JPH06162843A - Manufacture of bi oxide superconductor - Google Patents

Abstract

PURPOSE:To easily provide a Bi oxide superconductor excellent in superconductivity. CONSTITUTION:A green sheet 2, composed of a Bi oxide superconductor or its precursor powder, is arranged on a silver sheet to be temperature-increased at 0.1-1 deg.C per minute to 480 deg.C from room temperature in an oxygen atmosphere by using an electric furnace 5 to be kept for 1-8 hours at the temperature, then is temperature-increased to 875-885 deg.C to be kept for 1.5 hours at the temperature, and then is cooled at 200-300 deg.C per hour to below 830 deg.C. After that, the green sheet 2 is kept for 1-8 hours at a temperature below 830 deg.C to be quickly cooled at 300 deg.C per minute or more to 500 deg.C, and this procedure is repeated 5 times or more. Consequently, the quantity of the deposit of a different phase, deposited in a Bi oxide superconductor, and of oxygen, incorporated in a superconductive phase, can be restrained. In particular, crystal organization can be oriented by half-melting heat treatment in Bi oxide superconductor in which Bi:Sr:Ca:Cu=2:2: l:2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a Bi type oxide superconducting conductor applicable to magnets, coils, electric power application conductors and the like.

[0002]

2. Description of the Related Art So-called oxide high-temperature superconductors whose critical temperature exceeds liquid nitrogen temperature, represented by Y, Bi, and Tl systems, are used as magnets, coils, and various electric power application conductors by converting them into conductors and conductors. Attempts have been made to do so.

The most common of such attempts is to fill the powder of these oxide superconductors in a metal sheath material such as silver and reduce the diameter of the metal sheath material by a so-called powder-in-tube method. There is manufacturing technology. This method has great advantages over other methods in terms of workability in forming a wire and electromagnetic stability of the wire. For these metal sheath oxide superconducting wires, single-core round wires and tapes and multi-core round wires and tapes have already been devised and produced, and trial production of coils and conductors for cables has begun.

[0004]

However, it is difficult to obtain a uniform molded body with the above-mentioned metal sheath oxide superconducting wire. Further, since the outer peripheral portion is entirely covered with metal, the reaction between the oxide superconductor inside and oxygen in the atmosphere is suppressed, so that it is difficult to obtain high superconducting characteristics.

The present invention has been made as a result of extensive studies in view of the above problems of the prior art.
It is intended to provide a method for producing a Bi-based oxide superconducting conductor having excellent superconducting properties.

[0006]

In order to achieve the above-mentioned object, in the method for producing a Bi-based oxide superconductor according to the present invention, as shown in FIG. 1, a Bi-based oxide superconductor or its precursor powder is used. To prepare a green sheet 2 by a doctor blade method, laying the green sheet 2 on a silver sheet, and then raising the temperature from room temperature to 480 ° C. at 0.1 to 1 ° C. per minute in an oxygen atmosphere, After holding at the temperature for 1 to 8 hours, the temperature is raised to 875 to 885 ° C, and after holding at the temperature for 1.5 hours, the temperature is lower than 830 ° C to 200 to 300 ° C.
The process of cooling every hour at 0 ° C., then holding at a temperature of less than 830 ° C. for 1 to 8 hours, and rapidly cooling to 500 ° C. at 300 ° C./minute or more is repeated five times or more.

Next, an example of the method for producing the Bi-based oxide superconducting conductor of the present invention will be specifically described. The Bi-based oxide superconducting conductor or its precursor powder used in the method for producing a Bi-based oxide superconducting conductor of the present invention is prepared by adding an alcohol mixed solution containing a predetermined dispersant and kneading it, and then using polyvinyl butyral as a binder. Ethyl phthalate is added as a plasticizer and kneaded to obtain a slurry 1 having a predetermined viscosity.

In the doctor blade molding step, the slurry 1 is molded on the carrying tape 4 coated with silicon to have a width of 300 mm and a thickness of 500 to 700 μm by using the doctor blading apparatus shown in FIG.

After air-drying the molded slurry 1 at room temperature,
The green sheet 2 is obtained by drying at 30 ° C. to 40 ° C. for 20 to 30 minutes.

