JPH04310732A - Manufacture of composite body of oxide superconductor and metal - Google Patents

Abstract

PURPOSE:To suppress the generation of a crack caused by heat stress by successively laminating green sheets composed of oxide superconductor particles and metal particles so that the green sheet with high oxide superconductor content is arranged on an upper side. CONSTITUTION:A plurality of metal green sheets composed of a mixture of oxide superconductor particles and metal particles and stepwise increased in the content of a superconductor are successively laminated so that the green sheet with high oxide superconductor content is arranged on an upper side. Next, an oxide superconductor green sheet is laminated as the uppermost layer and the whole is baked during or after rolling to prepare an oxide superconductor/metal composite. This composite can be avoided from the crack or release generated in the interface or superconductor of a conventional bonded body or laminate.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a composite of an oxide superconductor and a metal.

0002

[Prior art] Oxide superconductor (hereinafter referred to as superconductor)
However, there are drawbacks such as difficulty in making complex shapes and difficulty in making large molded bodies.

[0003] In order to compensate for these drawbacks, superconductors are combined with materials such as metals to form composites. Methods of combining superconductors include a method of laminating a superconductor and a metal or coating (printing) a superconductor paste on a metal plate and firing it.

0004

[Problems to be Solved by the Invention] However, the problem with combining superconductors and metals is that in order to develop a superconducting state, they must be heated to extremely low temperatures using a refrigerant such as liquid helium or liquid nitrogen or a refrigerator. During cooling, cracks, peeling, etc. occur at the interface between the metal and the superconductor or at the superconductor because the thermal expansion coefficients of the superconductor and the metal differ. For this reason, the size of the superconductor and metal stack,
There are restrictions on the shape, usage conditions, etc.
This has been a hindrance to the practical application and application of superconductors.

An object of the present invention is to provide a method for manufacturing a superconductor-metal composite that suppresses the occurrence of cracks caused by thermal stress and is free from the above-mentioned problems.

[0006]

[Means for Solving the Problem] As a result of various studies on the above-mentioned drawbacks, the present inventors found that the value of the thermal expansion coefficient of a composite of a superconductor and a metal takes a value between that of a superconductor and a metal. They focused on this and found that by providing these composites as an intermediate layer between the superconductor and the metal, the occurrence of cracks caused by thermal strain can be suppressed. Furthermore, it has been found that this effect is remarkable when the metal has wettability to the superconductor when it is molten.

As a result of further investigation, the present inventors found that by changing the mixing ratio of superconductor particles and metal particles, the thermal expansion coefficient changes in proportion to the mixing ratio, and the metal particles are removed from the superconductor layer. The above problems can be avoided by providing multiple intermediate layers in which the mixing ratio of superconductor particles and metal particles is adjusted so that the coefficient of thermal expansion increases step by step, and by firing during or after rolling. The inventors discovered that a composite of a superconductor and a metal can be obtained and completed the present invention.

[0008] The present invention comprises a plurality of mixed green sheets of superconductor particles and metal particles in which the superconductor content is gradually increased on the upper surface of the metal green sheet, with the one with the higher superconductor content on the top. A method for manufacturing a composite of a superconductor and a metal, in which superconductor green sheets are laminated in order so that the superconductor green sheets are laminated on top, and then fired during or after rolling, and superconductor is contained on the top surface of the superconductor green sheets. A plurality of mixed green sheets of superconductor particles and metal particles whose content is gradually reduced are stacked one after another so that the one with the lowest superconductor content is on top, and then a metal green sheet is stacked on top. The present invention relates to a method for producing a composite of a superconductor and a metal, which is then fired during or after rolling.

[0009] In the present invention, the stepwise increase in the content of superconductor means that the content of superconductor in the mixed layer of superconductor and metal increases from the obtained metal layer side to the superconductor layer side. On the other hand, a gradual decrease in the superconductor content means that the superconductor content in the superconductor-metal mixed layer decreases from the obtained superconductor layer side to the metal layer side. It means that.

