JPH01246716A - Oxide superconductive wire - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to oxide superconducting wires that 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.

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 an in-phase reaction in the compacted powder inside. Methods of producing oxide superconductors are known.

``Problems to be Solved by the Invention'' However, in the case of oxide superconducting wires manufactured by the conventional method mentioned above, oxide superconductors are produced by causing a solid phase reaction in a compact obtained by compacting powder. is generated, so
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 inside each particle inside the oxide superconductor is The critical current inside the particle is 100 to 100 times higher than that of the oxide superconducting wire.
It has been observed that a current of 0x is flowing.

The present invention was made to solve the above-mentioned problems based on ideas based on the recent research results described above, and provides a high-performance oxide superconducting wire with high critical current density and high mechanical strength. The purpose is to

[Means for Solving the Problems J] The present invention provides a core made of a sintered body of an oxide superconductor, a reinforcing core material composited inside the core, and a reinforcing core material covering the core. A means for solving the problem is to provide a covering portion made of a solidified body of an oxide superconductor.

"Effect J: Compared to sintered bodies, solidified bodies of oxide superconductors have no pores and no grain boundaries, so they exhibit a high critical current density.
A solidified body without pores has higher mechanical strength than a sintered body, and the mechanical strength is improved because a reinforcing core material is composited in the core.

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. It consists of a reinforcing core material 2 composited inside the core 1, and a coating layer 3 made of a solidified body of oxide superconductor surrounding the core 1.

To manufacture the oxide superconducting wire A shown in FIG.
Prepare starting materials. 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, Pm
, Sm.

Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, L
1 of the periodic table such as u, [[[[indicates one or more elements of group A of the periodic table, elements of group VB of the periodic table such as Bi, or elements of group MB of the periodic table such as TI, B is Sr, Ba,
Ca.

Indicates one or more elements from group Ua of the periodic table such as Be, Mg, Ra, etc., and C represents rb of the periodic table such as Cu, Ag, and Au.
It represents two or more of group elements and Nb including Gu or Cu, and D represents 0 or O and AI. ) are used.

In addition, materials containing elements constituting the oxide superconductor include powders containing elements of group Ua of the periodic table, powders containing elements of group 1a of the periodic table, elements of group Vb of the periodic table, or elements of group llIb of the periodic table, and powders containing elements of group IIb of the periodic table, A mixed powder consisting of a powder containing an MB group element of the periodic table such as copper oxide powder, a calcined powder of this mixed powder, a mixed powder of the above mixed powder and calcined powder, etc. are used. The powders containing Group 111a elements of the periodic table used here include Be, S
These include compound powders or alloy powders such as carbonate powders, oxide powders, chloride powders, sulfide powders, and fluoride powders of each element of r, Mg, Ba, and Ra. Also, the periodic table m
Examples of powders containing group a elements include Sc, Y, La, Ce,
Pr.

Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,
Er, Tm, Yb.

Oxide powder, carbonate powder, chloride powder of each element of Lu,
Compound powders or alloy powders such as sulfide powders and fluoride powders are used, and powders containing group Vb elements of the periodic table include compound powders or alloy powders of elements such as Bi, and powders containing group llIb elements. Examples include compound powder or alloy powder of elements such as TI. Further, as the copper oxide powder, CuO, CutO, Cu30t
, Cuh03 and other powders are used.

By the way, to prepare the mixed powder, the above-mentioned powder method is usually used, but the method 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. After 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. In addition, during this pressing, a plurality of reinforcing core materials 2 (four in the drawing) made of a non-oxidizing metal material such as silver are inserted into the powder in an aligned manner and spaced apart from each other. . As a result, a rod-shaped molded body 4 whose cross-sectional structure is shown in FIG. 2 can be obtained.

The reinforcing core material 2 compounded inside the molded body 4 is a non-oxidizing material that does not deprive the molded body 4 of oxygen when heat treatment is performed later, and is also made of a material that has a reinforcing effect. Preferably, it is made of a metal material.

Note that 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 powder compact with a desired degree of compaction. It is. 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 4 was heated for 800 minutes in an atmosphere containing oxygen.
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, Y-B
When manufacturing an a-Cu-0 based oxide superconductor,
A treatment of heating to 800 to 950°C and then slowly cooling is preferred.

In addition, when producing B i-S r-Ca-Cu-0 based oxide superconducting wire, heat treatment is performed in two steps, such as heating at 890°C for 20 minutes and then heating at 880°C for 9 hours. It is preferable to rapidly cool the mixture after the heat treatment. Also, T I-c a-B a-Cu
In the case of -0 series, it is desirable to perform heat treatment at 880°C for 12 hours.

