JPH02267151A - Superconducting ceramic raw material powder, its production and production of superconducting ceramic using the same - Google Patents

Abstract

PURPOSE:To produce a powdery raw material for superconducting ceramic having dense texture and containing little weak bonds by dispersing coarse particles of superconducting ceramic in a suspension of fine particles of superconducting or non- superconducting filler to attach the fine particles on the surface of the coarse particle and drying the product. CONSTITUTION:Coarse particles of a superconducting ceramic are produced by crushing calcined superconducting ceramic. The diameter of the coarse particle is preferably about >=10mum. Separately, fine filler particles of the same or different kind of superconducting ceramic or of a non-superconducting substance of submicron order are suspended in a solvent such as acetone. The above coarse particles are dispersed in the suspension of fine filler particles to attach the fine particles on the surface of the coarse particle and the product is dried. The amount of attached fine particle is preferably about 5-20%. A powdery raw material for superconducting ceramic can be produced by this process. A superconducting ceramic having dense texture and high critical temperature and containing little weak bonds can be produced by forming and sintering the raw material powder.

Description

Detailed Description of the Invention The present invention relates to a raw material powder for superconducting ceramics, a method for producing the same, and a method for producing superconducting ceramics using the same, and in particular, to obtain superconducting ceramics with high density and excellent electrical properties. The present invention relates to a technique of using raw material powder in which fine filler particles are attached to the surface of coarse particles.

The present invention is particularly useful for producing high-quality superconducting ceramics by increasing the density of wires, tapes, bulks, thin films, etc. of oxide superconducting materials.

Mendanko 11 Oxide-ceramic superconducting materials that exhibit superconductivity at high temperatures, which was previously unanticipated, are being reported one after another.

The discovery of superconductivity dates back to 1911, but since then
Research has been carried out mainly on b-type compounds, and the substance that exhibits superconductivity at the highest temperature so far is NbaGe (23K
)Met. It was thought that it would be difficult to break this barrier of critical temperature 23, but recently, since La-Ba-Cu-0 with critical temperature 30 was reported, the situation has changed, and La-3rCu -0 (37-54K) was announced, and Y -B a exceeds the boiling point of liquid nitrogen (77K).
-CuO was announced. Along with this, the practical application of superconducting materials has become more familiar, and a large amount of research is currently being actively carried out.

Currently, rare earth (RE)-based superconducting ceramics are
Ba2Cu30. ; (La, XAE,)2CuOy
), bismuth type (B1-3r-Ca-Cu-0),
There is a great deal of interest in oxide superconducting materials such as thallium-based (T1.-BaCa-Cu-0).

Superconductors are put to practical use in the form of wires, tapes, bulks, sheets, thin films, and other molded products, but at the current stage, superconducting ceramic raw material powder is first prepared and then formed or formed. The process is to form a film and then sinter it.

Known methods for preparing raw material powder for superconducting ceramics include an in-phase reaction method involving calcination at high temperatures and a wet pyrolysis method.

The former method involves mixing metal oxides, carbonates, metal hydroxides, etc. and then heating the mixture at high temperatures to synthesize superconducting powder through an in-phase reaction.

The latter involves thermally decomposing the coprecipitate using oxalate, carbonate, citrate, etc.

One of the important issues in superconductors is how to increase the critical current density. In the case of oxide superconducting ceramics, when coarse particle powder calcined at high temperature is used as a raw material for a sintered body, only a low-density sintered body can be obtained. On the other hand, when a submicron-order fine powder such as a wet co-precipitated powder is used as a raw material, the sintered density increases, but there is a problem in that electrical characteristics deteriorate due to the presence of many grain boundaries. In order to increase the critical current density, it is necessary to increase the sintering density, but if submicron-order fine powder is used as a raw material for this purpose, there is a problem of deterioration of electrical properties due to weak bonding at grain boundaries. It is.

An object of the present invention is to develop a technique for obtaining superconducting ceramic raw material powder that makes it possible to manufacture superconducting ceramics that are denser and have fewer weak bonds.

