KR100290247B1 - Method for manufacturing barium titanate and perovskite type composite oxide - Google Patents

Abstract

The present invention relates to a method for producing barium titanate and perovskite-type composite oxides, and its purpose is to form raw materials in granular form and then thermally decompose them to obtain high purity fine grained barium titanate powder and perovskite having excellent composition and particle size uniformity. It is to provide a method for producing a complex composite oxide powder.

In order to achieve the above object, the present invention provides a method for preparing BaTiO ₃ powder, the method comprising the steps of: preparing a hydrated titania by adding ammonia water to an aqueous titanium chloride solution; Preparing a slurry by uniformly mixing an aqueous solution of barium nitrate or barium chloride with the hydrated titania; Spray drying or lyophilizing the slurry to dry the granules; Pyrolysing the dried granules; The present invention relates to a method for producing barium titanate comprising the step of pulverizing, and the present invention also provides a method for producing a perovskite-type complex oxide powder having an ABO ₃ form, the compound aqueous solution containing element B. Adding ammonia water to prepare a mixed hydrate; Preparing a slurry by uniformly mixing a compound aqueous solution containing element A in the prepared mixed hydrate; Spray drying or lyophilizing the slurry to dry the granules; Pyrolysing the dried granules; And it relates to a method for producing a perovskite-type composite oxide comprising the step of grinding.

Description

Method for manufacturing barium titanate and perovskite type composite oxide

The present invention relates to a method for producing barium titanate and perovskite-type composite oxides used in ferroelectrics, piezoelectrics and the like.

BACKGROUND ART In general, barium titanate powder is used as a ferroelectric and ferrite as an important component of an electronic ceramic, and is widely used as a raw material for ceramic capacitors, PTC (static thermistors), and piezoelectric materials.

The barium titanate powder is conventionally manufactured by synthesizing titanium oxide and barium carbonate by a solid phase reaction. However, according to the recent miniaturization of MLCC (thinning and high lamination of dielectrics) and low temperature baking, high purity with excellent particle size and composition uniformity Chemical synthesis techniques, such as hydrothermal synthesis, coprecipitation (oxalate method), alkoxide method (sol-gel method), etc., which can synthesize fine barium titanate powder, have been developed and their use is rapidly increasing.

However, all of these chemical synthesis methods are complicated in the manufacturing process and reaction occurs in the solution, so if the temperature, pH, concentration, and atmosphere of the solution are not managed well, non-uniformity of particle size and composition (Ba / Ti) is likely to occur, and expensive chemical The use of equipment and raw materials has the disadvantage of low productivity and high manufacturing costs.

Currently developed and commercially available chemical synthesis methods are three types of hydrothermal synthesis method, coprecipitation method (oxalate method) and alkoxide method, and the flow chart of each manufacturing process is shown in the first (ac) diagram. As follows.

A) hydrothermal synthesis

The hydrothermal synthesis reaction is performed by mixing titania and barium hydroxide into Ba-Ti ratio of 1.1-1.5: 1 to form a strong basic slurry as shown in the following Reaction Formula (1), and then heating it to 100-300 ° C. in a high temperature autoclave. To obtain grain-shaped barium titanate powder.

This hydrothermal synthesis method can produce high purity fine barium titanate powder with excellent composition, particle size uniformity and crystalline dispersibility, but it is difficult to match Ba / Ti = 1, and the manufacturing cost is expensive because the process is complicated and expensive equipment is required. There is this.

B) Coprecipitation method (oxalate method)

In the coprecipitation method, barium chloride and titanium chloride aqueous solution are mixed so that the ratio of Ba: Ti is 1: 1 and oxalic acid is added to the barium chloride (BaTiO (C ₂ O). ₄ ) ₂ · 4H ₂ O) is precipitated, washed well, filtered, dried and calcined at 800-1000 ° C. to obtain tetragonal barium titanate powder through the reaction of the following reaction formulas (3 to 5).

This coprecipitation method has the advantages of relatively simple process and low manufacturing cost, but it is difficult to control the composition so that Ba: Ti is 1: 1, and the precipitated titanium barium oxalate is a very large aggregate. This has the disadvantage that coarse aggregates remain as it is.

C) alkoxide method

The alkoxide method has various methods depending on which compound is used as a starting material. However, a method of preparing a crystalline barium titanate powder is a general method using a titanium alkoxide and an aqueous solution of barium hydroxide. The basic reaction of this synthesis method is shown in Scheme 6 below.

