JP3486156B2 - Method for producing crystalline barium titanate powder - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MLCC (multiayer ceramic capacito) required for next-generation ultra high frequency communication equipment.
r), a method for producing barium titanate used as a main raw material for producing filters and other parts, and more specifically, a fine and spherical particle having a particle size of about 1/10 or less of the particle size of barium titanate currently available. And a method for producing an ultrafine powder of crystalline barium titanate.

[0002]

2. Description of the Related Art Barium titanate represented by the chemical formula BaTiO ₃ is generally one kind of ferroelectric substance having a perovskite structure and has a very large dielectric constant, a relatively low price, and a thermal stability. Since it is excellent, it is used as a main raw material for MLCCs, filters, thermistors, varistors and the like.

Recently, electric circuits and elements manufactured based on the design of the electric circuits are being diversified and highly densified, while the size of products is extremely miniaturized.
There is a great industrial demand for a technique for producing a powder having an extremely small particle size while maintaining excellent crystallinity and purity.

For example, in the case of parts manufactured using barium titanate having a small particle size, the defective rate is greatly reduced, and the dielectric constant is increased due to the small particle size of the sintered body. The number can be reduced and the yield of the used raw material is improved. Also, the sintering temperature is lowered, and the energy consumption cost is reduced. Furthermore, the performances of MLCCs, filters, thermistors, and the like manufactured from ultrafine powders are expected to exhibit excellent performances even in the ultrahigh frequency band that will be a major medium in the telecommunications industry in the future.

Conventionally, the solid-phase reaction method and the oxalate precipitation synthesis method have been used as methods for producing barium titanate powder. The solid-state reaction method is a method for producing barium titanate powder by mixing titanium oxide and barium carbonate powder and then reacting them at a high temperature of 1,000 ° C. or higher. Is a method that is widely used all over the world because it has the advantage of low.

[0006] The oxalate precipitation synthesis method is a method in which production has been gradually advanced mainly in the United States recently, and it has an advantage that it is a relatively simple chemical synthesis method and has a high yield. .

However, each of the conventional methods for producing barium titanate powder has disadvantages. That is, since the solid-phase reaction method uses a high-temperature solid-state reaction, the minimum particle size of the produced powder is 1 μm.
It is around m and the shape of the particles is also very irregular. Therefore, it is unsuitable as a raw material for products requiring strict specifications and miniaturized products.

On the other hand, in the oxalate precipitation synthesis method, it is not easy to control the particle size and the entanglement of particles, and the stability of barium / titanium oxalate is high.
In order to produce barium titanate powder with high crystallinity, heat treatment at high temperature is necessary. Therefore, the average particle size of the finally produced powder cannot be less than about 0.5 μm.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the drawbacks of the conventional method, and has a particle size of about 1/10 or less than that of the conventional method and has a spherical shape. And a powder having high crystallinity is obtained,
It is an object of the present invention to provide a method for producing a crystalline barium titanate powder, which can improve not only the quality of the barium titanate powder itself but also the quality of electronic components and communication components produced using the barium titanate powder. To do.

[0010]

In order to achieve the above object, in the method for producing a crystalline barium titanate powder of the present invention, a sol precursor is produced using a partially acyloxylated titanium alkoxide and a barium compound. Then, the sol precursor is sprayed into a strong alkaline solution to coprecipitate, and then barium titanate powder is crystallized from the precipitation dispersion solution and purified by performing a water washing step.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Crystallization is carried out by a usual hydrothermal reaction, for example, a hydrothermal reaction in which energy is applied by using heating or microwaves, or the conditions of the coprecipitation step are changed, It is performed by co-precipitation and crystallization at the same time.

That is, in the method for producing a crystalline barium titanate powder according to the present invention, a sol precursor is produced using a partially acyloxylated titanium alkoxide and a barium compound, and the sol precursor is injected into a strong alkaline solution. By co-precipitating it, the average particle size is fine and spherical with a hydrothermal reaction or without a separate hydrothermal reaction. It is possible to produce a barium titanate powder having excellent properties.

The partially acyloxylated titanium alkoxide used in the present invention is prepared by using titanium alkoxide as a raw material, and the mixed solution of the sol precursor produced is stabilized in the state of an aqueous solution in order to stabilize in a sol state. It can be manufactured by adjusting the decomposition rate to maintain an appropriate level. That is, since the titanium alkoxide itself forms a gel in the state of an aqueous solution, it is not possible to directly use it to produce an excellent barium titanate powder. Therefore, in the present invention, a hydrolysis rate in an aqueous solution state is obtained by reacting a titanium alkoxide with a carboxylic acid and substituting a part of the unsubstituted or alkoxy-substituted alkoxy group with an acyloxy group, for example, an acetoxy group. Can be adjusted to an appropriate level so that the purified sol solution is stabilized without gelation.

