TWI908790B - Method for producing inorganic fine powder - Google Patents

Abstract

Disclosed is a method for producing an inorganic fine powder of which a volume-based cumulative 50% particle diameter D50 is in a range of 0.01 μm or more and 5.0 μm or less. The method of the present invention is characterized by comprising a step of producing a powder to be classified by dispersing a carboxylic acid-adsorbed inorganic raw material powder in which a carboxylic acid is adsorbed on an inorganic raw material powder having D50 of 10 μm or less in a gas phase to obtain the powder to be classified, and a dry classification step for performing dry classification of the powder to be classified. According to the present invention, it is possible to provide the method for producing the inorganic fine powder having an extremely small number of coarse particles and the volume-based cumulative 50% particle diameter D50 in the range of 0.01 μm or more and 5.0 μm or less with high productivity.

Description

Method for manufacturing inorganic micro powders

This invention relates to a method for manufacturing an inorganic micro powder.

Traditionally, conductive metal powders have been used as conductive materials for electronic components. In laminated ceramic capacitors (MCLLs), due to the rapid development of thinning of both the ceramic layer and the internal electrode layer, when using metal powders as internal electrodes, it is required that not only the average particle size be small, but also the particle size distribution of the powder be narrow in order to form a uniform electrode layer thickness. Furthermore, the powder must not contain large particles that could potentially short-circuit the electrodes by encasing the dielectric layer and coming into contact with the sides of adjacent internal electrodes.

To date, methods for classifying powders manufactured using various methods have been employed to produce powders with desired particle size distributions. These classification methods include, for example, classifying powders according to particle size based on differences in particle settling rates in the gas or liquid phase. Classification performed in the gas phase is called dry classification, while classification performed in the liquid phase is called wet classification. Although wet classification offers superior accuracy, it requires a liquid as the dispersion medium, and furthermore, drying and pulverization are necessary after classification. Therefore, dry classification is significantly less expensive.

However, in the past, when performing this dry classification, the powder would adhere to various parts of the classifier and block the powder supply port or the inside of the piping, making it difficult to operate for a long time. Furthermore, due to the low classification accuracy, there was a problem of low yield.

As a method aimed at solving such problems, Patent 1 discloses a method of dry-classifying powder by mixing powder with an additive composed of alcohols such as ethanol with a boiling point of less than 200°C, while the additive is vaporized.

In addition, in invention patent document 2, a method is disclosed in which powder is mixed with an additive consisting of an aqueous solution of alcohols such as ethanol containing 10% to 50% by mass, and the powder is dry-classified while the additive is vaporized.

Furthermore, Patent Document 3 discloses a method for dry-classifying the powder by mixing nickel powder with an additive composed of an organic solvent with a flash point above 80°C, such as diethylene glycol, while simultaneously vaporizing the additive. It also discloses a method for dry-classifying the powder by mixing nickel powder with an additive composed of water, while simultaneously vaporizing the additive.

In addition, in invention patent document 4, a method for dry fractionation of powder is disclosed by mixing powder with diethylene glycol monomethyl ether as a liquid additive.

[Previous Technical Literature] [Invention Patent Documents]

[Patent Document 1] International Publication No. 2010/047175. [Patent Document 2] International Publication No. 2010/057206. [Patent Document 3] International Publication No. 2010/106716. [Patent Document 4] International Publication No. 2012/124453.

[The problem that the invention aims to solve]

However, the inventors of this case discovered the following problems during their research: For example, although dry classification by adsorbing additives such as ethanol onto the powder allows the classifier to run for a long time, the resulting powder contains a large number of coarse particles. Therefore, in order to reduce the number of these coarse particles, the classification must be repeated multiple times. Furthermore, the following problem was also discovered: Although repeated classification can reduce the number of coarse particles, the time and cost involved reduce productivity, and consequently, significantly decrease the yield of the obtained powder.

Therefore, the purpose of this invention is to provide a method for manufacturing inorganic micropowders with a very small number of coarse particles and a volumetric 50% particle size _D50 ranging from 0.01 μm to 5.0 μm, which can be produced with high productivity. [Technical Means for Solving the Problem]

The above-mentioned objective is achieved by the present invention as described in (1) to (9) below. (1) A method for manufacturing inorganic micro powder, which is a method for manufacturing inorganic micro powder with a cumulative particle size _D50 of 50% in the volumetric metric range of 0.01 μm to 5.0 μm, comprising: a fractionated powder generation step, wherein adsorbed carboxylic acid inorganic raw material powder in which carboxylic acid is adsorbed in inorganic raw material powder with _D50 of 10 μm or less is dispersed in a gas phase to obtain fractionated powder; and a dry fractionation step, wherein the aforementioned fractionated powder is dry-fractionated.

(2) A method for manufacturing inorganic micro powder, wherein the cumulative 50% particle size _D50 on a volume basis is in the range of 0.01 μm to 5.0 μm, comprising: a step of generating a fractionated powder, wherein an inorganic raw material powder with a _D50 of 10 μm or less that is dispersed in the gas phase is used to generate a fractionated powder by adsorbing carboxylic acid onto the inorganic raw material powder in the dispersed state in the aforementioned gas phase to obtain fractionated powder; and a dry fractionation step, wherein the fractionated powder is dry-fractionated.

(3) The method for manufacturing inorganic micro powder as described in (2) above, wherein between the aforementioned fractionated powder generation step and the aforementioned dry fractionation step, there is: a recovery step, which recovers the aforementioned fractionated powder; and a dispersion step, which disperses the aforementioned fractionated powder obtained in the aforementioned recovery step in the gas phase.

