JPH01246717A - Oxide superconductive wire and its manufacture - Google Patents

Abstract

PURPOSE:To increase the critical current density by heating a wire material which consists of a sintered body of an oxide superconductor to fuse the outer circumference in a desired thickness, then, solidifying it, and providing a coverage of the solidified body. CONSTITUTION:A powder of an oxide superconductor or a mixture powder of it is baked temporarily, smashed, and pressed further to get a formation 3. Then the formation 3 is sintering-processed intermediately to obtain an intermediate sintered body 4. The intermediate sintered body 4 is inserted to a metallic tube body 5 to form a composite 6. Then, the composite 6 is diameter-reduction-processed to get a composite consolidated body 13, from which the outside sheath material is removed, to expose the inside consolidated body 14. After that, a thermal treatment is applied in the oxygen ambiance to the consolidated body 14 to obtain a sintered body. Since the oxide superconductor which consists of the sintered body has been sintered after consolidated sufficiently by the forging process in the diameter-reduction process, the solid phase reaction is made sufficiently, and a high critical current density is obtained. Furthermore, by the oxygen ion beam radiation at the solidification process of the outer circumference of the conductor 5, a uniform and high critical temperature is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an oxide superconducting wire, which is being developed for use in superconducting magnet windings, power transmission lines, etc., and a method for manufacturing the same.

"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.

Conventionally, as an example of a method for producing an oxide superconducting wire comprising this type of oxide superconductor, a plurality of raw material powders containing elements constituting the oxide superconductor are prepared, and this mixed powder is calcined. 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 atmosphere to cause a solid phase reaction in the compacted powder inside. A method of producing an oxide superconductor is known.

"Problems to be Solved by the Invention" However, in the case of oxide superconducting wire manufactured by the conventional method described above, the oxide superconductor is produced by causing a solid phase reaction in the compact obtained by compacting the powder. Since it is generated,
Inside the produced oxide superconductor, there are many grain boundaries formed by the interfaces of powder particles, and the grain boundaries have the disadvantage of having fine pores and defects. That is, such an oxide superconductor has a structure in which a large number of powder particles are bonded together,
Due to the structure in which current flows through the contact portions of the powder particles, there was a problem in that the critical current density could not be increased. In addition, the conventional oxide superconductors have the disadvantage of low mechanical strength due to the formation of fine pores in the grain boundaries, and cracks occur when coil processing is performed to manufacture superconducting magnets. There was an easy problem.

By the way, recent research has revealed that in the oxide superconducting wire mentioned above, although the overall critical current density is low, the superconducting current flowing through each particle inside the oxide superconductor is extremely high. It has been observed that a current that is 100 to 10 times higher than the critical current shown by the oxide superconducting wire flows inside the particles.

The present invention was made in order to solve the above-mentioned problems based on ideas based on the above-mentioned recent research results, and its purpose is to provide a high-performance oxide superconducting wire with a high critical current density. do.

"Means for Solving the Problems" The present invention provides a core wire portion made of a sintered body of an oxide superconductor;
A means of solving the problem was to provide a covering portion made of a solidified body of an oxide superconductor.

The method of the present invention involves heating a wire made of a sintered body of an oxide superconductor, melting the outer circumferential side of the wire to a required thickness, and then solidifying the wire, thereby forming a covering part made of a solidified body of an oxide superconductor, and a wire made of a sintered body of an oxide superconductor. The method of solving this problem was to manufacture an oxide superconducting wire consisting of a core wire portion made of a sintered body and a core wire portion made of a sintered body. In addition, a means to solve the problem was to perform solidification while irradiating an oxygen ion beam during the solidification.

"Operation" Compared to sintered bodies, solidified bodies of oxide superconductors exhibit a high critical current density because they have no pores and no grain boundaries. Also,
By leaving the sintered body of the oxide superconductor on the center side of the wire and melting only the outer peripheral side, the shape of the wire is maintained during melting and deformation is prevented. Note that if the oxide superconductor is irradiated with an oxygen ion beam during solidification, more oxygen atoms can be contained inside the oxide superconductor, and the properties will be improved.

The present invention will be explained in more detail below.

