JPH01175121A - Manufacture of oxide superconducting wire - Google Patents

Abstract

PURPOSE:To obtain a superconducting wire with high critical current density and excellent mechanical strength by adding acid and a basic material to a solution containing the constituting elements of an oxide superconductor to obtain a neutralized aqueous solution, crushing a mixture obtained by heating it to obtain a homogeneous fine grain powdery material, compressing it to the specific density and heat-treating it. CONSTITUTION:Citric acid or the like is added to an aqueous solution containing the elements constituting an oxide superconductor. A basic material such as ammonia is added into the aqueous solution and neutralizes it to obtain a neutralized aqueous solution with about pH 7. The neutralized aqueous solution is heated to obtain a sponge-shaped mixture. The mixture is crushed with a ball mill or the like to obtain mixed powder, it is dust-molded to produce a dust molded body 1. The molded body 1 is stored in a metal tube 2 to produce a composite body 3. The composite body 3 is shrinkage-processed by a rotary swaging device A, for example. The shrinkage processing is repeated until the density of a core becomes 75% or above of the theoretical density. A wire 13 thus obtained is heat-treated in the oxygen atmosphere to produce an oxide superconducting wire.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for producing an oxide superconducting wire that can be used for superconducting devices such as superconducting magnet coils, power transportation, and the like.

"Prior Art" Recently, various oxide-based superconducting materials have been discovered whose critical temperature (T c ) for transitioning from a normal conducting state to a superconducting state is higher than the temperature of liquid nitrogen.

As this type of oxide superconducting material, for example, the general formula A -
B -Cu-0 (A is La, Ce, Yb, Sc
, represents one or more elements of group IIIa of the periodic table such as Er,
B represents one or more elements of group Ila of the periodic table, such as Ba and Sr.

To manufacture this type of oxide superconductor by a powder method, a powder containing the Illa group element, a powder containing the Ila group element, and a copper oxide powder are mixed in an automatic mortar to prepare a mixed powder. After calcining the mixed powder, it is compacted into a predetermined shape, and the resulting compacted compact is heat-treated, and each element undergoes a solid phase reaction to produce a superconducting material. .

Further, as a method for manufacturing the A-B-Cu-0-based superconducting wire, filling a metal tube with the mixed powder or
Alternatively, a metal tube is filled with superconducting precursor powder obtained by heat-treating a mixed powder, and after filling, the metal tube is drawn using a die or the like to form a wire of a desired diameter, and then this wire is heat-treated. Each element undergoes a solid phase reaction inside the wire,
A method of obtaining a superconducting wire by producing an oxide superconductor in the core portion of the wire is known.

"Problems to be Solved by the Invention" By the way, in order to produce a high-quality oxide superconducting wire with a high critical current density by sintering the powder compact, a dense powder compact with a uniform composition must be heat-treated. It is necessary to carry out sufficient diffusion of each element during the solid phase reaction.

However, in the conventional powder mixing method described above, even if the raw material powders are mixed at a specified ratio during mixing, it is difficult to mix each element uniformly at the atomic level, and the distribution of each element cannot be completely uniform. As a result, the reactions of the elements become non-uniform, and superconductors are produced non-uniformly, making it impossible to manufacture oxide superconducting wires with high critical current density.

On the other hand, as a result of the present inventors measuring the compaction density of superconducting wire manufactured by the drawing method using a die, the compaction density was approximately 70 to 75% of the theoretical density (state of 0% porosity). there were. Therefore, according to the conventional method, since the core wire is heat-treated and sintered with insufficient consolidation density, the obtained superconducting wire does not undergo sufficient solid phase reactions of each element. There is a problem that a good critical current density cannot be obtained. In addition, as mentioned above, when superconducting wires are manufactured by sintering compacted compacts that are not sufficiently compacted, the internal porosity is relatively large, resulting in insufficient bending strength, etc. There are also problems with major dissatisfaction in terms of strength.

For this reason, when a superconducting wire is wound around a winding drum for use in winding a superconducting magnet, there is a risk that the superconductor is likely to crack, and the superconducting properties may be significantly degraded.

The present invention has been made in view of the above-mentioned problems, and aims to provide a method for producing an oxide superconducting wire having a uniform composition, a sufficiently high degree of compaction, exhibiting excellent superconducting properties, and having high mechanical strength. do.

