• Journal of Korean Society for Atmospheric Environment
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• v.14 no.6
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• pp.589-598
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• 1998

This study was conducted to investigate the chemical characteristics of Precipitation at Seoul, Yangpyong, Hongchon and Inje in the central part of Korean peninsula during the period from March 1994 to November 1997. The precipitation samples were collected by automatic wet-only sampler. The samples were analyzed for major anions (SO42-, NO3-, Cl-, F-) and cations(NH4+, Ca2+, Mg+, Na+, K+), in addition to acidity and electrical conductivity. The analytical instrument for water soluble ionic components was ion chromatography. The volume - weighted mean PH were 4.73, 4.87, 4.89 and 4.81 at Seoul, Yangpyong, Hongchon and Inje, respectively. The sums of cation concentrations was slightly greater than the sums of anion concentrations. Also, the highest ion component was SO42- in anions and NH4+ in cations. The mean equivalent ratios of SO42- to NO3- were found by 2.96, 2.71, 2.43 and 2.25 at Seoul, Yangpyong, Hongchon and Inje, respectively. The factor analysis was conducted in order to make the large and diverse data set as manageable levels and to qualitatively examine the relationship between the variables. It showed that major sources of pollutants in precipitation were from the anthropogenic in Seoul, the natural in Hongchon, and the anthropogenic and natural in Yangpyong and Inje.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.676-683
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• 2003

A laboratory experiment using artificial fracture rocks was used to understand the 3-dimensional dispersion of a tracer and the mixing process in a fractured network. In this experiment, 12cm polystyrene foam cubes with two electrodes for monitoring electric conductivity (EC) were used as artificial fractured rocks. Distilled water with 0.5mS/m was used as a tracer in water with 35mS/m and the difference of EC between the tracer and the water was monitored by a multipoint simultaneous measurement system of electrical resistance. The results showed that even if the fracture arrangement pattern was not straight in the direction of the flow, the tracer did not diffuse along individual fractures and an oval tracer plume, which was the distribution of tracer concentrations, tended to be form in the direction of the flow. The vertical cross section of the tracer distribution showed small diffusivity in the vertical direction. The calculated total tracer volume passing through each measurement point in the horizontal cross section showed while that the solute passed through measurement points near the direction of hydraulic gradient and in other directions, the passed tracer volumes were small. Using Peclet number as a criterion, it was found that the mass distribution at the fracture intersection was controlled in the stage of transition between the complete mixing model and the streamline routing model.

• Particle and aerosol research
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• v.15 no.4
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• pp.183-190
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• 2019

Here, we introduce porous graphene balls (PGB) showing superior electrochemical properties as supercapacitor electrode materials. PGB was fabricated via activation of graphene oxides (GO) by H₂O₂ and aerosol spray drying in series. Effect of activation on the morphology, specific surface area, pore volume, and electrochemical properties were investigated. As-prepared PGB showed spherical morphology containing pores, which lead to the effective prevention of restacking in graphene sheets. It also exhibited a large surface area, unique porous structures, and high electrical conductivity. The electrochemical properties of the PGB as electrode materials of supercapacitor are investigated by using aqueous KOH under symmetric two-electrode system. The highest specific capacitance of PGB was 279 F/g at 0.1 A/g. In addition, the high rate capability (93.8% retention) and long-term cycling stability (92.2%) of the PGB were found due to the facilitated ion mobility between the porous graphene layers.

• Carbon letters
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• v.23
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• pp.9-16
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• 2017

This paper introduces a nitrogen-doped ordered mesoporous carbon (NOMC) derived from glucosamine with hybrid capacitive behaviors, achieved by successfully combining electrical double-layer capacitance with pseudo-capacitance behaviors. The nitrogen doping content of the fabricated NOMC reached 7.4 at% while its specific surface area ($S_{BET}$) and total pore volume reached $778m^2g^{-1}$ and $1.17cm^3g^{-1}$, respectively. A dual mesoporous structure with small mesopores centered at 3.6 nm and large mesopores centered at 9.9 nm was observed. The specific capacitance of the reported materials reached up to $328Fg^{-1}$, which was 2.1 times higher than that of pristine CMK-3. The capacitance retention rate was found to be higher than 87.9% after 1000 charge/discharge cycles. The supplementary pseudocapacitance as well as the enhanced wettability and conductivity due to the incorporation of nitrogen heteroatoms within the carbon matrixes were found to be responsible for the excellent capacitive performance of the reported NOMC materials.

• Resources Recycling
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• v.14 no.1
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• pp.39-46
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• 2005

A solid-state high power torch with inter-electrode insert (IEI) was developed to treat solid waste (for example, incinerated ash), and it's operation characteristics were obtained in the plasma facility test for waste treatment. According to torch test from this study, at the non-transferred mode voltage is increased by gas volume proportionally, and at the transferred mode it is not affected to voltage change. Especially arc voltage is sustained stable at the range of 10% of total Fe in slag. In addition, Electrical conductivity is 0.05~0.25${\Omega}^{-1}cm^{-1}$, torch efficiency is 75~85% and Erosion rate is 2${\times}10^{-6}~6{\times}10^{-6}$ kg/s.

