JP3461654B2 - Manufacturing method of oxide superconductor - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxide superconductor having a high critical current density.

[0002]

2. Description of the Related Art Various materials have been proposed as oxide-based superconducting materials, but these oxide sintered bodies (bulk bodies) have been proposed.
Has a property that the critical current density is uniformly low regardless of its composition.

For example, the critical current density (hereinafter, J) of Y-based, Bi-based, Tl-based, and Hg-based oxide superconductors (bulk bodies)
(sometimes abbreviated as c) is generally 200 to 300 A / c
It is about m ² . For example, the Yc sintered body has a Jc of about 100 A / cm ² at most, and therefore, it has been attempted to manufacture it by a melting method, but in this case, the intended shape cannot be obtained. There are difficulties. Regarding the Bi-based sintered body, it was reported in one report that 1000 A / cm ² was obtained, and it was also reported that a maximum of 2500 A / cm ² was obtained. However, for the application to the superconducting current lead, at least 3000 A / cm ² or higher J
It is not satisfactory because c is required. For this reason, development is progressing in various fields in order to obtain an oxide superconductor capable of flowing a large amount of superconducting current.

[0004] To increase the Jc in the oxide superconductor material, and measures such as to align the crystal _orientation, it is necessary to a sintered body densified. It is also necessary to reduce impurities as much as possible. Therefore, it is no exaggeration to say that the sintering raw material determines the high Jc of the oxide superconductor.

In the conventional oxide superconductor, a raw material powder in which each component is blended so as to have a target composition is molded and sintered to obtain an oxide superconductor material. Calcined powder is used. The calcined powder was obtained by once calcining a mixture (including coprecipitated powder) in which each component was blended so as to have a target composition, and then crushing the calcined product several times. It is a powder. Here, for the pulverization after firing, the dry pulverization method using lycheiki and the like and the wet pulverization method using a ball mill are known, but it is considered that the wet pulverization method can obtain a more uniform and small particle size. ing. Further, in the wet pulverization method, it has been proposed to use a non-aqueous organic solvent in order to prevent the elution of each component into water (for example, JP-A 1-15).
No. 722).

[0006]

[Problems to be Solved by the Invention] This calcination powder production process, that is, the steps of weighing-mixing (or using coprecipitated powder) raw material powders of each component-calcination (baking) -crushing (calcination-
In the crushing process may be repeated several times), even if the weighing is performed accurately and the process control is strictly performed to adjust the composition of the obtained calcined powder to be substantially the same as the target oxide superconductor, It was also found that even if the inevitable impurities accompanying the raw materials were reduced as much as possible, there was a limit to the effect of improving Jc by itself. The present invention aims to overcome this limitation.

[0007]

[Means for Solving the Problems] The above object is to perform wet pulverization using a mixed organic solvent in which a nonpolar organic solvent and a polar organic solvent are mixed in the pulverization step of a calcined product in the process of producing calcined powder. It turns out that can be achieved by. That is, it is not effective to use the nonpolar organic solvent or the polar organic solvent alone, but when a mixed organic solvent of both is used, an extremely fine and uniform calcined powder with an average particle size of 2.5 μm or less is used. It was found that an oxide superconductor with a high critical current density can be obtained by sintering using this calcined powder.

Therefore, according to the present invention, the raw material formulation
In the method for manufacturing an oxide superconductor , the calcined product is crushed to obtain a calcined powder, and the calcined powder is molded and sintered .
When crushing the baked product, a non-polar organic solvent and
Characterized by wet milling using a mixed solvent of organic solvents
A method of manufacturing an oxide superconductor is provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to an oxide superconductor obtained by sintering a calcined powder as a precursor, and is based on the Bi-based, Y-based, Tl-based, and Hg-based known so far. It is possible to further increase Jc of any oxide superconductor (bulk body) such as. Known methods for producing calcined powder include a wet method for obtaining a raw material mixture in the form of coprecipitate and a dry mixing method for obtaining a raw material mixture by mixing powders (oxides, carbonates, etc.) of each component. However, the calcined powder according to the present invention may be produced by any method. When the dry mixing method is applied, it is advantageous to use a mixed organic solvent of a nonpolar organic solvent and a polar organic solvent when mixing the powders of the respective components.

