Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming multiple superposed electrolytic coatings
Patent
1997-03-03
1998-08-25
Gorgos, Kathryn L.
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming multiple superposed electrolytic coatings
205182, 205224, 505434, 505472, C25D 510, C25D 550, C23C 3924, B23K 3924
Patent
active
057980349
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of PCT/FR95/00262 filed Mar. 8, 1995.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for the preparation of a superconductor material of the mixed oxide type at a high critical temperature.
2. Description of the Related Art
Superconductivity is a phenomenon developing at temperatures below the critical temperature of a material, i.e. the temperature as from which the electrical resistance of said material becomes equal to 0 and a perfect diamagnetism is observed. This phenomenon is very interesting, because it permits power transmission at temperatures below the critical temperature without any energy loss.
The first superconductor materials discovered had very low critical temperatures requiring a cooling by means of liquid helium. In 1986, Bednorz and Muller discovered a new superconductor of the oxide type having a critical temperature above 30K and no longer requiring a cooling by liquid helium. Other mixed superconductor oxides were then found, such as e.g. the oxide YBa.sub.2 Cu.sup.3 O.sub.7-x, whose critical temperature is approximately 90K, so that there is no need for liquid helium for cooling it.
However, for most superconductor applications, it is necessary to prepare said materials in the form of either layers deposited on substrates in order to obtain thin films intended for microelectronics with a surface area of a few square centimeters and a thickness below 1 micrometer, or wires, ribbons or other conductors for high power electrical engineering and whose length will be several hundred or even several thousand meters and having a thickness of a few micrometers to a few millimeters.
For the preparation of thin films, it is possible to use conventional film vapour deposition methods such as laser ablation, cathode, radiofrequency and other sputtering processes, vapour deposition of organometallic compounds, etc. With these methods, products are obtained having an excellent electrical and magnetic quality, but the use of these methods for producing ribbons or products of great length is difficult to envisage due to the constraints involved in obtaining said quality. Thus, the excellence of the performance characteristics is only achieved on monocrystalline substrates, which are difficult to produce in great lengths. Moreover, in all these methods, the deposition rate is generally too slow to be able to produce at an acceptable cost layers with a thickness of a few micrometers over hundreds of meters. Finally, research has shown that for thicknesses exceeding 1 micrometer, the layers prepared lose their texture and consequently transmit lower current densities.
Moreover, for the preparation of very long products, consideration has been given to the use of powder metallurgy processes starting from the superconductor oxide in powder form or pulverulent precursor oxides which can be transformed into a superconductor by a heat treatment, filling a metal tube with these powders and then bringing it into the form of wires or ribbons by mechanical operations such as spinning, accompanied or not by intermediate annealing operations. The composites obtained are finally annealed in order to join together the superconductor grains and increase the power transmission capacity of the product obtained. However, this process suffers from the following disadvantages: oxide remains constant over the entire wire length, because a single necking is sufficient to reduce to zero the overall superconductivity and product.
A process for the preparation of long products is known, which makes use of the deposition of metal coatings by electrolytic processes, such as is described in U.S. Pat. No. 5,162,295.
According to this document, deposition takes place on a conductive substrate of layers of metals entering into the composition of the mixed superconductor oxide, the layers deposited then undergoing an oxidation treatment under conditions such that the mixed superconductor oxide is formed. However, this procedure suffers from the disad
REFERENCES:
patent: 4939308 (1990-07-01), Maxfield et al.
patent: 5120707 (1992-06-01), Maxfield et al.
patent: 5162295 (1992-11-01), Behi et al.
Gendre Philippe
Marquet Andre
Regnier Pierre
Schmirgeld-Mignot Lelia
Commissariat a l''Energie Atomique
Gorgos Kathryn L.
Wong Edna
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