Method for producing aminopolycarboxylic acid complex powder, additives, and ceramic powder

Abstract

To provide a water-soluble compound which is dissolved with a wide range of pH and is less likely to be solidified in a powder state.SOLUTION: An additive of ceramic powder contains aminopolycarboxylic acid complex powder of a rare earth element having an average particle diameter of 1 μm or more and 1,000 μm or less, and aminopolycarboxylic acid complex powder of the rare earth element, and is used for mixed with ceramic powder. A method for producing ceramic powder containing a rare earth compound in which a particle surface of ceramic powder is coated with a rare earth compound includes mixing an aqueous solution prepared by dissolving aminopolycarboxylic acid complex powder of the rare earth element in water, with ceramic powder and then removing moisture.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for producing aminopolycarboxylic acid complex powder, additives, and ceramic powder. [Background technology]

[0002] Rare earth compounds are frequently used as additives. For example, in multilayer ceramic capacitors, it is known that a highly reliable multilayer ceramic capacitor that does not suffer from insulation resistance defects can be obtained by uniformly dispersing rare earth oxides on the surface of ceramic particles, such as barium titanate-based ceramic particles, which are the main raw materials of the dielectric layer. (For example, Patent Document 1) In order to uniformly disperse the rare earth compound around the ceramic particles in this manner, the rare earth compound and ceramic particles are dispersed in a solvent using a media. Some rare earth compounds exhibit water solubility. For example, Patent Document 2 describes the use of a dysprosium citrate complex in the application of dispersing rare earth compounds on the surface of ceramic particles. Patent Document 3 describes the use of yttrium acetate tetrahydrate and the like in a similar application. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] WO2015 / 040881 pamphlet [Patent Document 2] Japanese Patent Publication No. 2007-204315 [Patent Document 3] Japanese Patent Publication No. 2013-163614 [Overview of the project] [Problems that the invention aims to solve]

[0004] When using rare earth compounds as additives, it is necessary that they dissolve at a pH that facilitates the dispersion of the main raw material and other additives. Therefore, solubility over a wide pH range is required. In addition, when a water-soluble compound of a rare earth element is provided as an aqueous solution, the volume increases and transportation becomes costly. On the other hand, when provided as a powder, it cements and causes blockages and handling troubles in the production and processing line. Therefore, there is a need to provide a water-soluble compound that is difficult to cement in powder form.

[0005] As a result of intensive studies by the present inventors, it has been found that an aminopolycarboxylic acid complex powder of a rare earth element with a specific particle size is difficult to cement and dissolves at a wide range of pH values.

Means for Solving the Problems

[0006] The present invention is based on the above findings, and provides an aminopolycarboxylic acid complex powder of a rare earth element having an average particle diameter of 1 μm or more and 1000 μm or less.

[0007] The present invention also provides an additive for ceramic powder, which contains an aminopolycarboxylic acid complex powder of a rare earth element and is used for mixing with ceramic powder.

[0008] The present invention also provides a method for producing a ceramic powder containing a rare earth compound. After mixing an aqueous solution in which an aminopolycarboxylic acid complex powder of a rare earth element is dissolved in water and the ceramic powder, moisture is removed to coat the particle surface of the ceramic powder with the rare earth compound.

Advantages of the Invention

[0009] According to the powder of the present invention, since it dissolves at a wide range of pH values, rare earth elements can be dissolved in a main raw material slurry in a highly dispersed state at a specific pH, and the rare earth compound and the main raw material can be efficiently mixed. In addition, even when the rare earth element is provided in powder form, it does not cement and can reduce blockages and handling troubles in the production and processing line. According to the present invention, there are also provided an additive capable of effectively improving the dispersibility of rare earth compounds in ceramic powder and providing a ceramic powder suitable for multilayer ceramic capacitors, and a method for producing the ceramic powder.

Brief Description of Drawings

[0010] [Figure 1] It is a SEM image showing the appearance of the mixed powder of barium titanate and dysprosium oxide obtained in Example 1. [Figure 2] It is a Dy element mapping diagram of the SEM image obtained in FIG. 1. [Figure 3] It is a Ti element mapping diagram of the SEM image obtained in FIG. 1. [Figure 4] It is a Ba element mapping diagram of the SEM image obtained in FIG. 1. [Figure 5] It is a SEM image showing the appearance of the mixed powder of barium titanate and dysprosium oxide obtained in Comparative Example 1. [Figure 6] It is a Dy element mapping diagram of the SEM image obtained in FIG. 5. [Figure 7] It is a Ti element mapping diagram of the SEM image obtained in FIG. 5. [Figure 8] It is a Ba element mapping diagram of the SEM image obtained in FIG. 5.

Modes for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail based on its preferred embodiments. This invention relates to a rare earth element aminopolycarboxylic acid complex powder. In aminopolycarboxylic acid complex powder, an aminopolycarboxylic acid complex refers to a complex in which an aminopolycarboxylic acid or a salt thereof is coordinated as a ligand to a central metal atom which is a rare earth element. Aminopolycarboxylic acid is a general term for chelating agents that have an amino group and multiple carboxyl groups in their molecule. Examples of aminopolycarboxylic acids include EDTA (ethylenediaminetetraacetic acid), iminodiacetic acid (IDA), ethylene glycol tetraacetic acid (EGTA), HEDTA (hydroxyethylethylenediaminetriacetic acid), NTA (nitrilotriacetic acid), DTPA (diethylenetriaminepentaacetic acid), TTHA (triethylenetetraminehexaacetic acid), and other aminopolysuccinic acids such as hydroxyiminodisuccinic acid. Furthermore, a salt of an aminopolycarboxylic acid refers to a salt in which some of the carboxyl groups in the aminopolycarboxylic acid are salts with cations other than rare earth elements, such as ammonium salts, sodium salts, and potassium salts. Among aminopolycarboxylic acids, aminopolyacetic acid is preferred due to its availability, and EDTA is the most preferred due to its widespread use. When the aminopolycarboxylic acid is EDTA, the EDTA ligand is usually coordinated to the central rare earth element in a molar ratio of 1:1.

[0012] Examples of rare earth elements include at least one element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu. Y, Dy, Gd, Tb, Ho, and Er are preferred in terms of corrosion resistance to air and reactivity with ceramic powder, with Dy being the most preferred.

[0013] The rare earth element aminopolycarboxylic acid complex powder used in this invention preferably has an average particle size of 1 μm or more and 1000 μm or less. The average particle size of the rare earth element aminopolycarboxylic acid complex powder is the particle size at which the cumulative volume from the smallest particle size side accounts for 50% by laser diffraction-scattering particle size distribution measurement (D 50 ) refers to.

[0014] The rare earth element aminopolycarboxylic acid complex powder has an average particle size (D50 ) being 1 μm or more makes it difficult for the powder to solidify even when left in the atmosphere. If the particle size is too small, it becomes difficult to produce, so from the viewpoint of ease of production, the average particle size is preferably 10 μm or more. By setting the average particle size to 10 μm or more, a device such as a high-speed stirrer is not required for production or processing for increasing the yield is not required, which is more preferable in terms of cost. Specific processing methods include bead mill pulverization, jet mill disintegration, and sieving. Further, from the viewpoint of the dispersibility of the rare earth compound in the ceramic powder, the average particle size is preferably 1000 μm or less, more preferably 500 μm or less. The average particle size (D 50 ) is the particle size at 50% volume-based integration from the small particle size side measured by the laser diffraction / scattering particle size distribution measurement method, and specifically, it can be measured by the measurement method described in the examples below. Making the average particle size of the aminopolycarboxylic acid complex powder 1 μm or more and 1000 μm or less can be achieved by processing means such as bead mill pulverization, jet mill disintegration, and sieving in addition to the production method described in the examples.

[0015] The aminopolycarboxylic acid complex powder of the rare earth element of the present invention preferably has a bulk density within a specific range. Specifically, a bulk density of 0.5 g / cm 3 or more is advantageous in terms of measures against solidification. From this viewpoint, a bulk density of 0.6 g / cm 3 or more is more preferable, and 0.7 g / cm 3 or more is even more preferable. Also, a bulk density of 1.2 g / cm 3 or less is advantageous in terms of measures against pulverization during transportation and work. From this viewpoint, a bulk density of 1.1 g / cm 3 or less is even more preferable. The bulk density of the aminopolycarboxylic acid complex powder of the rare earth element can be specifically measured by the measurement method described in the examples below.

[0016] The aminopolycarboxylic acid complex powder of the rare earth element of the present invention preferably has a specific surface area within a specific range. Specifically, a specific surface area of 0.5 m 2 / g or more is advantageous in terms of solubility. Also, the specific surface area is 5 m2 Having a specific surface area of ​​less than / g is advantageous in terms of preventing caking. From this perspective, a rare earth element aminopolycarboxylic acid complex powder with a specific surface area of ​​1 m² is advantageous. 2 / g or more 4m 2 It is preferable that the amount be less than or equal to 2m 2 / g or more 3.5m 2 It is more preferable that the amount is less than or equal to / g. The specific surface area can be measured by the measurement method described in the examples below.

[0017] The bulk density and specific surface area mentioned above can be achieved not only by the manufacturing method described in the examples, but also by processing such as bead mill grinding, jet mill crushing, and sieving, as well as by adjusting the manufacturing conditions (stirring conditions and precipitation temperature).

[0018] The rare earth element aminopolycarboxylic acid complex powder of the present invention is stable and does not form precipitates over a wide pH range when dissolved in water to form an aqueous solution. Specifically, it is preferably soluble in water, and when an aqueous solution with a concentration of 1 g / L is prepared, the aqueous solution does not produce precipitates derived from the aminopolycarboxylic acid complex in the pH range of 1.0 to 13.0 at 25°C. Specifically, 1 g of the rare earth element aminopolycarboxylic acid complex powder dissolves when mixed with 1 L of pH 1 nitric acid aqueous solution at 25°C, and also dissolves when mixed with 1 L of pH 13 ammonia aqueous solution at 25°C. Furthermore, no precipitate is visible when left standing for 24 hours at 25°C. This stable water solubility over a wide pH range is preferable because when the rare earth element aminopolycarboxylic acid complex of the present invention is mixed with ceramic powder as described later, the rare earth compound can be uniformly attached to the surface of each ceramic particle. In this context, rare earth compounds refer to aminopolycarboxylic acid complexes of rare earth elements and oxides of rare earth elements produced by their calcination.