"Means for solving the problem" In the present invention, an acid such as citric acid is added to an aqueous solution containing elements constituting an oxide superconductor, and then a basic material such as ammonia is added to this aqueous solution to neutralize it. The neutralized aqueous solution is then heated to obtain a mixture of the elements constituting the oxide superconductor, and this mixture is crushed to obtain a mixed powder, and this mixed powder is subjected to a powder compaction treatment. The compact is then filled into a metal sheath to form a composite, and the composite is subjected to diameter reduction processing to form a wire rod, and the degree of consolidation of the core wire within the wire is The solution was to set the density to 75% or more of the theoretical density and then heat treat it in an oxygen atmosphere.

The present invention will be explained in more detail below.

The oxide superconductor used in the oxide superconducting wire produced by the method of the present invention is of the A-B-Cu-0 series (however, A
are Y, Sc, La, Ce, Pr, Nd, Pm, Sm,
Eu.

B represents one or more elements of group IIIa of the periodic table, such as Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; B represents elements such as Sr, Ba, Ca, Be, Mg, and Ra; Indicates one or more elements from group IIa elements of the periodic table. ).

In order to manufacture an A-B-Cu-0 system superconducting wire by carrying out the method of the present invention, first, the above-mentioned A element, B element and Cu
Prepare an aqueous solution containing This aqueous solution is prepared by weighing and collecting soluble salts such as nitrates and acetates of each of these elements in a predetermined mixing ratio, and then dissolving them in a certain amount of water. The blending amount of each raw material is, for example, Y-Ba-Cu-0 based superconductor, Y:Ba
:Cu=1:2:3 (molar ratio) is preferable. In addition, the concentration of this aqueous solution is appropriately determined depending on the type of soluble salts to be dissolved, but is 0.5
It is desirable to set it to about 10%. In addition, in order to obtain the aqueous solution, oxides and carbonates of the respective elements, for example,
It may be created by weighing and collecting each raw material such as Y t O3, B a CO3, Cu 2 O, etc., placing it in a container, and adding a predetermined amount of nitric acid aqueous solution or acetic acid aqueous solution into this container to dissolve each raw material. .

Next, an acid is added to this aqueous solution. As the acid used here, carboxylic acids such as citric acid, succinic acid, and tartaric acid are preferred. The amount of acid added to the aqueous solution is appropriately selected depending on the type of acid used, and when citric acid is used, it is preferable to add about 5 to 20 parts by weight of citric acid to 100 parts by weight of the aqueous solution.

Next, a basic material is added to this aqueous solution to neutralize it, preferably to obtain a neutralized aqueous solution with a pH of about 7.

The basic material used here includes ammonia, ammonium carbonate, guanidine, ammonium acetate, etc., and aqueous ammonia is particularly preferably used. Basic materials such as ammonia water neutralize the acid in the aqueous solution and raise the pH.
It is preferable to add a tonne necessary to make it about 7.

Next, this neutralized aqueous solution is heated. By heating this neutralized aqueous solution, the water in the aqueous solution first evaporates, and then the acids and basic materials dissolved in the aqueous solution are thermally decomposed and gradually reduced, and finally A - B - Oxides or carbonates of each element constituting the Cu-0-based superconductor, such as Y 203. A spongy solid (mixture) in which BaCO3+CuO and the like are uniformly mixed is obtained.

Then, this mixture is further heated to make it thicker.

Note that when acids and basic materials undergo thermal decomposition, they foam and ignite, so place the neutralized aqueous solution in a large capacity container and heat it to prevent the contents from leaking due to foaming and to adjust the heating temperature. It is preferable to take appropriate measures such as:

Next, the mixture is pulverized using a device such as a ball mill or an automatic mortar to obtain a mixed powder with uniform particle size. The sponge-like mixture is an aggregate of fine particles with a particle size of about 0.1 to 0.6 μm, so by crushing this, a mixed powder of fine particles with a particle size of about 0.1 to 0.6 μm is obtained. can be easily obtained.

Subsequently, the mixed powder is heated, for example, at 500 to 1100°C.
- Perform calcination treatment by heating for about 100 hours. and,
The firing atmosphere in this calcination treatment has an oxygen content of 90
It is desirable that the oxygen atmosphere is at least vol%. If such a calcination treatment is performed, the density after the subsequent sintering treatment can be improved, and the constituent elements in the powder compact can be sufficiently reacted with each other.

