Superconductivity and thermal property of MgB ₂/aluminum matrix composite materials fabricated by 3-dimensional penetration casting method

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 MgBi ₂/Al composite material was about 25 W/K·m at 30 K, a value much higher than those found for NbTi or Nb ₃Sn superconducting wires normally used in practice, which are 0.5 and 0.2 W/K·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.