WO2014084428A1

WO2014084428A1 - Method for preparing barium titanate powder and barium titanate powder prepared by said method

Info

Publication number: WO2014084428A1
Application number: PCT/KR2012/010346
Authority: WO
Inventors: 최연규; 김현; 정원식; 차경진; 박지호
Original assignee: 삼성정밀화학(주)
Priority date: 2012-11-30
Filing date: 2012-11-30
Publication date: 2014-06-05
Also published as: KR101792278B1; KR20140072336A

Abstract

Disclosed are a method for preparing barium titanate powder and barium titanate powder prepared by said method. The disclosed method for preparing barium titanate powder comprises a primary calcination step and a secondary calcination step, thus preparing barium titanate powder having low content of fine particles, narrow particle size distribution and high crystalline properties.

Description

Method for producing barium titanate powder and barium titanate powder prepared by the method

A method for producing barium titanate powder and a barium titanate powder produced by the method are disclosed. More specifically, by including the first calcination step and the second calcination step, barium titanate by an oxalate process capable of producing fine barium titanate powder having a fine powder content, narrow particle size distribution, and high crystallinity A method for producing a powder and a barium titanate powder produced by the method are disclosed.

The barium titanate powder was conventionally manufactured by a solid phase reaction in which titanium dioxide (TiO ₂ ) and barium carbonate (BaCO ₃ ) were mixed and heat-treated at a high temperature, but recently, a small capacity of a multilayer ceramic capacitor (MLCC) has been increased. High purity / composition uniformity, fine grain / particle uniformity, non-aggregation / high dispersion, etc. are required according to high dielectric constant composition, dielectric thinning and high lamination), low temperature plasticization, high frequency and high performance. Various synthesis methods are used for the production of barium titanate powder. However, for mass production of barium titanate powder, a coprecipitation method, which is a kind of liquid phase method, in which barium titanate powder having a low manufacturing cost and a uniform composition can be obtained, must be used.

In the coprecipitation method, a liquid raw material containing barium (Ba) and titanium (Ti) is added to oxalic acid (H ₂ C ₂ O ₄ ) to barium titanyl oxalate [BaTiO (C ₂ O ₄ ) _{2 to} 4H ₂ O]. After the formation, the barium titanyl oxalate was calcined at high temperature to synthesize barium titanate (BaTiO ₃ ) powder having an appropriate size. However, during high temperature calcination, the barium titanate particles aggregate strongly together to form aggregates, and since these aggregates adversely affect the reliability of the electronic components, the aggregates are disaggregated to disintegrate and the final product titanium is used. Barium powder is prepared (see Korean Patent Publication Nos. 2003-0015011 and 2008-0070981). However, a large amount of fine particles are generated during the disintegration process, and high active regions (that is, regions where grain growth is likely to occur even at low temperatures) are formed, thereby causing abnormal grain growth and inorganic additives in the multilayer ceramic capacitor ( For example, rare earths, Mg, Mn, Cr, V, Y, Dy, etc.) cause excessive doping (soiling) there is a problem that causes a decrease in reliability and dielectric constant.

One embodiment of the present invention comprises a first calcination step and a second calcination step, by the oxalate process that can produce fine barium titanate powder having a fine powder content, narrow particle size distribution, high crystallinity Provided is a method for producing barium titanate powder.

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

One aspect of the invention,

Preparing an aqueous solution of barium chloride (BaCl ₂ ) and an aqueous solution of titanium tetrachloride (TiCl ₄ ) (preparing a raw material solution);

Adding bar water to the aqueous solution of oxalic acid (H ₂ C ₂ O ₄ ) to produce barium titanyl oxalate [BaTiO (C ₂ O ₄ ) _{2 to} 4H ₂ O] (hereinafter referred to simply as BTO). step);

Wet grinding the BTO (BTO wet grinding step);

Drying the wet milled BTO to obtain a BTO powder (BTO drying step);

First heat treating the BTO powder at 920 to 950 ° C. to produce barium titanate (BT) (first calcination step); And

It provides a method for producing barium titanate powder comprising the step (secondary calcination step) the second heat treatment of the BT at 820 ~ 890 ℃.

The method for producing the barium titanate powder, between the BTO production step and the BTO wet grinding step, the step of ripening the produced BTO, filtering the aged BTO, and washing the filtered BTO with excess water It may further comprise the step.

The method of manufacturing the barium titanate powder may further include obtaining a first BT powder by grinding the BT between the first calcination step and the second calcination step (BT grinding step).

The first BT powder may have an average particle diameter of 280 to 320nm and a fine powder content of 5 to 10% by weight (that is, a content of particles having a particle diameter of 70 nm or less).

The method of manufacturing the barium titanate powder may further include, after the secondary calcination step, disintegrating the secondary calcined BT to obtain a second BT powder (BT disintegration step).

Another aspect of the invention,

It provides a barium titanate powder prepared by the method for producing barium titanate.

The barium titanate powder may have a fine powder content of 3.5 wt% or less (that is, a content of particles having a particle diameter of 70 nm or less).

According to the method for producing the barium titanate powder by the oxalate process according to the embodiment of the present invention, by including the first calcination step and the second calcination step, the fine powder content, narrow particle size distribution, high crystallinity Fine barium titanate powder can be obtained.

1 is a flowchart illustrating a step-by-step method for producing a barium titanate powder according to an embodiment of the present invention.

FIG. 2 shows a series of processes in which barium titanyl oxalate is converted to barium titanate.

3 is a view showing a phenomenon occurring in the barium titanate in the second calcination step and / or disintegration step.

FIG. 4 is a SEM photograph prepared in Example 2 to illustrate necking phenomenon between barium titanate particles after the first calcination step and before the BT grinding step.

5 is a SEM photograph of the barium titanate powder prepared in Example 2. FIG.

6 is a SEM photograph of the barium titanate powder prepared in Comparative Example 1. FIG.

Figure 7 is a graph showing the particle size distribution of the barium titanate powder prepared in Example 2 and Comparative Example 1.

Hereinafter, a method of preparing barium titanate powder according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Although not shown in FIG. 1, first, a barium chloride (BaCl ₂ ) aqueous solution and a titanium tetrachloride (TiCl ₄ ) aqueous solution are prepared (a raw material aqueous solution preparation step). Aqueous solution of barium chloride is usually used by dissolving BaCl ₂ · 2H ₂ O in water, and its concentration range may be 0.2∼2.0 mol / L. When the concentration of the barium chloride aqueous solution is within the above range, the productivity of barium titanate (BT) to be described later is high compared to the volume of the barium chloride aqueous solution, and barium chloride is not precipitated. Titanium tetrachloride aqueous solution is usually used by diluting a high concentration of titanium tetrachloride solution, the concentration range may be 0.2 ~ 2.0 mol / L. When the concentration of the titanium tetrachloride aqueous solution is within the above range, the productivity of BT relative to the volume of the titanium tetrachloride aqueous solution is high, and titanium tetrachloride is not precipitated.

