JPH01201062A - Production of ceramic superconducting material - Google Patents

Abstract

PURPOSE:To densify a superconducting material and to improve a critical current density in producing the superconducting material by subjecting a raw material of oxide-based superconducting substance blended in a superconducting substance composition to kneading-calcining-grinding-molding and sintering, by specifying the grinding and sintering methods. CONSTITUTION:Each oxide powder blended in a superconducting composition is repeatedly calcined and ground until a single phase of superconducting mate rial is obtained and the powder is finally ground in an anhydrous organic disper sion medium by a ball mill or jet mill to give fine powder having <=1mu average particle diameter. The fine powder is molded, sintered at 900-970 deg.C for 2-100hr and the average crystal particle diameter of the sintered material is made <=3mu. In this method, when the average crystal particle diameter of the sintered material is >=3mu, uniform denseness is not sufficient and high critical current density JC can not be attained. The sintering condition should be made to select a lower temperature side than the above-mentioned range if the particle size of the fine powder before the sintering is small and uniform. But if the sintering temperature is <900 deg.C, sintering is insufficient and JC is extremely lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing an oxide-based high-temperature superconducting material, etc. The present invention facilitates producing a superconducting material having a high critical current density.

[Prior Art] Recently, Y, Ba2C:u30. - Various oxide-based ceramics, represented by the composition of (X is the degree of oxygen vacancy), have been discovered as so-called high-temperature superconducting materials that exceed the superconducting critical temperature (Tc) or liquid nitrogen temperature, and research is underway to put them into practical use.・Development is being promoted in all areas. When applying this to magnetically levitated trains, nuclear magnetic resonance tomography devices, superconducting propulsion ships, etc., conductors (e.g. wires, tapes) with a large amount of circulating current per unit cross-sectional area, i.e. critical current density (Jc ), it is necessary to establish manufacturing technology for superconducting materials with large values.

However, regarding the superconducting properties of these oxide-based ceramics, although it has been confirmed that Tc can be achieved in the high temperature range of 90 or higher in the basic material, ie, the powder of such ceramics, it is extremely difficult to achieve a large Jc. Partly because there is no accumulation of research and development results for practical application, very few effective and specific proposals for improving Jc have been reported.

[Problems to be Solved by the Invention] Production of ceramic superconducting materials such as Y1Ba2Cu3O7-X and oxides with similar forms is as follows: La2O3
゜Blending raw material powders such as Y2O3, SrCO3, BaC0, CuO, etc. in a predetermined ratio to form a superconducting material composition,
This is calcined to volatilize and remove unintended components such as carbonic acid, and then pulverized to produce ceramic superconducting material powder as an intermediate material, and this powder is pressure-molded to form the desired material. This is generally done by heat treatment (finish sintering) after shaping.

Incidentally, the smaller the particle size and the higher the dispersibility of the powder of the ceramitsu-based superconducting material, the more dense and compositionally uniform a sintered body, ie, the superconducting material, can be obtained. If the superconducting material is dense, the influence of grain boundaries will be reduced, so the critical temperature Tc,
The critical current density Jc and the critical magnetic field become higher. Thereby, it is possible to achieve high performance and miniaturization of electrical equipment. Furthermore, it becomes possible to perform fine and complicated processing, making it possible to apply it to electronic devices. Therefore, the densification of superconducting materials has an extremely large effect on improving the performance of electrical equipment and electronic devices.

However, the ceramic superconducting material powder obtained by the above conventional manufacturing method is La2O3,Y2O3゜5rC
Since a plurality of types of component raw materials in the form of O, . Pressure molded powders of this type have multiple compositions and are a mixture of coarse and fine particles.
Partial (semi-macro) non-uniformity of components is difficult to avoid,
Furthermore, since it is a mixture of a low melting point substance such as CuO (melting point: 1026°C) and a high melting point substance such as Y2O3 (melting point: 2410°C), it can be It is extremely difficult to achieve uniform diffusion of components through final sintering. In other words, in conventional methods, superconducting materials (bulk) are formed from homogeneous and dense sintered bodies.
is difficult to obtain. This is the critical temperature Tc, critical current density Jc, and critical magnetic field ■. This poses a major obstacle in terms of manufacturing technology to the improvement of manufacturing technology. In other words, from another perspective, if extremely fine powder of ceramic superconducting materials could be manufactured and obtained industrially, it would greatly contribute to improving and stabilizing the practical properties (e.g. TC, Jc) of ceramic superconducting materials. Therefore, there was a request to make this happen.

[Means for Solving the Problems] The present invention provides a method for producing a superconducting material from raw materials of an oxide-based superconducting material blended into a superconducting material composition through the steps of kneading, calcination, pulverization, shaping, and sintering. A uniform and dense sintered body is obtained by performing sintering in an appropriate manner, and the gist is that in the final pulverization of the calcination and pulverization process, the sintered body is treated with a whole mill in an anhydrous organic dispersion medium, or placed in a nitrogen stream. The powder is made into a fine powder of Mi conductive material with an average particle size of 1 micron or less, and the sintering after molding is
The process is carried out for 2 to 100 hours at a temperature of .degree. C. to 970.degree. C. to produce a superconducting material having an average crystal grain size of 3 microns or less. The above-mentioned "molding" refers to not only pressure-molding the superconducting material powder to directly form the desired final shape, but also applying another plastic processing etc. after pressure-forming to form the desired shape. Including those who are.

Further, in order to make the present invention even more effective, it is preferable to perform sintering after molding in a substantially pure oxygen atmosphere.

As the anhydrous organic dispersion medium used in the final pulverization, monohydric alcohols (for example, ethanol), monovalent ketones (for example, acetone), and other various types can be used. This selection may be made by taking into consideration the various conditions of each manufacturing plant (for example, the strength of the ball mill, processing time), the characteristics of the dispersion medium (for example, the boiling point), and other factors.

The sintering conditions (temperature, time) depend on the particle size of the fine powder before sintering (-after final pulverization).Specifically, if the particle size is small and uniform, the conditions are on the lower temperature side or the shorter time side. can be selected.

[Function] Critical temperature Tc, critical current density Jc of oxide-based superconducting material
, critical magnetic field■. The uniformity and density of the crystal grains of the sintered body (the bulk of the superconducting material) are closely related to the superconducting properties. Does it have a dominant influence on these?
This is the average particle size and particle size distribution of the superconducting material powder used as the raw material. The finer the average grain size and the narrower the grain size distribution width, the more uniformity and density of the crystal grains of the sintered body can be improved.

In this invention, as a measure to finely powder a superconducting material, each oxide powder blended to have a superconducting composition is repeatedly calcined and pulverized until it becomes a single phase of superconducting material, and then finally pulverized. is pulverized in an anhydrous organic dispersion medium using a wet ball mill or a jet mill to obtain a fine powder of superconducting material with an average particle size of 1 micron or less.In contrast to the conventional method, the powder method obtains an average particle size of 1 micron or less, with a particle size distribution. As a result, good pulverized powder with a maximum particle size of 5 microns or less can be obtained.

FIG. 1 shows a histogram of the particle size distribution of the pulverized powder obtained by the conventional method and the pulverized powder obtained by the wet whole mill among the powder methods. Conventional methods leave unpulverized powder on the order of several 1O microns,
It has a large average particle size of about 3 microns.

As specific ball milling conditions, high purity Al2O3 or ZR02 is used as the ball material, and the diameter is I.
Boil to Ommφ~lrom. Acetone, methanol, ethanol, etc. can be suitably used as the anhydrous organic dispersion medium. The use of ZrO□ balls with a larger specific gravity and a smaller particle size is more effective in making the particles finer. As an anhydrous organic dispersion medium, acetone is advantageous for drying after pulverization, or when operating for a long time, acetone has a low boiling point, so there is a risk of vaporization and a sudden increase in internal pressure. It is preferable to use , ethanol, or methanol. Also, water cannot be used because this superconducting material absorbs water and decomposes.

Next, a method of pulverizing using a jet mill will be explained. It is preferable to use a jet mill whose inside is lined with Al2O3 or the like because there is less contamination of the powder due to wear when the powder collides with the mill. The gas for transporting the powder may be compressed air, but dry air containing no moisture or nitrogen is preferable. The grinding conditions of a jet mill depend on the equipment, but 1
It is sufficient to select conditions that will reduce the particle size to .mu.m or less, and conventional general pulverization conditions may be used.

Basically, the molding may be carried out by conventional and common means. Among these, CIP (cold isostatic pressing) is effective in improving the compactness of the molded product.

The purpose of selecting the sintering conditions is to uniformly and precisely control the crystal grains of the sintered body. Specifically, the goal is to achieve an average crystal grain size of 3 microns or less (and a maximum crystal grain size of 5 microns or less), preferably an average crystal grain size of 2 microns or less (and a maximum crystal grain size of 5 microns or less). When the average crystal grain size is larger than 3 microns, uniform density is not sufficient and a high Jc cannot be achieved. In order to achieve this goal, it is appropriate to sinter powder having an average particle size of 1 micron or less (and a maximum particle size of 5 microns or less) at 900°C to 970°C for 2 to 100 hours. As for more detailed sintering conditions, depending on the particle size of the fine powder before sintering, if the particle size is small and uniform, the lower temperature side of the above range must be selected. Excessive (long-term) sintering at high temperatures causes abnormal grain growth and large anisotropy of grains, which causes stress to concentrate at grain boundaries and generate cracks, resulting in a significant decrease in Jc. It is.

Furthermore, in low-temperature sintering, since the sintering time can be extended, it is possible to make the sintered body denser and strengthen the bonding force between crystal grains. However, below 900°C, sintering becomes insufficient and Jc also decreases significantly.

Sintering should be performed under a substantially pure oxygen atmosphere. P.O.
2 affects the formation of superconducting phase during cooling after sintering,
A Po2 enriched atmosphere is advantageous. fat as oxygen partial pressure
...The above is desirable.

[Example 1 Y2O3, BaCO3, CuO powder in atomic ratio Y:B
The mixture was mixed in a ratio of a:Cu = 1 = 2.3, and kneaded in ethanol for 1δhr in a pot mill. This was dried in vacuum, calcined at 950°C for 8 hours, and pulverized and mixed using a ball mill twice.
2Cu307-x) Single phase. Then, for the final grinding, a ZrO ball with a diameter of 10 mm was used, and the powder was ground in ethanol for 2 hours.
Ball milling was performed for 4 hours, and the product was taken out and dried under vacuum. The obtained powder had an average particle size of 0.8 microns and a maximum particle size of 4 microns. This is 20mmφ thickness 2ffII
11 pellets were molded with CIP 7t/cm2,
Sintering was performed under various conditions in a pure oxygen atmosphere. The critical temperature Tc and critical current density Jc were measured using the four-terminal method. The critical temperature Tc was all above 90K. No.-
The table shows the measurement results of Jc. For comparison, the same sintering was performed using powder with an average particle size of 3 microns and a maximum particle size of 30 microns obtained by the conventional method, and the results are also shown in the same table. As a result, when the superconducting powder according to the present invention with an average grain size of 1 micron or less was sintered at 900°C to 970°C for an appropriate time, the average crystal grain size of the sintered body was 3 μm or less, showing good Jc. Ta. In particular, the Jc of a sintered body with an average crystal grain size of 2 microns or less is large. It is also clear from Table 1 that an O2-enriched atmosphere during sintering has a significant effect. Also, from the first surface metal body, 900 to 9
Sintering at 70°C for 2 to 100 hours is found to be suitable.

Example 2 Y2O3, mouth act3. CuO powder in atomic ratio Y:
The mixture was mixed in a ratio of Ba:Cu = 1:2:3, placed in a pot mill, and mixed in ethanol for 16 hours. The solids were vacuum dried, calcined at 925°C for 8 hours, and dry ground in a ball mill twice to produce a single phase superconducting material (
A powder of YBa2Cu307-X) was obtained. At this point, the particle size distribution of this powder was as shown in FIG. 2, with the median particle size being 1.6 μm. This powder was dry-pulverized using a jet mill. As shown in FIG. 3, the particle size distribution after pulverization had a median value of 0.9 μm, and no particles larger than 51 could be detected. This is 20mmφ and 2mm thick.
It was molded into a pellet under conditions of CIP 2t/cm2 and sintered under various conditions in a pure oxygen stream. The critical temperature Tc and critical current density Jc of this fired body were measured by a four-terminal method.

The critical temperature Tc was all over 90. JC in Figure 4
The relationship between the measurement results and firing temperature is shown. The firing time was 8 hours, and the maximum Jc value exceeded 100 OA/cm2. The value of Jc in the conventional method, as shown in the example work, was a maximum of 250 A/Cl112, and it is clear that the JC was improved by the final method.

[Effects of the Invention] According to the present invention, a sintered body of a dense ceramic superconducting material that is homogeneous and has a small crystal grain size can be obtained, and as a result, it has become possible to manufacture a superconducting material with a high critical current density. .

[Brief explanation of the drawing]

Fig. 1 shows the particle size distribution of the ceramic superconducting material according to the present invention and the ceramic superconducting material ground with a normal dry ball mill, and Fig. 2 shows the particle size distribution of the ceramic superconducting material ground twice with a normal dry ball mill. Figure, 3rd
The figure shows the particle size distribution after the superconducting material powder shown in Fig. 2 is pulverized with a jet mill, and Fig. 4 shows the criticality of superconductors obtained by firing the superconducting material powder pulverized with a jet mill at various temperatures. It is a figure showing the relationship between current density Jc and relative density.

Claims (3)

[Claims] 1. Raw materials for an oxide-based superconducting material blended to have a superconducting material composition are kneaded, then calcined and pulverized one or more times to obtain a superconducting material powder, and this powder is molded and sintered to form a superconducting material. In the method for producing a superconducting material, the final pulverization of the calcination-pulverization step is performed by ball milling in an anhydrous organic dispersion medium to obtain a fine powder of a superconducting material with an average particle size of 1 micron or less, and the fine powder is shaped and heated to a temperature of 900°C to 970°C. 1. A method for producing an oxide-based superconducting material, characterized in that sintering is performed for 2 to 100 hours to obtain a sintered body of a superconducting material having an average crystal grain size of 3 microns or less. 2. Raw materials for an oxide-based superconducting material blended to have a superconducting material composition are kneaded, then calcined and pulverized one or more times to obtain a superconducting material powder, and this powder is molded and sintered to form a superconducting material. In the method for manufacturing, in the final pulverization of the calcination-pulverization step, the powder of the superconducting material is placed in a nitrogen stream and subjected to jet mill treatment to obtain a fine powder of the superconducting material with an average particle size of 1 micron or less, and the fine powder is Molding, 900℃~970℃
A method for producing an oxide-based superconducting material, which comprises sintering at a temperature of 2 to 100 hours to obtain a sintered body of a superconducting material having an average crystal grain size of 3 microns or less. 3. 3. The method for producing an oxide-based superconducting material according to claim 1, wherein the sintering after shaping is performed in a substantially pure oxygen atmosphere.