As a result of repeated studies aimed at achieving the above-mentioned objective, we have developed a method that utilizes the characteristics of coarse particles with few grain boundaries while also using fine particles in order to increase the density. We came up with the idea of a composite superconducting ceramic raw material powder with fine particles attached, and obtained good results in trials. It has been found that superconducting ceramic fine particles of the same type or different type as the superconducting ceramic coarse particles can be used as the fine particles, or non-superconducting fine particles that dissolve in the superconducting phase or improve contact properties can be used. These are collectively called filler fine particles. Based on these findings, the present invention provides: 1) a superconducting ceramic raw material powder characterized in that filler fine particles are attached to the surface of superconducting ceramic coarse particles; a step of preparing superconducting ceramic coarse particles; a step of preparing a filler fine particle suspension in which the same or different types of superconducting ceramic filler fine particles or non-superconducting filler fine particles are suspended in a solvent; and the filler fine particle suspension. A superconducting ceramic comprising the steps of dispersing the superconducting ceramic coarse particles in a liquid and attaching filler fine particles to the surface of the superconducting ceramic coarse particles, and drying the superconducting ceramic coarse particles to which the filler fine particles have been deposited. A method for producing superconducting ceramic raw material powder in which fine filler particles are deposited on the surface of coarse particles, and 3) a method for producing superconducting ceramics in which the superconducting ceramic raw material powder is molded and then sintered. A method for producing superconducting ceramics is provided, which uses superconducting ceramic raw material powder having fine filler particles attached to the surface of the particles.

■11 Superconductivity has three important properties: (a) zero electrical resistance, (b) perfect diamagnetism, and (c) the Josephson effect, and these can be utilized in various fields. Applications are being considered. For example, since the electrical resistance is zero, large currents can be obtained with low loss in the fields of power transmission and power generation. There are great expectations for its application to magnetic levitation trains and accelerators that require the generation of high magnetic fields. Furthermore, magnetic shielding materials can be put to practical use by utilizing the perfect diamagnetic property. Furthermore, the Josephson effect can be used to develop high-speed computer devices and superconducting quantum interferometers (
Applications to SQUID) and photoresponsive superconducting switching devices are also seen as promising. As described above, the applications of superconductors are wide-ranging, and in order to put them into practical use, it is essential to establish the raw materials and processing sintering technology for manufacturing superconducting ceramic wires, tapes, bulks, thin films, sheets, etc. It is.

Known methods for synthesizing raw material powder for superconducting ceramics include an in-phase reaction method in which calcination is performed at a high temperature, and a coprecipitation method using oxalate, carbonate, or citrate.

Taking the production of YBa2Cu307-y as an example, in the solid phase reaction method, ¥203, BaCO3 and CuO powder are mixed at 1:4.
:6 molar ratio, calcined at a temperature of 900 to 950'C, and pulverized to obtain a relatively coarse synthetic raw material powder.

In the thermal decomposition method using oxalate, Y(NO3)3 ・
XH2O, 2Ba(NO3)2 and 3Cu(N03
) Oxalic acid is added to the raw material nitrate of 2.31120 to cause coprecipitation, and the coprecipitate is calcined to obtain a raw material powder. 2 instead of oxalic acid
The carbonate method involves coprecipitation using CO3. The citrate method is a method in which citric acid and ethylene glycol are added to the raw material nitrate and co-precipitated, and is also called the gel method. In the coprecipitation method, fine powder on the submicron order is obtained.

In addition, research is progressing on metal alkoxide hydrolysis methods, sol-gel methods, spray drying methods, and flame atomization methods as methods for obtaining fine particle raw material powders.

According to the present invention, it is possible to combine coarse grains and fine powders of raw material powder for superconducting ceramics.

By the way, examples of superconducting ceramics that are currently attracting attention include the following: (A) Rare earth RE system: REBa2Cu30y (RE: rare earth metal, excluding cerium, praseodymium, and terbium): (Lal -XAEX)2CuOy(AE: Ba.

Sr, Ca alkaline earth) La-based (B) Bismuth-based Bi 2Sr2Ca2C+J30y Bi 2sr2cacu20y (C) Thallium-based TIJa2CanCun+ 10° Example TIJa2CazCuaOy TIJa2CaCu20y TIBa2CalICun+tO y Example TIBazCa2Cu30y TIBa2CaCu++0y (D) BPBO-based (Ba1-XKx)BiO2 (E) Lead-based Pb2SrJCu30 (A+ rare earth or rare earth +5r) (F) Neodymium-based (Nd, Ce)zcuo4 (Nd, Ce, Sr)2CL104 Others, Ca
5r2(Cu, Bi)ao is known.

Targeting such superconducting ceramics, first, fired superconducting ceramics using the solid phase reaction method are crushed to a 10 μm diameter.
Superconducting ceramic coarse particles larger than m are prepared.

Next, a filler fine particle suspension is prepared in which superconducting ceramic filler fine particles or non-superconducting filler fine particles of the same or different types are suspended in a solvent.

