Superconducting Properties and Structures of MgB₂ Wires Prepared by External Diffusion Process

Abstract

 MgB₂ wires have been prepared by diffusion process using 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 drawn into a round wires of 1.0~0.8 mm in diameter without intermediate annealing. The composite wires were heat treated at 630℃ for 1~10 h in Ar gas atmosphere. Some of the specimens were hot pressed under 10 MPa and hot isostatic pressed (HIP) under 100 MPa during heat treatment. The MgB₂ core was synthesized through the diffusion reaction between outer Mg metal tube and inner B powder. The MgB₂ core forms denser structure without voids and cracks in comparison with conventional in-situ powder in tube (PIT) processed MgB₂ wires. The I_c value at 4.2 K for the HIP treated MgB₂ wire of 0.8 mm in diameter reaches to 31 A at 10 T, which corresponds to the J_c of 545 A/mm². The I_c and J_c values are much higher than that of conventional PIT processed MgB₂ wires.