JPH09235120A - Production of bismuth-based oxide superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a Bi-based oxide superconductor by which a dense oxide superconductor having a uniform composition can continuously be produced on the surface of a metallic substrate having the flexibility to readily obtain a long conductor good in adhesion to a metallic substrate. SOLUTION: A composite material comprising the first layer composed of Bi metal or a Bi alloy 2 applied to the surface of an Ag or an Ag alloy substrate 1 and the second layer composed of an oxide 3 containing at least Sr- Ca-Cu-O elements is heat-treated to form a Bi-based oxide superconductor layer 4 by mutual diffusion. Otherwise, a composite material prepared by applying a mixture of the Bi metal or the Bi alloy 2 with the oxide 3 containing at least the Sr-Ca-Cu-O elements to the surface of the Ag or Ag alloy substrate 1 is heat-treated to form the Bi-based oxide superconductor layer 4 by the mutual diffusion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magnetic resonance imaging apparatus (M
(RI) and other superconducting magnet wire rods, and a method for producing a high critical temperature Bi-based oxide superconductor, which is being developed as a conductive material for superconducting power transmission.

[0002]

2. Description of the Related Art Y-group, Bi-group, Tl-group, Hg-group, etc. oxide superconductors having a critical temperature Tc at which a transition from a normal conducting state to a superconducting state exceeds a liquid nitrogen temperature (77K). Has been discovered in recent years. In the Bi-based oxide superconductor, the phase of the composition represented by Bi ₂ Sr ₂ CaCu ₂ O _x has a Tc of about 80 K, and Bi ₂ Sr ₂ Ca ₂ Cu
It is known that the phase of the composition represented by ₃ O _Y has a Tc of about 105K. These phases having different Tc are usually generated in a mixed state, but it is known that when a part of Bi is replaced with Pb, a phase having a high Tc of 105 K is easily generated. These oxide-based superconductors
Nb that had to be cooled with liquid helium (4.2K)
Since it can be used under cooling conditions that are significantly more advantageous than conventional metal-based superconductors such as Ti and Nb ₃ Sn, research and development are being advanced as a superconducting material that is extremely promising in practice. Especially,
Bi-based oxide superconductors are attracting attention because they do not contain highly toxic elements such as Tl and Hg and can obtain a high Tc of 100 K or more.

However, since the oxide superconductor has extremely brittle mechanical properties, it has been conventionally processed into a wire shape by the following method, for example. That is, after calcining a plurality of raw material powders containing the elements constituting the oxide superconductor to remove unnecessary components, the calcined powders are filled in a metal tube such as Ag, swaged, drawn, A wire with a desired diameter or a tape with a desired thickness is processed by a method such as rolling, and this is heat-treated to cause a sintering reaction in the compressed mixed powder inside the metal tube to cause oxide superconductivity with the desired composition. It is a method of producing a body and manufacturing a superconducting wire.

[0004]

However, in the above-mentioned conventional method, it is difficult to mix the raw material powders completely and uniformly, and there is a problem that the superconductor as a whole does not have a completely uniform composition even if heat treatment is performed. It was In particular, with a long wire, it is not possible to generate a superconductor with a uniform composition over the entire length of the wire,
This results in the formation of a local portion having an unsuitable composition and insufficient superconducting properties, resulting in a problem that the properties of the entire wire are limited. In addition, the oxide superconductor formed inside the above wire is obtained by sintering a compacted powder compact by a sintering reaction, and since many fine pores are present inside the compact, It was less dense than metal-based superconductors, and it was difficult to increase the critical current density Jc, which is practically important.

From the above, the present inventor has previously proposed Japanese Patent Publication No.
No. -102976 was proposed. The present invention provides a Bi-based oxide superconductivity by mutual diffusion between an oxide composed of at least an element of Sr-Ca-O and an oxide composed of at least an element of Bi-Cu-O and containing no Sr. By this method, a dense oxide superconductor having a uniform composition can be continuously formed in a layered manner, and the thickness of the superconductor layer can be set to a desired size. It exerts a remarkable effect of being able to control and easily obtain a structure having a uniform crystal orientation. However, since the first layer is an oxide, its coating method is limited and relatively time-consuming. In addition, there is a problem of adhesion with the substrate, which is a problem in continuously producing the Bi-based oxide superconductor.

The present invention has been made in view of the above problems, and an object thereof is to continuously provide an oxide superconductor having a dense and uniform composition on the surface of a flexible metal substrate. The present invention is to provide a method for producing a Bi-based oxide superconductor, which can be easily produced to obtain a long conductor having good adhesion to a metal substrate.

[0007]

In order to solve this problem, the present inventor has proposed an intermetallic compound superconductor, such as Nb ₃ Sn or V ₃ Ga, which is hard to be directly processed due to its hard mechanical properties and brittleness. We focused on the method of manufacturing superconductors by the diffusion method, which was applied to the production of wire rods and was highly successful in industrialization. (For example, K. Tachikawa, Filamentary A15 Superconductors. P
lenum Press, (1980), p. 1). According to this diffusion method,
It continuously produces a dense superconducting phase with a uniform composition,
It is possible to obtain excellent superconducting properties.

The method for producing a Bi-based oxide superconductor according to the inventions of claims 1 to 9 uses this diffusion method as Bi-Sr-Ca.
It is applied to a method for producing a Bi-based oxide superconductor composed of an element of -Cu-O, and comprises a first layer made of Bi metal or Bi alloy coated on the surface of an Ag or Ag alloy substrate, and at least Sr-Ca. A composite comprising a second layer composed of an oxide containing an element of —Cu—O is heat-treated to form a Bi-based oxide superconductor layer by mutual diffusion.

The substrate 1 will be described in detail with reference to FIG.
Is made of Ag or an Ag alloy, and the Ag alloy contains Mg, Cu, etc. as an alloying element, and an alloying element that can be expected to improve mechanical strength without affecting the characteristics of the superconductor is added. . The first layer 2 is made of Bi metal or Bi alloy, and as Bi alloy, Bi-Cu, Bi-Pb,
An alloy composed of Bi-Cu-Pb is used. First layer 2
In the case of the Bi—Cu alloy, the composition ratio of the alloy is Cu: 0.05 to 1.0, B:
In the case of i-Pb alloy, Bi is set to 1 in atomic ratio and P
b: 0.2 to 1.5, and in the case of Bi-Cu-Pb alloy, the atomic ratio is Bi: 1 to Cu: 0.05 to.
1.0, Pb: The range of 0.2-1.0 is desirable. In the present invention, if the composition ratio deviates from these ranges, it becomes difficult to obtain good superconducting properties. The first layer 2
Is a constituent element that diffuses into the second layer 3 in a subsequent diffusion step, and preferably has a melting point as low as possible. The first layer 2 is coated on the base material 1. As a method thereof, Ag or Ag serving as the base material after melting each metal of Bi, Cu and Pb forming the first layer 2 at a predetermined composition ratio. A method of immersing an alloy tape or wire, thereby forming a first layer 2 having a predetermined thickness on the tape or wire surface (base material surface), or a metal forming the first layer on an Ag or Ag alloy pipe. There is a method in which the melted material is cast and then machined to a predetermined thickness to form the first layer 2 along the circumference of the inner surface of the pipe.

As the second layer 3, an Sr-Ca-Cu-O type oxide is used. The composition ratio of the oxide of the second layer 3 is, in atomic ratio, Sr: 1, Ca: 0.25 to 1.5, and Cu:
The range of 0.25 to 2.0 is preferable. In the present invention, if the composition ratio deviates from these ranges, it becomes difficult to obtain good superconducting properties. The second layer 3 is SrCO ₃ , CaCO ₃ ,
It is desirable that the raw material powder such as CuO is mixed at a predetermined composition ratio, and is manufactured through a process such as calcination, molding, and main firing, and that it has a melting point higher than that of the first layer. Here, the melting point of the second layer 3 is 9
At about 50 ° C to 1100 ° C, the melting point of the first layer 2 is 12
It is about 5 ° C to 850 ° C.

