JPH1059718A - Production of thallium-based superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a uniform, dense and high Tc Tl-based oxide superconductor by subjecting a 1st element composed of an element of Tl-O and a 2nd element composed of an element of Ba-Ca-Cu-O to diffusion heat treatment on the surface of a Ni-base material. SOLUTION: The Tl-base oxide superconductor is formed by subjecting the 1st element composed of at least composed of Tl-O and the 2nd element composed of at least the elements of Ba-Ca-Cu-O to diffusion heat treatment on the Ni or Ni-based alloy material. The 1st element is composed of the element of Tl-Ba-Ca-Cu-O preferably in the atomic ratio of Tl:Ba:Ca:Cu=1:0-1.0:0-1.0:0-1.0:0-1.0 and the 2nd element is composed of the element of Ba-Ca-Cu-O preferably in the atomic ratio of Ba:Ca:Cu=1:0.5-3.0:0.5-4.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is considered to be promising as a superconducting magnet wire for a magnetic resonance imaging apparatus (MRI-CT) or a conductive material for a superconducting power transmission. Particularly, the present invention is applicable to a liquid nitrogen temperature (77K) and a magnetic field. The present invention relates to a method for producing a Tl-based high-critical-temperature oxide superconducting wire, which is expected to be applied and is being researched and developed.

[0002]

BACKGROUND ART Y (yttrium) based on whose values the critical temperature T _c of the transition from normal conducting state to the superconducting state exceeds the liquid nitrogen temperature (77K), Bi (bismuth) group, Tl (thallium) group, Hg ( Oxide superconductors such as mercury) have been discovered. These oxide superconductors have been required to be cooled by liquid helium.
_Since superconducting materials can be used under significantly more advantageous cooling conditions than metal-based superconductors such as 3Sn, research and development are proceeding as superconducting materials that are extremely promising in practical use.

However, since the oxide superconductor has extremely brittle mechanical properties, the following method has been used as an example of a technique for processing the oxide superconductor into a wire shape. That is, after calcining a plurality of raw material powders containing elements constituting the oxide superconductor to remove unnecessary components, the calcined powder is filled in a metal tube of Ag or Ag alloy, and swaged.
It is processed into a tape of a desired thickness by a method such as drawing and rolling, and is subjected to a heat treatment to cause a sintering reaction in the compressed mixed powder inside the metal tube to generate an oxide superconductor having a desired composition. Manufactures superconducting wires.

[0004] However, in the conventional method for producing an oxide superconductor, it is difficult to completely and uniformly mix the raw material powders. Therefore, there has been a problem that the entire superconductor does not have a uniform composition even when heat treatment is performed. . In addition, when the metal base composite with the Tl-based oxide superconductor is Ag, Tl and Ag are about 29%.
Since it has a eutectic point of 0 ° C., depending on the amount of Tl contained therein, Ag is melted at a temperature much lower than 960 ° C., which is the melting point of pure Ag, and it is difficult to produce a Tl-based oxide superconducting wire. Was something. Although Ag has good workability, it has poor mechanical strength as a wire, and in practice, it has been necessary to take measures such as using a stainless steel tape or the like as a reinforcing material in order to obtain mechanical strength.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to make it possible to easily produce a Tl-based oxide superconducting wire and to form a superconducting material having a uniform composition. It is an object of the present invention to provide a method for producing a Tl-based oxide superconductor.

[0006]

Therefore, the present inventor has focused on a method of synthesizing a Tl-based oxide superconductor by a diffusion method which was previously made by the present inventor (Japanese Patent Laid-Open No. 6-219440). It has been found that a homogeneous and dense Tl-based oxide superconductor can be formed on a base material by a method of forming a wire rod which has been improved. That is, the invention of claim 1
i or at least Tl-
A first element composed of an element of O and at least Ba-
A method for producing a Tl-based oxide superconductor, which comprises producing a Tl-based oxide superconductor by diffusion heat treatment with a second element composed of a Ca-Cu-O element.

