JP3121863B2 - Method for producing Bi-based oxide superconducting conductor by melting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a Bi-based oxide superconducting conductor using a melting method, and relates to an improvement in the orientation and formation ratio of a superconducting phase after fusion and solidification, and an improvement in the thickness of a superconducting layer. The present invention relates to a method capable of improving the uniformity of the height.

[0002]

2. Description of the Related Art Conventionally, a method described below with reference to FIG. 6 has been known as an example of a method for manufacturing a superconducting conductor having a Bi-based oxide superconducting layer provided on an upper surface of a tape-shaped substrate. . In this method, first, a metal tape 1 of Ni or the like is prepared, and a raw material powder layer 2 of an element constituting a Bi-based oxide superconductor is formed on the upper surface of the metal tape 1. Next, a laser beam is irradiated from above the metal tape 1 to heat and melt only a part of a small area of the mixed powder layer 2 to form a fusion zone 3. In this state, the base material 1 is moved in the longitudinal direction at a constant speed, and the entire molten powder layer 2 in the longitudinal direction of the base material 1 can be heat-treated by gradually moving the minute molten zone 3. Has produced the oxide superconducting conductor 5 having the oxide superconducting layer 4.

[0003]

When the oxide superconducting conductor 5 is manufactured by the above-described method, the supply of the mixed powder layer 2 and the supply of the mixed powder That is, the three phenomena of the melting of the melt and the solidification of the melted portion are proceeding simultaneously. In a state where three phenomena are progressing in such a minute area, there is a high possibility that the balance of the three phenomena is lost even if a slight fluctuation occurs in the power of the laser beam. Then, even if a constant substrate moving speed is maintained, there is a problem that the amount of the melted portion changes, so that the thickness of the solidified portion becomes uneven and the crystal orientation deteriorates. In the above case, for example, Bi ₂ Sr ₂ Cu other than the oxide superconductor having the desired composition
There is a problem in that a non-superconducting phase typified by Oy or the like occurs and the superconducting characteristics deteriorate.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and has a target composition, a dense, uniform thickness Bi-based oxide superconductor having a high critical temperature, and is formed on a substrate by applying a melting method. It is an object of the present invention to provide a method that can be formed on a substrate.

[0005]

According to the first aspect of the present invention, a raw material powder layer containing an element constituting a Bi-based oxide superconductor is formed on an upper surface of a metal base material. Then, this raw material powder layer is heated in a heating furnace for 870-10.
After heating to 00 ° C to once melt the raw material powder layer,
While the melt-solidified layer to form a partially melted band part irradiated portion by irradiating a laser beam of melt-solidified layer after this, and then move the partial melting zone in the longitudinal direction of the base material melted Te The entire solidified layer is sequentially unidirectionally solidified to form an oxide superconducting layer.

[0006]

[Action] The raw material powder layer on the upper surface of the metal substrate is once melted in a heating furnace.
After that, the mixture is cooled and melted and solidified. At this stage, the raw material quantity powder layer becomes a dense and uniform thickness solidified layer with pores closed . If this molten solidified layer is unidirectionally solidified by a laser beam,
The two reactions of re-melting and solidification of the molten and solidified layer proceed, and the number of phenomena that occurs as compared with the conventional case where the three phenomena of supply of the raw material powder layer and melting and solidification of the layer progress. Is reduced. Therefore, even if a slight fluctuation occurs in the power of the laser beam, a dense oxide superconducting layer having a uniform thickness is generated. Since a dense oxide superconducting layer with a uniform thickness is generated, the orientation of the crystal grains during one-way melt solidification can be easily aligned, leading to an improvement in the crystal orientation of the resulting oxide superconducting layer, and a critical temperature and a critical temperature. Those with a high current density are generated.

Hereinafter, the present invention will be described in more detail. In order to manufacture the Bi-Sr-Ca-Cu-O-based oxide superconductor by carrying out the present invention, first, a starting material is prepared. As this starting material, a Bi compound, an Sr compound, a Ca compound, and a Cu compound are used. As the compound, any of oxides, chlorides, carbonates, sulfides, fluorides and the like of each element may be used. Specifically used in this example are Bi ₂ O ₃ powder, SrCO ₃ powder, CaCO ₃ powder and CuO powder. The compound used may be in the form of particles or powder, but preferably has the smallest possible particle size. In the case of manufacturing a Bi-based superconductor containing Pb, a Pb compound may be mixed in addition to the above compounds.

If the above powders are prepared, Bi: Sr: Ca:
The mixed powder is prepared by weighing Cu to a ratio of 2: 2: 1: 1: 2 and uniformly mixing with an automatic mortar over a required time. Here, when the ratio of the respective elements is 2: 2: 2: 3, the mixture is mixed at the ratio, and in the case where Pb is added in addition to the respective elements, a part of the Bi (for example, the number of Bis) Percent)
May be replaced with Pb. Next, the mixed powder is heated in the air at 800 to 850 ° C. for about 24 to 100 hours and calcined to remove unnecessary components. After calcining, the calcined product is pulverized to powder the calcined product.

Next, the above-mentioned powder is charged into a container 11 filled with an organic solvent 10 as shown in FIG. 1 to form a dispersion medium. Next, a tape-shaped metal substrate 12 is immersed in the dispersion medium and pulled up, and the metal substrate 12 having the thickness 1 shown in FIG.
The raw material powder layer 13 of about 0 to 100 μm is formed. The metal base material 12 is rich in flexibility and may be made of any metal as long as it can withstand the heat treatment described below, but the difference in thermal expansion coefficient between the metal base material 12 and the oxide superconductor is large. Considering that there is a possibility of causing a problem and that the oxide superconductor to be formed preferably has a structure similar to the crystal structure, a metal tape having a buffer layer formed on the upper surface thereof is preferable. Specifically, A
Ni tape or Hastelloy tape having a buffer layer formed of u, Ag, NiO, MgO, SrTiO ₃ or the like on the surface is preferable.

Next, the metal substrate 12 to which the raw material powder layer 13 is fixed is placed in a heating furnace such as an infrared image furnace for 870 minutes.
Heat and melt at a temperature of 1000 ° C. for about 1 minute to 1 hour.
When the raw material powder layer 13 is melted at this temperature, the whole or a part of the raw material powder layer 13 is melted.
The molten solidified layer 14 has a uniform thickness as shown in FIG. This molten solidified layer 1
No. 4 is obtained by melting and solidifying the raw material powder layer 13;
Voids and the like that existed inside the raw material powder layer 13 are closed, and unnecessary components contained in the raw material powder layer 13 are discharged, so that the density and purity are high, It is slightly thinner than the raw material powder layer 13 and has a uniform thickness.

Next, the molten and solidified layer 14 is irradiated with a laser beam from above as shown in FIG. 4 and is also irradiated with a laser beam from the back side of the metal substrate 12 corresponding to the irradiated portion of the laser beam. A small partial melting zone 15 shown in FIG. 4 is formed in a part of the solidified layer 14. Since the partial melting zone 15 is formed at a portion corresponding to the focal point of the laser beam, it is a narrow region having a width of about 2 mm. Irradiating the laser beam also from the back side of the metal base 12 is as follows.
When a laser beam is irradiated only from the upper side of the molten solidified layer 14, the surface portion of the molten solidified layer 14 is easily heated to the heating temperature by the laser beam, but the bottom portion of the molten solidified layer 14 is heated. If the metal base 12 is also heated by the laser beam from the back side of the metal base 12 and the metal base 12 is also heated, the temperature of the partial melting zone 15 can be made uniform between the front side and the bottom side.

When the partial melting zone 15 is formed, the metal base 12 is moved at a constant speed in the direction of arrow B in FIG.
By this process, the partial molten zone 15 gradually moves along the molten and solidified layer 14, and the portion after the partial molten zone 15 moves is solidified to form the oxide superconducting base layer 16. Since the oxide superconducting base layer 16 thus generated is generated by unidirectionally solidifying the melt-solidified layer 14 once melt-solidified in a heating furnace, unlike the case where the raw material powder layer 13 is directly melt-solidified, No thickness variation occurs. By performing heat treatment at 800 to 870 ° C. for several hours to several hundred hours after the directional solidification treatment, the entire oxide superconducting base layer 16 can be turned into an oxide superconducting layer 17, and the oxide superconducting conductor 18 shown in FIG. Can be obtained.

This is because the re-melting and solidification of the molten solidified layer 14 proceeds in the unidirectionally solidified minute area, and the supply of the raw material powder layer and the melting and solidifying of the layer are performed as in the conventional case. This is because the number of phenomena that occur is smaller than when two phenomena proceed, and even if a slight fluctuation occurs in the power of the laser beam, a superconducting base layer having a uniform thickness is generated. Since the superconducting base layer 16 having a uniform thickness is generated as described above, the orientation of the crystal grains at the time of melt-solidification can be easily aligned, leading to an improvement in the crystal orientation of the oxide superconducting layer 17, and the critical temperature and the critical current density can be reduced. The higher ones produce.

The oxide superconducting layer 17 obtained as described above has a uniform thickness and a high density, and vacancies existing in the raw material powder layer 13 are almost eliminated. Further, in the case of unidirectional solidification, the melt-solidified layer 14 originally having a high density is re-melted, so that the crystal orientation is smoothly performed. Therefore, the oxide superconducting layer 17 having excellent crystal orientation, high density, and high critical temperature and critical current density is provided.
Can be obtained.

The Bi-based oxide superconductor 18 manufactured by the above-described method has a critical temperature higher than the liquid nitrogen temperature (77 K). Since it has a denser crystal structure than an oxide superconductor simply produced by sintering a powder, it exhibits a high critical current density.

[0016]

EXAMPLE Bi ₂ O ₃ powder, SrCO ₃ powder, CaCO ₃ powder, and CuO powder were mixed with Bi: Sr: Ca: Cu = 2: 2:
Mix in a molar ratio of 1: 2 and mix in an automatic mortar for 1 hour. This mixed powder is 800-85 in air.
The mixture is calcined at 0 ° C. for 24 to 100 hours to pulverize the calcined product. Next, a Ni tape having a width of 2 mm and a thickness of 0.5 mm is prepared, and a container filled with ethanol is prepared.

Next, the pulverized material was mixed with ethanol in a container at a ratio of 400 g of the pulverized material to 1 liter of ethanol to prepare a dispersion medium, and a Ni tape was immersed in the dispersion medium and pulled up. A mixed powder layer having a thickness of 100 μm was formed thereon. Next, the Ni tape on which the mixed powder layer was formed was heated to 900 ° C. in an electric furnace to melt the mixed powder layer and then solidified to form a 50 μm thick melt-solidified layer. In this state, since the whole was heated and melted uniformly in the heating furnace, the raw material powder layer was a melt-solidified layer having a uniform thickness and no irregularities.

Next, a CO ₂ gas laser was irradiated from the front side of the molten solidified layer and the back side of the metal substrate, respectively, to form a 2 mm wide molten zone in a part of the molten solidified layer. At the same time N
The i-tape was moved at a speed of 5 mm / hour, the molten zone was also moved, and the entire melt-solidified layer was unidirectionally solidified. After solidification,
Heat treatment at 800 to 870 ° C. for 100 hours allowed an oxide superconductor to be obtained.

The obtained oxide superconductor was cooled with liquid nitrogen and its critical temperature (Tc) and critical current density (Jc) were measured. Tc = 82 K, Jc = 1000 A / cm ²
showed that.

[0020]

[Comparative Example] A raw material powder layer equivalent to the above was formed on a base material equivalent to the metal base material used in the above embodiment, and the process of once melting and solidifying this in a heating furnace was omitted. The same treatment as in the above example was performed to obtain an oxide superconducting conductor. When the critical temperature and critical current density of the obtained oxide superconducting conductor were measured, Tc = 78 K, Jc = 50 A / c
m ² . Note that in the oxide superconducting layer thus obtained, it was confirmed that fine irregularities were partially formed.

From the results described above, it has been found that by performing the method of the present invention, a Bi-based oxide superconducting conductor having a uniform thickness and excellent characteristics having a high critical temperature and a high critical current density can be produced. .

When the unidirectional solidification by the laser beam is performed, if the moving speed of the substrate 12 is set to 20 mm / hour or more, the moving speed is too fast to obtain satisfactory superconducting characteristics. Incidentally, in the oxide superconducting conductor manufactured by setting the moving speed to 20 mm / min, Tc
= 72K.

[0023]

As described above, according to the present invention, the raw material powder layer formed on the metal substrate is once melted and solidified to form a molten coagulated material.
After forming a solid layer, it is irradiated with a laser beam and solidified in one direction.
Since the oxide superconducting layer is formed , the thickness variation is small compared to the case where the raw material powder is directly unidirectionally solidified,
It is possible to obtain an oxide superconducting conductor having a Bi-based oxide superconducting layer which is dense and free of voids and has excellent crystal orientation. Therefore, the oxide superconducting conductor obtained by the method of the present invention exhibits excellent superconducting characteristics having a high critical temperature and a high critical current density.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state in which a raw material powder layer is formed on a metal substrate.

FIG. 2 is a sectional view showing a state in which a raw material powder layer is formed on a metal substrate.

FIG. 3 is a cross-sectional view showing a state in which a raw material powder layer is melted and solidified.

FIG. 4 is a cross-sectional view showing a state in which a molten solidified layer is unidirectionally solidified.

FIG. 5 is a sectional view of an oxide superconducting conductor.

FIG. 6 is a cross-sectional view for explaining a unidirectional solidification method in a conventional method.

[Explanation of symbols]

12 ... metal base material, 13 ... raw material powder layer, 14 ...
・ Molten solidified layer, 15 ・ ・ ・ Molten zone, 16 ・ ・ ・ Oxide superconducting base layer, 17
... oxide superconducting layer 18 ... oxide superconducting conductor.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideo Ishii 2-4-1 Nishi-Atsujigaoka, Chofu-shi, Tokyo Tokyo Electric Power Company R & D Center (72) Inventor Takushi Hara 2-4-1, Nishi-Atsujigaoka, Nishi-Chufu-shi, Tokyo No. Tokyo Electric Power Company Technical Research Institute (72) Inventor Takahiko Yamamoto 2-4-1 Nishi Azujigaoka, Chofu City, Tokyo Tokyo Electric Power Company Technical Research Institute (56) References JP-A-2-187003 (JP, A) Kaihei 2-51806 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 12/00-13/00 C30B 29/22

Claims (1)

(57) [Claims] 1. A raw material powder layer containing an element constituting a Bi-based oxide superconductor is formed on an upper surface of a metal substrate, and then the raw material powder layer is heated to 870 to 1000 ° C. in a heating furnace. The raw material powder layer is once melted and then cooled to form a melt-solidified layer, and thereafter, a part of the melt-solidified layer is irradiated with a laser beam to form a partially melted zone at the irradiated portion. Manufacturing the Bi-based oxide superconducting conductor by a melting method, wherein the partial molten zone is moved in the longitudinal direction of the base material, and the entire molten solidified layer is sequentially unidirectionally solidified to form an oxide superconducting layer. Method.