JPH03171517A - Manufacture of oxide superconductor wire material - Google Patents

Abstract

PURPOSE:To obtain a superconductor wire material, having an improved orientation property and high critical current density, by packing the halogenide particulate of a metallic element in a metal slender tube to form a desired shape, and then heat-treating the halogenide particulate in an oxidizing atmosphere including steam. CONSTITUTION:The halogenide particulate of a metallic element is mixed at a suitable ratio, packed in a silver or other metal slender tube, and wire-drawn and roll-treated to be formed into a desired shape and size. Then the halogenide particulate is oxidation-reacted in an oxidizing atmosphere including steam in a furnace having a given temperature gradient to form a superconducting wire material. This enables the generation of a nucleus to be restrained in the slender tube, and a large crystal to be produced in one direction to improve orientation property for obtaining a wire material having high critical current density. Also the manufacture of a coil or other specific shape articles can be eased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an oxide superconductor wire.

[Conventional technology and its problems]

An oxide superconductor whose critical temperature exceeds that of liquid nitrogen has been discovered, and research is being actively conducted to apply it to superconducting devices such as electromagnets and Josephson devices. Among these, the development of wire rods is an important point in producing superconducting electromagnets.

Until now, oxide superconducting wires have been produced by packing oxide superconductor powder into thin tubes (also called sheaths) such as silver sheaths, subjecting them to drawing, rolling, etc., and then heat-treating them. It's here. In this method, during the rolling process,
By applying a uniaxial force, it is possible to improve the conformation of the crystals of the plate-shaped oxide superconductor and improve the critical current density.

In order to improve crystal orientation through such mechanical orientation treatment and obtain an oxide superconductor with a large critical current density, it is necessary that the crystal grains of the oxide superconductor be large.

However, in this case, the size of the crystal is determined by the oxide superconductor powder used as a raw material, and in reality it is difficult to use powder larger than several tens of micrometers, so the critical current density is also 77K in the zero magnetic field. 1-3 inside
The limit is 10,000 A/cm.

As an oxide superconductor having relatively large crystals, there is a bismuth (lead) monostrontium calcium cuprate superconductor (hereinafter referred to as a Bi-based oxide superconductor). This B
I-based oxide superconductors have a very large crystal aspect ratio (ratio of length to thickness), so they are easily oriented, and therefore the critical current density in zero magnetic field shows a very large value. Due to the essential properties of Bi-based oxide superconductors, the binding force and the bond between grains are weak, and the critical current density drops to less than a few hundred 8/cm2 under a magnetic field of 1 Tesla or more. Ta.

On the other hand, yttrium-barium-copper oxide superconductors (hereinafter referred to as Y-based oxide superconductors) are oxide superconductors that have a large bottle-holding force. The binding force of this Y-based oxide superconductor is several times greater than that of the Bi-based oxide superconductor.

However, this Y-based oxide superconductor had a very small aspect ratio and therefore did not have good orientation.

Furthermore, in conventional methods for producing oxide superconductors, crystals of the superconductor do not grow within the sheath during heat treatment. This is because the oxide superconductor already exists inside the sheath as a polycrystalline powder, so there are too many crystal nuclei and larger crystals cannot be formed.

Within the series. Instead of oxide superconductor powder, a mixture of raw oxides (for example, diyttrium dioxide, barium oxide, or barium peroxide, and copper oxide for Y-based oxide superconductors) is filled in the oxide superconductor, and heat treatment is performed. The situation does not improve. In other words, because the temperature range in which solid-state reactions occur is extremely narrow (approximately 50'C), heat treatment easily generates many crystal nuclei of the oxide superconductor throughout the sheath, resulting in a polycrystalline state. This is because

The size of the crystal grains varies depending on the temperature of the heat treatment, but is at most several 10 μm.

Therefore, in order to grow large crystals of oxide superconductor within the sheath, it is necessary to suppress the generation of nuclei.

The present invention aims to suppress the generation of nuclei within the sheath, improve orientation by producing large crystal grains, and obtain an oxide superconductor with a high critical current density.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention utilizes fine particles of a halide of a metal element constituting an oxide superconductor.
An oxide superconductor wire is produced by packing the wire into a sheath), forming it into a desired shape or size through processes such as wire drawing and rolling, and then heat-treating it in an oxidizing atmosphere containing water vapor.

The oxide superconductor wire produced by the method of the present invention is. A mixture of metal element halide fine particles constituting the oxide superconductor in an appropriate ratio is placed in a thin tube of silver or other suitable metal (
Sheath), which is drawn and rolled to form the desired shape and size, and in some cases processed into a special shape such as a coil, and then heat treated in an oxidizing atmosphere containing water vapor. is formed.

That is, the present invention provides that when producing an oxide superconductor by performing an oxidation reaction using a metal halide as a raw material, if the metal halide is reacted with water vapor to perform an oxidation reaction, crystals or This is based on the discovery that it is possible to suppress the generation of nuclei that form the basis of long hair.

When a metal sheath is filled with the above halide mixture and exposed to an oxygen atmosphere containing water vapor, an oxidation reaction occurs due to the diffusion of water vapor that has penetrated from the outside of the metal sheath, generating nuclei. However, scanning electron microscopy confirmed that not many nuclei were generated, and many halides still remained in the area where the oxidation reaction was occurring, and that the area where nuclei were generated was limited. .

Thereafter, the reaction proceeds internally, and the crystals of the oxide superconductor grow around a small number of nuclei generated near the surface. This elongation process occurs in the C-axis direction from the surface to the center, and observation using a scanning electron microscope shows that plate-shaped crystals of the oxide superconductor are stacked on top of the metal sheath. .

If oxide superconductor particles are present in advance during the oxidation reaction, they serve as crystal growth nuclei and the crystal length can be further controlled.

Furthermore, if the inner diameter of the sheath is sufficiently small, or if the sheath is compressed and its width is sufficiently small, the conformation of the crystal will be further improved.

It is desirable that the raw material halide mixture has as fine particles as possible. Therefore, the spray drying method, which allows mixing on the atomic order, is the most suitable method for producing such a fine particle mixed powder.

If a sheath filled with such a halide is heat-treated by passing it through a furnace with a temperature gradient, the crystals will form huge crystals in one direction, and such wires will exhibit extremely high critical current densities. The metal halide used in the present invention preferably has a thickness of 100 μm or less.

This is because crystal growth tends to occur in the orientation direction if the thickness is up to this level.

The heat treatment in the present invention can be performed using only water vapor, but it may also be performed in an oxidizing atmosphere in which oxygen or other substances are added to the aquatic plants.

When heat-treating, it is desirable to use a furnace with a temperature gradient of 10°C/cm or more. If the temperature is less than 10°C/cm, many crystals will occur in various places on the sheath, causing large crystals to grow. This is because it becomes impossible to do so.

Further, when filling fine particles of a halide of a metal element into a capillary, an oxide superconductor may be added. If an oxide superconductor is added, it will serve as the core of the crystal length and the crystal length can be further controlled.

In the present invention, silver is typically used as the metal capillary, but other metals or other metals can be used as long as they do not react with the oxide superconductor at high temperatures and are permeable to water vapor. Alloys may also be used.

EXAMPLES The present invention will be explained in more detail with reference to Examples below.

r Example 1J This example was aimed at improving the orientation of an innotrium-barium-copper oxide superconductor (hereinafter referred to as Y-based oxide superconductor).

Y-based oxide superconductors have a large pinning force, which is several times larger than that of Bi-based oxide superconductors.
The orientation was not good because the aspect ratio was small.

Therefore, if giant crystals can be grown inside the sheath in the longitudinal direction of the sheath, it is expected that the wire will have extremely high conformation.

Therefore, an example of forming a superconductor wire represented by the chemical formula YBa2CuJ7-x will be shown here.

First, a fluoride prepared by a spray drying method so that the apparent compositional formula was YBazCuJ+:+ was prepared with an inner diameter of 1 mm,
A silver sheath with a wall thickness of 0.2 mm was filled. A bundle of 100 such sheaths was drawn and the diameter of the fluoride portion was approximately 50 μm. Furthermore, this wire is rolled, and the fluoride part is 10 μm in the short axis and 20 μm in the long axis.
It was made into a tape-shaped wire with an oval shape of m. This tape-shaped wire was placed in an electric furnace with a temperature gradient of 50° (1 cm).
I put it in at a speed of / hour. An oxygen stream containing water vapor was passed through the electric furnace. The maximum temperature of the electric furnace was 900°C. After this heat treatment was completed, the tape-shaped wire rod was annealed at 900°C in oxygen for 24 hours in an electric furnace with no temperature gradient, and further annealed at 400°C in oxygen for 24 hours.

The wire thus obtained was cut to an appropriate length and the critical current density in a magnetic field was measured. The results are shown in Table 1. Due to improved crystal orientation, the critical current density value (77K, 10
000 A/c).

Table 1 [Example 2] This example is an example in which an alloy is used as a metal sheath when molding a superconductor wire represented by YBazCu+Ot-X.

As in Example 1, the apparent m precept is YBazCu3F1.
The fluoride prepared by the spray drying method was packed into a sheath of yttrium-barium-copper alloy represented by the composition formula YzBaCu with an inner diameter of 1 mm and a wall thickness of 0.3, and
100 of these were bundled and wire-drawn to form a thin wire with a diameter of about 10 μm at the fluoride portion. This wire was placed into an electric furnace with a temperature gradient of 40°C/cm at a rate of 1cm/hour.

An oxygen stream containing water vapor was passed through the electric furnace.

The maximum temperature of the electric furnace was 930'C.

After this heat treatment is completed, the wire is annealed for 24 hours at 900'C in oxygen in an electric furnace with no temperature gradient.
Further, it was annealed at 400''C in oxygen for 12 hours.

The wire thus obtained was cut to an appropriate length and the critical current density in a magnetic field was measured. The results are shown in Table 2. Due to improved crystal orientation, the critical current density value (77K, zero magnetic field TeIO) reported for conventional wires has been improved.
OOO A/c+fl) A value larger than I order of magnitude is obtained.

Table 2 [Example 3] This example is for obtaining a tape-shaped wire of YBazCu: +O, -x. Similar to Example 1, a fluoride was prepared by spray drying so that the apparent composition was YBazCu3F+:v, and the inner diameter was 1 mm and the wall thickness was 0.2 mm.
One sheath was filled. When 100 such sheaths are bundled, each sheath has an outer diameter of approximately 0. The line was drawn to 1 mm. The cross section of the sheath is circular when the wire drawing is completed. Next, this bundle of sheaths was subjected to a rolling process.

In this week or so, the sheaths will be crushed and each sheath will be approximately 5μ thick.
It became a tape-like shape. This tape-shaped wire rod was put into an electric furnace with a temperature gradient of 60° (: / cm) at a rate of ICTI 1/hour. An oxygen stream containing water vapor was passed through the electric furnace. The maximum temperature of the electric furnace was After this heat treatment was completed, the wire was annealed for 24 cycles at 800°C in oxygen in an electric furnace with no temperature gradient.
Further, the mixture was heated in oxygen at 400°C for 7 hours for 7 hours.

The wire thus obtained was cut to an appropriate length and the critical current density in a magnetic field was measured. The results are shown in Table 3.

The sheath is crushed into a tape-like shape, and its width is sufficiently small, so the crystal orientation is improved compared to a sheathed tube, and as a result, the crystal orientation is also improved compared to a sheathed tube.
Since this was further improved, a large critical current density was also obtained.

Table 3 [Effects] In the present invention, when producing an oxide superconductor by performing an oxidation reaction using a metal halide as a raw material, the oxidation reaction is performed by reacting the metal halide with water vapor. By suppressing the generation of nuclei within the sheath and producing large crystal grains, an oxide superconductor with improved orientation can be obtained, and an oxide superconductor wire with a high critical current density can be produced. Moreover, the obtained oxide superconductor wire has a small decrease in field current density with respect to a magnetic field and is of practical use.

Furthermore, in the present invention, after forming the oxide superconductor into a desired shape or size, it is heat-treated in an oxidizing atmosphere containing water vapor. Since it is possible to manufacture objects, it is extremely easy to manufacture devices such as superconducting electromagnets, and therefore it can be applied to superconducting equipment used in a wide range of fields.

Claims (1)

[Claims] (1) Fine particles of the halide of the metal element constituting the oxide superconductor are packed into a thin metal tube, formed into a desired shape or size by a process such as wire drawing or rolling, and then placed in an oxidizing atmosphere containing water vapor. A method for producing an oxide superconductor wire characterized by heat treatment.