JP2764111B2 - Method for producing perovskite ceramic powder - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing perovskite-based ceramic powders, in particular high-quality perovskite-based ceramic powder materials having a uniform grain size and crystallization.

[Conventional technology]

Perovskite ceramic powders include, for example, barium titanate (BaTiO ₃ ), lead titanate (PbTiO ₃ ), calcium zirconate (CaZrO ₃ ), strontium titanate (Sr
TiO ₃ ) is a composite oxide generally represented by the ABO ₃ chemical formula, and these powders are useful as raw material powders for electric components such as ferroelectrics, ceramic heaters, and piezoelectrics.

Conventionally, perovskite-based ceramic powder, solid phase reaction method, alkoxide method, pyrolysis method of composite or mixed metal oxalate, product obtained by such methods as hydrothermal alloy method, using an electric furnace or gas furnace It is manufactured by calcining in the temperature range of about 400 to 1300 ° C and then pulverizing.

[Problems to be solved by the invention]

However, the perovskite ceramic powder formed by the process of calcining and pulverizing a product in the prior art has the following problems.

In the solid-phase reaction method, alkoxide method, thermal decomposition method of composite or mixed oxalate, hydrothermal synthesis method, and other conventional methods for producing perovskite ceramic raw material powder, even if any method is applied, In order to create the perovskite crystal structure described above, a calcining step of the raw material powder is required. However, even if a fine powder perovskite ceramic raw material powder is prepared by this calcining process, the original fine particles undergo grain growth due to the solid phase diffusion action between the fine particles, and the perovskite ceramic particles having the target crystal developed are developed. It was difficult to obtain ceramic raw materials.

For this reason, there is no problem if the sheet thickness is large when making a ceramic sheet using these raw material powders. However, recently, when the ceramic sheet is required to be thinner, a fine powder and a crystal structure are required. The need for a solid raw material powder is even higher. The current state of the art is that no well-known raw material powder has been obtained by the known techniques.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing a perovskite-based ceramic powder having a fine powder particle size and an extremely homogeneous crystal structure.

[Means for solving the problem]

In order to achieve the above object, a method for producing a perovskite-based ceramic powder according to the present invention comprises dispersing a perovskite (ABO ₃ ) -based ceramic raw material powder in an aqueous medium and then adding a carbonating agent or an oxidizing agent to dissolve the powder. Reacting with the A ion thus precipitated to precipitate carbonate or oxalate,
Subsequently, filtration, drying, and calcination are the structural features.

The production history of the perovskite (ABO ₃ ) -based ceramic raw material powder to be treated in the present invention is not particularly limited. That is, solid-state reactions of various metal carbonates and oxides,
Alcooxide method, oxalate method or hydrothermal synthesis method,
It is a powder having a crystal structure of perovskite obtained by a conventional method, and its crystallinity is not limited.

As such, for example, BaTiO ₃ , SrTiO ₃ ,
PbTiO ₃ , CaZrO _{3 and the} like are listed.
TiO ₃ is preferred.

In the present invention, first, such a raw material powder is dispersed in an aqueous medium by a desired means.

Since the raw material powder is preferably fine powder, when it is a coarse powder, it is desirable to perform a pulverizing operation prior to the dispersion treatment to obtain a fine powder.

In the dispersion operation, a slurry is prepared by dispersing the dispersion as uniformly as possible using a disperser such as a homogenizer, a colloid mill, or the like in which normal stirring, high-speed stirring, or strong shearing force acts. The slurry concentration is not particularly limited, but is 5 to 20% by weight.
In most cases, around 10 wt% is practical. The temperature may generally be room temperature, but may be in a heated state as needed.

Next, a carbonizing agent or an oxalate oxidizing agent is added to the prepared slurry and reacted with dissolved A ions to precipitate a fine precipitate of insoluble carbonate or oxalate.

That is, although the perovskite raw material powder represented by the ABO ₃ chemical formula has a low solubility in water, A ions corresponding to the state of the aqueous medium are dissolved in the prepared slurry with the above-mentioned dispersion treatment. The solubility is not limited to the A ion, and the A ion can be added and adjusted as needed.

In the present invention, this A ion (Ca ⁺⁺ , Ba ⁺⁺ , Sr ⁺⁺ , Pb ^++, etc.) is converted into fine particles of an insoluble salt with a carbonating agent or an oxidizing agent, and the fine particles of the perovskite raw material powder are converted by the fine particles. It is important that they are deposited or coated.

Here, the carbonating agent is a carbon dioxide gas, a carbonated water, an ammonium carbonate solution, an aqueous solution of ammonium bicarbonate and ammonia, and the oxalic oxidizing agent is an oxalic acid solution, an ammonium oxalate solution, or the like.

By causing such a carbonating agent or an oxidizing agent to act on the raw material slurry, the dissolved A ions quickly react to form fine particles of an insoluble carbonate or oxalate and deposit on the perovskite raw material powder.

After the reaction, the mixture is filtered, washed with water and dried to recover the raw material powder, and then calcined.

The calcination is performed by filling the raw material powder in a heat-resistant container such as a sagger and heat-treating it in a heating furnace such as a shuttle kiln in a temperature range of 400 to 1300 ° C., and then crushing using an appropriate crusher. Finish as a product.

This firing operation can be performed again if necessary.

(Operation)

According to the present invention, the A line in which the perovskite-based raw material powder is dissolved is converted into fine particles of insoluble carbonate and oxalate, and co-precipitated with the raw material powder to deposit or coat the surface of the raw material particles.

When such raw material powder is calcined, fine particles having a different composition are interposed between the particles of the raw material powder, and gas is generated by thermal decomposition, so that the solid diffusion action between the particles of the perovskite-based raw material powder is prevented. Thus, grain growth accompanying calcination is suppressed.

That is, the carbonate or oxalate of the A ion acts as a barrier agent against grain growth during calcination of the perovskite-based raw material powder, and after calcination, the composition becomes the original composition and becomes fine perovskite-based ceramic powder. Becomes

〔Example〕

Example 1. barium titanyl oxalate _{(BaTiO (C 2 O 4)} 2 · 4H
₂ O) a fine powder 1 barium titanate obtained by pyrolysis
Parts were sufficiently dispersed in 10 parts of water. Then, by blowing carbon dioxide gas with stirring, the Ba ions partially dissolved in water react with the carbon dioxide gas, and undissolved barium titanate (Ba
The barium carbonate fine particles generated are deposited on the TiO 3) particle surface. The end point of carbon dioxide injection is the pH of the slurry
, And stopped blowing when it reached 6.8. The obtained slurry is filtered, dried, crushed, and put in a sagger at 1100 ° C. for 4 hours.
Firing was performed for a long time to obtain a fine ceramic powder of barium titanate (the product of the present invention).

For comparison, a ceramic powder of barium titanate powder (comparative product) which was similarly calcined at 1100 ° C. for 4 hours without carbon dioxide treatment was obtained.

The particle sizes of these sample powders were determined by calcination by electron microscope observation.

FIG. 1 is an electron micrograph of a product of the present invention, and FIG. 2 is an electron micrograph of a product of a comparative example. As is clear from this photograph, the carbon dioxide-treated barium titanate (product of the present invention) prevents the growth of particles due to calcination, while the crystallization proceeds by calcination and barium titanate as a fine powder is formed. It turned out that.

When a multilayer capacitor was prepared using this barium titanate, a thin ceramic capacitor having a small dielectric loss and a large dielectric constant was obtained.

Example 2 712 parts of barium carbonate, 288 parts of titanium oxide and 2500 parts of water were put into a ball mill and mixed and pulverized for 4 hours. The obtained slurry was further sufficiently mixed with a stirrer, filtered, dried and then placed in a sagger. It was baked at 1100 ° C for 2 hours in a put shuttle kiln to produce barium titanate. Next, this was sufficiently pulverized by a pulverizer to obtain a powder having an average particle size of 0.7 μm or less.

This powder was added to a 10-fold amount of water, and a 3 wt% aqueous solution of ammonium carbonate (prepared with ammonium bicarbonate and aqueous ammonia) was added to the powder with sufficient stirring. After mixing for 30 minutes to allow a sufficient reaction, the mixture was filtered, dried, crushed, placed in a sagger, and fired at 1100 ° C. for 4 hours to obtain a fine ceramic powder of barium titanate.

On the other hand, a sample not subjected to the carbonation treatment with ammonium carbonate in the above was similarly calcined at 1100 ° C. for 4 hours to obtain a comparative sample.

When these two samples were observed with an electron microscope, it was confirmed that the carbonated product according to the present invention was a finer and sized powder.

Example 3. barium hydroxide _{Ba (OH) 2 · 8H 2} O) 289.9 parts of metatitanic acid [TiO (OH) 2] a slurry of (6 parts in terms of TiO2)
And 600 parts of water in an autoclave and stir at 9
The reaction was maintained at 5 ° C. for 2 hours. Next, solid-liquid separation was performed by a filtration device, and the obtained wet cake was placed in a washing device, and sufficiently washed with 600 parts of warm water to wash away excess barium hydroxide adhering to the crystals.

Next, filtration was performed again, and the obtained crystals were dried at 105 ° C. and then pulverized to obtain barium titanate fine powder. 1 part of barium titanate of this fine powder is dispersed in 10 parts of water, and ammonium oxalate in an amount of 3 wt% of the input amount of barium titanate is added little by little to the dispersion, and the mixture is stirred well for 30 minutes to react. I let it. Next, the slurry was filtered, dried and crushed, placed in a sagger, and fired at 950 ° C. for 4 hours to obtain a fine ceramic powder of barium titanate.

On the other hand, in the above, an untreated product which was not subjected to an oxalation reaction was fired at 950 ° C. for 4 hours to obtain a comparative sample.

When these two samples were observed with an electron microscope, the one according to the present invention was prevented from increasing in particle size due to firing,
It was found that it was a ceramic powder suitable for reducing the thickness of the multilayer capacitor and suitable for miniaturization of the capacitor.

