JPH0768694A - Superconductive composite and production thereof - Google Patents

Abstract

PURPOSE:To provide a superconductive composite generating no peeling or cracking even at the time of baking or at the time of cooling after the integration due to baking or heat treatment or at the time of cooling from room temp. to the temp. of liquid nitrogen, suppressing the reaction of a metal substrate with a superconductor and not lowered in superconductive characteristics. CONSTITUTION:A mixture layer containing silver and magnesia is formed on the surface of a metal plate (SUS 310S plate 1) by a flame spraying method and a noble metal layer 3 is formed on the surface of the mixture layer. Thereafter, the surface of the noble metal layer 3 is subjected to stretching treatment and, subsequently, a superconductive material is laminated to the surface of the polished noble metal layer 3 to be baked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting composite having high mechanical strength, excellent thermal shock characteristics, and application to a magnetic shield, and a method for producing the same.

[0002]

2. Description of the Related Art Since a superconductor, for example, a ceramics superconductor, has a drawback of being inferior in mechanical strength and thermal shock resistance, it has been attempted to combine a ceramics superconductor with a base material such as metal or ceramics to form a composite. ing. Among them, metal has an advantage that it is less likely to be restricted by size, shape and the like as compared with ceramics. However, ceramic superconductors have a low superconducting property such as a critical temperature (hereinafter referred to as Tc), a critical current density (hereinafter referred to as Jc), or a superconducting property due to reaction with many metal materials during firing and heat treatment. You may not get it. Therefore, it is known to use a noble metal layer as an intermediate layer between the ceramic superconductor and the metal. For example, Japanese Patent Laid-Open No. 4-1
In Japanese Patent Publication No. 99700, a noble metal such as gold or silver is diffusion-bonded as an intermediate layer on a metal substrate of an iron-nickel alloy by hot rolling to produce a composite base material, and Bi is formed on the composite base material.
A method for forming a superconductor is disclosed, and JP-A-3-19
No. 2615 discloses that an intermediate layer composed of a noble metal or an alloy layer thereof is melted at a temperature of 900 ° C. or higher on a metal substrate to form a coating layer having a thickness of 30 μm or more, and then a Bi-based system is formed on the coating layer. A method of forming a superconductor is shown.
Silver is used as a base material or an intermediate layer as described above, and also contributes to lowering the melting point during firing. Also, when the superconductor is melted during firing of the ceramic superconductor,
It is generally known that Tc, Jc, etc. are improved,
If silver is used, the superconductor can be easily melted uniformly.

[0003]

When compounding a ceramics superconductor and a metal plate, the problem is that the thermal expansion coefficient does not match and the reaction occurs when the ceramics superconductor and the metal plate are joined and integrated. This is the deterioration of superconducting properties. Furthermore, even when silver is used as an intermediate layer between the ceramics superconductor and the metal plate, the thermal expansion coefficient mismatches between the metal plate and / or the ceramics superconductor. The mismatch of the thermal expansion coefficients causes the cooling process after firing and heat treatment, or causes the superconducting state to occur, and thus causes cracks when cooling from room temperature to liquid nitrogen temperature, further 20K to 4.2K, and the shape and size. These restrictions are hindering the practical application and application of ceramics superconductors. When commercializing ceramics superconductors,
For example, when used for a magnetic shield body, a large-sized three-dimensional superconductor is required. In this case, magnetism leaks from the joint just by physically combining small superconductors to increase the size. That is, an integrated superconductor is required to obtain high magnetic shield performance. However, as disclosed in JP-A-4-199700, in order to perform diffusion bonding of a noble metal as an intermediate layer by hot rolling on a metal substrate of an iron-nickel alloy, under high temperature and high pressure in a reducing atmosphere. Therefore, not only is it difficult to fabricate a large-sized integrated composite substrate having a three-dimensional structure, but also the size of the device must be increased. Further, cracks are likely to occur in the noble metal layer due to the difference in thermal expansion between the iron-nickel alloy and the noble metal. In addition, if the ceramic superconductor formed on the metal composite substrate has a non-uniform defect in the structure, it is considered that the magnetism leaks from this defective part, and in order to obtain high magnetic shielding performance, the uniform superconducting property is required. It is desired to form a superconductor having However, as shown in JP-A-3-192615, when an intermediate layer made of a noble metal or an alloy thereof is melt-formed on a metal substrate at a temperature of 900 ° C. or higher, a large-sized three-dimensional integrated composite base material is obtained. In addition to being difficult to manufacture, the thickness of the noble metal or these alloy layers becomes non-uniform, and the noble metal and the superconductor are likely to partially react with each other, so that good superconducting properties may not be obtained. Further, peeling or cracking of the precious metal due to the difference in thermal expansion between the iron-nickel alloy and the precious metal is unavoidable. In addition to the above, there is also a method of forming a noble metal intermediate layer on the surface of an iron-nickel alloy by a thermal spraying method to produce a composite substrate, but since the thermal sprayed film is porous in this method, the metal substrate and the superconductor are passed through these pores. React with and it is difficult to obtain good superconducting properties. If the intermediate layer of the noble metal is thickened to suppress this reaction, the spray film is likely to be peeled off and the superconducting property is likely to be deteriorated. The present invention provides a superconducting composite and a method for producing the same that does not have the above-mentioned problems.

