JPH05325665A - Oxide superconductive multi-conductor wire rod - Google Patents

Abstract

PURPOSE:To improve superconducting stability and critical current density, and reduce anisotropy by forming an oxide superconductor in a prescribed cross sectional shape, burying at least three layers extendedly in the axial direction, and orienting the width direction to the outer peripheral surface side from the central axis. CONSTITUTION:In an oxide superconductive wire rod formed by embedding oxide superconductors (layers) 1 extendedly in the axial direction in an always conductive metallic sheath material 2, assuming that the layers 1 have a width (w) and a thickness (d), at least three layers having a cross sectional shape of 0.001w<=d<=0.3w are extendedly in the axial direction, and the width (w) direction is oriented to the outer peripheral surface side from the central axis. The cross section is formed in such a constitution as having line symmetrical axes as many as possible, and for example, when the layers 1 are arranged in the material 2 having a circular cross section, while orienting the width direction to the outer peripheral surface side with the axis as its center, the line symmetrical axes are formed innumerably in such a constitution as embedding the layers extendedly in the axial direction. Thereby, superconducting stability becomes excellent, and critical current density can be improved, and anisotropy can be also reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting multifilamentary wire, and more particularly to an oxide superconducting multifilamentary wire capable of eliminating anisotropy and achieving a high critical current density.

[0002]

2. Description of the Related Art As is well known, oxide superconductors having a critical temperature of more than 77.3K have a higher thermal conductivity than metal superconductors.
Since the problem of so-called cryogenic technology is largely solved, its use in the field of electric power / industrial electronic devices, for example, is drawing attention. The form of the oxide superconductor used in these fields is roughly classified into a long wire having a sheath material and a short bulk material having no sheath material. The long wire having the sheath material is used, for example, for forming a power transmission cable or a superconducting magnet. In addition, this type of superconducting wire is prepared by, for example, filling a powder of a calcined oxide superconductor into a metal tube that serves as a sheath material, and then subjecting it to surface-reducing processing by swaging, drawing, and rolling to draw a wire. Then, it is finally manufactured by heat treatment. FIG. 10 is a cross-sectional view of the tape-shaped superconducting wire obtained in this way, where 1 is an oxide superconductor and 2 is a sheath material. The reason why the superconducting wire is generally processed and manufactured into a tape shape in this manufacturing process is that the crystal grains in the oxide superconducting layer are easily aligned (orientated). By the way, in this kind of oxide superconductor,
Since there is a large anisotropy in the critical current density Jc of each crystal grain, in order to obtain a practical superconducting wire with a high critical current density Jc over the entire length of the wire, the crystal grains in the oxide superconductor 1 It is important to properly orient. In response to such a problem, the critical current density Jc can be improved by thinning the surface-reduction processing to a tape-shaped processing limit (from the surface of thickness) of about 0.1 mm. Heat treatment and press working or roll working are repeatedly applied to the formed product to increase the degree of crystal orientation. For example, in the case of Bi tape wire, a maximum of 54,000 A /
Those with a critical current density Jc (77.3K, 0T) of cm ² are also known. However, the tape wire material having an increased critical current density Jc is a so-called single-core wire (a wire material having only one oxide superconductor core in the wire material). Since the filament of the body is too thick, there is a problem that the superconducting coil configured has low superconducting stability. On the other hand, in consideration of such a problem of coil stability, attempts have been made to make a multi-core wire. That is, by making the multi-core wire rod, it is possible to make the filament thin without changing the thickness of the wire rod and to make it function as a superconducting wire rod suitable for the construction of a superconducting coil having stable superconductivity. The multifilamentary wire has a diameter of 1 to 2 mm by swaging and drawing by inserting the oxide superconductor into the covering material (tube) that forms the sheath material.
By reducing the surface area to form a composite, inserting and arranging this composite in the second coating material (tube), and performing the surface reduction processing again, the oxidation as shown in the cross-sectional structure in Fig. 11 is performed. We have obtained superconducting multi-core wire. In FIG. 11, 1 is an oxide superconductor and 2 is a sheath material.

[0003]

However, in the case of the oxide superconducting multifilamentary wire having the above structure, the ratio of the width w to the thickness d of each oxide superconductor 1 is close to 1, and each oxide superconductor 1
Since the crystal orientation of is not so good, the critical current density Jc is no more than about 10 ³ A / cm ² . To improve this point,
It has also been attempted to roll the oxide superconducting multifilamentary wire shown in FIG. 11 into a multifilamentary tape wire as shown in FIG. This multifilamentary tape wire material improves the orientation of the crystal grains of each oxide superconductor 1 and improves the critical current density Jc to about 10 ⁴ A / cm ² , but on the other hand, the critical current density in a magnetic field is increased. The anisotropy of Jc becomes a problem.

Here, the term "anisotropic" means that the critical current density Jc when an external magnetic field is applied perpendicularly to the tape wire surface is larger than that when the external magnetic field is applied parallel to the tape wire surface. It shows that it decreases sharply with increase. Figure 13
Shows an example of anisotropy in the case of a single-core tape wire, and the same tendency is observed in the case of a multi-core tape wire, although it is not so remarkable as in the case of a single-core tape wire. In FIG. 13, a curve a is the critical current density Jc when an external magnetic field is applied perpendicularly to the tape wire surface, and a curve b is a critical current density Jc when the external magnetic field is applied parallel to the tape wire surface. Show.

The anisotropy of the oxide superconducting wire in the magnetic field is large, for example, when the cylindrical coil is made of the oxide superconducting wire, the magnetic field component perpendicular to the tape surface becomes large at the coil end. There is a problem that the critical current density Jc is limited (suppressed) to a small value and a large current cannot flow through the coil. Further, in the tape wire, anisotropy appears strongly even if it is deteriorated by bending strain. That is, with respect to the bending (flat bending) of the tape wire in the thickness direction, even if the bending radius is small, the bending strain is small, and the deterioration of the critical current density Jc is also small, but the bending in the width direction (edge bending)
On the other hand, even if the bending radius is large, a large bending strain occurs and the critical current density Jc is greatly deteriorated. This anisotropy with respect to bending is a problem peculiar to the tape wire material, and, for example, when a solenoid coil is configured, it causes deterioration of the critical current density Jc in the rewound portions at both ends.

As described above, in the superconducting wire, the following characteristics are practically required, that is, the superconducting stability, the high critical current density Jc, the anisotropy, and the like are practically desired. The reality is that a superconducting wire having all the characteristics has not yet been realized.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an oxide superconducting multifilamentary wire having a superconducting stability, a high critical current density, and anisotropy reduced and suitable for a superconducting coil or the like. And

[0008]

The oxide superconducting multifilamentary wire of the present invention is an oxide superconducting wire formed by axially extending and embedding an oxide superconductor (layer) in a normal conductor metal sheath material. When the oxide superconductor (layer) has a width w and a thickness d, at least three having a cross-sectional shape of 0.001w ≦ d ≦ 0.3w are axially embedded and the width w direction is the central axis. To the outer peripheral surface side.

In the present invention, when the width w and the thickness d of the oxide superconductor axially stretched and embedded in the normal conductor metal sheath material are taken, the ratio of d to w (aspect ratio) is obtained.
Must have a cross-sectional shape of 0.001w ≦ d ≦ 0.3w. That is, when d / w ≤ 0.001, oxide superconductor (layer)
Of the oxide superconductor (layer) may be broken during surface-reduction processing, and as a result the reliability of the conductive function is likely to be impaired, and d / w ≧
At 0.3, the oxide superconductor (layer) becomes too thick, and it tends to be difficult for the crystal grains to perform the required orientation. For example, in a tape wire with a width of 2.5 mm, the width w of the oxide superconductor (layer) is set to a constant value of 2 mm, and the thickness is 1 to 1000 μm.
When the relationship with the critical current density Jc when changing in the range of m was obtained, it was as shown in FIG. Here, the thickness of the oxide superconductor (layer) that does not cause filament breakage and that can obtain a high critical current density Jc is 2 μm to 600 μm.
More preferably, it is 10 μm to 200 μm.