(4) A method for manufacturing inorganic micro powder, wherein the cumulative 50% particle size _D50 on a volume basis is in the range of 0.01 μm to 5.0 μm, comprising: a fractionated powder generation step, wherein inorganic raw material powder with _D50 of less than 10 μm is dispersed to obtain fractionated powder; and a dry fractionation step, wherein the fractionated powder is dry-fractionated; wherein the fractionated powder generation step is carried out in an atmosphere containing carboxylic acid in a gaseous state.

(5) The method for manufacturing inorganic micro powder as described in any of (2) to (4) above, wherein the proportion of the aforementioned carboxylic acid used is between 30 mol and 960 mol relative to the volume of the aforementioned inorganic raw material powder per ^m3 .

(6) The method for manufacturing inorganic micro powder as described in any of (1) to (5) above, wherein the boiling point of the aforementioned carboxylic acid is above 100°C and below 400°C.

(7) The method for manufacturing inorganic micro powder as described in any of (1) to (6) above, wherein the aforementioned carboxylic acid is selected from at least one of acetic acid, propionic acid, butyric acid and oleic acid.

(8) The method for manufacturing inorganic micro powder as described in any of (1) to (7) above, wherein the aforementioned dry classification step is carried out in a gas phase at a temperature of 60°C to 300°C.

(9) The method for manufacturing inorganic micropowder as described in any one of (1) to (8) above, wherein the inorganic component of the aforementioned inorganic raw material powder is selected from at least one of the group consisting of metals, metal oxides, glass, ceramics, and semiconductors. [Effects of the Invention]

According to the present invention, there is a method for manufacturing inorganic micropowders that can produce with high productivity a very small number of coarse particles and a cumulative 50% particle size D ₅₀ in the volumetric dimension of 0.01 μm to 5.0 μm.

The following is a detailed description of a preferred embodiment of the present invention. [Method for Manufacturing Inorganic Micropowder] 1. First Embodiment

The first embodiment of the present invention is a method for manufacturing inorganic micro powders in which the cumulative 50% particle size _D50 is in the range of 0.01 μm to 5.0 μm. The method comprises a step of generating fractionated powder by dispersing inorganic raw material powder containing adsorbed carboxylic acid in an inorganic raw material powder with _D50 of less than 10 μm in a gas phase to obtain fractionated powder; and a step of dry fractionation by dry fractionation of the fractionated powder.

This provides a method for manufacturing inorganic micropowders that can produce with high productivity a very small number of coarse particles and a cumulative 50% particle size _D50 in the range of 0.01 μm to 5.0 μm.

The superior performance is attributed to the following factors: Compared to dry fractionation by adsorbing additives such as ethanol onto powder, dispersing inorganic raw material powder containing adsorbed carboxylic acids in the gas phase significantly improves the dispersibility of the powder in the gas phase, thereby increasing fractionation accuracy. This drastically reduces the number of coarse particles in the produced inorganic micropowders. Furthermore, it reduces the number of fractionation stages, thus improving productivity.

Furthermore, by adsorbing carboxylic acids onto inorganic raw material powders, the flowability of the fractionated powder is improved, and the adhesion of the fractionated powder within the classifier is reduced, thereby increasing the yield. Also, the reduced adhesion within the classifier makes it less prone to clogging at the powder feed inlet or inside the piping, thus extending the classifier's uptime and improving productivity.

Furthermore, in this embodiment, since adsorbed carboxylic acid inorganic raw material powder pre-adsorbed with carboxylic acid is used, it is more advantageous to simplify and miniaturize the structure of the device for manufacturing inorganic micro powders compared to other embodiments, which will be detailed later. Also, since adsorbed carboxylic acid inorganic raw material powder pre-adsorbed with carboxylic acid is used, the powder has higher flowability and is less prone to adhesion within the classifier compared to adding inorganic raw material powder without adsorbed carboxylic acid to the classifier, resulting in smoother powder movement within the classifier.

In this manual, the cumulative 50% particle size ( _D50 ) of the volume datum, unless otherwise stated, refers to the 50% integral fraction of the volume datum of particle size distribution measured using a laser particle size distribution measuring device, which can be obtained by measurement using, for example, a laser diffraction/scattering type particle size distribution measuring device LA-960 (manufactured by HORIBA).

In this specification, grading refers to the process of grouping relatively larger particles into one group (in other words, coarse powder) and relatively smaller particles into another group (in other words, fine powder) based on their size. Specifically, in this specification, fine powder refers to a group of particles whose cumulative particle size _D50 is between 0.01 μm and 5.0 μm, based on a volumetric 50% ratio. Coarse powder refers to a group of particles with a _D50 greater than that of fine powder. Fine powder is used here to refer to the inorganic micro-powder manufactured in this invention.

Furthermore, coarse particles refer to particles with a very large particle size relative to the _D50 of the inorganic micro powder to be manufactured. They can be set to, for example, particles with a particle size more than 1.5 times the _D50 of the inorganic micro powder to be manufactured; or particles with a particle size more than _2.0 times the D50 of the target powder; or particles with a particle size more than 2.5 times the _D50 of the target powder.

2. Second Embodiment Furthermore, the method for manufacturing inorganic micropowder in the second embodiment of the present invention is a method for manufacturing inorganic micropowder with a cumulative 50% particle size _D50 in the range of 0.01 μm to 5.0 μm, comprising the following steps: a fractionated powder generation step in which carboxylic acid is adsorbed onto inorganic raw material powder with a _D50 of 10 μm or less in a dispersed state in the gas phase during generation, thereby obtaining fractionated powder; and a dry fractionation step in which the fractionated powder is dry-fractionated.

This provides a method for manufacturing inorganic micropowders that can produce with high productivity a very small number of coarse particles and a cumulative 50% particle size _D50 in the range of 0.01 μm to 5.0 μm.

The superior performance is attributed to the following factors: Compared to methods that involve mixing powder with additives such as ethanol and dry-sorting the powder while the additives are vaporized, the inorganic raw material powder, which is dispersed in the gas phase during generation, allows carboxylic acids to be adsorbed onto the inorganic raw material powder. This significantly improves the dispersibility of the powder being sorted in the gas phase, thereby increasing the sorting accuracy. Consequently, the number of coarse particles in the manufactured inorganic micro-powder is greatly reduced. This also reduces the number of sorting stages, improving productivity.

Furthermore, by adsorbing carboxylic acids onto inorganic raw material powders, the flowability of the fractionated powder is improved, and the adhesion of the fractionated powder within the classifier is reduced, thereby increasing the yield. Also, the reduced adhesion within the classifier makes it less prone to clogging at the powder feed inlet or inside the piping, thus extending the classifier's uptime and improving productivity.

Furthermore, in this embodiment, since the inorganic raw material powder is dispersed in the gas phase during generation, and carboxylic acid is adsorbed onto the inorganic raw material powder to obtain the fractionated powder, the number of steps for carboxylic acid adsorption is reduced compared to the aforementioned embodiment, which is advantageous from the perspective of further improving productivity. Moreover, this embodiment can more effectively suppress the uneven adsorption of carboxylic acid at different parts of the inorganic raw material powder, resulting in a final inorganic micro-powder with a very small number of coarse particles and a more ideal particle size distribution. Furthermore, since the amount of carboxylic acid adsorbed in the fractionated powder can be easily controlled by controlling the amount of carboxylic acid supplied, the final inorganic micro powder will have very few coarse particles and a more ideal particle size distribution.

3. Third Embodiment Furthermore, the method for manufacturing inorganic micropowder in the third embodiment of the present invention is a method for manufacturing inorganic micropowder with a cumulative particle size _D50 of 0.01 μm to 5.0 μm in a volumetric 50% range. It comprises the following steps: a fractionated powder generation step of dispersing inorganic raw material powder with a _D50 of 10 μm or less to obtain fractionated powder; and a dry fractionation step of dry fractionation of the fractionated powder; wherein the fractionated powder generation step is carried out in an atmosphere containing a gaseous carboxylic acid.

This provides a method for manufacturing inorganic micropowders that can produce with high productivity a very small number of coarse particles and a cumulative 50% particle size _D50 in the range of 0.01 μm to 5.0 μm.

The superior performance is attributed to the following factors: Compared to methods that involve mixing powder with additives such as ethanol and dry-sorting the powder while vaporizing the additives, dispersing the inorganic raw material powder in a gaseous atmosphere containing carboxylic acids to obtain the fractionated powder improves the dispersibility of the fractionated powder in the gas phase, thereby increasing the fractionation accuracy. This significantly reduces the number of coarse particles in the manufactured inorganic micropowder. Furthermore, it reduces the number of fractionation stages, thus improving productivity.

Furthermore, by adsorbing carboxylic acids onto inorganic raw material powders, the flowability of the fractionated powder is improved, and the adhesion of the fractionated powder within the classifier is reduced, thereby increasing the yield. Also, the reduced adhesion within the classifier makes it less prone to clogging at the powder feed inlet or inside the piping, thus extending the classifier's uptime and improving productivity.

Furthermore, in this embodiment, since the inorganic raw material powder is dispersed in an atmosphere containing gaseous carboxylic acid to obtain the fractionated powder, the number of steps for carboxylic acid adsorption is reduced compared to the first embodiment, which is advantageous from the perspective of further improving productivity. Moreover, this embodiment can more effectively suppress the uneven adsorption of carboxylic acid in different parts of the inorganic raw material powder, resulting in a significantly reduced number of coarse particles and a more ideal particle size distribution in the final inorganic micro-powder. Furthermore, since the amount of carboxylic acid adsorbed in the fractionated powder can be easily controlled by controlling the supply of carboxylic acid, the final inorganic micro-powder also results in a significantly reduced number of coarse particles and a more ideal particle size distribution.

Furthermore, in the aforementioned embodiments, although the reason for the improved dispersibility of the fractionated powder by obtaining the fractionated powder with carboxylic acid adsorbed on the inorganic raw material powder has not yet been determined, the inventors hypothesize as follows: That is, the inorganic raw material powder generally has functional groups such as hydroxyl groups on the surface of its constituent particles that can interact with carboxyl groups. Then, by adsorbing carboxylic acid onto the inorganic raw material powder, the functional groups such as hydroxyl groups on the surface of the constituent particles of the inorganic raw material powder interact with the carboxyl groups (-COOH) of the carboxylic acid, causing the portion of the carboxylic acid other than the carboxyl group, such as the hydrocarbon portion, to be located on the outer side of the metal powder particles. Therefore, it is believed that the increased dispersibility is due to the suppression of agglomeration of the inorganic raw material powder caused by the polar groups such as hydroxyl groups. Furthermore, when the inorganic raw material powder is, for example, metal powder, even without functional groups that interact with carboxyl groups such as hydroxyl groups, adsorption occurs through the reaction of carboxylic acid with metal to form carboxylic acid metal salts, or through the formation of coordination bonds between carboxyl groups and metal atoms on the surface of the metal powder. Therefore, carboxylic acid can be adsorbed more uniformly and in appropriate amounts onto the particle surface. Moreover, the more uniform and appropriate adsorption of carboxylic acid onto the particle surface suppresses the formation of polar groups such as hydroxyl groups. As described above, the adsorption in this invention can be either physical adsorption or chemical adsorption.

If the above-described composition is not met, satisfactory results cannot be obtained. For example, in the aforementioned embodiments, when the carboxylic acid is not adsorbed onto the powder being classified, the dispersibility of the powder in the gas phase cannot be sufficiently improved during the dry classification step. Consequently, the classification accuracy cannot be sufficiently improved, resulting in an increase in the number of coarse particles in the produced inorganic micro-powder. Furthermore, the required number of classification cycles increases, reducing productivity. Also, because the flowability of the powder being classified cannot be sufficiently improved, the adhesion of the powder within the classifier increases, reducing yield. Moreover, due to the increased adhesion within the classifier, the powder feed port or piping of the classifier becomes more prone to blockage, thus shortening the classifier's operating time and reducing productivity.

<Classifier> Figure 1 is a diagram showing an example structure of one type of classifier used in the method for manufacturing inorganic micropowders of the present invention. Furthermore, in the following description, the upper side of Figure 1 is referred to as "upper" and the lower side as "lower".

The classifier 1 is an airflow classifier that uses centrifugal force acting on powder to classify it, and it has a shell 3 for forming the classification chamber 10.

Upstream of the classification chamber (classification area) 10, there is a dispersion area 11 for dispersing the inorganic raw material powder before classification. The classification chamber 10 is the area for classifying the dispersed inorganic raw material powder.

Furthermore, the classifier 1 includes: an inlet 4 for guiding inorganic raw material powder into the dispersion zone 11; an air nozzle 5 for injecting high-pressure air (primary air) into the dispersion zone 11; a guide vane 6 for allowing secondary air to flow into the classification chamber 10 to form a swirling airflow within the classification chamber 10; a fine powder outlet 7 opening at the upper center of the classification chamber 10; and a coarse powder outlet 8 opening along the lower outer periphery of the classification chamber 10.

Next, a method for dispersing and classifying inorganic raw material powder using this classifier 1 will be explained.

Inorganic raw material powder is introduced into dispersion zone 11 through inlet 4. The inorganic raw material powder is dispersed by a dispersing force applied by primary air sprayed into dispersion zone 11. Then, the inorganic raw material powder is introduced into classification chamber 10 in a dispersed state.

In the classifying chamber 10, secondary air is introduced into the classifying chamber 10 by the guide vanes 6, causing the airflow to vortex within the classifying chamber 10 and exhausting from the upper center of the classifying chamber 10. Through the outward centrifugal force acting by this airflow vortex and the flow of gas moving towards the center, the inorganic raw material powder in the solid-gas mixture is separated into coarse powder and fine powder.

That is, the coarse powder moves radially outward within the classification chamber 10 due to the outward centrifugal force generated by the vortex of the airflow, and is recovered from the coarse powder outlet 8 at the lower periphery of the classification chamber 10. On the other hand, the fine powder moves radially inward within the classification chamber 10 due to the flow of gas moving towards the center, and is recovered from the fine powder outlet 7 at the upper center of the classification chamber 10.

The fine powder outlet 7 is connected to a suction pump (not shown), and the fine powder is discharged and recycled together with the air (exhaust air) in the classification chamber 10.

The process of generating the classified powder corresponds to the process performed in the dispersion zone 11, while the dry classification process corresponds to the process performed in the classification chamber (classification zone) 10. That is, the inorganic raw material powder that is dispersed in the dispersion zone 11, in other words, the powder introduced into the classification chamber 10, is the classified powder as referred to in this manual.

Furthermore, although the above description used examples of airflow classifiers that utilize centrifugal force generated by vortex airflow for classification, the classification method of the classifier is not particularly limited. For example, it could utilize centrifugal force generated by rotor rotation, gravity, or inertial force for classification.

Furthermore, in this invention, the powder generation step and the dry classification step are not limited to using the same apparatus; they can also be carried out using separate apparatuses. That is, after dispersing the inorganic raw material powder using a disperser to obtain the powder to be classified, a dry classifier can be used to classify the powder.

<Fractional Powder Generation Step> In the fractional powder generation step, carboxylic acid is adsorbed onto inorganic raw material powder and fractional powder is obtained dispersed in the gas phase.

(Inorganic raw material powder) The inorganic raw material powder is the raw material for the inorganic micro powder manufactured in this invention, and its cumulative 50% particle size _D50 is less than 10 μm.

Although the cumulative 50% particle size _D50 of inorganic raw material powders on a volumetric basis only needs to be below 10 μm, it is preferable to exceed 0.01 μm. In particular, for inorganic raw material powders, the cumulative 50% particle size _D50 on a volumetric basis, the _D50 of inorganic micro powders is preferably above 0.03 μm and below 2.5 μm, more preferably above 0.05 μm and below 1.2 μm, and even more preferably above 0.10 μm and below 0.80 μm.

Although the inorganic components of inorganic raw material powders are not specifically limited, they can include various metals, metal oxides, glasses, ceramics, semiconductors, etc.

Metals that make up inorganic raw material powders include, for example, silver, gold, platinum, copper, palladium, nickel, tungsten, zinc, tin, iron, cobalt, or alloys containing one or more of these.

Metal oxides (metal oxides other than ceramics) that make up inorganic raw material powders can be listed as such as nickel oxide, copper oxide, silver oxide, iron oxide, etc.

As a component of inorganic raw material powder, glass can include, for example, bismuth glass, tellurium glass, and silicate glass.

Ceramics that are composed of inorganic raw material powders include, for example, oxide ceramics, nitride ceramics, and boride ceramics. More specifically, they include alumina, silica, zirconia, barium titanate, calcium zirconate, alumina nitride, silicon nitride, and boron nitride. In addition, ceramics also include functional ceramics such as fluorescent bodies.

As semiconductors that make up inorganic raw material powders, examples include InP, GaP, InAs, GaAs, InGaP, InZnP, ZnSe, CdSe, CdS, etc.

In particular, the inorganic components of the inorganic raw material powder are preferably selected from at least one of the group consisting of metals, metal oxides, glass, ceramics, and semiconductors.

In this way, carboxylic acids can play their role more effectively, and the dispersibility of inorganic raw material powders can be further improved.

Furthermore, the aforementioned effects are even more pronounced when the inorganic component of the inorganic raw material powder is a metal, metal oxide, glass, or oxide ceramic. While the exact reason is not yet clear, the inventors speculate that it is due to the presence of a large number of hydroxyl groups on the particle surface of the inorganic raw material powder. The inventors speculate that, particularly when the inorganic component of the inorganic raw material powder is a metal, the portion forming metal oxides through oxidation on the powder surface contains a large number of hydroxyl groups, while the unoxidized portion forms carboxylic acid metal salts through reaction between the metal and carboxylic acid, or forms coordination bonds with metal atoms on the powder surface of carboxyl groups. This allows the carboxylic acid to be adsorbed more uniformly and in appropriate amounts, thus making the aforementioned effects even more pronounced. This effect is even more pronounced when the inorganic component of the inorganic raw material powder is composed of nickel.

Although the shape of inorganic raw material powder is not particularly limited, various shapes such as spheres, flakes, and granules can be listed, and one or more of these shapes can be selected for combination.

It should be noted that in this specification, spherical refers to the shape of particles with a major diameter to minor diameter ratio of 2 or less. Plate-like refers to the shape with a major diameter to minor diameter ratio of more than 2.

While not specifically limited, methods for manufacturing inorganic raw material powders include, for example, electrolysis, atomization, mechanical grinding, wet reduction, spray thermal decomposition, chemical vapor deposition, and physical vapor deposition.

Furthermore, the plurality of particles in an inorganic raw material powder may have the same composition as each other, or may contain particles with different compositions.

(Carboxylic acid) In the fractionated powder, the carboxylic acid is adsorbed onto the inorganic raw material powder. As an adsorbent in this invention, it can be either physical adsorption or chemical adsorption. Therefore, the dispersion of the fractionated powder in the gas phase becomes excellent, resulting in the easy and efficient acquisition of inorganic micropowders with the desired particle size distribution, and minimizing the number of coarse particles in the obtained inorganic micropowders.

As a carboxylic acid, although there is no particular limitation on any compound having a carboxyl group, examples include: formic acid, acetic acid, propionic acid, isobutyric acid, butyric acid, crotonic acid, isovaleric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lactic acid, oxalic acid, succinic acid, oleic acid, acrylic acid, methacrylic acid, etc. One or more of these can be selected and used in combination.

The boiling point of the carboxylic acid is preferably between 100°C and 400°C, more preferably between 105°C and 250°C, and even more preferably between 110°C and 200°C.

Therefore, in the process of generating the graded powder, carboxylic acid can be processed smoothly in a liquid state. While improving operability, when carboxylic acid is adsorbed onto the powder in a vaporized state, the sintering of inorganic raw material powder can be more effectively prevented, and carboxylic acid can be adsorbed onto the inorganic raw material powder with higher uniformity.

It should be noted that, unless otherwise stated, the term "boiling point" in this instruction manual refers to the boiling point at one atmosphere.

Furthermore, the carboxylic acid is preferably a monocarboxylic acid. This improves the dispersibility of the fractionated powder, allowing the benefits of this invention to be more significantly realized.

The carboxylic acid is preferably selected from at least one of acetic acid, propionic acid, butyric acid, and oleic acid, and more preferably acetic acid.

This improves the dispersibility of the fractionated powder, thus enhancing the effectiveness of the invention.

In the aforementioned first embodiment, the adsorbed carboxylic acid inorganic raw material powder, on which the cumulative 50% particle size D ₅₀ is less than 10 μm on a volume basis, is dispersed in the gas phase to obtain the fractionated powder.

First, prepare an adsorbed carboxylic acid inorganic raw material powder with carboxylic acid adsorbed on an inorganic raw material powder with a cumulative particle size D ₅₀ of less than 10 μm on a volume basis.

The method for manufacturing the adsorbed carboxylic acid inorganic raw material powder is not particularly limited, but preferably, for example, a method for adsorbing gaseous carboxylic acid onto the inorganic raw material powder.

