Recent advances in processing of Ag-clad Bi-2223 superconductors

Enhancements in the transport current properties of long lengths of multifilament Ag-sheathed (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconducting tapes were made as a function of increased packing density of precursor powder, improved mechanical deformation, and adjusted cooling rate. Improved processing parameters had a pronounced effect on the transport critical current (I{sub c}) of the superconducting tapes, at 77 K and zero applied magnetic field, an I{sub c} of 60 A was obtained in short length samples (4 cm), an I{sub c} of 54 A in a 164 m length, and 18 A in a 1,260 m length. These enhancements were based on the increase in packing density accompanied with improved mechanical deformation and cooling schedule. Maximum critical current values were two to three times higher in slow-cooled tapes than in fast-cooled tapes

Effect of lead content on the formation of the 2223 phase

Freeze-dried powders have been used for the formation of the high Tc (110 K) superconducting phase in the Bi-Sr-Ca-Cu-O system. Effects of lead content and oxygen partial pressure were investigated. It was shown that lead content and oxygen partial pressure were affecting liquid phase formation. Lead content affected the dissolution of the 2212 phase into the liquid phase from which the 2223 high Tc superconducting phase forms. Powder reacted as pellet with Bi{sub 1.8}Pb{sub 0.4}Sr{sub 2.0}Ca{sub 2.0}Cu{sub 3.0}O{sub x} composition shows essentially phase pure 2223 after 12 hrs at 845{degrees} C in 7%O{sub 2}

Processing and characterization of Ag-clad Bi-2223 superconductors

Practical applications of high-temperature superconductors will be governed by their current transport and mechanical characteristics. With careful control of the processing parameters high-quality long- length mono- and multifilament Bi-2223 conductors have been fabricated by the powder-in-tube technique. A critical current density (Jc) of up to 1.2 x 104 A cm{sup -2} has been observed at 77 K in a 1260-m-long multifilament conductor containing 37 monocore filaments. A high-temperature superconducting magnet and a prototype transformer were fabricated and characterized from such long-length conductors. Efforts further improve the current characteristics of the Bi-2223 tapes resulted in the development of the wire-in-tube technique. A Jc value >105 A cm{sup -2} at 77 K and in self field have been obtained in a Bi-2223 tape fabricated by the wire- in-tube method. Extensive studies on the in-situ strain characteristics of the mono- and multifilament conductors have been conducted. Multilayer silver/superconductor composite tapes, fabricated by a novel chemical etching technique, were also observed to exhibit improved strain tolerance characteristics

Advances in processing of Ag-sheathed (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} superconductors.

Advances in the processing and fabrication of Ag-sheathed (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) high-T{sub c} superconductors by the powder-in-tube technique continue to bring this material closer to commercial applications. Enhancement of the transport critical current density (J{sub c}) of Ag-sheathed Bi-2223 tapes was achieved by increasing the packing density of the precursor powder, improving mechanical deformation, and adjusting the cooling rate. Long lengths (>150 m) of multifilamentary Bi-2223 tapes have been fabricated and carry critical currents (I{sub c}) of >50 A (J{sub c} {approx} 25 kA/cm{sup 2}) at 77 K in self-field. A 1260-m-long tape carried an I{sub c} of 18 A (J{sub c} {approx} 12 kA/cm{sup 2}) from end-to-end. Several prototype coils have been assembled from these long-length tapes. Recent progress in the fabrication of Bi-2223 tapes is presented in this paper

Development of Ag-clad Bi-2223 superconductors for electric power applications.

Development of high-temperature superconductor technology will make possible the design and fabrication of smaller, lighter, and more efficient power devices such as motors, generators, transformers, transmission cables, and fault-current limiters. A prototype fault-current limiter, a 200-hp motor, and a 50-m-long transmission cable have already been demonstrated using Ag-clad Bi-2223 superconductor tapes. We have recently enhanced the transport current properties of long lengths of multifilament Ag-clad Bi-2223 tapes through increased packing density of precursor powder, improved mechanical deformation, optimization of conductor design, and adjusted cooling rate. These improved processing parameters had a pronounced effect on the transport critical current of the super-conducting tapes. Our improvements are briefly discussed and their implications are assessed in this paper