JPH01246719A - Manufacture of oxide superconductor - Google Patents

Abstract

PURPOSE:To increase the critical current density by forming a molten metal including elements of an oxide superconductor in a specific composition ratio, solidifying the molten metal to get a solid, and manufacturing an oxide superconductor from the solid as the basis. CONSTITUTION:Elements to compose an oxide superconductor are mixed to make a specific ratio of composition. Then, the mixture powder is baked temporarily, powdered, and an intermediate sintering process is applied to obtain an oxide superconductor powder. After that, the oxide superconductor powder is smashed in a crucible, and heated and fused in the ambiance presenting oxygen to obtain a molten metal. Then, the molten metal is cooled suddenly to solidify, and after holding for a specific time, it is cooled up to the room temperature. Then, the resultant solid is smashed into pieces. The smashed pieces are processed to make into a rod-form, which is inserted to a metallic tube body 2 to form a composite. Following that, the composite 3 is coldforged to reduce the diameter, and to a composite consolidated body 13 after the diameter reduction process, a sheath removal process and the final sintering process are applied to manufacture the oxide superconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for manufacturing oxide superconducting conductors, which are being developed for use in windings of superconducting magnets, power transmission lines, and the like.

"Prior Art" Recently, various oxide-based superconductors have been discovered whose critical temperature for transitioning from a normal conducting state to a superconducting state exceeds the temperature of liquid nitrogen. This kind of oxide superconductor is Y
-B a-Cu-0 series or B1-5 r-Ca-
These oxides are typified by Cu-0-based superconductors, and technological development is underway to manufacture superconducting wires comprising these oxide superconductors.

Conventionally, as an example of a method for manufacturing this type of oxide superconducting wire, a plurality of raw material powders containing elements constituting the oxide superconductor are prepared, and this mixed powder is calcined to remove unnecessary components. The calcined powder is filled into a metal tube and subjected to diameter reduction processing, and after the diameter reduction processing, heat treatment is performed in an oxygen atmosphere to cause a solid phase reaction in the compacted powder inside to produce an oxide superconductor. method is known.

"Problems to be Solved by the Invention" However, in the oxide superconducting wire manufactured by the conventional method described above, the elements constituting the oxide superconductor are not completely and uniformly mixed at the stage of producing the mixed powder. There is a problem in that oxide superconductors with the desired composition cannot be produced uniformly because the oxide superconductor is not produced uniformly, and the reaction of the elements during processing and sintering is a solid phase reaction, so a sufficient diffusion reaction of the elements cannot be expected. Therefore, there is a problem that an oxide superconductor having a desired composition cannot be uniformly produced. In addition, as mentioned above, since the oxide superconductor is produced by causing a solid phase reaction in the compact obtained by compacting the mixed powder that lacks uniformity, the grain boundaries of the produced oxide superconductor has the disadvantage of having minute pores and defects. That is, such an oxide superconductor has a structure in which current flows through the grain boundaries of powder particles containing vacancies and defects, so there is a problem in that the critical current density cannot be increased.

The present invention has been made to solve the above problems,
It is an object of the present invention to provide a method for manufacturing an oxide superconductor having a high critical current density.

[Means for Solving the Problems] The present invention provides a method for manufacturing an oxide superconductor comprising a multi-element oxide superconductor, in which each element constituting the oxide superconductor is mixed in a predetermined component ratio. A molten metal is formed, this molten metal is solidified to obtain a solidified body, this solidified body is crushed and the resulting crushed product is compression molded to obtain a rod-shaped body, and then this rod-shaped body is molded into a metal tube. to obtain a composite, and the composite is subjected to diameter reduction processing to form a composite consolidated body consisting of a consolidated body and a metal sheath, and then, after removing the metal sheath of this composite consolidated body, the consolidated body is The solution to this problem was heat treatment in an atmosphere containing oxygen.

``Effect'' An oxide superconductor with excellent properties is produced in a solidified body made from a molten metal with a predetermined component ratio due to a reaction by melt diffusion, which is faster than an in-phase reaction. The resulting rod-shaped body is filled into a metal tube and heat-treated to obtain a high-performance oxide superconducting conductor with a high critical current density.

The present invention will be explained in more detail below.

To practice the present invention and produce oxide superconducting conductors, starting materials are first prepared. As the starting material, a powder of an oxide superconductor, a material containing elements constituting the oxide superconductor, or a mixture thereof is used, and each element is weighed and mixed so as to have a predetermined composition ratio.

The oxide superconductor may be A-B-Cu-0 (where A is Y, Sc, La, Ce, Pr, Nd, P
m, Sm.

Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, L
Represents one or more of the elements of group MA of the periodic table such as u, group VB of the periodic table such as Bi, or elements of group M of the periodic table such as TI, A1, and B is S r, Ba, Ca, B
One or more of Group IIa elements of the periodic table, such as e and Ra. ) are used.

In addition, materials containing elements constituting the oxide superconductor include powders containing elements of group Ua of the periodic table, and powders containing elements of group Ua of the periodic table [[a
Group elements or periodic table group vb elements or periodic table 111
A mixed powder consisting of a powder containing a group B element and a copper oxide powder, a powder obtained by calcining this mixed powder, a mixed powder of the above mixed powder and calcined powder, etc. are used. Examples of powders containing elements of group Ila of the periodic table used here include Ca and Sr.

These include carbonate powders such as Ba and Ra, compound powders such as oxide powders, chloride powders, sulfide powders, and fluoride powders, and alloy powders. In addition, powders containing elements of group I [1a of the periodic table include Sc, Y, La, and Ce.

P r, Nd, Pn+, S a+, Eu, Gd, Tb,
Dy, Ho, E r, Tm.

Compound powders or alloy powders such as oxide powders, carbonate powders, chloride powders, sulfide powders, fluoride powders, etc. of each element of Yb and Lu are used, and Bi As a compound powder or alloy powder of elements such as T I
A compound powder or alloy powder of elements such as , A 1 is used. Further, as the copper oxide powder, Cuo,
Powders such as Cuyo, CLi2O2°Cu403 are used.

By the way, to prepare the mixed powder, the above-mentioned powder method is usually used, but it is not limited to this powder method.Each element is co-precipitated as a salt, and the precipitate is dried to prepare the mixed powder. It is also free to apply the coprecipitation method to obtain . In addition, compounds of the necessary elements are mixed in a predetermined ratio to form a mixed solution, acid is added to this mixed solution to form a sol, this sol-like substance is heated to gel, and this gel is further A sol-gel method may be applied in which the mixture is heated to form a solid phase and then pulverized to obtain a mixed powder.

Next, the mixed powder is heated and calcined at 750 to 950°C for 3 to 50 hours. When the calcining process is completed, the calcined product is further crushed to make the particle size uniform.

Next, the calcined powder was heated for 800 min in an oxygen gas atmosphere.
By heating at ~950°C for 3 to 50 hours and performing an intermediate sintering process of cooling after heating, a desired composition ratio (for example, YlBa2CLi2O?-δ (0≦8≦0.5) is obtained.
, Bi+Sr+Ca, Cu*0x1Tl, CatBaz
An oxide superconducting powder having a composition of CLI30X is obtained. In addition, in this intermediate sintering process, Y-B a-Cu-
When manufacturing a 0-based oxide superconductor, it is preferable to slowly cool it after heating, and B i-S r-Ca-Cu-
When manufacturing 0-based oxide superconductors, 2
It is preferable to perform a treatment such as heating for 0 minutes, then heating at 880° C. for 9 hours, and then rapidly cooling after heating.

The oxide superconducting powder thus obtained was placed in a crucible made of platinum or CaO, and heated for 13 hours in an oxygen atmosphere.
It is heated to about 00°C to melt and obtain a molten metal.

Next, this molten metal is rapidly cooled to a temperature range of 800 to 950°C to solidify it, and then this solidified body is maintained at 800 to 950°C for several hours to several tens of hours, and then cooled to room temperature. The process of rapidly cooling the molten metal can be carried out by a method in which the crucible is pulled out into the air from a heating furnace or a heating device, or by a method in which the crucible is rapidly cooled using a refrigerant. In the solidified body obtained by solidifying the molten metal in this manner, a uniform, high-quality oxide superconductor is produced by the melt diffusion reaction, which has a faster diffusion rate than the solid phase reaction.

In addition, when cooling the solidified body obtained from the molten metal to room temperature, it is preferable to slowly cool the Y-Ba-Cu-0 type solidified body, but rapid cooling is preferable for the B i-S r-Ca-Cu-0 type solidified body. It's okay to do that.

Next, the surface portion of the coagulated body thus obtained is scraped off to a thickness of 1 mm or less, preferably several microns to several hundred microns, and the scraped portion is ground using a grinder to obtain a powder (separated product). Mechanical cutting or the like may be used to scrape off the surface portion of the coagulated body, but it is also possible to perform grinding or the like to simultaneously scrape off and powderize. Note that the central portion of the solidified body after the surface portion has been scraped off is melted again and then solidified, and the surface is further repeatedly scraped off to be reused to obtain powder. Alternatively, the above-mentioned powder may be obtained by using a method in which the molten metal is jetted together with a carrier gas into a space at a temperature of 800 to 950° C. to be powdered.

This process is repeated to collect powder. The reason why only the surface portion of the solidified material is collected is that when the molten metal is solidified, sufficient oxygen is mainly supplied to the surface portion, and a highly pure and uniform oxide superconductor is generated at the surface portion. The purpose is to collect such highly pure and uniform oxide superconductors. Further, when powder is produced directly from molten metal using a carrier gas, if the particle size of the powder is several hundred μm or less, this powder is collected as it is and used in the following process.

Next, the powder collected as described above is subjected to pressing means such as applying hydrostatic pressure with a rubber press to obtain a rod-shaped body. In addition,
For this rod-shaped body, 800~
A heat treatment of heating at 950° C. for 6 to 50 hours may be performed to further improve the production rate of the oxide superconductor inside the rod-shaped body.

Next, the above-mentioned rod-shaped body I is inserted into the metal tube body 2 shown in FIG. 1 to create a composite body 3. The tube body 2 is made of CulAg
, AI, an alloy thereof, or a metal material such as stainless steel.

Note that it is necessary to select a material constituting the tube body from a non-oxidizing material that does not take away oxygen from the rod-shaped body, and preferably from a material that allows oxygen to permeate well. Therefore, it is preferable to use a noble metal or an alloy containing a noble metal, but a coating layer made of a non-oxidizing material may be formed on the inner peripheral surface of the tube.

Next, the composite body 3 is subjected to cold forging using a forging device such as a rotary swaging device shown in FIG. 1 to reduce the wire diameter to a desired wire diameter.

The rotary swaging device A shown in FIG. 1 includes a plurality of dies 6 that are movably provided by a drive device (not shown). These dice 6 are provided around the movement space when the rod-shaped composite body 3 is moved in its length direction, so as to surround this movement space.
A direction perpendicular to the movement space (direction of arrow a shown in FIG. 1)
It is held so as to be freely movable and rotatable around the movement space (in the direction of the arrow shown in FIG. 1). Further, a tapered surface 6a for reducing the diameter of the composite body 3 is formed on the inner surface of each die 6, so that the gap surrounded by the tapered surface 6a of each die 6 becomes tapered. ing.

To reduce the diameter of the composite 3, the rotary swaging device A is operated and one end of the composite 3 is pushed into the gap between the dies 6, as shown in FIG. Here, since the dice 6 are rotating while reciprocating at a predetermined interval in the direction of the arrow a in FIG.
is sequentially forged from one end side and is reduced in diameter to the wire diameter shown by the two-dot chain line in FIG. 1 to obtain a composite consolidated body 13. In this diameter reduction process, the composite body 3 is reduced in diameter while being forged by a plurality of dies 6 that reciprocate while rotating, so that the composite body 3 is reduced in diameter at a large processing rate without causing wire breakage. Diameter processing is possible.

In this example, the rotary swaging device A was used to reduce the diameter of the composite 3. However, when performing the diameter reduction process, other known forging methods may be used instead of using the rotary swaging device A shown in FIG. There is no problem with using a device, diameter reduction device, etc.

Once the diameter of the composite body 3 has been reduced to a desired wire diameter by the rotary swaging device A shown in FIG. An oxide superconducting conductor is produced by processing and final sintering.

That is, the tubular portion serving as the outer metal sheath is removed from the composite compacted body I3, thereby exposing the internal compacted body. To remove the metal sheath, the composite compacted body is immersed in a treatment solution such as an acid such as nitric acid or an alkaline solution such as caustic soda, and only the metal sheath is dissolved in the treatment solution. Various methods are used.

Note that as a method for removing the metal sheath, it is also possible to use mechanical cutting or passing the entire wire through a high-frequency induction heating furnace to selectively heat and melt only the metal sheath to remove it.

Next, the thus exposed compacted body is subjected to heat treatment to obtain a sintered body. This heat treatment is carried out by heating at 800 to 950 DEG C. for about 6 to 50 hours in an oxygen gas atmosphere, and then cooling. In addition,
When producing a Y-B a-Cu-0-based oxide superconductor, it is preferable to slowly cool it after heating.
r-Ca-Cu-0 system or Tica-B
When producing an a-Cu-0-based oxide superconductor, rapid cooling may be used.

Due to the heat treatment described above, each of the constituent elements in the compacted body undergoes a sufficient solid phase reaction with each other, and since the surface of the compacted body is exposed, oxygen is absorbed from the entire surface of the compacted body into its interior. It is efficiently diffused and sintered to obtain an oxide superconducting conductor.

Since the oxide superconductor manufactured in this way is formed using pure powder with a uniform composition formed from a molten solidified body, it exhibits an extremely high critical current density, and
This oxide superconductor exhibits a sufficiently high critical current density even in high magnetic fields. Furthermore, since the compact is heat-treated after being sufficiently compacted by the rotary swaging device A, a solid phase reaction is sufficiently carried out inside the compact, and an oxide superconductor with a high critical current density is produced. Furthermore, if a powder with a more uniform and pure composition is extracted from the surface part of the solidified body and a superconducting conductor is produced from this powder, an oxide superconductor with a uniform composition with less impurities can be produced. , an oxide superconducting conductor with a high critical current density can be obtained.

Note that it is preferable that a protective coating layer be formed on the outer surface of the oxide superconducting conductor obtained in this manner in order to prevent deterioration of superconducting properties and stabilize it, or for reinforcement. This protective coating layer can be formed by filling a molten bath with molten metal of a low melting point such as tin or solder, and coating the oxide superconducting conductor by immersing it in the molten metal while applying ultrasonic waves. Alternatively, methods such as coating with organic materials such as enamel or formal can be adopted for reinforcement.

Note that a coating layer made of amorphous carbon or the like may be formed using a film forming method.

If a protective coating layer is formed in this way,
In Y-B a-Cu-0 type superconductors, deterioration of superconducting properties due to moisture can be prevented.

"Example" Y, 03 powder, BaCO3 powder, and CuO powder
:Cu = 1:2:3 to obtain a mixed powder, and this mixed powder was heated at 900° C. for 24 hours to obtain a calcined powder. Next, the calcined powder was pulverized and further heated at 890° C. for 14 hours in an oxygen gas atmosphere to obtain an oxide superconductor having a composition of Y + B atc 11307-δ.

Next, this oxide superconductor was placed in a platinum crucible and heated to 1300° C. in an oxygen-existing atmosphere to melt the oxide superconductor and form a molten metal.

Next, this molten metal was rapidly cooled to 900°C in an oxygen gas atmosphere, held at 900°C for 10 hours, and then gradually cooled to room temperature at a rate of 200°C/hour to obtain a solidified body. Next, only the surface layer of this coagulated body was taken out and pulverized to obtain a powder.

The powder thus obtained was subjected to hydrostatic pressure using a rubber press to form a rod-shaped body having a diameter of 8V++. Next, this rod-shaped body is inserted into a silver tube having an outer diameter of 15 m + + + and an inner diameter of 10 mm, and is cold-worked using a rotary swaging device or a wire drawing machine to reduce the diameter to a diameter of 1.5 mm consisting of an oxide core and a silver sheath. A composite compact of 0 mfl was obtained. The silver sheath of this composite compact was then dissolved with dilute nitric acid to expose the oxide core. Next, this oxide core was heat-treated at 890° C. for 3 hours in an oxygen gas atmosphere to obtain an oxide superconducting conductor.

This oxide superconductor exhibits Jc=1.6XIO'A/am" in an OT (Tesla) magnetic field, and Jc=1.2 Indicated.

Incidentally, a mixed powder having the same composition as the above-mentioned mixed powder is calcined and filled into a silver sheath, the diameter of which is reduced using a rotary swaging device, the silver sheath is dissolved and removed, and the obtained oxidized powder is further heat-treated. Jc of physical superconducting conductor is 1X
Jc of other currently known oxide superconducting conductors is approximately 0.1 to IXIO
It is about 'A/am'.

However, these conventional oxide superconducting conductors have a Jc of 0.1-IX 10 even in an IT magnetic field.
It is known that the temperature decreases to 'A/cm'.

Therefore, it has been revealed that by carrying out the present invention, it is possible to obtain an oxide superconducting conductor with a high critical current density even in a strong magnetic field.

"Effects of the Invention" As explained above, according to the present invention, a solidified body is obtained by solidifying a molten metal in which a melt-diffusion reaction with a higher diffusion rate than a solid phase reaction is performed, and a uniform solidified body is obtained from this solidified body. Since a rod-shaped body is formed using a pulverized material having a similar composition, and an oxide superconducting conductor is manufactured from the rod-shaped body, there is an effect that a high-quality oxide superconducting conductor with a high critical current density can be manufactured. In addition, the oxide superconductor obtained by carrying out the present invention exhibits an excellent critical current density even in a high magnetic field because a uniform oxide superconductor with a uniform composition is produced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining the state in which a composite body is reduced in diameter by a rotary swaging device. ■...rod-shaped body, 2...tubular body, 3...complex,
6...Dice, 13...Composite consolidated body, 14...
- Consolidated body, A...Rotary swaging device.

Claims (1)

[Claims] In a method for producing an oxide superconductor comprising a multi-element oxide superconductor, a molten metal containing each element constituting the oxide superconductor in a predetermined component ratio is formed, and the molten metal is is solidified to obtain a coagulated body, this coagulated body is pulverized, the resulting pulverized product is compression molded to obtain a rod-shaped body, and then this rod-shaped body is filled into a metal tube to obtain a composite body,
The composite body is subjected to diameter reduction processing to form a composite consolidated body consisting of a consolidated body and a metal sheath, and then, after removing the metal sheath of this composite consolidated body, the consolidated body is heat-treated in an oxygen-present atmosphere. A method for producing an oxide superconducting conductor.