JPH0210091B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing ceramic raw material powder having a fine crystal grain size. Traditionally, ceramic raw material powders, such as
A solid phase reaction method is used to synthesize BaTiO ₃ , CaTiO ₃ , SrTiO ₃ , etc. However, this method has disadvantages in that the crystal grain size becomes large, 1 μm or more, and non-uniform because it requires high-temperature treatment. In addition, there is a method of synthesizing ceramic raw materials by chemical reaction in a solution. This solution reaction production method includes, for example, Ba, Sr, Ca,
There is a method of making an alcohol solution of metal alkoxides such as Ti, Zr, Sn, etc., mixing a predetermined amount of each, adding it to water, hydrolyzing it, precipitating it as a hydroxide of each metal, and filtering it to obtain a synthetic powder. . However, it should be noted that in this case, the same result can be obtained even if Ba, Sr, Ca, etc. are added as an aqueous solution of hydroxide or salt. However, in this method, the generated Ba
(OH) ₂ , Sr(OH) ₂ , Ca(OH) _{2 ,} etc. are mostly or partially dissolved in water, so they cannot form co-precipitates and can only be synthesized by evaporation and drying. Further, there is a drawback that there is no guarantee that the resulting precipitated crystals will be crushed to the same particle size as other metal hydroxides. The present invention aims to eliminate the drawbacks of the above-mentioned conventional examples and to provide a method capable of producing a fine powder ceramic raw material. That is, the gist of this invention is as follows: (i) In the first tank, oxalic acid, citric acid, tartaric acid,
and an aqueous solution of an organic acid or an organic acid salt consisting of an alkali metal salt or ammonium salt of oxalic acid, citric acid, or tartaric acid.
In a second tank, caustic soda and ammonium hydroxide are added to an aqueous solution of nitrate or chloride containing at least one of Ti, Zr, Sn, and Pb as a constituent element. Add a soluble hydroxide aqueous solution such as
(ii) mixing the slurry containing each precipitate obtained in the first step, passing through the slurry, and then washing with water; , a second step of drying, and (iii) a third step of calcining and pulverizing the obtained powder. In the above-mentioned step, in the first tank of the first step, oxalic acid, citric acid, tartaric acid, and an organic acid or an organic acid salt of an alkali metal salt or ammonium salt of oxalic acid, citric acid, or tartaric acid are used. Among them, organic acids or organic acid salts of alkali metal salts and ammonium salts of oxalic acid, citric acid, and tartaric acid include, for example, sodium oxalate, ammonium citrate, sodium citrate,
Potassium tartrate, etc. In addition, Bi, Nb, Zn, Y, and rare earth elements can be included as constituent elements used in the second tank of the first step. In particular, rare earth elements can suppress crystal grain growth. Furthermore, Mn, Al, and Si may be contained. These elements act as mineralizers. Each raw material is put into the first tank and the second tank at a predetermined ratio, and the completely precipitated slurry is mixed in the second process and further calcined in the third process. , it is possible to produce ceramic raw materials with no deviation in ratio. Also, when each precipitate obtained in the first step is mixed in the second step, the particle size is
With a diameter of 0.01 to 0.02 μm, a mixture in which each particle is adjacent to another primary particle can be obtained. After the mixture is filtered, it is washed with water and dried to obtain an active raw material that is easily reactive. By calcining this raw material in the third step, an ABO ₃ type ceramic raw material having a predetermined ratio is produced and can be agglomerated at the same time. Agglomerating ceramic raw materials into secondary particles reduces the specific surface area (m ² /gr) of the secondary particles when kneaded with a binder to make ceramic green sheets, for example, so that the amount of binder used can be reduced. This is also because the shrinkage rate can be reduced when the molded product is fired. Although it aggregates into secondary particles during the calcination stage, each raw material particle is just a mixture of fine particles, and the ceramic obtained by firing is also fine grained, so even if it is aggregated into secondary particles. There is no problem in obtaining fine grain ceramics. The processing temperature at the calcination stage is preferably 700-1000
Selected in the range of °C. This is because the ceramic raw material powder cannot be synthesized sufficiently at temperatures below 700℃, and at temperatures below 700℃,
This is because agglomeration will proceed too much if it exceeds this value. Note that the ceramic raw material powder obtained by the method of this invention is generally an ABO ₃ type oxide, but each precipitate obtained in the first step is
This tank does not correspond to B, but was selected from the viewpoint of elements that can be precipitated as organic acid salts in the first tank, and elements that can be precipitated as hydroxides in the second tank. be. In the second tank, the pH is adjusted to between 7 and 10, and the reason why the pH value is limited to this range is because the constituent elements will dissolve even if the pH value is lower or higher than this. Further, it is preferable that the PH value of the first tank and the PH value of the second tank match. This is the second step in which the slurry containing each precipitate is mixed, and the PH
This is to prevent a value shift from occurring, and also to prevent the hydroxide in the second tank from dissolving due to the influence of the PH value in the first tank. Further, in the second tank, hydrogen peroxide (H ₂ O ₂ ) may be added as a stabilizer. This is to prevent the solution from being hydrolyzed and precipitated. The present invention will be described in detail below with reference to examples. Example 1 The raw materials shown in the table below were prepared.

[Table] First, in the first tank, ammonium citrate was added to an aqueous solution of BaCl ₂ to adjust the pH to 9 to 9.5, and the solution was precipitated as barium citrate. In addition, in the second tank, TiCl ₄ , SnCl ₄ ,
Mix the aqueous solutions of SiCl ₄ and MnCl ₄ 4H ₂ O,
Add 15 ml of 30% hydrogen peroxide as a stabilizer, and add ammonium hydroxide (NH ₄ OH) to adjust the pH to 9 to 9.5 to obtain a precipitate containing Ti, Sn, Si, and Mn. . Furthermore, each precipitate slurry was mixed, filtered, and washed with water. When this water-washed raw material was mixed in a ball mill, successively filtered and dried, 0.02μ
A ceramic raw material powder in the form of fine particles of m was obtained. After that, it was calcined at a temperature of 900℃ for 1 hour, and Ba
(Ti, Sn)O ₃ -based calcined powder was obtained. Add a binder to this calcined powder, granulate it, and pressurize it.
It was molded at 1000 Kg/cm ² to form a disk of 10 mmφ and 1 mm thick, which was fired at 1300° C. for 2 hours to obtain a disk porcelain. Silver paste was applied to both sides of this porcelain disc and baked at 800°C for 30 minutes to form electrodes and obtain a capacitor. The dielectric constant (ε), dielectric loss (tan δ), temperature characteristic of dielectric constant (TC), and withstand voltage characteristics of this capacitor were measured, and the results are shown in the table below. Dielectric constant (ε) and dielectric loss (tanδ) are 1KHz,
It was measured under the condition of 1 Vr.ms, and the temperature characteristic (TC) of the dielectric constant was measured in the temperature range of -10°C to +85°C with +25°C as the standard.

【table】 Example 2 The raw materials shown in the table below were prepared.

[Table] First, in the first tank, Ba(NO ₃ ) ₂ , Ca
(NO ₃ ) ₂・4H ₂ O aqueous solutions were mixed, sodium oxalate was added to adjust the pH to 7 to 10, and barium oxalate (BaC ₂ O ₄ ) and calcium oxalate (CaCO _{3 )} were added. ) was precipitated as In addition, in the second tank, TiCl ₄ , ZrOCl ₂
8H ₂ O, SnCl ₄ , Bi(NO ₃ ) ₃・5H ₂ O, Pb(NO ₃ ) ₂ ,
Mix the aqueous solutions of Sm(NO ₃ ) ₃ and 6H ₂ O, add 15 ml of 30% hydrogen peroxide as a stabilizer, and further add caustic soda (NaOH) to adjust the pH to 7 to 10. A precipitate containing Ti, Zr, Sn, Bi, Pb, and Sm was obtained. Furthermore, each precipitate slurry was mixed, filtered, and washed with water. When this water-washed raw material was mixed in a ball mill, successively filtered and dried, it was found to have a particle diameter of 0.015 μm.
A ceramic raw material powder in the form of fine particles was obtained. After that, it was calcined at a temperature of 800℃ for 1 hour, and (Ba,
A calcined powder of Ca, Pb) (Ti, Zr, Sn, Bi) O ₃ system was obtained. This calcined powder was treated in the same manner as in Example 1 to prepare a capacitor, and its electrical characteristics were measured and the results are shown in the table below. Note that the firing temperature was 1120°C.

[Table] In addition, a multilayer capacitor was created using this raw material and its electrical characteristics were measured. To prepare the sample, binder, dispersant, etc. were added to the calcined raw material powder to form a paste, which was then printed to form a dielectric ceramic layer with a thickness of 20 μm, and an Ag:Pd ratio of 70:30 was used as the internal electrode. - Pd-based paste was printed and this was repeated alternately to make 10 dielectric ceramic layers. Next, it was fired at a firing temperature of 1120° C. for a firing time of 2 hours, and external connection electrodes were formed on both end faces to obtain a multilayer capacitor. The size of the obtained multilayer capacitor is 4mm×
It was 3 mm x 0.15 mm, and its capacitance was 0.43 μF. The thickness of each dielectric ceramic layer after firing was 12 μm. Example 3 The raw materials shown in the table below were prepared.

[Table] First, in the first tank, potassium tartrate was added to an aqueous solution of BaCl ₂ .2H ₂ O to adjust the pH to 9 to 9.5, and the solution was precipitated as barium tartrate. In addition, in the second tank, NdCl ₃ 6H ₂ O,
TiCl ₄ , Bi(NO ₃ ) ₃・5H ₂ O, MnCl ₄・4H ₂ O,
Mix each aqueous solution of _SiCl4 , add 10ml of 30% hydrogen peroxide as a stabilizer, add ammonium hydroxide ( _NH4OH ) to this, adjust the pH to 9 to 9.5,
A precipitate containing Nd, Ti, Bi, Mn, and Si was obtained. Furthermore, each precipitate slurry was mixed, filtered, and washed with water. When this water-washed raw material was mixed in a ball mill, successively filtered, and dried, the result was 0.01μ
A raw material powder in the form of fine particles of m was obtained. After that, it is calcined at a temperature of 800℃ for 1 hour.
(BaNd) (Ti, Bi) O ₇ -based calcined powder was obtained. This calcined powder was treated in the same manner as in Example 1 to prepare a capacitor, and its electrical characteristics were measured and the results are shown in the table below. Note that the firing temperature was 1100°C. In addition, the temperature characteristic (TC) of the dielectric constant is +10 to +25°C.
This is a value measured in a temperature range of +85℃.

【table】 Example 4 The raw materials shown in the table below were prepared.

[Table] First, in the first tank, oxalic acid was added to an aqueous solution of CaCl ₂ and aqueous ammonia was further added to adjust the pH to 9 to 9.5 to precipitate calcium oxalate. In addition, in the second tank, the aqueous solutions of TiCl ₄ and Nb ₂ Cl ₅ were mixed, and a 30% hydrogen peroxide solution was added as a stabilizer.
25 ml was added thereto, and the pH was adjusted to 9 to 9.5 by adding caustic soda (NaOH) to obtain a precipitate containing Ti and Nb. Further, each precipitate slurry was mixed, filtered, and washed with water. When this water-washed raw material was mixed in a ball mill, successively filtered and dried, it was found to have a particle diameter of 0.01 μm.
A finely divided raw material powder was obtained. After that, the Ca
(Ti, Nb) O ₃ -based calcined powder was obtained. A capacitor was prepared from this calcined powder in the same manner as in Example 1, and its electrical characteristics were measured. The results are shown in the table below. Note that the firing temperature was 1100°C. In addition, the temperature characteristic (TC) of the dielectric constant is -55 to +25℃.
This is a value measured in a temperature range of +125℃.

【table】

Claims (1)

[Claims] 1 (i) In the first tank, oxalic acid, citric acid, tartaric acid and these oxalic acids, Adding either an aqueous solution of an organic acid or an organic acid salt consisting of an alkali metal salt or ammonium salt of citric acid or tartaric acid.
Adjust the pH to 7 to 10 and precipitate as an organic acid salt. In a second tank, add caustic soda and hydroxide to an aqueous solution of nitrate or chloride containing at least one of Ti, Zr, Sn, and Pb as a constituent element. PH by adding aqueous solution of soluble hydroxide such as ammonium
(ii) mixing the slurry containing each precipitate obtained in the first step, passing through the slurry, and then washing with water; , a second step of drying; and (iii) a third step of calcining and pulverizing the obtained powder. 2. In the first step, the second tank further contains at least one of Bi, Nb, Zn, Y, rare earth elements, Mn, Al, and Si. A method for producing ceramic raw material powder according to item 1. 3 The calcination temperature in the third step is 700-1000℃
A method for producing ceramic raw material powder according to claim 1.