[0010] The superconductor used in the present invention is not particularly limited as long as it is an oxide. For example, if an yttrium-based superconductor or a bismuth-based superconductor is used, it is easy to process it into a sheet shape and has a critical temperature. is 77K or more, which is preferable.

[0011] The metal is not particularly limited as long as it is wettable to the superconductor when melted and does not significantly deteriorate the superconducting properties when mixed into the superconductor. It is preferable to use silver or an alloy containing 95% by weight or more of silver and one or more noble metals such as platinum, palladium, rhodium, ruthenium, osmium, and iridium. Especially the above precious metals are 0.1
It is preferable to use a silver alloy containing up to 5% by weight, preferably 0.2 to 3% by weight, since the critical current density (hereinafter referred to as Jc) is improved.

[0012] There are no particular restrictions on the method of forming each green sheet, but for example, the above-mentioned superconductor particles, metal particles, etc. are mixed together with an organic binder and a solvent, and then the mixture is supplied onto a film and then mixed using a doctor blade or the like. It can be formed by a method such as tape casting to a certain thickness.

[0013] The mixed green sheet of superconductor particles and metal particles can be formed by preparing a plurality of mixtures with different mixing ratios of superconductor particles and metal particles, and then using a method such as tape casting similar to that described above. can.

The solution in which the superconductor particles or metal particles are dispersed is prepared by adding an organic binder or plasticizer such as paraffin, polyisobutyl methacrylate, polyvinylpyrrolidone, or polyvinyl butyral to an alcohol, ketone, aromatic or aliphatic type. A solution dissolved in a hydrocarbon or the like is used.

[0015] If firing is performed in a temperature range where the metal particles and/or superconductor particles are partially melted, a highly dense and oriented sintered body can be obtained by simply holding the metal particles and/or superconductor particles at a high temperature for a short time.
This is preferable because the movement of base material components and the like becomes less likely to occur and deterioration of superconducting properties can be prevented. Note that the partial melting temperature refers to, for example, Japanese, Journal, Of, Applied, Physics (Japanese Journal, Of, Applied, Physics).
of Applied Physics)
Vol. 27, No. No. 12 (December 1988), L
Pages 2276-L2279 and the same magazine Vol. 28, No.
2 (February 1989), pages L213-L216, refers to the temperature at which a portion of the solid phase begins to form a liquid phase. The partial melting temperature in the present invention means a temperature at which a part of the solid phase in the metal and/or superconductor is melted and/or a temperature at which a liquid phase is generated by reaction of two or more solid phases. The range of this partial melting temperature varies depending on conditions such as composition and firing atmosphere. This partial melting temperature can be measured, for example, as the temperature of the endothermic peak of a differential thermal analyzer (DTA). The partial melting temperature range means a range of approximately the partial melting temperature, and refers to, for example, the temperature range from the start temperature to the end temperature of the endothermic peak of DTA.

[0016] After each green sheet is laminated, it is rolled. Although there is no particular restriction on the method of rolling, it is preferable to roll the green sheets with rolling rolls because this allows the green sheets to be made into long sheets. Further, rolling can be performed by other methods such as applying pressure from both sides using a press.

[0017] Mutual embedding occurs between the superconductor green sheets or the mixed green sheets of a plurality of superconductor particles and metal particles having different mixing ratios, and the metal green sheet layers by rolling. As a result, the composition changes continuously instead of changing stepwise when the layers are stacked one on top of the other, resulting in a more favorable state for reducing thermal stress. It is also preferable because it also promotes densification. Rolling in the partial melting temperature region is not particularly limited as long as it is a method that allows rolling at high temperatures.

When rolling in the partial melting temperature range, if too much pressure is applied, the liquid phase generated by partial melting will flow out.
There is a drawback that the content of the superconductor tends to be discontinuous, making it difficult to obtain a gradient. For this reason, the pressure to be applied is appropriately selected depending on conditions such as the composition of the superconductor, temperature, atmosphere, and the material of the metal. For example, in the case of a combination of bismuth-based superconductor and silver alloy, 0.5M
It is preferable to roll at a pressure of Pa to 150 MPa,
Preferably, the atmosphere is a mixed gas flow of oxygen and nitrogen for sintering. In the case of yttrium-based superconductors, 900℃~
0.5MPa to 150MPa in the temperature range of 1000℃
It is preferable that the rolling be carried out at a pressure of about 100 ml, and preferably in an oxygen atmosphere. Rolling at high temperatures not only promotes densification but also promotes compounding, which is extremely effective in improving superconducting properties.

