JPH0784341B2 - Method for producing oxide-based superconducting compact - Google Patents

Description

The present invention relates to a method for producing an oxide-based superconducting molded article.

[Conventional technology and its problems]

Oxide-based superconducting compacts consisting of alkaline earth metals, rare earth elements, copper and oxygen are made of oxides, carbonates, etc. of the metals mentioned above as raw materials. It is manufactured by crushing this product, molding it into a desired shape and sintering it. Critical temperature (T _C ), critical current density (J _C ) in the superconducting compact
The superconducting properties such as are greatly changed depending on the composition of raw materials, firing conditions, etc., and in order to obtain good superconducting properties, the mixing ratio of various starting materials, pre-firing conditions, etc. are controlled,
It is necessary to use a composite oxide having a composition and structure most suitable for developing a superconducting state, and perform sintering so as to obtain a dense compact while maintaining this composition and structure.

The sintering is conventionally performed in the air or an oxygen atmosphere. In the former case, although a dense compact can be obtained,
It was not possible to obtain a molded product exhibiting good superconducting properties because the composition and structure of the composite oxide changed due to a decrease in the amount of oxygen during sintering. In the latter case, although the composition and the structure are not significantly changed, a compact compact cannot be obtained due to poor sinterability. In particular, when the compact is molded into a ring, coil or the like, cracks are generated in the compact. Etc. tended to enter, resulting in deterioration of superconducting properties.

[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 an oxide-based conical conductive molded body that can obtain good superconducting properties. .

That is, the present invention, in producing an oxide-based superconducting molded body consisting of alkaline earth metal, rare earth element, copper and oxygen,
The raw material powder is 500 in a reduced pressure atmosphere with an oxygen partial pressure of 10 ^{-5 to} 200 Torr.
Pre-baked at ~ 1000 ℃, then crushed and classified, thus obtained fine powder with the same composition having a particle size of 0.05-1 μm and 6-
12 μm coarse powder is mixed with a fine powder in the range of 10 to 90 wt% and then molded, and then the molded body is sintered in an oxygen atmosphere and then fired in an oxygen atmosphere. And a method for producing an oxide-based superconducting compact.

In the present invention, the raw material powder is a powder of an alkaline earth metal, a rare earth element and an oxide of copper, a halide, a carbonate, a nitrate, or a sulfate, or a mixture of two or more thereof. It is desirable to use.

The present invention provides a mixed powder of various starting materials with an oxygen partial pressure of 10 ^{−5 to} 20 −20.
Pre-baking at 500-1000 ℃ in a reduced pressure atmosphere of 0 Torr to make a composite oxide that is in an oxygen-deficient state compared to the composition and structure required to develop a superconducting state, crush it, and sinter it in an oxygen atmosphere after molding. Depending on the circumstances, it is possible to obtain a dense sintered body with a density of 95% or more by simultaneously sintering it with a kind of reaction sintering with oxygen, and at the same time make it have the composition and structure necessary for manifesting the superconducting state. Is. Pre-firing of the raw material powder has a partial oxygen pressure of
If it exceeds 200 Torr, it will not be sufficiently deficient in oxygen, and it will not be possible to obtain a sufficiently dense sintered body when sintering in an oxygen atmosphere, and the oxygen partial pressure will be less than 10 ^-5 Torr. If so, oxygen is extremely deficient, and even if it is crushed and sintered in an oxygen atmosphere after molding, the composition and structure necessary for developing a superconducting state will not be obtained, so the oxygen partial pressure 10 ^-5 ~ 200Torr
Pre-fire in the atmosphere. The pre-baking is 1000 ° C
If the temperature exceeds 500 ° C., the respective raw materials are dissolved and the composition and structure required to develop the superconducting state are not obtained, and if the temperature is less than 500 ° C., the reaction does not proceed sufficiently, so the reaction is carried out within the temperature range of 500 to 1000 ° C.

As a method for obtaining a reduced pressure atmosphere having an oxygen partial pressure of 10 ^{−5 to} 200 Torr, the pre-firing furnace is evacuated as it is or in a state of being replaced with oxygen gas, and the pressure is reduced to a predetermined oxygen partial pressure. It is also possible to adjust the oxygen content in the inert gas to a predetermined oxygen partial pressure by substituting it with an inert gas such as argon or nitrogen, but to accelerate the decomposition of the raw material powder. In this case, preliminary firing is performed in a reduced pressure atmosphere.

The present invention further has a particle size of 0.05 to 1 μm and 6 to 12 obtained by crushing and classifying the pre-baked powder.
The ratio of the fine-grained powder is 100 μm and the coarse-grained powder is
Within the range of 10 to 90 wt%, after uniformly mixing and molding, the sintering process is performed to obtain a dense sintered body and the ratio of grain boundaries that can cause current path (path) disentanglement. To decrease the critical current density (J _C ) by increasing

Moreover, it is desirable to perform sintering and firing in an oxygen atmosphere at 600 to 1100 ° C.

[Action]

In the present invention, the oxygen partial pressure of the raw material powder is 10 ^{−5 to} 200 Torr.
Pre-calcined in a reduced pressure atmosphere at 500-1000 ° C to obtain a composite oxide that is in an oxygen-deficient state compared to the composition and structure required to develop the superconducting state, crush it, and sinter it in an oxygen atmosphere after molding. Therefore, it is possible to obtain a dense sintered body with a density of 95% or more by performing the sintering accompanied with a kind of reaction sintering with oxygen, and at the same time, have the optimum composition and structure for developing the superconducting state. Further, the pre-calcined powder is pulverized and classified to obtain a fine-grained powder having a specific particle size and a coarse-grained powder, which are uniformly mixed at a specific blending ratio, and then baked. Since the binding treatment is performed, the ratio of grain boundaries that can cause current path (path) entanglement is reduced in the obtained molded product, and a molded product exhibiting excellent superconducting properties can be obtained.

Example 1 Next, the present invention will be described more specifically by way of examples. BaCO ₃ , Y ₂ O ₃ and CuO were used as raw material powders, and the molar ratio of (Y +
Ba): Cu were mixed to be 1: 1. 500 g of the mixture,
After substituting with oxygen gas, it was evacuated, and pre-baked at 950 ° C. for 6 hours in an atmosphere reduced to an oxygen partial pressure of 6 × 10 ⁻³ Torr. The fired product thus obtained was crushed and classified to have an average particle size of 0.
A fine powder of 3 μm and a coarse powder having an average particle diameter of 7 μm were prepared, and both were uniformly mixed so that the ratio of the fine powder was 40 wt%. After that, the mixed powder obtained in this way
50mm, inner diameter 30mm, thickness 7mm ring and diameter 25mm, thickness 5
Molded into mm pellets. The compacts thus obtained are sintered in an oxygen atmosphere at 950 ° C. for 2 hours, then fired in an oxygen atmosphere at 800 ° C. for 6 hours, and slowly cooled at 800 to 400 ° C. at 1 ° C./min for superconductivity. A molded body was obtained.

[Example 2] A pre-baked powder of the same composition prepared in the same manner as in Example 1 was used, and a 5-turn coil having a wire diameter of 2 mm and an outer diameter of 50 m and an outer diameter of 10 mm,
After forming a pipe with an inner diameter of 8 mm and a length of 100 mm and sintering these in an oxygen atmosphere at 900 ° C for 2 hours, 85
It was fired at 0 ° C for 20 hours and gradually cooled at a temperature of 800 ° C / 400 ° C at 1 ° C / min to obtain a superconducting molded body free from cracks and the like.

[Comparative Example 1] A mixture of raw material powders having the same composition prepared in the same manner as in Example 1 was preliminarily prepared at 950 ° C for 6 hours under an atmosphere of oxygen partial pressure of 0.6 atm (the balance was nitrogen, and the total pressure was 1 atm). Baked. The pre-baked powder having an average particle size of 0.5 μm obtained by pulverizing and classifying the powder was subjected to molding, sintering and firing in the same manner as in Example 1 to obtain a superconducting molded body.

With respect to the superconducting compacts obtained in Examples 1 and 2 and Comparative Example 1, the superconducting properties such as density and critical temperature (T _C ) and critical current density (J _C ) were measured, and the results are summarized below. The results are shown in Table 1.

As is clear from Table 1, in each of the products of Examples 1 and 2 produced by the method of the present invention, a dense compact having a theoretical density of 95% or more was obtained, and T _C , J _{C and the} like were obtained. The superconducting property was also good. On the other hand, in the product of Comparative Example 1 in which the raw material powder was not pre-fired in an atmosphere of low oxygen partial pressure, the density of the molded body was low, and T _C , J _C, etc. were low.

〔The invention's effect〕

According to the method of the present invention, it is possible to obtain a dense ceramic superconducting molded body having excellent superconducting properties, and to exert a remarkable effect industrially.

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Claims (4)

[Claims] 1. When manufacturing an oxide superconducting compact comprising an alkaline earth metal, a rare earth element, copper and oxygen, the raw material powder is 500 to 500 in a reduced pressure atmosphere with an oxygen partial pressure of 10 ^{-5 to} 200 Torr.
After pre-baking at 1000 ° C, pulverization and classification were performed, and 6 to 12 fine particles of the same composition with a particle size of 0.05 to 1 µm were obtained.
Coarse with a coarse particle size of μm in the range of 10 to 90 wt% of fine particle size, and then molding, and then sintering the molded body in an oxygen atmosphere, and then firing in an oxygen atmosphere. A method for producing an oxide-based superconducting molded article, comprising: 2. The raw material powder is a powder of an alkaline earth metal, a rare earth element and an oxide of copper, a halide, a carbonate, a nitrate, or a sulfate, or a mixture of two or more of them. The method for producing an oxide-based superconducting molded article according to claim 1, wherein 3. The method for producing an oxide-based superconducting compact according to claim 1, wherein the sintering is performed in an oxygen atmosphere at 600 to 1100 ° C. 4. The method for producing an oxide-based superconducting molded article according to claim 1, wherein the firing in an oxygen atmosphere is carried out at 600 to 1100 ° C.