The green sheet 2 is cut into a predetermined size and placed on an Ag tape to form a composite. In order to remove the binder from the green sheet 2, the composite of the green sheet 2 and the Ag tape is 350 to 480 ° C.
(More preferably 450 ° C.) at a temperature of 0.1 to 1 ° C. per minute (more preferably 0.3 ° C. per minute), and the temperature is 1 to 1 ° C.
Hold for 8 hours (more preferably 8 hours).

In the present invention, the step of removing the binder is 350 to 480 ° C. for 1 to 8 hours,
This is because the binder is not sufficiently removed at a temperature of less than 0 ° C and less than 1 hour. Further, when the temperature exceeds 480 ° C. for 8 hours, the binder is completely removed, but the phase change of the Bi-based oxide superconductor increases the amount of precipitation of different phases and deteriorates the superconducting properties. In addition, the rate of temperature rise is 0.1 to 1 ° C.
The reason for setting every minute is that if the temperature is less than 0.1 ° C. per minute, the amount of precipitation of different phases increases due to the phase change of the Bi-based oxide superconductor before the temperature reaches the predetermined temperature, and the superconducting characteristics deteriorate. Also, if it exceeds 1 ° C. per minute, the binder is not sufficiently removed.

After removing the binder from the green sheet 2, the temperature of the green sheet 2 is raised to 875 to 885 ° C. (more preferably 880 ° C.) and kept at the temperature for 1.5 hours. After holding for a predetermined time in this way, it is cooled to less than 830 ° C. every 200 to 300 ° C. every hour and kept at 1
The step of holding for ~ 8 hours and then rapidly cooling to 500 ° C at 300 ° C / min or more is repeated 5 times or more (preferably 8 times), and then cooled to room temperature.

In the present invention, the holding temperature is 875-885.
The reason why the temperature is set to be 0 ° C is that the semi-molten amount becomes small at a temperature lower than 875 ° C, and almost all becomes a molten state at a temperature higher than 885 ° C, and in any case, the superconducting property is deteriorated.

Further, the semi-molten heat treatment is performed by cooling to 830 ° C. at 200 to 300 ° C. every hour, holding at the temperature for 1 to 8 hours, and then rapidly cooling to 500 ° C. at 300 ° C. or more per minute. This is because a later phase change to a superconducting phase is necessary and sufficient.

Similarly, at a cooling rate of less than 200 ° C./hour and a holding time of more than 8 hours, the amount of heterogeneous phase increases,
Further, if the cooling rate exceeds 300 ° C./hour and the holding time is less than 1 hour, the superconducting phase change does not sufficiently occur.

Here, the temperature is maintained at 830 ° C. for 1 to 8 hours, and then 50
The reason why the rapid cooling to 0 ° C. at 300 ° C./min or more is repeated five times or more is that the growth and the growth rate of the superconducting phase are improved by this repetition.

The reason why the material is rapidly cooled after being kept at the above temperature is that when gradually cooled, the amount of oxygen taken into the superconducting phase increases, causing a decrease in the critical temperature and a consequent decrease in the critical current density.

[0018]

In the method for producing the Bi-based oxide superconducting conductor of the present invention, the powder of the Bi-based oxide superconducting conductor or its precursor is dispersed in the organic solvent containing the organic binder, and the green sheet 2 is formed by the doctor blade method. Is placed on a silver sheet to form a composite, the organic matter contained in the green sheet 2 is removed by a binder removal step, and then the temperature rising rate, holding time, cooling rate, etc. of the green sheet 2 are strictly adjusted. Meanwhile, the heat treatment is performed, and then the material is rapidly cooled to room temperature. Therefore, it is possible to suppress the precipitation of a heterogeneous phase in the Bi-based oxide superconducting conductor and the amount of oxygen taken in the superconducting phase. In particular, B is Bi: Sr: Ca: Cu = 2: 2: 1: 2.
The crystal structure of the i-based oxide superconductor can be oriented by the half-melt heat treatment.

[0019]

【Example】

Bi (Example _{1) Bi 2 O 3, SrCO} 3, CaCO 3, and powder molar ratio of CuO: Sr: Ca: Cu =
The mixed powder mixed and mixed so as to be 2: 2: 1: 2 is calcined in the air at 800 ° C. for 50 hours, and then pulverized to obtain a calcined powder.