Next, the first layer 2 coated on the surface of the substrate 1
The second layer 3 is coated on the above to prepare a composite 6 in which the first layer 2 and the second layer 3 are in contact with each other. As shown in FIG. 2, the specific method for producing the composite is as follows. The Ag or Ag alloy base material 1 is dipped in a dissolved Bi-based metal or alloy to coat the surface of the base material with the metal forming the first layer 2. Then, after that, a method of coating the oxide forming the second layer 3 on the surface of the first layer 2 by pressing or the like can be adopted. In addition,
In FIG. 2, the Ag or Ag alloy base material 1 has a tape shape, but a wire shape base material may be used. Also,
As a method of coating the surface of the substrate 1 with the metal forming the first layer 2 or a method of coating the first layer 2 with the second layer 3, continuous coating by a spray method, a printing method, a vapor deposition method, or the like. Can also be adopted.

The composite body 6 thus produced is processed into a desired shape and then subjected to diffusion heat treatment. In this diffusion heat treatment, it is possible to obtain a superconductor having better characteristics by performing the primary diffusion heat treatment at a low temperature and then performing the secondary diffusion heat treatment at the next higher temperature. The primary diffusion heat treatment temperature is in the range of 100 ° C to 800 ° C, and the secondary diffusion heat treatment temperature is in the range of 800 ° C to 900 ° C. The primary heat treatment temperature is in the vicinity of the melting point of the first layer and is effective in increasing the adhesion between the first layer and the second layer, but it is possible to form the superconducting layer even if the primary heat treatment is omitted. . However, if the primary heat treatment is omitted, the component system of the first layer may rapidly melt and expand, causing cracks in the superconductor. Therefore, when the primary diffusion heat treatment temperature is omitted, it is necessary to increase the temperature rising rate during the secondary diffusion heat treatment by 1 ° C./minute or more in the temperature range of 600 ° C. or higher. The secondary heat treatment temperature is around the formation temperature of the Bi-based oxide superconductor, and a crystal structure having high Tc is formed.

On the other hand, the molten metal constituting the first layer 2 is cast into an Ag or Ag alloy pipe, and then machined to a predetermined thickness, and the first layer 2 is formed along the circumference of the inner surface of the pipe. In the case of a composite body in which the second layer 3 is filled in the inside thereof, or when it is processed into a round wire, the components of the first layer 2 are converted into the second layer 3 by diffusion heat treatment as shown in FIG.
It diffuses inside and reacts, and a Bi-based oxide superconducting layer 4 having a high Tc is formed between the second layer 3 and the Ag or Ag alloy base material 1.

The Bi of the method of the present invention thus obtained
For the base oxide superconductor, the Bi ₂ Sr ₂ CaC described above is used.
u ₂ O _x , Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _Y, and Bi partially substituted with Pb are included.

Next, the inventions of claims 10 to 17 will be described. These inventions use Bi or Ag on the surface of Ag or Ag alloy substrate.
Metal or Bi alloy and at least Sr-Ca-Cu-O
In the method for producing a Bi-based oxide superconductor, the composite coated with the mixture containing the element-containing oxide is heat treated to form a Bi-based oxide superconductor layer by mutual diffusion. FIG. 6 shows the principle diagram. The Ag or Ag alloy base material 1 is dipped in a mixture of the dissolved Bi metal or Bi alloy 2 and the oxide powder 3 containing at least an element of Sr-Ca-Cu-O to have a predetermined thickness on the surface of the base material. To form a mixture layer of. Next, this composite is heat-treated to produce a Bi-based oxide superconductor layer 4 by mutual diffusion. FIG. 7 shows a principle diagram when the present invention is applied to a pipe-shaped substrate.
Melted Bi metal or Bi alloy 2 and at least Sr-
A mixture with the oxide powder 3 containing the element of Ca-Cu-O is cast into the Ag or Ag alloy pipe 1 serving as a base material to form a composite. Then, the composite is heat-treated to produce a Bi-based oxide superconductor layer 4 by mutual diffusion.

Since the alloy composition, oxide composition, diffusion heat treatment conditions, and necessary mechanical processing in the inventions of claims 10 to 17 are the same as those of the inventions of claims 1 to 9,
Here, the description is omitted.

In the above-described embodiment, the obtained composite is heat-treated to produce a Bi-based oxide superconductor layer by mutual diffusion, but the present invention is not limited to these methods, and the obtained composite is obtained. A plurality of bodies may be bundled or stacked, or if necessary, these may be put into an Ag or Ag alloy sheath, and then the wire may be processed and then heat treated. According to this method, a Bi-based oxide superconducting wire having a multi-core structure can be manufactured.

[0018]

Next, embodiments of the present invention will be described. (Example 1) Raw material powders of SrCO ₃ , CaCO ₃ , and CuO were blended so as to have a composition of Sr ₂ CaCu ₂ O ₅ , and 9
Calcination at 00 ℃ for 6 hours to remove unnecessary components such as CO ₂
Then, after calcination at 1025 ° C. for 12 hours, pulverization and mixing were repeated to produce SrCaCu oxide powder.

On the other hand, the metals Bi and Cu compounded to have Bi-15 atomic% Cu are melted at 800 ° C., and the Ag tape is immersed therein for 2 to 3 seconds to give a thickness of about 80 μm on the surface of the Ag tape. Bi-15 atomic% Cu was coated. Then, the prepared SrCaCu oxide powder was applied to the Bi-15 atomic% Cu coated on the surface of the Ag tape for about 1 m.
It was coated with a thickness of m and then pressed into a tape-shaped composite sample having a width of 5 mm and a length of 30 mm. After subjecting this composite sample to the primary heat treatment at 700 ° C. for 10 hours, 84
A secondary diffusion heat treatment was performed at 0 ° C. for 20 to 100 hours to prepare a sample. Although the heat treatments of this embodiment were all performed in the atmosphere, the heat treatment atmosphere is not limited to the atmosphere, and similar results can be obtained by using a mixed gas of Ar and O ₂ , for example. FIG. 4 shows Ag, Bi, S of the cross section of the sample after the secondary diffusion heat treatment by an X-ray microanalyzer.
The surface analysis results of r, Ca, and Cu are shown. It can be seen that the Bi-based oxide superconductor having a thickness of about 80 μm is formed almost uniformly on the Ag base material.

The critical current Ic of this sample exceeds 4.2 A under a self-magnetic field of 4.2 K, and further exceeds 12 T.
Ic as a transport current of 300 A or more was obtained even under a strong magnetic field. This Ic is extremely high J of 75,000 A / cm ² or more when converted from the cross-sectional area of the superconductor.
c. In addition, measurement of 300 A or more was not possible due to the limits of the capacity of the energizing power source and the measuring rod.

It was found from this example that a Bi-based oxide superconductor having a uniform composition and high Ic and Jc values can be produced by the diffusion method. (Example 2) A Bi-Pb eutectic alloy having a composition of melted Bi-43.7 atom% Pb was used, with an outer diameter of 10 mm and an inner diameter of 7 m.
diameter of 4m by machining after casting into a m Ag pipe
A hole of m was opened, and SrCaCu oxide powder was enclosed in the hole. The SrCaCu oxide is a powder having the composition of Sr ₂ CaCu ₂ O ₅ produced by the same method as in Example 1. Then, a wire rod having a diameter of 1.5 mm and having a cross-sectional structure similar to that of FIG. 3 was formed by groove roll processing and wire drawing processing.

Next, at 100 ° C. for 10 hours, and then 600 ° C.
After performing the primary heat treatment for 10 hours at 840 ° C., the secondary diffusion heat treatment was performed at 840 ° C. for 20 to 100 hours in the same manner as in Example 1 to prepare a sample.

FIG. 5 shows the temperature dependence of the AC susceptibility of the sample. From this figure, it can be seen that a phase having a composition represented by Bi ₂ Sr ₂ CaCu ₂ O _x having a Tc of about 82 K and having a substantially uniform composition was formed.

[0024]

As is clear from the above examples, according to the manufacturing method of the present invention, it is possible to manufacture a high Tc Bi-based oxide superconductor which is dense, has no pores, and has a uniform composition.
It is possible to manufacture a Bi-based high Tc oxide superconducting wire having a large Jc and uniform characteristics in the length direction. Further, in the method of the present invention, unlike the normal powder sintering method, since the components of the first layer are diffused from one direction or the radial direction to generate an oxide superconductor, crystal grains grow in the diffusion direction,
There is also an effect that a high Tc oxide superconductor excellent in crystal orientation can be obtained. Furthermore, by adjusting the thickness of the first layer, it is possible to easily control the thickness of the generated superconducting layer (diffusion layer). In addition, the obtained oxide superconductor has flexibility because it is compounded with a metal base material such as Ag, suitable for continuous production, and has a feature that it can be formed into a desired shape. Therefore, the production of a magnetic shield or the like becomes easy by producing a long wire or forming a base material into a cylindrical shape. Furthermore, since the composite has good workability, it is easy to manufacture round wire rods, rectangular wire rods, tape wire rods, and the like. In particular, the round wire rod is useful for producing a superconducting magnet that requires a uniform magnetic field. Therefore, the method of the present invention can solve the problems in the conventional manufacturing method and provide a highly Tc-based Bi-based oxide superconductor that is excellent in denseness and uniformity and that has a desired shape and is highly flexible. It has a remarkable effect. Moreover, since the first layer is Bi metal or Bi alloy, the Ag, Ag alloy base material is continuously dipped and passed through the molten Bi metal or Bi alloy to coat the first layer,
Alternatively, the first layer can be cast into Ag, Ag alloy pipe. Further, since Bi metal or Bi alloy has a low melting point, the coating of the first layer is easy, and since it is a metal rather than an oxide, the adhesion to the Ag, Ag alloy base material is remarkably good. As described above, according to the present invention, continuous production of the Bi-based oxide superconductor is significantly facilitated.

Further, according to the invention of claims 10 to 17, a mixture having fluidity is obtained by dispersing high melting point Sr-Ca-Cu oxide powder in molten low melting point Bi metal or Bi alloy. It can be used to coat the substrate once.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of the manufacturing method of the present invention.

FIG. 2 is a diagram showing an example of a method for producing a composite according to the present invention.

FIG. 3 shows B by a diffusion reaction between a first layer metal 2 and a second layer oxide 3 formed on the inner surface of an Ag or Ag alloy pipe.
The figure which shows the principle which i-type oxide superconductor 4 produces | generates.

FIG. 4 shows Ag, Bi, and the like of Example 1 after the secondary diffusion heat treatment.
An X-ray photograph showing the results of surface analysis of Sr, Ca, Cu by an X-ray microanalyzer.

FIG. 5 is a diagram showing the temperature dependence of the AC susceptibility of Example 2 after the secondary diffusion heat treatment.

FIG. 6 is a view showing another embodiment of the present invention when the base material is a plate material.

FIG. 7 is a view showing another embodiment of the present invention when the base material is a pipe.

