JPH07126068A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To provide a production method capable of uniformly dispersing metal elements constituting an oxide superconductor, preventing deposition of a different phase and producing a single phase of a uniform oxide superconductor. CONSTITUTION:A water-soluble organopolymer chelating agent such as an EDTA-ED polymer is reacted with metal ions of constituent metal elements of an oxide superconductor such as a Y-Ba-Cu-O-based superconductor to synthesize a chelate polymer containing the constituent metal elements in a ratio in the oxide superconductor. This chelat polymer is heat treated to decompose and remove its organic components and subsequently heat treated in an oxidative atmosphere, thus producing the objective oxide superconductor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide superconductor, and more particularly to an improvement for producing an oxide superconductor having excellent uniformity using a water-soluble organic polymer chelating agent. .

[0002]

_2. Description of the Related Art Conventionally, as a method for producing an oxide superconductor, for example, in the case of producing a YBa ₂ Cu ₃ Oy type oxide superconductor, oxides or carbonates of the constituent metals Y, Ba, Cu are used. The solid-state reaction method of firing the mixture of is the mainstream, but when considering the mixture of these raw material powders as a bulk,
It is a mass of each element of Y, Ba and Cu, and is an extremely non-uniform aggregate at the atomic level.

Therefore, as a method for eliminating the non-uniformity in the solid-phase reaction method, for example, a solution method in which nitrates of Y, Ba and Cu are dissolved in water and the mixture is evaporated to dryness and heat-treated, Coprecipitation instantly when solidifying from the solution, a coprecipitation method of heat-treating the coprecipitate, the solution in a sol state by the reaction in the solution, then after changing to a gel state,
A sol-gel method of forming an oxide by heating a gel, or a method of reducing nonuniformity by using an alkoxide of each metal to reduce the difference in solubility in a solvent has been proposed.

Recently, in addition to the above-mentioned method, Y, Ba and Cu have been added to a water-soluble polymer solution which strongly interacts with metal ions.
After dissolving the ions to form a complex and evaporating and solidifying it,
A method of heat treatment has been proposed. The polymer used in this method is polyethylene glycol (a), polyvinyl alcohol (b), polyacrylic acid (c), or the like. These polymers and Y, Ba, Cu
The complex with is

[0005]

[Chemical 1]

It is represented by

[0007]

Among the above-mentioned conventional techniques, according to the solution method, precipitation starts from one having a low solubility in water in the process of evaporating and solidifying water from the mixed solution, and the precipitation is slow. When one of the nitrates precipitates in a pure form, the precipitation of the nitrate of the next element begins,
Finally, the most soluble nitrate precipitates. Each powder of the solid mixture thus obtained is a lump of a single element, which is a very heterogeneous aggregate at the atomic level.

On the other hand, the coprecipitation method is superior in homogeneity to the solution method because all the crystals are simultaneously and simultaneously precipitated, but it is still nonuniform at the atomic level.
Further, since the sol-gel method has no precipitation process and the alkoxide method has a small difference in solubility in a solvent, the heterogeneity is improved to some extent, but the homogeneity at the atomic level is not perfect.

Further, in the method of forming a complex with the water-soluble polymer, the binding force between the polymer complex and the metal ion is small, and the metal ion species (Y ³⁺ , Ba ²⁺ , Cu ²⁺ ) are used.
The difference in affinity due to is large. If the polymer strongly forms a complex with all the metal ions in the solution as shown in the above chemical formula 1, it is considered that when the solution is evaporated and solidified, the metal ion salt does not precipitate, When these polymers are used, it is inevitable that free metal ions remain in water. Moreover, since the abundance ratio of the remaining metal ion species is not the total element ratio, what is bonded to the polymer is solidified in an at random state (but the element ratio is different from the total element ratio) when evaporated and solidified, The metal ions remaining in the solution will be non-uniformly deposited.

