JPH0210089B2 - - 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 it requires high-temperature treatment, resulting in a large particle size of 1 μm or more and non-uniformity. In addition, there is a method of synthesizing ceramic raw materials by chemical reaction in a solution. As a manufacturing method using this solution reaction, for example, Ti ions and Ba etc.
Me ions are precipitated as titanyl barium oxalate (BaTiO(C ₂ O ₄ ) 4H ₂ O) using oxalic acid, and this precipitate is thermally decomposed at a temperature of 700°C or higher.
There is a method of synthesizing BaTiO ₃ (oxidation method). Although this oxalic acid method makes it possible to obtain fine particles of about 0.5 μm, this method has the following drawbacks. In other words, Ba and Ti can be precipitated at the same time, but other elements cannot be precipitated, and this method is used to obtain ceramic raw materials of systems other than BaTiO ₃ and composite systems of BaTiO ₃ and other systems. It is inappropriate as such. Furthermore, oxalate salts are expensive and disadvantageous in terms of industrial use. Furthermore, as a manufacturing method using this solution reaction, for example, an alcohol solution of metal alkoxide such as Ba, Sr, Ca, Ti, Zr, Sn, etc. is prepared, a predetermined amount of each is mixed, and then added to water and hydrolyzed.
There is a method of precipitating the 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 that (i) at least one of Ba, Sr, and Ca is used as a constituent element;
Species and constituent elements include at least Ti, Zr, Sn,
A soluble hydroxide aqueous solution such as caustic soda or ammonium hydroxide is added to an aqueous solution of nitrate or chloride containing one type of Pb to adjust the pH to 7 to 10, and at least hydroxides of Ti, Zr, Sn, and Pb are added. After precipitating only 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, while maintaining the pH within the above range, (ii) a second step in which the slurry containing each precipitate obtained in the first step is filtered, washed with water, and dried;
(iii) a third step of calcining and pulverizing the obtained powder. In the first step described above, oxalic acid, citric acid, tartaric acid, and organic acids or organic acid salts of alkali metal salts and ammonium salts of oxalic acid, citric acid, and tartaric acid are used. Examples of organic acids or organic salts of alkali metal salts and ammonium salts of citric acid and tartaric acid include sodium oxalate, ammonium citrate, sodium citrate, and potassium tartrate. In addition, in the above step, Bi, Nb, Zn, Y, and rare earth elements may be included as constituent elements to be precipitated as hydroxide in the first step, and these suppress grain growth of crystals. be able to. Furthermore, Mn, Al, and Si may be contained. These elements act as mineralizing agents. Furthermore, each raw material is added in a predetermined ratio in the first step, the completely precipitated slurry is passed through the second step, and further calcined in the third step, so that there is no difference in ratio. Ceramic raw materials can be produced. Furthermore, the precipitate obtained in the first step has a particle size of about 0.01 to 0.02 μm, and is a mixture of adjacent primary particles. Then, by washing with water and drying, an active raw material that is easily reactive can be obtained. 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 coagulated 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 in 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 synthesis of ceramic raw material powder does not take place sufficiently at temperatures below 700℃, and at temperatures below 700℃,
This is because aggregation will proceed too much if it exceeds this. Furthermore, during the reaction, hydrogen peroxide (H ₂ O ₂ ) may be added as a stabilizer. This is to prevent the solution from being hydrolyzed and precipitated. Hereinafter, this invention will be explained in detail according to examples. Example 1 The raw materials shown in the table below were prepared.

[Table] BaCl ₂ , TiCl ₂ , SnCl ₂ , SiCl ₄ and
Mix each aqueous solution of MnCl ₄ 4H ₂ O, add 15 ml of 30% hydrogen peroxide as a stabilizer, add ammonium hydroxide (NH ₄ OH) to adjust the pH to 9 to 9.5, and , hydroxides containing Sn, Si, and Mn were precipitated. After the hydroxide is completely precipitated, the pH is adjusted to 9~
Maintain the temperature at 9.5, add ammonium citrate aqueous solution,
It was precipitated as barium citrate. Next, the slurry of mixed precipitates was filtered and washed with water, and the washed raw materials were mixed in a ball mill, successively filtered and dried, and the result was 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 a temperature range of +10°C to +85°C with +25°C as a reference.

