Superconductivity and Thermal Property of MgB_2 /Aluminum Matrix Composite Materials Fabricated by 3-Dimensional Penetration Casting Method

摘要

Superconductive MgB_2/Al composite material with low and high volume fractions of particles were fabricated by our special pre-packing technique and 3-dimensional penetration casting method. The composite material showed homogeneous distribution of MgB_2 particles in the Al-matrix with neither any aggregation of particles nor defects such as cracks or cavities. The critical temperature of superconducting transition (T_c) was determined by electrical resistivity and magnetization to be about 37-39 K. Specific heat measurements further supported these T_c findings. The Meissner effect was also verified in the liquid He, in which a piece of the composite floated above a permanent magnet. The thermal conductivity of the MgB_2/Al composite material was about 25 W/Kcentre dot m at 30 K, a value much higher than those found for NbTi or Nb3Sn superconducting wires normally used in practice, which are 0.5 and 0.2 W/Kcentre dot m at 10 K, respectively. A billet of the superconducting material was successfully hot-extruded, forming a rod. The same as the billet sample, the rod showed an onset T_c of electrical resistivity of 39 K.