[0004]

As a result of various studies on the above-mentioned drawbacks, the present inventors have found that when a metal plate having excellent mechanical strength is used, the metal plate is prevented from being oxidized and the metal plate and the ceramics superconductor are combined. It has been found that it is important to bring the thermal expansion coefficient of the intermediate layer provided between the two close to the thermal expansion coefficient of the metal plate and the ceramics superconductor in order to prevent the reaction. Further, in forming the composite of the metal plate and the intermediate layer, if the intermediate layer is formed by a thermal spraying method, it is advantageous for size increase and integration, and it is important to make the intermediate layer forming the superconductor layer dense. I also confirmed that. That is, by providing an intermediate layer having a thermal expansion coefficient close to that of the metal plate and the ceramics superconductor between the metal plate and the ceramics superconductor, the generation of cracks due to thermal strain is suppressed, and further, the silver on the surface of the metal plate is suppressed. It was found that it is very effective to densify the noble metal layer after forming a mixture containing magnesia and magnesia by a thermal spraying method, forming a noble metal layer on the surface of the mixture, and stretching the noble metal layer surface. It came to completion. The present invention, between the metal plate and the superconductor layer, a mixture layer containing silver and magnesia from the metal plate side, a superconducting composite having a noble metal layer stretched on the upper surface thereof, and silver on the surface of the metal plate. A mixture layer containing magnesia was formed by a thermal spraying method, a noble metal layer was formed on the surface of the mixture layer, the surface of the noble metal layer was stretched, and then a superconductor material was laminated on the surface of the stretched noble metal layer. The present invention relates to a method for producing a superconducting composite which is post-baked.

The superconductor used in the present invention is an oxide type, and the composition thereof is not particularly limited, but if an yttrium type superconductor, a bismuth type superconductor, a thallium type superconductor or the like is used, the Tc is It is preferable because it is higher than the liquid nitrogen temperature. The mixture layer containing silver and magnesia and the noble metal layer are described as intermediate layers because they are formed between the metal plate and the superconductor layer, but these intermediate layers may be formed on one side of the metal plate or both sides. But there is no limit. Further, as a method of thermal spraying for forming a mixture layer containing silver and magnesia, a gas type, an arc type, a plasma type or the like can be used. The formation of the noble metal layer is not particularly limited, but it is preferably formed by the thermal spraying method. The thickness of the intermediate layer is not particularly limited, but if it is thin, the superconductor and the metal plate react with each other through the intermediate layer, and the superconducting property is likely to deteriorate. Therefore, the thickness is preferably 50 μm or more, and more preferably 100 to 600 μm. The mixture layer containing silver and magnesia is formed by the thermal spraying method as described above, and by a method other than the thermal spraying method, the mixture layer containing silver and magnesia is easily separated from the metal plate, and the thickness (200 μm or more) and It is difficult to form a three-dimensional structure. Since the metal plate is exposed to an atmosphere containing oxygen at a temperature of 800 ° C. or higher in the process of forming a superconductor, an iron-nickel alloy having excellent heat resistance and oxidation resistance, for example, SU.
It is preferable to use S304 and 301S, Hastelloy, Inconel or the like. The method for stretching the noble metal layer is not particularly limited, and can be stretched using sandpaper, a diamond wheel, a buff, a bite, a metal piece or the like as long as the surface has gloss. The surface roughness of the noble metal layer after the stretching treatment is preferably Ra of 1 μm or less because good superconducting properties can be obtained. If the stretching treatment of the noble metal layer is omitted, the metal plate and the superconductor react with each other to deteriorate the superconducting properties. The method for laminating the superconductor material on the surface of the noble metal layer is also not limited, but may be laminated by a method such as a thermal spraying method, a screen printing method, a transfer method, a spray coating method, a dip coating method or a green sheet laminating method. You can
The firing conditions are not particularly limited, and the conventionally known method is used. If necessary, heat treatment is performed after firing.

[0006]

EXAMPLES Examples of the present invention will be described below. The present invention is not limited to the scope of the examples below. Example 1 Silver powder (rare metallic, particle size 325-250 mesh) and magnesia powder (manufactured by Kojundo Chemical Laboratory, heavy,
Free powder, purity 99.9%) was weighed so as to have a ratio shown in Table 1 and dry-mixed for 1 hour with a V blender to obtain mixed powders a and b of silver and magnesia.

[0007]

[Table 1] Next, as a metal plate, the dimensions are 50 mm length x 50 mm width x thickness 1
After sandblasting a SUS310S plate of mm, as shown in FIG. 1, the entire surface (upper and lower surfaces) of the SUS310S plate 1 was sprayed with the mixed powder b of silver and magnesia obtained above by a known plasma spraying method, A mixture layer 2 of silver and magnesia having a surface thickness of 150 μm was formed.
Further, silver powder (rare metallic, particle size 325 to 250 mesh) was sprayed to a thickness of 100 μm as a noble metal layer on the upper surface of one side of the mixture layer 2 of silver and magnesia by a known gas spraying method, and this silver sprayed film was formed. The surface of was rubbed with sandpaper and stretched to obtain a base material for forming a superconductor on which the noble metal layer 3 was formed. When the surface of the noble metal layer after the stretching treatment was measured with a surface roughness meter, Ra was 0.8 μm.
On the other hand, the purity of 99.9 is set so that the atomic ratio of bismuth, strontium, calcium and copper is 2: 2: 1: 2.
% Or more bismuth oxide (manufactured by Kojundo Chemical Research Institute) 913.
29 g, strontium carbonate (made of rare metallic) 57
8.71 g, calcium carbonate (manufactured by Kojundo Chemical Laboratory) 1
96.17 g and cupric oxide (manufactured by Kojundo Chemical Laboratory Co., Ltd.) 3
11.82 g was weighed to obtain a raw material powder for superconductor. The raw material powder for superconductor was filled in a resin pot together with a resin ball and ion-exchanged water, and wet mixed for 60 hours under the condition of 60 rpm. After drying, put the mixture on a silver plate 8
It was calcined at 20 ° C. for 12 hours to obtain a calcined powder for superconductor.
The calcined powder was coarsely crushed, and then the resin pot was filled with zirconia balls and ethyl acetate, and wet crushed for 24 hours under the condition of 60 rpm. This was dried to obtain a bismuth-based superconductor powder A having an average particle size of 5.5 μm (hereinafter referred to as superconductor powder A). To 100 parts by weight of the obtained powder A for superconductor, 8 parts by weight of polyvinyl butyral resin (manufactured by Wako Pure Chemical Industries, reagent first grade) as an organic binder, and phthalate ester (manufactured by Wako Pure Chemical Industries, reagent first grade) as a plasticizer. 3 parts by weight and 50 parts by weight of butanol (manufactured by Wako Pure Chemical Industries, reagent first grade) were added and uniformly mixed, and then deaerated to obtain a superconductor slurry having a viscosity of 15 Pa · s. The superconductor slurry is supplied onto a polyester film (manufactured by Toray), and the thickness is 100 μm by the doctor blade method.
A green sheet for superconductor (hereinafter referred to as a green sheet) was obtained. Next, the above green sheet was thermocompression-bonded to the upper surface of the noble metal layer 3 of the previously obtained base material for forming a superconductor under the conditions of 60 ° C. for 10 minutes and 20 MPa to obtain a green sheet laminated base material for a superconductor. . The green sheet laminated base material for a superconductor obtained above is heated up to 500 ° C. in the atmosphere at a rate of 30 ° C./hour, and then at a rate of 100 ° C./hour.
After raising the temperature to 5 ° C. and holding at 885 ° C. for 15 minutes,
After cooling down to 0 ° C at a rate of 5 ° C / hour and holding for 1 hour, cool down to 800 ° C at 100 ° C / hour, and cool from 800 ° C to room temperature at 300 ° C / hour to obtain a film thickness of 31μ.
A bismuth-based ceramics composite (hereinafter referred to as a superconducting composite) having m superconductor layers 4 was obtained. The obtained superconducting composite was cut into a shape having a length of 50 mm and a width of 5 mm, and Tc and Jc of each sample were measured by the four-terminal method.
c was 91.4 to 92.6 K, and Jc at 77 K in a zero magnetic field was 2.9 to 3.4 (× 10 ⁷ A / m ² ) showing good superconducting properties. As a result of observing the appearance of the obtained superconducting composite, no peeling was observed between the SUS310S plate and the intermediate layer. Further, a heat cycle test was conducted at a liquid nitrogen temperature to 20 ° C. for 10 cycles, but no crack or peeling was observed.

