JPH08337424A - Production of bismuth-containing oxide superconducting wire - Google Patents

Abstract

PURPOSE: To increase Jc in a magnetic field or at the temp. (77K) of liq. nitrogen to a level fit for practical use without deteriorating a high Tc phase. CONSTITUTION: When a Bi-contg. oxide superconducting material having a compsn. represented by the general formula, (Bi, Pb)2 Sr2 Ca2 Cu3 O10 is produced, a wire of the material sheathed with a metal is heat-treated in the temp. range of 650-750 deg.C in an atmosphere contg. 0.5-5% gaseous oxygen in gaseous N2 and/or inert gas as an atmosphere of oxygen under reduced pressure after concluding sintering.

Description

Detailed Description of the Invention

[0001]

The present invention relates relates to a method of manufacturing a Bi-based oxide superconducting material, more particularly the production of Bi-based oxide superconducting wire which is used, for example, a magnet coil or the like, especially high-T _C phase The present invention relates to a method for producing a Bi-based oxide superconducting wire containing a large amount.

[0002]

2. Description of the Related Art Bi-based oxide superconducting materials have the general formula B
i ₂ Sr ₂ CaCu ₂ O ₈ (hereinafter referred to as Bi-2212) having a low T _C phase having a critical temperature (hereinafter referred to as T _C ) of about 80 K, and a general formula (Bi, Pb) ₂ Sr ₂
It is known that a high Tc phase having a Tc of about 110 K, which is represented by Ca ₂ Cu ₃ O ₁₀ (hereinafter referred to as Bi-2223), exists.

Since the higher the Tc of a superconducting material is, the more practical it is, a high Tc phase having a Tc of about 110 K, which is higher than the temperature of liquid nitrogen, that is, Bi-2223 has attracted attention as a practical material.

As a method for producing the wire made of Bi-2223, a metal sheath-processed superconducting material is used at a high temperature (8
Generally, a method of repeating the main baking treatment at 00 ° C. or higher (for example, Japanese Patent Laid-Open No. 5-203833).

[0005]

In order to put the superconducting material into practical use, it is necessary that the superconducting material has a high critical current density (hereinafter referred to as Jc). Liquid nitrogen temperature (77
It is necessary to maintain high Jc characteristics even at high temperatures such as K). Recently, it has been found that the introduction of a pinning center that traps magnetic flux lines generated by a superconducting current flowing in a superconducting material is indispensable in order to maintain high Jc characteristics even at high temperatures. Research and development of introducing pinning centers into Bi-based oxide superconducting materials.

However, a method of introducing a pinning center into a Bi-based oxide superconducting material having a high Tc phase has not been established, and there is a problem that its Jc characteristic has not yet reached a practical level.

The present invention has been made in view of the above problems, and puts the Jc characteristics of a Bi-based oxide superconducting material having a composition represented by the general formula (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ into practical use. Level (32000A / at liquid nitrogen temperature (77K)
(cm ² or more).

[0008]

In order to achieve the above object, a method for producing a Bi-based oxide superconducting material according to the present invention comprises:
A method for producing a Bi-based oxide superconducting material having a composition represented by the general formula (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ , wherein N ₂ gas and / or
Alternatively, the heat treatment is performed in a temperature range of 650 to 750 ° C. in a reduced pressure oxygen atmosphere containing 0.5 to 5% oxygen gas as an inert gas.

[0009]

According to the method for producing a Bi-based oxide superconducting material according to the present invention, 0.5 to 5% oxygen gas is added to N ₂ gas and / or an inert gas after the main-sintering of the metal sheath processed wire. Since the heat treatment is performed in a temperature range of 650 to 750 ° C. in a reduced pressure oxygen atmosphere containing Al, the superconducting property of the grain boundary of the high Tc phase is improved and the high Tc phase is improved by the heat treatment in the reduced pressure oxygen atmosphere after the main sintering. Part is decomposed and PbO, Ca ₂
A normal conductive precipitate containing PbO ₄ as a main component is generated, and it becomes possible to introduce a pinning center. This makes it possible to improve the Jc characteristic in a magnetic field or at a liquid nitrogen temperature (77K), as compared with a superconducting material produced by a conventional method.

