggested that the main reason of thermal stabilizaton is the substitution effect of large $Ba^{2+}$ ions into the $\Al^{3+}$ sites, which suppressed the surface diffusion of $\Al^{3+}$ ions.

• Carbon letters
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• v.15 no.2
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• pp.146-150
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• 2014

In this work, activated carbon nanofiber (ACNF) electrodes with high double-layer capacitance and good rate capability were prepared from polyacrylonitrile nanofibers by optimizing the carbonization temperature prior to $H_2O$ activation. The morphology of the ACNFs was observed by scanning electron microscopy. The elemental composition was determined by analysis of X-ray photoelectron spectroscopy. $N_2$-adsorption-isotherm characteristics at 77 K were confirmed by Brunauer-Emmett-Teller and Dubinin-Radushkevich equations. ACNFs processed at different carbonization temperatures were applied as electrodes for electrical double-layer capacitors. The experimental results showed that the surface morphology of the CNFs was not significantly changed after the carbonization process, although their diameters gradually decreased with increasing carbonization temperature. It was found that the carbon content in the CNFs could easily be tailored by controlling the carbonization temperature. The specific capacitance of the prepared ACNFs was enhanced by increasing the carbonization temperature.

• Progress in Superconductivity and Cryogenics
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• v.15 no.3
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• pp.1-4
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• 2013

We investigated the effect of Nb substitution for Ru on the structural and magnetic properties of $(Ru_{1-x}Nb_x)\;Sr_2(Sm_{1.4}Ce_{0.6})Cu_2O_z$ Samples. X-ray diffraction measurements indicated that nearly single-phase samples are formed in the range from x = 0 to 1.0. The superconducting transition temperature determined from the inflection in the field-cooled magnetic susceptibility decreased only slightly from $T_c$ = 25 K for x = 0 to $T_c$ = 22 K for x = 1.0, in consistent with the change in room temperature thermopower of the samples. However, the Nb substitution for Ru above x = 0.25 significantly suppressed the weak ferromagnetic component of the field-cooled magnetic susceptibility. It was also found that the Nb substitution for Ru results in an enhanced diamagnetic susceptibility with Nb content above x = 0.5 in both zero field-cooled and field-cooled magnetization measurements, in contrast to the behavior of the samples with $x{\leq}0.5$ in which the diamagnetic susceptibility decreases as the Nb content increases.