JP2010287504A - Silver coated superconductive particle powder and superconductive cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Bi2223 superconductive particle powder having a high critical current density (J<SB>c</SB>) and a superconductive cable using the Bi2223 superconductive particle powder. <P>SOLUTION: The silver coated Bi2223 superconductive particle powder is obtained by coating silver powder of nano order on the particle surface of Bi2223 superconductive particle powder or by coating a silver thin film on the Bi2223 superconductive particle powder by a sputtering or CVD method; and the superconductive cable can be manufactured by using the silver coated Bi2223 superconductive particle powder. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

An object of the present invention is to provide a Bi-based superconducting cable having a high critical current density ( _Jc ).

  In recent years, due to global environmental problems, attention has been focused on the development of technologies for improving the efficiency of energy use and creating new energy.

  As one way to increase the efficiency of energy use, research into the practical use of superconducting cables is being conducted in Japan, the US and Europe.

The superconductor _{cables, Bi2223 (Bi 2 Sr 2 Ca} 2 Cu 3 O x), Bi2212 (Bi 2 Sr 2 Ca 1 Cu 2 O x), YBCO (Y-Ba-Cu-O), MgB 2 Research and development are in progress.

Among these, Bi2223 has the highest _Tc , and the superconducting state is sufficiently generated under liquid nitrogen. In recent years, empirical research for practical application has been actively conducted.

  When Bi2223 is processed into a cable, generally, a method is adopted in which Bi2223 powder is put into silver or a tube containing silver, rolled and formed into a sheath, and then rolled.

Information necessary for comparing characteristics in a superconducting cable is critical current density ( _Jc ). _{J c} as Bi2223 polycrystalline bulk that is not cabled is only a ~100A / mm ² approximately, which is one of the major barriers to practical use.

JP 2007-87813 A JP 2004-119248 A JP-A-11-139824 JP-A-4-104985

In the above Patent Documents 1 to 4 described techniques, in which hardly yet Bi2223 high J _c of the cable is sufficient and says.

That is, in Patent Document 1 (Japanese Patent Laid-Open No. 2007-87813) and Patent Document 2 (Japanese Patent Laid-Open No. 2004-119248), Bi2212 including (Bi, Pb) 2223 is described. Is contained in a large amount, and the decrease in the volume fraction of the high _Tc phase (2223) is reduced.

Further, those containing Patent Document 3, (JP-A-11-139824 JP), are described for high _{J c} of by optimization of heat treatment conditions for the production Bi-2223-based, an impurity phase (non-superconducting phases) , and the resulting cable are those hard to say that having a high J _c.

  Further, Patent Document 4 (Japanese Patent Laid-Open No. 4-104985) describes that various oxides and the like are adhered to the surface of the superconductor, but it is considered that Ag is adhered more closely. Absent.

Therefore, in the present invention, and an object thereof is to provide a cable using a Bi2223 particles and the Bi2223 particles as stable and mass-produced high _{J c.}

  The above problem can be overcome by coating the surface of the superconducting particle powder comprising Bi2223 phase with separately prepared nano-order silver particles.

  Alternatively, the above problem can be overcome by coating the particle surface of Bi2223 particle powder with a silver thin film by sputtering or chemical vapor deposition.

That is, the present invention is a silver-coated superconducting particle powder in which the surface of a Bi-based superconducting particle powder is coated with silver particles having an average particle diameter of 1 to 100 nm, and the critical current density of the silver-coated superconducting particle powder is (J _c ) is a silver-coated superconducting particle powder characterized by being 190 A / mm ² or more (Invention 1).

The present invention also relates to a silver-coated superconducting particle powder in which the surface of a Bi-based superconducting particle powder is coated with a silver thin film, and the critical current density (J _c ) of the silver-coated superconducting particle powder is 190 A / mm. It is a silver-coated superconducting particle powder characterized by being ² or more (Invention 2).

  Moreover, this invention is a superconducting cable using the silver covering superconducting particle powder of this invention 1 or 2 (this invention 3).

