JP3281892B2 - Ceramic superconducting composite and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Superconductors, for example, ceramic superconductors, have the drawbacks of poor mechanical strength and thermal shock resistance, and must be partially melted during firing in order to obtain a high critical current density (Jc). Attempts have been made to combine ceramic superconductors with substrates such as metals and structural ceramics to form composites. Among them, metal has the advantage that it is less susceptible to restrictions such as size and shape than ceramics.

However, since the ceramic superconductor reacts with many metal materials and the superconductivity is deteriorated, it is necessary to form an intermediate layer between the metal substrate and the ceramic superconductor for the purpose of preventing the reaction.

[0004] For example, in the case of a bismuth-based superconductor, as shown in Japanese Patent Application Laid-Open No. 4-199700, a noble metal layer such as gold or silver is diffusion-bonded as an intermediate layer on a substrate of an iron-nickel alloy by hot rolling. Then, a method of producing a composite substrate and forming a bismuth-based superconductor on the composite substrate has been devised. In the case of a bismuth-based superconductor, it is known that superconductivity can be obtained even when magnesia is used in addition to gold and silver.

[0005]

When a superconductor is put into practical use, for example, used for a magnetic shield, a large-sized three-dimensional superconductor is required. In the case where the metal plate, the intermediate layer, and the ceramic superconductor are combined, a problem is a deterioration in superconductivity due to cracks, peeling, internal strain, reactions, and the like due to inconsistencies in the respective thermal expansion coefficients. The inconsistency in the coefficient of thermal expansion causes cracks and peeling during cooling from room temperature to liquid nitrogen temperature, and even 20K to 4.2K, in order to develop a superconducting state in addition to the cooling process during firing and heat treatment for complexing. And the shape and size are restricted, which hinders the practical application and application of ceramic superconductors.

However, in the case of the conventional method, in order to bond the iron-nickel-based alloy substrate and the noble metal intermediate layer, the bonding must be performed under high temperature and high pressure in a reducing atmosphere. Fabrication was difficult. Furthermore, cracks and peeling may occur due to the difference in thermal expansion between the iron-nickel alloy and the noble metal intermediate layer.

Although a method of forming a noble metal intermediate layer on the surface of an iron-nickel alloy by a thermal spraying method to obtain a composite base material can be considered, it is difficult to obtain a dense sprayed film, so that the noble metal intermediate layer must be thickened. It must be greatly affected by the coefficient of thermal expansion.

The present invention provides a ceramic superconducting composite free from the above problems and a method for producing the same.

[0009]

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 or the metal plate and the ceramic superconductor are connected. In order to prevent the reaction, it was considered important to make the thermal expansion coefficient of the intermediate layer provided between the two close to the thermal expansion coefficients of the metal plate and the ceramic superconductor.

For example, the thermal expansion coefficient of a bismuth-based superconductor is about 13 × 10 ⁻⁶ / ° C., whereas that of Inconel, which is an iron-nickel alloy, is about 16 × 10 ⁻⁶ / ° C. The intermediate layer has a silver content of about 21 × 10 ⁻⁶ / ° C. and a magnesia of about 14 × 10 ⁻⁶ / ° C., which are considered to be unlikely to cause a decrease in superconductivity due to the reaction. Although it is considered preferable to use magnesia as the intermediate layer from the above thermal expansion coefficient,
According to experiments performed by the present inventors, when a bismuth-based superconductor was independently formed on a silver substrate and a magnesia substrate without using a metal plate, a result showing superior superconducting characteristics on a silver substrate was obtained. .

That is, by providing an intermediate layer between the metal plate and the ceramic superconductor having a coefficient of thermal expansion close to that of the metal plate and further obtaining excellent superconducting characteristics, generation of cracks due to thermal strain is suppressed. This led to the completion of the present invention.

The present invention provides a ceramic superconducting composite in which an intermediate layer made of a mixture containing silver and magnesia is interposed between a metal plate and a ceramic superconductor layer, and a layer of a mixture containing silver and magnesia on the surface of the metal plate. To form
Furthermore, the present invention relates to a method for producing a ceramic superconducting composite in which a material for a ceramic superconductor is laminated on the surface of a layer of a mixture and then fired.

The ceramic superconductor used in the present invention is not particularly limited as long as it is an oxide. However, if a ceramic superconductor such as an yttrium-based superconductor, a bismuth-based superconductor, or a thallium-based superconductor is used, the critical temperature (hereinafter referred to as Tc) is obtained. Is preferable because the temperature is higher than the temperature of liquid nitrogen. Among them, bismuth-based superconductors are most suitable in the present invention.

In the present invention, the layer of the mixture of silver and magnesia is described as an intermediate layer to be formed between the metal plate and the ceramic superconductor layer. However, the layer may be laminated on one side of the metal plate or on both sides. There is no limitation.

The method of forming the intermediate layer is not particularly limited, but is preferably performed by a thermal spraying method. In addition, a gas type, a plasma type, or the like can be used as a thermal spraying method.
The thickness of the intermediate layer is not particularly limited, but if it is thin, the ceramic superconductor reacts with the metal plate through the intermediate layer, and the superconducting characteristics are apt to deteriorate.
It is from 00 μm to 600 μm.

SUS304 and 310 are used as metal plates.
Iron such as S, Hastelloy, Inconel 600 and 625
A nickel-based alloy plate, a nickel chrome steel plate, a silver plate, or the like is used.

The method of laminating the ceramic superconductor material on the surface of the intermediate layer containing silver and magnesia is not limited. However, thermal spraying, screen printing, transfer, spray coating, dip coating, green sheet lamination It can be laminated by a method such as a method.

The firing conditions are not particularly limited, and the firing is performed by a conventionally known method. If necessary, heat treatment is performed after firing.

[0019]

Embodiments of the present invention will be described below. Example 1 Silver powder (manufactured by Rare Metallic, particle size: 44 μm or less) and magnesia powder (manufactured by Kojundo Chemical Laboratory, heavy, free powder, purity: 99.9%) were weighed so as to have the proportions shown in Table 1. And mixed in a mortar for 15 minutes to obtain mixed powders a and b of silver and magnesia.

[0020]

[Table 1]

Next, as a metal plate, an Inconel 600 plate having a size of 50 mm in length × 50 mm in width × 1 mm in thickness was subjected to sandblasting, and then, as shown in FIG.
The superconducting layer 2 is formed by spraying the mixed powder a of silver and magnesia obtained above on one surface of the zero plate 1 by a known plasma spraying method to form an intermediate layer 2 having a thickness of 320 μm and containing a mixture containing silver and magnesia. A body forming substrate was obtained.

On the other hand, 913.29 g of bismuth oxide (manufactured by Kojundo Chemical Laboratories) having a purity of 99.9% or more so that the ratio of bismuth, strontium, calcium and copper becomes 2: 2: 1: 2 in atomic ratio, 578.71 g of strontium (manufactured by Rare Metallic), 196.17 g of calcium carbonate (manufactured by Kojundo Chemical Lab.), And 311.82 g of cupric oxide (manufactured by Kojundo Chemical Lab.) Were used as raw material powder for superconductors. .

The raw material powder for a superconductor was filled in a resin pot together with a resin ball and ion-exchanged water, and was wet-mixed at 60 rpm for 60 hours. After drying, the mixture was placed on a silver plate and calcined at 820 ° C. for 12 hours to obtain a calcined powder for a superconductor. The calcined powder was roughly pulverized, further filled in a resin pot together with zirconia balls and ethyl acetate, and wet pulverized at 60 rpm for 24 hours. This was dried to obtain bismuth-based superconductor powder A having an average particle size of 5 to 7 μm (hereinafter referred to as superconductor powder A).

An acrylic resin (manufactured by DuPont, # 520) was used as an organic binder in 100 parts by weight of the obtained superconductor powder A.
0) of 70 parts by weight, 2.5 parts by weight of a phthalate resin (D-160, manufactured by Mitsubishi Monsanto) as a plasticizer and 150 parts of 1,1,1-trichloroethane (Wako Pure Chemical Industries, Wako first grade). Parts by weight were added and uniformly mixed to obtain a superconductor slurry. The slurry for superconductor was cast on a polyester film (manufactured by Toray Industries Inc.) using a baker applicator, and dried at 60 ° C. for 10 hours.
By peeling off from the film, a superconductor green sheet (material for superconductor) having a thickness of 100 μm was obtained.

Next, on the upper surface of the intermediate layer 2 of the substrate for forming a superconductor obtained above, the green sheet for a superconductor obtained above was
Thermocompression bonding was performed at 30 ° C. at 30 ° C. to obtain a green sheet laminated substrate for a superconductor. The green sheet laminated substrate for superconductor obtained above is heated in air at a rate of 30 ° C./hour up to 500 ° C. and then at a rate of 100 ° C./hour.
After the temperature was raised to 5 ° C and held at 885 ° C for 15 minutes, 85
The temperature was lowered to 5 ° C at a rate of 5 ° C / hour.
After cooling to room temperature at a rate of / hour, a composite having the ceramic superconductor layer 3 having a thickness of 32 µm was obtained.

Next, the complex obtained above is placed in a nitrogen stream at 7
Heat treatment was performed at 00 ° C. for 15 hours to obtain a bismuth-based ceramic superconducting composite. As a result of measuring the Tc and critical current density (hereinafter referred to as Jc) of the obtained bismuth-based ceramic superconducting composite by a four-terminal method, Tc was found to be 91 K.
Jc at zero magnetic field at 77 K is 1.9 × 10 ⁷ A /
m ² . A heat cycle test at a temperature of liquid nitrogen to 20 ° C. was performed 10 times, but no crack was found.

Example 2 As a metal plate, the dimensions were 50 mm length × 50 mm width × 1 thickness.
mm SUS310S plate after sandblasting,
As shown in FIG. 2, the mixed powder b of silver and magnesia obtained in Example 1 was sprayed on the entire surface (upper and lower surfaces) of the SUS310S plate 4 by a known plasma spraying method, and the thickness of one side was 300 μm. A substrate for forming a superconductor in which the intermediate layer 2 made of a mixture containing silver and magnesia was formed was obtained.

Next, the calcined powder for superconductor obtained in Example 1 was pulverized in a mortar and heat-treated at 850 ° C. for 10 hours in the air. This is crushed in a mortar, and then classified to obtain a particle size of 30.
Bismuth-based superconductor powder B adjusted to ~ 150 µm
(Hereinafter referred to as superconductor powder B).

The above-mentioned superconductor powder B was sprayed on the previously-obtained base material for forming a superconductor by a known plasma spraying method, and then fired under the same conditions as in Example 1 to obtain a film having a thickness of 60%.
A composite having the ceramic superconductor layer 3 of μm was obtained.

Next, the composite obtained above was heat-treated under the same conditions as in Example 1 to obtain a bismuth-based ceramic superconducting composite. As a result of measuring Tc and Jc of the obtained bismuth-based ceramic superconducting composite by a four-terminal method,
Is 89K, and Jc at zero magnetic field at 77K is 0.9.
× 10 ⁷ A / m ² . A heat cycle test at a temperature of liquid nitrogen to 20 ° C. was performed 10 times, but no crack was found.

Example 3 As a metal plate, an Inconel 600 plate subjected to the same sand blast treatment as in Example 1 was used, and the entire surface (upper and lower surfaces) of the metal plate was obtained in Example 1 by a known plasma spraying method. A mixed powder a of silver and magnesia was sprayed to obtain a substrate for forming a superconductor in which an intermediate layer made of a mixture containing silver and magnesia having a thickness on one side of 320 μm was formed.

Next, the powder A10 for superconductor obtained in Example 1
To 0 parts by weight, 5 parts by weight of ethyl cellulose (45 cp, manufactured by Wako Pure Chemical Industries) as an organic binder and 30 parts by weight of terpineol (reagent first grade, Wako Pure Chemical Industries) as an organic solvent were added and uniformly kneaded. Thus, a paste for a bismuth-based superconductor was obtained.

