• Journal of Korea Foundry Society
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• v.26 no.2
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• pp.98-103
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• 2006

Metal-mold reactions between investment mold and TiAl alloys were investigated for the economic net-shape forming of TiAl alloys. The effect of mold preheating temperatures on the metal-mold reaction were investigated using a vacuum induction-melting furnace. In the case of TiAl alloys, there were no ${\alpha}$-case formation reactions. There were neither interstitial nor substitutional ${\alpha}$-case formations as TiAl alloys have both negligible solubility of oxygen and low activity in molten states. The fluidity of TiAl alloys increases with mold preheating temperature since they have a peritectic reaction that appears in the form of envelope, surrounding each particles of the primary constituent. The results of the investment casting of TiAl alloys confirm that the casting route in our study can be an effective approach for the economic net-shape forming of TiAl alloys.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.384-387
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• 1999

A new multi-seeding process for the growth of YBa$_2Cu_3O_x$ single crystals was developed. This process introduces an additional heating step to peritectic temperature and a subsequent slow cooling step to the growth temperature following the point when the crystals contacted. The crystal growth was resumed thereafter. The results obtained with this new process were compared with those of the conventional growth process, in which materials were only kept at the growth temperature. There was significant improvement in trapped magnetic field over the conventional multi-seeding process, which is believed to be due to complete elimination of liquid phase between crystals.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.242-246
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• 1999

For the fabrication of fault current limiting device using HTSC thick film, YBa$_2Cu_3O_x$ superconducting thick film was formed by surface diffusion process of the Y$_2BaCUO_5$ and the mixed compound of (3BaCuO$_2$+2CuO) expected to be liquid phase above the peritectic temperature of YBa$_2Cu_3O_x$. For the surface diffusion, the compounds of 3BaCuO$_2$+2CuO mixed with binder material was patterned on Y$_2BaCUO_5$ substrate by the screen printing method. After proper sintering, the characteristics of current limit on thick film fabricated was measured. The thick film was able to limit the current from 2.8213 mA$_{rms}$nu to 4.2034 mA$_{rms}$ with 500${\omega}$ load resistance, and from 4.1831 mA$_{rms}$ to 4.2150 mA$_{rms}$ with 10${\omega}$ load resistance.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.262-264
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• 2005

$Bi_{2}Sr_{2}CaCu_{2}O_{x}$(Bi-2212) and $Bi_{2}Sr_{2}Ca_{2}Cu_{3}O_{y}$(Bi-2223) high-$T_{c}$ superconductor(HTS) coating have been prepared by plasma spraying and heaat treatment. The Bi-2212 HTS coating later is synthesized through the peritectic reaction between Sr-Ca-Cu oxide coating layer and Bi-Cu oxide coating later, and $Bi_{2}Sr_{2}CaCu_{2}O_{y}$(Bi-2212) superconducting phase grow by partial melting process. The superconducting characteristic depends strongly on the conditions of the partial melting process. the Bi-2212 HTS layer consists of the whiskers grown in the diffusion direction. Above the 2212 layer, Bi-2223 phase and secondary phase was observed. The secondary phase is distributed uniformly over the whole surface. This is caused to the microcrack on the coatings surface. Despite everything, the film shows superconducting with an onset $T_{c}$ of about 115K. There are two changes steps. One changes (1step) at 115K is due to the diamagnetism of the Bi-2223 phase and the other changes (2step) at 78K is due to the diamagnetism of the Bi-2212 phase.

• Korean Journal of Crystallography
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• v.1 no.1
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• pp.29-34
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• 1990

Single crystals of the peritectic compound MgTiO3 up to 8 m diameter and 100mm long along the [1010] axis. were yon by the travelling solvent floating zone technique using a halogen lamp image furnace. The grown single crystal. which shows a solid solution range at high temperature, exsolves TiO2 component if it is annealed very slowly to room termperature. Grown boules were black but become translucent with pinkish brown color after tempering at 1100 t for 8-10 hours in oxygen atmosphere and showed distint chatoyancy along the (0001) plane. The grown crystal can be used as a new modified cat's eye gemstone. The optimum conditions were as follows ;Sintering temperature of the charge rod, 1300℃ the growth rate, 2-2.5mmh and the composition of the charge rod in molar ratio. MgO : TiO2 : 1:1.05.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.239-242
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• 2000

