JPH0832559B2 - Method for producing inorganic fine powder of perovskite type compound - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an inorganic fine powder of a perovskite compound (hereinafter referred to as “ABO ₃ ”).

Ceramics obtained by converting the ABO ₃ compound into ceramics have excellent dielectric properties, piezoelectric properties, and semiconductivity, and are very useful in the electronics field, and are used as capacitors, radio wave filters, ignition devices, thermistors, and the like.

2. Description of the Related Art Recently, as electronic devices have become smaller and lighter and have higher performance,
ABO ₃ ceramics are also required to be thinned and downsized, and studies have been made on thinning and downsizing in terms of technical aspects such as compounding, molding, and sintering in ceramicization. However, the limit has been reached for raw materials with a particle size of 0.8 μm or more produced by conventional solid-phase reaction. That is, it was made by a conventional solid-phase reaction
ABO ₃ raw materials include at least one or more carbonates or oxides of Mg, Ca, Sr, Ba and Pb (hereinafter referred to as group A elements) and Ti, Zr, Hf and Sn (hereinafter referred to as group B elements). ) Mixed with at least one or more oxides,
It is produced by treating at the above high temperature to form an ABO ₃ compound, mechanically pulverizing it with a ball mill, filtering and drying. For this reason, only ABO ₃ compounds of 0.8 μm or more can be obtained in the solid-phase reaction, and there is a limit to the downsizing and thinning of ceramics even if the ABO ₃ compound is used, no matter how compounding, molding and sintering techniques are used.

Problems to be Solved by the Invention JP-A-59-39726, JP-A-61-91016, JP-A-60-90825 and JP-A-61-31345 describe fine particle raw materials of ABO ₃ compounds. However, with these methods,
Since the step of washing with water is required, it becomes very difficult to control the A / B molar ratio, and it is economically disadvantageous. For example,
59-39726, JP-A 61-91016 discloses that fine particles are produced by reacting a hydroxide of titanium or zirconium with a water-soluble salt of barium, strontium or calcium in a strong alkaline aqueous solution.
Although ABO ₃ has been obtained, it is necessary to perform an operation to remove alkali metals Na, K, etc., which are not preferable in terms of electrical characteristics, and therefore it becomes difficult to control the molar ratio, resulting in high cost. In addition, JP-A-61
-31345, after the completion of the reaction, to prevent the deviation of the A / B molar ratio caused by the outflow of unreacted water-soluble A element component at the time of filtration, add a step to insolubilize the element A component once before filtration. However, the A / B molar ratio is controlled, but in any case,
Since the filtration and washing steps are indispensable, the accuracy of the molar ratio control is lacking, and the additional steps are economically disadvantageous.
Also, the A / B molar ratio factor of the ABO ₃ compound is ceramicization,
That is, it has been known that the densification or the sintered crystal grain size thereof is greatly affected, and the accuracy of the A / B molar ratio control is required to be at least three digits below the decimal point.

Therefore, the present inventors omit the commonly-used filtration and water washing steps by subjecting a mixed aqueous solution of a compound of a group A element and a compound of a group B element to atmospheric pressure heating reaction or hydrothermal reaction and then spray drying. It is possible to eliminate the deviation of the A / B molar ratio and the uneven distribution of the unreacted A element component caused by those steps, and when producing at the factory scale, find the merit that can be done in a continuous system,
The present invention has been completed.

Structure of the Invention Next, the method of the present invention will be described in detail.

As the at least one compound selected from the group A element compounds or at least one compound selected from the group B element compounds, commercially available products may be used as they are, or they may be prepared by an ordinary synthetic method. For example, hydroxides, oxides, organometallic compounds, salts and the like can be used. However, it cannot be used when the anion part of the compound exerts an unfavorable effect on the subsequent ceramic formation and the electrical characteristics of the ceramic. When using a hydroxide or oxide of Group B element, the particle size of this raw material is 0.3 μm or less, preferably
It is preferably 0.1 μm or less, and the reaction becomes difficult when it is 0.3 μm or more. Further, it goes without saying that the particle size of this raw material must be equal to or smaller than the particle size of the target-produced ABO ₃ compound.

The aqueous solution of a mixture of at least one compound selected from the group A element compounds and at least one compound selected from the group B element compounds is adjusted to pH 10 or higher as necessary. In most cases, the reaction does not proceed below pH 10.

The ABO ₃ compound is obtained by subjecting the aqueous alkaline mixture solution thus obtained to atmospheric pressure heating reaction or hydrothermal reaction. Needless to say, the atmospheric pressure heating reaction is a method of reacting by boiling under atmospheric pressure, and the hydrothermal reaction is usually under pressure.
It is a method of reacting at a temperature around 0 ° C to 300 ° C. The reaction conditions include reaction temperature, reaction pressure, reaction time, concentration of the mixture aqueous solution, and the like. Reaction temperature is usually 90
ABO ₃ compounds are produced at a temperature of ℃ or higher, but it is sufficient to raise the temperature to increase the reaction rate. As for the reaction time, a reaction temperature of 100 ° C. and normal pressure for 3 hours is sufficient, and correlates with the reaction temperature and pressure. Further, the concentration of the mixture aqueous solution affects the particle size of the produced ABO ₃ , and the lower the concentration, the larger the particle size tends to be. The preferred concentration is 0.2-0.9 mol / l
(ABO ₃ equivalent). However, these various conditions are somewhat different depending on the method of preparing the target-produced ABO ₃ compound or the aqueous solution mixture of the compound of the element A.

Next, the produced ABO ₃ compound-containing slurry is spray-dried. The spray drying is usually performed by a spray dryer, but the spray dryer is not limited to the spray dryer as long as the device satisfies the following conditions.

1) The A element component and the B element component do not go out of the system, and the A / B molar ratio does not shift.

2) Unreacted A element component and B element component are not unevenly distributed during drying, and unreacted A element component, B element component and generated ABO ₃
Are uniformly dried.

Since the powder obtained by the method of the present invention is present uniformly even if the unreacted A element component and B element component are present, it easily reacts in the main drying step, the calcination step, and the main firing step. Becomes ABO ₃ .

Furthermore, the ABO ₃ inorganic fine powder obtained after spray drying is calcined if necessary. The calcination temperature is limited by the intended particle size and crystal form of the inorganic fine powder. Taking barium titanate as an example, hydrous titanium oxide (particle size 0.05μ
The barium titanate having a Ba / Ti molar ratio of 1.000 obtained by the reaction of m) with barium hydroxide under atmospheric pressure is a cubic powder having a particle size of 0.1 μm or less, although it varies slightly depending on various conditions after drying. When barium titanate is treated at a high temperature, the grains grow and the crystal form also changes. Specifically, this barium titanate calcined at 1000 ° C. for 3 hours has an average particle size of 0.5 μm and its crystal form is a tetragonal crystal. Therefore, if you need 0.5μm tetragonal barium titanate, calcine at 1000 ℃
If you need a cubic crystal of μm, you can calcine at 850 ℃.

When the ABO ₃ compound is sintered, various additives are usually added for the purpose of adjusting the sinterability or electric characteristics of the sintered body. For example, regarding sinterability, there are grain growth inhibitors, curing agents, etc., and regarding electrical characteristics, there are shifters, depressors, reducing agents, reduction inhibitors, etc. Specifically, B, Bi, Li,
There are Y, Dy, Ce, Sm, Mn, Co, Ni, Nb and Si. If necessary, these additives can be contained in the ABO ₃ fine powder according to the intended use. The time of addition may be at the time of preparation of the aqueous solution of the mixture of the element A and the element B, at the time of reaction, after the reaction, or at the end of spray drying, but in order to make the content uniform, it is preferable to add in the step before spray drying .

Further, during dry molding of the ABO ₃ compound, a molding aid such as a binder or a plasticizer is usually added to the ABO ₃ compound raw material powder for the purpose of increasing the molding bulk density, etc., and the resulting granules are molded. It In the method of the present invention, it is also possible to obtain a granule raw material for molding by adding a molding auxiliary after the reaction formation of the ABO ₃ compound and spray-drying.

Example 1 Titanium chloride aqueous solution (Ti = 1, manufactured by Osaka Titanium Co., Ltd.)
Water (1800 wt., 6.5 wt%), 1800 ml of water, and 700 ml of 5 wt% ammonia water (Hayashi Junyaku Kogyo Co., Ltd. reagent grade 1) are added over about 1 hour to form a titanium hydroxide slurry, which is washed with a nutsche filter. Was performed to obtain a hydrous titanium oxide cake. The cake was found to have a TiO ₂ content of 11.46% by weight.

