JPH06183741A - Superconducting composite and its production - Google Patents

Abstract

PURPOSE:To produce a superconducting composite having a high mechanical strength and preventing the deterioration of its superconducting characteristics. CONSTITUTION:An Sr-Ca-Cu oxide layer which forms a layer reactive with an Ni alloy substrate by firing is formed on the Ni alloy substrate and they are integrated by successive or simultaneous primary firing. A Bi-contg. superconductor layer is then formed on the top of the Sr-Ca-Cu oxide layer and they are integrated by secondary firing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting composite and a method for producing the same.

[0002]

2. Description of the Related Art As one of superconductors whose critical temperature exceeds the boiling point of liquid nitrogen, a composite oxide containing bismuth (Bi), strontium (Sr), calcium (Ca) and copper (Cu) as main components is known. ing. As a method for obtaining a sintered body of the superconductor, a method of molding a superconductor powder and firing it at a temperature lower than its decomposition melting temperature or baking the superconductor on a silver substrate that does not generate a reaction product that deteriorates superconducting properties There is a way to integrate.

[0003]

However, when the superconductor is fired at a temperature lower than its decomposition and melting temperature, the sintered body does not become dense and the mechanical strength is low. In order to fire at a temperature above the decomposition melting temperature, it is essential to integrate it with a substrate having a desired shape, such as a silver substrate or a Ni alloy substrate, but a silver substrate that does not deteriorate superconducting properties has low mechanical strength. The liquid nitrogen temperature (7
If a Ni alloy substrate used at an extremely low temperature of 7.3 K) or less is used and a superconductor layer is directly formed on the surface of the Ni alloy substrate, the superconducting property of the superconductor tends to be deteriorated.

The present invention provides a superconducting composite and a method for producing the same for overcoming these drawbacks.

[0005]

According to the present invention, a reaction layer of the Ni alloy substrate and Sr-Ca-Cu oxide, a Sr-Ca-Cu oxide layer and a Bi-based superconductor layer are formed on a Ni alloy substrate. Sr-C in which a reaction layer with the Ni alloy substrate is formed by firing on the formed superconducting composite and Ni alloy substrate
After forming the a-Cu oxide layer, these are sequentially or simultaneously primary-fired to be integrated, and a Bi-based superconductor layer is further formed on the upper surface of the Sr-Ca-Cu oxide layer, and then secondary-fired. The present invention relates to a method for manufacturing an integrated superconducting composite.

Bi based superconductors include, for example, Bi, Sr and C.
The composition is mainly represented by a and Cu, and the ratio (atomic ratio) of Bi: Sr: Ca: Cu is generally 2: 2: 1: 2 or 2: 2: 2: 3. A part in which Pb is substituted and Pb is further added can be applied.

As the Ni alloy substrate, an alloy substrate containing Ni, which is called by a name such as stainless steel, Hastelloy, and Inconel, is shown, and it is preferable to use one having a thermal expansion coefficient close to that of a superconductor.

The Sr-Ca-Cu oxide has a melting point (liquid phase formation temperature) of 50 from the decomposition melting temperature of the Bi-based superconductor.
It is preferable that the temperature is higher than 0 ° C, and more preferable if it is higher than 100 ° C. Its composition is, for example, Sr: Ca: Cu ratio (atomic ratio) of 0.8: 0.2: 1 and 0.2: 0.8: 1.
And 0.02: 0.98: 1. It is also possible to prepare Sr-Cu and Ca-Cu compounds in advance and mix them at a desired ratio before forming.

A reaction layer of the Ni alloy substrate and the Sr-Ca-Cu oxide formed on the Ni alloy substrate and Sr-Ca-
Although the thickness of the Cu oxide layer is not strictly defined,
For example, the thickness of the reaction layer of the Ni alloy substrate and the Sr-Ca-Cu oxide and the Sr-Ca-Cu oxide layer is 20 to 50 μm.
The thing of about m is used. The method for forming these layers is not particularly limited, and for example, a screen printing method, a spray coating method, an electrodeposition method, a dipping method, a green sheet method or the like can be used.

The thickness of the Bi-based superconductor layer formed on the outermost surface (outermost layer) is not particularly limited because it depends on the application or its characteristics. The conditions for firing and integration are not particularly limited as long as the conditions are suitable for each firing since both primary firing and secondary firing differ depending on the individual materials. The firing atmosphere is also not particularly limited, but when the Sr—Ca—Cu oxide layer is formed, firing can be performed in a nitrogen atmosphere having an oxygen concentration of less than 10% or in a nitrogen atmosphere. In particular, firing in a nitrogen atmosphere is preferable because it is easy to prevent oxidation of the Ni alloy. In this case, it is preferable that oxygen is contained at about 5 to 10% at a low temperature of less than 300 ° C., and the temperature is gradually raised to smoothly decompose the organic binder contained in the layer formed on the Ni alloy substrate.

[0011]

The present invention comprises a Ni alloy substrate, a reaction layer of the Ni alloy substrate and Sr-Ca-Cu oxide, and Sr-Ca-Cu.
By forming the oxide layer and the Bi-based superconductor layer,
Since it is possible to prevent the Ni alloy substrate and the Bi-based superconductor layer from directly reacting with each other, it is possible to prevent deterioration of superconducting properties.

[0012]

EXAMPLES Examples of the present invention will be described below. Example 1 Bismuth trioxide (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%), lead monoxide (so that the ratio of bismuth, lead, strontium, calcium and copper in terms of atomic ratio is as shown in Table 1 Yellow) (made by Wako Pure Chemical Industries, special grade reagent), strontium carbonate (made by Rare Metallic Co., purity 99.9%), calcium carbonate (made by Kojundo Chemical Laboratory, purity 99.9%) and cupric oxide (high) Purity Chemical Laboratory Co., Ltd., purity 99.9%) was weighed and used as a starting material.

[0013]

[Table 1]

Next, the above starting materials were filled in a ball mill made of synthetic resin together with a steel ball covered with the synthetic resin and methanol, and wet-mixed and crushed for 60 hours under the condition of 50 rpm. Then, the pulverized product was taken out from the ball mill, dried at 100 ° C. for 24 hours, placed on an alumina baking plate, and baked in the air at 800 ° C. for 24 hours using an electric furnace. Sample No. 1 and No. 2 is 1
Additional firing for 20 hours at 000 ° C.

After cooling, the mixture was roughly ground in a mortar, and the ground product was filled in a synthetic resin ball mill together with zirconia balls and methanol, wet-ground for 48 hours at 50 rpm, and dried to obtain each powder. It was

After this, the sample No. 3 and No. Only the powder of No. 4 was placed on a calcined plate made of alumina, and sample N was placed in an oxygen furnace in a low oxygen atmosphere with a volume ratio of O ₂ : N ₂ = 1: 20.
o. 3 is 860 ° C. and sample No. 4 at 850 ℃ each 3
It was heated for 0 hour to obtain a bismuth-based superconductor. Next, the bismuth-based superconductor is roughly crushed in a mortar, and the crushed product is filled in a synthetic resin ball mill together with zirconia balls and methanol, wet-ground for 48 hours at 50 rpm, and dried to obtain a powder. Obtained.

Next, the sample No. 1-No. Methyl cellulose (manufactured by Wako Pure Chemical Industries) 12 to 100 g of each powder of 4
g and dibutyl phthalate (manufactured by Wako Pure Chemical Industries, Ltd.) are added,
To this, 18 g of terpineol (manufactured by Wako Pure Chemical Industries, Ltd.) and 18 g of diethylene glycol monobutyl ether were added and uniformly mixed to form a paste. Half of the obtained paste was used to obtain a green sheet using a baker applicator. The thickness of the green sheet is the same as sample No. 1 and N
o. The sample using the powder of No. 2 was 25 ± 5 μm and the sample No. 3 and No. 15 using the powder of No. 4
A thickness of 0 ± 20 μm was obtained. As the base film, a polyester film having a release agent treatment and a thickness of 50 μm was used.

After this, a 2 mm thick stainless steel plate (SUS
316) and the sample No. A paste using the powder of No. 1 was applied and dried to form a layer having a thickness of 50 μm. This was heated to 300 ° C. for 9 hours in a nitrogen gas stream having an oxygen concentration of 10% to decompose and remove organic substances, and then 10
The temperature was raised to 60 ° C. in 10 hours, and the temperature was maintained at 1060 ° C. for 0.5 hour (primary firing), and then cooled to room temperature in 12 hours.

