KR101606932B1 - A method of preparing barium titanate powder by oxalate process and barium titanate powder prepared by same - Google Patents

Abstract

A method for producing barium titanate powder and barium titanate powder produced by the method are disclosed. The disclosed method for producing barium titanate powder includes filling a barium titanyl oxalate powder and at least one kind of filler in a heating furnace after the synthesis of barium titanyl oxalate, followed by heat treatment. In addition, the barium titanate powder produced by the above-described production method has fine particle size distribution and high crystallinity.

Description

[0001] The present invention relates to a method for producing barium titanate powder by an oxalate process and a barium titanate powder prepared by the method,

A method for producing barium titanate powder and barium titanate powder produced by the method are disclosed. More particularly, the present invention relates to a process for producing barium titanate powder by an oxalate process comprising the steps of filling a barium titanyl oxalate synthesized with the synthesized barium titanyl oxalate powder and at least one kind of filler into a heating furnace, A barium titanate powder produced by the method is disclosed.

Conventionally, barium titanate powder has been produced by a solid phase reaction in which titanium dioxide (TiO ₂ ) and barium carbonate (BaCO ₃ ) are mixed and heat-treated at a high temperature. In recent years, barium titanate powder has been used as a small-capacity (MLCC) multilayer ceramic condenser It is required to have high purity / composition uniformity, fine particle / particle uniformity, non-cohesive / high dispersibility due to low temperature firing, high frequency and high performance due to high dielectric constant, high dielectric constant, high dielectric constant, And is produced by a synthetic method. Particularly, as the multilayer ceramic capacitor becomes thinner and more stable, it is required to have a barium titanate powder having a uniform particle size distribution and a high crystallinity at a particle diameter of 150 nm or less.

Prior art for producing such barium titanate powder is disclosed in Korean Patent Publication No. 2007-0031969 entitled "Method for producing ceramic powder having a perovskite structure, ceramic electronic component having a perovskite structure, A ceramic capacitor and a manufacturing method thereof ". However, in the method disclosed herein, barium titanate is synthesized by the solid phase method, and then the synthesized barium titanate powder is placed in a sealed container filled with water or a barium hydroxide aqueous solution having a pH of 7 or more to perform heat treatment. The drying process is added to increase the production cost and decrease the production yield. Furthermore, the crystallinity (c / a) of the barium titanate produced by the above-described production method is not more than 1.009 at a maximum of 200 nm and not only exceeds the crystallinity of more than 1.009 required for the production of a high-capacity miniaturized MLCC, There is a problem in that it can not overcome the fundamental limitation of the solid-phase reaction method which causes unevenness in particle size and the like. In addition, the above method also has a limitation in that it can not produce 100 nm-grade barium titanate of high crystallinity.

In addition, Korean Patent Publication No. 2005-0045580, "Barium titanate having a particle size of 100 nm" was prepared in the "Method of producing a composite oxide by a zero-gravity high-temperature heat treatment", but its crystallinity (c / a) was as low as 1.005.

One embodiment of the present invention relates to a method for producing barium titanyl oxalate, comprising the steps of filling a barium titanyl oxalate powder and at least one kind of filler in a heating furnace after the synthesis of barium titanyl oxalate, And a manufacturing method thereof.

Another embodiment of the present invention provides a barium titanate powder having a fine particle size distribution and a high crystallinity prepared by the above production method.

According to an aspect of the present invention,

A step of preparing an aqueous solution of barium chloride (BaCl ₂ ) and an aqueous solution of titanium tetrachloride (TiCl ₄ ) (raw material aqueous solution preparation step);

To produce barium titanyl oxalate [BaTiO (C ₂ O ₄ ) ₂ .4H ₂ O] by dropwise adding the aqueous solutions to an aqueous solution of oxalic acid (H ₂ C ₂ O ₄ ) (BTO production step);

Wet grinding the barium titanyl oxalate (wet grinding step);

Drying the wet-milled barium titanyl oxalate to obtain barium titanyl oxalate powder (drying step);

Filling the barium titanyl oxalate powder and at least one filler into a heating furnace (charging step); And

Barium titanate powder containing barium titanyl oxalate powder charged in the heating furnace to produce barium titanate and removing impurities contained in the barium titanyl oxalate powder (BT production and impurity removal step) Of the present invention.

