The Vickers microhardness of a BSCCO core in Ag-sheathed composites made by various deforming processes such as drawing, cold and hot hydrostatic extrusion, rolling, and uniaxial pressing have been measured. Because the hardness of a material, defined as the resistance to indentation, can be simply measured, it is used for density indication in the ceramic core. Complex microhardness profiles in BSCCO core cross-sections have been compared in composites deformed by the mentioned processes. These results give information on how the applied deforming process can effect the ceramic core density as well as its homogeneity and so influence the critical current density and current distribution in BSCCO/Ag superconducting tapes.

No abstract

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.