KR20090118748A - A method of preparing highly crystalline barium-titanate fine powder by oxalate process and highly crystalline barium-titanate fine powder prepared by the same - Google Patents

Abstract

PURPOSE: A method for preparing highly crystalline barium titanate fine powder by oxalate process is provided to improve crystallinity of the barium titanate fine powder. CONSTITUTION: A method for preparing highly crystalline barium titanate fine powder by oxalate process comprises the following steps of: preparing a barium chloride(BaCl2) aqueous solution and titanium tetrtachloride(TiCl4) aqueous solution; dropping the aqueous solutions of barium chloride and titanium tetrtachloride into an oxalic acid(H2C2O4) aqueous solution in order to produce a barium titanyl oxalate(BaTiO(C2O4)2·4H2O) crystal lump; wet fine grinding the barium titanyl oxalate crystal lump; drying the ground barium titanyl oxalate powder; and heat-treating the dried barium titanyl oxalate powder to produce a barium titanate crystal lump. Governing factor of crystallinity is controlled for the barium titanate in the heat-treating step.

Description

A method of preparing highly crystalline Barium-Titanate fine powder by oxalate process and highly crystalline Barium-Titanate fine powder prepared by the same}

The present invention relates to a method for preparing a highly crystalline barium titanate powder and to a highly crystalline barium titanate powder prepared by the method, and more particularly, to titanic acid by an oxalate process having a uniform particle size distribution and improved crystallinity. The present invention relates to a method for producing barium fine powder and to a fine barium titanate powder produced by the method.

The fine barium titanate powder is conventionally manufactured by solid phase reaction of heat treatment at high temperature by mixing titanium dioxide (TiO ₂ ) and barium carbonate (BaCO ₃ ), but recently, miniaturization of a multilayer ceramic capacitor (MLCC) High dielectric constant, dielectric thinning and high lamination), low temperature plasticization, high frequency and high performance, etc., require high purity / composition uniformity, fine grain / particle uniformity, non-aggregation / high dispersion, etc. It is manufactured by the synthesis method. In particular, even when the multilayer ceramic capacitor is thin and highly laminated, a fine barium titanate powder having a uniform particle size distribution and high crystallinity is required even when the particle diameter is 200 nm or less.

As a prior art for manufacturing such fine barium titanate powder, a method of manufacturing ceramic powder having a perovskite structure, a ceramic powder having a perovskite structure, a ceramic electronic component, and the manufacture of Korean Patent Publication No. 2007-0031969 Method, and multilayer ceramic capacitor and its manufacturing method. " The method presented here is a solid phase method, in which barium titanate is synthesized, and then the synthesized fine barium titanate powder is put into a sealed heating furnace filled with water or a barium hydroxide aqueous solution having a pH of 7 or higher and heat treated. In order to perform such a method, since a redrying process must be added after synthesis, production costs are increased and production yields are deteriorated. In addition, the crystallinity (c / a) is also 1.01.0 or less when the particle diameter is 200nm class, and does not meet the crystallinity of 1.01 or more required to manufacture a high capacity miniaturized multilayer ceramic capacitor, as well as low purity and composition nonuniformity There is a problem in that the fundamental limitations of the solid state reaction method such as particle size nonuniformity cannot be overcome. In addition, there is a problem in that the method cannot produce barium titanate having a high crystal grain size of 100 nm.

In addition, the Republic of Korea Patent Publication No. 2005-0045580 discloses a "method of producing a composite oxide by gravity-free high temperature heat treatment". Although the barium titanate having a particle diameter of 100 nm was prepared by the preparation method, the crystallinity (c / a) of the barium titanate was about 1.005, which was very low.

An object of the present invention is to provide a method for producing a fine barium titanate powder with improved particle size uniformity and a fine barium titanate powder produced by the method.

Still another object of the present invention is to provide a method for preparing fine barium titanate powder with improved crystallinity and a fine barium titanate powder prepared by the method.

The present invention to solve the above problems,

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

(b) spraying the aqueous solution and dropwise adding it to an aqueous solution of oxalic acid (H ₂ C ₂ O ₄ ) to generate a barium titanyl oxalate [BaTiO (C ₂ O ₄ ) ₂ .4H ₂ O] crystal mass;

(c) wet milling the barium titanyl oxalate crystal mass;

(d) drying the wet milled barium titanyl oxalate powder; And

(e) first heat treating the dried barium titanyl oxalate powder to produce barium titanate crystal mass;

The degree of crystallization of barium titanate is controlled by adjusting the crystallinity factor (Governing factor of crystallinity) during the first heat treatment of step (e), wherein the crystallinity factor (m / A) of the heating furnace is subjected to the first heat treatment It provides a method for producing a fine barium titanate powder defined by the weight (m) of the dried barium titanyl oxalate powder filled in the heating furnace per unit area (A).

