• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.277-284
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• 2004

Low carbon steels containing Si of up to $1.2\;wt\%$ were oxidized in air at 1373 K and 1523 K, i.e. below and above the eutectic temperature of FeO and $Fe_2SiO_4$. The influence of a impurity element, S on behavior of scale formation during oxidation was investigated by using $M\"{o}chssbauer$ spectroscopy and EDS. This allowed establishment of an interface oxidation model of Si-added steel depending on temperature and an impurity element. A compound of FeO and FeS was formed in the scale/matrix interface of low carbon steels containing S of up to $0.03\;wt\%$ oxidized above 1213 K of the eutectic temperature. This was flat formed between $Fe_2SiO_4$ nodules along the scale/matrix interface without selective oxidation. It is due to low viscosity and high wettability of the compound of FeO and FeS in liquid. Conventional metallographic examinations revealed that roughness of the scale/matrix interface in Si-added steels became flat as the content of S increased. It was independent of oxidizing temperature and Si content. Effects of oxidizing temperature and an impurity element content on descaling characteristics in Si-added steels were evaluated by using a hydraulic descaling simulator. Good descaling characteristics was attributable to this flatness of the scale/matrix interface.

• Applied Chemistry for Engineering
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• v.27 no.3
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• pp.335-341
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• 2016

In this study, impurity effects on diffusive-convection flow fields by physical vapor transport under terrestrial and microgravity conditions were numerically analyzed for the mixture of $Hg_2Cl_2-I_2$ system. The numerical analysis provides the essence of diffusive-convection flow as well as heat and mass transfer in the vapor phase during the physical vapor transport through velocity vector flow fields, streamlines, temperature, and concentration profiles. The total molar fluxes at the crystal regions were found to be much more sensitive to both the gravitational acceleration and the partial pressure of component $I_2$ as an impurity. Our results showed that the solutal effect tended to stabilize the diffusive-convection flow with increasing the partial pressure of component $I_2$. Under microgravity conditions below $10^{-3}g_0$, the flow fields showed a one-dimensional parabolic flow structure indicating a diffusion-dominant mode. In other words, at the gravitational levels less than $10^{-3}g_0$, the effects of convection would be negligible.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.21 no.2
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• pp.193-204
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• 2023

To ensure radiological safety margin in the transport and storage of spent nuclear fuel, it is crucial to perform source term and shielding analyses in advance from the perspective of conservation. When performing source term analysis on UO₂ fuel, which is mostly used in commercial nuclear power plants, uranium and oxygen are basically considered to be the initial materials of the new fuel. However, the presence of impurities in the fuel and structural materials of the fuel assembly may influence the source term and shielding analyses. The impurities could be radioactive materials or the stable materials that are activated by irradiation during reactor power operation. As measuring the impurity concentration levels in the fuel and structural materials can be challenging, publicly available information on impurity concentration levels is used as a reference in this evaluation. To assess the effect of impurities, the results of the source term and shielding analyses were compared depending on whether the assumed impurity concentration is considered. For the shielding analysis, generic cask design data developed by KEPCO-E&C was utilized.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.3
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• pp.117-124
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• 2010

For Ar=5, Pr=1.18, Le=0.15, Pe=2.89, Cv=1.06, $P_B$=20 Torr, the effects of impurity $(N_2)$ on thermally and solutally buoyancy-driven convection ($Gr_t=3.46{\times}10^4$ and $Gr_s=6.02{\times}10^5$, respectively) are theoretically investigated for further understanding and insight into an essence of thermo-solutal convection occurring in the vapor phase during the physical vapor transport. For $10K{\leq}{\Delta}T{\leq}50K$, the crystal growth rates are intimately related and linearly proportional to a temperature difference between the source and crystal region which is a driving force for thermally buoyancy-driven convection. Moreover, both the dimensionless Peclet number (Pe) and dimensional maximum velocity magnitudes are directly and linearly proportional to ${\Delta}T$. The growth rate is second order-exponentially decayed for $2{\leq}Ar{\leq}5$. This is related to a finding that the effects of side walls tend to stabilize the thermo-solutal convection in the growth reactor. Finally, the growth rate is found to be first order exponentially decayed for $10{\leq}P_B{\leq}200$ Torr.

• Bulletin of the Korean Chemical Society
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• v.35 no.12
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• pp.3475-3481
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• 2014

This paper describes how primary contaminants in ambient air affect the performance of the cathode in fuel cell electric vehicle applications. The effect of four atmospheric pollutants ($SO_2$, $NH_3$, $NO_2$, and CO) on cathode performance was investigated by air impurity injection and recovery test under load. Electrochemical analysis via polarization and electrochemical impedance spectroscopy was performed for various concentrations of contaminants during the impurity test in order to determine the origins of performance decay. The variation in cell voltage derived empirically in this study and data reported in the literature were normalized and juxtaposed to elucidate the relationship between impurity concentration and performance. Mechanisms of cathode degradation by air impurities were discussed in light of the findings.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.6
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• pp.532-537
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• 2003

Crystallographic, electric, magnetic and heat transition properties of $\alpha$-Fe$_2$O$_3$ have been studied with a small addition of Eu impurities. Hematite($\alpha$-Fe$_2$O$_3$) is a basic ferromagnetic material having rhombohedral structure, which is similar to perovskites structure. Eu is a rare earth element that has an electric configuration of 4f$^{7}$ 6s$^2$. X-ray diffraction pattern of Fe$_{1-x}$ Eu$_{x}$O$_3$ (x = 0.00, 0.04, 0.06) shows an increament of a value when the amount of Eu impurities increased. The VSM data show an increment of magnetization by increasing the amount of Eu impurity. The one with x=0.06 shows the largest increment of magnetic remanence. The magnetic remanence varied from 0.49$\times$10$^{-3}$ emu/g to 0.62$\times$10$^{-3}$ emu/g when Eu impurity is increased by 2 %. Coercivity is decreased as Eu impurity is increased. Resistances is reduced significantly by Eu impurity. There is a clear difference in temperature-dependent resistance depending on the amount of Eu impurities. Especially, there are cusps between 150 K to 175 K. It indicates the change of electronic quantum states inside the atoms by rare earth impurities in rhombohedral structure. Temperature-dependent heat capacity shows that the most effective amount of Eu impurities is 6 %. %.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.99-99
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• 1994

• Journal of the Korean Ceramic Society
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• v.29 no.1
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• pp.1-8
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• 1992

The effect of CaO impurity on the microstructural evolution during the sintering of ultrapure alumina(>99.999%) was studied under "clean" firing conditions. The sinterability of undoped alumina was low, but its microstructure was maintained uniform. In the case of CaO-doped alumina, the distribution of grain size and that of grain boundary dihedral angle became wider, and facetted pores observed frequently. When MgO was doped in addition to CaO, the sinterability increased drastically and the uniform microstructural characteristics resumed. This study suggests that the effect of CaO is to induce inhomogeneous microstructures presumably by anisotropic segregation to grain boundaries and pore surfaces, and that MgO suppresses the anisotropic segregation of Ca.

• Journal of Korea Foundry Society
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• v.24 no.3
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• pp.145-152
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• 2004

The eutectic Si in Al-8.5wt.%Si alloy was changed from large flake to fine lemellar(or fibrous) shape when the Sc amount in the Al-Si alloy reaches 0.2wt.%. The optimum amount of Sc for the best modification effect was 0.8wt.% and slight decrease of modification effect occurred over this value. The study on the distribution of the modifiers(Sr, Na, and Sc) and the measurement of the surface tension of the Al-8.5wt.%Si alloy melt added with Sr, Na, and Sc modifier, respectively, reveals that Sc modifies the eutectic Si by the decrease of surface tension, while Sr and Na modify the eutectic Si mainly by impurity induced twinning mechanism.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.621-624
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• 2002

In this study, outgassing characteristics of MgO films, and the plasma cleaning effects of the deposited MgO films by atmospheric pressure plasma on outgassing rate were compared. The MgO layer was heated up to 350 $^{\circ}C$ and the outgassing characteristics were observed for the heated conditions. As the main impurity species $H_2,\;H_2O,\;N_2,\;CO_2,\;and\;H_2O$ were released from this panel. Impurity species of plasma treatment panel were lower than non-treated panels for the heating temperature