JP3232794B2 - Method for producing fine barium carbonate for producing barium titanate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, in particular relates to a method for producing a suitable fine carbonate Barium as a raw material for an electronic material.

[0002]

2. Description of the Related Art Barium titanate ceramic capacitors, which are one of the electronic components, and in order to reduce the size and performance of a multilayer capacitor, have stable and stable electrical characteristics. Need to be secured. For this purpose, it is necessary that barium carbonate, which is one of the raw materials, has high purity and fineness.

[0003] As an industrial production method of barium carbonate, barite (BaSO ₄ ) has been conventionally reduced and roasted with carbon.
There are known methods of obtaining barium sulfide as an intermediate and reacting it with sodium carbonate or ammonium carbonate, or by directly blowing carbon dioxide gas. These reaction formulas are shown below.

[0004]

Embedded image BaSO ₄ + 4C → BaS + 4C
O BaS + Na ₂ CO ₃ → BaCO ₃ + Na
₂ S BaS + (NH ₄ ) ₂ CO ₃ → BaCO ₃ +
(NH ₄ ) ₂ S BaS + CO ₂ + H ₂ O → BaCO ₃ +
H ₂ S, however, strontium belonging to barite same alkaline earth metal and barium contained in which is a raw material, impurities such as calcium are included in carbonated barium impurities when barium carbonate production. Further, since barium sulfide is used as an intermediate, the sulfur content of barium sulfide is easily included as an impurity in the generated barium carbonate. In particular, the sulfur content is oxidized into barium sulfate during the production of barium titanate, and remains as an impurity in barium titanate.

Since all of these impurities have an adverse effect on the electrical characteristics of the barium titanate capacitor, it is desirable to remove them as much as possible. As a method for removing these impurities and purifying barium carbonate, generally, hydrochloric acid is added to barium sulfide obtained by reducing barite,
Barium, strontium, and calcium are changed to barium chloride, strontium chloride, and calcium chloride, respectively, and by utilizing the properties of these compounds having different water solubilities, recrystallization is repeated to reduce the strontium and calcium contents. A method of obtaining barium is employed.

The barium chloride thus purified is reacted with ammonium carbonate or ammonium hydrogen carbonate to obtain barium carbonate. The reaction formula is shown below.
The reaction is usually performed in an aqueous solution. In the case of ammonium bicarbonate, the reaction is performed while blowing an ammonium gas into the reaction solution so that the pH becomes constant.

[0007]

## STR2 ## BaCl ₂ + (NH ₄ ) ₂ CO ₃ → BaCO ₃ + 2NH ₄ Cl ─ (1) BaCl ₂ + NH ₄ HCO ₃ + NH ₃ → BaCO ₃ + 2NH ₄ Cl ─ (2) However, barium chloride The barium carbonate obtained by using the above contains chlorine as an impurity, and it has been difficult to remove this chlorine only by washing with water. That is, in the above reaction (1) or (2), after completion of the reaction, in a conventional manner, the generated barium carbonate is filtered and washed with water to remove impurities present on the surface and inside of the barium carbonate particles. No matter how much water washing is repeated, the content can hardly be reduced.

On the other hand, when a barium titanate capacitor is manufactured using barium carbonate in which chlorine remains, when a voltage is applied to the capacitor, the chlorine is contained in silver or silver-palladium alloy used for the electrode of the capacitor. At the same time as dissolving as ions, silver is also ionized and migrates into the barium titanate dielectric layer. If this amount is large, silver is deposited in the barium titanate dielectric layer, so that a current flows and the function as a capacitor is lost.

In order to reduce chlorine in barium carbonate, there is known a method in which barium chloride is changed to barium hydroxide and barium carbonate is applied to the barium hydroxide to obtain barium carbonate. The reaction formula of this method is shown below.

[0010]

Embedded image BaCl ₂ + 2NaOH → Ba (OH) ₂ + 2NaCl─ (3) Ba (OH) ₂ + CO ₂ → BaCO ₃ + 2H ₂ O─ (4) In the reaction formula (4), Is only water,
Theoretically, very high purity barium carbonate is obtained. However, in reality, barium hydroxide obtained by the reaction formula (3) contains NaCl or some Ba (OH) Cl as impurities.
Therefore, in order to obtain barium hydroxide crystals, it is necessary to repeat recrystallization of barium hydroxide. In this case, considering industrial production, the reaction formula
After suppressing the purity of barium hydroxide by (3) to a certain level, a method is adopted in which the reaction of reaction formula (4) is performed, and impurities such as NaCl are removed from the generated barium carbonate by filtration and washing with water. .

However, since the barium carbonate particles obtained by the reaction formula (4) have high purity, if they are washed with water for higher purity, there is a disadvantage that abnormal grain growth occurs and fine particles cannot be obtained. I was Also, the above reaction formula
Also in (1) or (2), after the reaction of barium chloride with ammonium carbonate or ammonium hydrogen carbonate, the produced barium carbonate is added together with by-produced ammonium chloride,
The present inventors have found that by aging in the presence of ammonium carbonate or ammonium hydrogen carbonate, barium carbonate with significantly reduced chlorine content as an impurity can be obtained, but the barium carbonate after aging has been obtained. When the particles are filtered and washed with water, there is a disadvantage that abnormal particle growth occurs as described above and fine particles cannot be obtained.

Further, when barium carbonate obtained by the conventional method is mixed with high-purity titanium oxide and calcined at 900 to 1450 ° C., the reactivity of barium carbonate is low. There is a problem that barium carbonate remains. The presence of such unreacted barium carbonate does not provide the expected electrical properties of a barium titanate capacitor, so raise the firing temperature or reduce the firing temperature until there is no unreacted barium carbonate. You need to increase the time.

However, such an operation causes non-uniformity of the barium titanate crystal particles, and as a result, only those having inferior electric characteristics can be obtained. The main object of the present invention is to provide a manufacturing method that can solve the problems described above, a suitable fine barium carbonate in the production of high quality barium titanate an easy get simply.

[0014]

Means for Solving the Problems and Actions The present inventors have conducted intensive studies to achieve the above object, and as a result, as expressed by the above reaction formula (1), (2) or (4). When reacting a soluble carbonate or carbon dioxide with a soluble barium salt, the barium salt is subjected to the above-mentioned reaction in excess, and when the carboxylic acid is added at any time from before the reaction to after the reaction, The present inventors have found a new fact that fine barium carbonate can be easily obtained, and have completed the method for producing fine barium carbonate according to the present invention.

That is, in the present invention, the carboxylic acid reacts with the excess barium salt in the reaction system to form a barium salt and deposits on the surface of the produced barium carbonate. It is suppressed from happening. Also,
Instead of adding an excess amount of the barium salt in advance, a carboxylic acid and a soluble barium salt may be added immediately after the reaction, and the barium salt of the carboxylic acid may be deposited on the surface of the resulting barium carbonate in the same manner as described above.

Further, the present inventors have found that barium carbonate obtained by the production method of the present invention has a BET specific surface area of 5 m ² / g or more, and is mixed with titanium oxide and fired at 900 to 1950 ° C. A new fact was found that unreacted barium carbonate had a reactivity when it did not. Therefore, if barium carbonate according to the present invention is used, high-purity and high-quality barium titanate containing no unreacted barium carbonate can be obtained at low cost.

The reason why the specific surface area of the BET is set to 5 m ² / g or more is as follows. That is, if the specific surface area is less than 5 m ² / g, the particles become large, and it is difficult to maintain the preferable average particle size of the barium titanate single crystal particles in the range of 0.5 to 1.5 μm. Become. However, if the specific surface area is too large, secondary agglomeration of the powder proceeds, and it becomes difficult to uniformly disperse the powder using a commonly used dispersing machine. Remaining undispersed secondary aggregated barium carbonate leads to residual unreacted barium carbonate, which also adversely affects the electrical properties of the resulting barium titanate capacitor. Therefore, barium carbonate of the present invention is preferably a specific surface area of BET is 5~25m ² / g, more preferably 10 to 20 m ² / g
It is.

