Carbon-Coating Layers on Boron Generated High Critical Current Density in MgB₂ Superconductor

Abstract

Boron particles with a homogeneous carbon-coating layer were employed as the precursor to fabricate MgB 2 superconductors to generate artificial two-dimensional (2D) fluxpinning centers. Systematic microstructure investigation reveals that the carbon layers are well-distributed in the MgB 2 matrix without agglomeration. The thickness of the carbon layers is smaller than the MgB 2 coherent length, which makes them transparent to supercurrent. The critical current density is increased because of the strong flux-pinning effects of the 2D carbon layers in the superconductor as highly efficient flux-pinning centers and the increased irreversibility field due to the carbondoping effects.

Research Progress of Electromagnetic Properties of MgB2 Induced by Carbon-Containing Materials Addition and Process Techniques

“…A higher g-C 3 N 4 content would induce large impurities and agglomerates in MgB 2 , which can damage the connectivity and decrease J c (H). Based on the GO and g-C 3 N 4 coating results, Li et al [105] have developed a carbon coating technique to tune the thickness of the 2D flux pinning centers from 1 to 5 nm.…”

Various effects of aliphatic amino acids on the critical current of the MgB2 superconductor

“…The increase of the FWHM of the XRD peaks of carbon-doped MgB2 reflects an increase of microstrain and should not result in a weakening of the overall point pinning. Instead, the enhanced shift towards surface pinning behavior at high field could be a result of a reinforced surface pinning strength that might be due to some carbon deposition on MgB2 grain surfaces [33][34][35][36][37]. From these measurements, it is however difficult to conclude whether this deviation really reflects a change in the flux pinning mechanism.…”

“…A more nuanced view appears from several reports dealing with graphene coated or generally carbon-encapsulated boron powders, which conclude to partial carbon-boron substitution in MgB2 and a residual carbon layer at the surface of the MgB2 grains that generates two-dimensional surface pinning centers and suppresses grain growth [33][34][35][36][37]. In the case of carbon nitride (C3N4) coated boron powders, BN nano-inclusions also form and contribute to performance enhancement [38], while for mixing of multiwall carbon nanotubes (MWCNT) to precursor powders, some MWCNTs remain inside the final MgB2 grains and influence the flux pinning mechanism [39].…”

Superconducting Joining Concept for Internal Magnesium Diffusion-Processed Magnesium Diboride Wires

“…The monofilament IMD wire for this study was produced using a pure Mg rod surrounded by carbon (C)-encapsulated amorphous B powder in a metallic iron (Fe) tube. The C-encapsulated B powder was obtained using the simultaneous pyrolysis of diborane (B 2 H 6 ) and dopant (C x H y ) gases in a hydrogen atmosphere. − For sealing the joint to minimize the evaporation of Mg during the heat treatment, the high-temperature sealing material Ceramabond 503 was used. Except for the heat treatment, the joint fabrication process was performed in the open air to make it more suitable for industrial applications.…”