Transport current improvements ofin situMgB2tapes by the addition of carbon nanotubes, silicon carbide or graphite

Various types of carbon nanotube (CNT), as well as SiC and graphite powders, were used at the 5 wt% level as additions to a mixture of commercial Mg and B powder for the fabrication of single-core, in situ tapes using two-axial rolling deformation in an Nb/Fe sheath and final heat treatment at 650 °C/0.5 h in Ar. Transport current measurements showed that well distributed CNT, SiC and graphite additions lead to an improvement of J c (μ 0 H ) characteristics. The presence of carbon-containing particles causes substitution of boron by carbon, which decreases the critical temperature and increases the upper critical field as well as the current density in high magnetic fields. The uniform distribution of CNTs or other carbon-containing particles is an important factor for effective carbon substitution. This observation may be important for the development of practical MgB 2 composite superconducting wires intended for magnets.