JPH0520942A - Manufacture of bithmuth-based superconductor - Google Patents

Abstract

PURPOSE:To increase a critical current density by forming a superconductive phase oriented with relation to crystal orientation by diffusing at least Ca and Cu among Sr, Ca and Cu in oxide having a predetermined composition ratio. CONSTITUTION:An oxide having a ratio expressed by Bi1.95+wSr1.39+xCa1.29+yCu1.00+z (-0.2<=w; z<=0.2; -0.2<=x<=0.7; -0.29<=y<=0.1) for a start composition ratio is used for a raw material. Next, a solidified material, that is a long wire, obtained by melting and one-way solidification is used for a base material. By heat diffusing at least Ca and Cu in the base material, a superconductive phase of a phase 2212 of Bi:Sr:Ca:Cu of 2:2:1:2 is generated. In this case, the phase 2212 is generated continuously for the whole length of the long wire, so a long conductor can be manufactured, and the superconductive phase is generated along the orientation obtained by oxide, thereby a critical current density can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a bismuth-based superconducting conductor, and more particularly to a method suitable for obtaining a wire-shaped bismuth-based superconducting conductor.

[0002]

2. Description of the Related Art In recent years, oxide-based materials have attracted attention as superconducting materials having a higher critical temperature. A technique for producing a superconducting wire using such a material has been actively researched.

As far as the bismuth-based material is concerned, one of the methods for producing a superconducting wire is, for example, Bi ₂ Sr ₂ Ca ₁ Cu ₂ O.
There is an example in which a raw material having _x as a starting composition is melted and unidirectionally solidified to be a wire rod. In particular, according to a method (laser pedestal method) in which a laser beam is applied to a raw material rod to form a narrow band melting region and the region is moved little by little, a superconducting wire rod having a relatively high critical current density is obtained. ..

[0004]

However, Bi ₂
A material having Sr ₂ Ca ₁ Cu ₂ O _x as a starting composition causes decomposition and melting, so that even if directional solidification (growth) is performed,
If the growth rate becomes faster, the orientation of the structure is disturbed, and there is a problem that the critical current density of the obtained bismuth-based superconducting conductor is relatively low even after the heat treatment after the growth.

Therefore, an object of the present invention is to obtain a bismuth-based superconducting conductor having a high critical current density,
An object of the present invention is to provide a method for manufacturing a bismuth-based superconducting conductor.

[0006]

According to the present invention, there is provided the above-mentioned technique.
In order to solve the surgical problem, Bi_{1.95 + w}Sr_{1.39 + x}Ca
_{1.29 + y}Cu_{1.00 + z}(−0.2 ≦ w; z ≦ 0.2; −0.
2 ≦ x ≦ 0.7; −0.29 ≦ y ≦ 0.1)
The starting material composition is an oxide having the following composition.
And a solidified body obtained by unidirectional solidification, that is,
A long wire is used as a base material. Oxides with such composition ratio
Gives a long line of highly oriented and almost single phase even if it grows at high speed.
The inventors of the present invention have found that So this
As a base material, at least Ca and Cu are thermally diffused
The superconducting phase on the surface of the base metal along the orientation of the base metal.
Bi: Sr: Ca: Cu is almost 2: 2: 1: 2.
2212 phases are generated. This 2212 phase is a long line
Since it is generated continuously over a long length, a long superconducting conductor
Can be manufactured. Thermal diffusion of Ca and Cu described above
Is an organic acid salt of Ca applied to the surface of the base material,
Heat treatment, then apply Cu organic acid salt and heat treatment
It is achieved by

[0007]

As described above, according to the present invention, at least Ca and Cu of Sr, Ca and Cu are diffused in an oxide having a predetermined composition ratio to obtain a crystallographically oriented superconducting phase. It is what Bi ₂ Sr _{2 has} good orientation even if it is grown at high speed from the viewpoint of industrial productivity.
In order to produce the Ca ₁ Cu ₂ O _x phase, the present invention uses
As the starting composition, not the oxide of Bi ₂ Sr ₂ Ca ₁ Cu _{2 but} the oxide having the above-mentioned specific composition ratio is used. This oxide has an orientation that can be obtained under high-speed growth.
It is significantly superior to the starting composition of Bi ₂ Sr ₂ Ca ₁ Cu ₂ . Therefore, using this oxide as a raw material,
First, after producing a long wire, at least Ca that forms a superconducting phase on its surface by a diffusion reaction with the above oxide.
When heat treatment is performed in the state of adding Cu and Cu, a superconducting phase is generated along the orientation obtained by the above oxide, so that a large critical current can be passed.

Any method can be used for producing the long wire made of the above-mentioned oxide as long as it is a unidirectional solidification method. In particular, a laser that can produce a large temperature gradient and a narrow melting zone can be used. Pedestal method is preferred. According to this method, a thin long wire having excellent orientation can be efficiently produced from the above oxide.

Further, at least Ca and C are present on the long line.
As a method of imparting u, an organic acid salt thermal decomposition method or a gas phase method is preferably used. The reason is that a film containing these elements can be formed on a long line with a high adhesive force, and the film thickness can be controlled. Therefore, the control for optimizing the diffusion region by heat treatment can be easily performed. Because.

In the present invention, the step of thermally diffusing at least Ca and Cu into a long wire may be performed by simultaneously applying all of these elements on the long wire and simultaneously diffusing them in a single heat treatment. The element may be applied to the long wire and heat-treated once, and then repeated.

The starting composition ratio of the oxide for obtaining the long wire is selected in the above-mentioned range because, within this range, the long composition is excellent in crystal orientation during unidirectional solidification. This is because a line can be obtained, but if it deviates from this range, the crystal orientation will be broken, and eventually good superconducting properties cannot be obtained.

[0012]

Example 1 Experimental Example 1 Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , and CuO were used, and Bi: Sr: Ca: Cu was blended in various composition ratios as shown below.

(1) Bi _1.95 Sr _1.39 Ca _0.29 Cu
_1.00 (2) Bi _1.75 Sr _1.19 Cu _0.80 (3) * Bi _1.65 Sr _1.09 Cu _0.70 (4) Bi _2.15 Sr _2.09 Ca _0.39 Cu _1.20 (5) * Bi _2.25 Sr _1.69 Ca _0.59 Cu _1.30 (6) Bi _1.95 Sr _1.39 Ca _0.29 Cu _1.00 (7) Bi _2.06 Sr _2.00 Cu _1.00 (8) Bi _1.95 Sr _1.69 Ca _0.29 Cu _1.00 (9) Bi _2.00 Sr _2.00 Cu _1.00 (The above sample numbers are marked with * are comparative examples. ) Each of the powders of the above Samples 1 to 9 was subjected to heat treatment at 750 ° C. for 12 hours, then at 800 ° C. for 96 hours, and pulverization after each heat treatment.
After being formed into a rod shape having a diameter of 4 mm and a length of 100 mm by P, heat treatment is again performed at 800 ° C. for 20 hours,
Then, melting and unidirectional solidification were performed by a laser pedestal method. At this time, regarding the growth rate, the feed rate of the raw material sintered rod was 50 mm / h and the pulling rate was 500 mm.
It was set to be / h. This makes the diameter 0.8 m
A fiber (long wire) having m and a length of 100 mm was obtained.

Each of the fibers thus obtained was further coated with an organic acid salt using toluene as a solvent and heat-treated. The organic acid salt was applied by immersing the fiber in an organic acid salt solution, slowly pulling it up, and then drying it at room temperature for 10 minutes and at 550 ° C. for 10 minutes.
By repeating this dipping and drying process 30 times,
A 3 μm thick film was formed on the fiber. Further, in the heat treatment, the fiber treated as described above is put into a furnace and heated to 840 ° C. at a rate of 0.33 ° C./min.
Heat treatment was performed at the same temperature for 100 hours.

The organic acid salt used for coating and heat treatment of the organic acid salt and the coating and heat treatment method were as follows for each sample. Toluene was used as the solvent of the organic acid salt.

For Samples 1 to 5, coating and heat treatment were repeated in the order of strontium naphthenate, calcium naphthenate, and copper naphthenate.

For Samples 6 and 7, coating and heat treatment were repeated in the order of calcium naphthenate and copper naphthenate.

For sample 8, strontium naphthenate, calcium naphthenate and copper naphthenate were added to S.
A mixture of r: Ca: Cu = 1: 1: 2 was applied and heat treated.

For sample 9, a mixture of calcium naphthenate and copper naphthenate mixed at a ratio of Ca: Cu = 1: 1 was applied and heat treated.

When the characteristics of each fiber thus obtained were evaluated, the results shown in Table 1 below were obtained. In Table 1, the critical temperature "Tc" and the critical current density "Jc (0T, 77.3K)" at the liquid nitrogen temperature (77.3K) in the zero magnetic field are shown.

[0021]

[Table 1] When observing the cross section of the obtained fiber with an optical microscope,
At the boundary between the bonded film by the fiber and an organic acid salt pyrolysis method obtained by unidirectional solidification, visible reaction phase with a thickness of 1μm is, when composition analysis by EDX, the phase Bi ₂ Sr ₂ Ca It was found to be ₁ Cu ₂ O _x .

