KR20100124776A

KR20100124776A - Manufacturing method for barium titanate

Info

Publication number: KR20100124776A
Application number: KR1020107020830A
Authority: KR
Inventors: 준야 후카자와
Original assignee: 니폰 가가쿠 고교 가부시키가이샤
Priority date: 2008-03-19
Filing date: 2009-03-19
Publication date: 2010-11-29
Also published as: WO2009125681A2; CN101977845A; JPWO2009125681A1; WO2009125681A3

Abstract

The present invention provides a method for easily producing barium titanate that is fine and has a low degree of aggregation and high crystallinity. The present method comprises a first step of obtaining the barium titanate obtained by heating the following amorphous particulate powder in air at 530 ° C. or higher and 700 ° C. or lower, and a reheating of barium titanate obtained in the first step at 700 ° C. or higher and 1000 ° C. or lower under reduced pressure. It is characterized by including 2 steps.
[Amorphous Fine Powder]
Titanium, barium, lactic acid and oxalic acid, the BET specific surface area is 6 m 2 / g or more, the molar ratio (Ba / Ti) of Ba atoms and Ti atoms is 0.98 to 1.02, 1120 to 1140 cm ^-1 derived from lactic acid And an infrared absorption spectral peak at 1040 to 1060 cm ⁻¹ .

Description

Manufacturing method of barium titanate {MANUFACTURING METHOD FOR BARIUM TITANATE}

The present invention relates to a method for producing barium titanate which is particularly preferably used as a dielectric material.

In recent years, with the rapid miniaturization, high performance, and high reliability of electronic devices, miniaturization of the elements constituting them and their starting materials is required. For example, the thickness of the dielectric currently used in a multilayer ceramic capacitor (MLCC) is about 700 to 800 nm, and the particle size of barium titanate (BaTiO ₃ ) fine particles serving as a raw material is reported to be 100 to 300 nm. As the miniaturization technology has the potential to change not only miniaturization and weight reduction of devices and devices, but also creation of new materials and high-performance materials, and even production methods, it will be a great breakthrough technology in the future.

In recent years, ceramics have also been deviceized in various forms. In the near future, it is expected that devices using the fine particles as they are will be developed. One example thereof is a composite dielectric of microparticles and polymers that are expected to be used at high frequencies.

One of the known methods for synthesizing barium titanate is pyrolysis of barium titanyl tetrahydrate. According to this method, barium titanate particles free of impurities and defects can be synthesized. The method which improved this method and developed further is also reported (for example, refer patent document 1).

However, when barium titanyl tetrahydrate is used as a raw material to synthesize barium titanate by pyrolysis, the value of c / a, which is the ratio of the c-axis to the a-axis of the lattice constant measured by the X-ray diffraction method of barium titanate obtained There was a problem that this was low and left the mold of the raw material, and aggregates were formed in which the primary particles were strongly aggregated (see Patent Document 2 and Non-Patent Document 1). In addition, the value of c / a becomes a measure of the dielectric constant of barium titanate, and when this value exists in the range of 1.005-1.008 in 50-215 nm of average particle diameters, it is known that the value of dielectric constant becomes large (refer patent document 2). ).

Japanese Patent Laid-Open No. 2003-26423 Japanese Patent Laid-Open No. 2006-117446

[Technical Report CREATIVE, Nippon Kagaku Kogyo Co., Ltd., 2002, p.61-P71]

An object of the present invention is to provide a method for producing barium titanate capable of eliminating the drawbacks of the prior art described above.

The present invention is the first step of obtaining the barium titanate by heating the following amorphous particulate powder in the air at 530 ℃ to 700 ℃

It is provided with the 2nd process of reheating barium titanate obtained by the 1st process at 700 to 1000 degreeC under reduced pressure, The manufacturing method of the barium titanate characterized by the above-mentioned.

[Amorphous Fine Powder]

Titanium, barium, lactic acid and oxalic acid, the BET specific surface area is 6 m 2 / g or more, the molar ratio (Ba / Ti) of Ba atoms and Ti atoms is 0.98 to 1.02, 1120 to 1140 cm ^-1 derived from lactic acid And an infrared absorption spectral peak at 1040 to 1060 cm ⁻¹ .

