JPH05178619A - Production of fine powder perovskite-structure compound - Google Patents

Abstract

PURPOSE:To produce a fine powdery perovskite-structure compd. appropriate as the material for the dielectric, piezoelectric, semiconductor, etc. CONSTITUTION:A thermal reaction is conducted in an alkaline suspension contg. a compd of the element selected from Ba, Pb, Sr, Mg and Ca and a compd. of the element selected from Ti, Zr, Hf and Sn in a specified molar ratio, the suspension contg. the perovskite-structure compd. grains as the reactional product is controlled to pH 7 to 11, solid is separated from liq., and the obtained wet cake is dry-heated and treated in an aq. suspension kept at pH 7 to 10 to produce the fine powdery perovskite-structure compd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fine powder of perovskite type compound suitable as a material for dielectrics, piezoelectrics, semiconductors and the like.

[0002]

TECHNICAL BACKGROUND AND PROBLEMS OF THE INVENTION Barium titanate,
Strontium titanate, lead titanate, lead zirconate,
So-called perovskite type compounds such as calcium stannate (collectively referred to as ABO ₃ compounds) have extremely excellent dielectric properties, piezoelectric properties, and semiconductor properties when the compounds are molded and then sintered.
As a so-called dielectric ceramic element such as a radio wave filter, an ignition element, and a thermistor, it is used in large quantities today in various application fields such as communication equipment and computers.
By the way, in recent years, there has been a marked trend toward miniaturization and high integration of electrodevices, and accordingly, demands for miniaturization and chipping of electronic elements applied to the devices have become stronger. As in the case of miniaturization and high capacity of multilayer capacitors, there are many perovskite type compounds such as barium titanate and strontium titanate as the dielectric material used in the microelectrode gap as sintered body constituent particles. Therefore, the smaller the particle size of the constituent particles, the more preferable.

By the way, as a method for producing the fine particles of the perovskite type compound as a dielectric material, for example, barium hydroxide as a group A compound and hydrous titanium oxide as a group B compound are used as starting materials, and both of them are mixed with a predetermined Ba. / Ti molar ratio, then heat reaction treatment under a predetermined alkali concentration under normal pressure or pressure, the obtained reaction-treated slurry is filtered and washed, and then the treated cake is dried and crushed. Is well known. In the wet method, however, fine particles of ABO ₃ compound can be obtained relatively easily, while unreacted Group B element remains in a solid state, while unreacted Group A element is partially or entirely dissolved in water. Since it remains in a sexual state and is removed in the process of filtration and washing, it tends to have a composition of group B element excess, and the degree of excess varies depending on the reaction conditions and the like. It is extremely difficult to control the composition of the / B molar ratio to a certain degree, and as a result, densification in the process of making the ABO ₃ compound into a ceramic and control of the sintered crystal grain size may be adversely affected. Further, in the above-mentioned wet method, since the reaction treatment is carried out in a strong alkaline medium, alkali metals such as Na and K tend to remain in the obtained ABO ₃ compound, and the result itself is used for sintering in the ceramization process. There are a number of problems that need to be solved, such as extremely difficult control of the crystal grain size, and significantly impairing the electrical characteristics of ceramics and their temporal stability.

The inventors of the present invention have, in the process of conducting various investigations to solve the above-mentioned problems, unreacted substances after the heating reaction treatment of the liquid to be reacted having a predetermined A / B molar ratio within a specific range. By combining and removing the pH adjustment and the heat treatment under a specific temperature condition in a specific order, the A / B molar ratio can be accurately controlled with an accuracy of 3% or less, and the alkali metal impurity is 100 ppm or less. The present invention has been completed based on the finding that it can be removed extremely efficiently.

[0005]

The present invention relates to a method for producing the perovskite type compound fine powder shown below. (1) at least one compound selected from the group A element compounds consisting of Ba, Pb, Sr, Mg and Ca, and T
i / Zr, Hf and at least one compound selected from the group B element compounds consisting of Sn and having an A / B molar ratio of 1
After subjecting the aqueous suspension of the above mixture containing the free alkali concentration of 0.1 mol / l or more to the reaction by heating at 80 ° C. or higher, and then adjusting the pH of the suspension to 7 to 11 Solid-liquid separation is performed, and the obtained wet cake is heat-treated at 300 ° C. or higher, and then the obtained heat-treated product is made into an aqueous suspension having a pH of 7 to 10, and then solid-liquid separated and dried. A method for producing a fine powder of a perovskite-type compound, comprising: (2) A / B molar ratio of 1.1 or more and a free alkali concentration of 0.1 mol / l or more The method for producing the fine powder of perovskite compound according to the item (1), and (3) the heating reaction treatment temperature of the suspension is 10
The method for producing perovskite-type compound fine powder according to item (1) above, wherein the temperature is 0 ° C. or higher.

In the present invention, various compounds can be used as the group A element compound, and mineral acid salts, organic acid salts, hydroxides and the like of the group A element can be used. Examples thereof include barium and strontium. Chloride, nitrate, acetate,
A hydroxide etc. can be mentioned. As the group B element compound, various compounds can be used, and examples thereof include mineral salts of group B elements, organometallic compounds, hydroxides, and the like. For example, for titanium and zirconium, chlorides can be used. , Nitrates, organometallic compounds, hydrated oxides and the like. Various alkaline compounds may be used, for example, NaOH and KO.
Examples thereof include caustic alkalis such as H and LiOH, as well as carbonates of alkali metals, and the above-mentioned ones may be partially used with an ammonium compound such as ammonium carbonate. In the present invention, A /
Various methods can be used for preparing an aqueous suspension of a mixture having a B molar ratio of 1 or more and a free alkali concentration of 0.1 mol / l or more. Preparation by adding an alkaline compound to a mixed system with a group B element compound, or by adding a group A element compound and a group B element compound to the alkaline compound system in any order or in parallel. You can A / B
Is 1 or more, preferably 1.1 to 2.0. If the molar ratio is too low, the ABO ₃ compound having the desired composition cannot be obtained, and the unreacted water-insoluble component is insoluble. The group B element compound of ( ₃ ) is excessively left in the produced ABO ₃ compound and the characteristics as a dielectric material are apt to be significantly impaired, and when the molar ratio is too much higher than the above, unreacted group A element compound is formed. Excessively remains in the ABO ₃ compound, and the removal treatment operations such as filtration and washing become complicated, and
Strict control of the desired A / B molar ratio becomes extremely difficult. Furthermore, the alkali concentration of the suspension is 0.1 mol / l or more,
Desirably, it is 0.1 to 1.5 mol / l, and when the molar ratio is too low, the fine particle size distribution A is uniform.
Crystal particles of the BO ₃ compound cannot be obtained, and when the alkali concentration is too high, it is not economically advantageous, and the treatment operation for washing and removing becomes extremely complicated.

The alkaline aqueous suspension prepared as described above is subjected to a heat reaction treatment under normal pressure or increased pressure to obtain fine ABO ₃ compound crystal particles having a uniform particle size distribution.
The heating reaction temperature varies depending on the concentration of the liquid to be reacted, the concentration of free alkali, the type of reactor, etc. and cannot be generally stated, but it is preferably 80 ° C. or higher, preferably about 100 to 200 ° C. If the treatment temperature is too lower than the above, it is not possible to obtain fine ABO ₃ compound crystal particles having a uniform particle size distribution, and if the temperature is too much higher than the above, the thermal cost will be increased from the viewpoint of the reactor. Not only is it unfavorable, but the reaction is likely to proceed locally, which is not preferable. Then, the aqueous suspension obtained by the heat reaction treatment as described above has a pH of 7 to 11, preferably 7.5 to 10.5, such as a mineral acid such as hydrochloric acid or nitric acid, a water-soluble organic substance. Most of the alkali metal impurities and unreacted soluble reacting components are removed by solid-liquid separation such as adjustment with acid etc., followed by decantation, filtration, and washing if necessary. To do. When the pH of the suspension is lower than the above range, the alkali metal impurities can be efficiently removed, but on the other hand, especially the A component in the produced ABO ₃ compound is unavoidable and the desired A / B ratio is not increased.
It is not preferable because an ABO ₃ compound having a molar ratio composition cannot be obtained.

The treated cake obtained by the solid-liquid separation treatment as described above is dried at 300 ° C. or higher, preferably 400
After heat treatment at ~ 700 ° C, an aqueous suspension having a pH of 7 to 10, preferably 7.5 to 9.5, is subjected to decantation treatment, filtration treatment and further washing treatment if necessary. A solid-liquid separation treatment such as simultaneous treatment is carried out to remove substantially all alkali metal impurities and unreacted soluble reacting components. If the heat treatment temperature is lower than the above range or the pH of the suspension is lower than the above range, the A component in the produced ABO ₃ compound is not particularly eluted, and If the heat treatment temperature is too high or the pH of the suspension is lower than the above range, the alkali metal impurities can be removed efficiently, but especially the A component in the ABO ₃ compound produced. elution can not be avoided in, or no longer be obtained ABO ₃ compound having a desired a / B mole ratio composition, ABO ₃ which further generated
It is not preferable because the compound particles become coarse. The ABO ₃ compound fine powder of the present invention obtained as described above has a uniform fine particle size distribution, has a good packing property at the time of molding and therefore has a significantly improved sinterability, and is dense at a lower temperature. A strong and excellent dielectric ceramic can be obtained.

[0009]

【Example】

Example 1 840 ml of water and 360 m of 400 g / l NaOH aqueous solution
Into a 3 liter four-necked flask containing 1 liter and maintained at 30 ° C., 0.75 mol /
800 ml of a mixed aqueous solution of 1 BaCl ₂ and 0.625 mol / l TiCl ₄ was added over 30 minutes (concentration of free alkali: 0.2 mol / l). After holding at the same temperature for 1 hour, the obtained aqueous slurry was put into a 3 l autoclave and subjected to hydrothermal reaction treatment at 150 ° C. for 1 hour. 25 ml of ammonium carbonate (1 mol / l) in the slurry after the hydrothermal treatment
Was added, and a dilute acetic acid aqueous solution was added to adjust the pH to 8 and the mixture was held for 30 minutes, then filtered, washed with water, and dried. Then, the obtained dried product is heated in an electric furnace at 600 ° C. in the atmosphere for 2
Heat treated for hours. Then, the obtained heat-treated product was made into an aqueous slurry, a dilute acetic acid aqueous solution was added to adjust the pH to 9 and held for 30 minutes, followed by filtration, washing with water and drying to obtain the desired barium titanate fine powder ( Sample A).

Example 2 1200 ml of water and 189.2 g of Ba (OH) ₂ powder were placed in a 3 l four-necked flask maintained at 30 ° C., while adding nitrogen gas while stirring, and adding 300 ml of 400 g / l NaOH aqueous solution. And then 1.25 mol / l TiC
l ₄ was added in an aqueous solution 400 ml 30 min (free alkali concentration: 0.5 mol / l). After holding at the same temperature for 1 hour, the obtained aqueous slurry was treated in the same manner as in Example 1 below to obtain the desired barium titanate fine powder (Sample B).

Example 3 The same procedure as in Example 2 was carried out except that ammonium carbonate was not added to obtain the desired barium titanate fine powder (Sample C).

Example 4 The same treatment as in Example 2 was carried out except that the hydrothermal treatment temperature was changed to 95 ° C. to obtain the desired barium titanate fine powder (Sample D). ..

Example 5 In Example 1, the heat treatment temperature in the electric furnace was set to 500 ° C.
In the same manner as in the case of the same example except that the same was changed to the above, the target barium titanate fine powder was obtained (Sample E).

Example 6 880 ml of water and 320 m of 400 g / l NaOH aqueous solution
in a 3 liter four-necked flask containing 1
With stirring while blowing nitrogen gas, 0.75 mol / l BaCl ₂ and 0.375 mol / l TiCl ₄ and 0.2
800 ml of a mixed aqueous solution of 5 mol / l ZrOCl ₂ was added over 30 minutes (free alkali concentration: 0.2 mol / l).
l). Thereafter, the same treatment as in Example 1 was carried out to obtain the desired barium titanium zirconate fine powder (Sample F).

Comparative Example 1 A hydrothermal reaction treatment was carried out in the same manner as in Example 1, and 25 ml of ammonium carbonate (1 mol / l) was added to the resulting slurry, and an aqueous acetic acid solution was added to adjust the pH to 5. Then, it was filtered, washed with water, and dried to obtain barium titanate fine powder (Sample G).

Comparative Example 2 Barium titanate fine powder was obtained in the same manner as in Comparative Example 1 except that the pH was not adjusted by adding an aqueous acetic acid solution (Sample H).

Comparative Example 3 In Example 1, after heat treatment in an electric furnace, the obtained treated product is made into an aqueous slurry, and the pH is not adjusted by adding a dilute acetic acid aqueous solution to the slurry. Without any treatment, fine barium titanate powder was obtained by the same treatment as in the case of the same example (Sample I).

Comparative Example 4 Barium titanate was obtained by filtering, washing and drying the slurry obtained by the hydrothermal reaction treatment obtained in the same manner as in Example 2 without adjusting the pH by adding a dilute aqueous acetic acid solution. A fine powder was obtained (Sample J).

Comparative Example 5 In Example 2, after the heat treatment in the electric furnace, the obtained treated product was made into an aqueous slurry, and the slurry was treated without adding a dilute aqueous acetic acid solution to adjust the pH. The barium titanate fine powder was obtained by the same treatment as in the example (Sample K).

Sample A obtained in the above Examples and Comparative Examples
Table 1 shows the results obtained by performing chemical analysis and specific surface area measurement for .about.K by conventional methods. When X-ray diffraction was performed on Samples A to K, Samples A to E and G to
K was cubic barium titanate and Sample F was cubic barium titanium zirconate.

[0021]

[Table 1]

[0022]

According to the method of the present invention, the desired A / B molar ratio is not controlled.
Fine ABO always controlled accurately ₃Compound particles
Easy to obtain and for dielectric ceramics
Alkali gold, which is highly disliked as a material
It can greatly reduce the residual of metal impurities.
It is of great industrial value.

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[Procedure amendment]

[Submission date] November 9, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

In the present invention, various compounds can be used as the group A element compound, and mineral acid salts, organic acid salts, hydroxides and the like of the group A element can be used. Examples thereof include barium and strontium. Chloride, nitrate, acetate,
A hydroxide etc. can be mentioned. As the group B element compound, various compounds can be used, and examples thereof include mineral salts of group B elements, organometallic compounds, hydroxides, and the like. For example, for titanium and zirconium, chlorides can be used. , Nitrates, organometallic compounds, hydrated oxides and the like. Various alkaline compounds may be used, for example, NaOH and KO.
Examples thereof include caustic alkalis such as H and LiOH, as well as carbonates of alkali metals, and the above-mentioned ones may be partially used with an ammonium compound such as ammonium carbonate. In the present invention, A /
Various methods can be used to prepare an aqueous suspension of a mixture having a B molar ratio of 1 or more and a free alkali concentration of 0.1 mol / 1 or more. Preparation by adding an alkaline compound to a mixed system with a group B element compound, or by adding a group A element compound and a group B element compound to the alkaline compound system in any order or in parallel. You can A / B
The molar ratio of A is 1 or more, preferably 1.1 to 2.0, and when the molar ratio is less than 1 , A of the desired composition is obtained.
BO ₃ compound can not be obtained, B group element compounds of unreacted water-insoluble, easily damaged significantly impair the excess remaining characteristics as a dielectric material in ABO ₃ compound generated desirability
I don't. Further, when the molar ratio is too much higher than the above-mentioned desirable range , the unreacted A group element compound is separated into the separated moisture.
Excessively remains in the cake, filtration, with the removal process operation by cleaning or the like becomes complicated, which is not preferable or Tsu Do desired A / tight control of B molar ratio coma difficulty. Further, the alkali concentration of the suspension is 0.1 mol / 1 or more, preferably 0.1 to 0.5 mol / 1, and the alkali concentration is
0.1 mol / 1 good Ri Beyond the can lower the inability to obtain crystal grains of uniform ABO ₃ compound having fine particle size distribution
Not desirable. Also, the alkali concentration is the above desirable
If too much on High than the range was not economically advantageous
Ri, preferred for the processing operation of the cleaning removal or Tsu Do Han Miscellaneous
Not good.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

