OXIDATION OF BI(PB)-SR-CA-CU-AG METALLIC PRECURSORS TO PRODUCE OXIDE/AG SUPERCONDUCTING MICROCOMPOSITES

Metallic precursor ribbons with nominal compositions of Bi1.4Pb0.6Sr2Ca3Cu4Ag3–11 were produced by vacuum induction melting followed by melt-spinning. Silver was added to aid in the alloy melting and metallic ribbon formation processes. These precursor ribbons were then subjected to a two-step treatment: first oxidation and then annealing under controlled atmosphere. Oxide/Ag superconducting microcomposites with zero resistance at 104–110 K and a critical current density of 600 A/cm2 at 77 K in zero field were produced in this way with excellent reproducibility. The oxidation kinetics, oxide structure, and oxidation mechanism were studied by a combination of thermogravimetry, optical and scanning electron microscopy, x-ray diffraction, and electron probe microanalysis. Three types of oxidation, combustion, fast and slow oxidation, were observed under different conditions, and they were found to be important for producing superconducting materials. While the combustion and fast oxidation produced distorted, inhomogeneous specimens, the slow oxidation produced nondeformed specimens with a relatively homogeneous mixture of oxide/Ag, from which the so-called “2223” superconducting phase can be formed after suitable annealing. © 1990, The Electrochemical Society, Inc. All rights reserved.