JP2565930B2 - Method for manufacturing ceramic superconducting compact - Google Patents

Description

The present invention relates to a method for producing a ceramics superconducting compact.

[Conventional technology]

Ceramic superconducting compacts such as alkaline earth metal, rare earth elements, oxide superconducting copper compacts composed of copper and oxygen,
The seaside temperature (T _c ) is high and its application is expected. As the manufacturing method Thus, for example, in the case of Y-Ba-CuO system, Y ₂ O _3, BaCO ₃ and CuO as raw material, pre-baked at about 900 ° C. by mixing these starting powders It is manufactured by pulverizing this into a desired shape, sintering it in a desired shape, sintering it at 900 to 1000 ° C. in the air or in an oxygen atmosphere for several hours, and then slowly cooling it to room temperature. Further, a heat treatment method has been used in which the oxygen partial pressure during the sintering process is changed, if necessary.

[Problems to be solved by the invention]

However the ceramic superconductor shaped bodies said produced by conventional methods, for the reasons described below critical current density (J _c) is low, the improvement of the critical current density (J _c) has been strongly desired.

(1) In order to obtain a dense sintered body, it is necessary to use a powder having a particle diameter as small as possible. However, when such a powder having a relatively small particle diameter is heated to a high temperature, the crystal of the sintered body is crystallized. The grains are likely to become coarse, and as a result, the critical current density (J _c ) decreases.

(2) Since the boundary energy of the crystal grain boundary is lowered by pre-baking or sintering at high temperature, recrystallization occurs or the grain boundary becomes a large tilt angle, and the crystal grain boundary becomes a potential barrier against electric current. As a result, the critical current density (J _c ) decreases.

(3) In order to obtain a high critical current density (J _c ) in an oxide-based superconducting compact with large current anisotropy, it is necessary to control the crystal orientation, but with the conventional method, high temperature and long time are required. By heating, the crystal grows freely and in an arbitrary orientation, so that it is almost impossible to control the crystal orientation.

(4) It has been attempted to change the oxygen partial pressure during the sintering treatment, but crystal orientation is rarely generated because the oxygen partial pressure is changed and the isotropic stress treatment is performed.

[Means for solving problems]

The present invention has been made as a result of intensive studies in view of the above points, and an object thereof is to provide a method for producing a ceramics superconducting compact capable of obtaining a high critical current density (J _c ). It is a thing.

That is, in the present invention, in the process of manufacturing a ceramics superconducting molded body, in the step of heating and cooling the ceramics superconductor or the precursor thereof, the molded body has a breaking strength in the range of 1/30 to 1/10. Is a method for manufacturing a ceramics superconducting molded body, which is characterized in that the anisotropic stress is applied.

The present invention, for example, applies an anisotropic stress such as a uniaxial tensile stress to a wire rod to a molded body in the heating and cooling step, thereby coarsening the crystal grains and heating the high-angle grains when heated to a high temperature. In order to prevent the generation of a field and to control the crystal orientation, and the stress is less than 1/30 of the breaking strength of the molded body, the effect of the stress load does not sufficiently occur, and the stress Is more than 1/10 of the breaking strength of the compact, the crystal orientation is disturbed, so it is necessary to apply a stress in the range of 1/30 to 1/10 of the breaking strength of the compact. is there.

In the method of the present invention, it is preferable that the ceramics superconductor to be heated and cooled or the molded body of the precursor thereof is coated with silver. Further, the ceramic superconducting molded article produced by the method of the present invention has particularly excellent characteristics when the ceramic is an oxide ceramic comprising an alkaline earth metal, a rare earth element, copper and oxygen.

It is desirable to apply the stress load in both the heating and cooling steps of the molded body in the present invention, but it is possible to obtain a similar effect by applying it only to the cooling step. As a method of applying a stress, for example, a ceramic superconductor or a precursor thereof can be continuously moved between a set of pulleys while the tension is applied between the pulleys. Alternatively, it is possible to apply the stress using a uniaxial tensile tester or a compressor.

[Action]

In the method of the present invention, in the step of heating and cooling the molded body of the ceramics superconductor or its precursor, anisotropic stress is applied to the molded body, so that the high critical current density ( It is possible to obtain a molded product having J _c ).

(1) Coarsening of crystal grains is prevented.

(2) Generation of large-angle tilt grain boundaries is prevented, and the potential barrier at grain boundaries is reduced. That is, the potential barrier is eliminated and the current flows easily between the grains by making the grain boundaries of the low-angle grain with lower boundary energy amorphous.

(3) Although it is heated to a high temperature for a long time, since stress is applied, crystal orientation becomes possible.

〔Example〕

Next, the present invention will be described more specifically by way of examples. Y ₂
O ₃ , BaCO ₃ and CuO are mixed so that Y: Ba: Cu = 1: 2: 3,
After pre-firing at 900 ° C., it was crushed, filled into a silver pipe having an outer diameter of 15 mm and an inner diameter of 10 mm, and wire-drawn into a diameter of 1 mm. The wire rod thus obtained is loaded with a tensile stress of 0.3 to 10 kg / mm ² by a method of suspending a weight giving a desired stress in an electric furnace, and 900 to 1000 at 10 ° C./min in the atmosphere. After heating to ℃ and holding for 5 hours, it was cooled to 300 ℃ at 2 ℃ / min.
For the superconducting wire obtained in this way, by the four-terminal method,
The critical current density (J _c , A / cm ² ) at 77 ° K and 0T was measured. The obtained results are first compared with the heating temperature and the load stress.
Shown in the table. The critical current density (J _c ) was measured when no load stress was applied, that is, when manufactured by the conventional method.
The results are also shown in Table 1. The breaking strength of the wire when heated to 900 to 1000 ° C. was about 30 kg / mm ² .

As is clear from Table 1, when heating and cooling the wire,
When a load stress within the range of the present invention (1 kg / mm ² and 3 kg / mm ² ) was applied, a high critical current density (J _c ) of 10 ³ A / cm ² or more was obtained in all cases. On the other hand, when the magnitude of the applied stress is outside the range of the present invention (0.3 kg / mm ² and 10 kg / mm ² ) and when no stress is applied (conventional example), only a low critical current density (J _c ) is obtained. There wasn't.

Further, as a result of investigating the longitudinal section of the wire produced by the method of the present invention by X-ray diffraction, it was confirmed that the crystal orientation was larger than that produced by the conventional method. Furthermore, it was found by observation with a transmission electron microscope that more non-crystalline disorder of atoms in the twin crystal and grain boundary layers was observed than in the conventional wire. On the other hand, it is confirmed that the conventional wire rods often have distinct high-angle grain boundaries, and there is a large difference in the degree of matching between crystal grains between the method of the present invention and the conventional method.

〔The invention's effect〕

According to the method of the present invention, it is possible to obtain a ceramics superconducting compact having a high critical current density (J _c ) value, which is a significant industrial effect.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location // C01G 1/00 H01B 12/00 ZAA H01B 12/00 ZAA C04B 35/00 ZAAK (73) Patent Right holder 999999999 Electric Power Development Co., Ltd. 6-15-1, Ginza, Chuo-ku, Tokyo (72) Inventor Yasuzo Tanaka 2-4-3 Okano, Nishi-ku, Yokohama-shi, Kanagawa Furukawa Electric Co., Ltd. Yokohama Research Laboratory (72) Invention Person Minoru Nakajima 2-4-3 Okano, Nishi-ku, Yokohama-shi, Kanagawa Furukawa Electric Co., Ltd. Yokohama Research Laboratory (56) Reference JP-A-63-282152 (JP, A)

Claims (5)

(57) [Claims] 1. When manufacturing a ceramics superconducting molded body, in the step of heating and cooling the molded body of the ceramics superconductor or its precursor, the molded body is in the range of 1/30 to 1/10 of its breaking strength. A method for manufacturing a ceramics superconducting molded body, characterized in that the anisotropic stress is applied. 2. The method for producing a ceramics superconducting molded article according to claim 1, wherein the molded body of the ceramics superconductor or its precursor is coated with silver. 3. The method for producing a ceramic superconducting compact according to claim 1, wherein the ceramic is an oxide ceramic. 4. The method for producing a ceramics superconducting compact according to claim 1, wherein the stress load is applied only to the cooling step. 5. A stress load is applied by tension between pulleys while continuously moving a molded body of a ceramics superconductor or its precursor between a pair of pulleys. The method for producing a ceramics superconducting molded article according to item 1.