발간논문

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This work was carried out to suggest a simple method for calculation of CO₂ laser beam absorptance on metal surface. Temperatures were measured from a series of locations on specimens during the irradiation of CO₂ laser beam on thin plate-shaped specimen. Absorptance was calculated by using modified finite differential method for two-dimensional unsteady-state heat transfer problem. Absorptance of laser beam increased when specimen temperature was increased, and calculated values were 9.3∼11.1% and 5.0∼5.5% for STS304 stainless steel and SM45C carbon steel for 82 W CO₂ laser beam. These absorptances were agreed well with other investigators results and theoretical values.

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A thermodynamic model which considered chemical and phase equilibria as well as mass and charge balance equations simultaneously was developed for the solvent extraction system of CoSO₄NaOH-CH₃COOH-D₂EHPA-Kerosene. Initial and equilibrium concentrations and activity coefficients of various solutes dissolved in the aqueous phase were calculated from the data of total concentrations of salutes. The difference between the activity coefficients of solutes calculated by Edwards equation and those by Debye-Hu¨ckel equation was increased with ionic charge in the experimental ranges. The distribution coefficients of extractant calculated by the model were increased with pH of the aqueous phase and the slope of Log(D_(HA)) vs. pH plot was nearly 1 as expected. The predicted distribution coefficients of cobalt calculated from the model were in good agreement with those obtained experimentally.

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The morphology and crystallographic feature of austenite formed from martensite during aging have been investigated in a Fe-10Cr-10Ni-2W maraging steel. The microstructure of solution-treated sample is fully martensite before aging. Four types morphology, such as lath-like, allotriomorph, Widmansta¨tten and wedge-shaped austenite. appeared in this maraging steel during aging. The reverted austenite is formed having both a Kurdjumov-Sachs(K-S) orientation relationship and a Nishiyama(N) orientation relationship with martensitic matrix. Furthermore, a wedge-shaped austenite is found to have a twin relationship between adjacent austenites. The twinned austenite is observed to have a very sharpy twin boundary, and longitudinal direction of the twin boundary is dependent upon both the beam direction and the orientation relationships between austenite and martensite.

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The maximum solubility of MgO was measured in the CaO-SiO₂-Fe_tO-MgO-∑xOy (MxOy = MnO, P₂O_5, Al₂O₃, TiO₂, CaF₂) slag in equilibrium with molten iron in the temperature range of 1550℃ to 1700℃. The effect of ∑MxOy on the MgO solubility and the method for calculating the maximum solubility of MgO using slag composition and temperature were discussed, respectively. Moreover , by applying above results to real operation as a means to prevent an erosion of refractory the optimum MgO content in LD slag was determined and summarized as follows; 1) The maximum solubility of MgO is increased with temperature, and decreased with basicity. The content of Fe_tO affects little on the maximum solubility of MgO. 2)The effect of ∑MxOy on the maximum solubility of MgO preserves a dilution effect due to increase in slag volume, and the amount of CaF₂ itself has an effect to lower the same amount of CaO.

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Circulating fluidized bed technology is received an increasing attention for pre-reduction of iron ores in the field of ironmaking by smelting reduction process. Cold-mode hydrodynamics of iron ore (particle diameter=0.065-1.0 ㎜) in a circulating fluidized bed(0.3t-ore/day) was investigated in this study. The bed with a 0.06 m in inside diameter and 3.75 m in height, was operated at superficial gas velocities between 1.4 and 9.2 m/s and at loads between 1 and 2 ㎏. Experimental results show that +0.25 ㎜ iron ore was degraded according to attrition or fragmentation with the turbulent mixing at high gas velocity, and the presence of -0.25 ㎜ fine iron ore leads the coarse iron ore to circulate at gas velocity lower than its terminal velocity. The axial holdup of iron ore in the riser was found to be greatly influenced by superficial gas velocity as well as size distribution of iron ore.

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