JPH03170303A - Production of superconductor - Google Patents

Abstract

PURPOSE:To obtain a superconducting ceramic thin film having excellent crystal orientation and high critical current density without causing the deviation of composition by coating a surface of a substrate with a molten mixture of a superconducting composition and an alkali halide and removing the alkali halide by evaporation. CONSTITUTION:A substrate is dipped into a solution produced by heating and melting a mixture of a Bi- or Tl-based superconducting composition and an alkali halide such as KCl, LiCl or NaCl to coat the surface of the substrate with the molten mixture. The substrate is preferably a fibrous or tape substrate having a melting point of >=600 deg.C, especially alumina fiber or silver tape surface- coated with SrTiO3. The objective thin film of superconducting ceramic can be produced by evaporating and removing the alkali halide from the molten mixture especially preferably at 770-850 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a superconductor, which forms a superconducting ceramic thin film with excellent superconducting properties on the surface of a base material. , relates to a method for producing superconductors that does not require complicated processes or special equipment.

[Conventional technology]

In recent years, superconducting ceramics that can be used even in the liquid nitrogen temperature range have been discovered, and this has had a major impact on the industry. As a typical example, Y-Ba-Cu-0 based oxide superconducting ceramics are well known. Also,
Recently, Bi-Sr-Ca-Cu-0 system or TffiBa-Ca-Cu-0 system oxide superconducting ceramics have been reported as new types of superconducting ceramics that do not contain rare earth elements. It has excellent stability against atmospheric moisture and carbon dioxide gas, has a constant oxygen content, and has stable superconducting properties.

However, in order to put these superconducting ceramics into practical use, it is essential to make them into wire or tape shapes, and it is difficult to sinter these hard and brittle ceramics in a dense manner while maintaining their superconducting structure. An important technical issue was whether to make it into wire or tape form.

Examples of methods for manufacturing wires, tapes, etc. made of superconducting ceramics include (1) Ceramics Magazine VOL 22 (1987) No.
6, page 526 describes a method for manufacturing wire rods, in which a silver pipe is filled with ceramic powder, the wire is drawn, the wire is wound into a coil shape, and then heat treated in an oxygen atmosphere. (2) According to an announcement by Argonne National Laboratory. , Y-Ba-Cu- in the polymer
(3) Japanese Journal
of Applied Physics, Vol. 2
6 (1987) Supplement 26-3 no 12
On page 11, a solution consisting of nitrates of Y, Ba, and Cu and Y20. , a method for manufacturing a wire rod in which powders of BaCo3 and CuO are mixed, shaped into a linear shape, and then fired. By forming a sol made from an organic metal compound into a tape shape and then sintering it,
A method for obtaining a tape-shaped oxide superconductor, (5) Kagaku Kogyo Nippo published on August 8, 2001, describes the method of filling a pure silver pipe with a Bi-based superconducting composition, and after wire drawing.
Repeat rolling, sintering and pressing until Tc=77.
3K, Jc = 20,000 A/cm2, and a method for obtaining a tape made of superconducting ceramic with good crystal grain orientation, and (6) JP-A No. 64-10530 describes L
A method has been proposed in which a substrate is immersed in a melt of an a-based superconducting compound, pulled up, rapidly cooled, and then annealed to produce a superconducting thin film.

[Problem that the invention seeks to solve]

However, the previously known methods for manufacturing superconductors as described above have various drawbacks. In other words, in method (1), the ceramic powder is heat-treated in a metal pipe, which makes it difficult to densify it, making it difficult to obtain sufficient superconducting contact between the particles of the sintered body, and causing significant changes in properties. The drawback is that it is difficult to precisely control the amount of oxygen that affects the method.

With method (2), it is difficult to maintain the shape from the time the polymer burns until the start of sintering, and when trying to sinter it densely, the crystal grains elongate, which affects the mechanical properties. The problem is that the superconducting properties tend to deteriorate or decompose, resulting in a significant drop in superconducting properties.

Method (3) has the problem that when the wire is sintered densely, the crystal grains become elongated, which deteriorates the mechanical properties of the resulting wire, and in particular, the flexibility tends to deteriorate. .

The method (4) has a problem in that it requires a long heat treatment after shaping.

In method (5), it was necessary to repeat pressing and sintering in order to improve the orientation of crystal grains, which was complicated.

In method (6), since the melting point of the superconducting composition is generally extremely high, there are problems in that the base materials that can be used are limited to those with particularly high heat resistance.

[Means for solving problems]

Therefore, the inventors of the present invention conducted intensive research to develop a method for manufacturing a superconductor that can solve the above-mentioned drawbacks, and as a result, they developed the present invention having the following gist and structure.

The gist of the present invention is to form a thin film made of superconducting ceramics by coating the surface of a base material with a melted mixture of superconducting composite material and alkali halide, and then evaporating and removing the alkali halide. This is a method for manufacturing a superconductor characterized by the following.

That is, in the present invention, after coating the surface of a flexible base material with a mixed melt of a superconducting composition and an alkali halide, when the alkali halide, which is a solvent, is evaporated off, the surface of the base material is coated. , a superconducting ceramic with extremely excellent crystal orientation is precipitated, and a superconductor is obtained.

In the present invention, the superconducting compound is a compound soluble in a melt of alkali halide, especially Bi-based or TI! ．． A system superconducting kumikaimono is suitable. Further, the alkali halide is KCl, LiCI! ．． and Na
It is at least one selected from Cl, and the base material preferably has a melting point of 600"C or more.

[Effect]

According to the present invention, it is necessary to coat the surface of a substrate with a mixed melt of a superconducting composition and an alkali halide, and then remove the alkali halide by evaporation. The reason is that after coating the surface of the base material with a mixed melt in which the superconducting composition is dissolved in an alkali halide solvent,
By gradually evaporating the alkali halide, which is a solvent, and concentrating the superconducting composition to create a supersaturated state, superconducting ceramics with no deviation in composition and excellent crystal orientation can be precipitated. This is because it is possible.

The coating of the melted mixture of the superconducting composition and the alkali halide can be done by coating the surface of the substrate with the mixture of the superconducting composition and the alkali halide and then heating and melting it, or by melting the superconducting composition and the alkali halide together. It is preferable to perform this by immersing the base material in a mixed melt of.

According to the present invention, the superconducting composition can be suitably used as long as it is a compound that is soluble in an alkali halide melt and crystallizes at a temperature of 600°C or higher; for example, A Bi-based or Tffi-based superconducting composition is preferable.

The mixture of the Bi-based or Tl-based superconducting composition and alkali halide is preferably melted at a temperature in the range of 770°C to 850°C. The reason for this is that it is difficult to melt a mixture of a Bi-based or Tl-based superconducting composition and an alkali halide at temperatures below 770°C;
This is because at temperatures above 0°C, the alkali halide evaporates extremely rapidly, making it difficult to obtain a stable mixed melt.

The Bi-based superconducting composition includes at least an element selected from the group consisting of bismuth, bismuth and alkhenium, bismuth and lead, bismuth and potassium, bismuth and yttrium, an alkaline earth metal, copper, and oxygen. For example, BiSrCaCut O
X, Biz SrzCa, -XY. Cu. Oy, Bi
．． −． PbXSr. Ca. Cu. OvSBi+-xAI
XSrCaCuz Ov, B i S rzy3C
az/3Ktyx Cu20v, B t2Srz Cu
z O. It is preferable to use one that generates CeraQ'7x such as v. The Tf-based superconducting composition is composed of at least thallium, an element selected from the group consisting of thallium and lead, an alkaline earth metal, copper, and oxygen, such as Tffi. Ba. Ca2Cui
O'. , T No. 5P bo. 5 S r x C a
A material that supports ceramics, such as 2 C Hz○3, is suitable.

The Bi-based superconducting ceramics and TI2-based superconducting ceramics ξ
Traditionally, Tsukusu had drawbacks such as requiring a long heat treatment during production, but according to the production method of the present invention,
A thin film of superconducting ceramics can be easily grown on the surface of a substrate, and the C-axis of the resulting superconducting ceramic crystal is oriented in a direction perpendicular to the surface of the substrate.
It is possible to form superconducting ceramic thin films with extremely high critical current densities.

According to the present invention, it is preferable to use an alkali halide that dissolves the target superconducting composition and can be removed by evaporation at as low a temperature as possible, for example,
KCI, LiCI! ．． It is advantageous to use at least one selected from NaCl and NaCl.

According to the present invention, the temperature at which the alkali halide is removed by evaporation from the mixed melt is particularly preferably 770°C to 850°C.

According to the present invention, the base material has a melting point of 600″C.
The above is desirable.

Further, as the base material, either a single crystal or a polycrystalline body can be used, and in particular, by using a single crystal body as the base material, the epitaxial film of the superconducting ceramic can be easily extended to a certain length. .

Examples of the base material include noble metals, noble metal-containing alloys,
AlltO3, cZroz, SiC, quartz, mullite, etc. are suitable, and the shape is preferably fibrous or tape-like.

Said A/! ．． O. , SiC, quartz, mullite, etc. as a base material, TiOz, MgO, etc. are added to the surface.
, cZroz, SrTiOi, a noble metal or an alloy containing a noble metal.

Moreover, in the present invention, in particular, S r T i O on the surface
Alumina fiber and silver tape coated with No. 3 can be suitably used as the base material.

