• 환경영향평가
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• 제17권6호
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• pp.321-333
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• 2008

Considering risks and artificial enrichments of metals in the soils of the study area, the study aims to analyze geology, grain size and geochemistry. Geology is mainly composed of gneisses and phyllites of metamorphic rocks, sandstones, siltstones, shales, tuffs of sedimentary ones and granites and andesites of igneous ones in the area. In the area, mean contents of metals are not meaningful in accordance with petrogenesis. The soil textures of the area are of S, lS and sL of sandy soil, L, scL, cL of loam and C, zC and sC of clayey soil. Mean contents of Ni, Cr, Co and Cu are meaningfully high in loam and clayey soil relative to sandy soil, whereas Ni, Zn, Cd contents are higher in clayey soil than in loam. Those differences imply the metallic contents are dependent to grain size. Based on the metal contents in the soils of the study area, Cu and Zn in loams and Pb in sandy soils are corresponded to soil contamination warning standards, and As showing 75mg/kg of maximum content in loams is assigned to soil contamination countermeasure standards, respectively. Artificial enrichment factor minimized wall rock and grain size relations is over 1 in Cr, Ni and Cu, but the factor is below 1 in average of other metals.

• 한국전기전자재료학회논문지
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• 제23권12호
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• pp.936-941
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• 2010

In this study, we have investigated the effects of Mn dopant on the bulk trap levels and grain boundary characteristics of $Bi_2O_3$-based ZnO (ZB) varistor using admittance spectroscopy and dielectric functions (such as $Z^*,\;Y^*,\;M^*,\;\varepsilon^*$, and $tan\delta$). Admittance spectra and dielectric functions show two bulk traps of $Zn_i^{..}$ (0.20 eV) and $V^{\bullet}_o$ (0.29~0.33 eV) in ZnO-$Bi_2O_3-Mn_3O_4$ (ZBM). The barrier of grain boundaries in ZBM could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.79 eV at lower temperature to 1.08 eV at higher temperature. The grain boundary capacitance $C_{gb}$ was decreased slightly with temperature as 1.3~1.8 nF but resistance $R_{gb}$ decreased exponentially. The relaxation time distribution can result from the heterogeneity of the barriers constituting the varistor. It is revealed that Mn dopant in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against the ambient temperature.

• 소성∙가공
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• 제7권2호
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• pp.168-176
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• 1998

Hot workability of the AA5083 alloy ws investigated by torsion test at temperature ranges of $350{\sim}520^{\circ}C$ and strain rates of 0.5, 1.0, and 3.0/sec. The flow stress and hot ductility of the AA5083 alloy as a function of deformation variables such as temperature and train rate were studied. The microstructural evolution of the AA5083 alloy was studied in relation to Zener-Hollomon parameter (Z=exp( /RT) Also the hot restoration mechanism of the AA5083 alloy was small when Z val-ues were higher than $1.73{\times}1016/sec(370^{\circ}C,\;0.5/sec)$ In addition the difference microstructures during hot deformation. It was found that the increase of flow curves and deformed microstructures during hot deformation. It was found that the increase of flow stress of the AA5083 alloy was small when Z val-ues were higher than $1.73{\times}1016/sec(370^{\circ}C.\;0.5/sec)$. However under the low Z values less than $1.73{\times}1016/sec(370^{\circ}C,\;0.5/sec)$ the flow stress increase with increasing the Z values. The large dispersoid particles in the matrix grain decreased the flow strain of the AA5083 alloy because it caused the stress concentration during hot deformation.

• 한국전자현미경학회:학술대회논문집
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• 한국현미경학회 2001년도 제32차 춘계학술대회
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• pp.41-42
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• 2001

• 한국작물학회:학술대회논문집
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• 한국작물학회 1997년도 추계 학술대회지
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• pp.86-87
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• 1997

• 한국자기학회지
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• 제13권1호
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• pp.15-20
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• 2003

Cu 금속 미분말은 확산속도가 CuO 보다 CuO 보다 빠르고 소결시 입자성장을 촉진시키기 때문에 기본조성 (N $i_{0.204}$C $u_{0.204}$Z $n_{0.612}$ $O_{1.02}$)F $e_{1.98}$ $O_{2.98}$에 들어가는 CuO대신 Cu/CuO의 비를 변화시켜 가면서 Cu가 ferrite에 미치는 영향을 조사하였다. Cu를 CuO 대신 치환함으로써 90$0^{\circ}C$에서 완전한 Spinel구조를 가짐을 XRD pattern을 통하여 확인하였고, Cu/CuO 비가 60%일 때가 투자율 1100, Ms 87 emu/g의 최적조건을 얻었다. Cu는 소결시 확산속도를 증가시켜 입자성장에 영향을 주었으며, CuO대신 Cu의 치환은 저온에서 투자율이 개선됨을 확인하고 소결온도를 3$0^{\circ}C$이상 낮출 수 있었다. 소결이 끝난 후에는 CuO와 같은 거동을 하는 것으로 확인되었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.293-296
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• 2001