Ti- butoxide (butoxide) or Ti- captive polyepoxide (Propoxide) solution in Ba (OH) ₂ aqueous solution was mixed by stirring ₆ ^2- Ba if Ti had a Ba ²⁺ is already formed (OH) ^{2 +} heat complex ( After the formation of the complex, it is decomposed to produce very fine cubic barium titanate powder of 0.01-0.1 μm.

This synthesis method provides high purity powder with excellent compositional uniformity and very fine particles, but titanium alkoxide is easy to react with water in the air, and it is easy to form hydrated titania by rapid Ti-OH reaction in solution. Is needed. In addition, the particles are too fine, must be subjected to a calcination process after synthesis and has the disadvantage that the alkoxide is expensive.

FIG. 2 (a-e) schematically shows the reaction mechanism of the conventional solid-phase synthesis method and the chemical synthesis method described in the above items a) -c), and schematically shows the atomic unit mixing. The solid phase synthesis method has a diffusion reaction distance in μm and the Ba / Ti composition is locally nonuniform after the reaction, whereas the chemical synthesis methods have reaction distances in atomic or molecular size. Forms very fine barium titanate powder.

Accordingly, the present inventors have repeatedly studied and experimented to solve the disadvantages of the prior art, and based on the results, the present invention proposes the present invention. The purpose of the present invention is to provide a method for producing a high-purity fine barium titanate powder and perovskite-type composite oxide powder having a particle size uniformity.

1 (a) is a process chart _showing a manufacturing process of BaTiO ₃ by the conventional hydrothermal synthesis method.

1 (b) is a process chart _showing the manufacturing process of BaTiO ₃ by the conventional coprecipitation method.

1 (c) is a process chart _showing a manufacturing process of BaTiO ₃ by the conventional alkoxycite method.

Figure 2 (a) is a schematic diagram showing the mixing mechanism of BaTiO ₃ powder by the conventional solid phase synthesis method.

Figure 2 (b) is a schematic diagram showing the mixing mechanism of BaTiO ₃ powder by the conventional oxalate method.

Figure 2 (c) is a schematic diagram showing the mixing mechanism of BaTiO ₃ powder synthesis by the conventional hydrothermal synthesis method.

Figure 2 (d) is a schematic diagram showing the mixing mechanism of BaTiO ₃ powder by the conventional alkoxycite method.

Figure 2 (e) is a schematic diagram showing an ideal mixing mechanism.

3 is a process chart showing an example of a BaTiO ₃ manufacturing process by the thermal decomposition synthesis method of the present invention.

4 is a TG / DTA curve for mixture granules showing Ba (NO ₃ ) ₂ Ti (OH) ₄ xH ₂ O form.

Figure 5 (a) is a graph showing the XRD peak of the mixture granules showing a Ba (NO ₃ ) ₂ Ti (OH) ₄ x H ₂ O form after spray drying.

Figure 5 (b) is a graph showing the XRD peak of the barium titanate powder granules after pyrolysis.

Figure 6 (a) is a scanning electron micrograph of the mixture granules showing Ba (NO ₃ ) ₂ Ti (OH) ₄ x H ₂ O form after spray drying.

Figure 6 (b) is a scanning electron micrograph of the barium titanate powder granules after pyrolysis.

7 (a) is a scanning electron micrograph of a barium titanate powder pyrolyzed at 800 ° C.

7 (b) is a scanning electron micrograph of a barium titanate powder pyrolyzed at 1000 ° C.

In order to achieve the above object, the present invention provides a method for preparing BaTiO ₃ powder, the method comprising the steps of: preparing a hydrated titania by adding ammonia water to a titanium chloride solution; Preparing a slurry by uniformly mixing an aqueous solution of barium nitrate or barium chloride with the hydrated titania; Spray drying or lyophilizing the slurry to dry the granules; Pyrolysing the dried granules; And relates to a method for producing barium titanate comprising pulverizing,

In addition, the present invention provides a method for producing a perovskite complex oxide powder having an ABO ₃ form, comprising the steps of preparing a mixed hydrate by adding ammonia water to the aqueous solution containing element B; Preparing a slurry by uniformly mixing a compound aqueous solution containing element A in the prepared mixed hydrate; Spray drying or lyophilizing the slurry to dry the granules; Pyrolysing the dried granules; And it relates to a method for producing a perovskite-type composite oxide comprising the step of grinding.

Hereinafter, the present invention will be described in detail.

