JP3248190B2 - Oxide superconducting wire, its manufacturing method and its handling method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxide superconducting wire,
The present invention relates to a method for manufacturing the same and a method for handling the same, and more particularly to an improvement for improving a strain resistance characteristic of a critical current density provided by a superconducting wire.

[0002]

2. Description of the Related Art In recent years, ceramic superconducting materials, that is, oxide superconducting materials, have attracted attention as superconducting materials exhibiting higher critical temperatures. Above all, 90K for yttrium, 110K for bismuth and 120K for thallium
Because of its high critical temperature, its practical use is expected.

[0003] As a method for obtaining a superconducting wire such as a long superconducting wire or a superconducting pattern wired on an appropriate substrate using a superconductor made of such an oxide superconducting material, a raw material powder is prepared by using a metal powder. There is known a method of producing a superconducting wire having a superconductor covered with a metal sheath by converting the raw material powder into a superconductor as desired by heating the raw material powder in a state covered with a sheath. The obtained superconducting wire can be more specifically applied to cables, bus bars, power leads, magnets, coils, and the like.

[0004]

In order to apply such a superconducting wire to a cable or a magnet, it is necessary to have a high critical current density in addition to a high critical temperature. In particular, it is necessary not only to secure a necessary critical current density in a magnetic field to be used, but also to be able to maintain a high critical current density under a used strain.

[0005] However, superconducting wires containing oxide superconductors have very poor strain resistance characteristics at the critical current density. For example, when they are bent at a certain curvature, the critical current density decreases.

[0006] Therefore, an object of the present invention is to provide a superconducting wire and a method of manufacturing the superconducting wire in which the critical current density does not significantly decrease even when strain is applied.

Another object of the present invention is to provide a preferred method of handling a superconducting wire as described above.

[0008]

The superconducting wire according to the present invention has a so-called multi-core structure, and includes a metal sheath,
A plurality of superconductors distributed independently in the thickness direction of the metal sheath within the metal sheath. The thickness dimension of each superconductor is set to 5% or less of the thickness dimension of the metal sheath.

The present invention relates to Bi-Sr-Ca-Cu-O
Or the component of (Bi, Pb) -Sr-Ca-Cu-O
Bi + Pb: Sr: Ca: Cu = 1.5-2.
5: 1.8 to 2.2: 1.5 to 2.5: 2.5 to 3.5
This is particularly advantageous when the superconductor is composed of a bismuth-based oxide superconductor having the following composition ratio .

The present invention also provides a method for manufacturing a superconducting wire including the above-described oxide superconductor. This manufacturing method comprises the steps of: preparing a plurality of wires made of an oxide superconductor covered with a first metal sheath; filling the plurality of wires into a second metal sheath; The plurality of strands so that the thickness of the superconductor contained in the strands is less than or equal to 5% of the thickness dimension of the second metal sheath and the second metal sheath is deformed into a tape shape. Performing a plastic working in which a compressive load is applied in the cross-sectional direction to the second metal sheath filled with the at least one time. The step of further filling the third metal sheath with the plurality of second metal sheaths each filled with a plurality of strands and performing plastic working may be further repeated at least once.

The present invention also provides a method for handling an oxide superconducting wire. The oxide superconducting wire includes a metal sheath having a dimension in a thickness direction, and a plurality of oxide superconductors distributed in the thickness direction independently of each other in the metal sheath. The thickness dimension is 5% of the thickness dimension of the metal sheath
Such an oxide superconducting wire is handled while controlling the strain (thickness of metal sheath / bending diameter) within a range of 0.3% or less.

[0012]

Once a crack has formed in a superconductor, it tends to propagate easily. This tendency is remarkable in oxide superconductors that are ceramics. Therefore,
If the magnitude of the strain exceeds a certain value, a crack occurs in the superconductor, and the crack once generated propagates to a portion where the strain is small, causing a decrease in critical current density. However, according to the present invention , since the superconductor is divided so that the thickness of the superconductor is equal to or less than a predetermined value,
Crack propagation can be prevented without reducing the amount of current that can flow. This makes it possible to improve the distortion resistance characteristics of the critical current density.

[0013]

Therefore, according to the present invention, a superconducting wire having a critical current density that does not decrease so much even when strain is applied can be obtained. Therefore, it becomes possible to apply the oxide superconducting wire, in which strain resistance is particularly problematic, to applications to which strain is applied, for example, a cable or a magnet without any problem.

In the present invention, when an oxide superconductor is used as the superconductor, such an oxide superconductor is preferably oriented c-axis in the thickness direction.

The above-described oxide superconductor may be any of yttrium, bismuth and thallium. However, bismuth-based oxide superconductors are particularly suitable. Bismuth-based oxide superconductor is B
i-Sr-Ca-Cu-O or (Bi, Pb) -Sr
-Ca-Cu-O, which contains Bi or (Bi, Pb) -Sr-Ca-C
wherein u is a 2223 composition, indicating a critical temperature of 110 K 22
More preferably, the 23 phases have their ab planes oriented in the direction of current flow. According to the invention, 1
A structure in which the a-b plane of the 2223 phase showing a critical temperature of 10K is oriented in the direction in which current flows can be easily obtained.

The bismuth-based oxide superconductor satisfies all of the requirements of higher critical temperature and critical current density, less toxicity and no need for rare earth elements, as compared with yttrium-based or thallium-based superconductors. It can be said that it is particularly preferable also in terms of

It should be noted that the yttrium-based and thallium-based materials can improve the degree of orientation to some extent, though not as much as the bismuth-based materials. Has been found.

In the present invention, the superconducting wire is in the form of a long wire in order to provide practicality in a wider range.

When the superconducting wire in the form of a long wire according to the present invention is further covered with an organic coating made of an organic substance, the superconducting properties of the superconducting wire can be further stabilized against bending of the superconducting wire. .

According to the above-described method for manufacturing an oxide superconducting wire according to the present invention, the thickness of the oxide superconductor covered with the metal sheath is divided into 5% or less of the total thickness of the superconducting wire. Is easy.

Further, the wire may be subjected to wire drawing before filling in the second metal sheath, which may reduce the thickness of each superconductor contained in the obtained oxide superconducting wire. It is valid.

Further, by the plastic working applied in the manufacturing method according to the present invention, the second metal sheath is preferably deformed into a rectangular tape shape.

In order to improve the critical current density, heat treatment is preferably performed after plastic working, and more preferably, plastic working and heat treatment are repeated a plurality of times.

Further, by changing the number of strands filled in the second metal sheath, it is possible to easily adjust the thickness of each superconductor contained in the oxide superconducting wire obtained in the plastic working step. Can be. For example, if the number of strands is increased, the thickness of the superconductor after plastic working can be easily reduced.

According to the present invention, the strain applied to the superconducting wire including the oxide superconductor is reduced by 0.3% as described above.
By controlling within the following range, deterioration of superconducting characteristics due to strain can be substantially prevented. Such distortion control is performed in various steps including, for example, heat treatment for producing a superconducting wire, and after production, feeding from a reel, winding on a reel, and further, a cable, a busbar, a power lead, This is performed in the case where a coil or the like is used. If the strain is controlled within the range of 0.3% or less as described above, the critical current density does not substantially decrease even if the strain is repeatedly applied, so that the superconducting wire can be used for various applications.

If the superconducting wire is heat-treated in a state of being wound with a curvature giving a strain of 0.3% or less, there is little or no deterioration in superconducting characteristics due to the strain during the heat treatment and at the time of unwinding, and particularly, bending. A superconducting wire exhibiting stable superconducting characteristics can be obtained.

[0027]

In order to obtain a superconducting wire containing an oxide superconductor according to the present invention, for example, the following manufacturing method is applied.

First, an oxide superconductor is filled in a first metal sheath to obtain a strand. This wire is subjected to wire drawing, thereby making it thinner. The plurality of wires thus thinned are then filled in a second metal sheath, and plastic working such as wire drawing and rolling is performed to further thin the wires. As a result, an oxide superconducting wire in which the thickness of the oxide superconductor contained in each individual wire is reduced to 5% or less of the entire thickness is obtained. This oxide superconducting wire has, for example, a rectangular tape shape.

In order to increase the critical current density of the oxide superconducting wire, the wire is further subjected to wire drawing and rolling, followed by heat treatment. And again,
Rolling and heat treatment may be performed. At this time,
Wire drawing may be combined with heat treatment instead of rolling.

In the case of a bismuth-based oxide superconductor, the temperature of the heat treatment is set slightly higher than the temperature at which the 2223 phase is predominantly formed, so that a structure having the intended high critical current density can be obtained. Can be.

If the powder to be filled in the first metal sheath is kept in a submicron state, a superconductor with good uniformity can be obtained.

The heat treatment temperature cannot be uniquely determined because an optimum temperature is selected depending on the heat treatment atmosphere. For example, when lowering the oxygen partial pressure of the heat treatment atmosphere, the heat treatment temperature becomes lower.

The metal sheath has a function of stabilizing the superconducting wire. As a metal that provides such a metal sheath, a metal that does not react with the superconductor, has good workability, and has a small specific resistance that functions as a stabilizing material is suitable.For example, silver, a silver alloy, gold, Alternatively, a gold alloy is used. In the manufacturing method according to the present invention, the first and second metal sheaths are used. In particular, the first metal sheath must not react with the superconductor, but the second metal sheath does not. It is not necessary to satisfy such conditions. Usually, however, these first and second metal sheaths are preferably silver,
It is composed of silver alloy, gold or gold alloy. In particular, as for the first metal sheath, a metal sheath in which only the surface in contact with the superconductor is covered with a layer made of a metal that does not react with the superconductor may be used. In that case, the other part of the metal sheath may be composed of another metal, such as copper, aluminum, or an alloy thereof, for example.

The plastic working includes, for example, wire drawing and rolling. To improve the critical current density,
In wire drawing, it is desirable that the degree of work is 80% or more.
% Is desirable. After such plastic working, heat treatment is preferably performed, and it is more effective that the plastic working and heat treatment are repeated a plurality of times to improve the critical current density. For example, when rolling is performed a plurality of times, it is desirable that the degree of working in one pass be 40% or more. When the rolling or the wire drawing is performed again after the heat treatment is performed, the degree of processing in such processing is sufficient to be about 10% to 30%. Rolling is performed using, for example, a roll or a press.

After the completion of the heat treatment, the obtained superconducting wire may be further covered with an organic substance. In order to coat the superconducting wire with the organic substance, for example, the superconducting wire is passed through a bath of the organic substance, or the surface of the superconducting wire is coated with the organic substance.

Hereinafter, an experimental example performed according to the present invention will be described.

Experimental Example 1 Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ and C
Using uO, Bi: Pb: Sr: Ca: Cu = 1.8
These were blended so as to have a composition ratio of 5: 0.41: 2.01: 2.19: 2.98. This blended product was placed in the air at 750 ° C. for 12 hours,
At 0 ° C. for 8 hours and further in a reduced pressure atmosphere of 1 Torr,
Heat treatment was performed at 760 ° C. for 8 hours. After each heat treatment, each was pulverized. The powder obtained through such a heat treatment was further pulverized by a ball mill to obtain a submicron powder. This powder was subjected to degassing at 800 ° C. for 10 minutes in a reduced pressure atmosphere.

The obtained powder was filled in a silver pipe having a diameter (outer diameter) of 12 mm and subjected to wire drawing until the diameter became 1.8 mm. Thereby, a strand was obtained. The wire obtained in this manner, as it is, or a desired number of wires is again filled in a silver pipe, and then subjected to wire drawing and rolling, and then subjected to heat treatment and further rolling. By performing processing and heat treatment,
Sample No. shown in Table 1 below. 1-5 were obtained.

[0039]

[Table 1] The thickness of the (individual) superconductor with respect to the thickness of the entire superconducting wire in each sample is No. 32% for 1; N
o. 15% for No. 2; 6.2 for 3
%, No. As for No. 4, 4.3% of No. 5 was 2.0%.

As described above, in order to obtain samples in which the thickness of the superconductor is variously changed with respect to the thickness of the entire wire, the method shown in FIGS. 1 and 2 was used.

