The reactivities of several oxide materials (OM) in direct contact with BSCCO powder has been tested at a temperature of approximately 845 • C in air. The OM such as BaZrO 3 , SrCO 3 , MgO and ZrO 2 showing little or no reactivity with BSCCO were mixed (10 wt%) with a BSCCO precursor powder and used for monocore tapes made by a standard powder-in-tube technique. The microstructure of the BSCCO+OM cores was analysed by SEM and XRD and the transport current properties-critical current, pinning force and resistance up to 16 T-were measured as a function of the magnetic field for various orientations with respect to the ab plane. The OM used influenced the electrical properties of the Bi-2223 phase in different ways. This is because the oxides react with BSCCO during the heat treatment and simultaneously affect the 2212 → 2223 phase transformation as well as the Bi-2223 grain growth and grain connectivity. Submicrometre commercial SrCO 3 powder was evaluated as the best material from all those tested, for resistive barriers in Bi-2223/Ag tapes.
Multi-core MgB 2 wire reinforced by stainless steel (SS) has been made by an in situ approach and subjected to additional deformations and mechanical stressing. A critical current density J c of 10 4 A cm −2 at 4.2 K was measured in an external field of 9.45-10 T. The filament density of drawn wire was increased by cold deformation without axial tension, which resulted in an increased J c by approximately 17%. SS reinforced wire shows a high resistance to mechanical stresses. Only 10% I c degradation was measured for wire twisted with L t = 7.14 mm. The presented SS reinforced wire has the highest irreversible strain ε irr = 0.9% so far published.
Nineteen-filament MgB 2 /Ti/Cu/SS composites have been made by an in situ approach using only drawing deformation to a filament size of 16.6-58 μm. Circular cables containing 133 filaments were assembled from 1 + 6 strands of diameter 0.25 mm and 0.375 mm. All wires and cables were heat treated at 800 • C/0.5 h in pure Ar atmosphere. The critical current densities J c of the different wire sizes were measured and EDX element mapping was done for some of them. It was found that the critical current density decreases with reduced filament size, especially below the filament diameter of 27 μm due to copper penetration through the thin Ti barrier (<10 μm) and consequent contamination of MgB 2 . In spite of Cu contamination, J c > 10 4 A cm −2 was measured at 4.2 K and field 5.5 T for the thinnest 16.6 μm filaments published up to now.
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