JPH01231219A - Manufacture of oxide superconducting material - Google Patents

Abstract

PURPOSE:To enable obtaining a superconducting oxide of high critical current density by pressurizing the raw material powder of an oxide superconducting material packed in a forming mold or a package in the specific decompressed atmosphere. CONSTITUTION:The powder of a YBCO oxide available from the crushing of T, Ba and Cu oxides or the sintered body of a carbonate powder is subject ed to pressed powder treatment so that the voids thereof will be 50 to 60%. A lower punch 8 is inserted in the lower part of a die 1 and a powder 14 after a pressing process is loaded on the lower punch 6 within a vessel 5. Then, an upper punch 7 is inserted in the upper part of the die 1. Thereafter, the vessel 5 is exhausted via an exhaust outlet 6 and pressure inside the vessel 5 is kept equal to or below 10Torr. The compact of YBCO so obtained is filled in a silver pipe and subjected to a drawing process and the like, together with the silver pipe. According to the aforesaid construction, it is possible to obtain a superconducting oxide wire material having high critical current density and superior characteristics.

Description

[Detailed description of the invention] [Industrial application field] The present invention is directed to yttrium-barium-copper-acid]
The present invention relates to a method for producing an acid (arsenic paste) superconducting material such as a (hereinafter referred to as YI13CO) superconducting material, and in particular to a method for producing an oxide superconducting material whose density is increased to improve its critical current density.

[Prior Art] In the process of processing YBCO-based superconducting material into a wire rod, oxides or carbonates of Y, Ba, and Cu are usually used as starting materials, and after mixing these in a predetermined amount,
Temporarily heat this mixed powder at a temperature of about 900'C,
A sintered body of YBCO powder particles is produced. Next, this sintered body is pulverized into powder with a predetermined particle size, and the YBCO-based powder obtained is press-molded into a compact having the size and shape of the entire powder.

Thereafter, after filling a metal pipe or the like with the molded body produced in the pressure forming step, the pipe is swaged or wire-drawn to a desired wire diameter.

Next, the wire produced in the above wire drawing process is given desired characteristics (
The sintering process is performed by heating to about 900'C in an oxidizing atmosphere so as to obtain a critical temperature Tc or critical current density Jc).

In this wire processing process, the pressure forming step has conventionally been carried out by a die forming method or a rubber press method.

FIG. 2 is a cross-sectional view showing a conventional pressure molding process using a die molding method. Punches 2 and 3 are inserted into the cylindrical die 1 from its upper and lower ends.

First, insert the lower punch 3 into the die 1, and
Insert the upper punch 2 into the die 1, which is loaded onto the punch 3 in the BCO superconducting material powder die 1, and press both punches 2.3 against each other as shown by the arrows in the figure. By pressing in the approaching direction, the powder 4 is compressed and molded.

[Problems to be Solved by the Invention] However, in this pressure forming process, when the powder 4 is charged into the die 1 and the upper punch 2 is inserted into the die 1, gas (air) also flows into the die 1. It will be sealed inside. Therefore, when the powder 4 is pressurized by the punch 2.degree. 3 to form an aggregate, the sealed gas enters between the powder particles, and the powder is molded with the gas remaining in the powder. Furthermore, as the applied pressure increases, the pressure of this trapped gas also increases.

In this case, the density of the press-molded body decreases due to the gas trapped between the powder particles, making it impossible to obtain a superconducting oxide with a high critical current density.

Furthermore, since the gas pressure in the press-molded body is high, springback (a phenomenon of slight expansion) and cracks are likely to occur in the press-molded body after the pressurizing force is removed.

For this reason, in the conventional manufacturing method, there is a problem that it is not possible to stably manufacture a YBCO-based superconducting material having a desired critical current density due to the intake of air during the pressure molding process. be.

This situation is the same when pressure molding is performed using a rubber press method, and the residual gas in the rubber bag is trapped between powder particles that are being aggregated by pressure, increasing the internal gas pressure.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a method for manufacturing an oxide superconducting material, which can obtain a superconducting material having a high density and a high critical current density, and can avoid the occurrence of cracks in the compact.

[Means for Solving the Problems] The method for producing an oxide superconducting material according to the present invention includes the steps of: compressing raw material powder of an oxide superconducting material so that the porosity becomes 60% or less; and molding this powder. Charge it into a mold or package,
It is characterized in that the powder in this mold or package is pressurized in a reduced pressure atmosphere of 10 Torr or less and molded into a predetermined shape.

Further, it is preferable that the raw material powder is subjected to powder compaction treatment so that the porosity becomes 50% or more.

In the present invention, the raw material powder of the oxide superconducting material charged into a mold or package is heated to 1 QTorr.

Pressure is applied to the following reduced pressure atmosphere. Therefore, air is removed from the powder in the mold, etc., not only from the surface but also from the inside before or during the molding pressurization.

Therefore, the amount of air remaining in the powder is extremely reduced, and a high-density pressed compact can be obtained, making it possible to produce a superconducting oxide with a high critical current density. Furthermore, since residual gas is significantly reduced, cracks do not occur in the molded product after the pressure is released.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing an example method of the present invention.

The container 5 is provided with an exhaust port 6 in the upper part of its side wall, and this exhaust port 6 is connected to a suitable exhaust means (not shown), so that the inside of the container 5 is exhausted through the exhaust port 6. It looks like this.

Further, a cylindrical die 1 is fixedly installed in the container 35 with its axial direction perpendicular.

Further, the punch 7.8 is disposed inside the container 5 with its base inserted airtightly into holes provided in the upper and lower walls of the container 5, and is driven by an appropriate driving means through this base. The punches 7 and 8 are driven upward and downward. Then, punch 7
．． 8 is adapted to be inserted into the die 1 disposed in the container 5 from its upper and lower end openings. Punch 7.
8 is provided with an exhaust passage 9 that opens at its tip, and this exhaust passage i? 8 is opened at the side of the punch 7.8 in the portion exposed from the die 1 to form an exhaust gas 1]10. Although the diameter of the exhaust passage 9 needs to be large enough to exhaust the residual gas in the powder 14, it is preferably as small as possible in order to prevent suction of the powder.

In the method of this embodiment, first, Y, Ba, Cu oxide or carbonate powders are blended in the same manner as in the conventional method, and then calcined to produce a sintered body of YBCO-based oxide. Then, this sintered body is crushed to obtain a powder of YBCO-based acid monomer.

Next, this powder is compacted so that the porosity becomes 50 to 60%. This is to provide the YBCO-based ¥A conductive material powder with an appropriate cohesive force before the pressure is reduced in the subsequent pressure molding process.

That is, if the cohesive force of the YBCO-based superconducting oxide powder is too weak, the fine powder may be discharged to the outside through the exhaust passage 9 or clog the exhaust passage 9 when the pressure is reduced. For this reason, the powder is subjected to a powder compaction treatment so that the porosity becomes 60% or less. On the other hand, if the cohesive force is too strong, it will be difficult to remove residual debris from the powder in the subsequent pressure molding step under a reduced pressure atmosphere. For this reason, it is preferable to ensure that the porosity of the powder after compaction is 50% or more.

Thereafter, the lower punch 8 is inserted into the lower part of the die 1, the above-mentioned compacted powder 14 is charged onto the lower punch 8 in the container 5, and then the upper punch 7 is inserted into the upper part of the die 1. Insert into. Then, the inside of the container 5 is evacuated through the exhaust port 6, and the inside of the container 5 is maintained at a pressure of 10 Tor+· or less. Then, the gas in the powder 14 is discharged into the container 5 through the exhaust passage 9 and further to the outside through the exhaust port 6.

Next, the punches 7.8 are moved in the direction of approaching each other as shown by the arrows in the figure, and the powder 14 is moved between them and the die 1.
Pressure mold. Even during this pressurization process, the gas inside the powder 14 is exhausted from the powder via the exhaust passage 9. In this way, most of the gas inside the powder disappears, and the resulting press-molded product has extremely low residual scum pressure. Therefore, the density of the compact is extremely high. Furthermore, since the residual gas pressure is low, no springback or cracks will occur in the molded product after the pressing force of the punches 7.8 is removed.