FIG. 1 shows an example of the oxide superconducting wire of the present invention. The oxide superconducting wire A shown in FIG. and a covering layer 2 made of a solidified body of oxide superconductor surrounding the oxide superconductor.

In order to carry out the present invention and manufacture the oxide superconducting wire A shown in FIG. 1, starting materials are first prepared. As the starting material, an oxide superconductor powder, a material containing elements constituting the oxide superconductor, or a mixture thereof is used.

The above-mentioned oxide superconductors include A-B-C-D system (where A is Y, Sc, La, Ce, Pr, Nd, P
m.

S m, E u, G d, T b, D y, Ho, E
Indicates one or more of the group MA elements of the periodic table such as r, T m, Y b, and Lu, or the group Vb elements of the periodic table such as Bi, or the group II b elements such as TI, and B teeth,
Sr, Ba, Ca, Be.

Represents one or more of the Ila group elements of the periodic table such as Mg and Ra, and C represents Cu or two or more of the periodic table Ib group elements such as Cu, Ag, and Au and Nb, including Cu or Cu. , D indicates O or 0 and AI. ) are used.

In addition, materials containing elements constituting the oxide superconductor include powders containing elements of group Ua of the periodic table and
A powder containing a group A element or a group VB element of the periodic table, and A1
A mixed powder consisting of a powder containing an element of group 11Ib of the periodic table, such as copper oxide powder, a calcined powder of this mixed powder, or a mixed powder of the above mixed powder and calcined powder, etc. are used. The powders containing Group Ila elements of the periodic table used here include Be, Sr, Ca, Mg, B
These include compound powders or alloy powders such as carbonate powders, oxide powders, chloride powders, sulfide powders, and fluoride powders of each element of a and Ra. In addition, powders containing group ma elements of the periodic table include Sc, Y, La, Ce, Pr, Nd,
Pm, Sm.

Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, L
Compound powders or alloy powders such as oxide powders, carbonate powders, chloride powders, sulfide powders, fluoride powders, etc. of each element of u are used, and powders containing group '■b elements of the periodic table include: It is a compound powder or alloy powder of an element such as Bi, and a compound powder or alloy powder of an element such as TI is a group (ii)b group element.

Further, examples of the copper oxide powder include CuO, Cu, and O.

Powders such as Q, u30t, Cu, 03 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 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 have a uniform particle size, mixed, and compacted by a pressing method such as a rubber press method to obtain a rod-shaped compact 3 shown in FIG. The method for compacting the pulverized material here is not limited to the method described above, and any method can be used as long as the pulverized material can be pressure-molded into a compacted compact of the desired compacted charcoal. . Note that a series of steps including calcination treatment, pulverization treatment, compaction treatment, etc. may be repeated one or more times. The calcination treatment is a treatment for decomposing and removing impurities such as carbonate and carbon, if they are contained in the mixed powder.

Next, the molded body 3 was heated for 800 minutes in an oxygen-containing atmosphere.
A rod-shaped intermediate sintered body is obtained by heating at ~950° C. for 6 to 50 hours and performing an intermediate sintering process of slow cooling or rapid cooling after heating. In addition, in this intermediate sintering process, 890
The heat treatment may be performed in two steps, such as heating at 880° C. for 20 minutes and then heating at 880° C. for 9 hours.

Next, the intermediate sintered body 4 manufactured as described above is inserted into a metal tube 5 shown in FIG. 3 to create a composite body 6. The tube body 5 is made of a metal material such as Cu, Ag, AI, an alloy thereof, or stainless steel. Note that the constituent material of the tube body 5 needs to be selected from a non-oxidizing material that does not take away oxygen from the intermediate sintered body 4, and preferably 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 6 is subjected to a diameter reduction process using a rotary swaging device B shown in FIG. This rotary swaging device B includes a plurality of dice IO movably provided by a drive device (not shown). These dice 10 are provided around a movement space when the rod-shaped composite body 6 is moved in its length direction so as to surround this movement space, and are arranged in a direction perpendicular to the movement space (in the direction perpendicular to the movement space). It is held movably in the direction of arrow a shown in FIG. 1) and rotatably around the movement space (in the direction of arrow a shown in FIG. 1). Further, a tapered surface 10a for reducing the diameter of the composite body 6 is formed on the inner surface of each die IO, so that the gap surrounded by the tapered surface 10a of each die IO becomes tapered. ing.

In order to reduce the diameter of the composite body 6, the rotary swaging device B is operated, and one end of the composite body 6 is pushed into the gap between the dies 10 as shown in FIG.
Sink into it. Here, the dice 10... are indicated by the arrow a in FIG.
Since the composite body 6 is rotated while reciprocating at a predetermined interval in the direction, the diameter of the composite body 6 is reduced while being sequentially forged from one end side to the wire diameter shown in FIG. 4, and a composite consolidated body 13 is obtained. In this diameter reduction process, the diameter is reduced while forging the composite body 6 using a plurality of rotating and reciprocating dies IO, so that the composite body 6 is reduced in diameter at a high processing rate without causing wire breakage. Diameter processing is possible.

In this example, the rotary swaging device B was used to reduce the diameter of the composite 6, but when performing the diameter reduction, other known forging methods could be used instead of using the rotary swaging device B shown in FIG. There is no problem in using a device, diameter reduction device, etc.

After the composite compact I3 is reduced in diameter to a desired wire diameter by the rotary swaging device B shown in FIG. 4, the composite compact I3 is subjected to the sheath removal process described below and a final sintering process to produce an oxide superconductor.

That is, the tubular portion serving as the outer metal sheath material is removed from the composite compacted body 13, thereby removing the inner compacted body 1.
Expose 4. To remove the metal sheath material, for example, the composite compacted body I3 is immersed in a treatment solution such as an acid such as nitric acid or an aqueous alkali solution such as caustic soda, and only the metal sheath material is dissolved in the treatment solution. chemical methods are used.

Note that as a method for removing the metal sheath material, 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 material to remove it.

Next, the compacted body exposed in this way! 4 is subjected to heat treatment to obtain a sintered body. This heat treatment is performed by heating at 800 to 950° C. for about 0.1 to 50 hours in an oxygen atmosphere, and then cooling slowly or rapidly.

Due to the above-mentioned heat treatment, the constituent elements in the compacted body I4 sufficiently cause a solid phase reaction with each other, and the surface of the compacted body I4 is exposed, so that the compacted body!
An oxide superconductor made of a sintered body in which oxygen is efficiently diffused from the entire surface of 4 into the interior! 5 is obtained. Oxide superconducting conductor 15 made of the sintered body produced in this way
Since it is sintered after being sufficiently compacted by forging during diameter reduction processing, a solid phase reaction occurs sufficiently, and the critical current density is approximately 103 to IO'A/cta''.

Furthermore, in this example, the oxide superconducting wire A shown in FIG. 1 is manufactured by performing the processing described below.

First, the oxide superconducting conductor 15 is introduced into a high frequency induction melting device to melt the outer peripheral side of the oxide superconducting conductor 15 to a required thickness, and then is cooled and solidified. Note that during this solidification, an oxygen ion beam may be irradiated to increase the oxygen concentration in the oxide superconductor.

To perform this melting and solidification, for example, a high frequency induction melting apparatus C shown in FIG. 5 is used.

The device shown in FIG. 5 consists of a heat-resistant tube 20 made of heat-resistant Pyrex glass, quartz glass, etc. and having an inner diameter of about 10 to 2 oIIIll, a high-frequency coil 21 arranged around the outer periphery of the heat-resistant tube 20, and a high-frequency coil 21 fixed to the outer surface of the heat-resistant tube 20. Sushi heat resistant tube 2
0 and a gas supply pipe 22 that communicates with the inside of the tank. A high frequency current of several kHz to several hundred kHz is applied to the high frequency coil 21 by a power source as shown in the diagram, so that the high frequency coil 21 generates tkw-io.

An output of approximately kW can be obtained. In addition, heat-resistant tube 2
Behind the terminal part of 0, there is an oxygen ion irradiation device 30...
is installed so that it can surround the oxide superconducting conductor 15 that has passed through the heat-resistant tube 20. These irradiation devices 30 are configured to be able to irradiate molecular, atomic, or ionic oxygen. In addition,
As the irradiation device 30, it is also possible to use a configuration that can irradiate oxygen ions together with a carrier gas such as an inert gas.

