JPH0610086B2 - Method for producing fine particles of bismuth titanate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing bismuth titanate fine particles, which is a ferroelectric material used for electronic parts such as capacitors.

[Outline of Invention]

According to the present invention, when bismuth titanate fine particles which are a ferroelectric material are synthesized, this synthesis is performed at pH 14.1 to 14.8.
This is carried out in an aqueous solution of No. 5 under a temperature condition of 150 ° C. or higher so that bismuth titanate fine particles having a fine and uniform particle size can be wet-synthesized without heat treatment.

[Conventional technology]

In recent years, miniaturization and high-density mounting of electronic parts have been rapidly progressing. Along with this, it has been desired to reduce the size and weight of the capacitor, which is one of the main components, like other electronic components, and to further increase the capacity and the high frequency resistance.

Therefore, in the above-mentioned capacitor, for example, a ceramic capacitor, in order to satisfy the above-mentioned demands, it is necessary to make the thickness of the ceramic layer thin and uniform. Is strongly desired. In addition, this atomization is
As raw materials for electrostrictive materials, piezoelectric materials, transparent ceramic materials, etc., they are strongly expected to improve sinterability and temperature characteristics.

In order to meet these demands, various research institutes are conducting research from various angles to obtain fine particles of a ferroelectric material, and bismuth titanate Bi ₄ (TiO ₄ ) having various excellent properties. ₃ is drawing attention.

Conventionally, as a method of producing the fine particles of bismuth titanate, bismuth oxide Bi ₂ O ₃ and titanium oxide TiO ₂ are pulverized and mixed in a ball mill, and a solid phase reaction is performed at a high temperature, and then a ball mill or the like is used. A method is known in which pulverization is carried out, and sieving is performed. However, the bismuth titanate fine particles obtained by such a production method have a poor particle size distribution of the fine particles obtained by finely pulverizing with a ball mill, and the inclusion of coarse particles is unavoidable. There is a drawback that metal oxides that are impurities are mixed.

Therefore, in order to solve the above-mentioned drawbacks, the applicant of the present invention has disclosed Japanese Patent Application No. 59-278503 (Japanese Patent Application Laid-Open No. 61-158).
No. 824) proposed a wet synthesis method of bismuth titanate fine particles. In this production method, a hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are wet-reacted in a strong alkaline aqueous solution (pH 14 to 14.9) to produce fine particle precipitates in an amorphous state. ,
The obtained fine particle precipitate is heat-treated. By this manufacturing method, the particle size is minute and uniform,
Moreover, it has become possible to produce fine particles of bismuth titanate in which metal oxides are not mixed.

[Problems to be solved by the invention]

However, in the method for producing bismuth titanate fine particles by the wet synthesis as described above, in order to precipitate bismuth titanate in an amorphous phase as crystalline fine particles, 400 ° C.
A heat treatment at a temperature above 10 ° C. is required, a heating device is required, and the manufacturing process becomes complicated. Furthermore, if the temperature of this heat treatment is low, a long heat treatment is required, and the manufacturing time becomes long.

In addition, by the above heat treatment, 0.1 μm from the amorphous phase
The crystalline substance Bi ₄ (TiO ₄ ) ₃ is deposited to some extent, but the crystalline substance is sintered by this heat treatment, and sintered particles having a large particle size may be mixed in the bismuth titanate fine particles. There is.

Alternatively, if the composition of the amorphous fine particles precipitates after the wet reaction is not constant, that is, the Bi / Ti molar ratio is not constant, substances other than Bi ₄ (TiO ₄ ) ₃ are mixed in the fine particles as impurities. There is also a risk of being lost.

The present invention has been proposed in view of the above-mentioned circumstances, the particle size is minute, and further, the particle size distribution is uniform, and bismuth titanate fine particles free of impurities are wet-reacted, and It is an object to provide a method for producing fine particles of bismuth titanate that can be synthesized without heat treatment.

[Means for solving problems]

The present inventors, as a result of extensive research over a long period of time to achieve the above-mentioned object, when a hydrolysis reaction of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are wet-reacted in an aqueous solution, By setting the pH and temperature of the aqueous solution within a predetermined range, it is possible to obtain fine particles of bismuth titanate in a single phase without heat treatment after bismuth titanate synthesis, and the particle diameter is fine and uniform. I found it.

