KR100489403B1 - METHOD OF PREPARING BaTiO3 POWDER - Google Patents

Abstract

A method for producing barium titanate powder is disclosed. After obtaining a mixed solution of a Ba metal salt and a Ti metal salt or a Ti-alkoxide, obtaining a coprecipitation of a mixed solution in which hydrogen peroxide water is added to the mixed solution and hydrothermally synthesizing the coprecipitate to synthesize barium titanate. Powder is prepared. Accordingly, spherical barium titanate powder having a uniform composition of high purity at a low temperature and low pressure and having a narrow particle size distribution can be manufactured. Therefore, an electronic component having excellent characteristics can be manufactured using the barium titanate powder.

Description

Method for producing barium titanate powder {METHOD OF PREPARING BaTiO3 POWDER}

The present invention The present invention relates to a method for preparing barium titanate (BaTiO ₃ ) powder by a hydrothermal synthesis method, and more particularly, to form a co-precipitate in the form of barium hydroxide (hereinafter, referred to as "Ba ₂ [Ti ₂ O ₅ (OH) ₆ ]"). It relates to a method for producing barium titanate powder which is then hydrothermally synthesized by coprecipitation to form a hydrothermal compound.

In general, barium titanate is an electronic material having a perovskite structure and has a high dielectric constant and is capable of controlling the dielectric constant according to additives. Therefore, barium titanate is actively applied as a multi-layer ceramic capacitor (MLCC) material. have. In addition, it is widely used as an ultrasonic vibrator and a positive temperature coefficient resistor (PTCR) material using piezoelectricity.

Recently, with the development of electronic products, as the electronic products become higher and smaller, semiconductor devices used as components of the electronic products are being integrated. Accordingly, in order to manufacture the semiconductor device, raw materials having fine particle size and physical and chemically uniform characteristics are required. In order to produce a raw material having the above characteristics, control of the initial manufacturing process is important. Therefore, in order to produce a spherical powder having a narrow particle size distribution having a uniform composition of high purity, a manufacturing method that is easy to control the initial manufacturing process is required.

Conventionally, barium titanate has been produced by a solid phase method using barium carbonate (hereinafter referred to as BaCO ₃ ) and titanium oxide (hereinafter referred to as TiO ₂ ) powder. Powders prepared by the solid phase method require a high temperature calcination process of 900 ° C. or higher and have low reactivity due to large particles. In addition, the use of ceramic balls in the grinding and mixing (milling) process, as well as the possibility of impurity incorporation, as well as low reactivity increases the firing temperature. As a result, high temperature grain growth occurs and the dielectric constant is lowered. An example of the production of barium titanate using the solid phase method is disclosed in US Pat. No. 5,362,693 (issued to Chu et al.).

In order to overcome the problems of the solid phase method, a hydrothermal synthesis method with little impurities and easy control of the initial powder has been developed and used for powder production. Conventional hydrothermal synthesis A method of synthesizing a compound through a dissolution-precipitation reaction using the pressure of steam generated by mixing hydroxides, salts, oxides and alkoxides of reactants in a closed vessel and adding a temperature of 100 ° C. or more to the mixed solution. Therefore, by synthesizing the fine powder at a relatively low temperature below 300 ℃ does not require a milling process of grinding and mixing the raw materials separately.

However, in the conventional hydrothermal synthesis method, due to the dissolution-precipitation process of 150 ° C. or more for a long time, the precipitated particles tend to be in the form of fine single crystals having a specific crystal plane rather than a sphere, thereby decreasing reactivity during sintering. Strong bases (NaOH, KOH) are used as mineralizers to lower the energy of the dissolution-precipitation process. Japanese Patent Laid-Open No. 60-215627 discloses a method of hydrothermally synthesizing BaTiO ₃ particles using the above strong base.

However, when the cations contained in the strong base, sodium (hereinafter referred to as Na) and potassium (hereinafter referred to as K), remain in the hydrothermal synthetic powder, most electrons remain as impurities in the synthesized powder without decomposing during drying or heat treatment. It lowers the physical properties of the material. In addition, when two or more cations are included in the composition, it is difficult to match the exact cation ratio (Ba / Ti) during powder synthesis of hydrothermal synthesis. In general, barium (hereinafter, Ba) is considerably shorter than that of titanium (hereinafter, Ti), and an excessive amount of Ba is added when raw materials are added. However, the general hydrothermal synthesis method using the precipitated hydroxides (Ba (OH) ₂ and TiO (OH) ₂ ) separately contains moisture (· xH ₂ O) in each raw powder, making it difficult to calculate the exact Ba excess.

Accordingly, the technical and problem of the present invention are to solve the above-mentioned problems, and an object of the present invention is to form a hydrothermal composite using a coprecipitate as a raw material for hydrothermal synthesis, thereby forming a particle size distribution having a high purity and uniform composition at low temperature. To provide a method for producing a narrow spherical powder.

The present invention for achieving the above object is a step of obtaining a mixed solution of Ba metal salt and Ti metal salt or Ti-alkoxide, adding hydrogen peroxide solution to the mixed solution to obtain a mixed solution, the mixed solution in ammonia water Dropping to form a co-precipitate and hydrothermally synthesizing the co-precipitate to synthesize barium titanate.

In this case, the Ba metal salt is BaCl ₂ or Ba (NO ₃ ) ₂ , the Ti metal salt is one selected from the group consisting of TiCl ₄ , TiO (NO ₃ ) ₂ and Ti-tetra-isopropoxide. The Ba / Ti ratio of the mixed aqueous solution is constant from 1 to 3. The co-precipitate is Ba ₂ [Ti ₂ O ₅ (OH) ₆ ], the pH of the co-precipitate is formed from 9 to 12. The coprecipitation is frozen and thawed to increase the input amount of the raw material of the hydrothermal synthesizer. The pH of the hydrothermal synthesis is 9 to 12. The synthesized powder of barium titanate was filtered and washed to obtain a raw powder.

According to the present invention, fine barium titanate powder of high purity can be synthesized in a short time at low temperature by preparing a co-precipitate and hydrothermally synthesizing the co-precipitate.

Hereinafter, with reference to the accompanying drawings, a manufacturing method of the present invention will be described.

1 is a manufacturing process chart of barium titanate powder according to the present invention.

Referring to FIG. 1, a mixed aqueous solution selected from the group consisting of a Ba metal salt having a determined concentration and a Ti metal salt and a Ti-alkoxide is prepared, and hydrogen peroxide corresponding to 10 moles of Ti is added to the mixed solution. A mixed solution dissociated with a peroxide ion of Ti ₂ O ₅ ⁺² is prepared by reaction with Ti ⁺⁴ . The mixed solution was added dropwise while stirring slowly to ammonia water of 10.4 normal concentration (N) to form a co-precipitate. At this time, the Ba / Ti ratio of the mixed aqueous solution to obtain the stoichiometric barium titanate (Ba / Ti = 1) of the final hydrothermal synthesis powder is 1 to 3. (S10 to S30)

In the above process, Ba ^{+ 2} ions and Ti ^{+ 4} ions were synthesized as Ba ₂ [Ti ₂ O ₅ (OH) ₆ ], which is a composite peroxide directly at room temperature.

At this time, the precipitation process of the co-precipitate is as follows.

Ti ⁺⁴ + H ₂ O _2- > Ti ₂ O ₅ ⁺²

_{^{2Ba +2 (aq) + Ti 2}} O 5 +2 (aq) + 6OH - -> Ba 2 [Ti 2 O 5 (OH) 6]

In order to increase the homogeneity and dispersibility of the reaction, the co-precipitate is reacted with an ultrasonic cleaner for 5 minutes.

In addition, by freezing and thawing the co-precipitate, the fine colloidal particles are aggregated to reduce the volume of the co-precipitate.

When the co-precipitate is frozen, fine colloidal co-precipitate powders of the co-precipitate are pushed out by the growth of the ice crystals, and the extruded co-precipitated powders are combined with the surrounding co-precipitation powders that are pushed by the growth of the ice crystals and loosely bound. Formed relatively large particles. Coagulated co-precipitated powders as described above are settled in the solution to reduce the volume present in the container. As a result, a larger amount of raw material can be added to the hydrothermal synthesis vessel of the same size than the colloidal co-precipitate, thereby increasing the efficiency of powder synthesis.

At this time, the synthesized co-precipitate is an amorphous composite peroxide, and the reaction solution containing the co-precipitate and ammonia water is put into a hydrothermal synthesis apparatus as it is and sealed, and then pressurized at 110 to 180 ° C. for 10 minutes to 5 hours to crystallize 35 nm or less. Obtain BaTiO ₃ powder. At this time, pressure is added to steam of water vapor and ammonia in the hydrothermal synthesis apparatus.

The hydrothermal synthesis reaction is as follows.

Ba ₂ [Ti ₂ O ₅ (OH) ₆ ] (amorphous)-> 2BaTiO ₃ (crystalline)

The synthesized powder is filtered, washed and dried to prepare a raw powder. (S70)

Hereinafter, a barium titanate powder manufacturing method using a hydrothermal synthesis method according to an embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a manufacturing process chart of barium titanate powder according to the present invention, Figure 2 is a graph showing the results of X-ray diffraction analysis according to the temperature of the coprecipitation used as a raw material of the hydrothermal synthesis obtained according to Example 1 3 is a graph showing an X-ray diffraction analysis result of barium titanate powder prepared at each temperature by hydrothermal synthesis using coprecipitation water obtained according to Example 1 of the present invention, and FIG. 4 is a ball obtained according to Example 1 Scanning electron microscope (SEM) photograph of the barium titanate powder prepared by the hydrothermal synthesis method using the precipitate, Figure 5 is a transmission electron microscope (TEM) of the barium titanate powder prepared by the hydrothermal synthesis method using the co-precipitate obtained according to Example 1 It is a photograph.

Example 1

Barium chloride (hereinafter referred to as BaCl ₂ ) and titanium chloride (hereinafter referred to as TiCl ₄ ) were dissolved in distilled water to prepare a raw material solution having 1 mol / l, respectively. (S10) Ti was added to a mixed aqueous solution of the aqueous solution containing the desired composition ratio. Hydrogen peroxide (H ₂ O ₂ ) water corresponding to 10 mole times was added and stirred to prepare a mixed solution. (S20) At this time, a mixed aqueous solution to obtain the stoichiometric barium titanate (Ba / Ti = 1) of the final hydrothermally synthesized powder. The Ba / Ti ratio was 1.65.

The mixed solution was slowly added dropwise to 10.4 N ammonia water solution to induce precipitation. (S30) After the precipitation was completed, the pH was adjusted to 12. The co-precipitated solution was placed in an ultrasonic cleaner and reacted for another 5 minutes. The co-precipitate was frozen and thawed to aggregate and sink the co-precipitate on the colloid to reduce the volume. (S40 to S50)

Referring to Figure 2, the crystalline barium titanate by the co-precipitation method is formed by heating to a relatively high temperature of 600 ℃ or more.

The co-precipitate product including the co-precipitate and ammonia water as a pH adjusting agent was sealed in a hydrothermal synthesis vessel. At this time, the pH was not adjusted separately and was the same as the conditions for preparing the coprecipitate. After maintaining for 2 hours at a synthesis temperature of 130 ℃ natural cooling to obtain a synthetic powder. (S60) At this time the pressure was 5MPa or less. The synthetic powder was filtered and washed until silver was detected with silver (AgNO ₃ ) aqueous solution, and Cl was not detected. After washing, the synthetic powder was dried at 80 ° C. for at least 10 hours, and the physical properties thereof were measured. (S70)

Referring to FIG. 3, crystalline BaTiO ₃ peaks can be confirmed at 90 ° C. or higher and distinct BaTiO ₃ peaks at 110 ° C. or higher. Referring to FIGS. 2 and 3, the weak BaCO ₃ peaks are reacted with carbon dioxide (CO ₂ ) introduced in an aqueous solution or air, and are decomposed at a high temperature so that they do not significantly affect the physical properties of the sintered body.

4 and 5, it can be seen that the fine primary particles (FIG. 5) having a diameter of about 30 nm form secondary particles (FIG. 4) having 0.5 micrometer or less. The specific surface area of the powder measured by the BET method is 77 m / g, which is very fine particles. The thermogravimetric (TG) result of the synthesized powder showed that the weight loss of the synthesized dry powder was less than about 5% of the initial weight of the powder, so that cracking did not occur even when immediately used for sintering.

Example 2

Barium nitrate (hereinafter referred to as Ba (NO ₃ ) ₂ ) and titanium nitrate (hereinafter referred to as TiO (NO ₃ ) ₂ ) were dissolved in distilled water to prepare a raw aqueous solution of 1 mol / l. At this time, the TiO (NO ₃ ) ₂ is precipitated by precipitation of 1 mol / l titanium chloride (hereinafter, TiCl ₄ ) aqueous solution in 10.4N ammonia water, filtered and washed with distilled water to remove Cl and added dilute nitric acid After melting, it was prepared by adding distilled water again.

A mixed solution was prepared by adding and stirring hydrogen peroxide (H ₂ O ₂ ) water corresponding to 10 mole times of Ti of the mixed aqueous solution to the mixed aqueous solution in which the raw material aqueous solution was mixed at a predetermined composition ratio. At this time, the Ba / Ti ratio of the mixed aqueous solution for obtaining the stoichiometric barium titanate (Ba / Ti = 1) of the final hydrothermal synthesis powder was 1.65.

The mixed solution was slowly added dropwise to 10.4N aqueous ammonia solution to induce precipitation. After the end of the precipitation pH was adjusted to 12. The solution in which the co-precipitate was formed was placed in an ultrasonic cleaner and reacted for 5 minutes. The co-precipitate was frozen and thawed to aggregate the co-precipitate on the colloid to reduce the volume.

The co-precipitate and a product containing ammonia water as a pH adjusting agent were sealed in a hydrothermal synthesis vessel. At this time, the pH was not additionally adjusted and was the same as that of the coprecipitation material. After maintaining for 2 hours at a synthesis temperature of 130 ℃ natural cooling to form a synthetic powder. At this time, the pressure was 5 MPa or less. The powder did not contain cations affecting the sintered body or chlorine (Cl) included in the case of Example 1, so that the hydrothermal synthesis process could be simplified by reducing the washing process. After drying at 80 ° C. for 10 hours or more, physical properties were measured, and all physical properties were the same as in Example 1.

Example 3

A mixed solution was prepared by dissolving barium nitrate (hereinafter, Ba (NO ₃ ) ₂ ) of a predetermined composition in distilled water and adding titanium tetra isopropoxide (hereinafter, Ti-tetra-isopropoxide). At this time, Ti-tetra-isopropoxide was hydrated on the mixed aqueous solution to form a gel, so that some nitric acid was added to dissolve it. Hydrogen peroxide (H ₂ O ₂ ) water corresponding to 10 mole times of Ti was added to the mixed aqueous solution, followed by stirring to prepare a mixed solution. In this case, the Ba / Ti ratio of the mixed solution for obtaining stoichiometric barium titanate (Ba / Ti = 1) was 1.65.

The mixed solution was slowly added dropwise to 10.4N aqueous ammonia solution to induce precipitation. After the end of the precipitation pH was adjusted to 12. The solution in which the co-precipitate was formed was reacted for 5 minutes in an ultrasonic cleaner, and the volume was reduced by coagulating the co-precipitate on the colloid by freezing and thawing the co-precipitate.

The co-precipitate and a product containing ammonia water as a pH adjusting agent were sealed in a hydrothermal synthesis vessel. At this time, the pH was not additionally adjusted and was the same as that of the coprecipitation. After maintaining for 2 hours at a synthesis temperature of 130 ℃ natural cooling to prepare a synthetic powder. At this time, the pressure was 5 MPa or less. Since the powder does not contain cations or Cl that affect the sintered body, the hydrothermal synthesis process can be simplified by reducing the washing process. After drying at 80 ° C. for 10 hours or more, physical properties were measured, and all physical properties were the same as in Example 1.

As described above, according to the present invention, the final Ba / Ti ratio can be easily controlled by performing hydrothermal synthesis on the co-precipitate having the Ba / Ti ratio determined using a raw material solution having a concentration of metal salts and alkoxides as raw materials. At a lower temperature than the conditions of hydrothermal synthesis, it was possible to synthesize a high purity fine barium titanate powder of fine tens of nanometers in a short time.

In addition, by using ammonia water, impurities such as Na or K are not included, and since the synthesis from hydroxide to oxide is induced by simple pressurization, long-term reactions such as dissolution and precipitation can be reduced.

Synthesis of high purity fine barium titanate powder can reduce the size of current electronic component products and improve electrical and dielectric properties.

Although described above with reference to the embodiments, those skilled in the art can be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below. I can understand.

1 is a manufacturing process chart of barium titanate powder according to the present invention.

Figure 2 is a graph showing the results of X-ray diffraction analysis according to the heat treatment temperature of the coprecipitation material used as a raw material of the hydrothermal synthesis obtained according to Example 1 of the present invention.

Figure 3 is a graph showing the X-ray diffraction analysis of the barium titanate powder prepared for each temperature by the hydrothermal synthesis method using a co-precipitate obtained in Example 1 of the present invention.

FIG. 4 is a scanning electron microscope (SEM) photograph of barium titanate powder prepared by hydrothermal synthesis using a coprecipitation material obtained in Example 1. FIG.

FIG. 5 is a transmission electron microscope (TEM) photograph of barium titanate powder prepared by hydrothermal synthesis using a coprecipitation material obtained in Example 1. FIG.

Claims (8)

Obtaining a mixed solution of a Ba metal salt selected from BaCl ₂ and Ba (NO ₃ ) ₂ and a Ti metal salt or Ti-alkoxide selected from TiCl ₄ , TiO (NO ₃ ) _2, and Ti-Tetra-isopropoxide; Adding hydrogen peroxide solution to the mixed aqueous solution to obtain a mixed solution; Dropping the mixed solution into ammonia water to form a co-precipitate under a pH of 9 to 12; And And hydrothermally synthesizing the co-precipitate under a pH of 9 to 12 to produce barium titanate. delete delete The method of claim 1, wherein the Ba / Ti ratio of the mixed aqueous solution is constant and the Ba / Ti ratio is 1 to 3. The method of claim 1, wherein the co-precipitate is Ba ₂ [Ti ₂ O ₅ (OH) ₆ ]. delete The method for producing barium titanate powder according to claim 1, wherein the coprecipitation is frozen and thawed to increase the input amount of the raw material of the hydrothermal synthesizer. The method for producing barium titanate powder according to claim 1, wherein the synthesized powder of barium titanate is filtered and dried to obtain a raw powder.