By adsorbing gaseous carboxylic acids onto inorganic raw material powder, the carboxylic acids can be adsorbed more uniformly onto the inorganic raw material powder. In this way, the effectiveness of this invention can be more significantly achieved.

While not particularly limited, methods for adsorbing gaseous carboxylic acids onto inorganic raw material powders include, for example, placing the inorganic raw material powder in an atmosphere containing gaseous carboxylic acids, or spraying a gas containing vaporized carboxylic acids onto the inorganic raw material powder.

Next, the adsorbed carboxylic acid inorganic raw material powder is dispersed in the gas phase to obtain the fractionated powder.

In the aforementioned second embodiment, the inorganic raw material powder with a cumulative volume 50% particle size _D50 of less than 10 μm, which is dispersed in the gas phase during generation, is subjected to adsorption of carboxylic acid onto the inorganic raw material powder to obtain the fractionated powder.

Methods for generating inorganic raw material powders that are dispersed in the gas phase during generation include gas-phase methods such as chemical vapor deposition and physical vapor deposition, as well as atomization and spray thermal decomposition methods. In particular, when inorganic raw material powders are generated using gas-phase methods or spray thermal decomposition methods, it is easier to adjust the particle size range of the inorganic raw material powders in this invention.

While the method for adsorbing carboxylic acid onto inorganic raw material powder is not particularly limited, it is preferably a method for adsorbing gaseous carboxylic acid onto inorganic raw material powder. Specifically, examples include spraying vaporized carboxylic acid onto inorganic raw material powder during the cooling process of inorganic raw material powder that is dispersed in the gas phase at a predetermined temperature.

This allows carboxylic acids to be adsorbed onto inorganic raw material powder with greater uniformity. As a result, particle aggregation can be more effectively suppressed, further improving dispersibility. Therefore, the effectiveness of this invention can be more significantly realized.

In addition, by having the inorganic raw material powder dispersed in the gas phase during generation, carboxylic acid is adsorbed onto the inorganic raw material powder to obtain the fractionated powder, thereby reducing the number of steps and further improving productivity.

In the second embodiment, it is preferable that between the fractionated powder generation step and the dry fractionation step, there is a recovery step for recovering the fractionated powder, and a dispersion step for dispersing the fractionated powder obtained in the recovery step in the gas phase.

This makes it easier to combine more suitable classifiers, thereby further improving the classification accuracy in subsequent dry classification steps and making the production of inorganic micro powders more efficient.

In the third embodiment of the present invention, inorganic raw material powder with a cumulative particle size _D50 of less than 10 μm in volumetric 50% is dispersed in an atmosphere containing carboxylic acid in gaseous state to obtain a graded powder.

First, prepare inorganic raw material powder with a cumulative particle size _D50 of less than 10 μm based on volumetric 50%. Then, obtain fractionated powder by dispersing this inorganic raw material powder in an atmosphere containing gaseous carboxylic acid.

By dispersing inorganic raw material powder in an atmosphere containing gaseous carboxylic acid, the carboxylic acid can be adsorbed onto the inorganic raw material powder with greater uniformity. This results in more effective suppression of particle aggregation and further improved dispersibility. Furthermore, the amount of carboxylic acid adsorbed on the inorganic raw material powder can be easily controlled. Therefore, the effectiveness of this invention can be more significantly realized. In addition, by dispersing the inorganic raw material powder in an atmosphere containing gaseous carboxylic acid, the number of steps can be reduced, further improving productivity.

In the second and third embodiments, although the amount of carboxylic acid used is not specifically limited, it is preferably used in a ratio of 30 mol to 960 mol relative to the volume of 1 ^m3 of inorganic raw material powder, more preferably in a ratio of 60 mol to 480 mol, and even more preferably in a ratio of 120 mol to 240 mol.

This allows for a more uniform adsorption of an appropriate amount of carboxylic acid onto the inorganic raw material powder, resulting in better dispersibility of the fractionated powder. Furthermore, the amount of carboxylic acid adsorbed onto the inorganic raw material powder is not excessive, leading to better physical properties when the manufactured inorganic micro-powder is paste-like.

It should be noted that the volume of the inorganic raw material powder in this invention is calculated based on the weight and real density of the powder.

Although the rate at which inorganic raw material powder is fed to the classifier, i.e., in the classifier 1 shown in Figure 1, the rate at which inorganic raw material powder is fed from the guide inlet 4 into the dispersion area 11 also depends on the size (capacity) of the classifier, it is preferably between 1 kg/hour and 20 kg/hour, more preferably between 3 kg/hour and 15 kg/hour, and even more preferably between 5 kg/hour and 12 kg/hour.

This improves both the dispersibility of inorganic raw material powders and the productivity of inorganic micro powders.

The supply pressure for dispersion, that is, the pressure of the dispersion air sprayed from the air nozzle 5 into the dispersion area 11 in the classifier 1 shown in Figure 1, is not particularly limited, but is preferably between 0.2 MPa and 1.0 MPa, more preferably between 0.4 MPa and 0.8 MPa, and even more preferably between 0.5 MPa and 0.7 MPa.

In this way, the dispersibility of inorganic raw material powders becomes better, and the productivity of inorganic micro powders also becomes better.

<Dry Classification Step> In the dry classification step, the powder to be classified obtained in the powder to be classified step is dry classified.

Because the fractionated powder adsorbed with carboxylic acids is properly dispersed in the gas phase, the fractionation accuracy of the dry fractionation process is improved. This results in a significantly reduced number of coarse particles in the produced inorganic micropowder. Furthermore, the improved fractionation accuracy allows for a reduction in the number of fractionation stages, thereby increasing productivity.