The alkaline aqueous suspension prepared as described above is subjected to a heat reaction treatment under normal pressure or pressure to obtain crystal particles of the ABO ₃ compound having a fine particle size distribution.
The heating reaction temperature varies depending on the concentration of the liquid to be reacted, the concentration of free alkali, the type of reactor, etc. and cannot be generally stated, but it is preferably 80 ° C. or higher, preferably about 100 to 200 ° C. If the treatment temperature is lower than 80 ° C., it is not desirable because fine ABO ₃ compound crystal particles having a uniform particle size distribution cannot be obtained. In addition the heating anti
From response processing temperature on much too the High and reactor than the desired range of the, was not even a beneficial thermal cost
And the reaction tends to proceed locally, which is not preferable.
Then, the aqueous suspension obtained by the heat reaction treatment as described above has a pH of 7 to 11, preferably 7.5 to 10.
Adjust to 5 with mineral acid such as hydrochloric acid or nitric acid, water-soluble organic acid, etc., and then perform decantation treatment, filtration treatment, and solid-liquid separation such as washing treatment if necessary. Most of alkali metal impurities and unreacted soluble reacting components are removed. When the pH of the suspension is lower than the above range, the alkali metal impurities can be removed efficiently, but on the other hand, especially A in the produced ABO ₃ compound can be removed.
Elution of the components is unavoidable, and A with the desired A / B molar ratio composition
BO ₃ compound is Mashi Nozomu not be obtained wards.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

The treated cake obtained by the solid-liquid separation treatment as described above is dried at 300 ° C. or higher, preferably 400
After heat treatment at ~ 700 ° C, an aqueous suspension having a pH of 7 to 10, preferably 7.5 to 9.5, is subjected to decantation treatment, filtration treatment and further washing treatment if necessary. A solid-liquid separation treatment such as simultaneous treatment is carried out to remove substantially all alkali metal impurities and unreacted soluble reacting components. Heat treatment humidity Ru only Hikuki than 300 ℃
In particular, the elution of the component A in the produced ABO ₃ compound is unavoidable, which is not desirable. On the other hand, the heat treatment temperature
If the temperature is much higher than the desired range,
The ABO ₃ compound described above is not preferable because it becomes coarse.
Yes. Further, the pH of the suspension is too lower than the above range.
And, while alkali metal impurities can be removed efficiently,
In particular, the A component in the ABO ₃ compound produced was eluted.
ABO ₃ compound having a desired A / B molar ratio composition
On the other hand, the pH of the suspension is below the above range.
If it is too high, the amount of remaining alkali metal impurities will increase.
Because possibly unwanted. The ABO ₃ compound fine powder of the present invention obtained as described above has a uniform fine particle size distribution, has good packing properties during molding, and thus has significantly improved sinterability, and is dense at lower temperatures. A strong and excellent dielectric ceramic can be obtained.

Claims (3)

[Claims] 1. At least one compound selected from the group A element compounds consisting of Ba, Pb, Sr, Mg and Ca, and at least one compound selected from the group B element compounds consisting of Ti, Zr, Hf and Sn. Is heated at 80 ° C. or higher to react it with an aqueous suspension of a mixture comprising A and B in an A / B molar ratio of 1 or more and a free alkali concentration of 0.1 mol / l or more, and then the pH of the suspension. Is adjusted to 7 to 11 and solid-liquid separation is performed, the obtained wet cake is heat-treated at 300 ° C. or higher, and then the heat-treated product obtained has a pH of 7 to 11
10. A method for producing a fine powder of a perovskite compound, which comprises forming an aqueous suspension of 10 and then solid-liquid separating and drying this. 2. The method for producing fine powder of perovskite type compound according to claim 1, wherein the A / B molar ratio is 1.1 or more and the free alkali concentration is 0.1 mol / l or more. 3. The process for producing fine powder of perovskite type compound according to claim 1, wherein the temperature of the heat reaction treatment of the suspension is 100 ° C. or higher.