JPH0769634A - Production of composition - Google Patents

Abstract

PURPOSE:To provide a producing method capable of obtaining a ABO3 type compound composed of uniform and spherical particles of <1mum, preferably <0.5mum particle diameter, having 1.000+ or -0.002mol ratio of A group element to B group element, excellent in crystallinity and extremely little in impurities such as alkali metals. CONSTITUTION:This producing method is composed of (a) a 1st process for obtaining a slurry mixture of at least one kind of salts of A group element composed of Mg, Ca, Sr, Ba and Pb and at least one kind of salts of B group element composed of Ti, Zr, Hf and Sn with water or an alkaline aq. solution, (b) a 2nd process for obtaining a hydrothermal synthetic powder by the hydrothermal reaction of the slurry mixture and after repeating cleaning several times, filtering and drying, (c) a 3rd process for allowing a mixture of the hydrothermal synthetic powder obtained in the 2nd process with the alkaline aq. solution to hydrothermally react. For instance, the obtained powdery barium titanate is 0.2-0.3mum in particle diameter, 0.999 in Ba/Ti ratio, 100ppm in Na content and 20ppm in Cl content.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a composition containing a perovskite type compound.

[0002]

2. Description of the Related Art In recent years, electronic devices have become significantly smaller and have higher performance. Correspondingly, the same applies to the ceramic electronic parts constituting the electronic device, and various improvements in the manufacturing process of the ceramic have been studied for the purpose of miniaturization and high performance, but the limit has almost been reached. Therefore,
In order to obtain ceramics that are even better than the current situation, it is necessary to improve the material.

For example, as the dielectric ceramics, 1
A uniform and spherical perovskite-type compound (hereinafter referred to as ABO ₃ type compound) having a size of μm or less, preferably 0.5 μm or less has been studied. The ABO ₃ type compound having such a particle size has a high surface energy when the particle size is small,
If the particle size distribution is uniform and spherical, packing at the time of molding is improved, so the sinterability is remarkably improved, and dense and strong ceramics can be obtained at a lower temperature. Further, a ceramic green sheet having a thickness of 10 μm or less is required in order to realize thinning and multi-layering of a monolithic ceramic capacitor, and in that case as well, 1 μm or less, preferably 0.5 μm or less of uniform thickness. Therefore, a spherical ABO ₃ type compound is required.

Conventionally, as a method for producing an ABO ₃ type compound such as barium titanate, barium carbonate and titanium oxide are reacted (calcined) at a high temperature of 1000 ° C. or more to synthesize barium titanate and mechanically A method of pulverizing and classifying (solid phase synthesis method) is known. Against this,
As a wet synthesis method, a metal alkoxide method, a hydroxide method,
Hydrothermal synthesis method and the like are known.

[0005]

However, in the case of the solid phase synthesis method, since barium titanate after calcination is solidified, even if it is mechanically pulverized and classified, it becomes a fine state of 1 μm or less. Is difficult. Further, since the particle shape thereof is a crushed product, when this was molded into an arbitrary shape and sintered, it lacked in sinterability. Further, as described above, in order to realize the thinning and multi-layering of the monolithic ceramic capacitor, it is necessary to form a ceramic green sheet having a thickness of 10 μm or less without any problem. When using barium titanate powder obtained by the method, the green density of the green sheet is reduced, or,
There was a problem that the thickness variation of the green sheet became large.

Further, regarding the wet synthesis method, in the case of the metal alkoxide method, the raw materials are expensive and there is a problem in industrialization. On the other hand, the hydroxide method has been attracting attention because the raw material is relatively inexpensive and the obtained powder has high sinterability.

For example, in JP-A-60-90825, a method of heating titanic acid and barium hydroxide at a temperature below the boiling point in the presence of a large amount of water is used. In this case, titanic acid is used. Must be adjusted in advance. For example, when titanic acid is precipitated by neutralizing an aqueous solution of a titanium compound, it is a colloid,
There is a problem that washing and filtration are industrially difficult.

