Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/01—Manufacture or treatment
  • H10N60/0268—Manufacture or treatment of devices comprising copper oxide
  • H10N60/0801—Manufacture or treatment of filaments or composite wires

Definitions

• the present invention relates to a method for producing superconducting Ag-sheathed ceramic tapes.
• the invention relates to a mechanical deformation met- hod including a placing of oxide Ag sheathed composite bar into a metallic outer tube, defo ⁇ ning the resultant bar to a wire and rolling the wire to a tape.
• the powder-in-tube method offers a simple approach to produce superconducting wires and tapes having good and reproducible properties (K. Heine et al. "High-field critical current densities in Bi 2 Sr 2 Ca 1 Cu 2 O 8+x /Ag wires " Appl. Phys. Lett. 55(23), 4 December 1989).
• a great potential market is expected in the Bi-based supercondutors produced by the powder-in-tube method.
• Bi-2223 and Bi-2212 tapes have been used to obtain high temperature superconducting prototypes, such as cables, magnets, motors, generators, fault current limiters, transformers, as well as superconducting magnetic energy storage units.
• J. can be enhanced by increasing J c (I c /A oxide ) of the super- conducting core and reducing the silver matrix.
• J c I c /A oxide
• a strip cutting technique experiments demonstrate that there are very large local variations of J c in a single filament tape . Tapes with average J c values of 12-15000A/cm 2 (77°K, 0T) had local J c values up to 76000 A/cm 2 which, however, depend on the local microstructure.
• the first one is the low oxide density in a tape compared with the theoretical density.
• the second is the inhomogeneous distribution of the filaments in the direction of width. Densification effect on the microstructure and J c in a Bi-2223 single filament tape has been reported by M.
• the highest relative density (true density/theoretical density) of a drawn wire was about 80 %.
• a green tape having a relative density of up to 90 % can be obtained by rolling the highest density wire (M. Satou, Y. Yamada, S. Murase, T. Kitamura and Y.
• a high compressive stress is essential for obtaining a high density in a green tape.
• a higher tensile sheath material than a pure Ag sheath would be effective to constrain the sheath in order to obtain this condition.
• An Ag alloy is a possibility.
• Cu or a Cu alloy would be even better.
• the Cu sheath was used as an additional outer sheath in the drawing process, then etched away before rolling.
• a Cu sheath was used as a supporting sheath in a hot extrusion process, whereafter a drawing and a rolling were performed to provide the final product.
• the highest densities were obtained for large deformation in one passage during extrusion.
• a hydrostatic extrusion does not allow a production of superconductors in their final form as reported in this paper. This paper claimed that the highest density and homogeneity were obtained in the tapes by conventional wire drawing and rolling without an additional Cu sheath.
• W reported by W.
• the object of the invention is to provide a method of improving superconducting performance of oxide superconductors and superconducting composites by enhancing density ofthe oxide core, reducing secondary non-superconducting phases, reducing the inhomogenity ofthe filament distribution during processing of oxide superconductors and superconducting composites. It is a further object ofthe invention to prepare oxide superconducting tapes having higher J c , J e and I c than conventionally-processed tapes.
• a feature of the invention is an improved mechanical deformation which involves an outer additional strong metal sheath during wire drawing and tape rolling processes.
• a method according to the invention of preparing an Ag alloy/ceramic superconducting tape includes a putting of a precursor powder into an Ag or Ag alloyed tube, drawing the bar into a wire of a predetermined diameter, cutting the wire to form a multifilament bar with an outer Ag or Ag alloyed tube, puttingthe resultantbar into ametal tube of e.g. Cu, Cu alloy, Al or steel. Deforming the multifilament bar by drawing, groove rolling, extru- sion, to form a wire and rolling the wire into a tape. The outer metal sheath will be removed either chemically or mechanically before heat treatment.
• ceramic refers to oxide superconductor, e.g. Bi(Pb)SrCaCuO, TlBaCaCuO, HgBaCaCuO, Y(Nd)BaCuO superconductors.
• Fig. 1 is a flow diagram illustrating the processing steps of the method according to the invention.
• Fig. 2 is a cross section of a superconducting composite bar and
• Fig. 3 is a cross section of a superconducting tape.
• the present invention is a method of improving the critical current density of oxide superconductor wires and tapes by a novel mechanical deformation process with an additional outer metal sheath.
• an outer strong metal sheath in additional to the Ag alloy sheath 3, an enhanced density of the oxide core 1, reduced non-superconducting secondary phases, improved texture ofthe grains, as well as increased oxide/ Ag ratio were obtained in the tapes resulting in a higher critical current density.
• the high compressive stress can be induced in the oxide core 1 by an additional outer strong sheath 4.
• the high tensile strength and toughness materials such as Cu can carry high deformation stress and strain without breaking so that working tools densify the oxide into a highly constrained condition.
• the fast transformation and diffusion are obtained by the highly dense oxide core 1. This results in a phase with a high purity and good texture.
• the outer Cu sheath 4 also gives a strong support for deforming high ratio superconducting oxide wires and tapes without breaking. During mechanical deformation, a contamination ofthe surface can be omitted by means of an outer protecting sheath.
• Fig. 1 shows the flow diagram of the processsing steps.
• the powder or powder bar was loaded into a pure Ag or Ag alloyed tube 2.
• a nominal composition (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x isused.
• the precursor powder consists ofBi- 2212 and secondary phases.
• the outer Cu tube may be used to prepare very high oxide ratio single filament. If so, the outer Cu sheath 4 have to be removed before bundling the single filament wires to form a multifila- ment bar.
• Bundled wires will be put into an Ag alloy tube 3 and then fit into a Cu tube 4 as shown in Fig. 2.
• the resultant bar will be deformed by swaging, drawing, extrusion, or groove rolling to a wire
• the wires are rolled into a tape shown in Fig 3
• Precursor powder was prepared by spray pyrolysis with a nominal stoichiometry of Bij ⁇ Pb 0 33 Sr, x7 Ca 2 Cu 3 ⁇ ⁇ The powder was pressed to a round bar with diameter of 16 mm and a length of 40 cm The billet was put into an Ag tube with an inner diameter of 18 mm and an outer diameter of 20 mm.
• a control tape to be compared with a tape according to the invention was made in same way but without an additional outer Cu sheath

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8107371

Family Applications (1)

Country Status (6)

Cited By (3)

Citations (1)

• 1999
  • 1999-12-20 JP JP2000590230A patent/JP2002533874A/ja active Pending
  • 1999-12-20 WO PCT/DK1999/000710 patent/WO2000038251A1/en not_active Ceased
  • 1999-12-20 SK SK799-2001A patent/SK7992001A3/sk unknown
  • 1999-12-20 AU AU16505/00A patent/AU1650500A/en not_active Abandoned
  • 1999-12-20 EP EP99959261A patent/EP1142037A1/en not_active Withdrawn
• 2001
  • 2001-06-22 NO NO20013175A patent/NO20013175L/no not_active Application Discontinuation

Patent Citations (1)

Also Published As

Similar Documents

Legal Events