A dispersant of 0.1% was added to 100 g of the calcined powder.
30 g of the mixed alcohol solution added with was added, 3 g of polyvinyl butyral (PVB) as a binder and 0.3 g of ethyl phthalate as a plasticizer were further added, and the mixture was kneaded for 20 hours. The viscosity of the obtained slurry 1 was 3000 poise.

The slurry 1 was molded into a width of 300 mm and a thickness of 600 μm on a carrying tape 4 coated with silicon by using the doctor blading device shown in FIG. The formed slurry 1 was cut into a width of 10 mm, air-dried at room temperature for 30 minutes, and then dried at 30 ° C to 40 ° C for 25 minutes to obtain a green sheet 2.

The green sheet 2 after drying has a thickness of 15
It was placed on a silver tape having a width of 0 μm and a width of 10 mm, heated to 450 ° C. at a temperature rising rate of 0.3 ° C./minute in an oxygen atmosphere using an electric furnace, and kept at this temperature for 8 hours. After the holding, the temperature was continuously raised to 880 ° C. and the temperature was held for 90 minutes. Further, it was continuously cooled to 830 ° C. at a cooling rate of 200 ° C./hour, kept at this temperature for 8 hours, and then rapidly cooled to 500 ° C. at 300 ° C./min. Further, the process of holding at 830 ° C. for 8 hours and then rapidly cooling to 500 ° C. at 300 ° C./min was repeated 8 times in total, and then taken out from the electric furnace and cooled in the atmosphere.

Jc of the obtained conductor was 45 at 77K and 0T.
8,000A / c at 000A / cm ² , 77K, 1T
It was 70000 A / cm ² at m ² , 4.2 K, and 10 T.

(Comparative Example 1) Bi was prepared in the same manner as in Example 1.
_A calcined powder of ₂ Sr ₂ CaCu ₂ O _x was prepared and had an inner diameter of 25 m.
It was filled in a silver pipe having an outer diameter of 40 mm and an outer diameter of 40 mm, and then processed into a width of 13 mm and a thickness of 0.15 mm by a wire drawing machine and flat roll rolling. This wire in the air for the same time as in Example 1,
It heat-processed by the temperature pattern.

Jc of the obtained conductor is 77K, 20 at 0T.
1500A / c at 000A / cm ² , 77K, 1T
It was 40,000 A / cm ² at m ² , 4.2 K, and 10 T, which was lower than that in Example 1.

[0026]

As described above, in the method for producing a Bi-based oxide superconducting conductor of the present invention, after the green sheet 2 made of the Bi-based oxide superconducting conductor or its precursor powder is placed on the silver sheet. Since the organic substance contained is removed by the binder removal step and then heat-treated while strictly adjusting the temperature rising rate, holding time, cooling rate, etc., and then rapidly cooled to room temperature, it is precipitated in the Bi-based oxide superconductor. It is possible to suppress the precipitation of different phases and the amount of oxygen taken into the superconducting phase. Especially Bi: Sr: Ca: Cu = 2: 2: 1: 2
In the Bi-based oxide superconductor, the crystal structure can be oriented by the semi-melting heat treatment. Therefore, according to the method for producing a Bi-based oxide superconducting conductor of the present invention, a Bi-based oxide superconducting conductor having excellent superconductivity can be easily produced.

[Brief description of drawings]

FIG. 1 is a schematic view of a doctor blading device used in the present invention.

[Explanation of symbols] 1 Slurry 2 Green sheet 3 Doctor blade 4 Carrying tape 5 Electric furnace

Claims (2)

[Claims] 1. A green sheet (2) is produced by a doctor blade method using a Bi-based oxide superconductor or a precursor powder thereof, and the green sheet (2) is placed on a silver sheet and then in an oxygen atmosphere. From room temperature to 480.
The temperature is raised at 1 to 1 ° C. per minute, held at the temperature for 1 to 8 hours, and then raised to 875 to 885 ° C., and the temperature is set to 1.5.
After holding for a period of time, it is cooled to below 830 ° C. every 200 to 300 ° C. every hour, and then at a temperature below 830 ° C. for 1 hour.
A method for producing an oxide superconducting conductor, characterized by holding for 8 hours and rapidly cooling to 300 ° C. per minute or more to 500 ° C. five times or more. 2. The composition of the Bi-based oxide superconductor or its precursor powder is Bi: Sr: Ca: Cu = 2: 2: 1:
2. The method for producing an oxide superconducting conductor according to claim 1, wherein the number is 2.