Next, sample No. Sample No. 1 is formed on the upper surface of the layer on which the paste using the powder of No. 1 is baked. Two green sheets obtained by using the powder of No. 3 were overlaid and thermocompression-bonded at 80 ° C., then heated to 300 ° C. in 12 hours in a nitrogen gas stream having an oxygen concentration of 5%, and kept at 300 ° C. for 2 hours. Then, the temperature was raised to 875 ° C. in 6 hours, the temperature was maintained at 875 ° C. for 0.2 hours (secondary firing), and then cooled to 850 ° C. for 1 hour at a rate of 5 ° C.,
Then, the mixture was cooled to room temperature for 12 hours to obtain a superconducting composite.

The obtained superconducting composite was measured for the critical temperature (hereinafter referred to as Tc) and the critical current density (hereinafter referred to as Jc) at which the electric resistance became 0 by the four-terminal method, and the Tc was 90.
The Jc at 77K was 11000 A / cm ² .

Example 2 Sample No. 2 was laminated on an Inconel plate having a thickness of 2 mm to have a thickness of 50 μm. The green sheet obtained by using the powder of No. 2 was thermocompression bonded at 80 ° C., then heated to 300 ° C. for 9 hours in a nitrogen stream having an oxygen concentration of 10% to decompose and remove organic substances, and then in a nitrogen atmosphere stream. The temperature was raised to 1060 ° C. in 10 hours, maintained at 1060 ° C. for 0.5 hour (primary firing), and then cooled to room temperature in 12 hours.

Next, sample No. Sample No. 2 was formed on the upper surface of the layer on which the green sheet obtained by using the powder of No. 2 was baked. After stacking three green sheets obtained by using the powder of No. 4 and thermocompression-bonding at 90 ° C., the temperature was raised to 300 ° C. in 12 hours in a nitrogen stream having an oxygen concentration of 5%, and kept at 300 ° C. for 2 hours. After 880
The temperature is raised to 6 ° C in 6 hours, the temperature is maintained at 880 ° C for 0.2 hours (secondary firing), cooled to 870 ° C, further maintained at 870 ° C for 40 hours, and then cooled to room temperature for 20 hours to obtain a superconducting composite. Got the body

When Tc and Jc of the obtained superconducting composite were measured by the four-terminal method, Tc was 105K and Jc at 77K was 1700 A / cm ² .

Comparative Example 1 Sample No. 1 was placed on the same stainless plate as in Example 1. Directly stack two green sheets obtained by using the powder of No.3 and 80 ℃
After thermocompression-bonding, a superconducting composite was obtained through the same steps as in Example 1. The Tc of the obtained superconducting composite was measured by the four-terminal method, but it was 77 K or less, and it did not show superconductivity at the liquid nitrogen temperature.

Comparative Example 2 Sample No. 2 was placed on the same Inconel plate as in Example 2. Directly stack the 3 green sheets obtained by using the powder of No. 4 and 90 ℃
After thermocompression-bonding, the superconducting composite was obtained through the same steps as in Example 2. When Tc and Jc of the obtained superconducting composite were measured by a four-terminal method, Tc was 79K and Jc at 77K was less than 10 A / cm ² .

[0026]

INDUSTRIAL APPLICABILITY The superconducting composite according to the present invention is a superconducting composite having high mechanical strength, no deterioration in superconducting properties, stable superconductivity at liquid nitrogen temperature, and industrially extremely suitable.

Claims (2)

[Claims] 1. A Ni alloy substrate and a S alloy on the Ni alloy substrate.
A superconducting composite in which a reaction layer with an r-Ca-Cu oxide, a Sr-Ca-Cu oxide layer, and a Bi-based superconductor layer are formed. 2. A Sr—Ca—Cu oxide layer, on which a reaction layer with the Ni alloy substrate is formed by firing, is formed on the Ni alloy substrate, and these are sequentially or simultaneously primary fired to be integrated. Furthermore, B is formed on the upper surface of the Sr-Ca-Cu oxide layer.
A method for producing a superconducting composite, which comprises forming an i-based superconductor layer and then performing secondary firing to integrate the layers.