Further, in JP-A-59-39726, a water-soluble barium salt such as barium chloride or barium nitrate is dissolved in an aqueous solution of titanium salt, and alkali is added to adjust the pH.
Is adjusted to 13 or more and heating at a boiling point or lower is proposed. However, since the barium titanate powder obtained by this method has a particle size of 0.02 to 0.03 μm, which is too fine, it has a problem that the density when molded is low and the shrinkage during sintering is large. Depending on the case, it may not be preferable.

With respect to the hydrothermal synthesis method, attention has recently been paid particularly to the fact that it is possible to obtain the barium titanate powder most suitable for withstanding the thinning and multi-layering of a monolithic ceramic capacitor.

For example, in JP-A-61-31345, a mixture of a group A element such as Ba and Sr and a group B element hydroxide such as Ti and Zr in a desired A / B ratio is prepared in an aqueous medium. A method has been proposed in which, after hydrothermal reaction, a group A element dissolved in an aqueous medium is made into a water-insoluble form, followed by filtration, washing with water and drying. However, in this case, the amount of the so-called insolubilizing agent that makes the group A element insoluble in water has to be determined for each production lot, which is complicated. That is,
In the hydrothermal reaction, the reaction rate varies depending on the production lot. Therefore, the concentration of group A element ions dissolved in the filtrate is analyzed each time, and the amount of the insolubilizer added is determined according to the value. There is a need.

Further, in JP-A-62-72525, any one of carbonate, chloride and nitrate compounds such as barium is dissolved in an aqueous solution of titanium tetrachloride to prepare sodium hydroxide or water. Add potassium oxide,
A method of heating in an autoclave has been proposed. However, as a result of detailed examination, alkali metal impurities such as Na and K could not be removed by any means. For example, in the synthesized barium titanate powder, 800-10
It became clear that about 00 ppm remained.

The object of the present invention is to provide uniform spherical particles of 1 μm or less, preferably 0.5 μm or less, and A
The molar ratio of the site element and the B site element is 1.000 ± 0.
It is an object of the present invention to provide a method for producing an ABO ₃ type compound having a crystallinity of 002, good crystallinity, and very few impurities such as alkali metals.

[0013]

That is, the gist of the method for producing a composition according to the present invention is (a) M
g, Ca, Sr, Ba, and Pb, at least one salt selected from the group A elements, at least one salt selected from group B elements consisting of Ti, Zr, Hf, and Sn, water or alkaline A first step of obtaining a mixture slurry with an aqueous solution, (b) a second step of hydrothermally reacting the mixture slurry to obtain a hydrothermal synthetic powder, (c) a hydrothermal synthetic powder obtained in the second step, And a third step of hydrothermally reacting the mixture with the alkaline aqueous solution.

In the third step, as the alkaline aqueous solution, for example, a barium hydroxide aqueous solution having a pH adjusted to 7 to 10 is used.

After the mixture slurry is prepared in the first step, the mixture slurry is hydrothermally treated in the next second step to obtain a synthetic powder. If the synthetic powder contains an alkali metal such as Li or Na, it is preferably washed. The number of times of washing may be arbitrarily repeated until the amount of alkali metal can be reduced to a certain amount. Then, it is filtered and dried to obtain a dry powder. This dry powder is brought to the next third step, mixed with an alkaline aqueous solution and the mixture hydrothermally reacted. Here, the alkali metal impurities including the ABO ₃ type compound can be further reduced.

[0016]

According to the present invention, there is a step of further mixing the powder obtained by hydrothermal synthesis with an alkaline aqueous solution, and subjecting this mixture to a hydrothermal reaction, in which the alkali contained in the ABO ₃ type compound is used. The amount of metal impurities can be reduced. The ABO ₃ type compound thus obtained has a small particle size, a uniform particle size, and a spherical shape, so that it has good reactivity and can lower the sintering temperature. Further, since the crushing step can be omitted, it is possible to prevent impurities from being mixed by crushing.

[0017]

EXAMPLES Example 1 0.1 mol of Ti (O—iC ₃ H ₇ ) ₄ and 30 ml of isopropyl alcohol (hereinafter referred to as IPA)
Is placed in a beaker made of polyfluorinated ethylene resin. Next, this solution is hydrolyzed with 135 ml containing 0.6 mol of an aqueous NaOH solution while being stirred with an ultra disperser. And 0.1 mol of BaCl ₂ · 2H
₂ O is charged (first step).

This mixture slurry was placed in a beaker made of polyfluoroethylene resin and mounted in an autoclave apparatus, and the polyfluoride was kept for 4 hours under the conditions of temperature: 170 ° C. and pressure: 16 kg / cm ^2. Using a stir bar made of ethylene oxide resin, 1
Hydrothermal synthesis was performed while stirring at 50 rpm. The precipitate obtained is taken out, washed with water and filtered several times,
A raw material powder was obtained by drying and crushing (second step). The particle diameter of this powder is 0.2 to 0.3 μm, and Ba / Ti
Ratio: 1.001, Na amount: 1000 ppm, Cl amount: 20 p
It was pm.

Next, 20 g of the powder and 200 ml of an aqueous barium hydroxide solution adjusted to pH = 10 were placed in a polyfluorinated ethylene resin beaker as above, and the beaker was autoclaved. It was attached to a heating device and subjected to hydrothermal treatment under the conditions of temperature: 200 ° C. and pressure: 15 kg / cm ² for 4 hours while stirring at 150 rpm using a stirring rod made of polyfluoroethylene resin. After completion of the treatment, filtration, drying and crushing were performed to obtain a raw material powder (third step). The powder has a particle size of 0.2 to 0.3 μm and a Ba / Ti ratio of 0.99.
9, Na amount: 100 ppm, Cl amount: 20 ppm. FIG. 1 is an X-ray diffraction pattern of the composition obtained by this method and shows that it has a cubic perovskite structure from the sharp peak of (110).

A brief description of each step is as follows:
Although Ba and Ti are charged in an equimolar ratio in the first step, a molar ratio shift occurs after the second step hydrothermal synthesis. To prevent this, at least 4 of the concentrations of Ba and Ti should be added.
The OH concentration is required to be twice, preferably 6 times or more.

Next, after the second step, washing is carried out, but washing is carried out several times with an alkaline aqueous solution in order to prevent Ba escape. The alkaline pH is at least 9 or higher. In addition,
The number of times of cleaning affects the reduction of impurities such as Na, K and Cl. Although Cl can be almost completely removed by washing 2-3 times, when an alkali metal impurity such as Na or K reaches a certain concentration, it does not decrease and is constant no matter how many times it is washed thereafter. In this example, the amount of residual Na remained at 1000 ppm after the third and subsequent washings. It is presumed that this is because alkali metal impurities such as Na are incorporated in the crystal lattice of barium titanate.

It was found that this reduction of residual Na can be solved by performing the re-hydrothermal treatment in the third step. This is
This is a very new fact that could not have been predicted from the known examples up to now. As the re-hydrothermal treatment condition, the higher the temperature, the better. However, when a polyfluorinated ethylene resin beaker is used, it is preferably 200 ° C or lower. A reaction time of 4 hours is sufficient.

In addition, regarding the solution at the time of rehydrothermal treatment,
It is necessary to make it alkaline so as to prevent Ba escape. Ammonia water, which gives alkalinity,
An aqueous solution containing an alkali metal such as a sodium hydroxide solution or a potassium hydroxide solution and an aqueous solution containing an alkaline earth metal such as a barium hydroxide solution are considered.

Among these, ammonia water is not preferable because under the condition of hydrothermal treatment, the ammonia volatilizes to cause Ba loss due to a decrease in pH, and the volatilized ammonia reacts with a beaker made of a polyfluoroethylene resin.
Further, an aqueous solution containing an alkali metal such as a sodium hydroxide solution cannot be used because it is one of the purposes to remove the alkali metal from the composition obtained by the present invention.

Therefore, an aqueous solution containing an alkaline earth metal such as a barium hydroxide solution is preferable. Particularly, a barium hydroxide solution is preferable, and the pH at that time is 7 to 10 and preferably 9 to 1
It is better to set it between 0. If the pH exceeds 10, the Ba / Ti ratio of the finally obtained powder will shift to the side with a large amount of Ba, and if the pH is 9 or less, Ba will be lost under hydrothermal treatment conditions.

[0026] (Example 2) 0.1 mol of Ti (O-iC ₃
H ₇ ) ₄ and 30 ml of IPA were put into a polyfluorinated ethylene resin beaker and stirred with an ultra disperser, and an aqueous solution containing 0.6 mol of NaOH 1
The hydrolysis is carried out with 35 ml. And 0.1 mol of Sr
Add Cl ₂ (first step).

A beaker made of a polyfluoroethylene resin containing the mixture slurry was mounted in an autoclave apparatus, and the temperature was 170 ° C. and the pressure was 16 kg / cm ² for 4 hours.
Use a stirring rod made of polyfluorinated ethylene resin to
Hydrothermal treatment was performed while stirring at rpm. The resulting precipitate was taken out, washed with water and filtered several times, then dried and crushed to obtain a raw material powder (second step). The particle diameter of this powder is 0.1 to 0.2 μm, and the Sr / Ti ratio is:
The amount was 1.002, the amount of Na was 900 ppm, and the amount of Cl was 10 ppm.

Next, 20 g of the above powder and 200 ml of a barium hydroxide aqueous solution adjusted to pH = 10 were placed in a polyfluorinated ethylene resin beaker, and this beaker was placed in an autoclave apparatus. Attached, temperature: 200 ℃, pressure: 15kg
The hydrothermal treatment was performed for 4 hours under the condition of / cm ² using a stirring rod made of polyfluoroethylene resin while stirring at 150 rpm. After completion of the treatment, filtration, drying and crushing were performed to obtain a raw material powder (third step).

As a result of observation with an electron microscope, the particle diameter and particle shape of this powder were 0.1 to 0.2 μm and spherical, Sr / Ti ratio: 0.998, Na amount: 80 ppm,
Cl amount: 10 ppm. Moreover, from the result of X-ray diffraction,
Strontium titanate having a cubic perovskite structure was formed.

As described above, the examples have been described with reference to barium titanate (BaTiO ₃ ) powder and strontium titanate (SrTiO ₃ ) powder.
CaTiO ₃ , (Ba, Ca) TiO ₃ , Ba (Ti, Z
Powders such as r) O ₃ and (Ba, Ca) (Ti, Zr) O ₃ can of course be manufactured by the same method.

[0031]

The ABO ₃ type powder produced according to the present invention has a spherical shape with a particle size of 0.1 to 0.3 μm and an A / B ratio within the range of 1.000 ± 0.002. is there.
Also, the crystallinity is good, and the impurities of alkali metal are extremely small. The ABO ₃ type powder having these characteristics can support not only thinning and multi-layering of a monolithic ceramic capacitor, but also high functionality and high reliability.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction pattern of barium titanate produced in Example 1.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01B 3/00 H 9059-5G

Claims (2)

[Claims] 1. (a) Mg, Ca, Sr, Ba, and P
to obtain a mixture slurry of at least one salt selected from the group A element consisting of b, at least one salt selected from the group B element consisting of Ti, Zr, Hf and Sn, and water or an alkaline aqueous solution. 1 step, (b) a second step of hydrothermally reacting the mixture slurry to obtain a hydrothermal synthetic powder, (c) a hydrothermal reaction of a mixture of the hydrothermal synthetic powder obtained in the second step and an alkaline aqueous solution And a third step of allowing the perovskite-type compound to be contained in the composition. 2. The method for producing a composition according to claim 1, wherein in the third step, a barium hydroxide aqueous solution having a pH adjusted to 7 to 10 is used as the alkaline aqueous solution.