JP2574161B2 - Manufacturing method of ceramic superconductor coil - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a superconducting coil, and more particularly to a novel method for producing a ceramic-based superconducting coil containing an oxide of a rare earth element. is there.

[Conventional technology]

The superconductivity phenomenon is a phenomenon in which the electric resistance is completely lost below a certain temperature, and the temperature at which the superconductivity occurs (critical temperature) differs depending on the material. Since a material having a higher critical temperature is easier to cool, the development of a material having a critical temperature as high as possible has been particularly prosperous recently. Also,
Not only the high critical temperature but also the upper limit current (critical current) that can flow in the superconducting state is an important point in the practical use of ceramic materials. For practical use, for example, wires must be used, but ceramic materials have a small current that can be passed per unit cross-sectional area, so the key to practical use is how high a critical current can be obtained. is there.

By the way, materials that cause superconductivity are alloys,
Ceramics are well known, and the development of ceramics materials has been particularly advanced in recent years, and the development of ceramics-based superconducting materials having a high critical temperature is constantly evolving. However, for practical use, superconducting materials were converted to long wires,
Despite the necessity of processing into a tape or the like, there is a problem that a ceramic-based superconducting material cannot be drawn like a metal material because it is hard and brittle. When a ceramic-based superconducting wire is used as a coil for a motor, it is necessary to wind the wire further.However, the wire breaks during this coil winding, or by applying a winding stress until it does not break, the superconductivity of the wire is increased. There are problems such as deterioration of characteristics.

[Problems to be solved by the invention]

Accordingly, an object of the present invention is to provide a novel method for directly manufacturing a coil of a ceramic-based superconducting material from a powder or a mixture of the raw material powders in view of the above points.

[Means for solving the problem]

The object is to fill a ceramic superconducting material powder or its raw material powder into a central portion of a metallic container, and to provide an electrically insulating ceramic powder between a filled layer of the ceramic superconducting material powder and an inner wall of the metallic container. A ceramic characterized by being filled and drawn together with a metal container, winding the obtained wire into a coil of a desired size, subjecting the obtained coil wound to a sintering process, and then removing the metal sheath of the coil. This is achieved by a method of manufacturing a superconducting coil.

The feature of the manufacturing method according to the specific invention of the present invention is that the powder of the ceramic-based superconducting material or its raw material powder is processed into a coil having a desired size and structure in advance by drawing and coiling using a metal container. Since sintering is performed, coil winding of a wire, which has conventionally been problematic, is not required, and various problems associated with coil winding are all eliminated.

The superconducting material is not particularly limited as long as it is a ceramic material, and is preferably a ceramic material containing an oxide of a rare earth element.

Such materials include, for example, barium, yttrium, copper, oxygen, barium, lanthanum,
There are ceramics containing copper / oxygen, strontium / lanthanum / copper / oxygen, barium / scandium / copper / oxygen, or calcium / lanthanum / copper / oxygen. It is a material composed of a certain composition of barium, yttrium, copper and oxygen. Furthermore, when using this yttrium-based superconducting material, its preferred compounding ratio is Ba:
Y: Cu: O = 2: 1: 3: 6 to 7 In the present invention, a ceramic powder having such a composition is used. The method for producing the powder may be a conventionally known method,
There is no particular limitation. For example, a solid process performed in a process of mixing raw material powders (for example, in the case of barium / yttrium / copper / oxygen based superconducting materials, barium carbonate, yttrium oxide, copper oxide, etc.) → sintering → re-powdering the sintered body It may be manufactured by such as. Further, in the present invention, a mixture of raw material powders such as barium carbonate, yttrium oxide, and copper oxide can be used. In the present invention, the powder of the ceramic-based superconducting material or a mixture of the raw material powders is hereinafter generally referred to as superconducting material powder.

In the method of the present invention, first, a ceramic-based superconducting material powder is filled in a central portion of a metallic container, and an electrically insulating ceramic powder is filled between a filling layer of the ceramic-based superconducting material powder and an inner wall of the metallic container. Then, the entire metal container is drawn to obtain a wire. Silver,
A bottomed pipe made of copper, stainless steel, aluminum or the like is preferable.

The wire obtained by wire drawing is wound into a coil having a desired size and shape, and the obtained coil wound is subjected to a sintering process to obtain a superconducting material powder and an electric insulating material present inside the coil wire. Sinterable ceramic powder.