Next, the intermediate sintered body produced 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, Ag1Al or 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 molded body 4, and preferably a material that allows oxygen to permeate well. Therefore, it is preferable to use precious metals or alloys containing precious metals.
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 is provided with a plurality of dice 0 that are movably provided by a drive device (not shown). These dice IO 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 (see Fig. 1). 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.

To reduce the diameter of the composite 6, the rotary swaging device B is operated and one end of the composite 6 is pushed into the gap between the dies 10, as shown in FIG. Here, since the dies 10 are rotating while reciprocating at a predetermined interval in the direction of arrow a in FIG. 4, the composite body 6 is sequentially forged from one end side and reduced in diameter as shown in FIG. The diameter is reduced to the wire diameter and it becomes a composite compacted body! 3 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 1O, so that the composite body 6 is reduced in diameter at a high processing rate without causing any 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 compacted body 13 is reduced in diameter to a desired wire diameter by the rotary swaging device B shown in FIG. 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 I3, thereby removing the inner compacted body I3.
Expose 4. To remove the metal sheath material, the composite compacted body 13 is immersed in a treatment liquid such as an acid such as nitric acid or an alkali aqueous solution such as caustic soda, and only the metal sheath material is dissolved in the treatment liquid. chemical methods are used.

In addition, as a method for removing the metal sheath material, mechanical cutting or passing the entire wire through a high frequency induction heating furnace,
It is also possible to use a method of selectively heating and melting only the metal sheath to remove it.

Next, the thus exposed compacted body I4 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. The heat treatment conditions at this time are the same as those for the intermediate heat treatment described above. It is preferable to set the conditions to suit each case where the heat treatment is performed, and to perform the heat treatment under conditions equivalent to those of the above-mentioned intermediate heat treatment.

Through such heat treatment, the above-mentioned compacted body! Since the constituent elements in I4 fully undergo a solid phase reaction with each other, and the surface of the compacted body I4 is exposed, oxygen is efficiently diffused from the entire surface of the compacted body I4 into its interior, resulting in sintering. An oxide superconducting conductor I5 consisting of solids is obtained.

Since this oxide superconducting conductor 15 is sintered after being sufficiently consolidated by forging during diameter reduction processing, it exhibits a critical current density of about I O' to l O'A/ca+'.

Furthermore, in this example, the above-mentioned oxide superconducting conductor 15 is subjected to the treatment described below to produce the oxide superconducting wire A shown in FIG. 1.

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 I5 to a required thickness, and then is cooled and solidified. Note that during this solidification, oxygen ion beam irradiation may be performed 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 20III11, a high-frequency coil 2I placed around the outer circumference of the heat-resistant tube 20, and a high-frequency coil 2I fixed to the outer surface of the heat-resistant tube 20. heat resistant tube 2
0 and a gas supply pipe 22 that communicates with the inside of the tank. The high frequency coil 21 is capable of obtaining an output of about 1 kW to 100 kW by applying a high frequency current of about several kHz to several hundred kHz from a power source as shown in the diagram. Furthermore, an oxygen ion irradiation device 30 is disposed behind the terminal end of the heat-resistant tube 20. These irradiation devices 30 are used to irradiate the oxide superconducting conductor I5 passed through the heat-resistant tube 20.
It is arranged so as to surround the outer periphery of.

The irradiation device 30 includes an oxygen ion generation source therein, and is configured to irradiate ionic, molecular, or atomic oxygen.

Note that, of course, as the irradiation device 30, one having a configuration that can irradiate oxygen ions together with a carrier gas such as an inert gas can be used.

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

Oxide superconductor! Oxide superconducting conductor after melting the outer circumferential side of 5! 5 is pulled out from the heat-resistant tube 20, the melted portion is cooled and solidified. By 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 I5, 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 on the outer peripheral side of the oxide superconducting conductor I5. An oxide superconducting wire A shown in FIG.
can be obtained. Furthermore, when the oxide superconducting conductor 5 is extracted 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.

By performing such cooling means, a more sufficient amount of oxygen can be supplied to the oxide superconductor 15.

Note that if the outer circumferential side of the oxide superconducting conductor I5 is completely melted, there is a risk that the melted portion will fall off, so the melt should be melted or semi-melted to an extent that can prevent falling off.

The coating layer 3 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. It becomes a superconductor, with a critical current density of 10
5 to 10'A/ca''.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 sintered material. .

In addition, the covering layer 3 has high mechanical strength because there are no fine pores found in ordinary sintered bodies, and since the core I made of the sintered body is reinforced by the reinforcing core material 2, the oxide The superconducting wire A has improved mechanical strength compared to an oxide superconducting wire made entirely of a sintered body. Therefore, the oxide superconducting IA does not produce defects such as clutter even when coiled to form a superconducting magnet.

