JP2876139B2 - Manufacturing method of oxide superconducting sintered body - Google Patents

Description

The present invention relates to a method for producing an oxide superconducting sintered body, and more particularly to a method for stabilizing the surface of an oxide superconducting sintered body.

(B) Prior art oxide superconductors manufactured by various methods, for example, typical
Y ₁ Ba ₂ Cu ₃ O _7- x and the like basically have low water resistance and have difficulty in surface resistance.

An oxide superconducting material Y ₁ Ba ₂ Cu ₃ O _7- x synthetic powder is molded in a mold or CIP (Cold Isostatic Pressing) at an appropriate pressure, and the molded body is sintered at 900 to 980 ° C. to form a bulk. In the method of manufacturing the method, the powder diameter can be reduced to, for example, 1 μm, and the bulk density can be increased to decrease the surface resistance. However, this method is not preferable because the Meissner effect with respect to the magnetic field decreases.

In order to increase the density by setting the powder diameter to 10 μm, sintering may be performed by raising the sintering temperature. It must be used, and it is extremely difficult to reach 90% or more of the theoretical density. Therefore, when the density is 70 to 90%, the Meissner effect is strong, but Jc (critical current density) is small,
There is a disadvantage that the surface resistance is also high.

Next, regarding the water resistance, as described above, the sintered body of Y ₁ Ba ₂ Cu ₃ O _7- x is basically weak in water, and for example, the superconducting property is remarkably overall only by immersing it in boiling water for 1 minute. Degradation, but as a countermeasure, Y ₁ Ba ₂ Cu ₃ O _7- x
After adding about 5 wt% of silver oxide to the synthetic powder of the above, molding and sintering, even if immersed in boiling water for 20 minutes, the superconductivity inside the sintered body is maintained to a degree that is slightly deteriorated. However, there is almost no effect on the improvement of the surface resistance.

As described above, after mixing and adjusting silver or silver oxide in the synthetic powder of Y ₁ Ba ₂ Cu ₃ O _7- x, the method of molding and sintering is such that silver or silver oxide is uniformly dispersed in the bulk. Therefore, there is little effect in improving the water resistance, and almost no effect is recognized in improving the surface resistance.

(C) Disclosure of the Invention The present invention is to solve the above-mentioned disadvantages, and to provide a method for lowering the surface resistance of a sintered oxide superconductor and further improving the water resistance.

That is, the present invention is characterized in that the oxide superconducting powder is molded, and then the molded body is coated with at least one of silver and silver oxide, and then fired to improve water resistance and conductivity. The present invention relates to a method for producing an oxide superconducting sintered body.

 Hereinafter, the method of the present invention will be described in detail.

After molding a typical fine powder of Y ₁ Ba ₂ Cu ₃ O _7- x as an oxide superconducting material by a mold press or CIP, a silver paste,
After at least one of silver oxide powder and silver powder is uniformly applied to the surface of the molded body to a predetermined thickness and dried sufficiently, the molded body is fired at 900 to 980 ° C, preferably 940 to 960 ° C for several tens of hours. As a result, silver diffuses inward from the surface during the sintering process and fills voids in the surface, forming a silver concentration distribution from the surface to the inside, which significantly improves water resistance and maintains superconductivity. In addition, the sinterability is improved and the surface resistance is reduced.

In the above, it is important and preferable to form a silver concentration distribution in which silver on the surface of the sintered body diffuses inward from the surface, and the silver concentration on the surface is high, and becomes lower toward the inside. .

In this case, the oxide superconductor is a crystal having a perovskite-type crystal structure of Y ₁ Ba ₂ Cu ₃ O _7- x, and of course, Y or Ba may be substituted. It can be applied to other oxide superconductors.

In the case of coating a molded article, there is a method such as application as one of the specific methods.

 Next, the present invention will be described with reference to examples.

(D) Example Example 1 An oxide superconducting powder having an average particle diameter of 10 μm of Y ₁ Ba ₂ Cu ₃ O _7- x was
Under pressure of 1 ton / cm ^2, a 4 mm thick 1 inch pellet was molded by pressure using a mold. A silver paste (manufactured by Fujikura Kasei Co., Ltd.) was applied to the surface of the molded body at a thickness of 20 μm, and then dried sufficiently. It was fired at a temperature of 950 ° C. for 20 hours in an oxygen atmosphere to produce an oxide superconductive sintered body.

 The surface resistance of this sintered body was as low as 5 mΩ · cm.

The sintered body was immersed in boiling water at 100 ° C for 20 minutes.
The superconducting properties were almost unchanged, although they were slightly white.

The Tc (critical temperature) of the pellet before immersion was 90K, and after immersion treatment, it was 89K when measured on a lightly polished surface.

Example 2 As in Example 1, Y ₁ Ba ₂ Cu ₃ O _7- x oxide superconducting powder (average particle size: 10 μm) was molded under the same conditions as in Example 1
Using an h (4 mm thick) pellet, the same silver paste as in Example 1 was applied to the surface of the pellet at a thickness of 10 μm, and then fired under the same conditions as in Example 1 to produce an oxide superconducting sintered body. did.

As a result, the surface resistance was low, and the results of the boiling water immersion test were the same as in Example 1.

Example 3 1 inch molded under the same conditions as in Example 1 with the same Y ₁ Ba ₂ Cu ₃ O _7- x oxide superconducting powder (average particle size of 10 μm) as in Example 1.
(Thickness: 4 mm) Silver oxide (AgO) powder having an average particle size of 3 μm was applied to the surface of the molded pellet, and then fired under the same conditions as in Example 1 to produce a sintered body.

As a result, the surface resistance was low as in the case of Example 1, and the result of the immersion test in boiling water was similar to that of Example 1, and there was almost no change.

Comparative Example 1 A mixed powder obtained by adding 5 wt% of silver oxide (AgO) to Y ₁ Ba ₂ Cu ₃ O _7- x oxide superconducting powder (average particle diameter: 10 μm) and mixing the same as in Example 1 was used in a mold at 1 ton / cm. ^Under the conditions of ² , a 1-inch (4 mm-thick) pellet was press-molded and fired in an oxygen atmosphere at 950 ° C. for 20 hours to produce an oxide superconducting sintered body.

The surface resistance of this oxide superconducting sintered body was 15 mΩ · cm, and Tc was 90K.

When this sintered body was immersed in boiling water at 100 ° C. for 20 minutes, the surface turned white, and Tc could not be measured only by light polishing.

Comparative Example 2 The same Y ₁ Ba ₂ Cu ₃ O _7- x oxide superconducting powder (average particle diameter: 10 μm) as in Example 1 was molded into a mold and 1 inch (4 mm thick) under the condition of 1 ton / cm ^2.
The pellets were molded under pressure and fired at 950 ° C. for 20 hours in an oxygen atmosphere.

The same silver paste as in Example 1 was applied to the surface of the fired pellet at a thickness of 20 μm, dried, and then dried again in an oxygen atmosphere.
Baking at 0 for 20 hours.

The surface resistance of the obtained sintered body was as high as 100 mΩ · cm, the results of the boiling water immersion test were poor, the whiteness was increased, and the Tc was significantly reduced.

(E) Effect of the Invention As described above, the present invention provides a compact obtained by press-molding a Y-Ba-Cu-O-based oxide superconducting powder or the like by coating the surface with silver or silver oxide and then sintering. Since silver diffuses inward from the surface to the surface of the obtained sintered body to form a silver concentration distribution such that the surface concentration is high and the inside is low, the water resistance of the sintered body surface is improved. However, the superconductivity can be maintained, and the surface resistance of the sintered body can be reduced.

In the above-described embodiment, the Y-Ba-Cu-O-based oxide superconductor has been described. However, it is needless to say that the method of the present invention can be applied to other types of oxide superconductors.

Claims (1)

(57) [Claims] After the oxide superconducting powder has been molded, at least one of silver paste, silver oxide and silver powder is applied to the surface of the molded body to a predetermined thickness, and after drying, the molded body is coated with 900 to 9%.
By sintering at 80 ° C., silver is formed in the sintering process to form a silver concentration distribution such that the silver concentration on the surface of the sintered body becomes higher as it goes inward and becomes lower, improving water resistance and maintaining superconductivity. A method for producing an oxide superconducting sintered body, characterized in that the superconducting sintered body further reduces the surface resistance.