Example 2 As a metal plate, an Inconel 600 plate having the same size as that of Example 1 was sandblasted, and then, as shown in FIG. 2, it was formed on one surface of the Inconel 600 plate 5 by a known plasma spraying method. Mixed powder a of silver and magnesia obtained in Example 1
Was sprayed to form a mixture layer 2 of silver and magnesia having a thickness of 150 μm. Further, the silver used in Example 1 was sprayed to a thickness of 100 μm as a noble metal layer on the upper surface of the mixture layer 2 of silver and magnesia by a known arc spraying method, and the surface of this silver sprayed film was stretched with a diamond wheel. Then, a base material for forming a superconductor on which the noble metal layer 3 was formed was obtained. When the surface of the precious metal layer after the stretching treatment was measured with a surface roughness meter,
Ra was 0.6 μm. On the other hand, a slurry for superconductor having a viscosity of 2 Pa · s was obtained in the same manner as in Example 1 except that the addition amount of butanol was 80 parts by weight. Next, the above superconductor slurry was spray-coated on the upper surface of the precious metal layer 3 of the superconductor-forming base material obtained above to obtain a superconductor material laminated base material. The superconducting material laminated base material obtained above was fired under the same conditions as in Example 1 to obtain a superconducting composite body in which the superconducting layer 4 having a film thickness of 27 μm was formed. For the obtained superconducting composite, Tc and Jc were measured in the same manner as in Example 1.
As a result of measuring and observing the appearance, Tc was 92.4-
At 93.1K, the Jc at 77K in zero magnetic field is 3.
It was 8 to 4.4 (× 10 ⁷ A / m ² ), and no peeling was observed between the metal substrate and the intermediate layer. Liquid nitrogen temperature ~ 20
A heat cycle test at 0 ° C. was performed for 10 cycles, but no crack or peeling was observed.

Example 3 The noble metal layer in Example 2 was changed from silver to gold, the method of forming the noble metal layer was a known plasma spraying method, and the heat treatment condition was 885 ° C.
A superconducting composite body having a superconducting layer having a film thickness of 30 μm was obtained in the same manner as in Example 2 except that the holding for 15 minutes was changed to the holding at 890 ° C. for 15 minutes. The obtained superconducting composite was measured for Tc and Jc and observed for appearance in the same manner as in Example 1. As a result, Tc was 90.2 to 91.2K.
Then, the Jc at 77K in the zero magnetic field is 2.3 to 2.9.
(× 10 ⁷ / m ² ), and no peeling was observed between the metal substrate and the intermediate layer. A heat cycle test was conducted at a liquid nitrogen temperature to 20 ° C. for 10 cycles, but no crack or peeling was observed.

Example 4 Bismuth oxide having a purity of 99.9% or more (so that the atomic ratio of bismuth, lead, strontium, calcium and copper is 1.8: 0.3: 1.8: 2: 3) 704.3 g of high purity chemical laboratory, 112.46 g of lead monoxide (high purity chemical laboratory), strontium carbonate (made of rare metallic) 446.28 g, calcium carbonate (high purity chemical laboratory) 336.18 g And 400.78 g of cupric oxide (manufactured by Kojundo Chemical Laboratory Co., Ltd.) was weighed to obtain a raw material powder for a superconductor. Next, the above-mentioned raw material powder for superconductor was filled in a resin pot together with resin balls and ion-exchanged water, and wet mixed for 60 hours under the condition of 60 rpm. After drying, the mixture was calcined at 800 ° C. for 12 hours to obtain a calcined powder for superconductor. The calcined powder is roughly crushed, and the resin pot is filled with zirconia balls and ethyl acetate, and the rate is 60 minutes per minute.
Wet milling was performed for 60 hours under the condition of rotation. After drying, 820 ℃
Was heat-treated for 20 hours, then the heat-treated powder was coarsely pulverized, and then the resin pot was filled with zirconia balls and ethyl acetate, and wet-pulverized for 24 hours under the condition of 60 rpm. This was dried to obtain a bismuth-based superconductor powder B having an average particle diameter of 4.5 μm (hereinafter referred to as superconductor powder B).

