JP2822328B2 - Superconductor manufacturing method - Google Patents

Description

The present invention relates to a method for producing a superconductor in which a Bi-based or Tl-based superconducting ceramic thin film having excellent superconductivity is formed on the surface of a substrate, In particular, the present invention relates to a method for manufacturing a superconductor that does not require complicated processes or special equipment.

[Prior Art] In recent years, superconducting ceramics that can be used even in the liquid nitrogen temperature range have been discovered, and have had a great impact industrially. As a typical example, a Y-Ba-Cu-O-based oxide superconducting ceramic is well known. Recently, Bi-Sr-Ca-Cu-O-based or Tl-Ba-
Ca-Cu-O based oxide superconducting ceramics have been reported. These oxide superconducting ceramics have excellent stability against moisture and carbon dioxide in the atmosphere, and have a stable oxygen content and stable superconductivity. There is a feature that there is.

However, in order to put these superconducting ceramics into practical use, it is indispensable to make them into a wire or tape.However, the hard and brittle ceramics must be sintered densely while maintaining the superconducting composition. It was an important technical issue whether to make a tape.

Examples of the method of manufacturing wires and tapes made of superconducting ceramics include, for example, (1) A method in which ceramic powder is filled in a silver pipe and drawn on page 526 of Ceramics Vol.22 (1987) No.6. (2) According to the publication of the Argonne National Research Report, a polymer is mixed with Y-Ba-Cu-O powder to form a wire, which is then wound into a coil and then heat-treated in an oxygen atmosphere. Method of manufacturing wire made of superconducting ceramics to burn flexible wire into flexible wire, (3) Japanese Journal of Applied Physics, Vol.26
(1987) Supplement 26-3, page 1211, Manufacturing a wire rod that mixes a solution consisting of nitrates of Y, Ba, and Cu with powders of Y ₂ O ₃ , BaCO ₃ , and CuO, shapes the wire, and fires it. (4) Japanese Patent Application Laid-Open No. 63-270316 discloses a method in which a sol made from an organometallic compound containing an element constituting an oxide superconductor is formed into a tape and then sintered to form a tape. (5) The Chemical Daily published on August 8, 1999, stated that a Bi-based superconducting composition was filled in a pure silver pipe, drawn, rolled, Repeat sintering and pressing, Tc = 77.3K, Jc
= A method of obtaining a tape made of a superconducting ceramic having superconducting properties of 20,000 A / cm ^{2 and} good crystal grain orientation; and (6) JP-A-64-10530 discloses a Y or La-based A method has been proposed in which a substrate is immersed in a melt of a superconducting compound, pulled up, rapidly cooled, and then annealed to produce a superconducting thin film.

[Problems to be Solved by the Invention] However, the conventionally known methods for manufacturing a superconductor as described above have various disadvantages. That is, in the method (1), since the ceramic powder is heat-treated in the metal pipe, it is difficult to densify the ceramic powder, it is difficult to obtain a sufficient superconducting contact between the particles of the sintered body, and the characteristics are greatly affected. There is a disadvantage that precise control of oxygen is difficult.

In the method (2), it is difficult to maintain the shape between the time when the polymer is burned and the time when the sintering is started. There is a problem that the superconductivity is easily deteriorated or deteriorated due to decomposition.

The method (3) has a problem in that if the wire is to be sintered densely, the mechanical properties of the wire obtained by growing crystal grains are deteriorated, and in particular, the flexibility tends to be deteriorated.

The method (4) has a problem that a long heat treatment is required after molding.

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

In the method (6), since the melting point of the superconducting composition is generally extremely high, there is a problem that the usable base material is limited to a particularly high heat-resistant material.

[Means for Solving the Problems] Accordingly, the present inventors have conducted intensive studies to develop a method of manufacturing a superconductor capable of solving the above-mentioned disadvantages, and as a result, have obtained a book having the following summary. The invention has been developed.

The gist of the present invention is to coat a mixed melt of a Bi-based or Tl-based superconducting composition and an alkali halide on the surface of a substrate,
This is a method for producing a superconductor, characterized in that a thin screen made of a Bi-based or Tl-based superconducting ceramic is formed by evaporating and removing an alkali halide at a temperature of from 840C to 840C.

That is, in the present invention, after coating a mixed melt of a Bi-based or Tl-based superconducting composition and an alkali halide on the surface of a flexible substrate, the alkali halide as a solvent is heated at 770 to 840 ° C. When it is removed by evaporation, Bi- or Tl-based superconducting ceramics with extremely excellent crystal orientation are deposited on the surface of the base material, and a superconductor is obtained.

In the present invention, a Bi-based or Tl-based superconducting composition which is a compound soluble in a molten alkali halide is used as the superconducting composition. Further, as the alkali halide, it is possible to use at least one selected from KCl, LiCl and NaCl, and as the base material,
The melting point is preferably 600 ° C. or higher.

[Action] According to the present invention, it is necessary to coat the surface of a base material with a mixed melt of a Bi-based or Tl-based superconducting composition and an alkali halide, and then remove the alkali halide by evaporation at 770 to 840 ° C. It is. The reason is that when the superconducting composition is dissolved in a solvent of alkali halide, after coating the mixed melt on the surface of the base material, the alkali halide, which is the solvent, is gradually evaporated to form the superconducting composition. This is because, by concentrating and producing a supersaturated state, superconducting ceramics having no composition deviation and extremely excellent crystal orientation can be deposited.

The coating of the mixed melt of the Bi-based or Tl-based superconducting composition and the alkali halide is performed by coating the base material surface with the mixture of the Bi-based or Tl-based superconducting composition and the alkali halide, and then heating and melting. Alternatively, it is preferable to perform the process by immersing the base material in a mixed melt of a Bi-based or Tl-based superconducting composition and an alkali halide.

In the present invention, a Bi-based or Tl-based superconducting composition that is soluble in an alkali halide melt and crystallizes at a temperature of 600 ° C. or higher is used as the superconducting composition. Said
The mixture of the Bi-based or Tl-based superconducting composition and the alkali halide is preferably melted in a temperature range of 770 ° C to 850 ° C. The reason is that it is difficult to melt a mixture of a Bi-based or Tl-based superconducting composition and an alkali halide at 770 ° C or lower, and at 850 ° C or higher, the evaporation of the alkali halide becomes extremely vigorous. This is because it is difficult to obtain a liquid.

The Bi-based superconducting composition comprises at least an element selected from the group consisting of bismuth, bismuth and aluminum, bismuth and lead, bismuth and potassium, bismuth and yttrium, an alkaline earth metal, copper and oxygen. And, for example, BiSrCaCu ₂ O _X , Bi ₂ Sr ₂ Ca _1-X
Y _X Cu ₂ O _Y , Bi _2-X Pb _X Sr ₂ Ca ₂ Cu ₃ O _Y , Bi _1-X Al _X SrCaCu ₂ O _Y , B
Those that produce ceramics such as iSr _2/3 Ca _2/3 K _2/3 Cu ₂ O _Y and Bi ₂ Sr ₂ Cu ₂ O _{7 + y} are suitable. The Tl-based superconducting composition is at least thallium, an element selected from the group consisting of thallium and lead, an alkaline earth metal, copper and oxygen, for example, Tl ₂ Ba ₂ Ca ₂ O
_X , Tl _0.5 Pb _0.5 Sr ₂ Ca ₂ Cu ₂ O _{3 and the} like which form ceramics are suitable.

Conventionally, Bi-based superconducting ceramics and Tl-based superconducting ceramics have disadvantages such as requiring a long-time heat treatment during production.However, according to the production method of the present invention, superconducting Since the ceramic thin film can be easily grown, and the c-axis of the obtained superconducting ceramic crystal is oriented in the direction perpendicular to the substrate surface, a superconducting ceramic thin film with an extremely large critical current density is formed. it can.

According to the present invention, it is preferable to use, as the alkali halide, one that dissolves the desired superconducting composition and that can be removed by evaporation at a low temperature, for example, any one selected from KCl, LiCl and NaCl. It is advantageous to use at least one.

In the present invention, it is necessary to evaporate and remove the alkali halide from the mixed melt at 770 ° C to 840 ° C.

According to the present invention, the base material preferably has a melting point of 600 ° C. or higher. Further, as the substrate, either a single crystal or a polycrystal can be used. In particular, by using a single crystal as a substrate, an epitaxial film of a superconducting ceramic can be easily grown.

As the base material, for example, a noble metal, a noble metal-containing alloy, Al ₂ O ₃ , cZrO ₂ , SiC, quartz, mullite, or the like is suitable, and its shape is desirably a fibrous form or a form on a tape.

When the above-mentioned Al ₂ O ₃ , SiC, quartz, mullite, etc. are used as the base material, TiO ₂ , MgO, cZrO ₂ , SrTi
It is desirable to coat O ₃ , a noble metal or an alloy containing a noble metal.

In the present invention, in particular, an alumina fiber coated with SrTiO _{3 on} its surface and a silver tape can be suitably used as the base material.