The titanium alkoxide is a compound in which four identical or different unsubstituted or alkoxy-substituted alkoxy groups are bonded to a titanium atom, and the alkoxy group is a linear or branched methoxy or ethoxy group. Unsubstituted alkoxy groups such as, propoxy, butoxy, pentyloxy, hexyloxy; and alkoxy-substituted alkoxy groups such as 2-methoxyethoxy, 2-ethoxyethoxy. From the viewpoint of easy synthesis, it is preferable that the same alkoxy group is bonded, and such an alkoxy group has 1 to 1 carbon atoms.
4 is preferable. That is, preferable titanium alkoxides include titanium tetramethoxide, titanium tetraethoxide, titanium tetrapropoxide and titanium tetrabutoxide.

A compound in which all unsubstituted or alkoxy-substituted alkoxy groups (hereinafter simply referred to as alkoxy groups) are replaced with acyloxy groups is difficult to form a sol by the addition of water because the acyloxy groups have low hydrolyzability. , Unable to produce barium titanate powder with excellent performance. Therefore, in order to achieve the stabilization of the sol precursor mixed solution, it is necessary to replace a part of the alkoxy groups in the titanium alkoxide with an acyloxy group, and among the four alkoxy groups of the titanium alkoxide, 2 to 3 are substituted. It is preferred to replace three with acyloxy groups. Further, the remaining alkoxy groups are hydrolyzed simultaneously with this exchange reaction and partially condensed to form a titanoxane bond, which forms a sol to obtain barium titanate having a desired fine particle size. Preferred for.
The titanium compound in which a part of the alkoxy group of the titanium alkoxide is replaced with an acyloxy group is called a partially acyloxylated titanium alkoxide in the present invention, and this is used for producing the barium titanate powder of the present invention. The degree of exchange of the alkoxy group with the acyloxy group is determined by NMR.
It can be confirmed by analysis etc.

Examples of the carboxylic acid used for the partial acyloxylation of titanium alkoxide include fatty acids such as formic acid, acetic acid, propionic acid, butanoic acid and isobutanoic acid. Acetic acid is particularly preferable because it is easy to handle and a partially acyloxylated titanium alkoxide that can maintain a stable sol is obtained. In the case of acetic acid, since a partially acyloxylated titanium alkoxide suitable for the present invention can be produced, it is preferable to use 4 to 10 mol, and particularly preferably 6.5 to 7.5 mol, per 1 mol of titanium alkoxide. . When the amount of acetic acid used is small, the exchange reaction to the acetoxy group is not sufficiently performed, and the obtained partially acyloxylated titanium alkoxide cannot be provided with sufficient stability. The reaction temperature at this time is 3
0 to 50 ° C. is preferable, and the reaction time is preferably 2 to 5 hours.

As the barium compound used for producing the sol precursor, barium chloride, barium acetate, barium nitrate, barium hydroxide or the like can be used. Unlike partially acyloxylated titanium alkoxides, barium compounds are not sensitive to hydrolysis, so it is possible to prepare a solution using water or a suitable organic solvent such as an alcohol, which is By mixing with the partially acyloxylated titanium alkoxide solution at a predetermined molar ratio, it is possible to produce a sol precursor mixed solution that is easy to inject. At this time, the barium compound can be used in an equivalent amount or more with respect to the partially acyloxylated titanium alkoxide. By using an excessive amount of barium compound, the atomic ratio of titanium to barium in the produced barium titanate can be set to about 1: 1, so that barium titanate having excellent physical properties can be produced.

Here, the injection of the sol precursor mixed solution is performed by using an apparatus produced by appropriately combining a pump, an injection nozzle and a flow rate controller. The pump and flow regulator can be selected to suit the required production rate. In addition, the injection nozzle is a two-flo
w) A nozzle is preferred, and the size of the nozzle hole is generally preferably 100 μm or less. According to the research results of the inventors, the smaller the diameter of the nozzle hole,
Fine particles tend to be produced.

As the gas for giving the pressure necessary for injection, a gas having a very low reactivity with the sol solution, such as nitrogen or argon, can be used.

