JPH07115949B2 - Method for manufacturing oxide superconductor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an oxide superconductor excellent in uniformity, reproducibility of production, and temperature characteristics.

2. Description of the Related Art A conventional method for manufacturing an oxide superconductor sintered body is to pulverize a raw material oxide or carbonate powder in an agate mortar,
After mixing, adding a binder and granulating, it is molded in a mold and baked in high temperature air.

Problems to be Solved by the Invention However, the conventional manufacturing method has problems in uniformity and reproducibility of production. For example, diameter
When a cylindrical sintered body with a thickness of 32 mm and a thickness of 30 mm was made and the uniformity of the characteristics inside it as a superconductor was examined, it was extremely bad. Moreover, there is a problem that the average value also greatly differs depending on the production lot.

The present invention has been made in view of the above points, and an object thereof is to provide a method for producing an oxide superconductor excellent in uniformity, reproducibility of production, and temperature characteristics.

Means for Solving the Problems In order to solve the above problems, in the material for a layered perovskite structure oxide superconductor, one kind of element is dissolved, and the remaining raw materials are mixed in the form of powder, Slurry is formed, and the obtained sludge is sprayed by a gas pressure into a high temperature container by gas pressure, and it becomes fine particles and is dried in the process of scattering and falling inside the container, and molding and firing the powder. This provides a method for producing an oxide superconductor excellent in uniformity, reproducibility of production, and temperature characteristics.

Effect The present invention can obtain a large-sized oxide superconductor excellent in uniformity, reproducibility of production, and temperature characteristics by the above-mentioned manufacturing method.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

(Example 1) A solution of yttrium nitrate was mixed with powders of barium nitrate and copper oxide so that the ratios of yttrium, barium and copper elements were each Y _0.3 Ba _0.7 Cu ₁ , and the mixture was mixed. (Slurry). The resulting slurry is sprayed with compressed air into a container kept at 290 ° C by the hot air blown into it using a narrow tube with a diameter of about 1 mm, and becomes fine particles, which dries in the process of scattering and falling inside the container. By doing so, powder having a particle size of 50 to 100 μm was obtained.

The powder thus obtained was calcined in air at 900 ° C. for 5 hours. After crushing and mixing this again, 900 ℃
It was fired in the air for 12 hours and then pulverized again. A binder (polyvinyl alcohol) was added to this in an amount of 5% by weight, and the mixture was granulated and molded into a disc having a thickness of 30 mm at a pressure of 200 kg / cm ² using a mold having a diameter of 40 mm. Next, this molded body was placed in an electric furnace and fired in air at 930 ° C. for 12 hours. After cooling to room temperature, heat treatment was performed at 900 ° C. for 5 hours.

Next, the electric resistance of this sintered body was measured at a liquid nitrogen (77 K) temperature, and as a result, it showed superconductivity. That is, the sintered body formed by such a method was a superconductor. When the obtained sintered body was examined by X-ray analysis, it showed a layered perovskite structure.

FIG. 1 shows a perovskite structure which is a constituent element of the layered perovskite structure which is the crystal structure of the present embodiment. In the figure, 1 is Cu, 2 is O, 3 is Y or Ba.
Is. The layered perovskite structure is one in which the components are stacked in layers with a certain period. It is considered that oxygen is appropriately eliminated in this structure of a material that is actually a superconductor.

About this material, oxide powder was used as a starting material, mixed in an agate mortar for 1 hour, and subjected to processing after molding in the same process as in this example. Uniformity and variation in characteristics between lots were measured and compared. As a result, the product obtained by the method of this example was significantly improved in both the uniformity of properties inside the sintered body and the variation in properties between lots, as compared with the agate mortar mixing method. Regarding the uniformity of properties inside the sintered body, the sintered body was cut into blocks of 5 mm square, and the critical temperatures of each were measured and compared. In the agate mortar mixing method, the variation was 5% or more, whereas in the present example, the variation was 3%.
% Or less. Also, make five sintered bodies each,
When the variation in the critical temperature was measured, the variation was about 10% or more in the agate mortar mixing method, whereas it was 7% or less in the present example. The reason for this is that, mainly in the method of the present example, a part of the material is solubilized and uniformly mixed with the powder, whereas in the agate mixing method, the powder and the powder are mixed. It is considered that the homogeneity is significantly different due to the mixing.

Further, by using the method of this example, the improvement of the critical temperature was observed. FIG. 2 shows the temperature dependence of the electric resistance of the superconductor. At the critical temperature, the electric resistance becomes zero. The critical temperature Tc ₁ of the present embodiment is the critical temperature Tc _{2 of} the superconductor prepared by the conventional agate mortar method.
Compared with, it was about 10% on the high temperature side. Considering the application of superconductivity, raising the critical temperature is extremely useful.
This improvement is one of the important effects of the present invention.

(Example 2) A solution of lanthanum nitrate was added to a powder of barium oxide and copper oxide, and the ratio of elements of lanthanum, barium and copper was La _1.84 Ba.
_The mixture was mixed so as to be contained in a ratio of _0.16 Cu _{1 to obtain} a slurry. The obtained slurry was subjected to the same process as in Example 1,
It was made into powder and then a sintered body was obtained. The electric resistance of the obtained sintered body was measured at a liquid helium (4K) temperature, and it showed superconductivity. That is, the sintered body formed by such a method was a superconductor. When the obtained sintered body was examined by X-ray analysis, it showed a layered perovskite structure.