To 100 parts by weight of the obtained powder B for superconductor, 5 parts by weight of ethyl cellulose (manufactured by Wako Pure Chemical Industries, 45 cp) as an organic binder and terpineol (manufactured by Wako Pure Chemical Industries, reagent first grade) as an organic solvent. 30 parts by weight was added and uniformly kneaded to obtain a bismuth-based superconductor paste (hereinafter referred to as a superconductor paste). After that, on the upper surface of the noble metal layer 3 of the base material for forming a superconductor obtained in Example 2,
The superconductor paste obtained above is applied by a dip coating method, dried and then heated in air to a temperature of 300 ° C. at a rate of 50 ° C./hour, and then at a rate of 100 ° C./hour for 84
After raising the temperature to 0 ° C and holding it at 840 ° C for 96 hours, 10
Cool down to room temperature at a rate of 0 ° C / hour and the film thickness is 100μ
A bismuth-based superconducting composite having m superconducting layers was obtained. The obtained superconducting composite was treated with T in the same manner as in Example 1.
As a result of measuring c and Jc and observing the appearance, Tc was 101.8 to 102.7K, and Jc at 77K in a zero magnetic field was 1.5 to 1.8 (× 10 ⁷ A / m ² ). ,
No peeling was observed between the metal substrate and the intermediate layer. A heat cycle test was conducted at a liquid nitrogen temperature to 20 ° C. for 10 cycles, but no crack or peeling was observed.

Comparative Example 1 A superconducting composite having a superconducting layer having a thickness of 28 μm was obtained in the same manner as in Example 1 except that thermal spraying of silver was not performed. The Tc and Jc of the obtained superconducting composite were measured by the same method as in Example 1. As a result, Tc was less than 77K, and superconducting properties were not obtained at 77K. Further, as a result of observing the appearance, the superconductor layer and the metal substrate reacted during the heat treatment through the gap between the mixed layer containing silver and magnesia, so that the intermediate layer film was swollen in some places.

Comparative Example 2 A superconductor layer having a thickness of 25 μm was prepared in the same manner as in Example 1 except that the mixture layer of silver and magnesia was not formed and the noble metal layer was not stretched. The formed superconducting composite was obtained. The Tc and Jc of the obtained superconducting composite were measured by the same method as in Example 1. As a result, Tc was less than 77K, and superconducting properties were not obtained at 77K. As a result of observing the appearance, the superconducting layer and the metal substrate reacted with each other through the gap between the noble metal layer (silver sprayed film) during the heat treatment, so that the silver sprayed film was swollen in some places.

Comparative Example 3 A superconducting composite having a superconducting layer having a thickness of 26 μm was obtained in the same manner as in Example 2 except that the noble metal layer was not stretched. As a result of measuring Tc and Jc of the obtained superconducting composite in the same manner as in Example 1, Tc was 89.8 to 92.0K, but Jc at 77K in a zero magnetic field was 0.3 to 1. .6 (× 10 ⁷ A
/ M ² ). Further, the appearance was observed by SEM and EDX analysis was performed, and as a result, many different phases other than the superconductor were confirmed.

[0015]

The superconducting composite according to the present invention is
Peeling, cracking, etc. do not occur even in the cooling process after being integrated by firing and in the cooling process after heat treatment or in the heat cycle test at room temperature and liquid nitrogen temperature, and the superconducting property does not deteriorate,
It is a superconducting composite which is industrially very suitable.

[Brief description of drawings]

FIG. 1 is a sectional view of a superconducting composite according to an embodiment of the present invention.

FIG. 2 is a sectional view of a superconducting composite according to another embodiment of the present invention.

[Explanation of symbols]

 1 SUS310S plate 2 Mixture layer of silver and magnesia 3 Noble metal layer 4 Superconductor layer 5 Inconel 600 plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shozo Yamana 4-13-1, Higashimachi, Hitachi-shi, Ibaraki Hitachi Chemical Co., Ltd. Ibaraki Research Institute

Claims (2)

[Claims] 1. A superconducting composite in which a mixture layer containing silver and magnesia is interposed between a metal plate and a superconductor layer and a noble metal layer stretched on the upper surface of the mixture layer. 2. A mixture layer containing silver and magnesia is formed on the surface of a metal plate by a thermal spraying method, a precious metal layer is formed on the surface of the mixture layer, and then the surface of the precious metal layer is stretched and then stretched. A method for producing a superconducting composite, comprising laminating a material for a superconductor on a surface of a noble metal layer and then firing the material.