Example 4. 148 parts of strontium carbonate and 80 parts of titanium oxide were pulverized and mixed in a ball mill, and the obtained powder was heated at 950 ° C for 2 hours.
After calcining, a solid phase reaction was carried out until a perovskite structure of strontium titanate (SrTiO ₃ ) was obtained, followed by pulverization with a pulverizer to obtain a raw material powder having an average particle size of 0.8 μm or less.

This raw material powder was sufficiently dispersed in 10 parts of water with respect to 1 part of the raw material powder by a stirrer, and 15 wt% ammonium carbonate based on the raw material powder was slowly added to the dispersion.
After sufficiently stirring, filtering, drying and crushing, the mixture was placed in a sagger and fired at 1100 ° C. for 2 hours in a shuttle kiln. When the obtained powder was lightly crushed and observed with an electron microscope in the same manner as in Example 1, an increase in the particle size due to firing was prevented as compared with the untreated product, and a strong microcrystalline strontium titanate titanate having a perovskite structure was obtained. Powder.

Example 5 100 parts of calcium carbonate and 80 parts of titanium oxide were mixed and pulverized with a ball mill, and then calcined at 1000 ° C. for 4 hours to obtain a calcined product having a perovskite structure of calcium titanate (CaTiO ₃ ). . The calcined product was pulverized by a pulverizer to prepare particles having an average particle size of 0.8 μm or less. 1 part of this powder
After uniformly dispersing in 0 parts of water, carbon dioxide gas was blown in, and when the pH of the slurry reached 6.8, the reaction was stopped, the mixture was aged for 30 minutes, and then filtered and dried to obtain a powder. Then, the powder was put in a sagger and fired at 1100 ° C. for 4 hours in an electric furnace to obtain a ceramic powder of calcium titanate.

Observation of this powder with an electron microscope revealed that the particle size was not increased due to firing compared to an untreated carbon dioxide gas product, and it was found to be a fine powder and a ceramic powder with crystals having a perovskite structure developed.

Example 6 221 parts of lead oxide (PbO) and 80 parts of titanium oxide were wet-mixed and pulverized with a ball mill, and dried, and then dried at 900 ° C.
After calcination for a time, a solid phase reaction was performed until a perovskite structure of lead titanate (PbTiO ₃ ) was obtained, and the mixture was further pulverized by a pulverizer into a powder having an average particle size of 0.8 μm or less. Next, this raw material powder was uniformly dispersed in 10 parts of water with respect to 1 part of the powder by a stirrer. 5 wt% ammonium oxalate was gradually added to the raw material powder, and after the addition was completed, the mixture was aged for 30 minutes, filtered, dried, and lightly pulverized to obtain a powder. This powder was placed in a sagger and calcined at 950 ° C. for 2 hours to obtain a ceramic powder of lead titanate.

This powder was observed with an electron microscope and compared with an untreated product of ammonium oxalate. As in Example 1, the powder was a fine-grained ceramic powder having fine particles and a fine crystal structure with good particle size distribution. It turns out.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, compared with the manufacturing method of the conventional perovskite-type ceramic powder, a fine and sized powder can be obtained.

Therefore, the perovskite-based ceramic powder obtained by the method according to the present invention can be effectively applied as an electroceramic powder that can follow a recent ceramic sheet required to be thinner.

[Brief description of the drawings]

The figure is an electron micrograph (magnification: 50) showing the particle structure of the barium titanate powder ceramic powder obtained in Example 1.
FIG. 1 shows a product of the present invention, and FIG. 2 shows a product of a comparative example.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeki Yamagata 9-15-1, Kameido, Koto-ku, Tokyo Inside the Research & Development Department, Japan Chemical Industry Co., Ltd. (72) Inventor Kazuo Ochiai 9-15-1, Kameido, Koto-ku, Tokyo No. Japan Chemical Industry Co., Ltd. Research and Development Department (56) References JP-A-64-3019 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01B 13/14-13/36

Claims (6)

(57) [Claims] 1. A perovskite (ABO ₃ ) -based ceramic raw material powder is dispersed in an aqueous medium, and then a carbonating agent or an oxalic oxidizing agent is added to react with dissolved A ions to precipitate a carbonate or an oxalate. A method for producing perovskite ceramic powder, which is followed by drying, drying and calcining. 2. The method according to claim 1, wherein the perovskite ceramic raw material powder is
The method for producing a perovskite-based ceramic powder according to claim 1, wherein the average particle diameter is in a range of 0.1 to 5 µm. 3. The method for producing a perovskite ceramic powder according to claim 1, wherein the carbonating agent is carbon dioxide or carbonated water. 4. The method for producing a perovskite ceramic powder according to claim 1, wherein the carbonating agent is an ammonium carbonate solution. 5. The method according to claim 1, wherein the oxidizing agent is oxalic acid or ammonium oxalate. 6. The method for producing a perovskite ceramic powder according to claim 1, wherein the perovskite ceramic powder is barium titanate.