JPH0699153B2 - Method for producing fine particles of sodium bismuth titanate - Google Patents

Description

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

[Outline of Invention]

The present invention, when synthesizing fine particles of bismuth sodium titanate which is a ferroelectric material, this synthesis is carried out in an alkaline solution having a pH of 13.4 or higher at a temperature condition of 130 ° C. or higher, and a fine and uniform titanic acid particle size is obtained. It is intended to wet-synthesize fine particles of sodium bismuth.

[Conventional technology]

In recent years, as integrated circuits (ICs) and large-scale integrated circuits (LSIs) have become highly integrated, and electric devices have become smaller and lighter, various individual electronic components such as capacitors, resistors, and coils have become smaller. It is progressing rapidly. In addition, the spread of high-efficiency automatic mounting technology for the purpose of rational production of complicated and multifunctional electronic products promotes the chipping of individual electronic components, and it has excellent dimensional accuracy and is small, lightweight, and high-quality chips. Mold parts are being used in large quantities.

By the way, in such a small and lightweight chip component, securing its performance is a major issue. For example, in the case of a chip type capacitor which is one of the main components, there is a large capacity and high frequency resistance. Research is underway to improve it. Generally, the electrical characteristics of a ceramic multilayer capacitor widely used as a chip type capacitor depend on the dielectric constant of the dielectric material used, the thickness of the dielectric layer, the number of stacked layers, etc. Further improvement is desired in terms of efficiency and sinterability.

In order to meet these demands, various research institutes have been conducting research on ferroelectric materials from various angles, and bismuth sodium titanate (Na _{1 / 2} Bi _1/2 TiO ₃ ) is attracting attention.

Conventionally, as a method for producing the fine particles of sodium bismuth titanate, bismuth oxide, titanium oxide and sodium hydroxide are pulverized and mixed in a ball mill, and after solid-phase reaction at high temperature, a ball mill or the like is used again. A method of pulverizing and sieving is known.

[Problems to be solved by the invention]

However, the bismuth sodium titanate fine particles obtained by such a production method have a poor particle size distribution, inevitably contain coarse particles, and require a long time for pulverization. There was a drawback that was mixed in.

The present invention has been proposed in view of the above-mentioned circumstances, the particle size is minute, and the particle size distribution is uniform, and the bismuth sodium titanate fine particles having no impurities are mixed by a wet reaction, Moreover, it is intended to be manufactured without heat treatment.

[Means for solving problems]

The present inventors have developed a synthetic method capable of wet-synthesizing fine bismuth sodium titanate fine particles having a good particle size distribution, and as a result of intensive research over a long period of time, as a result, in a sodium alkaline solution having a predetermined pH. It was found that by setting the reaction temperature to a predetermined value or higher, fine particles of bismuth sodium titanate in a single phase were obtained and the particle diameter was fine and uniform.

The present invention has been completed on the basis of such findings, wherein the hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are used, and the molar ratio Bi / Ti of bismuth and titanium is 0.1 to. It is characterized in that the reaction is carried out at a temperature of 130 ° C. or higher in an alkaline solution containing sodium ions having a pH of 13.4 or higher so as to be 0.9.

That is, in order to produce fine particles of bismuth sodium titanate in the present invention, a hydrolysis product of a titanium compound or a water-soluble titanium salt, and a water-soluble bismuth compound,
Wet-react in a strong alkaline aqueous solution (including Na ion) at high temperature using an autoclave to form a fine particle precipitate, and wash the obtained fine particle precipitate with water or warm water to remove alkali metal ions. It may be filtered and dried.

Here, the pH and temperature of the aqueous solution at the time of the wet reaction are important, and when the pH is set to 13.4 or higher and the temperature is set to 130 ° C. or higher, the bismuth sodium titanate Na _1/2 Bi _1/2 TiO ₃ fine particles are separated. Obtained as a phase.

According to the experiments conducted by the present inventors, it was found that Bi ₂ Ti ₂ O ₇ was produced in the above wet reaction when the pH of the aqueous solution was 13.4 or less. For example, the molar ratio of Bi and Ti (hereinafter abbreviated as Bi / Ti)
Set to 1: 2 and change the pH of the aqueous solution in an autoclave at 250 ℃
When the relative amount of fine particles of bismuth sodium titanate obtained by filtration and drying was measured for 8 hours, the results shown in FIG. 1 were obtained. The relative production amount of bismuth sodium titanate fine particles is a value obtained from the (200) peak area of the diffracted X-ray peak obtained by performing X-ray diffraction using a copper target and a nickel filter. (same as below). From this Fig. 1,
It was confirmed that the bismuth sodium titanate fine particles were synthesized as a single phase in a high yield in the range of pH 13.4 or higher. The pH of the alkaline solution at 13.4 is approximately 0.4 mol / l.
Of NaOH solution.

In the wet reaction, the reaction temperature may be 130 ° C or higher. For example, pH is 13.5 or higher, Bi / Ti = 1/2,
A wet reaction was carried out for 8 hours in an autoclave while changing the reaction temperature, and the relative amount of bismuth sodium titanate fine particles obtained by filtration and drying was measured, and the results shown in FIG. 2 were obtained. From this FIG. 2, it was confirmed that the production amount of bismuth sodium titanate fine particles increased as the reaction temperature increased, and the reaction temperature should be 130 ° C. or higher, preferably 150 ° C. or higher. The upper limit of the reaction temperature is as follows when an autoclave or the like is used.
It is considered possible up to about 400 ℃, but practically about 250 ℃.

On the other hand, the molar ratio Bi / Ti contained in the starting material Bi / Ti is Bi / Ti.
It is preferable that Ti is in the range of 0.1 to 0.9. For example,
Relative production of fine particles of bismuth sodium titanate obtained by carrying out wet reaction at 270 ° C for 3.5 hours in an autoclave by changing the mixing molar ratio of starting materials Bi and Ti with the pH of the aqueous solution being 13.5 or higher. Was measured, and the results shown in FIG. 3 were obtained. According to the analysis of the present inventors, Bi / T
It was found that when i is 1.0 or more, Bi ₄ (TiO ₄ ) ₃ is mixed and the production amount of bismuth sodium titanate fine particles is also reduced.
On the other hand, when Bi / Ti = 0.1 to 0.9, the bismuth sodium titanate fine particles can be synthesized in a single phase and with high yield, and the production amount is maximized especially near Bi / Ti = 0.5. It was confirmed that

Furthermore, in the above wet reaction, Bi / Ti = 1/2, p of the aqueous solution
When H was set to 13.5 or more, wet reaction was carried out at 220 ° C in an autoclave while changing the reaction time, and the relative amount of filtered and dried fine particles of sodium bismuth titanate was measured, and the results shown in Fig. 4 were obtained. Obtained. From FIG. 4, it was found that the relative production amount of fine particles increased depending on the time, and when the reaction time was about 60 minutes or more, the relative production amount was 98% or more, and thereafter became substantially constant.

[Action]

Wet reaction of a hydrolysis product of a titanium compound or a water-soluble titanium salt with a water-soluble bismuth compound in an alkaline aqueous solution (including Na ion) having a pH of 13.4 or more under the condition of a temperature of 130 ° C or more. As a result, fine particles of bismuth sodium titanate having a fine and uniform particle size and containing no impurities are synthesized without heat treatment.

〔Example〕

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

Example 1. 50 g of titanium chloride TiCl ₄ was placed in a beaker, and pure water was added dropwise to the beaker over 2 to 3 minutes to prepare an aqueous titanium chloride solution. To this aqueous solution, add sodium hydroxide NaOH solution and adjust the pH.
It was 7.0.

Next, 41.56 g of bismuth chloride BiCl ₃ was added to this solution, and then sodium hydroxide NaOH was added to adjust the pH to 7.0, and then pure water was added to make 500 ml.

Next, 50 ml of this aqueous solution was sampled, 12.8 g of sodium hydroxide NaOH was added thereto, and pure water was added to make 100 ml.

The aqueous solution thus prepared was reacted at 270 ° C. for 8 hours while stirring in a closed container (autoclave). After the reaction, impurities such as alkali ions are removed by repeating decantation on the produced white precipitate,
After further filtering and washing with water, it was 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. When the substance was identified based on the peak angle on the diffraction pattern shown in FIG. 5, it was confirmed that it was bismuth sodium titanate Na _1/2 Bi _1/2 TiO ₃ . In addition, the identification of this bismuth sodium titanate is Co-authored by Wang Tenho, Physics by Acta Physica Shinika (AC
TA PHYSICA SINICA), Volume 31, No.8, 1982.

Further, the lattice constant was calculated from the X-ray diffraction data of the fine particles of sodium bismuth titanate. As a result, it was confirmed that the obtained fine particles of sodium bismuth titanate were cubic crystals with a _o = 3.3954Å.

Furthermore, the bismuth sodium titanate fine particles are
As a result of firing at 0 ° C., 800 ° C. and 1000 ° C. for 3 hours, respectively, it was found that the crystal systems were all cubic and stable.

Example 2 50 g of titanium chloride TiCl ₄ was dropped into 100 ml of ice water over 2 to 3 minutes to prepare an aqueous titanium chloride solution. Sodium hydroxide NaOH was added to this aqueous solution to adjust the pH to 7.0, and then water was added to make 500 ml.

Next, 50 ml of this solution was sampled and 4.2 g of BiCl ₃ BiCl ₃ was added.
Subsequently, sodium hydroxide NaOH was added to adjust the pH to 7.0, and further 13.0 g of sodium hydroxide NaOH was added, and then water was added to make 100 ml.

Then, this aqueous solution was reacted at 250 ° C. for 8 hours while stirring in a closed container (autoclave). After the reaction, impurities such as alkali ions were removed by repeating decantation on the produced white precipitate, further filtered and washed with water, and then dried at 90 ° C. for 24 hours.

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 sodium bismuth titanate shown in FIG.

Example 3 50 g of titanium chloride TiCl ₄ was dropped into 100 ml of ice water over 3 to 5 minutes to prepare an aqueous titanium chloride solution. Sodium hydroxide NaOH solution was added to this aqueous solution to adjust the pH to 7.0, and then water was added to make 500 ml.

Then, 63.9 g bismuth nitrate _{Bi (NO 3) 3 · 5H} 2 O to the solution
Was added, and then sodium hydroxide NaOH was added to adjust the pH to 7.0, 200 g of sodium hydroxide NaOH was further added, and then water was added to 1000 ml.

Next, 100 ml of this aqueous solution was sampled and reacted at 250 ° C. for 1 hour while stirring in an airtight container (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 sodium bismuth titanate shown in FIG.

Example 4 100 ml of water was dropped into 50 g of titanium chloride TiCl ₄ over 3 to 5 minutes to prepare an aqueous titanium chloride solution. 140g in this aqueous solution
A white suspension was prepared by adding about 200 ml of NaOH solution (1 / l) to the suspension, and bismuth sulfate Bi ₂ (SO ₄ ) ₃ was added to the suspension.
3.06 g and sodium hydroxide NaOH were added to the specified amount to pH 7.0.
Then, water was further added to make 500 ml.

Next, 140 g of sodium hydroxide NaOH was added to this solution, and then water was added to make 1000 ml.

Next, 100 ml of this aqueous solution was sampled and reacted for 8 hours while stirring in a closed container (autoclave). After the reaction, impurities such as alkali ions are removed by repeating decantation on the produced white precipitate,
After further filtering and washing with water, it was dried at 100 ° C. overnight.

In the above operation, bismuth sodium titanate fine particles were synthesized by changing the reaction temperature, and the obtained bismuth sodium 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 exactly the same as the diffraction pattern of bismuth sodium titanate shown in FIG. 5 when analyzed by the X-ray diffraction method. It was found that these are fine particles of sodium bismuth titanate.

〔The invention's effect〕

As is clear from the above description, in the present invention,
Since the hydrolysis product of the titanium compound or the water-soluble titanium salt and the water-soluble bismuth compound are wet-reacted in a sodium ali solution having a pH of 13.4 or higher at a temperature of 130 ° C or higher, the particle size It is possible to synthesize fine particles of bismuth sodium titanate having a small particle size and a uniform particle size distribution without applying heat treatment.

Also, unlike the conventional method of mechanically micronizing using a ball mill or the like, since it is a wet synthesis, there is no mixing of metal oxides as impurities, and Bi / T of the resulting microparticles is
The composition ratio of i is kept accurate.

Furthermore, the fine particles of sodium bismuth titanate synthesized according to the present invention have a high activity and can lower the sintering temperature when used in, for example, a ceramic capacitor, so that PbO can be uniformly contained.

Therefore, it can be said that the obtained bismuth titanate fine particles are suitable for various electronic materials such as electrostrictive materials, piezoelectric materials and transparent ceramic materials.

[Brief description of drawings]

Fig. 1 is a characteristic diagram showing the pH dependence of the relative production amount of bismuth sodium titanate fine particles, Fig. 2 is a characteristic diagram showing the temperature dependence of the relative production amount of bismuth sodium titanate fine particles, and Fig. 3 is titanic acid. FIG. 4 is a characteristic diagram showing the Bi / Ti (molar ratio) dependency of the relative production amount of bismuth sodium fine particles, FIG. 4 is a characteristic diagram showing the wet reaction time dependency of the relative production amount of bismuth sodium titanate fine particles, and FIG. 5 is 2 is a diffraction X-ray spectrum of fine particles of sodium bismuth titanate produced by the production method of the present invention.

Claims (1)

[Claims] 1. A hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are adjusted so that a molar ratio Bi / Ti of bismuth and titanium is 0.1 to 0.9 and sodium ions having a pH of 13.4 or more are added. Temperature 130 in alkaline solution containing
A method for producing fine particles of sodium bismuth titanate, which comprises reacting at a temperature of not less than ° C.