JPH01149322A - Manufacture of ceramic superconductive wire - Google Patents

Abstract

PURPOSE:To obtain a long, mechanically and electrically stable superconductive wire with high strength and high current density by forming a sintered layer of ceramic superconductive substance on the periphery of a ceramic fiber strand. CONSTITUTION:A strand of ceramic fibers is covered with a mixture solution in which fine powder of ceramic superconductive substance or a component substance to produce it by heating in oxidative atmosphere is dispersed in a solvent. This covering substance is sintered, and the resultant sintered layer is covered with a stabilizing material consisting of conductive ceramic or conductive highpolymer. The ceramic fiber shall preferably be of SiC type or of oxide type. This allows easy formation of a long wire, wherein heat treatment in oxidative atmosphere can take place while it is long, and a practically applicable wire with high strength and critical current density can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a superconducting wire, and particularly to a method for manufacturing a ceramic superconducting wire.

(Conventional Technology) In recent years, especially since last fall, the development of ceramic superconductors has been progressing at a rapid pace all over the world.

This superconductor is Nb3G, which has the highest conventional critical temperature.
It greatly exceeds 23K of e, and is Ba-La-Cu-
0 series ceramics (critical temperature 35), La-8r-
Cu-0 ceramics (superconductivity starting temperature 37 or higher)
, La-Ca-Cu-0 ceramics, Y-Ba-C
In addition to u-0 series ceramics (zero resistance temperature of 93K), ceramics showing a critical temperature of 233 degrees or higher than room temperature have been reported this year.

In this way, it is possible that ceramic superconducting materials can be used at critical temperatures higher than the liquid nitrogen temperature or at room temperature.
In this case, there is no need to use expensive liquid helium, which is extremely advantageous economically, and when used in a superconducting generator or the like, the structure is simple and the efficiency of the heat engine is improved.

However, since ceramics are hard and brittle,
Unlike the Nb-Ti and Nb, Sn-based superconducting wires that are currently in practical use, it cannot be bent or coiled, and overcoming this point is the first step toward practical use.

Currently, there are two methods of manufacturing wire rods: (1) A method of heat-treating amorphous tape or wire rod in an oxygen atmosphere; A method of filling raw material powder inside a 0 alloy tube (for example, Cu-Ni alloy) and pulling both ends to produce a wire rod or The following methods have been proposed: (1) Filling a copper-based alloy tube with ceramics, subjecting it to heat treatment, rolling, etc., and forming it into a wire or tape shape.

However, the above method (■) requires extremely rapid cooling and can only yield extremely thin wire rods and FiiM tapes, so it has drawbacks as a method for obtaining practical wire rods. However, it is difficult to continuously manufacture long wire rods, and in method (■) above, the fixed length of the wire rod is limited by the outer diameter of the initial copper alloy tube, and the processing process is complicated. . In this case, it is desirable that the heat treatment for producing the ceramic superconductor be performed after forming, that is, near the final wire diameter, from the perspective of improving superconducting properties, but since it is covered with a copper alloy tube, oxygen is supplied inside after forming. This is extremely difficult and practically impossible.

Furthermore, wire rods manufactured by any of the above methods have problems in terms of strength, and have the disadvantage that they cannot be wound with high tension in order to counter electromagnetic force when forming a coil.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned difficulties, and it is possible to easily manufacture a long wire rod without requiring rapid cooling to make it amorphous. To provide a method for producing a ceramic superconducting wire, which can be heat-treated in an oxidizing atmosphere in the form of a long wire, and which can produce a practical wire with high strength and critical current density. Its purpose is to

[Structure of the Invention (Means for Solving Problems) The method for manufacturing a ceramic superconducting wire of the present invention is as follows: (a) A ceramic superconducting material or an oxidizing atmosphere is added to the outer periphery of the stranded wire obtained by twisting a plurality of ceramic fibers. (b) Next, sintering the deposited material; (c) It is characterized by a step of coating the outside of this sintered layer with a stabilizing material made of conductive ceramics or conductive polymer.

The above ceramic fiber is made of silicon carbide (SiC
) type or oxide type can be used.

These fibers are continuous filaments, with a diameter of 1000 to 1300
High heat resistance above ℃ and 200-250k Q/i
It has a tensile strength of n or more, and its average diameter is extremely small, for example, 10 to 13 μmφ, but of course, it is also possible to use a diameter larger than this. The former S
Examples of the iC fiber include Tyranno fiber (5i-Ti-C-0 fiber trade name manufactured by Ube Industries, Ltd.) and Nicalon (SiC fiber trade name manufactured by Nippon Carbon Co., Ltd.), and the oxidation of the latter As a physical fiber, SAFIL (UK 11perial Che 11ic
Al Industries PLC-ICI Al2
In addition to O3 fiber (trade name), Si02 fiber can also be used.

The above-mentioned fiber preferably has a volume resistivity of 10 5 Ωcm or less. When the volume resistivity is within the above range, when the temperature of the superconducting wire rises above the critical temperature,
This is because current flows through the fiber more easily and it becomes difficult to break down. 0. If the volume resistivity is high, the terminal voltage will rise when the temperature exceeds the critical temperature, making it easier to break down. 6. If the volume resistivity is small, loss will occur. It's less convenient.

The above ceramic fibers are used by forming a plurality of them into a twisted wire structure. In this way, good flexibility 5 and significantly greater strength can be achieved.

Examples of ceramic superconducting materials include YBa2
There are cu30x (x <14; perovskite) and those to which F, etc. are added.On the other hand, the constituent substances that generate it by heating in an oxidizing atmosphere include carbonates and oxides, such as Y2O3, BaCO3, Examples include CuO.

The above substances are dispersed in a solvent in the form of fine powder. In this case, it is preferable that the atomic ratio of each constituent element in the mixed solution matches the atomic ratio of the ceramic superconducting material. The fine powder of the superconducting material is preferably produced by a solid phase reaction method. That is, after uniformly mixing oxides, carbonates, etc., the process of heating in air is repeated, then this is compressed, and then sintered in an oxidizing atmosphere and pulverized can be used.

Further, as a solvent for the mixed solution, an enamel varnish having a low decomposition temperature, such as a polyurethane varnish or a polyvinyl alcohol resin solution, is used.

When applying the above liquid substance to the outer periphery of the stranded wires, it is possible to apply a paint that volatilizes at the sintering temperature to the gaps between the strands of the outermost layer, or to twist synthetic resin fibers in advance. It is possible to prevent the formation of a sintered layer in the line gaps and further improve flexibility.

The generation of a sintered layer of ceramic superconducting material is carried out at a temperature of 700 to 100 while adjusting oxidation in an oxygen stream or under oxygen pressure.
The properties are improved by heating to 0°C.

A stabilizing material is coated on the outside of this sintered layer, and as this stabilizing material, conductive ceramics or conductive polymer materials are used. The former conductive ceramic is Ti
There are carbides, borides, and nitrides such as C, NbC, WClTaC, ZrB, BN, and ZrN, and examples of the latter conductive polymer materials include polyacetylene and polypyrrole. These stabilizing materials preferably have a volume resistivity of 10 5 Ωcm or less. The reason for this is the same as in the case of ceramic fibers, but especially when conductive ceramics are used, the difference in thermal expansion of the constituent members of the wire can be reduced, which is extremely advantageous against thermal effects.

The stabilizing material coating can be applied in the melt, gas phase or ionic state.

An insulating coating is usually applied to the outside of the above-mentioned stabilizing material. Organic or inorganic materials are used as the insulating film, and the former organic insulating film is made of IJV cured urethane resin or PVF.
Examples of the latter inorganic insulating coating include alumina and polyborosiloxane resin.

(Function) In the method of the present invention, a mixed solution containing fine powder of a ceramic superconducting material or a constituent material that produces it by heating in an oxidizing atmosphere is coated on the outer periphery of a stranded wire made of ceramic fibers. Because it is post-sintered, long wire rods with good flexibility and high strength can be easily manufactured, and the difference in thermal expansion between the fiber and the ceramic superconducting material is small, and the adhesion is good. It is.

That is, by achieving the above-mentioned good adhesion and eliminating the need for processing ceramics, it is possible to manufacture long wire rods. Moreover, by using a mixed solution, a method similar to the manufacturing process of enamelled wire can be adopted.

<Example) Examples of the present invention will be described below.

The figure schematically shows an apparatus for manufacturing a ceramic superconducting wire according to the present invention, in which a coating device 3 and a baking furnace are provided between a delivery bobbin 1 on which ceramic fiber strands W are wound and a winding bobbin 2. 4 are arranged in order, and the fiber strands W pass through the coating device 3 and the baking furnace 4 a predetermined number of times via the guide reels 5 to 8, whereby the mixed solution contained in the coating tank 3b is passed through the coating roll 3a. A plurality of layers of resin are applied and baked on the outer periphery. Note that 9 is a drawing die.

