• Journal of Soil and Groundwater Environment
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• v.12 no.6
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• pp.100-106
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• 2007

The objective of this study was to evaluate the efficiency of $(NH_4)_2HPO_4$, $Na_2HPO_4{\cdot}12H_2O$, $CaHPO_4{\cdot}2H_2O$, $Ca(H_2PO_4)_2{\cdot}H_2O$ and $H_3PO_4$ for the stabilization of soils contaminated with multi-metals containing Pb, Cd and As. The application rate of stabilizers to soils was determined based on $PO_4/Pb_{total}$ molar ratio of 0.5, 1, 2, 4. The results of Korea Standard Test and TCLP (EPA Method 1311) showed the reduction of metal leachabilities below the regulatory limits for Pb and Cd when $H_3PO_4$ and $Ca(H_2PO_4)_2{\cdot}H_2O$ were applied. However, stabilization efficiency for Cd was low and in case of As leaching concentration increased rather. It is considered that $PO_4$ reacted effectively $Pb^{2+}$ due to leaching Pb under low pH condition created by adding $H_3PO_4$. Accordingly Pb was stabilized by dissolution and precipitation of hydroxypyromorphite. From the change of metals fraction using sequential extraction procedure when $H_3PO_4$ applied as a stabilizer, we confirmed that residual fraction increased more than 60% and this result was accorded with XRD analysis that detected only hydroxypyromorphite peak in $H_3PO_4$.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.137.2-137.2
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• 2011

Poly (sodium 4-styrenesulfonate) (PSS) is ionomer based on polystyrene that is electrical conductivity and isoviscosity. LiFePO4 has been a promising electrode material however its poor conductivity limits practical application. To enhance the electronic conductivity of LiFePO4, in this study we prepared LiFePO4- PSS composite by the hydrothermal method. LiFePO4 was heated at $170^{\circ}C$ for 12h and then different wt% PSS (0%, 2.91%, 4.75%, 7.36%, 10%) are added to LiFePO4 and milled at 300rpm for 10h. And then the obtained powders were subsequently heated at $500^{\circ}C$ for 1h under argon flow. The cathode electrode were made from mixtures of LiFePO4-PSS: SP-270- PVDF in a weighting ratio 75%: 25%:5%. The electrochemical properties of LiFePO4- PSS/Li batteries were analyzed by cyclic voltammetry and charge/discharge tests. LiFePO4-C/Li battery with 4.75 wt% PSS displays discharge capacity of 128 mAh g-1 at room temperature that is considerably higher than pure LiFePO4/Li battery ( 113.48 mAhg-1).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.361-362
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• 2007

Phospho-olivine $LiFePO_4$ cathode materials were prepared by hydrothermal reaction. Carbon black was added to enhance the electrical conductivity of $LiFePO_4$. The structural and morphological performance of $LiFePO_4$ and $LiFePO_4$-C powders were characterized by X-ray diffraction (XRD) and FE-SEM. $LiFePO_4/SPE/Li$ and $LiFePO_4$-C/SPE/Li cells were characterized electrochemically by charge/discharge experiments. The results showed that the discharge capacity of $LiFePO_4$-C/SPE/Li cell was 103 mAh/g at the first cycle. The discharge capacity of $LiFePO_4$-C/SPE/Li cell with 5 wt% carbon black was the largest among $LiFePO_4$-C/SPE/Li cells, 126 mAh/g at the first cycle and 123 mAh/g after 30 cycles, respectively. It was demonstrated that cycling performance of $LiFePO_4$-C/SPE/Li cell with 5 wt% carbon black was better than that of $LiFePO_4$/SPE/Li cell.

