JPH0477345A - Production of sintered superconducting material - Google Patents

Abstract

PURPOSE:To easily obtain a sintered superconducting material having a high critical current density by mixing a soln. contg. the compd. of the metal elements corresponding to the metal element composition of the superconducting material into the raw powder, forming the mixture and sintering the formed body. CONSTITUTION:The raw powder (e.g. a mixed powder of Bi2O3, PbO, SrCO3, CaCO3 and CuO in a specified molar ratio) for sintering a superconducting material is produced. A soln. contg. the compd. of the metal elements corresponding to the metal element composition (e.g. Bi:Pb:Sr:Ca:Cu=4:1:4:5:7) is then mixed into the raw material. The obtained mixture is formed, and the formed body is sintered to obtain the sintered superconducting material having a high sintered density. A soln. obtained by dissolving the naphthenates of Bi, Pb, Sr, Ca and Cu in toluene is exemplified as the soln. contg. the compd. of metal elements.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for sintering powder for sintering superconducting materials, and in particular, to a method for sintering powder for sintering superconducting materials, and in particular, it relates to a method for sintering powder for sintering superconducting materials. The present invention relates to a method of manufacturing a superconducting material sintered body having the following properties. The method of the present invention can be applied to any superconducting material such as a rare earth element-alkaline earth element-copper oxide system or a bismuth-alkaline earth element-copper oxide system.

(Prior art) Conventionally, sintered bodies of oxide-based high-temperature superconducting materials have been produced using dry mixing methods,
Raw material powder prepared by wet mixing method, multi-stage wet method, sol-gel method, flux method, hydrothermal method, etc. is calcined, pulverized,
It was manufactured by molding and sintering.

With the aim of homogenizing and increasing the density of sintered bodies, research is being actively conducted on each process.

As a method for preparing raw material powder, for example, the inventor of the present invention uses a mixed powder of raw material powders with an average particle size of 5 μm or less to prepare a powder with an average particle size of 1 μm.
It was discovered that a homogeneous sintered body could be obtained by sintering by pulverizing and then calcining, and a patent application has already been filed (Japanese Patent Application No. 101761/1999).

The adjustment of these raw material powders was aimed at homogenizing the particle composition and improving the critical current density.

However, since the raw material powder obtained by the above method has a fine particle size, the problem of poor sinterability (and therefore low sintered density) has been recognized again.

Examples of methods aimed at increasing the density of sintered bodies include:
A method in which a binder is added and molded after pulverizing the calcined raw material powder, and the molded product is degreased to increase the specific surface area and then fired (Japanese Patent Application Laid-Open No. 01-56351), which is molded into a superconductor precursor powder. In order to improve the properties, polyalkylene carbonate is added as a binder and mixed uniformly.
A method of performing pressure molding, debinding the molded body, completely volatilizing the binder, and then sintering it (Japanese Unexamined Patent Publication No. 01-208
357), a method of impregnating a molded green body or sintered body of high-temperature superconducting ceramics with a liquid containing a metal element compound corresponding to the metal element composition of the ceramic and sintering the same (Japanese Patent Application Laid-Open No. 01-298057), in a sealed container. A method of introducing a solution not only into the surface layer but also into the deep layer by introducing a metal salt solution such as naphthenic acid or the like into the gap and heat-treating the gap after reducing the pressure in the gap of the ceramic placed in the ceramic. 305844) etc. have been proposed.

(Problems to be Solved by the Invention) However, these methods have a drawback in that the steps are basically complicated. In particular, in the method of infiltrating a molded or sintered body with a metal salt, the infiltration treatment must be repeated repeatedly in order to obtain the infiltration effect, and even then, sufficient densification has not yet been achieved.

In order to solve the above-mentioned drawbacks, it is an object of the present invention to produce a high-density sintered body from a mixture with a homogeneous particle composition without requiring complicated processes such as degreasing, debinding, and infiltration. The objective is to develop a method for sintering superconducting materials that enables the sintering of superconducting materials.

(Means for Solving the Problem) The present inventor has been conducting research on a method for sintering superconducting materials using a powder method. As a result of a detailed study on increasing the density of sintered bodies, we found that in sintering powder for sintering superconducting materials, a solution containing a metal element compound corresponding to the metal element composition of the superconducting material is added to the raw material powder. It has been found that when first mixed, shaped and sintered, the sintered density is higher than before.

Based on this knowledge, the present invention provides a method for sintering a raw material powder for sintering a superconducting material by mixing a solution containing a metal element compound corresponding to the metal element composition of the superconducting material with the raw material powder. The present invention provides a method for producing a sintered body of a superconducting material, which comprises shaping and sintering a mixture.

