JP2622116B2 - Superconductor manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a highly stable oxide superconductor.

(Prior art) Conventionally, as a method for producing a superconductor mainly based on a copper oxide, a corresponding metal oxide or metal carbonate is finely crushed in a mortar, or the obtained fine powder is sieved, or Knead with a suitable binder, 800-1200
(Wu, MK, et al., Phys. Rev. Lett, 5
8,908 (1987)) and the addition of sodium carbonate to a homogeneous aqueous solution of the corresponding metal nitrate to form the poorly soluble metal carbonate.
Decarboxylation at 800 ° C and finally sintering at 1100 ° C or similar decarboxylation in the form of oxalate (Capone, D.
W. et al. Appl. Phys. Lett. 50, 543 (1987)) are known.

However, these manufacturing methods have a process of forming corresponding solid solutions of various metal oxides by a solid-phase reaction in the former, and in order to synthesize a material having a uniform composition, a high temperature of 1100 ° C. or more is required. It takes a long time. But,
In copper oxides, divalent copper is known to convert to monovalent copper at temperatures above 1050 ° C., which leads to a loss of superconductivity. In the latter method, since the water-soluble metal nitrate is used as a starting material, the metal salt is uniformly mixed at room temperature. However, it is necessary to decarbonate at 800 ° C. and degas and sinter at a high temperature of 1200 ° C. This treatment tends to cause bubbles and cracks inside the superconductor.

(Problems to be Solved by the Invention) In order to improve such a point, the present invention provides a method for producing a superconductor which enables uniform mixed sintering at a low temperature.

(Means for Solving the Problems) In the present invention, a mixed solution comprising desired various metal salts and a bidentate or higher chelating ligand is prepared, and the mixed solution is made into a spray state under an oxygen atmosphere or A process of contacting with a heated atmosphere or a flame in an inorganic oxygen atmosphere to burn and oxidize to synthesize oxide fine powder. If necessary, this fine powder is formed into a desired shape such as a film, a line, a disk, etc. together with a binder or without using a binder, and the formed product is sintered in the presence of oxygen. A conductor is obtained.

At this time, a metal nitrate, a perchlorate, a chlorate, or a bromate can be used as the metal salt for the purpose of sufficiently promoting the reaction. These salts are metal salts having oxidizing ions, and burn by heating to 450 ° C. or more to form oxides. In the present invention, this effect contributes to the synthesis of a superconductor at a lower temperature than before.

According to a preferred embodiment of the present invention, as a bidentate or higher chelating ligand, oxalic acid, hydroxo acids, or amino acids, or a polymer having a carboxylic acid group or a hydroxam group, or by using rubeanic acid, efficiently. A finely divided metal oxide can be produced. For example, as such a ligand, tartaric acid of oxalic acid and hydroxo acids, citric acid, gluconic acid, malonic acid, succinic acid, glutaric acid, ascorbic acid, ethylenediaminetetraacetic acid of amino acids, iminodiacetic acid, nitrilotriacetic acid, diethylenetriaminepentane Acetic acid, triethylenetetraminehexaacetic acid, L-amino acids and carboxylic acid-containing polymers include polyacrylic acid, polymethacrylic acid, polystyrene substituted with iminodiacetic acid, polyhydroxamic acid, rubeanic acid and the like.

In addition, before and after mixing with the metal salt and the chelating ligand, by adding an additive having a thickening action or a surfactant action with an organic substance having at least one hydrophilic portion, the granulating action is enhanced and uniformity is improved. A superconductor in the form of fine powder having a uniform particle size with a mixed composition can be obtained.

A manufacturing apparatus capable of performing the above manufacturing method is required to have a function of efficiently forming a solution of a raw material composition into fine droplets and performing combustion oxidation. The apparatus of the present invention includes a combustion chamber, a spray nozzle unit for supplying a raw material solution to the chamber in a mist state, a mechanism for supplying the raw material solution and pressurized air or oxygen to the nozzle unit, and the combustion chamber being heated. Or a mechanism for supplying air or oxygen or forming a flame in the chamber. This production apparatus supplies a mixed solution containing a metal salt and a chelating agent from a spray nozzle to a combustion chamber, thereby obtaining a superconductor as a metal oxide fine powder by deoxidizing and burning and oxidizing the mixed solution. Has functions. If a mechanism for collecting the generated metal oxide fine powder is added, the product can be collected more efficiently.

(Example of manufacturing method)

(Example 1) Y (NO ₃ ) ₃ , 0.2 mol / 1, Ba (NO ₃ ) ₂ 0.2 mol /, Cu (N
A solution obtained by mixing each aqueous solution of O ₃ ) ₂ and 0.2 mol / at a ratio of 1: 2: 3 at room temperature was mixed with a citric acid aqueous solution. The mixture was sprayed and brought into contact with a flame to deoxidize and burn and oxidize at the same time. The resulting oxide fine powder was pressed at 10 to 20 tons / cm ²
Sintered at 450-800 ° C. FIG. 1 shows an X-ray diffraction pattern of the sintered body. This is because Y _1.0 − which indicates a superconducting transition point of 92K.
X-ray diffraction pattern of oxygen-deficient perovskite (hereinafter abbreviated as ODP) structure of Ba _2.0 -Cu _3.0 system (Senba et al., Jan. J. App.
l.Hhys. 1987, April, L429-L431). This means that the superconducting ODP structure has a 150
This means that sintering was possible at temperatures as low as 550550 ° C. When the temperature change of the conductivity of the sample was determined by a four-terminal AC method, it was found that superconductivity was completely achieved at an absolute temperature of 85K, and the transition width, which was a measure of the quality of the sample, was 4.2K.

(Example) Y (ClO ₄ ) ₃ , 0.2 mol /, BaCl ₂ , 0.2 mol /, Cu (ClO ₄ )
₂ , Each 0.2 mol / aqueous solution was mixed at room temperature at a ratio of 1: 2: 3. This was mixed with a tartaric acid aqueous solution, a methanol solution of tetramethylammonium hydroxide was added, and the mixture was sprayed and brought into contact with a flame to burn and oxidize. The obtained oxide fine powder was pressed at 10 to 20 ton / cm ² and sintered at 600 to 800 ° C. When the temperature change of the conductivity of the sample was determined by a four-terminal AC method, it was found that superconductivity was completely reached at an absolute temperature of 82K, and the transition width was 8.5K.

Example 3 LaCl ₃ , 0.2 mol /, BaCl ₂ , 0.2 mol /, CuCl ₂ , 0.2 mol /
Were mixed at room temperature at a ratio of 6: 4: 1. This was mixed with an aqueous solution of ethylenediaminetetraacetic acid, and a 10% aqueous solution of tetramethylammonium hydroxide was gradually added. The mixed solution was sprayed, contacted with a flame, and burned and oxidized. The obtained oxide fine powder was pressed at 10 to 20 ton / cm ² and sintered at 600 to 800 ° C. Temperature change of conductivity of sample is 4
As determined by the terminal AC method, superconductivity was reached at an absolute temperature of 35K, and the transition width was 4.2K.

Example 4 GdCl ₃ , 0.2 mol /, SrCl ₂ , 0.2 mol /, CuCl ₂ , 0.2 mol /
Were mixed in a ratio of 0.5: 2.5: 4 at room temperature. This was mixed with an L-alanine solution to make the mixture into a spray, and then contacted with a flame to oxidize and burn. The obtained oxide fine powder was pressed at 10 to 20 ton / cm ² and sintered at 550 to 800 ° C.
When the temperature change of the conductivity of the sample was determined by a four-terminal AC method, superconductivity was reached at an absolute temperature of 85K, and the transition width was 3.8K.

Example 5 YNO ₃ , 0.2 mol /, BaNO ₂ , 0.2 mol /, CuNO ₂ , 0.2 mol /
Was mixed at a ratio of 1: 2: 3 at room temperature. Polyethylene glycol was added to the mixture, and the mixture was sprayed and brought into contact with a flame to oxidize and burn. The resulting oxide fine powder pressurized molded into a disk shape with 10-20 t / cm ²
Sintered at 600-800 ° C. When the temperature change of the conductivity of the sample was determined by a four-terminal AC method, superconductivity was reached at an absolute temperature of 88K, and the transition width was 1.8K.

(Example 6) EuCl ₃ , 0.2 mol /, BaCl ₂ , 0.2 mol /, CuCl ₂ , 0.2 mol /
Were mixed at room temperature in a ratio of 1: 2.5: 3. This was mixed with an aqueous solution of polymethacrylic acid, and the mixed solution was sprayed, contacted with a flame, and burned and oxidized. The obtained oxide fine powder was kneaded with a small amount of ethylene glycol, screen-printed on a YSZ substrate, and sintered at 600 to 700 ° C. When the temperature change of the conductivity of the sample was determined by a four-terminal AC method,
Superconductivity was reached at an absolute temperature of 89K, and the transition width was 1.5K.

Example 7 Y (ClO ₄ ) ₃ , 0.2 mol /, BaCl ₂ , 0.2 mol /, CuCl ₂ ,
0.2 mol / of each aqueous solution was mixed at a ratio of 1: 2: 3 at room temperature.
A small amount of an aqueous polyvinyl alcohol solution and lecithin were added thereto, mixed with a citric acid solution, and a 10% aqueous solution of dodecyltrimethyl hydroxide was gradually added. The mixture was sprayed and brought into contact with a flame to burn and oxidize. The obtained oxide fine powder is kneaded with a small amount of glycerin, and 10 to 20 tons / cm ²
It was extruded from the die with the pressure of 1 mm to form a wire rod having a diameter of 1 mm. This wire was sintered at 600 to 800 ° C. When the temperature change of the conductivity of the obtained wire sample was determined, superconductivity was reached at an absolute temperature of 89K, and the transition width was 1.5K.

In the above embodiment, the example in which the mist-like raw material mixed solution is brought into contact with the flame has been described. In the production method of the present invention, the metal salt contained in the raw material mixed solution is a metal salt having oxidizing ions, and is heated to 450 ° C. or more to burn and form an oxide. Therefore, it is possible to burn and oxidize the raw material mixed solution also by bringing it into contact with an atmosphere having such a temperature, for example, heated air or oxygen. In the same manner, a mixed solution prepared by mixing a chelating agent with a salt containing Y, Sc and a lanthanide-based element, an alkaline-earth-based element including Ba, and copper, charged to a predetermined composition, as a raw material, A fine powder of the substance was obtained.
Table 1 summarizes the results obtained after sintering the moldings at 500-800 ° C.

[Embodiment of Manufacturing Apparatus] FIG. 2 shows a block diagram of an embodiment of the manufacturing apparatus. This apparatus comprises a raw material container 6 for holding a mixed solution containing a metal salt and a chelating agent, a liquid sending pump 1 for feeding the mixed solution, a spray nozzle 2 for spraying the mixed solution in a mist, It comprises a pressurized air or pressurized oxygen supply section 3, a burner 4 for forming a flame for burning and oxidizing the injected mixed solution simultaneously with dehydration, and a combustion chamber 5 including the burner.

Using this apparatus, a fine powder of a metal oxide for producing a superconductor was obtained under the following conditions.

Composition of mixed solution: Y (NO ₃ ) ₃ , 0.01 to ₂ mol / aqueous solution Ba (NO ₃ ) ₂ , 0.01 to ₂ mol / aqueous solution Cu (NO ₃ ) ₂ , 0.01 to ₂ mol / aqueous solution Citric acid, 0.01 to 6 mol / aqueous solution Combustion chamber Internal temperature: 300-850 ° C The obtained fine powder is kneaded with a small amount of glycerin, and YSZ
It was screen printed on a substrate and sintered at 600-750 ° C. When the temperature change of the conductivity of the sample was determined by a four-terminal AC method, superconductivity was reached at an absolute temperature of 85K, and the transition width was 4.5K.

In the embodiment of the apparatus of the present invention, the same effect can be obtained even if the burner 4 is replaced with a jet port of heated air or oxygen.

(Effects of the Invention) As described above, according to the method of the present invention, a metal oxide fine powder uniformly mixed on an atomic scale with a predetermined composition of a superconductor can be efficiently obtained at a relatively low temperature. Using this metal oxide fine powder, a continuous metal oxide superconductor can be formed at a sintering temperature sufficiently lower than the conventional sintering temperature. Therefore, the present invention has a great advantage in solving the problem of lowering the superconducting transition point or losing superconductivity due to the chemical reaction between the superconductor, the substrate, and the core material, which tends to be caused by high-temperature sintering.

The device of the present invention can efficiently realize the method of the present invention.

High-temperature superconductors, especially materials that reach superconductivity above the temperature of liquid nitrogen with an absolute temperature of 77 K, are Josephson devices, power transport,
A wide range of industrial applications such as a high magnetic field generating magnet are expected, and the material processing has a great impact on the fact that the present invention can be manufactured by a low-temperature process.

[Brief description of the drawings]

FIG. 1 is a view showing an X-ray diffraction pattern (CuKα) of a superconductor having an oxygen-deficient perovskite structure obtained by the present invention, and FIG. 2 is a view showing an apparatus for manufacturing a superconductor of the present invention. 1 ... liquid feed pump, 2 ... injection nozzle, 3 ... pressurized air or pressurized oxygen supply unit, 4 ... burner, 5 ... combustion chamber, 6 ... material container.

Claims (9)

(57) [Claims] 1. A general composition formula (M1) x (M2) y (M3) zOw
(Where M1 is (B, Al, Ga, In, Tl, Sc, Y, La, Ce, Pr, Nd, Pm, S
m, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), one or more elements selected from the group consisting of M2, (Be, Mg, Ca, Sr, Ba, Ra, S
n, Pb), one or more elements selected from the group consisting of:
(M3 is (Cu), x, y, z, w are arbitrary atomic mole fractions) In the method for producing a superconductor represented by the following formula, a metal salt of M1, M2, M3 and a bidentate or higher chelate coordination And a step of preparing a mixed solution consisting of particles and contacting the mixed solution in a sprayed state with a heated atmosphere or a flame, burning and oxidizing simultaneously with drying to form a metal oxide. Manufacturing method of superconductor. 2. The method for producing a superconductor according to claim 1, wherein a salt selected from a nitrate, a perchlorate, a chlorate and a bromate is used as the metal salt. (3) The bidentate or higher chelating ligand is one or more compounds selected from oxalic acid, hydroxo acids, amino acids, polymers having a carboxylic acid group or a hydroxam group, and rubeanic acid. 3. The method for producing a superconductor according to claim 1, wherein the method comprises: 4. The hydroxo acids as a bidentate or higher chelating ligand is one or more acids selected from tartaric acid, citric acid, gluconic acid and ascorbic acid. Item 4. The method for producing a superconductor according to any one of Items 1, 2 and 3. 5. The superconductor according to claim 1, wherein the amino acids which are bidentate or higher chelating ligands are L-amino acids. Manufacturing method. 6. A polymer having a carboxylic acid group or a hydro (xam group) which is a bidentate or higher chelating ligand selected from polyacrylic acid, polymethacrylic acid, polystyrene substituted with iminodiacetic acid, and polyhydroxamic acid. The method for producing a superconductor according to any one of claims 1, 2, and 3, wherein the superconductor is a plurality of acids. 7. The method according to claim 1, wherein one or more organic additives are added in the step of preparing a solution comprising a metal salt and a bidentate or higher chelating ligand. The method for producing a superconductor according to any one of claims 6 to 13. 8. The method according to claim 1, wherein at least one of the organic additives comprises cellulose, glycerin, triethanolamine having a nitrification degree of 8% or more.
The superconductor according to any one of claims 1 to 7, wherein the superconductor is selected from ethylene glycol, propylene glycol, polyvinyl alcohol, polyacrylamide, polyethylene glycol, polypropylene glycol, cetyl methylcellulose, and polyvinylpyrrolidone. Production method. 9. The method for producing a superconductor according to claim 7, wherein at least one kind of the organic additive is an organic substance having a surfactant activity.