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

[Table] In the tank, Ba(NO ₃ ) ₂ , Ca(NO ₃ ) ₂ .
4H ₂ O, TiCl ₄ , ZrOCl ₂・8H ₂ O, SnCl ₄ , Bi
(NO ₃ ) ₃・5H ₂ O, Pb(NO ₃ ) ₂ , Sm(NO ₃ ) ₃・6H ₂ O
Mix each aqueous solution of Ti, add 15 ml of 30% hydrogen peroxide as a stabilizer, and further add caustic soda (NaOH) to adjust the pH to 7 to 10.
Hydroxides containing Zr, Sn, Bi, Pb, and Sn were precipitated. Further, sodium oxalate and a small amount of hydrochloric acid were added to precipitate barium oxalate (BaC ₂ O ₄ ) and calcium oxalate (CaC ₂ O ₄ ). Next, the slurry of mixed precipitates was 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 size 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] In the tank, BaCl ₂・2H ₂ O, NdCl ₃・
6H ₂ O, TiCl ₄ , Bi(NO ₃ ) ₃・5H ₂ O, MnCl ₄・
Mix the aqueous solutions of 4H ₂ O and SiCl ₄ , which are stabilizers.
10 ml of 30% hydrogen peroxide solution was added, and ammonium hydroxide (NH ₄ OH) was added to adjust the pH to 9 to 9.5 to precipitate hydroxides containing Nd, Ti, Bi, Mn, and Si. . Further, while maintaining the pH at 9 to 9.5, an aqueous potassium tartrate solution and a small amount of nitric acid were added to precipitate barium tartrate. Next, the slurry of mixed precipitates was filtered and washed with water. The water-washed raw materials were mixed in a ball mill and successively passed to obtain raw material powder in the form of fine particles of 0.01 μm. After that, it was calcined at a temperature of 800℃ for 1 hour, and (Ba,
A calcined powder of Nd)(Ti,Bi)O ₇ 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 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】 Example 4 The raw materials shown in the table below were prepared.

[Table] Mix aqueous solutions of CaCl ₂ , TiCl ₄ , and Nb ₂ Cl ₅ in a tank, and add 30% hydrogen peroxide solution 25 as a stabilizer.
ml was added thereto, and the pH was adjusted to 9 to 9.5 by adding caustic soda (NaOH) to precipitate hydroxides containing Ti and Nb. Further, a small amount of aqueous ammonia was added to maintain the pH at 9 to 9.5, and oxalic acid was added to precipitate calcium tartrate. Next, the slurry of mixed precipitates was 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) At least Ba, Sr, Ca as constituent elements
and at least Ti, Zr,
Add a soluble hydroxide aqueous solution such as caustic soda or ammonium hydroxide to an aqueous solution of nitrate or chloride containing at least one of Sn, Pb, and adjust the pH to 7 to 10. After precipitating only the oxide, an aqueous solution of an organic acid or organic acid salt consisting of oxalic acid, citric acid, tartaric acid, and an alkali metal salt or ammonium salt of these oxalic acid, citric acid, or tartaric acid is added while maintaining the pH within the above range. In addition, at least Ba, Sr, Ca
(ii) a second step in which the slurry containing each precipitate obtained in the first step is filtered, washed with water, and dried;
and (iii) a third step of calcining and pulverizing the obtained powder. 2 In the first step, at least Ti, Zr,
In addition to Sn and Pb, additional constituent elements include Bi,
A method for producing ceramic raw material powder according to claim 1, which comprises containing at least one of Nb, Zn, Y, rare earth elements, Mn, Al, and Si and precipitating it as a hydroxide. 3 The calcination temperature in the third step is 700℃~1000℃
The method for producing ceramic raw material powder according to claim 1, wherein the temperature is .degree.