Improving superconductivity and mechanical properties of Bi-2223/Ag-wire composite bulk by cold isostatic pressing

To improve superconductivity and mechanical properties of Bi-2223 sintered bulk, silver (Ag) wires of 0.4 mm in diameter were added to the bulk. The sample was sintered at 840°C for 50 hours in air. After treatment with cold isostatic pressing (CIP), the sample was re-sintered. When twenty-four Ag wires were composed, the critical current density (J_c) at 4.2 K and self-field increased from 1,200 A/cm² to 2,000 A/cm² with the CIP process. SEM observation results showed that high alignment and dense structures of Bi-2223 plate-like grains were formed around the interfacial region between the superconducting oxide and the metal Ag. The mechanical properties were measured by a three point bending test. The maximum bending stress of 60 MPa was obtained in the bulk without Ag wire, which was fractured separately. With the CIP process the maximum bending stress increased to 90 MPa for the composite. The composite did not fracture but only fine cracks were induced after the maximum bending stress.