According to one embodiment of the invention, the furnace is a Sagger or Tray.

According to another embodiment of the present invention, the crystallinity dominating factor is 0.52 g / cm ² It is as follows.

According to another embodiment of the present invention, the method for producing the barium titanate fine powder increases the crystallinity governing factor by performing gas discharge before the first heat treatment.

According to another embodiment of the present invention, the concentration of the barium chloride solution and titanium tetrachloride solution is 0.2 ~ 2.0 mol / l, respectively.

According to another embodiment of the present invention, the method for producing the barium titanate fine powder, between the step (b) and (c), the step of ripening the produced barium titanyl oxalate crystals, the aged barium Filtering the titanyl oxalate crystals, and washing the filtered barium titanyl oxalate crystals with excess water.

According to another embodiment of the present invention, the wet grinding of step (c) is performed by adding a nitrogen-containing additive selected from ammonia, amines, ammonium compounds, and amino acids.

According to another embodiment of the present invention, the drying of step (d) is carried out at a temperature of 400 ° C. or lower as a temperature higher than the boiling point of the solvent used for the wet grinding of step (c).

According to another embodiment of the present invention, the first heat treatment of step (e) is performed at a temperature in the range of 800 ~ 1000 ℃.

According to another embodiment of the present invention, the temperature increase rate from the drying temperature of the step (d) to the first heat treatment temperature of the step (e) is 0.5 ~ 10 ℃ / min.

According to another embodiment of the present invention, in the method for preparing the barium titanate fine powder, after the step (e), the barium titanate crystal mass produced by the first heat treatment is secondary at a temperature below the first heat treatment temperature. Further comprising the step of heat treatment.

According to another embodiment of the present invention, the method for producing the barium titanate fine powder, the step of grinding the barium titanate crystal mass produced by the first heat treatment between the first heat treatment and the second heat treatment of the step (e) It further includes.

According to another embodiment of the present invention, the method for preparing the barium titanate fine powder further includes adding barium carbonate (BaCO ₃ ) between the first heat treatment and the second heat treatment of step (e).

According to another embodiment of the present invention, the method for producing the barium titanate fine powder, the secondary heat treatment is carried out at a temperature of 600 ~ 1000 ℃ range.

According to another embodiment of the present invention, the rate of temperature increase to the second heat treatment temperature after the first heat treatment in the step (e) is 0.5 ~ 10 ℃ / min.

According to another embodiment of the present invention, the method may further include grinding the barium titanate crystal mass subjected to the second heat treatment.

In addition, the present invention to solve the above problems,

It provides a fine barium titanate powder prepared by the method of any one of the above embodiments.

According to the present invention, there can be provided a method for producing a barium titanate fine powder having improved particle size uniformity and a fine barium titanate powder produced by the method.

In addition, according to the present invention, there can be provided a method for producing barium titanate fine powder with improved crystallinity and a fine barium titanate powder prepared by the method.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart for explaining step by step the production method of fine barium titanate powder according to an embodiment of the present invention.

Hereinafter, a method of preparing the barium titanate fine powder according to one embodiment of the present invention will be described.

First, an aqueous solution of barium chloride (BaCl ₂ ) and an aqueous solution of titanium tetrachloride (TiCl ₄ ) are prepared (S10). Aqueous solution of barium chloride is usually used by dissolving BaCl ₂ · 2H ₂ O in water, and the preferred concentration range is 0.2 to 2.0 mol / l. When the concentration of the barium chloride solution is less than 0.2 mol / l, the productivity of the barium titanate to be described later compared to the volume of the barium chloride solution is not preferable, and when the concentration exceeds 2.0 mol / l solubility of barium chloride in water It is not preferable because barium chloride may precipitate out of the range. Titanium tetrachloride aqueous solution is usually used by diluting a high concentration of titanium tetrachloride solution, the preferred concentration range is 0.2 ~ 2.0 mol / l. If the concentration of the aqueous solution of titanium tetrachloride is less than 0.2 mol / l, the productivity of the barium titanate is not low relative to the volume of the aqueous solution of titanium tetrachloride, and if the concentration exceeds 2.0 mol / l, the solubility range of titanium tetrachloride in water is limited. Titanium tetrachloride is likely to precipitate outwardly, which is undesirable. The barium chloride aqueous solution and the titanium tetrachloride aqueous solution are preferably mixed at a ratio of 1 to 1.5 on a molar ratio (barium chloride / titanium tetrachloride), and more preferably at a ratio of 1 to 1.1. If the molar ratio is less than 1, the molar ratio of barium titanate, which is the final product, is very unlikely to be lowered to less than 1, and it is not preferable. If the molar ratio exceeds 1.5, the second phase (other phases other than barium titanate, Ba ₂ TiO ₉ ) is produced for example, which is undesirable. When the molar ratio of barium titanate, which is the final product, is lowered to less than 1, it is not preferable because the formation of the second phase and abnormal grain growth are caused.

Next, a mixed aqueous solution of the aqueous barium chloride solution and titanium tetrachloride solution or each of these aqueous solutions is added dropwise to the aqueous solution of oxalic acid (H ₂ C ₂ O ₄ ) using a high-speed jet nozzle to produce barium titanyl oxalate [BaTiO (C ₂ O). ₄ ) ₂ · 4H ₂ O] to produce a crystal mass (S20). At this time, the oxalic acid aqueous solution is preferably used in an amount larger than the barium chloride aqueous solution or titanium tetrachloride aqueous solution. The preferred concentration range of the oxalic acid aqueous solution is 0.2 to 5.0 mol / l. When the concentration of the aqueous solution of oxalic acid is less than 0.2 mol / l, the productivity of barium titanate is not preferable compared to the volume of the aqueous solution of oxalic acid, and when the concentration exceeds 5.0 mol / l, the possibility of out of the solubility of oxalic acid in water may be exceeded. This is not desirable. In this case, the temperature of the oxalic acid aqueous solution is preferably maintained at 20 to 100 ° C, more preferably at 50 to 90 ° C. It is preferable that the time for dropping the barium chloride aqueous solution and the titanium tetrachloride aqueous solution in the form of a mixed solution or separately by nozzle spraying to the oxalic acid aqueous solution is 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, it is more advantageous to use a hydraulic nozzle in terms of convenience or to obtain 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 adding a mixed solution containing barium (Ba) and titanium (Ti) ions to oxalic acid to form barium titanyl oxalate [BaTiO (C ₂ O ₄ ) ₂ .4H ₂ O] crystal mass is shown in the following scheme. It may be displayed as 1.

[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 barium titanyl oxalate crystals are aged, filtered, and washed with water (S30). It is advantageous in terms of productivity that the aging time is performed for 0.5 to 2 hours. Here, filtration means the process of isolate | separating only solid barium titanyl oxalate from the barium titanyl oxalate containing slurry using a centrifugal separator specifically. Thereafter, the filtered barium titanyl oxalate is washed with excess water until the pH of the washing liquid becomes neutral.

Thereafter, the barium titanyl oxalate crystal mass obtained by the above process is wet milled (S40). Here, the wet grinding is a method in which the barium titanyl oxalate crystal mass is added to a wet mill such as a beads mill, a ball mill, an attrition mill, and the like, together with a predetermined solvent to grind. Say Here, the solvent means an organic solvent such as alcohol or water such as deionized water, and the use of the organic solvent is advantageous in terms of crushing efficiency or particle size but increases in cost, and water is used. This simplifies the process and has the advantage of reducing costs. When water is used as the solvent, the amount thereof is preferably 1 to 10 parts by weight based on 1 part by weight of barium titanyl oxalate. When the amount of water used is less than 1 part by weight, it is not preferable because it is impossible to grind due to an increase in viscosity, and when the amount of use exceeds 10 parts by weight, the productivity of the barium titanyl oxalate particles is not low relative to the volume of water. The grinding time needs to be appropriately controlled due to a difference in grinding power depending on the grinding equipment, but when using a bead mill, it is usually preferably 10 to 300 minutes. By controlling the grinding time in this way, the particle size of the fine barium titanate powder, which is the final product, can be properly adjusted. It is desirable to add nitrogen-containing additives during this wet grinding process, thereby reducing acidity of the powder due to acidification of the mixture before and after grinding, high viscosity of the slurry after grinding, and the presence of chlorine ions in the produced barium titanyl oxalate. I can solve it. Here, as the nitrogen-containing additive, amines, ammonia, ammonium compounds, amino acids, and mixtures thereof may be used, and double ammonium compounds include ammonium hydroxide, ammonium carbonate, ammonium acetate, ammonium phosphate, ammonium oxalate, ammonium bicarbonate, and trimethyl. Ammonium hydroxide and the like can be used, and arginine, lysine and the like can be used as the amino acid. The content of such nitrogen-containing additive is preferably 0.5 to 20 mol parts with respect to 100 mol parts of barium titanyl oxalate. If the content is less than 0.5 mole parts, such as acidification and high viscosity of the slurry after pulverization, and if more than 20 mole parts, the titanium component is released from the barium titanyl oxalate crystals, the barium / titanium molar ratio is unbalanced Occurs.

Next, the wet milled barium titanyl oxalate is dried at a temperature of 400 ° C. or less to remove the used solvent (S50). As a result, dried barium titanyl oxalate powder is obtained. In this case, it is natural that the drying temperature should be above the boiling point of the solvent in order to evaporate and remove the solvent used.

Next, the dried barium titanyl oxalate powder is first heat-treated (S60). Primary heat treatment is carried out at a temperature in the range from 800 to 1000 ° C. When the heat treatment temperature is less than 800 ° C, barium titanate is hardly formed and is not preferable. When the heat treatment temperature is higher than 1000 ° C, the particle size of the fine barium titanate powder formed is too large, which is not preferable. The temperature increase rate from the drying temperature to the primary heat treatment temperature is preferably 0.5 to 10 ° C / min, more preferably 1 to 5 ° C / min. If the temperature increase rate is less than 0.5 ℃ / min is not preferable because the productivity of barium titanate is lowered, if the temperature exceeds 10 ℃ / min is not preferable because the temperature distribution is not uniform and the particle size of the fine barium titanate powder becomes uneven. By performing the first heat treatment as described above, barium titanyl oxalate crystals remove water and excess carbon dioxide present in the crystallized water and proceed through the same process as in Schemes 2 to 4 below. Get fine 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

For the first heat treatment of the dried barium titanyl oxalate powder, a sagger or a tray as shown in FIG. 2 may be used. Here, Sagger means a refractory soil container. Referring to FIG. 2, the sagger is a cube-shaped container having a bottom surface of a square shape having both a horizontal length and a vertical length a. However, the present invention is not limited thereto, and other various forms and furnaces of various materials may be used for the first heat treatment. We control the crystallinity (c / a) of barium titanate, the final product, by adjusting the weight (m) of the dried barium titanyl oxalate powder filled in the furnace per unit area (A) of a furnace such as Sagger. It turns out that it can be controlled. Thus, by defining a governing factor of crystallinity (hereinafter referred to simply as crystallinity governing factor) of barium titanate as described below, it is possible to obtain a crystallinity (c / a) of barium titanate of a desired value by adjusting it.

[Equation 1]

It is preferable that the crystallinity governing factor (m / A) has a value of 0.52 g / cm ² or less. When the value exceeds 0.52 g / cm ² , the moisture present in the barium titanyl oxalate crystal and the carbon dioxide gas generated during synthesis are not easily discharged, which is not preferable.

Thereafter, it is preferable to grind the barium titanate crystal mass produced through the first heat treatment process (S70), but the grinding process may be omitted. In this case, grinding may be performed by wet grinding using a mill such as a beads mill, an attention mill, and a ball mill with a predetermined solvent, a jet mill and a disk mill ( Such as a disk mill, dry grinding using a collision between raw materials or friction with a grinder without using a solvent. In this case, the pulverization is for resolving the agglomeration of the fine particles of the barium titanate powder, and after the wet pulverization, a drying step is further required, but it is not necessary to use a specially limited facility for drying. In case of using the equipment with high crushing efficiency in this stage of crushing process, it is possible to break the particles and generate a large amount of fine powder, which may lower the particle size distribution and crystallinity. Lowering it is desirable to break only the necking of the particles without breaking the particles themselves.

In addition, although it is preferable to further add barium carbonate (BaCO ₃ ) to the barium titanate crystal produced through the first heat treatment (S70), the addition process of the barium carbonate may be omitted. The barium carbonate addition process may be performed in parallel with the barium titanate grinding process, or may be performed alone without the grinding process. Hereinafter, the case where the barium carbonate addition process is performed in parallel with the grinding process will be described. First, the molar ratio of barium / titanium (Ba / Ti) in barium titanate is measured by using an analyzer such as XRF, and then an appropriate amount of barium carbonate (BaCO ₃ ) is added to barium titanate according to the molar ratio to grind. For example, when the barium / titanium molar ratio is in the range of 0.997 to 0.999, barium carbonate is added in the range of 0.08 to 2.28 parts by weight relative to 100 parts by weight of barium titanate, and when the molar ratio is in the range of 0.999 to 1.001, the amount of barium carbonate is 0.08 to 1.5. It is added in the sub range, and the barium carbonate is added in the range of 0.08 to 0.76 parts by weight when the molar ratio is in the range of 1.001 to 1.103.

 Accordingly, grain growth is suppressed in the subsequent secondary heat treatment, so that the barium titanate fine powder has a more uniform particle size distribution and maintains a final barium / titanium molar ratio. However, if the barium / titanium molar ratio of barium titanate after the first heat treatment is within a desired range, it is not necessary to add additional barium carbonate, and further grinding is not necessary unless the interparticle bonding phenomenon of the fine barium titanate powder is noticeable.

Next, the barium titanate crystal produced by the first heat treatment is subjected to a second heat treatment (S80). This secondary heat treatment process is performed at a temperature below the primary heat treatment temperature. That is, the secondary heat treatment is carried out at a temperature in the range of 600 ~ 1000 ℃. If the heat treatment temperature is less than 600 ° C., it is not preferable because there is almost no secondary heat treatment effect. If the heat treatment temperature is higher than 1000 ° C., the particle size of the fine barium titanate powder formed is too large, which is not preferable. It is preferable that it is 0.5-10 degrees C / min, and, as for the temperature increase rate to the secondary heat treatment temperature after the said 1st heat processing, it is more preferable that it is 1-5 degrees C / min. When the temperature increase rate is less than 0.5 ° C / min, the productivity of the barium titanate is lowered, which is not preferable. When the temperature exceeds 10 ° C / min, the temperature distribution is not uniform, and the particle size of the fine barium titanate powder is uneven, which is not preferable. By performing the secondary heat treatment in this way, a fine barium titanate powder having a uniform particle size distribution and high crystallinity can be obtained.

Finally, the barium titanate crystals subjected to the secondary heat treatment may be further ground, which may be omitted.

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 1-14

(Generation and aging of barium titanyl oxalate crystal)

A mixed aqueous solution was prepared by mixing 1320 L of an aqueous solution of barium chloride at a concentration of 1 mol / L and 1200 L of titanium tetrachloride aqueous solution at a concentration of 1 mol / L in a 4M ³ glass-lined reactor. 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 having a concentration of 1 mol / L prepared 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 90 ℃.

 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 barium titanyl oxalate crystals was obtained.

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

The barium titanyl oxalate slurry prepared above was filtered through a centrifugal separator and washed with excess water to have a pH of 6 or more, thereby obtaining a barium titanyl oxalate crystal mass.

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

To 50 kg of the barium titanyl oxalate crystal mass, 250 kg of dehydrated ion and 0.5 kg of 29% by volume ammonia water (8.4 mole parts relative to 100 mole parts of barium titanyl oxalate) were added and the resulting slurry was stirred in a mixing tank. At this time, the pH of the slurry was 9.3. Thereafter, the barium titanyl oxalate crystal mass was wet-pulverized so that the maximum particle size was 5 µm or less with a horizontal bead mill of 20 L. After grinding, the slurry had a pH of 5.1 and a viscosity of 1800 cP. The barium titanyl oxalate slurry thus obtained was dried in an oven at a temperature of 200 ° C. for 12 hours, and then the chlorine ion content was measured. As a result of the measurement, the chlorine ion content was 200 ppm.

(Primary heat treatment)

The dried barium titanyl oxalate crystal mass (weight = m) was charged at 800-1000 ° C. in an electric furnace (that is, Sagger having a form similar to that of FIG. 2 and having a bottom area A of Table 1 for each example). The heat treatment was performed while changing the temperature and / or m / A for each embodiment in the temperature range and 0.1 / 1.72 m / A range. As a result, barium titanate crystal mass was obtained. The crystallization degree (c / a), average particle size and particle size distribution (D ₁₀ / D ₅₀ , D ₉₀ / D ₅₀ ) of the prepared barium titanate crystals were measured together with the temperature and m / A values adopted during the first heat treatment. Table 1 shows. In addition, an SEM photograph of the barium titanate crystal mass prepared in Example 1 was taken (x50,000) and is shown in FIG. 3. In addition, for each barium titanate crystals prepared in Examples 1 to 14, the crystallinity (c / a) graph with respect to the crystallinity dominating factor (m / A) is shown in Fig. 4.

The crystallinity (c / a) is a crystal lattice by measuring 2Θ = 44 ~ 46.5 으로 under conditions of a speed of 2 sec / step and a step size of 0.02 at 40 kV, 200 mA using XRD (Dig Max 2000 series of Rigaku) The d-spacing values of the a-axis and the c-axis of are the indexes for evaluating the crystallinity of barium titanate using these ratios. In addition, the average particle diameter, and D ₁₀ / D ₅₀ and D ₉₀ / D _{50, which} are indicators of the particle size distribution, were taken by using a scanning electron microscope (SEM) image 30,000 times using a Jolm JSM-7400F, and then used an image analysis program. The size of the barium titanate particles was calculated from the average of the major and minor axis of the barium titanate particles, and the number of measured barium titanate particles was 800 or more. Here, the larger the D ₁₀ / D ₅₀ and the smaller the D ₉₀ / D ₅₀ , the better the particle size distribution. Where D _{10 ,} D _{50 , and} D ₉₀ refer to the particle diameters corresponding to 10%, 50%, and 90% of the total number of particles when the measured particles are arranged in order from smallest to largest. .

In Table 1, the c / a value is "-" when XRD analysis is observed as a cubic phase rather than a tetragonal phase, and thus the value cannot be measured.

Referring to Table 1 and FIG. 4, it can be seen that the crystallinity (c / a) is rapidly changed on the basis of the value of the crystallinity degree governing index (m / A) of 0.52 g / cm ² . In other words, when the value was 0.52 g / cm ² or less, the crystallinity was very high (> 1.008), but when it exceeds 0.52 g / cm ² , the crystallinity rapidly decreased. The result is that the lower the crystallinity governing index (m / A), the thinner the laminated thickness of the dried barium titanyl oxalate crystal agglomerate filled in Sagger during the first heat treatment, thereby facilitating the release of moisture and carbon dioxide gas. Judging. Further, in Example 1 Compared to 1-4 and Examples 11-14, even if the Sagger area (A) is different (i.e., A, each 87cm ² and 870cm ²⁾ equal to the crystallization dominated index (m / A) It can be seen that the value of crystallinity (c / a) hardly changes. In particular, in the case of Example 17, the value of crystallinity (c / a) was found to be highest (c / a = 1.0106).

Examples 18-23

Barium titanate crystal mass was prepared in the same manner as in Examples 1 to 17, except that gas was first discharged in a temperature range of 400 to 650 ° C. before the first heat treatment. However, in the case of gases, the crystallinity index controlled stylized fixing the value of (m / A) to 0.52g / cm ^2, it was adjusted to 0.69g / cm ² at the time of primary thermal treatment. That is, before the first heat treatment after the gas discharge, the gas discharged powder was filled again so that the crystallinity control factor became 0.69. In this case, the crystallinity, average particle diameter, and particle size distribution of the barium titanate particles obtained above were measured by the above-described measuring method, and the results are shown in Table 2 below.

In Table 2, the c / a value is "-" when XRD analysis is observed as a cubic phase rather than a tetragonal phase, and thus the value cannot be measured. In addition, the residual gas amount (wt%) was measured by measuring the weight of the electric furnace filled with barium titanyl oxalate powder before and after the gas discharge, respectively, and calculated by multiplying the weight after the gas discharge divided by the weight before the gas discharge.

Referring to Table 2, it can be seen that the crystallinity and particle size distribution are improved at the same particle size when the amount of residual gas decreases when the gas discharge temperature is increased and the size of the particles is equally adjusted after the first heat treatment. In addition, referring to Table 1 and Table 2, it can be seen that the gas crystallization and the particle size distribution are improved in the case of adopting the same crystallinity control index (m / A = 0.69) than in the case where the gas is discharged. have. These results indicate that the efficient removal of water and carbon dioxide as described above has a positive effect on the improvement of crystallinity. This can also lead to improved productivity.

 Although the present invention has been described with reference to the examples, these are merely exemplary, 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.

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

FIG. 2 is a diagram illustrating a method of calculating a governing factor of crystallinity of a fine barium titanate powder according to an embodiment of the present invention.

FIG. 3 is a SEM photograph of highly crystalline barium titanate particles having a particle diameter of 100 nm prepared by a manufacturing method according to an embodiment of the present invention.

FIG. 4 is a graph showing the change in crystallinity (c / a) of the fine barium titanate powder according to the crystallinity governing factor of FIG. 2.

Claims (18)

(a) preparing an aqueous solution of barium chloride (BaCl ₂ ) and an aqueous solution of titanium tetrachloride (TiCl ₄ ); (b) spraying the aqueous solution and dropwise adding it to an aqueous solution of oxalic acid (H ₂ C ₂ O ₄ ) to generate a barium titanyl oxalate [BaTiO (C ₂ O ₄ ) ₂ .4H ₂ O] crystal mass; (c) wet milling the barium titanyl oxalate crystal mass; (d) drying the wet milled barium titanyl oxalate powder; And (e) first heat treating the dried barium titanyl oxalate powder to produce barium titanate crystal mass; The degree of crystallization of barium titanate is controlled by adjusting the crystallinity factor (Governing factor of crystallinity) during the first heat treatment of step (e), wherein the crystallinity factor (m / A) of the heating furnace is subjected to the first heat treatment A method for producing a fine barium titanate powder defined by the weight (m) of the dried barium titanyl oxalate powder filled in the heating furnace per unit area (A). The method of claim 1, The heating furnace is a method of producing a barium titanate fine powder, characterized in that the Sagger or Tray. The method of claim 1, The crystallinity dominating factor is a method for producing a fine barium titanate powder, characterized in that 0.52g / cm ² or less. The method of claim 1, Method for producing a fine barium titanate powder, characterized in that to increase the crystallinity dominating factor by performing a gas discharge before the first heat treatment. The method of claim 1, In the step (b), the barium chloride aqueous solution and titanium tetrachloride aqueous solution is a method for producing a fine barium titanate powder, characterized in that before mixing. The method of claim 1, In the step (b), the barium chloride aqueous solution and titanium tetrachloride aqueous solution is a method for producing a fine barium titanate powder, characterized in that the mixing while being sprayed by a spray nozzle. The method of claim 1, Between steps (b) and (c), Aging the produced barium titanyl oxalate crystals; Filtering the aged barium titanyl oxalate crystals; And washing the filtered barium titanyl oxalate crystal with an excess of water. The method of preparing the barium titanate fine powder further comprises a. The method of claim 1, The wet grinding step (c) is a method for producing a fine barium titanate powder, characterized in that the addition of a nitrogen-containing additive selected from ammonia, amines, ammonium compounds, and amino acids. The method of claim 1, The drying of the step (d) is a method of producing a fine barium titanate powder, characterized in that carried out at a temperature below 400 ℃ as a temperature higher than the boiling point of the solvent used in the wet grinding of step (c). The method of claim 1, The primary heat treatment of step (e) is a method for producing a fine barium titanate powder, characterized in that carried out at a temperature in the range of 800 ~ 1000 ℃. The method of claim 1, Method for producing a fine barium titanate powder, characterized in that the temperature increase rate from the drying temperature of step (d) to the first heat treatment temperature of step (e) is 0.5 ~ 10 ℃ / min. The method of claim 1, After the step (e), further comprising the step of secondary heat treatment of the barium titanate crystal mass produced by the first heat treatment at a temperature below the first heat treatment temperature. The method of claim 12, Method for producing a fine barium titanate powder, characterized in that further comprising the step of adding barium carbonate (BaCO ₃ ) between the first heat treatment and the second heat treatment of step (e). The method of claim 12, And (a) pulverizing the barium titanate crystal mass produced by the first heat treatment between the first heat treatment and the second heat treatment in step (e). The method of claim 12, Method for producing a fine barium titanate powder, characterized in that the temperature increase rate to the secondary heat treatment temperature after the first heat treatment of step (e) is 0.5 ~ 10 ℃ / min. The method of claim 12, The secondary heat treatment is a method for producing a fine barium titanate powder, characterized in that carried out at a temperature in the range of 600 ~ 1000 ℃. The method of claim 12, Method for producing a fine barium titanate powder, characterized in that it further comprises the step of grinding the barium titanate crystal mass subjected to the second heat treatment. A fine barium titanate powder prepared by the process according to any one of claims 1 to 17.

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