Effect of SiC nanoparticle addition on the critical current density of MgB_2 tapes fabricated from MgH_2, B and MgB_2 powder mixtures

摘要

The effects of the addition of SiC nanoparticles were compared for MgB_2 tapes prepared from two different starting powders with respect to the improvement in the critical current, J_c, at 4.2 K and 10 T. The starting powder was prepared by blending premixed MgH_2 and B(MgH_2 + 2B) and premixed (MgH2 + 2B) and MgB_2 (30 percent MgB_2) in a ratio of 7:3. All tapes were fabricated by the in situ powder-in-tube method. The use of 30 percent MgB_2 as standard powder yields higher J_c values than MgH_2 + 2B in the case of the pure MgB_2 tape; however, the highest J_c (1.8 x 10~4 A cm~(-2)) was obtained for the tape from MgH_2 + 2B with 10 mol percent SiC additive. The tape from 30 percent MgB_2 contained regions with Si-free MgB_2 grains, while Si compounds were distributed homogeneously across the tape prepared from MgH_2 + 2B. Furthermore, the use of 30 percent MgB_2 instead of MgH_2 + 2B was found to reduce the effect of carbon substitution of the SiC additive. These data indicate that the technique, which enhances J_C-B characteristics of the pure MgB_2 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 MgB_2 tape by keeping (or improving) the overall reactivity between the standard powder and nanosized impurity particles.