[0019] In this invention, "water soluble" means the property of dissolving 1 g or more in 100 ml of water at 25°C. vinegar .

[0020] Furthermore, the present invention provides a ceramic powder additive used for mixing with ceramic powder, which includes a rare earth element aminopolycarboxylic acid complex powder. In this specification, the meaning of "used for mixing with ceramic powder" of the rare earth element aminopolycarboxylic acid complex powder is not limited to mixing the rare earth element aminopolycarboxylic acid complex powder with the ceramic powder in powder form, but also includes cases where the rare earth element aminopolycarboxylic acid complex powder is dissolved in a solvent such as water and then mixed with the ceramic powder.

[0021] For example, in the field of multilayer ceramic capacitors, it is known that highly reliable multilayer ceramic capacitors that do not suffer from insulation resistance defects can be obtained by uniformly dispersing oxides of rare earth elements on the surface of ceramic particles such as barium titanate, which are the main raw materials of the dielectric layer. As described above, rare earth element aminopolycarboxylic acid complex powders (especially rare earth element aminopolycarboxylic acid complex powders of specific particle sizes) are less prone to caking, and when dissolved in water, coarse particles are less likely to remain in the aqueous solution. Furthermore, these rare earth element aminopolycarboxylic acid complex powders are less prone to precipitation over a wide pH range and have high water solubility. Therefore, when an aqueous solution of rare earth element aminopolycarboxylic acid complex powder is mixed with ceramic powder, the rare earth element aminopolycarboxylic acid complex can be uniformly attached to the surface of the ceramic particles. By firing the ceramic powder on which the rare earth element aminopolycarboxylic acid complex is uniformly attached to the particle surface, a rare earth oxide-containing ceramic powder is obtained in which rare earth element oxides are uniformly attached to the surface of the ceramic particles. By using the obtained rare earth oxide-containing ceramic powder as a multilayer ceramic capacitor material, a highly reliable multilayer ceramic capacitor with suppressed insulation resistance defects can be obtained. Here, "uniformly attached" refers to a state in which differences in attachment thickness, attachment amount, and uneven distribution of attachment positions among particles are suppressed.

[0022] In contrast, conventional rare earth components were insufficient in terms of dispersing rare earth compounds with high dispersibility in ceramic powder for multilayer ceramic capacitors. For example, Patent Document 1 (Revised Publication No. 2015-040881) describes using a dispersion machine that employs dispersion media such as a ball mill or bead mill to disperse rare earth element oxides in ceramic powder in a solvent. However, when solvent-insoluble compounds such as rare earth element oxides are dispersed using dispersion media for extended periods to uniformly adhere to the surface of ceramic particles, the ceramic particles may be crushed or worn down, potentially degrading their performance. On the other hand, if dispersion media is used but only for a short time, there is a concern that coarse particles of the rare earth compound may remain (see Comparative Example 1 described later). Furthermore, as an example, in Patent Document 2 (JP 2007-204315 A) and Patent Document 3 (JP 2013-163614 A), organic acid complexes such as citrate complexes of rare earth elements are used instead of oxides of rare earth elements as rare earth components to be mixed with ceramic powder in a solvent. However, although organic acid complexes of rare earth elements are easily attached uniformly to the surface of ceramic particles, pH adjustment is necessary to prevent precipitation, or careful control is required to prevent solidification (see Comparative Examples 2 and 3 described later).

[0023] When a rare earth element aminopolycarboxylic acid complex is used for mixing with ceramic powder, the ceramic powder preferably has a primary particle size of 0.05 μm or more and 1 μm or less. A primary particle size of 0.05 μm or more has the advantage of suppressing aggregation of the ceramic powder and making it easier to disperse the aminopolycarboxylic acid complex in the ceramic powder. Furthermore, a primary particle size of 1.0 μm or less of the ceramic powder has the advantage of greatly improving the technical significance of the present invention, as it improves the dispersibility of rare earth compounds in ceramic powder. From this viewpoint, a primary particle size of 0.05 μm or more and 1 μm or less of the ceramic powder is more preferable, and a primary particle size of 0.1 μm or more and 0.5 μm or less is even more preferable. The primary particle size is measured by the specific surface area s(m²) measured by the BET method. 2 The particle size is determined from ( / g). The primary particle diameter d (μm) is d = 6 / (ρs) (where ρ is the true density (cm³). 3( / g)). The method for measuring the BET specific surface area of ​​the ceramic powder is the same as the method for measuring the specific surface area of ​​rare earth compounds such as aminocarboxylic acid complex powder described later in the examples.

[0024] Furthermore, as mentioned above, the ceramic powder is preferably a dielectric powder for ceramic capacitors in order to improve the reliability of the ceramic capacitor. Among the dielectric powders for ceramic capacitors, having a perovskite structure is preferable in that it possesses ferroelectric properties. Barium titanate is an example of a dielectric powder for ceramic capacitors having a perovskite structure. To further improve the reliability of the ceramic capacitor, a dielectric powder doped with Sr, Ca, etc., of barium titanate may also be used.

[0025] The additive material of the present invention can be in the form of a powder, flakes, or lumps. Taking advantage of the non-caking properties of the rare earth element aminocarboxylic acid powder mentioned above, it is preferable that it be in the form of a powder for ease of distribution. To the extent that the dispersibility of the rare earth compound in the ceramic powder described above can be improved, the additive may contain components other than the rare earth element aminopolycarboxylic acid complex powder. The proportion of the rare earth element aminopolycarboxylic acid complex powder in the solid content of the additive of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, most preferably 30% by mass or more, and may be 50% by mass or more. Solid content refers to the total of components excluding the solvent.

[0026] The following describes a method for producing ceramic powder containing rare earth compounds. The present invention's method for producing ceramic powder involves mixing an aqueous solution of a rare earth element aminopolycarboxylic acid complex powder in water with ceramic powder, and then removing the water to coat the particle surface of the ceramic powder with the rare earth compound.

[0027] When mixing an aqueous solution of a rare earth element aminopolycarboxylic acid complex powder with ceramic powder, the water, the rare earth element aminopolycarboxylic acid complex powder, and the ceramic powder may be mixed together in a container at the same time, or an aqueous solution may be obtained by mixing water and the rare earth element aminopolycarboxylic acid complex powder, and this aqueous solution may be mixed with the ceramic powder.

[0028] For improving the reliability of the resulting ceramic capacitor, it is preferable to mix the rare earth element aminopolycarboxylic acid complex powder with 100 moles of ceramic powder such that the amount of rare earth element in the rare earth element aminopolycarboxylic acid complex is between 0.1 mole and 10 moles, and more preferably between 1 mole and 5 moles.

[0029] Furthermore, regarding the amount of water used, it is preferable that the concentration of ceramic powder in the total amount of water, ceramic powder, and rare earth element aminopolycarboxylic acid complex powder is 5% by mass or more and 70% by mass or less, in order to uniformly adhere the rare earth element aminopolycarboxylic acid complex to the ceramic powder and to lower the viscosity and improve operability, and more preferably 10% by mass or more and 50% by mass or less.

[0030] The mixture of the resulting aminopolycarboxylic acid complex, ceramic powder, and water is then dehydrated to obtain a powder. Drying and / or calcination are convenient methods for removing moisture. For example, calcination can be carried out at 500°C to 1300°C. The calcination atmosphere can be an oxygen-containing atmosphere such as air. Under these calcination conditions, it becomes possible to coat the surface of the ceramic particles with rare earth oxides.

[0031] Furthermore, the mixing of ceramic powder, rare earth element aminopolycarboxylic acid complex, and water can be carried out by mechanical processing using a homogenizer, mill (bead mill, ball mill, etc.), mixer, grinder, paint shaker, etc. Disintegration processing using a dispersion media is particularly preferred. The dispersion time in the slurry is preferably 1 minute to 1 hour, and more preferably 2 minutes to 30 minutes.

[0032] When using a dispersion medium for mixing ceramic powder with a rare earth element aminopolycarboxylic acid complex and water, the material of the dispersion medium is not particularly limited, but from the viewpoint of suppressing the inclusion of metal impurities, ceramic media such as alumina, zirconia, silicon carbide, and silicon nitride are preferred. Zirconia as referred to here includes stabilized zirconia such as YSZ and PSZ.

[0033] From the viewpoint of shortening the dispersion time and improving dispersibility, the particle size of the dispersion media is preferably 0.015 mm or more and 2 mm or less, and more preferably 0.08 mm or more and 1 mm or less. From the viewpoint of shortening the dispersion time and improving dispersibility, the volume ratio of slurry to dispersion media is preferably 1:0.1 or more and 5 or less, and more preferably 0.5 or more and 1 or less.

[0034] Next, a preferred method for producing the aminopolycarboxylic acid complex powder of the present invention will be described. The aminopolycarboxylic acid complex powder of the present invention can be produced by mixing a water-soluble salt of a rare earth element with an aminopolycarboxylic acid in the presence of water and alkali. Examples of water-soluble salts include nitrates. In this process, it is preferable to wash the precipitated powder with ethanol and then heat it at 30 to 80°C for 5 to 24 hours in an atmospheric atmosphere with a relative humidity of 50% or less. By going through such an ethanol washing and drying process, particles with an average particle size of 1000 μm or less can be successfully produced. [Examples]

[0035] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples.

[0036] [Example 1] (Dy-EDTA complex powder) 0.44 mol of ethylenediaminetetraacetic acid was added to 200 ml of pure water, and dissolved in 150 ml of 24% by mass caustic soda. To this aqueous solution, an aqueous solution of 0.44 mol of dysprosium nitrate n hydrate dissolved in 150 ml of pure water was added, and the mixture was stirred at 100 rpm with a stirrer at room temperature for 2 hours. After filtering the precipitated solid, it was washed three times repeatedly with 150 ml of ethanol, and dried at 50°C for 10 hours in an atmospheric atmosphere with 50% relative humidity to obtain 135 g of dysprosium-EDTA complex powder. This was used as one batch, and the required number of batches for the experiment were prepared. The obtained dysprosium-EDTA complex powder was measured for specific surface area, bulk density, and average particle size using the following method, and the specific surface area was found to be 3.2 m². 2 The bulk density is 0.84 g / cm³ / g. 3 The average particle size was 29.3 μm. The obtained dysprosium-EDTA complex powder dissolved when 1 g was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, and also dissolved when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C. In both cases, no precipitate formed when the dissolved solution was left to stand at 25°C for 24 hours. When 20 g of the obtained dysprosium-EDTA complex was left in air at 24°C and 78% relative humidity for 72 hours, the dysprosium-EDTA complex remained in powder form and could be sieved with a 500 μm ultrasonic sieve with a 100% sieving efficiency without solidification. The average particle size remained almost unchanged before and after the 72-hour period.

[0037] (Method for measuring specific surface area) The specific surface area was measured using the BET single-point method with a Macsorb model-1201 fully automatic specific surface area meter manufactured by Mountec. The gas used was a nitrogen-helium mixture (30 vol%). As a pretreatment before measurement, the powder was placed in a glass cell and set in the apparatus, and nitrogen gas was circulated through the glass cell and dried at 150°C for 60 minutes.

[0038] (Method for measuring bulk density) Using a multi-functional powder property measuring instrument, the Multi-Tester MT-1000 (manufactured by Seishin Corporation), the bulk density was measured according to "7-2. Measurement Method of Static Bulk Density (Vastly Packed Bulk Density)" in the instruction manual, except that the powder was not supplied without passing through a sieve.

[0039] (Method for measuring average particle size) Measurements were taken using a Nikkiso Co., Ltd. Microtrac MT3300EXII. During measurement, ethanol was used as the dispersion medium. The sample was added to the sample circulation chamber of the Microtrac MT3300EXII, and the dispersion treatment was performed using the ultrasonic device built into the MT3300EXII at an output of 40W for 300 seconds. After the device determined that the concentration was appropriate, D 50 We measured it.

[0040] (Dispersibility test with barium titanate powder) Barium titanate powder (primary particle size 0.1 μm, manufactured by Kyoritsu Material Co., Ltd., BTHP-100) was mixed with pure water to obtain a 10% by mass barium titanate slurry. The pH of this slurry was 10.0 at 25°C. To the barium titanate slurry, 100 moles of barium titanate were mixed with 4 moles of the dysprosium-EDTA complex powder (Dy) and φ0.1 mm YTZ beads (manufactured by Nikkatoh Co., Ltd.) in a container such that the volume ratio of slurry:YTZ beads = 1:2. The mixture was then shaken in a paint shaker for 3 minutes. The resulting slurry was dried at 120°C and then calcined at 1000°C for 3 hours in an air atmosphere to obtain a mixed powder of barium titanate and dysprosium oxide. Figures 1 to 4 show the results of observing this powder with a scanning Auger electron microscope. In Figures 1 to 4, it can be seen that the Dy compound (dysprosium oxide) is uniformly dispersed around the barium titanate, and there are no coarse particles. For the mixing test with this barium titanate powder, the dysprosium-EDTA complex powder was not used after drying, but rather after being left in an air environment at 24°C and 78% relative humidity for 72 hours, and before ultrasonic sieving.

[0041] [Comparative Example 1] (Dysprosium Oxide Powder) Dysprosium oxide powder (manufactured by Nippon Yttrium Co., Ltd.) was prepared. The prepared dysprosium oxide powder had a specific surface area of ​​10 m². 2 / g, average particle size 0.5 μm, bulk density 0.5 g / cm³ 3 That was the case. The dispersibility test with the barium titanate powder was carried out in the same manner as above, except that the dysprosium oxide powder was used instead of the dysprosium-EDTA complex powder, to obtain a mixed powder of barium titanate and dysprosium oxide. Figures 5 to 8 show the results of observing this powder with a scanning Auger electron microscope. In Figure 6, it can be seen that coarse particles of the Dy compound (dysprosium oxide) are particularly present in the area indicated by the arrow.

[0042] [Example 2] (Y-EDTA complex powder) In Example 1, dysprosium nitrate was replaced with yttrium nitrate. Aside from this change, the Y-EDTA complex powder was obtained in the same manner as in Example 1. The specific surface area of ​​the obtained complex powder was 1.3 m². 2 The bulk density is 0.88 g / cm³ / g. 3 The average particle size was 32.3 μm. The obtained yttrium-EDTA complex powder dissolved when 1 g was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, and also dissolved when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C. In both cases, no precipitate formed when the dissolved solution was left to stand at 25°C for 24 hours. The obtained complex powder was left in air at 24°C and 78% relative humidity for 72 hours. It remained in powder form and could be sieved with a 500 μm ultrasonic sieve with a 100% sieving efficiency without solidification. The average particle size remained almost unchanged before and after the 72-hour period. Furthermore, the dispersibility test with the barium titanate powder was carried out in the same manner as in Example 1, except that Y-EDTA complex powder was used instead of the dysprosium-EDTA complex powder and 4 mol parts of Y were used, to obtain a mixed powder of barium titanate and yttrium oxide. When this powder was observed with a scanning Auger electron microscope, the Y compound (yttrium oxide) was uniformly dispersed around the barium titanate, and there were no coarse particles.

[0043] [Example 3] (Ho-EDTA complex powder) In Example 1, dysprosium nitrate was replaced with holmium nitrate. Aside from this change, the Ho-EDTA complex powder was obtained in the same manner as in Example 1. The specific surface area of ​​the obtained complex powder was 1.0 m². 2 The bulk density is 0.93 g / cm³ / g. 3 The average particle size was 27.5 μm. The obtained holmium-EDTA complex powder dissolved when 1 g was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, and also dissolved when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C. In both cases, no precipitate formed when the dissolved solution was left to stand at 25°C for 24 hours. The obtained complex powder was left in air at 24°C and 78% relative humidity for 72 hours. It remained in powder form and could be sieved with a 500 μm ultrasonic sieve with a 100% sieving efficiency without solidification. The average particle size remained almost unchanged before and after the 72-hour period. Furthermore, a dispersibility test with the barium titanate powder was carried out in the same manner as in Example 1, except that Ho-EDTA complex powder was used instead of the dysprosium-EDTA complex powder and 4 mol parts of Ho were used, to obtain a mixed powder of barium titanate and holmium oxide. When this powder was observed with a scanning Auger electron microscope, it was found that Ho compounds (holmium oxide) were uniformly dispersed around barium titanate, and there were no coarse particles.

[0044] [Example 4] (Production of Yb-EDTA complex powder) In Example 1, dysprosium nitrate was replaced with ytterbium nitrate. Apart from this change, an aminopolycarboxylic acid complex powder was obtained in the same manner as in Example 1. The specific surface area of ​​the obtained complex powder was 2.6 m². 2 The bulk density is 0.99 g / cm³ / g. 3 The average particle size was 29.1 μm. The obtained ytterbium-EDTA complex powder dissolved when 1 g was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, and also dissolved when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C. In both cases, no precipitate formed when the dissolved solution was left to stand at 25°C for 24 hours. When the obtained complex was left in air at 24°C and 78% relative humidity for 72 hours, it remained in powder form and could be sieved with a 500 μm ultrasonic sieve with a 100% sieving efficiency without solidification. The average particle size remained almost unchanged before and after the 72-hour period. Furthermore, the dispersibility test with the barium titanate powder was carried out in the same manner as in Example 1, except that Yb-EDTA complex powder was used instead of the dysprosium-EDTA complex powder and 4 mol parts of Yb were used, to obtain a mixed powder of barium titanate and ytterbium oxide. When this powder was observed with a scanning Auger electron microscope, the Yb compound (ytterbium oxide) was uniformly dispersed around the barium titanate, and there were no coarse particles.

[0045] [Comparative Example 2] (Citrate complex of Dy) 0.2 mol of dysprosium nitrate and 0.6 mol of citric acid monohydrate were dissolved in 550 g of ethanol, and then 150 ml of caustic soda was added and the mixture was stirred for 2 hours. The precipitate was filtered and washed three times with 150 ml of ethanol, and then dried at 50°C for 10 hours under an air atmosphere to obtain a dysprosium-citric acid complex. The specific surface area of ​​the obtained complex powder was 0.4 m². 2 The bulk density is 0.74 g / cm³ / g. 3 The average particle size was 78.6 μm. When 1 g of the obtained dysprosium-citric acid complex was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, it dissolved, and when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C, it also dissolved. In both cases, no precipitate formed when the dissolved solution was allowed to stand at 25°C for 24 hours. Furthermore, when the obtained dysprosium-citric acid complex was left in air at 24°C and 78% relative humidity for 72 hours, it solidified into a large mass, and only 2% could be sieved through a 500 μm sieve. In other words, it solidified into a single large mass in the atmosphere. Therefore, it was not possible to conduct a dispersibility test with the barium titanate powder.

[0046] [Comparative Example 3] Dysprosium acetate powder was obtained by dissolving 0.3 mol of dysprosium oxide (0.6 mol as element Dy) in 172.2 ml of an 80% by mass aqueous solution of acetic acid heated to 90°C, and then cooling and crystallizing the solution. The specific surface area of ​​the obtained dysprosium acetate powder was 5.0 m². 2 / g, bulk density is 1.0g / cm³ 3 The average particle size was 30.0 μm. The obtained dysprosium acetate powder dissolved when 1 g was mixed with 1 L of pH 1 nitric acid aqueous solution at 25°C, but did not dissolve when 1 g was mixed with pH 13 ammonia aqueous solution at 25°C. No precipitate formed when the solution dissolved in 1 L of pH 1 nitric acid aqueous solution was left to stand at 25°C for 24 hours. Furthermore, the mixture with pH 13 aqueous solution did not dissolve even after being left to stand at 25°C for 24 hours. The obtained dysprosium acetate powder was left in air at 24°C and 78% relative humidity for 72 hours. It remained in powder form and could be sieved with a 500 μm ultrasonic sieve with a 100% sieving efficiency without solidification. The average particle size remained almost unchanged before and after the 72-hour period. Furthermore, the dispersibility test with the barium titanate powder was carried out in the same manner as in Example 1, except that dysprosium acetate powder was used instead of the dysprosium-EDTA complex powder, to obtain a mixed powder of barium titanate and dysprosium oxide. When this powder was observed with a scanning Auger electron microscope, coarse particles of the Dy compound (dysprosium oxide) were found to be present.

[0047] [Example 5] In the method for preparing the dysprosium-EDTA complex described in Example 1, stirring at 1000 rpm with a high-speed stirrer instead of 100 rpm with a stirrer resulted in a specific surface area of ​​4.1 m². 2 / g, bulk density is 0.8g / cm³ 3 A dysprosium-EDTA complex powder with an average particle size of 8.3 μm was obtained. The obtained dysprosium-EDTA complex powder dissolved when 1 g was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, and also dissolved when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C. In both cases, no precipitate formed when the dissolved solution was left to stand at 25°C for 24 hours. The dysprosium-EDTA complex with an average particle size of less than 10 μm was left in air at 24°C and 78% relative humidity for 72 hours, as in Example 1. It could be sieved with a 500 μm ultrasonic sieve with a 100% sieving efficiency and did not solidify. The average particle size hardly changed before and after the 72-hour period. A dispersibility test was performed with the barium titanate powder in the same manner as in Example 1, except that the obtained dysprosium-EDTA complex powder was used in place of the complex powder obtained in Example 1, to obtain a mixed powder of barium titanate and dysprosium oxide. When this powder was observed with a scanning Auger electron microscope, the Dy compound (dysprosium oxide) was uniformly dispersed around the barium titanate, and there were no coarse particles.

[0048] [Example 6] In the method for preparing the dysprosium-EDTA complex described in Example 1, stirring at 10,000 rpm with a high-speed stirrer instead of 100 rpm with a stirrer resulted in a specific surface area of ​​4.8 m². 2 / g, bulk density is 0.7g / cm³ 3 A dysprosium-EDTA complex with an average particle size of 1.0 μm was obtained. This dysprosium-EDTA complex powder, with an average particle size of 1.0 μm, dissolved when 1 g was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, and also dissolved when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C. In both cases, no precipitate formed after the solution was left to stand at 25°C for 24 hours. This dysprosium-EDTA complex with an average particle size of 1.0 μm was left in air at 24°C and 78% relative humidity for 72 hours, as in Example 1. It could be sieved with a 500 μm ultrasonic sieve with a 100% sieving efficiency and did not solidify. The average particle size hardly changed before and after the 72-hour period. A dispersibility test was performed with the barium titanate powder in the same manner as in Example 1, except that the obtained dysprosium-EDTA complex powder was used in place of the complex powder obtained in Example 1, to obtain a mixed powder of barium titanate and dysprosium oxide. When this powder was observed with a scanning Auger electron microscope, the Dy compound (dysprosium oxide) was uniformly dispersed around the barium titanate, and there were no coarse particles.

[0049] [Example 7] In the method for preparing the dysprosium-EDTA complex described in Example 1, the amount of ethanol used for ethanol washing in Example 1 was changed from 150 ml to 20 ml, and the washing was repeated three times. The mixture was then dried at 50°C for 10 hours in an atmospheric environment with a relative humidity of 50%, resulting in a specific surface area of ​​0.6 m². 2 / g, bulk density is 1.1g / cm³ 3 A dysprosium-EDTA complex powder with an average particle size of 800 μm was obtained. This dysprosium-EDTA complex powder, with an average particle size of 800 μm, dissolved when 1 g was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, and also dissolved when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C. In both cases, no precipitate formed after the solution was left to stand at 25°C for 24 hours. This dysprosium-EDTA complex was left in the air for 72 hours, similar to Example 1, but there was no change in the average particle size and it did not solidify. The average particle size remained almost unchanged before and after the 72-hour period. A dispersibility test was performed with the barium titanate powder in the same manner as in Example 1, except that the obtained dysprosium-EDTA complex powder was used in place of the complex powder obtained in Example 1, to obtain a mixed powder of barium titanate and dysprosium oxide. When this powder was observed with a scanning Auger electron microscope, the Dy compound (dysprosium oxide) was uniformly dispersed around the barium titanate, and there were no coarse particles.

