JPH02255555A - Production of high density oxide superconductor - Google Patents

Abstract

PURPOSE:To increase relative density and critical current density by impregnating an oxide superconducting base material with a soln. contg. a specified starting material blend and by carrying out drying, dewaxing and sintering. CONSTITUTION:A Ba-La-Cu-O or Ba-Y-Cu-O type oxide superconducting base material is impregnated with a soln. contg. 10-100g/l starting material blend having the same ratio among the metallic elements as the superconducting base material. The impregnated material is dried, dewaxed by heating to 400-600 deg.C and sintered at a temp. at which superconductivity is rendered. This temp. is decided according to the compsn. of the base material.

Description

DETAILED DESCRIPTION OF THE INVENTION [A. Field of Industrial Application] The present invention relates to a method for producing an oxide superconductor in which current density is improved by increasing relative density.

[Mouth, conventional technology]

Attempts have been made to use oxide superconductors in various electrical devices as films and tape wires.

For example, in the case of membranes, they can be applied to the surface of metals or dense ceramics, when the raw material for oxide superconductors is powder, it is as a slurry, and when it is soluble, it is as a solution.
An oxide superconducting film is produced by coating each of them using an appropriate method, drying and firing, and in the case of tape wires, the oxide superconducting powder is filled into a metal pipe and then rolled using a cold rolling machine. The wire rod was produced by stretching the pipe and applying pressure to form it into a tape shape, which was then fired.

[C.6 Problems to be Solved by the Invention] The higher the relative density of an oxide superconductor, the higher the current density, and the wider the range of applications.

However, in the conventional method, the superconducting oxide is a plate-like crystal, and the crystals grow in random directions during the firing process, creating voids, so the relative density of the produced oxide superconductor is extremely low. For example, the relative density of the film was around 50%, and even if a tape wire is produced by applying high pressure with a cold rolling machine, the relative density of the oxide superconductor that is the core material is only 75%. It was only %. As described above, since the structure of the oxide superconductor manufactured by the conventional method was porous, there was a drawback that a current with a high current density could not be passed through the structure. For this reason, many researchers have been searching for a manufacturing method that increases the relative density, but this has not yet been put to practical use.

[Means for Solving Problems 23] Therefore, the present inventors investigated a method of filling voids in an oxide superconductor with a superconducting oxide having the same composition. He discovered that the relative density could be unexpectedly improved by manufacturing and impregnating it with a solution consisting of the same metal element ratio, and completed a similar invention.

That is, in the present invention, a molded oxide superconducting substrate (hereinafter referred to as the substrate) is impregnated with a solution containing a raw material mixture having the same metal element ratio as that of the substrate, then dried, degreased, and then The object of the present invention is to provide a method for producing an oxide superconductor having a high relative density and produced by firing.

The present invention will be explained in detail below.

The material of the substrate of the present invention is Ba-La-Cu-0 series, Ba-
Y-CuO system, 5a-Er-Cu-0 system, B1-5r-
Ca-Cu-0 system, B1-Pb5r-Ca-Cu-0 system, T jl! It is a known oxide superconductor such as -Ba-Ca-Cu-0 system, and specific compounds include La+, 5B
ao, 2CL104, YBazCu30. ,
ErBa2CuiOx.

Bi25rzCazCu30x + Bl+, 4Pb
o, hSrzCazC1l+Ox +T l zBaz
Examples include cazcuzOX.

The substrate may be manufactured according to a known manufacturing method in which raw materials are adjusted, formed, and fired to form the intended superconducting oxide, and this application is not particularly limited thereto.

Further, the shape is not similarly limited, but in order to improve the impregnation described later, it is preferable that the thickness is thin.

Next, the impregnation step will be explained.

A solution containing a raw material mixture with the same metal element ratio as that of the substrate is a solution that uses soluble compounds as raw materials and combines these raw materials appropriately so that the metal element ratio is the same as that of the substrate. It means a solution made by dissolving the obtained raw material mixture in a solvent.

It was previously shown that there are multiple metal elements constituting the base. Normally, it is difficult to blend compounds containing many metal elements as raw materials, so it is preferable to use compounds containing one or two metal elements as raw materials, combine them to adjust the metal element ratio, and then blend them. .