The filler may comprise a porous gas adsorbent material.

The filler may comprise at least one material selected from zeolite, activated carbon and glass wool.

The filler may have at least one shape selected from a particle shape, a wool shape, a wire shape, and a plate shape.

The filling amount of the filler may be 200 to 10,000 parts by volume per 100 parts of the charged amount of the barium titanyl oxalate powder.

The impurities may include at least one of water and carbon.

The impurities may be removed in the form of at least one of water vapor and carbon dioxide gas.

The heating furnace may be a sagger or a tray.

Wherein the barium titanate powder is produced by aging the barium titanyl oxalate produced between the BTO production step and the wet pulverization step; Filtering the aged barium titanyl oxalate; And washing the filtered barium titanyl oxalate with an excess of water.

The wet pulverization step may be performed by adding at least one nitrogen-containing additive selected from ammonia, an amine, an ammonium compound and an amino acid to the barium titanyl oxalate.

The method for producing barium titanate powder may further include pulverizing barium titanate produced in the BT production step and the impurity removal step.

According to another aspect of the present invention,

And barium titanate powder prepared by the above production method.

According to one embodiment of the present invention, barium titanyl oxalate powder and at least one kind of filler are synthesized after the synthesis of barium titanyl oxalate, A method for producing a powder can be provided.

According to another embodiment of the present invention, barium titanate powder having a fine particle size distribution and a high crystallinity can be prepared by the above production method.

Hereinafter, a method for producing barium titanate powder according to an embodiment of the present invention will be described in detail.

First, an aqueous solution of barium chloride (BaCl ₂ ) and an aqueous solution of titanium tetrachloride (TiCl ₄ ) are prepared (raw material aqueous solution preparation step). The aqueous barium chloride solution is usually prepared by dissolving BaCl ₂ .2H ₂ O in water, and its concentration range may be from 0.2 to 2.0 mol / l. When the concentration of barium chloride aqueous solution is less than 0.2 mol / l, the productivity of barium titanate described below is low compared to the volume of barium chloride aqueous solution. When the concentration exceeds 2.0 mol / l, the solubility range of barium chloride There is a possibility that barium chloride will precipitate out. The titanium tetrachloride aqueous solution is usually diluted with a high concentration titanium tetrachloride solution, and its concentration range may be from 0.2 to 2.0 mol / l. When the concentration of the titanium tetrachloride aqueous solution is less than 0.2 mol / l, the productivity of barium titanate is lower than that of the aqueous solution of titanium tetrachloride. When the concentration exceeds 2.0 mol / l, the solubility of titanium tetrachloride There is a possibility of titanium precipitation.

Next, barium titanyl oxalate (BTO: BaTiO (C (O)) is added dropwise to the mixed aqueous solution of the aqueous solution of barium chloride and aqueous solution of titanium tetrachloride or each of the aqueous solutions thereof by dropping it in an aqueous solution of oxalic acid (H ₂ C ₂ O ₄ ) ₂ O ₄ ) ₂ .4H ₂ O] (BTO production step). At this time, the oxalic acid aqueous solution may be used in a larger amount than the aqueous solution of barium chloride or aqueous solution of titanium tetrachloride. The concentration range of the oxalic acid aqueous solution may be 0.2 to 5.0 mol / l. If the concentration of oxalic acid aqueous solution is less than 0.2 mol / l, the productivity of barium titanate is low relative to the volume of oxalic acid aqueous solution. If the concentration exceeds 5.0 mol / l, the solubility of oxalic acid in water may be out of the range. Also in this case, the temperature of the oxalic acid aqueous solution may be maintained at 20 to 100 ° C, for example, 50 to 90 ° C. The time for which the aqueous solution of barium chloride and the aqueous solution of titanium tetrachloride are injected into the oxalic acid aqueous solution separately in the form of a mixed solution or separately is 1 to 3 hours. This drop time can be achieved by adjusting the injection speed of the nozzle. Injection nozzles can use a first-flow or second-flow nozzle depending on the flow of the fluid, and the use of a first-flow nozzle may be more advantageous in terms of convenience and obtaining uniform sediment. The first nozzle may be a full con, a hollow con, or a flat nozzle. The process of adding barium chloride aqueous solution and aqueous titanium tetrachloride solution to oxalic acid aqueous solution to produce barium titanyl oxalate [BaTiO (C ₂ O ₄ ) ₂ .4H ₂ O] can be represented by the following reaction formula 1.