By using the silver-coated superconductive particle powder according to the present invention, a high _Jc cable can be obtained.

  First, the silver-coated superconductive particle powder according to the present invention will be described.

The composition of the Bi-based superconducting particle powder used in the present invention generally has the following chemical composition formula:
Formula: (Bi.Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _Δ
Formula: Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _Δ
A composition corresponding to the Bi2223 phase represented by

  The particle size of the superconductive particle powder is not particularly limited, but it is 0.1 to 500 μm, preferably a particle powder having an average particle size of 0.5 to 200 μm, or two or more points within the range of these average particle sizes. Any of the particle | grains powder which mixed particle | grains by arbitrary weight may be sufficient.

  The silver-coated superconducting particle powder according to the present invention 1 is obtained by coating the particle surface of the Bi-based superconducting particle powder with silver particles having an average particle diameter of 1 to 100 nm.

As for the average particle diameter of the silver particle which coat | covers the particle | grain surface of Bi type | system | group superconducting particle powder used for this invention 1, 1-100 nm is preferable. When the particle size of the silver particles exceeds 100 nm, the bulk density of the Bi-based superconducting particle powder does not increase during wire processing, and the particle surface of the Bi-based superconducting particle powder cannot be sufficiently covered. _{Since c} cable cannot be obtained, it is not preferable. A more preferable average particle diameter of silver particles is 1 to 80 nm.

The state of the silver particles before coating may be an aqueous / organic solvent-based dispersion slurry or dry powder, and is preferably in the state of a dispersion slurry. Although the silver concentration in a dispersion | distribution slurry is not specifically limited, 1-30 wt% may be sufficient.
The solvent of the dispersion slurry is water, glycerin, ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, tetraethylene glycol, methanol, ethanol, isopropanol, 1-propanol, 1-butanol, 2-butanol, 2-methyl- 1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol , 3-methyl-2-butanol, 2,2-dimethyl-1-propanol, 1-octanol, 1-decanol, cis-9-octadecen-1-ol, cyclohexanol, methylcyclohexanol, 2-ethylhexanol, hexane Diacid 2-isopropyl-5-methylcyclohexanol, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, phenol, terpineol, prenol, isovaleric acid, senecioic acid, tiglic acid, 3-methyl-3-butene- 2-ol, angelic acid, geraniol, nerol, farnesol, nerolidol, cineol, 1,2,4-butanetriol, benzyl alcohol, polyvinyl alcohol aqueous solution, n-hexane, cyclohexane, toluene, formalin, chloroform, benzene, heptane, Examples include octane, nonane, and decane, and at least one of them may be used.

  The dispersant for dispersing silver particles in a solvent is not limited, but polyvinyl alcohol, sodium polyacrylate, polyethylene glycol, cellulose, sucrose, oleic acid, sodium oleate, oleylamine, stearic acid, sodium stearate, etc. Can be used.

  In the present invention 1, the method of coating the Bi-based superconducting particle powder with nano-order silver particles is not particularly limited. For example, while mixing the Bi-based superconducting particle powder and the silver-dispersed solvent with a lyi machine, It is obtained by volatilization. As another coating method, it can also be obtained by diluting a silver dispersion solvent with a solvent, adding Bi-based superconducting particle powder thereto, mixing well, and then evaporating the solvent with an evaporator. You can choose the method that suits your production. For example, the drying may be performed at 100 ° C. with a ventilation dryer after the coating treatment. Conditions such as temperature may be appropriately selected depending on the dispersion solvent. Moreover, you may heat-process after application | coating and drying. The heat treatment makes the silver coating on the surface of the Bi-based superconducting particles more ideal. For example, the heat treatment may be performed in air at 200 ° C. for 2 hours.

  Bi-based superconducting particle powder and coated silver are weight ratios expressed by (coating silver weight) / (Bi2223 superconducting particle powder weight), although not particularly limited, 0.001 to 2 wt%, preferably 0.005 to 1.5 wt%. The optimum ratio may be selected according to the method and conditions of cable formation.

