JPH01122522A - Manufacture of oxide superconducting fiber - Google Patents

Abstract

PURPOSE:To obtain high strength and good flexibility by dispersing a material capable of serving as an oxide superconductor in an aqueous solution containing a water soluble polymer, wet-spinning this spinning raw liquid in an organic solvent which is a nonsolvent for the water soluble polymer, then heat-treating it. CONSTITUTION:A material containing Cu as an oxide superconductor or a material capable of serving as an oxide superconductor by heat treatment is dispersed or solved in an aqueous solution containing a water soluble polymer made of a polyvinyl alcohol polymer to produce a spinning raw liquid. This spinning raw liquid is wet-spun in an organic solvent made of methanol which is compatible with water and a nonsolvent for the water soluble polymer to form precursor fibers of superconducting fibers, then the precursor fibers are heat-treated. Oxide superconducting fibers with high strength and good flexibility are thereby obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for manufacturing an oxide superconductor made into a wire that can be used for superconducting magnets, superconducting power transmission lines, and the like.

Moon-jD Jin 9'' (Mission) Conventionally, Nb3Ge or Nb3Sn was used as a superconductor.
etc. = 3- intermetallic compounds are known. However, the critical temperature (Tc) of these materials is extremely low, at most 23.3K (Nb5Ge), and when these materials are used, industrial production is difficult and requires cooling with liquid helium, which is less economical. This has been a significant constraint on the use of these materials for a wide range of industrial applications.

Recently, it has been discovered that oxide superconductors have extremely high critical temperatures, and research in this field has become active. Materials with high critical temperatures (hereinafter abbreviated as high-temperature superconducting materials) include superconductors of grade 40 (La
+-zSrz), cuo4[Chem, l, ett,
.

429 (1987)], B as a superconductor in 90
a2Y+CL13O,-, [Phys, Rev, l,
ett, 58 (1,987) 405], and in addition to Y, superconducting phenomena of magnitude 90 have already been observed in Lu, Yb, Tm, Er, etc.

With the advent of 90-grade high-temperature superconducting materials, liquid nitrogen (77K
), and there are prospects that industrial problems in cooling will be greatly improved.

Problems that C6 Ming aims to solve Applications of high-temperature superconductivity include applications in the electronics field, as typified by Josephson devices, and electrical equipment fields, as typified by superconducting generators, magnetic levitation trains, and superconducting power transmission lines. It is broadly divided into applications.

Application to the electronics field is also a very important issue, but when considering the magnitude of the impact it will have on industry and society, it is the application of high temperature superconductivity to electrical equipment that is important.

Superconducting magnet technology is an elemental technology for the application of high-temperature superconductivity to electrical equipment. Things that use superconducting magnets include MHD power generation, magnetic floating trains, high-energy particle accelerators, superconducting generators, superconducting transformers, and N.
Examples include MR-CT. If high-temperature superconductors can be used in the field of magnets, the economic efficiency of superconducting magnet application equipment will be greatly improved. It is also expected that the drastic improvement in economic efficiency will open up new fields of application or application to superconducting power transmission lines.

In order to use a high-temperature superconductor in a magnet, it must be a wire that can be wrapped around the magnet. Furthermore, a major problem in practical use of superconducting magnets is stabilization of the magnet.

Intermetallic superconductors like conventional Nb5Ge or Nb3Sn? Here, for example, a Cu5n alloy rod,
Nb or +lb alloy rods are tightly bundled and heat treated to reduce Nb or +lb alloy rods.
After forming a b3Sn compound layer, the superconductor is made into a wire by an extremely complicated method of repeating the drawing process many times to make the wire into a wire.

However, since high-temperature superconductors, ie, oxide superconductors, are made of ceramics, they have the problem of being significantly more difficult to form into wires than conventional superconductors.

In order to solve these problems, a method has already been proposed in which a hole is made in a silver alloy ingot and the material is filled with oxide superconductor powder or powder of a substance that can be made into an oxide superconductor through heat treatment to form a wire and then heat treated. ing.

However, when a high-temperature superconductor, that is, an oxide superconductor, is packed into a hollow metal tube made of silver or the like and made into a wire, (1) it is extremely difficult to make an ultra-fine wire with a diameter of 100 μm to 200 μm or less; (2) There have been extremely serious problems, such as the difficulty of maintaining a high temperature superconductor, that is, an oxide superconductor, without disconnection and with uniform conductivity over the entire line area.

