Study On SiC Doped MgB₂ Superconducting Bulk

MgB2 is a newly discovered superconducting material with 39K critical transition temperature and large coherence length. Comparing with high temperature superconductors (HTS), it has weak link-free grain boundaries, so that it can be produced to wires and tapes with high critical current density (Jc). Moreover, comparing with low temperature superconductors, MgB2 could be used instead of liquid helium (4.2K), at temperature between 20-30K which could be obtained by refrigerated cooling technology with low cost. However, MgB2 has poor flux pinning property and low critical field (Hc2) and irreversibility field (Hirr), which limit the practical applications of MgB2 in a broad field. Therefore, the doping of nano particles is an important means to improve the magnetic behavior and superconducting properties of MgB2.In this paper we presented an effective method of producing pinning centers which lead to an enhancement of the critical current densities in MgB2 superconductor via powder metallurgy technology. Nano SiC doped MgB2 bulks fabricated using magnesium(Mg), amorphous boron (B) and nano SiC powder as starting materials were synthesized by conventional pressureless sintering (PLS) and spark plasma sintering (SPS) methods. The effects of the fabrication parameters (including sintering routes, sintering temperature and sintering time) on the phase formation and micreostructure of the MgB2 bulks were investigated by the X-ray diffraction, Scanning Electronic Microscope (SEM). Meanwhile the effects of the ratio of Mg and B atom in initial powders, the content of SiC doping and the sintering methods on the superconductiing properties of MgB2 bulks were discussed emphatically. Lastly, the density, microstructure and superconducting properties of the MgB2 bulks sintered by different methods were compared.The results showed that the nano SiC doped MgB2 bulks with less impurity and high superconducting properties could be synthesized by both the conventional vacuum sintering and the sparking plasma sintering. For the conventional pressureless sintering (PLS), the MgB2 bulk with the ratio of Mg and B atom of 1.1:2 with 5wt.% SiC doping was sintered at a temperature of 720℃for 1 hour in the flowing argon...