JP2563411B2 - Manufacturing method of oxide superconducting wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a method for producing a superconducting wire using an oxide superconductor.

(Prior Art) In recent years, since it was announced that Ba-La-Cu-O-based layered perovskite type oxides may have a high critical temperature, research on oxide superconductors has been conducted at various places. (Z.Phys.B Condensed Matter 64,189-193 (198
6)). Among them, a defect perovskite type having an oxygen defect represented by a Y-Ba-Cu-O system (LnBa ₂ Cu ₃ O _7-δ)
Type) (δ represents oxygen deficiency, usually 1 or less, Ln is Y, L
a, Sc, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu
Oxide superconductor of at least one element selected from the above, and part of Ba can be replaced by Sr etc.) has a critical temperature of 90K or higher and is higher than liquid nitrogen. (Phys.Rev.Lett.Vol.58 No.9,908)
−910).

Conventionally, in converting this oxide superconductor into a wire rod, after filling the metal tube with the oxide superconductor powder and reducing the surface to the final wire diameter, the metal layer is removed, and then heat treatment for firing and It was obtained by applying a heat treatment for introducing oxygen. The oxide superconducting wire thus obtained may have pores or cracks inside because the oxide superconductor uniformly thermally expands or contracts when the temperature changes during production or use. Since it is small, a high critical current density can be obtained.

However, the oxide superconductor is a crystalline oxide and has poor ductility and flexibility. Further, if it is left as it is, it is weak against mechanical stress, and if it is distorted by a certain value or more, the superconducting property is deteriorated or disappears. Therefore, in the above-described conventional oxide superconducting wire, it is difficult to obtain a practical mechanical strength depending on the application, and the superconducting property is reduced or disappears due to the strain caused by the mechanical stress. There was a problem that the critical current density could not be obtained.

(Problems to be Solved by the Invention) As described above, it is difficult to obtain practical mechanical strength of an oxide superconducting wire obtained by a conventional manufacturing method depending on its application, and a desired critical current There was a problem that the density could not be obtained.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a method for producing an oxide superconducting wire having a high critical current density and improved mechanical strength.

[Structure of the Invention] (Means for Solving the Problems) That is, in the method for producing an oxide superconducting wire of the present invention, a metal core material is arranged in a metal tube in the longitudinal direction, and the metal core material It is characterized in that an oxide superconductor powder is filled between the metal tube and the metal tube, wire drawing is performed, the outer metal layer is removed, and then heat treatment is performed in an oxygen-containing atmosphere.

The metal core material used in the present invention is preferably excellent in heat resistance, thermal conductivity, conductivity and drawability, and examples of such a metal include silver, gold, platinum, palladium, or alloys thereof. To be done.

It is also possible to use an oxidizing metal such as copper or a copper alloy as the core material, but in this case, in order to generate an oxygen deficiency layer or a contamination layer on the oxide superconductor surface during heat treatment, silver, gold, The superconducting property is deteriorated as compared with the case of using platinum, palladium, or an alloy thereof.

The metal tube may be made of any metal, but it is preferable to use copper from the viewpoint of drawability and economical efficiency. However, in the case of calcination as needed after the wire drawing process, the use of silver, gold, platinum, palladium, or an alloy thereof makes it possible to obtain a wire having more excellent superconducting properties.

Although various oxide superconductors can be used in the present invention, a practical effect is particularly large when a rare earth element-containing perovskite-type oxide superconductor having a high critical temperature is used.

The oxide superconductor containing a rare-earth element and having a perovskite structure may be any as long as it can realize a superconducting state, and is an LnBa ₂ Cu ₃ O _7-δ system (δ is an oxygen deficiency and is usually a number of 1 or less. , Ln are Y, La, Sc, Nd, Sm, Eu, Gd,
At least one selected from Dy, Ho, Er, Tm, Yb and Lu
Examples are oxides having a perovskite type in a broad sense, such as a defective perovskite type having an oxygen defect such as a kind of element and part of Ba can be replaced with Sr, etc., and a layered perovskite type such as an Sr-La-Cu-O type. Is done. In addition, rare earth elements are also defined in a broad sense, and include Sc, Y, and La systems. As a typical system, in addition to the Y-Ba-Cu-O system, Y is Eu, Dy, Ho, Er,
Systems substituted with rare earths such as Tm, Yb and Lu, Sc-Ba-Cu-O
System, Sr-La-Cu-O system, and a system in which Sr is replaced by Ba or Ca.

The oxide superconductor used in the present invention can be obtained, for example, by the following manufacturing method.

First, the constituent elements of the perovskite-type oxide superconductor such as Y, Ba, and Cu are sufficiently mixed. During mixing, Y ₂ O ₃ , Cu
An oxide such as O can be used as a raw material. Also,
In addition to these oxides, compounds such as carbonates, nitrates, and hydroxides that are converted into oxides after firing may be used. Further, an oxalate obtained by a coprecipitation method or the like may be used. The elements constituting the perovskite-type oxide superconductor are basically mixed so as to have a stoichiometric composition, but may be slightly shifted depending on the production conditions and the like. For example, in the Y-Ba-Cu-O system, Y2 mol and Ba2 mol, Cu3 mol
Is the standard composition, but in practice, Ba2 ± 0.
A deviation of about 6 mol and Cu3 ± 0.2 mol is not a problem.

After mixing the above-mentioned raw materials, they are calcined, pulverized into a desired shape, and fired at about 850 to 980 ° C. Calcination is not always necessary. The calcination and the calcination are preferably performed in an oxygen-containing atmosphere capable of supplying sufficient oxygen. After firing into a desired shape, heat treatment is performed in an oxygen-containing atmosphere to impart superconductivity. The heat treatment is usually performed in an oxygen-containing atmosphere.
It is carried out by holding at 300 to 700 ° C, or by gradually cooling to 600 ° C or less after firing.

The thus obtained oxide superconductor has an oxygen-defective perovskite structure (LnBa ₂ Cu ₃ O
_7-δ (δ is usually 1 or less)). In addition, Ba is Sr, Ca
And at least one of Cu may be replaced with Ti, V, Cr, Mn, Fe, Co, Ni, Zn or the like.

This substitution amount can be appropriately set within a range that does not deteriorate the superconducting property, but an excessively large amount of replacement deteriorates the superconducting property, so the amount is set to 80 mol% or less, and in practice, to about 20 mol% or less.

The oxide superconducting wire according to the present invention is manufactured, for example, as follows.

First, the fired product obtained by firing and crystallizing the oxide superconductor is pulverized by a known means such as a ball mill. At this time, the oxide superconductor is divided into fine powders from the cleavage plane.
The pulverization is desirably performed until the average particle size becomes about 1 to 5 μm and the ratio of diameter to thickness becomes 3 to 5. If necessary, the pulverized powder may be classified and used in the above range.

Next, this oxide superconductor powder is filled in a metal tube in which a metal core material is arranged in the length direction of the tube, and both ends are sealed with the metal material. After sealing, the metal pipe is forged by a swaging machine or the like in the warm, and then drawn cold to reduce the outer diameter of the metal pipe to 1/10 or less of the original outer diameter, preferably 1/20 or less. Reduce the diameter. After the diameter reduction processing, rolling processing may be performed as necessary.

When the desired outer diameter is obtained in this way, if necessary, calcination is performed at 850 to 940 ° C., and then the metal layer on the outer periphery is removed by etching, laser processing, or the like. Then, heat treatment for firing is performed at 850 to 980 ° C. for 8 to 80 hours in an oxygen-containing atmosphere. After firing, 660 ° C. or less is gradually cooled at a rate of about 1 ° C./minute in an oxygen-containing atmosphere, and oxygen is introduced into oxygen vacancies in the crystal structure of the oxide superconductor to improve superconductivity. The heat treatment for introducing oxygen is 300 to 700.
You may perform by hold | maintaining at 50 degreeC for 3 to 50 hours.

(Operation) In the oxide superconducting wire obtained by the present invention, the outer periphery of the oxide superconductor during heat treatment is not restricted by the metal, so that the volume contraction of the oxide superconductor is smoothly performed. For this reason,
As the oxide superconductor is densified, pores and cracks are less likely to occur inside the oxide superconductor, and the critical current density is improved.

Further, since the wire rod has the metal core material, the mechanical strength of the wire rod is improved.

Therefore, it is possible to obtain an oxide superconducting wire having a high critical current density with improved mechanical strength.

(Example) Hereinafter, the Example of this invention is described.

Example 1 First, BaCO ₃ powder and Y ₂ O ₃ were used as raw materials for an oxide superconductor.
Powders and CuO powders were used, and these were compounded so that the molar ratio of Y: Ba: Cu = 1: 2: 3, thoroughly mixed and pulverized. Then, the mixture was fired at 900 ° C. for 8 hours and then pulverized, and the pulverized material was fired at 900 ° C. for 24 hours in the air and then pulverized using a ball mill, and classified to have an average particle size of 2 μm and a diameter-to-thickness ratio. Three
.About.5 perovskite type oxide superconductor powders were obtained.

Next, as shown in FIG. 1 (a), the obtained oxide superconductor powder 1 was prepared by arranging a silver core material 2 having a diameter of 3 mm and a length of 100 mm in the length direction of the tube. , Length 100mm
Was filled in a copper tube 3 having one end sealed with a copper material, and the other end was sealed with a copper plug.

After this, using a swaging machine at room temperature, the outer diameter is 2 mm.
The wire was obtained by cold forging.

Next, the silver layer around the wire was removed by etching using HNO _3, and after firing at 950 ° C for 24 hours in an oxygen-containing atmosphere, it was gradually cooled from 600 ° C at 1 ° C / min. (B)
As shown in, an oxide superconducting layer 5 was formed on the outer periphery of the silver layer 4 to obtain an oxide superconducting wire 6.

The external magnetic field of the oxide superconducting wire thus obtained is 0T, 77
The critical current density at K was 5000 A / cm ² . Also, 20
Critical current density in an external magnetic field 0T, 77K when tensioned in 00kgf / cm ² is 4800A / cm ^2, reduction of the superconducting properties were slightly.

Example 2 As shown in FIG. 2 (a), a copper pipe was used as the metal core material.
It has a shape that closely adheres to the inner wall of 11 and has an outer circumferential arc length of 15 mm and a thickness.
A strand having an outer diameter of 1.8 mm filled with oxide superconductor powder 13 was obtained in the same manner as in Example 1 except that a silver core material 12 having an arcuate cross section having a length of 3 mm and a length of 100 mm was used.

After that, the obtained wire is further rolled by a roller die to have a thickness of 1 mm and a width of 2.5 mm as shown in FIG. 2 (b).
Made into a tape shape.

After that, the copper layer on the outer periphery was removed by etching using HNO _3, and after firing at 950 ° C. for 24 hours in an oxygen-containing atmosphere, it was slowly cooled from 600 ° C. at 1 ° C./min. ), An oxide superconducting wire having a silver layer 15 on one side surface of the oxide superconducting layer 14 was obtained. In addition, in FIG. 2B, the same reference numerals are given to members common to those in FIG.

The external magnetic field of the oxide superconducting wire thus obtained is 0T, 77
The critical current density at K was 5500 A / cm ² . Also, 20
When a tension of 00 kgf / cm ² was applied, the critical current density was 5200 A / cm ² in an external magnetic field of 0 T and 77 K, and the deterioration of superconducting properties was slight.

Comparative Example An oxide superconducting wire was obtained in the same manner as in Example 1 except that the silver rod was not used.

The critical current density of this oxide superconducting wire at an external magnetic field of 0 T and 77 K was 1000 A / cm ² . Further, the critical current density at an external magnetic field of 0 T and 77 K when a tension of 2000 kgf / cm ² was applied was 10 A / cm ² , and the deterioration of the superconducting properties was greater than that of the oxide superconducting wire of the present invention.

[Effects of the Invention] As described above, the oxide superconducting wire obtained by the method for producing an oxide superconducting wire of the present invention has improved mechanical strength as compared with the conventional oxide superconducting wire, and has a critical value. The current density is also high.

Therefore, the use of the present invention makes it possible to expand the uses of the oxide superconducting wire.

[Brief description of drawings]

FIG. 1 is a perspective view showing a part of the procedure of one embodiment for producing an oxide superconducting wire according to the present invention, and FIG. 2 (a) is the procedure of another embodiment for producing an oxide superconducting wire according to the present invention. 2 (b) and 2 (c) are perspective views showing a part of FIG.
It is sectional drawing showing a part of procedure following FIG. 1,13 …… Oxide superconductor powder 2,12 …… Silver core material 3,11 …… Copper tube 4,15 …… Silver layer 5,14 …… Oxide superconductor 6,16 …… Oxide superconducting wire

Claims (5)

(57) [Claims] 1. A metal core material is arranged in a length direction in a metal tube, oxide superconductor powder is filled between the metal core material and the metal tube, and then wire drawing is applied to the outer periphery. The method for producing an oxide superconducting wire, characterized in that the metal layer is removed, and then heat treatment is performed in an oxygen-containing atmosphere. 2. The method for producing an oxide superconducting wire according to claim 1, wherein the metal core material is made of silver, gold, platinum, palladium, or an alloy thereof. 3. The method for producing an oxide superconducting wire according to claim 1 or 2, wherein the oxide superconductor is a perovskite type oxide superconductor containing a rare earth element. . 4. An oxide superconductor comprising Ln element (Ln is at least one element selected from rare earth elements), Ba and Cu
Is substantially contained in an atomic ratio of 1: 2: 3.
A method for producing an oxide superconducting wire according to the item. 5. The oxide superconductor is LnBa ₂ Cu ₃ O _7-δ (δ
Represents an oxygen defect) and has an oxygen deficiency type perovskite structure. 5. The method for producing an oxide superconducting wire according to claim 1, wherein the perovskite structure is an oxygen deficiency type perovskite structure.