Fabrication of ex situ processed MgB2 wires using nano carbon doped powder

Abstract We fabricated ex situ MgB 2 wires using C-doped MgB 2 powder as a precursor in order to improve the core density of the wires and their C doping content. The C-doped powder was prepared with Mg, B, and nano carbon (NC) powders by the in situ technique and then MgB 2− x C x ( x  = 0, 0.01, and 0.03) wires were fabricated by the ex situ technique using the powder-in-tube method. The phase formation, lattice change, and microstructure were characterized and correlated with the T c and J c variations. We observed that the ex situ wire had a higher core density than the in situ wire, however its morphology consisted of agglomerated particles, indicating that sintering and grain growth did not occur completely, even though the sintering was conducted at high temperature (1000 °C). As the C content increased, T c decreased, while the decrease of J c with increasing magnetic field became smaller. The J c of MgB 1.97 C 0.03 wire made by the ex situ technique was 3.34 kA/cm 2 at 6.6 T and 5 K which is comparable to that of the in situ wire (4.81 kA/cm 2 at 6.6 T and 5 K).