In other words, the production of stabilized superconducting wires is the most important issue for the practical application of high-temperature superconducting materials, and the most important issue for this purpose is the production of ultrafine wires of high-temperature superconductors, that is, oxide superconductors. The current situation is that there is a strong demand for this.

Steps for resolving problem D1 In view of the above-mentioned current situation, the inventors of the present invention have conducted intensive studies and have discovered that an oxide superconductor or a substance that can become an oxide superconductor through heat treatment is dispersed in an aqueous solution containing a water-soluble polymer. Alternatively, by dissolving and preparing a spinning stock solution, wet-spinning this spinning stock solution in an organic solvent that is compatible with water and a non-solvent for the water-soluble polymer to obtain precursor fibers of superconducting fibers, and then heat-treating the solution. They discovered that oxide superconducting fibers can be obtained and completed the present invention.

The present invention will be explained in detail below.

The oxide superconductor used in the present invention is not particularly limited as long as it forms a ceramic sintered body through heat treatment and exhibits a superconducting phenomenon below a certain temperature. Preferably.

Specifically, (La, Ba), Cub4 and general formula LnB
a2Cu3O7□ (However, Ln is Y, Lu, Yb,
Tm, Er, Ho, Dy.

At least one of Gd, Eu, and Sm, χ is 0<x
≦05. ). Part of each of the above Ln, Ba, Cu, and O is F.
etc. may be replaced.

Examples of substances that can be turned into oxide superconductors by heat treatment include those consisting of oxides, nitrates, carbonates, etc. of the respective metals forming the oxide superconductor described in 1.

Specifically, (a) an oxide, nitrate or carbonate of Ln (however, Ln
n is Y, Lu, Yb, Tm, Er,
Ho, Dy, Gd, Eu.

At least one type of Sm) (b) Ba oxide, nitrate or carbonate; and (c) Cu oxide, nitrate or carbonate. The above (b) may be Ba acetate or fluoride. Also, for (c) above, C
It may be gluconate or fluoride of u.

More specifically, as in Section 1 (a), y2o.

Y(No3)2 etc., and as above (b) BaCO3
゜Ba(NO3)2. BaFt etc. are Cub as the above (c).

Cu(NO3)2. Examples include CuF2.2H3O.

A spinning stock solution may be prepared by dispersing or dissolving each of these components in an aqueous solution containing a water-soluble polymer. Before dispersing or dissolving the mixture in an aqueous solution, the mixture is heated at a temperature of 800°C to 100°C (1°C
A more excellent effect can be obtained by using a material calcined for 1 to 5 hours under these conditions.

The oxide superconductor used in the present invention or the substance that can become an oxide superconductor by heat treatment is preferably used in the form of a powder, and particularly has an iJ of 51 m or less, preferably 1 μm or less, and more preferably iJ: 0.5 μm or less. It is preferable to use it as a fine powder.

The water-soluble polymer used in the present invention is a polyvinyl alcohol polymer (hereinafter referred to as polyvinyl alcohol).
(sometimes abbreviated as A), cellulose derivatives such as methylcellulose, hydroxyethylcellulose, and hydroxyethylmethylcellulose, polyvinylpyrrolidone, polyacrylamide, and polyethylene glycol, among which PVA-based polymers are most preferably used.

There are no particular restrictions on the saponification degree or polymerization degree of the PVA polymer as long as it is within the water-soluble range, but the saponification degree is usually 70.
~100 mol%, preferably 85-1.00 mol%, most preferably 95-100 mol%, degree of polymerization 500
~20,000, preferably from 1,000 to 15 (100).

The polyvinyl alcohol polymer in the present invention includes not only ordinary unmodified polyvinyl alcohol but also so-called modified polyvinyl alcohol. Examples of the modified polyvinyl alcohol include saponified copolymers of vinyl acetate and a comonomer copolymerizable with vinyl acetate. Comonomers include vinyl esters other than vinyl acetate (for example, vinyl propionate, vinyl stearate, vinyl benzoate, saturated branched HFi vinyl fatty acids, etc.);
Unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid or their alkyl esters; unsaturated polyhydric carboxylic acids such as maleic acid, maleic anhydride, fumaric acid, and itaconic acid; or partial or complete esters thereof; acrylonitrile, methacrylonitrile,
Acrylamide, methacrylamide, olefin sulfonic acid (e.g. ethylene sulfonic acid, allyl sulfonic acid, methalylsulfonic acid, etc.) or its salts, ethylene, propylene, butene, α-octene, α-dodecene,
Examples include α-olefins such as α-octadecene, vinyl ethers, and silane-containing monomers. The proportion of these comonomers in the copolymer is less than 20 mol %, preferably less than 10 mol %.

