JP2005162595A - Barium titanate powder and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide barium titanate powder having excellent low-temperature sinterability, and a method for manufacturing the same. <P>SOLUTION: For the BaTiO<SB>3</SB>powder, the length ratio c/a of the a axis and c axis of a perovskite structure is ≥1.008 and the value obtained by dividing the average grain size by the diameter of the equivalent BET specific surface area calculated from the BET specific surface area is 1-1.5. The method for manufacturing the BaTiO<SB>3</SB>powder comprises firing the mixture which is a mixture containing a titanium compound and a barium compound and yields BaTiO<SB>3</SB>by firing at a temperature at which the BaTiO<SB>3</SB>is generated, wherein the firing of the mixture is performed by exposing the mixture to an atmosphere containing one or more of Cl, Br, and I at 200°C and in a temperature range where the BaTiO<SB>3</SB>is generated, then heating the mixture in an atmosphere substantially containing none of Cl, Br, I, and F at the temperature at which the BaTiO<SB>3</SB>is generated or above. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a barium titanate powder and a method for producing the same.

  Since barium titanate has a high dielectric constant, it is used in multilayer capacitors.

  A multilayer capacitor using barium titanate is formed by alternately laminating dielectric layers made of barium titanate and electrode layers for applying a voltage to the dielectric layer. The multilayer capacitor is manufactured by laminating and sintering a barium titanate powder layer and a powder layer of an electrode layer material. An expensive platinum group metal is used as the electrode layer, but a change to an inexpensive metal such as nickel is desired in order to reduce costs. However, since nickel has a low melting point, it is necessary to sinter at a temperature of about 1200 ° C. or lower, which is lower than the conventional sintering temperature of about 1400 ° C., which is excellent in low-temperature sinterability and a relatively low temperature of 1200 ° C. or lower. There has been a demand for a barium titanate powder that gives a high density of 95% or more of the theoretical density even when sintered at a low temperature.

The barium titanate powder has an average particle diameter of 0.88 μm and a BET specific surface area of 2.2 m ² / g (the BET specific surface area equivalent diameter calculated from the BET specific surface area is 0.45 μm. The value divided by the equivalent surface area diameter is 2.0.) Barium titanate powder having a c / a of 1.0105 is known, and as its production method, a mixture of an aqueous titanium tetrachloride solution and an aqueous barium chloride solution is known. Has been proposed in which a precipitate is taken out and dried, and then dried and held at 1060 ° C. in an air atmosphere and baked (see, for example, Patent Document 1). The obtained barium titanate has not been sufficiently sintered at low temperature.

JP 2002-53320 A

  An object of the present invention is to provide a barium titanate powder excellent in low-temperature sinterability and a method for producing the same.

  As a result of intensive studies on the barium titanate powder excellent in low-temperature sinterability and the production method thereof, the length ratio c / a of the a-axis to the c-axis of the perovskite structure is within a certain range, and The BET specific surface area equivalent diameter calculated from the BET specific surface area was determined, and the barium titanate powder having a value obtained by dividing the average particle diameter by the BET specific surface area equivalent diameter was found to be excellent in low-temperature sinterability. It was. Further, the inventors of the present invention provide a method for producing barium titanate, comprising a mixture containing a titanium compound and a barium compound, wherein the mixture that produces barium titanate by firing is fired at a temperature higher than that at which barium titanate is produced. Baking the mixture is exposed to an atmosphere containing one or more halogens selected from the group consisting of chlorine, bromine and iodine at any temperature within a certain temperature range, and then at a temperature above that at which barium titanate is formed. Found that a barium titanate powder excellent in low-temperature sinterability can be produced by heating the mixture in an atmosphere substantially free of any of chlorine, bromine, iodine and fluorine. It came to be completed.

  That is, according to the present invention, the length ratio c / a between the a-axis and the c-axis of the perovskite structure is 1.008 or more, and the value obtained by dividing the average particle diameter by the BET specific surface area equivalent diameter calculated from the BET specific surface area is 1. Provided is a barium titanate powder characterized by being 1.5 or less. Further, the present invention is a mixture containing a titanium compound and a barium compound, wherein the mixture that gives barium titanate by firing is fired at a temperature higher than the temperature at which barium titanate is produced. Baking is exposed to an atmosphere containing one or more halogens selected from the group consisting of chlorine, bromine and iodine in a temperature range of 200 ° C. or higher and lower than the temperature at which barium titanate is formed, and then barium titanate The method for producing barium titanate powder is characterized in that the mixture is heated in an atmosphere substantially free of any of chlorine, bromine, iodine and fluorine at a temperature higher than the temperature at which is produced.

  Since the barium titanate powder of the present invention is excellent in low-temperature sinterability, it is possible to produce a multilayer capacitor using an inexpensive metal having a low melting point such as nickel for the electrode layer. And according to the manufacturing method of this invention, since the barium titanate powder of this invention excellent in low-temperature sintering property can be manufactured, this invention is very useful industrially.

  In the barium titanate powder of the present invention, the length ratio c / a between the a-axis and the c-axis of the perovskite structure is 1.008 or more, the average particle diameter is equivalent to the BET specific surface area equivalent diameter calculated from the BET specific surface area of the powder. The value obtained by dividing (hereinafter also referred to as “BET diameter ratio”) is 1 or more and 1.5 or less. Here, the BET specific surface area can be measured by a BET one-point method, and the average particle diameter can be measured by a laser diffraction scattering method particle size distribution measuring device or the like. The value of the BET diameter ratio is theoretically 1 when the particles constituting the powder are spheres having a completely uniform particle diameter, and increases as the aggregation of the particles increases. Further, the value of c / a increases as the crystallinity increases (the crystal has fewer defects). The inventors have found that when such c / a is 1.008 or more and the BET diameter ratio is 1.5 or less, the barium titanate powder becomes a powder excellent in sinterability at low temperatures. I found it. The BET diameter ratio is preferably 1.3 or less, and more preferably 1.2 or less. Moreover, since it becomes a powder excellent in low-temperature sintering property, the value of c / a is preferably 1.0090 or more, more preferably 1.0095 or more. The upper limit of c / a is about 1.011.

  Further, the average particle size is preferably smaller than 0.3 μm because it is excellent in low temperature sinterability, but when it is less than 0.05 μm, the aggregation of particles becomes strong and the low temperature sinterability of the barium titanate powder tends to decrease. There is.

Further, when the average value of the density of each particle is low, it may be low due to a void inside the particle or a hydroxyl group, and the low temperature sinterability is low. tends to decrease, preferably has an average density of the particles is 5.80 g / cm ³ or more, more preferably 5.90 g / cm ³ or more, it is 5.95 g / cm ³ or more Further preferred. The average density of the particles can be measured with a helium-substituted true density measuring device or a precision pycnometer.

In addition, the lighter bulk density of the barium titanate powder and the higher bulk density of the barium titanate powder are barium titanate powders that are more excellent in low-temperature sintering, so the lighter bulk density is 1.4 g / cm ³ or more. In addition, barium titanate powder having a bulk density of 1.8 g / cm ³ or more is preferable. The light bulk density of the powder is calculated by “powder mass / powder volume” after filling the powder into the container, and the heavy bulk density is tapped (usually about 3 cm high) after filling the container with the powder. It is calculated by “powder mass / powder volume” after being dropped about 100 times.

Next, the production method of the present invention will be described in detail.
The length ratio c / a between the a-axis and the c-axis of the perovskite structure is 1.008 or more, and the value obtained by dividing the average particle diameter by the BET specific surface area equivalent diameter calculated from the BET specific surface area is 1 or more and 1.5 or less. The barium titanate powder of the present invention is a mixture containing a titanium compound and a barium compound, and is produced by firing a mixture that gives barium titanate by firing at a temperature higher than that at which barium titanate is produced. In the method, the firing of the mixture is exposed to an atmosphere containing one or more halogens selected from the group consisting of chlorine, bromine and iodine in a temperature range above 200 ° C. and below the temperature at which barium titanate is formed, Above the temperature at which barium titanate is formed, it is added in an atmosphere substantially free of chlorine, bromine, iodine and fluorine. That can be produced the present inventors have found by performing with.

  In the production method of the present invention, a mixture containing a titanium compound and a barium compound is used. As the titanium compound and barium compound, oxides, carbonates, hydroxides, hydroxide gels, and the like can be used. As a mixture of the titanium compound and barium compound, a composite compound of titanium and barium can also be used. Specific examples of the titanium compound include titanium dioxide and titanium tetrachloride neutralized precipitates (titanium hydroxide or hydroxide gel). Specific examples of the barium compound include barium carbonate, hydroxide. Examples thereof include barium and barium acetate. Specific examples of the composite compound of titanium and barium include, for example, barium titanyl oxalate tetrahydrate. In the present invention, it can be used as a titanium compound or a barium compound. The mixture containing a titanium compound and a barium compound can contain, for example, a flux composed of a borate salt or an ammonium salt for the purpose of improving the crystallinity of the obtained barium titanate.

  In the production method of the present invention, a mixture containing a titanium compound and a barium compound and giving barium titanate by firing can be prepared by mixing the titanium compound and the barium compound by dry or wet mixing. The flux can be mixed at the same time. The mixture can be pulverized in advance before firing. Examples of apparatuses that can be used for mixing and pulverizing include industrially used ball mills, vibration mills, Henschel mixers, vertical granulators, dynamic mills, and the like. In order to obtain fine barium titanate, the mixture is preferably fine, and therefore, it is preferable to use a ball mill, a vibration mill or the like having a grinding ability.

  And the manufacturing method of this invention is a manufacturing method of barium titanate by baking the mixture containing a titanium compound and a barium compound at temperature higher than the temperature from which this mixture turns into barium titanate, The manufacturing method of this invention In this case, the mixture is fired by exposing the mixture to an atmosphere containing halogen in a temperature range of 200 ° C. or higher and lower than the temperature at which barium titanate is generated. In the method of the present invention, the mixture may be exposed to a halogen-containing atmosphere in a temperature range of 200 ° C. or higher and lower than the temperature at which barium titanate is formed. The exposure time is usually 1 minute or longer and 10 hours. There may be times when the mixture is not exposed to halogen in the temperature range. The temperature range at which the mixture is exposed to the halogen-containing atmosphere is preferably a temperature range of 300 ° C. or higher and 800 ° C. or lower, and more preferably a temperature range of 500 ° C. or higher and 700 ° C. or lower.

  In the production method of the present invention, the halogens are chlorine, bromine and iodine, with chlorine being preferred. Examples of the halogen in the atmosphere containing halogen include molecular halogen, hydrogen halide, halide vapor, and the like. Molecular halogen and hydrogen halide are preferable, hydrogen halide is more preferable, and hydrogen chloride is more preferable. The content of molecular halogen and halogen compound in the atmosphere is preferably 0.5% by volume to 50% by volume, more preferably 1% by volume to 30% by volume, and even more preferably 3% by volume to 20% by volume. It is. Nitrogen, oxygen, air, argon, or a mixed gas thereof can be used as a gas other than the molecular halogen and the halogen compound in the atmosphere.

  Thereafter, at a temperature equal to or higher than the temperature at which the mixture becomes barium titanate, the mixture is heated and fired in an atmosphere substantially not containing fluorine in addition to the halogen. The time for heating the mixture at a temperature equal to or higher than the temperature at which the mixture becomes barium titanate is usually from 10 minutes to 10 hours. As one embodiment of the production method of the present invention, a mixture containing a titanium compound and a barium compound is placed in a furnace and heating is started. Then, a hydrogen chloride-containing atmosphere is set in the furnace in a temperature range of 500 ° C. to 700 ° C. Introduced into the atmosphere, the mixture was exposed to a halogen-containing atmosphere, and then the atmosphere was replaced with air up to 700 ° C. while heating was continued, and in the air atmosphere at a temperature higher than the temperature at which the mixture became barium titanate while continuing heating. An example of the method for producing barium titanate by heating and baking at 1 is shown.

  The temperature at which the mixture containing the titanium compound and the barium compound becomes barium titanate can be determined by thermal analysis (TG-DTA) or the like. When the temperature at which barium titanate is generated is determined by thermal analysis, the peak temperature appearing in the obtained chart may be determined. The temperature differs depending on the starting barium compound and titanium compound, but is generally in the temperature range of more than 800 ° C. and 1000 ° C. or less.

  The barium titanate powder generated by firing may have a halogenated compound in the firing atmosphere attached to the surface of the barium titanate powder particles, but can be easily removed by washing with water. The water used for washing preferably contains a carbonate to reduce barium elution.

The powder obtained after firing is washed, and further maintained in an atmosphere substantially free of chlorine, bromine, iodine and fluorine at a temperature in the range of 800 ° C. to 1100 ° C. to refire the powder. It is preferable to do. Air is usually used as the atmosphere when refiring.
The obtained barium titanate powder can be further washed, classified and pulverized by a method generally used industrially.

  In this way, barium titanate powder having a ratio c / a of 1.008 or more and a BET diameter ratio of 1 or more and 1.5 or less can be produced. Further, the barium titanate powder produced by the production method of the present invention is a fine particle and becomes a barium titanate powder that can be easily dispersed in primary particles. Furthermore, since the barium titanate powder produced by the production method of the present invention has few aggregated particles and the degree of aggregation is light, the pulverization energy required for breaking the aggregation is small, and it is agglomerated by a short time ball mill or vibration mill. In addition, it is possible to prevent coarse foreign matters from being mixed due to ball defects in a ball mill or a vibration mill, and generation of aggregated particles due to mill packing.

The barium titanate powder of the present invention is excellent in low-temperature sinterability, dispersibility, and filling characteristics. The obtained sintered body has few pores, the surface is smooth, and the size is in the range of 1 mm × 1 mm of the surface. However, there are almost no pores or protrusions of 0.5 μm or more. Therefore, it is suitable as a raw material for multilayer capacitors, dielectric filters, PDP display electrode insulators, inorganic EL dielectric layers, and the like. Among them, a barium titanate powder having a light packaging density of 1.4 g / cm ³ or more and a heavy bulk density of 1.8 g / cm ³ or more is a doctor blade molding method used when manufacturing a multilayer capacitor. In the above, since the amount of the solvent used when producing the barium titanate powder slurry for forming the doctor blade is small, it is more suitable as a raw material for the multilayer capacitor. As the solvent used here, a normal organic solvent such as toluene, ethanol, acetone or the like can be used as the organic solvent. In the aqueous solvent, since barium titanate is dissolved in water, ammonia, ammonia carbonate, carbonate An aqueous solvent that is adjusted to be alkaline with ammonium hydrogen or the like to prevent dissolution of barium titanate can be used. As the dispersant, a cationic, anionic, polyester, polycarboxylic acid amine, vinyl compound, or the like can be used. If necessary, it can be crushed in an organic solvent, and ultrasonic dispersion, a ball mill, a vibration mill, a rod mill, or the like can be employed. As the molding method, slip casting, tape molding or the like can be employed.

  In multilayer capacitors using barium titanate, the thinner the dielectric layer made of a barium titanate sintered body, the higher the capacitance of the capacitor per unit volume. It is requested to do. In recent years, it has been studied to reduce the thickness to about 1 μm. In order to produce such a thin dielectric layer, the average particle size of fine particles is less than that of the barium titanate powder used as a raw material. Since a fine powder having a particle size of 3 μm or less is required, a fine particle having an average particle size of 0.3 μm or less among the barium titanate powder of the present invention is suitable for manufacturing a capacitor having a thin dielectric layer. Furthermore, in recent years, build-up substrates have been developed in which barium titanate powder is kneaded with resin and filled into a substrate without being sintered, and among the barium titanate powders of the present invention, A powder having a high bulk density is suitable as a raw material for a build-up substrate because the resin can be filled with a high density.

EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited by these.
In the following examples, firing was performed twice. In the first firing, the mixture containing the titanium compound and the barium compound is exposed to a halogen-containing atmosphere in a temperature range of 200 ° C. or higher and lower than the temperature at which barium titanate is generated. Above the generating temperature, the mixture was heated in air. The powder obtained after firing was washed with water, and further held in air at a temperature in the range of 800 ° C. to 1100 ° C. for second firing.
1. Measurement of average particle size The average particle size was determined by dispersing the powder in a 0.2% by weight sodium hexametaphosphate aqueous solution and carrying out ultrasonic treatment, followed by laser diffraction scattering method particle size distribution analyzer (manufactured by Malvern, UK, Master Measured using a sizer 2000).

2. Measurement of BET Specific Surface Area and BET Specific Surface Area Equivalent Diameter The BET specific surface area of the powder was measured with a BET specific surface area measuring device (manufactured by Shimadzu Corporation, Flowsorb II2300 type) by the BET one-point method. The BET specific surface area equivalent diameter is calculated from the value of the obtained BET specific surface area by 6 ÷ (theoretical density of barium titanate (g / cm ³ )) ÷ (BET specific surface area (m ² / g)). A surface area equivalent diameter (μm) was used. The theoretical density of barium titanate was 6.02 g / cm ³ of tetragonal crystal.

3. Generation phase identification, measurement of c / a The generation phase was identified by an X-ray diffraction measurement device (Rigaku, RINT type). The obtained X-ray diffraction pattern was analyzed by the Rietveld method to determine the ratio c / a between the a axis and the c axis.

4). Measurement of Ba / Ti ratio The peak intensities of Ba and Ti were measured using a fluorescent X-ray apparatus (manufactured by Philips (Netherlands), PW1480 type). A calibration curve was prepared from a standard sample whose composition was determined by chemical analysis, and the Ba / Ti ratio was determined using it.

5). Measurement of Halogen Content Using a fluorescent X-ray apparatus (manufactured by Philips (Netherlands), PW1480 type), the intensity of the peak corresponding to the halogen was measured. Further, after the particles were dissolved in acid, the amount of chlorine was measured by chemical titration, and the amount of halogen was calculated from the peak intensity ratio using the peak of the standard sample.

6). Measurement of Particle Density The average density of powder particles was measured using a density measuring device (manufactured by Yuasa Ionics, Ultrapycnometer UPY-4 type). Pellets obtained by uniaxially molding the powder dried at 120 ° C. at a pressure of 300 kg / cm ² were measured as samples.

7). Measurement of light heavy bulk density Using 50 g of powder, the powder was put into a 100 mL measuring cylinder made of glass, the volume at that time was read, and the light bulk density was calculated by dividing the mass by the volume. Thereafter, the sample was dropped 100 times from a height of 5 cm, tapped, the volume was read again, and the bulk density was calculated by dividing the mass by the volume. In addition, it measured after confirming that the volume reduction of the powder was saturated in the middle of 100 times of tapping.

8). Measurement of molded body bulk density and sintered body bulk density The bulk density of the molded body was calculated from the volume obtained by measuring the size of the molded body and the measured mass. The density of the sintered body was determined by the Archimedes method using water.

9. Measurement of slurry viscosity After adding 1/3 times the mass of ethanol to the powder, and adding 0.2% by weight of the dispersant SN-9228 (trade name) manufactured by San Nopco, stirring and ultrasonic dispersion treatment were performed. To give a 75% by weight slurry. Using a B-type viscometer, No. Viscosity was measured under the condition of 12 prm with 4 rotors.

Example 1
Barium carbonate (Nippon Kagaku, LC-1 (trade name), BET specific surface area 10.2 m ² / g), Titanium dioxide (Ishihara Techno, PT-401M (trade name), BET specific surface area 20.7 m ² / g , Measuring the loss on ignition of rutile ratio (50.7%) (weight loss when moisture and volatile components are removed by heating to 700 ° C.), and correcting the weight shift due to volatile components such as moisture, About 1.1 kg of powder was weighed so that the molar ratio of barium carbonate to titanium dioxide was 1: 1. Using a 10 L polyethylene pot and a 15 mmφ iron core plastic ball, the mixed powder weighed by a dry ball mill was mixed for 20 hours. The BET specific surface area after mixing was 13.8 m ² / g. As a result of analyzing the mixture by TG-DTA, the production temperature of barium titanate was 820 ° C. The mixture was fired using a tubular furnace (furnace core tube volume 20 L) having a quartz glass furnace core tube. The temperature inside the furnace was raised to a nitrogen atmosphere, and the temperature was raised. At 600 ° C., an atmosphere of 3% by volume of hydrogen chloride—97% by volume of nitrogen was introduced, switched to an air atmosphere at 700 ° C. and heated to 950 ° C. The first firing was performed while maintaining the time. The pressure in the firing atmosphere is all atmospheric pressure (about 0.1 MPa). After firing, the obtained barium titanate powder was dispersed in an aqueous solution of ammonium hydrogen carbonate having a concentration of 0.8% by weight, filtered and washed. The washed powder was dried at 130 ° C. and held in an air atmosphere at 900 ° C. for 3 hours to perform second firing. Further, the powder was pulverized for 20 hours by a ball mill using a 10 L polyethylene pot and a plastic ball with a core of 15 mmφ.

As a result of X-ray diffraction analysis, the obtained powder was a BaTiO ₃ single phase and c / a was 1.0095. The average particle size was 0.130 μm. The BET specific surface area was 8.57 m ² / g, and the BET diameter ratio was 1.12. The particle bulk density was 5.88 g / cm ³ , the Ba / Ti ratio by fluorescent X-ray was 1.000, and the chlorine content was 26 ppm by weight. The loosed bulk density of 1.61 g / cm ^3, OmoSoTakashi density was 2.04 g / cm ^3.

Next, when this powder was dispersed in ethanol and the viscosity was measured as a slurry of 75% by weight, it was 13160 mPa · s. Further, the powder was formed into a cylindrical shape of 13 mmφ by uniaxial pressing, and further a pressure of 1.5 t / cm ² was applied by a hydrostatic press to produce a compact. The bulk density of this molded body was 3.65 g / cm ³ . This molded body was sintered in air at 1100 ° C. for 3 hours, and the density of the obtained sintered body was measured to be 5.82 g / cm ³ (96.7% of the theoretical density). Sintering was carried out at 1200 ° C. for 3 hours, and the density of the obtained sintered body was measured to be 5.74 g / cm ³ (95.3% of the theoretical density).

  In addition, the result of each following Example and each comparative example was shown in Table 1 (however, a sintered compact density is a result in 1100 degreeC sintering).

Example 2
Baking and washing were performed in the same manner as in Example 1 except that the first baking temperature was changed to 900 ° C. As a result of XRD analysis, the obtained powder was a BaTiO ₃ single phase and c / a was 1.0089. The average particle size was 0.130 μm. The BET specific surface area was 8.65 m ² / g, and the BET diameter ratio was 1.13. The average density of the particles was 5.86 g / cm ³ , the Ba / Ti ratio by fluorescent X-ray was 1.001, and the chlorine content was 35 ppm by weight. The lightly loaded bulk density was 1.55 g / cm ³ and the heavyly loaded bulk density was 2.00 g / cm ³ . As a result of sintering in the same manner as in Example 1, the molded body density was 3.59 g / cm ³ , and the sintered body density was 5.85 g / cm ³ (97.2% of the theoretical density) when sintered at 1100 ° C. It was 5.76 g / cm ³ (95.7% of the theoretical density) after sintering at 1200 ° C.

Example 3
The firing and cleaning were performed in the same manner as in Example 1 except that the first firing temperature was changed to 850 ° C. and the second firing temperature was 1000 ° C. As a result of XRD analysis, the obtained powder was a BaTiO ₃ single phase and c / a was 1.0097. The average particle size was 0.145 μm. The BET specific surface area was 7.27 m ² / g, and the BET diameter ratio was 1.06. The light bulk density was 1.44 g / cm ³ and the heavy bulk density was 2.00 g / cm ³ . The Ba / Ti ratio by fluorescent X-ray was 0.998, and the chlorine content was 46 ppm by weight. Further, as a result of sintering at 1100 ° C. in the same manner as in Example 1, the sintered body density was 5.92 g / cm ³ (98.3% of the theoretical density).

Example 4
Baking and washing were performed in the same manner as in Example 1 except that the second baking temperature was 950 ° C. As a result of XRD analysis, the obtained powder was a BaTiO ₃ single phase and c / a was 1.0095. The average particle size was 0.185 μm. The BET specific surface area was 6.49 m ² / g, and the BET diameter ratio was 1.20. The light bulk density was 1.45 g / cm ³ and the heavy bulk density was 1.92 g / cm ³ . The Ba / Ti ratio by fluorescent X-ray was 0.997, and the chlorine content was 29 ppm by weight. Further, as a result of sintering at 1100 ° C. in the same manner as in Example 1, the sintered body density was 5.9 g / cm ³ (99.5% of the theoretical density). Further, as a result of sintering at 1100 ° C. in the same manner as in Example 1 except that the sintering temperature was lowered to 1050 ° C. and the sintering temperature was changed to 1050 ° C., the sintered body density was 5.91 g / cm ³ (theoretical). 98.2% of the density).

Example 5
Baking and washing were performed in the same manner as in Example 1 except that the first baking temperature was changed to 900 ° C. As a result of XRD analysis, the obtained powder was a BaTiO ₃ single phase and c / a was 1.0096. The average particle size was 0.159 μm. The BET specific surface area was 7.12 m ² / g, and the BET diameter ratio was 1.14. The light bulk density was 1.47 g / cm ³ and the heavy bulk density was 2.00 g / cm ³ . The Ba / Ti ratio by fluorescent X-ray was 0.998.

Example 6
Firing and washing were performed in the same manner as in Example 1 except that the atmospheric gas introduced at 600 ° C. was changed to 10% by volume of hydrogen chloride and 90% by volume of nitrogen. As a result of XRD analysis, the obtained powder was a BaTiO ₃ single phase and c / a was 1.0083. The average particle size was 0.160 μm. The BET specific surface area was 7.19 m ² / g, and the BET diameter ratio was 1.15. The loosed bulk density of 1.56 g / cm ^3, OmoSoTakashi density was 2.01 g / cm ^3. The Ba / Ti ratio by fluorescent X-ray was 0.998.

Example 7
Using the barium titanate powder obtained in Example 1, a 1: 9 mixed solution of toluene / ethanol was added as a solvent to a concentration of 50% by weight, and SN-9228 (trade name) manufactured by San Nopco was added as a dispersant (titanium). An amount of 1% by weight with respect to the barium acid powder was added.) And pulverized and mixed for 2 hours by a ball mill using Hypra Ball (trade name, iron-made nylon ball) to obtain a slurry. Using the slurry, molding was performed by a slip casting method, and the molded body was dried and then sintered by being held at 1200 ° C. for 3 hours in an air atmosphere. The density of the sintered body increased to 5.75 g / cm ³ (95.6% of the theoretical density). A 5 mm × 5 mm range of the surface of the obtained sintered body was observed with a scanning electron microscope, but no pores (holes) or protrusions having a size of 0.5 μm or more were observed.

Example 8
Using the barium titanate powder obtained in Example 2, a 1: 9 mixed solution of toluene / ethanol as a solvent was added to a concentration of 50% by weight, and Texahol (trade name) manufactured by San Nopco was added as a dispersant (barium titanate). An amount of 1% by weight with respect to the powder was added.) And pulverized and mixed for 2 hours by a ball mill using Hypra Ball (trade name, iron-made nylon ball) to obtain a slurry. Using the slurry, molding was performed by a slip casting method, and the molded body was dried and then sintered by being held at 1200 ° C. for 3 hours in an air atmosphere. The density of the sintered body increased to 5.69 g / cm ³ (94.6% of the theoretical density). A 5 mm × 5 mm range on the surface of the obtained sintered body was observed with a scanning electron microscope, but no pores or protrusions having a size of 0.5 μm or more were observed.

Comparative Example 1
Baking and washing were performed in the same manner as in Example 1 except that the entire baking process was performed in an air atmosphere. As a result of XRD analysis, the obtained powder was a BaTiO ₃ single phase and c / a was 1.0073. The average particle size was 0.162 μm. The BET specific surface area was 7.30 m ² / g, and the BET diameter ratio was 1.19. The average density of the particles was 5.84 g / cm ³ and the Ba / Ti ratio by fluorescent X-ray was 0.998. The lightly loaded bulk density was 1.40 g / cm ³ and the heavyly loaded bulk density was 1.78 g / cm ³ . As a result of sintering in the same manner as in Example 1, green density 3.39 g / cm ^3, 1100 sintered body density of ° C. is 4.67g / cm ³ (77.6% of theoretical density), the 1200 ° C. The sintered body density was 4.94 g / cm ³ (82.1% of the theoretical density).

Comparative Example 2
The first baking was carried out in the same manner as in Example 1 except that the baking temperature was 850 ° C. and the entire baking process was performed in an air atmosphere. As a result of XRD analysis, the obtained powder was mixed with BaCO ₃ , BaO and TiO ₂ in addition to BaTiO ₃ .

Comparative Example 3
In the first baking, baking and cleaning were performed in the same manner as in Example 1 except that after introducing an atmosphere of 3% by volume of hydrogen chloride and 97% by volume of nitrogen at 600 ° C., the atmosphere was changed to the end of the first baking. Carried out. In the XRD analysis of the powder immediately after the first firing, the formation of barium chloride was observed. As a result of XRD analysis, the powder obtained after washing and refiring was a BaTiO ₃ single phase, and c / a was 1.0085. The average particle diameter was 0.282 μm, and coarse particles of 3 μm or more were observed. The BET specific surface area was 6.69 m ² / g, and the BET diameter ratio was 1.89. The light bulk density was 1.33 g / cm ³ and the heavy bulk density was 1.88 g / cm ³ . The Ba / Ti ratio by fluorescent X-ray was 0.996, and the chlorine content was 260 ppm by weight.

Comparative Example 4
An aqueous solution of titanium tetrachloride (manufactured by Sumitomo Sitix) diluted with water to 2.5 mol / L in terms of titanium dioxide and a 5% by weight sodium hydroxide aqueous solution were adjusted to pH 3. The liquid was poured into 1 L of ion-exchanged water cooled with ice while adjusting to be in the range of 7 to 4.3. The resulting precipitate of hydrated titanium dioxide was filtered and washed using a suction filter. The BET value of the powder obtained by drying the precipitate at 110 ° C. was 200 to 240 m ² / g. Weigh 15 g of precipitate in terms of titanium dioxide, add ion-exchanged water to make a suspension, and further barium hydroxide octahydrate (Wako Pure Chemical Industries, Ltd.) so that Ba / Ti = 1.4. And the solution was hydrothermally treated in an autoclave at 150 ° C. for 1 hour. After the hydrothermal treatment, the solid in the solution was filtered, washed, dried at 110 ° C., and fired at 600 ° C. in an air atmosphere. As a result of XRD analysis, the obtained powder was a BaTiO ₃ single phase and c / a was 1.0007. The average particle size was 0.131 μm. The BET specific surface area was 11.1 m ² / g, and the BET diameter ratio was 1.46. The average density of the particles was 5.76 g / cm ³ , the Ba / Ti ratio by fluorescent X-ray was 0.997, and the chlorine content was 57 ppm by weight. The light bulk density was 1.08 g / cm ³ and the heavy bulk density was 1.45 g / cm ³ . As a result of sintering in the same manner as in Example 1, the compact density was 3.28 g / cm ³ , and the sintered body density at 1100 ° C. was 4.58 g / cm ³ (76.1% of the theoretical density), 1200 ° C. The sintered body density was 5.16 g / cm ³ (85.7% of the theoretical density).

Comparative Example 5
Hydrothermal treatment was performed under the same conditions as in Comparative Example 4, and the same procedure as in Comparative Example 4 was performed except that the firing temperature was changed to 800 ° C. As a result of XRD analysis, the obtained powder was a BaTiO ₃ single phase and c / a was 1.0060. The average particle size was 0.389 μm. The BET specific surface area was 7.26 m ² / g, and the BET diameter ratio was 2.83. Further, the light bulk density was 1.07 g / cm ³ and the heavy bulk density was 1.45 g / cm ³ . When this powder was dispersed in ethanol and the viscosity was measured as a slurry of 75% by weight, it was 26460 mPa · s. As a result of sintering in the same manner as in Example 1, green density 3.50 g / cm ^3, 1100 sintered body density of ° C. is 4.33g / cm ³ (71.9% of theoretical density), the 1200 ° C. The sintered compact density was 4.98 g / cm ³ (82.7% of the theoretical density).

Claims (9)

  The length ratio c / a between the a-axis and the c-axis of the perovskite structure is 1.008 or more, and the value obtained by dividing the average particle diameter by the BET specific surface area equivalent diameter calculated from the BET specific surface area is 1 or more and 1.5 or less. The barium titanate powder characterized by the above-mentioned.   The barium titanate powder according to claim 1, wherein the average particle size is 0.05 µm or more and 0.3 µm or less. The barium titanate powder according to claim 1 or 2, wherein the light bulk density is 1.4 g / cm ³ or more and the heavy bulk density is 1.8 g / cm ³ or more. The barium titanate powder according to claim 1, wherein the average density of the particles is 5.8 g / cm ³ or more.   In a method for producing barium titanate, which is a mixture containing a titanium compound and a barium compound, and bakes a mixture that gives barium titanate by firing at a temperature higher than that at which barium titanate is produced. Above, in a temperature range below the temperature at which barium titanate is produced, exposed to an atmosphere containing one or more halogens selected from the group consisting of chlorine, bromine and iodine, and then above the temperature at which barium titanate is produced In the method for producing barium titanate powder, which is carried out by heating in an atmosphere substantially free of any of chlorine, bromine, iodine and fluorine.   The production method according to claim 5, wherein the total content of molecular halogen or hydrogen halide in an atmosphere containing halogen is 0.5 vol% or more and 30 vol% or less.   The production method according to claim 5, wherein the halogen is chlorine.   The production method according to claim 5, wherein the pressure of the atmosphere containing halogen is atmospheric pressure. The powder obtained after firing is washed, and further maintained in an atmosphere substantially free of chlorine, bromine, iodine and fluorine at a temperature in the range of 800 ° C. to 1100 ° C. to re-fire the powder. The manufacturing method according to claim 5, wherein: