JP2966442B2 - Bi-based oxide superconductor and method for producing wire thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention is promising as an isoconducting magnet wire for magnetic resonance tomography (MRI-CT), a conductive material for superconducting power transmission, and a magnetic shielding material. Is under development
The present invention relates to a method for producing a Bi-based high critical temperature oxide superconductor.

(Prior art) Recently, critical temperature at which transition from normal conducting state to superconducting state
Oxide superconductors such as Y (yttrium) group, Bi (bismuth) group, Tl (thallium) group, and the like, in which Tc has a value exceeding the boiling temperature of liquid nitrogen, have been discovered. In a Bi-based oxide superconductor, the phase of the composition represented by Bi ₂ Sr ₂ CaCu ₂ O _X has a Tc of about 80 K,
A phase having a composition represented by Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _Y having a Tc of about 105 K is usually produced in a mixed state, but recently, a part of Bi has been replaced by Pb to 105 K It is known that the proportion of the phase having a high Tc is large. Since these oxide-based superconductors can be used under significantly more advantageous cooling conditions than conventional metal-based superconductors such as Nb-Ti and Nb ₃ Sn, which had to be cooled with liquid helium, Research and development are proceeding as superconducting materials that are extremely promising in practical use. In particular, Bi-based oxide superconductors have attracted attention because they can obtain Tc of 100 K or more without containing any toxic elements such as Tl. Since the oxide superconductor has extremely brittle mechanical properties, the following method is used as an example of a method of processing into a wire shape. That is, a plurality of raw material powders containing the elements constituting the oxide superconductor are calcined, unnecessary components are removed, and then the calcined powder is formed into a wire having a desired diameter or a tape having a desired thickness. This is a method for producing an oxide superconductor having a desired composition by subjecting it to a heat treatment by a solid phase reaction to produce a superconducting wire.

(Problems to be Solved by the Invention) However, in the conventional production method, it is difficult to completely and uniformly mix the raw material powders, so that even when heat treatment is performed, the entire superconductor does not have a completely uniform composition. was there. In particular, it was practically impossible to produce a superconductor having a uniform composition over the entire length of a long wire. For this reason, a local portion having insufficient superconducting characteristics is formed with an inappropriate composition, and as a result, there is a problem that the characteristics of the entire wire are limited by the local characteristics.

The oxide superconductor formed inside the above-mentioned wire is obtained by sintering a compact obtained by compressing powder by a solid-phase reaction, and has a large number of fine pores inside. For this reason, there is a problem in that it lacks in denseness as compared with conventional alloys and intermetallic compounds, and it is difficult to increase the critical current density Jc which is practically important.

Further, in the Bi-based oxide-based superconductor, a long time such as several hundred hours is required for heat treatment in order to generate a high Tc phase.

The present invention makes it possible to obtain a dense oxide superconductor having a uniform composition, and it is also possible to extremely easily control the minute adjustment of component elements and the addition of other elements, and to obtain a high Tc by a short-time heat treatment. It is an object of the present invention to provide a Bi-based oxide superconductor that can be used and a method for manufacturing a wire rod.

(Means for Solving the Problems) In order to achieve the object, a method for producing a Bi-based oxide superconductor of the present invention comprises dissolving a compound containing Bi, Sr, Ca, and Cu in an inorganic acid, and dissolving the compound in distilled water. Dilute, add hydroxylic acid, polyhydric alcohol, heat and stir to generate organic acid salts,
The gel-like reaction product obtained by dehydration and cooling is thermally decomposed,
Heat treatment is performed after the precursor is formed.

Further, the method for producing a Bi-based oxide superconductor of the present invention comprises dissolving at least a compound containing Sr and Ca in an inorganic acid, adding a hydroxyl acid and a polyhydric alcohol to form an organic acid salt, and then dehydrating. Precursor A obtained by subjecting the obtained reaction product to thermal decomposition treatment, and precursor B produced by subjecting a compound containing at least Bi and Cu to the same treatment are mixed and heat-treated.

Here, the precursor refers to an ash-like substance obtained after removing water, residual gas and organic components contained in the gel by thermal decomposition of the gel-like organic acid salt. In addition, examples of the inorganic acid include nitric acid, hydrochloric acid, and sulfuric acid. Examples of the hydroxyl acid include citric acid, tartaric acid, and polyacrylic acid, and the use of citric acid or polyacrylic acid is preferred. Examples of the polyhydric alcohol include dihydric or higher polyhydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol, glycerin, and trihydroxybenzene, and the use of ethylene glycol or diethylene glycol is preferred.

Further, the Bi-based oxide superconductor produced in the present invention is a mixture of Bi ₂ Sr ₂ CaCu ₂ O _X , Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _Y and Bi described above, and a part of Bi of the precursor B. Includes compositions substituted with Pb.

Further, in the method for producing a Bi-based oxide superconductor of the present invention, the primary or the mixture of the precursor A and the precursor B obtained by the above-described production method has a primary temperature in the range of 600 ° C to 820 ° C. Heat treatment and 830 ° C to 870 performed after this heat treatment
Heat treatment consisting of a second heat treatment in the range of ° C. is performed.

Further, the method for producing a conductive wire such as a Bi-based oxide of the present invention,
After the above-mentioned primary heat treatment, it is obtained by forming the material into a linear material and then performing a secondary heat treatment.

(Examples) Hereinafter, the manufacturing method of the present invention will be described in detail based on examples.

Raw materials such as Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO, and Pb ₃ O ₄ to replace Bi ₂ O _{3 as} necessary are weighed to a predetermined composition ratio, and nitric acid, hydrochloric acid, sulfuric acid, etc. And then diluted with distilled water. Here, the reason for using the inorganic acid is Bi ₂ O
₃ , for converting SrCO ₃ , CaCO ₃ , CuO, and Pb ₃ O ₄ into water-soluble metal ions. Then, after adding a predetermined amount of hydroxylic acid such as citric acid, tartaric acid and polyacrylic acid and a polyhydric alcohol such as ethylene glycol and diethylene glycol, the mixture is heated and stirred at about 90 ° C. to generate an organic acid salt. Here, hydroxyl acid is used to generate a complex compound (chelate compound) of a metal ion and hydroxyl acid. The polyhydric alcohol is used for binding a complex compound (chelate compound) of the generated metal ion and hydroxyl acid in a polymer state. The solution containing the organic acid salt is dehydrated and cooled, and the gel-like reaction product is thermally decomposed at about 350 ° C. to obtain a precursor. The heat decomposition here removes water and residual gas contained in the gel, and further decomposes the organic matter of the organic acid salt. After pulverizing this precursor, a primary heat treatment is performed, and further pulverization and molding are performed, followed by a secondary heat treatment to obtain a superconductor.

In the case of Bi-Sr-Ca-Cu-O system, its composition ratio (atomic ratio)
Means that Bi is 0.5 to 1.5, Ca 0.5 to 1.5, Cu 0.7 to 2.0 as Sr is 1.
Is desirably within the range. Here, since the above compound takes the form of an oxide, the content of O is theoretically calculated from the amount of the above element. In addition, the amount of addition of inorganic acids (such as nitric acid, hydrochloric acid, and sulfuric acid), hydroxyl acids (such as citric acid, tartaric acid, and polyacrylic acid) and polyhydric alcohols (such as ethylene glycol and diethylene glycol) used when preparing an organic acid salt is also described. It is theoretically calculated by calculating the total ionic valence from the amounts of the above elements.

In the present invention, when the composition ratio is out of these ranges, it is difficult to obtain good superconducting characteristics. In the above compound, a part of Bi was added to P at a composition ratio (atomic ratio) of 0.05 to 0.5.
Substitution with b is more effective in obtaining excellent superconducting properties.

Here, the gel of the organic acid salt is continuously applied on the base tape by a method such as a printing method, or the fibrous base material is immersed in the gel of the organic acid salt and continuously passed therethrough. If a method such as coating is adopted, a Bi-based superconductor wire can be produced.

Further, the precursor composition is not directly set as the target superconductor composition, but is formed separately into a high melting point component (precursor A) and a low melting point component (precursor B), and the two are mixed and subjected to a primary heat treatment. And superconducting by the diffusion reaction between both precursors in the secondary heat treatment,
A Bi-based oxide superconductor can be obtained. In this case, selection of an appropriate composition of the precursor A and the precursor B plays a very important role in producing a superconductor by a diffusion reaction.

Here, the precursor A contains elements of Sr, Ca or Sr, Ca, Cu, and their atomic ratio is Ca0.25 to 1.0, Cu
0 to 1.5, and the precursor B is Bi, Cu or
contains the elements i, Ca, and Cu, and their atomic ratio is C
It is preferable that a is in the range of a0 to 1.0 and Cu is in the range of 0.25 to 1.5.

Further, a part of Bi of the precursor B is 0.05 to 0.5 with respect to Bi1.
Substitution with Pb at the atomic composition ratio is more effective in obtaining excellent superconducting properties.

Further, the molar ratio of the mixture of the precursor A and the precursor B described above,
It is more effective to set the precursor B in the range of 0.5 to 2.0 with the precursor A as 1 in order to obtain excellent isoconductivity.

According to this production method, the melting point of the precursor B of the low melting point component is 70
Since the temperature is as low as 0 to 750 ° C., it becomes a melt in the secondary heat treatment, and a high Tc superconductor can be generated by a rapid diffusion reaction in the secondary heat treatment. Since the melting point of the precursor A is 1000 ° C. or higher, the diffusion reaction is a solid-liquid phase reaction. Also,
The fineness of the precursor according to the present invention is also effective in accelerating the diffusion reaction.

Next, heat treatment for generating the precursor (including the mixture of the precursor A and the precursor B) Bi-based superconductor obtained in the above-described process is performed. In this heat treatment, a material having better performance can be provided by performing a first heat treatment at a lower temperature and then performing a second heat treatment at a higher temperature.

The primary heat treatment aims at decomposing and completely removing residual gas, moisture, and organic substances remaining in the precursor, and the primary heat treatment temperature is 600 ° C to 820 ° C, preferably 650 ° C.
In the range of ℃ ~ 800 ℃. Since this precursor has a very high reactivity, it is desirable that the first heat treatment is performed in an inert atmosphere such as an Ar gas stream. The primary heat treatment is desirably performed at a temperature equal to or lower than the melting point of the precursor.

Next, the secondary heat treatment temperature is 830 ° C. to 870 ° C., preferably 84 ° C.
In the range of 5 ° C to 865 ° C, it is near the generation temperature of Bi-based high critical temperature isoconductor, and forms a crystal structure with high Tc. Although it is possible to generate a superconducting phase even if the primary heat treatment is omitted, the sample is rapidly expanded or expanded due to the generation of carbon dioxide gas and moisture due to residual gas remaining in the precursor and decomposed organic substances. It may shrink, become porous, or crack. Therefore, when the primary heat treatment is omitted, the temperature increase during the secondary heat treatment should be 40
Slower than 400 ° C in the temperature range of 0 ° C or higher,
Preferably, it is performed at a rate lower than 1 ° C./min to remove residual gas and the like. Alternatively, the temperature of the secondary heat treatment may be temporarily stopped at about 400 ° C., and the temperature may be increased again after removing the residual gas and the like. In this case, the heating rate does not need to be reduced as described above.

Further, the above-described secondary heat treatment is performed in a plurality of times, and after the sample is given superconductivity by the previous secondary heat treatment, further processing steps such as pressing, rolling, and extrusion are performed, and the secondary heat treatment is performed again. And the superconductivity can be improved.

Further, as another mode of using the present invention for forming a superconducting wire, a material after the first heat treatment is processed into a long wire, and then a second heat treatment is performed to produce a high Tc Bi-based oxide superconducting wire. be able to. The material after the primary heat treatment is processed by filling it into a metal sheath of Ag or the like, processing it by sandwiching it between metal plates, or forming it into a linear shape on a substrate tape.

Further, Bi is caused by a diffusion reaction between the precursor A and the precursor B.
When a base oxide superconductor is generated, a more uniform and dense structure can be obtained, and the superconductivity can be improved.

Example 1 Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO and raw material powder were used as Bi ₂ Sr ₂ Ca ₂ Cu ₃
Weigh so that the composition ratio of O _Y , and add distilled water to this,
The mixture was dissolved by adding concentrated nitric acid, and after adding a specified amount of citric acid monohydrate and ethylene glycol, the mixture was heated and stirred on a hot plate stirrer. When the reaction started, the color of the solution became clear blue, and as the reaction proceeded, a fine white precipitate was formed, and the evaporation of water occurred with the generation of NOx, and the amount of the solution decreased. When the reaction was completed, the sample became a viscous sol, and swelled like a sponge due to generation of NOx. When this was cooled, it solidified and became a gel. This gel was pyrolyzed at 350 ° C. for 1.5 hours in an electric furnace to obtain a precursor. This precursor was pulverized, and after a heat treatment at 780 ° C. for 8 hours as a primary heat treatment, the pulverization was repeated. FIG. 1 shows the particle size distribution of the pulverized precursor. The precursor is composed of fine particles having a particle size of about 10 μm or less. This powder was pressed under a load of 2 tons to form a tape having a width of 4 mm, a length of 30 mm and a thickness of about 1 mm, and subjected to a secondary heat treatment at 860 ° C. for 20 hours. In addition, all the heat treatments of this example were performed in the air. When the Tc of this sample was measured by the DC four-terminal method, a zero resistance temperature of 60 K was obtained.

Example 2 A raw material powder of Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO, Pb ₃ O ₄ was prepared using Bi _1.8
The precursor was weighed so as to have a composition ratio of Pb _0.2 Sr ₂ Ca ₂ Cu ₃ O _Y , and a precursor was produced in the same manner as in Example 1. This precursor was pulverized, and after a heat treatment at 780 ° C. for 8 hours as a primary heat treatment, the pulverization was repeated. Press this powder with a load of 2 tons to
4mm, length 30mm, thickness of about 1mm molded into a tape, 845 ℃
A secondary heat treatment was applied at ~ 865 ° C for 20 hours. In addition, all the heat treatments of this example were performed in the air. The results of measurement by the DC four-terminal method revealed that when the heat treatment was performed at a temperature of 855 ° C. or higher, superconductivity was exhibited at a temperature of liquid nitrogen (−196 ° C. = 77 K) or higher. Especially at 860 ° C., the zero resistance temperature of the sample was about 102K.

Example 3 A precursor prepared in the same manner as in Example 2 was subjected to heat treatment at 780 ° C. for 8 hours as a primary heat treatment, and then pulverization was repeated.
Pressing this powder with a load of 2 tons, width 4 mm, length 30 mm,
It was formed into a tape having a thickness of about 1 mm, and subjected to a secondary heat treatment at 860 ° C. for 20 hours. This sample was pressed into a 4mm-wide, 30mm-long, 1mm-thick tape with a load of 3 tons.
A secondary heat treatment was performed at 0 ° C. for 20 hours. In addition, all the heat treatments of this example were performed in the air. When the Tc of this sample was measured by a DC four-terminal method, a zero resistance temperature of about 105K was obtained. The conventional solid-phase reaction method requires heat treatment for several hundred hours to obtain high Tc. From this result, it was confirmed that the heat treatment can be reduced to 40 hours according to the present production method.

Example 4 A raw material powder of Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO, and Pb ₃ O ₄ was prepared using Bi _1.8
The precursor was weighed so as to have a composition ratio of Pb _0.2 Sr ₂ Ca _1.8 Cu ₃ O _Y , and a precursor was produced in the same manner as in Example 1. This precursor was pulverized, and after a heat treatment at 780 ° C. for 8 hours as a primary heat treatment, the pulverization was repeated. This powder was pressed with a load of 2 tons and molded into a tape shape with a width of 4 mm, a length of 30 mm and a thickness of about 1 mm.
A second heat treatment was performed at 20 ° C. for 20 hours. This sample was press-worked again at a load of 3 tons and heat-treated at 860 ° C. for 20 hours. Then, the sample was pressed further at a load of 3 tons and heat-treated at 860 ° C. for 20 hours. In addition, all the heat treatments of this example were performed in the air. When the Tc of this sample was measured by a DC four-terminal method, a zero resistance temperature of about 106 K was obtained. FIG. 2 shows this transition curve.

Example 5 A raw material powder of SrCO ₃ and CaCO ₃ was weighed so as to have a composition of Sr ₂ Ca ₂ O ₄ , and a precursor was prepared in the same manner as in Example 1 to obtain a precursor A. Further, Bi ₂ O ₃ , CuO raw material powder is converted to Bi ₂ Cu ₂ O ₅
Was weighed so as to have the composition described above, and a precursor was prepared in the same manner as in Example 1 to obtain a precursor B. Both are mixed well at a molar ratio of 1; 1.3, and the first heat treatment is performed at 700 ° C. for 10 hours.
The grinding was repeated.

This mixed powder was filled into an Ag tube with an inner diameter of 5 mm, an outer diameter of 8 mm, and a length of 80 mm, plugged, processed into a 2.5 mm square rod shape with a groove roll, and then formed into a 1 mm thick, 5 mm wide tape with a flat roll. Rolled. Here, after performing a secondary heat treatment at 860 ° C. for 10 hours, rolling was performed to a thickness of 0.3 mm, and a heat treatment was performed again at 860 ° C. for 10 hours. In addition, all the heat treatments of this example were performed in the air.

The Tc of this sample was measured by the DC four-terminal method.
A zero resistance temperature of K was obtained. Also, its critical current density J
When c was measured, a value approximately 15 times higher than that of the sample of Example 1 was obtained under a magnetic field of 1 T at 4.2 K.

Example 6 A raw material powder of SrCO ₃ , CaCO ₃ , and CuO was weighed so as to have a composition of Sr ₂ CaCu ₂ O ₅ , and a precursor was prepared in the same manner as in Example 1 to obtain a precursor A. Raw materials of Bi ₂ O ₃ , Pb ₃ O ₄ , CaCO ₃ , and CuO were weighed so as to have a composition of Bi _1.8 Pb _0.2 CaCu _1.5 O _5.5 , and a precursor was prepared in the same manner as in Example 1. And precursor B. Both were well mixed at a molar ratio of 1: 1 and primary heat treatment was performed at 650 ° C. for 10 hours, and then pulverization was repeated.

This mixed powder was filled into an Ag tube with an inner diameter of 5 mm, an outer diameter of 8 mm, and a length of 80 mm, plugged, processed into a 2.5 mm square rod shape with a groove roll, and then formed into a 1 mm thick, 5 mm wide tape with a flat roll. Rolled. Here, after performing a secondary heat treatment at 855 ° C. for 10 hours, rolling was performed to a thickness of 0.3 mm, and a secondary heat treatment was performed again at 855 ° C. for 10 hours. In addition, all the heat treatments of this example were performed in the air.

The Tc of this sample was measured by the DC four-terminal method.
A zero resistance temperature of 7K was obtained. Also, its critical current density
When Jc was measured, it was about 20K at 77K compared to the sample of Example 2.
A twofold higher value was obtained.

(Effects of the Invention) As is clear from the above description, according to the method for producing a Bi-based oxide superconductor of the present invention, a dense Bi-based high Tc oxide superconductor having a very uniform composition can be produced. . In particular, the present invention produces a precursor A of a high melting point component and a precursor B of a low melting point component having an appropriate composition and mixes both to diffuse between the two precursors in the first heat treatment and / or the second heat treatment. Since the superconductor is generated by the reaction, a more uniform and dense Bi-based oxide superconductor can be provided. Therefore, when this manufacturing method is applied to wire production,
It is possible to produce a Bi-based high Tc oxide superconductor wire having a large Jc and uniform properties in the length direction. Also, Bi
In a base oxide-based superconductor, a long time such as several hundred hours is required for heat treatment to generate a high Tc phase.However, in this manufacturing method, a high Tc phase is obtained by a heat treatment for several tens of hours. The time can be shortened and the efficiency of the manufacturing process can be increased.

Therefore, the present manufacturing method can solve the problems of the conventional manufacturing method, and can provide a Bi-based high Tc oxide superconductor excellent in uniformity and denseness.