• Journal of Engineering Education Research
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• v.14 no.3
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• pp.38-44
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• 2011

The purpose of this study is to provide the information of decision making that can be used to improve curriculum of engineering education by surveying and analyzing that educational needs of ${\bigcirc}{\bigcirc}$ university' engineering students about program outcomes. The conclusions of this study are as follows. First, it was found that engineering students surveyed valued much of the necessity of PO2(analysis experiment), PO3(design capability), PO6(teamwork) among program outcomes. In addition, it was found that engineering students surveyed thought their ability was low in PO3(design capability), PO4(problem solving), PO10 (knowledge of current events). Second, it was found that the order of educational needs about program outcomes was PO3(design capability), PO2(analysis experiment), PO1(knowledge application), PO5(practical ability), PO4(problem solving) which suggested that engineering students surveyed had high educational needs for engineering program outcomes. On the other hand, it was found that engineering students surveyed showed lower awareness of PO7, PO10, PO11 which had characteristics of humanities. It is necessary that systematic establishment of course completion system in basic design, element design and comprehensive design by giving weight to design education that aims to strengthen design capability should be made in curriculum of engineering education. It was found that there was considerable difference in educational needs about program outcomes especially in PO1(analysis experiment), PO4(problem solving), PO5(practical ability), PO6(teamwork) according to grade, gender and specialty and therefore this should be considered in designing curriculum. It is judged that operation of flexible education program should be arranged if learning achievement through regular curriculum Is limited.

• Journal of Wetlands Research
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• v.14 no.2
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• pp.255-263
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• 2012

The stream has various environments and they are serving as main habitats of aquatic organisms. The distribution of phytoplankton is affected by water environment, especially pH, nitrogen and phosphorus. To reveal the relationship between phytoplankton distribution and water environment, we measured pH, $NO_3{^-}$ and $PO{_4}^{3-}$ concentration, and abundance of phytoplankton at 10 sites in the upper stream of Dorim-cheon. pH value ranged 5.05 to 7.56. $NO_3{^-}$ and $PO{_4}^{3-}$ concentrations ranged 0.4 ~ 4.9ppm and 0.02 ~ 0.99ppm, respectively. A point source of $NO_3{^-}$ was Seoul National University but concentration was not high and dropped to normal range at 400m downstream. $NO_3{^-}/PO{_4}^{3-}$ ratio ranged 28 to 152 except site 4 (0.4) where was affected by $PO{_4}^{3-}$ point source. Water pH, $NO_3{^-}$ and $PO{_4}^{3-}$ concentrations increased with downstream and were related to the input of irrigation water from Han-river between site 5 and 6. Bacillariophyceae alge dominated this stream. Phytoplankton density increased abruptly at downstream of site 5. In general, phytoplankton density did not increase until the $NO_3{^-}$ concentration of 3.5ppm and $PO{_4}^{3-}$ concentration of 0.07ppm. Phytoplankton density was low at sites where $NO_3{^-}/PO{_4}^{3-}$ ratio was larger than 50.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.133-133
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• 2009

Phospho-olivine $LiFePO_4$ and $LiTi_{0.1}Fe_{0.9}PO_4$ cathode materials were prepared by the solid-state reaction. To improve conductivity we carried out electrochemical performance of $Ti^{2+}$ doped $LiFePO_4$. The $Ti^{2+}$ doped $LiFePO_4$ started 3.36 V of flat voltage on discharge curve and showed a gentle decline in the curve compared to undoped $LiFePO_4$ without great changes of capacity. And so, we could achieve to improve electrochemical performance as reversible, cycle life. Similarly, $LiFePO_4$ doping with $Ti^{2+}$ was showed the effect of dopant which was obtained the improved discharge capacity as 140 mAh/g and good cycling performance.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.137.1-137.1
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• 2011