[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 and used as starting raw material powder.

Next, the above starting material powder was filled in a zirconia pot together with zirconia balls and methanol, and wet mixed and pulverized at 60 revolutions per minute for 100 hours. After drying, the crushed material was placed on an alumina baking plate and heated at 920°C in the air.
℃ at a rate of 200℃/hour, and 10℃ at 950℃.
After being fired for 1 hour, it was cooled at a rate of 100°C/hour, then ground in an alumina mortar, then heated at a rate of 100°C/hour in an oxygen atmosphere, and then re-fired at 950°C for 10 hours and then brought to 100°C.
/ hour, and then filled in a zirconia pot with zirconia balls and re-pulverized to obtain superconductor particles with an average particle size of 4.8 μm.

To 100 g of the superconductor particles, 6 g of polyvinyl butyral resin (manufactured by Wako Pure Chemical Industries, Ltd., reagent first class), 3 g of phthalate ester (manufactured by Wako Pure Chemical Industries, Ltd., reagent first class) and butanol (
After adding and mixing 45 g of Wako Pure Chemical Industries, Ltd., reagent grade 1), deaeration and solvent removal were performed to obtain a slurry whose viscosity was adjusted to 10,000 cp at 20°C. After this, the slurry is made to a thickness of 100 μm.
The superconductor green sheet a (hereinafter referred to as sheet a) having a thickness of 0.6 mm was obtained by tape casting using a doctor blade method and drying.

On the other hand, using the superconductor particles obtained above and silver particles (manufactured by Tanaka Massey, particle size 2 μm), a thickness of 0.6 mm was obtained.
mixed green sheets b, c and d (hereinafter referred to as sheets b, c
and d), and a silver green sheet e (hereinafter referred to as sheet e) having a thickness of 0.6 mm was obtained using the same silver particles as above. Table 1 shows the content of superconductor particles and silver particles in each sheet. Note that sheets b, c, and d, and sheet e were produced through the same process as sheet a.

[0023]

[Table 1]

Next, sheets d, c and b are placed on the upper surface of sheet e.
After stacking 6 sheets a on top,
Sandwiched between twin rolls, rolled at 103N per 1cm width to a thickness of 2mm, then slit to a width of 5mm.
It was made into a tape shape of mm. Next, this tape was placed on a zirconia baking plate and heated to 350°C in an air stream at a rate of 25°C/hour, then heat treated at 920°C for 10 hours, and then cooled at a rate of 50°C/hour. A composite of superconductor and metal was obtained.

The critical temperature (hereinafter referred to as Tc) and Jc of the obtained composite of superconductor and metal were measured by the four-probe method, and Tc was 91K and Jc was 77K, which was 1.2×10 7
It was A/m2.

Next, 10 superconductor-metal composites cut into 200 mm x 5 mm sizes were tested at 0°C to 300°C in a dry thermal shock tester (manufactured by Tabai, model: TSR-63).
A dry thermal shock test was conducted by performing 50 cycles at -0°C. As a result, no cracks or peeling occurred in any of the 10 pieces.

Example 2 Bismuth trioxide (manufactured by Kojundo Kagaku Kenkyujo) 685.99% or higher in purity was prepared so that the ratio of bismuth, strontium, calcium and copper was 2:2:1:2 in atomic ratio. 0
g, 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 and used as starting raw material powder.

