Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Process of making wire – tape – cable – coil – or fiber
Reexamination Certificate
1997-03-10
2001-10-09
Beck, Shrive P. (Department: 1762)
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Process of making wire, tape, cable, coil, or fiber
C505S430000, C505S230000, C505S704000
Reexamination Certificate
active
06300285
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preparing superconductive wire or tape, and more particularly to a process of preparing superconductive wire or tape wherein at least one reduction or deformation stage is conducted at sub-ambient temperatures, e.g., at liquid nitrogen temperatures.
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 wires, tapes or similar shapes. Ideally such wires or 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 wire 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 wire, and finally sintering the reduced wire.
Generally, conventional deformation processing provides long lengths of a desired form such as rod, wire, tube or tape, consolidates the superconductor powder, and induces a desirable texture into the high temperature superconductive material (referred to as Deformation Induced Texture—DIT). High relative densities and sharp textures in the superconducting phase are required attributes for all high performance high temperature superconductive conductors. Certain high temperature superconductive materials show marked texturing via certain methods of deformation processing. It is well known that high performance high temperature superconductive conductors that contain Bi-2223 are fabricated using an iterative thermomechanical process in which certain types of deformation are interspersed with high temperature heat treatments. The deformation provides the desired density and texture in the high temperature superconductive material and the heat treatments result in chemical reactions that heal microcracks. Ultimately, the result is a composite within which the Bi-2223 grains are textured and connected.
Previous techniques have focused on wire drawing and tape rolling to achieve high density and texture. Such processes have routinely been performed at room or ambient temperatures or at elevated temperatures. Although high performance conductors have been fabricated using a deformational process at room temperature, microstructural analysis of the resultant composites continues to indicate that there is much room for improvement. Accordingly, alternatives to the conventional processing were sought whereby improvement in the properties of the resultant high temperature superconductive composites could be realized.
An object of the present invention is to provide an improved reduction or deformation process for the preparation of high temperature superconductive wires or tapes.
Another object of the present invention is to provide such a reduction or deformation process for the preparation of high temperature superconductive wires or tapes whereby improvements in texture and uniformity of the superconductive material thickness, increased filament uniformity and increased density of the superconductive material can be achieved.
Still another object of the present invention is to provide, via an alternative reduction or deformation process, a high temperature superconductive composite having a higher density of the superconductive material and an improved uniformity of superconductive thickness in the composite as well as improved filament uniformity.
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 an improvement in a process of preparing a composite high temperature oxide superconductive wire including filling a metal tube with an oxide superconductive powder material, reducing the cross-sectional dimensions of the tube through a multiple of cross-sectional reduction steps, and sintering the oxide superconductive powder material to produce a resultant composite high temperature oxide superconductive wire, the improvement comprising at least one cross-sectional reduction step being conducted at sub-ambient temperatures.
The present invention further provides the product formed by the process of having at least one cross-sectional reduction step conducted at sub-ambient temperatures, such a superconductive wire including an oxide superconductor core surrounded by a metal sheath, the metal sheath further characterized as having a dislocation density of greater than about 10
12
/cm
2
, and the oxide superconductor core further characterized as having substantial uniformity in cross sectional dimensions.
DETAILED DESCRIPTION
The present invention concerns a process of preparing a superconductive article, e.g., a superconductive wire or tape, such a process including at least one cross-sectional reduction of the wire or tape at a sub-ambient processing temperature and the resultant product therefrom.
In the process of the present invention, a cross-sectional reduction step is conducted at sub-ambient temperatures. By “sub-ambient”
0
is meant that the temperature is intentionally depressed from an otherwise ambient temperature, i.e., room temperature. Preferably, the cross-sectional reduction step is conducted at temperatures of less than about 200 K, more preferably at temperatures of less than about 100 K.
Cross-sectional reduction steps can include drawing, extruding, rolling, pressing, ironing, or swaging, all of which can result in a reduction in the cross sectional dimensions of any particular article after such processing. By conducting at least one cross-sectional reduction step at the sub-ambient temperatures, it has now been found that improved compaction of the superconductive material can be achieved via increased strength of the metal surrounding the superconductive material.
The present superconductive article generally includes a high temperature oxide superconductive material such as a high temperature oxide superconductive ceramic material. By “high temperatures” is generally meant that such a material exhibits superconductivity at temperatures above about 35 K, and preferably exhibits superconductivity at the temperature of liquid nitrogen, about 78 K.
In preparing the superconductive wire or tape including a high temperature oxide superconductive ceramic material, oxide superconductive powder can be prepared from bismuth-based superconductive materials such as a bismuth-strontium-calcium-copper oxide, e.g., Bi
2
Sr
2
Ca
2
Cu
3
O
x
(Bi-2223) or Bi
2
Sr
2
Ca
1
Cu
2
O
x
, (Bi-2212) or a bismuth-lead-strontium-calcium-copper oxide, e.g., (Bi
2−x
Pb
x
)Sr
2
Ca
2
Cu
3
O
x
, from rare earth-based superconductive materials including yttrium-based superconductive materials such as a yttrium-barium-copper oxide, e.g., YBa
2
Cu
3
O
x
, or from thallium-based superconductive materials such as a thallium-barium-copper oxide, e.g., Tl
2
Ba
2
Ca
2
Cu
3
O
x
.
Numerous other oxide superconductive compositions are well known as exemplified by MBa
2
Cu
3
O
x
where M is neodymium (Nd), dysprosium (Dy), erbium (Er), thulium (Tm), gadolinium (Gd), samarium (Sm), europium (Eu), ytterbium (Yb), holmium (Ho) or mixtures thereof, La
2−x
Sn
x
CuO
4
, La
2
CuO
4
doped with fluorine, YBa
2
Cu
3
O
x
doped with fluorine, EuBa
2
(Cu
1−y
M
y
)
3
O
x
where M is chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni) or zinc (Zn), and BaKBiO
3
. Those acquainted with the art will appreciate that the list of superconductors, especially high temperature ceramic-type oxide superconductors, is long and continues to grow on a regular basis and that basic high temperature ceramic-type oxide superconductor compositions may generally be doped with various metals, metalloids and non-metals. The purpose of the present invention is to provide an improved proces
Bingert John F.
Michels William
Roberts Peter R.
Beck Shrive P.
Cottrell Bruce H.
The Regents of the University of California
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