Superconductor technology: apparatus – material – process – High temperature devices – systems – apparatus – com- ponents,... – Superconducting wire – tape – cable – or fiber – per se
Reexamination Certificate
1998-03-12
2001-06-05
Kunemund, Robert (Department: 1765)
Superconductor technology: apparatus, material, process
High temperature devices, systems, apparatus, com- ponents,...
Superconducting wire, tape, cable, or fiber, per se
C505S236000, C505S430000, C505S450000
Reexamination Certificate
active
06243598
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of preparing rare earth-barium-cuprates superconductors by melt texturing of the superconducting material on a metallic substrate.
2. Description of the Related Art
Heretofore, melt texturing of rare earth-barium-cuprate superconducting materials on silver substrates have been prohibited in air by the high melting point of the material in air exceeding the melting point of silver in air.
It has previously been demonstrated, however, that the melting point of RE
1+y
Ba
2−y
Cu
3
O
7−x
(0≦y≦0.9, 0≦x≦1) (RE) phases decreases as the partial oxygen pressure, i.e. p(O
2
), decreases. Furthermore, it is well known that the melting point of silver increases as p(O
2
) decreases.
SUMMARY OF THE INVENTION
Given the above, the present invention recognizes that it is possible to produce rare earth-barium cuprate superconductors on silver substrates by melting several RE123 phases below the melting point of silver at low p(O
2
). As such, the method of this invention is based on the principle of changing the melting points (peritectic decomposition temperature) of the rare earth-barium-cuprate superconductors (RE123, RE=Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof), including the non-superconducting Pr123 phase of the above formulation and of the melting point of silver as a function of p(O
2
)
More specifically, the invention provides a method of preparing a rare earth-barium-cuprate superconductor, preferably in the form of metallic tapes or wires, using a thick film or powder-in-tube process by supporting on a metallic substrate a mixture of seed crystals or aligned platelets of a rare earth-barium cuprate phase having a high melting point and a rare earth-barium-cuprate powder phase having a lower melting point. The material supported on the substrate is then subjected to a heat treatment at a temperature below the melting point of the high melting rare earth-barium-cuprate seed crystals and the metallic substrate and above the melting point of the low melting powder. This treatment may be performed in an atmosphere having a partial pressure of oxygen lower than the partial pressure of oxygen in air. Subsequently, the heat treated supported material is cooled below the melting temperature of the material and annealed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
According to a preferred embodiment of the present invention, a highly textured microstructure of the RE123 material is obtained by providing on a silver substrate a mixture of RE
1+y
Ba
2−y
Cu
3
O
7−x
(0≦y≦0.9, 0≦x≦1) material comprising one phase of aligned RE123 platelets or seed crystals having a relatively high melting point and a second phase of a RE123 powder having a melting point lower than that of the RE123 platelets. The mixture is placed in an environment having a reduced partial pressure of oxygen sufficient to raise the melting point of silver to a temperature at least above the melting point of the lower melting RE123 phase. The mixture is then heated to a temperature above the melting point of the RE123 powder but below the melting point of the RE123 platelets and of the silver substrate. Subsequently, the material is solidified by nucleation and expitaxial growth of the low melting point RE123 phase on the platelets or crystals during cooling. As a final step in the process, the solidified material is annealed in pure oxygen to provide the finished superconductor product.
Using the above-described process, RE123/silver wires and tapes having a highly aligned RE123 material are produced using conventional “powder in tube” and “thick film” technologies. For example, wires and tapes produced with a “powder-in-tube” process requires placing the RE123 mixture inside a silver tube. The tube is evacuated, sealed, and pulled or stretched and then shaped into a tape or wire. After shaping, the tube is subjected to the heat treatment described above. Similarly, using a “thick film” process, the RE123 mixture is coated onto a metallic substrate having a shape of a tape or wire before heat treatment.
Superconductive tapes and wires may also be prepared using other metallic substrates such as nickel and/or stainless steel coated with an inert buffer layer known in the art, such as silver, barium zirconate, magnesium oxide and RE
2
BaCuO
5
.
REFERENCES:
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patent: 5474976 (1995-12-01), Kondoh et al.
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patent: 5536704 (1996-07-01), Yamada et al.
patent: 5591698 (1997-01-01), Song et al.
patent: 5856277 (1999-01-01), Chen et al.
patent: 5866515 (1999-02-01), Dorris et al.
patent: 5872081 (1999-02-01), Woolf
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patent: 0756336 (1997-01-01), None
S.I. Yoo et al., “Melt Processing for Strong Flux Pinning in RE-Ba-Cu-O (RE: Nd, Sm, Eu, Gd) Superconductors”, Journal of Electronic Materials, vol. 24, No. 12, Dec. 1995, pp. 1923-1930.
Haldor Topsoe A/S
Kunemund Robert
Ostrolenk, Faber, Gerb & Soffen, LLL
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