Example 1 Fine powder of a superconducting material was produced by a solid phase reaction method as follows. That is, Y2O3 is 2259, aaco
Mix 4679 g of 3 and 239 g of CUO and heat this in air at 950° C. for 8 hours, which is repeated 3 times. The resulting powder is pressed by applying a compression force of 1.5 t/d. Then, after sintering in air at 950°C for 12 hours,
The mixture was gradually cooled to 0°C, maintained at this temperature for 2 hours, and then ground into powder. Superconducting fine powder 500 produced in this way
g to polyurethane varnish (cresol solution, 120℃
90 minutes solids content 70% ) 1000 (mixed in +.

This mixed solution was stored in the coating tank 3b, and the ceramic fiber strands W were made by collectively twisting 1,000 pieces of Charon (manufactured by Nippon Carbon Co., Ltd.) into SiC fibers with an outer diameter of 10 μmφ. A primary sintered layer having a thickness of 6.8 .mu.l was formed on the ceramic fiber strands W by passing it through a baking furnace 4 having a coating apparatus of 5 and a furnace temperature of 300 to 400 DEG C. six times.

Next, it was heated at 950° C. for 2 hours to form a sintered layer.

The thickness of this sintered layer was 3.5 μf. Furthermore, as a result of measuring the characteristics of the wire with TiC coated on the outer periphery of this sintered layer, the critical temperature (Tc) was 88K, and the critical current density (Jc
) is (0,5~1.0)X 10” A/cノ(at
77K).

Example 2 500 g of fine powder of a superconducting material produced by the solid phase reaction method in the same manner as in Example 1 was uniformly mixed in a 20% ethanol solution of polyvinyl alcohol resin, and the outer diameter was 1.
1000 SiC fibers of 0 μlφ were coated and baked on a twisted wire. The film thickness at this time was 6.7 μl.The thickness of the sintered layer, which was then sintered at 950° C. for 2 hours, was 2.8 μl. Furthermore, as a result of measuring the characteristics of the wire with WC coated on the outer periphery, Tc = 83, Jc =
It was (0,3-0.7)×10′ eight pano (at77K).

[Effects of the Invention] As described above, according to the method for manufacturing a ceramic superconducting wire of the present invention, by forming a sintered layer of a ceramic superconducting material on the outer periphery of a stranded ceramic fiber wire, sintering at high temperature and for a long period of time is possible. It is possible to easily produce a long mechanically and electrically stable wire rod without fiber breakage even under such conditions, and a superconducting wire with high strength and current density can be obtained.

Since the superconducting wire manufactured according to the present invention has excellent flexibility, a plurality of these wires can be used to easily form an aggregated wire, stranded wire, or braided wire, and the wire obtained in this way can be used to After coiling with high tension, it can be impregnated with enamel varnish to produce superconducting magnets.

[Brief explanation of the drawing]

The figure is a schematic diagram showing an embodiment of an apparatus used in the method of manufacturing a ceramic superconducting wire of the present invention. 3... Coating device 4... Baking furnace W... Ceramic fiber stranded wire L...
・・・・・・Mixed solution

Claims (8)

[Claims] (1) (A) Fine powder made of a ceramic superconducting material or a constituent material that generates it by heating in an oxidizing atmosphere is dispersed in a solvent around the outer periphery of a stranded wire made by twisting multiple ceramic fibers. (b) Next, sintering the deposited material; and (c) coating the outside of this sintered layer with a stabilizing material made of conductive ceramics or conductive polymer material. A method for manufacturing a ceramic superconducting wire, comprising the steps of: (2) The method for manufacturing a ceramic superconducting wire according to claim 1, wherein the ceramic fiber is a silicon carbide fiber or an oxide fiber. (3) The method for manufacturing a ceramic superconducting wire according to claim 1 or 2, wherein the superconducting material is a Y-Ba-Cu-O ceramic. (4) The method for producing a ceramic superconducting wire according to any one of claims 1 to 3, wherein the fine powder of the superconducting substance is produced by a solid phase reaction method. (5) The method for producing a ceramic superconducting wire according to any one of claims 1 to 4, wherein the solvent is an enamel varnish having a low decomposition temperature. (6) Ceramic fiber has a volume resistivity of 10
The method for manufacturing a ceramic superconducting wire according to claim 2, wherein the ceramic superconducting wire has a resistance of ^5 Ωcm or less. (7) The stabilizing material made of conductive ceramics or conductive polymer material has a volume resistivity of 10^5Ωcm.
A method for manufacturing a ceramic superconducting wire according to any one of claims 1, 3 to 6 below. (8) The ceramic superconducting wire according to any one of claims 1 to 7, wherein the sintered layer is formed on the outer periphery of the stranded wire excluding the strand gaps in the outermost layer constituting the stranded wire. manufacturing method.