JPH01261205A - Method for producing oxide superconductor and apparatus for producing the same - Google Patents

Abstract

PURPOSE:To obtain a homogeneous oxide superconductor, having sharp superconductivity transition and excellent in critical current characteristics, by bringing a solid substance containing constituent elements of the oxide superconductor into contact with a melt containing the constituent elements thereof and reacting both. CONSTITUTION:A solid substance containing at least constituent elements of a superconductor is brought into contact and reacted with a melt containing at least constituent elements of the superconductor. Alternatively, a method for reacting a composite material having a solid substance containing the constituent elements of the oxide superconductor on the surface of a core material with a melt containing at least the constituent elements of the oxide superconductor to form the oxide superconductor on the surface of the core material can be also adopted. Either form of metallic and oxide states containing the constituent elements of the oxide superconductor may be used as the above-mentioned solid substance and melt.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing an oxide superconductor, and particularly to a method suitable for producing an oxide superconductor having a high critical temperature.

[Conventional technology]

Recently, Y-B with a critical temperature of 90 to 120
a-Cu-0 system, B i-3r-Cu-0 system, T
Oxide superconductors such as the Q-Ba-Ca-Cu-0 system have been discovered one after another. A common method for producing these oxide superconductors is to sinter a green compact obtained by stirring and mixing powders of each oxide or carbonate constituting the oxide superconductor. Incidentally, articles related to this species include Science Asahi (May 1987 issue, pages 68 to 73).

[Problem to be solved by the invention]

However, oxide superconductors produced by conventional methods involve a solid phase-solid phase reaction, which has the disadvantage that it is difficult to react sufficiently and it is difficult to obtain uniform performance with a sharp superconducting transition. Also.

It is a sintered body and has many voids, making it difficult to obtain a dense one.

Furthermore, although the crystal structure of these oxide superconductors is not necessarily clear at present, they have a multi-layered perovskite crystal structure and have anisotropy in their critical current, so the sintered body has a large Another problem is that it is difficult to obtain a critical current.

In addition, especially in T Q -B a -Ca -Cu-0 based oxide superconductors, the constituent elements TQ or TQ oxide have a high vapor pressure and evaporate during firing, making it difficult to form a good superconductor. It has disadvantages such as being difficult to obtain.

Therefore, an object of the present invention is to provide a method for producing an oxide superconductor that is homogeneous, has a sharp superconducting transition, and has excellent critical current characteristics, eliminating the above-mentioned drawbacks.

[Means to solve the problem]

The above objective is achieved by adopting a manufacturing method based on bringing a solid substance containing at least the constituent elements of the oxide superconductor into contact with a molten substance containing at least the constituent elements of the oxide superconductor to cause a reaction. be done.

In addition, by bringing a composite comprising a solid substance containing the constituent elements of an oxide superconductor on the surface of the core material into contact with a melt containing at least the constituent elements of the oxide superconductor and causing a reaction, the surface of the core material It is also possible to adopt a method of forming an oxide superconductor.

Also, by placing the melt in a generally sealed container, it is possible to prevent the constituent elements with high vapor pressure from evaporating.

[Function] The method of the present invention employs a so-called solid phase-liquid phase reaction in which a solid substance containing the constituent elements of an oxide superconductor and a molten substance are brought into contact and reacted. Since the crystal growth rate can be increased compared to the above, a dense and homogeneous oxide superconductor can be obtained.

In addition, the solid substance and the molten substance in this method may be either in a metallic state or an oxide state containing the constituent elements of the oxide superconductor, and the molten substance has a property that lowers the melting point and improves the reactivity. Li, K.

Alkaline earth metal elements such as Na can also be added.

Furthermore, since a solid phase-liquid phase reaction is used, it is easy to form an oxide superconductor with aligned crystal directions, and at this time, by controlling the temperature gradient, the crystal orientation can be further improved. encouraged.

〔Example〕

The present invention will be explained in detail below.

