JPH05262578A - Ceramic superconducting form - Google Patents

Abstract

PURPOSE:To provide the subject form giving excellent superconducting characteristics esp. under magnetic field. CONSTITUTION:2-30vol.% of pores of submicron order playing as a role of the pinning sites for magnetic flux are dispersed uniformly in a ceramic superconducting form. Thereby, magnetic flux will be pinned, and the superconducting characteristics of the ceramic form can be improved esp. under magnetic field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is particularly useful in magnetic fields.
The present invention relates to a ceramics superconducting compact that exhibits high superconducting properties.

[0002]

2. Description of the Related Art In recent years, Y- which exhibits superconductivity at liquid nitrogen temperature
Ba-Cu-O system, Bi- (Pb) -Sr-Ca-Cu
Ceramic superconductors such as -O type and Tl-Ba-Ca-Cu-O type have been found, and researches for practical use as conductors for magnets, power cables and the like have been actively pursued.

[0003]

By the way, in order to improve the superconducting properties of these ceramic superconductors, in addition to increasing the space factor of the superconductor phase, many pinning sites for restraining magnetic flux are provided in the ceramic superconductor. Although it may be distributed, in the latter case, an effective pinning site has not been found yet, so that there is a problem in that a high value of superconducting properties cannot be obtained particularly under a magnetic field.

[0004]

DISCLOSURE OF THE INVENTION The present invention has conducted intensive studies in view of the above situation, and found that the fine pores contained in the ceramic superconductor have a function of pinning the magnetic flux, and further research is conducted. The present invention has thus been completed. That is, the present invention is characterized in that submicron-order pores of 2 to 30% by volume are uniformly dispersed and contained in the ceramic superconducting compact.

In the present invention, the submicron order pores are pores having a diameter of about 1 μmφ or less, which may be vacuum or may contain gas. The reason why the size of the pores is limited to the submicron order is that if the size exceeds the submicron order, the pinning effect of the pores cannot be sufficiently obtained. In the present invention, the reason why the content of submicron-order pores is limited to 2 to 30% by volume is that if the content is less than 2% by volume, the effect as a pinning site for restraining the magnetic flux in the ceramic superconductor is not sufficiently exhibited. is there. On the other hand, if it exceeds 30% by volume, the pores are united with each other and the pores cannot be maintained in a fine state, and moreover, the space factor of the superconductor phase is reduced and Jc is lowered. The content of pores is particularly preferably 5 to 15% by volume.

The ceramic superconducting molded article of the present invention comprises:
Any ceramic superconductor other than the above-described Bi-based ceramic superconductor is applied. The ceramics superconducting compact of the present invention is a usual powder sintering method, that is, powder compacting a raw material powder that can be a ceramics superconductor into a desired shape, or filling the raw material powder into a metal pipe, It is manufactured by a method in which it is drawn into a predetermined shape to form a composite wire rod, and these powder compacts or composite wire rods are heated and sintered at a predetermined temperature. It is preferable to use the above fine powder because fine pores are dispersed in the obtained oxide superconducting molded body. The ceramic superconducting compact of the present invention is also excellent in crystal orientation, and it is considered that this is because the raw material powder is so fine that the powder particles can easily rotate and move during stretching. As a method for producing a submicron-order raw material fine powder, a method in which a solution in which constituent elements of an oxide superconductor are dissolved is sprayed in a high-temperature oxidizing atmosphere to react with a precursor powder is suitable. As the method of spraying the solution, an ultrasonic atomizer, a gas nozzle sprayer, or the like is applied.

The raw material powders that can be used as the above-mentioned ceramics superconductor include the above-mentioned Y-based, Bi-based, Tl-based ceramics superconductor powders, etc., and react with the ceramics superconductor by heat treatment in an oxygen-containing atmosphere. An intermediate, such as a mixture of constituent elements of a ceramic superconductor,
Alternatively, a coprecipitated mixture, or a primary raw material powder of the oxide or carbonate of the above-mentioned constituent elements is mixed in a predetermined amount to form a mixed raw material, and an oxygen-deficient complex oxide powder obtained by calcination of the mixed raw material is used Be done. To fill the raw material powder into the metal pipe, in addition to the method of directly filling the raw material powder, the raw material powder is preliminarily molded into a predetermined shape by the CIP method or the molded body is further heat-sintered. And the like are used. When the raw material powder is processed into a compact or a sintered compact as described above and then filled, the density of the obtained ceramic superconducting compact increases, and the characteristics such as Jc are further improved.

