KR20040056506A - A method for preparing fine particles of barium titanate using emulsion - Google Patents

Abstract

PURPOSE: Provided is a process for producing monodisperse barium titanate fine particles by using an emulsion, and therefore the barium titanate fine particles have a spherical shape, a uniform particle diameter, and a size of less than 1 micron. CONSTITUTION: The process for producing the barium titanate fine particles comprises the steps of: dissolving a barium-titanium complex alkoxide in 40-60vol% of octanol to prepare an octanol solution; adding 30-50vol% of dimethyl sulfoxide to the octanol solution to make the total solvent of 90vol% and then stirring and mixing to prepare an emulsion solution, wherein the octanol solution and the dimethyl sulfoxide are heated each at 21-60deg.C before mixing; mixing the emulsion solution and a solution obtained by dissolving water in 10vol% of ethanol to produce the barium titanate and stirring the reaction solution to grow the produced particles.

Description

A method for preparing barium titanate fine particles using an emulsion {A METHOD FOR PREPARING FINE PARTICLES OF BARIUM TITANATE USING EMULSION}

Field of invention

The present invention relates to a method for producing barium titanate fine particles using an emulsion, and more particularly, to a method for producing a monodisperse barium titanate fine powder having a spherical shape, uniform particle size and a size of 1 micron or less. It is about.

Prior art

To make high-density ceramic products with uniform microstructures highly reliable and reproducible: ① spherical, ② narrow particle size distribution, no aggregation between particles, that is, monodispersion, ③ microparticles less than 1 micron, ④ Raw material powder with uniform composition and high purity is required. As a means for producing such a raw material powder, a method of hydrolyzing metal alkoxide in an organic solvent has recently been noted.

This method is called alkoxide method or hydrolysis control method. In 1968, Stoverber hydrolyzed silicon alkoxide while using ammonia as a catalyst in ethanol to produce spherical silica fine particles having a size of 0.5 to 1.0 micron. Started with. Thereafter, titania fine particles (JP-A 62-91418, Pyung 1-33939) and zirconia fine particles (JP-A 62-91421) were produced using an ethanol solvent.

However, monodisperse barium titanate particles are not produced by the above conventional method. The main reason is that the hydrolysis rate of the composite alkoxide of barium and titanium, which is a precursor, is very fast. That is, as the lower alcohol solvent such as ethanol used in the conventional method, the hydrolysis rate of the very fast barium titanium composite alkoxide cannot be properly controlled, so that monodisperse fine particles cannot be obtained.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method capable of producing monodisperse barium titanate fine particles having a spherical shape, a narrow particle size distribution, and a size of 1 micron or less.

1 is a scanning electron micrograph (SEM) of barium titanate particles prepared according to an embodiment of the present invention.

2 is a scanning electron micrograph of a barium titanate aggregate prepared according to a comparative example.

In order to achieve the above object of the present invention, the present invention comprises the steps of dissolving the barium titanium complex alkoxide in 40 to 60% by volume of octanol to prepare an octanol solution; Preparing an emulsion solution by adding 30 to 50% by volume of dimethyl sulfoxide to the octanol solution so that the sum of the solvents is 90% by volume, followed by mixing with stirring; And mixing the emulsion solution with a solution obtained by dissolving water in 10% by volume of ethanol to produce barium titanate, and growing the resultant particles while stirring the reaction solution to provide a method for producing barium titanate fine particles. do.

Hereinafter, the present invention will be described in more detail.

In the present invention, the complex alkoxide of barium titanium is hydrolyzed in a mixed solvent of octanol, dimethylsulfoxide and ethanol to form spherical particles with a uniform particle size and a size of 1 micron or less. Disperse barium titanate fine particles are synthesized.

In applying the method, the most important manufacturing principle and the difference from the conventional method is to make the complex alkoxide in the state of fine emulsion of tens to hundreds of nanometers (nanometer) size in the intermediate stage during the production. In the conventional method, alkoxides are hydrolyzed by mixing water with an alkoxide in an organic solvent, and oligomers formed at this time merge with each other to form a nucleus, and oligomers in a solvent adhere to the formed nucleus to grow to form fine particles. Done. In contrast, in the present invention, dimethyl sulfoxide is mixed with the octanol solution in which the complex alkoxide is dissolved, and the complex alkoxide is instantaneously made into a liquid bead state of tens to hundreds of nanometers (this is called an "emulsion state"). By adding water diluted with ethanol to this emulsion solution, a unique method of hydrolyzing the emulsion already produced is used. The emulsion state is a state in which a liquid solute is dispersed in a liquid solvent. In the present invention, a mixed solution of octanol and dimethyl sulfoxide becomes a solvent, and a complex alkoxide in the form of a dozen to several hundred nanoporous liquid beads becomes a solute.

The reason for the composite alkoxide to be in an emulsion state is as follows. Complex alkoxides are well soluble in octanol but are rarely soluble in dimethyl sulfoxide. Therefore, when dimethyl sulfoxide is added to the octanol solution in which the complex alkoxide is dissolved, the solubility of the complex alkoxide suddenly decreases, and therefore, a significant amount (as the solubility decreases) of the complex alkoxide precipitates in the liquid phase and is dispersed in the solution. The reason for adopting this method is that since the hydrolysis speed of the composite alkoxide is so fast, monodisperse fine particles of barium titanium cannot be obtained by the production mechanism of the conventional method.

Looking at the method of producing barium titanium monodisperse fine particles using the principle and the production mechanism in more detail as follows. The octanol solution is prepared by dissolving 0.15 to 0.35 mol / 1 of barium titanium complex alkoxide in 40 to 60 vol% of octanol in the final mixed solvent. When the barium titanium composite alkoxide is dissolved in octanol but is not readily dissolved at room temperature, the barium titanium composite alkoxide can be easily dissolved by stirring with heating at about 50 ° C. The concentration of the barium titanium composite alkoxide needs to be controlled to 0.15 to 0.35 mol / l. At less than 0.15 mol / l, the concentration of the hydrolyzate is low, so that an emulsion, which is a preliminary material of barium titanate fine particles, is not produced. If it exceeds l, excess particles are generated in the solution, and the particles stick to each other during the growth of particles to form aggregates.

To the octanol solution prepared above, 30-50% by volume of dimethylsulfoxide was added and mixed with stirring so that the total solvent was 90% by volume to prepare an emulsion solution. When dimethyl sulfoxide is added, the fine bead-like liquid of barium titanium composite alkoxide precipitates instantly, and the solution is in an emulsion state.

When dimethyl sulfoxide is mixed with the octanol solution in which the barium titanium complex alkoxide is dissolved, the dissolved barium titanium complex alkoxide precipitates. In order for the precipitate to be uniformly formed throughout the solution, the mixture of the octanol solution and dimethyl sulfoxide is mixed. The castle should be good. In order to achieve this, the two solutions are preferably heated to 21 to 60 ° C., respectively. At less than 21 ° C., the octanol solution and dimethyl sulfoxide are not mixed at all. If the temperature exceeds 60 ° C., the hydrolysis reaction occurring in the next step after mixing proceeds so fast that spherical fine particles are not obtained but only aggregates are formed.

Since the emulsion solution is produced by mixing the octanol solution and dimethyl sulfoxide, the mixing ratio of these two solutions is very important. When the volume amount after mixing octanol and dimethyl sulfoxide is 90 volume%, it is preferable that the volume ratio which dimethyl sulfoxide occupies among these is 30-50 volume%. When the volume ratio of dimethyl sulfoxide occupies less than 30% by volume or more than 50% by volume, the balance between the amount of emulsion formation and the amount of complex alkoxide dissolved in the mixed solvent is poor, resulting in agglomerates or polydispersions not spherical particles. This is because fine particles are obtained.

Mixing the emulsion solution with a solution obtained by dissolving 0.06 to 0.25 mol / l of water in 10% by volume of ethanol to produce barium titanate fine particles, and the same size having a process of growing the resulting particles while stirring the reaction solution It is to provide a method for producing barium titanate fine particles. The concentration of water should be controlled to 0.06 to 0.25 mol / l, but when it is less than 0.06 mol / l, it takes a long time to produce the barium titanate particles in the solution by hydrolysis, and if it exceeds 0.25 mol / l, barium titanate The particle size distribution of the fine particles becomes wider, so that they become so-called polydispersions or aggregates which are not spherical fine particles.

According to the method of the present invention, a predetermined amount of barium titanate in which a liquid bead emulsion is hydrolyzed is produced, and after the formation, oligomers formed by hydrolysis of the composite alkoxide dissolved in the solvent without precipitation on their surfaces are produced. The particle growth process adsorbed is progressed to obtain barium titanate fine particles having the same size.

It is desirable to stir the solution so that uniform mixing and grain growth of the solution occur uniformly throughout the solution. As the stirring method, for example, stirring with a magnetic stirrer, stirring with a propeller type stirrer, stirring using ultrasonic waves, etc. are not particularly limited.

The growth rate of the barium titanate fine particles is very fast up to about 1 minute after adding ethanol solution to the mixed solution of octanol solution and dimethyl sulfoxide, but becomes slow with the growth of the particles. It lasts up to 1 hour and after 5 minutes the particle size reaches about 90% of the final particle size. Therefore, barium titanate particles having a different particle diameter can be obtained by appropriately selecting the grain growth time. For example, the particle size obtained after one hour of grain growth is about 0.5 micron.

The monodisperse barium titanate fine particles can be obtained by recovering the barium titanate fine particles grown to the size desired by the above production method by centrifugation, and drying them in an oven and a vacuum dryer controlled at about 200 ° C. The particle size distribution of the produced barium titanate fine particles has a normal distribution, and more than 68% of all particles are contained within ± 10% of the average particle diameter, thereby obtaining highly monodisperse fine particles.

Hereinafter, preferred examples are provided to aid in understanding the present invention. However, the following examples are only presented to aid the understanding of the present invention, and the present invention is not limited to the following examples.

Examples and Comparative Examples

Example 1

The barium titanium composite alkoxide (0.15 mol / l) was dissolved in 40 vol% octanol while heating at 50 ° C., and 50 vol% dimethyl sulfoxide was added and mixed with stirring. At this time, the octanol solution and dimethyl sulfoxide were heated to 40 ° C. before mixing. To this mixed solution, distilled water (0.06 mol / l) dissolved in 10% by volume of ethanol was mixed and hydrolyzed while stirring. After granulation at room temperature for 1 hour, the fine particles and the solvent were separated by a centrifuge, and the separated precipitate was dried for 6 hours in a vacuum dryer at 200 ° C. A scanning electron microscope (SEM) photograph of the barium titanate fine particles thus obtained is shown in FIG. 1. As shown in FIG. 1, it can be seen that the barium titanate powder obtained is spherical, having an average particle diameter of 0.5 micron, and particles of the same size without aggregation at all.

Example 2

The barium titanium composite alkoxide (0.35 mol / l) was dissolved in 60 vol% octanol while heating at 50 ° C., and 30 vol% dimethyl sulfoxide was added and mixed with stirring. At this time, the octanol solution and dimethyl sulfoxide were heated to 40 ° C. before mixing. To this mixed solution, distilled water (0.25 mol / l) dissolved in 10% by volume of ethanol was mixed and hydrolyzed while stirring. After granulation at room temperature for 1 hour, the fine particles and the solvent were separated by a centrifuge, and the separated precipitate was dried for 6 hours in a vacuum dryer at 200 ° C. It was confirmed that the barium titanate fine particles obtained in this example were also monodisperse fine particles having a spherical shape and an average particle diameter of 1 micron or less and no aggregation at all, like the barium titanate fine particles obtained in Example 1.

Comparative Example 1

A barium titanium composite alkoxide (0.40 mol / l) was added to a solution in which 65 vol% octanol was dissolved while applying 50 ° C. heat to 25 vol% dimethyl sulfoxide, followed by mixing with stirring. At this time, the octanol solution and dimethyl sulfoxide were heated to 40 ° C. before mixing. To this mixed solution, distilled water (0.30 mol / l) dissolved in 10% by volume of ethanol was mixed and hydrolyzed while stirring. After granulation at room temperature for 1 hour, the fine particles produced by centrifugation and the solvent were separated, and the separated precipitate was dried for 6 hours in a vacuum dryer at 200 ° C. The scanning electron microscope (SEM) photograph of the obtained barium titanate microparticles | fine-particles was shown in FIG. As shown in Fig. 2, it can be seen that the barium titanate fine particles obtained under conditions outside the scope of the present invention are aggregates, not spherical fine particles.

By the synthesis method of the present invention, spherical monodisperse barium titanate fine particles having a spherical shape and an average particle diameter of 1 micron or less and without aggregation can be obtained. Since the barium titanate fine particles are spherical fine particles having a uniform particle diameter, they are optimal as raw material powders for ceramic sintered bodies. In addition, it can be used for various purposes such as electronic materials, pigments, cosmetics, jewelry, fillers.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (4)

Preparing an octanol solution by dissolving barium titanium complex alkoxide in 40 to 60% by volume of octanol; Preparing an emulsion solution by adding 30 to 50% by volume of dimethyl sulfoxide to the octanol solution so that the sum of the solvents is 90% by volume, followed by mixing with stirring; And Mixing the emulsion solution with a solution obtained by dissolving water in 10% by volume of ethanol to produce barium titanate, and growing the resulting particles while stirring the reaction solution. The manufacturing method of the barium titanate microparticles | fine-particles which consist of these. The method of claim 1, further comprising heating each of the octanol solution and dimethyl sulfoxide to 21 to 60 DEG C before mixing. The method of claim 1, wherein the barium titanium composite alkoxide is dissolved at a concentration of 0.15 to 0.35 mol / 1. The method of claim 1, wherein the water is dissolved 0.06 to 0.25 mol / l.