In any case, the calcined powder is produced by once calcining the raw material mixture and then pulverizing the calcined product. In the present invention, this pulverization is performed by using a nonpolar organic solvent and a polar organic solvent. It is essential to carry out the wet pulverization using the mixed organic solvent. Nonpolar organic solvents that can be used include benzene, n-hexane, cyclohexane, and the like, and polar organic solvents that can be used include alcohols such as methanol and ethanol, acetone, and methyl ethyl ketone.

In the wet pulverization of a fired product as a precursor of an oxide superconductor, there has been no study so far on the relationship between the affinity of the precursor and a solvent, the separability, the pulverization efficiency and the like. The present inventors have found that, when a mixed organic solvent of both is used, an oxide superconductor having a high Jc can be obtained more uniformly than in the case of using the nonpolar organic solvent alone or the polar organic solvent alone. We found that it became a fine calcined powder. The reason is not always clear, but it can be thought about as follows.

The non-polar organic solvent is a superconducting oxide (precursor)
The efficiency of pulverization and mixing cannot be increased because of poor affinity with. On the other hand, polar organic solvents are superconducting oxides (precursors)
If a polymer is formed by reacting on the surface of, and it adheres, it becomes difficult to separate and remains as an impurity, and it may cause ignition in the heating in the furnace in the subsequent process. Further, the polar organic solvent easily absorbs moisture, and the absorbed moisture reacts with the superconducting oxide to generate impurities such as hydroxide, resulting in composition shift, and the impurities themselves deteriorate superconducting properties. However, a mixture of both in an appropriate amount has good affinity with the superconducting oxide, is non-reactive, and has good separability, and can be uniformly pulverized to a fine particle size, and at the same time the superconducting oxide can be Since there is little influence on the purity, the sintered product of this powder becomes an oxide superconductor having a high Jc.

In this case, the effect is different depending on the mixing ratio of the nonpolar organic solvent and the polar organic solvent.
This mixing ratio may be selected within an appropriate range depending on the type of organic solvent used and the type of target superconducting oxide. Generally, the non-polar organic solvent is 30 to 99.5% by weight, and the balance is a polar organic solvent, so that it does not react with superconducting oxide and has good affinity (good compatibility). ， The separability is also good. The more preferable mixing ratio is 70 to 96% by weight of the nonpolar organic solvent and the balance of the polar organic solvent. Wet grinding using this mixed organic solvent can be performed by a ball mill or the like.

As described above, when the superconducting oxide (precursor) is wet-milled using the mixed solvent, the average particle size becomes 2.
It is possible to make uniform fine particles of 5 μm or less, and by compacting and sintering these fine particles, a high-density sintered body can be obtained.
As a result, Jc can be increased.

On the other hand, in order to improve Jc, the composition of the calcined powder is as close as possible to the target composition of the superconducting oxide, and the carbon content and the water content in the calcined powder are also improved. Needs to be small. These points will be described below.

First, it is necessary to use high-purity raw material powder for producing the calcined powder. Bismuth-based oxide superconductor such as Bi _1.85 Pb _0.35 Sr _1.90 Ca _2.05
In order to obtain a sintered body of Cu _3.05 O _x , it is necessary to prepare a high-purity calcined powder having a composition ratio as close as possible to the composition ratio. The starting materials for such calcined powder are Bi ₂ O ₃ and P
Powders of bO, SrCO ₃ , CaO and CuO are used, but it is necessary that the raw material powders themselves have high purity. Also _, when producing such raw materials by the coprecipitation method, it is necessary to avoid mixing impurities.

However, the component amount of the calcined powder is precisely controlled so as to obtain the component composition of the oxide superconductor material, and a high-purity raw material is used to reduce impurities accompanying the raw material as much as possible. However, carbon and water may be contained in the calcined powder due to atmospheric moisture and carbon dioxide during the calcined powder manufacturing process.
This adversely affects Jc of the oxide superconductor.

The route by which carbon is mixed from the atmosphere can be considered as follows. That is, when moisture in the atmosphere comes into contact with a trace amount of a substance that does not form a superconducting crystal, a hydroxide is formed, and this hydroxide reacts with carbon dioxide gas in the atmosphere to form a carbonate, and this carbonate is The content as C is increased, and finally C precipitates at the grain boundaries. When C is deposited on the crystal grain boundaries in this manner, the superconducting current flowing between the grains is obstructed.

