JPH09263971A - Superconducting composite body and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a superconducting composite body high in critical current density and magnetic shielding effect uniform in superconducting characteristics and suitable for a large-sized product and to provide a method capable of easily producing a large-sized product. SOLUTION: This superconducting composite body is the one in which a densed noble metal film essentially consisting of silver is formed on the surface of a base material, a silver layer is formed on the upper face, and a superconducting layer is furthermore formed on the upper face. As for the method for producing the superconducting composite body, a noble metal film essentially consisting silver is formed on the surface of a base material, thereafter, the noble metal film is subjected to densifying treatment, next, the upper face is coated with silver paste, which dried and baked, furthermore, a superconducting precursory body is formed on the upper face, and subsequently, firing is executed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a superconducting composite suitable for a magnetic shield and the like and a method for producing the same.

[0002]

2. Description of the Related Art High-temperature superconductors have low mechanical strength.
Attempts have been made to form a composite with a base material such as structural ceramics or metal. However, since the high temperature superconductor reacts with many ceramics and metallic materials during firing, the superconducting properties may be deteriorated or may not be obtained. Therefore, on heat-resistant nickel-based alloy base materials such as stainless steel and Inconel,
In order to prevent the reaction between the superconductor and the substrate, an oxide ceramics or a noble metal containing silver as a main component is provided as an intermediate coating, and the superconductor is baked on the intermediate coating.

Further, when the superconductor is put into practical use, for example, when it is used for an application such as a magnetic shield, a large and three-dimensional superconductor is required. It is effective to form a noble metal coating by the method. For example, as shown in JP-A-6-209182, a manufacturing method has been proposed in which a silver and superconductor layer is formed on a base material by a plasma spraying method. However, since there are many pores in the sprayed precious metal coating, when heat treatment such as baking the superconductor is performed, the base material and the superconductor react through these pores, and superconducting properties cannot be obtained. A method of alternately repeating thermal spraying of superconductors is used. However, in such a method, the work is complicated and time-consuming, and the cost is high. further,
Since the surface of the sprayed noble metal coating has large irregularities, the orientation of the superconducting crystal particles is poor, and there is a problem that good superconducting properties cannot be obtained.

[0004]

The invention according to claim 1 provides a superconducting composite having a high critical current density and a magnetic shielding effect, uniform superconducting properties, and suitable for a large-sized product. The invention according to claim 2 provides a method for producing a superconducting composite, which has a high critical current density and a high magnetic shield effect, has uniform superconducting properties, and can easily produce a large-sized product. In addition to the effect of the invention described in claim 2, the invention described in claim 3 provides a method for manufacturing a superconducting composite, which can easily manufacture a particularly large product and can easily manufacture a product having a three-dimensional structure. is there. In addition to the invention described in claim 2, the invention described in claim 4 provides a method for producing a superconducting composite having a particularly excellent magnetic shield effect.

[0005]

According to the present invention, a densified noble metal film containing silver as a main component is formed on the surface of a substrate,
The present invention relates to a superconducting composite having a silver layer formed on its upper surface and a superconductor layer formed on its upper surface. In the present invention, a noble metal coating containing silver as a main component is formed on the surface of a base material, the noble metal coating is densified, and then a silver paste is applied to the upper surface, dried and baked, and the upper surface is further coated. The present invention relates to a method for producing a superconducting composite, which comprises firing the superconducting precursor after forming the superconducting precursor. The present invention also relates to the method for producing a superconducting composite, wherein the noble metal coating is formed by a thermal spraying method. The present invention also relates to a method for producing a superconducting composite, which comprises coating, drying and baking a silver paste, and then smoothing the surface.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the kind and composition of the base material are not particularly limited, but since heat treatment is performed at a temperature of 800 ° C. or higher in an atmosphere containing oxygen in order to develop superconducting properties, Material with excellent heat resistance and oxidation resistance,
For example, in addition to ceramics, stainless steel, Inconel,
It is preferable to use a nickel-based alloy such as incoloy.

In order to form the noble metal coating containing silver as a main component, it is preferable to form the noble metal coating by a thermal spraying method, because the three-dimensional structure can be easily formed on the surface and the film can be thickened. Various methods such as arc spraying, gas spraying, plasma spraying, HVOF spraying (supersonic gas spraying) can be used as the spraying method.

The noble metal coating is densified in order to reduce voids (pores) in the coating that are generated when the noble metal coating is formed by a thermal spraying method or the like, and the method is not particularly limited. A method of polishing and stretching the silver coating with a grindstone, a buff or the like, or stretching with a cutting tool, a metal piece or the like, and in the case of a flat plate, stretching can be performed using roll rolling or a mechanical press.