Since the present invention relates to such a BaTiO _3, other various perop Perovskite - Type manufacturing method for manufacturing the framework of the BaTiO ₃ in that, the perop Perovskite - Type compound oxide to a method for producing a complex oxide in powder form, the following BaTiO ₃ The present invention will be described based on the manufacturing method.

In the present invention, ammonia water is added to an aqueous titanium chloride solution to prepare hydrated titania.

The aqueous solution of titanic acid chloride is preferably in the range of 0.5-2.0 mol / l, which is in consideration of economical efficiency and the gel state obtained.

The concentration of the ammonia water is preferably 5-30%, which is 30% or less for sufficient reaction, and 5% or more in consideration of the additive effect.

It is preferable that the final pH of the mixture of the aqueous solution of titanic chloride and aqueous ammonia is 7-10, because less than 7 gelation is insufficient, and it is difficult to exceed 10.

Aqueous ammonia is added to the aqueous titanium chloride solution to obtain hydrated titania, and it is preferably washed sufficiently to remove Cl components using pure water. At this time, the obtained hydrated titania has the form of Ti (OH) ₄ .XH ₂ O.

In the present invention, a slurry is prepared by uniformly mixing an aqueous solution of barium nitrate or barium chloride with the hydrated titania.

The barium nitrate or barium chloride aqueous solution is added in an amount such that BaTiO ₃ of a desired form is obtained. In the case of pure BaTiO ₃ , the concentration of the barium nitrate or barium chloride solution is preferably 0.5-2.0 mo1 / 1 as the concentration of the titanium chloride solution.

The slurry obtained by mixing as described above is preferably adjusted with water so that the solid content concentration is 10-50%. If it is less than 10%, it is not good in terms of productivity, and if it exceeds 50%, barium nitrate or barium chloride tends to be insoluble. have.

In the present invention, the slurry is spray-dried or lyophilized to dry the granules.

After mixing the hydrated titania and barium nitrate aqueous solution, spray-drying or lyophilizing to 100 ° C. or more with sufficient stirring, and rapidly evaporating water, Ba (NO ₃ ) ₂ · Ti by a reaction as shown in the following Reaction Formula (7) (OH) ₄ · xH ₂ O and the mixture in the form of hydrated titania and barium nitrate mixed uniformly to the molecular level size is formed in the form of granules.

The spray drying may be used a conventional spray dryer, it is preferable that the internal temperature of the chamber of the spray dryer is 100 ℃ or more, because less than 100 ℃ may be undried. In addition, the lyophilization can be carried out through a conventional method.

The size of the granules is preferably about 10-l00㎛ average size, because less than 10㎛ there is a fear that the uniformity is lowered, if it exceeds 100㎛ there is a fear that sufficient drying does not occur.

In the present invention, the dried granules are pyrolyzed.

The pyrolysis is preferably performed at 650-1200 ° C., since the chemical reaction may not be completed at less than 650 ° C., and the particle size tends to be too large above 1200 ° C.

When the granules are pyrolyzed in this way, the crystal water and OH ⁻ ions contained in the hydrated titania of the mixture are first removed, followed by fine TiO ₂ particles and Ba (NO ₃ ) ₂ particles, and Ba (NO) as the temperature increases. ₃ ) After ₂ is decomposed into BaO and NO _x gas, TiO ₂ and BaO finally react to form tetragonal barium titanate powder. Inferring such a reaction roughly by temperature is considered to have a mechanism such as the following reaction formula (8).

It is also possible to use barium chloride as a starting material instead of barium nitrate, and the reaction mechanism is similar to that of barium nitrate.

In addition, in the present invention, the powder is pulverized after the pyrolysis to prepare a powder having a desired particle size.

The pulverization can be carried out in a conventional manner, preferably wet grinding methods such as bead mills, ball mills, planetary mills and the like. At this time, the grinding time is preferably about 1-5 hours, but when pulverized in this way has a particle size of 0.2-1.0㎛.

The flowchart of the barium titanate powder manufacturing process described above is shown in FIG. 3, and the preferred conditions of each manufacturing process are briefly described as follows.

A) Hydration titania manufacturing

Ti-hydrate is precipitated by slowly adding 10-20% ammonia water to the TiC1 ₄ 0.5-2.0mo1 / 1 aqueous solution until the final pH is 7-10. The hydrated titania thus prepared is sufficiently washed with pure water to completely remove Cl ⁻ .

B) mixing

The hydrated titania and barium nitrate or barium chloride solution prepared above are mixed so that the Ba: Ti ratio is 1: 1 and then sufficiently stirred.

Spray dry or freeze drying

The mixed slurry prepared above is spray dried or lyophilized with sufficient stirring to prevent phase separation from occurring. At this time, the solid concentration of the slurry is preferably 10-50%, the drying temperature is 100-300 ℃, the granule size is preferably adjusted to 10-100㎛.

D) Pyrolysis and Grinding

The granules prepared above were thermally decomposed at 650-1200 ° C., and then ground for 1-5 hours using a bead mill or a ball mill (planetary mill), where the particle diameter was 0.2-1.0 μm and the Ba: Ti ratio was close to 1: 1. High purity barium titanate powder is formed.

In the above, the method for producing BaTiO ₃ powder has been described in detail, but the method for producing the perovskite composite oxide powder of the present invention can be carried out by the same method.

In the present invention, in the case of producing the ABO ₃ type perovskite complex oxide powder, representative examples of the applicable elements are as follows. That is, the elements corresponding to A include Sr, Ca, Mg, Pb, Ba, and the like, and the elements corresponding to B include Ti, Zr, Hf, and Sn, and A and B are the elements, respectively. At least 1 type can be selected from these. However, this invention is not limited to this.

That is, a compound aqueous solution containing element B is used instead of the aqueous titanium chloride solution, and a compound aqueous solution containing element A is used instead of barium nitrate or barium chloride solution, and these ratios can be carried out in a conventional method or in a desired ratio. have. In addition, although the concentration of the starting material, pyrolysis temperature or particle size may vary slightly depending on the type of perovskite to be obtained, it may be solved by applying a conventional method.

In the compound aqueous solution containing element B, the compound may, for example, be a chlorinated compound. In the compound aqueous solution containing element A, the compound may be, for example, a nitriding or chloride compound.

According to the present invention as described above, barium titanate and perovskite-type composite oxides are obtained, and these oxides are prepared in various forms by adding a composition compound that can be substituted with Ba (A) and Ti (B) at an appropriate ratio. Of perovskite-type complex oxide powder can be easily produced. For example, Sr, Ca, Mg, and Pb may be dissolved in the Ba position, and Zr, Hf, and Sn elements may be dissolved in the Ti position.

The substance added for the substitutional employment is preferably added at the time of mixing titania (mixed hydroxide) and barium nitrate (nitride or chloride compound).

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

10% ammonia water was added slowly to the TiCl ₄ 1mo1 / 1 aqueous solution with stirring to a final pH of 10 to precipitate titania, and washed sufficiently with pure water to completely remove Cl ⁻ . The hydrated titania and barium nitrate thus prepared were mixed so as to have a Ba: Ti ratio of 1: 1, and then sufficiently stirred to prepare a mixed slurry. The mixed slurry was spray dried with sufficient stirring to prevent phase separation from occurring. At this time, the solid concentration of the slurry was 30%, the drying temperature was 200-120 ° C., and the granule size was adjusted to 10-100 μm to obtain granules. The obtained Ba (NO ₃ ) ₂ Ti (OH) ₄ xH ₂ O granules were pyrolyzed to show the TG / DTA thermal analysis curve in FIG. 4. As can be seen in FIG. 4, the reaction of Scheme (8) is well illustrated.

Example 2

After mixing 1.0 mo1 / 1 of barium nitrate solution with 1.0 mo1 / 1 of hydrated titania, spray-drying at a slurry solid concentration of 30%, drying temperature of 250 ° C (spray dryer inlet temperature), and disk rotation speed of 10,000 rpm with sufficient stirring. Granules were made. The granules were pyrolyzed at 950 ° C. for 2 hours to obtain barium titanate powder having a particle diameter of 0.5 ± 0.3 μm and a Ba / Ti ratio of 0.990.

5 (a) and (b) are XRD analysis results of the granules after spray drying and the powders after pyrolysis. As can be seen in Figure 5 (a), (b), after drying, the granules are mixed with amorphous titanium hydrate and barium nitrate, and after calcination, it can be seen that the powder is tetragonal barium titanate with good crystallinity.

6 (a) and (b) are scanning electron micrographs of the granules after spray drying and the powder after pyrolysis. FIG. 6 (a) shows the barium titanate mixed granules after spray drying. Showing barium titanate powder.

7 (a) and 7 (b) are scanning electron micrographs of powders obtained by setting the pyrolysis temperature at 800 ° C. and 1000 ° C., respectively. By comparing these pictures, it is possible to control the particle size of the powder according to the thermal decomposition temperature. Could know. The 800 ° C pyrolysis powder of FIG. 7 (a) has a particle diameter of 0.2 ± 0.1 μm, and the 1000 ° C pyrolysis powder of FIG. 7 (b) has a very uniform particle size of 0.6-0.3 μm.

Example 3

After mixing 0.2 mol / l of zirconia hydride with 0.8 mol / l of hydrated titania, 1.0 mol / l of aqueous barium nitrate was added thereto, followed by spray drying and pyrolysis under the same conditions as in Example 1 to perform Ba: (Ti + zr). Barium titanate zirconate powder having a ratio of 1: 1 and a Ti: Zr of 8: 2.

The obtained barium titanium zirconate powder was excellent in particle size and composition uniformity and showed high purity.

According to the pyrolysis synthesis method (Pyrorisis Synthesis) according to the present invention can obtain the following improvement effect. That is, a tetragonal barium titanate powder (perovskite-type complex oxide powder) having a uniform Ba / Ti composition and particle size and excellent crystallinity can be obtained. The manufacturing process is simple and the composition and particle size control are easy. In addition, when mixing the hydrated titania and barium nitrate, it is possible to easily prepare the perovskite-type composite oxide powder by adding a composition compound that can be substituted with Ba and Ti. In addition, the synthesis process is dramatically shortened, so the process management is easy and the productivity is improved. The starting material uses chloride and nitrate compounds which are the lowest of Ba (A) and Ti (B) compounds. Low input and discharge significantly reduces manufacturing costs and facilitates wastewater management.

Claims (16)

A method of preparing BaTiO ₃ powder, comprising: preparing hydrated titania by adding ammonia water to an aqueous titanium chloride solution; Preparing a slurry by uniformly mixing an aqueous solution of barium nitrate or barium chloride with the hydrated titania; Spray drying or lyophilizing the slurry to dry the granules; Pyrolysing the dried granules; And Barium titanate production method comprising the step of grinding. The method of claim 1, wherein the aqueous titanium chloride solution is a concentration of 0.5-2.0 mol / l barium titanate production method. The method of claim 1, wherein in the step of preparing a slurry by uniformly mixing a barium nitrate or barium chloride solution with the hydrated titania, a Zr, Hf or Sn component is added to replace a part of the Ti component in the titanium chloride solution. Barium titanate production method characterized in that. The method of claim 1, wherein in the step of preparing a slurry by uniformly mixing barium nitrate or barium chloride solution with titania hydration, Sr, Ca, Mg or Pb to replace a part of Ba component in barium nitrate or barium chloride solution. A method for producing barium titanate, comprising adding a component. The method of claim 1, wherein the ammonia water has a concentration of 5-30% barium titanate production method. The method for producing barium titanate according to claim 1, wherein the final pH of the mixture obtained by adding ammonia water to the aqueous titanium chloride solution is 7-10. The method of claim 1, wherein the barium nitrate or barium chloride aqueous solution has a concentration of 0.5-2.0 mol / l. The method of claim 1, wherein the ratio of the aqueous solution of titanium chloride and the aqueous solution of barium nitrate or barium chloride is 1: 1 in a molar ratio of Ba: Ti. The method for producing barium titanate according to claim 1, wherein the slurry obtained by mixing the hydrated titania and the barium nitrate or barium chloride aqueous solution has a solid content of 10-50%. The method for producing barium titanate according to claim 1, wherein the spray drying is performed at a chamber internal temperature of 100 캜 or more. The method of claim 1, wherein the granules obtained by drying have an average size of 10-l00 μm. The method for producing barium titanate according to claim 1, wherein the pyrolysis is performed at 650-1200 ° C. The method for producing barium titanate according to claim 1, wherein the grinding is wet grinding by a bead mill or a ball mill or a planetary mill, and the grinding time is 1-5 hours. Preparation of a perovskite-type complex oxide powder having the form of ABO ₃ (A: at least one selected from Sr, Ca, Mg, Pb, and Ba: B: at least one selected from Ti, Zr, Hf, and Sn) A method for producing a mixed hydrate by adding ammonia water to a compound aqueous solution containing element B; Preparing a slurry by uniformly mixing a compound aqueous solution containing element A in the prepared mixed hydrate; Spray drying or lyophilizing the slurry to dry the granules; Pyrolysing the dried granules; And pulverizing. 15. The method of claim 14, wherein in the compound containing element B, the compound is a chloride compound. 15. The method for producing a perovskite-type composite oxide according to claim 14, wherein in the compound containing element A, the compound is a nitride or chloride compound.