[Example 1] YxOs, BaC0at CuO powder was converted into Y:Ba:Cu
After mixing and stirring so that the ratio is 1:2:3,
The pressure-molded pellets were calcined at 900'C x 5 hours. After re-pulverizing this, it was press-molded again and heat-treated in an oxygen stream at 910° C. for 5 hours to obtain a sintered body having a diameter of 27 m and a thickness of 1.5+ m.

Apart from this, B a : Cu : K is 2:2:1
B.sub.a COa, Cu.sub.2 O, and KO granular powders were blended so that the ratio was as follows, and the mixture was melted in a platinum crucible. This is 950
The sintered body was immersed in the melt and held for 1 hour, then taken out and cooled to room temperature at a rate of 100°C/h in an oxygen stream.

The obtained oxide superconductor has a width of 2 mm and a thickness of 1.5 mm.
A rod-shaped sample with a length of 25 m and a length of 25 m was cut to measure the critical temperature and critical current density using the 4-terminal resistance method. As a result, the critical temperature at which the resistance becomes zero was 92, and the critical current density in liquid nitrogen and zero magnetic field was 730 A/J, showing excellent performance. Furthermore, as a result of microstructure observation using a scanning electron microscope, it was confirmed that the crystals of the plate-shaped oxide superconductor were oriented with good directionality.

[Example 2] 'rQzOa, BacO3, CaC0a, and CuO powders were blended so that the ratio of TQ:Ba:Ca:Cu was 2:2:2:3, mixed and stirred, and then pressure molded to a diameter of 30 mm.
Pellets with a thickness of 2IIn were made, placed in a platinum boat, and fired at 840° C. for 1 hour. At this time, the same phase and liquid phase coexisted, and the solid phase was taken out. A rod-shaped sample with a width of 21 m, a thickness of 1.5 rIn, and a length of 251 m was cut out from this same phase as in Example 1, and the critical temperature was measured. Although a slight transition was observed around 100 K, it was found to be 4.2 K.
Even after cooling to a certain temperature, it did not become completely superconducting.

Next, the same composition as above was placed in a platinum boat and fired for 840"C1h with the lid covered with a platinum plate.The critical temperature of the solid phase obtained at this time was 120" and completely A high critical temperature at which the electrical resistance becomes zero was obtained.

An analysis of the residue in the platinum boat, which was in a liquid phase at 840°C, revealed that when the platinum boat was not covered, most of it was oxides mainly composed of Cu and Ba, and T
Almost no fl is contained, and when the platinum boat is covered, TQ is also present. From this, a Tl2-Ba-Ca-Cu-○ based oxide superconductor with excellent performance can be obtained. It has been found that it is effective to prevent TQ in the liquid phase from evaporating.

[Execution tooth 3] The surface of a long piece of nimonic alloy core material with a thickness of 0 mm, 1 mm and a width of 5 cm was plated with Cu with a thickness of 10 μm, and the outer side of the Y- Ba-Cu-0
The sintered body of the oxide superconductor is crushed.

A paste made by adding an organic binder was applied. This was subjected to heat treatment of 9106CX for 5 hours to evaporate the organic binder to produce a long composite material.

Next, as shown in FIG. 1, the composite material 1 wound around the supply spool 3 was passed through the melt 2 contained in the container 4, and was continuously wound up by the winding respool rule 8. It was set in reaction tank 9, and oxide superconductors were continuously manufactured by the method of the present invention. At this time, the composition of the melt was the same as in Example 1, and the electric furnace 7 with a temperature gradient
The temperature was continuously changed from 950° C. to room temperature so that the heat treatment could be performed while oxygen gas was flowing.

Further, the melt 2 was heated by a heater 5 provided outside the container 4 and maintained at 950°C.

A lid 6 was provided on the container 4 to prevent the constituent elements in the melt from evaporating.

The obtained oxide superconductor was uniformly formed on the surface of the nimonic alloy core tape with a thickness of about 30 μm.

The critical temperature for zero electrical resistance was 92.1 K, measured using a 3 cm long sample cut from the obtained tape.

The critical current density in liquid nitrogen was as large as 4200 A/aJ.

In addition, the crystal structure observed using a scanning electron microscope confirmed that plate-shaped crystal grains were oriented parallel to the tape surface.

[Example 4] The same method as in Example 3 was carried out for the B1-3r-Ca-0 based oxide super THI body. The melt in this case is p
A B1-Pb-Cu-0-based composition was added with about 10% of b, and the temperature was 870°C.

[Example 5] The same method as in Example 3 was conducted for a TQ-8r-Ca-Cu-0 based oxide superconductor. The melt in this case was a TQ-B a -Cu-〇-based composition, and the temperature was 840°C.

It goes without saying that a superconducting coil can be obtained by insulating and winding the long tapes produced in Examples 3 to 5 above.

〔Effect of the invention〕

The present invention has been described above in detail, including examples.According to the present invention, since a solid phase-liquid phase reaction is used, the crystal growth rate is fast and the crystal orientation is excellent, resulting in a homogeneous in,
Oxide superconductors with sharp critical temperature transitions and large critical current densities can be easily obtained.

Moreover, various modifications can be applied to the composition of the solid phase substance and the liquefied substance.

Further, by using the elongated oxide superconductor obtained by the method of the present invention, a superconducting application device using liquid nitrogen as a refrigerant can be easily obtained.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing a manufacturing method for explaining one embodiment of the present invention. 1... Composite, 2... Melt, 3... Supply spool. 4... Container, 5... Heater, 6... Lid, 7...
·Electric furnace. 8... Spool for winding, 9... Reaction tank.

Claims (10)

[Claims] 1. Oxide superconductor characterized in that an oxide superconductor is formed by bringing a solid substance containing at least the constituent elements of the oxide superconductor into contact with a molten substance containing at least the constituent elements of the oxide superconductor and causing a reaction. How the body is manufactured. 2. 2. The method of manufacturing an oxide superconductor according to claim 1, wherein the solid material and the melt material are both oxides, or either one of them is an oxide. 3. By bringing a composite composed of a solid substance containing the constituent elements of an oxide superconductor on the surface of the core material into contact with a melt containing at least the constituent elements of the oxide superconductor and causing a reaction, the surface of the core material is oxidized. 1. A method for producing an oxide superconductor, the method comprising forming an oxide superconductor. 4. By continuously passing a composite consisting of a solid substance containing constituent elements of an oxide superconductor on the surface of the core material through a melt containing at least constituent elements of the oxide superconductor, the composite material is formed on the surface of the core material. A method for producing an oxide superconductor, which comprises continuously forming an oxide superconductor. 5. A method for manufacturing an oxide superconductor according to claim 4, characterized in that a temperature gradient is provided on the exit side from the melt. 6. Claims 1, 2, 3, 4,
Or the method of manufacturing an oxide superconductor according to claim 5, wherein the melt is in a substantially sealed container. 7. A supply device for a composite in which a solid substance containing constituent elements of an oxide superconductor is formed on the surface of a core material, and the composite supplied from the supply device is contacted and reacted to form an oxide superconductor. a container for storing a molten material containing at least constituent elements of an oxide superconductor; a winding device for winding up the oxide superconductor obtained by the reaction in the container; An apparatus for producing an oxide superconductor, comprising: a temperature control device for controlling the temperature; and a temperature gradient control device for gradually changing the temperature of the oxide superconductor discharged from the container. 8. It is characterized by being formed by winding a superconductor obtained by contacting and reacting a solid substance containing at least the constituent elements of the oxide superconductor with a molten substance containing at least the constituent elements of the oxide superconductor. superconducting coil. 9. By bringing a composite composed of a solid substance containing the constituent elements of an oxide superconductor on the surface of the core material into contact with a melt containing at least the constituent elements of the oxide superconductor and causing a reaction, the surface of the core material is oxidized. A superconducting coil characterized in that it is formed by winding a superconductor formed into a physical superconductor. 10. By continuously passing a composite consisting of a solid substance containing constituent elements of an oxide superconductor on the surface of the core material through a melt containing at least constituent elements of the oxide superconductor, the composite material is formed on the surface of the core material. A superconducting coil characterized in that it is formed by winding a superconductor in which an oxide superconductor is continuously formed.