JP5057643B2 - Manufacturing method of sintered barium titanate - Google Patents

Description

The present invention relates to a method for producing a barium titanate sintered body .

  In recent years, with the miniaturization of electronic devices, for example, multilayer ceramic capacitors, which are representative examples of multilayer ceramic electronic components, have been made thinner and multilayered in order to meet the demand for smaller size and larger capacity in the market. However, the ceramic green sheets used in the dielectric layer manufacturing process have been made finer for ceramic powder used to reduce the film thickness.

  Here, as a method for achieving atomization of a ceramic powder prepared by a solid phase method using a metal oxide or a metal carbonate as a raw material powder, one disclosed in Patent Document 1 below It has been known.

FIG. 4 is a conventional process diagram of mixing and pulverizing raw material powders in a ceramic manufacturing method. As shown in FIG. 4, first, a slurry is prepared by previously blending a plurality of kinds of raw material powders, and then the slurry is pulverized and dried, followed by calcination. The pulverization here is carried out using a forced stirring mill configured by filling fine balls (commonly called beads) inside the pulverization container. According to the forced stirring mill described above, a smaller diameter medium can be used as compared with a conventional ball mill in which a ball for pulverization is placed in a pot and rotated. There is an advantage that a corresponding pulverized particle size can be achieved.
JP 2003-306385 A

  However, as described above, in the conventional manufacturing method, since a plurality of types of raw material powders are mixed before pulverization and then pulverized by a forced stirring mill, the pulverizability of the plurality of types of raw material powders used is different. If different, under the same pulverization conditions, depending on the material to be pulverized, overpulverization and insufficient pulverization are likely to occur simultaneously, and the slurry that has been excessively pulverized tends to agglomerate. The target pulverized particle size could not be obtained, and there was a problem that uniform slurry was difficult to obtain due to the difference in particle size.

  In addition, when a plurality of raw material powders are used as described above, when raw material powders having a large particle diameter are used in either of them, the coarse particles and the fine particles cannot be uniformly dispersed. There was a risk that a partially inhomogeneous composition could be formed in the powder.

  In addition, if excessive grinding conditions are used to solve the shortage of grinding, the amount of impurities mixed due to the media during grinding and the lining material of the grinding container increases, and there is a problem that high purity powder cannot be obtained. It was.

Therefore, according to the present invention, it is possible to easily obtain an ultrafine and homogeneous barium titanate powder and to reduce the amount of impurities during pulverization. By using the barium titanate powder thus obtained, homogeneous and fine crystals can be obtained. It aims at providing the manufacturing method of the barium titanate sintered compact comprised by particle | grains.

The method for producing a barium titanate sintered body according to the present invention includes a raw material powder composed of any one of Ti oxide, carbonate compound and chloride, and Ba oxide, carbonate compound and chloride. The raw material powder composed of the above compound is individually pulverized using a media forced stirring mill or a ball mill so that the average particle diameter of the raw material powder is 100 nm or less, and each slurry is prepared. When using a high pressure dispersion apparatus, a mixing step, each of the slurry to prepare a mixed slurry by blowing one another with high pressure gas, the calcining step of calcining the mixed powder prepared by drying the mixture slurry And a molding step of forming a molded body using the calcined powder produced in the calcining step, and a firing step of firing the molded body at a temperature of 1150 ° C. or lower. .

According to the present invention, a raw material powder composed of any one compound of Ti oxide, carbonate compound, and chloride , and a raw material powder composed of any compound selected from Ba oxide, carbonate compound, and chloride . Even if the pulverization properties are different from each other, each raw material powder is mixed after pulverization by separately pulverizing before calcination by changing the pulverization conditions so as to achieve the target particle size distribution. The particle size of the raw material powder to be adjusted can be adjusted appropriately. By adopting such a production method, it is possible to suppress aggregation of the raw material powder due to overgrinding, and to suppress contamination of impurities (contamination) from the mill or ball generated during overgrinding.

Further, in the step of preparing each of the slurry, more using the media forced stirring type mill or a ball mill because of object to be crushed gives high dispersion state even when fine, 100 n m is the average particle size of the raw material powder Grind to the following.

Et al is, in the mixing step is the next step, Ru with a high-pressure dispersing device or media-less dispersing device because it reduces the contamination of the media and mill during mixing. Furthermore, in this manufacturing method, a calcining step of calcining the mixed powder produced by drying the mixed slurry, a molding step of forming a molded body using the calcined powder produced in the calcining step, and the molding And a firing step of firing the body at a temperature of 1150 ° C. or lower. By such a manufacturing method, firing at a temperature of 1150 ° C. or lower, which has not been conventionally possible as a sintering temperature for barium titanate, can be easily performed.

  Hereinafter, an example of barium titanate powder, which is a material for a multilayer ceramic capacitor, will be described in detail with reference to FIG. FIG. 1 is a process diagram showing a method for producing a ceramic according to the present invention. In the method for producing ceramics of the present invention, it is important to first pulverize each of a plurality of types of raw material powders to be used. In particular, in the present invention, it is preferable to use a media forced stirring mill as the pulverizer. FIG. 2 is a schematic cross-sectional view of a media forced stirring mill according to the present invention. The media forced stirring type mill A includes a stirring container 1, and a slurry introduction port 3 is provided at one end of the stirring container 1, and a slurry discharge port 5 is also provided at the other end.

  In the stirring vessel 1, a plurality of disks 9 are provided as stirring rotating bodies held by the main shaft 7. The disk 9 is configured to rotate at a predetermined peripheral speed by rotationally driving the main shaft 7. In the media forced stirring mill, a rotor or a pin may be used as the rotating body for stirring in addition to the disk 9 described above. A space for removing the main shaft 7 and the disk 9 in the stirring container 1 is filled with a grinding medium (not shown), and the medium is filled with fine balls called beads. The ball diameter is preferably 300 μm or less from the viewpoint of making the final size of the object to be ground in the present invention finer. Moreover, as a medium, what uses materials, such as an alumina and a zirconia, can be used conveniently. The filling rate of the medium is 80 to 98% of the effective internal volume of the stirring container 1, more specifically, the effective internal volume of the stirring container 1. Further, the volume concentration of the raw material powder in the slurry is set to 2% by volume or more. Further, the peripheral speed of the disk is set to 3 m / second or more. In particular, 4 to 10 m / sec is preferable.

  Next, slurry containing raw material powder is introduced from the slurry inlet 3 of the stirring vessel 1 while the disk 9 is rotated at a predetermined peripheral speed. Next, the slurry wet-mixed with the media in the media forced stirring mill is discharged from the slurry discharge port 5.

  This slurry is obtained, for example, by dispersing raw material powder in a liquid such as water or ethanol. In the present invention, it is preferable to add a suitable dispersant to the slurry.

And according to this invention, the average particle diameter after grind | pulverizing raw material powder can be 100 nm or less, especially 80 nm or less, and contamination can be 500 ppm or less.

  On the other hand, in the conventional method of pulverizing under the same conditions after mixing plural kinds of raw material powders to be used, if the pulverization properties of these raw material powders are different, Over-pulverization and insufficient pulverization tend to occur at the same time, and the over-pulverized slurry tends to agglomerate. It becomes difficult to obtain a uniform slurry due to the difference between the two.

  In addition, when a plurality of raw material powders are used as described above, when either one of the raw material powders having a large particle size is used, the particle size becomes a particle size that depends on the particle size of the raw material powder, and calcining is performed. It is difficult to form a partially uniform composition with respect to the powder, which also prevents homogenization.

  Furthermore, when excessive grinding conditions are employed in order to solve the shortage of grinding, the amount of impurities mixed due to the media during grinding or the lining material of the grinding container increases, and high purity powder cannot be obtained.

Next, the other raw material powders are pulverized in the same manner as described above, and these pulverized single slurries are mixed to prepare a mixed slurry. The mixer when preparing the mixture slurry, in terms of suppressing contamination of impurities from the media, Ru with a high-pressure dispersing device or media-less disperser. FIG. 3 is a schematic sectional view showing a medialess disperser. As shown in FIG. 3, the medialess disperser B includes a stirring vessel 21, and a slurry introduction port 23 is provided at one end of the stirring vessel 21, and a slurry discharge port 25 is also provided at the other end. ing.

  In the stirring vessel 21, a plurality of stirring blades 29 are provided as stirring rotating bodies held by the main shaft 27. The stirring blade 29 is configured to rotate at a predetermined peripheral speed by rotationally driving the main shaft 27.

  The high-pressure dispersing device is a method of spraying pulverized single slurry together with high-pressure gas. In some cases, it can be sprayed onto ceramic equipment. In this way, the mixing of impurities from the media can be suppressed by the method of spraying single slurry together with high-pressure gas. The pressure is preferably 100 MPa or more.

  Each condition in the wet mixing process as described above is obtained based on the result of an experiment described later. According to the manufacturing method including the wet mixing step under such conditions, a slurry having a very small particle size distribution and a small amount of impurities mixed into the raw material powder can be obtained.

More specifically, for example, in the perovskite complex oxide represented by the general formula ABO ₃ , the A / B molar ratio variation as the composition variation can be set to 0.01 or less. That is, in the present invention, since the single slurries prepared in advance are mixed with each other, the ceramic powder contained in the single slurry is diluted, and therefore diluted as compared with the case of directly mixing the ceramic powder. The composition variation can be reduced by that amount. The variation in the A / B molar ratio is the difference between the maximum value and the minimum value when the composition for 10 primary particles is obtained by TEM.

Further, in the present invention, as raw material powder, Ba, of Ti, oxides, carbonates compounds, can be used any compound of the chloride, in particular, the perovskite type complex represented by a general formula ABO ₃ in obtaining an oxide powder, for example a divalent besides Ba as an element occupying the a site, Mg, Ca, and Sr, also Zr is tetravalent besides Ti as an element occupying the B sites have free Good .

  Next, after the discharged mixed slurry is dried, it is calcined at a temperature of 1000 ° C. or lower, and then the calcined powder is crushed so as to maintain the above-mentioned average particle diameter. The pulverized mixed raw material powder is then formed into a desired shape and then fired to obtain a ceramic sintered body. When the fine ceramic powder obtained by the production method of the present invention is used, the firing temperature can be easily reduced to 1150 ° C. or lower, which has not been conventionally achieved as a sintering temperature for barium titanate.

First, barium titanate is selected as the composite oxide according to the present invention, and BaCO ₃ having a purity of 98% and an average particle size of about 0.25 μm and TiO ₂ having a purity of 97% and an average particle size of 30 nm are used as the raw material powder. Got ready.

Next, each raw material powder was put in a stirring vessel, water as a solvent and polyacrylate as a dispersing agent were added, and each pre-dispersed slurry was prepared by stirring in the stirring vessel for 30 minutes. . At this time, the solid content ratio of the raw material powder to water was dispersed such that BaCO ₃ was 40 mass% and TiO ₂ was 10 mass%.

  Next, the pre-dispersed slurry was pulverized and mixed using a media forced stirring mill, a ball mill, or a high-pressure disperser. The grinding conditions are shown in Table 1. The media was zirconia, and the grinding conditions were adjusted as the media diameter, media filling rate, peripheral speed, residence time, pressure, flow rate, and number of passes through the mill. Each sample was prepared under the following conditions.

  The mixed slurry was prepared so that the Ba / Ti ratio of each slurry prepared by pulverization was 1. The mixed slurry was dried at a temperature of 110 ° C. for 10 hours.

The conditions for pulverization and mixing in the sample of the present invention were as follows. That is, no. In No. 1, the two types of pre-dispersed slurry obtained were each pulverized and dispersed with a media forced stirring mill. BaCO ₃ media forced stirring mill conditions were media 0.05φZrO ₂ , bead filling rate 85%, peripheral speed 6 m / s, residence time 3 min, 2 passes. The TiO ₂ media forced stirring mill conditions were media 0.05φZrO ₂ , bead filling rate 85%, peripheral speed 12 m / s, and residence time 3 min. Next, the obtained two kinds of slurries were prepared so that the Ba / Ti molar ratio = 1.000, and a single slurry was sprayed together with a high-pressure gas in a high-pressure dispersion device to be dispersed and mixed. The treatment was performed at a pressure of 150 MPa, a flow rate of 500 ml / min, and one pass.

No. In No. 2, no. Two types of slurry pulverized with a media forced stirring mill under the same conditions as 1 were prepared so that the Ba / Ti molar ratio = 1.000, and dispersed and mixed with a bead mill. The medium was 0.05φZrO ₂ , the bead filling rate was 85%, the peripheral speed was 4 m / s, and the residence time was 5 min.

No. In No. 3, the two types of pre-dispersed slurry obtained were pulverized and dispersed with a ball mill. The ball mill conditions for BaCO ₃ were 1 L polypot, media 0.5φZrO ₂ , filling rate 60%, peripheral speed 1 m / s, and rotation time 72 Hr. The ball mill conditions for TiO ₂ were media 0.5φZrO ₂ , filling rate 60%, peripheral speed 1 m / s, and rotation time 150 Hr.

  Next, the obtained two types of slurries were prepared so as to have a Ba / Ti molar ratio = 1.000, and dispersed and mixed in a high-pressure dispersion apparatus. The treatment was performed at a pressure of 150 MPa, a flow rate of 500 ml / min, and one pass.

No. In No. 4, no. Two types of slurry pulverized by a ball mill under the same conditions as in No. 3 were prepared so that the Ba / Ti molar ratio = 1.000, and dispersed and mixed in a media forced stirring mill. The medium was 0.05φZrO ₂ , the bead filling rate was 85%, the peripheral speed was 4 m / s, and the residence time was 5 min.

No. which is a comparative example (process B). For 5 to 7, first, BaCO ₃ powder and TiO ₂ powder were prepared so that the Ba / Ti molar ratio = 1.000, and 1% polyacrylate dispersant was added to the powder weight. And it was made to disperse | distribute so that solid content ratio might be 30 weight% in pure water, and it stirred for 30 minutes with the stirrer, and obtained the pre-mixed slurry.

No. In No. 5, the obtained premixed slurry was pulverized and mixed in a media forced stirring mill. The media forced agitation mill conditions were media 0.05φZrO ₂ , bead filling rate 85%, peripheral speed 12 m / s, and residence time 8 min.

No. In No. 6, the premixed slurry was pulverized and mixed in a media forced stirring mill. The media forced agitation mill conditions were media 0.05φZrO ₂ , bead filling rate 85%, peripheral speed 6 m / s, and residence time 8 min.

  No. In No. 7, the premixed slurry was dispersed and mixed with a high-pressure dispersing device. The treatment was performed at a pressure of 245 MPa, a flow rate of 500 ml / min, and 3 passes.

  Next, the above No. 1 to 7 parts by weight of glass powder as a sintering aid and 3 parts by weight of polyvinyl alcohol as a binder are added to 100 parts by weight of the mixed powder to perform granulation. Was used to form a molded body having a diameter of 12 mmΦ and a thickness of 2 mm at a pressure of 100 MPa.

Next, this molded body was degreased by heat treatment at 500 ° C. for 2 hours in the atmosphere, and then baked for 2 hours at 1100 ° C. in a reducing atmosphere, and further at 1000 ° C. in the atmosphere. Re-oxidation treatment was performed to obtain a ceramic sintered body. Next, an In · Ga alloy was applied to the upper and lower surfaces of the obtained ceramic sintered body, and used as a material for property evaluation. The amount of impurities was determined by ICP analysis of the mixed powder. The average particle size of the obtained powder after pulverization and the crystal particles after sintering was obtained as an average value of 20 from an electron micrograph. The amount of unreacted BaCO ₃ and the lattice constant c / a in the mixed powder were determined from the X-ray diffraction pattern by the Rietveld method. The relative dielectric constant of the ceramic sintered body was determined by measurement after holding at 1 MHz, 1 v, and 1 minute using an LCR meter. Table 1 shows the results.

As is apparent from the results in Table 1, No. Reference numerals 1 and 3 represent samples of the present invention obtained by pulverizing the raw material powders and then mixing them with a high-pressure dispersing apparatus . The amount of impurities after mixing was suppressed to 500 ppm or less. The residual amount of BaCO ₃ was as low as 1% or less, and the tetragonal c / a was also as high as 1.007 or more. In all cases, the average particle size after pulverization was 95 nm or less, and the crystal particle size after sintering was also 150 nm or less. Moreover, the characteristic which satisfy | fills the dielectric constant of 900 or more was acquired as a result of the sintered compact. In addition, No. Reference numerals 2 and 4 are reference examples.

No. 5-7 have shown the sample outside the range of this invention grind | pulverized after mixing raw material powder. The amount of impurities was as large as 500 ppm or more, the unreacted content of BaCO ₃ was as large as 6% or more, and the tetragonal c / a was as low as 1.002 or less. The average particle size after pulverization was 110 to 160 nm, and the crystal particle size after sintering was 180 to 250 nm. For this reason, the relative dielectric constant of the obtained sintered body was significantly reduced.

It is process drawing which shows the grinding | pulverization and mixing of the raw material powder in the manufacturing method of the barium titanate sintered compact of this invention. It is a schematic sectional drawing of the media forced stirring type mill concerning this invention. It is a cross-sectional schematic diagram which shows the media-less disperser concerning this invention. It is the conventional process drawing of mixing and crushing of raw material powder in the manufacturing method of a barium titanate sintered compact .

Explanation of symbols

A Media forced stirring mill 1 Stirring vessel 3 Slurry inlet 5 Slurry outlet 7 Main shaft 9 Disk B Medialess disperser 21 Stirrer vessel 23 Slurry inlet 25 Slurry outlet 27 Main shaft 29 Stirring blade

Claims (1)

A raw material powder composed of any one compound of Ti oxide, carbonate compound and chloride, and a raw material powder composed of any compound selected from Ba oxide, carbonate compound and chloride, respectively. , Using a media forced stirring mill or a ball mill, pulverizing the raw material powder so that the average particle size is 100 nm or less, and producing each slurry,
Using a high pressure dispersion apparatus, a mixing step of preparing a mixed slurry by blowing one another each of the slurry with high pressure gas,
A calcining step of calcining the mixed powder produced by drying the mixed slurry;
A molding step of forming a molded body using the calcined powder produced in the calcining step;
A firing step of firing the molded body at a temperature of 1150 ° C. or lower;
The manufacturing method of the barium titanate sintered compact characterized by comprising.

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