The critical current density (J _c ) of the silver-coated superconducting particle powder according to the present invention 1 is 190 A / mm ² or more, preferably 220 A / mm ² or more, more preferably 250 A / mm ² or more.

  The silver-coated superconducting particle powder according to the present invention 2 is obtained by coating the particle surface of a Bi-based superconducting particle powder with a silver thin film.

  The method for coating the Bi-based superconducting particle powder surface according to the present invention 2 with silver is not particularly limited, but sputtering, chemical vapor deposition (CVD), or the like may be used.

  Bi-based superconducting particle powder and coated silver are 0.001 to 2 wt%, preferably 0.005 in a weight ratio represented by (weight of coated silver) / (weight of Bi-based superconducting particle powder). 1.5 wt%. The optimum ratio may be selected according to the method and conditions of cable formation.

In the second aspect of the present invention, it is preferable to employ a powder sputtering method as a method for coating Bi-based superconducting particles by sputtering. The powder sputtering method can be performed with reference to a method disclosed in Japanese Patent Application Laid-Open No. 2006-96953 or Japanese Patent Application Laid-Open No. 2002-157918. The apparatus which performs powder sputtering can use the apparatus marketed normally.
As a normal operation, the Bi-based superconducting particle powder is introduced into a rotary chamber of a powder sputtering apparatus and then evacuated under reduced pressure. Thereafter, a commonly used sputtering gas such as argon gas is introduced, and the pressure is adjusted within a range of 1 × 10 ⁻³ to 1 × 10 ⁻² Torr. Power is applied to excite plasma to sputter a silver target, and silver is coated on Bi-based superconducting particle powder. After performing sputtering to a desired thickness, the powder is taken out to obtain Bi-based superconducting particle powder coated with silver.

  Other vacuum deposition methods according to the second aspect of the present invention can be performed using CVD (Chemical Vapor Deposition), PVD (Physical Vapor Deposition), thermal CVD, plasma CVD, photo-CVD, or the like. As the CVD method, for example, a compound disclosed in Japanese Patent Application Laid-Open No. 7-215981 can be used.

  The thickness of silver to be coated is preferably 0.05 to 1 μm, more preferably 0.05 to 0.15 μm. If the thickness of the silver to be coated is less than 0.05 μm, the conductivity becomes insufficient, which is not preferable. Even when the thickness of the silver to be coated is thicker than 1 μm, sufficient conductivity can be obtained, but it is not preferable from the viewpoint of productivity because the sputtering time becomes unnecessarily long.

The critical current density (J _c ) of the silver-coated superconducting particle powder according to the present invention 2 is 190 A / mm ² or more, preferably 220 A / mm ² or more, more preferably 250 A / mm ² or more.

  The superconducting cable using the silver-coated superconducting particle powder according to the present invention 3 is a step of filling a metal sheath using the silver-coated superconducting particle powder of the present invention 1 or 2 as generally known, A process of forming a wire by plastic processing of a metal sheath filled with raw materials, a process of producing a strand by bundling the wire, and inserting a strand into a metal pipe for strand insertion to form a multi-core structure And a step of drawing the multi-core structure to form a tape-shaped wire.

The critical current density (J _c ) of the silver-coated superconducting particle powder according to the present invention 3 is 190 A / mm ² or more, preferably 220 A / mm ² or more, more preferably 250 A / mm ² or more.

<Action>
By using the silver-coated superconducting particle powder according to the present invention, resistance at the contact portion between Bi-based superconducting particle powder particles, loss due to bond deficiency between the particles is less likely to occur, and Bi is coated. Since the superconducting particle powder content is large, the superconducting current is not unevenly distributed without breaking the superconducting state, and the Bi-based superconducting particle powder particles are not distributed in the bulk or the cable without any resistance or loss. The present inventors presume that a large critical current density (J _c ) that could not be obtained in the past can be obtained. Furthermore, a cable having a high critical current density (J _c ) can be obtained by using the silver-coated superconducting particle powder according to the present invention.

  A typical embodiment of the present invention is as follows.