Example 3 A solution of rare earth nitric oxide (Lu, Yb, Tm, Er, Ho, Dy, Gd, Eu, Sm, Nd nitric oxide) was added to powders of barium nitrate and copper nitrate, rare earth, barium, The copper element ratios are 0.4 and
Various types of slurry were mixed to obtain 0.6. The obtained slurry was pulverized through the same process as in Example 1 to obtain a sintered body. The electric resistance of the obtained sintered body was measured at a liquid helium (4K) temperature, and it showed superconductivity.

That is, the sintered body formed by such a method was a superconductor. Further examination by X-ray analysis showed a layered perovskite structure.

As described above, according to the method of the present invention, it is possible to obtain an oxide superconductor excellent in uniformity, reproducibility of production, and temperature characteristics.

According to the manufacturing method of the present embodiment, any material can be applied to the oxide superconductor having the layered perovskite structure. FIG. 1 shows the crystal structure of Example 1, but in the case of Examples 2 to 3, Cu, which was used in each Example instead of Y and Ba in this structure, was used. , And elements other than O have been replaced.

Regarding Examples 2 to 3 as well, the uniformity of characteristics inside the sintered body and the variation in characteristics between lots were measured and compared. As a result, the product obtained by the method of this example was significantly improved in both the uniformity of properties inside the sintered body and the variation in properties between lots, as compared with the agate mortar mixing method. In the agate mortar mixing method, the variation was 5% or more, while in the present example, it was 3% or less.
Further, when five sintered bodies were prepared and the variation in the critical temperature thereof was measured, the variation was about 10% or more in the agate mortar mixing method, whereas the variation in the present example was 7%. % Or less. The reason for this is that in all of the methods, in the method of the present embodiment, a part of the material is dissolved and is uniformly mixed with the powder, whereas in the agate mortar mixing method, the powder and powder are mixed. Therefore, it is considered that the uniformity is significantly different.

Further, also in Examples 2 to 3, as in the case of Example 1, improvement in the critical temperature was observed. The critical temperature of this example is about 10 as compared with the critical temperature of the superconductor prepared by the agate mortar method which is a conventional method.
It was on the high temperature side. Raising the critical temperature is extremely useful from the viewpoint of application of superconductivity, and this improvement is one of the important effects of the present invention.

Further, in this example, the raw material was solubilized using nitric oxide, but it is clear that if the solubilization is possible, the method of the present invention can be applied and the effects of the present invention can be obtained in view of the principle.

Further, from Examples 1 to 3, it is considered that the method of the present invention can be applied to any material as long as it is an oxide superconductor having a layered perovskite structure.

In the present invention, only one of the raw materials was made into a solution, and the other materials were mixed in the form of powder. If all raw materials are solubilized and this method is applied, the amount of water to be evaporated is much higher than that of the present invention. Therefore, a large amount of energy such as electric power is required for spray drying, which is not preferable. Further, if all of them are sprayed in the form of a liquid, precipitation of some materials occurs depending on the difference in solubility at the time of drying, and the uniformity is impaired, which is not preferable. In the present invention, since only one type of component is dissolved, such segregation does not cause non-uniformity.

In this embodiment, yttrium or rare earth is used as a solution, but these may be added in the form of powder, or barium or copper in the form of solution. However, from the viewpoint of energy saving during hot air drying, it is preferable to make the solution with the smallest amount into a solution.

Effects of the Invention As described above, the present invention is one of the materials for the layered perovskite structure oxide superconductor, which is made into a solution,
The rest of the raw materials are mixed in the form of powder, made into mud, and the obtained mud is sprayed into the high temperature container by gas pressure through a thin tube, and it becomes fine particles and is dried in the process of scattering and falling inside the container. The present invention provides a method for producing an oxide superconductor excellent in uniformity, reproducibility of production, and temperature characteristics by molding and firing the powder obtained by the above.

[Brief description of drawings]

FIG. 1 is a structural diagram showing a perovskite structure which is a constituent element of the layered perovskite structure which is the crystal structure of the oxide superconductor used in the present invention, and FIG. 2 shows the effect of raising the critical temperature of the present invention. It is a graph. 1 ... Cu, 2 ... O, 3 ... Y or Ba.

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Claims (3)

[Claims] 1. A layered perovskite structure oxide superconducting material, one of the elements is made into a solution, the rest of the raw materials are mixed in the form of powder, and the obtained slurry is gas-pressured through a thin tube. A method for producing an oxide superconductor, characterized in that a powder obtained by spraying into a high-temperature container by means of particles and drying in the process of scattering and falling inside the container is molded and fired. 2. The oxidation according to claim 1, wherein an A-Ba-Cu oxide (where A is Y, a rare earth) is used as the layered perovskite structure superconductor oxide. Method for manufacturing superconductors. 3. Rare earths such as La, Lu, Yb, Tm, Er, Ho, Dy, Gd,
Eu, Sm, Nd are used, The manufacturing method of the oxide superconductor of Claim (2) characterized by the above-mentioned.