올리빈 구조의 $LiFePO_4$ 정극 활물질은 $650^{\circ}C$에서 고상법으로 제조되었다. $LiFePO_4$의 전자전도도를 향상시키기 위하여 graphite nanofiber(GNF)를 각각 3wt%, 5wt%, 7wt%, 9wt% 첨가하여 $LiFePO_4$-C를 제조하였다. 제조된 분말의 입자 형태를 확인하기 위하여 X-ray diffraction(XRD)과 File Electronic Scaning Electromicroscopy(FE-SEM)를 측정하였다. XRD결과로부터 제조된 분말은 모두 순수한 결정 구조를 나타내었고 입자의 크기는 약 200nm였다. 5wt% GNF를 첨가한 $LiFePO_4$-C는 기타 첨가량에 비해 방전용량이 가장 높았다. 첫 사이클의 용량은 151.73mAh/g 나타났고 50 사이클 뒤에도 92% 이상을 유지하고 있었다. 첨가하지 않은 것에 비해 43% 증가하였다. $LiFePO_4$-C(3wt%), $LiFePO_4$-C(7wt%), $LiFePO_4$-C(9wt%)의 첫 사이클 방전용량은 각각 147.94mAh/g, 136.64mAh/g, 121.07mAh/g 나타났다. $LiFePO_4$-C(5wt%)에 비해 용량은 떨어쪘지만 순수한 $LiFePO_4$보다 많이 높았다. 임피던스 결과를 보면 기타 첨가량에 비해 $LiFePO_4$-C(5wt%)의 저항 제일 낮았다. 이는 충방전 결과와 일치하였다. graphite nanofiber의 첨가로 인하여 $LiFePO_4$ 정극 활물질의 전자전도도가 높아지고, 따라서 전기화학적 특성도 크게 향상되었다.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.433-436
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• 2013

Carbon-coated $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials are first reported in this work, prepared by the mechanochemical process with a complex metal oxide as the precursor and sucrose as the carbon source. X-ray diffraction pattern of the composite material indicates that both olivine $LiMnPO_4$ and monoclinic $Li_3V_2(PO_4)_3$ co-exist. We further investigated the electrochemical properties of our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials using galvanostatic charging/discharging tests, where our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite electrode materials exhibit the charge/discharge efficiency of 91.9%, while $Li_3V_2(PO_4)_3$ and $LiMnPO_4$ exhibit the efficiency of 87.7 and 86.7% in the first cycle. The composites display unique electrochemical performances in terms of overvoltage and cycle stability, displaying a reduced gap of 141.6 mV between charge and discharge voltage and 95.0% capacity efficiency after $15^{th}$ cycles.

• Analytical Science and Technology
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• v.24 no.5
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• pp.378-386
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• 2011

The goal of this study is to understand the influence of temperature on phosphorus release rate from soil into water. As the temperature increases, $PO_4$-P reaches equilibrium more quickly and the equilibrium concentration increases, and thus the $PO_4$-P concentration increases, and pH decreases. The $PO_4$-P concentration affects pH. $PO_4$-P released from turbidity is not adsorbed onto the turbidity. $PO_4$-P was independent on the turbidity and yet $PO_4$-P was steadily increasing. However, $PO_4$-P was dependent upon the turbidity concentration as the turbidity releases $PO_4$-P. The total phosphorous (T-P) and turbidity were directly linked because T-P changed with the turbidity. T-P includes the $PO_4$-P content of water and the phosphorus content of the turbidity. As the temperature decreases, density of water increases, and the precipitation of turbidity decreases, resulting in an increases in T-P concentration. As the temperature increases, the T-P concentration decreases, but the PO4-P release rate from turbidity increases. At the same time, even at different temperatures, the T-P concentrations of the samples were about the same. When the lake gets deepened, the water temperature decreases, hence, the phosphorus release rate from soil into water was decreased. This mechanism is of great interest because phosphorus is released from soil sediment into the lake water.

• Transactions on Electrical and Electronic Materials
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• v.13 no.4
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• pp.177-180
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• 2012

In this study, we prepared $LiFePO_4$- poly (sodium 4-styrenesulfonate) (PSS) composite by the hydrothermal method and ball-milling process. Different wt% PSS were added to $LiFePO_4$. The cathode electrodes were made from mixtures of $LiFePO_4$-PSS: SP-270: PVDF in a weighting ratio of 70%: 25%: 5%. $LiFePO_4$-PSS powders were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM). The electrochemical properties of $LiFePO_4$-PSS/Li batteries were analyzed by cyclic voltammetry, charge/discharge tests, and AC impedance spectroscopy. A Li/$LiFePO_4$-PSS battery with 4.75 wt% PSS shows the best electrochemical properties, with a discharge capacity of 128 mAh/g.