Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Process of making wire – tape – cable – coil – or fiber
Reexamination Certificate
1995-11-07
2001-02-27
Kopec, Mark (Department: 1751)
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Process of making wire, tape, cable, coil, or fiber
C505S492000, C505S501000, C505S740000, C174S125100
Reexamination Certificate
active
06194352
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to cabled superconducting oxide conductors and to a method for their manufacturing. The present invention further relates to a method for healing defects introduced into the oxide superconductor composite during cabling and thereby improving superconducting properties.
BACKGROUND OF THE INVENTION
Since the discovery of oxide superconducting materials with transition temperatures above about 20 Kelvin the possibility of using them to obtain greater efficiency in electrical and magnetic applications has attracted considerable interest. However, to be practical outside the laboratory, most electrical and magnetic applications require flexible cabled lengths of conductor manufacturable with high packing factors which can be manufactured at reasonable cost and with high engineering current-carrying capacity. High packing factor forms are needed because limited space constraints and high overall current requirements are major design issues. Conductors which are flexibly cabled, that is, composed of twisted, helically wound, braided or otherwise transposed bundles of electrically, and sometimes mechanically, isolated conductor strands, are desired in many applications, including coils, rotating machinery and long length cables. In comparison to monolithic conductors of comparable composition and cross-section, cabled forms which are made from a number of isolated conductors strands will have much higher flexibility. Substantially mechanically isolated cable strands have some ability to move within the cable, although some degree of mechanical locking of the strands is desired for stability and robustness of the conductor to stay together during handling and winding. Electrical isolation of the cable strands is preferred but not required. In low temperature superconducting conductors, cables which are made from a number of substantially electrically isolated and transposed conductor strands have been shown to have greatly reduced AC losses in comparison to monolithic conductors. See “
Superconducting Magnets”
by Martin Wilson (1983,1990), pp 197, 307-309. It has been proposed that the same relation will hold for high temperature superconductors. Flexibility increases in proportion to the ratio between the cable cross-section and the strand cross-section. AC losses are believed to decrease in relation to cable cross-section, strand cross-section and twist pitch. Thus, the greater the number of strands in a cable of given dimension, the more pronounced these advantages will be.
However, it has not been considered feasible to form oxide superconductors in high winding density, tightly transposed configurations because of the physical limitations of the material. Superconducting oxides have complex, brittle, ceramic-like structures which cannot by themselves be drawn into wires or similar forms using conventional metal-processing methods and which do not possess the necessary mechanical properties to withstand cabling in continuous long lengths. Consequently, the more useful forms of high temperature superconducting conductors usually are composite structures in which the superconducting oxides are supported by a matrix material, typically a noble metal, which adds mechanical robustness to the composite.
Even in composite forms, the geometries in which high-performance superconducting oxide articles may be successfully fabricated are constrained by the relative brittleness of the composite, by the electrical anisotropy characteristic of the oxide superconductor, and by the necessity of “texturing” the oxide material to achieve adequate critical current density. Unlike other known conductors, the current-carrying capacity of a superconducting oxide composite depends significantly on the degree of crystallographic alignment and intergrain bonding of the oxide grains, together known as “texturing”, induced during the composite manufacturing operation.
Known processing methods for obtaining textured oxide superconductor composite articles include an iterative process of alternating anneal and deformation steps. The anneal is used to promote reaction-induced texture (RIT) of the oxide superconductor in which the anisotropic growth of the superconducting grains is enhanced. Each deformation provides an incremental improvement in the orientation of the oxide grains (deformation-induced texturing or DIT).
The texture derived from a particular deformation technique will depend on how closely the applied strain vectors correspond to the slip planes in the superconducting oxide. Thus, superconducting oxides such as the BSCCO family, which have a micaceous structure characterized by highly anisotropic preferred cleavage planes and slip systems, possess a highly anisotropic current-carrying capacity. Such superconducting oxides are known to be most effectively DIT textured by non-axisymmetric techniques such as pressing and rolling, which create highly aspected (greater than about 5:1) forms. Other methods of texturing BSCCO 2223 have been described in U.S. Ser. No. 08/302,601, filed Sep. 8, 1994 entitled “Torsional Texturing of Superconducting Oxide Composite Articles”, which describes a torsional texturing technique; U.S. Ser. No. 08/041,822 filed Apr. 1, 1993, entitled “Improved Processing for Oxide Superconductors” now issued as U.S. Pat. No. 5,635,456; and U.S. Ser. No. 08/198,912 filed Feb. 17, 1994, entitled “Improved Processing of Oxide Superconductors” which is now issued as U.S. Pat. No. 5,635,456 which describes an RIT technique based on partial melting. These techniques have been observed to provide the greatest improvement in the Jc's of BSCCO 2223 samples when used in combination with a highly non-axisymmetric DIT technique, such as rolling.
Although superconducting oxide composite articles may be textured by various methods, including magnetic alignment, longitudinal deformation (DIT) or heat treatment (RIT), not all texturing methods are equally applicable to, or effective for, all superconducting oxides. For example, known techniques for texturing the two-layer and three-layer phases of the bismuth-strontium-calcium-copper-oxide family of superconductors (Bi
2
Sr
2
Ca
1
Cu
2
O
x
and Bi
2
Sr
2
Ca
2
Cu
3
O
x
, also known as BSCCO 2212 and BSCCO 2223, respectively) are described in Tenbrink et al., “Development of Technical High-T
c
Superconductor Wires and Tapes”, Paper MF-1, Applied Superconductivity Conference, Chicago(Aug. 23-28, 1992), H. B. Liu and J. B. Vander Sande, submitted to Physica C, (1995), and Motowidlo et al., “Mechanical and Electrical Properties of BSCCO Multifilament Tape Conductors”, paper presented at Materials research Society Meeting, Apr. 12-15, 1993. Micaceous oxides such as the BSCCO family which demonstrate high current carrying capacity in the absence of biaxial texture have been considered especially promising for electrical applications because they can be textured by techniques which are readily scalable to long-length manufacturing.
Liquid phases in co-existence with solid oxide phases have been used in processing of oxide superconductors. One type of partial melting, known as peritectic decomposition, takes advantage of liquid phases which form at peritectic points of the phase diagram containing the oxide superconductor. During peritectic decomposition, the oxide superconductor remains a solid until the peritectic temperature is reached, at which point the oxide superconductor decomposes into a liquid phase and a new solid phase. The peritectic decompositions of Bi
2
Sr
2
CaCu
2
O
8+x
, (BSCCO 2212, where 0≦x≦1.5), into an alkaline earth oxide and a liquid phase and of YBa
2
Cu
3
O
7−&dgr;
(YBCO 123, where 0≦&dgr;≦1.0) into Y
2
BaCuO
5
and a liquid phase are well known. Kase et al. in IEEE Trans. Mag. 27(2), 1254 (1991) report obtaining highly textured BSCCO 2212 by slowly cooling through the peritectic point, a RIT technique because BSCCO 2212 totally melts and reforms during melt textured growth, any texturing induced by deformation prior to the melting will not influence
Barnes William L.
Otto Alexander
Riley, Jr. Gilbert N.
Seuntjens Jeffrey M.
Snitchler Gregory L.
American Superconductor Corporation
Clark & Elbing LLP
Kopec Mark
Scozzafava Mary Rose
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