According to a second aspect of the present invention, the first element is Tl
-Ba-Ca-Cu-O, whose atomic ratio is set to Tl as 1, Ba: 0 to 1.0, and Ca: 0 to 1..
0, Cu: 0 to 1.0, and the second element is composed of an element of Ba—Ca—Cu—O. 0.0, Cu: 0.
It is characterized by being in the range of 5 to 4.0.

According to a third aspect of the present invention, the raw material of the first and second elements is one or more fluorides selected from TlF, BaF ₂ , CaF ₂ and CuF ₂ . A fourth aspect of the present invention, the first element, V further V ₂ O ₅ as one of Tl in an atomic ratio of: is added within an amount of 0.2 to 4.0.

According to a fifth aspect of the present invention, a second element is coated on the surface of a substrate made of Ni or a Ni-based alloy, preliminarily heat-treated, and then the first element is coated thereon. Diffusion heat treatment.

According to a sixth aspect of the present invention, the first element and the second element
The composite powder obtained by mixing the powders with the elements described above is filled in a sheath material made of Ni or a Ni-based alloy and subjected to diffusion heat treatment. The invention according to claim 7 is characterized in that, after the diffusion heat treatment, in an atmosphere containing oxygen or oxygen of 50 mol% or more,
Annealing is performed in the range of 300 ° C. to 650 ° C.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. In the present invention, Ni or a Ni-based alloy is used as the base material. Ni, which is the base material, does not diffuse into the superconductor layer during the heat treatment, so that it does not deteriorate the superconducting properties. Further, since it is extremely excellent in corrosion resistance, it is subjected to high-temperature heat treatment in the air or in an atmosphere containing oxygen. Can withstand enough. Also, Ni is liable to exhibit a cubic texture with uniform crystal orientations by performing appropriate processing such as rolling and recrystallization heat treatment. Tl generated on this crystallographically oriented Ni substrate
The base oxide superconductor can be expected to orient the crystal under the influence of the texture of the Ni base material. Further, Ni or Ni-based alloy has mechanical strength twice or more that of Ag which has been widely used in oxide superconducting wires, and the price is one order of magnitude lower than Ag. In addition, the cost required for manufacturing the oxide superconducting wire can be significantly reduced. Ni-based alloys applicable in the present invention include Nimonic alloy, Inconel
(Inconel) alloy.

A Tl-based oxide superconductor is formed on the surface of the substrate by a diffusion heat treatment of the first element and the second element. The first element desirably has a melting point as low as possible to promote diffusion during heat treatment of the composite,
An oxide or fluoride composed of at least an element of Tl-O is used. This first element is Tl-Ba-C
It is composed of an element of a-Cu-O, and its atomic ratio is set to 1 for Tl and 0 to Ba: 0 to obtain preferable superconducting properties.
1.0, Ca: 0 to 1.0, and Cu: 0 to 1.0 are desirable. The first element has a melting point of 700 ° C.
The melting point is about 850 ° C., but by adding V ₂ O ₅ which forms a eutectic system with Tl ₂ O ₃ , the melting point is 385 ° C. to 55 ° C.
It can be lowered to about 0 ° C. V ₂ O ₅ is preferably added in the range of V: 0.2 to 4.0, where Tl is 1 in atomic ratio.

The second element also functions as a base when diffusing the composite, and desirably has a melting point as high as possible, and uses an oxide composed of at least Ba-Ca-Cu-O. Ba-Ca-C of this second element
The atomic ratio of u is preferably Ba to obtain favorable superconducting properties.
Is set to 1, Ca: 0.5 to 3.0, Cu: 0.5 to
It is desirable to be in the range of 4.0. The second element has a melting point of 900 ° C. or higher.

The above-mentioned first and second elements are obtained by mixing the raw material powders in a predetermined composition ratio, then performing calcination for removing unnecessary components, and then pulverizing into fine powders. Note that the first and second
As raw materials for the elements of TlF, BaF ₂ , CaF ₂ , C
The use of a fluoride such as uF ₂ has the advantage that the critical current characteristics of a generated T1-based oxide high-temperature superconductor in liquid nitrogen under a magnetic field can be improved.

In the present invention, a first element,
The second element is coated, and the composite is subjected to a diffusion heat treatment to produce a Tl-based oxide superconductor. Specific methods include (1) a tape or wire made of Ni or a Ni-based alloy. First, the second element is coated on the substrate in the form of a spray, screen printing, spin coating, or the like, and then subjected to a preliminary heat treatment to increase the adhesion to the substrate, A method of producing a composite tape, a wire, or the like by continuously coating the first element on the surface in a similar manner; and (2) a method of forming the first element and the second element in a Ni or Ni-based alloy base sheath. The composite obtained by filling the mixed powder of the elements of the above, drawing, repeating flat roll rolling and heat treatment, tape,
There is a method for producing a wire or the like.

Then, a Tl-based oxide superconductor is obtained by applying a diffusion heat treatment to the tape or the linear composite thus obtained. After the diffusion heat treatment, if the produced tapes, wires, and the like are annealed in an atmosphere containing oxygen or oxygen of 50 mol% or more, a material having better performance can be provided. Here, the reason why the annealing atmosphere is an atmosphere containing oxygen or oxygen of 50 mol% or more is that, if the atmosphere contains less than 50 mol% of oxygen such as in the air, the characteristics cannot be improved even if annealing is performed. .

[0017]

As described above, according to the present invention, the Tl-based oxide superconductor is divided into a first element having a low melting point phase and a second element having a high melting point phase, and the Tl-based oxide superconductor is formed by a diffusion method. Ni body
This is a method of synthesizing on a substrate. At this time, Ni substrate and Tl
The adhesion to the base oxide superconducting layer is extremely good, and Ni does not diffuse into the Tl-based oxide superconducting layer by diffusion heat treatment, so that the superconductivity inherent to the Tl-based oxide high-temperature superconductor is lowered. I won't let you. Ni, which is a base material, is extremely excellent in corrosion resistance, and thus can sufficiently withstand high-temperature heat treatment in the air or in an atmosphere containing oxygen.

Further, Ni is liable to exhibit a cubic texture with uniform crystal orientations by performing appropriate processing such as rolling and recrystallization heat treatment. The Tl-based oxide superconductor generated on the crystal-oriented Ni base material can be expected to be crystal-oriented under the influence of the texture of Ni. Further, Ni or Ni-based alloy has mechanical strength twice or more that of Ag which has been widely used in oxide superconducting wires, and the price is one order of magnitude lower than Ag. In addition, the cost required for manufacturing the oxide superconducting wire can be significantly reduced.

Further, when a Tl-based oxide superconductor is produced by a diffusion method, the superconducting characteristics such as critical current are improved by using a fluoride or a V-based oxide as the first element which is a low melting point component. Is done. When a fluoride such as TlF is added to the first element, the magnetic field characteristics are remarkably improved due to a change in the crystal structure of the generated Tl-based oxide superconductor.
7K, a Tl-based oxide superconductor having a uniform and dense structure having a large transport current under a magnetic field can be formed on a Ni substrate. Further, when an oxide of V ₂ O ₅ having a eutectic composition with Tl ₂ O ₃ is added to the first element, the melting point can be further lowered, and the second element, which is a high melting point component, can be used.
Diffusion with the element is promoted, and the Tl-based oxide superconducting diffusion layer, which is much thicker than the Tl-based oxide superconducting diffusion layer by the diffusion method previously filed by the present inventors, can be uniformly formed without changing the heat treatment conditions. It can be produced on a Ni substrate.
For example, the thickness of the Tl-based oxide superconducting diffusion layer can be as large as about 600 μm, depending on the heat treatment conditions. Further, since the added V-based oxide is extruded to the outside without being taken into the Tl-based oxide superconducting diffusion layer, it promotes generation of a superconducting phase, but does not deteriorate superconducting characteristics. Further, the growth of the superconducting crystal grains can be promoted, and the crystal grain boundaries that hinder the transport current can be reduced. Such an effect is due to T _{2 in} addition to V ₂ O ₅
It can also be obtained by adding an oxide which forms a eutectic system having a low melting point with l ₂ O ₃ .

As described above, according to the present invention, by performing diffusion heat treatment on the composite, the components of the first element diffuse and react in the second element, and the base material of Ni or a Ni-based alloy is formed. on the surface of, the uniform generation thick Tl group oxide ultrafine conductive layer of dense high T _c, it is possible to provide an oxide high temperature superconductor suitable for practical use.

[0021]

【Example】

(Example 1) Raw material powders of BaCO ₃ , CaCO ₃ , and CuO were blended to have a composition of BaCa ₂ Cu ₂ O ₅ ,
Unnecessary components such as CO ₂ were removed by calcination at 900 ° C. for 18 hours, and pulverized by a ball mill to a particle size of about several microns. An acrylic binder was added to this fine powder to form a paste, thereby producing a second element that was a high melting point component. Then, this paste-like second element is
Thickness 0.1 made by rolling into a tape shape with a flat roll
mm, width 7mm, length 30mm on the surface of Ni substrate,
It was coated to a thickness of about 0.2 mm by a screen printing method.
After sufficiently drying, the binder was removed by heat treatment at 400 ° C. for 6 hours, followed by heat treatment at 900 ° C. for 12 hours to bring the second element into close contact with the Ni substrate. On the other hand, raw materials of TlF and BaO were blended so as to have a composition of Tl ₂ BaOF ₂ , and kneaded sufficiently in an agate mortar to prepare a first element. This mixed powder, which is the first element, is suspended in ethanol and slurried to a thickness of about 0.1 mm and applied to the surface of the second element coated on a Ni substrate by a spray method. To produce a composite. This complex is placed in an atmosphere containing Tl ₂ O ₃ vapor for 83 hours.
Diffusion heat treatment was performed at 0 ° C. for 2 hours. In the cooling process of the diffusion heat treatment, the cooling is slowly performed at a rate of 0.1 ° C./min up to 800 ° C., and then 1.7 ° C./min.
Cooled at the speed. Further, at 600 ° C. in an oxygen stream,
A sample was prepared by annealing for 2 hours. When the composition distribution of the sample cross section was analyzed by an electron probe microanalyzer, no diffusion of Ni from the substrate to the superconducting diffusion layer was observed. The change due to the magnetic field of the I _c at 77K samples shown in curve 1 of FIG. Curve 2 in FIG. 1 is the case where Tl ₂ O ₃ is used as the raw material powder of the first element, and the other sample preparation conditions are the same as curve 1. Curve 1 gives a transport current of about 70 A under zero magnetic field,
It is about 3.5 times that of curve 2. The transport current at 77 K in the curve 2 sharply decreases due to the application of an external magnetic field, but the curve 1 does not show a significant decrease in the transport current even under a magnetic field of 1.5 T. Thus, when TlF was used instead of Tl ₂ O ₃ , the I _c characteristics under a magnetic field at 77 K were significantly improved. (Example 2) A composite of a nimonic alloy substrate having the same dimensions as the substrate of Example 1 and a second element having the same composition as that of Example 1 was produced by the same method. Next, Tl ₂
The raw material powders of O ₃ and V ₂ O ₅ were blended so that the atomic ratio of Tl was 1 and V was 0.64, and kneaded sufficiently in an agate mortar to produce a first element. This was applied to the surface of the second element coated on the Ni substrate in the same manner as in Example 1. Next, the composite was subjected to diffusion heat treatment at 800 to 880 ° C. for 10 minutes to 2 hours in an atmosphere containing Tl ₂ O ₃ vapor. FIG. 2 shows the relationship between the thickness of the generated diffusion layer and the heat treatment temperature. In Curve 3 in which V ₂ O ₅ was added to the first element, a diffusion layer having a thickness approximately three times that of Curve 4 in which V ₂ O ₅ was not added was generated, and the diffusion was significantly promoted. After diffusion heat treatment, V was added without any solid solution in the superconducting phase, T _c represents a 117K, I _c is increased substantially in proportion to the thickness of the diffusion layer. (Example 3) A first element and a second element used in the sample of curve 1 of Example 1 were mixed in a Ni base sheath having an outer diameter of 10 mm and an inner diameter of 7 mm at a molar ratio of 1: 1. The composite obtained by filling the mixed powder thus obtained was subjected to groove roll and flat roll rolling to prepare a tape-shaped composite wire having a width of 7 mm and a thickness of 0.3 mm. Next, this composite wire was subjected to a diffusion heat treatment under the same conditions as in Example 1, and after the diffusion heat treatment, annealed in oxygen at 600 ° C. for 12 hours to produce a Tl-based oxide superconductor tape material. This tape material, 77
K showed an I _c value of about 40 A at zero magnetic field. Since the Ni base material has a strong (100) <001> texture by the heat treatment after processing, it is considered to be effective in growing the Tl-based oxide superconductor layer in contact with the Ni base material in a preferred orientation.

[Brief description of the drawings]

[1] Example 1 of the sample, 77K, a diagram showing a change in the I _c under a magnetic field, curve 1 is for using TlF as raw material powder of the first element, curve 2 TlF Is not used. The magnetic field is applied in a direction perpendicular to the current and parallel to the sample surface.

FIG. 2 is a graph showing the relationship between the thickness of a diffusion layer formed in the sample of Example 2 and the temperature of diffusion heat treatment. Curve 3 is a curve obtained by adding V ₂ O ₅ to the first element, and curve 4 ( (Broken line) is V ₂ O
₅ is not added. The diffusion heat treatment time is 2 hours which is constant for each temperature.

[Explanation of symbols]

Curve 1: Sample using TlF for the first element Curve 2: Sample not using TlF for the first element Curve 3: Sample obtained by adding V ₂ O ₅ to the first element Curve 4: First element Sample without V ₂ O ₅

Claims (7)

[Claims] 1. The method according to claim 1, wherein the surface of the Ni or Ni-based alloy substrate is
A first element composed of at least an element of Tl-O;
A method for producing a Tl-based oxide superconductor, which comprises producing a Tl-based oxide superconductor by diffusion heat treatment with at least a second element composed of Ba-Ca-Cu-O. 2. The method according to claim 1, wherein the first element is Tl-Ba-Ca-
It is composed of an element of Cu—O, and its atomic ratio is Ba: 0 to 1.0, Ca: 0 to 1.0, and Cu: 0, where Tl is 1.
~ 1.0, and the second element is Ba-Ca
-Cu-O element, whose atomic ratio is Ba to 1
The manufacturing method of the Tl-based oxide superconductor according to claim 1, wherein Ca: 0.5 to 3.0 and Cu: 0.5 to 4.0. 3. The first and second elements are characterized in that the raw material is T
1 selected from IF, BaF ₂ , CaF ₂ and CuF ₂
The method for producing a Tl-based oxide superconductor according to claim 1 or 2, wherein the method is a kind or two or more kinds of fluorides. 4. A method according to claim 1, wherein the first element further comprises V ₂ O ₅ added in an atomic ratio of Tl of 1 to V: 0.2 to 4.0. Any one of
3. The method for producing a Tl-based oxide superconductor according to 1.). 5. A second element is coated on the surface of a substrate made of Ni or a Ni-based alloy, preliminarily heat-treated, and further,
The method for producing a Tl-based oxide superconductor according to any one of claims 1 to 4, wherein the element is coated and the obtained composite is subjected to diffusion heat treatment. 6. A method of filling a composite powder obtained by mixing powders of the first element and the second element into a sheath material made of Ni or a Ni-based alloy and performing a diffusion heat treatment. The T according to any one of claims 1 to 4, characterized in that:
A method for producing an l-based oxide superconductor. 7. Oxygen or 50 mol% after the diffusion heat treatment.
300 ° C to 650 ° C in the above atmosphere containing oxygen
The annealing is performed in the range of (1) to (6).
The method for producing a Tl-based oxide superconductor according to any one of the above.