Next, a mixed aqueous solution of the aqueous barium chloride solution and titanium tetrachloride solution or each of these aqueous solutions is added (for example, dropwise) to the aqueous solution of oxalic acid (H ₂ C ₂ O ₄ ) using a high-speed jet nozzle to add barium titanyl oxal. A rate [BaTiO (C ₂ O ₄ ) _2. 4H ₂ O] (hereinafter referred to simply as BTO) is generated (BTO generation step, S1). At this time, the oxalic acid aqueous solution may be used in an amount larger than the barium chloride aqueous solution or titanium tetrachloride aqueous solution. Specifically, the concentration range of the oxalic acid aqueous solution may be 0.2 ~ 5.0 mol / L. When the concentration of the oxalic acid aqueous solution is within the above range, the productivity of BT relative to the volume of the oxalic acid aqueous solution is high, and oxalic acid may be completely dissolved in water. In this case, the temperature of the oxalic acid aqueous solution may be maintained at 20 ~ 100 ℃, for example, 50 ~ 90 ℃. The aqueous solution of the barium chloride solution and the titanium tetrachloride solution in the form of a mixed solution or separately sprayed onto the oxalic acid solution may be added dropwise for 1 to 3 hours. This dropping time can be achieved by adjusting the injection speed of the nozzle. The injection nozzle may use a hydraulic or two-fluid nozzle depending on the flow of the fluid, and the use of the hydraulic nozzle may be more advantageous in terms of convenience or in obtaining a uniform precipitate. As the hydraulic nozzle, a full cone, a hollow cone, a flat, or the like may be used. As such, a process of generating BTO [BaTiO (C ₂ O ₄ ) ₂ .4H ₂ O] by adding an aqueous barium chloride solution and an aqueous titanium tetrachloride solution to the oxalic acid solution may be represented as in Scheme 1 below.

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

Next, the produced BTO may be aged, filtered, and washed with water (S2). It may be advantageous in terms of productivity that the aging time is 0.5 to 2 hours. Here, filtration means the process of separating only solid-state BTO from the BTO containing slurry using a centrifugal separator specifically. Thereafter, the filtered BTO may be washed with excess water until the pH of the washing liquid is neutral.

Then, wet grinding the BTO obtained through the above process (BTO wet grinding step, S3). Here, the wet grinding means a method in which BTO is mixed with a predetermined medium and put into a wet grinding machine such as a beads mill, a ball mill, an attrition mill, and the like. Here, the medium means an organic medium such as alcohol or water such as deionized water, and the use of an organic medium is advantageous in terms of crushing efficiency or particle size, but has a disadvantage of increasing cost. This simplifies the process and has the advantage of reducing costs. When water is used as the medium, its amount may be 1 to 10 parts by weight based on 1 part by weight of BTO. When the amount of water used is within the above range, the viscosity is moderate, so that grinding is easy, and the productivity of BTO is high relative to the volume of water. Grinding time needs to be appropriately controlled due to the difference in grinding force depending on the grinding facility, it may be 10 ~ 300 minutes when using a bead mill. By controlling the grinding time as described above, the particle size of the final product BT powder can be properly adjusted. Nitrogen-containing additives such as ammonia can be added during this wet grinding process, which can solve the problem of acidification of the mixture before and after grinding, high viscosity of the slurry after grinding, and reduction of the dielectric properties of the powder due to the presence of chlorine ions in the produced BTO. have.

Next, the wet milled BTO is dried at a temperature of 400 ° C. or lower to remove the used medium (BTO drying step, S4). As a result, dried BTO powder is obtained. In this case, it is natural that the drying temperature should be above the boiling point of the medium in order to evaporate and remove the medium used.

Subsequently, the BTO powder is charged into a heating furnace, and then subjected to a first heat treatment at 920 to 950 ° C. to produce barium titanate (BT) (first calcination step, S5). When the primary heat treatment temperature is out of the above range, barium titanate having a target particle size (ie, an average particle diameter of 280 to 320 nm) cannot be obtained. In the first calcination step (S5), impurities including water and / or carbon may be removed. The temperature increase rate from the drying temperature of the BTO drying step (S4) to the first heat treatment temperature of the first calcination step (S5) may be 0.5 ~ 10 ℃ / min, for example 1 ~ 5 ℃ / min. If the temperature increase rate is within the above range, the productivity of BT is high, the temperature distribution is uniform, and the particle size of the BT powder is uniform. By performing the first calcination step (S5) as described above, the BT and the tens to hundreds of nm size BT through the process as shown in the following reaction scheme 2 to 4 by removing the excess carbon dioxide and water present in the crystal water of the BTO crystals Get powder.

Scheme 2

BaTiO (C ₂ O ₄ ) ₂ 4H ₂ O → BaTiO (C ₂ O ₄ ) ₂ + 4H ₂ O

Scheme 3

BaTiO (C ₂ O ₄ ) ₂ + 1/2 O ₂ → BaCO ₃ + TiO ₂ + 2CO ₂

Scheme 4

BaCO ₃ + TiO ₂ → BaTiO ₃

Sagger or Tray may be used as a heating furnace for heat treatment of the dried BTO powder. Here, Sagger means a refractory soil container. The sagger may be, for example, a cuboid shaped container having a square bottom surface.

Thereafter, the first BT powder is pulverized through the first calcination step S5 to obtain a first BT powder (BT crushing step S6). However, this BT grinding step (S6) may be omitted. The BT grinding step S6 may be performed by wet grinding using a mill such as a beads mill, an attention mill, and a ball mill with a predetermined medium, It may also be performed by dry grinding using friction between the raw materials or friction with the pulverizer without using a medium such as a jet mill and a disk mill. The BT grinding step S6 is for separating (ie, breaking) large BT particles into small BT particles. In the BT grinding step (S6), the destruction of the particles is caused to generate a large amount of fine powder, thereby widening the particle size distribution and lowering the crystallinity.

Next, when the BT grinding step (S6) is performed by wet grinding, the wet milled BT is dried at a temperature of 400 ° C. or less to remove the used medium (first BT drying step, S7). As a result, a dried first BT powder is obtained. The first BT powder may have an average particle diameter of 280 ~ 320nm and the fine powder content of 5 ~ 10% by weight. The average particle diameter of the first BT powder has a close correlation with the primary heat treatment temperature of the first calcination step (S5), and accordingly sets a target average particle diameter of the first BT powder first, and then the target average. The primary heat treatment temperature may be determined to achieve a particle diameter.

On the other hand, when the BT grinding step (S6) is performed by dry grinding, the first BT drying step (S7) can be omitted.

Hereinafter, the phenomenon occurring in the first calcination step S5 and the BT grinding step S6 will be described in detail with reference to FIG. 2.

FIG. 2 shows a series of processes in which barium titanyl oxalate (BTO) is converted to barium titanate (BT).

Referring to FIG. 2, in the first calcination step (S5), BTO is thermally decomposed to generate barium titanate particles BT1, and at this time, barium titanate particles (barium titanate particles are removed from the BTO while impurities (water vapor and / or carbon dioxide) are removed). An oxygen deficient layer ('VL' in FIG. 3) is formed in BT1). Thereafter, the barium titanate particles BT1 are grain-grown and selectively necked to form aggregates and barium titanate particles BT2 having a larger particle size than these and optionally aggregated. The oxygen depletion layer has a high activity against grain growth, and when the barium titanate particles (BT1) are used in the dielectric layer of the multilayer capacitor, abnormal grain growth may occur during chip firing. Also referred to. Accordingly, the barium titanate particles BT1 have a large amount of grain growth in the oxygen deficient layer and a small amount of grain growth in the remaining portions, resulting in an overall nonuniform grain growth (this is called abnormal grain growth). Is converted to). Thereafter, the barium titanate particles BT2 are necked to each other to form the aforementioned aggregate. Subsequently, the agglomerates are separated into smaller barium titanate particles BT3 in the BT milling step S6 to form fine powder FP, wherein the oxygen depletion layer contained in the barium titanate particles BT3 is external. Is exposed. As a result, barium titanate powder (BT3 + FP) having a high fine powder content is obtained. In the present specification, the "fine powder content" refers to the content of fine particles having a particle diameter of 70 nm or less contained in the barium titanate (BT) powder.

Then, referring again to Figure 1, the first BT powder is heat-treated at 820 ~ 890 ℃ secondary (second calcination step, S8). If the secondary heat treatment temperature is less than 820 ° C., there is almost no secondary heat treatment effect. If the secondary heat treatment temperature is higher than 890 ° C., the fine powder content in the final BT powder after disintegration is high and the crystallinity is also low. The temperature increase rate from the drying temperature of the first BT drying step S7 to the secondary heat treatment temperature of the second calcination step S8 may be 0.5 to 10 ° C./min, for example, 1 to 5 ° C./min. have. When the said temperature increase rate is within the said range (0.5-10 degreeC / min), productivity of barium titanate will be high, temperature distribution will become uniform, and the particle size of barium titanate powder will be uniform. Thus, by performing the second calcination step (S8), it is possible to obtain a fine barium titanate powder having a fine powder content, narrow particle size distribution and high crystallinity.

Next, disintegration of the BT passed through the second calcination step (S8) to obtain a second BT powder (BT disintegration step, S9). In this specification, “disintegration” means simply breaking the necking of particles without breaking the particles, and “crushing” means breaking one particle and separating it into two or more pieces. However, this BT disintegration step S9 may be omitted. The BT pulverization step S9 may be performed by wet pulverization using a pulverizer such as a beads mill, an attention mill, and a ball mill together with a predetermined medium. It may also be carried out by dry pulverization using friction between the raw materials or friction with the crusher without using a medium such as a jet mill and a disk mill. The BT disintegration step (S9) is for solving the aggregation between the particles of the BT powder. In the case of using the BT disintegration step (S9), if the equipment having a high disintegration efficiency is used, particle breakage is caused and a large amount of fine powder is generated, which may result in a narrow particle size distribution and a decrease in crystallinity. It is desirable to lower the breaking strength to break only the necking of the particles without breaking the particles themselves.

Finally, when the BT disintegration step S9 is performed by wet disintegration, the wet disintegration BT is dried at a temperature of 350 ° C. or less to remove the used medium (second BT drying step, S10). . As a result, a dried second BT powder is obtained. The second BT powder may have a fine powder content of 3.5% by weight or less.

On the other hand, when the BT disintegration step S9 is performed by dry disintegration, the second BT drying step S10 may be omitted.

Hereinafter, the phenomenon occurring in the barium titanate in the secondary calcination step S8 and / or the disintegration step S9 will be described in detail with reference to FIG. 3.

Referring to FIG. 3, in the secondary calcination step S8 and / or the disintegration step S9, oxygen is replenished in the oxygen deficiency layer VL included in the barium titanate particles BT3 (that is, BaTiO). _3-x + 1 / 2O _2x → BaTiO ₃ , real number with 0 <x <3). Accordingly, the barium titanate particles BT4 in which abnormal grain growth is suppressed are formed by removing the oxygen depletion layer VL. Thereafter, the fine powders FP are recombined or redoped with the barium titanate particles BT4 to form barium titanate particles BT5 having a low fine content. Specifically, the recombination or redistribution may be performed by rearranging the fines FP after migration to the barium titanate particles BT4.

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 1-4 and Comparative Examples 1-4

(BTO generation and ripening)

1320 l of barium chloride solution at 1 mol / l concentration and 1200 l of titanium tetrachloride solution at 1 mol / l concentration were mixed well in a 4M ³ glass-lined reactor to form a mixed aqueous solution. Thereafter, the mixed aqueous solution was sprayed at a rate of 2.5 l / min using a full con type nozzle to 2520 l of an oxalic acid aqueous solution of 1 mol / l concentration, filled in a 6M ³ reactor. A diaphragm pump was used to supply the mixed aqueous solution during nozzle spraying. At this time, the oxalic acid solution was sprayed while stirring with a stirrer, the stirring speed of the stirrer was maintained at 150rpm, the temperature of the oxalic acid solution was maintained at 70 ℃.

After the dropwise addition of the mixed aqueous solution for 2 hours, the reaction temperature was maintained for 1 hour, and then air-cooled with stirring to mature for 1 hour. As a result, a slurry containing BTO was obtained.

(Filtration and washing of the resulting BTO slurry)

The BTO slurry prepared above was filtered with a centrifugal separator and washed with excess water so that the pH of the washing solution was 6 or more to obtain BTO.

(Wet grinding and drying of the produced BTO)

50 kg of the BTO, 250 kg of deionized water, and 0.5 kg of 29% by volume ammonia water (8. 4 mol parts relative to 100 mol parts of BTO) were added to a mixing tank and stirred to form a slurry. At this time, the pH of the slurry was 9.3. Thereafter, the BTO was wet milled with a 20 L horizontal beads mill (medium: deionized water) such that the maximum particle size was 5 µm or less. After grinding, the slurry had a pH of 5.1 and a viscosity of 1800 cP. Thus obtained BTO slurry was dried in an oven at a temperature of 200 ℃ for 12 hours to prepare a BTO powder.

(1st calcination, wet grinding and drying)

After the dried BTO powder was put into an electric furnace, the target average particle diameter of the BT produced after the first calcination was set to 300 nm, and the first heat treatment was performed at 950 ° C. for 2 hours. As a result, BT-A powder was obtained. Thereafter, the BT-A powder was wet pulverized for 30 minutes at a speed of 5 m / s (ie, 1500 rpm) with a 20 L horizontal beads mill (medium: deionized water). The BT slurry formed after pulverization was dried for 24 hours at 150 ℃ oven. As a result, a first BT powder was obtained.

(Second calcination, wet crushing and drying)

After the first BT powder was added to the electric furnace, the second heat treatment was performed for 2 hours while changing the heat treatment temperature in the temperature range of 820 ~ 920 ℃ according to each Example and Comparative Example. As a result, BT-B powder was obtained. Thereafter, the BT-B powder was wet pulverized at a circumferential speed of 5 m / s (ie, 1500 rpm) with a 20 L horizontal beads mill (medium: deionized water). At this time, the wet disintegration was terminated when the D 50 of the barium titanate measured by the particle size analyzer (Malvern, mastersizer-2000) reached 0.85 to 0.87 μm. The BT slurry formed after the wet disintegration was dried for 24 hours at 150 ℃ oven. As a result, a second BT powder was obtained. In Comparative Example 1, however, the second calcination and subsequent steps were omitted.

Evaluation example

Evaluation Example 1 Characterization of Barium Titanate (BT-B) Powders After Secondary Calcining and Before Wet Disintegration

The average particle diameter, specific surface area, average necking angle, full width at half maximum (FWHM) and crystallinity (c / a) and the presence or absence of fine powder was measured or evaluated in the following manner, and the results are shown in Table 1 below.

(Average particle size, average necking angle and derivative presence)

The presence of the average particle diameter, average necking angle and derivative is calculated or observed by using an image analysis program (Image Pro Plus ver 4.5) after taking a scanning electron microscope (SEM) photograph 50,000 times using a Jeol JSM-7400F. It was. In this case, the number of BT-B particles measured was 800 or more. In calculating the average particle diameter, the particle diameter of each BT-B particle was calculated by the average of the long axis and the short axis of each BT-B particle.

(Crystallinity (c / a) and half width)

The crystallinity (c / a) is measured at 2θ = 44 to 46.5 degrees (°) under conditions of a speed of 2 sec / step and a step size of 0.02 at 40 kV and 200 mA using XRD (D / Max 2000 series of Rigaku Corporation). The d-spacing values of the a-axis and the c-axis of the crystal lattice were obtained. The half width was obtained by precise analysis of the (111) plane and the (222) plane in the same manner as the crystallinity measuring method. However, 2θ regions of the (111) plane and the (222) plane were 38 to 40 degrees (°) and 83 to 84 degrees (°), respectively.

(Specific surface area)

The specific surface area was analyzed using a specific surface area meter (Mountech, Macsorb HM-1220).

On the other hand, in order to help the understanding of the average necking angle, a SEM photograph of the BT-B powder prepared in Example 2 was taken and shown in FIG. Referring to FIG. 4, it can be seen that two barium titanate particles of the BT-B powder prepared in Example 2 are necked to each other. In this case, the necking angle is represented by theta (θ), and it can be seen from Table 1 that the value is 87 degrees (°).

Table 1

	Secondary calcination temperature (℃)	Average particle size (nm)	Specific surface area (m ² / g)	Average necking angle (°)	Half width		Crystallinity (c / a)	Differential presence
	Secondary calcination temperature (℃)	Average particle size (nm)	Specific surface area (m ² / g)	Average necking angle (°)	(111) flat	(222) flat	Crystallinity (c / a)	Differential presence
Comparative Example 1	-	310	3.76	107	0.124	0.146	1.0100	existence
Example 1	820 ± 5	312	3.36	79	0.108	0.138	1.0105	existence
Example 2	840 ± 5	315	3.24	87	0.107	0.137	1.0110	Nonexistence
Example 3	860 ± 5	317	3.12	90	0.107	0.137	1.0110	Nonexistence
Example 4	890 ± 5	317	2.94	96	0.107	0.137	1.0110	Nonexistence
Comparative Example 2	900 ± 5	322	2.88	104	0.106	0.137	1.0110	Nonexistence
Comparative Example 3	910 ± 5	323	2.82	108	0.103	0.136	1.0110	Nonexistence
Comparative Example 4	920 ± 5	344	2.76	109	0.103	0.136	1.0110	Nonexistence

Referring to Table 1, the barium titanate (BT-B) powder prepared in Examples 1 to 4 has a smaller average particle diameter and average necking angle than the barium titanate (BT-B) powder prepared in Comparative Examples 2 to 4. The degree of abnormal grain growth appeared to be small. However, the specific surface area and the half width decreased generally as the secondary calcination temperature increased, and the derivative did not exist when the secondary calcination temperature was above 840 ℃.

Evaluation Example 2: Characterization of Barium Titanate Powder (Second BT Powder) After Secondary Calcining, Wet Disintegration, and Drying

With the secondary heat treatment temperature adopted in the second calcination, the particle size (D50), specific surface area, full width at half maximum (FWHM), crystallinity (c / a) and fine powder content of the prepared second BT powder In the same manner as measured or evaluated, the results are shown in Table 2 below.

(D50 and fine powder content)

D50 and fine powder content was calculated by using an image analysis program (ImagePro Plus ver 4.5) after scanning electron microscopy (SEM) of 50,000 times using a Jeol JSM-7400F. In this case, the number of the measured second BT particles was 800 or more. In the calculation of D50, the particle diameter of each second BT particle was calculated as an average of the long axis and the short axis of each second BT particle. Here, D50 refers to the particle size of the particles corresponding to 50% of the total number of particles when the measured particles are arranged in order from smallest to largest. The fine powder content refers to the percentage of the area occupied by the fine powder having a particle size of less than 70nm of the total area occupied by all the BT particles in the SEM image.

(Specific surface area, half width and crystallinity (c / a))

The specific surface area, half width, and crystallinity (c / a) were measured in the same manner as in Evaluation Example 1.

TABLE 2

	Secondary calcination temperature (℃)	D50 (nm)	Specific surface area (m ² / g)	Half width		Crystallinity (c / a)	Fine content (%)
	Secondary calcination temperature (℃)	D50 (nm)	Specific surface area (m ² / g)	(111) flat	(222) flat	Crystallinity (c / a)	Fine content (%)
Comparative Example 1	-	0.87	3.79	0.124	0.146	1.0100	6.6
Example 1	820 ± 5	0.85	3.47	0.110	0.140	1.0103	3.3
Example 2	840 ± 5	0.86	3.30	0.107	0.137	1.0105	0.7
Example 3	860 ± 5	0.87	3.38	0.108	0.137	1.0105	1.2
Example 4	890 ± 5	0.87	3.45	0.110	0.139	1.0105	2.8
Comparative Example 2	900 ± 5	0.86	3.58	0.120	0.140	1.0100	5.6
Comparative Example 3	910 ± 5	0.87	3.75	0.123	0.146	1.0100	6.1
Comparative Example 4	920 ± 5	0.87	3.81	0.124	0.146	1.0100	6.9

Referring to Table 2, the barium titanate powder prepared in Examples 1 to 4 (second BT powder) has a smaller D50 or the same as the barium titanate powder prepared in Comparative Examples 1 to 4 (second BT powder). In addition, the specific surface area and half width are small, the crystallinity is high, and the fine powder content is low.

Meanwhile, SEM photographs of the barium titanate powder (second BT powder) prepared in Example 2 and SEM photographs of the barium titanate powder (first BT powder) prepared in Comparative Example 1 were taken, and FIGS. 5 and 6, respectively. Indicated. 5 and 6, the barium titanate powder prepared in Example 2 (second BT powder) (see FIG. 5) is the barium titanate powder prepared in Comparative Example 1 (first BT powder) (see FIG. 6). Compared with, the content of fine powder is very small, and the shape of the particles also has a regular shape of spherical shape.

Evaluation Example 3: Measurement of Particle Size Distribution

Particle size distribution of barium titanate powder (second BT powder) prepared in Example 2 and particle size distribution of barium titanate powder (first BT powder) prepared in Comparative Example 1 using a particle size analyzer (Mastersizer-2000, Malvern) Distribution was measured and the result is shown in FIG. Referring to FIG. 7, the barium titanate powder (second BT powder) prepared in Example 2 was found to have a smaller particle size distribution than the barium titanate powder (first BT powder) prepared in Comparative Example 1.

Although the present invention has been described with reference to the drawings and embodiments, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims

Preparing an aqueous solution of barium chloride (BaCl 2 ) and an aqueous solution of titanium tetrachloride (TiCl 4 ) (preparing a raw material solution);

Adding the aqueous solution to an aqueous solution of oxalic acid (H 2 C 2 O 4 ) to produce barium titanyl oxalate [BaTiO (C 2 O 4 ) 2 .4H 2 O] (hereinafter simply referred to as BTO). step);

Wet grinding the BTO (BTO wet grinding step);

Drying the wet milled BTO to obtain a BTO powder (BTO drying step);

First heat treating the BTO powder at 920 to 950 ° C. to produce barium titanate (BT) (first calcination step); And

Method for producing a barium titanate powder comprising the second heat treatment (second calcination step) the BT at 820 ~ 890 ℃.
The method of claim 1,

Between the BTO generation step and the BTO wet grinding step,

Aging the generated BTO;

Filtering the aged BTO; And

Method for producing a barium titanate powder further comprises the step of washing the filtered BTO with excess water.
The method of claim 1,

Between the first calcination step and the second calcination step, the method for producing barium titanate powder further comprising the step of pulverizing the BT to obtain a first BT powder (BT grinding step).
The method of claim 3,

The first BT powder is a method for producing barium titanate powder having an average particle diameter of 280 ~ 320nm and fine powder content of 5 ~ 10% by weight (that is, the content of particles having a particle diameter of less than 70nm).
The method of claim 1,

After the second calcination step, a method for producing barium titanate powder further comprising the step of pulverizing the secondary calcined BT to obtain a second BT powder (BT crushing step).
Barium titanate powder produced by the method according to any one of claims 1 to 5.
The method of claim 6,

Barium titanate powder having a fine content of 3.5% by weight or less (ie, a content of particles having a particle diameter of 70 nm or less).