The thickness of the noble metal coating after the densification treatment is 5
0 to 400 μm is preferable, and 100 to 300 μm is more preferable. If the thickness is less than 50 μm, the base material and the superconductor react with each other during baking, so that the superconducting property tends to be deteriorated or not obtained. If it exceeds 400 μm, cracks are likely to occur in the superconductor due to the difference in thermal expansion between the base material, the noble metal and the superconductor.

As a component of the noble metal coating, an alloy of silver and gold may be used as long as silver is the main component, and platinum, palladium, etc. may be contained. If necessary, MgO may be formed in the underlayer of the silver coating layer, or MgO and silver may be sprayed together to form a coating film of a mixture of both.

When the precious metal coating is formed by the thermal spraying method or the like, the surface roughness of the precious metal coating after the densification treatment is Ra.
When the (center line average roughness) is 5 μm or less, the reaction between the base material and the superconductor is suppressed, the orientation of the superconducting crystal particles is improved, and a superconductor having a high Jc with few defects is obtained, which is preferable. .

The silver paste may contain platinum, palladium, rhodium or the like as long as it contains silver as a main component and does not contain impurities that react with the superconductor to deteriorate the characteristics. The method of applying the silver paste is not particularly limited, and it can be applied by a dip coating method, brush coating or the like. The baking temperature of the silver paste is 80
0-900 degreeC is preferable. The smoothing treatment after baking the silver paste is not particularly limited, and can be smoothed with a grindstone, a buff, a bite, sandpaper, a metal piece or the like.

The superconducting precursor is, for example, a powder for a superconductor, an organic binder such as ethyl cellulose, polyvinyl butyral resin or acrylic resin, a phthalate ester, a plasticizer such as benzyl n-butyl phthalate, butanol, isopropyl alcohol or acetic acid. Ethyl, a solvent such as water is added, these are mixed to prepare a slurry, a green sheet is prepared by a doctor blade method using the slurry,
A method of laminating this on the surface of the sprayed precious metal film or a method of forming by screen printing method, spray coating method, dip coating method, etc., further gas type, arc type using powder for superconductor or rod for superconductor It can be formed by a thermal spraying method such as a plasma method. The thickness of the superconducting precursor is not particularly limited, but it is preferably in the range of 10 to 500 μm.

The amount of the organic binder, plasticizer and solvent used in preparing the above-mentioned slurry is such that the superconducting precursor powder 10
5 to 30 parts by weight, 0.5 to 0.5 parts by weight
It is preferably in the range of 20 parts by weight and 5 to 50 parts by weight.

There is no particular limitation on the type of superconductor, and it is possible to use Y-based, Tl-based superconductors as well as Bi-based superconductors. For example, in the case of Bi-based superconductors, Bi ₂ Sr ₂ C is used.
ACu ₂ O _x , (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _y, etc. can be used as a representative composition. Furthermore, Sb, Ag,
A composition containing Pt or the like, a composition deviated from the stoichiometric composition, a composition in which a part of the main element is replaced with another element, or the like can also be used.

The baking temperature of the superconducting precursor is appropriately selected depending on the mixing ratio of each raw material and the like, but is 800 to 950.
The firing is preferably performed in the range of 0 ° C., and the atmosphere is preferably an atmosphere containing oxygen. In the present invention, the noble metal coating formed by the thermal spraying method or the like may be heat-treated before and after the densification treatment, if necessary, and the heat treatment temperature is preferably lower than 940 ° C.

In the superconducting composite according to the present invention, the base material and the superconductor do not react with each other even when heat treatment such as baking the superconductor is carried out. It has excellent superconducting properties.

[0018]

The present invention will be described below with reference to examples. Examples 1 to 5, Comparative Example 1 B ₂ iO so that the composition ratio of bismuth, strontium, calcium and copper is 2: 2: 1: 2 in atomic ratio.
₃ (manufactured by Kojundo Chemical Laboratory, purity 99.9% by weight), 22
8.3 g, SrCO ₃ (manufactured by Kojundo Chemical Laboratory, purity 9
9.9 wt%), 144.7 g, CaCO ₃ (manufactured by Kojundo Chemical Laboratory, purity 99.9 wt%) 49.0 g and Cu
O (manufactured by Kojundo Chemical Laboratory, purity 99.9% by weight) 77.
9 g was weighed and used as a starting material.

The above starting materials were filled in a ball mill made of synthetic resin together with steel balls covered with synthetic resin and 330 g of water, and wet mixed for 24 hours to prepare a mixed powder.
This mixed powder was placed in an alumina bowl, calcined at 800 ° C. for 10 hours in the atmosphere using an electric furnace, coarsely crushed, and then filled in a ball mill made of synthetic resin together with balls made of zirconia and 330 g of ethyl acetate, It was wet pulverized for 48 hours to obtain a calcined powder (powder for superconductor) having an average particle size of 5 μm.

