JPH07277710A - Production of perovskite-type multiple oxide powder - Google Patents

Abstract

PURPOSE:To provide a method for producing easily at low cost perovskite-type multiple oxide powder useful as e.g. a ceramic feedstock and having such characteristics as to be fine and highly dispersible to submicron levels and, besides, sharp in the distribution of both primary and secondary particle diameters. CONSTITUTION:In producing the perovskite-type multiple oxide powder expressed by formula ABO3 (A is at least one kind of alkaline earth metal; B is at least one kind of tetravalent metallic element), an aqueous slurry of at least one kind of an alkaline earth metal hydroxide is incorporated with at least one kind of compound of tetravalent metal and an alkali at least equivalent to the tetravalent metal under agitation to carry out a reaction, and the resultant slurry containing the reaction product is aged at about 50-200 deg.C.

Description

Detailed Description of the Invention

[0001]

The present invention relates to fine particles, high dispersibility,
The present invention also relates to a method for producing a perovskite type complex oxide powder having a narrow particle size distribution width. More specifically, condensers,
The present invention relates to a method for producing a perovskite-type composite oxide powder, particularly a barium titanate-based dielectric material powder, which is useful as a material for ceramic electronic components such as PTC elements and semiconductors.

[0002]

2. Description of the Related Art (1) As a method for producing a perovskite type complex oxide powder, (1) powders of carbonates or oxides of elements constituting the complex oxide are mixed and pulverized, and then calcined at a temperature of 1000 ° C. or higher. A so-called dry method of mechanically pulverizing and pulverizing, (2) a method of firing oxalates of both metals produced by adding oxalic acid to an aqueous solution of barium and titanium at high temperature, (3) alkoxide of barium and titanium A method of hydrolyzing the mixed solution of (4) a method of mixing titanium oxide and barium hydroxide at a ratio of Ba / Ti = 1.2, and performing a hydrothermal treatment at 110 to 370 ° C. in an autoclave,
(5) A method is known in which hydrous titanium oxide having a water content of 95% by weight and barium hydroxide are mixed so that the molar ratio of barium to titanium is 2 to 3, and the mixture is heated to 100 ° C.

[0003]

The dry method (1) requires a high temperature (about 1300 to 1400 ° C.). Further, high temperature calcination causes sintering to start, resulting in coarse primary particles including abnormal particle growth, which are aggregated. Therefore, there is a problem in that barium titanate-based oxide powder having a fine and uniform secondary particle diameter cannot be obtained by pulverization after firing. There is also a problem that it is difficult to avoid mixing of impurities in the crushing process. The oxalate method of (2) needs to be carried out at a firing temperature of 600 ° C. or higher,
Some coarsening and agglomeration of primary particles are unavoidable,
There is a problem similar to the method (1). Further, since oxalic acid is used in a large amount, there is a problem that the cost becomes high.
The method (3) of hydrolysis is a liquid phase reaction as compared with the methods (1) and (2), so that the uniformity is remarkably improved.
There is an advantage that the target compound can be obtained at room temperature. However, the generated crystals have many lattice distortions due to lattice defects,
Poor crystal perfection. Therefore, although the primary particles are small, there is a problem that they are strongly aggregated to form coarse secondary particles. Further, there is a problem that the alkoxide as a raw material is expensive and the cost becomes high. In the method (4) of hydrothermal treatment, the reaction rate is slow because titanium oxide is a relatively stable compound. Therefore, high temperature and high pressure (300
(85 ° C., 85 atm or more), and the generated secondary particles of barium titanate are coarse and non-uniform, and the method (5) is based on the external shape of the obtained barium titanate. However, there is a problem that the material becomes a square shape due to the shape of the hydrous titanium oxide. Further, since the primary particles are too fine, there is a problem that they are likely to aggregate.

An object of the present invention is a fine perovskite type composite oxide powder which is fine and highly dispersible in a submicron level and has a sharp distribution of primary and secondary particle diameters, for example, ceramic raw materials. The purpose of the present invention is to provide a manufacturing method capable of easily and inexpensively manufacturing a powder useful as the above. The present invention intends to satisfy the market demand for electronic parts such as miniaturization, large capacity, high performance, high reliability, and low price by providing the ceramic raw material powder.

[0005]

The present invention provides a compound represented by the formula (1) ABO ₃ (1) [wherein A represents at least one alkaline earth metal and B represents at least one tetravalent metal element]. In the method for producing a perovskite-type composite oxide powder represented, at least one tetravalent metal compound and at least one tetravalent metal equivalent or excess equivalent alkali in an aqueous slurry of at least one alkaline earth metal hydroxide. And are added under stirring to react with each other, and a slurry containing the reactant is aged at about 50 to 200 ° C., preferably about 100 to 200 ° C. for 0.1 to 10 hours, preferably about 0.1 to 3 hours. A method for producing a perovskite type complex oxide powder is provided.

The present invention is a method for obtaining a perovskite-type crystal having an extremely high degree of perfection by carrying out a coprecipitation reaction at a room temperature using an inexpensive raw material, and then performing an aging treatment, preferably a hydrothermal treatment. is there. The crystals obtained by the method of the present invention have a fine average primary particle size of about 0.01 to 1 μm, and almost no aggregation occurs. Therefore, the average secondary particle diameter is also about 0.01 to 1 μm, which shows extremely high dispersibility. Further, the distribution of the primary particle diameter and the secondary particle diameter is sharp, and the outer shapes of the primary and secondary particles are almost spherical, so that the powder has good fluidity and packing property. Therefore, it is easy to supply high-performance ceramics by using the powder obtained by the method of the present invention. The alkaline earth metal hydroxide used in the present invention includes Mg, Ca,
It means a hydroxide of Sr and Ba. Examples of the tetravalent metal element used in the present invention include Ti, Zr, Sn and the like. Compounds of tetravalent metals include chlorides of these metals,
Examples thereof include halides such as bromide, and water-soluble monovalent salts such as nitrates. As the alkaline component used in the present invention,
Examples thereof include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, and organic amines such as ammonium hydroxide, dimethylamine and NN′-dimethylbenzylamine.

The alkali component may be added at any stage before the addition of the aqueous solution of the tetravalent metal compound to the aqueous slurry of the hydroxide of alkaline earth metal, at the same time as the addition of the aqueous solution, or after the addition. The addition amount of the alkali component may be approximately equal to or more than that of the tetravalent metal compound. It is preferable to remove carbonate ions and carbon dioxide in the water and the atmosphere used as much as possible so that carbonation of the alkaline earth hydroxide does not occur in the coprecipitation reaction and the subsequent aging treatment reaction. Stirring during the coprecipitation reaction is a necessary operation, and the aging treatment reaction is also preferably carried out under sufficient stirring. After aging treatment,
Fine, highly dispersible perovskite type crystals are obtained by filtration, washing with water and drying according to a conventional method. The dried product may be further calcined at about 800 ° C., then washed and dried. For cleaning, it is preferable to use pure water from which carbonate ions and the like have been removed.

In the present invention, a known rare earth element for forming a semiconductor, such as Y, Sc, La, etc., or Bi, N is used.
It is also possible to add an aqueous solution of a water-soluble salt of an element such as b or Sb during the coprecipitation reaction to cause the coprecipitation reaction. At this time, it is preferable that the amount of the alkali component to be added be increased by the equivalent amount of these additional elements. According to the method of the present invention, the crystals of the perovskite-type composite oxide ABO _{3 have} substantially no aggregation, the primary particles and the secondary particles have substantially the same particle diameter, and the average secondary particle diameter is about 0. 01 to 1.
It is obtained in the range of 0 μm, preferably in the range of about 0.01 to 0.5 μm, and the BET specific surface area in the range of about 1 to ²⁰ m ² / g. The method for producing a perovskite-type composite oxide of the present invention is based on a large difference in pH required for hydroxide formation between an alkaline earth metal and a tetravalent metal element compound during a coprecipitation reaction, resulting in heterogeneous precipitation formation. This is to solve the defect of the conventional manufacturing method. That is, in the production method of the present invention, an alkaline earth metal element that has a high solubility and does not form a hydroxide unless the pH is high is left as a hydroxide from the beginning, and an aqueous solution of a tetravalent metal and an alkali component are added thereto. It is a manufacturing method that has succeeded in solving the defects of the conventional manufacturing method by enabling a coprecipitation reaction close to ideal. As a result, it is possible to obtain a coprecipitate having a composition close to that of a perovskite type complex oxide, and the subsequent hydrothermal reaction in the liquid phase results in a lower temperature and a higher degree of perfection than in conventional production methods. Therefore, it is possible to provide a manufacturing method capable of easily obtaining crystals of a perovskite complex oxide having a high temperature.

[0009]

EFFECTS OF THE INVENTION The present invention provides a method for producing fine and highly dispersible perovskite type complex oxide crystals, which have hitherto not been obtained, at low temperature and with good reproducibility by using inexpensive raw materials. . Further according to the invention, by varying the temperature of the aging treatment between about 50 ° C. and 200 ° C., preferably the temperature of the hydrothermal treatment between about 100 ° C. and 200 ° C.,
Provided is a method for easily and reproducibly producing crystals of a perovskite-type composite oxide having various primary particle diameters and secondary particle diameters. The production method of the present invention meets diversified demands for crystals of perovskite type complex oxides.

The present invention will be described in more detail based on the following examples. In the following examples, parts and% mean parts by weight and% by weight, respectively, unless otherwise specified. Example 1 0.1 mol of Ba (OH) ₂ .8H ₂ O was added to 500 ml of deionized water (about 25 ° C.) with stirring, and after dispersion and dissolution, 0.1 mol of TiCl ₄ solution (about 25 C) was added. Subsequently, 0.4 mol of a 4 mol / liter sodium hydroxide aqueous solution (about 25 ° C.) was added, and the mixture was stirred for 0.25
Held for hours. The slurry obtained by the above reaction was placed in an autoclave as it was, and hydrothermal treatment was carried out at 170 ° C. for 2 hours. Then, it was filtered under reduced pressure, further washed with deionized water, and dried. The obtained barium titanate powder is X
As a result of line diffraction, it was found to be cubic. As for the particle size distribution, the average particle size is 0.10 according to the laser diffraction scattering method.
It was 6 μm, and the standard deviation was 0.016 μm, which was extremely fine and had a narrow distribution width. The BET specific surface area was 6 m ² / g. Also, when observed by a scanning electron microscope, almost all the particles were spherical, and particles having an average diameter of about 0.1 μm were dispersed without agglomeration. The electron micrograph (10,000 times) showing the crystal structure of the obtained powder is shown in FIG. 1, and the particle size distribution is shown in FIG.

Example 2 0.06 mol of Ba (OH) ₂ .8H ₂ O and 0.04 mol in 500 ml of deionized water (about 25 ° C.) with stirring.
After Smol (S) (OH) ₂ .8H ₂ O was added and dispersed and dissolved,
A 095 molar TiCl ₄ solution (about 25 ° C.) was added. Then, a 4 mol / liter sodium hydroxide aqueous solution (about 2 mol
(5 ° C.) 0.4 mol was added and the mixture was kept under stirring for 0.25 hours. The slurry obtained by the above reaction was placed in an autoclave as it was, and hydrothermally treated at 150 ° C. for 2 hours. Then, it was filtered under reduced pressure, washed with water and dried. Obtained (Ba _0.60 S
The powder having a composition of r _0.40 ) TiO ₃ showed a B
It was found to be a cubic solid solution having the same crystal structure as aTiO ₃ . The average particle size is 0.122μ
m, the standard deviation was 0.024 μm, and the BET specific surface area was 8.5 m ² / g. Observation with a scanning electron microscope revealed that almost all the particles were substantially spherical, their diameter was about 0.1 μm, and they were dispersed without aggregation.

Example 3 To 500 ml of deionized water (about 20 ° C.), 0.1 mol of Ba (OH) ₂ .8H ₂ O was added with stirring, and after dispersion and dissolution, 4 mol / l of potassium hydroxide was added. 0.4 mol of an aqueous solution (about 20 ° C.) was added. Then, 0.09 mol of TiCl ₄ solution (about 20 ° C.) and 0.01 mol of SrC were added.
l ₄ aqueous solution of (approximately 20 ° C.) was added and 100 ml simultaneously. Then, it heated at 70 degreeC and hold | maintained under stirring for about 2 hours. Then, it was filtered under reduced pressure, washed with deionized water, and dried. The obtained Ba (Ti _0.90 Sr _0.10 ) O
As a result of X-ray diffraction, the powder having the composition of ₃ was found to be a cubic solid solution having the same crystal structure as BaTiO ₃ .
The particle size distribution is such that the average particle size is 0.196 μm and the standard deviation is 0.0.
The BET specific surface area was 12.1 m ² / g. Observation with a scanning electron microscope revealed that almost all the particles were almost spherical and had a diameter of about 0.2.
It was μm and was dispersed without agglomeration.

Comparative Example 1 0.12 mol of Ba (OH) ₂ .8H ₂ O was added to 500 ml of deionized water (about 20 ° C.) with stirring, and after dispersion and dissolution, 0.1 mol of TiO ₂ was added. After adding and dispersing,
It was kept under stirring for about 0.25 hours. The obtained slurry was put into an autoclave and hydrothermally treated at 170 ° C. for 2 hours. Then, it was filtered under reduced pressure, washed with deionized water, and dried. As a result of X-ray diffraction, the obtained powder was a mixture of cubic barium titanate and titanium oxide.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the crystal structure of the composition obtained in Example 1.

FIG. 2 is a graph showing the particle size distribution of the composition obtained in Example 1.

Claims (4)

[Claims] 1. A perovskite-type complex oxide represented by the formula (1) ABO ₃ (1) [wherein A represents at least one alkaline earth metal and B represents at least one tetravalent metal element]. In the method for producing a powder, at least one tetravalent metal compound and tetravalent metal and an equivalent or excess equivalent of alkali are added to an aqueous slurry of at least one alkaline earth metal hydroxide with stirring. A method for producing a perovskite type complex oxide powder, which comprises reacting and aging a slurry containing a reactant at about 50 to 200 ° C. 2. Aging is carried out in an autoclave at a rate of about 100-.
The method for producing a perovskite type complex oxide powder according to claim 1, wherein the hydrothermal treatment is performed at 200 ° C. 3. The method for producing a perovskite-type composite oxide powder according to claim 1, wherein the tetravalent metal compound is a tetravalent metal halide or a tetravalent metal nitrate. 4. The method for producing a perovskite complex oxide powder according to claim 1, wherein the perovskite complex oxide powder is a barium titanate-based dielectric powder.