In the present invention, in order to make the anisotropy as small as possible, it is desirable that the transverse section has as many axially symmetrical axes as possible. For example, as shown in the sectional view of FIG. A structure in which an oxide superconductor (layer) 1 is embedded in an electric conductor metal sheath material 2 while being oriented in the outer peripheral surface side about the axis in the width direction and extending in the axial direction,
Anisotropy can be eliminated by making the axis of line symmetry innumerable. The elimination of the anisotropy is not limited to the case where the cross section is circular, and the oxide superconductor (layer) 1 to be stretched and embedded in the sheath material 2 is selected and set to 3 or more, and the cross section is also set. For 3 ≦ n
In the case of a regular n-sided polygon (the larger n is, the better), it is possible to use any of those having different degrees. Figure 3
As shown in a sectional view in FIG. 3, the hexagonal shape has a smaller line symmetry axis in the cross section than the circular cross section, but the oxide superconductor (layer) 1 is oriented to the outer peripheral surface side as described above. As a result, the anisotropy can be reduced. Furthermore, the cross section may be elliptical, but in this case, it is preferable to set the ratio of the major axis a and the minor axis b to about 1 ≦ a / b ≦ 2.

In the present invention, in order to reduce the anisotropy, the oxide superconductor (layer) 1 is embedded in the normal conductor metal sheath material 2 while being oriented toward the outer peripheral surface side and being stretched and embedded in the axial direction. It is selected and set to 3 or more. That is, when the number is 2 or less, there is no difference from the case of the conventional tape wire, and the anisotropy can be reduced by selecting and setting the number 3 or more. For example, as shown in a sectional view in FIG. 4, even when the number of oxide superconductors (layers) 1 is four, the anisotropy is reduced.
That is, as shown in FIG. 5, the critical current density Jc (curve a) when a magnetic field is applied in parallel to two of the four oxide layers and perpendicular to the two, and 45 ° in all the oxide layers. It can be seen that the difference from the critical current density Jc (curve b) when a magnetic field is applied to form the angle is relatively small and the anisotropy is reduced.

Further, the wire rod according to the present invention is characterized in that the critical current density Jc when the wire rod itself is twisted is small. In the metal-based superconducting wire currently used, the wire is twisted to further improve the superconducting stability when coiled and to reduce AC loss. A large bending strain is added to cause a significant deterioration of the critical current density Jc.
On the other hand, in the case of the wire according to the present invention, when such twisting is performed, the strain applied to the layer of the oxide superconductor is small, so that the critical current density Jc does not deteriorate.

In the present invention, the oxide superconductor (layer) that is embedded in the sheath material while being oriented on the outer peripheral surface side and stretched and embedded in the axial direction is, for example, an oxide superconductor containing a rare earth element represented by Y system. Body, La-Sr-Cu-O system, Bi-Sr-Ca-
Cu-O-based, Tl-Ba-Ca-Cu-O-based, and Nd-Ce-Cu-O-based oxide superconductors are examples. As a specific example, in the case of an oxide superconductor containing a rare earth element, Re M ₂ Cu ₃ O _7-δ (however,
Re is at least one element selected from rare earth elements such as Y, La, Sc, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and M is Bi, S
At least one element selected from r and Ca, δ is an oxygen deficiency and is usually a number, and a part of Cu is Ti, V, Cr, Mn, Fe, Co, N
i, Zn, etc. can be substituted). Bi-based oxide superconductors include Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x and Bi ₂ (Sr, C
a) ₃ Cu ₂ O _{x and the} like are exemplified, and Tl-based oxide superconductors include Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _y and Tl ₂ (Ba, Ca) ₃ Cu ₂ O _y.
And the like, and may be the one in which Ag or Ag ₂ 0 is added.

In the present invention, the sheath material is required to be not oxidized by the oxide superconductor embedded therein at room temperature, heat treatment temperature, etc., and is an electrically good conductor which can bypass the current flowing when the superconductivity is broken. Good. And specifically, for example, Ag, Au, Pt, Pd, Cu or an alloy composed of two or more of these, more preferably
Ag is mentioned, and in order to increase the mechanical strength of these metals, trace amounts of metal oxides such as SnO ₂ , ZnO, Al ₂ O _{3 are used.}
It may be a complex to which is added. .

