JPH0431021B2 - - Google Patents

Description

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

[Prior art and its problems]

Superconducting materials are already used in high-energy particle accelerators,
It has been put into practical use in the form of superconducting magnets in MRI-CT physical property research equipment for medical diagnosis, etc.
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 9T
It is widely used as a wire for generating magnetic fields. The Tc (critical temperature at which a superconducting state exists) of the Nb-Ti alloy is 9K. In addition, compound superconducting materials have been developed as materials with significantly higher Tc than Nb-Ti alloys, and currently Nb ₃ Sn (Tc: 18K) and Nb 3 Sn (Tc: 18K) are being developed.
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. Cooling superconducting materials with Tc below 23 K requires expensive liquid helium, which hinders their widespread application. As a material to break down this Tc wall,
In 1986, Mr. Muller et al.
Since the announcement that signs of superconductivity were observed in -La-Cu-O-based oxides, the race to develop oxide-based superconducting materials has accelerated. In 1986 Tc was 40K
By the beginning of 1987, it was already 77K.
A Y-Ba-Cu-O superconducting material has been developed that exceeds the liquid nitrogen temperature of , and its Tc has 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 high-temperature superconducting materials that can be used at liquid nitrogen temperatures increases expectations for the aforementioned application fields. However, no method has yet been proposed that can easily produce a superconducting material having a high Tc value and a superconducting film that is less likely to crack during heat treatment.

Accordingly, an object of the present invention is to provide a method for easily producing a superconducting material in which a superconducting film having a high Tc value and hardly cracking occurs during heat treatment is formed.

[Means for solving problems]

This invention prepares a superconducting material consisting of a base material and a superconducting film by thermally spraying powder of a composite oxide superconducting material containing Cu _x O _y groups onto the surface of a base material, and then coats the superconducting material with When producing a superconducting material by heat treatment, after starting thermal spraying, the powder is sprayed in a semi-molten state onto the surface of the base material, and then the powder is sprayed in a completely molten state onto the surface of the base material. By thermal spraying, an intermediate layer having a porosity larger than that of the superconducting film is formed between the base material and the superconducting film, so that during the heat treatment of the superconducting material, the superconducting film The feature is that it prevents cracks from occurring.

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 a plasma spraying apparatus used in the method of manufacturing a superconducting material according to the present invention.

As shown in FIG. 1, the plasma spraying apparatus 1 includes:
From a vacuum vessel 4, a thermal spray nozzle 5 provided within the vacuum vessel 4, a tungsten electrode 6 provided within the thermal spray nozzle 5, and a plasma power source 7 connected between the thermal spray nozzle 5 and the electrode 6. It's summery.

The base material 2 is placed in the vacuum vessel 4 facing the thermal spray nozzle 5, the pressure inside the vacuum vessel 4 is reduced, and a differential gas such as argon, helium, etc.
Powder of complex oxide superconducting material containing Cu _x O _y group (10
100 μm) respectively, and then the plasma power source 7 is activated to spray the thermal spray nozzle 5.
A plasma arc is generated between the electrode 6 and the electrode 6.

The superconducting material 8 is manufactured using the plasma spraying apparatus 1 as follows. That is, the pressure inside the vacuum container 4 is reduced, the working gas is supplied into the rear end of the thermal spray nozzle 5, and the inside of the front end of the thermal spray nozzle 5 is
Powder of a composite oxide superconducting material containing Cu _x O _y groups is supplied, and power is supplied from the plasma power supply 7 to the electrode 6 . In this case, the power from the plasma power source 7 is adjusted so that the powder is in a semi-molten state for a predetermined time from the start of thermal spraying, and then the power from the plasma power source 7 is adjusted so that the powder is in a completely molten state. Adjust. As a result, the base material 2, the intermediate layer 3A formed on the surface thereof and made of a superconducting material with a high porosity, that is, a coarse structure, and the intermediate layer 3A formed on the surface thereof.
Formed on the surface of, the porosity is small, i.e.
A superconducting material 8 consisting of a superconducting film 3B with a dense structure is manufactured.

In this way, between the base material 2 and the superconducting film 3B, an intermediate layer 3A having a top and cushion function is formed.
is formed, so during the subsequent heat treatment, the base material 2
The difference in thermal expansion coefficient between the superconducting film 3B and the superconducting film 3B prevents cracks from occurring in the superconducting film 3B.

The heat treatment conditions for the superconducting material 8 are as follows. That is, the superconducting material 8 is heated to a temperature of 500 to 980°C, and then heated to a temperature of 20°C in an oxygen-containing atmosphere.
The superconducting material 8 is cooled at a rate of ℃/min or less.

Here, the reason why the heating temperature was set in the range of 500 to 980°C is because below 500°C, the crystals of the superconducting film 3B
This is because it is impossible to form an orthorhombic crystal in which a superconducting phenomenon occurs and the amount of oxygen vacancies in the superconducting film 3B becomes large.On the other hand, when the temperature exceeds 980°C, a chemical reaction occurs between the base material 2 and the superconducting film 3B. This is because the superconducting phenomenon does not appear in the film 3B.

〔Example〕

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 into the thermal spray nozzle 5 as a working gas. Then, 8KW of power is supplied from the plasma power supply 7 to the electrode 6, and Y _0.3 −Ba _0.7 −Cu ₁ −
Powder of superconducting material consisting of O _3-y (particle size from 10
100 μm) into the thermal spray nozzle 5, and
The pressure inside the vacuum container 4 was reduced to 80 mbar, and an intermediate layer 3A having a thickness of 50 μm was formed on the surface of the base material 2. The porosity of the intermediate layer 3A was 20%.
Next, the power from the plasma power source 7 was increased to 25 KW to form a superconducting film 3B having a thickness of 100 μm on the surface of the intermediate layer 3A. Superconducting film 3B
The porosity was 2%. Next, the superconducting material 8 thus obtained was placed in a heating furnace and heated to a temperature of 930°C for 30 minutes, and then cooled at a rate of 20°C/min. Then, when the state of peeling of the superconducting film 3B was examined, no peeling was observed at all. Then, Tc
and Jc (critical current density was investigated. As a result, Tc is
90K, Jc was 150A/cm ² .

〔Effect of the invention〕

As explained above, according to this invention, Tc
This brings about the effect that it is possible to easily produce a superconducting material having a large value of Jc and a superconducting film that is less prone to cracking during heat treatment.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a plasma spraying apparatus used in the method of manufacturing a superconducting material according to the present invention. In the drawings, 1... plasma spraying device, 2...
... Base material, 3A ... Intermediate layer, 3B ... Superconducting film,
4... Vacuum container, 5... Thermal spray nozzle, 6... Electrode, 7... Power source, 8... Superconducting material.

Claims (1)

[Claims] 1 A superconducting material consisting of a base material and a superconducting film is prepared by spraying powder of a composite oxide superconducting material containing a Cu _x O _y group onto the surface of a base material, and then heat treatment is performed on the superconducting material. When producing a superconducting material, after starting thermal spraying, the powder is thermally sprayed in a semi-molten state onto the surface of the base material, and then the powder is thermally sprayed in a completely molten state onto the surface of the base material, In this way, an intermediate layer having a porosity greater than that of the superconducting film is formed between the base material and the superconducting film, thereby preventing cracks in the superconducting film during heat treatment of the superconducting material. A method for producing a superconducting material, characterized by preventing generation of superconducting materials.