Distilled water was added to 240.2 g of the hydrous titanium oxide cake to prepare Ti
After adjusting to a slurry of O ₂ 60 g / l, the reaction system was placed in a nitrogen atmosphere, 108.7 g of Ba (OH) ₂ · 8H ₂ O was added, and distilled water was further added to obtain 0.7 mol / l (calculated as BaTiO ₃ ), Ba / The slurry was adjusted to a Ti molar ratio of 1.000. The slurry was heated to the boiling temperature over about 1 hour and reacted at the boiling temperature for about 3 hours.

After the reaction was completed, the slurry was concentrated to 0.9 mol / l, and the inlet temperature was 250 ° C, the outlet temperature was 120 ° C, and the atomizer rotation number was 25000 using a spray dryer manufactured by Okawara Kakoki Co., Ltd.
It was spray dried at rpm to obtain barium titanate fine powder.

From the X-ray diffraction and the electron micrograph of the produced barium titanate fine powder, it was found that the produced barium titanate fine powder was a cubic crystal with an average particle size of 0.08 μm. The Ba / Ti molar ratio measured by fluorescent X-ray was 1.000.

Example 2 As in Example 1, hydrous titanium oxide / Ba (OH) ₂ .8H ₂
After preparing O mixed slurry 0.7 mol / l (BaTiO ₃ conversion),
The slurry was charged into a heat-resistant nickel alloy autoclave (volume: 1) (500 ml), heated at 100 ° C./hr while stirring at 500 rpm, and reacted at 250 ° C. for 2 hours.

After the reaction, spray drying was carried out in the same manner as in Example 1 using a spoo dryer to obtain barium titanate fine powder.

X-ray diffraction and electron micrograph were the same as in Example 1. Further, the Ba / Ti molar ratio was quantified by fluorescent X-ray, and the result was 1.000.

Example 3 100 g of titanium isopropoxide (manufactured by Rare Metal Co., Ltd.) having a purity of 99.99% was dissolved in 150 ml of isopropyl alcohol (Hayashi Pure Chemical Co., Ltd. special grade) and heated under reflux for 2 hours. In a nitrogen atmosphere, the titanium isopropoxide solution was kept at 80 ° C. in a 45 wt% Ba (OH) ₂ .8H ₂ O aqueous solution 246.6.
Gradually drop by roller pump over 1 hour 30 minutes,
Then water, slurry concentration 0.7 mol / l, Ba / Ti molar ratio 1.
Adjusted to 000. Thereafter, the atmospheric pressure heating reaction or the hydrothermal reaction was performed in the same manner as in Example 1 or Example 2, and then spray drying was performed to obtain barium titanate inorganic fine powder. Both of the compositions obtained by the room temperature heating reaction and the hydrothermal reaction were subjected to X-ray diffraction,
From electron micrographs and fluorescent X-ray quantification results of the Ba / Ti molar ratio, it was found to be cubic barium titanate having a particle size of 0.09 μm and a Ba / Ti molar ratio of 1.000.

Example 4 Under a nitrogen atmosphere, 75.83 g (0.2970 mol) of purity 99.99% barium isopropoxide (manufactured by Rare Metal Co., Ltd.) and 85.17 g (0.3000 mol) of purity 99.99% titanium isoporopoxide (manufactured by Rare Metal Co., Ltd.) And were dissolved in 350 ml of isopropyl alcohol and heated under reflux for 2 hours.

Distilled water (65 ml) was added dropwise to the solution over 1 hour to hydrolyze the alcoholate, and once cooled to room temperature, water was added to give a slurry concentration of 0.5 mol / l (calculated as BaTiO ₃ ), a Ba / Ti molar ratio of 0.990.
Adjusted to.

Thereafter, a room temperature heating reaction or a hydrothermal reaction is performed in the same manner as in Example 1 or Example 2 to obtain a Ba / Ti molar ratio of 0.9 with a particle size of 0.07 μm.
90 cubic barium titanates were obtained.

Example 5 Hydrous titanium oxide cake (1
1.46 wt%) Distilled water is added to 200.0 g to obtain a slurry concentration of 60 g /
Adjusted to l. After placing the reaction system in a nitrogen atmosphere, Sr (OH) ₂
The · 8H ₂ O76.24g was added to the slurry.

After adjusting the final slurry concentration to 0.7 mol / l (converted to SrTiO ₃ ), strontium titanate fine powder was obtained in the same manner as in Example 1 or Example 2 below. Results of quantifying the Sr / Ti molar ratio of the strontium titanate from fluorescent X-rays
It was 1.000.