Next, the calcined product thus calcined is subjected to a powder compaction treatment to produce a powder compact. For example, cold isostatic pressing, hot isostatic pressing (1-
Methods such as isostatic pressing such as 11P) are preferably used, but the method is not limited to these methods, and any method can be used as long as the above-mentioned starting material can be pressure-molded into a powder compact with a desired compaction density. , any method can be used. For example, a metal tube filled with the above-mentioned starting material is subjected to drawing processing using a die, rotary swaging processing, rolling processing, etc., one type or a combination of two or more types, to reduce the diameter of the metal tube, and the above-mentioned mixed powder is transformed into the desired powder. A method of forming a green compact with a high degree of compaction may also be used. The compacting pressure in the above-mentioned powder compacting process is determined depending on the type of starting material, the compaction degree of the compact to be achieved, etc., and is usually 1.5 to 10 tons.
/ am”.

Subsequently, the powder compact was heated at 800 to 1100°C for 1 to 10 minutes.
A firing process is performed in which the material is heated for 0 hours and then slowly cooled. and,
The firing atmosphere is preferably an oxygen atmosphere having an oxygen content of 90% by volume or more.

Furthermore, the above-mentioned starting material may be repeatedly subjected to a series of treatments consisting of calcination treatment, powder compaction treatment, and firing treatment once or twice or more.

Next, the powder compact produced as described above is housed in a metal tube (metal sheath) 2 as shown in FIG. 1 to produce a composite 3. The tube body 2 used here includes Cu
SAg, A (! or alloys thereof, or metal materials such as stainless steel are used. The material for forming the tube body 2 is not limited to metal materials as long as it can be plastically worked. , powder compact l during heat treatment
It is necessary to select a non-oxidizing material that does not take away oxygen from the surface. 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 2.

Next, in this example, the composite body 3 is subjected to a diameter reduction process using a rotary swaging device A as shown in FIG.

This rotary swaying device A includes a plurality of dice 6 movably provided by a drive device along the illustrated path.
・It is equipped with the following. 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 performing diameter reduction processing on the composite body 3 is formed on the inner surface of each die 6, and the gap surrounded by the tapered surface 6a of each die 6 is formed first. It has become narrowed.

To reduce the diameter of the composite body 3, the rotary swaging device A is operated and one end of the composite body 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 vertical direction in FIG.
is sequentially forged from one end side and reduced in diameter to the wire diameter shown by the two-dot chain line in FIG. In this diameter reduction process, since the composite body 3 is forged and reduced in diameter by a plurality of dies 6 that rotate and reciprocate, a large processing rate can be achieved without causing wire breakage in the composite body 3 during the diameter reduction process. Diameter processing is possible.

Such diameter reduction processing is performed until the wire diameter of the wire rod 13 reaches a desired wire diameter and the consolidation density of the core wire within the wire rod 13 is 75% of the theoretical density.
% or more, preferably 77% or more. If the compaction density of the core wire is less than 75% of the theoretical density, the compaction density is too small and there is a limit to the sintered density even if the core wire is subjected to post-process heat treatment. This causes the inconvenience that the characteristics become extremely poor. If the desired wire diameter and consolidation density cannot be achieved by processing using the rotary swaging device A, a rotary swaging device equipped with a die having a forming gap smaller than the forming gap of the die 6 of this device A may be used. It is necessary to repeatedly reduce the diameter using a swaging device or the like.

The wire rod 13 thus obtained is subjected to the treatment described below to produce an oxide superconducting wire.

First, the tube portion serving as the outer metal sheath is removed from the wire 13, thereby exposing the core wire portion. To remove the metal source here, for example, a chemical method may be used in which the composite is immersed in a treatment liquid such as an aqueous acid or alkali solution, and only the metal source is dissolved in the treatment liquid. In this method, when copper, silver, or an alloy of these is used for the metal sheath, dilute nitric acid is used as the treatment liquid, and when aluminum is used for the metal sheath, caustic soda is used as the treatment liquid. When stainless steel is used, aqua regia or the like is used as the treatment liquid, but the combination of the sheath material and the treatment liquid is not limited to these. After such a removal operation, it is desirable to immediately wash or neutralize the surface of the core wire to eliminate the influence of the treatment liquid on the core wire.

Note that cutting may be another method for removing the metal sheath, but if this cutting is used, if the core wire is small in diameter, it may cause inconveniences such as bending during the removal operation. .

For this reason, in this example, we adopted the chemical method described above, which is unlikely to cause the above-mentioned disadvantages to the core wire, but if there is little risk of bending, a method of removing the metal sheath by cutting may also be used. , both a method of chemically removing the metal source and a method of mechanically removing the metal source may be used in combination.

Next, the core wire thus exposed is subjected to heat treatment. This heat treatment is performed at, for example, 800 to 1100°C.
This is done by slowly cooling the mixture for about 1 to 100 hours. The treatment atmosphere in this heat treatment is preferably an oxygen atmosphere with an oxygen content of 90% by volume or more.