[Reaction Scheme 1]

BaCl ₂ .2H ₂ O + TiOCl _2. + 2H ₂ C ₂ O ₄ 2H ₂ O? BaTiO (C ₂ O ₄ ) ₂ .4H ₂ O + 4HCl

The resulting barium titanyl oxalate can then be aged, filtered and washed with water. The aging time is preferably 0.5 to 2 hours in terms of productivity. Here, filtration refers to a step of separating only solid phase barium titanyl oxalate from barium titanyl oxalate-containing slurry using a centrifugal separator. The barium titanyl oxalate filtered with excess water can then be washed until the pH of the wash is neutral.

Thereafter, barium titanyl oxalate obtained through the above process is wet pulverized (wet pulverization step). Here, wet grinding refers to a method of pulverizing barium titanyl oxalate together with a predetermined medium into a wet pulverizer such as a beads mill, a ball mill, and an attrition mill. Here, the medium means water such as organic medium such as alcohol and deionized water. If organic medium is used, it is advantageous from the viewpoint of grinding efficiency and particle size control, but there is a disadvantage that cost is increased. This has the advantage of simplifying the process and reducing costs. When water is used as the medium, the amount thereof may be 1 to 10 parts by weight based on 1 part by weight of barium titanyl oxalate. When the amount of the water used is less than 1 part by weight, the powder can not be pulverized due to viscosity increase. When the amount is more than 10 parts by weight, the productivity of barium titanyl oxalate to the volume of water is low. The milling time needs to be appropriately controlled by the difference in milling power depending on the milling equipment, and it may be 10 to 300 minutes when using the bead mill. By controlling the milling time in this way, the particle size of the final product, barium titanate powder, can be appropriately controlled. It is possible to add a nitrogen-containing additive during the wet milling process, thereby solving the problem of acidification of the mixture before and after the milling, high viscosity of the slurry after milling, and reduction of the dielectric property of the powder due to the presence of chloride ion in the barium titanyl oxalate produced . Examples of the nitrogen-containing additive include amines, ammonia, ammonium compounds, amino acids, and mixtures of two or more thereof. Examples of the ammonium compounds include ammonium hydroxide, ammonium carbonate, ammonium acetate, ammonium phosphate, ammonium oxalate, ammonium bicarbonate, Ammonium hydroxide, a mixture of two or more thereof, and the like, and examples of the amino acids include arginine, lysine, and mixtures thereof. The content of such a nitrogen-containing additive may be 0.5 to 20 moles per 100 moles of barium titanyl oxalate. When the content is less than 0.5 molar parts, a phenomenon such as acidification and high viscosity of the slurry after grinding appears. When the amount exceeds 20 molar parts, the titanium component escapes from the barium titanyl oxalate crystal and the barium / titanium molar ratio becomes unbalanced Occurs.

Next, the wet milled barium titanyl oxalate is dried at a temperature of 400 DEG C or lower to remove the used medium (drying step). As a result, a dried barium titanyl oxalate powder is obtained. In this case, it is natural that the drying temperature should be equal to or higher than the boiling point of the medium in order to evaporate and remove the used medium.