8 parts by weight of polyvinyl butyral resin, 3 parts by weight of phthalate and 50 parts by weight of butanol were added to 100 parts by weight of the calcined powder and mixed, and then deaerated to obtain a slurry having a viscosity of 15 Pa · sec. A 180 μm thick polyester film (manufactured by Toray Industries, Inc.)
Green sheet for superconductors with a thickness of 0.1 mm supplied by the doctor blade method (hereinafter referred to as a green sheet)
(Superconducting precursor) was obtained.

Further, 100 parts by weight of silver powder (manufactured by Tanaka Kikinzoku International Co., Ltd.), 2 parts by weight of ethyl cellulose, and 40 parts by weight of a 1: 1 mixed solution of terpineol and butyl carbitol in a weight ratio were weighed. A silver paste was prepared by uniformly mixing in a mortar.

Separately from the above, a silver coating was formed by plasma spraying on a 1 mm thick Inconel substrate whose surface was blasted. The surface of this silver sprayed coating was roughly ground with sandpaper, and then cut into a piece having a width of 20 mm and a length of 40 mm. Further, the surface of the silver sprayed coating after cutting was densified by sanding and stretching with sandpaper to obtain a composite substrate on which a silver coating having a surface roughness Ra of 0.8 μm and a thickness of 0.2 mm was formed. Obtained. Next, the silver paste obtained above was dip-coated on the upper surface of this composite substrate except for Comparative Example 1, and then dried at 80 ° C. Table 1 shows the number of times the dip coating and the drying were performed as one step. Then, the silver paste was baked in the air at 830 ° C. for 30 minutes. Further, for Examples 1, 2 and 4, after this,
The surface was smoothed using an Inconel piece so that the surface roughness Ra was 0.6 μm.

Next, the green sheet obtained above was burned with the respective silver paste-baked composite base material and the silver paste, and then the surface was re-polished.
A laminate was obtained by pressure bonding for 10 minutes at a temperature of 10 MPa.
This laminated body is put in an electric furnace and heated up to 300 ° C in the atmosphere for 5
0 ° C./hour, heating from 300 ° C. to 880 ° C. at a rate of 100 ° C./hour, holding at 880 ° C. for 0.5 hour, then
2 ° C / hour up to 0 ° C, 10 from 850 ° C to 500 ° C
The superconductor was baked at 0 ° C./hour and cooled from 500 ° C. to room temperature at a rate of 50 ° C./hour. Then oxygen partial pressure 1
Heat treatment was performed at 790 ° C. for 10 hours in an atmosphere of kPa to obtain a superconducting composite. The critical current density Jc (A / cm ² ) of the obtained superconducting composite was measured in liquid nitrogen (77 K) by the 4-terminal method. Table 1 shows the results. The samples used for the evaluation were produced 10 each under each condition, and the critical current density was an average value thereof.

Separately from the Jc evaluation sample, a magnetic shield having a diameter of 60 mm and a length of 200 mm was prepared under the same conditions as those described above and shown in Table 1 except for the bonding condition of the green sheet. The green sheets were adhered with a paste having the same composition. 1 at 77K on the obtained magnetic shield
An external magnetic field of 0 ^-5 T was applied, and the internal magnetic field was measured by the pickup coil at the center inside the magnetic shield to determine the shield effect (external magnetic field / internal magnetic field). Table 1 shows the results.

[0025]

[Table 1]

As shown in Table 1, the superconducting composite according to the present invention is excellent in high critical current density and magnetic shield effect.

[0027]

The superconducting composite according to the first aspect of the present invention has a high critical current density and a high magnetic shield effect, has uniform superconducting properties, and is suitable for large-sized products and products having a three-dimensional structure. Claim 2
The method for producing a superconducting composite described above has a high critical current density and a high magnetic shield effect, uniform superconducting properties, and a large-sized product can be easily produced, and is industrially very suitable. The method for producing a superconducting composite according to claim 3 has the effects of the method for producing a superconducting composite according to claim 2, and particularly large-sized products can be easily produced. The method for producing a superconducting composite according to claim 4 has the effects of the method for producing a superconducting composite according to claim 2, and is particularly excellent in the magnetic shielding effect.

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Claims (4)

[Claims] 1. A superconducting composite in which a densified noble metal film containing silver as a main component is formed on the surface of a base material, a silver layer is formed on the upper surface thereof, and a superconductor layer is further formed on the upper surface thereof. 2. A noble metal coating containing silver as a main component is formed on the surface of a base material, the noble metal coating is densified, and then a silver paste is applied to this upper surface, followed by drying and baking. A method for producing a superconducting composite, which comprises firing a superconducting precursor after forming a superconducting precursor on the substrate. 3. The method for producing a superconducting composite according to claim 2, wherein the noble metal coating is formed by a thermal spraying method. 4. A silver paste is applied, dried and baked, and then the surface is smoothed.
A method for producing the superconducting composite described.