  The particle size of the silver coating the Bi-based superconducting particle powder was measured using a transmission electron microscope (TEM: JEOL Ltd., JEM-1200EXII). The average value was obtained by selecting 120 particles for randomization and measuring the particle size.

  The average particle diameter of the Bi-based superconducting particle powder and the state confirmation of the silver-coated superconducting particle powder are confirmed by a scanning electron microscope (SEM: Hitachi High-Technologies Corporation, S-4800 FE-SEM (TYPE-I)). It was measured. The average value was obtained by selecting 120 particles for randomization and measuring the particle size.

  The production phase of the Bi-based superconductive particle powder was measured with a powder X-ray diffractometer (XRD: Rigaku Corporation, RINT 2500).

  The composition analysis of the Bi-based superconducting particle powder and the coating amount of silver were obtained by dissolving the sample with an acid and analyzing it using a plasma emission spectrometer (ICP: Seiko Electronics Co., Ltd., SPS4000).

The critical current density (J _c ) of the Bi-based superconducting particle powder coated with silver was measured as follows.

First, a pellet-shaped molded body having a diameter of 20 mmφ and a thickness of 1.0 mm was prepared from silver-coated Bi2223 superconductive particle powder at 3 ton / cm ² . Subsequently, after firing with 3 ton / cm ² pressure applied, it was rapidly cooled to room temperature. This polycrystal was cut into strips, and the critical current density (J _c ) at 77 K was determined by the four probe method.

<< Preparation of Bi2223 superconductive particle powder >>
Bi2223 superconducting particle powder was produced by the following three methods.

(A) Bi ₂ O ₃ (Aldrich Sigma reagent, purity 99.999%), SrCO ₃ (Aldrich Sigma reagent, purity 99.9%), CaCO ₃ (Aldrich Sigma reagent, purity 99.0) %), CuO (Aldrich Sigma reagent, purity 99.5%) was used as a raw material. Each raw material was weighed so that the atomic ratio of Bi: Sr: Ca: Cu was 2.1: 2.0: 2.0: 3.1, and pulverized and mixed in an agate mortar for 30 minutes. At this time, ethanol, IPA, MEK, and 2 (-2-methoxyethoxy) ethanol were appropriately added in minute amounts. Thereafter, it was formed into a pellet having a diameter of 30 mmφ and a thickness of 15 mm at 300 kg / cm ² , calcined at 750 ° C. for 2 hours, and then pulverized in an agate mortar, followed by ² ton / cm ^{2 with a} diameter of 30 mmφ and a thickness of 8. A 5 mm pellet shaped body was prepared, calcined at 820 ° C. for 6 hours, and ground again in an agate mortar for 15 minutes. Furthermore, a Bi2223 superconducting particle was produced by producing a pellet-shaped molded body having a diameter of 30 mmφ and a thickness of 5 mm at 3 ton / cm ² and firing in an atmosphere of 844 ° C. for 24 h and O ₂ / N ₂ = 20/80 vol%. A powder was obtained.
When the obtained powder was analyzed by ICP, Bi: Sr: Ca: Cu = 2.1: 2.0: 2.0: 3.1, which was the same as the charged composition. The average particle size was 45 μm. From the XRD Rietveld analysis, 98% was the Bi2223 phase, and the product phase was judged to be almost single phase.