Next, the above starting material powder was filled into a zirconia pot together with zirconia balls and methanol, and wet mixed at 60 revolutions per minute for 100 hours. After drying, the crushed product was placed on an alumina firing plate and heated to 800°C in the air at a rate of 200°C/hour, fired at 800°C for 10 hours, cooled at a rate of 100°C/hour, and then crushed in an alumina mortar. After that, the temperature was raised at a rate of 100°C/hour in an atmosphere of O2/N2 = 1/10, and after re-firing at 880°C for 20 hours, it was cooled at a rate of 100°C/hour. It was filled with zirconia balls and re-pulverized to obtain superconductor particles with an average particle size of 4.3 μm.

Hereinafter, using the same materials as in Example 1 and going through the same steps as in Example 1, sheets a, b, and 0.6 mm thick were prepared.
c, d and e were obtained. Table 2 shows the content of superconductor particles and silver particles in each sheet.

[0030]

[Table 2]

Next, in the same manner as in Example 1, sheets d, c, and b are laminated in this order on the upper surface of sheet e, and 6 sheets of sheet a are laminated on top.
After repeating 3N rolling to a thickness of 2 mm, it was slit to form a tape with a width of 5 mm. Next, this tape was placed on a zirconia baking plate and heated to 350°C at a rate of 25°C/hour in an air stream, and further heated for 8 hours.
After heat treatment at 90°C for 20 hours, it was cooled at a rate of 50°C/hour to obtain a composite of superconductor and metal.

When the Tc and Jc of the obtained superconductor-metal composite were measured by the four-terminal method, the Tc was 90K and the Jc was 1.2×10 7 A/m 2 at 77K.

A dry thermal shock test similar to that in Example 1 was conducted, but no cracks or peeling occurred in all 10 samples.

Comparative Example 1 Six sheets of sheet a and four sheets of sheet e obtained in example 1 were laminated, and then rolling was repeated under the same conditions as in example 1 to form sheets of 1.2 mm and 0.8 mm, respectively. After adjusting the thickness, they were stacked on top of each other, and the same steps as in Example 1 were carried out to obtain a superconductor-metal composite.

When the Tc and Jc of the obtained superconductor-metal composite were measured by the four-terminal method, the Tc was 91K and the Jc was 8.9×10 6 A/m 2 at 77K. In addition, when a dry thermal shock test similar to that in Example 1 was conducted, 1
Cracks occurred in 9 out of 0, and peeling occurred in 6 of them.

Comparative Example 2 Six sheets of sheet a and four sheets of sheet e obtained in example 2 were laminated, and then rolling was repeated under the same conditions as in example 2 to form sheets of 1.2 mm and 0.8 mm, respectively. After adjusting the thickness, they were stacked on top of each other, and the same steps as in Example 2 were carried out to obtain a superconductor-metal composite. When the Tc and Jc of the resulting superconductor-metal composite were measured using the four-terminal method, Tc was 90K and Jc was 7.9×106A at 77K.
/m2.

Further, when a dry thermal shock test similar to that in Example 1 was conducted, cracks occurred in 8 out of 10 samples, and peeling occurred in 6 of them.

[0038]

[Effects of the Invention] The superconductor-metal composite of the present invention not only avoids the occurrence of cracks and peeling that were observed in conventional bonded bodies, interfaces of laminates, and superconductors, but also
It is necessary as an intermediate material between a superconductor and a metal, such as a bonding material for a superconducting element, a terminal material for a superconducting circuit board, etc. It is also a composite of a superconductor and a metal that is extremely suitable industrially because it facilitates the production of magnetically shielded containers.

Claims (2)

[Claims] Claim 1: A plurality of mixed green sheets of oxide superconductor particles and metal particles each having a stepwise increasing content of oxide superconductor are placed on the top surface of the metal green sheet. A composite of an oxide superconductor and a metal, which is laminated in order so that the largest amount is on the top, and then an oxide superconductor green sheet is laminated on top, and then fired during or after rolling. Manufacturing method. [Claim 2] A plurality of mixed green sheets of oxide superconductor particles and metal particles in which the content of oxide superconductor is gradually reduced are placed on the upper surface of the oxide superconductor green sheet. A composite of an oxide superconductor and a metal, which is laminated in order such that the one with the lowest content is on the top, and then a metal green sheet is laminated on top, and then fired during or after rolling. Manufacturing method.