Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Applying hot isostatic fluid pressure to preform using...
Reexamination Certificate
2000-05-30
2003-09-02
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Applying hot isostatic fluid pressure to preform using...
C264S614000, C264S619000, C505S431000, C505S432000, C029S599000
Reexamination Certificate
active
06613270
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the production and processing of high T
c
superconducting bismuth-strontium-calcium-copper-oxide materials.
Since the discovery of the copper oxide ceramic superconductors, their physical and chemical properties have been widely studied and described in many publications, too numerous to be listed individually. These materials have superconducting transition temperatures (T
c
) greater than the boiling temperature (77° K.) of liquid nitrogen. However, in order to be useful for the majority of applications, substantially single phase superconducting materials with high critical current densities (J
c
) are needed. In general, this requires that the grains of the superconductor be crystallographically aligned, or textured, and well sintered together. Several members of the bismuth-strontium-calcium-copper-oxide family (BSCCO), in particular, Bi
2
Sr
2
CaCu
2
O
8
(BSCCO 2212) and Bi
2
Sr
2
Ca
2
Cu
3
O
10
(BSCCO 2223) have yielded promising results, particularly when the bismuth is partially substituted by dopants, such as lead ((Bi,Pb)SCCO).
Composites of superconducting materials and metals are often used to obtain better mechanical properties than superconducting materials alone provide. These composites may be prepared in elongated forms such as wires and tapes by the well-known “powder-in-tube” or “PIT” process which includes, for multifilamentary articles, the three stages of: forming a powder of superconductor precursor material (precursor powder formation stage); filling a noble metal billet with the precursor powder, longitudinally deforming and annealing it, forming a bundle of billets or of previously formed bundles, and longitudinally deforming and annealing the bundle to provide a composite of reduced cross-section including one or more filaments of superconductor precursor material in a surrounding noble metal matrix (composite precursor fabrication stage); and subjecting the composite to successive asymmetric deformation and annealing cycles and further thermally processing the composite to form and sinter a core material having the desired superconducting properties (thermomechanical processing stage). General information about the PIT method described above and processing of the oxide superconductors is provided by Sandhage et al., in JOM, Vol. 43, No. 3 (1991) pages 21 through 25, and the references cited therein, by Tenbrink, Wilhelm, Heine and Krauth, Development of Technical High-Tc Superconductor Wires and Tapes, Paper MF-1, Applied Superconductivity Conference, Chicago (Aug. 23-28, 1992), and Motowidlo, Galinski, Hoehn, Jr. and by Haldar, Mechanical and Electrical Properties of BSCCO Multifilament Tape Conductors, paper presented at Materials research Society Meeting, Apr. 12-15, 1993.
In the composite precursor fabrication stage, longitudinal deformation operations, i.e., wire drawing and/or extrusion, which form the billet or bundle into an elongated shape such as a wire or tape are followed by low temperature anneals, typically on the order of 200° C. to 450° C. at 1 atm in air for silver, to relieve strain energy introduced by deformation, without causing substantial reaction of the precursor powder or melting or grain growth in the silver.
FIG. 1
(prior art) is a typical annealing curve showing silver hardness as a function of annealing temperature. In some instances, a high temperature thermal anneal, typically on the order of 600° C. at 1 atm in air for silver, has been performed prior to the first bundle deformation step in the stage to bond the billets to one another. In other instances, where high strain deformations involving reductions of 100% or more have been performed, a high temperature thermal anneal, typically on the order of 600° C. at 1 atm in air for silver, has been included as the last step in the stage in order to relieve the strain energy in the matrix material prior to thermomechanical processing.
The deformation portions of the deformation and annealing cycles in the thermomechanical processing stage, are asymmetric deformations which create alignment of precursor grains in the core (“textured” grains) which facilitate the growth of well-aligned and sintered grains of the desired superconducting material during later thermal processing stages. Examples are rolling and the isostatic pressing cycle described in U.S. patent application Ser. No. 07/906,843 (US '843) filed Jun. 30, 1992 entitled “High Tc Superconductor and Method for Making It”, which is herein incorporated in its entirety by reference. They may be followed by anneals to relieve strain energy in the metal portions of the composite precursor. A series of heat treatments is also typically performed during the thermomechanical processing stage to promote powder reactions, including final thermomechanical treatment stages employed to more fully convert the filaments to the desired final, highly textured superconducting phase, preferably BSCCO or (Bi,Pb)SCCO 2223. The thermomechanical processing may be carried out by any conventional method, such as for example those described in Sandhage et al, supra, Tenbrink et al, supra, Haldar, supra, and in U.S. Pat. No. 5,635,456 issued Jun. 3, 1997, entitled “Improved Processing for Oxide Superconductors,” and U.S. Pat. No. 5,661,114 issued Aug. 26, 1997, entitled “Improved Processing of Oxide Superconductors”, and U.S. patent application Ser. Nos. 08/468,089, (US '089) filed Jun. 6, 1995, entitled “Improved Deformation Process for Superconducting Ceramic Composite Conductors”, now issued as U.S. Pat. No. 6,247,224, and 08/651,169 (US '169) filed May 21, 1996, entitled “A Novel reaction for High Performance (Bi,Pb)
2
Sr
2
Ca
2
Cu
3
O
y
Composites”, now issued as U.S. Pat. No. 5,798,318, all of which are hereby incorporated in their entirety by reference.
The general process is practiced in several variants depending on the starting powders, which may be, for example, metal alloys having the same metal content as the desired superconducting core material in the “metallic precursor” or “MPIT” process, or mixtures of powders of the oxide components of the desired superconducting oxide core material or of a powder having the nominal composition of the desired superconducting oxide core material in the “oxide powder” or “OPIT” process. OPIT precursor powders may be prepared by reacting raw powders such as the corresponding oxides, oxalates, carbonates, nitrides or nitrates of the metallic elements of the desired superconducting oxide. One or more subsequent chemical reactions, some of which typically occur inside the formed filaments, create the superconducting material in combination with greater or lesser amounts of non-superconducting secondary phases. Because the desired superconducting material is formed by a series of chemical reactions, its performance will depend on the quality and chemical composition of the starting materials and on the subsequent processing conditions, such as temperature, time, and atmosphere. Different processing conditions will give rise to different phases or different ratios of phases, some of which, being easier to mechanically texture or more likely to achieve complete reaction into the final superconducting material, are more desirable than others. Various intermediate reactions may be deliberately promoted in order to create more desirable intermediate phases or to increase the ratio of the final superconducting material to the secondary phases in the finished product.
For example, it has been observed that the orthorhombic phase of BSCCO 2212 responds better to the asymmetric deformation required for deformation-induced texturing resulting in a denser, less porous oxide grain structure, and so, undergoes texturing to a much greater extent than the corresponding tetragonal phase. Moreover, the orthorhombic phase of (Bi,Pb)SCCO 2212 represents doping of lead into the BSCCO solid state structure with the concomitant conversion of the lead-free tetragonal phase into the orthorhombic phase. The lead-doped orthorhombic phase
Carter William L.
Li Qi
Masur Lawrence J.
Parella Ronald D.
Parker Donald R.
American Superconductor Corporation
Fiorilla Christopher A.
Hale and Dorr LLP
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