"Example 1" A mixed powder was prepared by mixing Y2O powder (4N), B a C03 powder (3N), and CuO powder (3N), and a calcination treatment was performed in which the mixed powder was heated at 900°C for 24 hours. The calcined powder was then compacted using a rubber press. During this molding, a diameter I is formed inside the calcined powder.

Insert 5 Ag1A of 0III in a lined state and spaced from each other so that it becomes a rod shape with an overall diameter of 10 mm.
It was compacted. 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 the wire rod to mm. Next, the Ag sheath of this wire was dissolved and removed with a nitric acid aqueous solution to expose the core wire with a diameter of 1.0 mm, and heat treatment was performed at 890°C for 14 hours in an oxygen atmosphere to remove the oxidized sintered body. A superconducting conductor was obtained. The critical current density of this oxide superconductor is 5XlO'A at 77K.
/ca+'' was shown.

Next, this superconducting conductor is passed through a high frequency induction heating device with an output of 50 kW at a linear speed of 5 ffl/min, and a high frequency of 100 kHz is applied by the high frequency induction heating device to melt the surface layer portion of the oxide superconducting conductor to a thickness of about 100 μm. The wire was pulled out of the induction heating furnace and the molten layer was solidified to obtain an oxide superconducting wire.

The oxide superconducting wire produced in this way has a critical temperature
90 to 1 critical current density 2 X l O'A/cm''.

Further, the obtained oxide superconducting wire was able to maintain a round wire shape with a circular cross section, and no deformation due to melting and solidification was observed. In addition, this oxide superconducting wire was
When it was bent to a diameter of 0m+e, fine racks were generated on the surface, but due to the reinforcing effect of the silver wire placed inside, no definitive defects occurred. When the oxide superconducting wire bent as described above was returned to its original straight shape and the critical current density was measured, it exhibited a value almost equal to the value before bending.

“Example 2” A mixed powder was prepared by mixing B i,o powder, S rCOs powder, and CuO powder so that Bi:Sr:Ca:Cu=l:1:1:2, and this mixed powder 8
A calcining treatment was performed by heating at 00° C. for 10 hours, and the calcined powder was compacted into a rod shape with a diameter of 10 ais+ using a rubber press.

Thereafter, the rod-shaped body was sintered at 820° C. for 10 hours in an atmosphere containing oxygen to obtain a rod-shaped sintered body. Next, this sintered body was inserted into a sheath made of Ag and swaged to a diameter of 1°5111 m to obtain a wire rod. Next, A of this wire
The sheath made of G was dissolved and removed with dilute nitric acid to expose a core wire with a diameter of 1.0 mm, and further heat treatment was performed in the atmosphere at 870° C. for 8 hours to obtain an oxide superconducting conductor made of a sintered body. This B i-S r-Ca-Cu-0 based oxide superconductor has a critical current density of 3X10 at 77K.
It showed 3A/am'.

Next, this superconducting conductor was passed through a high frequency induction heating furnace with an output of 50 kW at a linear speed of 10 n+/min, and
A high frequency of 0 kHz was applied to melt the surface layer portion of the oxide superconducting conductor to a thickness of about 50 μm, and the conductor was pulled out from 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 round wire shape with a circular cross section.

This oxide superconducting wire is Critical temperature: 100K.

It showed a critical current density of 5 X l O'A/cm''.

"Effects of the Invention" As explained above, the present invention includes a core made of a sintered body of an oxide superconductor, a reinforcing core material inside the core, and an oxide superconductor on the outer peripheral side of the core. The coating layer on the outer circumferential side has no fine pores or grain boundaries that exist in a sintered body, so 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. In addition, the coating layer has high mechanical strength because it does not have the fine pores found in sintered bodies, and since the core is also composited with a reinforcing core material, the overall mechanical strength is also high. Therefore, even when coil processing is performed using the oxide superconducting wire of the present invention, cracks do not occur, and a superconducting magnet with excellent superconducting properties without cracks in the winding can be manufactured.

[Brief explanation of the drawing]

1 to 5 are for explaining one embodiment of the present invention, and FIG. 1 is a cross-sectional view of an oxide superconducting wire, and FIG. 2 is a cross-sectional view of an oxide superconducting wire.
The figure is a cross-sectional view of a rod-shaped molded body, Figure 3 is a cross-sectional view of a composite body, Figure 4 is a cross-sectional view showing the state in which diameter reduction is being performed using a rotary swaging device, and Figure 5 is FIG. 3 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, ■... Core portion, 2... Reinforcement core material, 3... Covering layer, 6
... Composite, ■3... Composite consolidated body, 14... Consolidated body, 15... Oxide superconducting conductor.

Claims (1)

[Claims] A core made of a sintered body of an oxide superconductor, a reinforcing core material composited inside the core, and a covering part made of a solidified body of an oxide superconductor provided to cover the core. An oxide superconducting wire comprising: