JP2008127258A - Method for manufacturing ceramic powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a ceramic powder, by which the ceramic powder, from which a dense hardly shrinkable sintered compact can be obtained at a low sintering temperature, can be easily obtained with good productivity. <P>SOLUTION: The method for manufacturing the ceramic powder includes a process for synthesizing nanosize ceramic particles and at the same time, covering each submicron size particle with the nanosize ceramic particles by subjecting a raw material, obtained by previously mixing a material constituting nanosize ceramic particles and a ceramic powder comprising submicron size ceramic particles, to hydrothermal synthesis. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a ceramic powder that can be sintered at a low temperature and suppresses shrinkage during firing, a ceramic powder produced by the method for producing the ceramic powder, and the ceramic powder. The present invention relates to a molded body obtained by using a sinter and a sintered body.

  Industrial machinery parts as structural materials, and materials constituting electronic parts such as circuit boards, capacitors, oscillators, and high-frequency devices, oxide-based ceramic materials such as zirconia and alumina, silicon nitride, silicon carbide, etc. Non-oxide ceramic materials are used.

  Generally, the above parts are manufactured through a manufacturing process in which a ceramic material made of ceramic powder of a submicron size or larger is used, formed by a dry or wet forming method, and then fired. Usually, the firing temperature is required to be 1300 ° C. or higher when obtaining a structural component, and 1100 ° C. or higher when obtaining an electronic component.

  On the other hand, at the present time when demands for global energy saving and low environmental load are increasing, it is recognized that realizing an energy-saving manufacturing process is a very important problem. Therefore, it can be said that reducing the firing temperature when obtaining the above-mentioned component using a ceramic material is a very important issue.

  In addition, in general, if the firing temperature is lowered, the shrinkage rate can be suppressed as compared with the case of firing at a higher temperature, and therefore, from the viewpoint of preventing the generation of cracks and improving the yield, Is preferably low.

  Further, depending on the parts using the ceramic material, there are cases where a reduction in the firing temperature is required due to individual specific circumstances. For example, in a multilayer ceramic capacitor (MLCC) that is an electronic component having a structure in which an internal electrode layer and a dielectric layer are stacked, a manufacturing process is performed in which the internal electrode layer and the dielectric layer are simultaneously fired. When manufactured, the melting point of the metal material used for the internal electrode layer needs to be higher than the sintering temperature of the ceramic material constituting the dielectric layer. Therefore, the ceramic material constituting the dielectric layer can be sintered at a low temperature. The lower the temperature, the wider the selection range of metals that can be used as the internal electrode layer. For example, a cheaper metal can be used as the internal electrode layer. Therefore, in the production of MLCC, it is desired to lower the firing temperature. Of course, the low temperature firing also suppresses the occurrence of cracks during shrinkage, so that an improvement in the yield of MLCC is also expected.

  Barium titanate is known as a representative ceramic material constituting the dielectric layer of the MLCC. In recent years, the demand for higher performance of MLCCs, such as higher capacity and higher frequency, has been increasing. To meet these demands, barium titanate is made of high purity, homogeneous composition and fine particles. Techniques have been proposed for making ceramic powders having an appropriate particle size distribution. For example, as related arts for producing barium titanate, oxalate method (for example, see Patent Documents 1 and 2), alkoxide method (for example, see Patent Document 3), hydrothermal synthesis method (for example, Patent A liquid phase method such as Document 4 and Non-Patent Documents 1 and 2) is disclosed.

However, in order to sinter the barium titanate powder obtained by these liquid phase methods, 1200 degreeC or more is required. Although it can be said that the firing temperature for obtaining the sintered body is somewhat lower than that produced by the solid phase method, it is not at a level that can be said to be very low temperature firing.

  On the other hand, a sol-gel method in which ceramic powder obtained by hydrolysis or thermal decomposition reaction of a metal alkoxide precursor solution is formed and sintered is also known. There is a problem that it cannot be solved automatically.

  Moreover, since the primary particle diameter of barium titanate obtained by the sol-gel method is so-called nano-sized, it can be said that it has low-temperature sinterability, but it also has problems due to being nano-sized ceramic particles. . That is, first, since the particles exist as secondary particles (aggregated particles) having a non-uniform particle size, there is a problem that molding is not easy and the density of the molded body does not increase. Secondly, there is a problem that the compaction of the compact during drying and sintering is large and the conditions for the synthesis reaction are complicated. Third, in order to obtain a dense sintered body, a firing temperature of 1100 ° C. or higher is necessary. After all, it cannot be said to be a low-temperature firing, and the shrinkage rate associated with firing increases, resulting in a decrease in yield. There is a problem that.

  In contrast, attempts have been made to make use of the low-temperature sintering characteristics of nano-sized ceramic particles by mixing nano-sized ceramic powder with sub-micron-sized ceramic powder. However, since the nano-sized ceramic particles are highly cohesive, they are not completely crushed and distributed uniformly in the molded body, and a large number of voids are generated in the molded body before firing. The shrinkage problem and low temperature sintering have not been realized.

JP 2004-26641 A JP-T-2004-521850 JP 2000-128631 A JP 2002-221926 A H. Xu, L .; Gao, “Hydrogenetic synthesis of high-purity BaTiO3 powders: control of powder phase and size, 58 sintering density, and 80 liters. H. Xu, L .; Gao, “Tetragonal Nanocrystalline Barium Titanate powder: Preparation, Characterization, and Dielectric Properties”, J. Am. Am. Ceram. Soc. , 86 (2003) 203-205.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is to provide a ceramic powder capable of obtaining a sintered body that is dense and hardly shrinks at a low firing temperature. Another object of the present invention is to provide a method for producing a ceramic powder that can be obtained simply and with high productivity.

  As a result of repeated research, it has been found that the above problems can be solved by the following means, and the present invention has been completed.

That is, according to the present invention, first, a material comprising nano-sized ceramic particles and a ceramic powder composed of sub-micron-sized ceramic particles are used in advance, and this is hydrothermally synthesized. There is provided a method for producing ceramic powder, which comprises a step of simultaneously coating nano-sized ceramic particles on the surface of submicron-sized ceramic particles while synthesizing the ceramic particles.

  The method for producing a ceramic powder according to the present invention is a method for producing a ceramic powder comprising submicron sized ceramic particles whose surface is coated with nano-sized ceramic particles. In other words, by the method for producing ceramic powder according to the present invention, a ceramic powder composed of submicron-sized ceramic particles whose surface is coated with nano-sized ceramic particles can be obtained.

  In the method for producing ceramic powder according to the present invention, it is preferable to hydrothermally synthesize ceramic powder made of ceramic particles of submicron size while pulverizing. In this case, it is preferable to pulverize ceramic powder made of ceramic particles of submicron size with a ball mill.

  In the method for producing a ceramic powder according to the present invention, it is preferable that the nano-sized ceramic particles and the submicron-sized ceramic particles are made of the same material.

In the method for producing ceramic powder according to the present invention, the ceramic powder is barium titanate (BaTiO ₃ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), titania (TiO ₂ ), lead titanate (PbTiO ₃ ). , Lithium niobate (LiNbO ₃ ), silicon carbide (SiC), aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), lithium molybdate (Li ₂ MoO ₄ ), titanium nitride (TiN), or mullite (3Al ₂ O ₃ · 2SiO ₂ ) ceramic powder is preferable.

  Next, according to the present invention, there is provided a ceramic powder having a ceramic particle diameter of 0.1 to 1 μm manufactured by any one of the above-described methods for manufacturing a ceramic powder.

  The ceramic powder according to the present invention is preferably one that can be sintered at a firing temperature of 1000 ° C. or less.

  Next, according to the present invention, there is provided a molded body having a relative density of 95% or more formed by molding any one of the ceramic powders described above.

  Next, according to the present invention, there is provided a sintered body composed of sintered grains having a tetragonal crystal structure, which is obtained by molding and firing any one of the above ceramic powders.

  The sintered body according to the present invention preferably has a shrinkage ratio during firing of 20% or less. This means that it is a sintered body that has not shrunk by more than 20% from the compact before firing.

  Next, according to the present invention, a method for coating nano-sized ceramic particles onto sub-micron-sized ceramic particles composed of the same material as the ceramic particles, the material constituting the nano-sized ceramic particles And a ceramic particle coating method comprising hydrothermal synthesis of a raw material obtained by previously mixing ceramic powder made of submicron ceramic particles of the same material as the ceramic particles.

  In the present specification, nano-sized ceramic particles are also referred to as nanoparticles. The submicron ceramic particles are also called core particles, and the coated core particles are also called coated particles.

  In this specification, the nano size refers to 1 nm or more and less than 100 nm, and the submicron size refers to 0.1 μm or more and less than 1 μm. In the present invention, the preferred size of the nanoparticles is 10 nm or more and 50 nm or less, and the preferred size of the core particles is 0.1 μm or more and 0.5 μm or less.

  The method for producing a ceramic powder according to the present invention includes a step of hydrothermally synthesizing a raw material in which a material constituting nano-sized ceramic particles and a ceramic powder composed of submicron-sized ceramic particles are preliminarily mixed. In addition, while synthesizing the nano-sized ceramic particles, the nano-sized ceramic particles are coated on the surface of the sub-micron-sized ceramic particles, so that the resulting ceramic powder is nano-sized on the surface of the sub-micron-sized ceramic particles. The ceramic particles are composed of uniformly coated ceramic particles, and the density of the molded body can be made extremely high during molding and firing, and can be sintered at a low temperature. . In addition, since submicron ceramic particles are present in a state where nano-sized ceramic particles are filled, sintering with reduced shrinkage is possible.

  In general, it is known that sintering is possible at a low temperature by molding ceramic powder made of nano-sized ceramic particles. Therefore, conventionally, in order to form and fire ceramic powder composed of nano-sized ceramic particles, and to extract low-temperature sinterability that is a characteristic of nano-sized ceramic particles, ceramic powder composed of nano-sized ceramic particles; Forming and firing a mixture of ceramic powder made of ceramic particles of submicron size by a wet or dry mechanical method is performed. However, nano-sized ceramic particles of less than 100 nm have strong cohesive force and are difficult to exist as primary particles, and therefore exist as aggregated particles having a particle size distribution width. For example, it is difficult to crush and disperse the agglomeration of nano-sized ceramic particles through a ball mill process because the agglomeration force is strong. Therefore, when molded and fired using ceramic powder composed of nano-sized ceramic particles, the density of the molded body is low, and firing at high temperature is necessary for sintering, and shrinkage due to firing is large. turn into. In addition, when a ceramic powder composed of nano-sized ceramic particles and a ceramic powder composed of sub-micron-sized ceramic particles are mixed and molded by a wet or dry mechanical method, the nano-sized ceramic particles are uniformly distributed. In addition to being introduced into the compact, in addition to the formation of voids in the compact due to the aggregation of nano-sized ceramic particles, the shrinkage during firing and the high temperature required for sintering Can occur. According to the ceramic powder manufacturing method and the ceramic powder obtained according to the present invention, these problems can be avoided.

  Since the method for producing a ceramic powder according to the present invention uses a hydrothermal synthesis method, a ceramic powder composed of ceramic particles having high purity, excellent composition uniformity, and uniform particle diameter can be obtained.

  The method for producing a ceramic powder according to the present invention has a simpler production process, excellent productivity, and less capital investment compared to other means capable of synthesizing nano-sized ceramic powder, such as the sol-gel method. That's it. Nevertheless, it is possible to produce a ceramic powder that can be easily molded, can increase the density of the compact, and can be sintered at a low temperature, for example, a barium titanate ceramic powder.

Ceramic powder produced by the ceramic powder production method according to the present invention, for example, barium titanate ceramic powder, is made of ceramic particles of submicron size, and is formed by press molding, casting molding, extrusion molding, isostatic pressing. Conventionally known ceramic forming methods such as tape forming (doctor blade method etc.) can be applied. Therefore, it is related to production of a molded body and a sintered body, and is excellent in production efficiency.

  According to the barium titanate-based ceramic powder produced by the method for producing ceramic powder according to the present invention, it is involved in the production of a multilayer ceramic capacitor, and the selection range of metals that can be used as internal electrode layers is widened, so that inexpensive metals are used. It becomes possible to do. Multilayer ceramic capacitors may be manufactured by laminating an internal electrode layer and a dielectric layer and sintering them simultaneously. The melting point of the metal used for the internal electrode layer must be higher than the sintering temperature of the molded body. This is because the barium titanate ceramic powder produced by the method for producing ceramic powder according to the present invention can be fired (sintered) at a low temperature. Moreover, the firing energy is reduced, and a low environmental load is realized. Furthermore, since the shrinkage rate is reduced, the yield can be improved, the manufacturing cost of the multilayer ceramic capacitor can be reduced, and this is extremely useful industrially.

  Hereinafter, embodiments of the present invention will be described with appropriate reference to the drawings, but the present invention should not be construed as being limited thereto. Various changes, modifications, improvements, and substitutions can be added based on the knowledge of those skilled in the art without departing from the scope of the present invention. For example, the drawings show preferred embodiments of the present invention, but the present invention is not limited by the modes shown in the drawings or the information shown in the drawings. In practicing or verifying the present invention, the same means as described in this specification or equivalent means can be applied, but preferred means are those described below.

  FIG. 1 is a schematic view showing an example of an apparatus used in the method for producing ceramic powder according to the present invention. The apparatus shown in FIG. 1 includes an outer heat-resistant pressure-resistant container 1 and an inner chemical-resistant container 5 for containing materials constituting nano-sized ceramic particles and ceramic powder made of sub-micron-sized ceramic particles. And a heater 4 for maintaining the container 6 at a predetermined temperature. A rotating shaft rod 3 is disposed outside the container 6, and the container 6 can be rotated under heating and pressurizing conditions. The container 6 is preferably composed of, for example, a chemical-resistant container 5 made of tetrafluoroethylene resin and a heat-resistant pressure-resistant container 1 made of stainless steel. However, the container is not limited as long as it does not break with respect to the temperature in hydrothermal synthesis, does not break when heated or when pressure is applied, and does not react with the solvent by the solvent.

It is also possible to place the ball 2 for pulverizing and mixing in the container 6 and simultaneously perform the synthesis of the ceramic powder and the coating reaction while preventing the core particles from aggregating. However, if the nanoparticles can be synthesized by hydrothermal synthesis, the pulverizing and mixing balls 2 may or may not be introduced. For example, a ZrO ₂ ball having a diameter of 5 mm can be used as the pulverizing and mixing ball, but the type and diameter of the pulverizing and mixing ball 2 are not limited as long as they do not affect impurities in the reaction. Whether or not the pulverizing and mixing balls 2 are introduced into the container 6, a ceramic powder that can be sintered at a low temperature and with low shrinkage can be obtained.

In the method for producing a ceramic powder according to the present invention, in order to obtain a ceramic powder coated with nanoparticles of the same kind (same material) as the core particles, the surface charge of the ceramic particles must be considered. That is, ceramic particles having different surface charges, positive and negative surface charges attract each other, so that the nanoparticles are coated on the core particle surface by so-called heteroaggregation. On the other hand, if the core particles and nanoparticles are different (different materials) ceramic particles, the surface state of positive and negative charges can be adjusted by adjusting the pH, and coated particles can be formed by heteroaggregation. It is. However, in general, the same kind of ceramic particles have the same surface charge only by pH adjustment, and does not cause hetero-aggregation. Therefore, uniform coating cannot be performed. In the method for producing a ceramic powder according to the present invention, for example, in the case of a barium titanate powder, a polyethyleneimine (PEI) having a positive charge at a pH of 11 or less is added to break up the aggregation of the core particles. The core particles are crushed and PEI is adsorbed on the surfaces of the core particles. By performing this step, the surface charge of barium titanate is positively charged at pH 11 or less. Since the isoelectric point of barium titanate is 6, and when the pH is higher than that isoelectric point, it becomes a negative charge, and when it is lower, it becomes a positive charge. It is possible to perform a coating reaction by heteroaggregation.

In the method for producing a ceramic powder according to the present invention, for example, in order to obtain a nano-sized barium titanate ceramic powder, an aqueous barium hydroxide (Ba (OH) ₂ ) solution and titanium tetraisopropoxide ([(CH 3) 2 CHO) are used. ] ₄ Ti) solution are mixed. In this case, the ratio of Ba to Ti is 1: 1, preferably 1.03 to 1.5: 1, and a little Ba component is mixed. This is because when barium hydroxide is dissolved, a little amount of barium carbonate is generated, and by increasing the pH of the aqueous solution, the generated barium titanate is decomposed, that is, unreacted due to elution of the barium component. This is to reduce the change in composition and composition.

  Examples of titanium tetraisopropoxide that is a titanium alkoxide include, but are not limited to, a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, an isobutyl group, and a normal pentyl group. The solvent for dissolving the titanium alkoxide is not limited as long as the titanium alkoxide is soluble, and alcohols such as methyl, ethyl, isopropyl, and normal butyl alcohol, and aliphatic hydrocarbons such as hexane, heptane, octane, benzene, toluene, and xylene. A solvent of aromatic hydrocarbons can be used, and a mixed system of these solvents may be used. Desirably, it is preferable to use a solvent that is compatible with water, and to add an alcohol if it is not compatible. This is because it can be hydrolyzed uniformly by being compatible with an aqueous barium hydroxide solution, so that fine ceramic particles can be prepared.

  In the method for producing a ceramic powder according to the present invention, the ceramic powder composed of the core particles is preferably dispersed in advance using a dispersant of polyethyleneimine (PEI). This is because the ceramic powder composed of the agglomerated core particles can be crushed, and the surface of each core particle can be coated with the nanoparticles during the coating reaction.

  In the method for producing ceramic powder according to the present invention, a mixed solution of barium and titanium is placed in a container 6 and a slurry of core particles dispersed by the PEI is added. Preferably, the pulverizing and mixing balls 2 are put in the container 6 and the hydrothermal synthesis step is simultaneously performed while performing the ball mill step. Thus, the nanoparticles can be synthesized and the nanoparticles can be coated on the surface of the core particles. Preferred nanoparticles that can be synthesized include those having a particle size of 20 nm or more and 50 nm or less. This is the same even when the grinding and mixing balls 2 are not inserted.

  The rotation speed of the container 6 may be any as long as the pulverizing and mixing ball 2 always rotates in accordance with the rotation without jumping in the container 6. If so, the surface of the nanoparticles produced by hydrothermal synthesis can be activated, and the aggregated particles (core particles) can be uniformly, homogeneously and activated. The rotation direction of the container 6 may be any of horizontal, vertical, and diagonal directions. Solid-liquid separation can be performed by existing separation methods such as filtration and centrifugation.

The ceramic powder made of the coated particles produced can be dried by one or a combination of drying methods such as natural drying, ventilation drying, heat drying, vacuum drying, freeze drying, etc., but it prevents aggregation during drying. Therefore, it is desirable that the drying temperature is as low as possible. From the viewpoint of preventing aggregation during drying, freeze-drying is most desirable. The dried ceramic powder can be used as a molding material as it is.

  FIG. 2 is a TEM (transmission electron microscope) photograph of coated particles of a ceramic powder in which the nanoparticles and core particles are both barium titanate, produced by the method for producing a ceramic powder according to the present invention. In FIG. 2, it can be observed that approximately 20 nm nanoparticles are uniformly coated on the surface of the core particles.

  FIG. 3 is a photograph taken by SEM (scanning electron microscope) of the coated particles of the ceramic powder in which the nanoparticles and the core particles are both barium titanate prepared by the method for producing ceramic powder according to the present invention. . According to FIG. 3, in addition to the coated particles, there is a homogeneous aggregated particle having a uniform diameter of 0.1 to 0.2 μm by aggregation of nanoparticles that are not involved in the coating of about 20 nm. It is confirmed that

  Furthermore, FIG. 4 is a graph showing the X-ray diffraction measurement results of the ceramic powder produced by the method for producing ceramic powder according to the present invention, in which both the nanoparticles and the core particle are barium titanate. It can be understood that the manufactured product is indeed barium titanate powder.

  The ceramic powder produced by the method for producing a ceramic powder according to the present invention uses submicron-sized core particles, and, as described above, nanoparticles that are not involved in coating are submicron-sized agglomerates. Since it is in the form of particles, it can be applied to conventionally known ceramic forming methods. The ceramic powder may be packed in a mold, press-molded, and hydrostatic-pressure molded (dry molding), or the ceramic powder may be dispersed and cast-molded, and then tape-molded (wet molding). In any case, abnormal grain growth is suppressed during sintering by molding a ceramic powder composed of core particles coated with nanoparticles and aggregated particles of uniform diameter obtained by agglomerating homogeneous nanoparticles. Moreover, since the activity of the nanoparticles is high, it leads to an improvement in sinterability.

  For example, the mold is filled with barium titanate powder produced by the method for producing ceramic powder according to the present invention, press-molded, sintered after isostatic pressing, and sintered at 900 to 1000 ° C., A dense sintered body can be obtained at a firing temperature lower by about 300 to 400 ° C. than the conventional one. In addition, when a conventional barium titanate powder composed only of core particles not coated with nanoparticles is molded, when the molded body is fired, in the case of a firing temperature of 1300 ° C. and a relative density of 95%, Whereas the shrinkage rate is 17%, the molded body using the barium titanate powder produced by the method for producing ceramic powder according to the present invention is fired at a temperature lower by 300 ° C. or more than the conventional one, and is 95% or more. In the case of relative density, the shrinkage rate can be suppressed to 17% or less.

  By using the barium titanate powder produced by the method for producing ceramic powder according to the present invention, in which both the nanoparticles and the core particles are barium titanate, the resulting molded body is fired to lower the characteristics. Thus, a sintered body of barium titanate composed of square-phase sintered grains having a size of 1 μm or less without abnormal grain growth is obtained. FIG. 5 is a photograph of the sintered body by SEM (scanning electron microscope), and FIG. 6 is a graph showing the X-ray diffraction measurement result of the sintered body. FIG. 5 confirms the shape of the sintered grains of the sintered body. Also, usually, in the case of tetragonal type, that is, tetragonal barium titanate, the 45 degree peak is separated into two as measured by X-ray diffraction. That is, it is confirmed to be composed of a tetragonal crystal phase.

Next, the present invention will be described more specifically with reference to the following examples. In the following description, barium titanate powder is used as the ceramic powder. However, as long as the gist of the present invention is not exceeded, other types of barium titanate ceramic powder and oxide ceramics (Al ₂ It can be applied to other ceramic powders such as O ₃ , ZrO ₂ , TiO ₂ , PbTiO ₃ , LiNbO _3, etc., and is not limited. The nano-sized ceramic particles and the sub-micron-sized ceramic particles are not limited to those made of different types and the same kind of materials, and the materials are limited as long as they enable a hydrothermal synthesis reaction and a coating reaction. do not do.

Example 1 (1) 6.1645 g of barium hydroxide (Ba (OH) ₂ .8H ₂ O) was added to and dissolved in 38 ml of distilled water at 80 ° C. to obtain a barium hydroxide solution. Slightly produced BaCO ₃ was removed by filtration. Then, 3.7002 g of titanium tetraisopropoxide ([(CH ₃ ) ₂ CHO] ₄ Ti) was dissolved in 8 ml of isopropyl alcohol, and this was added to the barium hydroxide solution to obtain a mixed solution.

  (2) The amount of barium titanate powder composed of 0.3 μm core particles is 1% by volume with respect to the amount of barium titanate powder composed of nanoparticles to be synthesized, and this is 1% by mass of polyethyleneimine (PEI) To obtain a barium titanate dispersion slurry. Since PEI has a positive charge, the surface of barium titanate has a positive charge.

(3) Next, the barium titanate-dispersed slurry was added to the above mixed solution, placed in a Teflon (registered trademark) container (chemical resistant container), and ZrO ₂ balls having a diameter of 5 mm for crushing and crushing were added. . Furthermore, this Teflon (registered trademark) container was set in a stainless steel container (heat-resistant pressure-resistant container), and hydrothermal synthesis was performed. Specifically, a container formed by setting a Teflon (registered trademark) container in a stainless steel container is raised to 100 ° C. at a temperature rising rate of 5 ° C./min while being rotated at a rotation speed of 150 rpm, and held for 2 hours. And cooled to obtain a precipitate in the container. The precipitate was washed and then freeze-dried to obtain barium titanate powder.

  When the obtained barium titanate powder was subjected to X-ray diffraction, it was confirmed that it was certainly a barium titanate powder. Furthermore, when the powder form and the particle form were observed by SEM and TEM, it was observed that the surface of the core particle was coated with nanoparticles of about 20 nm, and the powder form was involved in the coated particles and the coating. The nanoparticles that did not exist were composed of aggregated particles. The coated particles are about 0.5 μm larger than the size of the core particles (0.3 μm), and the agglomerated particles are submicron-sized and have a uniform diameter of approximately 0.12 to 0.2 μm. It was.

  (4) Using the obtained barium titanate powder, press molding was performed at 2000 N, and further, hydrostatic pressure molding was performed by applying a pressure of 100 MPa in still water to obtain four compacts. The average relative density of the four molded bodies obtained was 52% (see FIG. 7). Compared to the relative density in Comparative Example 1 described later, this is a considerably high value (see FIG. 7).

  (5) Next, the obtained four compacts were individually raised at a heating rate of 100 ° C./h to a predetermined temperature (800 ° C., 900 ° C., 1000 ° C., 1100 ° C.) for 5 hours. Sintered at normal pressure to obtain barium titanate sintered bodies having different firing temperatures.

  And the relative density and shrinkage | contraction rate (linear shrinkage rate) of the obtained sintered compact were measured. The results are shown in FIGS. The relative density was 96% at a firing temperature of 900 ° C. and the shrinkage was 22%, and the relative density was 98% and the shrinkage was 22% at 1000 ° C., confirming that low temperature sintering was possible.