To fabricate YBa$_2$Cu$_3$O$_{x}$ thick film using diffusion process, $Y_2$BaCuO$_{5}$ and BaO+CuO as the material of substrate and the doping material were selected. CeO$_2$ in the doping material was mixed. As another doping material, YBa$_2$Cu$_3$O$_{x}$ was prepared for the comparison with BaO+CuO doping material. Each doping material was patterned on $Y_2$BaCuO$_{5}$ substrate by the screen printing method and then was annealed above peritectic reaction temperature of YBCO with a few step. It could be observed by X-ray diffraction patterns and SEM photographs that through the diffusion process of the $Y_2$BaCuO$_{5}$ and BaO+CuO, the YBa$_2$Cu$_3$O$_{x}$ phase was formed. With an amout of addition of CeO$_2$, the thickness of a formed YBa$_2$Cu$_3$O$_{x}$ decreased. x/ decreased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.91-92
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• 2006

The important merit of Bi-2212/Ag wire is to apply cable as round wire state. Bi-2212 high Tc superconducting wires were fabricated in order to apply Rutherford cable near the future. Various Ag ratio from 0.22 to 0.42 of Ag tubes for PID (powder-In-Tube) process were used to investigate the workability and to prevent breakage of filaments during drawing. In order to find proper heat treatment condition, we investigated micro-structure of Bi-2212/Ag wires by using differential thermal analysis, XRD and SEM. The effect of atmosphere on the peritectic decomposition temperature of precursor was investigated. The shape of grain was observed by SEM to investigate Bi-2212 phase formation in filaments. The higher of Ag ratio of mono filament had the higher critical current density, Jc. The wire with 0.42 of Ag ratio showed 7,886 A/cm2 of Jc at 77K.

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.35-40
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• 2022

To fabricate large grain YBCO bulk superconductors by melt process, Sm123 single crystal with a high melting point are mostly used as seeds. However, it also uses Y123 film deposited on MgO single crystal substrate. This study investigated the growth behavior of the Y123 grain during a melt process when single grain YBCO bulk was used as a seed. Single grain Y123 bulk was grown when the seed size was small. When the seed size was relatively large, multiple grains were grown but the grains were still large. Y123 seed crystal was completely decomposed during high temperature anneal at 1040℃ and new Y123 crystals were nucleated during a slow cooling stage below a peritectic temperature. Thereafter, newly formed Y123 crystals from the seed area are thought to grow into the Y1.8 powder compact. The crystallographic orientations of newly nucleated Y123 grains are independent of the crystallographic orientation of Y123 seed. It is thought that the crystallographic orientation of newly nucleated Y123 crystal can be controlled by using Y211-free Y123 single crystal as a seed of homo-seeding melt growth.

• Progress in Superconductivity
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• v.13 no.2
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• pp.133-138
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• 2011

To reduce the processing cost of the single grain REBCO (RE: Rare-earth elements) bulk superconductors, a cost-effective process should be developed. One possible way of developing the cost-effective process is the use of low-cost precursor powders. In this study, the single grain YBCO superconductors were fabricated using a home made powder. $YBa_2Cu_3O_{7-y}$ (Y123) powders were synthesized at $850-900^{\circ}C$ in air by the powder calcination method with repeated crushing and heat treatment steps. The processing parameters for the fabrication of single grain Y123 bulk superconductors, $T_{max}$ (maximum temperature), $T_p$ (peritectic temperature) and a cooling rate through $T_p$ were optimized. To enhance the flux pinning capacity of the single grain Y123 samples, $Y_2BaCuO_5$ (Y211) particles were dispersed in the Y123 matrix by adding $Y_2O_3$ powder to the calcined Y123 powder. Applying the optimized processing condition, the single grain Y123 superconductors with $T_c=91\;K$ and $J_c=1.5{\times}10^4\;A/cm^2$ at 2 T were successfully fabricated using a home made powder. The levitation forces and trapped magnetic field at 77 K measured using a Nd-B-Fe permanent magnet of 5300 G were 47 N and 3000 G, respectively, which are comparable to those obtained for the samples fabricated using a commercial grade Y123 powders.

• Korean Journal of Materials Research
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• v.2 no.3
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• pp.202-206
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• 1992

The $CeO_2$-added Y-Ba-Cu-O oxides were prepared by the partial melt process involving the peritectic reaction, liquid + 2-1-1 phase ${\rightarrow}$ 1-2-3 phase, to investigate the effect of the dopant on microstructure and superconductivity. During the peritec reaction, all the added $CeO_2$ was converted to $BaCeO_3$ particles which were finely dispersed in large 1-2-3 grains. Superconducting transition temperature($T_{c}R=0$ point) of the partial-melted samples was as high as 90K regardless of $CeO_2$ content up to 5wt%, which is owing to the separation of the second phase from the 1-2-3 superconducting phase.