Next, the barium titanyl oxalate powder and at least one kind of filler are charged into a heating furnace (charging step). The filler can increase the dispersibility of the barium titanyl oxalate powder and reduce the packing density, thereby enabling air communication to the gaps between the filler and / or powder particles filled in the heating furnace in the BT production and impurity removal steps to be described later, and Facilitates heat transfer between the filler and / or particles to promote uniform heating and smooth discharge of generated gas. The filler may include a porous gas adsorbing material. In this case, the filler may further perform a function of adsorbing and removing the gas generated in the BT generation and the impurity removal step described later. In addition, the filler may include zeolite, activated carbon, and / or glass wool, and may have a particle shape, a wool shape, a wire shape, and / or a plate shape. When the filler is in the form of particles, the barium titanyl oxalate powder is mixed with the filler before or after being filled in the heating furnace, and when the filler has a shape other than a particle shape, the barium titanyl oxalate powder Are dispersed inside and / or outside the filler. The filling amount of the filler may be 200 to 10,000 parts by volume, for example, 500 to 2,000 parts by volume, for 100 parts by volume of the barium titanyl oxalate powder. If the filling amount of the barium titanyl oxalate powder is less than 200 parts by volume with respect to 100 parts by volume of the filling amount of the barium titanyl oxalate powder, the filling density of the barium titanyl oxalate powder becomes high, It is not economical from the side.

 Next, barium titanyl oxalate powder charged in the heating furnace is heat-treated to produce barium titanate, and impurities contained in the barium titanyl oxalate powder are separated and removed (BT formation and impurity removal step). The impurities may comprise moisture and / or carbon. These impurities can be removed in the form of steam and / or carbon dioxide gas during heat treatment. In this step, the filler is filled in the heating furnace as described above, so that the barium titanyl oxalate powder is uniformly dispersed in the heating furnace and the packing density is lowered, so that heat is uniformly transferred to each of the powder particles, (Water vapor, carbon dioxide gas, etc.) is smoothly discharged, the nucleation temperature of barium titanate is lowered, and the particle size becomes smaller. The grain boundary of barium titanate is uniformly formed, the crystallinity is high and the particle size distribution becomes uniform. Further, when the filler includes a porous gas-absorbing material, the gas generated during the heat treatment is adsorbed on the filler to be removed, so that uniform nucleation and grain growth of barium titanate are achieved and crystallinity is increased. If moisture or gas generated during the heat treatment remains in the heating furnace, further evaporation of moisture remaining in the barium titanyl oxalate powder or further separation of carbon components is suppressed, As shown in FIG. The heat treatment temperature may be 800 to 1,000 ° C. When the heat treatment temperature is lower than 800 ° C, barium titanate is hardly produced, which is undesirable. When the heat treatment temperature is higher than 1000 ° C, the resulting barium titanate powder becomes too large in particle size. The heating rate from the drying temperature to the heat treatment temperature may be 0.5 to 10 ° C / min, for example, 1 to 5 ° C / min. If the rate of temperature rise is less than 0.5 占 폚 / min, the productivity of barium titanate is lowered. If the heating rate is more than 10 占 폚 / min, the temperature distribution is not uniform and the barium titanate fine powder becomes uneven in particle size. By performing the heat treatment in this way, water and excess carbonic acid present as crystal water are removed in the barium titanyl oxalate crystal, and barium titanate powder of several tens to several hundreds of nanometers in size is obtained through the process of the following Reaction Schemes 2 to 4 .

[Reaction Scheme 2]

BaTiO (C ₂ O ₄ ) ₂ .4H ₂ O? BaTiO (C ₂ O ₄ ) ₂ + 4H ₂ O

[Reaction Scheme 3]

BaTiO (C ₂ O ₄ ) ₂ + 1/2 O _{2 -} > BaCO ₃ + TiO ₂ + 2CO ₂

[Reaction Scheme 4]

BaCO ₃ + TiO _{2 -} > BaTiO ₃

Sagger or Tray may be used as a heating furnace for the heat treatment of the dried barium titanyl oxalate powder. Here, Sagger refers to refractory earth containers. The sagger may be, for example, a hexagonal container having a square bottom surface.