At the time of pressure molding of this powder 14, the atmospheric pressure was set to 10 Torr.
The reason why the atmospheric pressure is set below 10 Torr is because if it is higher, the gas in the powder cannot be sufficiently removed and the density of the compact cannot be made sufficiently high, so the effect of improving the critical current density is lowered. This is because it will be insufficient.

Next, the YBCO molded body thus obtained is filled into a silver pipe and subjected to wire drawing processing etc. together with the silver pipe to obtain a wire rod of a predetermined wire diameter. Thereafter, only the silver pipe is removed by acid treatment, and then a predetermined firing treatment is performed to obtain a YBCO-based oxide superconducting material.

Since this superconducting material has a high density, it has a high critical current; a superconducting oxide wire with extremely excellent characteristics can be obtained.

Next, we will explain the results of actually manufacturing superconducting oxide wires using the example method of the present invention.
A powder having a composition of 07-J was prepared, and a press-molded body was prepared under the conditions shown in Table 1 below.

Examples 1 to 4 in Table 1, Comparative Examples 1.2 and Conventional Example were all pressure molded using the molding apparatus shown in FIG. 1 described above. The size of each of these pressure-molded bodies is 7 mm in diameter, 100 + IIn in length, and the molding pressure is 2.5 tons. The porosity of the obtained molded body was measured using a mercury porosimeter, and the apparent density was calculated. The results are also shown in Table 1 above.

Next, each of the molded bodies produced by the above method had a wall thickness of III.
After filling and sealing in a Wl silver pipe, it was reduced in diameter by swaging until the diameter became 2.0 mm and turned into a wire rod. Thereafter, the silver seal on the surface layer was dissolved in methanol nitric acid, and then heat-treated in an oxidizing atmosphere at 900° C. for 10 hours. The obtained superconducting oxide wire was immersed in liquid nitrogen, and its critical current density was measured. This result also applies to the first
It is also shown in the table. Note that the critical current density is expressed as an index as a ratio to the conventional example, with the critical current density of a superconductor manufactured by a conventional method being 1.

As is clear from Table 1, the YBa2 CL1307-a superconductors manufactured by the invention method of Examples 1 to 4 have a higher apparent density and critical current than those manufactured by the conventional method. A remarkable improvement effect is observed in both density.

On the other hand, in Comparative Example 1, the pressure reduction treatment during pressure molding was insufficient and the atmospheric pressure (50Tθrr, ) was high, so the effect of improving the critical current density was small.

Further, in Comparative Example 2, the porosity before the vacuum treatment was as high as 65%, so fine powder was discharged to the outside.

In addition, Examples 1 to 3 are the empty ii! before depressurization treatment. Rate 5
Since it is 0% or more, in the case of Example 4 (porosity llO%
), it is sufficiently degassed and its apparent density and critical current density are high.

[Effects of the Invention] As explained above, according to the present invention, when the powder of oxide superconducting material such as YBCO-based material is pressure-molded, the porosity is 6.
10 Torr after powder compaction so that it is 0-6 or less
Since the molding is carried out under pressure under the following reduced pressure atmosphere, a molded body with high clarity can be obtained, the occurrence of cracks etc. after molding can be avoided, and it is possible to produce an oxide superconducting material with a high critical current density. can.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the embodiment method of the present invention, and FIG. 2t2 is a cross-sectional view showing the conventional method. 1; Dice, 5: Container, 6, 10; Exhaust port, 7° 8; Bunch, 9; Exhaust passage, 14; Superconducting oxide raw material powder

Claims (2)

[Claims] (1) After compacting the raw material powder of the oxide superconducting material so that the porosity becomes 60% or less, this powder is charged into a mold or package, and the powder in this mold or package is heated to 10 Torr.
1. A method for producing an oxide superconducting material, which comprises forming the material into a predetermined shape by applying pressure in a reduced pressure atmosphere below r. (2) The method for producing an oxide superconducting material according to claim 1, wherein the powder after the compaction treatment has a porosity of 50% or more.