Method for the production of barium titanate powder

Abstract

A process for the production of barium titanate powder, comprising the following steps: Addition of an aqueous slurry of anatase titanium dioxide hydrate, which has a specific surface area according to BET in the range of 200 m² 2 / g up to 400 m 2 / g and exhibits a half-width of diffraction of the (101) plane measured by X-ray diffraction in the range of 2.3° to 5.0°, to an aqueous solution of barium hydroxide, while the aqueous solution of barium hydroxide is maintained at a temperature in the range of 80 °C up to its boiling point under normal pressure in order to cause a reaction of the barium hydroxide with the titanium oxide hydrate and thereby obtain an aqueous suspension of barium titanate precursor; and Performing a hydrothermal treatment with the barium titanate precursor thus obtained for a period of not less than 24 hours, yielding barium titanate particles.

Description

Field of expertise

[0001] The present invention relates to a process for producing barium titanate powder, particularly to a process for producing barium titanate powder consisting of uniform fine particles with increased tetragonality and superior dispersibility. State of the art

[0002] In recent years, there has been a strong demand for a significant improvement in the properties of elements configuring electronic components and raw materials for manufacturing electronic components, with a reduction in size, improvement in performance, and reduction in weight of various electronic components.

[0003] For example, multilayer ceramic capacitors (MLCCs) have been increasingly required to reduce layer thickness. Therefore, barium titanate used in dielectric layers in MLCCs has been increasingly required to have uniform fine particles and high tetragonality, as well as superior dispersibility.

[0004] As methods for producing barium titanate, a solid-phase method, an oxalic acid method, a sol-gel method, and the like have been known so far. However, in order to produce fine barium titanate particles, particularly those with a particle diameter of about 250 nm or less, preferably about 150 nm or less, and thereby meet the current demand for reducing the film thickness of the MLCC, a hydrothermal method, which is a wet process, is advantageous. Since the solid-phase method and the oxalic acid method involve a calcination process, uniform particles are difficult to obtain, and furthermore, the resulting particles are easily clumped together, making fine particles difficult to obtain. The sol-gel method uses an expensive alkoxide as a raw material, and therefore the sol-gel method has a problem with production cost.

[0005] Various methods for producing barium titanate by the hydrothermal method are already known. For example, a method in which an aqueous solution of barium salt in the presence of a carboxylic acid is added to a slurry of titanium oxide hydrate and reacted with it to produce barium titanate seed particles, the resulting slurry containing the barium titanate seed particles is subjected to hydrothermal treatment to obtain spherical barium titanate particles, and the resulting spherical barium titanate particles are then fired at a temperature of 800°C to 1200°C (Patent Literature 1).

[0006] This process allows for the production of fine barium titanate particles with a relatively large BET specific surface area and high tetragonality. However, since the process requires calcination of barium titanate seed particles, it is difficult to obtain particles with a uniform particle diameter. Due to particle aggregation, it is also difficult to obtain fine particles. When using such barium titanate as a dielectric material in the manufacture of MLCCs, it is difficult to meet the requirement for reducing the layer thickness of the MLCC. Prior art can also be found in DE 11 2014 003 886 T5. State of the artPatent literature

[0007] Patent Literature 1: JP 2002-211926A Brief description of the inventionTechnical problem

[0008] The invention was completed to solve the above-mentioned problems in the production of barium titanate powder. An object of the invention is to provide a process for producing barium titanate powder consisting of uniform fine particles with high tetragonality and superior dispersibility. Solution to the problem

[0009] The invention provides a process for producing barium titanate powder, which comprises the following steps: Adding an aqueous slurry of anatase titanium oxide hydrate, which has a BET specific surface area in the range of 200 m 2 / g up to 400 m 2 / g and a half-width of the diffraction peak of the (101) plane measured by X-ray diffraction in the range of 2.3° to 5.0°, to an aqueous solution of barium hydroxide, while maintaining the aqueous solution of barium hydroxide at a temperature in the range of 80 °C to its boiling point under atmospheric pressure to cause the barium hydroxide to react with the titanium oxide hydrate and thereby obtain an aqueous slurry of barium titanate precursor; and

[0010] Subjecting the thus obtained barium titanate precursor to a hydrothermal treatment for a period of not less than 24 hours to obtain barium titanate particles.

[0011] A particularly preferred process for producing barium titanate powder according to the invention comprises the following steps: Simultaneously adding an aqueous solution of titanium tetrachloride and an aqueous solution of an alkali to water maintained at a temperature of 45 to 65 °C, while maintaining the temperature of the resulting reaction mixture in the range of 45 °C to 65 °C and its pH in the range of 1.5 to 3.5 to simultaneously neutralize the titanium tetrachloride with the alkali, thereby obtaining an aqueous slurry of anatase titanium oxide hydrate having a BET specific surface area in the range of 200 m 2 / g up to 400 m 2 / g and a half-width of the diffraction peak of the (101) plane measured by X-ray diffraction in the range of 2.3° to 5.0°;

[0012] Adding the aqueous slurry of anatase titanium oxide hydrate to an aqueous solution of barium hydroxide while maintaining the aqueous solution of barium hydroxide at a temperature in the range of 80 °C to its boiling point under atmospheric pressure to cause the barium hydroxide to react with the titanium oxide hydrate and thereby obtain an aqueous slurry of barium titanate precursor; and

[0013] Subjecting the thus obtained barium titanate precursor to a hydrothermal treatment for a period of not less than 24 hours to obtain barium titanate particles.

[0014] According to the invention, the temperature of the hydrothermal treatment in the above-mentioned hydrothermal treatment step, that is, in the step of hydrothermally treating the barium titanate precursor to obtain barium titanate particles, is preferably 250 °C or less. Advantageous effects of the invention

[0015] According to the process of the invention, barium titanate powder consisting of uniform fine particles with high tetragonality and having superior dispersibility is obtained. Brief description of the drawings Fig. Figure 1 is a scanning electron micrograph (50,000x magnification) of an example of barium titanate obtained by the process of the invention. Description of the embodiments

[0016] The process for producing barium titanate powder according to the invention comprises the following steps: Adding an aqueous slurry of anatase titanium oxide hydrate, which has a BET specific surface area in the range of 200 m 2 / g up to 400 m 2 / g and a half-width of the diffraction peak of the (101) plane measured by X-ray diffraction in the range of 2.3° to 5.0°, to an aqueous solution of barium hydroxide, while maintaining the aqueous solution of barium hydroxide at a temperature in the range of 80 °C to its boiling point under atmospheric pressure to cause the barium hydroxide to react with the titanium oxide hydrate and thereby obtain an aqueous slurry of barium titanate precursor; and

[0017] Subjecting the thus obtained barium titanate precursor to a hydrothermal treatment for a period of not less than 24 hours to obtain barium titanate particles.

[0018] If the BET specific surface area of ​​the anatase titanium oxide hydrate used is greater than 400 m 2 / g, the resulting barium titanate exhibits lower tetragonality. If the BET specific surface area of ​​the anatase titanium oxide hydrate used is less than 200 m 2 / g, the anatase titanium oxide hydrate has high crystallinity, but on the other hand has low reactivity towards barium hydroxide, so that the obtained barium titanate particles have lower tetragonality.

[0019] In particular, according to the invention, the anatase titanium oxide hydrate used preferably has a BET specific surface area in the range of 200 m 2 / g up to 350 m 2 / g and particularly preferably in the range of 220 m 2 / g up to 330 m 2 / g on.

[0020] Furthermore, if the anatase titanium oxide hydrate used has a half-width of the (101) plane diffraction peak measured by X-ray diffraction of less than 2.3°, it has high crystallinity but low reactivity toward barium hydroxide, and therefore the resulting barium titanate particles have low tetragonality. On the other hand, if the anatase titanium oxide hydrate used has a half-width of more than 5.0°, the resulting barium titanate particles have low tetragonality.

[0021] In particular, the anatase titanium oxide hydrate used in the invention preferably has a half-width of the diffraction peak of the (101) plane measured by X-ray diffraction in the range of 2.3° to 4.0°, and more preferably in the range of 2.3° to 3.5°.

[0022] As described above, the aqueous slurry of anatase titanium oxide hydrate, which has a BET specific surface area in the range of 200 m 2 / g up to 400 m 2 / g and a half-width of the diffraction peak of the (101) plane measured by X-ray diffraction in the range of 2.3° to 5.0°, preferably obtained by simultaneously adding an aqueous solution of titanium tetrachloride and an aqueous solution of an alkali, each having a temperature maintained in the range of 45°C to 65°C, to water maintained in advance at a temperature in the range of 45°C to 65°C to simultaneously neutralize the titanium tetrachloride with the alkali, while maintaining the pH of the resulting reaction mixture in the range of 1.5 to 3.5, preferably in the range of 2.0 to 3.5.

[0023] Therefore, according to the invention, the most preferred process for producing barium titanate powder comprises the following steps: Simultaneously adding an aqueous solution of titanium tetrachloride and an aqueous solution of an alkali to water maintained at a temperature of 45 to 65 °C, while maintaining the temperature of the resulting reaction mixture in the range of 45 °C to 65 °C and its pH in the range of 1.5 to 3.5 to simultaneously neutralize the titanium tetrachloride with the alkali, thereby obtaining an aqueous slurry of anatase titanium oxide hydrate having a BET specific surface area in the range of 200 m 2 / g up to 400 m 2 / g and a half-width of the diffraction peak of the (101) plane measured by X-ray diffraction in the range of 2.3° to 5.0°;

[0024] Adding the aqueous slurry of anatase-type titanium oxide hydrate to an aqueous solution of barium hydroxide while maintaining the aqueous solution of barium hydroxide at a temperature in the range of 80 °C to its boiling point under atmospheric pressure to cause the barium hydroxide to react with the titanium oxide hydrate and thereby obtain an aqueous slurry of barium titanate precursor; and

[0025] Subjecting the thus obtained barium titanate precursor to a hydrothermal treatment for a period of not less than 24 hours to obtain barium titanate particles.

[0026] As described above, according to the invention, the aqueous slurry of anatase titanium oxide hydrate is preferably obtained by simultaneously neutralizing titanium tetrachloride with an alkali. Here, "simultaneous neutralization of titanium tetrachloride with the alkali" refers to simultaneously adding an aqueous solution of titanium tetrachloride and an aqueous solution of an alkali to a container containing water and mixing them in the container to neutralize the titanium tetrachloride with the alkali.

[0027] In the above-described simultaneous neutralization of titanium tetrachloride with alkali, the concentration of titanium oxide hydrate in the slurry when the simultaneous neutralization is completed is not particularly limited, and usually it is preferably in the range of 10 g / L to 50 g / L as TiO2. If the concentration of titanium oxide hydrate in the slurry is higher than 50 g / L as TiO2 when the simultaneous neutralization is completed, amorphous titanium oxide hydrate is likely to be formed, and therefore it becomes difficult to obtain anatase titanium oxide hydrate. On the other hand, if the concentration of titanium oxide hydrate in the slurry is less than 10 g / L as TiO2 when the simultaneous neutralization is completed, the productivity is likely to be low.

[0028] Furthermore, in the above-described simultaneous neutralization of the titanium tetrachloride with the alkali, the temperatures of the water, the aqueous solution of titanium tetrachloride and the aqueous solution of the alkali do not all need to be the same, but preferably the temperatures are close to each other and most preferably, in particular, are all the same.

[0029] As the aqueous alkali solution, an aqueous solution of an alkali metal hydroxide, such as sodium hydroxide and potassium hydroxide, ammonia, and the like, is preferably used. Instead of the aqueous alkali solution, a solid alkali compound can also be added directly.

[0030] Even if the pH of the resulting reaction mixture in the above-described simultaneous neutralization of the titanium tetrachloride with the alkali is in the range of 1.5 to 3.5, if the neutralization temperature is lower than 45 °C, no anatase titanium oxide hydrate can be obtained, and the BET specific surface area of ​​the resulting titanium oxide hydrate exceeds 400 m 2 / G.

[0031] If the neutralization temperature is higher than 65°C, the titanium tetrachloride is hydrolyzed, likely forming rutile titanium oxide hydrate, or the half-width of the titanium oxide hydrate becomes less than 2.3°. Rutile titanium oxide hydrate has low reactivity with barium hydroxide, and the resulting barium titanate particles exhibit lower tetragonality. Even if the half-width of the titanium oxide hydrate is less than 2.3°, the resulting barium titanate particles exhibit lower tetragonality.

[0032] On the other hand, even if the neutralization temperature is in the range of 45 °C to 65 °C, if the pH of the resulting reaction mixture is higher than 3.5, anatase titanium oxide hydrate cannot be obtained, and the BET specific surface area of ​​the resulting titanium oxide hydrate exceeds 400 m 2 / g. When using such a titanium oxide hydrate, the resulting barium titanate particles exhibit lower tetragonality.

[0033] When the pH of the resulting reaction mixture is less than 1.5, a large amount of chloride ions remain as impurities in the produced titanium oxide hydrate, and as a result, its reactivity toward barium hydroxide deteriorates, and thus the obtained barium titanate particles have lower tetragonality.

[0034] Thus, according to the invention, titanium tetrachloride is neutralized simultaneously with the alkali in water to yield titanium oxide hydrate, the resulting slurry is filtered and washed with water to remove chloride ions and the like generated during the neutralization therefrom, and the resulting cake is dispersed in water, thereby obtaining the aqueous slurry of titanium oxide hydrate, which can be preferably used in the step of obtaining an aqueous slurry of the barium titanate precursor.

[0035] The aqueous slurry of anatase titanium oxide hydrate, which has a BET specific surface area in the range of 200 m 2 / g up to 400 m 2 / g and having a half-width of the diffraction peak of the (101) plane in the range of 2.3° to 5.0° as measured by X-ray diffraction, is added to an aqueous solution of barium hydroxide while maintaining the aqueous solution of barium hydroxide at a temperature in the range of 80 °C to its boiling point under atmospheric pressure to cause the barium hydroxide to react with the titanium oxide hydrate as described above, thereby obtaining an aqueous slurry of barium titanate precursor.

[0036] The barium titanate precursor obtained by the reaction of barium hydroxide with titanium oxide hydrate usually consists of fine particles of barium titanate with a BET specific surface area in the range of 50 m 2 / g up to 200 m 2 / g. Since the reaction between barium hydroxide and titanium oxide hydrate is a reaction under normal pressure, the obtained barium titanate precursor has a Ba / Ti ratio less than 1, but it was confirmed by powder X-ray diffraction that the obtained barium titanate precursor has a crystal structure of barium titanate.

[0037] The aqueous solution of barium hydroxide may contain a water-soluble organic solvent, as long as the reaction of the barium hydroxide with the titanium oxide hydrate is not impaired. Examples of such water-soluble organic solvents include ethylene glycol, diethylene glycol, polyethylene glycol, and the like.

[0038] When the barium titanate precursor is obtained by reacting barium hydroxide with hydrated titanium oxide, the barium hydroxide and hydrated titanium oxide are preferably used in such a manner that the Ba / Ti molar ratio is in the range of 1.1 to 3.0 when the addition of the anatase hydrated titanium oxide aqueous slurry to the barium hydroxide aqueous solution is completed. When the Ba / Ti molar ratio is less than 1.1 in the reaction of barium hydroxide with hydrated titanium oxide, the alkalinity of the resulting reaction system is low, so the reactivity between the barium hydroxide and hydrated titanium oxide deteriorates. When the Ba / Ti molar ratio is greater than 3.0, the reactivity between the barium hydroxide and hydrated titanium oxide is unproblematic; however, since the barium hydroxide, which does not contribute to the reaction, is used in excess, this raises the problem of high production costs.

[0039] In the above-described step of obtaining the aqueous slurry of the barium titanate precursor, the temperature at which the barium hydroxide reacts with the titanium oxide hydrate is important. Even though the anatase titanium oxide hydrate has a BET specific surface area in the range of 200 m 2 / g up to 400 m 2 / g and a half-width of 2.3° to 5.0° as described above, if the reaction temperature with the barium hydroxide is lower than 80°C under normal pressure, barium titanate particles with high tetragonality cannot be obtained. The upper limit of the reaction temperature is a temperature up to the boiling point of the reaction mixture containing the barium hydroxide.

[0040] According to the method of the invention, the barium titanate precursor obtained as described above is subjected to hydrothermal treatment for a period of not less than 24 hours. The resulting slurry is filtered, washed with water, and then dried to obtain the desired barium titanate powder consisting of uniform fine particles with increased tetragonality. If one wishes to synthesize barium titanate only by hydrothermal treatment without proceeding through the barium titanate precursor, the reaction of barium hydroxide with titanium oxide hydrate proceeds simultaneously with the particle growth of the resulting barium titanate particles, and as a result, a large number of hydroxy groups are incorporated into the barium titanate particles, making it difficult to obtain barium titanate particles with high tetragonality.

[0041] The aqueous slurry of the barium titanate precursor subjected to hydrothermal treatment preferably contains the barium titanate precursor in a concentration ranging from 0.4 mol / L to 1.0 mol / L as BaTiO3.

[0042] The aqueous slurry of the barium titanate precursor can be subjected to hydrothermal treatment while maintaining the obtained concentration without concentrating or diluting it.

[0043] The aqueous slurry of the barium titanate precursor is usually placed in an autoclave as it is and then subjected to hydrothermal treatment at a temperature exceeding its boiling point under normal pressure, which is usually not more than 250 °C and preferably in the range of 105 °C to 250 °C.

[0044] In the process of the invention, the hydrothermal treatment is carried out for a period of 24 hours or more, usually in the range of 24 to 1000 hours, preferably in the range of 24 to 500 hours, and most preferably in the range of 24 to 200 hours. According to the invention, the particle diameter of the resulting barium titanate can be controlled by the temperature at which and the time during which the hydrothermal treatment is carried out.

[0045] That is, the particle diameter of the barium titanate increases with increasing temperature at which the hydrothermal treatment is performed, while the particle diameter of the barium titanate increases with increasing time for the hydrothermal treatment. Specifically, according to the present invention, a barium titanate with a larger particle diameter and higher tetragonality is obtained by conducting the hydrothermal treatment for a longer period of time. If the hydrothermal treatment is conducted for a shorter period than 24 hours, the resulting barium titanate particles do not grow sufficiently and therefore exhibit low tetragonality.

[0046] After the aqueous slurry of the barium titanate precursor is subjected to hydrothermal treatment in this way, the contents of the autoclave are cooled to normal temperature, the resulting slurry is filtered, washed with water, and then dried to obtain barium titanate powder. The drying temperature is usually in the range of 100°C to 150°C.

[0047] The barium titanate powder thus obtained consists of uniform fine particles with superior tetragonality and usually has a BET specific surface area in the range of 3 m 2 / g up to 70 m 2 / g, preferably in the range of 4 m 2 / g up to 20 m 2 / g, on.

[0048] In the invention, the tetragonality of barium titanate is evaluated based on the c / a ratio, which can be determined by powder X-ray diffraction of the barium titanate powder. The barium titanate powder obtained according to the invention has a c / a ratio of 1.008 or more, thus exhibiting tetragonality in this sense. The resulting barium titanate powder thus exhibits superior tetragonality. Since the barium titanate obtained in this way exhibits high tetragonality only through the hydrothermal treatment of the barium titanate precursor, as explained above, it is unnecessary to further calcine and crush the resulting barium titanate.

[0049] As described above, the barium titanate particles obtained by the invention exhibit high tetragonality and superior dispersibility. Furthermore, the barium titanate particles with high tetragonality also exhibit high dielectricity and are therefore suitable for use as a dielectric material. Consequently, the barium titanate powder obtained by the invention can be advantageously used as a dielectric material, meeting the requirement for reducing film thickness in MLCC production.

[0050] The invention will be described in detail with reference to examples, but the present invention is not limited to examples. ExamplesExample 1 (Preparation of an aqueous slurry of titanium oxide hydrate)

[0051] 500 ml of pure water was added to a beaker and then heated to 55 °C. Simultaneously, 350 ml of an aqueous solution of titanium tetrachloride (manufactured by Osaka Titanium Technologies Co., Ltd., 3.8 mol / L as TiO2) was added to the water at a rate of 2.5 ml / minute and 7 L of pure water was added to the water at a rate of 50 ml / minute. At the same time, a sodium hydroxide solution having a concentration of 30 wt% was also added to the water. While maintaining the resulting mixture at a pH of 2.5 and a temperature of 55 °C to neutralize the titanium tetrachloride simultaneously with the alkali, sodium hydroxide, an aqueous slurry of titanium oxide hydrate having a concentration of 14 g / L as TiO2 was obtained.

[0052] The resulting aqueous slurry was filtered and then washed with water to remove sodium ions and chloride ions. Pure water was added to the resulting cake, yielding an aqueous slurry of anatase titanium oxide hydrate with a concentration of 110 g / L as TiO2. (Preparation of an aqueous slurry of barium titanate precursor)

[0053] In a reaction vessel with a capacity of 5 liters, 567 ml of pure water and 959 g of barium hydroxide octahydrate (manufactured by Sakai Chemical Industry Co., Ltd.) were added and then heated to 100 °C to dissolve the barium hydroxide octahydrate in water, thereby preparing an aqueous barium hydroxide solution.

[0054] The aqueous slurry of titanium oxide hydrate was added to the aqueous solution of barium hydroxide over 1 hour while maintaining the temperature at 100 °C, and they were reacted with each other at 100 °C for 2 hours, thereby obtaining an aqueous slurry of barium titanate precursor with a concentration of 0.66 mol / L as BaTiO3. The Ba / Ti molar ratio in the resulting reaction mixture was 2.3 when the addition of the aqueous slurry of titanium oxide hydrate to the aqueous barium hydroxide solution was completed. (Hydrothermal treatment of the aqueous slurry of the barium titanate precursor)

[0055] The above-obtained aqueous slurry of the barium titanate precursor with a concentration of 0.66 mol / L as BaTiO3 was placed in an autoclave vessel and then subjected to hydrothermal treatment at 180 °C for 120 hours. The contents of the autoclave were then allowed to cool to room temperature. The resulting aqueous slurry was filtered, washed with water, and then dried at 130 °C to yield barium titanate powder.

[0056] Fig. Figure 1 is a scanning electron micrograph (50,000x magnification) of the barium titanate powder obtained above. The invention provides barium titanate powder consisting of uniform fine particles. Example 2

[0057] Barium titanate powder was obtained in the same manner as in Example 1, except that the aqueous slurry of the barium titanate precursor was subjected to hydrothermal treatment at a temperature of 180 °C for 48 hours. Example 3

[0058] Barium titanate powder was obtained in the same manner as in Example 1, except that the aqueous slurry of the barium titanate precursor was subjected to hydrothermal treatment at a temperature of 200 °C for 24 hours. Example 4

[0059] Barium titanate powder was obtained in the same manner as in Example 1, except that the aqueous slurry of the barium titanate precursor was subjected to hydrothermal treatment at a temperature of 160 °C for 168 hours. Example 5

[0060] Barium titanate powder was obtained in the same manner as in Example 1, except that the aqueous slurry of the barium titanate precursor was subjected to hydrothermal treatment at a temperature of 200 °C for 180 hours. Example 6

[0061] Barium titanate powder was obtained in the same manner as in Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a pH of 3.5 and a temperature of 45 °C and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 170 °C for 96 hours. Example 7

[0062] Barium titanate powder was obtained in the same manner as in Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a pH of 2.0 and a temperature of 45 °C and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 200 °C for 24 hours. Comparative Example 1 (Preparation of an aqueous slurry of titanium oxide hydrate)

[0063] 500 mL of pure water was added to a beaker and maintained at a temperature of 60 °C. Simultaneously, 350 mL of an aqueous solution of titanium tetrachloride (manufactured by Osaka Titanium Technologies Co., Ltd., 3.8 mol / L as TiO2) was added to the water at a rate of 2.5 mL / minute and 7 L of pure water was added to the water at a rate of 50 mL / minute. A sodium hydroxide solution having a concentration of 30 wt% was added to the water. While simultaneously adjusting the resulting mixture to a pH of 2.0 and a temperature of 60 °C to simultaneously neutralize the titanium tetrachloride, an aqueous slurry of titanium oxide hydrate having a concentration of 14 g / L as TiO2 was obtained.

[0064] The aqueous slurry was filtered and then washed with water to remove sodium ions and chloride ions. Pure water was added to the resulting cake, yielding an aqueous slurry of anatase titanium oxide hydrate with a concentration of 110 g / L as TiO2. (Preparation of an aqueous slurry of barium titanate precursor)

[0065] In a reaction vessel with a capacity of 5 liters, 567 ml of pure water and 959 g of barium hydroxide octahydrate (manufactured by Sakai Chemical Industry Co., Ltd.) were added and then heated to 100 °C to dissolve the barium hydroxide octahydrate in water, thereby preparing an aqueous barium hydroxide solution.

[0066] The aqueous slurry of titanium oxide hydrate was added to the aqueous solution of barium hydroxide over 1 hour while maintaining the temperature at 100 °C, and they were reacted with each other at 100 °C for 2 hours, thereby obtaining an aqueous slurry of barium titanate precursor with a concentration of 0.66 mol / L as BaTiO3. The Ba / Ti molar ratio in the resulting reaction mixture was 2.3 when the addition of the aqueous slurry of titanium oxide hydrate to the aqueous barium hydroxide solution was completed. (Hydrothermal treatment of the aqueous slurry of the barium titanate precursor)

[0067] The above-obtained aqueous slurry of the barium titanate precursor with a concentration of 0.66 mol / L as BaTiO3 was placed in an autoclave vessel and then subjected to hydrothermal treatment at 190 °C for 0.5 hours. The contents of the autoclave were then allowed to cool to room temperature. The resulting aqueous slurry was filtered, washed with water, and then dried at 130 °C to yield barium titanate powder. Comparison example 2

[0068] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a temperature of 50 °C and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 180 °C for 20 hours. Comparison example 3

[0069] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a temperature of 50 °C and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 205 °C for 2 hours. Comparison example 4

[0070] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a pH of 3.0, the reaction of titanium oxide hydrate and barium hydroxide was carried out at a temperature of 100 °C for 5 hours, and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 130 °C for 0.5 hour. Comparison example 5

[0071] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a temperature of 50 °C, the reaction of titanium oxide hydrate and barium hydroxide was carried out at a temperature of 80 °C for 5 hours, and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 200 °C for 2 hours. Comparison example 6

[0072] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a pH of 3.0, the reaction of titanium oxide hydrate and barium hydroxide was carried out at a temperature of 95 °C for 5 hours, and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 180 °C for 0.5 hour. Comparison example 7

[0073] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a temperature of 50 °C, the reaction of titanium oxide hydrate and barium hydroxide was carried out at a temperature of 100 °C for 2 hours, and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 110 °C for 2 hours. Comparison example 8

[0074] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a pH of 5.0 and at a temperature of 20 °C, the reaction of titanium oxide hydrate and barium hydroxide was carried out at a temperature of 70 °C for 2 hours, and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 150 °C for 160 hours. Comparison example 9

[0075] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a pH of 2.5 and at a temperature of 55 °C and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 250 °C for 2 hours. Comparison example 10

[0076] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a temperature of 45 °C and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 180 °C for 20 hours. Comparison example 11

[0077] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a temperature of 80 °C and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 200 °C for 24 hours. Comparison example 12

[0078] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a pH of 1.5 and at a temperature of 20 °C and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 160 °C for 40 hours. Comparison example 13

[0079] Barium titanate powder was obtained in the same manner as in Comparative Example 1, except that the simultaneous neutralization of titanium tetrachloride was carried out at a pH of 4.0 and at a temperature of 40 °C and the hydrothermal treatment of the barium titanate precursor was carried out at a temperature of 170 °C for 24 hours.

[0080] The reaction conditions in the above-described Examples 1 to 7 and Comparative Examples 1 to 13, the pH and temperatures at which titanium tetrachloride was simultaneously neutralized with sodium hydroxide, the reaction temperature at and reaction time during which the titanium oxide hydrate was reacted with barium hydroxide to obtain the barium titanate precursor, and the temperature at and time during which the aqueous slurry of the barium titanate precursor was subjected to hydrothermal treatment are shown in Table 1.

[0081] The properties of the titanium oxide hydrate used in Examples 1 to 7 and Comparative Examples 1 to 13 and the properties of the barium titanate powder obtained in Examples 1 to 7 and Comparative Examples 1 to 13 are shown in Table 2. (Crystal structure of titanium oxide hydrate)

[0082] A small amount of the aqueous slurry of titanium oxide hydrate obtained by simultaneously neutralizing titanium tetrachloride with sodium hydroxide was taken, filtered, washed with water, and dried to yield a powder. The crystal structure of the powder was examined using a powder X-ray diffraction apparatus (RINT-TTR III, manufactured by Rigaku Corporation, radiation source: CuKα).

[0083] Furthermore, the half-width was calculated from the reflection of the (101) plane and used as an index of the crystallinity of the titanium oxide hydrate. As shown in Table 2, the reflection of the titanium oxide hydrate was very broad in Comparative Examples 8, 12, and 13, and thus the titanium oxide hydrates obtained therein were judged to be amorphous. (c / a ratio of barium titanate)

[0084] The barium titanate powder was subjected to powder X-ray diffraction using a powder X-ray diffraction apparatus (RINT-TTR III, manufactured by Rigaku Corporation, radiation source: CuKα), and then the c / a ratio was determined using the WPPF method. (Specific surface area of ​​titanium oxide hydrate powder and barium titanate powder)

[0085] The specific surface area of ​​each of titanium oxide hydrate powder and barium titanate powder was measured by a single-point BET method using a fully automatic specific surface area meter (HM Model 1220, manufactured by Mountech Co., Ltd.) after 30 minutes of degassing at 205 °C. Table 1 Production of titanium oxide hydrate Production of barium titanate precursor Hydrothermal treatment PH value Temperature (°C) Temperature (°C) Time (h) Temperature (°C) Time (h) Example 1 2,5 55 100 2,0 180 120 Example 2 2,5 55 100 2,0 180 48 Example 3 2,5 55 100 2,0 200 24 Example 4 2,5 55 100 2,0 160 168 Example 5 2,5 55 100 2,0 200 180 Example 6 3,5 45 100 2,0 170 96 Example 7 2,0 45 100 2,0 200 24 Comparison example 1 2,0 60 100 2,0 190 0,5 Comparison example 2 2,0 50 100 2,0 180 20 Comparison example 3 2,0 50 100 2,0 205 2,0 Comparison example 4 3,0 60 100 5,0 130 0,5 Comparison example 5 2,0 50 80 5,0 200 2,0 Comparison example 6 3,0 60 95 5,0 180 0,5 Comparison example 7 2,0 50 100 2,0 110 2,0 Comparison example 8 5,0 20 70 2,0 150 160 Comparison example 9 2,5 55 100 2,0 250 2,0 Comparison example 10 2,0 45 100 2,0 180 20 Comparison example 11 2,0 80 100 2,0 200 24 Comparison example 12 1,5 20 100 2,0 160 40 Comparison example 13 4,0 40 100 2,0 170 24 Table 2 Titanium oxide hydrate Barium titanate Specific surface Crystal structure*) Half-width Specific surface c / a (m 2 / g) (°) (m 2 / g) Example 1 255 A 2,5 7,4 1,010 Example 2 255 A 2,5 10,5 1,008 Example 3 249 A 2,4 11,7 1,008 Example 4 249 A 2,4 10,1 1,009 Example 5 255 A 2,5 4,9 1,010 Example 6 322 A 3,1 8,7 1,008 Example 7 284 A 3,0 8,6 1,008 Comparison example 1 270 A 2,5 20,6 1,006 Comparison example 2 256 A 2,5 11,8 1,007 Comparison example 3 256 A 2,5 17,1 1,006 Comparison example 4 226 A 2,4 48,3 1,005 Comparison example 5 256 A 2,5 21,7 1,006 Comparison example 6 226 A 2,4 25,2 1,006 Comparison example 7 256 A 2,5 68,4 1,003 Comparison example 8 409 On 6,3 8,1 1,007 Comparison example 9 255 A 2,5 17,0 1,006 Comparison example 10 284 A 3,0 13,7 1,007 Comparison example 11 158 A 1,6 10,2 1,007 Comparison example 12 401 On 5,5 15,9 1,006 Comparison example 13 422 On 6,5 14,7 1,006 *) "A" stands for "anatase" and "Am" stands for "amorphous".

[0086] As shown in Table 2, the barium titanate powder obtained by the process of the invention has a specific surface area in the range of 4 m 2 / g up to 20 m 2 / g and a c / a ratio of 1.008 or more. The barium titanate powder obtained by the process of the invention thus consists of fine particles with increased tetragonality.

[0087] Furthermore, the process of the invention does not require calcination of the barium titanate powder obtained by hydrothermal treatment of barium titanate precursor, and accordingly, the process of the invention usually provides barium titanate powder having superior dispersibility without decomposition of the resulting barium titanate powder.

Claims

[1] A process for producing barium titanate powder comprising the following steps: Adding an aqueous slurry of anatase titanium oxide hydrate, which has a BET specific surface area in the range of 200 m 2 / g up to 400 m 2 / g and a half-width of the diffraction peak of the (101) plane measured by X-ray diffraction in the range of 2.3° to 5.0°, to an aqueous solution of barium hydroxide, while maintaining the aqueous solution of barium hydroxide at a temperature in the range of 80 °C to its boiling point under atmospheric pressure to cause the barium hydroxide to react with the titanium oxide hydrate and thereby obtain an aqueous slurry of barium titanate precursor; and Subjecting the thus obtained barium titanate precursor to a hydrothermal treatment for a period of not less than 24 hours to obtain barium titanate particles. [2] The method according to claim 1, wherein in the step of subjecting the barium titanate precursor to hydrothermal treatment to obtain barium titanate, the hydrothermal treatment is carried out at a temperature of 250°C or less. [3] A method according to claim 1, comprising the following steps: Simultaneously adding an aqueous solution of titanium tetrachloride and an aqueous solution of an alkali to water maintained at a temperature of 45 °C to 65 °C, while maintaining the temperature of the resulting reaction mixture in the range of 45 to 65 °C and its pH in the range of 1.5 to 3.5, to simultaneously neutralize the titanium tetrachloride with the alkali, thereby obtaining an aqueous slurry of anatase titanium oxide hydrate having a BET specific surface area in the range of 200 m 2 / g up to 400 m 2 / g and a half-width of the diffraction peak of the (101) plane measured by X-ray diffraction in the range of 2.3° to 5.0°; Adding the aqueous slurry of anatase-type titanium oxide hydrate to an aqueous solution of barium hydroxide while maintaining the aqueous solution of barium hydroxide at a temperature in the range of 80 °C to its boiling point under atmospheric pressure to cause the barium hydroxide to react with the titanium oxide hydrate and thereby obtain an aqueous slurry of barium titanate precursor; and Subjecting the thus obtained barium titanate precursor to a hydrothermal treatment for a period of not less than 24 hours to obtain barium titanate particles. [4] The method according to claim 3, wherein in the step of subjecting the barium titanate precursor to hydrothermal treatment to obtain barium titanate, the hydrothermal treatment is carried out at a temperature of 250°C or less.

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