Examples of soluble compounds containing metal elements include organic compounds such as naphthenates, octylates, stearates, acetylacetonates, alkoxides, etc., and inorganic compounds such as nitrates and acetates.

Next, the solvent will be explained. Specifically, examples of organic solvents include butanol, toluene, xylene, pyridine, etc., and examples of inorganic solvents include water, and these solvents are used alone or in combination.

Various methods of dissolution can be considered, such as blending all the raw materials in advance and then adding them to a solvent and stirring to dissolve them, but in this application, the dissolution method is not particularly limited.

The concentration of the solution is related to many factors that affect impregnation, such as the size of the substrate, the state of the voids, and the viscosity of the solvent used.
Taking these into consideration, it can only be determined experimentally, but as a guide, the concentration is approximately 0 to 100 g/6.

Methods for impregnating the substrate with the solution include tobuzuke, brush coating,
Follow conventional methods such as spraying.

To achieve sufficient and speedy impregnation, it is necessary to heat the solution (to lower the viscosity) and, if the substrate size is large, to also heat the substrate, or to perform it under reduced pressure, or to use a combination of both. It is preferable to do so.

Next, the drying and degreasing steps will be explained.

? After drying the substrate impregnated with the liquid 8 according to a conventional method, the substrate is heated to a temperature of 400 to 60°C for the purpose of decomposing and volatilizing organic matter.
Perform degreasing treatment at 0°C.

The relative density of the sintered body tends to increase by repeating the impregnation-drying-degreasing process described above.
From the viewpoint of cost effectiveness, it is desirable to carry out the process no more than 20 times, since the relative density will not improve much if the process is repeated more than once. The most preferred number of repetitions is about 10 to 15 times.

The degreased substrate is fired in a conventional manner. The firing temperature is determined depending on the composition of the substrate and is set at a temperature that exhibits superconducting performance.

Hereinafter, the present invention will be explained based on examples.

[E, Example]

1) Substrate manufacturing BizOs, PbO+5rCOz, CaC0z and C
Each powder of uO has a metal element ratio of Bt:Pb:Sr:Ca:C
u = Q, 7:0.3:1:1:1.5 (element ratio), added to methanol and mixed thoroughly,
Dry. A plasticizer (dibutyl phthalate), a binder (polyvinyl butyral), and a dispersant (
Add ethyl oleate) and solvent (xylene),
Mix again to form a slurry.

After defoaming, the slurry is formed into a sheet using a coating machine, dried, degreased at 500℃ for 1 hour, and then divided into 5X20X
A 0.2 m molded body was obtained.

Subsequently, after firing at 850°C for 1 hour, the Bi
A superconducting substrate having a composition of: b, 4Pbo, 1srzcazcu+ox was manufactured.

2) Bismuth naphthenate, lead naphthenate, strontium naphthenate, calcium naphthenate, and copper naphthenate as raw materials for producing a solution for impregnation are prepared in an elemental ratio of Bi:Pb:Sr:Ca:Cu of 0.7:0. The ratio was 3:1:1:1.5.

The raw material formulation was dissolved in the solvent toluene to a concentration of 20 g/l to prepare a solution for impregnation.

3) Impregnation, drying and degreasing After soaking the substrate in the solution for 1 hour,
It was dried at 0°C and degreased for an hour.

This soaking, drying, and degreasing process was repeated, and the number of times is shown in Table 1.

4) Firing and measurement Each degreased substrate was fired in an electric furnace at 850° C. for IO hours, and then allowed to cool in the furnace to obtain an oxide superconductor.

The relative density, critical temperature, and critical current density of the obtained oxide superconductor were measured, and the results are shown in Table 1. The relative density was measured by the underwater gravimetric method, and the critical temperature and critical current density were measured by the four-probe method.

Note that the above measurements were also performed on the substrate manufactured by the conventional method, and the obtained results are also listed in the same table.

table ■ has a significantly higher relative density than that obtained by conventional methods.

Therefore, the critical current density was also dramatically improved.

Claims (1)

[Claims] A method for producing a high-density oxide superconductor, which comprises impregnating an oxide superconducting substrate with a solution containing a raw material mixture having the same metal element ratio as that of the substrate, drying, degreasing, and firing.