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To develop the advanced Zr alloy for nuclear fuel cladding, the microstructure and corrosion characteristics of Zr-xNb binary alloys were studied of Nb addition. Microstructural observation and corrosion behavior of Zr-xNb alloys with niobium content were carried to develop an advanced nuclear fuel cladding materials. Niobium addition results in refining the final grain size, increasing precipitation in matrix and reducing corrosion resistance of the alloy in 360℃, 18.9㎫ water. The alloy with 0.2 wt.% Nb, especially, showed the highest corrosion resistance in this study which was related to columnar structure of the oxide and relatively high content of tetra-ZrO₂. This supports that the corrosion behavior of the Zr-Nb alloy significantly depended on the microstructure and composition of the oxide. mom the XRD analysis, SEM study and TEM observation on the oxide having equal oxide thickness, the 0.2 wt.% Nb alloy showing the best corrosion resistance had higher fraction of tetra-ZrO₂ and columnar structure than other alloys. Therefore, it is considered that the corrosion of Zr-xNb binary alloy would be controlled by the oxide characteristics like tetra-ZrO₂ and equiaxed structure.

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A two-dimensional coupled cellular automaton-continuum model was developed to predict the solidification grain structures and the deflection behavior of columnar grains solidified in a flowing melt. Al-Cu alloys were solidified on an inclined Cu chill in order to investigate the deflection behavior of columnar grains in the upstream flow. The growth velocity of a dendrite was determined by the KGT model based on the calculated temperature and solute profiles around a dendrite tip during solidification. The effects of flow velocity and solute content on the deflection angle of the columnar grains were investigated through experiments, and the results were compared with computer simulations. It was found that the present model could predict the deflection behavior of the columnar grains solidified in a flowing melt.

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A coupled numerical model was developed to predict macrosegregation in continuously cast steel billets. Continuum formulation was adopted to investigate macroscopic transport behavior of momentum, heat and species in the continuous casting process. In order to model fluid flow damping in the mushy zone solidification was considered to occur in two successive stages. In the first stage with the solid fraction below a certain critical value, the relative viscosity concept was employed to treat fluid flow in the dilute mushy zone. In the second stage with the solid fraction above critical value, the permeability concept was used to treat the concentrated mushy zone as a porous medium. Turbulent fluid flow during continuous casting was treated by the standard k-ε model. Thermal and solutal convections were also considered in the simulation of solute redistribution in the mushy zone. The effect of interdendritic flow on surface temperature, metallurgical length and centerline segregation were investigated. It is suggested that the present model can be successfully applied to simulate the macrosegregation in continuous casting of steel billets.

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P-type 20% Bi₂Te₃-(80-x)% Sb₂Te₃-x% Sb₂Se₃ (0≤x≤7) alloy powders, fabricated by mechanical alloying and melting/grinding processes, were hot pressed and their thermoelectric properties were characterized with the Sb₂Se₃ content and the powder processing method. The Seebeck coefficient and electrical resistivity of the hot-pressed 20% Bi₂Te₃-(80-x)% Sb₂Te₃-x% Sb₂Se₃ alloys increased with increasing the Sb₂Se₃ content due to the reduction of the hole concentration. Although the total thermal conductivity of the hot-pressed 20% Bi₂Te₃-(80-x)% Sb₂Te₃-x% Sb₂Se₃ alloys decreased with increasing the Sb₂Se₃ content due to the reduction of κ_(el), the lattice thermal conductivity κ_(ph) was not lowered. The figure-of-merit of the hot-pressed 20% Bi₂Te₃-(80-x)% Sb₂Te₃-x% Sb₂Se₃ alloys decreased with increasing the Sb₂Se₃ content, because the increment of the electrical resistivity was much larger than the decrement of the thermal conductivity and the increment of the Seebeck coefficient.

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MgO thin films have been widely used as a surface protective layer in AC type plasma display panels (PDPs) due to its very low sputtering yield and large secondary electron emission capability. In this work, MgO thin films were prepared on soda lime glass substrates by rf magnetron sputtering method using a MgO target in order to analyze the effect of deposition parameters on their preferred orientation, microstructure and plasma damage properties. The preferred orientation of MgO films was changed from (200) to (111) as the distance from the target to the substrate decreased from 70 ㎜ to 20 ㎜. The MgO film deposited at a high gas pressure and at a long target-to-substrate distance has (200) preferred orientation and very high surface roughness as well as a tendency of columnar growth. However, by increasing the RF power and decreasing the target-to-substrate distance and the gas pressure, films were found to have (111) and (222) preferred orientation. Plasma erosion rate was minimized for the case of (111) preferred orientaion.

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Carbon was expected to dissolve into slag as carbide ion(C^(2-)_2) at low oxygen partial pressure. In order to clarify these mechanisms of carbon dissolution, carbon solubility was measured both in acidic and basic slags with changing oxygen partial pressure and temperature. In basic slags, carbon solubility in MO-B₂O₃ decreased with the oxygen partial pressure and increased with basicity, which confirms the carbide ion formation mechanism. But in acidic slags, carbon solubility in MO-B₂O₃ decreased with basicity and oxygen partial pressure. In order to explain these phenomena, the probable mechanism was discussed and suggested on the basis of experimental results. The model of nitrogen dissolution into slag was compared to that of carbon dissolution and it was found that the change of the dissolution behaviors with basicity were very similar.

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The effect of oxygen blowing under reduced pressure on decarburization and temperature changes were studied using an RH vacuum degasser. The decarburization rate was increased from 0.17 to 0.19min^(-1) by oxygen blowing during decarburization. It was caused by the increase of effective reaction area such as cavity and splash formed by oxygen blowing on melt surface. The carbon content below 20ppm was obtained by oxygen blowing. An average TDR (temperature drop-rate) during decarburization was decreased to -0.6℃/min by oxygen blowing. It was caused by post combustion of the carbon monoxide gas generated from melt decarburization in RH vacuum vessel.

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