[0015]

In the oxide superconducting multifilamentary wire according to the present invention, the oxide superconductor (layer) arranged and embedded in the multifilament is formed into a preferable shape for crystal grain orientation, and only a high critical current density Jc can be flowed. On the other hand, by giving a predetermined directionality, on the other hand, the anisotropy is significantly reduced or eliminated.
That is, when forming a coil to form a superconducting magnet, the critical current density Jc depends on the angle between the magnetic field and the wire.
Of the critical current density Jc
It can be said that this is suitable for the construction of a large-current type (large-capacity type) superconducting device with superconducting stability, since the difference in the degree of deterioration is eliminated.

[0016]

Embodiments of the present invention will be described below with reference to FIGS.

Example 1 Oxide superconductor fine powder prepared by the oxalate coprecipitation method was first prepared. As a result of IPC analysis, this fine powder was Bi: Pb: Sr: Ca: Cu.
= 1.72: 0.34: 1.83: 1.97: 3.13. Then, about 100 g of this oxalate coprecipitated powder was placed in a MgO sample dish and calcined in the air at 800 ° C for 40 hours. After this calcination, 1 ~
A calcinated powder was obtained by crushing to a diameter of about 10 μm, and the phase of this calcinated powder was examined by X-ray diffraction. As a result, (Bi, Pb) ₂ Sr ₂ Ca
It was a mixed phase of Cu ₂ O _x (low Tc phase) and Ca ₂ Pb O ₄ , CuO. The above calcined powder was filled in an Ag tube having an outer diameter of 6 mm and an inner diameter of 5 mm,
A tape wire with a width of 2.5 mm and a thickness of 0.15 mm was created by applying drawing (drawing) and rolling (rolling). This tape wire is cut to a length of 100 mm and 700 ℃ x 2
The processing strain was removed by applying a heat treatment for 0 hr.

Next, as shown in a perspective view in FIG.
The Ag core wire 4 having an outer diameter of 2 mm is concentrically inserted and arranged in the Ag pipe 3 having an inner diameter of 8 mm and the inner diameter of 7 mm, while the tape wire obtained above is inserted so that the width direction thereof faces the outer peripheral surface side of the Ag pipe 3. After the placement, the surface is reduced to an outer diameter of 2 mm by drawing (Example 1a), or an intermediate heat treatment is performed for 20 hours when the outer diameter is reduced to 3 mm, and then the surface is reduced again to an outer diameter of 2 mm ( Example 1b). After surface-reducing each of the outer diameters to 2 mm, heat treatment was performed at 835 ° C. for 50 hours in an argon gas atmosphere containing 7.7% oxygen to obtain an oxide superconducting multifilamentary wire. With respect to each of the oxide superconducting multifilamentary wire rods configured as described above, several portions were cut and the width w and the thickness d of the oxide superconductor (layer) 1 in each cross section were measured by a micrograph. , D / w was 0.038.

The critical current Ic of the oxide superconducting multifilamentary wire was measured in liquid nitrogen by the four-terminal method. The result was measured by pressing to obtain an oxide superconducting single-core wire (Comparative Example 1), roll. Table 1 shows a comparison with the case of the oxide superconducting single core wire obtained by processing (Comparative Example 2) and the conventional oxide superconducting multi-core wire (Comparative Example 3).

Table 1 Example 1a Example 1b Comparative Example 1 Comparative Example 2 Comparative Example 3 Critical Current Density Jc (A / cm ² ) 8700 9800 33,000 10,200 2,300 Example 2 In the case of Example 1, drawing reduction was performed. Under the same conditions except that a hexagonal die was used, an oxide superconducting multi-core wire having a final hexagonal cross-section with an outer diameter of 4 mm was obtained under the same conditions as shown in FIG. This oxide superconducting multifilamentary wire was heat-treated in the air at 700 ° C for 20 hours to remove processing strain, and then placed in an Ag tube with an outer diameter of 12 mm as shown in Fig. 8.
Seven wires were inserted and arranged, and wire drawing was performed again to obtain a final multifilamentary oxide superconducting wire having an outer diameter of 2 mm. About this oxide superconducting multifilamentary wire, several places are cut and the width w and the thickness d of the oxide superconductor (layer) 1 in each cross section are cut.
(Approximately 5 μm) was measured with a micrograph, d / w
Was 0.034.

Table 2 shows the results of measuring the critical current Ic of the above-mentioned oxide superconducting multifilamentary wire in liquid nitrogen by the four-terminal method together with the case of the oxide superconducting multifilamentary wire with a hexagonal cross section. ..

Table 2 Primary cross-section hexagonal wire rod Secondary multi-core wire rod Critical current density Jc (A / cm ² ) 7.200 4.300 Example 3 In the case of Example 1, SnO ₂ reinforced Ag (SnO) was used instead of Ag core wire 4. ₂ content 1%) ... Example 3a ... or Al ₂
O ₃ reinforced Ag (Al ₂ O ₃ content: 1%) ... An oxide superconducting multifilamentary wire having an outer diameter of 2 mm was obtained under the same conditions except that Example 3b was used. About this oxide superconducting multi-core wire,
When the width w and the thickness d (about 5 μm) of the oxide superconductor (layer) 1 in each cross section were cut at several positions and measured by a micrograph, d / w was 0.038.

Table 3 shows the results of measuring the critical current Ic of the above oxide superconducting multifilamentary wire in liquid nitrogen by the 4-terminal method. Further, FIG. 9 shows the results of measuring the critical current Ic by the four-terminal method in liquid nitrogen while applying tensile stress to these oxide superconducting multifilamentary wires. In FIG. 9, curve a shows the case of Example 3a, and curve b shows the case of Example 3b.

[0024] The oxide superconducting multifilamentary wire according to the present invention is not limited to the above-exemplified constitution, and it is needless to say that various modifications can be made within the scope of the invention.

[0025]

As described above, since the oxide superconducting multifilamentary wire according to the present invention is a multifilamentary wire, it is possible to miniaturize the filament without reducing or lowering the critical current density Jc. Since it is possible, it is possible to form a coil with excellent superconducting stability, and the anisotropy in a magnetic field is greatly improved. In other words, the present invention provides a superconducting wire that has the characteristics of superconducting stability, high critical current density Jc, and the absence of anisotropy, which are required for practical use in superconducting wires. It can be said to bring many advantages in the industrial field.

[Brief description of drawings]

FIG. 1 is a curve diagram showing an example of the relationship between the thickness of an oxide superconducting layer and a high critical current density in an oxide superconducting multifilamentary wire according to the present invention.

FIG. 2 is a cross-sectional view showing an example of a cross-sectional structure of an oxide superconducting multifilamentary wire according to the present invention.

FIG. 3 is a cross-sectional view showing another example of the cross-sectional structure of an oxide superconducting multi-core wire according to the present invention.

FIG. 4 is a cross-sectional view showing still another example of the cross-sectional structure of the oxide superconducting multi-core wire according to the present invention.

FIG. 5 is a curve diagram showing an example of anisotropy of the oxide superconducting multifilamentary wire according to the present invention.

FIG. 6 is a perspective view schematically showing an example of a manufacturing embodiment of an oxide superconducting multifilamentary wire according to the present invention.

FIG. 7 is a cross-sectional view showing another example of the cross-sectional structure of the oxide superconducting multifilamentary wire according to the present invention.

FIG. 8 is a cross-sectional view showing still another example of the cross-sectional structure of the oxide superconducting multifilamentary wire according to the present invention.

FIG. 9 is a curve diagram showing a characteristic example of an oxide superconducting multifilamentary wire according to the present invention.

FIG. 10 is a perspective view showing a structure of a conventional oxide superconducting single-core wire.

FIG. 11 is a cross-sectional view showing the structure of a conventional oxide superconducting multifilamentary wire.

FIG. 12 is a perspective view showing another structure of a conventional oxide superconducting multifilamentary wire.

FIG. 13 is a curve diagram showing an anisotropy example of a conventional oxide superconducting single-core wire.

[Explanation of symbols]

1 ... Oxide superconductor 2 ... Sheath material 3 ... Ag tube
4 ... Ag core wire 5 ...

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Murase 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Research Institute

Claims (1)

[Claims] 1. An oxide superconducting wire comprising an oxide superconductor which is axially stretched and embedded in a normal conductor metal sheath material, wherein the oxide superconductor has a width w and a thickness d of 0.001.
An oxide superconducting multifilamentary wire characterized in that at least three wires having a cross-sectional shape of w ≦ d ≦ 0.3w are embedded in an axial direction and the width w direction thereof is oriented from the central axis to the outer peripheral surface side. ..