Superconductor technology: apparatus – material – process – High temperature – per se – Having tc greater than or equal to 150 k
Patent
1991-08-16
1993-05-18
Beck, Shrive
Superconductor technology: apparatus, material, process
High temperature , per se
Having tc greater than or equal to 150 k
505701, 427 62, 4274432, B05D 512, B05D 118
Patent
active
052121526
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the protection of oxide superconductors from degradation.
BACKGROUND OF THE INVENTION
The recently discovered oxide superconducting ceramic materials, with superconducting transition temperatures (T.sub.c) in the range above that of liquid nitrogen (77.degree. K), are technologically very exciting materials. However, they are not known to suffer extensive chemical degradation in the atmosphere, particularly in the presence of water vapour and carbon dioxide. In addition, they are highly oxidising and are able to oxidise metals, including gold, in bulk solution and in condensed moisture films. This reactivity will limit their eventual use and methods of eliminating the degradation must be sought prior to commercial exploitation.
It is therefore an object of the present invention to provide a method of protecting such superconductors from degradation.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of treating an oxide superconductor to prevent degradation thereof the method comprising treating the superconductor with a solution of a metal which is capable of being oxidised by the superconductor to form on those regions of the surface area of the superconductor treated with the solution an insulating, non-porous protective film of an oxide which is stable against further oxidation.
The invention also provides an oxide superconductor in which at least a portion of the surface area of the superconductor is coated with an insulating, non-porous protective film of a metal oxide which is stable against further oxidation by the superconductor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is applicable particularly to the treatment of copper-containing superconducting oxides. All oxide superconductors containing copper and/or an oxidised cuprate peroxide complex will be subject to degradation as described above and will therefore be suitable for treatment. Classes of copper containing superconductors to which the invention is applicable are given in Table I, together with specific examples of each class.
TABLE 1 ______________________________________
Classes of super conductor
Examples
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La--Ba--Cu--O La.sub.1.8 Sr.sub.0.2 CuO.sub.4 - X
Y--Ba--U--O Y Ba.sub.2 Cu.sub.3 O.sub.7 - X
(Pb) Bi--Sr--Ca--Cu--O
Bi.sub.2 Sr.sub.3 - X Ca.sub.x Cu.sub.2 O.sub.8 - X
Tl--Ba--Ca--Cu--O Tl.sub.2 Ba.sub.2 CaCu.sub.3 O.sub.10
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- X
In addition rare earth, and other, elements may dope the above.
It has been found that the provision of the metal oxide film acts as an effective barrier to protect the superconductor from corrosion and environmental degradation. The oxide film is so effective that untreated superconductors which would normally be attacked and quickly destroyed by atmospheric moisture are (when treated in accordance with the invention) totally stable when exposed to the atmosphere.
The method of the invention can most conveniently be effected by dipping the superconductor into the solution of the metal ions which give rise to the protective oxide film and simultaneously applying an appropriate oxidising electrochemical potential. For superconductors which have a degree of porosity, the solution will penetrate the interstices within the superconductor so that the protective metal oxide is deposited on the interior surface area.
The metal ion in the treatment solution must be one which can be oxidised on the superconductor surface to give an oxide film which is stable against oxidation by the highly oxidising superconductor. Suitable metal ions include Mn.sup.2+, Ti.sup.3+, Pb.sup.2+ and Sn.sup.2+.
In the case where the metal ion in an aqueous treatment solution is Mn.sup.2+ and the superconductor contains Cu.sup.3+ ions, the reaction process is essentially
In the above example, the oxidation of Mn.sup.2+ to MnO.sub.2 may also be effected by an appropriate applied external potential (voltage).
The preferred concentration of the metal ion
REFERENCES:
Vasquez et al, "Wet chemical techniques for passivation of YBa.sub.2 Cu.sub.3 O.sub.7-x ", Appl. Phys. Lett. 55(117) Oct. 1989, p. 1801-1803.
Osteryoung, et al., Electrochemical Formation of Polypyrrole Films on YBa2Cu3O7-x, Journal of the Electrochemical Society, Oct. 1988, vol. 135, No. 10, see the whole document.
Hepburn Beverley J.
Lyon Stuart B.
Beck Shrive
British Technology Group Limited
King Roy V.
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