• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.363-368
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• 1999

Multiseeding 방법을 사용하여 Y-Ba-Cu-0 초전도_ 시료를 제조하였다. Multiseeding은 여러개의 종자를 동시에 사용함으로써 단시간에 큰 size의 시료를 제조하고자 하는 의도에서 시도되었다. 또한 field-cooled 상태에서 포획 자기장의 크기를 측정함으로써 입자간 결합 상태와 시료의 품질을 평가하였다. 일반적인 방법으로 제조할 경우 포획 자기장 값은 입계를 지나면서 크게 감소하였는데, 이는 입계에 존재하는 잔류액상 및 미반응 211 입자 등에 기인한 결과이다. 입계를 따라 미반응상들이 잔류하는 현상을 억제하기 위해 본. 연구에서는 종자들간의 간격을 조절하였다. 그 결과 종자결정들간의 간격을 최대한 좁게 배열하였을 때 포획자기장의 크기가 입계에서 감소하지 않는 결과를 얻었다. 이와 같이 종자간의간격이 충분히 가까울 경우에는, 결정성장 초기에 두 입자가 하나로 결합될 수 있으므로 입계에 미반응 액상이 잔류하는 현상을 억제할수 있었던 것으로 생각된다.

• 한국초전도ㆍ저온공학회논문지
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• 제14권3호
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• pp.1-4
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• 2012

Effects of artificial holes on the cooling efficiency of single grain YBCO bulk superconductors were studied. Single grain YBCO bulk superconductors without artificial holes, with six 2.4 mm holes and six holes filled with Bi-Pb-Cd-Sn metal solder were fabricated by a top-seeded melt growth process for powder compacts with/without holes. Simulation for the cooling rate to a liquid nitrogen temperature (77 K) of YBCO samples was carried out using a finite element method (FEM) and the results are compared with the actual cooling rates of samples in liquid nitrogen. The simulated cooling times for the YBCO sample without holes, with six holes and with six holes filled with the metal solder were 80, 47 and 75 sec. respectively, which are similar to the actual cooling times of 84, 52 and 78 sec. estimated for the same samples cooled in liquid nitrogen. The shorter cooling time of the sample with artificial holes are attributed to the increased surface areas associated with the presence of artificial holes. The metal filling into the holes did not give any remarkable effect on the cooling efficiency.

• 한국초전도ㆍ저온공학회논문지
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• 제19권3호
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• pp.27-32
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• 2017

The effects of artificial holes on the trapped magnetic fields and magnetic levitation forces of very large single-grain $Y_{1.5}Ba_2Cu_3O_{7-y}$ (Y1.5) bulk superconductors were studied. Artificial holes were made for Y1.5 powder compacts by die pressing using cylindrical dies with a diameter of 30 mm or 40 m, or rectangular dies with a side length of 50 mm. The single grain Y1.5 bulk superconductors (25 mm, 33 mm in diameter and 42 mm in side length) with artificial holes were fabricated using a top-seeded melt growth (TSMG) process for the die-pressed Y1.5 powder compacts. The magnetic levitation forces at 77 K of the 25 mm single grain Y1.5 samples with one (diameters of 4.2 mm) or six artificial holes (diameters of 2.5 mm) were 10-17% higher than that of the Y1.5 sample without artificial holes. The trapped magnetic fields at 77 K of the Y1.5 samples with artificial holes were also 9.6-18% higher than that of the Y1.5 sample without artificial holes. The 33 mm and 42 mm single grain Y1.5 samples with artificial holes (2.5 mm and 4.2 mm in diameter) also showed trapped magnetic fields 10-13% higher than that of the Y1.5 samples without artificial holes in spite of the reduced superconducting volume fraction due to the presence of artificial holes. The property enhancement in the large single grain Y1.5 bulk superconductors appears to be attributed to the formation of the pore-free regions near the artificial holes and the homogeneous oxygen distribution in the large Y123 grains.

• 한국재료학회지
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• 제23권6호
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• pp.309-315
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• 2013

$GdBa_2Cu_3O_{7-y}$(Gd123) powders were synthesized by the solid-state reaction method using $Gd_2O_3$ (99.9% purity), $BaCO_3$ (99.75%) and CuO (99.9%) powders. The synthesized Gd123 powder and the Gd123 powder with $Gd_2O_3$ addition ($Gd_{1.5}Ba_2Cu_3O_{7-y}$(Gd1.5)) were used as raw powders for the fabrication of Gd123 bulk superconductors. The Gd123 and Gd1.5 bulk superconductors were fabricated by sintering or a top-seeded melt growth (TSMG) process. The superconducting transition temperature ($T_{c,onset}$) of the sintered Gd123 was 93 K and the transition width was as large as 20 K. The $T_{c,onset}$ of the TSMG processed Gd123 was 82 K and the transition width was also as large as 12 K. The critical current density ($J_c$) at 77 K and 0 T of the sintered Gd123 and TSMG processed Gd123 were as low as a few hundreds A/$cm^2$. The addition of 0.25 mole $Gd_2O_3$ and 1 wt.% $CeO_2$ to Gd123 enhanced the $T_c$, $J_c$ and magnetic flux density (H) of the TSMG processed Gd123 sample owing to the formation of the superconducting phase with high flux pinning capability. The $T_c$ of the TSMG processed Gd1.5 was 92 K and the transition width was 1 K. The $J_cs$ at 77 K (0 T and 2 T) were $3.2{\times}10^4\;A/cm^2$ and $2.5{\times}10^4\;A/cm^2$, respectively. The H at 77 K of the TSMG-processed Gd1.5 was 1.96 kG, which is 54% of the applied magnetic field (3.45 kG).