• Bulletin of the Korean Chemical Society
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• v.16 no.7
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• pp.600-603
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• 1995

A series of samples in the Sm1-xSrxCoO3-y(x=0.00, 0.25, 0.50, 0.75 and 1.00) system has been prepared at 1200 ℃ under ambient atmosphere. The X-ray diffraction patterns of the samples with x=0.00 and 0.25 are indexed with orthorhombic symmetry like GdFeO3 and x=0.50 appears to be perfectly cubic. In the tetragonal system (x=0.75), the structure is similar to that of SrCoO2.80. The composition of x=1.00, SrCoO2.52, shows the brownmillerite-type structure. The reduced lattice volume is increased with x value in this system. The chemical analysis shows the τ value (the amount of the Co4+ ions in the system) is maximized at the composition of x=0.50. Nonstoichiometric chemical formulas are determined by the x, τ and y values. The electrical conductivity has been measured in the temperature range of 78 to 1000 K. The activation energy is minimum for those of x=0.25 and x=0.50 with metallic behavior. First-order semiconductor-to-metal transition of SmCoO3 is not observed. Instead, a broad, high-order semiconductor-to-metal transition is observed. In general, the effective magnetic moment is increased with increasing τ values at low temperature. At high temperature, the magnetic moment is maximum for that of x=0.00. The 3d-electrons are collective and give ferromagnetism in x=0.50.

• Korean Journal of Soil Science and Fertilizer
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• v.48 no.5
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• pp.326-331
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• 2015

High salinity and sodicity of soils play a negative role in producing crops in reclaimed tidal lands. To evaluate the effects of soil ameliorants on salt removal in a highly saline and sodic soil of reclaimed tidal land, we conducted a column experiment with treating gypsum, compost, and phosphate at 0-2 cm depth and measured the salt concentration of leachate and soil. Electrical conductivity of leachate was $45-48dSm^{-1}$ at 1 pore volume (PV) of water and decreased to less than $3dSm^{-1}$ at 3 PV of water. Gypsum significantly decreased SAR (sodium adsorption ratio) of leachate below 3 at 3 PV of water and soil ESP (exchangeable sodium percentage) below 3% for the whole profile of soil column. Compost significantly decreased ESP of soil at 0-5 cm depth to 5% compared with the control (20%). However, compost affected little the composition of cations below a depth of 5 cm and in leachate compared with control treatment. It was concluded that gypsum was effective in ameliorating reclaimed tidal lands at and below a soil layer receiving gypsum while compost worked only at a soil layer where compost was treated.

• Journal of the Korean Ceramic Society
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• v.56 no.1
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• pp.65-70
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• 2019

Simple fabrication of a powdered Ge-reduced graphene oxide (Ge-rGO) composite via spray pyrolysis and reduction is introduced herein. Successful incorporation of the rGO nanosheets with Ge hindered the aggregation of Ge and conferred enhanced structural stability to the composite by alleviating the mechanical stress associated with drastic volume changes during repeated cycling. The Li-ion storage performance of Ge-rGO was compared with that of powdered Ge metal. The reversible discharge capacity of Ge-rGO at the $200^{th}$ cycle was $748mA\;h\;g^{-1}$ at a current density of $1.0A\;g^{-1}$ and Ge-rGO showed a capacity of $375mA\;h\;g^{-1}$ even at a high current density of $5.0A\;g^{-1}$. The excellent performance of Ge-rGO is attributed to the structural robustness, enhanced electrical conductivity, and formation of open channels between the rGO nanosheets, which facilitated electrolyte penetration for improved Li-ion diffusion.

• Journal of the Korean institute of surface engineering
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• v.55 no.6
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• pp.441-447
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• 2022

Silicon-based materials are one of the most promising anode active materials in lithium-ion battery. A carbon layer decorated on the surface of silicon particles efficiently suppresses the large volume expansion of silicon and improves electrical conductivity. Carbon coating through chemical vapor deposition (CVD) is one of the most effective strategies to synthesize carbon- coated silicon materials suitable for mass production. Herein, we synthesized carbon coated SiOx via pilot scale CVD reactor (P-SiO_x@C) and carbon coated SiO_x via industrial scale CVD reactor (I-SiO_x@C) to identify physical characteristic changes according to the CVD capacity. Reduced size silicon domains and local non-uniform carbon coating layer were detected in I-SiO_x@C due to non-uniform temperature distribution in the industrial scale CVD reactor with large capacity, resulting in increased surface area due to severe electrolyte consumption.

• Journal of Ecology and Environment
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• v.39 no.1
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• pp.61-70
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• 2016

Major objectives of the study were to analyze chemical and biological influences of the river ecosystem on the artificial weir construction at three regions of Sejong-Weir (S_j-W), Gongju-Weir (G_j-W), and Baekje-Weir (B_j-W) during 2008-2012. After the weir construction, the discharge volume increased up to 2.9 times, and biological oxygen demand (BOD) and electrical conductivity (EC) significantly decreased (p < 0.05). Also, the decrease of total phosphorus (TP) was also evident after the weir construction, but still hyper-eutrophic conditions, based on criteria by , were maintained. Multi-metric model of Index of Biological Integrity (IBI) showed that IBI values averaged 21.0 (range: 20-22; fair condition) in the B_wc, and 14.3 (range: 12-18; poor condition) in the A_wc. The model values of IBI in S_j-W and G_j-W were significantly decreased after the weir construction. The model of Self-Organizing Map (SOM) showed that two groups (cluster I and cluster II) of B_wc and A_wc were divided in the analysis based on the clustering map trained by the SOM. Principal Component Analysis (PCA) was similar to the results of the SOM analysis. Taken together, this research suggests that the weir construction on the river modified the discharge volume and the physical habitat structures along with distinct changes of some chemical water quality. These physical and chemical factors influenced the ecosystem health, measured as a model value of IBI.