발간논문

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The importance of textures for physical and technological properties of materials was recognized during the last years. The exact quantitative analysis of texture was given in the form of the correct pole figures. In order to estimate the effect of the intensity correction of the pole figures on the texture analysis, ODF-analysis prediction of the properties were carried out with the simulated pole figures including the intensity incorrectness which can be caused by defocusing, absorption and mis-adjustment. If the incorrectness of the intensity is small, the ODF-analysis can be determined within 10% errors without intensity correction. It depends not only on the size of slits or collimator and the diffraction angle but also on the type of texture. In the case of the β-fiber type texture of fcc metals, the analysis was carried successfully out with the {111}, {200} and {220} pole figures which were measured up to 70°tilt-angle and not corrected the perversion of intensity. In the case of the (α+γ)-fiber type texture of bcc metals, the analysis was carried successfully out with the corrected {110}, {200} and {211} pole. figures which were measured up to 75°tilt-angle.

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An attempt is made to see numerically the effect on the solidification of cooling during filling process and the residual flow after finishing filling process in a casting process. Emphasis is given to simultaneous analysis of fluid flow and heat transfer in the whole casting process from filling to the end of solidification. To treat the free surface, MAC method is employed in the SIMPLER algorithm of the finite volume approach. Thermal stresses during solidification is calculated based on temperature distributions through the finite element analysis. Results show the distinct difference between the present analysis and the conventional analysis, which just deals with solidification process only.

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Thermoelectric properties of the polycrystalline (Bi_(0.2)Sb_(0.8))₂Te₃, fabricated by mechanical alloying and hot-pressing, were investigated with addition of BN as scattering centers. The Seebeck coefficient of the hot-pressed (Bi_(0.2)Sb_(0.8))₂Te₃ was not affected by addition of BN. The thermal conductivity of the hot-pressed (Bi_(0.2)Sb_(0.8))₂Te₃ decreased with increasing the volume fraction of BN due to the reduction of k_(el) However, the lattice thermal conductivity k_(ph) was little varied with addition of BN. The figure-of-merit of the hot-pressed (Bi_(0.2)Sb_(0.8))₂Te₃ was 3.05×10^(-3)/K without addition of BN and was lowered with increasing the volume fraction of BN, because the increase of the electrical resistivity was larger than the reduction of the thermal conductivity due to the grain refinement.

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Fe₂O₃-TiO₂ films were formed by MOCVD technique, and their corrosion resistance and photoelectrochemical property were examined in acidic, neutral and alkaline solutions. The corrosion resistance was examined by an anodic polarization test, and the photocurrent response by a photoelectrochemical polarization test. The photocurrent and quantum yield maximum of the films depended on the titanium cationic fraction(X_η) in the films. They decreased in the range of X_η=0.0-0.70, then increased in the range of X_(Ti)=0.70-0.95, and finally decreased in the range of X_(Ti)=0.95-1.0 with increasing X_η value. The increase in the photocurrent and quantum yield maximum in the range of X_η=0.70-0.95 was attributed to the amorphous structure. Such a change in the photocurrent and quantum yield maximum was independent to the solution pH. The corrosion resistance of the films increased with increasing X_η value of the film in acidic, neutral and alkaline solutions. Therefore, the films with X_η=0.70-0.95 can be concluded to have high photocurrent response and high corrosion resistance.

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Liquid Fe-13Cr-5V-1.2C alloy and solid low carbon steel were solidified and bonded in a tube after holding at temperatures for 285sec. The effects of mutual diffusion between two alloys on the microstructural change was investigated. Primary solidified layer bonded on the low carbon steel surface was formed as planar type. Alloy contents and hardness values droped nearby the bonded interface within primary solidified layer. Reaction layer formed in the vicinity of the bonded interface within 30∼40㎛ distance had lower alloy contents than cellular type structure. It is suggested that uphill diffusion of carbon from low carbon Fe-0.2C steel into the Fe-13Cr-5V-1.2C alloy at 1200℃ had produced low Cr content austenite. The austenite was transformed to auto-tempered martensite, which were identified as reaction layer.

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A 1/10 scale water model experiment was performed to measure the residence time distributions(RTD) of the 300 ton ladle of a RH process. The effects of distance of the snorkels(center to center distance : 170㎜, 210㎜, 250㎜, 290㎜, 330㎜,) and the flow rate(circulation rate : 13.20 L/min, 16.20 L/min, 19.47 L/min) on RTD were investigated. The RTD of the ladle of the RH process differs from that of plug flow or completely mixed reactor. As the distance of the snorkels becomes shorter, the RTD of the ladle approaches that of the completely mixed reactor. And the distance of the snorkels becomes longer, the RTD of the ladle approaches that of the plug reactor. The shapes of the normalized RTDs are not changed by the increase of the flow rates.

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Three mechanisms of the degradation behavior of iron ore fines(IOF) sized 1000㎛ 50 5000㎛ during fluidizedbed reduction have been investigated: mechanical degradation(MD), thermal degradation(TD) and reactional degradation(RD). The effects of operational parameters such as ore type, temperature, superficial gas velocity, and reducing gas composition have also been studied. The degradation in three mechanisms has been quantitatively evaluated by the amount of IOF smaller than 1000㎛ which was produced and by the weight change of IOF in the bed during fluidization. The reactional degradation become the most predominant aspect among the three and the thermal degradation is the least when the IOF has a low water content, while the degradations of all three aspects are not much different in contribution when the IOF has a high water content. For the effect of operating parameters, the IOF of a lower sphericity showed a higher degradation in the cold fluidization under inert atmosphere but this effect was lessened or negligible under a fluidized-bed reduction at a high temperature. A higher water content in the IOF demonstrated a higher degradation at a high temperature. In the fluidized-bed reduction, the degradation was little affected by the reaction temperature, the superficial gas velocity, and the reducing gas composition. In addition, all three aspects of degradation were mostly completed in the early stage, within 15 minutes, of the operations. The present study is expected to provided useful parameters critical in the determination of reactor size in a scale-up of a fluidized-bed system.

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