1 is an X-ray diffraction chart of amorphous particulate powder used in Example 1. FIG.
2 is an FT-IR chart of the amorphous fine particle powder used in Example 1. FIG.
FIG. 3 is a scanning electron microscope image of the amorphous fine particle powder used in Example 1. FIG.
4 is an X-ray diffraction diagram of barium titanate obtained in the first step of Example 1. FIG.
FIG. 5 is a scanning electron microscope image of barium titanate obtained in Example 2. FIG.
FIG. 6 is a scanning electron microscope image of barium titanate obtained in Comparative Example 3.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated based on the preferable embodiment. The manufacturing method of this invention is largely divided, and is equipped with the following two steps of processes.

(1) 1st process: The specific amorphous particulate powder is heated at 530 degreeC or more and 700 degrees C or less in air, and barium titanate is obtained.

(2) 2nd process: The barium titanate obtained by the 1st process is reheated at 700 degreeC or more and 1000 degrees C or less under reduced pressure.

Hereinafter, each process is demonstrated.

First, the amorphous fine particle powder used as a raw material in the manufacturing method of this invention is demonstrated. This amorphous particulate powder can be suitably used as a raw material for producing perovskite-type barium titanate powder, similarly to barium titanyl tetrahydrate. Amorphous fine particle powder contains titanium, barium, lactic acid, and oxalic acid. In addition, the amorphous fine particle powder has a BET specific surface area of 6 m 2 / g or more, and a molar ratio (Ba / Ti) of Ba atoms and Ti atoms is 0.98 to 1.02. In addition, the amorphous particulate powder has infrared absorption spectral peaks at 1120 to 1140 cm ⁻¹ and 1040 to 1060 cm ⁻¹ derived from lactic acid. This amorphous particulate powder is amorphous in X-ray diffraction analysis and is a novel material first developed by the inventors.

The amorphous fine particle powder has an average particle diameter of 3 μm or less, more preferably 0.3 μm or less, still more preferably 0.1 μm or less, and particularly preferably 0.0001 to 0.1 μm in average particle diameter obtained from a scanning electron microscope (SEM). It is The particle diameter of this range is remarkably fine compared with the barium titanyl tetrahydrate oxalate normally used for manufacture of barium titanate. In addition, as is apparent from the examples described later, the amorphous fine particle powder is in a highly dispersed state without excessive aggregation of the primary particles in the above range. A high dispersion state is advantageous in that barium titanate having a high relative dielectric constant is easily obtained as an amorphous particulate powder as a raw material. Usually, when barium titanyl tetrahydrate is used as a raw material, the barium titanate obtained also has an aggregate structure derived from barium titanyl tetrahydrate which is a raw material. Therefore, when the barium titanate is pulverized, the particles are damaged by the pulverization, and as a result, the dielectric constant may be lowered.

Further, the amorphous particulate powder has a BET specific surface area of 6 m 2 / g or more as described above, preferably 10 m 2 / g or more and 200 m 2 / g or less, more preferably 20 m 2 / g or more and 200 m 2 / g or less. .

The amorphous particulate powder contains Ba atoms and Ti atoms, and the molar ratio (Ba / Ti) of Ba atoms and Ti atoms is 0.98 to 1.02 as described above, preferably 0.99 to 1.00. If the Ba / Ti ratio is within this range, the amorphous fine particle powder becomes a preferred raw material for producing perovskite-type barium titanate powder.

The amorphous particulate powder contains oxalic acid groups and lactic acid groups in the chemical structure as well as titanium and barium. Particularly due to the inclusion of lactic acid groups, the amorphous particulate powder has infrared absorption spectral peaks at 1120 to 1140 cm ⁻¹ and 1040 to 1060 cm ⁻¹ , respectively, derived from lactic acid. Although the chemical composition of the amorphous fine particle powder is not clear, it is considered to be a complex organic acid salt containing Ba and Ti which contain Ba and Ti in the above ranges and which also contain oxalic acid groups and lactic acid groups in an appropriate blending ratio. The deorganic acid treatment of such amorphous fine particle powder by heat enables easy production of perovskite-type barium titanate powder from the amorphous fine particle powder without by-product barium carbonate.

In addition, the amorphous fine particle powder not only has the above-described characteristics, but also has a chlorine content of preferably 70 ppm or less, more preferably 50 ppm or less, even more preferably 15 ppm or less. This makes it easy to reduce the amount of chlorine contained in the barium titanate obtained from the amorphous particulate powder. It is particularly preferable to reduce the amount of chlorine contained in barium titanate from the viewpoint of securing the reliability thereof when producing a dielectric such as a multilayer capacitor using barium titanate powder as a raw material.

Amorphous fine particle powder can contain a subcomponent element for the purpose of adjusting the dielectric characteristic and temperature characteristic of a perovskite-type barium titanate powder. As the minor component element, for example, a rare earth element, Li, Bi, Zn, Mn, Al, Ca, Sr, Co, Ni, Cr, Fe, Mg, Zr, Hf, V, Nb, Ta, Mo, W, Sn and At least 1 sort (s) of element chosen from the group which consists of Si is mentioned. As the rare earth element, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the like can be used. Content of a subcomponent element can be arbitrarily set according to the dielectric characteristic made into the objective. For example, it is preferable to adjust content in amorphous particulate powder so that it may be contained in 0.001 to 10 weight% in a perovskite type barium titanate.

The amorphous fine particle powder is preferably prepared by contacting a solution containing a titanium component, a barium component and a lactic acid component (Liquid A) and a solution containing a oxalic acid component (Liquid B) in a solvent containing an alcohol to carry out the reaction. .

As a titanium source used as the titanium component in A liquid, titanium chloride, titanium sulfate, a titanium alkoxide, or the hydrolyzate of these titanium compounds can be used. As a hydrolyzate of a titanium compound, what hydrolyzed, for example, aqueous solutions, such as titanium chloride and a titanium sulfate, with alkaline solutions, such as ammonia and sodium hydroxide, hydrolyzed the titanium alkoxide solution with water, etc. can be used. Of these, the titanium alkoxide is particularly preferably used because the by-products are alcohols only, and incorporation of chlorine and other impurities can be avoided. Specific examples of the titanium alkoxide include titanium methoxide, titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium butoxide and the like. Among them, titanium butoxide is particularly preferably used in terms of various physical properties such as industrial availability, good stability of the raw material itself, and good separation of butanol itself. Titanium alkoxide can also be used as a solution dissolved in solvent, such as alcohol.

As a barium source which becomes a barium component in A liquid, barium hydroxide, barium chloride, barium nitrate, barium carbonate, barium acetate, barium lactate, barium alkoxide, etc. can be used, for example. Among them, barium hydroxide is particularly preferably used because it is inexpensive and can react without mixing chlorine or other impurities.

As lactic acid source used as the lactic acid component in A liquid, lactic acid alkali metal salts, such as lactic acid, sodium lactate, potassium lactate, ammonium lactate, etc. are mentioned. Among them, lactic acid is particularly preferably used in that there are no by-products and incorporation of unnecessary impurities can be avoided.

In the present invention, titanium lactic acid such as hydroxybis (lactate) titanium, which is a component source of both the titanium component and the lactic acid component, can also be used.

As a solvent which dissolves a titanium component, a barium component, and a lactic acid component, water can be used, for example. Or a mixed solvent of water and alcohol.

Solution A is preferably a transparent solution in which the titanium component, the barium component and the lactic acid component are dissolved, so that the desired amorphous fine particle powder can be produced smoothly. For this purpose, solution A is preferably prepared by step I of preparing a transparent solution comprising a titanium source, lactic acid source and water, and step II of adding a barium source to the solution.

In the operation in step I, a titanium source is added to an aqueous solution in which the lactic acid source is dissolved, or a lactic acid source is added to a suspension containing the titanium source and water. When using a liquid titanium compound, a lactic acid source may be added to a titanium compound as it is, and then water may be added to manufacture an aqueous solution. The temperature which adds a lactic acid source will not be specifically limited if it is more than the freezing point of the solvent to be used.

The amount of the lactic acid source in the A liquid is represented by a molar ratio (lactic acid / Ti) to Ti in the Ti component, preferably 2 to 10, more preferably 4 to 8. This is because if the molar ratio of lactic acid to Ti is less than 2, hydrolysis reaction of the titanium compound is likely to occur, or it is difficult to obtain an aqueous solution in which a stable titanium component is dissolved. On the other hand, even if this molar ratio exceeds 10, it is because an effect is saturated and it is not industrially advantageous.

Although the compounding quantity of the water in process I will not be restrict | limited especially if it is an amount which turns into the transparent liquid in which each component melt | dissolved, Usually, the density | concentration of Ti becomes like this. Preferably it is 0.05-1.7 mol / L, More preferably, it is 0.1-0.7 mol / L. The concentration of lactic acid is preferably 0.1 to 17 mol / L, more preferably 0.4 to 2.8 mol / L.

The barium source described above is then added in step II to the clear solution comprising the titanium source, lactic acid source and water obtained in step I. The amount of addition of the barium source is made such that the molar ratio (Ba / Ti) of Ba to Ti in the titanium component is preferably 0.93 to 1.02, more preferably 0.95 to 1.00 in consideration of the reaction efficiency. The reason is that when the molar ratio of Ba to Ti is less than 0.93, the reaction efficiency tends to decrease, and (Ba / Ti) of the amorphous fine particle powder obtained may be 0.98 or less. On the other hand, when it exceeds 1.02, (Ba / Ti) of amorphous fine particle powder will become easy to become 1.02 or more. The temperature which adds a barium source will not be specifically limited if it is more than the freezing point of the solvent to be used.

A liquid can also be adjusted in concentration with water and / or alcohol as needed. The alcohol which can be used is 1 type (s) or 2 or more types of C1-C4 including methanol, ethanol, propanol, isopropanol, butanol, etc., for example.

As for the density | concentration of each component in A liquid, titanium component becomes like this. Preferably it is 0.05-1.7 mol / L, More preferably, it is 0.1-0.7 mol / L. The barium component is preferably 0.0465 to 1.734 mol / L, more preferably 0.095 to 0.7 mol / L, as Ba. The lactic acid component is preferably 0.1 to 17 mol / L, more preferably 0.4 to 5.6 mol / L, as lactic acid.

A liquid may contain a minor component element for the purpose of adjusting the dielectric properties and temperature characteristics of the perovskite-type barium titanate powder as necessary. As the minor component element, for example, a rare earth element, Li, Bi, Zn, Mn, Al, Ca, Sr, Co, Ni, Cr, Fe, Mg, Zr, Hf, V, Nb, Ta, Mo, W, Sn and At least 1 sort (s) of element chosen from the group which consists of Si is mentioned. Examples of the rare earth element include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and the like. It is preferable to add a subcomponent element as compounds, such as an acetate, a carbonate, nitrate, a lactate, or an alkoxide. The addition amount of the compound containing a subcomponent element can be arbitrarily set according to the dielectric characteristic made into the objective. For example, it is preferable that the quantity converted into the element in the compound containing a subcomponent element is 0.001 to 10 weight% with respect to the perovskite type barium titanate powder.

On the other hand, liquid B is a solution containing oxalic acid. It is particularly preferable to use amorphous B powder having a high BET specific surface area as a B solution of oxalic acid dissolved in alcohol. As alcohol, 1 type, or 2 or more types are mentioned among the C1-C4 monovalent lower alcohols, such as methanol, ethanol, propanol, isopropanol, butanol, etc., for example.

In the liquid B, the concentration of oxalic acid is preferably 0.04 to 5.1 mol / L, more preferably 0.1 to 2.1 mol / L. By setting it as this range, since the target amorphous particulate powder is obtained in high yield, it is preferable.

As a method of bringing A liquid and B liquid into contact with a solvent containing alcohol, a liquid A is added to liquid B under stirring, or a liquid and liquid B are simultaneously added to a solution containing alcohol (C liquid) under stirring. The method of doing is preferable. Among them, the method of adding A liquid and B liquid to a solution containing alcohol (C liquid) at the same time with stirring is particularly preferable in terms of producing amorphous particulate powder having a uniform chemical composition ratio. In this case, as alcohol which can be used for C liquid, 1 type, or 2 or more types of C1-C4 monovalent lower alcohols, such as methanol, ethanol, a propanol, isopropanol, butanol, etc. are mentioned, for example. In particular, it is preferable to use the same alcohol as in A liquid and B liquid. In this case, the solvent amount of the alcohol of the liquid C is not particularly limited.

The addition amount of the liquid A to the liquid B, or the amount of the liquid A and the liquid B to the liquid C is an amount such that the molar ratio of oxalic acid (oxalic acid / Ti) in liquid B to Ti in liquid A is preferably 1.3 to 2.3. It is preferable because it is possible to obtain amorphous particulate powder in high yield. The stirring speed may be such that the slurry containing the amorphous fine particles generated from the start of addition to the end of the reaction is always in a state showing fluidity, and is not particularly limited.

The contact temperature of A liquid and B liquid is below the boiling point of the solvent to be used, and if it is more than a freezing point, it will not specifically limit. When the addition is carried out continuously at a constant speed, it is preferable because the amorphous fine particle powder having a BET specific surface area or a Ba / Ti molar ratio within the above-described range and small fluctuation and stable quality can be easily obtained.

After the contact of liquid A and liquid B is completed, a aging reaction is performed as necessary. When this aging is completed, the reaction of the produced amorphous fine particles is completed, and therefore, it is preferable in that the amorphous fine particle powder having a BET specific surface area and a Ba / Ti molar ratio within the above-mentioned range can be easily obtained. Although there is no restriction | limiting in particular in the temperature in aging, Preferably it is 10-50 degreeC. It is preferable that aging time is 3 minutes or more. Aging temperature means the mixture whole temperature after contact of A liquid and B liquid.

After completion of aging, solid-liquid separation is carried out by a conventional method, followed by washing, drying and pulverization as necessary to obtain the target amorphous particulate powder. In this case, when titanium alkoxide is used as the titanium source and barium hydroxide is used as the barium source, there is an advantage that a washing step for washing impurities such as chlorine can be omitted.

As the means for pulverization, pulverization with a rotary knife such as a food processor, a roll mill, a pin mill, or the like can be used. It is preferable that the amorphous fine particle powder obtained in this way is added to a grinding | pulverization process in order to improve the dispersibility. In some cases, pulverization may be performed directly without performing pulverization after drying. In either case of pulverization after pulverization or pulverization without pulverization, the pulverization treatment eliminates coagulated coarse powder (for example, 2 μm or more) and increases dispersibility. have. For this grinding treatment, a grinding device such as a jet mill can be used. The amorphous fine particle powder after grinding | pulverization is an average primary particle diameter calculated | required by SEM, Preferably it is 0.3 micrometer or less, More preferably, it is 0.1 micrometer or less, More preferably, it is a fine particle of 0.0001-0.1 micrometer, and there are few aggregated coarse powders, and dispersibility This powder becomes high. In addition, disintegration generally refers to an operation of pulverizing a bulk material, and pulverization generally refers to an operation of making the powder fine to a fine powder level of several μm or less.

The amorphous fine particle powder obtained in this way is a fine grain which has the above-mentioned particle diameter. This amorphous fine particle powder is added to the 1st process of heating at 530 degreeC or more and 700 degrees C or less, Preferably it is 570-610 degreeC in air under atmospheric pressure. The amorphous particulate powder is thermally decomposed by heating in the first step to produce barium titanate. When the heating temperature in the first step does not reach 530 ° C., the pyrolysis of the amorphous fine particle powder is not sufficiently completed, so that decomposition gas is generated in the reheating under reduced pressure of the second step, which is a subsequent step. Commercially available heating furnaces capable of vacuuming under reduced pressure cannot be used for reactions in which a large amount of gas is generated at a high temperature since the exhaust gas exhaustion countermeasures are not sufficiently considered. Therefore, generation of decomposition gas in the second step is not preferable from the viewpoint of industrial production of barium titanate. Therefore, it is significant from an industrial standpoint that substantially all of the amorphous particulate powder is converted to barium titanate in the first step. "Substantially all" means that the amorphous particulate powder is converted to barium titanate to such an extent that no harm caused by the gas generated due to the thermal decomposition of the amorphous particulate powder in the second step is not caused. On the other hand, when the heating temperature in the first step exceeds 700 ° C., the conversion of the amorphous fine particle powder to barium titanate is sufficiently performed. On the other hand, grain growth of barium titanate proceeds and fine barium titanate cannot be obtained.

The temperature increase rate in the first step is preferably 0.2 to 10 ° C / min, particularly 0.5 to 5 ° C / min, in that oxidation is sufficiently performed. After reaching the target temperature at this temperature raising rate, the temperature is preferably maintained for 0.2 to 20 hours, more preferably 0.5 to 5 hours. By setting it as the heating time of this range, thermal decomposition of an amorphous fine particle powder can fully advance, and generation | occurrence | production of the gas of thermal decomposition products in the 2nd process under reduced pressure mentioned later is prevented.

The temperature rising in a 1st process can also carry out this in multiple stages. For example, after heating up at a first temperature increase rate to reach a predetermined temperature, the temperature is maintained for a predetermined time, and then the temperature is raised at a second temperature increase rate to reach a predetermined temperature, and then the temperature is maintained for a predetermined time. By holding, the 1st process can be performed.

The first step can be performed while the amorphous fine particle powder is left in the heating furnace while air is passed through. Alternatively, the rotary kiln can be used while the air is circulated in a state in which the amorphous particulate powder is flowed (electrically transmitted) using a rotary kiln or the like.

After completion of the first step, the second step is then performed. In the second step, the intermediate product obtained in the first step is heated under reduced pressure to be converted to barium titanate. The second step is a continuous operation from the first step and can be performed by further raising the temperature from the heating temperature in the first step. In some cases, after completion of the first step, the second step may be performed after cooling to room temperature once and then grinding or pulverizing as necessary. In addition, in the case of the former, that is, in the case of further increasing the temperature from the heating temperature in the first step, the temperature increase rate is not particularly limited.

Since almost all of the amorphous particulate powder was converted to barium titanate in the first process, generation of gas due to thermal decomposition of the amorphous particulate powder is hardly observed in the second process. Therefore, no problem occurs even if a heating furnace capable of vacuum suction is used in the second step.

Heating temperature in a 2nd process is 700 degreeC or more and 1000 degrees C or less, Preferably you may be 800-950 degreeC. When heating temperature is lower than 700 degreeC, the crystallinity of the barium titanate obtained falls and it is not easy to raise a dielectric constant. When heating temperature is higher than 1000 degreeC, particle | grain growth of barium titanate advances and the particle diameter of the barium titanate obtained becomes large. It is also conceivable to perform reheating of the barium titanate in the second step in air. However, in the case of reheating in air and reheating under reduced pressure, comparing the values of c / a, which is the ratio of the c-axis and a-axis lattice constants of barium titanate with the same particle diameter, c / a when reheated under reduced pressure is Since it becomes a high value, ie, the crystallinity of barium titanate becomes high, it is advantageous to reheat under reduced pressure.

The second step is performed under reduced pressure. The pressure condition is preferably 200 Pa to 10 ^-4 Pa, more preferably 10 Pa to 10 ^-2 Pa. Although performing a 2nd process in inert gas, such as nitrogen gas, can also be considered, In this case, crystallinity of the barium titanate obtained cannot fully be improved. By heat-processing at high temperature under reduced pressure according to this invention, the crystallinity can be improved, suppressing grain growth of barium titanate.

In the heating in the second step, after reaching the target temperature at the above-mentioned heating rate, it is preferable to maintain the temperature for preferably 0.2 to 20 hours, more preferably 1 to 10 hours. It is preferable at the point of sufficiently raising the temperature and increasing the relative dielectric constant sufficiently.

A 2nd process can be performed using a stationary heating furnace similarly to a 1st process. Alternatively, a rotary kiln or the like may be used.

The target barium titanate is obtained by the heat treatment in the second step. The obtained barium titanate is added to the grinding treatment in accordance with a conventional method to form powder of the desired particle size. Although the obtained barium titanate has a small particle size of primary particles, the degree of aggregation is low and the dispersibility is high. In addition, crystallinity also increases. The higher the crystallinity of the barium titanate relative to the relative dielectric constant, the higher the dielectric constant.

The perovskite-type barium titanate powder obtained according to the present invention preferably has an average particle diameter of 0.02 to 0.3 µm, more preferably 0.05 to 0.15 µm, and preferably a BET specific surface area, obtained from a scanning electron microscope (SEM). Is 6 m <2> / g or more, More preferably, it is 8-20 m <2> / g, and a change of a particle size is small. In addition, the degree of aggregation of the primary particles of barium titanate is low, and the dispersibility is high. In addition to these physical properties, the chlorine content is preferably 70 ppm or less, more preferably 50 ppm or less, and the molar ratio of Ba and Ti is preferably 0.98 to 1.02, more preferably 0.99 to 1.00.

Moreover, the perovskite type barium titanate powder obtained is high in crystallinity as mentioned above. Specifically, the average particle diameter determined from the scanning electron microscope (SEM) is preferably 40 to 150 nm, more preferably 50 to 130 nm. The value of c / a, which is the ratio of the c-axis to the a-axis of the lattice constant measured by the X-ray diffraction method, is preferably 1.0050 to 1.0100, more preferably 1.0055 to 1.0100.

The perovskite-type barium titanate powder, which is a dielectric material produced according to the method of the present invention, is preferably used as a raw material of, for example, a multilayer ceramic capacitor. The barium titanate powder is mixed with a conventionally known additive, an organic binder, a plasticizer, and a dispersant, and mixed in a suitable solvent to disperse the slurry into a slurry, and a sheet is formed to obtain a ceramic sheet used for producing a multilayer ceramic capacitor. .

In order to manufacture a multilayer ceramic capacitor from the ceramic sheet, first, a conductive paste for forming an internal electrode is printed on one surface of the ceramic sheet. After drying the paste, a plurality of the ceramic sheets are laminated and pressed in the thickness direction to form a laminate. Subsequently, this laminated body is heat-processed, a binder removal process is performed, and it bakes and produces a fired body. Further, Ni paste, Ag paste, nickel alloy paste, copper paste, copper alloy paste and the like are applied to the fired body and baked to obtain a multilayer capacitor.

In addition, when the perovskite-type barium titanate powder produced according to the method of the present invention is blended with a resin such as an epoxy resin, a polyester resin, a polyimide resin, or the like to form a resin sheet, a resin film, an adhesive or the like, printing It can be used as a material such as a wiring board or a multilayer printed wiring board, an electrode ceramic circuit board, a glass ceramic circuit board, and a circuit peripheral material.

In addition, the perovskite-type barium titanate powder produced according to the method of the present invention is a catalyst used in the reaction of exhaust gas removal, chemical synthesis, or the like, a surface modifier of a printing toner that provides an antistatic and cleaning effect, In addition, it can be used suitably also as a piezoelectric body, an optoelectronic material, a semiconductor, a sensor, etc.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the scope of the present invention is not limited to this embodiment.

EXAMPLE 1

(1) Preparation of amorphous particulate powder

To 8.56 g of tetra-n-butyl titanate, 18.22 g of lactic acid and then 30 g of pure water were added in portions under stirring at 25 ° C. to prepare a clear liquid. Subsequently, 7.75 g of barium hydroxide octahydrate was added, dissolved at 25 ° C, and diluted with ethanol to prepare 100 ml of A solution. Apart from this, 6.67 g of oxalic acid dihydrate was dissolved in 100 ml of ethanol at 25 ° C. to obtain a B liquid.

Subsequently, the total amount of solution A and solution B was added dropwise simultaneously for 5 minutes to 100 ml of ethanol (C solution) under stirring at 25 ° C. After completion of the dropwise addition, the mixture was aged at 25 ° C. for 15 minutes to obtain a precipitate. This precipitate was filtered off and dried at 80 ° C. to obtain a powder. It was 1.00 when this powder was measured for the Ba / Ti molar ratio by the fluorescent X-ray method. Moreover, it was 67 m <2> / g when the BET specific surface area was measured using the fully automatic specific surface area meter (Macsorb model-1201). Moreover, it was 30 nm when the average particle diameter was measured. Moreover, it was 2 ppm when chlorine content was measured by ion chromatography. The average particle diameter was made into the average value of the particle diameter of 200 particle | grains extracted arbitrarily by the scanning electron microscope observation at 70,000 times magnification.

In addition, the X-ray diffraction chart of the obtained powder is shown in FIG. 1, and an FT-IR chart is shown in FIG. In addition, a scanning electron microscope image is shown in FIG. As apparent from the results shown in FIG. 1, no diffraction peaks were observed in the obtained powder, and it was found that they were amorphous. In addition, as apparent from the results shown in FIG. 2, absorption peaks of 1120 to 1140 cm ⁻¹ and 1040 to 1060 cm ⁻¹ derived from lactic acid were observed.

(2) production of dielectric materials

4 g of the amorphous fine particle powder was allowed to stand in an electric furnace, and heated up to 580 ° C. at an elevated temperature rate of 1 ° C./min in air under atmospheric pressure, and then maintained for 2 hours. Thus, barium titanate was obtained (1st process). Detailed operating conditions in the first step are as follows. 4 shows an X-ray diffraction diagram of the barium titanate obtained by the first step.

[Operation conditions]

Room temperature to 250 ° C .: temperature increase rate 1 ° C./min

250 ° C .: 1 hour of holding time

250 to 580 ° C: temperature rising rate of 1 ° C / min

580 ° C .: retention time 2 hours

The barium titanate was then reheated by vacuum evacuation at a pressure of 1 Pa using a Tamman tubular kiln (manufactured by Motoyama Co., Ltd.), raising the temperature to 800 ° C. at 3.5 ° C./min under this condition, and then holding it for 1 hour. Then, the electric furnace was turned off and it cooled slowly to room temperature, exhausting (2nd process).

(3) evaluation

(A) Ba / Ti molar ratio, (b) average particle diameter, (c) ratio c / a of a-axis, and (d) BET specific surface area were measured with respect to the obtained barium titanate particle | grains by the following method. These results are shown in Table 1 below. In addition, the ratio c / a of the c-axis to the a-axis of (c) is a measure of the degree of the dielectric constant of barium titanate. When the value is within the range of 1.0050 to 1.0100 at an average particle diameter of 40 to 150 nm, the relative dielectric constant is high. Means that.

(a) Ba / Ti molar ratio

It measured by the fluorescent X-ray method.

(b) average particle diameter

By the scanning electron microscope, it calculated | required with the average value of 200 or more particle | grains extracted arbitrarily at 70,000 times magnification.

(c) the ratio c-a to a-axis c / a

It measured by X-ray diffraction method and computed lattice constants c and a from Rietveld analysis.

(d) BET specific surface area

It was measured using a fully automatic specific surface area meter (Macsorb model-1201).

[Examples 2 and 3]

Barium titanate particles were obtained in the same manner as in Example 1 except that the heating temperature of the second step was set to the temperature shown in Table 1. The measurement similar to Example 1 was performed about the obtained barium titanate particle. The results are shown in Table 1. In addition, the scanning electron microscope image of the barium titanate powder obtained in Example 2 is shown in FIG.

[Comparative Examples 1 and 2]

Barium titanate particles were obtained in the same manner as in Example 1 except that the second step was carried out in air (at atmospheric pressure) and the heating temperature of the second step was set to the temperature shown in Table 2. The measurement similar to Example 1 was performed about the obtained barium titanate particle. The results are shown in Table 2.

(Comparative Example 3)

Barium titanate particles were obtained in the same manner as in Example 2 except that the starting material was used for barium titanyl tetrahydrate (average particle size: 88 µm). The measurement similar to Example 1 was performed about the obtained barium titanate particle. The results are shown in Table 2. Moreover, the scanning electron microscope image of the obtained barium titanate powder is shown in FIG.

As is clear from the results shown in Tables 1 and 2, it was found that the barium titanate obtained in each example has a large value of c / a despite the extremely small average particle diameter. From this, it is judged that the barium titanate obtained in each Example is high in crystallinity. High crystallinity in the particle size range of the example means that the dielectric constant of barium titanate is high. On the other hand, when the barium titanate obtained by each comparative example was compared with the same particle diameter in the relationship of an average particle diameter and c / a, it turned out that the value of c / a is small. From this, it is judged that barium titanate obtained in each comparative example is low in crystallinity and low in dielectric constant when compared with the same particle diameter in the relationship between the average particle diameter and c / a. 5 and 6 show that the barium titanate obtained in the examples is fine and has a low degree of aggregation.

According to the present invention, barium titanate which is fine and has a low degree of aggregation and high crystallinity can be easily produced.

Claims

A first step of obtaining the barium titanate by heating the following amorphous particulate powder at 530 ° C. to 700 ° C. in air;
And a second step of reheating the barium titanate obtained in the first step at 700 ° C to 1000 ° C under reduced pressure.
(Amorphous Fine Particle Powder)
Titanium, barium, lactic acid and oxalic acid, the BET specific surface area is 6 m 2 / g or more, the molar ratio (Ba / Ti) of Ba atoms and Ti atoms is 0.98 to 1.02, 1120 to 1140 cm ^-1 derived from lactic acid And an infrared absorption spectral peak at 1040 to 1060 cm ⁻¹ .

The method for producing barium titanate according to claim 1, wherein the amorphous fine particle powder has a chlorine content of 70 ppm or less.

A rare earth element, Li, Bi, Zn, Mn, Al, Ca, Sr, Co, Ni, Cr, Fe, Mg, Zr, Hf, V, Nb, as claimed in claim 1 or 2; A method for producing barium titanate, further comprising at least one subcomponent element selected from the group consisting of Ta, Mo, W, Sn and Si.