Superconductor technology: apparatus – material – process – High temperature devices – systems – apparatus – com- ponents,... – Superconducting wire – tape – cable – or fiber – per se
Reexamination Certificate
1997-07-29
2002-04-09
Yamnitzky, Marie (Department: 1774)
Superconductor technology: apparatus, material, process
High temperature devices, systems, apparatus, com- ponents,...
Superconducting wire, tape, cable, or fiber, per se
C505S236000, C505S237000, C505S431000, C505S704000, C174S125100, C029S599000, C428S702000, C428S930000
Reexamination Certificate
active
06370405
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to high temperature ceramic superconductors. More particularly, it relates to multifilamentary superconductor structures that include a multiplicity of thin and uniform filaments; and to the manufacture of such structures from near net shape precursors.
BACKGROUND OF THE INVENTION
Superconductors are materials having essentially zero resistance to the flow of electrical current at temperatures below a critical temperature, Tc. A variety of copper oxide ceramic materials have been observed to exhibit superconductivity at relatively high temperatures, i.e., above 77K. Since the discovery of the first copper oxide based superconductor about ten years ago, these superconducting ceramics have attracted wide interest, and their physical and chemical properties have been widely studied and described in many publications.
Composites of superconducting materials and metals are often used to obtain better mechanical and electrical properties than superconducting materials alone provide. These composites are typically prepared in elongated wires, elements and cables by a variety of known processes such as the well-known powder-in-tube (“PIT”) process in which a metal container is filled with a precursor powder and the filled container is then deformed and thermomechanically processed to form filamentary composites having the desired superconducting properties, and a variety of coated conductor (“CC”) processes in which a superconductor material or a precursor thereof is deposited on a substrate which is then further processed to form a composite including a superconducting filament. However formed, a multiplicity of filaments may be bundled and/or cabled, with additional deformation and thermomechanical processing steps as needed, to provide multifilamentary composites.
To be commercially viable, high-temperature superconductor (HTS) wire must have high performance (e.g., high critical current density of the superconductor, Jc) and low cost. In the past, considerable efforts have been directed to improving the Jc of superconducting ceramics through densification and crystallographic alignment or texture of the superconducting grains; more recently, there has been increasing interest in and efforts to develop manufacturing technologies through which long lengths of HTS wires can be fabricated with higher, and commercially acceptable, price to performance (as measured by $/kA m) ratios.
At this time, it is known in the HTS community that the highest performing BSCCO (both 2212 and 2223) contain highly aspected (an “aspected” element has, in transverse cross-section, a width greater than its height) filaments with dimensions on the order of 10 ×100 microns, and that composite Bi-2223 conductors fabricated using PIT techniques can achieve relatively high Jc performance if asymmetric deformation resulting in an aspected element is employed. For example, using asymmetric deformation, a Jc value of 69,000 A/cm2 at 77K and self field has been reported (Q. Li et al., Physica C, 217 (1993) 360); and it has been predicted that the Jc performance of Bi-2223 conductors may be improved drastically if the thickness of the superconducting layer is decreased from the 30 micron level used by Li et al. to the three micron level. A Jc value in excess of 100,000 A/cm2 (77K, 0 T) has been estimated for the Bi-2223 layer (about 1.5 micron thick) that is immediately adjacent to the Ag in conventionally fabricated elements. Other HTS wire types have shown short length performance, e.g., coated conductors based on Y-123 which are fabricated using thin film techniques using such equipment as vacuum systems, lasers and ion guns.
It is difficult to achieve filament thicknesses in the range of 3 microns using conventional PIT techniques in which axisymmetric deformation is used to prepare a round multifilamentary precursor that is subsequently rolled into a highly aspected element, for two principal reasons. First, the strain path for each filament is a function of its position within the composite, and filaments in the edges of the final element will be less textured and will have a lower performance level than those in the central region of the element. Second, the pre-deformation cross-section of each filament is typically circular, and it is difficult to achieve a thin and wide filament by deforming an initially round filament.
A variety of deformation processing procedures have been proposed. Copending application Ser. No. 08/468,089, filed Jun. 6, 1995 now U.S. Pat. No. 6,247,224 entitled “Simplified Deformation-Sintering Process for Oxide Superconducting Articles”, and incorporated herein by reference in its entirety, describes a method for preparing a highly textured oxide superconductor article in a single, rather than a multiple step, deformation-sinter process. In the procedure described a precursor article, including a plurality of filaments extending along the length of the article and comprising a precursor oxide having a dominant amount of a tetragonal BSCCO 2212 phase and a constraining member substantially surrounding each of the filaments, is subjected to a heat treatment at an oxygen partial pressure and temperature selected to convert a tetragonal BSCCO 2212 oxide into an orthorhombic BSCCO 2212 oxide. Thereafter, the article is roll worked in a single high reduction draft in a range of about 40% to 95% in thickness so that the filaments have a constraining dimension is substantially equivalent to a longest dimension of the oxide superconductor grains, and is then sintered to obtain a BSCCO 2212 or 2203 oxide superconductor. Other procedures are disclosed in copending application Ser. No. 08/651,688, filed Nov. 11, 1995 and entitled “Improved Breakdown Process for Superconducting Ceramic Composite Conductors”, which application is also here incorporated by reference in its entirety.
To be practical outside the laboratory, most electrical and magnetic applications require flexible cabled lengths of conductor manufacturable with high fill factors (i.e. a high volume percent of superconductor in the composite multifilament structure) in addition to high current-carrying capacity. Thus, in addition to making individual filaments with high Jc, considerable effort also has been directed to the manufacture of cables and the like which include a multiplicity of HTS filaments. For example, copending application Ser. No. 08/554,814, filed Nov. 11, 1995, now U.S. Pat. No. 6,247,225, entitled “Cabled Conductors Containing Anisotropic Superconducting Compounds and Method for Making Them,” and also hereby incorporated by reference in its entirety, discloses a cabled conductor comprising a plurality of transposed strands each comprising one or more preferably twisted filaments preferably surrounded or supported by a matrix material and comprising textured anisotropic superconducting compounds which have crystallographic grain alignment that is substantially unidirectional and independent of the rotational orientation of the strands and filaments in the cabled conductor. The cabled conductor is made by forming a plurality of suitable composite strands, forming a cabled intermediate from the strands by transposing them about the longitudinal axis of the conductor at a preselected strand lay pitch, and, texturing the strands in one or more steps including at least one step involving application of a texturing process with a primary component directed orthogonal to the widest longitudinal cross-section of the cabled intermediate, at least one such orthogonal texturing step occurring subsequent to said strand transposition step. In one embodiment, the filament cross-section, filament twist pitch, and strand lay pitch are cooperatively selected to provide a filament transposition area which is always at least ten times the preferred direction area of a typical grain of the desired anisotropic superconducting compound. For materials requiring biaxial texture, the texturing step may include application of a texturing process with a second primary component in a predet
Antaya Peter D.
Christopherson Craig J.
Craven Christopher A.
DeMoranville Kenneth L.
Garrant Jennifer H.
American Superconductor Corporation
Hale and Dorr LLP
Yamnitzky Marie
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