JP2767750B2 - Method for producing oriented oxide superconductor - Google Patents

Description

The present invention relates to a method for producing an oriented oxide superconductor,
In particular, the present invention relates to a method for producing an oxide superconducting film exhibiting superconductivity at a temperature of liquid nitrogen or higher.

[Prior art] Bi-Pb-Sr-Ca-Cu-O system (110K class), La-Sr-Cu-
O system (40K class), La-Ba-Cu-O system (90K class) and Y-Ba
-Cu-O-based (90K class) oxide is a material exhibiting superconductivity.

For the production of a thick film body for processing these materials into a wire, etc., various raw material oxide powders are compounded in a predetermined compounding amount of each composition, or a powder material obtained by calcining the compound and a plasticizer and a binder. , A dispersant and a solvent, mixed and processed into a sheet by a doctor blade method, and then the sheet is subjected to a temperature suitable for each superconducting oxide (for example, 840 to 800 for a Bi-Pb-Sr-Ca-Cu-O system). (850 ° C.) for hundreds of hours in the air, in a semi-molten state, and then cooled to obtain a thick film.

[Problems to be Solved by the Invention] However, when a thick film is produced by the above method, the crystal particles of the oxide superconductor are plate-like crystals, and thus the crystal particles generated during the strong heat treatment are To grow in a chaotic direction. Therefore, a dense thick film cannot be obtained, and the superconducting current flows in parallel with the crystal plane of the plate-like crystal, which causes a problem that the critical current density is low as a result of disordered crystal orientation.

[Means for Solving the Problems] The present inventors studied sheet processing materials, processing conditions, heat treatment conditions, and the like in order to improve the crystal orientation. As a result, the crystal orientation of the film was greatly improved by hot pressing. Found to be.

That is, the present invention is to mix the oxide superconductor powder, plasticizer, binder, dispersant and solvent, and after defoaming,
It is processed into a sheet and dried, and the resulting dried sheet is 65 ~
This is a method for producing an oriented oxide superconductor, which comprises hot pressing at 100 ° C. and 5000 to 10,000 kg / cm ² and then firing the sheet.

The compounding of the oxides and carbonates used as the raw material compounds in the present invention varies depending on the superconductor to be produced.For example, in the Bi-Pb-Sr-Ca-Cu-O system, the metal atom ratio is as follows. It is blended so that it may be in the proper range.

Bi: 0.6 to 1.1 Pb: 0.2 to 0.4 Sr: 0.7 to 1.1 Ca: 0.7 to 1.1 Cu: 1.4 to 2.2 In the Ba-Y-Cu-O system, the atomic ratio of Ba: Y: Cu = 2: 1: 3 What is necessary is just to mix | blend so that it may become.

When the content is outside the above range, the critical temperature of the obtained superconductor becomes low.

When mixing the compounds having the above mixing ratios, it is preferable that the compounds are mixed with an alcohol (methanol, ethanol, isopropanol, etc.) for 24 hours and then dried at 100 ° C.

The obtained mixed powder is mixed at an appropriate temperature (for example, Bi
-Pb-Sr-Ca-Cu-O system, 780-820 ° C, Ba-Y-Cu-
Calcination at about 850-900 ° C for O-system for 10-20 hours to decompose the carbonic acid component, and then calcining the powder at a temperature of 845-860 ° C in the presence of oxygen, usually in air for 10-100 Heat treatment for a long time.

A binder, a plasticizer, a dispersant, and a solvent are blended with the strongly heat-treated calcined powder, and sufficiently crushed and mixed to form a slurry.

The binder used above gives shape retention at the time of sheet molding, for example, polyvinyl butyral, polyvinyl alcohol, polyacrylate, nitrocellulose, polymethacrylate, ethyl cellulose, etc. are used, and the plasticizer softens the binder. For example, dibutyl phthalate, butylbenzyl phthalate, butyl stearate, dimethyl phthalate and the like are used.
In addition, the dispersant prevents aggregation of the slurry, and for example, ethyl oleate, fatty acid (glycerin trioleate), natural fish oil, octadiene and the like are used.

As the solvent, methanol, ethanol, butanol, lower alcohols such as isopropanol, xylene, aromatic solvents such as toluene, other trichloroethylene, ethyl acetate, methyl ethyl ketone and the like,
In particular, it is preferable to use a mixed solvent of an alcohol solvent and an aromatic solvent as a solvent, for example, a mixed solvent of toluene / ethyl acetate, ethyl alcohol / trichloroethylene and the like.

 The mixing ratio of these is as follows: calcined powder: 100 parts by weight Binder: 2 to 5 parts by weight Plasticizer: 2 to 5 parts by weight Dispersant: 1 to 2 parts by weight Solvent: 40 to 60 parts by weight

The mixing of the calcined powder and the binder is performed in a ball mill, and the mixing time is preferably at least 10 hours or more.

The slurry-like mixture obtained by mixing and pulverizing is defoamed by stirring under reduced pressure with a rotary pump or the like, and then processed into a sheet having a thickness of 100 to 300 μm.

The sheet is formed by extending the sheet on a plastic sheet such as polyethylene or polypropylene by a doctor blade method, but a method such as a calendar roll method or an extrusion method may be employed.

After drying the formed sheet at room temperature, 5000 ~ 10
Apply a load of 000 kg / cm ² and maintain that state for 10-20 minutes. The load is usually a hydraulic press. Little improvement in crystal orientation at 5000 kg / cm ² less than the load, 10000 kg / cm
Even if a load of ² or more is applied, the improvement in the effect is small.

After the pressure treatment is completed, the compounded additives are removed by volatilization or burning at a temperature of 400 to 500 ° C (degreasing treatment), and then various oxide superconductors are synthesized in air or at an appropriate partial pressure of oxygen. Temperature (for example, in the case of Bi-Pb-Sr-Ca-Cu-O system 84
(5 to 860 ° C) for 10 to 120 hours, and then allowed to cool in a firing furnace.

Since the obtained film has a high critical temperature and a high critical current density, it can be used as a superconductor as it is or after being processed into a wire.

Example 1 Example 1 Powders of Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ and CuO were prepared so that the metal atomic ratio was Bi: Pb: Sr: Ca: Cu = 0.96: 0.24: 1: 1: 1.6. After mixing with methanol for 24 hours, the mixture was dried at 100 ° C. The dried powder was calcined in air at 800 ° C. to decompose the carbonic acid component. The calcined powder was formed into a size of 20 mmφ × 10 mmt, and was sintered at 850 ° C. for 60 hours in the air.

The sintered body is pulverized, and polyvinyl butyral 3 parts by weight dibutyl phthalate 3 parts by weight Ethyl oleate 1 part by weight Ethanol 23 parts by weight Xylene 23 parts by weight is added to 100 parts by weight of the obtained powder, and mixed and pulverized for 24 hours. Degassed under reduced pressure.

The obtained paste was spread on a polyethylene sheet and processed into a sheet having a thickness of 200 μm. The sheet was dried at room temperature and cut into square pieces of 20 mm × 10 mm.

Remove the polyethylene sheet from these square pieces and apply a load of 20 tons (10000 kg / cm ² ) with a hydraulic press while heating to 70 ° C.
Added for 0 minutes.

The pressurized square piece was subjected to a strong heat treatment in air at 850 ° C. for 14 hours and then allowed to cool in a furnace.

The critical temperature and critical current density of the obtained film were measured by a four-terminal method under cooling with liquid helium. The orientation of the film was measured by X-ray diffractometer using the (002) plane diffraction line intensity (I
₍₀₀₂₎ ) and (200) plane diffraction line intensity (I ₍₂₀₀₎ ) were determined by the following equation.

The results are shown in Table 1.

Examples 2 and 3 Table 1 shows the results obtained in Example 1 when the heat treatment temperature of the pressure piece was changed.

Example 4 Table 1 shows the results when the same experiment as in Example 1 was performed for YBa ₂ Cu ₃ O _x .

Comparative Examples 1 and 2 The same procedure was performed as in Example 1 except that the square pieces were not hot pressed (Comparative Example 1).

Further, the same procedure was performed as in Example 4 except that the square pieces were not hot-pressed (Comparative Example 2).

 The results obtained are shown in Table 1.

[Effects of the Invention] According to the method of the present invention, the sheet formed from the sintered paste is pressed under heating to improve the orientation of the plate-like crystals, and the oxide superconductivity having a high critical current density A body membrane can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B28B 3/00-5/12 C04B 35/00-35/22 C01G 1/00 H01B 13/00 565

Claims (1)

(57) [Claims] 1. A powder of an oxide superconductor is mixed with a plasticizer, a binder, a dispersant and a solvent, defoamed, processed into a sheet, and dried. ° C, 500
A method for producing an oriented oxide superconductor, wherein the sheet is calcined after hot pressing at 0 to 10,000 kg / cm ² .