Another group of modified polyvinyl alcohols are post-modifications of vinyl acetate homopolymers or saponified products of the aforementioned copolymers. Examples of post-modification include acetalization, urethanization, phosphoric acid esterification, sulfuric acid esterification, and sulfonic acid esterification.

The spinning stock solution used in the present invention contains an oxide superconductor (preferably in powder form) or a substance that can become an oxide superconductor by heat treatment (preferably in powder form). It can be prepared by dispersing or dissolving it in an aqueous polymer solution.

The weight ratio of the above-mentioned oxide superconductor or a substance that can become an oxide superconductor by heat treatment to the water-soluble polymer in the spinning stock solution is such that the latter is 15% by weight or less and 3% by weight or more, preferably 3% by weight or more relative to the former. It is preferable that the amount is 8% by weight or less and 3% by weight or more.

Further, when preparing the above-mentioned spinning stock solution, it is permissible to use a dispersant of a substance that can become an oxide superconductor by heat treatment of the above-mentioned oxide superconductor. In this case, the dispersant is an anionic emulsifier,
Nonionic emulsifiers and cationic emulsifiers can be used. For example, polyoxyethylene (10) ocdylphenyl ether, sodium dodecyl sulfate, etc. can be used.

Further? Polymer-based dispersion stabilizers such as polyacrylic acid and its salts, neutralized products of copolymers of borisdyrene and maleic anhydride, and neutralized products of maleic anhydride-ibutene copolymers can also be used.

The total solid content concentration in the above-mentioned spinning dope is not particularly limited, but is usually selected from a range of about 20 to 70% by weight.

The above-mentioned spinning stock solution is then wet-spun in an organic solvent that is compatible with water and is a non-solvent for the water-soluble polymer, and then dried to obtain a continuous precursor fiber.

Examples of organic solvents that are compatible with water and are non-solvents for water-soluble polymers used in the present invention include methanol, ethanol,
Lower alcohols such as isopropanol and propatool;
Ketones such as acetone and methyl ethyl carbon can be used, but methanol is preferably used from the viewpoint of wet spinnability.

It is also possible to use a small amount of water in combination with the organic solvent to form a mixed solvent. In this case, the volume ratio of [organic solvent/water] is preferably 10,010 to 50,150.

Further, the temperature is preferably 50°C or less.

The spinning draft is preferably fl, 1 to 2.0, preferably 0.
．． 8 to 1.2 is good.

The precursor fibers are then heat treated. Of course, there is no problem in stretching the film as appropriate prior to the heat treatment. The heat treatment conditions include, for example, 95% in the presence of oxygen.
An example is a method of baking at a temperature of 0° C. to 1000° C. for several minutes to several hours, preferably several minutes to several tens of minutes, and then slowly cooling.

The diameter of the oxide superconducting fiber obtained by the production method of the present invention is not limited in any way, but in view of practicality, the diameter is usually 1000 μm or less. A preferred diameter is 500 μm or less, a more preferred diameter is 200 μm or less, and an especially preferred diameter is 1.
It is 0 μm or less. Although there is no restriction on the lower limit, it is usually 1 μm or less.

According to the manufacturing method of the present invention, an oxide superconducting fiber having an arbitrary diameter as described in item 1, a porosity of 10% by volume or less, a tensile strength of IMPa or more, and a critical temperature (Tc) of 80 or more is produced. Obtainable.

The oxide superconducting fiber obtained by the production method of the present invention does not contain any inorganic substances other than the oxide superconductor, such as alkali metals, so it is free from various problems caused by alkali metals. It is.

E1 action and effects of the invention The oxide high temperature superconducting fiber of the present invention has high strength and good flexibility, and is extremely effectively used as a superconducting fiber for superconducting magnets and superconducting power transmission lines. Although the oxide high-temperature superconducting fiber of the present invention may be used alone, it is preferable to use it as a stabilized superconducting wire by wrapping a single fiber with a metal such as copper or aluminum. When producing a stabilized superconducting wire, the use of high temperature superconducting fibers having a diameter of 200 μm or less, preferably 100 μm or less increases the cooling effect and improves the flexibility of the superconducting wire.

Specific applications of the oxide high temperature superconducting wire of the present invention include MHD power generation, magnetic levitation trains, superconducting generators, NM
Examples include R-CT and high energy accelerator.

The present invention will be explained in more detail below using Examples.

Measurement method: The critical temperature (Tc) and current density (Jc) of the superconducting fiber were determined by measuring the electrical resistance of the superconducting fiber using a standard four-terminal method. This terminal was a platinum wire with a diameter of 70 μm, and a silver conductive adhesive was used to adhere the sample. Sample temperature was measured using a (chromel-gold + 0.007% iron) thermocouple.

The tensile strength and elongation of the superconducting fibers were measured using an Instron type tensile tester at room temperature with a jack distance of J6-5 mm and a tensile speed of 0.033 m/sec.

Y, 0320g, BaCO369,9g and CuO
After thoroughly mixing 43.3 g of the mixture, it was calcined at 950° C. for 5 hours, then crushed and passed through an 846 mesh filter to obtain calcined powder with a diameter of 15 μm or less.

Reference example 2 Y20! +2 [1g, BaCO369.9g and CuO43.3g were well mixed, held at 950°C for 5 hours, and then cooled to room temperature at a rate of 100°C/hour under an oxygen gas flow to form a single orthorhombic crystal. YBa2Cu3O
An oxide superconductor of 7-z was obtained. Crush this, 846
By passing through the Metsusoyu filter, the diameter is 15 μm.
The following oxide superconductor powder was obtained.

Kamako L plate” - Y(NO3)3・6H20Log, Ba(No3)2
13.6g and CI(NO3)2.38,018.9
Dissolve each g in distilled water, mix and make a total of 3O
It was made into an aqueous solution of 0 mρ. This was placed in a syringe equipped with a syringe needle with a diameter of 0.8 mm, and injected into a 2CO3 aqueous solution of 300 mρ at a concentration of 07 mol/ρ to obtain a fine coprecipitate powder. At this time, a KOH aqueous solution was appropriately added so that the I)H of the system was 7 to 8. The obtained powder was filtered and washed three times with water.
After washing with alcohol, it was dried at 45°C. followed by 85
Calcination was performed at 0° C. for 2 hours to obtain a fine powder of 0.2 μm or less.

Example I The powder log of 15 μm or less prepared in Reference Example 1 was dispersed in 15 g of distilled water. (This is called liquid A) Separately prepared 5% polyvinyl alcohol (hereinafter referred to as PVA)
(Polymerization degree 1700, saponification degree 985 mol%, Na content: 0.05 wt% or less PVA used as sodium acetate) 40% aqueous solution of ammonia partially neutralized isobutyne-maleic anhydride copolymer (viscosity 50 cps ( 3O°C
), pH=7.85) was added and mixed well.

(This will be referred to as Solution B.) Subsequently, Solution A was added to Solution B, and the total amount was concentrated to 3 Og on a hot plate while stirring well to obtain a stock solution.

Next, methanol was used as a coagulating liquid, wet spinning was performed to form a filament, and the filament was wound onto a bobbin. This filament was heated at 40℃
After drying in a dryer, the fibers were placed in a furnace at 980°C and held for 5 minutes, and cooled to room temperature under a flow of oxygen gas at a rate of 100°C/BH to obtain oxide superconducting fibers with a diameter of 110 μm.

The critical temperature (Tc) of this fiber was 82 and the critical current (Jc) at 77K was 2.5 A/cm'.

In addition, the tensile strength is 3.0 MPa and the breaking elongation is 2.9%.
Met.

Example 2 Using the oxide superconductor powder prepared in Reference Example 2, PVA
As polymerization degree 2400, saponification degree 98.5 mol%, Na
Minutes: An oxide superconducting fiber was obtained in the same manner as in Example 1 except that 0.05 wt% or less of sodium acetate was used.

The Tc of this fiber was 8]K, and the Jc at 77K was 1, OA/cm2. Also, the tensile strength is 2.1M
Pa, and the elongation at break was 2.5%.

Example 3 1.0 g of powder having an average particle size of 0.2 μm prepared by the coprecipitation method of Reference Example 3 was dispersed in 15 g of distilled water.