[0010]

As a result of repeated studies on a method for making the above problems uniform, the present inventors have found that the organic polymer has a strong bonding force with metal ions and high stability. Using a chelating agent, it was found that when the metal element constituting the oxide superconductor is chelated and present in the polymer, the homogeneity at the atomic level is maintained even when it is evaporated and solidified, and the present invention I arrived.

That is, in the method for producing an oxide superconductor of the present invention, a water-soluble organic polymer chelating reagent is reacted with a metal ion of a constituent metal element of the oxide superconductor, and the metal element is converted into the oxide superconductor. It is characterized in that a chelating polymer contained at a forming ratio is prepared, the chelating polymer is heat-treated to decompose and remove organic components, and then heat-treated in an oxidizing atmosphere, wherein the water-soluble organic polymer chelating reagent is EDTA. -At least one selected from ED polymer, polyethyleneimine derivative, polyvinylamine derivative, polyallylamine derivative, polypropyleneimine derivative, polyschiff base chelating agent, and Diels-Alder adduct chelating agent of maleic anhydride to conjugated diene polymer It is characterized by that.

The present invention will be described in detail below. The method for producing an oxide superconductor according to the present invention is characterized by using a water-soluble organic polymer chelating reagent. Organic polymer chelating agents include those having a polydentate ligand in a chain polymer. In particular, EDTA (ethylenediaminetetraacetic acid) is the most chelating ligand currently synthesized, and the polyamide obtained by the reaction of this with ED (ethylenediamine) is shown below. Form a chelating polymer as shown.

[0013]

[Chemical 2]

Since this chelate polymer forms a chelate with four coordinations with respect to one metal ion, it is extremely stable and has a strong binding force. Therefore, not all of the metal ions in the water will bind to this chelating polymer, leaving free metal ions in the water.

As the polymer having a large chelating power like the EDTA-ED polymer, polyethyleneimine derivatives such as poly (N-carboxymethyl) ethyleneimine and polyvinyl such as poly (N, N-dicarboxymethyl) vinylamine are used. Amine derivative, poly (N,
Examples include polyallylamine derivatives such as N-dicarboxymethyl) allylamine, polypropyleneimine derivatives, polyschiff base chelates, and Diels-Alder adduct chelates of maleic anhydride to conjugated diene polymers. For example, when chelated with poly (N-carboxymethyl) ethyleneimine,

[0016]

[Chemical 3]

As described above, and when chelated with poly (N, N-dicarboxylmethyl) vinylamine,

[0018]

[Chemical 4]

It becomes as follows. When chelated with poly (N, N-dicarboxylmethyl) allylamine,

[0020]

[Chemical 5]

It becomes as follows. The chelates represented by the above chemical formulas 3, 4, and 5 have a strong chelating power similarly to the chelate represented by the chemical formula 2. Further, the above chemical formula 3, chemical formula 4, chemical formula 5
The chelate represented by the formula (2) has a smaller chelate molecular weight than the chelate represented by formula (2), and is considered to be further liberated during sintering.

According to the present invention, the above chelate polymer is used as a starting material. In order to produce the chelate polymer, first, nitrates, sulfates, acetates, etc. of the metal elements constituting the oxide superconductor to be obtained are prepared, and these are made to have a metal ratio that exhibits superconducting properties. The mixture is weighed and mixed, and for example, the organic polymer chelating reagent (0.1 M) having a molecular weight of 70,000 to 80,000 is added to the aqueous solution at a volume ratio of 1: 1 with respect to a 0.1 M aqueous solution of metal salts. . Next, after evaporating water from this solution to dryness,
The solid obtained is dried at a temperature of 100 to 120 ° C. for 5 to 20 hours. In this solid substance, the metal captured by the chelate is uniformly dispersed at the atomic level.

