Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Process of making wire – tape – cable – coil – or fiber
Reexamination Certificate
2000-10-25
2003-04-29
Dunn, Tom (Department: 1725)
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Process of making wire, tape, cable, coil, or fiber
C505S470000
Reexamination Certificate
active
06555504
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an oxide superconducting wire and a production method therefor, and more particularly, relates to an oxide superconducting wire having an insulating layer and a production method therefor.
BACKGROUND ART
Conventionally, a bismuth-based oxide superconducting wire is known as one type of oxide superconducting wire. The bismuth-based oxide superconducting wire can be used at a liquid nitrogen temperature and can yield a relatively high critical current density. Moreover, since the bismuth-based oxide superconducting wire can be relatively easily elongated, applications thereof to superconducting cables and magnets are expected.
When such an oxide superconducting wire is applied to a magnet, it is required to have an insulating layer, from the viewpoint of coiling efficiency and the like.
The above-described bismuth-based oxide superconducting wire is used as a tape-shaped wire in many cases for the following reasons. That is, the critical current density of an oxide superconductor exhibits considerably high anisotropy, and therefore, it is necessary to align polycrystals of the oxide superconductor in order to achieve a high critical current density.
The bismuth-based oxide superconducting wire is deformed into a tape by plastic deformation such as rolling. The polycrystals of precursor of the oxide superconductor are aligned by the plastic deformation.
The width of the tape-shaped oxide superconducting wire varies within the range of ±0.2 mm in the above-described plastic deformation process. It is therefore necessary to adopt a method for reliably forming an insulating layer over the entire surface of the tape-shaped wire even when the width of the wire varies. As a result, it has been considered to adopt a method of forming an insulating layer in the above tape-shaped wire in which an insulating-film base is applied to a tape-shaped wire by putting the tape-shaped wire between felts impregnated with the insulating-film base and the tape-shaped wire is then subjected to baking. The tape-shaped wire in such an insulating layer forming method using felts is coated solely with a layer of the insulating-film base of approximately 1.5 &mgr;m in thickness in one operation of applying the insulating-film base. For this reason, in such an insulating layer forming method using the felts, an operation of applying the insulating-film base and a baking operation are usually repeated about ten times.
However, when the above insulating layer forming method is applied to a tape-shaped bismuth-based oxide superconducting wire, the critical current density of the tape-shaped oxide superconducting wire decreases substantially after an insulating layer is formed. This is due to the following reasons.
When the above insulating layer forming method is applied to a tape-shaped oxide superconducting wire, the tape-shaped wire is heated at a high temperature in the baking process. The temperature of the tape-shaped wire is raised by the high-temperature heating. The tape-shaped wire is composed of oxide superconducting filaments and a metal covering layer formed around the oxide superconducting filaments. With the above-described increase in temperature of the tape-shaped wire, the metal covering layer and the oxide superconducting filaments in the tape-shaped wire are thermally expanded. In this case, strain occurs in the tape-shaped wire due to a difference in coefficient of thermal expansion between the metal covering layer and the oxide superconducting filaments. For this reason, a mechanical strain is exerted on the oxide superconducting filaments. As a result, superconducting properties are deteriorated, for example, the critical current density of the tape-shaped oxide superconducting wire is lowered.
When the insulating-film base applying and the baking are repeated about ten times, it is necessary to put the tape-shaped wire into a baking furnace a predetermined number of times. In this case, since the tape-shaped wire is led into the baking furnace a plurality of times, the direction of travel of the tape-shaped wire occasionally changes by using a roller, although this depends on the configuration of an apparatus for applying and baking the insulating-film base. Since the tape-shaped wire is bent along the roller, it is subjected to bending.
In order to move the tape-shaped wire in the felts and the baking furnace, it is necessary to constantly apply a fixed tension to the tape-shaped wire. Such bending of the tape-shaped wire and application of tension thereto also put excessive mechanical strain on the oxide superconducting filaments. As a result, the superconducting properties of the tape-shaped oxide superconducting wire are deteriorated, and the critical current density is lowered.
As described above, it is difficult to form an insulating layer in the conventional tape-shaped oxide superconducting wire without deteriorating the superconducting properties.
The present invention has been developed to solve the above problems, and an object of the invention is to provide an oxide superconducting wire which allows an insulating layer to be formed without deteriorating the superconducting properties, and to provide a production method therefor.
DISCLOSURE OF INVENTION
According to a first aspect of the present invention, an oxide superconducting wire includes an oxide superconducting filament, a matrix, a covering layer, and an insulating layer. The matrix is made of silver and is placed so as to enclose the oxide superconducting filament. The covering layer, placed so as to enclose the matrix, contains silver and manganese, and has a thickness of 10 &mgr;m to 50 &mgr;m. The insulating layer is placed so as to enclose the covering layer.
Since the covering layer is made of a material containing silver and manganese, the mechanical strength thereof can be increased. This ensures sufficient strength to withstand the tension and bending applied to the oxide superconducting wire when forming the insulating layer. That is, since the covering layer of the oxide superconducting wire thus has sufficient strength, it is possible to prevent the exertion of excessive mechanical strain on the oxide superconducting filament in the process of forming the insulating layer, the process of constructing a magnet, a cable, or the like by using the oxide superconducting wire, and in the case in which stress is applied to the oxide superconducting wire by a temperature change due to cooling and electromagnetic force when operating an equipment using the oxide superconducting wire, such as a magnet. As a result, it is possible to prevent deterioration of the superconducting properties of the oxide superconducting filament. For this reason, the critical current density of the oxide superconducting wire is prevented from being lowered.
While manganese is used as an element to be contained in the covering layer in order to increase the strength thereof, it has a relatively low reactivity with an oxide superconductor. For this reason, it is possible to inhibit the problem that the element in the covering layer in a sintering process for generating the oxide superconductor hinders the generative reaction of an oxide superconductor. Since the matrix of silver is interposed between the oxide superconducting filament and the covering layer, manganese in the covering layer can be reduced by the matrix from diffusing to the oxide superconducting filament. This more reliably reduces the above problem in which the generative reaction of the oxide superconductor is hindered by manganese in the covering layer.
Since the thickness of the covering layer is within the range of 10 &mgr;m to 50 &mgr;m, the covering layer can be formed without causing fatal defects, such as cracks, in the production procedure for the oxide superconducting wire. Moreover, the oxide superconductor can be generated reliably because gas generated with the generative reaction of the oxide superconductor can be reliably released from the wire. In the case in which the thickness of the covering laye
Ayai Naoki
Hayashi Kazuhiko
Saga Nobuhiro
Cooke Colleen P.
Dunn Tom
Sumitomo Electric Industries Ltd.
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