外部拡散法MgB2超伝導線材の組織と超伝導特性

Abstract

MgB2 wires have been prepared through diffusion process in pure Mg metal tube. Amorphous B powder mixed with 5 mol% SiC nano-sized powder addition was encased in a Mg tube, and then the tube was inserted into a pure iron tube to form the Fe/Mg/B(powder) composite wires. The composite was initially drawn into around wires of 1.0 ~ 0.8 mm in diameter without intermediate annealing. The composite wires were heat treated at 630℃ for 5 h in Ar gas atmosphere. Some of the specimens were hot isostatic pressed (HIP treated) under 100 MPa during heat treatment. The MgB2 core was synthesized through the diffusion reaction between outside Mg metal tube and inside B powder with SiC addition. The MgB2 core forms denser structure without voids and cracks in comparison with conventional in-situ powder in tube (PIT process) MgB2 wires. The Ic values at 4.2 K for MgB2 wire of 1.0 mm and 0.8 mm in diameter with HIP reach to 145 A and 164 A at 5 T, which correspond to the Jc of 1680 A/mm2 and 2930 A/mm2, respectively. These values are much higher than that of PIT processed MgB2 wire.