According to the present invention, the atmosphere for evaporating and removing the alkali halide from the mixed melt of the Bi-based or Tl-based superconducting composition and the alkali halide is not limited to a specific atmosphere, but may be reduced pressure, normal pressure or pressure. Although any atmosphere under pressure can be used, it is advantageous to carry out in an oxidizing atmosphere, particularly when producing an oxide superconductor film.

Further, in the present invention, when the obtained superconducting ceramics has a low Tc phase, it is preferable that the superconducting ceramics be subjected to a heat treatment to make it a high Tc phase.

The temperature of the heat treatment is desirably 830 ° C to 860 ° C.

Example Next, an example of the present invention will be described in detail.

Example 1 Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , and CuO were converted to a chlorine composition Bi: Sr: Ca: Cu =
The mixture was mixed at 1.6: 0.4: 1.6: 2.0: 2.8 and heated at 800 ° C. for 12 hours. The obtained calcined body was pulverized, fired at 840 ° C., and then furnace-cooled to room temperature. The process from grinding to furnace cooling was repeated several times.

A 100-fold molar ratio of KCl was added to the obtained powder, and mixed using ethanol. The mixed powder was applied to a silver tape and heated at 840 ° C. for about 3 hours to evaporate KCl. At this time, Bi-Sr-Ca dissolved in KCl during the evaporation process
-Cu-O was concentrated and reached a supersaturated state, and was gradually deposited on the substrate to obtain a superconducting tape.

Example 2 (1) Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO are elementally composed of Bi: Sr: Ca: C
u = 1.6: 0.4: 1.6: 2.0: 2.8
Heated for 2 hours. The obtained calcined body was pulverized, and then KCl having a molar ratio of 100 times was added to the powder, and the mixture was mixed with ethanol.
%, And 19.0% of butyl carbitol acetate were added and kneaded to prepare a paste.

(2) A surface of alumina fiber (15 μm) was coated with a SrTiO ₃ film by a sol-gel method.

(3) After applying the paste obtained in the above (1) to the alumina fiber obtained in the above (2) and drying it,
Heat at 840 ° C. for about 5 hours to evaporate the KCl. At this time, Bi-Sr-Ca-Cu dissolved in KCl during the evaporation process
-O was concentrated and reached a supersaturated state, and was gradually deposited on the base material to obtain a superconducting wire.

Example 3 (1) Tl ₂ O ₃ , BaCO ₃ , CaCO ₃ , CuO were added to the elemental composition, Tl: Ba:
The mixture was mixed so that Ca: Cu = 2: 2: 2: 3 and heated at 800 ° C. for 12 hours. The obtained calcined body was crushed, and a 20-fold molar ratio of NaCl was added to the obtained powder, and mixed using ethanol,
Further, 1.0% of ethyl cellulose and 19.0% of butyl carbitol acetate were added to the powder and kneaded to prepare a paste.

(2) A MgO film was coated by applying a magnesium chloride solution to the surface of the alumina fiber (15 μm) and performing a heat treatment.

(3) The paste obtained in the above (1) was applied to the alumina fiber obtained in the above (2), dried, and then heated at 840 ° C. for about 5 hours to evaporate NaCl. At this time, Tl-Ba-Ca dissolved in NaCl during the evaporation process
-Cu-O was concentrated and reached a supersaturated state, and was gradually deposited on the substrate to obtain a superconducting wire.

Example 4 This example is basically the same as Example 1, except that the superconducting tape obtained in Example 1 was further subjected to a heat treatment at 845 ° C. for 150 hours.

Example 5 (1) Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO are elemental compositions (molar ratio)
Bi: Sr: Ca: Cu = 1.6: 0.4: 1.6: 2.0: 2.8 mixed at 80
Heated at 0 ° C. for 12 hours.

The obtained calcined body was pulverized, converted into a Bi-based superconducting ceramic, mixed with 100 mol of KCl to 1 mol of the powder, placed in a platinum crucible and heated at 800 ° C. to obtain a molten liquid.

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

(3) Then, KCl 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 the above (3) is heated at 840 ° C for 150 hours.
Heated for hours.

Example 6 (1) Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO are elemental composition (molar ratio)
Bi: Sr: Ca: Cu = 1.6: 0.4: 1.6: 2.0: 2.8 mixed at 80
Heated at 0 ° C. for 12 hours. The obtained calcined body was pulverized, and NaCl was added to 1 mol of powder in terms of Bi-based superconducting ceramic.
0 mol was mixed, and this was put into a platinum crucible and heated at 800 ° C. to obtain a molten liquid.

