JPH01246720A - Manufacture of oxide superconductor - Google Patents

Abstract

PURPOSE:To increase the critical current density by forming a molten metal including elements to compose an oxide superconductor in a specific composition ratio, solidifying the molten metal into a solid, filling the solid or only the surface separated from the solid in a metal tube, and then processing it. CONSTITUTION:Elements to compose an oxide superconductor are mixed to make a specific composition ratio. Then the mixture powder is baked temporarily and powdered, and the resultant powder is sintered intermediately to obtain an oxide superconductive powder. After that, the oxide superconductive powder is poured in a crucible, heated, and fused to obtain a molten metal. Then, the molten metal is cooled suddenly to solidify, and the resultant solid is cooled up to the room temperature. Then, only the surface part of the solid is scraped to get a powder. The powder is pressured to make a rod-form body 1, which is inserted to a metallic tube body 2 to form a composite 3. Then, the composite 3 is cold-forged to reduce the diameter, and to the resultant composite consolidated body 13, a sheath removal process and the final sintering process are applied to make an oxide superconductor. Furthermore, the powder of the purer composition ratio is picked up from the surface of the solidified body, and a superconductor is manufactured from the powder.

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. At the same time, 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-present atmosphere to cause a solid phase reaction in the compacted powder inside to produce an oxide superconductor. There are known ways to do this.

"Problems to be Solved by the Invention" However, in the oxide superconducting wire manufactured by the conventional method described above, each element constituting the oxide superconductor is completely mixed in q- at the stage of producing the mixed powder. 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 oxide superconductors have a problem in that the critical current density cannot be increased because of the structure in which current flows through grain boundaries of powder particles containing vacancies and defects.

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 with a predetermined component. A composite is obtained by forming a molten metal containing the same ratio, solidifying the molten metal, and filling a metal tube with the solidified material. The method of solving the problem was to form a composite consolidated body consisting of a metal sheath, then remove the metal sheath from the composite consolidated body, and then heat treat the consolidated body in an oxygen-containing atmosphere.

In addition, a method for solving the problem was to separate only the surface portion of the obtained solidified body, fill it in a metal tube to reduce its diameter, and perform heat treatment to produce an oxide superconducting conductor.

"Operation" An oxide superconductor with excellent properties is produced by a melt-diffusion reaction in a solidified body made from a molten metal with a predetermined component ratio, and this solidified body is filled into a metal tube and heat-treated to create a superconductor with high properties. Obtain an oxide superconducting conductor. In addition, since the surface portion of the solidified body obtained from the molten metal is supplemented with a sufficient amount of oxygen and an oxide superconductor is generated, by extracting and separating only this surface portion, the desired composition ratio can be achieved. A pure oxide superconductor isolate is obtained, and based on this, oxide superconductor conductors with high properties are manufactured.

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
s+, 5LIl.

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 MB of the periodic table such as T I, A I, and B is S r, Ba, Ca
, Be, Ra, and other elements of the Ua group of the periodic table. ) are used.

In addition, materials containing elements constituting the oxide superconductor include powders containing elements of group Ua of the periodic table, elements of group Ua of the periodic table, elements of group Vb of the periodic table, or elements of group 1 [1b of the periodic table].
A mixed powder consisting of a powder containing a group 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. The powder containing the Ua group element of the periodic table used here is C
a, 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. Further, examples of powders containing elements of Group Ma of the periodic table include Sc, Y, La, and Ce.

Pr, Nd, Pm, S+++, Eu, Gd, Tb, Dy
, Ho, Er, 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 Compound powder or alloy powder of elements such as T
Compound powders or alloy powders of elements such as I and A1 are used. Furthermore, as the copper oxide powder, Cuo
, Cufo, Cuto t.

A powder such as Cu2O3 is 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.
An intermediate sintering process of heating at ~950°C for 3 to 50 hours and cooling after heating is performed to obtain a desired composition ratio (for example, Y IB arc Li2O7-i (0≦i≦0.
5), B f's r, Catc Ll! OX, T
An oxide superconducting powder having a composition of 1tCatB atCL+305 is obtained. In addition, in this intermediate sintering process,
When producing a Y-B a-Cu-0-based oxide superconductor, it is preferable to slowly cool it after heating.
When producing an S r-Ca-Cu-0-based oxide superconductor, it is preferable to heat it at 890°C for 20 minutes, then heat it at 880°C for 9 hours, and then rapidly cool it 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 and 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 solidified body for Y-Ba-Cu-0 type, but rapid cooling for B i-8r-Ca-Cu-0 type. There is no problem.

Next, the surface portion of the coagulated body thus obtained is scraped off to a thickness of lam or less, preferably several microns to several hundred microns, and the scraped portion is ground by a grinder to obtain a powder (separated material). 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. The solidified material after the surface portion has been scraped off is melted again and then solidified, and the surface is further scraped off repeatedly to be reused to obtain powder. In addition, the molten metal can be heated to 800~
By using a method of ejecting into a space at a temperature of 950° C. and pulverizing, the above-mentioned scraping step and pulverizing step may be omitted.

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 is.

Next, the powder is subjected to pressing means such as applying hydrostatic pressure with a rubber press to obtain a rod-shaped body. Note that this rod-shaped body may be heated to 800 to
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 rod-shaped body 1 described above is inserted into a metal tube 2 shown in FIG. 1 to create a composite body 3. The tube body 2 is made of Cu, Ag
s It is formed from a metal material such as Al, an alloy thereof, or stainless steel.

The material for forming the tube must be a non-oxidizing material that does not take away oxygen from the rod-shaped body, preferably a material that allows oxygen to pass through 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 along the illustrated path. 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 Moeki 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, but when performing the diameter reduction, other known forging methods could be used instead of using the rotary swaging device A shown in FIG. There is no problem in using a device, diameter reduction device, etc.

After reducing the diameter of the composite body 3 to a desired wire diameter by performing the diameter reduction process using the rotary swaging device A shown in FIG. A final sintering process is performed to produce an oxide superconducting conductor.

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 performed in an oxygen gas atmosphere at a temperature of 800 to 950
C. for about 6 to 50 hours, and then cooled. In addition, when manufacturing a Y-Ba-Cu-0-based oxide superconductor, it is preferable to slowly cool it after heating.
When producing an I-ca-B 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 efficiently transferred from the entire surface of the compacted body to the inside. It is well diffused and sintered to obtain an oxide superconductor.

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. Further, since the compacted body is heat-treated after being sufficiently compacted by the rotary swaging device A, a solid phase reaction is sufficiently carried out inside the compacted body, and an oxide superconductor with a high critical current density is generated. 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 Y;Ba
: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 IB atc L1307-8.

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 made into a powder with an outer diameter of 15 mm and an inner diameter of 10 mm.
The wire was filled into a silver tube and reduced in diameter by cold working using a rotary swaging device or a wire drawing machine to obtain a wire rod with a diameter of 1.0 +++ m consisting of an oxide core and a silver paste.

The silver sheath of this wire 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 J c = 1.5 x 10 'A/cm'' in the absence of a magnetic field, and 5
Even in a magnetic field of T, J c = 1 and OX 10 'A/am' were exhibited.

Incidentally, a mixed powder having the same composition as the mixed powder described above is calcined and filled into a silver sheath, and the diameter of this is reduced using a rotary swaging device, and then the silver sheath is dissolved and removed. Jc of a superconducting conductor is I
X l O'A/cm, and the Jc of other currently known oxide superconductors is approximately 0, j ~ I
It is approximately X l O'A/cm'.

However, these conventional oxide superconducting conductors have a Jc of 0.1 to 0.1 even in an IT magnetic field! X 10
It is known that the value 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 that undergoes a melt-diffusion reaction with a higher diffusion rate than a solid phase reaction, and a uniform solidified body is obtained from this solidified body. Since the oxide superconducting conductor is manufactured using powder having a specific composition, it is possible to manufacture a high-quality oxide superconducting conductor with a high critical current density. 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.

In addition, sufficient oxygen is supplied to the surface side of the solidified material obtained from the molten metal, producing an oxide superconductor with excellent characteristics. Therefore, if only this surface portion is collected to produce an oxide superconductor, criticality will occur. This has the effect of producing excellent oxide superconducting conductors with high current density.

[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, I3...Composite consolidated body, I4...
・Consolidated body,

Claims (2)

[Claims] (1) In a method for manufacturing 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. The solidified body obtained by solidifying this molten metal is filled into a metal tube to obtain a composite body, and the composite body is subjected to diameter reduction processing to form a composite consolidated body consisting of a consolidated body and a metal sheath. After removing the metal sheath of the composite compact,
A method for producing an oxide superconducting conductor, which comprises heat-treating a compact in an oxygen-present atmosphere. (2) In a method for manufacturing an oxide superconductor comprising a multi-element oxide superconductor, a molten metal containing each element constituting the oxide superconductor at a predetermined component ratio is formed. This molten metal is solidified and only the surface portion of the solidified body is separated to obtain a separated product, and then this separated product is filled into a metal tube to obtain a composite, and the composite is subjected to diameter reduction processing. After forming a composite consolidated body consisting of a consolidated body and a metal sheath, and then removing the metal sheath of this composite consolidated body,
A method for producing an oxide superconducting conductor, which comprises heat-treating a compact in an oxygen-present atmosphere.