(Ii) Bi ₂ O ₃ (Aldrich Sigma reagent, purity 99.999%), PbO (Aldrich Sigma reagent, purity 99.999%) SrCO ₃ (Aldrich Sigma reagent, purity 99.9%) , CaCO ₃ (Aldrich Sigma reagent, purity 99.0%), CuO (Aldrich Sigma reagent, purity 99.5%) were used as raw materials. Each raw material is weighed so that the atomic ratio of Bi: Pb: Sr: Ca: Cu is 1.8: 0.4: 2.0: 2.0: 3.2, and ground in an agate mortar for 30 minutes. Mixed. At this time, ethanol, IPA, MEK, 2 (-2-methoxyethoxy) ethanol, etc. were added while adding a trace amount appropriately. Thereafter, it was molded into a pellet with a diameter of 30 mmφ and a thickness of 15 mm at 300 kg / cm ² , calcined at 720 ° C. for 2 hours, and then a pellet with a diameter of 30 mmφ and a thickness of 8.5 mm at ² ton / cm ² . And calcined at 820 ° C. for 6 hours and ground again in an agate mortar for 15 minutes. Furthermore, a Bi2223 superconducting particle was produced by producing a pellet-shaped molded body having a diameter of 30 mmφ and a thickness of 5 mm at 3 ton / cm ² and firing in an atmosphere of 844 ° C. for 24 h and O ₂ / N ₂ = 20/80 vol%. A powder was obtained. When the obtained powder was analyzed by ICP, Bi: Pb: Sr: Ca: Cu = 1.8: 0.4: 2.0: 2.0: 3.2, which was the same as the charged composition. The average particle size was 28 μm. The produced phase was a Bi2223 phase single phase from XRD.

_{(C) Bi (CH 3 COO) 3} ( Aldrich Sigma reagent, _{99.99% purity), Pb (CH 3 COO)} 2 · 3H 2 O ( Aldrich Sigma reagent, 99.99% purity), Ba (CH ₃ COO) ₂ (Aldrich Sigma reagent, purity 99.0%), Sr (CH ₃ COO) ₂ xH ₂ O (Aldrich Sigma reagent, purity 99.995%), Ca (CH ₃ COO ) ₂ · H ₂ O (Aldrich Sigma reagent, purity 99.0%), Cu (CH ₃ COO) ₂ × H ₂ O (Aldrich Sigma reagent, purity 99.0%) were used as raw materials. Each raw material so that the atomic ratio of Bi: Pb: Ba: Sr: Ca: Cu is 1.8: 0.4: 0.045: 2.0: 2.0: 3.2, and the total raw material weight is 250 g. Were weighed and lightly pulverized and mixed in an agate mortar. This was transferred to an evaporating dish, and water, ethylene glycol, and citric acid corresponding to 8 times the total metal molar concentration were added and heated to 220 ° C. while stirring well to obtain a gel. Subsequently, while mixing well, the temperature was raised to 370 ° C. to obtain a black-like powder. A powder formed by pulverizing for 30 minutes with a laika machine is used to produce a pellet-shaped molded body having a diameter of 30 mmφ and a thickness of 8.5 mm at ² ton / cm ² , and calcined at 787 ° C. in an argon stream. After pulverization for 30 minutes, a pellet-shaped formed body having a diameter of 30 mmφ and a thickness of 5 mm was prepared at 3 ton / cm ² and fired in an O ₂ / N ₂ = 20/80 vol% atmosphere to obtain Bi2223 superconductive particle powder. It was. When the obtained powder was analyzed by ICP, Bi: Pb: Ba: Sr: Ca: Cu = 1.8: 0.4: 0.045: 2.0: 2.0: 3.2 It was the same. The average particle size was 22 μm. The produced phase was a Bi2223 phase single phase from XRD.

<Preparation of nano-order silver particles and silver particle dispersion>
(I) To a 1 L beaker, 160 g of silver nitrate, 151.2 g of butylamine and 800 ml of methanol were added, and stirred for 2 hours to prepare solution A. Separately, 248.8 g of ascorbic acid was taken into a 10 L beaker, 1600 ml of water was added and dissolved by stirring, and then 800 ml of methanol was added to prepare solution B. The liquid A was added dropwise to the place where the liquid B was well stirred over 5 hours. After completion of dropping, stirring was continued for 3.5 hours. After completion of stirring, the mixture was allowed to stand for 30 minutes to precipitate the solid. After removing the supernatant by decantation, 2000 ml of water was newly added, and the supernatant was removed by stirring, standing, and decantation. This purification operation was repeated three times. The precipitated solid was dried in a drier to remove moisture and obtain nano-order silver particles. 200 g of toluene was added to the silver particles, and the mixture was pulverized with zirconia beads for 30 hours in an alumina ball mill to prepare a 25% silver nanoparticle dispersion. The primary particle of the obtained silver particle was 80 nm.

(II) 4.0 g of silver nitrate, 50 ml of toluene and 9.4 g of oleylamine were weighed in a beaker and stirred at room temperature to dissolve the silver nitrate. Subsequently, 8.3 g of ascorbic acid was added and stirred for 2 hours. The reaction solution had a blackish yellow color. Subsequently, silver nanoparticles were agglomerated and precipitated using a mixed solution of acetone and methanol-water, and the supernatant solution was removed by decantation to remove excess salts and amines. After the purification operation was repeated three times, the aggregate was dried under reduced pressure. Subsequently, 3.92 g of toluene was added to prepare a 25% dispersion of silver nanoparticles. The primary particle of the obtained silver particle was 8 nm.

<< Silver coating on Bi2223 superconductive particle powder >>
(A) The Bi2223 superconducting particle powder (a) obtained above (50 g) and the silver particle dispersion (3.2 g) (I) above were weighed, and (a) was pulverized and mixed with a reiki machine. (I) was added dropwise over 60 minutes. Then, it dried for 2 hours at 70 degreeC with the explosion-proof dryer, and also silver-coated Bi2223 superconducting particle powder was obtained by performing heat processing in air at 250 degreeC for 4 hours. The silver coating amount of the obtained powder was 1.6% in terms of (coating silver weight) / (Bi2223 superconducting particle powder weight).

(B) 50 g of the Bi2223 superconducting particle powder obtained in (a) and 0.2 g of the silver particle dispersion (II) obtained above are respectively weighed, and (a) is pulverized and mixed with a likai machine. (II) was added dropwise over 30 minutes. Then, it dried for 2 hours at 70 degreeC with the explosion-proof dryer, and also silver-coated Bi2223 superconducting particle powder was obtained by performing heat processing for 4 hours at 200 degreeC in the air. The silver coating amount of the obtained powder was 0.1% in terms of (coating silver weight) / (Bi2223 superconducting particle powder weight).

(C) 50 g of the Bi2223 superconductive particle powder obtained in (c) and 2.2 g of the silver particle dispersion (II) obtained above were respectively weighed. 2.2 g of toluene was added to the weighed (II), and (A) was added dropwise over 60 minutes to the place where it was pulverized and mixed with a lykai machine. Then, it dried for 2 hours at 70 degreeC with the explosion-proof dryer, and also silver-coated Bi2223 superconducting particle powder was obtained by performing heat processing for 4 hours at 180 degreeC in the air. The silver coating amount of the obtained powder was 1.1% in terms of (coating silver weight) / (Bi2223 superconducting particle powder weight).

(D) After introducing 50 g of the Bi2223 superconducting particle powder obtained in (c) above into a rotary chamber of a powder sputtering apparatus (homemade production apparatus by Toda Kogyo Co., Ltd.) and exhausting the inside of the chamber Then, Ar was introduced as a sputtering gas and adjusted to 5 × 10 ⁻³ Torr. While rotating the rotary chamber at 10 rpm, the sputtering process was performed for 100 minutes with an input power of 1 kW. The silver coating amount of the obtained powder was 0.07% in terms of (coating silver weight) / (Bi2223 superconducting particle powder weight).

Example 1
The critical current density ( _Jc ) was measured using the silver-coated Bi2223 superconducting particle powder (A). First, a pellet-shaped molded body having a diameter of 20 mmφ and a thickness of 1.0 mm was produced from the powder of (A) at 3 ton / cm ² . Subsequently, it was baked in air at 848 ° C. for 24 hours under a pressure of 3 ton / cm ² and rapidly cooled. The obtained sample was cut into a strip shape, and the critical current density (J _c ) at 77 K was measured. As a result, it was 192 A / mm ² .

Example 2
The critical current density ( _Jc ) was measured using the silver-coated Bi2223 superconductive particle powder of (B) above. A sample produced in the same manner as in Example 1 was cut into a strip shape, and the critical current density (J _c ) at 77 K was measured. As a result, it was 222 A / mm ² .