This is to supply sufficient oxygen necessary for the superconductor produced in the core wire to be treated, and to produce a single-phase, uniform superconductor exhibiting good superconducting properties in the core wire.

In addition, the oxygen gas used to make the treatment atmosphere for this heat treatment the above-mentioned specific oxygen atmosphere has a purity of 90%.
Those with higher purity are preferred.

Then, the above-mentioned specific oxygen atmosphere can be obtained by flowing the oxygen gas with such high purity toward the object to be treated. It is preferable that the flow rate of the high-purity oxygen gas at this time is usually in the range of 0.5 to 5 C/min.

Furthermore, this heat treatment is preferably performed under pressurized conditions exceeding atmospheric pressure. In this case, the pressure of oxygen gas is preferably determined in the range of 1.5 to 5 atm.

In addition, the oxygen atmosphere in this heat treatment may contain elements of group II of the periodic table such as S, Se, Te, Po, and F.
, C1, Br, etc., gases of group ■b elements of the periodic table, or H
Inert gases such as e, Ne, Ar, Kr, Xe, and Rn can be mixed. Each element other than oxygen in the heat treatment atmosphere becomes a constituent element of the obtained superconductor and contributes to improving the superconducting properties of the superconductor.

In addition, during the slow cooling in the above heat treatment, 400 to 600
The crystal structure of the oxide superconductor may be maintained at a temperature range of .degree. C. for a predetermined period of time to promote the transformation of the crystal structure from a tetragonal structure to an orthorhombic structure.

The core wire whose consolidation density has been improved to 75% or more by processing with the rotary swaging device is such that the heat treatment causes a sufficient solid phase reaction between the constituent elements in the core wire, and the surface of the core wire is Since the core wire is exposed, oxygen atoms are efficiently diffused from the entire surface of the core wire into the core wire. Therefore, the above-mentioned core wire has, for example, A
A -B-Cu-0-based oxide superconductor is produced, and thereby an oxide-based superconducting wire exhibiting good superconducting properties is obtained.

Then, such an oxide-based superconducting wire can be subjected to a coating treatment to form a protective coat layer, if necessary. As the material for forming this protective coat layer, for example, low melting point metals such as tin and lead, alloys such as solder, etc. are suitably used.

As a method for forming this protective coat layer, methods such as electroplating, melt plating, and solder plating are suitably used. Alternatively, a method may be used in which the powder of the low melting point metal or the alloy powder is applied to the surface of the oxide superconducting wire to a predetermined thickness and then the powder is sintered. By forming a protective coating layer in this way, it is possible to reliably prevent, for example, the dissipation of oxygen elements from the superconductor or the adhesion of moisture to the superconductor, so that the good superconducting properties of the oxide-based superconducting wire can be maintained for a long time. It can be made stable over time.

According to this manufacturing method, by performing forging at least once using the rotary swaging device A, the powder compact in the composite body 3 is sufficiently consolidated, and the core wire has a consolidation density of 75% or more of the theoretical density. A wire rod 13 is obtained, and then, after removing the metal sheath from this wire rod 13, heat treatment is performed in an oxygen atmosphere so that each element in the core wire undergoes a solid phase reaction, and the elements are smoothly diffused. From this, it is possible to produce an oxide superconducting wire that has low porosity, high mechanical strength such as bending strength, and exhibits good superconducting properties that are uniform in the longitudinal direction. Therefore, the oxide superconducting wire obtained in this way is resistant to bending and has good flexibility, so it can be wound without cracking and is suitable for winding for superconducting magnets. Become something.

Furthermore, if the compact 1 is fired in a specific oxygen atmosphere to form the composite 3, the sintered density of the compact 1 can be significantly improved by the firing process.
By reducing the diameter of the composite 3, it is possible to obtain a wire having a core wire with an extremely high degree of consolidation. Then, after removing the tube part of this wire and exposing the core wire part,
Further, by heat treatment in an oxygen atmosphere, an oxide-based superconducting wire exhibiting good superconducting properties can be manufactured.

In this example, rotary swaging was used to reduce the diameter of the composite 3, but the present invention is not limited to this, and processing methods such as rolling may also be suitably used.

Examples are shown below.

"Example" Based on the method of the present invention, a Y-B a-Cu-0 based superconducting wire was manufactured. First, Y:Ba:Cu=1:2
:9.0791g of Y t O3 so that
BaCO3 31.7451g, CuO 19.18g
58g was weighed and put into a beaker.

Next, put 80ml of 60% nitric acid aqueous solution into the beaker.
Each raw material powder was completely dissolved. Next, 120 g of citric acid was added to this aqueous solution and thoroughly stirred to completely dissolve it.

Next, while checking the pH of this aqueous solution with a hydrogen ion concentration meter, 28% ammonia water was added to neutralize it to obtain a blue transparent liquid (neutralized aqueous solution) with a pH of 7. Next, this neutralized aqueous solution was heated to 200°C. This heating causes the neutralized aqueous solution to
The water evaporates and becomes a viscous liquid, followed by foaming, likely due to thermal decomposition of ammonium nitrate and citric acid, forming a porous mass, which then decomposes with ignition, leaving a spongy mass of the mixed material. Ta. When this mixed material was investigated by X-ray diffraction, Y to s,
It turned out to be a mixture of BaCO3 and Cuo.

The mixture was further crushed in an automatic mortar for 30 minutes to obtain a powder. This pulverization process can be easily performed because the mixture is in the form of porous lumps, and the particle size is 0.1 to 0.6.
A powder of about μm size could be obtained.

Next, this powder was calcined by heating at 900°C for 24 hours in an oxygen stream, and then pulverized in a ball mill, and then subjected to powder compaction at a compacting pressure of 2.5 t/cm'. A rod-shaped powder compact was obtained. next,
This powder compact was heated at 890°C in an oxygen gas atmosphere.
A heat treatment was performed for 12 hours. A powder compact having an outer diameter of 6.9 mm was obtained by repeating a series of steps consisting of pulverization, compaction, and heat treatment three times.

Next, this green compact was filled into a silver tube having an outer diameter of 10 mm and an inner diameter of 7 mm to form a composite. Next, using a rotary swaging device equipped with a die having a configuration similar to that shown in FIG.
The diameter was gradually reduced while cold forging until it became a wire rod.

When we measured the consolidation density of the wire rod after forging, it was found that the theoretical density was 8.
It was 2%.

Next, the wire was immersed in nitric acid to dissolve and remove the silver sheath to expose the core wire. And further in an oxygen atmosphere 8
A heat treatment of heating to 90° C. for 12 hours and then slow cooling was performed to generate an oxide superconductor and obtain a superconducting wire.

The superconducting wire manufactured as described above has a critical temperature
91 showed a critical current density of about 11000 A/cm2 (at 77 K). Note that the core wire portion of the oxide superconducting wire exhibited a consolidation density of 91% or more.

From the above, it is clear that the oxide-based superconducting wire manufactured by implementing the present invention has high mechanical strength due to the high degree of compaction in the core wire portion, and has excellent superconducting properties such as critical current density. became.

"Effects of the Invention" As explained above, according to the manufacturing method of the present invention, an acid and a basic material are added to a solution containing constituent elements of an oxide superconductor to obtain a neutralized aqueous solution, and this is heated. The resulting mixture is pulverized to obtain a starting material in the form of homogeneous fine particles, which is then consolidated to 75% or more of the theoretical density and heat treated to produce superconducting wire. Since a diffusion reaction can be caused and the sintered density can be improved, it is possible to produce a superconducting wire with high critical current density and excellent mechanical strength. In addition, since the mixture obtained by heating the neutralized aqueous solution is an aggregate of fine particles, fine particle powder can be easily obtained by crushing it, and since superconducting wire is manufactured from this fine particle powder, atomic This has the effect of allowing the solid phase reaction to occur smoothly and producing superconducting wires with excellent properties.

Therefore, when the oxide-based superconducting wire manufactured according to the present invention is wound around a winding drum to be used as a winding wire for a superconducting magnet, it can be wound without causing cracks.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a rotary swinging device used in carrying out the present invention. 1...Powder compact, 2...Tube body (metal tube), 3...
・Composite, 6...Dice, 13...Wire, A...
Rotary swaging device.

Claims (1)

[Claims] An acid such as citric acid is added to an aqueous solution containing elements constituting an oxide superconductor, then a basic material such as ammonia is added to this aqueous solution for neutralization, and then this neutralized aqueous solution is heated to A mixture of elements constituting the oxide superconductor is obtained, this mixture is pulverized to obtain a mixed powder, this mixed powder is subjected to powder compaction treatment to form a compact, and then the compact is made into a compact. After filling a metal sheath to form a composite, the composite is subjected to diameter reduction processing to form a wire rod, and the compaction density of the core wire within the wire rod is reduced to 75% of the theoretical density.
% or more, and then heat-treated in an oxygen atmosphere.