JPH01163921A - Manufacture of superconductive fiber - Google Patents

Abstract

PURPOSE:To obtain a high density and an even quality and to realize the superconductive property and a good mechanical strength by melting a ceramics type superconductive substance, discharging it in a fiber form from a nozzle, and then applying a heat treatment to realize the superconductive property. CONSTITUTION:A ceramics type superconductive substance is heated at a temperature higher than its melting point, and resultant molten substance is discharged from a nozzle into the space, the space at a high temperature 750 to 950 deg.C, preferably, and a fibriform substance is formed. In this case, as soon as the fibriform substance is solidified, a metal membrane is attached, or after that, the fibriform substance is left for a specific time in the high temperature space. After that, the fibriform substance is heat-treated to realize the superconductive property. Consequently, a superconductive fiber of not only a high density, but also of a superconductive property at the level suitable for a practical use and a good mechanical strength can be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing ceramic superconducting fibers, and in particular, a method for producing high-density, small-diameter superconducting fibers by spinning a molten substance. It is related to.

[Prior Art] Recently, oxide-based superconductors have been found to have a Tc (superconductivity initiation temperature) much higher than the liquid nitrogen temperature compared to conventional metal-based or intermetallic-based superconducting materials. It is expected to have a wide range of applications in various industrial fields.

Such oxide superconductors are so-called ceramics, and thin films for electronic devices are manufactured using thin film forming techniques such as vapor deposition, sputtering, and CVD.

[Problems to be Solved by the Invention] On the other hand, attempts have been made to manufacture superconducting fibers made of ceramic superconductors, and, for example, methods of manufacturing ceramic fibers using a sol-gel method are being considered. This method is similar to the method for manufacturing ceramic fibers, in which superconductor fine particles are mixed with a spinnable solvent, extruded through a nozzle to form fibers, and then heated to a temperature at which the superconductor fine particles are sintered. This is a method of producing fibers by heating. However, the superconducting fibers produced by this method have low density, low mechanical strength, and poor superconducting properties, and in particular, the critical current density is several hundreds of amperes/ej, which is far from the practically required value. It remains at about ampere. This is because a large number of grain boundaries and pores are present inside the superconducting fiber produced in this manner, and these are the cause of impeding improvement in superconducting properties.

The present invention eliminates the drawbacks of the above-mentioned conventional techniques regarding the production of ceramic superconducting fibers, has a high density, does not have clear grain boundaries as seen in general sintered bodies, and is also practical. The object of the present invention is to provide a method for manufacturing superconducting fibers having superconducting properties and mechanical strength properties that do not cause any problems.

[Means for Solving the Problem] In order to achieve the above object, the present inventor conducted various studies to find a new process in view of the limitations of the method of sintering fine superconductor powder. As a result, instead of sintering fine superconductor powder, we melted the superconducting material at high temperatures, spun it, and then recrystallized it while cooling or slow cooling. The present invention was based on the discovery that it is possible to produce superconducting fibers that do not have distinct grain boundaries as seen in sintered bodies.

That is, the present invention, which relates to a method for producing superconducting fibers, involves heating a ceramic-based superconducting material above its melting point and releasing the resulting molten material into a space, preferably into a high-temperature space, to produce a fiber-shaped material. If necessary, a metal film is attached at the same time as the fibrous material solidifies, or the fibrous material is left in the high temperature space for a certain period of time, and then the fibrous material is heat-treated to make it superconducting. It is characterized by causing the expression of

The present invention will be explained in more detail below.

The superconducting material used in the present invention is a ceramic-based superconducting material, which includes perovskite ceramics and bismuth-based composite oxide ceramics.

Perovskite ceramics have the general formula ABCuO (A: 237-x Y, L a r Nd r S m r E u
+ G d + D y , Ho.

Er, Tn+, Yb or Lu, B: Ba or Sr.

X: Usually expressed as 0 to 0.35). In addition, bismuth-based composite oxides include Bi and Sr, which are easily available in terms of resources.

It is not only composed of elements such as Ca and Cu, but also has a critical temperature of 110', which is about 20' higher than that of conventional Y-Ba-Cu oxide. It is also said to be a chemically stable substance that does not react with water. For example, Bi −8r −
The preferred elemental ratio of Ca-Cu-based oxide is Bl:S
r: Ca: Cu = 1: 1: 1:
2, Bi OSrCO3, Cab, CuO23
'' are weighed and mixed and heat-treated at 750 to 880°C in an oxygen-containing atmosphere.

Such ceramic-based oxide superconducting materials are prepared by conventional methods, such as powder mixing of constituent element oxides, hydroxides, inorganic acid salts, and organic acid salts, coprecipitation method, sol-gel method, spray drying method, etc. . The prepared raw materials are put into a container made of an appropriate material either as they are or after being subjected to a predetermined heat treatment to form a superconductor crystal structure, and heated to a temperature higher than the melting point to melt the material to form a molten substance. For example, in the case of perovskite ceramics, the melting point is about 1200°C, so it is heated to about 1500°C, Bi - Sr - Ca -
In the case of Cu-based oxide, the melting point is about 900°C, so it is heated to about 1200°C to form a molten substance. The material for the container is preferably a material that does not react with superconducting substances, and Mg
Ceramics such as AR20a and aluminum nitride that do not contain O or Sl are preferable. W when using a metal container
, Ta, etc. may be used, but in order to suppress the reaction with the superconducting substance, it is desirable to use a ceramic container. Heating methods include a resistance heating method, a high frequency heating method, and a method using a halogen lamp. The atmosphere during melting is preferably an argon atmosphere.

After the superconducting substance is melted, the molten substance is immediately discharged in the form of fibers from a nozzle provided at the bottom or lower side of the container. At that time, it may be pulled out by gravity, but
A diffused pressure may be applied inside the container and the material may be discharged from the nozzle. The appropriate drawing/discharging speed is 0.6 to 3 m/win in the range of 900 to 1500°C.

The atmosphere in the space in which the fibrous material is released may be argon or the like, but an oxygen-containing atmosphere is preferable.

The temperature of this space is preferably 750 to 950°C. Although a fibrous material can be obtained by quickly cooling the drawn fibrous material to room temperature or liquid nitrogen temperature, the material produced by rapid cooling in this way is amorphous and has a non-uniform chemical composition. At low temperatures, this material exhibits semiconducting electrical resistance and does not exhibit superconductivity. Therefore, in order to impart superconductivity to a fibrous material prepared by rapid cooling, it must be heat-treated at a temperature of 750°C or higher, at which crystallization progresses, but since it is amorphous, crystallization progresses slowly and each crystal is The grains are also small. Furthermore, due to the non-uniform chemical composition, a second phase that does not exhibit superconductivity precipitates at grain boundaries, deteriorating the superconducting properties of the fibrous material.

On the other hand, when a fibrous material is drawn into a high-temperature space of 750 to 880°C for Bi-Sr-Ca-Cu oxides and 850 to 950°C for perovskite ceramics, the composition becomes uniform and the crystal growth is slow. Since the process proceeds inside the fiber, it is easy to obtain a high-density fibrous polycrystalline superconductor. For this purpose, it is preferable to allow the drawn fibrous material to remain in such a high temperature space for a certain period of time (eg, 1 hour).

The obtained fibrous material may be heat-treated in space or on the hearth to develop superconductivity, but in order to form continuous long fibers, it is preferable to heat-treat the material while winding it up at the same time as drawing it out. .

Note that, after being pulled out from the nozzle, the fibrous material can be solidified and a metal film can be attached to the surface at the same time. In this case, the metal film is preferably a metal that does not melt during heat treatment and does not react with the superconducting fibers, such as Au,
Ag, Cu, etc. are good.

In addition to vapor deposition, the metal film may be deposited by thermal CVD. Superconducting fibers with a metal film can have increased mechanical strength compared to fibers without a metal film.

Moreover, in the present invention, various operations may be added after the heat treatment. B
In the case of l -Sr -Ca -Cu-based oxides, after heat treatment at 750 to 880°C, the material is slowly cooled until the furnace temperature reaches about 600°C, and then taken out from the furnace and rapidly cooled.

Next, examples of the present invention will be shown.

[Example 1] A superconducting material 50 having a chemical composition of YBa2Cu306,8 was prepared in advance by a conventional method. was placed in a container made of high-purity alumina and heated to 1350° C. using a high-frequency heating method. At this time, the inside of the container was made into an argon atmosphere.

After the superconducting material was completely melted, 2 atmospheres of argon pressure was applied inside the container, and the fibrous material was discharged into an electric furnace heated to 950° C. through a nozzle with a diameter of 0.1 mm. The discharge velocity is 1.5 m/sin.

A is applied to the fiber surface of the fibrous material immediately after release by thermal CVD.
After depositing a metal film consisting of g, it was deposited on the hearth. In addition, thermal CVD uses AgCg as a raw material, and 1 (lcs
The deposition rate was set at a deposition rate of /ll1in.

After treating the fiber-shaped material deposited on the hearth at 950°C for 1 hour, it is slowly cooled, and when it reaches 700°C, oxygen gas is introduced into the furnace to create an oxygen atmosphere, followed by cooling at 5°C/sin. did. The obtained fibrous material had a diameter of 0.15 m and a superconductivity initiation temperature Tc of 85 mm.

[Example 2] Bi:Sr:Ca with the element ratio prepared in advance by a conventional method:
Superconducting material 5 having a chemical composition of Cu=1:1:1:2
0 g was placed in a container made of high-purity alumina and heated to 1200° C. using a high frequency method. At this time, the inside of the container was made into an oxygen atmosphere.

After the superconducting material was completely melted, argon pressure of 2 atmospheres was applied inside the container, and the fibrous material was discharged from a nozzle with a diameter of 0.1 mm into an electric furnace heated to 850°C. The discharge velocity is 1.5 m/a+in.

A is applied to the fiber surface of the fibrous material immediately after release by thermal CVD.
After depositing a metal film consisting of g, it was deposited on the hearth. In addition, thermal CVD uses AgCjl as a raw material, and Loz/
The test was carried out under the condition of a deposition rate of sin.

The fibrous material deposited on the hearth was treated at 850° C. for 1 hour, then gradually cooled, and when it reached 600° C., it was taken out from the furnace and rapidly cooled. The obtained fibrous material had a diameter of 0.15 mm and a superconductivity onset temperature of 100 mm.

[Effects of the Invention] As detailed above, according to the present invention, a ceramic superconducting substance is once melted, and after being discharged in the form of fibers from a nozzle, superconductivity is developed by heat treatment. It is possible to produce superconducting fibers that have no clear grain boundaries or pores like those found in sintered bodies, are dense and homogeneous, and have mechanical strength and superconducting properties that pose no practical problems. It is possible.

In particular, Bl-8r-Ca-Cu based oxide superconducting materials have a lower melting point than Y-Ba-Cu-0 based superconducting materials that have been studied in the past. Therefore, since it can be melted at 900°C, it is suitably used in the melt spinning manufacturing method shown in the present invention. Furthermore, there is no need to perform long-time oxygen atmosphere treatment, and the manufacturing process can be shortened.

The superconducting fiber obtained in the present invention can be used not only as a winding of a superconducting coil, but also as a superconducting wire for power transmission. Furthermore, if it is made into a cloth or felt shape, it can be used as a magnetic shielding material. Furthermore, when a superconducting fiber is produced and a metal film is attached at the same time, when it is used as a superconducting coil winding or a superconducting power transmission line, there is no need to later form a metal film as a stabilizing material for the superconducting wire. Economical.

Claims (5)

[Claims] (1) The molten material obtained by heating a ceramic superconducting material above its melting point is discharged into space from a nozzle to form a fibrous material, and then the fibrous material is heat-treated to develop superconductivity. A method for producing superconducting fibers characterized by: (2) The molten material obtained by heating the ceramic superconducting material above its melting point is discharged into space from a nozzle to form a fibrous material, and at the same time as the fibrous material solidifies, a metal film is attached. A method for producing superconducting fibers, which comprises heat-treating the fibrous material to develop superconductivity. (3) The molten material obtained by heating a ceramic superconducting material above its melting point is discharged from a nozzle into a high-temperature space to form a fiber-shaped material, and after remaining in the high-temperature space for a certain period of time, the molten material is A method for producing superconducting fibers, which comprises heat-treating a shaped substance to develop superconductivity. (4) The method according to claim 3, wherein the high temperature space is maintained at a temperature of 750 to 950°C at which crystals of the ceramic superconductor precipitate. (5) The molten material obtained by heating a ceramic superconducting material above its melting point is discharged from a nozzle into a high-temperature space to form a fibrous material, and at the same time as the fibrous material solidifies, a metal film is attached. . A method for producing superconducting fibers, which comprises leaving the fiber-shaped material in the high-temperature space for a certain period of time, and then heat-treating the fiber-shaped material to develop superconductivity.