JPH01242420A - Production of raw powder for high-temperature superconducting ceramic - Google Patents

Abstract

PURPOSE:To obtain the title easy-to-sinter raw powder for a superconducting ceramic by forming a precipitate from a mixed soln. of a Bi salt, an alkaline earth element salt, and a copper salt and a specified mixed soln., and sintering the precipitate. CONSTITUTION:A mixed soln. of a bismuth salt, an alkaline-earth element salt, and a copper salt is brought into contact with a mixed soln. of an ammonium salt and an amine to form a precipitate, and the precipitate is water- washed or not, separated by filtration, dried, and then calcined to obtain the desired raw powder. The raw powder is shown by the formula (A is Mg, Ca, Ba, and Sr). In the formula, two kinds of the alkaline-earth elements mentioned above are preferably combined and used as A, or more preferably Ca and Sr are combined. In addition, 1<x<4, 0.8<y<2.5, and 4<z<7 are preferably fulfilled. When two kinds of alkaline-earth elements are combined and used as A, the ratio of the two kinds is preferably controlled to 0.5w-1.5 or more preferably to about 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing raw material powder for easily sinterable Bi, alkaline earth, and Cu oxide-based high-temperature superconducting ceramics.

(Prior art and its problems) It has become known that Bi-alkaline earth element-Cu# compound ceramics is a superconducting material with a critical temperature of over 100 degrees. Since it does not use expensive rare earth elements such as Cu oxide-based superconducting ceramics, it is expected to be economical and to be applied in many fields.

These Bi-alkaline earth element-Cu acid oxidation group-based high-temperature superconducting ceramics become superconducting even when cooled with an inexpensive refrigerant such as liquid nitrogen, so Nb-, which only exhibits a superconducting state in liquid helium, If it can be used in superconducting magnets instead of Ti-based superconducting alloys, there will be great economic benefits.

However, the superconducting ceramics that have been produced so far have had problems in that their critical current density is low (and the temperature range of the transition from normal conduction to barrier conduction is wide and lacks steepness).

It has been pointed out that the reason for these problems is that superconducting ceramics are porous and have a low density.

Hitherto, Bi-alkaline earth element-Cu acid oxidation group-based high-temperature superconducting ceramics have been produced by pressurizing and sintering raw material powders prepared by dry or wet mixing.

In the dry mixing method, powders of oxides or carbonates of constituent components of superconducting ceramics, such as Bi201, CaC0,
, 5rCO, , CuO powder is used as a starting material, and it is crushed and mixed in a ball mill, mill, mortar, etc., and then sintered to produce raw material powder for superconducting ceramics.
This is the way to do it.

On the other hand, the wet mixing method uses the same starting materials as the dry mixing method.
This is a method in which a solvent that does not react with the starting materials and does not substantially dissolve them is added and mixed mechanically.

Both of the above heating methods are technically easy and highly safe methods, but the obtained raw material powder has a large particle size of 1 to 5 μm or more, the particle size distribution is not uniform, and there is also a large variation in components. .

Therefore, high-temperature superconducting ceramics made by sintering this raw material powder have a problem of low density and low critical current density.

Furthermore, in the multi-stage wet method, components are precipitated from a solution of each component of superconducting ceramics in multiple stages, but there are drawbacks such as requiring complicated steps.

(Technical means for solving the problems) The present invention solves the drawbacks of the conventional mixing method and wet method.
This is a method for producing easily sinterable superconducting ceramic raw material powder.

In the present invention, a precipitate formed by contacting a mixed solution of a bismuth salt, an alkaline earth element salt, and a copper salt with a mixed solution of an ammonium salt and an amine is filtered and separated with or without water washing, dried, and then Bi characterized by being calcined
- A method for producing raw material powder for alkaline earth element-Cu oxide superconducting ceramics.

The Bi-alkaline earth element-Cu oxide based superconducting ceramic in the present invention has the following general formula, Bi+AxCu
yoz, where A represents at least one alkaline earth element selected from Mg, Ca, Ba, and Sr. As A, it is preferable to use a combination of the above two types of alkaline earth elements, and particularly preferable is a combination of Ca and Sr.

In the above formula, 1<x<4.0.8<y<2.5.4
The range <z<7 is preferable. When two types of alkaline earth elements are used in combination as A, the composition ratio of the two types of elements is preferably larger than 0.5 and smaller than 1.5, and particularly preferably around 1.

As the bismuth salt, alkaline earth element salt, and copper salt of the present invention, hydrochloride, nitrate, etc. can be used.