FIGS. 1 and 2 show a plurality of strands 3 in which an oxide superconductor 1 is covered with a first metal sheath 2. In FIG. 1, the seven strands 3
Is filled in the metal sheath 4. On the other hand, in FIG.
The strands 3 are filled in the second metal sheath 5. In these states, plastic working such as rolling is performed. Thereby, in FIG. 1, a rectangular tape-shaped superconducting wire 6 is obtained, and in FIG. 2, a rectangular tape-shaped superconducting wire 7 is also obtained.

When these superconducting wires 6 and 7 are compared, in the superconducting wire 6 shown in FIG. 1, the thickness of each oxide superconductor 1 is 30 times the thickness of the entire superconducting wire 6.
%. On the other hand, in the superconducting wire 7 shown in FIG. 2, the thickness of each oxide superconductor 1 is set to about 15% of the entire thickness of the superconducting wire 7.

As described above, the thickness of each superconductor contained in the superconducting wire obtained by plastic working can be adjusted by the number of strands filled in the second metal sheath. In each of the above-described samples, the ratio of the thickness of each superconductor is changed by the method shown in FIGS.

For each of the superconducting wires thus obtained, strain-critical current density (at liquid nitrogen temperature)
The characteristics were compared. The results are shown in Table 1.

[0045] Each numeral shown in Table 1, when the critical current density when not give distortion and J _CO, the critical current density when given a predetermined strain was _{J C, J C / J CO} × 100
The value calculated in [%] is shown.

From Table 1, it was found that the thickness of each superconductor was 5% or less of the total thickness of the wire rod. 4 and no. 5
It can be seen that this has excellent strain resistance characteristics.

Experimental Example 2 Bi: Pb: Sr: Ca: Cu = 1.78: 0.44:
Oxides or carbonates containing the respective elements are mixed so as to have a composition of 1.99: 2.23: 2.98, and the mixture is heat-treated so that the ratio of Bi + Pb: Sr: Ca: Cu is about 2:
A powder composed of a 2212 phase of 2: 1: 2 and a non-superconducting phase was prepared.

This powder was degassed at 720 ° C. for 10 hours in a reduced pressure atmosphere of 8 Torr.

The obtained powder was first coated with a silver pipe having an outer diameter of 12 mm and an inner diameter of 8 mm, and was drawn to an outer diameter of 1 mm. 1296 multifilamentary wires were used. Next, this was wire-drawn to an outer diameter of 1 mm, and then 0.1 mm
It was rolled to a thickness of 7 mm.

Further, this wire was heat-treated at 840 ° C. for 50 hours, then rolled at a working ratio of 11.8%, and then wound around a 50 mm diameter alumina / silica ceramic cylinder. In such a wound state, the wire is
It had a curvature giving a strain of 0.3%.

In the above state, the wire was heat-treated at 840 ° C. for 50 hours. The critical current density at the liquid nitrogen temperature of the wire immediately after the heat treatment was 7000 A / cm ² .

Next, the wire was unwound from the cylinder, and the wire was bent and returned to a linear shape on the circumferential surface of the cylinder having the same diameter 40 times, and the critical current density was measured in the same manner. Was obtained.

Experimental Example 3 Bi: Pb: Sr: Ca: Cu = 1.78: 0.44:
So as to have a composition of 1.96: 2.25: 2.99:
An oxide or carbonate containing each element was mixed, and heat treatment was performed to prepare a powder composed of a 2212 phase and a non-superconducting phase.

This powder was degassed at 700 ° C. for 7 hours in a reduced pressure atmosphere of 11 Torr.

The obtained powder was prepared with an outer diameter of 12 mm and an inner diameter of 8 m
m, and the wire was drawn to an outer diameter of 1 mm. Then, the wire was further inserted into a large-diameter silver pipe to produce 1,260 multifilamentary wires. Next, the multifilamentary wire is drawn to an outer diameter of 1 mm.
It rolled until it became thickness of mm.

The two obtained wires are superposed and adhered to each other, and heat-treated at 840 ° C. for 50 hours in a state of being adhered to each other.
It was rolled at a working ratio of 15%.

The two-layer wire thus obtained is
It was wound around a ceramic bobbin having a diameter corresponding to a strain of 0.29%, and heat-treated at 840 ° C. for 50 hours.

[0058] The two wires thus superposed and adhered to each other are
The bobbin was wound into a bobbin having the same diameter, and further wound around a Teflon (trade name) pipe having the same diameter in a spiral at a pitch of 60 mm.

The wound product was bent to have a radius of 100 mm and 200 mm, respectively, and these bending operations were repeated 10 times.

After the heat treatment, after each rewinding, and each bending
For each after return, the criticality of the wire in liquid nitrogen
The current density was measured. The results were all 8000 A /
cm ^TwoWas obtained.

Experimental Example 4 Bi: Pb: Sr: Ca: Cu = 1.76: 0.43:
An oxide or carbonate containing each element was mixed so as to have a composition of 1.98: 2.20: 3.02, and heat treatment was performed to prepare a powder composed of a 2212 phase and a non-superconducting phase.

This powder was subjected to a degassing treatment at 710 ° C. for 12 hours in a reduced pressure atmosphere of 15 Torr.

The obtained powder was first coated with a silver pipe having an outer diameter of 12 mm and an inner diameter of 8 mm, and was drawn to an outer diameter of 1 mm, and then further put into a large-diameter silver pipe. 1296 multifilamentary wires were used. Next, this was wire-drawn to an outer diameter of 1 mm.
Rolling was performed to a thickness of 17 mm.

Next, this wire was heat-treated at 840 ° C. for 50 hours, then rolled at a working ratio of 11.8%, and wound around a 50 mm diameter alumina / silica ceramic cylinder. In this wound state, the wire is
It had a curvature giving a strain of 0.3%.

In the above state, the wire was heat-treated at 840 ° C. for 50 hours.

Next, the wire is fed out of the above-mentioned cylinder,
After passing through the bath of Formal at a linear speed of 20 m / min, 3
Baking at 50 ° C. was performed 10 times, and 30 to 5 times.
A 0 micron thick formal coating was applied. At this time, in all the steps, the strain was controlled to 0.3% or less.

This wire was wound around a bobbin having a diameter of 50 mm to produce a coil. This coil exhibited a critical current density of 6000 A / cm ² at liquid nitrogen temperature.

Experimental Example 5 Bi: Pb: Sr: Ca: Cu = 1.82: 0.42:
An oxide or a carbonate containing each element was mixed so as to have a composition of 1.99: 2.22: 3.01, and a powder composed of a 2212 phase and a non-superconducting phase was prepared by heat treatment.

This powder was degassed at 700 ° C. for 15 hours in a reduced pressure atmosphere of 10 Torr.

The obtained powder was prepared with an outer diameter of 12 mm and an inner diameter of 8 m
m, and the wire was drawn to an outer diameter of 1 mm. Then, the wire was further inserted into a large-diameter silver pipe to produce 1,260 multifilamentary wires. Next, the multifilamentary wire is drawn to an outer diameter of 1 mm.
It rolled until it became thickness of mm.

Further, this wire was heat-treated at 840 ° C. for 50 hours, and then rolled at a working ratio of 15%.

This wire was wound around a ceramic bobbin having a diameter corresponding to a strain of 0.29% and heat-treated at 840 ° C. for 50 hours.

Next, the wire rod is fed out from the above-described bobbin,
After passing through a bath of Formal, the furnace at 400 ° C
This was baked for 0 seconds, and this was repeated 10 times. At this time, in all the steps, the strain was controlled so as to be suppressed to 3% or less. As a result, a wire having a formal coating having a thickness of 40 microns was obtained.

This wire was wound as a conductor of a cable around a 50 mm diameter stainless steel tube at a pitch of 50 mm and bent at a radius of 70 cm.

When the critical current density of the wire at the liquid nitrogen temperature was measured for each of the heat treatment, the formal coating, the rewinding, and the bending, a value of 7500 A / cm ² was obtained in each case. .

[Brief description of the drawings]

FIG. 1 is an illustrative sectional view showing a plastic working step included in a method for manufacturing an oxide superconducting wire according to the present invention.

FIG. 2 is a view corresponding to FIG. 1 and shows a state in which the number of strands 3 is increased from that in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxide superconductor 2 1st metal sheath 3 Element wire 4,5 2nd metal sheath 6,7 Superconducting wire

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-105409 (JP, A) JP-A-1-169815 (JP, A) JP-A-1-134822 (JP, A) JP-A 64-64 19617 (JP, A) JP-A-1-144524 (JP, A) JP-A-1-321605 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 12/10 H01B 13 / 00

Claims (14)

(57) [Claims] 1. A metal sheath having a dimension in a thickness direction, and a plurality of oxide superconductors distributed in the thickness direction independently of each other in the metal sheath, wherein the oxide superconductor is Bi- A bismuth-based oxide superconductor having a component of Sr—Ca—Cu—O or (Bi, Pb) —Sr—Ca—Cu—O, wherein the bismuth-based oxide superconductor is Bi + Pb: Sr:
Ca: Cu = 1.5-2.5: 1.8-2.2: 1.5
２．５2.5: 2.5-3.5, wherein the thickness dimension of each of the oxide superconductors is 5% or less of the thickness dimension of the metal sheath. Superconducting wire. 2. The oxide superconducting wire according to claim 1, wherein the oxide superconductor is c-axis oriented in a thickness direction. 3. The oxide superconducting wire according to claim 1, further comprising an organic substance covering the metal sheath. 4. Bi-Sr-Ca-Cu-O or (B
i, Pb) have a component of -Sr-Ca-Cu-O, Bi
+ Pb: Sr: Ca: Cu = 1.5-2.5: 1.8-
Has a composition ratio of 2.2: 1.5 to 2.5: 2.5 to 3.5
Preparing a plurality of wires made of a bismuth-based oxide superconductor covered by a first metal sheath, filling the plurality of wires into a second metal sheath, and including the plurality of wires in each of the wires 5% of the thickness dimension of the second metal sheath in the thickness direction of the second metal sheath.
Performing plastic working in which a compressive load is applied in a cross-sectional direction to the second metal sheath filled with the plurality of strands at least once so as to deform the second metal sheath into a tape shape, A method for producing an oxide superconducting wire, comprising a step. 5. The oxide superconducting wire according to claim 4 , further comprising a step of drawing each of the wires before filling the plurality of wires into the second metal sheath. Manufacturing method. 6. The plastic working step, said second metal sheath is deformed into flat tape shape, claim 4
3. The method for producing an oxide superconducting wire according to item 1. 7. The method for producing an oxide superconducting wire according to claim 4 , further comprising a step of heat-treating the oxide superconductor after the plastic working step. 8. The method for producing an oxide superconducting wire according to claim 7 , wherein the plastic working step and the heat treatment step are repeated a plurality of times. 9. A step of adjusting the thickness of each oxide superconductor contained in the oxide superconducting wire obtained in the plastic working step, based on the number of the wires filled in the second metal sheath. Claims further comprising:
5. The method for producing an oxide superconducting wire according to 4 . 10. The method according to claim 1, further comprising:
The method for producing an oxide superconducting wire according to claim 7 , further comprising a step of coating the metal sheath with an organic substance. 11. The step of coating with an organic substance,
The method for producing an oxide superconducting wire according to claim 10 , comprising a step of passing the wire through a bath of an organic substance. 12. The step of coating with the organic substance,
The method for manufacturing an oxide superconducting wire according to claim 10 , further comprising applying an organic substance to a surface of the wire. 13. The heat treatment step includes heat-treating the superconducting wire in a state where the superconducting wire is wound with a curvature that gives a strain of 0.3% or less (strain = thickness of the superconducting wire / bending diameter).
The method for producing an oxide superconducting wire according to claim 7 , further comprising a step of extending from a state in which the curvature is given. 14. A metal sheath having a thickness dimension,
A plurality of oxide superconductors distributed in the thickness direction independently of each other in the metal sheath, wherein the oxide superconductor is formed of Bi-Sr-Ca-Cu-O or (Bi, Pb)- A bismuth-based oxide superconductor having a component of Sr—Ca—Cu—O, wherein the bismuth-based oxide
Material superconductor is Bi + Pb: Sr: Ca: Cu = 1.5
-2.5: 1.8-2.2: 1.5-2.5: 2.5-
A composition ratio of 3.5, wherein the thickness dimension of each of the oxide superconductors is 5% of the thickness dimension of the metal sheath;
A method for handling an oxide superconducting wire as described below, wherein the strain (thickness of metal sheath / bending diameter) is controlled within a range of 0.3% or less. Handling method.