For the stretching process applied to the above-mentioned multilayer composite billet, any processing method such as extrusion, drawing, swaging, rolling, forging, and press compression can be applied, but the rolling processing method or the press compression processing method is a superconductor. It is preferable because the density of the layer can be further increased. The heat treatment applied to the composite wire obtained by drawing the composite billet is performed in order to react the raw material powder with the ceramic superconductor. This last heat treatment is preferably performed after the drawn material is formed into a magnet coil or the like because cracks and the like are less likely to occur in the ceramic superconductor inside. The ceramic superconducting compact containing 2 to 30% by volume of submicron-order pores of the present invention can be produced, for example, by using a submicron-order fine powder as a raw material powder, and the submicron-order pores described above can be produced. Is not lost by the conventional manufacturing method as described above.

[0009]

The ceramic superconducting molded article of the present invention contains the submicron-order pores in an amount of 2 to 30% by volume, and the pores act as effective pinning sites for magnetic flux, especially under a magnetic field. High superconducting properties can be obtained.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 First, a raw material powder was prepared by an aerosol method. That is, B
i: Sr, Ca, Cu nitrate is added to Bi: Sr: Ca: C
u were mixed so that the atomic ratio was 2: 2: 1: 2, and these were dissolved in water to prepare raw material solutions of various concentrations. Next, this raw material solution is atomized using an ultrasonic atomizer, and this atomized material is introduced into a quartz tube heated to 800 to 930 ° C by using air as a carrier gas to react and generate a superconducting precursor powder. The precursor powder was sucked and collected on the filter. When the spraying speed is set to 0.05 ml / sec, the precursor powder with 3 kinds of particle size distribution is prepared by changing the spraying speed to 0.05 ml / sec ± 20% or 0.05 ml / sec ± 50%. did. A small amount of a binder is added to the thus obtained three kinds of precursor powders, and the mixture is press-molded under various pressures within the range of 1 to 50 MPa to obtain 20 × 5 × 1 mm.
It was used as a bar material. Next, this bar is exposed to air at 860 ℃ × 20
The ceramics superconducting rod-shaped body was manufactured by performing heat treatment for a period of time.

Comparative Example 1 Bi: Sr: Ca: Cu was used as the starting material for each of BiCO _3, SrCO _3, CaCO _{3, and} CuO in an atomic ratio of 2: 2: 1: 2.
And mix to obtain 8
Preliminary firing at 50 ° C for 20 hours, pulverizing and mixing the preliminarily fired body into a preliminarily fired powder, and press-molding the preliminarily fired powder for 20 ×
It was made a 5 x 1 mm bar. Next, in the atmosphere,
A ceramic superconducting rod was manufactured by performing heat treatment at 60 ° C for 20 hours. With respect to various ceramics superconducting rods thus obtained, the C-axis orientation of the crystal and J
c was measured. The results are shown in Table 1 together with the spray rate of the aqueous solution of the aerosol method, the particle size of the precursor powder, the content of pores in the superconducting molded body, and the like. Jc is in liquid nitrogen (77
K) Measured by a 4-terminal method under a magnetic field of 1T. The particle size of the precursor powder and the size of the pores in the superconducting compact were measured by a scanning electron microscope, and the crystal orientation was measured by an X-ray diffraction method.

[0012]

[Table 1]

As is clear from Table 1, the products of the present invention (No.
1 to 5) were excellent in crystal orientation and Jc. The higher the pressing pressure, and the smaller the pores in the superconducting molded body, the higher the value of Jc. Pore content is 10
The peak of Jc was obtained in the case of the volume%. On the other hand, No. 6 of the comparative example has a low porosity content, and therefore the pinning effect due to the porosity is not sufficiently exerted, and No. 7 has too much porosity and the pores are coalesced and coarsened. As a result, the Jc decreased in each case. In Nos. 8 and 9, the dispersion of the particle size of the precursor powder was large, and as a result, the pores in the superconducting compact were coarsened, the crystal orientation was poor, and the effect of pinning the magnetic flux in the pores was reduced. Has dropped. In No. 10, since the precursor powder, that is, the particles of the calcined powder were coarse, the pores in the oxide superconducting molded body were large and the Jc was considerably lowered. The case of the Bi-based oxide superconducting molded article has been described above, but the present invention is also applicable to oxide superconducting molded articles of other systems as long as submicron-order pores are uniformly dispersed and contained. , The same effect is exhibited.

[0014]

As described above, the ceramic superconducting molded article of the present invention has excellent superconducting properties especially under a magnetic field, and when used as a conductor for a magnet coil or the like, a remarkable effect is exhibited.

Claims (1)

[Claims] 1. Porosity of submicron order is 2 to 30
A ceramic superconducting compact characterized by being contained in a uniformly dispersed manner by volume%.