When the content of oxygen gas in the N ₂ gas and / or the inert gas is less than 0.5%, the high T
The decomposition of the c phase proceeds more than necessary, and the crystal grains of the normal conductive precipitate become too large, which is not preferable. On the other hand, if the oxygen gas content exceeds 5%, there will be no precipitation of the normal conductive precipitates, making it impossible to introduce pinning centers. Therefore, the content of the oxygen gas in the N ₂ gas and / or the inert gas atmosphere is preferably in the range of 0.5 to 5%.

When the temperature of the heat treatment is lower than 650 ° C., there is no precipitation of the normal conductive precipitates and it becomes impossible to introduce a pinning center. When the temperature is higher than 750 ° C., the decomposition of the high Tc phase is more than necessary. And the crystal grains of the normal conductive precipitate become too large, which is not preferable. Therefore, the temperature range of the heat treatment is preferably 650 to 750 ° C.

Further, the longer the heat treatment time is, the more the Jc characteristics are improved.
The Jc of the superconducting material becomes larger at 00 hours. However, when it exceeds 100 hours, there is almost no difference in time effect, and for example, the Jc characteristics are almost the same between 100 hours and 200 hours.

[0013]

EXAMPLES Examples of the method for producing a Bi-based oxide superconducting material according to the present invention will be described below.

First, as raw material powders, Bi ₂ O ₃ and Pb are used.
O, SrCO ₃ , CaCO ₃ , and CuO are prepared, and Bi:
Pb: Sr: Ca: Cu = 1.8: 0.4: 1.8:
After mixing and mixing so as to have a molar ratio of 2.2: 3.0, calcining twice at 800 ° C. for 24 hours in the air atmosphere, crushing and mixing well, and then an outer diameter of 6 mm, Inner diameter 4
Fill a mm silver pipe. Next, the silver pipe filled with the calcined powder is drawn and rolled into a tape shape having a width of 3 mm and a thickness of 0.1 mm, for example. The silver tape thus produced was cut into a length of 20 mm, baked in an air atmosphere at 840 ° C. for 96 hours, and then cut to 7 tons.
Pressing is performed at a pressure of / cm ² . 84 more after this
After firing at 0 ° C. for 24 hours, press treatment is performed at a pressure of 7 ton / cm ² , and firing is performed again at 840 ° C. for 24 hours.
After performing the above-mentioned sintering process, further heat treatment was performed under the following conditions.

Table 1 below shows each heat treatment condition, Tc of the obtained Bi type oxide superconducting material and Jc at the liquid nitrogen temperature. The heat treatment conditions include oxygen partial pressure,
The heat treatment temperature and heat treatment time were changed. Sample N in Table 1
o is a serial number including the examples and comparative examples, and * is described in the remarks column in the comparative examples. Sample No. 13 is
A conventional example manufactured without the heat treatment is shown.

[0016]

[Table 1]

FIG. 1 is a graph showing the relationship between the oxygen partial pressure and the Jc value prepared based on Table 1, and the section A in FIG. 1 shows the range of the present invention. In addition, the numbers in the figure indicate the sample No. in Table 1. Is shown.

As is clear from FIG. 1 and Table 1, the Bi-based oxide superconducting materials (Sample Nos. 2, 4, 9, 10) obtained by the method according to the example are all related to the comparative example. Bi-based oxide superconducting material obtained by the method (Sample N
o. Jc value higher than 1, 11-13).
As described above, the oxygen gas content in the reduced pressure oxygen atmosphere during the heat treatment after the main sintering of the metal sheath processed wire is 0.5.
By setting the content to ˜5%, a high Jc value can be obtained.

