한국초전도ㆍ저온공학회논문지 (Progress in Superconductivity and Cryogenics)

  • 제21권2호
  • /
  • Pages.40-44
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  • 2019
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  • 1229-3008(pISSN)
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  • 2287-6251(eISSN)
한국초전도저온학회 (The Korean Society of Superconductivity and Cryogenics)
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Effects of a compaction method for powder compacts on the critical current density of MgB2 bulk superconductors

  • Kang, M.O. (Korea Atomic Energy Research Institute) ;
  • Joo, J. (Sungkyunkwan University) ;
  • Jun, B.H. (Korea Atomic Energy Research Institute) ;
  • Choo, K.N. (Korea Atomic Energy Research Institute) ;
  • Kim, C.J. (Korea Atomic Energy Research Institute)
  • 투고 : 2019.06.16
  • 심사 : 2019.06.21
  • 발행 : 2019.06.30
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초록

In this study, the effects of the compaction method for (Mg+2B) powders on the apparent density and superconducting properties of $MgB_2$ bulk superconductor were investigated. The raw powders used in this study were nano-sized boron (B) and spherical magnesium (Mg). A batch of a powder mixture of (Mg+2B) was put in a steel mold and uniaxially pressed at 1 ton or 3 tons into pellets. Another batch of the powder mixture was uniaxially pressed at 1 ton and then pressed isostatically at $1800kg/cm^2$ in the water chamber. All pellets were heat-treated at $650^{\circ}C$ for 1 h in flowing argon gas for the formation of $MgB_2$. The apparent density of powder compacts pressed at 3 ton was higher than that at 1 ton. The cold isostatic pressing (CIP) in a water chamber allowed further increase of the apparent density of powder compacts, which influenced the pellet density of the final products ($MgB_2$). The compaction methods (uniaxial pressing and CIP) did not affect the formation of $MgB_2$ and superconducting critical temperature ($T_c$) of $MgB_2$, but affected the critical current density ($J_c$) of $MgB_2$ significantly. The sample with the high apparent density showed high $J_c$ at 5 K and 20 K at applied magnetic fields (0-5 T).

키워드

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Fig. 1. FE-SEM images of (a) Mg and (b) B used as raw powders.

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Fig. 2. Schematic drawings of (a) uniaxial pressing and (b) cold isostatic pressing (CIP).

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Fig. 3. Volume change of pellets after uniaxial pressing, CIP and heat treatment.

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Fig. 4. Histogram of an apparent density before/after heat treatment as a function of the compaction condition.

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Fig. 5. Powder X-ray diffraction patterns of MgB2 prepared with various compaction methods.

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Fig. 6. Normalized M-T curves of MgB2 prepared with various compaction methods.

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Fig. 7. Jc-B curves at 5 K and 20 K of MgB2 prepared with various compaction methods.

TABLE I COMPACTION INFORMATION OF PELLETS.

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TABLE II APPARENT DENSITY AND VARIATION OF DENSITY CHANGE BEFORE/AFTER HEAT TREATMENT WITH VARIOUS COMPACTION CONDITIONS.

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TABLE III CRITICAL CURRENT DENSITY OF MGB2 AT 3 T, 5 K AND 20 K PREPARED WITH VARIOUS COMPACTION CONDITIONS.

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