A strong alkaline solution is stored in the coprecipitation tank. At this time, the characteristics of the barium titanate powder produced also slightly change depending on the components of the alkaline solution, but the more important factor is the pH of the alkaline solution. That is, if the pH is too low, the efficiency of precipitation of the injected sol solution will decrease, so it is preferable to maintain the pH at 13 or higher. In particular, by maintaining the pH of the coprecipitate at 13.7 or higher, precipitation and crystallization occur simultaneously, so that it is possible to obtain crystallized barium titanate powder without separate hydrothermal reaction. it can. The coprecipitation tank used at this time is preferably made of a material that does not cause problems such as corrosion due to the strong alkaline solution.

In the present invention, coprecipitation means a phenomenon in which a sol precursor obtained from a partially acyloxylated titanium alkoxide and a barium compound is brought into contact with a strong alkaline solution to simultaneously precipitate. Since the precipitation efficiency of each precursor compound changes depending on the concentration and volume of the alkaline solution or the temperature of the solution, the above conditions are adjusted according to the desired efficiency. In particular, when the temperature of the alkaline solution is high, for example, 80 to 100 ° C., precipitation and crystallization occur at the same time, and it is not necessary to perform a separate hydrothermal reaction step. Furthermore, in order to prevent the entanglement of particles precipitated in the solution and to bring about coprecipitation under normal conditions,
It is preferred to stir the coprecipitation bath solution in a suitable manner.
In the present invention, the mixture in which the precipitation phase obtained through the above coprecipitation step is dispersed in the solution is referred to as a precipitation dispersion solution.

The precipitate-dispersed solution thus obtained is stirred until it becomes uniform, then transferred to an autoclave reactor having excellent alkali resistance, and hydrothermal reaction is carried out under appropriate conditions.
At this time, the energy required for the hydrothermal reaction can be supplied in various forms. For example, electrical heating or microwaves and the like can be used to carry out the hydrothermal reaction. The hydrothermal reaction is preferably carried out by appropriately adjusting reaction conditions such as time and temperature depending on the desired reaction state and the degree of entanglement of particles.

According to the results of the study conducted by the present inventors, it is preferable that the reaction temperature is about 100 to 160 ° C. and the reaction time is about 30 minutes to 3 hours in the case of electric heating. In the case of the hydrothermal reaction utilizing, the reaction time is preferably about 5 to 30 minutes, and as the material of the reactor,
A microwave absorption factor that is extremely low should be selected. In all cases, vigorous stirring is required in the course of the reaction in order to obtain a homogeneous powder by hydrothermal reaction.

As described above, the sol precursor mixed solution is
In a high temperature alkaline solution of 80 to 100 ℃, or at pH 1
When co-precipitated with a super strong alkaline solution of 3.7 or more, barium titanate powder with high crystallinity can be obtained only by performing the co-precipitation step at room temperature without performing a separate hydrothermal reaction. In the present invention, a mixture of barium titanate powder dispersed in a solution thus obtained only by the coprecipitation step or obtained through the coprecipitation step and the hydrothermal reaction,
It is called a powder dispersion solution.

The powder dispersion solution thus produced is subjected to an appropriate method such as a centrifugal separation method to carry out a purification step of collecting the powder. At this time, the rotation speed of the centrifuge is
3,000 to 12,000 rpm is preferable. In addition, in order to completely remove impurities such as various metal ions and water-soluble compounds remaining in the manufactured barium titanate, several washing steps are performed. The water washing step is performed using distilled water or an aqueous solution containing an appropriate additive. Here, as the additive, use a substance that does not affect the overall composition while maintaining the pH of the solvent at 10 to 11, such as an aqueous barium hydroxide solution or an aqueous ammonia solution, particularly a dilute solution thereof. Is preferred.

In order to remove residual moisture from the barium titanate powder obtained by such a purification step, it is preferable to put the powder in an oven and perform a drying step of drying it at an appropriate temperature. At this time, if the drying temperature is too low, the removal rate of water decreases, but if the drying temperature is too high, a sintering phenomenon occurs between the fine powders. In the present invention, it is more preferable to perform drying at a temperature of about 50 to 150 ° C.

Various characteristics of the barium titanate powder finally obtained through the drying step can be measured and analyzed by various analysis methods. For example, the measurement and the analysis can be performed by a scanning electron microscope (SEM), an X-ray diffraction analyzer (XRD), an infrared spectrometer (IR), a BET, a Raman spectrometer and a thermal analyzer (TGA).

[0028]

Example 1 0.1 mol of titanium tetraisopropoxide was mixed with 7 mol of glacial acetic acid and reacted at 40 ° C. for 3 hours to obtain a partially acetoxylated titanium isopropoxide solution. At this time, vigorous stirring was performed in order to maximize the reaction efficiency.

Then, a small amount of distilled water was mixed with the produced partially acetoxylated titanium isopropoxide solution to cause a slight hydrolysis reaction, and the solution was allowed to stand for stabilization, and the solution became transparent. . Then, it was mixed with a barium acetate solution, stirred, and then left to stand to form a sol mixed solution. Then the nozzle size is 50 μm and 1
Using a spray device having a twin nozzle of 00 μm, the formed sol solution was sprayed with argon at room temperature into a coprecipitation tank containing a potassium hydroxide solution having a pH of 13.5 until a precipitate was formed. I left it as it was.

Then, the obtained precipitate dispersion solution was transferred to a reactor for hydrothermal synthesis lined with polytetrafluoroethylene, and then heated at 120 ° C. for 2 hours while heating with an electric heater and a temperature controller. A hydrothermal reaction was carried out.
Then, from the powder dispersion solution obtained after completion of the hydrothermal reaction, only the powder was collected using a centrifuge. At this time, the rotation speed of the centrifuge was 8,000 rpm. Then, the powder purified by several washings was
It was placed in an oven at 20 ° C. and dried.

The particle size of the barium titanate thus obtained was measured using a scanning electron microscope, and it was found that it had a very fine particle morphology, as shown in FIG. For reference, FIG. 2 is a scanning electron micrograph showing a commercially available barium titanate product using a conventional hydrothermal reaction method. As is clear from the comparison between FIG. 1 and FIG. 2, the average particle size of the powder produced by the method for producing crystalline barium titanate powder of the present invention is about 20 to 30 nm, and the average particle size of commercial products is Remarkably smaller than (inside and outside 500 nm). Further, as is clear from the X-ray diffraction spectrum shown in FIG. 3, it contained only the pure barium titanate crystal phase.

Example 2 Example 1 except that 0.15 mol of barium acetate was used.
A barium titanate powder is produced by the same method as
Purified.

The barium titanate powder thus obtained was measured using a scanning electron microscope, and as a result, a powder having a much finer particle size than that of a commercially available product was obtained as in Example 1. Was given. Further, as shown in FIG. 4, by adding an excessive amount of barium compound, the average particle diameter of the powder could be slightly reduced. As a result of X-ray diffraction, the crystallinity of the obtained barium titanate powder was very high, and the crystal phases of other substances were not observed.

According to the present embodiment, by using an excess amount of barium compound with respect to titanium, the barium: titanium atomic ratio of the finally obtained barium titanate powder is adjusted to be about 1: 1. Turned out to get.

Example 3 The temperature of the coprecipitation tank containing the strong alkaline solution was set to 100.
The steps up to coprecipitation were carried out in the same manner as in Example 1 except that the sol precursor mixed solution was sprayed to carry out coprecipitation while maintaining the temperature at ℃.

As a result, the reaction for crystallization of barium titanate is carried out simultaneously with the coprecipitation in the coprecipitation tank maintained at a high temperature, so that a separate hydrothermal reaction utilizing an autoclave is not possible. Was needed.

As a result, as in the case of Example 1, it was possible to produce a powder having a significantly finer particle size than the commercially available product. As a result of the analysis by X-ray diffraction, the crystallinity of the obtained barium titanate powder was very high, and the crystal phase of other substances was not observed.

Example 4 The steps up to coprecipitation were carried out in the same manner as in Example 1 except that a coprecipitation tank containing a super strong alkaline solution having a pH of about 14 was used.

The powder dispersion solution thus obtained is
The crystallization reaction in the coprecipitation tank was carried out at the same time as the coprecipitation so that the improvement of the crystallinity was hardly observed even if the hydrothermal reaction was carried out separately. Therefore, in this case, since coprecipitation and crystallization of barium titanate are simultaneously performed in the coprecipitation tank, a separate hydrothermal reaction utilizing an autoclave is not necessary.

As a result, as in Example 1, it was possible to produce a powder having a significantly finer particle size than the commercially available product. As a result of X-ray diffraction analysis, the crystallinity of the obtained barium titanate powder was very high, and the crystal phase of other substances was not observed.

Example 5 Titanic acid was prepared in the same manner as in Example 1 except that a microwave having a frequency of 2.45 GHz was used as the energy source for the hydrothermal reaction and a reactor made of polytetrafluoroethylene was used. Barium powder was produced.

FIG. 5 shows a scanning electron micrograph of barium titanate powder synthesized using microwaves.
The produced powder had an average particle size of about 50 to 60 nm, had a shape close to a sphere, and had a powder shape with a uniform particle size. The entanglement phenomenon between particles was also very small. As shown in FIG. 6, as a result of the analysis by X-ray diffraction analysis spectrum, the crystallinity of the barium titanate powder was very high, and the crystal phase of other substances was not observed.

[0043]

As described above, a new sol precursor was found by the method for producing the crystalline barium titanate powder of the present invention, and each step using the sol precursor was developed to obtain the existing one. The effect of being able to produce a barium titanate powder having a fine and spherical particle shape, which was not obtained with the above product, was obtained.

By using such fine barium titanate powder, the quality of various related parts used in the electronic and information communication fields can be improved, and the unit production cost of the product can be reduced.

[Brief description of drawings]

FIG. 1 is a scanning electron microscope (SEM) photograph of the barium titanate powder produced in Example 1, which is a method for producing a crystalline barium titanate powder of the present invention.

FIG. 2 is a scanning electron micrograph of a barium titanate product manufactured by a conventional hydrothermal reaction method.

FIG. 3 is a view showing an X-ray diffraction spectrum of barium titanate powder produced in Example 1.

4 is a scanning electron micrograph of barium titanate powder produced according to Example 2. FIG.

FIG. 5 is a scanning electron micrograph of the barium titanate powder produced in Example 5, which was hydrothermally reacted using microwaves.

6 is a view showing an X-ray diffraction spectrum of barium titanate powder produced according to Example 5. FIG.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Zhao Eixiang 53-1501, Misumi Apartment, 235-1, Cheonggyeong-ri-dong, Dongdaemun-gu, Seoul, Republic of Korea (72) Inventor Shen Shun, Nam-gu, Seoul, Republic of Korea 41, Feng-dong, Jungli Apartment 102-1608 (72) Inventor, Kim Young Dae, 39-1, Shimogetsu-dani, Seongbuk-gu, Seoul, Republic of Korea, Kist Apartment B202 (72), Inventor, Li Soyang, Mayor of Gyeonggi Province No. 5 in Iwantong Cave Second Apartment of Yanggwa Sumiko 207-1103 (56) Reference JP-A-3-5322 (JP, A) JP-A-3-170674 (JP, A) JP-A-3-33015 (JP, A) ) JP-A-2-271918 (JP, A) JP-A-2-59426 (JP, A) JP-A-2-44026 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C01G 1/00-25/00 C04B 35/46

Claims (13)

(57) [Claims] 1. A sol precursor is produced using a partially acyloxylated titanium alkoxide and a barium compound, and the sol precursor is sprayed into a strong alkaline solution to coprecipitate,
A method for producing crystalline barium titanate powder, which comprises crystallizing barium titanate powder from a precipitation dispersion solution. 2. The method for producing crystalline barium titanate powder according to claim 1, wherein the pH of the strong alkaline solution is 13 or more. 3. The method for producing a crystalline barium titanate powder according to claim 1, wherein the precipitation-dispersed solution is heated in an autoclave for hydrothermal reaction to crystallize the barium titanate powder. 4. The method for producing a crystalline barium titanate powder according to claim 1, wherein the precipitation-dispersed solution is subjected to hydrothermal reaction using microwaves to crystallize the barium titanate powder. 5. The production of crystalline barium titanate powder according to claim 2, wherein the strong alkaline solution has a pH of 13.7 or higher, and the barium titanate powder is directly crystallized from the precipitation dispersion solution. Method. 6. The crystalline barium titanate powder according to claim 1, wherein the strong alkaline solution is heated to 80 to 100 ° C. and used to directly crystallize the barium titanate powder from the precipitation dispersion solution. Production method. 7. The method for producing a crystalline barium titanate powder according to claim 1, wherein a partially acyloxylated titanium alkoxide obtained by a substituent exchange reaction of a titanium alkoxide with a carboxylic acid is used. 8. The method for producing a crystalline barium titanate powder according to claim 7, wherein the titanium alkoxide is selected from the group consisting of titanium tetramethoxide, titanium tetraethoxide, titanium tetrapropoxide and titanium tetrabutoxide. 9. The method for producing crystalline barium titanate powder according to claim 7, wherein the carboxylic acid is acetic acid. 10. The method for producing a crystalline barium titanate powder according to claim 9, wherein 4 to 10 mol of the acetic acid is used with respect to 1 mol of the titanium alkoxide. 11. The method for producing a crystalline barium titanate powder according to claim 1, wherein the barium compound is selected from the group consisting of barium chloride, barium acetate, barium nitrate and barium hydroxide. 12. The barium compound is used in an amount equal to or more than the equivalent of the partially acyloxylated titanium alkoxide,
A method for producing the crystalline barium titanate powder according to claim 1. 13. The crystalline barium titanate according to claim 1, wherein the crystallized barium titanate powder is recovered and then washed with an aqueous barium hydroxide solution or an aqueous ammonia solution. Powder manufacturing method.