발간논문

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In order to develop of an advanced spent fuel management process based on the molten salt technology, it is necessary to choose the optimum materials for the process piping and equipment handling molten salt. The corrosion behavior of five Fe-Ni binary alloys at different concentrations of LiCl and LiCl-Li₂O was investigated in the temperature range of 650-850℃. In a molten salt of LiCl, an internal oxidation occurred in all the alloys. The corrosion rate of the alloy showed the parabolic kinetics and it increased with an increase in Fe content in the alloys. In a mixed molten salt of LiCl-Li₂O, an internal oxidation occurred in Fe-rich alloy and a porous scale consisting of LiFeO₂ and Ni was formed in Ni-rich alloy. The corrosion rate increased with an increase in Ni content in the alloys.

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Oxidation behavior and morphological changes of oxide films in molten magnesium alloy containing various amount of Ca were investigated. With increasing Ca content, the ignition of molten alloys maintained to 700℃ in the air was delayed dramatically. The oxide films formed at 700℃ in Ca containing magnesium were compact, thin and dense. The oxide films in Ca-containing magnesium alloys also consisted of the mixture of MgO and CaO. Therefore, the continuous oxidation of Ca-containing magnesium alloys was suppressed by the formation of dense oxide films on the surface of molten magnesium alloys.

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The continuous casting process has been adopted increasingly in recent years to save both energy and labor. It has experienced a rapid development in the production of semi-finished steel products, replacing the conventional route of ingot casting plus rolling. To achieve this good merit, however, more studies about thermal and dynamical interactions between roll and slab are needed. So this paper shows the results of the dynamic bulging in thin slab casting, which is one of the critical factors in designing and operating the continuous casting machine. The dynamic bulging between two supporting rolls under ferro-static pressure and slab-self weight has been computed in terms of creep and elastic-plasticity. The strain and strain rate distributions in solidified shell undergoing a series of bulging are calculated with working boundary conditions.

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Amorphous ribbons with composition of Fe_(73.5)Cu₁Nb₃Si_(13.5)B_9 (FINEMET) and Fe_(76)Si_(14.5)B_(9.5) used soft magnetic materials have been annealed between about 427℃ and 627℃. This annealing process produced a series of partially crystallized samples with different crystallite sizes and coercivities (H_c). The nanocrystalline structure of α-Fe(Si) embedded in an amorphous matrix was investigated by synchrotron radiation X-ray diffractometer (SRXRD). To measure the crystallite size, Fourier analysis was performed. A series of crystallite with 28 ㎚∼150 ㎚ were estimated. And then magnetic properties of the specimens were tested by vibrating sample magnetometer (VSM). In this study, we analyzed the dependency of coercivity (H_c) with crystalline size of FINEMET and Fe_(76)Si_(14.5)B_(9.5) using Fourier analysis and VSM. The best soft magnetic properties (H_c = 4.57 Oe in FINEMET and H_c = 6.98Oe in FeSiB) were observed for the smallest grain sizes of about 28 ㎚ in FINEMET and 41 ㎚ in FeSiB. With increasing crystallite size (D), coercivity was steeply increased, which was followed by the D^6-power law (up to D = 50 ㎚). The variation of the soft magnetic properties with the average grain size was discussed.

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The effects of microstructure before high temperature annealing on secondary recrystallization in conventional grain-oriented electrical steels are investigated. Before high temperature annealing, the cold rolled specimens were annealed at 600 and 850℃ for 200s in 25%H₂+75%N₂, in order to make the recovered and recrystallized microstructure, respectively. For the observation of grain size and precipitates, specimens were extracted at 700, 800, 900, 950 and 1000℃ during the heating step of high temperature annealing. For the recrystallized specimen before high temperature annealing, secondary recrystallization was nearly completed at 950℃ during high temperature annealing. However, in case of the recovered specimen, secondary recrystallization was formed at a higher temperature than 950℃. After high temperature annealing, better magnetic properties were obtained in the recovered specimen than in the recrystallized specimen.

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Carbon in slag might be dissolved as carbide or carbonate ion, depending on various conditions such as oxygen potential and slag basicity, etc. Carbonate solubilities were measured for CaO bearing slag systems at 1600℃ under different thermodynamic conditions by using equilibration techniques. Carbonate solubility increased with activity of (CaO). The reaction mechanism of the carbonate dissolution in slag can be expressed reaction between CO₂ gaseous phase and oxygen ion to form carbonate (CO^(2-)_3). Carbonate capacities of various slags depended not only on oxygen ion but also activity coefficient of carbonate ion. The activity coefficient of carbonate ion in CaO-SiO₂ slag changed with CaO content, but that of CaO-Al₂O₃ slag did not change remarkably. Substitution of MgO by CaO on solubility of carbonate had a similar effect as in the case of carbide in CaO-SiO₂-MgO slag. The critical oxygen potential for carbide and carbonate stability found to be 10^(-10) atm.

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The extraction characteristic and stoichiometric relation for the solvent extraction of indium from sulfuric acid solution was studied with Versatic Acid-10. The results showed that the extraction efficiency of indium increased with increasing pH of solution and concentration of Versatic Acid-10 as extractant. And, up to 45℃, the higher reaction temperature was, the more indium was extracted. On the other hand, the indium was extracted by solvated organo-metal compound with one molecule of the Versatic Acid-10 monomer like [In(OH)R₂·RH] and the extracted species were not associated with each other. The extraction relation and equilibrium constant would be as follows : [In(OH)^(2+)]_(aq)+3/2[R₂H₂]_(org)=[In(OH)R₂·RH]_(org)+2[H^+]_(aq), Kc=3.31×10^(-6) at 18℃.

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The vibration properties of the pure Al plate and pure Cu plate, 12 ㎜ wide and 164∼254 ㎜ long, were investigated by cantilever beam and RFDA to get the following results. (1) The results by cantilever beam method and RFDA show that the resonance frequency decreases as the specimen length increases or the thickness decreases. (2) When measuring the vibration by the cantilever beam method, the vibration damping coefficients are stable at the specimen with 184 ㎜ or higher length. (3) When measuring the vibration damping coefficient by the cantilever beam method, the mean vibration damping ratio of Al specimen 1.6∼0.8 ㎜ thick is 3.1×10^(-2) and 4.0×10^(-2) in Cu specimen of 2.0∼1.2 ㎜ (4) When measuring the vibration damping properties by the RFDA, vibration damping coefficients are similar regardless of the length and thickness of a specimen and the mean vibration damping ratios of Al and Cu were 2.1×10^(-2) and 2.7×10^(-2), respectively. (5) As a result of (3) and (4), The relationship, between the vibration damping ratio measured by the cantilever beam method and it by the RFDA was founded as g_s=(δ_o/δ_r)×(1/1.5).

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