JPS61256923A - Production of pulverous perovskite type oxide powder - Google Patents

Abstract

PURPOSE:To easily produce the titled uniform pulverous powder having good crystallinity by brining an aq. soln. contg. ions of prescribed components into reaction with an excess oxalic acid in the presence of ethanol and decomposing thermally the precipitate obtd. with ammonia, etc., at high pH. CONSTITUTION:The aq. soln. contg. the constituting metallic element ions of the perovskite type oxide expressed by the general formula; PbZr1-xTixO3 (where 0<=x<=1.0) is brought into reaction with the excess oxalic acid of 10-25mol% of the total molar number of the above-mentioned ions in the presence of ethanol to form the precipitate. A basic gas or basic aq. soln. such as gaseous ammonia or aq. ammonia of which the oxalate such as ammonium oxalate formed by reacting with an oxalic acid is insoluble in an aq. ethanol soln. and is decomposed to evaporate by heating is thereafter brought into reaction with the aq. ethanol soln. contg. the above-mentioned borate. The resultant precipitate is theremally decomposed at about 600-800 deg.C after filtration and sepn., by which the pulverous perovskite type oxide powder having easy dispersibility is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to perovskite-type oxides of the general formula Pbzr.
, -xTix03 (where X is O<, x<1:
1.0) (hereinafter abbreviated as PZT).

PZT, either by itself or in the form of a solid solution of other perovskite compounds, is a material that is widely used as a ferroelectric or piezoelectric material in capacitors and the like.

Many of these materials are used as sintered bodies obtained by baking and solidifying their powders. In that case, the quality of the material obtained is significantly influenced by the degree of sintering, so in order to obtain a good material, it is necessary that the raw material powder has excellent properties.

On the other hand, in recent years, there has been active development of so-called composite materials in which piezoelectric powders such as PZT are dispersed in polymer materials, but in order to improve the performance of these materials, it is necessary to use uniform and easily dispersible fine particles with good crystallinity. It is requested that it be a powder.

Prior Art The following method is known as a conventional method for producing PZT powder.

(1) A method in which oxide powders of each constituent metal element are mixed and the mixture is heated at high temperature to cause a solid phase reaction.

(2) A method of dropping sulfuric acid into an aqueous solution containing ions of each constituent metal element to coprecipitate each metal element as an oxalate salt, and then thermally decomposing the coprecipitated oxalate salt0 (3) Each composition A method in which a mixture of alkoxides of metal elements is hydrolyzed, coprecipitated, and the coprecipitated hydrolyzate is thermally decomposed.

However, all of these methods have a number of problems, and it is difficult to say that they are necessarily satisfactory. For example, the solid phase reaction in (1) not only has problems with the manufacturing process in that it requires high temperatures and long periods of time, but also makes it difficult to sinter the product powder. There is a problem in that it requires the use of a promoter.0 In the coprecipitation method (2), the solubility of the oxalate of each constituent metal element in water, which is the coprecipitation medium, differs, so each constituent metal element is mixed into the desired component. It is difficult to co-precipitate at a specific ratio, and therefore it is difficult to obtain a single composition of the desired composition.

Co-precipitation method (3) has the advantage of being able to obtain products with high purity and high uniformity, but it is difficult to manufacture and expensive because each constituent metal element needs to be an alkoxide. Become.

One of the inventors of the present invention, in order to eliminate the drawbacks of the conventional method,
First, we improved the oxalate method in (2) above, and found that oxalic acid is soluble in ethanol, and that the oxalate of Zr ions, Ti ions, and pb io/ Taking advantage of the property that Pb is completely insoluble in ethanol,
An aqueous solution of Zr and Ti salts, preferably lead nitrate, titanium, zirconium oxynitrates, is contacted with oxalic acid in the presence of ethanol to obtain a precipitate of PZT precursor, which is pyrolyzed to produce PZT fine particles. Invented a method for producing powder.

(Japanese Unexamined Patent Publication No. 59-3972 and Unexamined Japanese Patent Application No. 59-131
(Refer to Publication No. 505) According to this method, a fine powder with uniform particle size and easy sinterability can be obtained, but the obtained fine PZT powder contains some Pb,
It is deficient in Zr and Ti, which induces mutual fusion of fine particles during thermal decomposition, and the thermal decomposition temperature is 700°C.
℃ to 800℃ or higher.Objective of the InventionThe present invention aims to solve the above-mentioned problems, and its purpose is to easily produce uniform fine particles with a desired PZT composition and good crystallinity. It is an object of the present invention to provide a method for producing PZT fine powder which can be obtained at a low thermal decomposition temperature without causing mutual fusion of the fine particles obtained in the thermal decomposition step.

Structure of the Invention As a result of intensive research to achieve the above object, the present inventors have found that an aqueous solution containing ions of constituent metal elements of PZT is brought into contact with oxalic acid in the presence of ethanol to form a precipitate of oxalate. When precipitating using an excessive amount of oxalic acid, ammonia gas or ammonia water is added to the precipitate to raise the pH to 8 or higher, and a small amount of Pb remains in the solution.

At the same time as Zr and Ti ions are completely precipitated, excess oxalic acid reacts with ammonia to precipitate ethanol-insoluble ammonium oxalate. This ammonium oxalate is interposed between the precipitated metal salt particles and prevents the fine particles from adhering to each other during thermal decomposition, resulting in easily dispersible fine particles with good crystallinity and a low thermal decomposition temperature. I was able to find out what happened. The present invention was completed based on this knowledge.

The gist of the present invention is 1) general formula Pbzr1-xTixO3 (where X is O
≦X≦1.0) An aqueous solution containing constituent metal element ions of a perovskite-type oxide represented by ≦X≦1.0 is brought into contact with oxalic acid in the presence of ethanol to generate a precipitate of a precursor of the oxide. In the method for producing perovskite-type oxide fine powder by thermally decomposing this precursor precipitate, oxalic acid is used in excess of 10 to 25 mol% of the total number of moles of the constituent metal element ions, and the constituent metal element ions are After reacting an aqueous solution containing oxalic acid with oxalic acid in the presence of ethanol to generate a precipitate, the oxalate salt produced by reacting with oxalic acid is added to the ethanol aqueous solution containing the precipitate, which is insoluble in the ethanol aqueous solution. Contact with a basic gas or basic aqueous solution that forms a salt and decomposes and evaporates by heating, and when the pf (pf) is 8 or more, ammonium oxalate is simultaneously formed, and this is thermally decomposed. A method for producing perovskite-type oxide fine powder.

If the titanium raw material used in the method of the present invention contains chlorine ions in the precipitate, it will have an adverse effect when the thermal decomposition product is sintered, and especially if it contains PB, it will be difficult to chloride, which is insoluble in the mixed aqueous solution. Since lead is produced and the material becomes impure, it is preferable to use titanium oxynitrate obtained by dissolving titanium hydroxide, which contains little chlorine ions, in nitric acid. When using inexpensive titanium tetrachloride as a starting material, for example, titanium tetrachloride is mixed with twice the volume of distilled water to make a titanium tetrachloride aqueous solution, and ammonia is added dropwise to this to form a titanium hydroxide precipitate. When titanium oxynitrate is obtained by dissolving titanium hydroxide obtained by washing with water to remove chlorine ions in nitric acid, titanium oxynitrate containing less chlorine ions can be obtained.

As the raw material for zirconium and candy, it is preferable to use zirconium oxynitrate and lead nitrate. These may be commercially available products dissolved in water.

Oxalic acid ethanol is made by dissolving oxalic acid in a large amount of ethanol. The amount of oxalic acid is from 10 to the total number of moles of cations.
The excess amount is 25 mol%. This excess is necessary for subsequent contact with basic gases or basic aqueous solutions to form the oxalate salt. If it is less than 1.0 mol%, the amount of oxalate produced will be small and the effect will be small.If it exceeds 1.25 mol%, the oxalate produced will be too excessive and the presence of oxalate will be reduced. On the contrary, the effectiveness decreases. If the amount is 30 mol% in excess, the effect will be halved.

The ratio of oxalic acid to ethanol is preferably about 200 mols of ethanol per 1 mol of oxalic acid.

Next, the oxalic acid ethanol K is brought into contact with an aqueous solution containing ions of metal elements constituting PZT to form a precipitate of the metal oxide precursor. In this case, contact methods include (1) a method of dropping an aqueous solution of constituent metal element ions into an aqueous solution of constituent metal element ions, and (2) a method of dropping an aqueous solution of constituent metal element ions into an aqueous solution of constituent metal element ions. ) method is preferred. The reaction temperature at this time may be from 0 to room temperature.

A lower temperature is preferable in that fine particles are formed.

The ethanol aqueous solution containing the obtained precipitate is brought into contact with a basic gas or a basic aqueous solution in which the oxalate salt produced by reaction with oxalic acid is insoluble in the ethanol aqueous solution and decomposes and evaporates upon heating. Examples of the basic substance include ammonia and tetramethylammonium.

Among them, ammonia is preferred because it is inexpensive and easily available.

(Ammonia will be explained below as a representative.) The amount of ammonia used is the amount that will raise the pH to 8 or higher and convert excess oxalic acid into oxalic acid ammonium salt. ◇If the pH is lower than 8, a small amount of Pb, Zr,
It is difficult to completely precipitate Ti ions.

The ammonium oxalate thus produced is insoluble in the ethanol aqueous solution, so it is interposed between the oxalate particles of all the constituent metal element ions, and when it is thermally decomposed, PZT
Prevents fusion of particles and produces easily dispersible fine particles with good crystallinity.

Therefore, the PZT fine particles obtained by this K have excellent sinterability, and thermal decomposition and crystallization are completed at a temperature lower than that of particles not subjected to ammonia treatment by 100° C. or more.

It is desirable to filter the obtained precipitate and redisperse it in ethanol to remove nitrate ions and chloride ions contained in the precipitate. After drying, the precipitate is crushed to obtain a PZT oxide precursor powder. For example, 6
Calcinate at 00 to 800°C for thermal decomposition. In this case, T
Since the formation temperature of the solid solution varies depending on the i/Zr ratio, it is desirable to determine the thermal decomposition temperature by examining the ratio using X-ray powder diffraction or the like.

In the case of PbTiO3, it can be completely thermally decomposed and crystallized at 600°C. The resulting fine powder has a very fine particle size of 0.1 μm, and the particle shape is almost spherical and has excellent crystallinity. On the other hand, if no ammonia treatment is applied, the temperature will be 700 to 800℃ (700℃ if chlorine ions are completely removed).
) is required. As described above, the method of the present invention is economical since the thermal decomposition temperature is low.

Example 1: Double the volume of distilled water was added to a commercially available TiG14 solution to make a titanium tetrachloride aqueous solution, and aqueous ammonia was added to this to make titanium hydroxide. After washing and filtration, concentrated nitric acid was added to make titanium oxynitrate. Toshida. T in this titanium oxynitrate solution
i? The l1 degree was 0.025697d.

A titanium oxynitrate solution of 30.0 d of titanium oxynitrate was mixed with an aqueous solution prepared by dissolving lead nitrate in an equimolar amount with respect to TILt and Ti in 40.0 d of distilled water. This mixed aqueous solution was mixed with 280 ethanol of ethanol in an amount equivalent to 2.2 mol of Ti.
ml K dissolved in oxalic acid in ethanol solution at room temperature at a rate of 3.9 m/mi, H. Further, ammonia water 601 was added dropwise to this at a rate of 1.811 Lt/min to obtain a white precipitate. The pH at this time was 9.0. The resulting coprecipitate was washed twice with ethanol, dried, and ground, followed by heat treatment at 600° C. for 2 hours. The obtained powder was examined by X-ray diffraction and was found to be single-phase Pb.
No coexistence of unreacted substances was observed in TiO3.

Moreover, this PbTi0. Particles of the powder were easily dispersed by ultrasonic dispersion in water, and when observed with a scanning electron microscope, the particle size was 0.10 μm.

Example 2゜ Titanium oxynitrate solution 3o, omz and T obtained in Example 1
Equimolar amounts of zirconium oxynitrate and Ti for i
An aqueous solution in which twice the molar amount of lead nitrate was dissolved in distilled water 70.0117 was mixed. This is 4.4 for Ti.
After dropping a molar amount of oxalic acid into an oxalic acid ethanol solution dissolved in ethanol 400 at a rate of 1.2 d/min at room temperature, 2.8 d of ammonia water 801 was added.
A white precipitate was obtained by dropping at a rate of /min. The pH at this time was 10.0. The obtained precipitate was washed twice with ethanol and then dried.

The pulverized material was heat treated at 800° C. for 2 hours in air. When the obtained powder was examined by X-ray diffraction, PZ
In the T phase, no unreacted substances were observed. The particles of this PZT powder were easily dispersed by ultrasonic dispersion in water, and when observed with a scanning electron microscope, the particle size was 0.10 μm.

Comparative Example 1゜Into a mixed aqueous solution of lead, zirconium, and titanium prepared in the same manner as in Example 2, 20.0 dl min of oxalic acid ethanol prepared in the same manner as in Example 2 was added at room temperature.
A white precipitate was obtained by dropping the precipitate at a rate of 0.
After washing with ethanol twice, dry.

The pulverized material was heat treated at 800° C. for 2 hours in air. When the obtained powder was examined by X-ray diffraction, PZ
In addition to T, the presence of unreacted PbO and PbZrO3 was observed. When this powder was observed with a scanning electron microscope, it was found that
Particle fusion was observed, and the particle size was 0.80 μm.It was also observed that even ultrasonic dispersion did not eliminate this fusion at all.Effects of the Invention According to the method of the present invention, It has excellent effects such as:

1) After co-precipitating the constituent metal element ions as oxalates in the presence of ethanol, the constituent metal elements are brought into contact with a basic gas such as ammonia or a basic aqueous solution to adjust the pH to 8 or higher. It is possible to completely precipitate ions and easily obtain a uniform fine powder of PZT with the desired composition and good crystallinity. Since the oxalic acid basic salt is present in the coprecipitate particles of the constituent metal element ions, the phenomenon of mutual fusion of fine particles does not occur during thermal decomposition, and furthermore, the thermal decomposition temperature can be lowered.

3) Since the PZT oxide obtained has the above-mentioned properties, its piezoelectricity can be used for applications such as ultrasonic diagnostic equipment, flaw detectors, pressure sensors, buzzers, microphones,
It can be advantageously used in speakers, stereo pickups, piezoelectric actuators, etc.

Furthermore, when composited with rubber or synthetic resin polymer and used in blood pressure monitors, wide-surface speakers, etc., it is easy to form a thin film.

Patent applicant Goto, director of the Institute for Inorganic Materials, Science and Technology Agency
Excellent

Claims (1)

[Claims] 1) An aqueous solution containing constituent metal element ions of a perovskite oxide represented by the general formula PbZr_1_-_xTi_xO_3 (where x represents 0≦x≦1.0) in the presence of ethanol. In the method for producing perovskite-type oxide fine powder by contacting with oxalic acid to form a precipitate of a precursor of the oxide and thermally decomposing the precursor precipitate, oxalic acid is used to remove all of the constituent metal element ions. The aqueous solution containing the constituent metal element ions is reacted with oxalic acid in the presence of ethanol to form a precipitate, and then the ethanol aqueous solution containing the precipitate is added to the ethanol aqueous solution containing the precipitate. The oxalate produced by reacting with citric acid is brought into contact with a basic gas or a basic aqueous solution that is insoluble in the ethanol aqueous solution and decomposes and evaporates upon heating to raise the pH to 8 or higher and at the same time form ammonium oxalate. 1. A method for producing perovskite-type oxide fine powder, which comprises: 2) The method for producing perovskite-type oxide fine powder according to claim 1, wherein the basic gas or basic aqueous solution is an ammonia gas or an ammonia aqueous solution.