MgB 2 commercial powder was encased in a Ni tube and rolled into a monocore tape of about 5 mm in width and 0.3 mm in thickness. Different kinds of metal powder, i.e., In, Sn, Ag, Cu and Ni, were added to the MgB 2 core. Addition of the low melting point metal powder, e.g., In and Sn, has been found to enhance significantly the value in MgB 2 tapes. Annealing at a low temperature yields further increase in the of tapes with In and Sn addition. The enhancement in by the In addition and the low temperature annealing reaches a factor of 6-7. The of the tapes with 10vol% In addition, annealed at 200 C for 10 h is on the order of 10 5 A/cm 2 at 4.2 K and 0.5 T. The TEM observation shows that In fills up the gaps among MgB 2 grains. The additional annealing produces better impregnation of In in the core. The improvement in grain linkage seems to be the probable origin for the enhancement in by the In addition. The optimum amount of In addition to the MgB 2 core is likely 10-15vol%. Ag, Cu and Ni powder addition yields no apparent effect on of PIT MgB 2 tapes.Index Terms-Critical current, metal powder addition, MgB 2 superconductor, powder in tube.
Nb 3 Sn superconductors with excellent high field performance are prepared by the reaction between the Ta Sn core and the Nb (Nb Ta) sheath. The mechanism of the formation of thick Nb 3 Sn layers by the reaction has been studied. No stable compound richer in Sn exists in the Ta Sn system, and Sn has stronger affinity to Nb than to Ta. Furthermore, Nb in the sheath diffuses into the core at the reaction. These seem to be possible origins for the enhancement of the diffusion of Sn from the core to the sheath synthesizing thick Nb 3 Sn layers. Ta in the core is incorporated into the Nb 3 Sn layer at the reaction. Subsequently, the effect of the Cu addition to the Ta Sn core of the composite has been studied. The Cu addition appreciably decreases the reaction temperature, and reduces the grain size of Nb 3 Sn. The Cu addition enhances the J c in lower field, while it reduces the J c in higher fields. A variety of J c versus magnetic field performance can be obtained by adjusting the amount of Cu addition to the core. The amount of Cu addition and the TaSn ratio in the core, as well as the reaction temperature of the specimen have been optimized. The development of Nb 3 Sn conductors capable of generating fields over 20 T at 4.2 K seems to be promising through the present process.
Newly discovered MgB2 superconducting tapes have been prepared by PIT process. The critical current (Ic) of the Ni-sheathed MgB2 tapes with 10 vol% In and Sn addition excesses 300 A at 4.2K, corresponding to above the critical current density (Jc) of 40,000 A/cm2. The addition of powder metals with low melting point improves the Ic for the MgB2 superconducting tapes.
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