JP2556545B2 - Method for manufacturing oxide superconducting wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an oxide superconducting wire used for a power cable, a magnet, a power storage link, a magnetic shield, or the like.

[Conventional technology and its problems]

In recent years, (Ln _1-X Sr _X ) CuO ₄ , (Ln _1-X Ba _X ) ₂ CuO ₄ , LnBa ₂
An oxide superconductor having a layered perovskite structure, such as Cu ₃ O ₇ , LnBa _{2 -X} Sr _X Cu ₃ O ₇ (where Ln is Y, Sc or a rare earth element), has been found.

These oxide superconductors become superconducting at liquid N ₂ temperature or higher, so they are much more economical than conventional metal superconductors that exhibit superconductivity at liquid He temperature, and their use in various fields is being studied. .

By the way, since the above oxide superconductors are brittle, they cannot be plastically processed like metal materials, and powder metallurgy is mainly used for processing these into wire rods and the like.

The raw material powder used in the powder metallurgy method as described above is Y
Taking a Ba-Cu-O-based superconductor as an example, the raw material is Y ₂
Compounds such as O ₃ , BaCO ₃ and CuO can be processed into oxide superconducting compacts by mixing the above compounds so that Y: Ba: Cu becomes 1: 2: 3, and then mixing this mixture. Powder in oxygen atmosphere
It is heated to 850-1,000 ℃ and calcined, and this calcined product is crushed with a ball mill etc., classified and processed into calcined powder, and this calcined powder is molded into a desired shape, which is then oxygen-containing. It is performed by a method of sintering in an atmosphere.

By the way, the crystal structure of the above oxide superconductor is
As shown in Fig. 3 for YBa ₂ Cu ₃ O _7- δ (δ ≈ 0.1 to 0.3) superconductors, transition element ions such as Cu are present in the center of the cube, and Ba, Y, etc. with large radii of activity in the corners. It is a metal ion, and oxygen is arranged face to face. In the oxide superconductor having such a crystal structure, since the electron cloud of the transition element ion at the center is not spherically symmetric, the crystal anisotropy is electrically strong, the magnetic field current is small in the C-axis direction, and the perpendicular to the C-axis. A large value is shown in the direction parallel to the normal surface, that is, the surface including the a and b axes.

However, in the conventional method for producing a molded oxide superconducting body, the crystal grains of the superconductor forming the molded body are randomly oriented, and the crystal orientation is such that a high critical current is obtained particularly in the energizing direction. Critical current density (below
There is a problem that only an oxide superconducting compact having a low J _c ) can be obtained.

[Means for solving the problem]

As a result of earnest research in view of such circumstances, the present invention has found that the cooling condition after the heat treatment at a predetermined temperature has a great influence on the superconducting properties of the obtained superconductor, and further research is conducted on this point. As a result, the method of the present invention can be achieved.

That is, according to the present invention, after the raw material powder of the oxide superconductor is formed into a linear body having a desired shape, the linear body is heated at a predetermined temperature in an oxygen-containing atmosphere and then cooled. Is cooled under a cooling condition in which the cooling temperature gradient in the longitudinal direction of the linear body is 10 ° C./cm or more and the cooling rate is 5 ° C./min or less.

In the present invention, the raw material powder of the oxide superconductor is subjected to heat treatment at a predetermined temperature in an oxygen-containing atmosphere to a linear body having a desired shape, by sintering the raw material powder, or This is to adjust the amount of oxygen in the crystal, which is then performed at 10 ° C / c.
Cooling at a temperature gradient of m or more and at a cooling rate of 5 ° C./min or less is necessary for orienting the highly conductive surface of the oxide superconductor crystal including the a and b axes in the longitudinal direction of the linear body. That is, the effect is not sufficiently exhibited with a temperature gradient of less than 10 ° C./cm. Further, the reason for slow cooling at a rate of 5 ° C./min or less is to allow the above orientation to be sufficiently performed over time and to convert the crystal structure from a tetragonal crystal to an orthorhombic crystal that becomes a superconductor.

In the present invention, the reason why the crystal plane including the highly conductive a and b axes of the oxide superconductor is oriented in the longitudinal direction of the linear body by increasing the cooling temperature gradient to 10 ° C./cm or more is that the line during cooling is linear. It is considered that thermal stress strongly acts in the longitudinal direction of the sheet and the stress is relaxed by orienting the plane including the a and b axes having a small axial ratio in the longitudinal direction.

Further, since the above-mentioned orientation becomes stronger as the temperature of the linear body becomes higher, it is preferable to raise the heating temperature to the solid-liquid coexisting temperature.

In the present invention, the oxide superconducting raw material powder contains, for example, Y
₂ O ₃ , BaCO ₃ , CuO, and other raw material compounds that can be oxide superconductors are mixed in a prescribed mixing ratio, and this is heated to 850 to 1,000 ° C. and calcined, and the calcined body is crushed and classified. The calcined powder obtained by the above is used.

As a method of forming the raw material powder into a linear body, Ag,
A method of filling the raw material powder into a pipe of Cu or an alloy thereof and performing a stretching process, or a method of coating the metal or alloy around the raw material powder by a conform method, or a raw material powder in a paste form Then, a method of coating on a metal substrate or a method of melting the raw material powder and depositing the melt on the metal substrate is applied.

For the above-mentioned metal substrate, a metal or alloy material that does not generate oxide scale at high temperatures, such as SUS, Hastelloy alloy, and Pt, is suitable.

In the present invention, the predetermined temperature for heating the linear body formed by molding the raw material powder in the oxygen atmosphere is less than 900 ° C., and the desired crystal orientation in the subsequent cooling step of the cooling conditions defined in the present invention is sufficient. If it is not expressed, and if it exceeds 1,200 ° C, a large amount of other compounds such as Y ₂ BaCuO ₅ are generated in the cooling process, and the superconducting property is deteriorated.

In the present invention, as the heating furnace capable of gradually cooling at a cooling rate of 5 ° C./min or less and having a large cooling temperature gradient of 10 ° C./cm or more, for example, a furnace having a structure shown in FIG. 1A is used.

That is, the furnace shown in FIG. 1A is an electric resistance type heating furnace, and in order to rapidly heat the linear body 1 to a predetermined temperature, the outer wall on the inlet side of the furnace is covered with a heat insulating material 2, and the heating element 3 is a furnace. The structure is densely arranged from the inlet side to the center and gradually coarsely arranged from the center to the outlet side so that a large temperature gradient and gradual cooling are possible. Further, a reflecting plate 4 is provided in the central portion of the furnace so as to promote heating immediately before the start of cooling and to obtain a high temperature gradient from the beginning of cooling.

FIG. 8B shows the temperature history of the linear body when the linear body was run in the electric resistance heating furnace. It can be seen that after the linear body enters the furnace, the linear body is rapidly heated to a predetermined temperature to a predetermined temperature T ₁ and then cooled at a constant temperature gradient.

FIG. 2 (a) is a structural explanatory view of an induction heating furnace, in which the linear body 1 is run in an induction coil 5 for heating, and a heat insulating material 2 is stretched on the inlet / outlet side wall of the furnace to keep the furnace warm. To improve rapidity and accelerate the rapid heating by placing the reflector 4 near the inlet of the furnace, and further disposing the gas nozzle 6 outside the outlet of the furnace.
It has a structure in which a gas such as N ₂ or Freon is blown onto the linear body 1 so that a large cooling temperature gradient can be obtained. The heating furnace of this structure can shorten the furnace length.

FIG. 2B shows the temperature history of the linear body by the heating furnace. The linear body rapidly reaches the predetermined temperature T ₁ , and an extremely large cooling temperature gradient is obtained during cooling.

〔Example〕

 The present invention will be described in detail below with reference to examples.

Example 1 Y ₂ O ₃ , BaCO ₃ and CuO were mixed and mixed so that the molar ratio of Y: Ba: Cu was 1: 2: 3, which was then heated in the atmosphere at 920 ° C. for 20 hours and then heated. Is crushed with a ball mill into a Y ₁ Ba ₂ Cu ₃ O _x calcined powder, which is packed into a Pd pipe with an outer diameter of 6 mm and an inner diameter of 4 mm, which is then stretched to form a 0.5 mmφ linear wire. Molded into a body.

The linear body thus obtained was run in the heating furnace shown in FIG. 1 or 2 and heat-treated under various conditions in the atmosphere to obtain an oxide superconducting wire.

Example 2 The same calcined powder used in Example 1 was heated to 1,350 ° C. to be melted, and a Pt wire of 0.5 mmφ was run in this melt to produce Y ₁ B.
A solidified body of a ₂ Cu ₃ O _x was adhered to a thickness of 10 μm to form a linear body. The linear body thus obtained was run in the heating furnace shown in FIG. 1 or 2 and heat-treated under various conditions to obtain an oxide superconducting wire.

In the above Examples 1 and 2, the temperature T of the linear body at the outlet of the heating furnace
₂ was 40 ° C.

Conventional Example 1 The same linear body as that used in Example 1 or 2 was heat-treated in a batch furnace.

The critical temperature ( _Tc ) and the critical current density ( _Jc ) of each of the superconducting wire rods thus obtained were measured. The results are shown in Table 1.

As is apparent from Table 1, the method products (1 to 8) of the present invention have higher T _c and J _c values than the comparative method products (9 to 13) or the conventional method products (14, 15). .

Among the comparative method products (9 to 13), No. 10 has a cooling temperature gradient, and Nos. 11 and 13 have cooling temperatures outside the limit values of the method of the present invention, so that T _c and J _c values are low. It was No of these
No. 13 was because the crystal structure was not completely converted to the orthorhombic crystal that becomes a superconductor because the cooling rate was too fast, and it can be made into a superconductor by reannealing in an oxygen-containing atmosphere. No. 9 had a low heating temperature, so that sufficient crystal orientation could not be obtained, and No. 12 had a too high heating temperature, so that a compound of Y ₂ BaCuO ₅ was formed and T _c and J _c were low. When X-ray diffraction was performed on each of the superconducting wire rods according to the method of the present invention, it was confirmed that the crystal planes including the a and b axes were oriented parallel to the longitudinal direction of the wire rods.

In the present example, the linear body was run in the heating furnace, but when the linear body is short, the linear body is fixed and the heating furnace or burner is moved to heat and cool the linear body. It doesn't matter.

Although the above embodiments have been described with respect to a Y-Ba-Cu-O-based superconductor, the method of the present invention can also be applied to oxide superconductors containing other alkaline earth metals, rare earth elements, copper and oxygen as main components. Of course.

〔effect〕

As described above, according to the method of the present invention, since the crystal planes including a and b axes having high conductivity are oriented in the longitudinal direction of the superconducting wire, an oxide superconducting wire having excellent superconducting properties such as J _c can be easily obtained. It can be produced and has a remarkable industrial effect.

[Brief description of drawings]

FIG. 1A is a structural explanatory view showing an embodiment of a heating furnace for carrying out the method of the present invention, FIG. 1B is a temperature history diagram of a linear body by the heating furnace, and FIGS. Examples of the structure of the heating furnace and the temperature history diagram of the linear body showing the examples are shown in FIG. 3, and FIG. 3 shows an example of the crystal structure of the oxide superconductor YBa ₂ Cu ₃ O _7-
It has a crystal structure of δ (δ ≈ 0.1 to 0.3). 1 ... Linear body, 3 ... Heating element, 5 ... Induction coil.

 ─────────────────────────────────────────────────── ─── Continuation of front page (73) Patent holder 999999999 Electric Power Development Co., Ltd. 6-15-1 Ginza, Chuo-ku, Tokyo (72) Inventor Yuyuki Kikuchi 2-4-3 Okano Nishi-ku, Yokohama-shi, Kanagawa Furukawa Electric Industry Co., Ltd. Yokohama Research Laboratory (72) Inventor Yasumi Tanaka 2-4-3 Okano, Nishi-ku, Yokohama-shi, Kanagawa Furukawa Electric Co., Ltd. Yokohama Research Laboratory (72) Inventor Tsukushi Hara Nishitsujiga, Chofu-shi, Tokyo Oka 2-4-1 Tokyo Electric Power Co., Inc. Technical Research Institute (72) Inventor Kiyoo Mitsui 7-2-1 Nakayama, Sendai City, Miyagi Prefecture Tohoku Electric Power Co., Inc. (72) Inventor Kiyoshi Ogawa Toyohira-ku, Sapporo-shi, Hokkaido Satozuka 461-6 Hokkaido Electric Power Co., Inc. Research Institute (72) Inventor Juntaka Yoshino 6-15-1, Ginza Ginza, Chuo-ku, Tokyo (56) Reference text Patent flat 1-260717 (JP, A) JP Akira 64-10518 (JP, A)

Claims (1)

(57) [Claims] 1. A raw material powder for an oxide superconductor is formed into a linear body having a desired shape by a desired method, the linear body is heated at a predetermined temperature in an oxygen-containing atmosphere, and then cooled. In the production of an oxide superconducting wire, the linear body is cooled under cooling conditions such that the cooling temperature gradient in the longitudinal direction of the linear body is 10 ° C / cm or more and the cooling rate is 5 ° C / min or less. Method.