Thereafter, the barium titanate produced through the heat treatment process (that is, the BT production and the impurity removal step) may be pulverized, but such a pulverization step may be omitted. The pulverization may be carried out by wet pulverization using a pulverizer such as a beads mill, an atrition mill, and a ball mill together with a predetermined medium, a jet mill and a disk mill Disk mill or the like may be used for the pulverization between the raw materials without using the medium or the dry grinding using the frictional force with the grinder. The pulverization step is intended to solve the intergranular agglomeration of the barium titanate powder. After the wet pulverization, a drying process is additionally required, but it is not necessary to use facilities specially limited for drying. In the case of using an apparatus having an excessively high grinding efficiency in the grinding step, the grinding strength is lowered as much as possible to reduce the grain size distribution and crystallinity, It is preferable to cut only the necking between the particles without destroying the particles.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments, but the present invention is not limited thereto.

Example

Examples 1 to 8

(Formation and aging of barium titanyl oxalate)

1320 L of a 1 mol / L aqueous solution of barium chloride and 1200 L of a 1 M / L aqueous solution of titanium tetrachloride were mixed well in a 4M ³ glass-lined reaction tank to prepare a mixed aqueous solution. Thereafter, the mixed aqueous solution was injected at a rate of 2.5 L / min using a full cone type nozzle into 2520 L of a previously prepared 1 mol / l oxalic acid aqueous solution filled in a 6 M ³ reactor. A diaphragm pump was used to supply the mixed aqueous solution during nozzle injection. At this time, the oxalic acid solution was sprayed while stirring with a stirrer, the stirring speed of the stirrer was maintained at 150 rpm, and the temperature of the oxalic acid solution was maintained at 90 ° C.

 After the dropwise addition of the mixed aqueous solution for 2 hours, the reaction temperature was maintained for 1 hour, and the mixture was air-cooled while stirring and aged for 1 hour. As a result, a slurry containing barium titanyl oxalate was obtained.

(Filtration and washing of the resulting barium titanyl oxalate slurry)

The barium titanyl oxalate slurry prepared above was filtered with a centrifuge and washed with excessive water to a pH of the washing solution of 6 or more to obtain barium titanyl oxalate.

(Wet grinding and drying of the resulting barium titanyl oxalate)

50 kg of barium titanyl oxalate, 250 kg of deionized water and 0.5 kg of 29 vol.% Ammonia water (8.4 molar parts relative to 100 molar parts of barium titanyl oxalate) were added to a mixing vessel and stirred to produce a slurry. At this time, the pH of the slurry was 9.3. Thereafter, the barium titanyl oxalate was wet pulverized so as to have a maximum particle diameter of 5 탆 or less with a 20-liter horizontal bead mill. After milling, the slurry had a pH of 5.1 and a viscosity of 1800 cP. The thus obtained barium titanyl oxalate slurry was dried in an oven at a temperature of 200 ° C for 12 hours, and the chlorine ion content thereof was measured. As a result of the measurement, the chlorine ion content was 200 ppm.

(Heat treatment)

100 g of dried barium titanyl oxalate and 10 g of skin (20 g) of filler 667 parts as shown in the following Table 1 were charged together in a 1 L Sagger, and the temperature and selective The heat treatment was carried out while changing the type of the filler. As a result, barium titanate was obtained. The crystallization degree (c / a), the average particle size and the particle size distribution (D ₁₀ / D ₅₀ , D ₅₀ / D ₉₀ ) of barium titanate were measured with the temperature employed in the heat treatment.

The crystallinity (c / a) was determined by measuring XRD (D / Max 2000 series by Rigaku) at 40 kV, 200 mA at a rate of 2 sec / step and 0.02 step size, And the d-spacing values of the a-axis and the c-axis of the barium titanate were measured. D ₁₀ / D ₅₀ and D ₅₀ / D _{90, which} are the indexes of the average particle size and the particle size distribution, were measured by scanning electron microscope (SEM) photographs using a JSM-7400F manufactured by Jeol Co., Pro Plus ver 4.5) was used to calculate the size of the barium titanate particles on the average of the major axis and the minor axis of the barium titanate particles. The number of barium titanate particles measured was 800 or more. Here, the larger the D ₁₀ / D ₅₀ and the D ₅₀ / D ₉₀ , the better the particle size distribution. Here, D _10, D _{50, and} D ₉₀ represent the particle diameters of particles corresponding to the order of 10%, 50%, and 90% of the total number of particles when the measured particles are arranged in the order of small particle size to large particle size. do.

Comparative Examples 1 to 3

Barium titanate was prepared in the same manner as in Examples 1 to 3 except that no filler was filled in the sagger, and the crystallinity (c / a), the average particle diameter and the particle size distribution (D ₁₀ / D ₅₀ , and D ₅₀ / D ₉₀ ) were measured and are shown in Table 1 below. In each of the cases of Comparative Examples 1 to 3, the charged amount of barium titanyl oxalate dried was 10 g in the same manner as in Examples 1 to 3.

Note 1) Particle size: 2 to 3.5 μm, apparent density: 0.25 g / cm ³ or more, plate shape.

2) Particle diameter: 2 to 9 탆; apparent density: 0.001 to 0.003 g / cm ³ ;

3) Specific surface area: 1200 m ² / g or more, apparent density: 0.45 to 0.5 g / cm ³ , plate shape.

In Table 1, the c / a value is "- " when XRD analysis is not a tetragonal phase but is observed as a cubic phase and can not be measured.

Referring to Table 1 above, barium titanate of Examples 1 to 3 and Examples 4 to 8 was crystallized at a lower heat treatment temperature as compared with the barium titanate of Comparative Examples 2 to 3, as well as at such a relatively low heat treatment temperature , It was found that they have generally high crystallinity, small average particle size and uniform particle size distribution.

 While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (12)

A step of preparing an aqueous solution of barium chloride (BaCl ₂ ) and an aqueous solution of titanium tetrachloride (TiCl ₄ ) (raw material aqueous solution preparation step); To produce barium titanyl oxalate [BaTiO (C ₂ O ₄ ) ₂ .4H ₂ O] by dropwise adding the aqueous solutions to an aqueous solution of oxalic acid (H ₂ C ₂ O ₄ ) (BTO production step); Wet grinding the barium titanyl oxalate (wet grinding step); Drying the wet-milled barium titanyl oxalate to obtain barium titanyl oxalate powder (drying step); Filling the barium titanyl oxalate powder and at least one filler into a heating furnace (charging step); And Barium titanate powder containing barium titanyl oxalate powder charged in the heating furnace to produce barium titanate and removing impurities contained in the barium titanyl oxalate powder (BT production and impurity removal step) ≪ / RTI > The method according to claim 1, Wherein the filler comprises a porous gas adsorbent material. 3. The method of claim 2, Wherein the filler comprises at least one material selected from zeolite, activated carbon and glass wool. The method according to claim 1, Wherein the filler has at least one shape selected from a particle shape, a wool shape, a wire shape, and a plate shape. The method according to claim 1, Wherein the filled amount of the filler is 200 to 10,000 parts by volume per 100 parts of skin charged with the barium titanyl oxalate powder. The method according to claim 1, Wherein the impurity comprises at least one of water and carbon. The method according to claim 6, Wherein the impurities are removed in the form of at least one of water vapor and carbon dioxide gas. The method according to claim 1, Wherein the heating furnace is a sagger or a tray. The method according to claim 1, Between the BTO generation step and the wet grinding step, Aging the resulting barium titanyl oxalate; Filtering the aged barium titanyl oxalate; And And washing the filtered barium titanyl oxalate with an excess of water. The method according to claim 1, Wherein the wet pulverization step is performed by adding at least one nitrogen-containing additive selected from ammonia, an amine, an ammonium compound and an amino acid to the barium titanyl oxalate. The method according to claim 1, And b) grinding the barium titanate produced in the BT production and the impurity removal step. delete