JPH0534288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a superconducting material.

[Conventional technology and its problems]

Superconducting materials are already used in high-energy particle accelerators,
In MRI-CT physical property research equipment for medical diagnosis, etc.
It has been put into practical use in the form of superconducting magnets. Applications include generators, energy storage and conversion, linear motor cars, magnetic separation devices for resource recovery, nuclear fusion reactors, power transmission cables, magnetic shielding materials, etc.
Furthermore, superconducting elements using the Josephson effect are expected to be applied to ultra-high-speed computers, infrared detectors, low-noise amplifiers, etc., and if these are put into full-scale practical use, they will have significant industrial and social impact. The magnitude of the impact is still difficult to measure.

A typical superconducting material developed so far is Nb-Ti alloy, which is currently widely used as a wire for generating magnetic fields up to 9T. Nb−
Tc of Ti alloy (critical temperature at which superconducting state exists)
is 9K. In addition, compound-based superconducting materials have been developed as materials with Tc much higher than Nb-Ti alloys, and currently Nb ₃ Sn (Tc: 18K) and V ₃ Ga
(Tc: 15K) has been made into wire and put into practical use. Furthermore, a Tc of 23K has been obtained with Nb ₃ Ge.

Although efforts have been made to obtain high Tc superconducting materials for many years, Tc23K has become a major barrier to conventional alloy-based and compound-based superconducting materials. Expensive liquid He is required to cool superconducting materials with Tc below 23K.
This hinders the widespread application of superconducting materials. In 1986, Mr. Mu¨ller of IBM Zurich and others proposed Ba-La as a material to break down this Tc wall.
Since the announcement that signs of superconductivity were observed in -Cu-O-based oxides, the race to develop oxide-based superconducting materials has accelerated. In 1986, Tc was 40K, but in early 1987, a Y-Ba-Cu-O superconducting material was developed that exceeded the liquid nitrogen temperature of 77K, and Tc reached approximately 93K. Furthermore, vigorous development has continued since then, and there have been reports of the development of superconducting materials that exhibit superconducting phenomena at room temperature, although there are currently safety issues. The discovery of a high-temperature superconducting material that can be used at liquid nitrogen temperatures has raised expectations for the aforementioned application fields, but actual application requires the development of processing techniques such as wire rods and coatings. must be accompanied by

Conventionally, with regard to the above-mentioned film formation, attempts have been made to form a film made of an oxide superconducting material on the surface of a base material by sputtering or electron beam evaporation.

[Problem that the invention seeks to solve]

However, in the conventional method described above, the thickness of the film that can be stably formed is about 1 μm at most, which limits the power supply capacity, and the film formation speed is slow, so it takes a long time to form a film of a predetermined thickness. It takes.

An object of the present invention is to provide a method for producing a superconducting material, which allows a thick film to be formed stably and in a short period of time, and which also allows easy control of the amount of oxygen in an oxide superconducting material.

[Means for solving problems]

This invention sprays a powder made of a composite oxide superconducting material containing a Cu _x O _y group onto the surface of a base material by thermal spraying to form a film made of the material on the surface, and then: A superconducting material consisting of the base material and the film obtained in this way,
Heated at 700 to 980℃ for a specified time in an oxygen-containing atmosphere, cooled slowly, and heated to 400℃ in the same atmosphere.
The film is characterized in that it is heated to 600° C. for a predetermined period of time, thereby controlling the crystal structure and oxygen content of the film.

Next, one embodiment of the method for manufacturing a superconducting material according to the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the method for manufacturing a superconducting material according to the present invention.

Using a plasma spraying apparatus 1 as shown in FIG. 1, Y-Ba-Cu-O
A film 3 of a composite oxide superconducting material containing a Cu _x O _y group such as a Cu x O y group is formed. Note that the thermal spraying apparatus 1 may be other than one that uses plasma as a heat source.

The plasma spraying apparatus 1 includes a vacuum vessel 4, a thermal spray nozzle 5 provided in the vacuum vessel 4, a tungsten electrode 6 provided in the thermal spray nozzle 5, and connected between the thermal spray nozzle 5 and the electrode 6. It consists of a plasma power supply 7.

A plate-shaped or rod-shaped base material 2 is installed in a vacuum vessel 4 facing a thermal spray nozzle 5, and while the pressure inside the vacuum vessel 4 is reduced, a working gas such as argon or helium and Cu _x O are injected into the thermal spray nozzle 5. Powder (10 to 100 μm) of a composite oxide superconducting material containing a _y group is continuously supplied, and the plasma power source 7 is activated to generate a plasma jet from the spray nozzle 5 toward the electrode 6. In this way, the powder is melted to 40-100% of its volume and sprayed onto the surface of the substrate 2.