In the present invention, the sintering temperature at which barium carbonate and titanium oxide are reacted is 900 to 1450 ° C.
The reason was as follows. That is, if the firing temperature is lower than 900 ° C., the reaction takes a long time, resulting in poor productivity and is not practical. On the other hand, when the temperature exceeds 1450 ° C.,
There is a problem that the generated barium titanate crystal particles are likely to be non-uniform. The firing temperature is 1000-1350
C. is more preferred.

The disappearance of barium carbonate can be confirmed by X-ray diffraction, as described in Examples below.
The production method of the present invention has an effect that the produced barium carbonate is sufficient to impart the above-mentioned reactivity, and the content of impurities can be significantly reduced. Examples of the soluble barium salt in the present invention include barium chloride and barium hydroxide. Examples of the soluble carbonate in the present invention include ammonium carbonate, ammonium hydrogen carbonate, sodium carbonate and the like.

In the present invention, specific examples of the reaction for obtaining barium carbonate include, besides carbonate, a reaction between barium hydroxide represented by the above-mentioned reaction formula (4) and carbon dioxide. Also, a reaction between barium chloride represented by the above reaction formula (1) or (2) and ammonium carbonate or ammonium bicarbonate, a reaction between barium chloride represented by the following reaction formula (5) and sodium carbonate, Equation (6)
And the reaction between barium chloride and carbon dioxide.

[0021]

BaCl ₂ + Na ₂ CO ₃ → BaCO ₃ + 2NaCl─ (5) BaCl ₂ + CO ₂ + H ₂ O + 2NH ₃ → BaCO ₃ + 2NH ₄ Cl─ (6) In the reaction formula (6), In order to neutralize hydrochloric acid by-produced, it is necessary to carry out the reaction while adding ammonia or sodium hydroxide. Usually, the reaction is carried out while maintaining the pH at 6 to 8.

In the reaction, the barium salt is added in an excess amount to the carbonate, preferably 1.01 to 1 mol of the carbonate.
加 え る 3 mol, more preferably 1.04 to 1.6 mol. This is to produce a barium salt of a carboxylic acid which is deposited on the surface of the produced barium carbonate. The reaction for producing barium carbonate is performed by adding an aqueous solution of a carbonate to an aqueous solution of a barium salt or by blowing a carbon dioxide gas. At this time, it is preferable to carry out the reaction continuously in order to obtain fine barium carbonate particles. In order to carry out the reaction continuously, it is only necessary to feed a barium salt and a carbonate or a carbon dioxide gas into a reaction vessel having a high-speed rotating blade and a small reaction volume while discharging the reaction product from the other. Specifically, for example, a pump is used as a reaction vessel, and the reaction is performed in a casing of the pump. In the case of carbon dioxide gas, it takes a certain amount of time to dissolve it in water, so that the reaction vessel also needs a certain size. Therefore, if necessary, the pumps may be connected in two or more stages in series. However, in the case of a pump having a sufficiently large casing volume and a large number of rotations, one pump may be used. As the pump, for example, a centrifugal pump, an axial pump or the like can be used.

The continuous reaction is preferable especially when barium hydroxide is reacted with carbon dioxide. In the reaction between barium hydroxide and carbon dioxide, the temperature is usually 25 to 50 ° C.
The residence time in the reaction vessel is preferably 1 second or less, and the other time is about several seconds.

The carboxylic acid added immediately after the reaction includes, for example, citric acid, carboxymethylcellulose, oxalic acid, malonic acid, succinic acid, maleic acid, adipic acid, acrylic acid and the like.
Preference is given to using polybasic carboxylic acids having one or more carboxyl groups. The amount of the carboxylic acid to be added varies depending on the type of the carboxylic acid used, the number of carboxyl groups in one molecule, and the like, but is usually 0.2% by weight or more based on the produced barium carbonate. If the amount of the carboxylic acid is less than 0.2% by weight, the amount of the barium salt of the carboxylic acid deposited is insufficient, so that particles may grow during filtration and washing of the produced barium carbonate.

It is preferable to add the carboxylic acid immediately after the completion of the reaction. Instead of reacting the barium salt in an excessive state, the carboxylic acid and the barium salt are added in the process of reacting the theoretical amount of the barium salt with the carbonate or immediately after the reaction. The barium carbonate particles thus obtained have a BET specific surface area of 5 m ² / g or more. The barium carbonate particles are filtered and washed in the final step, but the barium salt of carboxylic acid is deposited on the surface, so that the particle growth is suppressed.

In order to obtain a barium titanate capacitor from the obtained barium carbonate particles, barium carbonate and titanium oxide are mixed, fired, and reacted as shown in the following reaction formula.

[0027]

## STR5 ## BaCO ₃ + TiO ₂ → BaO.Ti
Since the calcination of O ₂ + CO ₂ is performed at a temperature of 900 ° C. or more as described above, the carboxylic acid deposited on the surface of the barium carbonate particles is decomposed into carbon dioxide gas and water by the calcination, and the carboxylic acid is deposited in the barium titanate crystal. And does not act as impurities.

[0028]

EXAMPLES Next, fine barium carbonate of the present invention and a method for producing the same will be described with reference to Test Examples and Examples. Test Example 1 Pumps P ₁ and P ₂ were used as reaction vessels as shown in FIG.
And it was used as the connecting P ₃ into three stages. Details of each pump are as follows.

(A) First-stage pump P ₁ : centrifugal pump (Nissau-Warman pump manufactured by Taiheiyo Metal Co., Ltd.), suction port diameter 4 inches (101.6 mm), discharge port diameter 3 inches (7
6.2 mm), 400 l / min, impeller rotation speed 19
30 rpm (b) Second stage pump P ₂ : centrifugal pump (manufactured by Honda Pump Co., Ltd.), suction port diameter 3 inch (76.2 mm), discharge port diameter 3 inch (76.2 mm), 300 l / min, impeller rotation Number 1450 rpm (c) Third stage pump P ₃ : centrifugal pump (manufactured by Kansui Pump Co., Ltd.), suction port diameter 3 inches (76.2 mm), discharge port diameter 2 inches (50.8 mm), 200 liter / min, impeller Rotation speed 1450 rpm A 100 m ³ barium hydroxide aqueous solution having a concentration of 50 g / liter and a temperature of 30 ° C. was prepared, and as shown in FIG.
It was charged into the suction port of the pump P ₁ in the ³ / h flow rate. At the same time by blowing carbon dioxide gas in the flow path of barium hydroxide to the pump P ₁ so as to PH6.1～6.3, at pump P _1, P ₂ and P _3, was carried out continuously reacting .
At this time, the reaction rate, the discharge port of the pump P ₁ of the first stage 5
2% 81% in the discharge port of the pump P ₂ of the second stage, was 95% at a discharge port of the pump P ₃ of the third stage.

An aqueous solution of carboxymethylcellulose (CMC) having a concentration of 10 g / liter was added to the reaction slurry immediately after it was discharged from the discharge port of the third stage pump P ₃ , with an addition amount of 0% and 0% based on barium carbonate produced. 0.05%, 0.1%,
Slurries were added at different flow rates so as to be 0.5% and 1.0% (both are wt%, the same applies hereinafter) to obtain a slurry. This slurry was immediately filtered and washed with water.
Next, the obtained water-containing cake was dried at 170 ° C. and pulverized to obtain barium carbonate particles. The electron micrographs are shown in FIGS. In addition, the average diameter and BE of each barium carbonate particle determined from the electron micrograph were
Table 1 shows the specific surface area of T.

[0031]

[Table 1] In addition, the specific surface area of BET was measured using "Chisoubu U2" manufactured by Yuasa Ionics Co., Ltd. From FIG. 2 to FIG. 6 and Table 1, by adding CMC, much finer particles were obtained as compared with the case where CMC was not added (FIG. 2). %, The effect of preventing the growth of particles is remarkable. Test Example 2 Instead of carboxymethylcellulose, the concentration was 10 g /
The liter of citric acid aqueous solution was changed at the respective flow rates such that the addition amounts were 0%, 0.02%, 0.2%, 1.0% and 5.0% with respect to the produced barium carbonate, and in addition to added to the reaction slurry after exiting from the discharge port of the pump P ₃ stages to give the barium carbonate particles in the same manner as in test example 1. The electron micrographs are shown in FIGS. In addition, the average diameter of each barium carbonate particle obtained from the electron micrograph and B obtained in the same manner as described above.
Table 2 shows the specific surface area of ET.

[0032]

[Table 2] From FIG. 7 to FIG. 11 and Table 2, compared with the case where citric acid was not added (FIG. 7), by adding citric acid,
It can be seen that much finer particles were obtained, and particularly when the amount of citric acid added was 0.2% or more, the effect of preventing the growth of the particles was remarkable. Test Example 3 15 m ³ of an aqueous solution of ammonium bicarbonate having a concentration of 51 g / liter was prepared, and ammonium gas was blown into the solution to absorb the solution, thereby adjusting the pH to 9.8. Then, set the temperature to 3
It was kept at 0 ° C. On the other hand, a 167 g / liter barium chloride aqueous solution (15 m ³⁾ was prepared at a temperature of 60 ° C., and each was reacted at 4 m ³ / hour in the same manner as in Test Example 1. Immediately after the reaction, an aqueous solution of carboxymethylcellulose (CMC) was added so as to be 0% and 0.5% with respect to the produced barium carbonate, and the resulting slurry was filtered and washed, and the wet cake was dried at 170 ° C. The particles were crushed to obtain barium carbonate particles.

As a result, in the case where CMC was not added, the specific surface area was 5.6 m ² / g, while the specific surface area was 5.6 m ² / g.
In the case where C was added, it was 10.8 m ² / g. Example 1 The barium carbonate having a BET specific surface area of 15.9 m ² / g obtained in Test Example 1 was reacted with high-purity titanium oxide (manufactured by Toho Titanium Co.) to produce barium titanate at 900 ° C. When calcined, the presence or absence of disappearance of the peak of barium carbonate was examined by X-ray diffraction. The test was performed under the following conditions. (1) Mixing of raw materials The molar ratio of high purity titanium oxide / barium carbonate is 1.03.
The following components were mixed so that

Barium carbonate 40.4 g High-purity titanium oxide 16.8 g Pure water 120 g Zircon beads (diameter 1.7 mm) 60 g Dispersant 2.4 g (Dispersant is pure in 5 g of "Poise 532A" manufactured by Kao Corporation) (2) Dispersion operation The composition of the above (1) was placed in a 300 cc glass container and dispersed for 60 minutes by a disperser (manufactured by Red Devil). (3) Separation of beads The dispersion liquid was passed through a screen having a mesh diameter of 1 mm to separate beads. (4) Drying It was dried for 24 hours by a constant temperature dryer at 105 ° C. (5) Pulverization The dried product was crushed in an agate mortar for 5 minutes. (6) Firing 4 g of the obtained crushed product is put into a 5 cc porcelain crucible, and
Calcination was performed at 2 ° C. for 2 hours to obtain barium titanate. After firing, the product was subjected to X-ray diffraction to confirm the presence or absence of a peak of barium carbonate. (7) Results X-ray diffraction of the product is shown in FIG. Comparative Example 1 BET was used instead of 40.4 g of barium carbonate obtained in the test example.
Commercially available barium carbonate having a specific surface area of 6.5 m ² / g.
Except that the molar ratio of high-purity titanium oxide / barium carbonate was 1.03 using 0 g,
It was mixed with titanium oxide and baked at 900 ° C. for 2 hours. X-ray diffraction of the reaction product is shown in FIG. Example 2 Barium titanate was obtained in the same manner as in Example 1 except that the firing temperature was changed from 900 ° C. to 960 ° C. The product was subjected to X-ray diffraction to confirm the presence of a barium carbonate peak. FIG. 14 shows the result of X-ray diffraction. Comparative Example 2 A barium titanate was obtained in the same manner as in Comparative Example 1, except that the firing temperature was changed from 900 ° C. to 960 ° C. The product was subjected to X-ray diffraction to confirm the presence of a barium carbonate peak. FIG. 15 shows the result of X-ray diffraction.

12 and 13, and FIGS. 14 and 15, the presence of barium carbonate peaks in Comparative Examples 1 and 2, whereas the peaks of barium carbonate in Examples 1 and 2 were completely eliminated. Example 1, 2
It can be seen that the barium carbonate used in Example 1 has excellent reactivity. Further, with respect to the other barium carbonates obtained in Test Examples 1 to 4, when calcination was carried out in the same manner as in Examples 1 and 2, it was confirmed that the peak of barium carbonate had disappeared by X-ray diffraction.

[0036]

As described above, the fine barium carbonate of the present invention has a BET specific surface area of 5 m ² / g or more, and is unreacted carbonate when mixed with titanium oxide and calcined at 900 to 1450 ° C. Since it has reactivity in the absence of barium, it has the effect that it can be suitably used for producing high quality barium titanate capacitors. However, it is needless to say that the barium carbonate of the present invention is not limited to the raw material for producing barium titanate, but can be applied to other various uses.

Further, according to the method for producing fine barium carbonate of the present invention, since abnormal particle growth after barium carbonate is generated is suppressed, there is an effect that fine barium carbonate with high purity can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a reaction route in Test Example 1 of the present invention.

FIG. 2 shows that the amount of CMC added was 0 in Test Example 1 of the present invention.
5 is an electron micrograph (magnification: 4,000 times) showing the particle structure of barium carbonate formed at the time of%.

FIG. 3 is an electron micrograph (magnification: 4000 times) showing the particle structure of barium carbonate formed when the amount of CMC added is 0.05% in Test Example 1 of the present invention.

FIG. 4 is an electron micrograph (magnification: 4000 times) showing the particle structure of barium carbonate produced when the amount of CMC added is 0.1% in Test Example 1 of the present invention.

FIG. 5 is an electron micrograph (magnification: 4000 times) showing the particle structure of barium carbonate formed when the amount of CMC added is 0.5% in Test Example 1 of the present invention.

FIG. 6 is an electron micrograph (magnification: 4000 times) showing the particle structure of barium carbonate produced when the amount of CMC added is 1.0% in Test Example 1 of the present invention.

FIG. 7 is an electron micrograph (magnification: 4000 times) showing the particle structure of barium carbonate formed when the amount of citric acid added is 0% in Test Example 2 of the present invention.

FIG. 8 is an electron micrograph (magnification: 4000 times) showing the particle structure of barium carbonate formed when the amount of citric acid added is 0.02% in Test Example 2 of the present invention.

FIG. 9 is an electron micrograph (magnification: 4000 times) showing the particle structure of barium carbonate formed when the amount of citric acid added is 0.2% in Test Example 2 of the present invention.

FIG. 10 is an electron micrograph (magnification: 4000 times) showing the particle structure of barium carbonate produced when the amount of citric acid added is 1.0% in Test Example 2 of the present invention.

FIG. 11 is an electron micrograph (magnification: 4000 times) showing the particle structure of barium carbonate produced when the amount of citric acid added was 5.0% in Test Example 2 of the present invention.

FIG. 12 is a graph showing X-ray diffraction when fired at 900 ° in Example 1 of the present invention.

FIG. 13 is a graph showing X-ray diffraction when firing at 900 ° in Comparative Example 1 of the present invention.

FIG. 14 is a graph showing X-ray diffraction when firing at 960 ° in Example 2 of the present invention.

FIG. 15 is a graph showing X-ray diffraction when firing at 960 ° in Comparative Example 2 of the present invention.

[Description of Reference Numerals] P ₁ first stage pump P ₂ second stage pump P ₃ third stage pump

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-167216 (JP, A) JP-A-49-90300 (JP, A) JP-A-50-37698 (JP, A) JP-A-59-90 50028 (JP, A) JP-A-55-20229 (JP, A) JP-A-50-147498 (JP, A) JP-A-6-345424 (JP, A) JP-B-46-10059 (JP, B1) Patent 102330 (JP, C2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01F 11/18 C01G 23/00 C04B 35/46 H01G 4/12 310

Claims (1)

(57) [Claims] 1. A process for producing barium carbonate wherein a soluble barium salt is reacted with a soluble carbonate or carbon dioxide, wherein the soluble barium salt is in excess of a stoichiometric amount required for reacting with the soluble carbonate or carbon dioxide. A method for producing fine barium carbonate for producing barium titanate, wherein the reaction is carried out in a state, and a carboxylic acid is added at any time from before the reaction to after the reaction.