[Brief description of the drawings]

FIG. 1 is a graph showing the particle size distribution of the organic acid salt precursor obtained according to Example 1 of the present production method, and the left side of the vertical axis represents the frequency% with respect to the particle diameter of a bar graph (histogram) in the figure. On the right side,% below the sieve with respect to the particle size of the curve in the figure is shown.
The horizontal axis represents the particle size. FIG. 2 is a diagram showing a temperature change of the electric resistance of the Bi-based oxide superconductor sample obtained by Example 4 of the present production method. The vertical axis represents the electric resistance of the sample, and the horizontal axis represents the temperature. .

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-197352 (JP, A) JP-A-63-291856 (JP, A) JP-A-64-79060 (JP, A) JP-A-2- 275718 (JP, A) JP-A-3-93609 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 29/00 C01G 1/00 C04B 35/00 H01B 12/00

Claims (12)

(57) [Claims] 1. A compound containing Bi, Sr, Ca, and Cu is dissolved in an inorganic acid, a hydroxyl acid and a polyhydric alcohol are added to form an organic acid salt, and the reaction product obtained by dehydration is heated. Bi is characterized by performing heat treatment after decomposing and forming a precursor
A method for producing a base oxide superconductor. 2. The compound comprising the elements Bi, Sr, Ca, and Cu, wherein the atomic ratio is Bi 0.5-1.5,
2. The method for producing a Bi-based oxide superconductor according to claim 1, wherein the Cu content is in a range of 0.5 to 1.5 and a Cu of 0.7 to 2.0. 3. The method according to claim 1, wherein a part of Bi of the compound is 0.05 to
3. The method for producing a Bi-based oxide superconductor according to claim 1, wherein Pb is substituted at a composition atomic ratio of 0.5. 4. A precursor obtained by dissolving at least a compound containing Sr and Ca in an inorganic acid, adding a hydroxyl acid and a polyhydric alcohol to form an organic acid salt, and then dehydrating the reaction product to obtain a precursor. A method for producing a Bi-based oxide superconductor, comprising mixing a body A and a precursor B produced by performing the same treatment on a compound containing at least Bi and Cu, and performing a heat treatment. 5. The precursor A contains Sr, Ca or the elements Sr, Ca, Cu, and the atomic ratio thereof is Ca 0.25 to 1.0,
Cu0-1.5, and the precursor B is Bi, Cu or B
contains the elements i, Ca, and Cu, and their atomic ratio is C
The method for producing a Bi-based oxide superconductor according to claim 4, wherein a is in the range of a0 to 1.0 and Cu is in the range of 0.25 to 1.5. 6. A part of Bi of the precursor B is converted to Bi1.
The method for producing a Bi-based oxide superconductor according to claim 4 or 5, wherein Pb is substituted with an atomic composition ratio of 0.05 to 0.5. 7. A precursor according to claim 4, wherein the molar ratio of the mixture of the precursor A and the precursor B is in the range of 0.5 to 2.0 with the precursor A being 1. 3. The method for producing a Bi-based oxide superconductor according to 1.). 8. The heat treatment according to claim 1, wherein said heat treatment comprises a first heat treatment in the range of 600.degree. C. to 820.degree. C. and a second heat treatment in the range of 830.degree. The method for producing a Bi-based oxide superconductor according to any one of the above. 9. The heat treatment comprises only a secondary heat treatment at 830 ° C. to 870 ° C., and when the temperature is raised to 400 ° C. or more, the heating rate is 400
2. The method according to claim 1, wherein the temperature is made slower than the case where the temperature is lower than ℃.
8. The method for producing a Bi-based oxide superconductor according to any one of items 7 to 7. 10. The Bi according to claim 1, wherein the heat treatment comprises only a second heat treatment at 830 ° C. to 870 ° C., and the temperature is temporarily stopped at about 400 ° C.
A method for producing a base oxide superconductor. 11. The Bi according to claim 8, wherein the secondary heat treatment is divided into a plurality of times, and intermediate processing such as pressing, rolling, and extruding is performed between them.
A method for producing a base oxide superconductor. 12. A method for producing a Bi-based oxide superconducting wire according to claim 8, wherein the material is formed into a linear material after the primary heat treatment, and a secondary heat treatment is performed.