Improved critical current density in ex situ processed carbon-substituted MgB2 tapes by Mg addition
Abstract:We have studied the effect of planetary ball-milling of filling powder with mineral oil on the carbon substitution and the critical current density (J c) of Fe-sheathed MgB2 tapes fabricated through an ex situ process in a powder-in-tube (PIT) technique. Although tapes using powder with oil treatment show weak coupling, the J c properties of those tapes are enhanced due to carbon substitution for boron. The ball-milling treatment with the oil on the filling powder with Mg addition further enhances the J c property of tapes. The J c values of the tapes reach about 9 kA cm−2 at 4.2 K and 10 T. The ball-milling produces a fresh clean surface by the grinding of large grains with a damaged surface and promotes a carbon substitution reaction. Mg addition compensates for the deviation in composition which occurs in the reaction. Some of the boron which is released from MgB2 at the reaction can act as an obstacle to the supercurrent path. The additional Mg consumes the boron at the formation of MgB2 and improves the grain coupling.
Document Type: Research Article
Publication date: June 1, 2012