• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2000년도 추계총회,초청강연,특별강연,연구발표회
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• pp.89.2-89
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• 2000

• Journal of Radiation Protection and Research
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• 제21권1호
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• pp.51-58
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• 1996

2년간의 온실실험을 통하여 벼, 콩, 배추, 무의 생육초기와 생육후기에 $^{54}Mn,\;^{60}Co,\;^{85}Sr,\;^{137}Cs$의 혼합용액을 산성 양질사토로 상층부를 채운 재배상자내 담수 또는 토양의 표면에 가하고 작물수확 직후에 지하 $15{\sim}20cm$까지 토양길이에 따른 방사성 핵종의 농도분포를 조사하였다. 방사성 핵종의 농도는 토양깊이에 따라 지수함수적으로 감소하는 경향으로 처리한 방사능의 80%이상이 지하 $3{\sim}4cm$ 이내 에 분포하였다. 핵종간 지하로의 이동성은 대체로 $^{85}Sr>^{54}Mn>^{60}Co{\geq}^{137}Cs$의 순이었다. 재배작물간에 이동 정도는 벼 재배토양에서 가장 높았고 N, P, K의 시비량이 가장 적었던 콩 재배토양에서 가장 낮았다. 두 처리시기간 지하분포 양상의 차이는 침적후 시간경과에 따라 단위시간당 지하 1cm 밑으로 이동하는 방사능량이 감소한다는 것을 나타내었다. 작물의 생육 초기에 방사성 핵종을 가한 후 실시된 염화칼리와 석회의 동시첨가로 핵종의 지하이동은 밭작물에서는 변화가 없거나 다소 억제되었으나 벼에서는 약간 촉진되었다.

• 한국환경농학회지
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• 제16권4호
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• pp.304-310
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• 1997

오이의 파종 2일전 및 파종후 네 차례에 걸쳐 Mn-54, Co-60, Sr-85, Cs-137의 혼합용액을 온실내 재배상자의 토양에 처리하고 처리시기별 및 수확시기별 열매에 대한 전이계수($m^2$/㎏-fresh)를 측정하였다. 전이계수는 핵종, 처리시기 및 수확시기에 따라 최고 약 60배의 변이를 보였다. 처리시기에 따른 전이계수의 변화양상은 핵종간 및 수확시기간에 차이가 있었다. 핵종간에 전이계수는 대체로 Sr-85 > Mn-54 > Co-60 > Cs-137의 순이었다. 파종전 토양과의 혼합처리시 전이계수는 생육초기 토양표면 처리에 비해 Mn-54, Co-60, Cs-137의 경우 다소 높았으나 Sr-85의 경우 차이가 없었다. 생육초기 토양표면에 처리된 방사성 핵종의 토양층위별 농도는 재배종료후 토양 깊이에 따라 지수함수적으로 감소하고 처리량의 $80{\sim}99%$가 토심 3cm 이내에 분포하는 것으로 나타났다.핵종의 토양 침투성은 Sr-85 > Mn-54 > Co-60 > Cs-137의 순이었다. 본 연구결과는 오이의 재배기간중 토양의 방사능 오염시 열매내 방사성 핵종의 농도예측, 오이의 수확,소비 및 오이밭 제염 대책수립에 활용될 수 있다.

• Current Applied Physics
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• 제18권11호
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• pp.1431-1435
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• 2018

Using first-principles calculations, we successfully investigate the electrochemical performance of the monoclinic $NaMnO_2$ for the sodium ion batteries. $NaMnO_2$ possesses a voltage window of 3.54-2.52 V and theoretical reversible capacity of $136mAh\;g^{-1}$. Besides, we find that the metallicity of the monoclinic $NaMnO_2$ gradually increases during Na extraction. Moreover, the computational Na migration energy barrier in the monoclinic $NaMnO_2$ is 0.18 eV, ensuring ideal conductivity and reversible capacity. Although the Jahn-Teller distortion effects limit the enhancement of the reversible capacity of the monoclinic $NaMnO_2$, it is still a right cathode material for the sodium ion batteries. The computational results are well in consistent with the experimental investigations.

