Fabrication and characteristics of long MgB2 wire with high superconducting properties

Abstract

Appling the in situ powder-in-tube method, 11 meter long Fe-sheath MgB2 superconducting wires with outer diameter 1.75mm were fabricated, using 99.5% Mg powder and 99.9% amorphous boron powder doped with 30 nm SiC powder as starting materials. This procedure begins with ball-milling of the mixture powder immersed in acetone solution in a jar and subsequently drying in vacuum. Then the iron tube loaded with the powder mixture was grooved, swaged and drawn to the final wire size. The transition temperature, microstructure, lattice constant and chemical element distribution were evaluated by SQUID, XRD, SEM and EDS, respectively. It was found that TC(onset) and ΔTC are 35.1K and 5.3K, respectively. All samples containing a small amount of MgO, exhibit rather uniform microstructure. Besides, by nano-SiC doping, the MgB2 lattice distortion due to substitution of boron by carbon, results in forming effective flux pining centers, which significantly improves the critical current, and the C element was uniformly distributed in the MgB2 matrix. The standard four_probe measurement shows that all the 10 sample points, which were evenly cut at 1 meter intervals of the 11 meter length wire, have good superconducting homogeneity with critical current values fluctuating within 10% under the applied fields vavying from 10 to 18 Tesla, and all Jc values are above 104A/cm2, with the highest value reaching 1.2×104A/cm2 at 4.2K and 10T.