JPH0497939A - Oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor excellent in superconductivity by filling silver in the void of the sintered bulky body of an oxide superconductor. CONSTITUTION:The void in the sintered bulky body of this oxide superconductor is filled with silver. The superconductivity of the superconductor is improved due to the presence of silver between the crystal grains and proximity effect, and the stability of the bulky body and consequently the stability in superconductivity are improved. When the void is narrowed and difficult to fill, the density of the sintered bulky body is lowered to enlarge the void, and the lowering of the superconductivity or stability due to the lowered density is sufficiently compensated by the improvement of superconductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an oxide superconductor having excellent superconducting properties, which is obtained by filling voids in a sintered bulk body with silver.

BACKGROUND ART Conventionally, a sintered bulk body made of an oxide superconductor, such as a wire or a sheet body, with a silver coating layer provided on the outer periphery has been known.

However, there are problems in that superconducting properties such as critical temperature and critical N flow density are poor, and the stability is poor.

Means for Solving the Problems The present invention overcomes the above problems by filling voids in a sintered bulk body of an oxide superconductor with silver.

That is, the present invention provides an oxide superconductor characterized in that voids inside a sintered bulk body made of an oxide superconductor are filled with silver.

By filling the voids inside the sintered bulk body made of a functional oxide superconductor with silver, the superconducting properties improve, possibly due to the proximity effect caused by the presence of silver between crystal grains, and the sintered bulk body improves. The stability, and thus the stability of the superconducting properties, is improved.

In the above, reason 1 such as narrow voids: If filling with silver is more difficult, the density of the sintered bulk body is lowered to enlarge the voids, thereby making it possible to fill with silver to achieve the above configuration. In this case, the superconducting properties can be improved by more than the decrease in the superconducting properties or the decrease in the stability due to the decrease in density.

Examples of Constituent Elements of the Invention In the present invention, there are no particular limitations on the oxide superconductor forming the sintered bulk body. For example, YBa2Cu30
Y-based oxide superconductors such as a and Yt b Bab Cu0c, Bat-d Kd Ba-based oxide superconductors such as BiO3, Nd2-e Cee Cu0n-t
d-based oxide superconductor, Bi25r Pbz 5r2Ca
2Cu30h or Bi25r2Cal-t CLII O
Bi-based oxide superconductors such as J, La-based oxide superconductors, TI-based oxide superconductors, Pb-based oxide superconductors, etc., and those in which the above-mentioned components such as Y are replaced with other rare earth elements. , or those in which components such as Ba are replaced with other alkaline earth metals, or those in which O components are replaced with F or the like can be used.

For example, oxide superconductors are produced by mixing raw materials at a predetermined composition ratio using a wet mixing method such as a coprecipitation method or a sol-gel method, or any other suitable mixing method, and then calcining the mixture.
It can be obtained by subjecting it to a sintering treatment to form a superconductor.

In the oxide superconductor of the present invention, voids inside a sintered bulk body are filled with silver. For example, it can be manufactured by immersing a sintered bulk body with voids that can be filled with silver into a molten silver solution, or by degassing the sintered bulk body in a vacuum container if necessary. This can be done by pouring molten silver into a container. According to the above method, there is an advantage that filling voids in the sintered bulk body with silver and forming a coating layer of silver on the outer periphery of the sintered bulk body as necessary can be accomplished in the same process.

FIGS. 1 to 3 show an example of the process using the vacuum container described above. In this method, first, a sintered bulk body 1 having a void that can be filled with silver is placed in a vacuum container 2 (Fig. 1).
. Next, the gas inside the vacuum container 2 is removed via a vacuum pump or the like to reduce the pressure (FIG. 2). Thereby, the molten silver can smoothly penetrate into the voids inside the sintered bulk body 1. Next, the silver melt 3 is placed in the vacuum container 2.
The molten silver is injected into the internal voids of the sintered bulk body 1, and the molten silver is applied to the outer periphery of the sintered bulk body 1, and the molten silver is cooled and solidified (Fig. 3). ). When the silver melt enters the internal voids of the sintered bulk body 1, the fluidity of the silver melt may be maintained or increased by heating as necessary.

In the above manufacturing method, the sintered bulk body having voids that can be filled with silver is formed, for example, by a method of controlling the density of a molded body or a green compact made of oxide superconductor powder, etc. be able to. The sintered bulk body is formed by using, for example, the above-mentioned raw material mixture of the oxide superconductor,
Alternatively, the pulverized powder of the sintered body is compacted and the compacted body is sintered, or the oxide superconductor powder is extruded through an organic binder made of polymer or the like. This may be carried out by any suitable method such as a method in which a molded body is sintered.

Incidentally, in the case of oxide superconductor powder with a particle size of 0.1-10 μ-, the powder bulk has a density that is about 1/2 or less of the density of the compact formed by packing it in a predetermined container closest to each other. In the usual case, a sintered bulk body with voids that can be filled with silver is produced by sintering it.
Obtainable.

Based on the density of the sintered bulk body, 3.5 g/e
By setting the density to about 1+ or less, voids that can be filled with silver are usually formed, but the density is not limited to this because there is a large density difference depending on the type of oxide superconductor.

The external shape of the sintered bulk body to be formed is arbitrary, such as a linear body, a sheet body, or a secondary molded form such as a coil.

In addition, from the point of forming a sintered bulk body having voids that can be filled with silver, a binder made of a polymer or the like that disappears by thermal decomposition etc. when sintering the oxide superconductor powder is used.
A preferred method is to mold a mixture with oxide superconductor powder into a predetermined shape, and then sinter the molded body in which the oxide superconductor powder is held in shape with a binder.

In the above case, the size of the voids formed within the sintered bulk body can be controlled based on the amount of binder used. Further, based on homogeneous mixing of the binder and the oxide superconductor powder using a solvent or the like, voids can be uniformly formed in the sintered bulk body. Furthermore, the powder bulk body can be formed by various molding methods such as extrusion molding, injection molding, coating by imparting fluidity by using a solvent, and casting.

In the above case, after the organic components in the molded body are removed by degreasing treatment, the molded body is subjected to sintering treatment to obtain the desired sintered bulk body.

Effects of the Invention According to the present invention, since the voids inside the sintered bulk body are filled with silver, the superconducting properties such as critical temperature and critical current density are excellent, and the stability of the sintered bulk body and, by extension, the stability of the superconducting properties are improved. It can be made into an oxide superconductor with excellent properties.

Example Y 203, Ba CO3, and CuO powders were mixed in a predetermined amount, calcined at 750 to 850°C for 12 hours, and then ground, and the powder was press-molded into a bulk body with a diameter of 20 m+ and a thickness of 1 mm. This was then sintered at 900-1000°C for 12 hours and annealed in oxygen at 500°C to form YBa2 CU3.
Obtain an oxide superconductor consisting of 0a, crush it to powder with a particle size of 0.1 to 1Oμ, and add 100 parts by weight of the powder to 50 parts by weight of polyvinyl alcohol, 5 parts by weight of dibutyl phthalate,
parts by weight and 20 parts by weight of toluene were mixed in a pressure kneader to obtain a molded material.

Next, the above molded material was extruded to obtain a string having an outer diameter of 1.0M, and the string was degreased in a nitrogen gas atmosphere.

The degreasing treatment was performed at a heating rate of 200°C/hour to 200°C, then at a heating rate of 5°C/hour to 750°C, and then to 20°C.
Cooling was performed at a rate of 0°C/hour.

The resulting degreased body was then heated at a rate of 200°C/hour, sintered at 900-1000°C for 12 hours, and then annealed with oxygen at 500°C to form an oxide superconductor consisting of a series of rods. A sintered bulk body was obtained.

By the way, the critical temperature of said sintered bulk body is 92, and the critical current density is 600 A/c++i (77,
3K.

The same applies hereafter).

Further, after being left at room temperature for 30 days, the critical temperature was 82, and the critical current density was 20 OA/cd.

Note that the apparent density was 3.0 g/cil.

Next, the sintered bulk body was placed in a vacuum container and heated to 500°C.
After being left under a reduced pressure of 0.1 Torr for 20 minutes, molten silver was injected, left at 500° C. for 30 minutes, and then gradually cooled.

The obtained oxide superconductor had the internal voids of the sintered bulk body filled with silver and had a 0.5 m thick silver layer around the outer periphery.

Its apparent density was 8.0 g/c+7.

Also, the critical temperature is 92 and the critical current density is 100
It was 0 A/cJ.

Furthermore, after being left at room temperature for 30 days, the critical temperature is 89, and the critical current density is 800 A/cj.
Met.

The above critical temperature was determined by measuring the change in electrical resistance due to temperature using the four-terminal method under a current density of 0.1 A/c+J without cooling with liquid helium, and the generated voltage between the voltage terminals was O. This is the temperature at that time.

The critical current density was determined by gradually increasing the current value while cooling the power lead with liquid nitrogen and measuring the change in voltage between the voltage terminals due to the applied current using the four-terminal method. It is the value obtained by dividing the old current I, at which the voltage appeared, by the cross-sectional area of the superconductor.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 are explanatory diagrams of each T degree illustrating the method for manufacturing an oxide superconductor of the present invention. 1. Sintered bulk body of oxide superconductor 2/Vacuum container 3; Silver melt patented person Mitsubishi Cable Industries Co., Ltd. Agent Tsutomu Fujimoto Gas No. 2

Claims (1)

[Claims] 1. An oxide superconductor characterized in that voids inside a sintered bulk body made of the oxide superconductor are filled with silver.