As the filler fine particles, particles having uniform particle diameters on the submicron order (d<1 μm) are used. Preferably, the calcined powder is produced by the coprecipitation method described above.

As the solvent, a chemically stable solvent having a low boiling point, low viscosity, and high purity (low water content) is used, such as acetone, toluene, xylene, benzene, alcohol, and ethyl acetate.

As the non-superconducting filler fine particles, additives such as PbO which are solid-dissolved in the superconducting phase, or additives such as Ag which improve contact properties can be used.

Examples of usable non-superconducting fine particles include PbO, Ag2o,
These include Pb and Ag. After adding a solvent to the filler particles, they are uniformly dispersed using an ultrasonic cleaner.

Superconducting ceramic coarse particles are dispersed in a suspension of filler fine particles, and the filler fine particles are attached to the surfaces of the superconducting ceramic coarse particles.

After sieving, the superconducting ceramic coarse particles to which filler fine particles are attached are dried at a temperature of 100 to 200°C. Fine filler particles can be added in an amount of 5 to 20% relative to the coarse particles.

As the coarse particles, it is preferable to use particles with as few grain boundaries as possible. In this respect, single crystal or near-single crystal particles are used. For example, in the case of rare earth yttrium, heating to 1000-1.050'C makes it semi-molten, and cooling at 10°C/hour to a temperature range of 920-960'C produces a mixture of superconducting and non-superconducting phases. is obtained. By separating the superconducting phase, pulverizing it, and separating the superconducting phase again by magnetic levitation separation, single crystal coarse particles of 10K or more are obtained. Even in the case of bismuth-based materials, single crystal coarse particles of 10K or higher can be obtained by holding the temperature at around 1000°C, cooling slowly to 850'C at a rate of 10°C/hour, and then pulverizing. Such single crystal particles are used if necessary.

<Example 1> YBa2CuJy was produced by solid phase reaction, which was calcined at 970'C in an oxygen atmosphere for 20 hours and slowly cooled. It was ground in a ball mill to prepare coarse particles with an average particle size of 20 μm.

On the other hand, 20 g of fine particles of YBa2CuJ with an average particle size of 0.5 μm were prepared by a wet co-precipitation method, and acetone 5
0 cc was added and subjected to an ultrasonic cleaner to prepare a suspension.

20 g of the above coarse particles were added to this suspension, and the mixture was placed in an ultrasonic cleaner for 15 minutes.

This mixture was poured into a 10μm sieve, and the sieve material was filtered through a 10μm sieve.
It was dried at 0°C for 5 hours.

10% of the fine particles were attached to the coarse particles.

Using this raw material powder, one-way press at room temperature
After molding into a bulk of 20 mm diameter x 5 mm thickness at a pressure of 000 kg/cm2, it was molded in an oxygen atmosphere of 2 kg/cm2.
It was baked for 0 hours and slowly cooled to room temperature over 20 hours.

The relative density of the resulting product increased from 85% to 95% when only coarse particles were used.

Critical current density Je (77K) is 100 A/cm2
It increased from 500 A/cm” to 500 A/cm”.

The present invention aims to create superconducting ceramics that are more dense and have fewer weak bonds through the use of a new concept raw material powder, which is a composite superconducting ceramic raw material powder in which fine filler particles are attached to the surface of coarse superconducting ceramic particles. made possible the production of The present invention targets superconducting ceramics with high critical temperatures, which have been in the spotlight recently, and is useful for increasing the density of wires, tapes, bulks, thin films, etc., and producing high-quality superconducting ceramics.

Claims (1)

[Scope of Claims] 1) A superconducting ceramic raw material powder, characterized in that filler fine particles are attached to the surface of superconducting ceramic coarse particles. 2) A step of preparing superconducting ceramic coarse particles by pulverizing fired superconducting ceramics, and preparing a filler fine particle suspension in which the same or different types of superconducting ceramic filler fine particles or non-superconducting filler fine particles are suspended in a solvent. a step of dispersing the superconducting ceramic coarse particles in the filler fine particle suspension to adhere the filler fine particles to the surface of the superconducting ceramic coarse particles; and drying the superconducting ceramic coarse particles to which the filler fine particles are attached. A method for producing a superconducting ceramic raw material powder in which fine filler particles are attached to the surface of superconducting ceramic coarse particles. 3) A method for producing superconducting ceramics in which superconducting ceramic raw material powder is molded and then sintered, characterized in that superconducting ceramic raw material powder in which filler fine particles are attached to the surface of superconducting ceramic coarse particles is used as superconducting ceramic raw material powder. Method for manufacturing superconducting ceramics.