JPS63303851A - Sintered body of superconducting ceramic - Google Patents

Abstract

PURPOSE:A sintered body having a thin insulative layer on the surface and rhombic crystalline parts in the inside, having thus superior superconductive characteristics, produced by calcining a mixture consisting of a specified compsn. consisting of an oxide of a rare earth element, an oxide of an alkaline earth metal, an oxide of Cu, etc., and sintering a mixture after adding a specified proportion of Bi2O3 to the calcined product. CONSTITUTION:The sintered body of the superconducting ceramic of this invention is formed by adding 0.01-10pts.wt. Bi2O3 or 0.01-10pts.wt. Bi2O3 plus 0.01-16pts.wt. Pr6O11 to 100pts.wt. specified calcined product, molding the mixture, and then sintering the molded body. Said calcined product is obtd. by calcining a mixture consisting of 0.5-30wt.% oxide of a rare earth element, 20-80wt.% carbonate or oxide of an alkaline earth metal, and 10-50wt.% oxide of Cu.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a superconducting ceramic sintered body. Superconducting ceramics are formed into linear or strip shapes and are used in generators, transformers, other electrical equipment, and electronic devices such as D1Cefson elements.

BACKGROUND OF THE INVENTION Recently, superconducting materials, which are typical functional materials, have been rapidly developed.

Conventionally, several metal elements, alloys of these metals, intermetallic compounds, organic materials, ceramics, and the like have been known as superconducting materials.

However, their superconducting transition temperatures are generally low; for example, niobium titanium alloys, vanadium-gallium compounds,
Research was underway to apply niobium titanium alloys to superconducting magnets, etc., but they needed to be cooled to below an absolute temperature of 25, and expensive liquid helium was indispensable as a coolant.

Recently, La, Sr, Cu oxides, Y, H
a. Ceramic superconducting materials such as Cu oxide have been developed and are attracting attention. These are relatively inexpensive oxide systems, and the typical Y-Ba-Cu-0 system is 80
Since it exhibits superconducting properties at temperatures above 200 ft, it has the advantage of being able to use inexpensive liquid nitrogen as a coolant.

Conventionally, in the production of these ceramic superconducting materials, La203, Y203, SrCO3, BaCO
3. A method has been adopted in which raw material powder in the form of oxides or carbonates such as Cu 2 O is calcined, pulverized, pressure-molded, and then sintered.

The smaller the particle size and the higher the dispersibility of the raw material powder, the more dense the superconducting material can be obtained.

Problems to be Solved by the Invention In order for these ceramic materials to exhibit excellent superconducting properties, it is necessary to sufficiently increase the oxygen concentration in the ceramic materials. Moreover, as a result, Y Ba2Cu
In 307-type Y-Ha-Cu-0 ceramics, etc., the orthorhombic layered perovskite structure is stable, and this structure is thought to be the crystal structure that enables a high Tc (critical temperature for superconductivity). There is.

If the material is treated in an oxygen-enriched state, sufficient oxygen is supplied to the raw material powder, and the oxygen atoms enter the crystal lattice to form a lattice, it becomes a pure orthorhombic crystal, with high density and critical The temperature (τC) is high and the current density is high, resulting in good superconducting properties.

However, even when processed in an oxygen-enriched state, depending on the state of the raw material powder, sufficient oxygen may not be supplied, resulting in a sintered body containing a mixture of orthorhombic and tetragonal crystals, with a low density and chalk-like structure. Therefore, it may not exhibit excellent superconductivity.

The present invention aims to obtain a sintered body with high density without impairing its superconducting properties, and furthermore, it aims to provide a means for promoting the supply of oxygen to the material during the cooling process after sintering. be.

Means for Solving the Problems The present invention has investigated these problems, particularly a method for stably obtaining a sintered body with high density, and found that by blending a small amount of Bi2O3 into raw material powder and molding it, a liquid can be produced. The present invention was completed based on the knowledge that an orthorhombic superconducting ceramic sintered body can be obtained by promoting phase sintering and sintering while supplying sufficient oxygen.

That is, the gist of the present invention is as follows.

(1) A mixture containing 0.5 to 30% by weight of rare earth element oxide, 20 to 80% by weight of alkaline earth metal carbonate or oxide, and 10 to 50% by weight of copper oxide is prepared. Bi2O30.01~1 to 100 parts by weight of baked product
A superconducting ceramic sintered body formed by molding and sintering a mixture containing 0 parts by weight.

(2) A mixture containing 0.5 to 30% by weight of a rare earth element oxide, 20 to 80% by weight of an alkaline earth metal carbonate or oxide, and 10 to 50% by weight of a copper oxide is prepared. Bi2O3 and Pr6 to 100 parts by weight of the baked product
A superconducting ceramic sintered body formed by molding and sintering a mixture of 0.01 to 10 parts by weight of each of ou and ou.

(3) Calcining a mixture containing 0.5 to 30% by weight of rare earth element oxide, 20 to 80% by weight of alkaline earth metal carbonate or oxide, and 10 to 50% by weight of copper oxide. Bi2O30-01 to 10 to 100 parts by weight of
A superconducting ceramic sintered body prepared by blending parts by weight, molding and sintering, and polishing at least a part of the surface of the sintered body.

(4) Calcining a mixture containing 0.5 to 30% by weight of rare earth element oxide, 20 to 80% by weight of alkaline earth metal carbonate or oxide, and 10 to 50% by weight of copper oxide. Bi2O3 and Pr60 in 10033 parts of the
A superconducting ceramic sintered body prepared by blending 0.01 to 10 parts by weight of each of 11 to 10% by weight, molding and sintering, and polishing at least a portion of the surface of the sintered body.

Function As shown in FIG. 1, the present invention involves calcining a mixture containing a rare earth element oxide, an alkaline earth metal carbonate or oxide, and a copper oxide in a specific ratio to form a raw material powder. do. Bi2O3 is added to this as a sintering aid and oxygen source.
A mixture of Bi2O3 and Pr6O11 alone or a small amount of Bi2O3 and Pr6O11 is molded and sintered.

As a result, Bi2O3 becomes a liquid phase at the sintering temperature, penetrates into grain boundaries, and promotes sintering. Furthermore, since the Bi2O3 phase itself has the property of easily passing oxygen, sufficient oxygen diffusion through the grain boundaries becomes possible during sintering. Also, during cooling after sintering,
Since the added Pr6O11 is reduced and releases oxygen,
1203 and/or Pr6O1, such as 0 or more, where oxygen is supplied not only from the outside but also from the inside
1 increases the stability of the orthorhombic structure, making it possible to obtain an excellent superconducting material.

The rare earth element for forming the raw material powder is, for example, La%Eu, Dy, HOlEr, Tm, Yb or Y, and the alkaline earth metal is, for example, Ca.
, Sr or Ba. A typical example of the copper oxide is CuO1Cu20.

The method for obtaining the raw material powder is not particularly limited, and can be produced by, for example, the oxalic acid ethanol method previously proposed by the present inventors or the usual oxide/carbonate solid phase kneading method.

In addition, in the oxalic acid ethanol method, an aqueous solution of nitrates of rare earth elements, alkaline earth metals, and Cu is added to an alcoholic solution of oxalic acid to precipitate the oxalates of rare earth elements, alkaline earth metals, and Cu. Aqueous ammonia was added dropwise to the precipitated solution to adjust the pH to 2 to 7, and the mixture of the rare earth element, alkaline earth metal, and Cu oxalate obtained by filtering the solution was calcined.
This is a method of crushing.

Although Bi2O3 used in the present invention can be commercially available, it is preferable to use Bi2O3 synthesized by an alkoxide method because it yields particles with a particle size on the order of submicrons.

Bi2O3 is a substance that has a melting point of 825°C and is easily permeable to oxygen, and when added to the raw material powder, it forms a grain boundary layer, but within the range of the amount added, it does not cover the entire grain, so it is inherently superconducting. Even if Bi2O3, which does not exhibit this, is used, the superconducting properties will not be impaired.

Moreover, the Bi2O3 main component phase that has passed through the liquid phase escapes to the sample surface. As a result, the surface layer becomes an insulating layer with a thickness of about 1100 JL and does not exhibit superconducting properties.

However, the internal structure consists mainly of orthorhombic crystals that exhibit superconducting properties. The results of measuring these substances by X-ray diffraction are shown in FIG. Therefore, after sintering, the sample surface is approximately 110
By polishing to about 0.01L, a dense superelectric material can be extracted from the inside.

In addition, this insulating layer is very thin, so when it is used for semiconductor chips, lead wires, or parts that use a sintered body alone, there is no need to coat it with an insulating layer and it can be used effectively as is. be able to. Furthermore, it also serves as a protective film, making it a superconductor that is resistant to changes over time.

In the present invention, Bi2O3 and
The formation of orthorhombic crystals can be advantageously achieved by adding Pr6O11, which releases oxygen by a reduction reaction. The blending amount of Pr6O11 for this purpose is almost the same as that of Bi2O3.

Next, a method for producing a sintered body using the ceramic composition of the present invention will be explained in more detail.

First, a mixture containing 0.5 to 30% by weight of a rare earth element oxide, 20 to 80% by weight of an alkaline earth metal carbonate or oxide, and 10 to 50% by weight of a copper oxide is calcined. .

The calcination temperature is 700 to 1000°C, preferably 8°C.
The temperature is 50 to 850°C. This is because if the temperature is too high, the particle size will increase and the copper will melt, which is not preferable. Calcination time is 1 to 10 hours, preferably 2 to 6 hours.

The atmosphere for calcination may contain at least 20% oxygen by volume and other inert gases, but a high oxygen content is preferable, and a pressure of about 1 to 10 kgf/c2 is sufficient. be.

A raw material powder is obtained by calcination, and in the present invention, Bi2O3 and/or Pr are added to this as a sintering aid and an oxygen supplying agent.
6O11 is added and sintered after molding.

Regarding molding, if the calcined state is left as it is, the particles will fuse and become lumpy, making it impossible to form a molded product with uniform grain size. Therefore, the grain size is reduced to submicron level using an appropriate pulverizer, and then molded using an appropriate molding machine. It is preferable to form a molded article with desired dimensions and shape.

This molded body is sintered at a temperature of 825°C to tooo°C, preferably 850°C to 950°C, a sintering time of IH-48H, preferably 5H to 20H, an atmosphere of oxygen of 20% by volume or more and 1 to 10
As a result of sintering at kgf/cm2 of 0 or more, a dense sintered body having a thin insulating layer on the surface and excellent orthorhombic superconducting properties inside can be obtained.

Example Hereinafter, the present invention will be specifically explained with reference to Examples.

A YBa2Gu30-Bi2O3 sintered body to which 2.5% by weight of B12O3 has been added is manufactured according to the flowchart shown in Fig. 1. First, Y2O3, BaCO3, and CuO are blended and mixed to have a composition of YBa2Cu307. death,
After calcining in an oxygen gas atmosphere at 850°C, 5H, and pulverizing it, 2.5% Bi2O3 powder was added and kneaded again, uniaxial compression at 300kgf/cm2, 2000k.
Diameter 10m], thickness 2 with cold isostatic pressure of gf/c112
A molded body of mm was molded. Sintering at 950℃, 8H,
This was carried out in an oxygen stream to obtain a sintered body. In addition, as a comparative material, a sintered body without using Bi2O3 powder was manufactured under the same conditions.

Table 1 shows the measurement results of the bulk densities of the sintered bodies according to the present invention and comparative materials.

As is clear from Table 1, the sintered body according to the present invention showed an improvement in bulk density, and a clear reduction in pores was also observed when observed using a scanning electron microscope.

As explained above, Bi2O3 is a substance that does not exhibit superconductivity, so its behavior was investigated. As a result, X in Figure 2
As shown in the line diffraction results, it was found that the old 203 acts as a sintering aid and then escapes to the surface of the sintered body.

The surface layer to which Bi2O3 has migrated is a thin layer with a thickness of approximately 100 gm, and is a layer containing the γ-Bi2O3 phase (Fig. 2 (b)).
)), and is an insulating layer that does not exhibit superconductivity. However, an X-ray diffraction image showing the presence of tetragonal + orthorhombic crystals inside was obtained (Figure 2 (a)), and electron microscopic observation revealed that orthorhombic crystals with internal twins were present in other crystals. Similar observations were made to superconducting materials.

The surface layer of the obtained sintered body was ground down and its superconducting properties were measured. The results are shown in FIG. 3. As shown in this graph, a superconducting phenomenon was exhibited at about 90, and the resistance completely became zero at 82.

Effects of the Invention According to the present invention, a dense sintered body having a thin insulating layer on the surface and excellent orthorhombic superconducting properties inside can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of the present invention, FIG. 2(a),
(b) is an X-ray diffraction chart of the sintered body, and FIG. 3 is a graph showing the results of electrical resistance measurement.

Claims (4)

[Claims] (1) A mixture containing 0.5 to 30% by weight of rare earth element oxide, 20 to 80% by weight of alkaline earth metal carbonate or oxide, and 10 to 50% by weight of copper oxide is prepared. Bi_2O_30.01 to 100 parts by weight of baked product
A superconducting ceramic sintered body formed by molding and sintering a mixture of ~10 parts by weight. (2) A mixture containing 0.5 to 30% by weight of a rare earth element oxide, 20 to 80% by weight of an alkaline earth metal carbonate or oxide, and 10 to 50% by weight of a copper oxide is prepared. Bi_2O_3 and Pr are added to 100 parts by weight of the baked product.
A superconducting ceramic sintered body formed by molding and sintering a mixture of 0.01 to 10 parts by weight of _6O_1_1. (3) Calcining a mixture containing 0.5 to 30% by weight of rare earth element oxide, 20 to 80% by weight of alkaline earth metal carbonate or oxide, and 10 to 50% by weight of copper oxide. Bi_2O_30.01 to 100 parts by weight of
A superconducting ceramic sintered body prepared by blending 10 parts by weight, molding and sintering, and polishing at least a portion of the surface of the sintered body. (4) Calcining a mixture containing 0.5 to 30% by weight of rare earth element oxide, 20 to 80% by weight of alkaline earth metal carbonate or oxide, and 10 to 50% by weight of copper oxide. Bi_2O_3 and Pr_
A superconducting ceramic sintered body formed by blending 0.01 to 10 parts by weight of 6O_1_1, molding and sintering, and polishing at least a part of the surface of the sintered body.