JPH01226723A - Method for synthesizing particulate oxide raw material - Google Patents

Abstract

PURPOSE:To provide oxide raw material for synthesizing oxide high temp. superconductor, capable of being synthesized at a low temp. and sintered, by mixing metal salt soln. and oxalic acid, etc., in the presence of a water-soluble org. solvent having smaller dielectric constant than water, when the precipitate of metal oxalate is produced. CONSTITUTION:The mixed soln. (S1) of acetate, nitrate, etc. of Bi, Sr, Ca, copper, etc., is prepd. so as to make the compsn. of the targeted oxide high temp. superconductor. When the mixed soln. (S1) is added with ammonium oxalate or ammonium carbonate soln. (S2), the aq. soln. contg. one or more kinds of water-soluble org. solvents having <=50 dielectric constant is added to both S1 and S2, or one side S1 or S2 to synthesize a soln. contg. particulate metal oxalate precipitate. The title material is obtd. by spray-drying and heat decomposing, or spray-heat decomposing. The water-soluble org. solvent above- mentioned decreases the solubility of metal oxalate and the dielectric constant of the soln., and thereby, contributes to increasing the number of generating crystal nuclei and making precipitated particles corpuscular.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for synthesizing raw materials for oxide high temperature superconductors.

1° "i-Technology and its Problems" Conventionally, chemical methods for synthesizing oxide high-temperature superconducting materials include (1) solid phase reaction method, (2) evaporation method, and (3)
Co-precipitation method, (4) metal alkoxide method, etc. are known.

However, the solid phase reaction method described in (1) above involves mixing reagents such as bismuth, strontium, calcium, copper, etc. in the form of oxides, carbonates, etc. in a mortar, ball mill, etc., and repeating the steps of calcining and pulverizing. Although this method attempts to obtain a powder with the desired phase homogeneity, the resulting particle size generally increases, and the problem of sample contamination during the grinding process is unavoidable.

The evaporation method (2) is a method in which a dry sample is obtained by heating a mixed solution of metal salts with a predetermined composition ratio to remove the solvent, and a raw material powder is obtained by pulverizing and calcining this. When removing the solvent, non-uniformity of the composition and fluctuations in the overall composition tend to occur due to differences in solubility of each component, decomposition, sublimation, etc., and a pulverization process is required, resulting in the problem of sample contamination.

In the coprecipitation method (3), a precipitant is added to a mixed solution of metal salts to form precipitated particles of a single or double salt, which are then filtered,
By drying and firing, it is possible to synthesize fine particle raw materials with a size of 1 μm or less to several μm relatively easily. However, in the case of a multi-component system, complete simultaneous precipitation is theoretically impossible, and it is difficult to obtain a precipitate with a desired composition ratio.

In the metal alkoxide method (4), it is possible to synthesize ultrafine particles of several tens of nanometers by hydrolyzing a metal alkoxide solution, but the metal alkoxide as a starting material is very expensive, and in the case of a multicomponent system, , an organic solvent is required in which the solubility of each metal is high enough to cause no practical problems, and synthesis of composite alkoxides is difficult.
It has the same drawbacks as the coprecipitation method regarding the non-uniformity of the composition of precipitated particles.

"Summary of the Invention" The purpose of the present invention is to eliminate these drawbacks and provide a synthetic raw material for oxide high-temperature superconductors that is fine-grained and homogeneous, can be synthesized at low temperatures, and has easy sinterability. shall be.

In the process of researching a raw material synthesis method for oxide high-temperature superconductors, the present inventor discovered that when metal oxalate precipitates are formed, a solvent is added to an aqueous solution of oxalic acid, ammonium oxalate, and/or ammonium carbonate. By adding a water-soluble organic solvent such as ethanol with a dielectric constant lower than that of water, the precipitate formed when mixing ■ and ■ becomes finer.
The inventors have discovered that by spray-drying this, fine particles that can be easily thermally decomposed can be produced without requiring operations such as adjusting the amount of each component at pH 1 of the starting solution, and have thus arrived at the present invention.

That is, the present invention involves: (1) preparing a mixed solution of metal salts such as acetate and nitrate so as to have the desired composition of an oxide high-temperature superconductor; In particular, an aqueous solution containing at least one type of water-soluble organic solvent with a dielectric constant of 50 or less,
In addition to both or one of (2), a solution containing fine metal oxalate precipitates is synthesized.

Furthermore, by spray drying this solution under appropriate conditions, particles that can be easily thermally decomposed can be obtained, or by spray pyrolysis, it is possible to obtain fine particle raw material powder with a particle size of 2 to 3 μm or less after thermal decomposition. Features. The present invention will be explained in detail below.

First, the amount of water-soluble organic solvent added to the metal salt mixed solution and oxalic acid, ammonium oxalate, or ammonium carbonate is such that the water:organic solvent ratio in the total solution is 1 = 5 with respect to the saturated solution.
~lO:1, and the saturated solution:solvent ratio is 1:1 to 1:10
shall be. The reasons for adding a water-soluble organic solvent are, firstly, to reduce the solubility of metal oxalate and increase the number of crystal nuclei, and secondly, to reduce the dielectric constant of the solution and facilitate the formation of ionic aggregates. Both contribute to an increase in the number of crystal nuclei generated and to the atomization of precipitated particles. Here, if the ratio of water to organic solvent is larger than this, the degree of decrease in solubility and dielectric constant will be small, whereas if it is smaller than this, crystallization will easily occur during treatment.

In addition, if the ratio of the saturated solution to the solvent is too high, it becomes difficult to collect using a cyclone after spray drying, and if another collection method is required, the production efficiency will decrease. Table 1 shows examples and physical properties of the water-soluble organic solvents used.

In order to make the precipitated particles fine and homogeneous, it is necessary to mix (1) and (2) quickly with vigorous stirring using a stirrer or the like.

The conditions for spray drying include sample inlet and outlet temperatures, atomizing air volume, and sample delivery so that the sample dries quickly and the granulated particles are as fine as possible with a collectable size. It is necessary to adjust the amount of liquid and the amount of air sucked at the cyclone inlet so that the larvae can be collected with good yield. The optimum conditions for these conditions differ depending on the concentration of the sample solution, the volume of the drying chamber, the shape of the cyclone, etc.

Although the thermal decomposition temperature varies depending on the composition of the sample, for example, in the case of B14Sr3Ca3Cu40y, it was confirmed by X-ray diffraction that it exhibited a superconducting phase crystal structure after firing at 820°C for 3 hours (Figure 1).

In the case of spray pyrolysis, it is introduced into a furnace at about 600 to 1800°C, or under high temperature conditions such as plasma or chemical flame. In this case as well, various conditions related to spraying, such as temperature, spray droplet diameter, and residence time, include the amount of sample solution, concentration, type of solvent, shape of processing container, etc.
It is necessary to select optimal conditions depending on conditions such as the sample collection method. Further, if the thermal decomposition and crystallization of the obtained particles have not led to superconducting phase synthesis, an appropriate heat treatment is performed.

The particle size of the fine particles obtained through the processes of spray drying-pyrolysis and spray pyrolysis is fine particles with a primary particle size of 2 to 3 μm or less, and the composition analysis results of the bulk and micro regions using an analytical electron microscope. It was confirmed that the stoichiometry was maintained and the composition was uniform.

The thus obtained fine particles have a superconducting phase synthesized at low temperatures, and are fine and easily sinterable.

In addition, compared to other chemical synthesis methods, there is no need to control precipitation conditions during the process and there is no need to worry about compositional fluctuations, and it can be widely applied to cases where the target element or composition is changed. Moreover, mass production by scaling up the processing equipment is easy.

"Example" Next, the present invention will be explained with reference to Examples.

(Example 1) A nitrate solution 5001 of BiaSr3CaaCu40y of 0.02 M/I was prepared, and twice the volume of water-ethanol = 1:1 solution was mixed therein. A solution of 0.5 mol/I was mixed. These were rapidly mixed and stirred at room temperature, and the resulting solution was spray-dried under the following conditions. Two-fluid nozzle spray, drying chamber inlet temperature 200℃, outlet temperature 10
0℃, spray air pressure 1.5Kg/cm2, suction air amount, 0
．． 40m3/min, sample liquid flow rate 10cm3/m
The ino collection particles were agglomerated particles with a diameter of 2 to 5 μm, and by heat-treating them at 820° C. for 3 hours, particles exhibiting a superconducting phase crystal structure of 2 to 3 μm or less were obtained. The sintered body created using this raw material has a superconducting transition temperature Tc = 9
4K and was densified to 95% of the theoretical density.

(Example 2) Ethylene glycol was used as an organic solvent to be added to the metal nitrate aqueous solution and oxalic acid solution of Example 1. The concentration of water-ethylene glycol solution is water: ethylene glycol = 3
:1.

The spray drying conditions were the same as in Example 1, except that the sample solution temperature was 5.
It was kept at 0°C. By heat-treating the spray-dried particles at 820° C. for 3 hours, a superconducting crystalline phase similar to that shown in FIG. 1 was obtained.

The particle size was 2-3 μm.

(Example 3) A solution containing metal oxalate prepared under the same conditions as in Example 1 was sprayed into a reaction tube of an electric furnace kept at 900°C, and generated particles were collected using a cyclone and a filter. The primary particle size was 0.5 to 2 μm. This particle is bismuth,
These are oxides and carbonates of strontium, calcium, and copper, and after being heat-treated at 800° C. for 1 hour, they exhibited a superconducting crystalline phase.

"Effects of the Invention" As explained above, the present invention can easily produce a fine particle raw material with a homogeneous composition for an oxide high temperature superconductor that can be synthesized at a lower temperature than the conventional one, is easy to sinter, and is easy to sinter. This is expected to promote the practical application of superconducting materials, such as improving critical current density.

[Brief explanation of the drawing]

Figure 1 shows superconducting phase fine particle powder X produced by this method.
In the line diffraction pattern, (000) in the figure represents the plane index corresponding to each diffraction peak.

Claims (1)

[Claims] A metal salt solution such as bismuth, strontium, calcium, copper, etc. and an oxalic acid or ammonium oxalate solution or an ammonium carbonate solution are mixed in an aqueous solution containing at least one water-soluble organic solvent having a dielectric constant of 50 or less. A method for synthesizing particulate raw materials for use in oxide high-temperature superconductors by mixing and spray-drying-pyrolyzing or spray-pyrolyzing the mixture.