(Detailed Description of the Invention) The superconducting material used in the present invention is not particularly limited, including its type. It goes without saying that superconducting materials with as high a superconducting temperature as possible, which are currently of great interest, are preferable. Examples include rare earth element-alkaline earth element-copper oxide system and bismuth-alkaline earth element-copper oxide system. The details of these are omitted as there are many references.

The superconducting material raw material powder used in the present invention can be produced by a known method such as a dry mixing method, a wet mixing method, a multi-stage wet method, a sol-gel method, a flux method, or a hydrothermal method. In particular, if it is desired to homogenize the particle composition, it is desirable to adjust the particle size in advance by the method already disclosed by the present inventor.

The solution of metal element compounds used in the present invention is obtained by dissolving a plurality of metal element compounds corresponding to a desired superconducting material in a solvent according to their compositions.

Examples of the metal element compound include oxides, hydroxides, halides, organic acid salts, inorganic acid salts, alkoxides, and the like. Particularly preferred compounds include metal-oxygen-
Those with carbon bonds, specifically, metal salts of organic acids or inorganic acids such as naphthenic acid, octylic acid, stearic acid, oxalic acid, citric acid, benzoic acid, nitric acid, carbonic acid, and salt, ethanol, and propylene chloride. Tools, metal alkoxides of alcohols such as butanol, and the like.

There are no particular restrictions on the metal concentration in the solution, and the upper limit is determined by the solubility of the compound, etc. In order to provide a sufficient densification effect, it is generally desirable to use 3 to 40% by weight in terms of the metal element compound.

As the solvent, any solvent may be used as long as it can dissolve the above-mentioned metal element compound or react with it if necessary. For example, hydrocarbons such as toluene and hexane, methanol,
Alcohols such as ethanol, ketones such as acetone,
Organic acids such as naphthenic acid, oleic acid, stearic acid,
Examples include nitric acid aqueous solution, ammonia aqueous solution, water, and mixtures thereof. It is desirable to use these in appropriate combinations depending on the type of metal element compound used.

The method of mixing the solution containing the metal element compound into the raw material powder is not particularly limited and may be any commonly used method. For example, a mortar, a ball mill, etc. may be used. The mixed amount of the solution may be within a range that provides a sufficient addition effect and allows molding, and is generally desirably about 0.1 to 10% by weight based on the raw material powder.

As for the molding and sintering methods, conventional methods are sufficient. For example, regarding the molding method, uniaxial molding using a mold,
Examples include CIP molding. Regarding the sintering method,
Examples include pressureless sintering, pressure sintering such as hot press, and the like.

It was confirmed that the superconducting material sintered body produced in this way has a higher sintered density than a case where a solution containing a metal element compound is not mixed.

(Example and Comparative Example n Bigot, PbO, SrCOs, CaCO
A raw material powder for sintering was produced using a wet mixing method using CuO as a raw material. Metal element composition is Bi:Pb:Sr:
Adjustment was made so that Ca:Cu = 4:I:4:5 near (near) ratio. The average particle size is O6 by mixing using a ball mill.
A mixed powder of 9 μm was obtained and used as a raw material powder.

A solution containing a metal element compound was prepared by dissolving bismuth naphthenate, lead naphthenate, strontium naphthenate, calcium naphthenate, and copper naphthenate in toluene in accordance with the above-mentioned raw material compounds. The composition ratio of each metal element was the same as that of the mixed powder, and the metal concentration in the solution was 40% in terms of metal compound.

The raw material powder and solution were mixed using an agate mortar. The mixing amount of the solution was 2%.

As a comparative example, a sample containing only raw material powder without mixing a solution containing a metal element compound was prepared.

These powders were uniaxially molded using a mold and heated at 850°C for 48°C.
Sintered in the atmosphere for an hour.

The composition, X-ray diffraction pattern, and density of the sintered body were evaluated. Regarding the composition and X-ray diffraction pattern,
Although no difference was observed between the present invention and the comparative example, as for the density, as shown in Table 1, it was confirmed that the sintered density was higher when the solution containing the metal element compound was mixed.

Table 1 (2) Compared to conventional high-density methods, there is no need to go through complicated steps, and it is possible to shorten the steps and save labor.

(3) This has the advantage that critical current density, which is one of the characteristics of superconductivity, can be improved over conventional values.

Name of agent: Motohiro Kurauchi (Effects of the invention) (1) The present invention has the advantage of increasing the density of the sintered body.

Claims (1)

[Claims] (1) In sintering a raw material powder for sintering a superconducting material, a solution containing a metal element compound corresponding to the metal element composition of the superconducting material is mixed with the raw material powder, the resulting mixture is shaped, and then sintered. A method for manufacturing a superconducting material sintered body, characterized by: