JP2010228993A - Production method of dielectric particle aggregate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method of spherical and minute dielectric particle aggregates. <P>SOLUTION: The production method of dielectric particle aggregates includes steps of electrostatically charging a slurry containing dielectric particles and a solvent, spraying the slurry to produce charged droplets, and vaporizing the solvent in the droplets to aggregate dielectric particles. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing dielectric particle aggregates. Such dielectric particle aggregates are used, for example, in the production of ceramic sintered bodies.

  Conventionally, dielectric particle aggregates have been used in various applications such as the production of ceramic sintered bodies.

  As a method for producing dielectric particle aggregates, Patent Document 1 describes a method in which dielectric particles are dispersed in a solvent to form a slurry, and then the slurry is spray-dried by a rotating disk method or the like. The dielectric particle aggregate obtained by such a method has an average particle diameter in the range of about 20 μm to about 200 μm and is truly spherical.

  Patent Document 2 discloses a dielectric particle synthesized by a hydrothermal synthesis method and having an average particle diameter in the range of 0.05 μm to 0.2 μm and non-spherical.

  By the way, for example, when using dielectric particles for the production of a ceramic sintered body, the ceramic sintered body is obtained by pressure-molding and firing dielectric particle aggregates. Here, if the dielectric particle aggregates are spherical and minute, the dielectric particle aggregates are more uniformly and densely formed during the pressure forming, and the ceramic sintered body is more uniformly and densely formed. Can be.

  However, in the methods described in Patent Documents 1 and 2, it is difficult to form a spherical and minute dielectric particle aggregate, and a manufacturing method capable of forming such a dielectric particle aggregate is required. It was.

Japanese Patent Publication No. 7-17460 JP 2007-277031 A

  The present invention provides a method for producing a true spherical and fine dielectric particle aggregate.

  A method for producing dielectric particle aggregates according to an aspect of the present invention includes a step of charging a slurry containing dielectric particles and a solvent, a step of spraying the slurry to generate charged droplets, and the droplets And evaporating the solvent to agglomerate the dielectric particles.

  According to the method for producing a dielectric particle aggregate according to one embodiment of the present invention, a dielectric particle aggregate having a true spherical shape is provided by aggregating dielectric particles in a charged droplet. be able to.

It is sectional drawing explaining the manufacturing method of the dielectric material particle aggregate concerning one Embodiment of this invention. It is the photograph which expanded the barium titanate aggregate obtained by Example 1 5000 times with the scanning electron microscope. It is the graph showing the particle size distribution of the barium titanate aggregate in FIG. The vertical axis represents the circularity, the horizontal axis represents the particle size (μm), and each point represents each particle. It is the photograph which expanded the barium titanate aggregate obtained by Example 1, and which processed the focused beam by 8000 times with the scanning ion microscope. It is the photograph which expanded the barium titanate aggregate obtained by Example 2 5000 times with the scanning electron microscope.

  Below, the manufacturing method of the dielectric particle aggregate which concerns on one Embodiment of this invention is demonstrated in detail based on FIG. 1 for the manufacturing method using the spraying apparatus 1 as an example.

  The dielectric particle aggregate produced according to this embodiment can be used for various applications.

  For example, when such dielectric particle aggregates are used in the production of ceramic sintered bodies, the dielectric particle aggregates are spherical and minute when forming the dielectric particle aggregates. And can be densely molded. Therefore, a more uniform and dense ceramic sintered body can be produced.

  First, the spray device 1 shown in FIG. 1 will be described.

  The spraying device 1 is hollow and has a cylindrical syringe 2 having an opening 2 a at the lower end, an applied voltage supply line 3 connected to the syringe 2, and an applied voltage supply line 3. A power source 4 and a conductive substrate 5 positioned below the syringe 2 and connected to the ground are provided. The diameter of the opening 2a is set to be very small, for example, 100 μm or less. The power supply 4 can adjust the applied voltage.

  The spray device 1 has a function of spraying a sample as follows.

  First, a sample is supplied into the syringe 2. As the sample, for example, a liquid or slurry is used. The supplied sample is not lowered downward from the opening 2a because the surface tension exceeds the gravity due to the minute diameter of the opening 2a.

  Next, by applying a voltage from the power source 4 to the sample in the syringe 2 via the applied voltage supply line 3, the sample is charged and an electric field is generated. Since the substrate 5 is conductive, an electrostatic force is generated between the sample and the substrate 5 by the electric field. Due to the electrostatic force, an electric attractive force is generated between the sample and the substrate 5. When the sum of the electric attractive force and gravity exceeds the surface tension, the sample is sprayed toward the substrate 5 from the opening 2a.

  By such spraying, droplets are generated from the charged sample. Since the droplets are charged, the sample droplets repel each other due to the electric repulsion, so that the sample droplets can be miniaturized. By such miniaturization, the liquid contained in the droplets can be efficiently evaporated. Since it evaporates in this way, it is not necessary to apply an external force such as wind pressure or centrifugal force to the sample.

  Below, the manufacturing method of the dielectric particle aggregate using the spraying apparatus 1 is demonstrated.

  (1) Prepare dielectric particles.

  As the dielectric particles, those formed of a dielectric material such as barium titanate, calcium titanate, strontium titanate, or lead zirconate titanate can be used. In particular, it is desirable to use a dielectric material having a high dielectric constant. As a dielectric material having a high dielectric constant, a piezoelectric material, a pyroelectric material, or a ferroelectric material can be used. Among them, a material having a ferroelectric property is used from the viewpoint of dielectric constant. It is desirable. In the case where the dielectric particles have a perovskite structure, it is desirable to use those having a tetragonal crystal structure from the same viewpoint.

  The average particle diameter of the dielectric particles is set to 0.001 μm or more and 3 μm or less, for example. The dielectric particles are produced by, for example, a hydrothermal synthesis method.

  (2) The dielectric particles and the solvent are mixed to prepare the slurry 6.

  The mixing of the dielectric particles and the solvent is performed by dispersing the dielectric particles in the solvent using, for example, a ball mill, a bead mill, or a vibration mill. As the solvent, ethanol, polyethylene glycol, or the like can be used. Of these, it is desirable to use ethanol. Note that when the dielectric particles and the solvent are mixed, a plasticizer, a dispersant, a lubricant, or the like may be further mixed.

  (3) The slurry 6 is sprayed to form dielectric particle aggregates.

  Specifically, it is performed as follows.

  First, the slurry 6 is supplied into the syringe 2.

  Next, a voltage is applied from the power source 4 to the slurry 6 in the syringe 2 via the applied voltage supply line 3, thereby charging the slurry 6 and generating an electric field. The charged slurry 6 is sprayed by an electrostatic force generated due to the electric field.

  Charged droplets are generated by spraying the slurry 6. Since the charged droplets repel each other by an electric repulsive force, the droplets of the slurry 6 can be made finer and the solvent contained in the droplets can be efficiently evaporated. In addition, it is desirable not to heat at the time of this spraying.

  By the above method, dielectric particle aggregates can be produced.

  Such dielectric particle aggregates are presumed to be formed by polarization of dielectric particles in the charged droplets, and evaporation of the solvent in the droplets in a state where the polarized dielectric particles aggregate together. Is done.

  The dielectric particle aggregates thus produced are true spherical and minute. The true spherical shape of the dielectric particle aggregate is presumed to be formed by evaporation of the solvent in the droplet in a state where the charged dielectric particles aggregate in the charged droplet. The In addition, the minute shape of the dielectric particle aggregate is presumed to be caused by the above-described formation of the aggregate in the miniaturized droplet.

  In addition, the dielectric particle aggregate is formed by polarization of the dielectric particles and evaporation of the solvent, and it is estimated that the density is uniform because no external force such as wind pressure or centrifugal force is applied during the aggregation. .

  In the step (1), when a dielectric material having a high dielectric constant is used, dielectric particles can be efficiently aggregated when the slurry 6 is sprayed. This is presumably because the dielectric particles are easily polarized in the charged droplets, and the dielectric particles are likely to aggregate in the charged droplets.

  Moreover, when ethanol is used as the solvent in the step (2), the dielectric particles can be efficiently aggregated. It is estimated that this is because the solvent can be efficiently evaporated when the slurry 6 is sprayed.

  Further, in the step (2), by appropriately adjusting the concentration of the dielectric particles in the slurry 6, a dielectric particle aggregate having a desired size can be produced. For example, when the concentration of dielectric particles in the slurry 6 is increased, the shape of the dielectric particle aggregate can be increased. This is presumed to be due to the change in the amount of dielectric particles that aggregate in the charged droplets depending on the concentration of the dielectric particles.

  Moreover, when spraying the slurry 6 in the step (4), it is desirable not to heat it. As a result, the density of dielectric particle aggregates can be formed more uniformly. In addition, according to this embodiment, since the droplets are miniaturized, the solvent can be efficiently evaporated without heating.

  The present invention is not limited to the above-described embodiments, and various changes and improvements can be made without departing from the scope of the present invention.

  Examples of the present invention will be described below.

Example 1
First, tetragonal barium titanate (average particle size: 0.1 μm) was added to ethanol and mixed for 5 hours by a bead mill to prepare a slurry having a barium titanate mass concentration of 55%. Next, the slurry was sprayed by applying a voltage of 30 KV using the above-mentioned spraying apparatus, and ethanol was evaporated to obtain a barium titanate aggregate.

  A scanning electron micrograph of the obtained barium titanate aggregate is shown in FIG. The image analysis of the photograph shown in FIG. 2 was performed using commercially available software called “MacView”, and the circularity and the average particle diameter were measured. The results are shown in Table 1 and FIG. In addition, a particle size is based on the equivalent circle diameter prescribed | regulated to JISR1670: 2006. The circularity conforms to JIS B2711: 2005.

As shown in Table 1, the barium titanate aggregate has a circularity close to 1 and a small average particle size. Therefore, the barium titanate aggregate is truly spherical and minute.

  Further, the obtained barium titanate aggregate was subjected to focused ion beam processing to form a cross section. FIG. 4 shows a scanning ion micrograph of the barium titanate aggregate subjected to such processing. As shown in FIG. 4, many voids are observed in the cross section (arrows in the figure). For the voids in the cross section, the distance between the centers of gravity with the closest void was measured, and the standard deviation of the distance between the centers of gravity was determined. The results are shown in Table 2. The distance between the centers of gravity was measured using “MacView”. Moreover, the standard deviation was calculated | required about three different cross sections.

As shown in Table 2, the standard deviation of the distance between the centers of gravity is small. Therefore, since the distances between the voids are almost uniform, it is estimated that the voids are uniformly scattered in the cross section. From this, it is estimated that the density inside barium titanate is uniform.

Example 2
First, tetragonal barium titanate (average particle size: 0.1 μm) was added to ethanol and mixed for 5 hours by a bead mill to prepare a slurry having a barium titanate mass concentration of 1%. Next, the slurry was sprayed in the same manner as in Example 1 to obtain barium titanate aggregates.

  A scanning electron micrograph of the obtained barium titanate aggregate is shown in FIG. When FIG. 2 is compared with FIG. 5, the particle diameter of the barium titanate aggregate shown in FIG. Therefore, it is estimated that the particle size of the barium titanate aggregate obtained can be increased by increasing the mass concentration of barium titanate in the slurry.

DESCRIPTION OF SYMBOLS 1 Spraying apparatus 2 Syringe 2a Opening part 3 Applied voltage supply line 4 Power supply 5 Board | substrate 6 Slurry

Claims (6)

Charging a slurry containing dielectric particles and a solvent;
Spraying the slurry to generate charged droplets;
Evaporating the solvent in the droplets to agglomerate the dielectric particles;
A method for producing dielectric particle aggregates, comprising: In the manufacturing method of the dielectric particle aggregate according to claim 1,
The step of aggregating the dielectric particles includes
A method for producing a dielectric particle aggregate, comprising the step of evaporating the solvent while polarizing the dielectric particles in the charged droplets. In the manufacturing method of the dielectric particle aggregate according to claim 1,
The step of generating the droplet includes
A method for producing a dielectric particle aggregate comprising the step of spraying the slurry by applying an electrostatic force to the slurry. In the manufacturing method of the dielectric particle aggregate according to claim 1,
The step of aggregating the dielectric particles includes
A method for producing a dielectric particle aggregate, comprising: a step of evaporating the solvent while refining the charged liquid properties by repelling the charged liquid properties by an electric repulsive force. In the manufacturing method of the dielectric particle aggregate according to claim 1,
The method for producing an aggregate of dielectric particles, wherein the dielectric particles are ferroelectric. In the manufacturing method of the dielectric particle aggregate according to claim 1,
The method for producing an aggregate of dielectric particles, wherein the dielectric particles have a perovskite structure and are tetragonal.