Furthermore, by improving the flowability of the powder being classified, the adhesion of the powder within the classifier is reduced, thereby increasing the yield. Also, by reducing adhesion within the classifier, the powder feed port or piping of the classifier becomes less prone to clogging, thus extending the classifier's operating time and improving productivity.

This enables the production of inorganic micro-powders with a very small number of coarse particles with high productivity.

While the gas phase temperature for the dry fractionation step is not particularly limited, it is preferably above 60°C and below 300°C, more preferably above 100°C and below 250°C, and even more preferably above 150°C and below 200°C.

This method effectively prevents problems such as particle deformation or deterioration of particle components caused by heat. Furthermore, the increased airflow velocity enhances centrifugal force and prevents water vapor adhesion to the particles, thus further improving classification accuracy. Additionally, it improves productivity. Moreover, it significantly reduces the number of coarse particles in inorganic micropowders.

The airflow rate during the dry classification step, i.e., the airflow rate generated by the suction pump connected to the micronized powder outlet 7 in the classifier 1 shown in Figure 1, is not particularly limited, but is preferably between 5.0 ^m³ /min and 30 ^m³ /min, more preferably between 6.0 ^m³ /min and 20 ^m³ /min, and even more preferably between 7.0 ^m³ /min and 9.0 ^m³ /min. This allows for more efficient classification of the powder being classified.

The suction pressure for dry classification, i.e., the suction pressure generated by the suction pump connected to the micronized powder outlet 7 in the classifier 1 shown in Figure 1, is not particularly limited, but is preferably between -60 kPa and -5 kPa, more preferably between -50 kPa and -10 kPa, and even more preferably between -40 kPa and -15 kPa. This allows for better classification of the powder being classified.

By dry classification of the powder to be classified, the powder is classified into micro powder and coarse powder. The powder to be classified into, for example, micro powder with a cumulative particle size _D50 of 50% based on volume (between 0.01 μm and 5.0 μm), and coarse powder with a _D50 greater than that of micro powder. The micro powder is recycled as the inorganic micro powder produced by this invention.

In the above manner, inorganic micro powders with a cumulative particle size _D50 of 0.01 μm to 5.0 μm in volumetric 50% can be manufactured.

The inorganic micro powder produced in this way has a very small number of coarse particles. Furthermore, the adsorption of carboxylic acids on the inorganic micro powder also prevents secondary agglomeration.

Furthermore, according to the above method, the number of classification cycles can be reduced due to the improved classification accuracy. Additionally, the adhesion of the powder being classified within the classifier is reduced, thereby improving yield. Moreover, by reducing adhesion within the classifier, the powder feed port and piping are less prone to clogging, thus extending the classifier's operating time and improving productivity.

Furthermore, although the dry grading step can be performed only once, it can also be repeated several times. This can further improve grading accuracy.

While the yield of inorganic micropowders in the dry fractionation step is not specifically limited, it is preferably above 80%, more preferably above 85%, and even more preferably above 88%. This makes the effectiveness of the invention more significant.

Furthermore, in this instruction manual, the yield of inorganic micropowders in the dry classification step is a value obtained by using the following formula based on the powder weight before classification (i.e., the weight of the powder being classified) and the powder weight after classification (i.e., the weight of the inorganic micropowder): Yield (%) = (Powder weight after classification / Powder weight before classification) × 100

Although the inorganic micro powder produced by the method of the present invention only needs to have a cumulative particle size _D50 of 50% on a volume basis in the range of 0.01 μm to 5.0 μm, the _D50 of the inorganic micro powder is preferably 0.03 μm to 2.0 μm, more preferably 0.05 μm to 1.0 μm, and even more preferably 0.10 μm to 0.60 μm.

This allows for the acquisition of inorganic micropowders with a more desirable particle size distribution. Furthermore, in the prior art, when _D50 is within this range, coarse particles easily become a problem, and the adverse effects caused by coarse particles are particularly prone to occur. In contrast, in this invention, even when _D50 is within this range, the aforementioned problems can be prevented more effectively. That is, when the _D50 of the inorganic micropowder is within the aforementioned range, the effectiveness of this invention is more significantly realized.

Regarding the inorganic micro powder produced by the method of the present invention described above, when the integral fraction of the volume criterion of particle size distribution measured by the laser particle size distribution measuring device is set to 10% as D ₁₀ [μm], the integral fraction of 50% as D ₅₀ [μm], and the integral fraction of 90% as D ₉₀ [μm], the value of (D ₉₀ - D ₁₀ )/D ₅₀ is preferably between 0.30 and 0.90, more preferably between 0.35 and 0.80, and even more preferably between 0.40 and 0.75.

(D ₉₀ - D ₁₀ )/D ₅₀ is an indicator of the uniformity of particle size distribution. The smaller the value of (D ₉₀ - D ₁₀ )/D ₅₀ , the narrower the particle size distribution, which means that the particle size is more uniform.

This results in a more uniform particle size for inorganic micropowders, making them suitable for a variety of applications.

Furthermore, in the method for manufacturing the inorganic micro powder of the present invention, the number of coarse particles obtained by the following measurement is preferably less than 30, more preferably less than 15, and even more preferably less than 5.

This allows for a more effective prevention of various problems caused by coarse particles in inorganic micro powders.