As the ammonium salt, carbonate, bicarbonate, etc. can be used. The amount used may be at least the equivalent molar amount of the alkaline earth element salt.

As the amines, primary, secondary or tertiary amine compounds can be used, but secondary amine compounds (R, NH; R is an alkyl group having 1 to 4 carbon atoms) are particularly preferred. The amount used should be at least 1.5 times the amount of the above copper salt by mole.

The winter solvent is not particularly limited as long as it dissolves them, and for example, water, water-alcohol, alcohol, etc. can be used.

In the present invention, the precipitate can be formed, for example, by adding a mixed solution of an ammonium salt and an amine to a mixed solution of a bismuth salt, an alkaline earth element salt, and a copper salt while stirring the mixed solution. After forming a precipitate under the above conditions, if amines are further added in an amount equivalent to or more than the total number of moles of bismuth salt, alkaline earth element salt, and copper salt, the rate of formation of a copper compound precipitate is improved.

The formed precipitate can be directly separated by filtration and dried, but the precipitate may be washed with water, then separated by filtration and dried.

After drying, the powder is pre-sintered. Temperature of pre-sintering is 500~9
50°C is preferred. When the pre-sintering temperature is lower than 500°C, it is not preferable because dehydration and thermal decomposition of the mixed powder do not proceed sufficiently. Further, when the preliminary sintering temperature is higher than 950°C, the particles of the mixed powder become coarse, which is not preferable.

Superconducting ceramics can be obtained by molding the raw material powder of superconducting ceramics obtained by the method of the present invention under high pressure and sintering at 700 to 950°C.

(Effects of the present invention) The raw material powder of Bi-alkaline earth element-Cu oxide superconducting ceramics obtained by the method of the present invention has a uniform composition and particle size because the constituent element compounds co-precipitate. are submicron-sized particles and have good sinterability. The superconducting ceramic obtained by sintering this powder is a dense ceramic with a density of 5.3 g/cff1 or more, and the current density is also higher than that of conventional ceramics.

(Example) Examples of the present invention are shown below.

Example 1 250% of an aqueous solution of 0.04 mol of ammonium carbonate was mixed with 300% of an aqueous solution of 0.04 mol of diethylamine,
Aqueous solution of ammonium carbonate and diethylamine was added for 8 layers.

Next, while stirring the ammonium carbonate/diethylamine aqueous solution, 0.02 mol of bismuth nitrate, 0.02 mol of calcium nitrate, 0.02 mol of strontium nitrate, and 0.0 mol of copper nitrate. A coprecipitate was obtained by adding 450 g of an aqueous solution in which 4 mol of O was uniformly dissolved.

Further, while stirring the aqueous solution of the coprecipitate, 300 d of an aqueous solution of 0.34 mol of diethylamine was added, and after stirring for about 1 hour, the mixture was left in the apparatus overnight to complete the precipitation reaction.

The coprecipitate was separated by filtration, dried, pulverized, pre-sintered at 750°C for 2 hours, and then molded into an IT/CFFL press at 900°C.
The mixture was sintered for 5 hours to obtain a superconducting ceramic sintered body.

This superconducting ceramic had a density of 5.53 g/d, a critical temperature (T c ) of 105 K, and a critical current density of 418 A/cut.

Example 2 Example 1 except that in the filtration separation and drying of the coprecipitate, the coprecipitate was washed with distilled water, filtered, separated, and dried.
I did the same thing.

The density of this superconducting ceramic is 5.61 g/c4, the critical temperature (Tc) is 106, and the critical current density is 4.
23 A/CTI+.

Comparative Example 1 Bismuth oxide 0.5 mol, calcium carbonate 0.5 mol,
Powders of 0.5 mol of strontium carbonate and 1 mol of oxide were dry mixed using a crusher. 8 times this powder in the air.
20" C was fired for 12 hours. This powder was lt/cff
After press molding, it was sintered at 900°C for 6 hours to obtain a ceramic sintered body.

The density of this ceramic is 4.45 g/cffl, the critical temperature (Tc) is 92, and the critical current density is 195 A.
/c-ia.

Claims (1)

[Claims] A precipitate formed by contacting a mixed solution of a bismuth salt, an alkaline earth element salt, and a copper salt with a mixed solution of an ammonium salt and an amine is separated by filtration with or without water washing, dried, and then calcined. A method for producing raw material powder for Bi-alkaline earth element-Cu oxide superconducting ceramics, characterized by: