KR20050061697A - A method for preparation of barium titanate powder with sol-gel reaction - Google Patents

Abstract

The present invention relates to a method for producing barium titanate particles by a sol-gel reaction, and more particularly, to prepare a titanium alkoxide prepared under a nitrogen atmosphere in place of a titanium alkoxide dissolved in alcohol using a stirrer and a static mixer. It is a series of single processes of sol-gel reaction with an aqueous solution of barium and calcination, pulverization and washing without first drying and then washing, controlling the molar ratio of barium / titanium elements of barium titanate particles, and having an average particle size of 0.1. In the method for producing barium titanate particles which can be used in a wide range of fields such as multi-layer ceramic capacitors (MLCC), static characteristic thermistors (PCT), and piezoelectric bodies, having a particle size distribution of -0.3 µm, with a uniform particle size. It is about.

Description

A method for preparation of barium titanate powder with sol-gel reaction

The present invention relates to a method for producing barium titanate particles by a sol-gel reaction, and more particularly, to prepare a titanium alkoxide prepared under a nitrogen atmosphere in place of a titanium alkoxide dissolved in an alcohol using a stirrer and a static mixer. It is a series of single processes of sol-gel reaction with an aqueous solution of barium and calcination, pulverization and washing without first drying and then washing, controlling the molar ratio of barium / titanium elements of barium titanate particles, and having an average particle size of 0.1. In the method for producing barium titanate particles which can be used in a wide range of fields such as multi-layer ceramic capacitors (MLCC), static characteristic thermistors (PCT), and piezoelectric bodies, having a particle size distribution of -0.3 µm, with a uniform particle size. It is about.

Barium titanate is chemically labeled as BaTiO ₃ and is one of the ferroelectric materials having a perovskite structure, which has a large dielectric constant, relatively low cost, and excellent thermal stability, thus enabling multilayer ceramic capacitors (MLCC), It has been used as a main raw material in products such as PCT, filter, and varistor. Recently, electric circuits and devices designed and manufactured based on them are becoming more diversified and higher in density. While the density of circuits increases significantly, the current trend of miniaturizing the size of the product shows that the technology of producing powders with excellent crystallinity and purity and small particle size is of great industrial significance. Have For example, in the case of parts made of barium titanate having a small particle size, first, the defective rate is greatly reduced, and due to the small grain size in the sintered body, the dielectric constant increases, thereby reducing the number of layers required, thereby improving the efficiency of using raw materials, and sintering. As the temperature decreases, the associated costs such as energy costs are reduced. In addition, the performance of multi-layer ceramic capacitors (MLCCs), static thermistors (PCTs), filters, varistors and other products manufactured as ultra-fine powders will excel in the ultra-high frequency bands that will form the main media in the communications industry in the future. Judging.

In general, barium titanate was synthesized by mixing and grinding a solid phase of titanium dioxide and barium carbonate. However, such a solid-phase mixed grinding method is not only difficult to secure uniformity between lots according to the particle size and purity of raw materials, but also has difficulty in controlling the size of the barium titanate particles to a certain limit or less, resulting in poor sinterability.

Therefore, in order to improve the uniformity and particle size problems between lots, liquid phase synthesis has recently been widely used. Typical liquid synthesis methods include oxalate method (coprecipitation method), hydrothermal synthesis method, and sol-gel method (alkoxide method).

First, the oxalate method is also called co-precipitation method, oxalic acid is added to the reaction solution of barium chloride and titanium tetrachloride aqueous solution to precipitate barium titanyl oxalate, which is washed, filtered and dried, and then calcined at high temperature. A method for producing barium titanate particles. The oxalate method has the advantage of relatively simple process and low manufacturing cost, but has the disadvantage that the size of the primary particles is relatively large, 0.1 ~ 1 ㎛.

The hydrothermal synthesis method is a method of producing crystalline barium titanate particles by mixing titanium gel hydrate and barium hydroxide aqueous solution under high temperature and high pressure (US Pat. No. 4,643,984). Since the hydrothermal synthesis method causes a violent exothermic reaction of titanium tetrachloride as a reactant in air, it must be dissolved in distilled water before mixing reaction to make an aqueous titanium tetrachloride solution. In addition, since a reactor for high temperature and high pressure is required, there is a limit in cost reduction, resulting in an expensive product.

In addition, the sol-gel method is also called an alkoxide method, and it is common to synthesize | combine using a titanium alkoxide and the barium hydroxide aqueous solution (Japanese Patent No. 2002-060219). In the case of the sol-gel method, a fine powder having a particle size of 0.1 to 0.3 μm can be obtained, and since the reactor for high temperature and high pressure is unnecessary, it is inexpensive and easy to manage, but the alcohol solution of titanium alkoxide, which is a reactant In case of preparing, it is easy to react with moisture in the air, so careful process control is required, and there is a hassle of process explosion-proof device against alcohol. Also. It includes a step of obtaining solid particles from the reaction solution of the alcohol solution of the titanium alkoxide and the aqueous solution of barium hydroxide and then washing with boiling pure water to separate the solid-liquid separation, which is required because the produced particles may be lost during washing. As a separation method, a process such as winssim separation is required, and a process control for controlling the molar ratio of elements of barium / titanium during the process is required.

Accordingly, the present inventors have made efforts to improve side reactions and management problems and process complexity problems caused by the use of titanium alkoxide, which is a reaction raw material in the sol-gel method. Titanium alkoxide prepared under nitrogen atmosphere is sol-gel reacted with barium hydroxide aqueous solution using a stirrer and a static mixer, and then dried and washed, and then calcined, pulverized and washed. The present invention has been completed by knowing that the particle size distribution having a size of 0.1 to 0.3 µm has a uniform particle size and that the barium / titanium element molar ratio of the barium titanate particles can be controlled in each step by removing the cleaning step.

Therefore, it is possible to control the barium / titanium element molar ratio in a series of single processes using titanium alkoxide directly, and the particle size distribution is uniform and fine. It is an object of the present invention to provide a method for producing barium titanate particles which can be used in the present invention.

The present invention provides a method for producing barium titanate by sol-gel reaction,

Preparing a reaction solution by a sol-gel reaction using a stirrer and a static mixer at 40 to 100 ° C. at a reaction temperature of 0.1 to 1.0 M barium hydroxide solution and titanium alkoxide in a nitrogen atmosphere;

Firstly drying the prepared reaction solution to obtain barium titanate dried particles, and calcining them at a temperature of 800 to 1100 ° C. to produce barium titanate particles; And

The barium titanate particles are characterized by a method for producing barium titanate particles comprising the step of pulverizing the prepared barium titanate particles, followed by washing with water and secondary drying to produce purified barium titanate particles.

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

The present invention is a method for preparing barium titanate particles by direct drying and calcining by direct sol-gel reaction of titanium alkoxide with barium hydroxide aqueous solution at a constant molar ratio using a stirrer and a static mixer, followed by grinding, washing and secondary drying. In the related art, since titanium alkoxide easily reacts with a small amount of water in the air, the titanium alkoxide is dissolved and used in an alcohol solution. However, the present invention simplifies the process by mixing titanium alkoxide and barium hydroxide by using a stirrer and a static mixer. At the same time, there is no need for a process of removing by-products due to the use of alcohol, and there is an advantage in that the molar ratio of the barium / titanium element of the barium titanate particles in each step can be easily controlled by removing the cleaning process after the first drying. Accordingly, the present invention relates to a method for producing barium titanate particles having a uniform particle size distribution having an average particle size of 0.1 to 0.3 μm and having a molar ratio of barium / titanium element of almost 1: 1 in a single process according to the present invention. .

As described above, the method for producing barium titanate particles according to the present invention will be described in detail.

First, an aqueous solution of barium hydroxide at a concentration of 0.1 to 1.0 M and titanium alkoxide are mixed under a nitrogen atmosphere by using a stirrer and a static mixer, and a reaction solution is prepared by a sol-gel reaction at a reaction temperature of 40 to 100 ° C. The barium hydroxide aqueous solution dissolves barium hydroxide in pure water from which carbon dioxide (CO ₂ ) is removed to obtain an aqueous solution having a concentration of 0.1 to 1.0 M. The barium hydroxide can be used in the form of a general hydrate, it is preferable to use barium hydroxide octahydrate (Ba (OH) ₂ · 8H ₂ O) in the present invention. When the concentration of the barium hydroxide aqueous solution is less than 0.1 M concentration, after the reaction, it becomes an excess state of titanium and becomes unsuitable as a dielectric ceramic powder. There is a problem that it becomes unsuitable as a dielectric ceramic powder. In addition, the titanium alkoxide is directly mixed under a condition that does not occur with a small amount of water in the air through the reaction under a nitrogen atmosphere and a method of mixing using a stirrer and a static mixer instead of dissolving in an existing alcohol solution. It is added to the sol-gel reaction to simplify the process. The titanium alkoxide may use a reaction material of conventional barium titanate particles, and for example, one selected from titanium isopropoxide and titanium butoxide may be used.

The barium hydroxide aqueous solution and the titanium alkoxide may be mixed and used in a molar ratio range of 1.0 to 1.5, more preferably 1.0 to 1.2, in an element molar ratio of barium / titanium. When the elemental molar ratio of barium / titanium is less than 1.0, it becomes an excessive state of titanium and is unsuitable as a dielectric ceramic powder. When the elemental molar ratio of barium / titanium exceeds 1.5, it becomes an excess state of barium and barium carbonate is formed, resulting in dielectric The problem of becoming unsuitable as a ceramic powder arises. In the sol-gel reaction, it is preferable to use a reaction temperature of 40 to 100 ° C., more preferably 60 to 90 ° C., in which the general reaction is carried out. An ongoing problem arises.

Next, the prepared reaction solution is first dried to obtain dry barium titanate particles having a tetragonal structure, which are calcined at a temperature of 800 to 1100 ° C. to produce barium titanate particles.

The primary drying is carried out using an oven, fluid bed dryer and spray-dry under normal conditions. In the preparation of barium titanate particles by a conventional sol-gel reaction, a washing process is provided before the first drying process. However, in the present invention, the first drying process is performed immediately after the sol-gel reaction so as not to be washed. The loss of the remaining unreacted barium was suppressed, and the barium / titanium element molar ratio of the barium titanate particles was controlled for each process. The barium titanate dry particles have a molar ratio of barium / titanium element of 1.0 to 1.2.

In addition, the heating rate during calcination is 0.5 to 10 ℃ / min, the holding temperature is preferably 800 to 1100 ℃. The dry particles are grown through calcination to obtain uniform fine particles of barium titanate of 0.1 to 0.3 μm, and the particles are uniform.

Next, the barium titanate particles prepared above are pulverized, and then washed with water and secondaryly dried to produce purified barium titanate particles.

The grinding may be a wet mill such as a planetary mill, a ball mill and a bead mill, and a dry mill such as an atomizer and a jet mill. When using the wet machine requires a drying process. The pulverized barium titanate particles are washed with water and secondly dried to remove excess unreacted barium, and water washing is preferably used with 0.001 to 0.05 l / g of pure water.

As described above, barium titanate prepared by a series of single processes in which titanium alkoxide is directly incorporated into barium hydroxide under a nitrogen atmosphere of the present invention and mixed using a stirrer and a static mixer has an average particle size of 0.1 to 0.3 μm. It forms a homogeneous tetragonal crystal structure and can be widely used as a material for many electric / electronic parts such as multilayer ceramic capacitors (MLCC) and ceramic filters.

Hereinafter, the present invention will be described in more detail based on the following examples, but the present invention is not limited to the examples.

Example 1

The barium hydroxide was dissolved in pure water from which carbon dioxide was removed with a nitrogen gas purge to prepare 0.4 L of an aqueous 0.4 M barium hydroxide solution, and the barium hydroxide solution and titanium isopropoxide were kept at 1.1 barium / titanium molar ratio to 80 ° C. The mixture was mixed well in the reaction tank of barium and titanium for 1 hour to prepare a reaction solution.

The reaction solution was first dried in an oven to obtain barium titanate dried particles, which were calcined at 1000 ° C. to obtain barium titanate particles. At this time, the dried barium titanate particles showed a uniform particle shape with an average particle size of 0.1 μm as shown in FIG. 1.

The calcined barium titanate particles were washed to remove excess barium, and then pulverized with a bead mill to produce barium titanate particles.

As shown in FIG. 2, the barium titanate particles obtained by the pulverization showed a uniform particle shape with an average particle size of 0.2 μm, a uniform particle size distribution as shown in FIG. 3, and a barium / titanium molar ratio of 1.0. It was confirmed that the particles were barium titanate having a crystal structure.

Example 2

The same process as in Example 1, but calcining at a temperature of 950 ℃ to prepare barium titanate particles.

The barium titanate particles obtained above were found to have a uniform particle shape with an average particle size of 0.15 μm and exhibit a tetragonal crystal structure.

Example 3

The same process as in Example 1, but calcining at a temperature of 1050 ℃ to prepare barium titanate particles.

The barium titanate particles obtained above were found to have a uniform particle shape with an average particle size of 0.22 μm and exhibit a tetragonal crystal structure.

Example 4

In the same manner as in Example 1, barium titanate particles were prepared by performing a reaction using titanium butoxide.

The barium titanate particles obtained above were found to have a uniform particle shape with an average particle size of 0.3 μm and exhibit a tetragonal crystal structure.

Comparative example

Barium titanate particles were prepared in the same manner as in Example 1 except that titanium isopropoxide was dissolved in isopropanol to prepare 0.4 M titanium isopropoxide solution.

The barium titanate particles obtained above was confirmed to have an average particle size of 0.2 ~ 0.3 ㎛.

As described above, the barium titanate particles prepared by the sol-gel reaction of the titanium alkoxide mixed directly with the barium hydroxide aqueous solution according to the present invention have a uniform particle size distribution of 0.1 to 0.3 μm in average, and thus are multi-layered. It can be widely used as a raw material such as ceramic capacitor (MLCC), static characteristic thermistor (PCT) and piezoelectric body.

Figure 1 shows a SEM photograph of the first dry barium titanate particles in Example 1 according to the present invention.

Figure 2 shows a SEM photograph of the barium titanate particles prepared in Example 1 according to the present invention.

Figure 3 shows the particle size distribution of the barium titanate particles prepared in Example 1 according to the present invention.

Figure 4 shows the change in the molar ratio of the barium / titanium element according to the change in the amount of washing water washed with the barium titanate particles prepared in Example 1 according to the present invention.

Figure 5 shows the XRD photograph of the first dried barium titanate dried particles (a) and barium titanate particles (b) after the calcination process prepared in Example 1 of the present invention.

Claims (5)

In the method for producing barium titanate by sol-gel reaction, Mixing the aqueous solution of barium hydroxide at a concentration of 0.1 to 1.0 M with titanium alkoxide using a stirrer and a static mixer under a nitrogen atmosphere, and preparing a reaction solution by sol-gel reaction at a reaction temperature of 40 to 100 ° C .; Firstly drying the prepared reaction solution to obtain barium titanate dried particles, and calcining them at a temperature of 800 to 1100 ° C. to produce barium titanate particles; And After grinding the prepared barium titanate particles, washing with water and secondary drying to produce purified barium titanate particles Method for producing barium titanate particles, characterized in that it comprises a. The method for producing barium titanate particles according to claim 1, wherein the barium hydroxide aqueous solution and the titanium alkoxide are mixed and used in an element molar ratio of barium / titanium in the range of 1.0 to 1.5. The method for producing barium titanate particles according to claim 1, wherein the barium titanate dry particles have a barium / titanium element molar ratio in the range of 1 to 1.2, an average particle size of 0.05 to 0.1 m, and a tetragonal crystal structure. . The method for producing barium titanate particles according to claim 1, wherein the barium titanate particles have an average particle size of 0.1 to 0.3 µm and have a tetragonal crystal structure. The method for producing barium titanate particles according to claim 1, wherein the water washing uses 0.001 to 0.05 l / g of pure water.