• Bulletin of the Korean Chemical Society
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• 제27권9호
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• pp.1310-1314
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• 2006

Sulfur-substituted $LiMn_{0.9}Cr_{0.1}O_{2-x}S_x$ $(0\;\leq\;x\;\leq\;0.1)$ layered oxides have been prepared by solid state reaction under inert atmosphere. From powder X-ray diffraction analyses, all the present lithium manganates were found to be crystallized with monoclinic-layered structure. Electrochemical measurements clearly demonstrated that, in comparison with the pristine $LiMn_{0.9}Cr_{0.1}O_2$, the sulfur-substituted derivatives exhibit smaller discharge capacities for the entire cycle range but the recovery of discharge capacity after the initial several cycles becomes faster upon sulfur substitution. The effect of the sulfur substitution on the chemical bonding nature of $LiMn_{0.9}Cr_{0.1}O_{2-x}S_x$has been investigated using X-ray absorption spectroscopic (XAS) analyses at Mn and Cr K-edges. According to Mn K-edge XAS results, the trivalent oxidation state of manganese ion remains unchanged before and after the substitution whereas the local structure around manganese ions becomes more distorted with increasing the substitution rate of sulfur. On the other hand, the replacement of oxygen with sulfur has negligible influence on the local atomic arrangement around chromium ions, which is surely due to the high octahedral stabilization energy of $Cr^{+III} $ ions. Based on the present experimental findings, we have suggested that the decrease of discharge capacity upon sulfur substitution is ascribable to the enhanced structural distortion of $MnO_6$ octahedra and/or to the formation of covalent Li-S bonds, and the accompanying improvement of cyclability would be related to the depression of Mn migration and/or to the pillaring effect of larger sulfur anion.

• 환경영향평가
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• 제24권4호
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• pp.344-351
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• 2015

본 연구에서는 비소로 오염된 지역의 토양 및 지하수에 동전기적 기술을 사용하고 배양된 토양 미생물과 배양액을 주입하여 토양 내의 토착 미생물을 활성화하여 비소의 이동도를 상승시키는 것이 주요목표이다. 생물학적 동전기법은 미생물의 전기적 이동을 이용하여 기존의 생물학적 복원에서 문제시 되어온 늦은 분해속도와 낮은 제거효율의 단점을 극복할 수 있었다. 이는 전극의 전해액 대신 토양 미생물과 배양액을 혼합 주입하여 유기물질을 전자 공여체로 이용하는 다양한 토양 미생물이 Fe, Mn 등을 환원하게 된다. 이에 따라 주변의 금속 산화 미생물이 As(III)를 As(V)로 변환시킴으로써 As(III)의 이동도가 증가하게 되고, 이로 인해 As의 이동도가 기존 동전기법의 약 30%에 비해 60 ~ 70%정도로 상승함을 확인하였다.

• Journal of Ecology and Environment
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• 제44권3호
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• pp.185-195
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• 2020

Background: The flathead grey mullet Mugil cephalus has the widest distribution among mugilid species. Recent studies based on mitochondrial DNA sequences showed that the species comprises at least 14 different groups, three of which occur in the northwest Pacific. We analyzed the otolith microchemistry of M. cephalus at several locations in Korea to improve understanding of migration pattern and population origin. Results: We collected 123 sagittal otoliths from seven locations and determined their concentrations of eight elements (⁷Li, ²⁴Mg, ⁵⁵Mn, ⁵⁷Fe, ⁶⁰Ni, ⁶³Cu, ⁸⁸Sr, and ¹³⁸Ba) using laser ablation inductively coupled plasma mass spectrometry. Mean otolith elemental ratios differed significantly among the locations. The Sr:Ca, Fe:Ca, and Ba:Ca ratios were significantly higher than others, and useful chemical signatures for investigating the habitat use of M. cephalus populations. We identified five diverse and complicated migration patterns using the otolith data that we collected: estuarine resident (type I), freshwater migrant (type II), estuarine migrant (type III), seawater resident (type IV), and seawater migrant (type V). A canonical discriminant analysis plot revealed separation of two groups (type II in the Yellow Sea vs. other types in remaining locations). Two locations on Jeju Island, despite their close proximity, had fish with quite different migration patterns, corroborating previous molecular studies that distinguished two groups of fishes. Conclusion: We successfully showed that the migration patterns of the Korean mullet varied by location. Only fish from the western sector of Jeju had a unique migration pattern, which is likely confined population in this area. Among the eight otolith elements measured, the Sr:Ca ratio was found to be the best indicator of migration pattern and population origin.

• Journal of Welding and Joining
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• 제7권4호
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• pp.30-37
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• 1989

Effect of heat treatment on mechanical properties of an overlay weldment was investigated. Over welding was carried out on the structural C-Mn mild steel substrate to take required test specimens. Shielded metal arc welding process with 13Cr-0.2Ni stick electrode was applied. The heat treatment temperatures and holding times were $450{\circ}C., 550{\circ}C., 650{\circ}C., 750{\circ}C., 850{\circ}C.$ and 0.5hr, 2hr, 10hr, respectively. Mechanical tests and microscopic inspection were also carried out to investigate welds soundness. Test results indicated that carbon migration was dominant near bonded zone. At temperature of around 650.deg. C, carburized layer and decarburized layer were formed remarkably along overlay welds region and C-Mn mild steel region, respectively. The wideth of these layers became wider with increasing heat treatment temperature and/or holding time at the elevated temperature, and this relationship agreed with Larson-Miller parameter. Side bending test results demonstrated that the crack free region of overlay welds could be deduced from the relationship between temperature and holding time.

• 한국세라믹학회지
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• 제52권5호
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• pp.331-337
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• 2015

$LaBO_3$ (B = Cr, Mn, Fe, Co, and Ni) perovskites, the most common perovskite-type mixed ionic-electronic conductors (MIECs), are promising candidates for intermediate-temperature solid oxide fuel cell (IT-SOFC) cathodes. The catalytic activity on MIEC-based cathodes is closely related to the bulk ionic conductivity. Doping B-site cations with other metals may be one way to enhance the ionic conductivity, which would also be sensitively influenced by the chemical composition of the dopants. Here, using density functional theory (DFT) calculations, we quantitatively assess the activation energies of bulk oxide ion diffusion in $LaBO_3$ perovskites with a wide range of combinations of B-site cations by calculating the oxygen vacancy formation and migration energies. Our results show that bulk oxide ion diffusion dominantly depends on oxygen vacancy formation energy rather than on the migration energy. As a result, we suggest that the late transition metal-based perovskites have relatively low oxygen vacancy formation energies, and thereby exhibit low activation energy barriers. Our results will provide useful insight into the design of new cathode materials with better performance.

• Journal of Electrochemical Science and Technology
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• 제4권3호
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• pp.102-107
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• 2013

The electrochemical properties of Mg-doped $LiFe_{0.48}Mn_{0.48}Mg_{0.04}PO_4$ and pure $LiFe_{0.5}Mn_{0.5}PO_4$ olivine cathodes are examined and the lattice parameters are refined by Rietveld analysis. The calculated atomic parameters from the refinement show that $Mg^{2+}$ doping has a significant effect in the olivine $LiFeMnPO_4$ structure. The unit cell volume is 297.053(2) ${\AA}^3$ for pure $LiFe_{0.5}Mn_{0.5}PO_4$ and is decreased to 296.177(1) ${\AA}^3$ for Mg-doped $LiFe_{0.48}Mn_{0.48}Mg_{0.04}PO_4$ sample. The doping of $Mg^{2+}$ cation with atomic radius smaller than $Mn^{2+}$ and $Fe^{2+}$ ion induces longer Li-O bond length in $LiO_6$ octahedra of the olivine structure. The larger interstitial sites in $LiO_6$ octahedra facilitate the lithium ion migration and also enhance the diffusion kinetics of olivine cathode material. The $LiFe_{0.48}Mn_{0.48}Mg_{0.04}PO_4$ sample with larger Li-O bond length delivers higher discharge capacities and also notably increases the rate capability of the electrode.