Thereafter, the bismuth-based superconductor paste obtained above was applied to the upper surface of the intermediate layer of the base material for forming a superconductor obtained earlier by dip coating, dried, and dried under the same conditions as in Example 1. To obtain a composite having a ceramic superconductor layer having a thickness of 30 μm.

Next, the composite obtained above was heat-treated under the same conditions as in Example 1 to obtain a bismuth-based ceramic superconducting composite. As a result of measuring Tc and Jc of the obtained bismuth-based ceramic superconducting composite by a four-terminal method,
Is 92K, and Jc at zero magnetic field at 77K is 2.2.
× 10 ⁷ A / m ² . A heat cycle test at a temperature of liquid nitrogen to 20 ° C. was performed 10 times, but no crack was found.

Example 4 As a metal plate, the dimensions were 50 mm long × 50 mm wide × 1 thickness.
3 mm, the mixed powder b of silver and magnesia obtained in Example 1 was sprayed onto one surface of the silver plate 5 by a known plasma spraying method, as shown in FIG. A substrate for forming a superconductor, on which an intermediate layer 2 made of a mixture containing silver and magnesia having a thickness of 100 μm was formed.

Next, the slurry for the superconductor obtained in Example 1 was applied to the upper surface of the intermediate layer 2 of the base material for forming a superconductor obtained above by a spray coating method, dried, and then dried in the same manner as in Example 1. The composite was fired under the conditions to form the ceramic superconductor layer 3 having a thickness of 30 μm.

Next, the composite obtained above was heat-treated under the same conditions as in Example 1 to obtain a bismuth-based ceramic superconducting composite. As a result of measuring Tc and Jc of the obtained bismuth-based ceramic superconducting composite by a four-terminal method,
Is 92K, and Jc at zero magnetic field at 77K is 2.1.
× 10 ⁷ A / m ² . A heat cycle test at a temperature of liquid nitrogen to 20 ° C. was performed for 10 cycles, but no crack was observed.

EXAMPLE 5 Bismuth oxide having a purity of 99.9% or more (bismuth, lead, strontium, calcium, and copper was adjusted to have an atomic ratio of 1.8: 0.3: 1.8: 2: 3). 704.3 g, high purity chemical laboratory, 112.46 g lead monoxide (high purity chemical laboratory), 446.28 g strontium carbonate (rare metallic), 336.18 g calcium carbonate (high purity chemical laboratory) And 400.78 g of cupric oxide (manufactured by Kojundo Chemical Laboratory) were weighed to obtain a raw material powder for a superconductor.

Next, the raw material powder for a superconductor was filled in a resin pot together with a resin ball and ion-exchanged water.
The wet mixing was performed at 60 rpm for 60 hours. After drying, the mixture was calcined at 800 ° C. for 12 hours to obtain a calcined powder for a superconductor. The calcined powder is roughly pulverized, and further filled in a resin pot together with zirconia balls and ethyl acetate.
The wet pulverization was performed for 60 hours under the condition of 0 rotation.

After drying, the mixture is heat-treated at 820 ° C. for 20 hours, then the heat-treated powder is coarsely pulverized, and further filled in a resin pot together with zirconia balls and ethyl acetate.
The wet pulverization was performed for 24 hours under the condition of 0 rotation. This is dried to obtain a bismuth-based superconductor powder C having an average particle size of 4 to 6 μm.
(Hereinafter referred to as superconductor powder C).

To 100 parts by weight of the obtained superconductor powder C, 5 parts by weight of ethylcellulose (45 cp, manufactured by Wako Pure Chemical Industries) as an organic binder and terpineol (first-class reagent, Wako Pure Chemical Industries, Ltd.) as an organic solvent were used. 30 parts by weight were added and uniformly kneaded to obtain a bismuth-based superconductor paste.

Next, the bismuth-based superconductor paste obtained above was applied to the upper surface of the intermediate layer of the base material for forming a superconductor obtained in Example 2 by a screen printing method, dried and then heated to 300 ° C. in the air. Is heated at a rate of 50 ° C./hour,
A bismuth-based material in which a ceramic superconductor layer having a thickness of 100 μm is formed by heating to 840 ° C. at a rate of 00 ° C./hour, holding at 840 ° C. for 96 hours, and cooling to room temperature at a rate of 100 ° C./hour. A superconducting composite was obtained.

Tc and Jc of the obtained bismuth-based superconducting composite were measured by a four-terminal method.
At K, the Jc at zero field at 77K is 1.0 × 10
^{It was 7} A / m ² . A heat cycle test at a temperature of liquid nitrogen to 20 ° C. was performed for 10 cycles, but no crack was observed.

Comparative Example 1 A superconductor having a 310 μm-thick silver layer formed through the same process as in Example 1 except that only the silver powder was used instead of the mixed powder of magnesia and silver of Example 1. A substrate for forming was obtained. A bismuth-based ceramic superconducting composite having a ceramic superconductor layer having a thickness of 35 μm was obtained through the same steps as in Example 1 below.

As a result of measuring the Tc and Jc of the obtained bismuth-based ceramic superconducting composite by a four-terminal method,
Tc was 89K, and Jc at zero magnetic field at 77K was 0.6 × 10 ⁷ A / m ² . Liquid nitrogen temperature ~ 2
When a heat cycle test at 0 ° C. was performed, cracks occurred at the ninth cycle.

Comparative Example 2 A superconductor formed of a magnesia layer having a thickness of 320 μm through the same steps as in Example 2 except that only magnesia powder was used instead of the mixed powder of magnesia and silver of Example 2. A substrate for forming was obtained.

Thereafter, through the same steps as in Example 3, the film thickness becomes 3
A bismuth-based ceramic superconducting composite having a 0 μm ceramic superconductor layer formed thereon was obtained. As a result of measuring the Tc and Jc of the obtained bismuth-based ceramic superconducting composite by a four-terminal method, Tc was 88 K, and Jc in a zero magnetic field at 77 K was 0.4 × 10 ⁷ A / m ² .
A heat cycle test at a temperature of liquid nitrogen to 20 ° C. was performed, but no crack was observed.

[0048]

The ceramic superconducting composite according to the present invention is free from cracks, peeling, etc. even after being integrated by firing and firing, and also in a cooling process after heat treatment or a heat cycle test between room temperature and liquid nitrogen temperature. In addition, the superconducting composite does not deteriorate in superconductivity and is industrially extremely suitable.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a bismuth-based ceramic superconducting composite according to one embodiment of the present invention.

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

FIG. 3 is a sectional view of a bismuth-based ceramic superconducting composite according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inconel 600 board 2 Intermediate layer 3 Ceramic superconductor layer 4 SUS310S board 5 Silver board

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C01G 29/00 ZAA C01G 29/00 ZAA // B32B 7/02 105 B32B 7/02 105 (72) Inventor Shuichiro Shimoda Hitachi, Ibaraki Hitachi Chemical Industry Co., Ltd.Ibaraki Research Center 4-3-1, Hitachi Chemical Co., Ltd. (72) Inventor Shozo Yamana 4-3-1, Higashimachi, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd.Ibaraki Research Center Examiner Mayumi Koishi (56) References JP-A-63-274018 (JP, A) JP-A-4-349187 (JP, A) JP-A-2-160545 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name ) B32B 15/00-15/20 C01G 1/00

Claims (3)

(57) [Claims] 1. A ceramic superconducting composite in which an intermediate layer made of a mixture containing silver and magnesia is interposed between a metal plate and a ceramic superconductor layer. 2. A ceramic superconducting composite, comprising: forming a layer of a mixture containing silver and magnesia on the surface of a metal plate; laminating a material for ceramics superconductor on the surface of the layer of the mixture; Manufacturing method. 3. The method for producing a ceramic superconducting composite according to claim 2, wherein the layer of the mixture containing silver and magnesia is formed by thermal spraying.