FIG. 2 is a graph showing the relationship between the heat treatment temperature and the Jc value, which was prepared based on Table 1. Section B in FIG.
Indicates the scope of the present invention. In addition, the numbers in the figure indicate the sample No. in Table 1. Is shown.

As is clear from FIG. 2 and Table 1, the Bi-based oxide superconducting material (Sample No. 4) obtained by the method according to the example was Bi-obtained by the method according to the comparative example.
It has a higher Jc value than the oxide superconducting materials (Samples Nos. 7, 8, and 13). As described above, the temperature during the heat treatment after the main sintering of the metal sheath processed wire is 650 to 75.
By setting the temperature to 0 ° C., a high Jc value can be obtained.

FIG. 3 is a graph showing the relationship between the heat treatment time and the Jc value prepared based on Table 1, and the numbers in the figure indicate the sample No. in Table 1. Is shown.

As is clear from FIG. 3 and Table 1, the sample No. 1 having a heat treatment time of 1 hour was used. 3 and sample No. 3 having a heat treatment time of 10 hours. 4 and sample No. 4 having a heat treatment time of 100 hours. 5 and sample N with heat treatment time of 200 hours
o. Comparing with No. 6, the longer the heat treatment time, the more
The value will be higher. However, the sample No. 5 and sample No. As is clear from the comparison with No. 6, the effect of extending the heat treatment time is not so great for 100 hours or longer, and
The Jc value after heat treatment hardly changes with time.

FIG. 4 is an SEM cross-section of a silver-sheathed wire.
3A and 3B show a state before the heat treatment of the method of the present invention, and FIG. 6B shows a cross section after the heat treatment of the method of the present invention.

By applying the heat treatment of the method of the present invention,
It can be seen that pinning centers (spotted ones that appear white in the figure (b)) are introduced into the wire.

[0025]

As described in detail above, according to the method for producing a Bi-based oxide superconducting material according to the present invention, the general formula (Bi,
Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ Bi having a composition represented by
A method for producing a metal-based oxide superconducting material, comprising: performing a main-sintering of a metal-sheathed wire; and then applying a reduced pressure oxygen atmosphere containing 0.5 to 5% oxygen gas in N ₂ gas and / or an inert gas. Since the heat treatment is performed in the temperature range of 650 to 750 ° C., a high T is obtained by the heat treatment in the reduced pressure oxygen atmosphere after the main sintering.
The superconducting property of the grain boundary of the c phase is improved, part of the high Tc phase is decomposed, and normal-conducting precipitates containing PbO and Ca ₂ PbO ₄ as the main components are generated, enabling the introduction of pinning centers. Become. This makes it possible to improve the Jc characteristics in a magnetic field and at liquid nitrogen temperature (77K), as compared to the superconducting material produced by the conventional method, and provides a superior material for forming power cables, magnets, etc. can do.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between oxygen partial pressure and Jc value created based on Table 1.

FIG. 2 is a graph showing a relationship between a heat treatment temperature and a Jc value, which is created based on Table 1.

FIG. 3 is a graph showing the relationship between heat treatment time and Jc value, which was created based on Table 1.

4A and 4B are views of a cross section of a superconducting wire observed with an SEM, in which FIG. 4A is before the heat treatment of the present invention, and FIG. 4B is after the heat treatment.

Claims (1)

[Claims] 1. A compound represented by the general formula (Bi, Pb) ₂ Sr ₂ Ca ₂ C
A method of manufacturing a u ₃ Bi-based oxide composition represented by O ₁₀ superconducting wire, after the sintering of the metal sheath working wire, N ₂
650 to 750 in a reduced pressure oxygen atmosphere containing 0.5 to 5% oxygen gas in the gas and / or the inert gas
A method for producing a Bi-based oxide superconducting wire, which comprises performing heat treatment in a temperature range of ° C.