JP2565954B2 - Method for manufacturing superconductor coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing a superconductor coil using an oxide superconductor.

(Prior Art) In recent years, since it was announced that Ba-La-Cu-O-based layered perovskite type oxides may have a high critical temperature, research on oxide superconductors has been conducted at various places. (Z.Phys.B Condensed Matter 64,189-193 (198
6)). Among them, a defect perovskite type ((LnBa ₂ Cu ₃ O having an oxygen defect represented by a Y-Ba-Cu-O system.
_7-δ type) (δ represents oxygen deficiency and is usually 1 or less, Ln is
At least one element selected from Y, La, Sc, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and part of Ba is Sr.
, Etc.)) oxide superconductor has a critical temperature of 90
Since it has a high temperature above K and above the boiling point of liquid nitrogen, it is attracting attention as a very promising material (Phys.Ruv.Lett.Vo
l.58 No.9,908-910).

By the way, since such an oxide superconductor is obtained as a sintered body of crystalline oxide or a powder thereof, when these are used as, for example, a superconductor coil, first, the metal tube is filled with the oxide superconductor powder. After that, it is made into a long wire by drawing it, and then a coil is produced by winding this superconductor wire on an appropriate winding frame.
Attempted to use.

Further, since the superconductor characteristics of this oxide superconductor deteriorate due to strain and the like generated during winding, after winding the above-mentioned wire into a required coil shape, the oxide superconductor powder is densified and oxygen defects δ It is said that it is appropriate to introduce oxygen into the alloy and perform heat treatment to improve superconductor characteristics.

Conventionally, this heat treatment is performed in two steps: firing for densification under a temperature condition of about 800 ° C to 1000 ° C and annealing for supplying oxygen under a temperature condition of about 300 ° C to 700 ° C. This is because annealing is performed in a temperature range where the oxygen absorption capacity is high because oxygen is released from the crystal at the firing temperature.

(Problems to be solved by the invention) However, in the heat treatment in the method for manufacturing a superconductor coil as described above, annealing is performed under a temperature condition of about 300 ° C. to 700 ° C. at which oxygen absorption of the oxide superconductor is high. However, even if silver, which is not oxidized even at high temperature and has an excellent oxygen supply ability, is used as the material of the metal tube, under the temperature conditions described above, the diffusing power of oxygen in the silver decreases and sufficient superconductivity is reduced. Long-term heat treatment is required to obtain body characteristics.

Further, as described above, since the heat treatment is performed after the coil is wound, there is a problem that the supply of oxygen is insufficient inside the wound body, and the superconducting characteristics are likely to be non-uniform as a whole.

Furthermore, in the firing process for densification described above,
The volume of the oxide superconductor is reduced due to the sintering, and cracks are generated in the oxide superconductor, or voids are generated between the metal tube and the oxide superconductor. When such voids occur, the critical current density decreases and the mechanical strength decreases, and the amount of strain generated by external stress increases with this decrease in strength, and this increase in strain decreases the superconducting properties. There is also the problem of doing so.

The present invention has been made in order to solve such conventional problems, it is possible to uniformly supply oxygen to the entire oxide superconductor in a short time even after forming into a coil shape, While preventing the generation of cracks in the superconductor, by preventing the generation of voids between the metal tube and the oxide superconductor, an object of the present invention is to provide a method for producing a superconductor coil having excellent superconducting properties. To do.

[Structure of the Invention] (Means for Solving the Problems) In the method for producing a superconductor coil of the present invention, an oxide superconductor powder is mixed in a tube material made of silver or a silver alloy to form an oxide superconductor by heating. In a method for manufacturing a superconductor coil, which comprises a step of winding a powder-filled wire into a desired coil shape, and a step of heat-treating a wound body obtained by this winding step in an oxygen-containing atmosphere, The process is performed in an oxygen-containing atmosphere pressurized to 10 atm to 1000 atm.

Although many oxide superconductors are known, the use of a rare earth element-containing perovskite-type oxide superconductor having a high critical temperature has a high practical effect. The oxide superconductor containing a rare earth element and having a perovskite type structure may be any as long as it can realize a superconducting state. For example, LnBa ₂ Cu ₃ O _7-δ system (Ln is Y, La, S
At least one element selected from rare earth elements such as c, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu, and δ represents an oxygen defect, usually a number of 1 or less; Some can be replaced with Ca, etc. ) Defect perovskite type having oxygen defects such as
An oxide having a perovskite type in a broad sense such as a layered perovskite type such as Sr—La—Cu—O system is exemplified. In addition, the rare earth element is defined in a broad sense and includes Sc, Y and La systems. As a typical system, in addition to the Y-Ba-Cu-O system, a system in which Y is substituted with a rare earth element such as Eu, Dy, Ho, Er, Tm, Yb, and Lu, Sc-Ba-Cu-O system, Sr -La-Cu-O system,
Furthermore, a system in which Sr is substituted with Ba, Ca, etc. can be mentioned.

The oxide superconductor powder used in the present invention is produced, for example, as follows.

First, the constituent elements of the perovskite-type oxide superconductor such as Y, Ba, and Cu are sufficiently mixed. When mixing, Y ₂ O ₃ ,
In addition to using oxides and carbonates such as BaCO ₃ and CuO as raw materials, compounds such as nitrates and hydroxides that are converted into oxides after firing may be used. Further, an oxalate obtained by a coprecipitation method or the like may be used. The elements composing the perovskite type oxide superconductor are basically mixed so as to have a stoichiometric composition, but there may be a slight deviation in relation to manufacturing conditions. For example, Y-
In the Ba-Cu-O system, Ba 2mol and Cu 3mol are standard compositions with respect to Y 1mol, but in practice, Ba 2 ± 0.6mo with respect to Y 1mol.
l, Cu 3 ± 0.4mol deviation is not a problem.

Then, after thoroughly mixing the above-mentioned raw materials, 850-980 ° C
Bake at a temperature of about. Then, if necessary, heat treatment is performed in an oxygen-containing atmosphere, preferably in an oxygen atmosphere, or by gradually cooling to about 300 ° C. in a similar atmosphere to introduce oxygen into oxygen defects δ and improve superconductivity. be able to. This heat treatment is usually performed at about 300 to 700 ° C.

Next, the fired product is ball mill, sand grinder,
Grind by other known means. At this time, the perovskite-type oxide superconductor is divided from the cleavage plane into a fine powder. This pulverization is preferably performed so that the average particle size is 0.1 to 5 μm.

The oxide superconductor powder obtained in this manner has an oxygen-defective perovskite structure (LnBa ₂ C
u ₃ O _7−δ (δ is usually 1 or less)). Note that Ba
It is also possible to replace it with Sr, Ca, etc., and further replace a part of Cu with Ti, V, Cr, Mn, Fe, Co, Ni, Zn, etc. The amount of substitution can be appropriately set within a range that does not deteriorate the superconducting characteristics, but is set to 80 mol% or less because excessively large amount of substitution deteriorates the superconducting characteristics.

The method for producing the superconductor coil of the present invention will be described in more detail. First, the oxide superconductor powder produced by the method as described above or the mixed powder used as the raw material of the oxide superconductor described above is made of silver or a silver alloy. Fill into the pipe material. As this silver alloy, use of an alloy such as a silver-silver alloy or a silver-manganese alloy is preferable because it is excellent in wire workability. However, if the contents of copper and manganese are large, the characteristics of the oxide superconductor are deteriorated, so it is preferable to add a small amount (about 5% by weight). Next, after the powder is solidified from the pipe material by a swaging machine or the like, it is elongated by processing such as wire drawing and processed into a wire material. The shape of the wire may be circular, oval, tape-shaped, etc. In particular, since the shape of the oval or tape is fixed in the heat treatment in a pressurized atmosphere, the direction of deformation is fixed. It is effective.

Next, this wire is wound around, for example, an appropriate winding frame to form a coil having a required shape.

Then, the coil-shaped molded body is heat-treated in an oxygen-containing atmosphere pressurized to 10 atm to 1000 atm. As described above, by performing the heat treatment for the purpose of densifying the oxide superconductor and improving the superconducting property in the pressurized atmosphere, the oxygen supply capacity is improved almost in proportion to the pressure, and the oxide superconductor powder is also improved. It is possible to prevent the generation of voids between the metal tube and the oxide superconductor due to the decrease in the volume.

The reason for limiting the pressure in this heat treatment to the above range is that if the pressure is less than 10 atm, the effect of improving the oxygen supply capacity by pressurization cannot be sufficiently obtained, and if it exceeds 1000 atm, the handleability is reduced in terms of equipment safety. is there.

Further, the atmosphere of this heat treatment may be made to satisfy the above-mentioned pressure by oxygen gas, but at a high pressure of around 1000 atm, since oxygen alone is dangerous, an inert gas such as argon or nitrogen and oxygen are used. The total pressure may be increased by using a mixed gas.
In such a case, the oxygen partial pressure in the atmosphere is 10 atm to 500
It is preferable to be atm. By increasing the overall pressure in this way, the denseness of the oxide superconductor is improved.

Also, this heat treatment is performed at a temperature of 850 ° C to 940 ° C for 6 hours
The objective is fully achieved by carrying out the operation for about 48 hours.
After this, if necessary, in the same atmosphere,
It may be gradually cooled to about 0 ° C., or may be kept at a temperature of about 300 ° C. to 600 ° C. for several hours.

(Operation) The amount of oxygen introduced into the oxygen vacancies δ of the oxide superconductor increases almost in proportion to 1/2 of the atmospheric pressure. In the method for producing a superconductor coil of the present invention, the oxide superconductor wire is Since the coil-shaped molded body molded using is heat-treated in a pressurized atmosphere, it becomes possible to sufficiently introduce oxygen even by a heat treatment for a shorter time than in the conventional case, and it is wound in multiple layers. Oxygen can also be supplied to the oxide superconductor inside the coil by the applied pressure, and the superconducting characteristics are improved uniformly. Further, it is possible to prevent the generation of cracks in the oxide superconductor and the formation of voids between the metal tube and the oxide superconductor by the pressure applied during the heat treatment.