(2) An alumina fiber was immersed in the melt obtained in the above (1).

(3) Then, while immersed, heat at 800 ° C for 3 hours to add KCl
Was removed by evaporation to obtain a superconducting ceramic wire.

(4) The superconducting wire obtained in (3) above is
Heated for hours.

Example 7 (1) Tl ₂ O ₃ , BaCO ₃ , CaCO ₃ , and CuO are mixed so that the element composition (molar ratio) Tl: Ba: Ca: Cu = 2: 2: 2: 3, and 800 ° C.
For 12 hours. The obtained calcined body was pulverized, and converted to Tl-based superconducting ceramic, and NaCl was added to 200 mol of powder in 1 mol.
The mixture was mixed in a mole, and the mixture was put in a platinum crucible and heated at 800 ° C. to obtain a melt.

(2) 0.07 mol of metal strontium and 0.07 mol of titanium tetraisopropoxide are mixed in 300 g of 2-ethoxyethanol.
Into a homogeneous solution, and this solution is evaporated with an evaporator.
It was concentrated to 100 g.

(3) An alumina fiber (fiber diameter: 15 μm) is immersed in the solution obtained in the above (2), and after pulling it up, 500
Heat treated at 10 ° C. for 10 minutes.

(4) After repeating step (3) for 40 times, heat treatment was performed at 1000 ° C. for 1 hour to obtain an alumina fiber having a 0.2 μm thick strontium titanate layer.

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

(6) Then, the mixture was heated at 800 ° C. for 3 hours to evaporate and remove NaCl to obtain a superconducting ceramic wire.

(7) The superconducting ceramic wire was heat-treated at 840 ° C. for 150 hours.

Example 8 This example is similar to Example 6 in terms of a base tree, but is similar to Example 6.
At 0 ° C, KCl was removed by evaporation to obtain a superconducting wire ceramic wire.

Example 9 This example is basically the same as Example 6, but
Using the apparatus shown in FIG. 1, continuous fibers of superconducting ceramics were produced. The alumina fiber 2 sent out from the uncoiler 1 is mixed at a temperature of 773 ° C. with a heating device 4 at a temperature of 773 ° C. in a molten state.
The melt 5 was coated by immersion in the solution, and KCl was evaporated and removed by heating at 800 ° C. with a heating device 4 ′ to obtain a superconducting ceramic continuous fiber.

The superconducting tapes and wires obtained in Examples 1 to 9 were cut to a predetermined length, and the change in electric resistance in a zero magnetic field was measured while controlling the temperature of the test piece for measuring superconductivity. The current density was measured in liquid nitrogen. The results are shown in Table 1.

[Effects of the Invention] As described above, according to the present invention, a superconducting ceramic wire or a superconducting ceramic tape having excellent flexibility, superconducting characteristics and mechanical strength can be manufactured by a simple process using a special device. The superconducting ceramic wire and the resulting superconducting ceramic tape are highly practical materials in various fields such as the electronics, energy, and medical fields. It is informative.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus for producing continuous superconducting ceramic fibers used in Example 9. DESCRIPTION OF SYMBOLS 1 ... Uncoiler, 2 ... Alumina fiber 3 ... Guide, 4 and 4 '... Heating device 5 ... Mixed melt of superconducting composition and KCl 6 ... Recoiler, 7 ... Container 8 ... Superconductivity Ceramic continuous fiber

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Takeya 7-12-11 Roppongi, Minato-ku, Tokyo (56) References JP-A 1-275435 (JP, A) JP-A 2-26807 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 1/00-57/00 H01B 12/00 H01L 39/00-39/24

Claims (6)

(57) [Claims] 1. A method of coating a surface of a base material with a mixed melt of a Bi-based or Tl-based superconducting composition and an alkali halide, and removing the alkali halide by evaporation at 770 to 840 ° C. A method for producing a superconductor, comprising forming a thin film. 2. The production of a superconductor according to claim 1, wherein the coating of the mixed melt is carried out by coating a mixture of a superconducting composition and an alkali halide on the surface of a substrate and then heating and melting the mixture. Method. 3. The method for producing a superconductor according to claim 1, wherein the coating of the mixed melt is performed by immersing a base material in a melt obtained by heating and melting a mixture of a superconductive composition and an alkali halide. 4. The method according to claim 1, wherein the alkali halide is at least one selected from KCl, LiCl and NaCl. 5. The method according to claim 1, wherein the base material has a melting point of 600 ° C. or higher. 6. The method for manufacturing a superconductor according to claim 1, wherein said base material is in the form of a fiber or a tape.