[0050] [Comparative Example 4] In the method for preparing the dysprosium-EDTA complex described in Example 1, the step of repeatedly washing with 150 ml of ethanol three times as performed in Example 1 was omitted, and the complex was dried at 50°C for 10 hours in an atmospheric atmosphere with a relative humidity of 50%. Drying and agglomeration resulted in an average particle size of 1800 μm and a specific surface area of ​​0.3 m². 2 / g, bulk density is 1.3g / cm³ 3 A dysprosium-EDTA complex powder was obtained. This dysprosium-EDTA complex powder, with an average particle size of 1800 μm, dissolved when 1 g was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, and also dissolved when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C. In both cases, no precipitate formed after the solution was left to stand at 25°C for 24 hours. This dysprosium-EDTA complex was left in the air for 72 hours, similar to Example 1, but there was no change in the average particle size and it did not solidify. A dispersibility test was performed with the barium titanate powder in the same manner as in Example 1, except that the obtained dysprosium-EDTA complex powder was used in place of the complex powder obtained in Example 1, to obtain a mixed powder of barium titanate and dysprosium oxide. When this powder was observed with a scanning Auger electron microscope, coarse particles of the Dy compound (dysprosium oxide) were found.

[0051] [Comparative Example 5] In the method for preparing the dysprosium-EDTA complex described in Example 1, stirring at 20,000 rpm with a high-speed stirrer instead of 100 rpm with a stirrer resulted in a specific surface area of ​​5.3 m². 2 / g, bulk density is 0.5g / cm³ 3 A dysprosium-EDTA complex with an average particle size of 0.5 μm was obtained. This dysprosium-EDTA complex powder, with an average particle size of 0.5 μm, dissolved when 1 g was mixed with 1 L of pH 1 aqueous nitric acid solution at 25°C, and also dissolved when 1 g was mixed with pH 13 aqueous ammonia solution at 25°C. In both cases, no precipitate formed after the solution was left to stand at 25°C for 24 hours. When this dysprosium-EDTA complex with an average particle size of 0.5 μm was left in air at 24°C and 78% relative humidity for 72 hours, as in Example 1, it solidified and only 30% could be sieved through a 500 μm sieve. A dispersibility test was performed with the barium titanate powder in the same manner as in Example 1, except that the obtained dysprosium-EDTA complex powder was used in place of the complex powder obtained in Example 1, to obtain a mixed powder of barium titanate and dysprosium oxide. When this powder was observed with a scanning Auger electron microscope, coarse particles of the Dy compound (dysprosium oxide) were found to be present.

[0052] The measurement and evaluation results for the above examples and comparative examples are summarized in Table 1 below. Furthermore, Table 1 also shows the results of confirming the solubility of the complex powders obtained in each example and each powder obtained in the comparative example by determining whether 1 g or more dissolves in 100 ml of pure water at 25°C.

[0053] [Table 1]

[0054] As described above, the powder of rare earth EDTA complex, a representative example of rare earth aminopolycarboxylic acid complexes, is D 50 If the particle size is 1 μm or larger, it will not solidify. 50 If the particle size is 1000 μm or less, it exhibits good dispersibility in barium titanate powder, a typical example of ceramic powder, and it was confirmed that the aqueous solution does not form precipitates in a wide pH range of 1 to 13.

Claims

1. A ceramic powder additive used for firing after mixing with ceramic powder, containing a water-soluble rare earth element aminopolycarboxylic acid complex powder with an average particle size of 1 μm to 1000 μm.

2. The ceramic powder additive according to claim 1, wherein 1 g of the aminopolycarboxylic acid complex powder dissolves when mixed with 1 L of an aqueous nitric acid solution at pH 1, and also dissolves when mixed with 1 L of an aqueous ammonia solution at pH 13.

3. Bulk density is 0.5 g / cm³ ３ 1.2g / cm or more ３ The additive according to claim 1 or 2, which is as follows:

4. The additive according to any one of claims 1 to 3, wherein the aminopolycarboxylic acid complex powder of the rare earth element is EDTA (ethylenediaminetetraacetic acid) complex powder.

5. Bulk density 0.5 g / cm³ ３ 1.2g / cm or more ３ The following is true, with a specific surface area of ​​0.5 m². ２ / g or more 5m ２ The additive according to claim 2, wherein the amount is less than or equal to / g.

6. Bulk density is 0.7 g / cm ３ or more and 1.1 g / cm ３ or less, and the specific surface area is 2 m ２ / g or more and 3.5 m ２ / g or less. The additive according to claim 5.

7. The additive according to any one of claims 1 to 6, wherein the rare earth element is one selected from Dy (dysprosium), Ho (holmium), and Yb (ytterbium).

8. An additive according to any one of claims 1 to 6, used for mixing with a powder made of a dielectric material for ceramic capacitors.

9. The additive according to claim 8, used for mixing with the powder made of the dielectric having a perovskite structure.

10. An additive according to any one of claims 1 to 9, used for mixing with barium titanate powder.

11. A method for producing ceramic powder containing rare earth compounds, A method for producing ceramic powder, comprising mixing an aqueous solution of a water-soluble rare earth element aminopolycarboxylic acid complex powder having an average particle size of 1 μm to 500 μm with ceramic powder and firing the mixture, thereby coating the particle surface of the ceramic powder with a rare earth compound.

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