JPH08119633A - Production of fine barium titanate particles - Google Patents

Abstract

PURPOSE: To obtain fine barium titanate particles free from corrosive ions at a low cost by bringing a suspension consisting of fine TiO2 particles, a water- soluble barium compd., an alkaline compd. and water into an aq. soln. reaction in an autoclave. CONSTITUTION: Fine TiO2 particles of <=80μm particle diameter are mixed with a water-soluble barium compd., an alkaline compd. and water so that the molar ratio of Ba to Ti is regulated to 0.8-3 and the resultant suspension of >=pH 13.3 is charged into an autoclave and brought into an aq. soln. reaction at >=130 deg.C for >=1hr to obtain the objective fine barium titanate particles of 30-80μm particle diameter.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a dielectric material, a piezoelectric material,
The present invention relates to a method for producing fine particles of barium titanate used as an electrostrictive material.

[0002]

2. Description of the Related Art A fired body of barium titanate (BaTiO ₃ ) is used as various functional materials such as a dielectric material of a capacitor, a piezoelectric material and an electrostrictive material. The BaTiO ₃ particles used as the firing raw material are required to be further finer and have a uniform particle size for such applications.

For example, in recent years, capacitors have been required to have smaller capacities, lighter weights, and lower prices as well as other electronic parts, as well as to have larger capacities. In order to meet such a demand, a monolithic ceramic capacitor (barium titanate capacitor) using a BaTiO ₃ fired body as a dielectric material has been receiving attention. Since the BaTiO ₃ fired body has a very high dielectric constant, a compact and large-capacity capacitor can be realized.

Here, in order to further reduce the thickness of such a barium titanate capacitor while keeping the thickness uniform, it is necessary that the BaTiO ₃ particles used as the firing raw material be fine. . Further, in a monolithic ceramic capacitor, an additive such as lead may be added to the dielectric material layer in order to improve sinterability and temperature characteristics. At this time, if the sintering temperature of the dielectric material layer is high, part of the added lead or the like is evaporated, and the composition of the dielectric material layer becomes non-uniform. In this case, if the BaTiO ₃ particles used as the raw material are fine particles, the sintering temperature can be kept low, so that evaporation of lead or the like during sintering can be suppressed and a dielectric material layer having a uniform composition can be formed. Become.

As described above, BaTiO ₃ particles are desired to be made into fine particles as a raw material for a dielectric material of a capacitor, and also as a raw material for an electrostrictive material, a piezoelectric material, and a transparent ceramic material, for the purpose of improving their characteristics. Desired. In addition, recently, with the aim of improving the characteristics of synthetic resins,
Various inorganic powder materials have been added.
Even when BaTiO ₃ particles are used as the inorganic powder material, if the BaTiO ₃ particles are fine particles, the surface property can be improved in resin processing such as molding, which is extremely convenient.

Therefore, such fine BaTiO ₃
Various manufacturing methods have been proposed in order to obtain particles. First, the BaTiO ₃ powder has been mainly manufactured by the solid phase reaction so far. That is, barium carbonate (BaCO ₃ )
The powder and the titanium oxide powder are wet-mixed in a ball mill, the mixture is dried and pressed, and then the temperature is set to 1000 to 1
BaTiO ₃ [tetragonal (a ₀
= 0.3994 nm, b ₀ = 0.4038 nm)]. Then, the obtained BaTiO ₃ is mechanically pulverized into fine particles, and coarse particles are removed by sieving or the like.

However, the BaTiO ₃ powder thus obtained by solid-phase reaction and mechanical pulverization has a considerably large particle size and is non-uniform, and contamination with impurities cannot be avoided. Next, BaT, which is relatively fine and has a uniform particle size,
As a method for obtaining iO ₃ particles, a titanyl oxalate / barium complex salt was synthesized, and this was thermally decomposed to form BaTiO ₃ particles [tetragonal (a ₀ = 0.3994 nm, b ₀ = 0.403).
8 nm)].

However, this method has complicated steps,
Since organic materials are used, the manufacturing cost is considerably higher than that of the solid phase reaction method. Also, B produced by this method
The particle size of the aTiO ₃ powder is at most 0.2-0.
Since it is about 5 μm, it cannot be said that it can sufficiently meet the recent demand for fine particles. Furthermore, recently, a method of obtaining BaTiO ₃ fine particles (cubic crystal) using a metal alkoxide has been proposed. According to this method, a relatively fine BaTiO ₃ powder having a particle size of 20 nm to 30 nm can be obtained, but the production cost is higher than in the case of the oxalate method, and practical use is hindered.

As another manufacturing method, there is a method of manufacturing BaTiO ₃ fine particles (cubic crystals) using titanium tetrachloride, titanium sulfate, etc. as main raw materials.
No. 4 is disclosed. This publication describes that, according to this method, a fine BaTiO ₃ powder having a uniform particle size can be obtained at low cost. However, titanium tetrachloride as the raw material is difficult to handle because of its high reactivity. On the other hand, when titanium sulfate is used, it is necessary to remove the sulfate ion after completion of hydrolysis, which is very troublesome. In any case, a slight amount of chlorine ion or sulfate ion was obtained in some cases BaTiO ₃
May be mixed in particles. When corrosive ions such as chlorine ions are mixed in the BaTiO ₃ fine particles, for example, in the multilayer ceramic capacitor, copper is used for the electrode lead-out.
Nickel metal is often used and may corrode.

Therefore, the present invention has been proposed in view of such conventional circumstances, and fine barium titanate particles can be obtained without containing corrosive ions such as Cl ions and SO ₄ ions. It is an object of the present invention to provide a method for producing barium titanate fine particles which can be produced at low cost.

[0011]

In order to achieve the above object, the method for producing fine particles of barium titanate of the present invention comprises:
The method comprises the steps of mixing titanium oxide fine particles with a water-soluble barium compound, an alkaline compound and water to form a suspension, and a step of reacting the suspension with an aqueous solution in a pressure vessel. The particle size is 80 nm or less, the pH during the aqueous solution reaction is 13.3 or more, and the reaction temperature is 130.
It is characterized in that the temperature is not lower than ° C.

The titanium oxide fine particles and the water-soluble barium compound are characterized in that Ba / Ti (molar ratio is 0.8 to 3. First, barium titanate ( In order to produce the BaTiO ₃ ) fine particles, titanium oxide fine particles as a raw material and a water-soluble barium salt are prepared.The titanium oxide (TiO ₂ ) fine particles may be either rutile type TiO ₂ or anatase type TiO _2. It may be a mixture of these.

However, since the particle size of the TiO ₂ fine particles is reflected in the particle size of the finally obtained BaTiO ₃ fine particles, a particle size of 80 nm or less, more preferably 50 nm or less is used. Examples of the water-soluble barium salt include barium nitrate Ba (NO ₃ ) ₂ and barium acetate Ba.
(CH ₃ COO) ₂ , barium hydroxide Ba (OH) ₂ ,
The hydrated salt _{Ba (OH) 2 · 8H 2} O, barium chloride B
aCl ₂ or the like can be used.

In order to produce a sufficient amount of BaTiO ₃ fine particles, it is important that the molar ratio of Ba and Ti (Ba / Ti) in the TiO ₂ fine particles and the water-soluble barium salt is within an appropriate range. Figure 1 shows Ba / Ti (molar ratio) and B
The relationship between the amount of aTiO ₃ particles produced is shown below.
0.8 to 3 is suitable for a / Ti (molar ratio), preferably 0.8 to 2, and more preferably 0.95 to 2.0.
Is. When Ba / Ti (molar ratio) is out of this range, the amount of BaTiO ₃ particles produced is small.

Next, the TiO ₂ fine particles and the water-soluble barium salt are put into a strong alkaline aqueous solution and reacted with stirring in an autoclave. The alkaline compound of the strong alkaline aqueous solution includes LiOH, NaOH, KOH,
NH ₄ OH, and the like. The reaction conditions are the pH of the reaction solution
Is 13.5 or more, preferably 13.7 to 14.7, more preferably 13.8 or more, the reaction temperature is 130 ° C. or more, preferably 140 to 250 ° C., and the reaction time is 1
It is at least 3 hours, preferably at least 3 hours. For example, FIG.
Shows the relationship between the pH of the reaction solution and the production amount of barium titanate fine particles. When the pH and the reaction temperature are out of the above ranges, a sufficient amount of BaTiO ₃ fine particles is not produced.

The barium titanate particles produced through the aqueous solution reaction under the above conditions are, for example, perovskite type, cubic system (a ₀ = 0.4025 nm or so),
After that, it is filtered, washed with water and dried to be used for various purposes.
Here, the BaTiO ₃ fine particles thus produced have a fine particle size of 30 nm to 80 nm, reflecting the particle size of the TiO ₂ fine particles as the raw material, and are uniform without containing coarse particles and impurity particles. is there. Further, since a raw material that produces corrosive ions such as chlorides and sulfuric acid compounds is not used, corrosive ions are not mixed. Further, since it is produced without using an organic compound, the manufacturing cost can be kept low.

Thus, fine and highly pure BaTiO 3
If ₃ form fine particles for firing the dielectric material layer of the capacitor, it is possible to form in thin and uniform thickness of the dielectric material layer, additives uniformly contained lead such because the firing temperature is kept low Be punished. Therefore, small,
Capacitors with large capacity and excellent characteristics can be obtained. Moreover, since the corrosive ions are not mixed, the corrosion of the leader line caused by it is also avoided.

Further, such BaTiO ₃ fine particles are optimal as a raw material for electrostrictive materials and piezoelectric materials, and when used as an inorganic powder material added to a synthetic resin, good moldability is obtained. .

[0019]

[Function] A TiO ₂ fine particle having a particle size of 80 nm or less is mixed with a water-soluble barium compound, an alkaline compound and water to form a suspension having a predetermined pH, and this suspension is placed in a pressure vessel at a predetermined reaction temperature. When the aqueous solution is reacted with
Fine BaTiO ₃ reflecting the particle size of iO ₂ fine particles
The fine particles are produced in high purity without containing corrosive ions.

[0020]

EXAMPLES Specific examples of the present invention will be described below based on experimental results. Example 1 16 g of rutile type TiO _{2 having} a particle size of 40 nm and 68 g of barium nitrate Ba (NO ₃ ) _{2 were} mixed with 1.5 N · NaO.
Pour into 300 ml of H solution to make a suspension, temperature 150 ° C
The reaction was carried out in the autoclave of 5 for 5 hours with stirring.
The pH of the suspension was 14.0. Next, the powder produced by this reaction was washed with water by decantation, filtered, further washed with water, and dried at a temperature of 150 ° C. for one day.

The X-ray diffraction spectrum of the resulting powder obtained as described above was observed and compared with that of the JCPDS card. The measurement result of the X-ray diffraction spectrum is shown in FIG. The X-ray diffraction was performed under the conditions of time constant 1 using a copper target and a nickel filter. As a result, the resulting powder was cubic BaTiO ₃ (a ₀ =
It was determined to be 0.4025 nm).

In addition, FIG. 4 shows an electron micrograph of the obtained BaTiO ₃ powder. From this photo, BaTiO ₃
The particle size is 40 nm, which shows that the particle size is uniform. Furthermore, the obtained BaT is shown in FIGS.
iO ₃ shows the thermal analysis results of the fine particles, the BaTiO ₃
The fine particles have almost no peak of exothermic heat and no weight loss. This suggests that the amount of impurities is small and the purity is high. Example 2 In this example, first, TiO ₂ particles were produced, and BaTiO ₃ particles were produced using the produced TiO ₂ .

51 g of titanium tetrachloride was dropped into 100 ml of ice water, 100 ml of 5N NaOH was added thereto, and water was further added to bring the total amount to 400 ml. This solution was reacted at a temperature of 100 ° C. for 5 hours while stirring with a magnetic stirrer. Next, this reaction product was filtered, washed with water, and dried at a temperature of 150 ° C. for one day to obtain TiO ₂ . The obtained TiO ₂ had a particle size of 30 nm.
It had a rutile structure.

This rutile TiO having a particle size of 30 nm
And ₂ 16g, barium chloride BaCl ₂ · 2H ₂ O50g
Were added to 250 ml of 1N NaOH solution, and water was further added to make the total amount 300 ml. The pH of this suspension was 13.8. This suspension is heated to a temperature of 130
The reaction product was reacted in an autoclave at ℃ for 5 hours, and the obtained reaction product was washed with water by decantation, separated by filtration, further washed with water, and dried at a temperature of 150 ° C for one day.

The X-ray diffraction spectrum of the powder thus obtained was observed under the same conditions as in Example 1, and the same diffraction pattern as that shown in FIG. 3 was obtained. Then, by comparing this diffraction pattern with a JCPDS card, the obtained powder was cubic BaTiO 3.
It was determined to be ₃ (a ₀ = 0.4072 nm). Further, it was found from the electron micrograph of the BaTiO ₃ powder that the particle size was 30 nm and that the particles were uniform. Example 3 16 g of anatase type TiO _{2 having} a particle size of 50 nm,
35g of barium hydroxide Ba (OH) ₂ and 1N ・ KO
It is put into 300 ml of H solution to make a suspension, and the temperature is 170 ° C.
The reaction was carried out in the autoclave of 5 for 5 hours with stirring.
The pH of the suspension was 14.2. Next, the reaction product was washed with water by decantation, separated by filtration, further washed with water, and dried at a temperature of 150 ° C. for one day.

With respect to the powder thus obtained, an X-ray diffraction spectrum was observed under the same conditions as in Example 1, and as a result, the same diffraction pattern as in FIG. 3 was obtained. Then, by comparing this diffraction pattern with a JCPDS card, the obtained powder was cubic BaTiO 3.
It was determined to be ₃ (a ₀ = 0.4025 nm). Moreover, it was found from the electron micrograph of the BaTiO ₃ powder that the particle size was uniform at 50 nm. Example 4 16 g of rutile type TiO _{2 having} a particle size of 40 nm and 53 g of barium nitrate Ba (NO ₃ ) ₂ were added to 300 ml of a 1N LiOH solution to prepare a suspension, which was stirred in an autoclave at a temperature of 180 ° C. for 5 hours. While reacting. The pH of the suspension was 13.9. Next, the reaction product was washed with water by decantation, separated by filtration, further washed with water, and dried at a temperature of 150 ° C. for one day.

The X-ray diffraction spectrum of the produced powder thus obtained was observed under the same conditions as in Example 1, and as a result, the same diffraction pattern as in FIG. 3 was obtained. Then, by comparing this diffraction pattern with a JCPDS card, the obtained powder was cubic BaTiO 3.
It was determined to be ₃ (a ₀ = 0.4024 nm). Further, it was found from the electron micrograph of the BaTiO ₃ powder that the particle size was uniform at 40 nm. Example 5 16 g of anatase type TiO _{2 having} a particle size of 80 nm,
35g of barium hydroxide Ba (OH) ₂ and 1N ・ Na
It is put into 300 ml of OH solution to make a suspension, and the temperature is 220.
The reaction was carried out in an autoclave at ℃ for 5 hours with stirring. The pH of the suspension was 14.2. next,
The reaction product was washed with water by decantation, filtered,
Further, it was washed with water and dried at a temperature of 150 ° C. for 24 hours.

The X-ray diffraction spectrum of the powder thus obtained was observed under the same conditions as in Example 1, and as a result, the same diffraction pattern as in FIG. 3 was obtained. Example 6 16 g of rutile TiO _{2 having} a particle size of 70 nm and 50 g of barium chloride BaCl ₂ .2H ₂ O were mixed with 2N.Na.
Add to 300 ml of OH solution to make a suspension, and set the temperature to 250.
The reaction was carried out in an autoclave at ℃ for 5 hours with stirring. The pH of the suspension was 14.2. next,
The reaction product is washed with water by decantation, filtered,
Further, it was washed with water and dried at a temperature of 150 ° C. for 24 hours.

The X-ray diffraction spectrum of the produced powder thus obtained was observed under the same conditions as in Example 1, and as a result, the same diffraction pattern as in FIG. 3 was obtained. By comparing this pattern with the JCPDS card,
It was determined to be cubic BaTiO ₃ (a ₀ = 0.4023 nm). In addition, it was found from the electron micrograph of the BaTiO ₃ powder that the particle size was uniform at 60 nm. Comparative Example 1 16 g of rutile TiO _{2 having} a particle size of 40 nm and 53 g of barium nitrate Ba (NO ₃ ) ₂ were added to 300 ml of a 1N NaOH solution to give a suspension, which was in a boiling state while stirring with a magnetic stirrer. And reacted for 5 hours.
The pH of the suspension was 13.9. Next, the reaction product was washed with water by decantation, separated by filtration, further washed with water, and dried at a temperature of 150 ° C. for one day.

As a result of observing the X-ray diffraction spectrum of the powder thus obtained under the same conditions as in Example 1, BaTiO ₃ was obtained although a diffraction peak corresponding to the rutile TiO ₂ as a raw material was observed. The diffraction peak of was only slightly visible. And anatase TiO ₂ 16g of Comparative Example 2 particle size 50 nm,
Barium chloride BaCl ₂ · H ₂ O 50 g and 0.1N
-Adding to 300 ml of NaOH solution to make a suspension, the mixture was reacted in an autoclave at a temperature of 150 ° C for 5 hours with stirring. The pH of the suspension was 12.8. Next, the reaction product was washed with water by decantation, separated by filtration, further washed with water, and dried at a temperature of 150 ° C. for one day.

X-ray diffraction spectrum of the powder thus obtained was observed under the same conditions as in Example 1. As a result, a diffraction peak corresponding to the anatase-type TiO ₂ as a raw material was observed, but BaTiO ₃ The diffraction peak of was only slightly visible. Comparative Example 3 16 g of rutile TiO ₂ having a particle size of 0.2 μm,
Barium chloride BaCl ₂ · 2H ₂ O 49g and 1N ·
Pour into 300 ml of NaOH solution to make a suspension, temperature 1
The reaction was carried out in an autoclave at 40 ° C with stirring for 5 hours. The pH of the suspension was 13.9. Next, the reaction product was washed with water by decantation, separated by filtration, further washed with water, and dried at a temperature of 150 ° C. for one day.

X-ray diffraction spectrum of the powder thus obtained was observed under the same conditions as in Example 1. As a result, a diffraction peak corresponding to the starting material rutile TiO ₂ was observed, but BaTiO ₃ The diffraction peak of was only slightly visible. Next, the amount of Cl ions and SO ₄ ions mixed in the barium titanate particles produced in Examples 1 to 6 was measured. Table 1 shows the results. For comparison, barium titanate particles (comparative example 4) produced by an aqueous solution reaction using titanium tetrachloride as a raw material were similarly measured for the mixed amounts of Cl ions and SO ₄ ions. The results are also shown in Table 1.

[0033]

[Table 1]

As shown in Table 1, the barium titanate particles produced in Comparative Example 4 contained 243 ppm of Cl ions, while the barium titanate particles produced in Examples 1 to 6 were mixed. Almost no Cl ions and SO ₄ ions are mixed in the particles. From the above results, when fine particle titanium oxide having a particle size of 80 nm or less and a water-soluble barium salt are reacted in an aqueous solution at a predetermined pH and a reaction temperature, fine barium titanate fine particles reflecting the particle size of titanium oxide used as a raw material are corroded. It was found that the product can be obtained in a high purity without containing a sex ion.

[0035]

As is apparent from the above description, in the method for producing BaTiO ₃ fine particles of the present invention, a step of mixing TiO ₂ fine particles with a water-soluble barium compound, an alkaline compound and water to form a suspension is provided. And a step of reacting the suspension with an aqueous solution in a pressure vessel, wherein the particle size of the TiO ₂ fine particles is 80 nm or less, and the pH during the aqueous solution reaction.
Is 13.3 or higher and the reaction temperature is 130 ° C or higher,
Fine BaTiO ₃ fine particles reflecting the particle size of the TiO ₂ fine particles used as a raw material can be produced with high purity without containing corrosive ions.

If such a sintered body of BaTiO ₃ fine particles is used as a dielectric material, for example, it is possible to obtain a compact capacitor having a large capacity and high reliability. The BaTiO ₃ sintered body also exhibits excellent characteristics as a piezoelectric material and an electrostrictive material, and can greatly contribute to the improvement of the performance of various electronic devices.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship of Ba / Ti (molar ratio) when an aqueous solution reaction of TiO ₂ fine particles and a water-soluble barium compound is carried out.

FIG. 2 is a characteristic diagram showing the relationship between the pH of the reaction solution and the production amount of barium titanate fine particles when the TiO ₂ fine particles and the water-soluble barium compound are reacted in an aqueous solution.

FIG. 3 is a characteristic diagram showing an X-ray diffraction spectrum of barium titanate fine particles produced by the production method of the present invention.

FIG. 4 is an electron micrograph showing a particle structure of the barium titanate fine particles.

FIG. 5 is a characteristic diagram showing a relationship between temperature and weight of the barium titanate fine particles.

FIG. 6 shows the temperature and endothermic amount of the barium titanate fine particles,
It is a characteristic view which shows the relationship of a calorific value.

Claims (5)

[Claims] 1. A method comprising: mixing titanium oxide fine particles, a water-soluble barium compound, an alkaline compound and water into a suspension, and reacting the suspension with an aqueous solution in a pressure vessel. The titanium oxide fine particles have a particle size of 80 nm or less, a pH of 13.3 or more upon reaction with an aqueous solution, and a reaction temperature of 13
A method for producing fine particles of barium titanate, which is 0 ° C. or higher. 2. The method for producing fine particles of barium titanate according to claim 1, wherein the titanium oxide fine particles are rutile type titanium oxide, anatase type titanium oxide or a mixture of rutile type titanium oxide and anatase type titanium oxide. . 3. A method for producing fine particles of barium titanate, characterized in that titanium oxide and a water-soluble barium compound have a Ba / Ti (molar ratio of 0.8 to 3). 4. The method for producing barium titanate according to claim 2, wherein the pH in the reaction with the aqueous solution is 13.7 or more and 14.7 or less. 5. The reaction temperature for the aqueous solution reaction is 140.
It is -250 degreeC, The manufacturing method of the barium titanate of Claim 1 characterized by the above-mentioned.