(Example) Next, the Example of this invention is described.

Example 1 2 mol of BaCO ₃ powder having a particle size of 1 to 5 μm, 0.5 mol of Y ₂ O ₃ powder, and C
3 mol of uO powder was thoroughly mixed and calcined in the air at 900 ° C for 48 hours to react, and the calcined product was further oxygenated.
After firing at 500 ℃ for 24 hours to react, introduce oxygen into the oxygen vacant space, pulverize with a ball mill, average particle size 0.5μ
m perovskite type oxide superconductor powder was obtained.

Next, use this oxide superconductor powder with an outer diameter of 200 mm and an inner diameter of 16 m.
One end of m × 70 mm in length is put into a silver tube sealed with silver material, and after pressing with a press pressure of 1 ton / cm ² , a silver plug is attached to the other end and welding is performed leaving a vent hole. The wire was cold drawn to an outer diameter of 2 mm to produce an oxide superconductor wire.

Next, the dimension of the winding part of this oxide superconductor wire is the diameter.
Thirty layers were wound around a reel of 30 mm × 200 mm in length to produce a coil-shaped molded body.

After this, the coil-shaped molded body is placed in a firing furnace, and pressurized to 100 atm with oxygen gas in the firing furnace,
In this state, heat treatment was performed under the condition of 900 ° C. for 24 hours, and further heat treatment was performed at 500 ° C. for 24 hours to manufacture the target superconductor coil.

When the superconducting properties of the superconducting coil thus obtained were measured, the critical temperature was 90 K and the critical current density at 77 K was 3100 A / cm ^2, which was a good result. The density in the superconductor wire was 98% as determined from the cross-sectional structure, and it was a good value, and no void was observed. Furthermore, when a current of 10 A was passed through this superconductor coil and the strength of the generated magnetic field was measured, it was 60 G.

On the other hand, for comparison with the present invention, a superconductor coil was produced under the same conditions except that the heat treatment in the above example was carried out under the condition of oxygen gas of 1 atm, and the characteristics of this superconductor coil were measured in the same manner. The critical temperature
90K, critical current density 900A / cm ² , density in supercurrent conductor wire 8
The generated magnetic field was 5% and the magnetic field was 15G.

Example 2 Using the same coil-shaped molded body produced in Example 1, heat treatment was performed with argon gas at a partial pressure of 800 atm and a partial pressure of 20 atm.
A superconductor coil was produced under the same conditions as in Example 1 except that the superconducting coil was used in an atmosphere of a mixed gas of 0 atm of oxygen gas.

The characteristics of the superconductor coil thus obtained were measured in the same manner as in Example 1, and the critical temperature
90K, critical current density 4800A / cm ² , density within superconductor wire 99
%, Good results were obtained with a generated magnetic field of 120 G.

[Effects of the Invention] As is clear from the above examples, according to the method for manufacturing a superconductor coil of the present invention, a heat treatment for the purpose of densifying an oxide superconductor and improving superconducting properties is performed at 10 atm to 1000 a.
Since it is performed in an oxygen-containing atmosphere pressurized to tm, oxygen can be uniformly supplied to the entire oxide superconductor of the coil-shaped formed body by a heat treatment for a relatively short time, and Since the generation of voids can be prevented,
Superconducting coils with excellent superconducting properties can be manufactured at low cost. In addition, the obtained superconductor coil also has excellent coil performance.

Claims (5)

(57) [Claims] 1. A step of forming a wire material in which a tube material made of silver or a silver alloy is filled with an oxide superconductor powder or a mixed powder which becomes an oxide superconductor by heating into a required coil shape, and a step of forming the coil shape. In a method for manufacturing a superconductor coil having a step of heat-treating a molded body in an oxygen-containing atmosphere, the heat-treating step is performed in an oxygen-containing atmosphere pressurized to 10 atm to 1000 atm. Production method. 2. The method for producing a superconductor coil according to claim 1, wherein the oxygen partial pressure in the pressurized oxygen-containing atmosphere is in the range of 10 atm to 500 atm. 3. The method for producing a superconductor coil according to claim 1, wherein the oxide superconductor is a perovskite type oxide superconductor containing a rare earth element. 4. The superconductor according to claim 1, wherein the oxide superconductor contains rare earth elements, Ba and Cu in an atomic ratio of substantially 1: 2: 3. Body coil manufacturing method. 5. The oxide superconductor is LnBa ₂ Cu ₃ O _7-δ.
(Ln represents at least one element selected from rare earth elements, and δ represents oxygen deficiency.) The oxygen-defective perovskite structure has a superconducting structure according to claim 1. Coil manufacturing method.