[Explanation of symbols]

1 ... Ag or Ag alloy substrate 2 ... Bi metal or Bi alloy 3 ... Sr-Ca-Cu oxide 4 ... Bi-based oxide superconductor 5 ... Ag or Ag alloy surface with Bi metal or B
Composite tape coated with i alloy 6 ... Composite

Claims (17)

[Claims] 1. A B coated on the surface of an Ag or Ag alloy substrate.
a first layer of i-metal or Bi-alloy and at least Sr
The composite consisting of the second layer composed of the oxide containing the element —Ca—Cu—O is heat treated and Bi
A method for producing a Bi-based oxide superconductor, which comprises forming a base oxide superconductor layer. 2. The method for producing a Bi-based oxide superconductor according to claim 1, wherein the first layer is a metal containing only Bi element. 3. The first layer is a Bi—Cu alloy, and the atomic ratio thereof is within the range of Cu: 0.05 to 1.0, with Bi = 1. A method for producing the Bi-based oxide superconductor described. 4. The first layer is a Bi—Pb alloy, the atomic ratio of which is within the range of Pb: 0.2 to 1.5 with Bi = 1. A method for producing the Bi-based oxide superconductor described. 5. The first layer is a Bi—Cu—Pb alloy, the atomic ratio of which is Bi: 1 and Cu: 0.05 to
1.0, Pb: It exists in the range of 0.2-1.5, The manufacturing method of the Bi based oxide superconductor of Claim 1 characterized by the above-mentioned. 6. The second layer is at least Sr—Ca—
An oxide containing an element of Cu-O, the atomic ratio of which is Sr = 1, Ca: 0.25 to 1.5, Cu: 0.25 to
6. Within the range of 2.0. 6.
2. The method for producing a Bi-based oxide superconductor according to any one of 1. 7. The first layer is formed on the surface of the base material by immersing the base material in a melt of a metal or an alloy forming the first layer. 2. A method for producing a Bi-based oxide superconductor according to item 1. 8. The first layer is formed on the surface of the base material by casting a melt of the metal or alloy forming the first layer into the pipe-shaped base material. One of
The method for producing a Bi-based oxide superconductor according to item 1. 9. A Bi-based oxide superconducting material, characterized in that a first layer is produced by the method according to claim 8, and a composite comprising the first layer and the second layer is processed into a wire and then heat-treated. Body manufacturing method. 10. A composite in which the surface of an Ag or Ag alloy substrate is coated with a mixture of a Bi metal or a Bi alloy and an oxide containing at least an element of Sr—Ca—Cu—O is heat treated to cause interdiffusion. The method for producing a Bi-based oxide superconductor, comprising forming a Bi-based oxide superconductor layer by: 11. The Bi alloy is a Bi—Cu alloy,
The atomic ratio is Cu: 0.05-1.
It exists in the range of 0, The manufacturing method of the Bi based oxide superconductor of Claim 10 characterized by the above-mentioned. 12. The Bi alloy is a Bi—Pb alloy,
The atomic ratio is Pb: 0.2 to 1.5 with Bi as 1.
11. B according to claim 10, characterized in that
Method for producing i-based oxide superconductor. 13. The Bi alloy is a Bi—Cu—Pb alloy having an atomic ratio of Cu: 0.05 when Bi is 1.
-1.0, Pb: It exists in the range of 0.2-1.5, The manufacturing method of the Bi based oxide superconductor of Claim 10 characterized by the above-mentioned. 14. The at least Sr—Ca—Cu—O
The atomic ratio of the oxide containing the element is Ca: 0.25 to 1.5 and Cu: 0.25 to 2.0 with Sr as 1.
The method for producing a Bi-based oxide superconductor according to any one of claims 10 to 13, characterized by being within the range. 15. The base material B mixed with the oxide.
The composite is formed on the surface of a substrate by immersing in a melt of an i metal or a Bi alloy.
2. The method for producing a Bi-based oxide superconductor according to any one of 1. 16. The composite material is formed on the surface of the base material by casting a melt of Bi metal or Bi alloy mixed with the oxide into a pipe-shaped base material. 16. The method for producing a Bi-based oxide superconductor according to any one of 15. 17. A method for producing a Bi-based oxide superconductor, which comprises subjecting the composite formed by the method of claim 16 to wire processing and then heat treating.