• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2041-2046
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• 2004

Recently series of steam explosion experiments have been performed in the TROI facility to identify the influence of corium compositions on the occurrence of a spontaneous steam explosion varying corium melt composition. The compositions of the corium were 0 : 100, 50 : 50, 70 : 30, 80 : 20 and 87 : 13 at weight percent of $UO_2$ to $ZrO_2$, and the mass of the corium was about 10kg. Corium melt at 0 : 100 weight percent (pure zirconia) caused a strong spontaneous steam explosion, and melt at 70 : 30 weight percent(eutectic corium) led to a weak steam spike, while melts at other compositions did not result in spontaneous steam explosions, when they came into contact with 67cm deep water pool at room temperature. It seems that the explosivity of pure zirconia is stronger than that of corium at other compositions and a steam explosion is not likely to occur with corium melts at non-eutectic compositions which are included in mushy zone region.

• Bulletin of the Korean Chemical Society
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• v.30 no.1
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• pp.133-136
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• 2009

A newly designed Ag/$Ag^+$ reference electrode in a quartz tube with a tungsten tip junction (W-tip-Quartz- REF) was fabricated and its electrochemical performance was compared with a conventional Pyrex tube-based Ag/$Ag^+$ reference electrode (Py-REF). The results of the electrochemical potential measurements with the W-tip-Quartz- REF and the Py-REF in the LiCl-KCl eutectic melts for a wide temperature range proved that the oxide layer on the surface of the tungsten metal tip provided a high ionic conduction. Stability of our newly designed W-tip- Quartz-REF was tested by measuring a junction potential for 12 hours at 700${^{\circ}C}$. The results of the cyclic voltammetric measurement indicated that the Ag/$Ag^+$ reference electrode in the quartz tube with a tungsten tip junction can provide a good performance for a wide temperature range.

• Metals and materials international
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• v.24 no.6
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• pp.1386-1393
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• 2018

The solubility of $TiO_2$ in $NaF-CaF_2-BaF_2$ ternary eutectic melts was investigated at the temperature range of $1025-1150^{\circ}C$. The least-squares equation was obtained from the relationship between the reciprocal temperature and the natural logarithm of the titanium concentration in the melts saturated with $TiO_2$. The corresponding partial molar enthalpy of dissolution of $TiO_2$ was found to be 188 kJ/mol. The titanium saturation concentration was 3.73 wt% at $1100^{\circ}C$. From the titanium concentration change with the added amount of $TiO_2$ at different holding time after a final stirring, it was found that not only complete dissolution of $TiO_2$ but also enough sedimentation of excessive $TiO_2$ should be guaranteed to obtain more reliable solubility data. The holding time of 10 h was found to be enough for the excessive $TiO_2$ particles to settle down in our experimental conditions. It is noteworthy that in case of adding $TiO_2$ in excess of its solubility, the $Ba_{1.12}(Ti_8O_{16})$ phase was observed at the lower and bottom of the solidified salt ingots.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.22-22
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• 2010

Eutectic composition phase with low melting point which solidifies at the final stage affects the solidification cracking at the intercellular or interdendritic area of welds and castings. If sufficient amount of eutectic composition liquid does not exist between the solidifying phases, the discontinuities remain as cracks. However, abundant amount of liquid eutectic composition existing in the final stage can flow into the discontinuities easily and heal the cracks. By flowing of liquid eutectic and healing of discontinuities, the possibility of cracking can be reduced when the amount of eutectic liquid is sufficient. For the solidification of pure metals, liquid eutectic does not exist and the interlocking of growing solid phases can be realized without interruption of liquid film. Therefore there is little possibility of solidification cracking in the case of welds and castings of pure metal. In a practical sense, the effective way to reduce or prevent the solidification cracking is making the composition of molten pool or melts near to the eutectic composition.

• Journal of the Korean Ceramic Society
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• v.26 no.4
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• pp.505-513
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• 1989

The sintering behavior and grain growth of ZnO in 99.0mol% ZnO-1.0mol% Bi2O3 which are the basic compositions of ZnO varistor were studied. The microstructrual observation confirmed that the final sintered density was mainly determined at the initial stage of sintering, i.e. grain rearrangement and grain growth which were induced by the penetration of eutectic melts formed at eutectic temperature(74$0^{\circ}C$). But when the liquid penetration was terminated, the grain growth did not promote further densification. Activation energy of the grain growth of ZnO in the system of 99.0mol% ZnO-1.0mol% Bi2O3 was 44.8$\pm$1.8Kcal/mol.

• Journal of the Korean Ceramic Society
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• v.23 no.2
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• pp.13-20
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• 1986

Composite polycrystals including ${\gamma}$-$6Bi_2O_3$.$SiO_2$ crystal which have needlelike regular structure are useful for the high resolution optical devices. For the purpose of obtaining the composite polycrystals described above the melts of eutectic composition in the three eutectic systems including $6Bi_2O_3$.$SiO_2$ composition were unidirectionally solidified at a rate of 0.05 and 0.25 cm/h under a thermal gradient of 10$0^{\circ}C$/m. Composite polycrystals of relatively regular structure in which needlelike ${\gamma}$-$6Bi_2O_3$.$SiO_2$ crystals were arrayed in parallel with $2Bi_2O_3$.$B_2O_3$ crystal matrix were obtained when the eutectic melt of $6Bi_2O_3$.$SiO_2 -2Bi_2O_3$.$B_2O_3$ system was solidified at a rate of 0.25 cm/h. Partial structural irregularity however was found in the obtained composite polycrystals.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.653-660
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• 2022

The interaction between UN and CdCl₂ in the LiCl-KCl molten eutectic was studied at 1023 K. The chlorination was monitored by sampling and recording the redox potential of the medium. At 1023 K the chlorination of UN with cadmium chloride in the molten LiCl-KCl eutectic proceeds completely and results in the formation of uranium chlorides. The melts of the LiCl-KCl-UCl₃ or LiCl-KCl-UCl₄ compositions can be obtained by the end of experiment depending on the presence of metallic cadmium in the reaction zone. The higher the concentration of the chlorinating agent, the faster the reaction rate. At [CdCl₂]/[UN] = 1.65 (10% excess) the reaction proceeds to completion in about 7.5 h. At [CdCl₂]/[UN] = 7 the complete chlorination takes 2.5-3 h.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.348-348
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• 2011

Carbon nanotube (CNT) field effect transistors and sensors use CNT as a current channel, of which the resistance varies with the gate voltage or upon molecule adsorption. Since the performance of CNT devices depends very much on the CNT/metal contact resistance, the CNT/electrode contact must be stable and the contact resistance must be small. Depending on the geometry of CNT/electrode contact, it can be categorized into the end-contact, embedded-contact (top-contact), and side-contact (bottom-contact). Because of difficulties in the sample preparation, the end-contact CNT device is seldom practiced. The embedded-contact in which CNT is embedded inside the electrode is desirable due to its rigidness and the low contact resistance. Fabrication of this structure is complicated, however, because each CNT has to be located under a high-resolution microscope and then the electrode is patterned by electron beam lithography. The side-contact is done by depositing CNT electrophoretically or by precipitating on the patterned electrode. Although this contact is fragile and the contact resistance is relatively high, the side-contact by far has been widely practiced because of its simple fabrication process. Here we introduce a simple method to embed CNT inside the electrode while taking advantage of the bottom-contact process. The idea is to utilize a eutectic material as an electrode, which melts at low temperature so that CNT is not damaged while annealing to melt the electrode to embed CNT. The lowering of CNT/Au contact resistance upon annealing at mild temperature has been reported, but the electrode in these studies did not melt and CNT laid on the surface of electrode even after annealing. In our experiment, we used a eutectic Au/Al film that melts at 250$^{\circ}C$. After depositing CNT on the electrode made of an Au/Al thin film, we annealed the sample at 250$^{\circ}C$ in air to induce eutectic melting. As a result, Au-Al alloy grains formed, under which the CNT was embedded to produce a rigid and low resistance contact. The embedded CNT contact was as strong as to tolerate the ultrasonic agitation for 90 s and the current-voltage measurement indicated that the contact resistance was lowered by a factor of 4. By performing standard fabrication process on this CNT-deposited substrate to add another pair of electrodes bridged by CNT in perpendicular direction, we could fabricate a CNT cross junction. Finally, we could conclude that the eutectic alloy electrode is valid for CNT sensors by examine the detection of Au ion which is spontaneously reduced to CNT surface. The device sustatined strong washing process and maintained its detection ability.

• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.863-866
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• 2011

The electrode reaction of $Eu^{3+}$ in a LiCl-KCl eutectic melt has been re-examined using cyclic voltammetry (CV). In this work, for the first time, the kinetic details of a $Eu^{3+}/Eu^{2+}$ redox system have been completely elucidated, along with the thermodynamic property, through a curve fitting applied to experimental CV data, which were obtained in a wide scan rate range of 0.5 to 10 V/s. The simulated results showed an excellent fit to all experimental CV data simultaneously, even though the curve fittings were performed within a large dynamic range of initial transfer coefficient values, formal potentials, and standard rate constants. As a result, a proper formal potential, transfer coefficient, and standard rate constant for the $Eu^{3+}/Eu^{2+}$ redox system were successfully extracted using the CV curve fitting.

• Journal of Welding and Joining
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• v.21 no.5
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• pp.534-539
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• 2003

An efficient soldering process using the longitudinal ultrasonic vibration is introduced in this work for electronic packaging. The effects of the process parameters such as the ultrasonic frequency, amplitude, dimension of the metal bump and solder are analyzed through a viscoelastic lumped model. The viscoelastic properties of the eutectic solder were measured for calculation and evaluation of heat generation capability of the solder. Experiments were conducted to verify the possibility of the proposed ultrasonic soldering method by inserting the Cu and Au bumps into the solder block. Localized heating due to ultrasonic vibration melts the solder near the metal bump, which demonstrates the applicability of the ultrasonic soldering method to the high-density electronic packaging.