The oxide superconducting conductor 15 is fed into the heat-resistant tube 20 at a predetermined linear speed, and the high frequency coil 2I is energized to heat the oxide superconducting conductor I5. In addition, oxide superconducting conductor! 5 is passed through the heat-resistant tube 20, the passing speed and the output of the high-frequency coil 21 are adjusted so that only a predetermined thickness of the outer peripheral surface of the oxide superconducting conductor 15 is melted.

When the oxide superconducting conductor 15 is pulled out from the heat-resistant tube 20 after the outer peripheral side of the oxide superconducting conductor I5 is melted, the melted portion is cooled and solidified. Through this treatment, the coating layer 2 made of the solidified body of the oxide superconductor can be formed on the outer peripheral side of the oxide superconducting conductor 15, and the coating layer 2 made of the solidified body of the oxide superconductor and the sintered body of the oxide superconductor can be formed. It is possible to obtain the oxide superconducting wire A shown in FIG. 1, which includes a core wire portion l made of a solid body. Further, when the oxide superconducting conductor 15 is pulled out from the heat-resistant tube 20 and cooled, the oxygen ion irradiation device 30 can be operated to irradiate the entire circumference with oxygen ions while cooling. Note that if the outer circumferential side of the oxide superconducting conductor 15 is completely melted, there is a risk that the melted portion will fall off, so this melt should be melted to an extent that can prevent falling off.

The coating layer 2 formed by melting and then solidifying the oxide superconductor 15 has no pores inside and has a much higher density than the sintered body, so it is a dense and homogeneous oxide. Becomes a superconductor. Therefore, this portion of the covering layer 2 exhibits a higher critical current density than the sintered body. Therefore, the oxide superconducting wire A produced in this manner is superior in that it exhibits a higher critical current density than an oxide superconductor made entirely of a sintered body.

Furthermore, since the coating layer 2 does not have fine pores that are found in ordinary sintered bodies, its mechanical strength is high.

Therefore, the oxide superconducting wire A does not produce defects such as cracks even if it is processed into a coil to form a superconducting magnet. Furthermore, if the oxide superconducting wire A is manufactured while irradiating oxygen ions, it is possible to cool the oxide superconductor 15 while supplying even more oxygen to the inside of the crystal. Oxygen is sufficiently taken in to produce a more homogeneous oxide-based superconducting material with a high critical temperature, and an oxide superconducting wire A is obtained.

[Example 1] Calcination treatment in which a mixed powder is prepared by mixing Y, 03 powder (4N), B a CO3 powder (3N), and CuO powder (3N), and this mixed powder is heated at 900° C. for 24 hours. The calcined powder was compacted into a rod shape with a diameter of 10 mm using a rubber press. Thereafter, the rod-shaped body was sintered at 890° C. for 14 hours in an atmosphere containing oxygen to obtain a rod-shaped sintered body.

Next, this sintered body was inserted into an Ag sheath with a diameter of 1.5 mm.
A wire rod was obtained by swaging to III11.

Subsequently, the Ag sheath of this wire was dissolved and removed with a nitric acid aqueous solution to reduce the diameter to 1.

The core wire of 0.0 mm was exposed and further heat treated at 890° C. for 14 hours in an oxygen atmosphere to obtain an oxide superconducting conductor made of a sintered body. The critical current density of this oxide superconductor is 5 x 103A at 77K.
/cm”.

Next, this superconducting conductor was passed through a high frequency induction heating furnace with an output of 50 kW at a linear speed of 5 m/min, and heated at 100 kW in the high frequency induction heating furnace.
A high frequency of Hz is applied to melt the surface layer of the oxide superconductor to a thickness of about 100 μm, and the material is pulled out from a high frequency induction heating furnace and solidified, while an ion beam (accelerating voltage :1.5 kV) from four directions to provide sufficient oxygen to the superconductor, and then solidify the molten layer to obtain an oxide superconducting wire. The oxide superconducting wire thus obtained was able to maintain a circular cross-section.

This oxide superconducting wire has IO'A/cm' at 77K.
The critical current density was 95K, and the critical temperature was 95K.