The present invention has been completed based on such findings, and a hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are mixed in an aqueous solution at pH 1
The reaction is performed at 4.1 to 14.85 and a temperature of 150 ° C. or higher.

That is, in order to produce bismuth titanate fine particles in the present invention, a hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are used in an autoclave or the like at high temperature in a strong alkaline aqueous solution. Wet reaction may be carried out to generate a fine particle precipitate, and the obtained fine particle precipitate may be washed with water or warm water to remove alkali ions such as K ⁺ , Na ⁺ , Li ^+, and then filtered and dried.

Here, the pH and temperature of the aqueous solution at the time of the wet reaction are important, and bismuth titanate Bi ₄ (TiO ₄ ) can be obtained by setting the pH to 14.1 to 14.85 and the temperature to 150 ° C. or higher.
₃ fine particles are obtained as a single phase.

According to the experiments of the present inventors, in the above wet reaction, BiOCl is produced when the aqueous solution has a pH of 12.0 or less, and
It was found that Bi ₂ O ₃ was produced at pH 14.9 or higher. For example, while changing the pH of the aqueous solution, the molar ratio of Bi and Ti (hereinafter abbreviated as Bi / Ti) is set to 4/3, titanium is obtained by performing a wet reaction in an autoclave at 220 ° C. for 4 hours, filtering and drying. When the relative amount of the bismuth acid fine particles produced was measured, the results shown in FIG. 1 were obtained. The relative production amount of bismuth titanate fine particles is a value calculated from the (171) peak area of the diffracted X-ray peak obtained by performing X-ray diffraction using a copper target and a nickel filter (the same applies below). . From this FIG. 1, pH 14.1 to 14.
Within the range of 85, it was confirmed that the bismuth titanate fine particles were synthesized as a single phase in a high yield.

In the wet reaction, the reaction temperature may be 150 ° C or higher. For example, changing the reaction temperature to adjust the pH to 14.
47, Bi / Ti = 4/3, 3 in autoclave
When the relative amount of bismuth titanate fine particles obtained by carrying out a wet reaction for a time, filtering and drying was measured, the results shown in FIG. 2 were obtained. From this FIG. 2, the production amount of bismuth titanate fine particles increases as the reaction temperature increases,
It was confirmed that the reaction temperature should be 150 ° C. or higher, preferably 170 ° C. or higher.

On the other hand, the molar ratio of Bi and Ti contained in the starting material Bi / T
It is preferable that i is in the range of Bi / Ti = 1.1 to 1.6. For example, the relative molar ratio of bismuth titanate fine particles obtained by changing the mixing molar ratio of the starting materials Bi and Ti to adjust the pH of the aqueous solution to 14.47, performing a wet reaction at 220 ° C. for 8 hours in an autoclave, and filtering and drying. When the amount produced was measured, the results shown in FIG. 3 were obtained. From FIG. 3, when Bi / Ti is 1.0 or less, Na _1/2 Bi _1/2 TiO _{2
When 3 and 3} are mixed and Bi / Ti is 1.7 or more, Bi ₂ O ₃
It can be seen that the amount of bismuth titanate fine particles produced is also reduced due to the inclusion of the above. On the other hand, Bi / Ti = 1.1-
Within the range of 1.6, bismuth titanate fine particles Bi
It was confirmed that ₄ (TiO ₄ ) ₃ is a single phase and can be synthesized in a high yield, and the maximum production amount is obtained particularly near Bi / Ti = 1.3.

Furthermore, in the above-mentioned wet reaction, the reaction time is changed to
i / Ti = 4/3, the pH of the aqueous solution was set to 14.47, and after wet reaction at 220 ° C. in an autoclave,
When the relative amount of the filtered and dried bismuth titanate particles produced was measured, the results shown in FIG. 4 were obtained. From this FIG. 4, it was found that the relative production amount of fine particles increased depending on the time, and became substantially constant at 95% or more when the reaction time was about 20 minutes or more.

[Action]

A hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are added in an aqueous solution to pH 14.
By the wet reaction under the conditions of 1 to 14.85 and a temperature of 150 ° C. or more, the particle size is fine and uniform,
Bismuth titanate fine particles free of impurities can be synthesized without heat treatment.

〔Example〕

Hereinafter, the present invention will be described with reference to more specific examples. Needless to say, the present invention is not limited to the examples below.

Example 1 50 g of titanium chloride TiC ₄ was added to 100 m of ice water.
A titanium chloride aqueous solution was prepared by dropwise addition over 3 minutes. To this aqueous solution, add sodium hydroxide NaOH solution and
After adjusting to 7.0, water was added to make the length 500 m.

Next, 50 m of this solution was sampled and bismuth nitrate Bi was added.
(NO ₃ ) ₃ .5H ₂ O was added in an amount of 17.0 g, sodium hydroxide NaOH was added to adjust the pH to 7.0, and 12 g of sodium hydroxide NaOH was further added.
It was set to 00m. The pH of this aqueous solution was 14.5.

Next, this aqueous solution was reacted at 250 ° C. for 3 hours while stirring in a closed container using an autoclave. After the reaction, the white precipitate formed was repeatedly decanted to remove impurities such as alkali ions, further filtered and washed with water, and then dried at 100 ° C. overnight.

The fine particles obtained by the above operation were analyzed by the X-ray diffraction method.
Results are shown in FIG. The diffraction pattern shown in FIG. 5 is ASTM (The American Society for Testing Material).
It was found that the fine particles were orthorhombic (orthorhombic phase) bismuth titanate fine particles, which was in agreement with s) card 12-213. An electron microscope (TEM) photograph of the bismuth titanate fine particles is shown in FIG.

The lattice constant was calculated from the X-ray diffraction data of the bismuth titanate fine particles. As a result, the obtained bismuth titanate fine particles had a _o = 5.438, b _o = 32.70,
It was confirmed to be an orthorhombic crystal with c _o = 5.415.

Example 2 2 to 100 m of water in 50 g of titanium chloride TiC ₄ .
An aqueous solution of titanium chloride was prepared by dropping in three portions. To this aqueous solution, 40 g of sodium hydroxide NaOH was added to form a white suspension, and bismuth sulfate Bi ₂ (S
24.81 g of O ₄ ) ₃ was added, and sodium hydroxide NaOH
Was added to adjust the pH to 7, and then water was added to 500 m.

Next, 50 m of this solution was sampled, and sodium hydroxide N
8 g of aOH was added, and water was further added to make 100 m. The pH of this aqueous solution was 14.3.

Next, this aqueous solution was reacted at 220 ° C. for 1 hour while stirring in a closed container using an autoclave. After the reaction, the white precipitate formed was repeatedly decanted to remove impurities such as alkali ions, further filtered and washed with water, and then dried at 80 ° C. overnight.

When the fine particles obtained by the above operation were analyzed by the X-ray diffraction method, the diffraction pattern was exactly the same as that of the bismuth titanate fine particles Bi ₄ (TiO ₄ ) ₃ shown in FIG. In addition, the TEM photograph of the fine particles was a crystal having a shape and size similar to the crystal shown in FIG. Therefore, the fine particles are orthorhombic bismuth titanate fine particles B.
It was found to be i ₄ (TiO ₄ ) ₃ .

Example 3 50 g of titanium chloride TiC ₄ was added to 200 m of ice water.
A titanium chloride aqueous solution was prepared by dropwise addition over 5 minutes. Concentrated ammonia water NH ₄ OH was added to this aqueous solution to form a white suspension, and ammonia water NH ₄ OH was added to this suspension to adjust the pH to 8, and water was added to adjust the volume to 500 m.

Next, 50 m of this solution was sampled, and bismuth chloride BiC was collected.
After adding 11.08 g of ₃ , sodium hydroxide NaO
H solution and water were added to make 100 m. PH of this aqueous solution
Was 14.7.

Then, the above aqueous solution was reacted at 290 ° C. for 3 hours while stirring in a closed container using an autoclave. After the reaction, impurities such as alkali ions were removed by repeating decantation with respect to the produced white precipitate, further filtered and washed with water, and then dried at 90 ° C. overnight.

When the fine particles obtained by the above operation were analyzed by the X-ray diffraction method, the diffraction pattern was exactly the same as that of the bismuth titanate fine particles Bi ₄ (TiO ₄ ) ₃ shown in FIG.
In addition, the TEM photograph of the fine particles was a crystal having a shape and size similar to the crystal shown in FIG. Therefore, the fine particles are orthorhombic bismuth titanate fine particles Bi.
It was found to be ₄ (TiO ₄ ) ₃ .

Example 4 3 to 100 m of water was added to 50 g of titanium chloride TiC _4.
An aqueous solution of titanium chloride was prepared by dropwise addition in five portions. About 200 g of 140 g / sodium hydroxide NaOH solution was added to this aqueous solution to form a white suspension, and 11.08 g of bismuth bisulfate BiC ₃ and a predetermined amount of sodium hydroxide NaOH were added to this suspension to adjust the pH to 7.0. Then, water was further added to make the length 500 m.

Next, 120 g of sodium hydroxide NaOH was added to this solution.
After the addition, water was added to adjust the thickness to 1000 m.

Next, 100 m of this aqueous solution was sampled and reacted for 1 hour while stirring in a closed container using an autoclave. After the reaction, the white precipitate formed was repeatedly decanted to remove impurities such as alkali ions, further filtered and washed with water, and then dried at 100 ° C. overnight.

In the above operation, bismuth titanate fine particles were synthesized by changing the reaction temperature, and the obtained bismuth titanate fine particles were subjected to X-ray diffraction. The results are shown in Table 1.

As is clear from Table 1, the fine particles obtained by the above-mentioned operation were analyzed by the X-ray diffraction method and the results were as shown by the diffraction pattern of the bismuth titanate fine particles Bi ₄ (TiO ₄ ) ₃ shown in FIG. Exactly the same, and TEM of this fine particle
The photograph was a crystal of similar shape and size to the crystal shown in FIG. Therefore, it was found that the fine particles were orthorhombic bismuth titanate fine particles Bi ₄ (TiO ₄ ) ₃ .

〔The invention's effect〕

As is clear from the above description, according to the present invention, a hydrolysis product of a titanium compound or a water-soluble titanium salt,
A water-soluble bismuth compound and a pH of 14.1-1 in an aqueous solution
Since bismuth titanate fine particles are synthesized by a wet reaction under the conditions of 4.85 and a temperature of 150 ° C or higher, bismuth titanate fine particles having a fine particle size and a uniform particle size distribution should be subjected to heat treatment. Can be synthesized without. Therefore, the obtained bismuth titanate fine particles are
It is suitable for various electronic materials such as electrostrictive materials, piezoelectric materials and transparent ceramic materials.

Further, since it is not necessary to perform heat treatment after the wet reaction,
Bismuth titanate fine particles Bi ₄ (TiO ₄ ) ₃ having no composition variation and no mixing of sintered particles and the like caused by heat treatment are obtained. further,
A heating device is not required, and manufacturing time can be shortened or productivity can be improved.

[Brief description of drawings]

1 is a characteristic diagram showing the pH dependence of the relative production amount of bismuth titanate fine particles, FIG. 2 is a characteristic diagram showing the temperature dependence of the relative production amount of bismuth titanate fine particles, and FIG. 3 is a bismuth titanate fine particle. Fig. 4 is a characteristic diagram showing the Bi / Ti (molar ratio) dependency of the relative production amount of bismuth, Fig. 4 is a characteristic diagram showing the wet reaction time dependency of the relative production amount of bismuth titanate fine particles, and Fig. 5 is the production of the invention. The diffraction X-ray spectrum of the bismuth titanate fine particles produced by the method is shown in FIG. 6, and FIG. 6 is an electron micrograph of the obtained bismuth titanate fine particles.

Claims (1)

[Claims] 1. A pH value of a hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound in an aqueous solution.
14.1 to 14.85, a method for producing bismuth titanate fine particles, characterized by reacting at a temperature of 150 ° C or higher