(This will be referred to as liquid C.) Add 5 g of distilled water to 10 g of a separately prepared 5% PVA (polymerization degree 33O0, saponification degree 98.7 mol%, Na content, 0.05% or less as sodium acetate) aqueous solution.
, 30% aqueous solution of partially neutralized ammonia of isobutyne-maleic anhydride-N-phenylmaleimide copolymer (viscosity 520 cp (30 °C), pH = 8', 2) OJO
g and mixed. (This will be referred to as Solution D.) Subsequently, Solution C was added to Solution B and the total amount was concentrated to 35 g on a hot plate while stirring well to obtain a stock solution.

Next, a mixed liquid of [methanol/)1,0] -90/10 (weight ratio) was used as a coagulating liquid, and the filament was formed by wet spinning and wound onto a bobbin. This filament was dried in a dryer at 40°C, then placed in a 980°C oven for 5 minutes, and cooled to room temperature under a flow of oxygen gas at a rate of 100°C to obtain an oxide superconducting fiber with a diameter of 70 μm. .

The Tc of this fiber was 83 and the Jc at 77K was 150 A/cm'. Also, the tensile strength is 25MP
a, the elongation at break was 2.5%.

Claims (17)

[Claims] (1) Prepare a spinning dope by dispersing or dissolving an oxide superconductor or a substance that can become an oxide superconductor through heat treatment in an aqueous solution containing a water-soluble polymer;
A method for producing oxide superconducting fibers, which comprises wet-spinning this spinning stock solution in an organic solvent that is compatible with water and is a non-solvent for water-soluble polymers to obtain precursor fibers for superconducting fibers, followed by heat treatment. . (2) The method for producing an oxide superconducting fiber according to claim 1, wherein the oxide superconductor or the substance that can become an oxide superconductor by heat treatment contains Cu. (3) The oxide superconductor has the general formula LnBa_2Cu_3O
_7_-_x (However, Ln is Y, Lu, Yb, Tm, E
At least one of r, Ho, Dy, Gd, Eu, and Sm, and x represents 0<x≦0.5. ) The method for producing an oxide superconducting fiber according to claim 2, wherein the oxide superconducting fiber is represented by: (4) The oxide superconductor is YBa_2Cu_7_-_x(
The method for producing an oxide superconducting fiber according to claim 3, wherein 0<x≦0.5. (5) Substances that can become oxide superconductors by heat treatment include (a) Ln oxide, nitrate or carbonate (however, Ln
is Y, Lu, Yb, Tm, Er, Ho, Dy, Gd, E
(b) Ba oxide, nitrate, carbonate, acetate, or fluoride; and (c) Cu oxide, nitrate, carbonate, gluconate, or fluoride. A method for producing an oxide superconducting fiber according to claim 2. (6) The method for producing an oxide superconducting fiber according to claim 5, wherein Ln is Y. (7) The method for producing an oxide superconducting fiber according to claim 1, wherein the water-soluble polymer is a polyvinyl alcohol polymer. (8) The method for producing an oxide superconducting fiber according to claim 1, wherein the organic solvent that is compatible with water and is a non-solvent for the water-soluble polymer is methanol. (9) The diameter of the oxide superconducting fiber is substantially 1000 μm
A method for producing an oxide superconducting fiber according to claim 1, which is as follows. (10) The diameter of the oxide superconducting fiber is substantially 500 μm
A method for producing an oxide superconducting fiber according to claim 9 as follows. (11) The diameter of the oxide superconducting fiber is substantially 200 μm
A method for producing an oxide superconducting fiber according to claim 10, which is as follows. (12) The diameter of the oxide superconducting fiber is substantially 100 μm
A method for producing an oxide superconducting fiber according to claim 11, which is as follows. (13) The method for producing oxide superconducting fibers according to claim 12, wherein the oxide superconducting fibers have a diameter of substantially 10 μm or less. (14) The method for producing an oxide superconducting fiber according to claim 1, wherein the oxide superconductor or the substance that can become an oxide superconductor by heat treatment is in powder form. (15) The method for producing an oxide superconducting fiber according to claim 14, wherein the powder has a substantially average particle size of 15 μm or less. (16) The method for producing an oxide superconducting fiber according to claim 15, wherein the powder has a substantially average particle size of 1 μm or less. (17) The method for producing an oxide superconducting fiber according to claim 16, wherein the powder has a substantially average particle size of 0.5 μm or less.