JPH04314534A - Composite material of oxide superconductor and its manufacture - Google Patents

Abstract

PURPOSE:To provide a composite material of oxide superconductor and its manufacture, while the occurrence of cracks is suppressed and simultaneously superconductivity is prevented from being lowered. CONSTITUTION:The sheet of silver particle, the sheet of oxide superconductor powder, the mixed sheet of oxide superconductor powder with silver particle and base material are laminated from upper side in order, and then the laminate is integrally baked.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconductor (hereinafter referred to as superconductor) composite material and a method for producing the same.

0002

BACKGROUND OF THE INVENTION Conventionally, superconducting materials have had drawbacks such as difficulty in producing complex three-dimensional shapes and difficulty in producing large molded bodies.

[0003] In order to compensate for these drawbacks, attempts have been made to combine superconductors with materials such as metals to form composites. Specifically, a laminate of a superconductor and a base material such as metal ceramics, or printing or coating a superconductor layer on the surface of the base material,
There is a method of forming it by a method such as thermal spraying and then firing it.

0004

[Problems to be Solved by the Invention] However, problems in the composite of superconductors and metals include mismatching coefficients of thermal expansion due to the joining and integration of the superconductor and the base material, or problems due to the superconductivity of the base material components. This was due to the deterioration of superconducting properties due to diffusion into the body layer.

The mismatch in thermal expansion coefficients causes cracks to occur during the cooling process after integration by firing or during cooling from room temperature to liquid nitrogen temperature and further from 20K to 4.2K, and the shape, size, etc. are restricted. This has been an obstacle to the practical use and application of superconductors. Furthermore, when ceramics are used as a base material, there is a problem in that the size of the ceramics is limited.

[0006] An object of the present invention is to provide a superconductor composite material and a method for producing the same that are free from the above-mentioned problems.

[0007]

[Means for Solving the Problem] As a result of various studies on the above-mentioned drawbacks, the present inventors focused on the fact that the value of the coefficient of thermal expansion of a mixture of a superconductor and a metal takes a value intermediate between the two. It has been found that by providing these mixtures on a base material, the occurrence of cracks caused by thermal strain can be suppressed.

[0008] Furthermore, the properties of the superconductor layer are degraded by diffusion of the base material components into the superconductor layer;
It has been found that this problem can be prevented by providing a barrier layer between the superconductor layer and the superconductor layer containing the base particles.

[0009] Furthermore, it is also possible to solve the problem of the problem that when each layer is formed into a sheet and the layers are laminated and integrated, mutual embedding occurs and the composition changes stepwise at these interfaces. I understand.

The inventors of the present invention have conducted further studies in view of the above points, and have found that a superconductor composite having a complex shape can be created by laminating an integrated laminated sheet onto the surface of a base material that has been previously processed into a desired shape. The inventors discovered that the material can be easily produced and completed the present invention.

The present invention provides a superconductor composite material comprising a silver layer, a superconductor layer, a mixed layer of superconductor and silver, a mixed layer of superconductor and base material, and a base material, and a silver particle sheet from above,
A superconductor composite material in which a superconductor powder sheet, a mixed sheet of superconductor powder and silver particles, a mixed sheet of superconductor powder and base material particles, and a base material are laminated in this order and then baked and integrated. Regarding the manufacturing method.

The superconductor used in the present invention is not particularly limited as long as it is an oxide, but it is preferable to use an yttrium-based superconductor, a bismuth-based superconductor, a thallium-based superconductor, or the like.

In the present invention, the base material is a nickel-based alloy, an iron-based alloy, etc., has excellent oxidation resistance at a temperature of 800 to 950°C, and has a coefficient of thermal expansion of (12±2)×10-6/
It is preferable to use one at ℃. In the present invention, the object can be achieved even if a three-dimensional shaped base material is used as the base material.

[0014] Regarding the mixing ratio of the superconductor and silver, if the volume ratio of silver is 10 to 50%, the effect as a barrier is large and it is preferable from the viewpoint of economy and matching of the coefficient of thermal expansion. The thickness of the silver layer is preferably in the range of 5 to 200 μm, and 1
A range of 0 to 50 μm is more preferable because environmental resistance is improved. The thickness of the mixed layer of superconductor and silver and the mixed layer of superconductor and base material are 5 to 400 μm, respectively.
It is preferably in the range of 10 to 400 μm, and more preferably in the range of 10 to 200 μm and 20 to 200 μm.

The thickness of the superconductor layer varies depending on the application, but for example, in the case of a magnetic shield, the thickness varies from 0.2 to 1 mm depending on the magnetic field.
The range is preferably 0 mm, especially 10-3T.
(10 Gauss) level magnetic field can be shielded with about 1 mm.

There are no particular restrictions on the method of processing silver particles, superconductor powder, and a mixture of the superconductor powder and silver particles, base particles, etc. into a sheet, but for example, the above materials may be processed into a sheet using an organic binder, a plasticizer, etc. It can be processed by a tape casting method in which the film is mixed with a solvent, supplied onto a film, and molded to a certain thickness using a doctor blade.

[0017] The particle size of the superconductor powder is from several μm to several tens of μm.
The range is preferably m. The particle size of the silver particles is preferably smaller than the superconductor powder, and the particle size of the base particles is preferably similar to the particle size of the superconductor powder.

In the present invention, a base material having a three-dimensional shape means a base material having a three-dimensional shape such as a cylinder, a prism, a cube, a hemisphere, or a cylinder.

[0019]

[Examples] Examples of the present invention will be described below. Example 1 The ratio of yttrium, barium and copper is 1:2 in atomic ratio
:3, 112.91 g of yttrium oxide (manufactured by Shin-Etsu Chemical Co., Ltd.) with a purity of 99.9% or more, barium carbonate (
394.68 g (manufactured by Kojundo Kagaku Kenkyusho) and 238.64 g of copper oxide (manufactured by Kojundo Kagaku Kenkyusho) were weighed to obtain raw material powder for superconductors.

Next, the above raw material powder for superconductor was filled in a plastic pot together with zirconia balls and methanol, and wet mixed at 60 revolutions per minute for 100 hours. After drying, the mixture was placed on an alumina baking plate and heated to 920°C in the air at a rate of 200°C/hour.
After being held at 0°C for 10 hours, the temperature was lowered at a rate of 100°C/hour, and then coarsely ground with a mortar, re-fired under the same conditions as above, cooled, and coarsely ground again with a mortar. Furthermore, the pulverized product was filled in a zirconia pot together with zirconia balls and pulverized to obtain yttrium-based superconductor powder having an average particle size of 3.7 μm.

To 100 g of the superconductor powder, 7 g of polyvinyl butyral resin (manufactured by Wako Pure Chemical Industries, Ltd., reagent 1st class), 3.5 g of phthalate ester (manufactured by Wako Pure Chemical Industries, Ltd., reagent 1 class) and butanol (manufactured by Wako Pure Chemical Industries, Ltd., reagent 1) were added. After adding and mixing 45 g of the slurry, the solvent was removed to obtain a slurry whose viscosity was adjusted to 10 Pa·s (100 poise) at 20°C. After that, the slurry was supplied onto a 100 μm thick polyester film (manufactured by Toray Industries) and tape cast using a doctor blade method.
A superconductor powder sheet a having a thickness of 0.8 mm was obtained by drying.

On the other hand, 75 g (75 g) of the superconductor powder obtained above
volume%) and silver particles (purity 99.9%, particle size 2.5 μm
) 7.0 g of the same polyvinyl butyral resin and 3.5 g of phthalate ester as above were added to 40 g (25% by volume), and then a 0.4 mm thick mixed sheet b and 75 g of superconductor powder were prepared in the same manner as above. 7.0 g of the same polyvinyl butyral resin and 3.5 g of phthalate ester as above were added to 40 g of particles of iron alloy (manufactured by Hitachi Metals, trade name: YEF50, particle size: 8.5 μm), and the same method as above was used. A mixed sheet c having a thickness of 0.5 mm was obtained. In addition, 100 g of silver particles similar to the above were mixed with 4.0 g of polyvinyl butyral resin.
4g, phthalate ester 2.2g and butanol 33g
After adding and mixing uniformly to form a slurry, tape casting was performed using a doctor blade method, and dried to form a slurry of 0.2
A sheet d of mm was obtained.

Next, each of the sheets obtained above was rolled using a twin roll so that sheet a had a thickness of 0.2 mm, mixed sheet b and mixed sheet c both had a thickness of 0.1 mm, and sheet d had a thickness of 0.2 mm.
It was rolled to a thickness of 0.05 mm. Next, each sheet was cut into 30 cm square pieces, and the sheet c was placed on an iron alloy (manufactured by Hitachi Metals, trade name: YEF50) base material with dimensions of 30 cm square and thickness of 1 mm.
1 sheet, 1 sheet B, 5 sheets A, and 1 sheet D were laminated in this order, and after heating these to 80°C,
They were bonded together under a pressure of MPa.

[0024] After that, the bonded product was placed on a zirconia baking plate, and the temperature was raised to 500°C at a rate of 20°C/hour in a mixed gas flow of 5% by volume of oxygen and 95% by volume of nitrogen, and then to 930°C. The temperature was raised at a rate of 50 °C/hour, held at 930 °C for 10 hours, and then lowered to 500 °C at a rate of 50 °C/hour, and at 500 °C, the atmosphere was changed to oxygen.
After holding at 00°C for 20 hours, the temperature was lowered again at a rate of 50°C/hour, and cooled to room temperature to obtain an integrated superconductor composite material.

[0025] The obtained superconductor composite material was subjected to 10 cycles of a heat cycle test at a temperature of liquid nitrogen to 20°C, but no cracks were observed. 5×5 again
The critical temperature (hereinafter referred to as Tc) and critical current density (hereinafter referred to as J
When Tc was measured, Tc was 90K and 77K.
Jc was 1.4 x 107 A/m2. Furthermore, 1000
After leaving it for a while and testing its environmental resistance, no whitening of the superconductor surface was observed.