According to the present invention, the atmosphere in which the alkali halide is evaporated and removed from the molten mixture of the superconducting composite material and the alkali halide is not limited to a specific atmosphere;
Although either normal pressure or pressurized atmosphere can be used, it is advantageous to carry out the process in an oxidizing atmosphere, especially when producing oxide superconductor films.

Furthermore, in the present invention, when the obtained superconducting ceramic ξ is in a low Tc phase, it is preferable to heat treat it to convert it into a high Tc phase.

Further, the temperature of the heat treatment is preferably 830°C to 860°C.

〔Example〕

Next, embodiments of the present invention will be described in detail.

Example l l2 B L Os , SrCOs , CaCO,,
, CuO has the elemental composition Bi:Sr:Ca:Cu=1.6:
0.4:1.6:2. Mix so that o: 2.8,
Heated at 800'C for 12 hours. The obtained calcined body was pulverized, fired at 840 degrees, and then cooled in a furnace to room temperature.

The process from crushing to furnace cooling was repeated several times.

100 times the molar ratio of K (l) was added to the obtained powder and mixed using ethanol. This mixed powder was spread on a silver tape and heated at 840°C for about 3 hours to evaporate KCI. At this time, during the evaporation process, Bi-Sr-CaCu-0 dissolved in K(l) was concentrated and reached a supersaturated state, and gradually precipitated on the base material to obtain a superconducting tape.

Example 2 (1) BizOs, SrCOa, CaCOa, Cu
O is the element group Bi:Sr:Ca:Cu=1.6go. 4
:1,6:2. o: Mixed to 2.8, 800
Heated at °C for 12 hours. The obtained calcined body is pulverized, and then 100 times the molar ratio of KCI1 is added to the powder, mixed using ethanol, and 1. 0% and 19.0% butyl carbitol acetate were added and kneaded to form a paste.

(2) A film of S r Ti O 3 was coated on the surface of an alumina fiber (15 μm) by a sol-gel method.

(3) The paste obtained in (1) above was applied to the alumina fiber obtained in (2) above, dried, and then heated at 840° C. for about 5 hours to evaporate KCl. At this time, B dissolved in KCj2 during the evaporation process
i-Sr-Ca-Cu-0 was concentrated and reached a supersaturated state, and gradually precipitated on the base material to obtain a superconducting wire.

Example 3 (1) TffiZ 03 , BaCO3 , CaCO.
, CuO in the elemental group or TI! ．． :Ba:Ca:C
Mix in a ratio of u-2:2:2:3,
It was heated at 800°C for 12 hours. The obtained calcined body was pulverized, 20 times the molar ratio of NaCl was added to the obtained powder, mixed using ethanol, and 1.0% of ethyl cellulose and butyl carbitol acetate were added to the powder. 19.0% was added and kneaded to make a paste.

(2) By applying a magnesium chloride solution to the surface of Aluminum fiber (15 μm) and heat-treating it, M
A film of gO was coated.

(3) The paste obtained in (1) above was applied to the alumina fiber obtained in (2) above, dried, and then heated at 840°C for about 5 hours to evaporate NaCl. . At this time, T4, which had been dissolved in NaCl during the evaporation process! -Ba-Ca-CuO was concentrated and reached a supersaturated state, and gradually precipitated on the base material to obtain a superconducting wire.

Example 4 This example is basically the same as Example 1, but the superconducting tape obtained in Example 1 was further treated at 845°C for 15
A heat treatment of 0 hours was applied.

Example 5 (1) B iz C)+, SrCO3, CaC
O3, CuO elemental composition (molar ratio) Bi:Sr:Ca:
l5Cu=1. 6:0. 4:1. 6:2.
O:2. The mixture was mixed in a ratio of 8 to 8, and heated at 800°C for 12 hours.

The obtained calcined body was pulverized, and 100 mol of KCI was mixed with 1 mol of powder in terms of Bi-based superconducting ceramic.
This was placed in a platinum crucible and heated at 800°C to form a molten liquid.

(2) A silver tape (thickness: 1 mm, width: 3 mm, length: 200 mm) was immersed in the melt obtained in (1) above.

(3) Next, KCI was evaporated and removed by heating at 800° C. for 3 hours while immersed, to obtain a superconducting tape.

(4) The superconducting tape obtained in (3) above was heated to 840°C.
Heat treatment was performed for 150 hours.

Example 6 (1) Bi203, SrCO3, CaCO3, Cu
The elemental composition (molar ratio) of O is Bi:Sr:Ca:Cu=1.
Mixed at a ratio of 6:0.4:1.6:2.0:2.8,
Heated at 800'C for 12 hours.

The obtained calcined body was pulverized, and 200 mol of NaCI was mixed with 1 mol of Bi-based superconducting ceramic powder, which was placed in a platinum crucible and heated at 800'C to melt. It was made into a liquid.

(2) Alumina fiber was immersed in the melt obtained in (1) above. (3) Then, while immersed, it was heated at 800"C for 3 hours to evaporate KCI and obtain a superconducting ceramic wire. .

(4) The superconducting wire obtained in (3) above was heated to 840°C.
It was heated for 100 hours.

Example 7 (1) Tzz 03, BaCO. , CaCO3,
CuO is divided into elemental composition (molar ratio) Tl:Ba:Ca
:Cu=2:2:2:3 and calcined at 800°C for 12 hours. The obtained calcined body was pulverized, and 200 mol of NaCI was mixed with 1 mol of powder in terms of TN-based superconducting ceramic, and this was placed in a platinum crucible and heated at 800°C to form a molten liquid. .

(2) 0.07 mol of metallic strontium and 0.07 mol of titanium tetraisoproboxide were dissolved in 300 g of 2-ethoxyethanol to form a homogeneous solution, and this solution was concentrated using an evaporator until it reached 100 g.

(3) After immersing an alumina fiber (fiber diameter 15 μm) in the solution obtained in (2) above and pulling it up,
Heat treatment was performed at 00°C for 10 minutes.

(4) After repeating the step (3) above 40 times, 10
Heat treatment was performed at 00'C for 1 hour to obtain an alumina fiber on which a strontium titanate layer with a thickness of 0.2 μm was formed.

(5) The alumina fiber obtained in step (4) above was immersed in the melt obtained in step (1) above, and then pulled up to coat it with the melt.

(6) Next, NaCI was evaporated off by heating at 800°C for 3 hours to obtain a superconducting ceramic wire.

(7) The superconducting ceramic wire rod was heated to 150°C at 840°C.
Heat treated for hours.

Example 8 This example is basically the same as Example 6, except that 78
KCI was removed by evaporation at 0°C to obtain a superconducting ceramic wire.

Example 9 This example is basically the same as Example 6, except that continuous fibers of superconducting ceramics ξ were produced using the apparatus shown in FIG. By immersing the alucina fiber 2 sent out from the uncoiler 1 in the mixed melt 5 of the superconducting composition and KCI, which has been heated to 773°C by the heating device 4 and is in a molten state, 5 was coated and further heated at 800° C. with a heating device 4° to evaporate and remove KCI, thereby obtaining a superconducting ceramic continuous fiber.

The superconducting tapes and wires obtained in Examples 1 to 9 were cut into constant lengths, and changes in electrical resistance in zero magnetic field were measured while controlling the temperature of the test pieces for measuring superconducting properties. In addition, current density was measured in liquid nitrogen. These results are shown in Table I.

19 Table 1 [Effects of the Invention] As described above, according to the present invention, superconducting ceramic wires and superconducting ceramic tapes with excellent flexibility, superconducting properties, and mechanical strength can be produced by a simple process. The superconducting ceramic wires and superconducting tapes obtained can be easily manufactured without using special equipment, and have practical applications in various fields such as electronics, energy, and medical fields. It is an expensive material and is industrially useful.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a superconducting ceramic continuous fiber manufacturing apparatus used in Example 9. 1- Uncoiler 2- Aluminum fiber 3- Guide 4, 4" - Heating device 5 - Mixed melt of superconducting & IItc material and KCI 6
- Recoiler 7 - Container 8 - Superconducting ceramic continuous fiber

Claims (1)

[Claims] 1. A thin film made of superconducting ceramics is formed by coating the surface of a base material with a melted mixture of a superconducting composition and an alkali halide, and then evaporating and removing the alkali halide. A method for producing a superconductor. 2. The method for producing a superconductor according to claim 1, wherein the coating of the mixed melt is performed by coating the surface of the substrate with the mixture of the superconducting composition and the alkali halide, and then heating and melting the mixture. 3. The method for producing a superconductor according to claim 1, wherein the coating of the mixed melt is performed by immersing the substrate in a melt obtained by heating and melting a mixture of a superconducting composition and an alkali halide. 4. The method for producing a superconductor according to claim 1, wherein the superconducting composition is a compound soluble in a melt of alkali halide. 5. The method for producing a superconductor according to claim 1, wherein the superconducting composition is a Bi-based or Tl-based superconducting composition. 6. The method for producing a superconductor according to claim 1, wherein the alkali halide is at least one selected from KCl, LiCl, and NaCl. 7. The method for producing a superconductor according to claim 1, wherein the base material has a melting point of 600° C. or higher. 8. The method for producing a superconductor according to claim 1, wherein the base material is in the form of a fiber or a tape.