Next, the sufficiently dried solid material is pulverized and then treated at 350 to 500 ° C. for 0.5 to 3 hours to decompose and remove organic components in the solid material. At this time, the atmosphere is an oxidizing atmosphere such as air. The carbon residue after this treatment is preferably 0.1% or less. By this heat treatment, the metal element in the chelate polymer is dissociated from the chelate and becomes a uniform mixture of Y ₁ Ba ₂ Cu ₃ Oy.

Thereafter, this mixture was placed in an oxidizing atmosphere,
A uniform oxide superconductor can be produced by heat treatment at a temperature sufficient to form an oxide superconductor. The firing temperature at this time varies depending on the type of oxide superconductor to be obtained, but for example, when YBa ₂ Cu ₃ Oy is produced, a temperature range of 860 to 920 ° C. is desirable.

In the case of producing a sintered body, the oxide superconductor synthesized by the above heat treatment is further added to 860-950.
The firing may be performed in an oxidizing atmosphere at ℃.

Further, in the above-mentioned manufacturing method, the carbon component can be removed by repeating the decomposition and removal step of the organic component, and the heat treatment step for synthesizing the oxide superconductor is carried out plural times, or the annealing is performed after firing. By performing the treatment, the crystallinity can be increased and the characteristics can be improved.

Further, when the polymer to be used is thermoplastic, it is possible to obtain an oxide superconducting sintered body having a desired shape by forming the chelate polymer into a desired shape before heat treatment and then performing heat treatment and firing. You can Further, it is also possible to manufacture a coiled wire material whose surface exhibits superconductivity by applying a chelate polymer to a desired base material, for example, the surface of a coiled wire material thickly, followed by heat treatment and baking.

[0028]

According to the constitution of the present invention, when a chain polymer having a polydentate ligand is dissolved in an aqueous solution of a metal salt of a constituent metal element of an oxide superconductor, the metal ion is trapped by the chelate and Each constituent metal element is bonded at random to the main chain while maintaining a constant ratio.

According to the above-mentioned methods, even if the metal ions are homogeneously dissolved at the atomic level, the coexisting metal ions are individually precipitated due to the difference in solubility between the metal compounds immediately before the water is completely removed. The obtained powder is a simple metal compound at the atomic level, and the powder system as a whole is not uniform at the atomic level.

In the present invention, when the water in the chelate polymer aqueous solution is evaporated and solidified, each metal remains chemically bonded at random to the polymer chain even when the water is completely removed. Since the metal ion maintains the blended element ratio and is uniform at the atomic level in any portion, it is possible to obtain a uniform oxide superconductor by heat-treating and firing this chelate polymer.

The chelate polymer molecule is a linear polymer and exhibits thermoplasticity unless strong intermolecular interaction occurs. By taking advantage of this thermoplasticity, molding and processing this polymer into a desired shape, and then heat treating it, it is possible to produce oxide superconductors of any shape.

Even when thermoplasticity cannot be obtained, a viscous polymer solution is prepared, applied on the surface of a desired substrate, and heat-treated and fired to obtain a coated body having an oxide superconductor on the surface. Can be produced.

[0033]

【Example】

Example EDTA dianhydride and ethylenediamine were stirred in dimethylsulfoxide (DMSO) for 1 week to give

[0034]

[Chemical 6]

Weight average molecular weight of 3.4 × 10
A water-soluble chain polymer of ³ was obtained. The reaction is carried out in a nitrogen atmosphere, ethylenediamine is refluxed by adding metallic Na, DM
As SO, CaH ₂ was added, heated, and then distilled under reduced pressure to be used.

Next, 25 ml of 0.1M Y (NO ₃ ) ₃ .6H ₂ O and 0.1M Ba (NO ₃ ) were used so that the molar ratio of Y: Ba: Cu was 1: 2: _3. ) ₃ to 50 ml
And 0.1 ml of Cu (NO ₃ ) ₃ / 3H ₂ O 75 ml
Were mixed, to which 0.1M repeating unit of the organic polymer chelating reagent was added at a volume ratio of 1: 1. This is 5 at 60 ℃ using a rotary evaporator.
Film solid obtained by evaporation to dryness for 110 hours
And dried for 12 hours to obtain a chelate polymer powder. When the distribution state of the metal element was observed on this powder by an energy dispersive micro area analyzer (EPMA), it was confirmed that Y, Ba and Cu elements were uniformly dispersed in the order of micron.