Example 3
The critical current density ( _Jc ) was measured using the silver-coated Bi2223 superconductive particle powder of (C) above. A sample produced in the same manner as in Example 1 was cut into a strip shape, and the critical current density (J _c ) at 77 K was measured. As a result, it was 233 A / mm ² .

Example 4
The critical current density ( _Jc ) was measured using the silver-coated Bi2223 superconducting particle powder (D). A sample produced in the same manner as in Example 1 was cut into a strip shape, and the critical current density (J _c ) at 77 K was measured. As a result, it was 239 A / mm ² .

Example 5
The critical current density ( _Jc ) was measured using the silver-coated Bi2223 superconductive particle powder of (C) above. First, a pellet-shaped molded body having a diameter of 20 mmφ and a thickness of 1.0 mm was produced from the powder of (A) at 2.8 ton / cm ² . Subsequently, it was baked in an atmosphere of 844 ° C. for 24 hours under an O ₂ / N ₂ = 20/80 vol% state with a pressure of 2.8 ton / cm ² being applied, and then rapidly cooled. The obtained sample cut into strips, critical current density _{(J c)} results of measuring the at 77K, was 251A / mm ^2.

Example 6
After degassing the silver-coated Bi2223 superconducting particle powder of (C) above, it was filled in a silver pipe having an outer diameter of 25 mmφ and an inner diameter of 22 mmφ, and was drawn to an outer diameter of 20 mmφ. This was put into a pipe having an outer diameter of 23 mmφ and an inner diameter of 22 mmφ, and Sr ₆ V ₂ O ₁₁ was filled as a high-resistance material powder around the periphery. This was drawn until the outer diameter became 1.5 mmφ. Further, the 60 wires were bundled and fitted into a silver pipe having an outer diameter of 14.5 mmφ and an inner diameter of 14.1 mmφ, and was drawn until the outer diameter became 1.2 mm. Next, the tape-shaped wire was obtained by rolling this until it became thickness 0.25mm. This was baked at 845 ° C. for 30 hours to obtain a superconducting cable using silver-coated Bi2223 superconducting particle powder. Was 248A / mm ² was measured critical current density _{(J c)} in which the 77K.

Example 7
A superconducting cable was produced in the same manner as in Example 6 using the silver-coated Bi2223 superconducting particle powder of (D) above. Was 250A / mm ² was measured critical current density _{(J c)} in which the 77K.

Comparative Example 1
When the critical current density (J _c ) at 77 K was measured in the same manner as in Example 1 using the Bi2223 superconductive particle powder of (a) above, it was 115 A / mm ² .

Comparative Example 2
When the critical current density (J _c ) at 77 K was measured using the Bi2223 superconducting particle powder of (a) above in the same manner as in Example 1, it was 156 A / mm ² .

Comparative Example 3
When the critical current density (J _c ) at 77 K was measured in the same manner as in Example 1 using the Bi2223 superconductive particle powder of (c) above, it was 143 A / mm ² .

Comparative Example 4
A superconducting cable using Bi superconducting particle powder was obtained in the same manner as in Example 6 using the Bi2223 superconducting particle powder of (c) above. Was 187A / mm ² was measured critical current density _{(J c)} in which the 77K.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Since the present invention has a high critical current density ( _Jc ), it is very useful as a superconductor, particularly a superconducting cable.

Claims (3)

A Bi-based silver-coated superconducting particles having an average particle diameter of the particle surface of the superconducting particles are coated with silver particles 1 to 100 nm, the critical current density of the silver-coated superconducting particles (J _c) is 190A / Mm ² or more Silver-coated superconductive particle powder, The particle surface of the Bi-based superconducting particles a silver-coated superconducting particles coated with silver thin film, the critical current density of the silver-coated superconducting particles (J _c) is 190A / mm ² or more Silver coated superconducting particle powder. A superconducting cable using the silver-coated superconducting particle powder according to claim 1.