Microstructure and superconducting properties of nanocarbon-doped internal Mg diffusion-processed MgB₂wires fabricated using different boron powders

Abstract

MgB2/Nb/Monel monofilament wires were fabricated using four different boron powders by an internal Mg diffusion (IMD) process. The microstructure, morphology and the critical current density (Jc) of the used boron powders and the formative MgB2 layers were analyzed and compared. It was found that the purity and particle size of the boron powder influence the superconducting properties of MgB2 wires; further that the optimized heat-treatment condition also depends on the quality of the boron powder. The highest Jc was obtained in the MgB2 layer made using amorphous boron (AB) powder, although a certain amount of voids existed in the superconducting layer. The IMD-processed MgB2 layer fabricated using high-purity boron (HB) powder had also a high Jc compared with the powder-in-tube (PIT) process and a few unreacted boron particles remained in it. MgB2 wire fabricated using low-purity boron (LB) powder had a high cost-performance ratio compared with the others, which is expected to allow the fabrication of large-scale and low-cost superconducting wires for practical application. However, the enhancement of the Jc was not found in the MgB2 layer manufactured using the ball-milled LB (MLB) powder as expected due to the increased percentage of impurity.

Homogeneity of SiC distribution in IMD MgB2 wires

“…Purity and particle size of boron powder are identified as the main two factors [18][19][20]. A previous work of our group has shown that the boron powder purity has a more strong influence on the properties of MgB 2 wires than the particle size [21]. Additionally, the dispersion of dopants in the boron powder matrix is also quite critical, as the subsequent processing steps like cold working and heat treatment will not improve the dispersion.…”

High-field superconductivity in C-doped MgB2 bulk samples prepared by a rapid synthesis route

“…The MgB 2 bulk sample manufacturing process consists of a combination of the Internal Magnesium Diffusion (IMD) and the Powder-in-Closed-Tube (PiCT) techniques 26 , 27 . Samples prepared by IMD are typically characterized by high electrical connectivity 28 . The PiCT technique allows in turn achieving a high density of the reacted MgB 2 phase and a high reproducibility of the sample properties 27 .…”

Scanning Hall-probe microscopy for site-specific observation of microstructure in superconducting wires and tapes for the clarification of their performance bottlenecks

“…Furthermore, this study also first clarifies the direct relationship between the performance of the wire and its microstructure based on the hybrid microscopy of the SHPM and SEM. In fact, recent high-performance MgB 2 wires have been fabricated without SiC: C doping by other methods [40][41][42].…”