Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-02-12
2001-03-06
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C174S125100, C174S126200, C505S231000, C505S431000, C505S501000
Reexamination Certificate
active
06195870
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to superconductive tapes and more particularly to superconductive tapes prepared under low pressure compressive annealing. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).
BACKGROUND OF THE INVENTION
The discovery of high temperature superconductive materials in the late 1980's was soon followed by a desire to form such materials into tapes or similar shapes. Ideally such tapes should be physically strong, flexible, highly conductive and able to withstand strong magnetic fields without loss of current carrying capacity.
Processes generally referred to as “powder in a tube” have been developed. For example, a general process of fabricating superconductive tape involves initially preparing a superconductive powder, filling a tube or pipe of silver with the superconductive powder, sealing the pipe or tube, subjecting the pipe or tube to reducing or deforming operations to form tape, and finally sintering the reduced tape at high temperatures.
Efforts to further develop conventional thermomechanical processing methods have been largely unsuccessful in improving the critical current density, J
c
, of BSCCO superconducting tapes. Limited current density remains an obstacle in the commercial application of BSCCO high temperature superconductors. Conventional processing involves iterative cycles of mechanical deformation to develop texture and reduce porosity followed by thermal annealing to react components, to relieve stress and to heal microcracks caused by the deformation. Texture and deformation hardening and cracking may limit the ability to obtain the desired grain texture through deformation alone. In addition, the oxide core density of the superconductive tapes decreases during the annealing, causing J
c
to decrease as well.
It is an object of the present invention to provide a process of improving critical current density in superconductive tapes by a low pressure compressive annealing of the tapes.
It is a further object of the invention to provide a process of low pressure compressive annealing of superconductive tapes in the absence of tape deformation, i.e., where such low pressure compressive annealing does not subject the tapes to deformation.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a process of preparing a high temperature oxide superconductive tape including heating an oxide superconductive precursor tape at ambient pressure and at temperatures of from about 810° C. to about 840° C. for a sufficient period of time, pressing said oxide superconductive precursor tape under high pressure of greater than about 0.1 GPa at ambient temperature, and heating said oxide superconductive precursor tape under low compressive uniaxial pressures insufficient to deform said oxide superconductive precursor tape at temperatures of from about 810° C. to about 840° C. for periods of time from about 100 hours to about 200 hours.
In one embodiment of the present invention, the high temperature oxide superconductive tape includes a bismuth-strontium-calcium-copper oxide as the superconductive material.
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Baldonado Patrick S.
Bingert John F.
Holesinger Terry G.
Peterson Dean E.
Zhu Yuntian T.
Arbes Carl J.
Cottrell Bruce H.
The Regents of the University of California
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