The sintering temperature depends on the ceramic used,
In the case of the above-described superconducting material powder, the temperature is 700 to 1000 ° C., preferably about 800 to 950 ° C., and the time required for sintering is 1 to 24.
About an hour. In order to supply a sufficient amount of oxygen to the superconducting material powder in the wire during the sintering, it is preferable to adopt a conventionally known method, for example, sintering in an oxygen atmosphere.

Since the metal sheath derived from the metal container exists on the surface of the coil obtained through the sintering process, the metal sheath is then removed by a method such as chemical treatment or mechanical removal. As the treatment chemical, an acid, an alkali, or the like appropriate for the type of metal to be removed may be used in combination of two or more as needed.

The obtained superconducting coil may be used as it is because the surface layer is an electric insulating layer, but it is more preferable that the insulating layer is formed by coating and baking the insulating varnish on the surface.

〔Example〕

Hereinafter, the method of the present invention will be described more specifically based on examples.

Example 1 Outer diameter of a silver pipe sealed at one end and having a 6 mm inner diameter and a 0.5 mm wall thickness
A copper mandrel of 5 mm is inserted and installed concentrically, and an electrically insulating ceramic powder (yttrium oxide and copper oxide having an average particle size of about 5 μm) is inserted into a ring-shaped cross section formed between the silver pipe and the mandrel. : 1 weight ratio mixture) under vacuum, then densely withdraw the copper mandrel, and in the resulting hole as a superconducting ceramic material, the composition is barium, yttrium, copper, oxygen, and the mixing ratio is Ba: Y: Cu : O
= 2: 1: 3: 6.1 The material powder having an average particle size of about 5 μm prepared densely under vacuum was drawn and drawn using a cassette die to obtain a wire having an outer diameter of 1 mm. Next, this wire rod has an outer diameter of 10m.
m, wound tightly around the surface of a ceramic cylinder with a flow of 50 mm to form a coil.
After sintering for 4 hours and cooling to room temperature, the silver extraction of the coil was dissolved and removed with a 10% by weight aqueous nitric acid solution, washed sufficiently with water and dried to obtain a superconducting coil having a ceramic electric insulating layer on the surface.

Example 2 A material powder having an average particle diameter of about 5 μm prepared at a mixing ratio of Ba: Y: Cu: O = 2: 1: 3: 7.0 was subjected to electrical insulation treatment in the same manner and under the same conditions as in Example 1. A coil was obtained.

Example 3 As a ceramic-based superconducting material, the composition was barium / lanthanum / copper / oxygen, and the mixing ratio was Ba: Y: Cu: O = 0.15:
Using a material powder having an average particle size of about 5 μm prepared at 0.85: 1: 4, a coil subjected to electrical insulation treatment was obtained in the same manner and under the same conditions as in Example 1.

The critical temperature and critical current density of each wire obtained in each example were measured by the following methods, and the results shown in Table 1 were obtained.

(Measurement method of critical temperature and critical current density) 1) Critical temperature A sample (2 to 3 cm in length) was cooled to a current density of 0.1 A / cm ^{2 with} liquid helium, and the electrical resistance change and temperature change were determined by the four-terminal method. The temperature at which the electric resistance value became zero was determined by measuring with a -Y recorder.

2) Critical current density A sample (2 to 3 cm in length) is immersed in liquid helium together with a power lead, and while gradually increasing the current value, the IR drop and the change in current are measured by a four-terminal method using an XY recorder. The current value at which the drop appears was determined.

[Effects of the Invention] As described above, according to the manufacturing method of the present invention, it is possible to directly manufacture a ceramic superconducting material powder or a coil of the raw material powder by using a mixture thereof.
Therefore, coil winding of the wire rod, which has many problems in the related art, is unnecessary, and all the various problems associated with the coil winding are eliminated. Further, since the coil obtained by the method of the present invention has an electrically insulating ceramic on its surface layer, there is no need for an electrical insulation treatment.

Claims (2)

(57) [Claims] An electric insulating ceramic powder is filled between a filling layer of a ceramic-based superconducting material powder and an inner wall of a metallic container by filling a central portion of a metallic container with a powder of a ceramic-based superconducting material or a raw material powder thereof. Is filled, and the whole metal container is drawn, the obtained wire is coil-wound to a desired size, the obtained coil winding is subjected to a sintering step, and then the metal outer skin of the coil is removed. A method for manufacturing a ceramic superconductor coil. 2. The composition of the superconducting material is barium / yttrium / copper / oxygen, barium / lanthanum / copper / oxygen / strontium / lanthanum / copper / oxygen, barium / scandium / copper / oxygen, or calcium / lanthanum / copper.
The method for producing a ceramic superconductor coil according to claim 1, wherein the method is oxygen.