Example 6 B in a nitrogen atmosphere was added to the hydrous titanium oxide slurry (about TiO ₂ 60 g / l) obtained in Example 1 whose Ti content was measured in advance.
a _0.9 Sr _0.1 each content had been quantified Ba beforehand Ba and Sr to be the _{TiO 3 (OH) 2 · 8H} 2 O and Sr
(OH) was added ₂ · 8H ₂ O, then water was added a slurry concentration
After adjusting to 0.7 mol / l (calculated as Ba _0.9 Sr _0.1 TiO ₂ ), Ba _0.9 S was prepared in the same manner as in Example 1 or Example 2 below.
r _0.1 TiO ₃ fine powder was obtained. Quantitative analysis with fluorescent X-ray gives Ba, S
The molar ratio of r and Ti was as specified.

Example 7 The BaTiO ₃ composition obtained in Example 1 was calcined at 850 ° C. for 3 hours, wet-milled for 3 hours using partially stabilized zirconia balls and a resin pot, and then polyvinyl alcohol and polyethylene glycol were added to BaTiO ₃ respectively. It was added 1.0 wt% and 0.5 wt% in solid content basis relative to _3, and granulated by a spray drier. After dry molding the granules at a pressure of 1500 kg / cm ² , up to 600 ℃ 50 ℃ / hr, up to a predetermined temperature 250 ℃ / hr
The temperature was raised by, and firing was performed at a predetermined temperature for 2 hours.

As a comparison product, a commercially available barium titanate (average particle size 1.
0 μm) was molded and fired in the same manner as above. The bulk density of the obtained sintered body was measured with an analytical balance and a micrometer, and the electrical characteristics (dielectric constant at 20 ° C; tan δ and Curie point, dielectric constant at Curie point) were measured by Yokogawa Hewlett-Packard LCR. Table 1 shows the results measured by the meter 4274A.

EFFECTS OF THE INVENTION As described above, in the method of the present invention, if the charged amounts of the starting materials of the group A element and the group B element or the A / B molar ratio before the reaction are strictly adjusted, the desired A / B molar ratio can be obtained. It is possible to easily and inexpensively obtain a finely divided fine particle ABO ₃ compound, and furthermore, there is no uneven distribution of unreacted A element and B element components caused by the conventional washing with water and drying step, and the produced ABO ₃ compound can be obtained. Unreacted A element component and B element component are uniformly mixed. Furthermore, by adding the additives and molding aids usually required for ceramization before spray drying, a granular ceramic raw material for molding can be obtained very rationally.

Claims (7)

[Claims] 1. An alkaline earth metal such as Mg, Ca, Sr, or Ba and P.
A predetermined A / B molar ratio mixture aqueous solution of at least one compound selected from the group A element compounds consisting of b and at least one compound selected from the group B element compounds consisting of Ti, Zr, Hf and Sn is prepared. A method for producing an inorganic fine powder of a perovskite-type compound, which comprises subjecting the aqueous solution of the mixture to a reaction under atmospheric pressure or a hydrothermal reaction, spray-drying the reaction mixture, and calcining if necessary. 2. A mixture aqueous solution which comprises mixing at least one hydroxide and / or oxide of a group A element with at least one hydroxide and / or oxide of a group B element.
Item 6. A method for producing an inorganic fine powder according to item. 3. The inorganic fine powder according to claim 1, wherein at least one hydroxide and / or oxide of the group A element is mixed with at least one organometallic compound of the group B element to obtain an aqueous solution of the mixture. Manufacturing method. 4. The inorganic fine powder according to claim 1, wherein at least one organometallic compound of Group A element is mixed with at least one hydroxide and / or oxide of Group B element to obtain an aqueous mixture solution. Body manufacturing method. 5. The method for producing an inorganic fine powder according to claim 1, wherein at least one organometallic compound of group A element is mixed with at least one organometallic compound of group B element to obtain an aqueous mixture solution. . 6. At least one hydroxide and / or oxide of the group A element is barium hydroxide, and at least one hydroxide and / or oxide of the group B element is hydrous titanium oxide. The method for producing an inorganic fine powder according to item 2, wherein the perovskite type compound is barium titanate. 7. At least one hydroxide and / or oxide of the group A element is strontium hydroxide, and at least one hydroxide and / or oxide of the group B element is hydrous titanium oxide. The method for producing an inorganic fine powder according to claim 2, wherein the perovskite compound is strontium titanate.