The base material 2 and the coating 3 are coated by the thermal spraying device 1 described above.
After obtaining the superconducting material 8 consisting of
℃ for a specified period of time, then 20℃/min.
Cool to a temperature of 400 to 600℃ at the following rate, or cool to room temperature once, then cool to a temperature of 400 to 600℃.
The sample is reheated to a temperature of 0.degree. C., maintained in this temperature range for a predetermined period of time, and then slowly cooled to room temperature.

The reason why the superconducting material 8 is heat-treated in this way is as follows.

When the molten particles of the superconducting material 8 adhere to the surface of the base material 2 by thermal spraying, the molten particles are immediately cooled. Therefore, the crystal structure of most of the film 3 formed on the surface of the base material 2 is tetragonal, which is stable at high temperatures. As a result, the superconducting phenomenon does not sufficiently appear in the film 3. Therefore, the temperature range of the film 3 mentioned above,
That is, when heated from 700 to 980° C., the crystal structure of the film 3, which originally tends to be orthorhombic, easily changes from tetragonal to orthorhombic. As a result, a superconducting phenomenon completely appears in the film 3 (see FIG. 2).

Next, the reason why the superconducting material 8 is held at a temperature of 400 to 600°C for a predetermined period of time is to compensate for the amount of oxygen in the film 3 that has been lost due to the heating in the previous stage, and to make the superconducting phenomenon appear. be. As is clear from Figure 2, the amount of oxygen absorbed is particularly large in the temperature range of 400 to 600°C. Therefore, in this temperature range,
By adjusting the heating time, the amount of oxygen in the film can be easily controlled.

In addition, the cooling rate was set to 20℃/min or less because
This is because if it exceeds 20°C/min, the risk of cracking in the film increases, the film becomes easier to peel off, and the amount of oxygen vacancies in the film increases.

Next, embodiments of the invention will be described.

Vacuum vessel 4 of plasma spraying apparatus 1 shown in FIG.
A copper plate-shaped base material 2 is set inside the spray nozzle 5, and a mixed gas of argon gas and helium gas (Ar: 20/min, He: 40/min) is continuously supplied as plasma gas into the thermal spray nozzle 5. and plasma power supply 7
A power _{of 15} KW is supplied between the thermal spray nozzle 5 and the _{electrode 6} from Then, the atmospheric pressure inside the vacuum container 4 is
The pressure was reduced to 80 mbar, and a film 3 made of a superconducting material having a film thickness of 150 μm was formed on the surface of the base material 2.

Next, the base material 2 and the film 3 obtained in this way
The superconducting material 8 consisting of The mixture was held and then slowly cooled to room temperature to produce a plate-shaped superconducting material.

A test piece from the superconducting material produced in this way (base material thickness 2 mm, coating 0.15 mm, width 5 mm, length 50 mm)
This was cut out and immersed in liquid nitrogen (77K), and the critical current density (Jc) was examined by four-terminal resistance measurement method. The critical temperature (Tc) was also measured using a similar method. Furthermore, X
The crystal structure of the film was also investigated by line diffraction. As a result, the crystal structure of the film was orthorhombic, with Jc of 80A/cm ² and Tc of 90K.

Furthermore, when we investigated the Meissner effect, we found that
The effect was confirmed at 77K.

Next, the strength of the film was investigated. This was evaluated by subjecting a test piece having the same dimensions as the above-mentioned test piece to the three-point bending test shown in FIG. 3, and determining the bending angle of the test piece when cracking occurred in the film. As a result, no cracks occurred in the film even when the test piece was bent up to 4.4 degrees.

〔Effect of the invention〕

As explained above, a thick film made of a superconducting substance can be stably formed on a substrate in a short time, and furthermore, the amount of oxygen in the film can be easily controlled, which is an extremely useful effect. brought about.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the state in which a superconducting film is formed on a base material by the method of the present invention, and FIG.
The figure is a graph showing the relationship between temperature, absorbed oxygen amount, and crystal structure, and FIG. 3 is a front view showing a three-point bending test. 1... Plasma arc thermal spraying device, 2... Base material,
3... Film, 4... Vacuum container, 5... Thermal spray nozzle, 6... Electrode, 7... Plasma power source, 8... Superconducting material.

Claims (1)

[Claims] 1 Cu _x O _y is applied onto the surface of the base material by thermal spraying.
A powder made of a composite oxide superconducting substance containing groups is sprayed to form a film made of the substance on the surface, and then the superconducting material made of the base material and the film thus obtained is exposed to oxygen. Heating at 700 to 980℃ for a specified period of time in a containing atmosphere,
1. A method for producing a superconducting material, which comprises heating the film at 400 to 600° C. for a predetermined time in the same atmosphere after slow cooling, thereby controlling the crystal structure and oxygen content of the film.