Such mixing of water and carbon from the atmosphere cannot be avoided even if the starting raw material is carefully selected to have a high purity. It turns out that there are many opportunities to mix in the process. This is probably because in the pulverized state after firing, the moisture in the atmosphere is easily absorbed due to the rapid increase in the specific surface area and the increase in active sites.

However, it has been clarified that such wet grinding using the mixed organic solvent according to the present invention can prevent such contamination of water and carbon from the atmosphere. For example, in Bi-based superconductors, the C content in the calcined powder is 0.
Both components can be simultaneously reduced to below 10%, in some cases below 0.05%, and to a water content below 0.5% by weight. Such effects are
The use of polar organic solvents alone does not give as good a mixture. In the case of Y-based superconductors, similarly, the C content in the calcined powder was reduced to 1.0% by weight or less, preferably 0.50% or less, and the water content was reduced to less than 1.0%. can do.

Therefore, the object of the present invention to increase the Jc of the oxide superconductor is to produce a calcined powder as a sintering raw material for the superconductor sintered product by wet pulverizing the superconductor oxide after firing. In this case, it can be advantageously achieved by a method for producing a calcined powder, which is characterized in that wet pulverization is performed using a mixed solvent of a nonpolar organic solvent and a polar organic solvent. The oxide superconductor made of a sintered body using the calcined powder obtained by this production method is of Bi type, and has a Jc of 3000 A / cm ² or more, preferably 500 A / cm ² or more, as shown in Examples described later.
0A / cm ² to reach even the intended Y-reach 500A / cm ^2.

[0022]

【Example】

Example 1 _{Bi 2 O 3, PbO, SrCO} 3, Ca
Powders of O and CuO were converted into Bi: Pb: Sr: Ca: Cu.
The molar ratio of 1.85: 0.35: 1.90: 2.05: 3.
Weighed to be 05. On the other hand, prepare a mixed solvent such that the weight ratio of benzene: methanol is 9: 1, add this mixed solvent and mix the powder well, and after mixing, remove the solvent by vacuum drying method and recover. did.

Next, the powder mixture is heated to 800 ° C. in the atmosphere.
Firing was carried out for 10 hours, the same solvent as above was added to the obtained fired product, and wet pulverization was performed. After pulverization, the solvent was removed and recovered in the same manner as above. A ball mill using zirconia balls (ZrO ₂ 98%) having a diameter of 8 mm was used for the wet pulverization. The C%, H ₂ O%, average particle size and yield of the obtained powder were measured, and the results are shown in Table 1. This powder was fired again in the atmosphere at 800 ° C. for 10 hours to obtain a calcined powder.

The resulting calcined powder was made into a sintered body in the steps of "press molding"-"sintering"-"intermediate compression"-"sintering"-"intermediate compression"-"sintering". The conditions of these steps are as follows. Press molding: Press molding into a disk-shaped green compact having a diameter of 20 mm and a thickness of 2 mm at 3.0 ton / cm ² . Sintering: All are 850 degreeC x 50 hours. Intermediate compression: CIP method (cold isotropic compression method) compressed to 3.0 ton / cm ² .

A test piece was cut out from the obtained sintered body, the critical current density (Jc) was measured, and the results are also shown in Table 1.

Example 2 Example 1 was repeated except that the solvent used was a mixed solvent of benzene: methanol at a weight ratio of 5: 5. The same measurement as in Example 1 was performed, and the results are shown in Table 1.

Example 3 As the raw material powder, Y ₂ O ₃ ,
Example 1 was repeated except that each powder of BaCO ₃ and CuO was weighed so that the molar ratio of Y: Ba: Cu was 1: 2: 3. The solvent used is the same as in Example 1.
However, the firing of this raw material powder was performed twice in the air at 940
℃ × 50 hours. The same items as in Example 1 were measured, and the results are shown in Table 1.

Comparative Example 1 Example 1 was repeated except that the solvent was changed to a benzene: methanol weight ratio of 10: 0 (benzene alone). The same measurement as in Example 1 was performed, and the results are shown in Table 1.

Comparative Example 2 Example 1 was repeated except that the solvent was changed to a benzene: methanol weight ratio of 0:10 (methanol alone). The same measurement as in Example 1 was performed, and the results are shown in Table 1.

Comparative Example 3 Example 3 was repeated except that the solvent was changed to a benzene: methanol weight ratio of 10: 0 (benzene alone). The same measurement as in Example 1 was performed, and the results are shown in Table 1.

[0031]

[Table 1]

The measuring method of each item in Table 1 is as follows. Carbon content (C%): In order to prevent the reaction with moisture and carbon dioxide in the atmosphere, a part of it is sampled from the powder handled in dry air, heated to a high temperature of 1000 ° C or more, and burned. The carbon dioxide gas that comes out in a closed state is quantified with an infrared spectroscope. Moisture content (H ₂ O%): Moisture generated when heated to 300 ° C. is measured using a Karl Fischer moisture meter. Average particle diameter: The median diameter is measured using a laser diffractometer (manufactured by Shimadzu Corporation, particle size distribution measuring device for Shimadzu laser diffraction, SALD-1100). Critical current density (Jc): A strip-shaped test piece having a cross section of 1 mm square is cut out from a sintered body, an electrode for Jc measurement and a lead wire are attached, and measurement is performed by a four-terminal method.

As can be seen from the results in Table 1, in the Bi-based oxide superconductors, the critical current density of 100 was obtained in Comparative Examples 1 and 2 in which the solvent was benzene alone or ethanol alone.
It was 0 A / cm ² , but the critical current density was 5000 or 30 in Examples 1 and 2 which used a solvent in which both were mixed.
It has been improved to 00 A / cm ² . Particularly, in Example 1, a calcined powder having a low C% and a H ₂ O% and a small particle size was obtained, and it can be considered that this resulted in a high critical current density.

Similarly, in the case of the Y-based oxide superconductor, the critical current density is 100 A / cm ² to 500 A / cm ² in Example 3 in which 10% of methanol is mixed, as compared with Comparative Example 3 in which benzene is used alone. Has improved. It can be seen that this improvement effect is also due to the smaller particle size.

[0035]

As described above, a non-polar solvent such as benzene or a polar solvent such as methanol is used as the sintering raw material powder used for producing the sintered body of the oxide superconductor. In comparison with the case of mixing and wet pulverizing, the nonpolar solvent and the polar solvent are mixed and used as in the present invention.
Sintering raw material powder (calcined powder) of good quality (low C concentration and H ₂ O concentration, small particle size) can be manufactured,
Oxide superconductors sintered using this exhibit a high critical current density.

Continuation of the front page (56) Reference JP-A-4-237910 (JP, A) JP-A-2-204358 (JP, A) JP-A-1-45722 (JP, A) JP-A-1-9812 (JP , A) JP-A-50-18396 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 35/45 C01G 1/00

Claims (5)

(57) [Claims] 1. A raw material mixture is fired, and the fired product is crushed.
And a calcined powder, a process for the preparation of oxides superconductors The calcined powder was molded and sintered, grinding the calcination product
Use a mixed solvent of non-polar organic solvent and polar organic solvent
Production of oxides superconductor, characterized by wet milling Te
Law . 2. The mixed solvent comprises a nonpolar organic solvent of 30 to 9
The method for producing an oxide superconductor according to claim 1 , wherein the balance is 9.5% by weight and the balance is a polar organic solvent . 3. The fired product has an average particle diameter of 2.5 μm or less.
The method for producing an oxide superconductor according to claim 1, which is pulverized into a calcined powder . 4. The oxide superconductor is a bismuth oxide superconductor, and the calcined powder thereof has a carbon content of 0.1% by weight or less, a water content of 0.5% by weight or less, and an average particle diameter of 2.0.
The method for producing an oxide superconductor according to claim 1, 2 or 3 , wherein the thickness is not more than μm. 5. The oxide superconductor is a yttrium-based oxide superconductor, and the calcined powder thereof has a carbon content of 0.5% by weight.
Below, the water content is less than 1.0 wt% and the average particle size is 2.
It is 5 micrometers or less, The manufacturing method of the oxide superconductor of Claim 1, 2 or 3 .