“Example 2” B! Bi: z03 powder, 5rCOa powder and CuO powder:
A mixed powder was prepared by mixing Sr:Ca:Cu=l:I:I:2, and this mixed powder was heated at 800°C.
The powder was calcined by heating for 10 hours, and the calcined powder was compacted into a rod shape with a diameter of 10 a+m using a rubber press.

After this, the rod-shaped body was heated at 820°C for 8 hours, and further heated at 850°C.
Both were sintered at ℃ for 2 hours in an oxygen atmosphere to obtain rod-shaped sintered bodies. Next, the sintered body was inserted into a sheath made of Ag and swaged to a diameter of 1.5 mff1 to obtain a wire rod. Next, the Ag sheath of this wire was dissolved and removed in a dilute nitric acid aqueous solution to expose the core wire with a diameter of 1.0 ms+, and then heat-treated in the atmosphere at 870°C for 10 hours to form an oxide made of a sintered body. A superconducting conductor was obtained. The critical current density of this oxide superconductor was 1xLO3A/am'' at 77K.

Next, this superconducting conductor was passed through a high frequency induction heating furnace with an output of 50 kW at a linear speed of 5 m/min, and heated at 100 kW in the high frequency induction heating furnace.
A high frequency of Hz was applied to melt the surface layer portion of the oxide superconducting conductor to a thickness of about 100 μm, and the conductor was pulled out of a high frequency induction heating furnace to solidify the molten layer to obtain an oxide superconducting wire. The obtained oxide superconducting wire was able to maintain a circular cross-sectional shape and was not deformed.

This oxide superconducting wire is Critical temperature: 103K.

The critical current density was 5×I O3A/cm”.

"Effects of the Invention" As explained above, the present invention includes a core wire made of a sintered body of an oxide superconductor inside, and a coating layer made of a molten solidified body of an oxide superconductor on the outer peripheral side. Since the outer peripheral side coating layer does not have fine pores or grain boundaries that exist in a sintered body, it exhibits an extremely high critical current density. Therefore, the oxide superconducting wire of the present invention exhibits a higher critical current density than an oxide superconducting wire made of a sintered body. Furthermore, since the coating layer does not have fine pores that are found in sintered bodies, the mechanical strength is also increased. Therefore, even when coil processing is performed using the oxide superconducting wire of the present invention, cracks do not occur, and a crack-free superconducting magnet can be manufactured.

In addition, by heating the sintered oxide superconductor to melt and solidify the outer circumferential side to the required thickness, we have created an oxide superconductor that is dense with no pores, has high mechanical strength, and has a high critical current density. This has the effect that the wire can be manufactured easily.

In addition, by irradiating an oxygen ion beam during solidification, it is possible to supply a sufficient amount of oxygen to the oxide superconductor and manufacture an oxide superconducting wire, which makes it possible to manufacture an oxide superconducting wire that is more homogeneous and has a higher critical temperature. effective.

[Brief explanation of the drawing]

Figures 1 to 5 show one embodiment of the present invention; Figure 1 is a cross-sectional view of an oxide superconducting wire, Figure 2 is a cross-sectional view of a rod-shaped body, and Figure 3 is a cross-sectional view of a composite wire. FIG. 4 is a cross-sectional view showing a state in which the diameter is reduced using a rotary swaging device, and FIG. 5 is a perspective view showing a state in which heat treatment is performed using a high-frequency induction heating device. . A... Oxide superconducting wire, B... Rotary swaging device, C... High frequency induction heating device, 1... Core wire portion, 2... Coating layer, 3... Rod-shaped body,
6... Composite, 13... Composite consolidated body, I4... Consolidated body, 15... Oxide superconducting conductor.

Claims (3)

[Claims] (1) An oxide superconducting wire characterized by comprising a core wire portion made of a sintered body of an oxide superconductor and a covering portion made of a solidified body of an oxide superconductor. (2) By heating the outer periphery of a wire made of a sintered body of an oxide superconductor, melting the outer circumference of the wire to a required thickness, and then solidifying the coated part made of a solidified body of an oxide superconductor. and a core wire portion made of a sintered body of an oxide superconductor. (3) The method for producing an oxide superconducting wire according to claim 2, wherein the outer peripheral side of the wire is melted to a required thickness and then, when solidified, the surface thereof is irradiated with an oxygen ion beam.