JPH11228139A - Method for producing titanium-containing composite oxide powder - Google Patents

Abstract

(57) [Problem] To provide a method capable of inexpensively producing a homogeneous and fine titanium-containing composite oxide powder widely used as a dielectric or a piezoelectric by a simple process. The particle size is 100 nm or less or the specific surface area is 15 m.
² / g or more of titania particles and an aqueous solution in which a metal salt is dissolved to form a suspension, and an organic solvent and a dispersant are added to the obtained suspension to form a suspension. An emulsion forming step of forming an emulsion, and a combustion step of spray-burning the obtained emulsion to form a composite oxide powder,
A method for producing a titanium-containing composite oxide powder, comprising:

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a homogeneous and fine titanium-containing composite oxide powder.

[0002]

2. Description of the Related Art Titanium-containing composite oxides such as barium titanate, strontium titanate, zirconium titanate, and lead titanate have excellent dielectric properties and piezoelectric properties, and are widely used in multilayer capacitors and actuators. It's being used. In recent years, the thickness of the laminate has been decreasing due to a demand for miniaturization of devices, and accordingly, a uniform and fine raw material powder has been required.

[0003] In response to these requirements, the sol-gel method (E. Wu
et al., Mat.Res.Soc.Symp.Proc., Vol. 32, 169-174 (198
4)), hydrothermal synthesis method (H. Kumazawa et al., J. Mat. Sci., Vo
l. 31, 2599-2602 (1996)), solution method (M. Leoni et al., JM
at. Sci. lett., Vol. 15, 1302-1304 (1996)) and the like have been studied. However, the sol-gel method is expensive because it uses expensive alkoxide raw materials,
The hydrothermal synthesis method and the solution method have a problem that the processes are complicated because calcination, drying, and crushing steps are required.

Japanese Patent Application Laid-Open No. 8-169715 discloses that
There is disclosed a method of synthesizing composite oxide fine particles by self-igniting metal oxide fine particles of titanium dioxide and an aqueous metal nitrate solution containing metal ions of barium nitrate together with fuel (for example, a water-soluble amino acid). In the above-described method of forming composite oxide fine particles by self-ignition, a temperature distribution is easily formed, and it is difficult to obtain uniform composite oxide fine particles. As a result, there is a problem that the second phase, which is a composite oxide having another composition, tends to precipitate. For example, the BaT shown in FIG.
In the X-ray diffraction pattern of iO ₃ , Ba ₂ TiO
_A second phase peak considered to be ₄ is observed. Therefore, it is difficult to obtain homogeneous composite oxide fine particles by the self-ignition method. Further, although the above-mentioned publication allows formation of fine particles, it does not refer to raw materials and products as to specific particle diameters.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a simple and convenient process for producing a uniform and fine titanium-containing composite oxide powder widely used as a dielectric or piezoelectric material. The purpose is to establish a method that can be manufactured at low cost.

[0006]

The method for producing a titanium-containing composite oxide powder of the present invention comprises mixing titania particles having a particle size of 100 nm or less or a specific surface area of 15 m ² / g or more with an aqueous solution in which a metal salt is dissolved. A suspension formation step of forming a suspension, an emulsion formation step of adding an organic solvent and a dispersant to the obtained suspension to form the suspension into an emulsion, and spray-burning the obtained emulsion to form a composite And a combustion step for producing oxide powder.

Preferably, the metal salt is a salt of an alkaline earth element.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a titanium-containing composite oxide powder according to the present invention comprises emulsifying a suspension of titania particles having a specific range of particle size or specific surface area and an aqueous solution of a metal salt to form the emulsion. By spray combustion to obtain a homogeneous fine powder composite oxide powder. In this emulsion combustion method, a composite oxide powder can be directly synthesized from an aqueous solution of titania particles and a metal salt. Therefore, it does not require expensive alkoxide raw materials as in the sol-gel method,
Further, unlike the hydrothermal synthesis method and the solution method, steps such as drying, calcination, and pulverization are not required, so that the steps are simplified and the production can be performed at low cost.

As the starting material, titania particles having a particle size of 100 nm or less can be used. An aqueous solution in which the other metal element forming the composite oxide is dissolved exists together with the titania particles as an aqueous phase of the emulsion. For this reason, when the emulsion is sprayed and burned, the other metal element diffuses into the titania particles, whereby a homogeneous composite oxide powder can be formed. On the other hand, when the particle size of the titania particles exceeds 100 nm, since the particle size of the titania particles is large, other metal elements do not sufficiently diffuse into the titania particles when the emulsion is spray-burned, and unreacted titania remains. Alternatively, the second phase is undesirably precipitated.

Even if the particle size of the titania particles exceeds 100 nm, the titania particles have a specific surface area of 15
If it is at least m ² / g, it can be used as a starting material. Since the specific surface area is large, the other metal element can sufficiently enter the inside of the porous body in the solution preparation stage. For this reason, the diffusion distance between the titania particles and the metal element during the emulsion combustion becomes shorter, and a homogeneous composite oxide powder can be formed.

The composition of the starting material titania particles of the present invention is not particularly limited, except that it contains titanium. For example, a binary composite oxide composition such as barium titanate and strontium titanate may be used.
The composition may be such that the component and the fourth component are further added. The titania particles may be either crystalline particles or amorphous particles. The titania particles may be in the form of a powder or in the form of a sol in which the particles are dispersed in water.

The kind of the other metal element salt to be used is not limited. Any metal nitrate, metal acetate, or water-soluble metal salt may be used. However, care must be taken because metal halides such as chlorides may form harmful organic halides when the emulsion is burned. In the production method of the present invention, first, titania particles and an aqueous solution of a salt of a metal element are mixed to form a suspension, and then the obtained suspension is emulsified. Emulsification is performed using the usual W /
A method of forming an O-type emulsion can be applied. An aqueous solution of titania particles and a metal element salt is confined in this emulsion.

In this emulsion combustion method, one water droplet in the formed W / O type emulsion forms one reaction field,
That is, it corresponds to one generated particle. For this reason, if the water droplet diameter is larger than 10 μm, the reaction field may be too large to be non-uniform, and the generated particles may be large, which is not preferable. The type of the organic solvent used for forming the emulsion is not particularly limited. Any organic solvent, such as hexane, octane, kerosene, gasoline, etc., that can produce an aqueous solution and a W / O emulsion may be used.

The type and amount of the dispersant used are not particularly limited. Cationic surfactants, anionic surfactants, nonionic surfactants may be used, depending on the type of aqueous solution, organic solvent and required water droplet diameter,
What is necessary is just to change the kind and addition amount of a dispersing agent. In the emulsion combustion step, the reaction of complex oxide formation proceeds by the combustion of the organic solvent holding the emulsion, so that the carbon dioxide concentration in the reaction atmosphere is much higher than that in the atmosphere. For this reason, the alkaline earth element usually easily forms a carbonate in such an atmosphere, but does not form a carbonate when forming a composite oxide with titanium.
Although the cause is not clear, it is thought that it is closely related to the production rates of alkaline earth elements and titania, and the chemical stability of the produced composite oxide.

[0015] The combustion temperature during the emulsion combustion is not particularly limited, but is preferably in the range of 700 to 1200 ° C. 7
If the temperature is lower than 00 ° C., the combustion temperature is too low, and the organic solvent may not completely burn and may remain, which is not preferable. Combustion temperature is 1
If the temperature exceeds 200 ° C., the combustion temperature is too high, and the generated powder may undesirably aggregate and sinter to grow grains.

The combustion atmosphere is not particularly limited. However, if oxygen is not sufficient, carbon components in the organic solvent may remain due to incomplete combustion. Therefore, it is desirable to supply oxygen (air) to such an extent that the organic solvent in the emulsion can be completely burned.

[0017]

The present invention will be specifically described below with reference to examples. (Example 1) Suspension forming step A commercially available titania sol (STS-01, manufactured by Ishihara Techno: titania particle diameter: 7 nm) and a commercially available barium nitrate dissolved in deionized water were used to prepare 0.01 to 0.3 mol / mol. L of barium nitrate aqueous solution, the molar ratio of titanium to barium is Ti / Ba = 1 /
A predetermined amount was mixed so as to be 1 to obtain an aqueous phase.

Emulsion formation step Commercial kerosene was used as the organic solvent. As the dispersant, sun soft No. manufactured by Taiyo Kagaku Co., Ltd. 818H was used in an amount of 5 to 10% by weight based on kerosene. The kerosene containing the dispersant was used as an oil phase. The water phase and the oil phase were mixed such that the ratio of water phase / oil phase = 40 to 70/60 to 30 (% by volume). The mixed solution is 1000-1000 using a homogenizer.
Stir at 20,000 rpm for 5 to 30 minutes,
An O-type emulsion was obtained. From the result of observation with an optical microscope, the water droplet diameter in the above emulsion was about 1 to 2 μm.
Met.

Combustion Step The W / O emulsion prepared as described above is used in JP-A-7-8
Using an emulsion combustion reactor described in No. 190, the emulsion was sprayed, the oil phase was burned, and the metal ions present in the aqueous phase were oxidized to form a composite oxide powder. The synthesis conditions are such that the spray flow rate of the emulsion, the amount of air (oxygen amount), and the like are controlled so that the sprayed emulsion droplets are completely burned and the flame temperature is a constant temperature of 800 to 1000 ° C. I did it. The generated powder was collected by a bag filter installed at the rear of the reaction tube.

The crystal phase of the obtained composite oxide powder was changed to powder X
It was identified by the line diffraction method. (Example 2) A commercially available titania powder (average particle diameter: 100 nm) was used instead of titania sol as a titanium source.
A composite oxide powder was synthesized by the same process as in Example 1,
The crystal phase of this composite oxide powder was identified. Comparative Example 1 Commercially available titania powder (average particle diameter 200 nm, specific surface area 9 m ² ) instead of titania sol as a titanium source
/ G) except that a ground product was used, a powder was synthesized by the same process as in Example 1, and the crystal phase of the synthesized powder was identified.

FIG. 1 shows the X-ray diffraction patterns of the powders synthesized in Example 1, Example 2, and Comparative Example 1. Example 1,
In Example 2, a single phase of barium titanate (indicated by a circle in FIG. 1) was obtained, whereas in Comparative Example 1, the solid phase shown in FIG.
In addition to the barium titanate marked, unreacted titania, a barium-rich second phase (Ba ₂ TiO ₄ ), and the like are observed, indicating that barium titanate does not become a single phase. Further, when the powder synthesized in Example 1 was observed by SEM, the product was fine spherical particles having a particle diameter of several hundred nm and a relatively uniform particle diameter. (Example 3) An aqueous metal salt solution to be mixed with the titania sol of Example 1 was an aqueous solution of zirconium oxynitrate of 0.01 to 2 mol / L, and the molar ratio of titanium to zirconium was Ti /
A predetermined amount was mixed so that Zr = 1/1 to obtain an aqueous phase. Otherwise, a composite oxide powder was synthesized by the same process as in Example 1, and the crystal phase of this composite oxide powder was identified. FIG. 2 shows an X-ray diffraction pattern of the composite oxide powder synthesized in Example 3. It can be seen that a single phase of zirconium titanate was obtained. (Example 4) A metal salt aqueous solution to be mixed with the titania sol of Example 1 was a 0.01 to 2 mol / L strontium nitrate aqueous solution, and the molar ratio of titanium to strontium was Ti / S
A predetermined amount was mixed so that r = 1/1 to obtain an aqueous phase. Otherwise, a composite oxide powder was synthesized by the same process as in Example 1, and the crystal phase of the composite oxide synthesized powder was identified. FIG. 3 shows an X-ray diffraction pattern of the powder synthesized in Example 4. It can be seen that a single phase of strontium titanate was obtained. (Example 5) An aqueous metal salt solution to be mixed with the titania sol of Example 1 was an aqueous solution of calcium nitrate of 0.01 to 2 mol / L, and the molar ratio of titanium to calcium was Ti / Ca = 1 /
A predetermined amount was mixed so as to be 1 to obtain an aqueous phase. Otherwise, a composite oxide powder was synthesized by the same process as in Example 1, and the crystal phase of this composite oxide powder was identified. It can be seen that a single phase of calcium titanate was obtained. (Example 6) The aqueous metal salt solution mixed with the titania sol of Example 1 was used as the aqueous barium nitrate solution of Example and the aqueous solution of zirconium oxynitrate of Example 3, and the molar ratio of barium, titanium, and zirconium was Ba / Ti / Zr = 1. /
A predetermined amount was mixed so as to be 0.5 / 0.5 to obtain an aqueous phase. Otherwise, a composite oxide powder was synthesized by the same process as in Example 1, and the crystal phase of this composite oxide powder was identified. It was confirmed that a desired single phase of Ba (Zr _0.5 Ti _0.5 ) O ₃ was obtained.

[0022]

According to the production method of the present invention, stable titanium oxide can be used as a raw material. Moreover, since other metal salts are present in the solution state around the titanium particles, and the metal salts are immediately converted to oxides by the combustion and solid-dissolve in the titanium oxide, a uniform composite oxide can be easily obtained in powder form. Can be. At this time, by specifying the particle diameter or the specific surface area of the titanium oxide, a fine and uniform composite oxide powder can be produced by a low-cost and safe process.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction pattern of barium titanate synthesized in Example 1, Example 2, and Comparative Example 1.

FIG. 2 is an X-ray diffraction pattern of a zirconium titanate powder synthesized in Example 3.

FIG. 3 is an X-ray diffraction pattern of a strontium titanate powder synthesized in Example 4.

Claims (1)

[Claims] 1. A particle diameter of 100 nm or less or a specific surface area of 15 m.
² / g or more of titania particles and an aqueous solution in which a metal salt is dissolved to form a suspension, and a suspension is obtained by adding an organic solvent and a dispersant to the obtained suspension. A method for producing a titanium-containing composite oxide powder, comprising: an emulsion forming step of preparing a composite oxide powder by spray-burning the obtained emulsion to form a composite oxide powder.