Example 2 685.0 g of bismuth oxide (manufactured by Kojundo Kagaku Kenkyusho) with a purity of 99.9% or more so that the ratio of bismuth, strontium, calcium, and copper was 2:2:1:2 in atomic ratio.
, Strontium carbonate (manufactured by Kojundo Kagaku Kenkyusho) 434.
0g, calcium carbonate (manufactured by Kojundo Kagaku Kenkyusho) 147.
1g and cupric oxide (manufactured by Kojundo Kagaku Kenkyusho) 233.9
g was weighed, mixed and dried in the same manner as in Example 1.

[0027] Next, this was placed on an alumina firing plate and heated to 820°C in the air at a rate of 200°C/hour, held at 820°C for 10 hours, and then lowered at a rate of 200°C/hour. This was coarsely pulverized in an alumina mortar, and then filled in a plastic pot with zirconia balls and acetate, and pulverized finely. After drying, it was recalcined at 820°C for 10 hours, then coarsely ground in an alumina mortar, and then filled in a zirconia pot with zirconia balls and ground to produce bismuth-based superconductor powder with an average particle size of 5.2 μm. Obtained.

Thereafter, the same steps as in Example 1 were carried out until the thickness was 0.
8 mm superconductor powder sheet a, 0.4 mm thick mixed sheet b, 0.8 mm thick mixed sheet c, and 0.4 mm thick mixed sheet c.
A 2 mm sheet d was obtained. Each of these sheets was used in Example 1.
Similarly, using twin rolls, sheet a and sheet c were rolled to a thickness of 0.2 mm, sheet b to a thickness of 0.1 mm, and sheet d to a thickness of 0.05 mm.
It was cut into m square pieces, then laminated on the same iron alloy base material as in Example 1 in the same manner as in Example 1, and further bonded under the same conditions and steps as in Example 1.

[0029] After that, the bonded product was placed on a zirconia baking plate, and the temperature was raised to 500°C at a rate of 20°C/hour in a mixed gas flow of 5% by volume of oxygen and 95% by volume of nitrogen, and then to 850°C. Raise the temperature at a rate of 100℃/hour to 850℃
The temperature was maintained for 1 hour at
After being held at 850°C for 10 hours, the temperature was lowered to 200°C at a rate of 50°C/hour, and then cooled to room temperature to obtain an integrated superconductor composite material.

[0030] The obtained superconductor composite material was subjected to 10 cycles of a heat cycle test at a temperature of liquid nitrogen to 20°C, but no cracks were observed. 5×5 again
When Tc and Jc of the superconducting composite material cut into 0 mm dimensions were measured using the four-terminal method, Tc was 86K and 77K.
Jc at K was 1.9 x 107 A/m2.

Comparative Example 1 A superconductor composite material in which five sheets of sheet a obtained in Example 1 were laminated onto the same iron alloy base material as in Example 1, and then integrated through the same steps as in Example 1. I got it.

[0032] When the obtained superconductor composite material was subjected to 10 cycles of a heat cycle test at a liquid nitrogen temperature to 20°C, cracks occurred in the superconductor layer. Further, when the same environmental resistance test as in Example 1 was carried out, a part of the surface of the superconductor turned white.

Comparative Example 2 One sheet C and five sheets A obtained in Example 2 were placed on a cylinder made of iron alloy (manufactured by Hitachi Metals, trade name: YEF50) with a thickness of 1 mm, a diameter of 20 cm, and a length of 30 cm. They were laminated in order, and the same steps as in Example 2 were carried out to obtain an integrated superconductor composite material.

[0034] The obtained superconductor composite material was subjected to 10 cycles of a heat cycle test at a temperature of liquid nitrogen to 20°C, but no cracks were observed. However, Tc
is 84K and Jc at 77K is 7.2×106A/m2
This value was lower than that of the superconductor composite material obtained in the example.

[0035]

Effects of the Invention The superconductor composite material of the present invention does not generate cracks during the cooling process after being integrated by firing, or even when cooled from room temperature to liquid nitrogen temperature, or even from 20K to 4.2K, and has high superconductivity. Physical properties are not deteriorated, and by providing a silver layer on the surface, environmental resistance is improved without deterioration of superconducting properties, making it extremely suitable industrially.

Claims (4)

[Claims] 1. An oxide superconductor composite material comprising a silver layer, an oxide superconductor layer, a mixed layer of the oxide superconductor and silver, a mixed layer of the oxide superconductor and a base material, and a base material. 2. The oxide superconductor composite material according to claim 1, wherein the base material has a three-dimensional shape. [Claim 3] The order from the top is a silver particle sheet, an oxide superconductor powder sheet, a mixed sheet of oxide superconductor powder and silver particles, a mixed sheet of oxide superconductor powder and base material particles, and a base material. 1. A method for producing an oxide superconductor composite material, which comprises bonding the materials together in a manner similar to the above, followed by firing and integrating the materials. 4. The method for producing an oxide superconductor composite material according to claim 3, wherein the base material has a three-dimensional shape.