Then, this was treated in air at 450 ° C. for 1 hour to decompose and remove organic components, and then the temperature rising / falling rate was 3 ° C.
/ Min and heat-treated at 880 ° C for 10 hours to synthesize an oxide superconductor. When the obtained oxide superconductor was subjected to X-ray diffraction measurement, it was found to be a single phase of Y ₁ Ba ₂ Cu ₃ Oy. Further, this was fired in air at 920 ° C. to prepare an oxide superconducting sintered body.

The density of the obtained sintered body was measured by the Archimedes method, and the critical temperature and the critical current density in liquid nitrogen (70K) were also measured.

Comparative Example 1 (Solution Method) Y: Ba: Cu = 1.2: 3 in a molar ratio of 0.
1M of Y a _{(NO 3) 3 · 6H 2} O and 25 ml, 0.1
50 ml of M Ba (NO ₃ ) ₃ and 0.1 M Cu
_{(NO 3) 3 · 3H 2} O were mixed 75 ml, after dried, and calcined at 880 ° C., and calcined at 920 ° C., was subjected to characteristic evaluation in the same manner as in Example.

Comparative Example 2 (EDTA Chelate) In the example, 2% of 0.1M Y (NO ₃ ) ₃ .6H ₂ O was added so that the molar ratio was Y: Ba: Cu = 1: 2: 3.
5 ml and 50 ml of 0.1 M Ba (NO ₃ ) ₃
75 ml of 0.1 M Cu (NO ₃ ) ₃ .3H ₂ O was mixed, and 4.38 g of EDTA powder was added to this and heated to 90 ° C. to completely dissolve it. Thereafter, this solution was dried, decomposed and removed, heat-treated and fired under the same conditions as in the example to produce a sintered body, and the characteristics were evaluated.

Comparative Example 3 (Solid Phase Method) Using Y ₂ O ₃ , BaCO ₃ and CuO powders, Y: B
The mixture was weighed and mixed so that the a: Ca ratio was 1: 2: 3, molded, and then fired at 920 ° C., and the characteristics were evaluated in the same manner as in Example 1.

Table 1 shows the measurement results of the above characteristics.

[0043]

[Table 1]

According to Table 1, according to the method of the present invention, the density of the sintered body is highest, the densification is advanced, and the Jc value is also highest, which is superior to the methods of other comparative examples. I understand.

The difference between the density and Jc of Example and Comparative Example 2 is considered to be the effect of the polymerization according to the present invention.

[0046]

As described in detail above, according to the present invention,
By using the organic polymer chelate, it is possible to uniformly disperse the metal elements constituting the oxide superconductor,
A single phase of a uniform oxide superconductor can be produced by suppressing the precipitation of different phases. Moreover, since a polymer is used, a sintered body of any shape can be obtained, and the utilization of the oxide superconductor can be expanded.

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Claims (2)

[Claims] 1. A water-soluble organic polymer chelating reagent is reacted with a metal ion of a constituent metal element of an oxide superconductor,
An oxide characterized in that a chelate polymer containing the metal element in a ratio to form an oxide superconductor is prepared, the chelate polymer is heat-treated to decompose and remove organic components, and then heat-treated in an oxidizing atmosphere. Superconductor manufacturing method. 2. The water-soluble organic polymer chelating reagent,
EDTA-ED polymer, polyethyleneimine derivative,
The oxide superconductor according to claim 1, which is at least one selected from a polyvinylamine derivative, a polyallylamine derivative, a polypropyleneimine derivative, a polyschiff base chelating agent, and a Diels-Alder adduct chelating agent of maleic anhydride to a conjugated diene polymer. Manufacturing method.