Experimental Example 2 Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ and CuO were blended so that Bi: Sr: Ca: Cu had various composition ratios as shown below.

(10) Bi _1.95 Sr _1.39 Ca _0.29 C
u _1.00 (11) Bi _1.75 Sr _1.19 Cu _0.80 (12) * Bi _1.65 Sr _1.09 Cu _0.70 (13) Bi _2.15 Sr _2.09 Ca _0.39 Cu _1.20 (14) * Bi _2.25 Sr _1.69 Ca _0.59 Cu _1.30 (15) Bi _1.95 Sr _1.39 Ca _0.29 Cu _1.00 (16) Same as above (17) Bi _2.00 Sr _2.00 Cu _1.00 (18) Same as above (Samples marked with * indicate comparative examples.) Using the powders of Samples 10 to 18 above The same operation as in Experimental Example 1 was performed, and the diameter was 0.8 mm and the length was 100 mm.
Fiber (long wire) was obtained.

Each of the fibers of Samples 10 to 18 thus obtained was subjected to sputtering and heat treatment under the following conditions.

Samples 10 to 14 were sputtered using a compound of SrCO ₃ , CaCO ₃ and CuO as a sputtering substance, and then heat-treated.

For samples 15 and 17, a compound of CaCO ₃ and CuO was used as a sputtering substance, and after sputtering, heat treatment was performed.

For samples 16 and 18, CaCO
₃ , sputtering and heat treatment were repeated in the order of CuO.

In the above-mentioned sputtering, 3 μm (Sample 1
6 and 18 were set to obtain the film thickness (for one sputtering operation). Samples 10-1
In Nos. 5 and 17, SrCO ₃ , CaCO ₃ and CuO, or CaCO ₃ and CuO were mixed in equimolar ratios and sintered at 900 ° C. for 20 hours, and used as the sputtering material. For each sample, the condition of heat treatment performed after sputtering is 840 ° C.
The temperature was raised at a rate of 0.33 ° C./minute until the temperature was maintained for 100 hours.

The characteristics of each fiber thus obtained were evaluated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0030]

[Table 2] Also, when observing the cross section of the obtained fiber with an optical microscope, the thickness at the boundary between the fiber obtained by the unidirectional solidification method and the film bonded by the sputtering method was the same as in Experimental Example 1. A reaction phase of 1 μm is visible, and when the composition is analyzed by EDX, this phase shows Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _x.
It turned out to be

Other Comparative Experimental Example Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ and CuO were mixed in a composition ratio of Bi: Sr: Ca: Cu = 2: 2: 1: 2, and 800 12 hours at ℃, then 86
Each of the heat treatments at 0 ° C. for 96 hours and the pulverization after each heat treatment were repeated, and the obtained powder was subjected to CIP to obtain a diameter of 4 m.
After forming into a rod shape of m and 100 mm in length,
Heat treatment was performed at 00 ° C. for 2 hours, and then melting and directional solidification were performed by a laser pedestal method. At this time, as the growth rate, the feed rate of the raw material sintering rod was 10 mm.
/ H, and the pulling speed was set to 100 mm / h. This gives a diameter of 0.8 mm and a length of 100 m.
m fibers were obtained. In addition, 84
After performing a heat treatment at 0 ° C. for 96 hours, the characteristics of the obtained fiber were evaluated. It shows that the critical current density is 88
K, the liquid nitrogen temperature at zero magnetic field (77.3K)
The critical current density was 5000 A / cm ² .

The composition of the phase observed in the cross section was analyzed by EDX. As a result, most of the phases were Bi ₂ Sr ₂ Ca.
_{It was 1} Cu ₂ O _x .

[0033]

As described above, according to the present invention, while a fiber grown at a high speed, that is, a long wire is used as a precursor,
A bismuth-based superconducting conductor having excellent performance in terms of critical current density can be manufactured. Therefore, by producing a superconducting wire by such a method, the possibility of practical application to power cables and magnets is increased.

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location // H01B 12/04 ZAA 8936-5G

Claims (1)

Claims 1. Bi _{1.95 + w} Sr _{1.39 + x} Ca _{0.29 + y} Cu
_{1.00 + z} (−0.2 ≦ w; z ≦ 0.2; −0.2 ≦ x ≦
0.7; a step of obtaining a long wire by melting and unidirectionally solidifying an oxide whose starting composition ratio is a ratio represented by −0.29 ≦ y ≦ 0.1), and at least Ca and A method for producing a bismuth-based superconducting conductor, comprising the step of thermally diffusing Cu into the long wire.