Pavol Kovac
Functional superconductors are usually composite wires consisting of superconducting filaments inside a severall metallic sheaths playing the role of inter-diffusion protection (diffusion barrier) and also the role of electrical and mechanical stabilization. Up to now, MgB2 phase is the lightest existing superconducting compound with specific mass of only 2.5 gcm-3. The combination of MgB2 filaments with Ti-barriers and Al-stabilization outer sheath would provide a composite wire with the minimal mass. But, pure Al is too soft to be used for the outer sheath of composite wires subjected to apparent cold deformation by drawing or rolling. Therefore, micro-structure and properties Al+Al2O3 material produced by powder metallurgy was carefuly tested and then successfully utilized for composite MgB2/Ti/Al+Al2O3 wire. Mechanical and electrical properies of such wire were examined at low temperatures and used also for the superconducting coil made by wind and react process with utilization of self-insulated 15 µm Al2O3 layer created on the wire surface by the anodic oxidation. Very thin and high temperature resistant Al2O3 layer offers high space factor which maximize the current density and winding efficiency. High electrical performance and also tolerance to axial stress have been obtained for MgB2/Ti/Al+Al2O3 wires at low temperatures. Such lightweight MgB2 composite conductors can be especially interesting for future high power density aircraft engines and also for some of space applications (e.g. active magnetic shielding), where the total mass of system is important issue.
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