Effect of SiC nanoparticle addition on the critical current density of MgB2 tapes fabricated from MgH2, B and MgB2 powder mixtures

The effects of the addition of SiC nanoparticles were compared for MgB2 tapes prepared from two different starting powders with respect to the improvement in the critical current, Jc, at 4.2 K and 10 T. The starting powder was prepared by blending premixed MgH2 and B(MgH2+2B) and premixed (MgH2+2B) and MgB2 (30% MgB2) in a ratio of 7:3. All tapes were fabricated by the in situ powder-in-tube method. The use of 30% MgB2 as standard powder yields higher Jc values than MgH2+2B in the case of the pure MgB2 tape; however, the highest Jc (1.8 x 104 A cm-2) was obtained for the tape from MgH2+2B with 10 mol% SiC additive. The tape from 30% MgB2 contained regions with Si-free MgB2 grains, while Si compounds were distributed homogeneously across the tape prepared from MgH2+2B. Furthermore, the use of 30% MgB2 instead of MgH2+2B was found to reduce the effect of carbon substitution of the SiC additive. These data indicate that the technique, which enhances Jc-B characteristics of the pure MgB2 tape, does not promise further improvement through the addition of nanosized impurity particles. It is concluded that we should improve the fabrication technique of the MgB2 tape by keeping (or improving) the overall reactivity between the standard powder and nanosized impurity particles