  In addition, when X-ray diffraction of the sintered body was performed, the sintered grain structure of the sintered body was separated into two 45-degree peaks and was tetragonal, that is, a tetragonal barium titanate sintered body. It was confirmed that. Further, when the sintered body was observed using a scanning electron microscope, it was confirmed that the sintered body was a tetragonal type, that is, a sintered body of barium titanate composed of sintered grains of a tetragonal phase. done.

  (Example 2) In preparation of the barium titanate dispersion slurry, the amount of barium titanate powder composed of 0.3 μm core particles was 5% by volume with respect to the amount of barium titanate powder composed of nanoparticles to be synthesized. Except for the above, barium titanate powder was produced in the same manner as in (1) to (4) of Example 1, and four compacts were obtained using it. The average relative density of the four molded bodies obtained was 57% (see FIG. 7). Compared to the relative density in Comparative Example 2 described later, this is a considerably high value (see FIG. 7).

  Then, four compacts were fired under the same conditions as (5) of Example 1, a sintered body was obtained, and the relative density and shrinkage rate (linear shrinkage rate) of the sintered body were measured. The results are shown in FIGS. At 900 ° C., the relative density was 90% and the shrinkage was 11%. At 1000 ° C., the relative density was 96% and the shrinkage was 16%. Compared with the sintering temperature (1300 ° C or higher) and shrinkage rate (17%) of the compact formed by molding submicron-sized conventional barium titanate powder, it can be sintered at a temperature lower by 300 ° C or higher. Moreover, the shrinkage could be suppressed.

  FIG. 10 is a SEM photograph of the sintered body fired at 1000 ° C. in Example 2. FIG. 10 confirmed that the size of the sintered grains was 1 μm or less. FIG. 11A is a SEM photograph of the fracture surface of the sintered body fired at 900 ° C. in Example 2.

  (Example 3) In preparation of the barium titanate dispersion slurry, the amount of barium titanate powder composed of 0.3 μm core particles was 10% by volume with respect to the amount of barium titanate powder composed of nanoparticles to be synthesized. Except for the above, barium titanate powder was produced in the same manner as in (1) to (4) of Example 1, and four compacts were obtained using it. The average relative density of the four molded bodies obtained was 59% (see FIG. 7). Compared to the relative density in Comparative Example 3 described later, this is a considerably high value (see FIG. 7).

(Example 4) Barium titanate powder was prepared in the same manner as (1) to (3) of Example 1 except that ZrO ₂ balls for pulverization and disintegration were not used in hydrothermal synthesis. Manufactured. When preparing the barium titanate-dispersed slurry, the amount of barium titanate powder composed of 0.3 μm core particles is 1% by volume with respect to the amount of barium titanate powder composed of nanoparticles synthesized.

  About the obtained barium titanate powder, when the powder form and particle form were observed by SEM and TEM, it was observed that the surface of the core particle was coated with nanoparticles of about 20 nm, and the powder form was coated. It was composed of particles and aggregated particles in which nanoparticles that were not involved in the coating were aggregated. The coated particles are about 0.5 μm larger than the size of the core particles (0.3 μm), and the agglomerated particles are submicron-sized and have a uniform diameter of approximately 0.12 to 0.2 μm. It was.

  Next, using the obtained barium titanate powder, four molded bodies were obtained in the same manner as in (4) of Example 1. The average relative density of the obtained four compacts was 52%, which was the same as the relative density of the compacts in Example 1.

(Example 5) In carrying out hydrothermal synthesis, ZrO ₂ balls for pulverization and disintegration were not used. In preparing the barium titanate-dispersed slurry, the amount of barium titanate powder composed of 0.3 μm core particles was 5% by volume with respect to the amount of barium titanate powder composed of synthesized nanoparticles. Except these, it carried out similarly to (1)-(4) of Example 1, and manufactured the barium titanate powder, and obtained the 4 molded object using it. The average relative density of the obtained four compacts was 57%, which was the same as the relative density of the compacts in Example 2.

  Then, four compacts were fired under the same conditions as (5) of Example 1, a sintered body was obtained, and the relative density and shrinkage rate (linear shrinkage rate) of the sintered body were measured. As a result, the relative density was 95% and the shrinkage rate was 7% at 900 ° C., and the relative density was 97% and the shrinkage rate was 16% at 1000 ° C. Compared to the sintering temperature (1300 ° C or higher) and shrinkage rate (17%) of the molded body formed by molding submicron-sized conventional barium titanate powder, it can be sintered at a temperature lower than 400 ° C, Moreover, the shrinkage could be suppressed.

  The molded body in Example 5 can be densified at a lower temperature than the molded body of Example 1, and shrinkage can be suppressed. FIG. 11B is a SEM photograph of the fracture surface of the sintered body fired at 900 ° C. in Example 5.

FIG. 11A according to Example 2 and FIG. 11B according to Example 5 are compared, and the fracture surface of the sintered body is observed. It can be seen that dense sintering is progressing. This is because, in Example 2, since hydrothermal synthesis is performed while introducing a ZrO ₂ ball for pulverization and disintegration and adding a ball mill process, nanoparticles highly active against sintering are synthesized. Conceivable. That is, since the nanoparticles not involved in the coating are also highly active, the sintered particles formed by agglomerating the agglomerated particles formed by agglomeration of the agglomerated particles are sintered by the agglomerated particles in Example 5 being sintered Since it becomes larger than the grain, it is considered that the sinterability is lowered.

(Example 6) When hydrothermal synthesis was performed, ZrO ₂ balls for pulverization and disintegration were not used. In preparing the barium titanate-dispersed slurry, the amount of barium titanate powder composed of 0.3 μm core particles was 10% by volume with respect to the amount of barium titanate powder composed of synthesized nanoparticles. Except these, it carried out similarly to (1)-(4) of Example 1, and manufactured the barium titanate powder, and obtained the 4 molded object using it. The average relative density of the obtained four compacts was 59%, which was the same as the relative density of the compacts in Example 3.

  (Comparative example 1) It is an example at the time of mixing mechanically the ceramic powder which consists of core particles, and the ceramic powder which consists of nanoparticles.

(A) To 61 ml of distilled water at 80 ° C., 6.1645 g of barium hydroxide (Ba (OH) ₂ .8H ₂ O) was added and dissolved to obtain a barium hydroxide solution. Slightly produced BaCO ₃ was removed by filtration. Then, 3.7002 g of titanium tetraisopropoxide ([(CH ₃ ) ₂ CHO] ₄ Ti) was dissolved in 8 ml of isopropyl alcohol, and this was added to the barium hydroxide solution to obtain a mixed solution.

(B) This mixed solution is put in a Teflon (registered trademark) container (chemical resistant container), and a ZrO ₂ ball having a diameter of 5 mm for pulverization / disintegration is reduced to half the volume of the Teflon (registered trademark) container. added. Furthermore, this Teflon (registered trademark) container was set in a stainless steel container (heat-resistant pressure-resistant container, 100 ml), and hydrothermal synthesis was performed. Specifically, a container formed by setting a Teflon (registered trademark) container in a stainless steel container is raised to 100 ° C. at a temperature rising rate of 5 ° C./min while being rotated at a rotation speed of 150 rpm, and held for 2 hours. And cooled to obtain a precipitate in the container. And after wash | cleaning a deposit, the barium titanate powder which consists of nanoparticles was obtained by freeze-drying.

  When the obtained barium titanate powder was subjected to X-ray diffraction, it was confirmed to be a (ceramic) powder of barium titanate. Furthermore, when the powder form and the particle form were observed by SEM, the nanoparticles (primary particles) of the barium titanate powder were 10 to 50 nm, and there were aggregated particles in which the nanoparticles were aggregated. The particles had a substantially uniform diameter of submicron size and a form with a narrow particle size distribution width.

  (C) The amount of barium titanate powder composed of 0.3 μm core particles is 1% by volume with respect to the amount of barium titanate powder (comprised of nanoparticles) obtained. Barium titanate powder in which nanoparticles and core particles were mechanically mixed was obtained by dry mixing for a minute.

  (D) Using the obtained barium titanate powder, press molding was performed at 2000 N, and further, hydrostatic pressing was performed by applying a pressure of 100 MPa in still water to obtain four compacts. The average relative density of the four molded bodies obtained was 46% (see FIG. 7). Compared with the relative density in the previous Example 1, it is a considerably low value (see FIG. 7).

  (E) Next, the obtained four compacts were individually raised to a predetermined temperature (800 ° C., 900 ° C., 1000 ° C., 1100 ° C.) at a heating rate of 100 ° C./h for 5 hours, Sintered at normal pressure to obtain barium titanate sintered bodies having different firing temperatures.

  And the relative density and shrinkage | contraction rate (linear shrinkage rate) of the obtained sintered compact were measured. The results are shown in FIGS. At a firing temperature of 900 ° C., the relative density was 85% and the shrinkage was 19%. At 1000 ° C., the relative density was 95% and the shrinkage was 23%. It was confirmed that low temperature sintering was possible. Compared with Example 1, it can be seen that the low-temperature sinterability is small and the shrinkage is not suppressed. That is, it is impossible to obtain a ceramic powder that can be sintered at low temperature and can be sintered at low temperature by simply mechanically mixing the nanoparticles and the core particles.

  (Comparative Example 2) (a) of Comparative Example 1 except that the amount of barium titanate powder composed of 0.3 μm core particles was 5% by volume with respect to the amount of barium titanate powder composed of nanoparticles. In the same manner as in (d), barium titanate powder was produced, and four compacts were obtained using it. The average relative density of the four molded bodies obtained was 48% (see FIG. 7). Compared with the relative density in the previous Example 2, it is a considerably low value (see FIG. 7).

  And the four molded object was baked on the same conditions as (e) of the comparative example 1, the sintered compact was obtained, and the relative density and shrinkage | contraction rate (linear shrinkage rate) of the sintered compact were measured. The results are shown in FIGS. At 900 ° C., the relative density was 64% and the shrinkage was 10%. At 1000 ° C., the relative density was 90% and the shrinkage was 19%. Compared to Example 2, it can be seen that the low-temperature sinterability is small and the shrinkage is not suppressed.

  (Comparative Example 3) (a) of Comparative Example 1 except that the amount of barium titanate powder composed of 0.3 μm core particles was 10% by volume with respect to the amount of barium titanate powder composed of nanoparticles. In the same manner as in (d), barium titanate powder was produced, and four compacts were obtained using it. The average relative density of the four molded bodies obtained was 51% (see FIG. 7). Compared with the relative density in the previous Example 3, it is a considerably low value (see FIG. 7).

(Comparative Example 4) Using only barium titanate powder composed of 0.3 μm core particles, press molding at 2000 N, and further hydrostatic pressing by applying a pressure of 100 MPa in still water, 5 compacts Got. Next, the obtained five compacts were individually heated at a predetermined temperature (1100 ° C, 1200 ° C, 1250 ° C, 1300 ° C, 1350 ° C) at a heating rate of 100 ° C / h.
C.) and fired at normal pressure for 5 hours to obtain sintered bodies of barium titanate having different firing temperatures. And the relative density and shrinkage | contraction rate (linear shrinkage rate) of the obtained sintered compact were measured. The results are shown in FIGS.

  The method for producing a ceramic powder according to the present invention is suitably used as a means for producing a ceramic powder for constituting an electronic component material, for example. When the ceramic powder produced by the method for producing ceramic powder according to the present invention is a barium titanate powder, the barium titanate powder is a dielectric material such as a multilayer ceramic capacitor (MLCC), a thermistor, and a resistor. It is suitable as a material for constituting piezoelectric materials, semiconductors, and other various electronic component materials.

It is a schematic diagram which shows an example of the apparatus used with the manufacturing method of the ceramic powder concerning this invention, and is a figure showing the apparatus which can perform a ball mill process and a hydrothermal synthesis process simultaneously. It is the photograph by the TEM (transmission electron microscope) of particle | grains of the ceramic powder produced with the manufacturing method of the ceramic powder concerning this invention. It is the photograph by the SEM (scanning electron microscope) of particle | grains of the ceramic powder produced with the manufacturing method of the ceramic powder concerning this invention. It is a graph which shows the X-ray-diffraction measurement result of the ceramic powder produced with the manufacturing method of the ceramic powder concerning this invention. It is the photograph by SEM (scanning electron microscope) of the sintered compact obtained by shape | molding and baking using the ceramic powder produced with the manufacturing method of the ceramic powder concerning this invention. It is a graph which shows the X-ray-diffraction measurement result of the sintered compact shown by FIG. It is a graph which shows the result of an Example, ratio (volume%) of the quantity of the barium titanate powder which consists of 0.3 micrometer core particles with respect to the quantity of the barium titanate powder which consists of nanoparticles, and the relative density (%) of a molded object ). It is a graph which shows the result of an Example, and shows the relationship between the calcination temperature (degreeC) required in order to obtain a sintered compact, and the relative density (%) of a sintered compact. It is a graph which shows the result of an Example, and shows the relationship between the calcination temperature (degreeC) required in order to obtain a sintered compact, and the shrinkage | contraction rate (%) of a sintered compact. It is a photograph by SEM of the sintered compact baked at 1000 degreeC in Example 2 among Examples. (A) is the photograph by SEM of the fracture surface of the sintered compact baked at 900 degreeC in Example 2 in Example, (b) is 900 degreeC in Example 5 in Example. It is the photograph by SEM of the fracture surface of the sintered body which baked.

Explanation of symbols

1: heat-resistant pressure-resistant container 2: ball for grinding and mixing 3: rotating shaft rod 4: heater 5: chemical-resistant container 6: container

Claims (11)

Using a raw material in which the material constituting the nano-sized ceramic particles and the ceramic powder made of sub-micron-sized ceramic particles are mixed in advance, this is hydrothermally synthesized,
A method for producing ceramic powder, comprising synthesizing nano-sized ceramic particles and simultaneously coating nano-sized ceramic particles on the surface of sub-micron ceramic particles.   The method for producing a ceramic powder according to claim 1, wherein the ceramic powder composed of the submicron ceramic particles is hydrothermally synthesized while being pulverized.   The method for producing a ceramic powder according to claim 2, wherein the ceramic powder comprising the submicron-sized ceramic particles is pulverized by a ball mill.   The method for producing ceramic powder according to any one of claims 1 to 3, wherein the nano-sized ceramic particles and the submicron-sized ceramic particles are made of the same material. The ceramic powder is barium titanate (BaTiO ₃ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), titania (TiO ₂ ), lead titanate (PbTiO ₃ ), lithium niobate (LiNbO ₃ ), carbonized. Ceramic powder of silicon (SiC), aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), lithium molybdate (Li ₂ MoO ₄ ), titanium nitride (TiN), or mullite (3Al ₂ O ₃ · 2SiO ₂ ) The method for synthesizing ceramic powder according to any one of claims 1 to 4.   The ceramic powder with which the diameter of the ceramic particle manufactured by the manufacturing method of the ceramic powder as described in any one of Claims 1-5 is 0.1-1 micrometer.   The ceramic powder according to claim 6, which can be sintered at a firing temperature of 1000 ° C or lower.   A molded body obtained by molding the ceramic powder according to claim 6 or 7 and having a relative density of 95% or more.   A sintered body formed by sintering and sintering the ceramic powder according to claim 6 or 7 and having a crystal structure of tetragonal crystal.   The sintered body according to claim 9, wherein a shrinkage rate during firing is 20% or less. A method of coating nano-sized ceramic particles onto sub-micron-sized ceramic particles composed of the same material as the ceramic particles,
A ceramic particle comprising hydrothermal synthesis of a material comprising nano-sized ceramic particles and a ceramic powder composed of sub-micron-sized ceramic particles of the same material as the ceramic particles. Coating method.