JPH035358A - Production of orientable oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain a film of an oxide superconductor having high crystal orientability and superconducting characteristics at the temp. of liq. nitrogen or above by successively subjecting powder of an oxide superconductor to forming into a sheet shape, pressing under specified temp. and pressure conditions and sintering. CONSTITUTION:Powder of an oxide superconductor such as a Bi-Pb-Sr-Ca-Cu-O type oxide superconductor is mixed with a plasticizer such as dibutyl phthalate, a binder such as polyvinyl butyral, a dispersant such as ethyl oleate and a solvent, preferably an alcoholic-arom. mixed solvent. The resulting slurry is defoamed under reduced pressure and this defoamed slurry is formed into a sheet shape, dried at ordinary temp., hot pressed at 65-100 deg.C under 1,000-10,000kg/cm<2> pressure for 10-20min, dewaxed and sintered to obtain an orientable oxide superconductor.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing an oriented oxide superconductor, and in particular a method for producing an oxide superconducting film exhibiting superconducting properties at temperatures above liquid nitrogen temperature. It is related to.

[Prior art] B1-Pb-3r-(:a-(:u-0 series is IOK class)
, La-5r-Cu-0 system (grade 40), La
-Ba-Cu-0 system (grade 90) and Y-Ha-Cu-
0 series (grade 90) oxides are materials that exhibit superconductivity.

The production of thick film bodies for processing these materials into wire rods, etc. involves blending various raw material oxide powders in predetermined amounts for each composition, or using a powder material obtained by calcining this blend, a plasticizer, and a binder. , a dispersant, and a solvent are mixed and processed into a sheet by a doctor blade method, and then heated at a temperature suitable for each superconducting oxide (for example, B1-Pb-5r-Ca-C;
In the case of the u-0 series, it was ignited in air at 840 to 850° C. for several hundred hours, brought to 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 manufactured by the above method, the crystal grains of the oxide superconductor may be plate-shaped crystals.
This is because the crystal grains generated during the ignition process grow in a disordered direction. Therefore, a dense thick film cannot be obtained, and since the superconducting current flows parallel to the crystal planes of the plate-shaped crystals, there is a problem that the critical current density is low as a result of disordered crystal orientation.

[Means for solving the problem] In order to improve this crystal orientation, the present inventors conducted research on sheet processing materials, processing conditions, heat treatment conditions, etc., and as a result, the crystal orientation of the film body was significantly improved by heat pressing. I found out that it can be done.

That is, in the present invention, oxide superconductor powder is mixed with a plasticizer,
After mixing with the binder, dispersant and solvent and defoaming, it is processed into a sheet and dried.
(b) A method for producing an oriented oxide superconductor, which comprises hot pressing the sheet at 0° C. and 1000 to 10000 kg/cm 2 and then firing the sheet.

The composition of oxides and carbonates used as raw material compounds in the present invention varies depending on the superconductor to be produced, but for example, in the B1-Pb-5r-Ca-Cu-0 system, the metal atomic ratio is as follows. It is blended in such a way that it falls within a certain range.

Bi: 0.6-1.1 Pb: 0.2-0.4 Sr: 0.7-1.1 Ca: 0.7-1.1 Cu: 1.4-2.2 Also, Ba-Y -Cu-0 system Ba:Y:(:um
They may be blended in an atomic ratio of 2:1:3.

If the composition is outside the above range, the critical temperature of the resulting superconductor will be low.

When mixing each compound in the above mixing ratio, use alcohol (methanol, ethanol, isopropanol, etc.)
Preferably, the mixture is mixed for 24 hours and then dried at 100°C.

The obtained mixed powder is heated at an appropriate temperature (for example, B1
-780 to 820° for Pb-5r-Ca-Cu-0 system
(about 850-900℃ for C1Ba-Y-Cu-0 system)
The powder is calcined for 10 to 20 hours to decompose the carbonic acid component, and then the calcined powder is ignited for 10 to 100 hours in the presence of oxygen at a temperature of 845 to 860°C.

A binder, a plasticizer, a dispersant, and a solvent are added to this ignited fired powder, and the powder is thoroughly ground and mixed to form a slurry.

The binder used above provides shape retention during sheet forming, such as polyvinyl butyral, polyvinyl alcohol, polyacrylic ester, nitrocellulose, polymethacrylic ester, ethyl cellulose, etc., and the plasticizer softens the binder. For example, dibutyl phthalate, butylbenzyl phthalate, butyl stearate, dimethyl phthalate, etc. are used.

Further, the dispersant prevents agglomeration of the slurry, and for example, ethyl oleate, fatty acid (glycerol trioleate), natural fish oil, octadiene, etc. are used.

Solvents include lower alcohols such as methanol, ethanol, butanol, isopropanol, xylene,
Examples include aromatic solvents such as toluene, trichlorethylene, ethyl acetate, methyl ethyl ketone, etc. Particular solvents include mixed solvents of alcohol solvents and aromatic solvents, such as toluene/ethyl acetate, ethyl alcohol/
It is preferable to use a mixed solvent such as trichlorethylene).

The mixing ratio of these is Calcined powder: 100 parts by weight Pine mites 2-5 parts by weight Plasticizer = 2-5 parts by weight Dispersant: 1 to 2 parts by weight Solvent: 40-60 parts by weight It is.

The firing powder and binder are mixed in a ball mill.
It is desirable that the mixing time be at least 10 hours.

The slurry-like mixture obtained by mixing and pulverizing is degassed by stirring while reducing the pressure using a rotary pump or the like, and then processed into a sheet having a thickness of 100 to 300 um.

This sheet forming is carried out by spreading the sheet on a plastic sheet such as polyethylene or polypropylene by a doctor blade method, but methods such as a calender roll method and an extrusion method may also be employed.

After drying the formed sheet at room temperature,
Apply a load of 10,000 kg/cm2 and maintain that state for 10 to 20 minutes. A hydraulic press is usually used to apply the load. A load of less than 1000 kg/cm2 has little effect on improving crystal orientation, and a load of 10,000 kg/cm2 or more Even if a load is applied, there is little improvement in effectiveness.

After the pressure treatment is completed, the additives are removed by volatilization or combustion at a temperature of 400 to 500°C (degreasing treatment).
Temperatures at which various oxide superconductors can be synthesized in air or at an appropriate oxygen partial pressure (for example, B1-Pb-3r-Ca-(:
In the case of u-0 series, ignition treatment is performed at 845 to 860° C. for 10 to 120 hours, and then allowed to cool in a firing furnace.

Since the obtained membrane has a high critical temperature and a high critical current density, it can be used as a membrane or processed into a wire for various purposes as a superconductor.

[Example] Example I Biz03. PbO, SrCO3, CaC01 and C
The uO powder was prepared in a metal atomic ratio of Bi:Pb:Sr:Ca:fl; u=0.96:0.
The mixture was blended in a ratio of 24:1:1:1.6, methanol was added, mixed for 24 hours, and then dried at 100°C.

The dry powder was calcined in air at 800°C to decompose the carbonic acid component. The calcined powder was molded into a size of 20 mmφ x 10 mmt, and sintered in air at 850° C. for 60 hours.

3 parts by weight of polyvinyl butyral 3 parts by weight of dibutyl phthalate ethyl oleate per 100 parts by weight of powder obtained by pulverizing the sintered body
Add 1 part by weight of ethanol, 23 parts by weight of xylene, and add 24 parts by weight of
The mixture was mixed and ground for a period of time, and then defoamed under reduced pressure.

The resulting paste was spread on a polyethylene sheet to form a sheet with a thickness of 200 μm. This sheet was dried at room temperature and cut into square pieces of 20 mm x 10 mm.

The polyethylene sheet was removed from this square piece, and a load of 20 tons was applied for 10 minutes using a hydraulic press while heating it to 70'C.

The pressurized square pieces were ignited in air at 850°C for 14 hours, and then allowed to cool in the furnace.

The critical temperature and critical current density of the obtained film were measured by the four-terminal method while cooling with liquid helium. In addition, the orientation of the film was measured using an X-ray diffractometer, and the (002) plane fold line strength fb
. . 2)) and (200) plane fold line strength [1tool)
It was calculated using the following formula.

The same procedure as in Example 4 was carried out except for the following differences (Comparative Example 2).

The results obtained are shown in Table 1.

Table 1 The results are shown in Table 1.

Example 2.3 Table 1 shows the results obtained by changing the ignition temperature of the pressurized piece in Example 1.

Example 4 Table 1 shows the results of an experiment similar to Example 1 conducted on YBaiCuiOx.

Comparative Example 1.2 The same procedure as in Example 1 was carried out except that the square pieces were not hot pressed in Example 1 (Comparative Example 1).

Also, in Example 4, the square pieces were not heat pressed [Effects of the invention]

Claims (1)

[Claims] (1) Oxide superconductor powder is mixed with plasticizer, binder,
After mixing with a dispersant and a solvent and defoaming, it is processed into a sheet and dried, and the resulting dry sheet is heated at 65 to 100°C for 1
A method for producing an oriented oxide superconductor, which comprises hot pressing the sheet at a pressure of 000 to 10,000 kg/cm^2 and then firing the sheet.