The dynamic softening mechanisms of AISI 316, AISI 304 and AISI 430 stainless steels were studied with torsion test in the temperature range of $900 - 1200^{\circ}C$ and the strain rate range of $5.0x10^{-2}-5.0x10^0/sec$. The austenitic stainless steels, such as AISI 316 and AISI 304 were softened by dynamic recrystallization (DRX) during hot deformation. Also, the evolutions of flow stress and microstructure of AISI 430 ferritic stainless steel show the characteristics of continuous dynamic recrystallization (CDRX). To establish the quantitative equations for DRX of AISI 316 stainless steel, the evolution of flow stress curve with strain was analyzed. The critical strain (${\varepsilon}_c$) and strain for maximum softening rate (${\varepsilon}^{*}$) could be confirmed by the analysis of work hardening rate ($d{\sigma}/d{\varepsilon}={\theta}$). The volume fraction of dynamic recrystallization ($X_{DRX}$) as a function of processing variables, such as strain rate ( $\varepsilon$ ), temperature (T), and strain ( $\varepsilon$ ) were established using the ${\epsilon}_c$ and ${\varepsilon}^{*}$. For the exact prediction the ${\varepsilon}_c,\;{\varepsilon}^{*}$ and Avrami' exponent (m') were quantitatively expressed by dimensionless parameter, Z/A, respectively. It was found that the calculated results were agreed with the experimental data for the steels at my deformation conditions. Also, we can reasonably conclude that the DRX, CDRX and grain refinement of stainless steels can be achieved by large strain deformation at high Z parameter condition.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 1999년도 제1회 학술대회논문집(KIASC 1st conference 99)
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• pp.3-9
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• 1999

The grain morphology, the changes in morphology and Jc with the thermo-mechanical treatment (TMT) history, the field dependence of Jc and the nature of intergranular bonding were studied in $T_{10.8}$$Pb_{.2}$$Bi_{0.2}$$Sr_{1.8}$$Ba_{0.2}$$Ca_{2.2}$$Cu_{3}$$O_{z}$/Ag tapes. As a result, incorporation of intermediate rolling during the final heat-treatment resulted in of plate-like TI-1223 grains, and thus enhanced Jc. Jc's near 2.5$\times$104 A/cm2 at 77 K and 0 T were obtained in just rolled tapes with an excellent reproducibility. The high Jc's seem to grain-connectivity easy recovery of excellent grain-connectivity during final heat-treatment after inter -mediate rolling, probably due to retarded T1 evaporation and excessive Ca content in the present composition. The strong field dependence of Jc even in low fields, however, indicated that there still existed significant weak-links and the degree of directional grain-alignment was far from the desired one. The intergranular binding in the tapes seemed to be mainly dominated by SIS junctions.

• 한국전기전자재료학회논문지
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• 제23권5호
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• pp.368-373
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• 2010

In this study, we have investigated the effects of Cr dopant on the bulk trap levels and grain boundary characteristics of $Bi_2O_3$-based ZnO (ZB) varistor using admittance spectroscopy and dielectric functions (such as $Z^*,\;Y^*,\;M^*,\;{\varepsilon}^*$, and $tan{\delta}$). Admittance spectra show more than two bulk traps of $Zn_i$ and $V_o$ probably in different ionization states in ZnO-$Bi_2O_3-Cr_2O_3$ (ZBCr) system. Three kinds of temperature-dependant activation energies ($E_{bt}'s$) were calculated as 0.11~0.14 eV of attractive coulombic center, 0.16~0.17 eV of $Zn_{\ddot{i}}$, and 0.33 eV of $V_o^{\cdot}$ as dominant bulk defects. The grain boundaries of ZBCr could be electrochemically divided into two types as a sensitive to ambient oxygen i.e. electrically active one and an oxygen-insensitive i.e. electrically inactive one. The grain boundaries were electrically single type under 460 K (equivalent circuit as parallel $R_{gb1}C_{gb1}$) but separated as double one ($R_{gb1}C_{gb1}-R_{gb2}C_{gb2}$) over 480 K. It is revealed that the dielectric functions are very useful tool to separate the overlapped bulk defect levels and to characterize the electrical properties of grain boundaries.

• 한국세라믹학회지
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• 제48권1호
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• pp.69-73
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• 2011

A $ZrO_2$ thin film as a corrosion protective layer was deposited on Zircaloy-4 (Z-4) clad material using $N_2O$ as a reactive gas by RF reactive magnetron sputtering at room temperature. The Z-4 substrate was located in plasma or out of plasma during the $ZrO_2$ deposition process to investigate mechanical and corrosive properties for the plasma immersion. Tetragonal and monoclinic phases were existed in $ZrO_2$ thin film immersed in plasma. We observed that a grain size of the $ZrO_2$ thin film immersed in plasma state is larger than that of the $ZrO_2$ thin film out of plasma state. In addition, the corrosive property of the $ZrO_2$ thin films in the plasma was characterized using the weight gains of Z-4 after the corrosion test. Compared with the $ZrO_2$ thin film immersed out of plasma, the weight gains of $ZrO_2$ thin film immersed in plasma were larger. These results indicate that the $ZrO_2$ film with the tetragonal phase in the $ZrO_2$ can protect the Z-4 from corrosive phenomena.