The determination of the number of coarse particles mentioned above can be performed, for example, as follows: First, 1.0 g of inorganic micro-powder is mixed with 20 mL of ethanol and treated with an ultrasonic cleaner (e.g., Honda Electric Corporation, W-113) for 1 minute to prepare a dispersion. 30 μL of this dispersion is weighed and dropped onto an aluminum sample stage, then dried to remove the dispersion medium, thereby preparing a sample for measurement. The sample is then observed using a scanning electron microscope (SEM) (e.g., Hitachi High-Tech Corporation, SU-1510) at 10,000x magnification with a 50° visual field. The total number of inorganic micro powder particles with a cumulative particle size D ₅₀ greater than 1.5 times the volume 50% particle size is obtained, and this value is taken as the number of coarse particles.

[Applications of Inorganic Micro Powders] Although the applications of inorganic micro powders produced by the method of the present invention are not particularly limited, for example, inorganic micro powders produced using conductive metal powders as inorganic raw material powders can be used as conductive powders.

Examples of materials that can be used to make conductive metal powders include, for example, silver, gold, platinum, copper, palladium, nickel, tungsten, zinc, tin, iron, cobalt, or alloys containing at least one of these. Two or more of the aforementioned materials can also be combined to make conductive powders.

Conductive powders are suitable for use as conductive materials in electronic components. As conductive materials in electronic components, they are used to form conductive parts. While their applications are not particularly limited, they are especially suitable for forming internal conductors (internal electrodes) or terminal electrodes in multilayer ceramic electronic components such as multilayer ceramic capacitors, multilayer ceramic inductors, and multilayer piezoelectric actuators. Conductive powders used in this type of application require particularly high reliability.

The conductive powder manufactured by the method of this invention has a small average particle size, a narrow particle size distribution, and contains almost no coarse particles. Therefore, when the conductive powder is used in internal electrodes, it can form an electrode layer of uniform thickness and effectively prevent short circuits caused by conductive powder particles contacting both sides of the internal electrode. Thus, even in applications requiring particularly high reliability, satisfactory performance can be achieved. Therefore, the conductive powder manufactured by the method of this invention exhibits even more significant advantages when used to form internal conductors (internal electrodes) or terminal electrodes of multilayer ceramic electronic components such as multilayer ceramic capacitors, multilayer ceramic inductors, and multilayer piezoelectric actuators.

Conductive powder can also be used, for example, as a conductive paste made by mixing glass frit and an organic vehicle, to form conductive parts of electronic components.

While the above description pertains to a preferred embodiment of the invention, the invention is not limited thereto.

For example, the apparatus used in the method for manufacturing inorganic micro powders of the present invention is not limited to those described in the above embodiments.

Furthermore, in the method for manufacturing the inorganic micro powder of the present invention, two or more of the methods described in the first to third embodiments can be combined.

More specifically, for example, the inorganic raw material powder containing adsorbed carboxylic acid can be dispersed in the gas phase, and then the carboxylic acid can be added to the powder to allow it to be adsorbed, thereby obtaining the classified powder. That is, the method described in the first embodiment and the method described in the third embodiment can also be combined.

Alternatively, for example, an inorganic raw material powder with a _D50 of less than 10 μm that is dispersed in the gas phase during generation can be generated. While the inorganic raw material powder is dispersed in the gas phase, carboxylic acid is adsorbed onto the aforementioned inorganic raw material powder to obtain fractionated powder. The fractionated powder is then recovered, and additional carboxylic acid is adsorbed onto the recovered powder. In this case, when additional carboxylic acid is adsorbed, the powder may be in an undispersed state or a dispersed state in the gas phase. That is, the method described in the second embodiment can be combined with the method described in the first embodiment, or the second embodiment and the third embodiment can be combined.

Alternatively, the method described in the first embodiment can be combined with the method described in the second embodiment and the method described in the third embodiment.

In such cases, the order of the combinations of methods corresponding to each embodiment (especially the order of methods for adsorbing carboxylic acids) is not particularly limited. [ Example ]

Although specific embodiments are given below to illustrate the invention in more detail, the invention is not limited to these embodiments. Furthermore, in the following description, unless otherwise specified, temperature and humidity conditions are applied at room temperature (25°C) and relative humidity of 50%. Also, for various measurement conditions, unless otherwise specified, the values are also at room temperature (25°C) and relative humidity of 50%. Furthermore, the integral fraction values _{D10 (} 10%), _D50 (50%), and _D90 (90%) for the volumetric basis of inorganic raw material powders and inorganic micro powders were obtained by measurement using a laser diffraction/scattering type particle size distribution measuring device LA-960 (manufactured by HORIBA). Additionally, the boiling points of the carboxylic acids used in the embodiments described below are summarized in Table 1.

[Table 1]

[1] Manufacturing of Inorganic Micropowders

(Example 1) In this embodiment, inorganic micro powder is produced by using the method described in the first embodiment above, that is, by dispersing the adsorbed carboxylic acid inorganic raw material powder in the gas phase to obtain the fractionated powder. A more detailed description is as follows.

First, nickel powder with a cumulative particle size _D50 of 0.31 μm on a volume basis was prepared as the inorganic raw material powder.

The nickel powder was left to stand in an atmosphere containing acetic acid, which is a carboxylic acid, thereby obtaining nickel acetate powder adsorbed. In addition, the acetic acid used was of near 100% purity (manufactured by FUJIFILM Wako Pure Chemical Corporation, premium grade 99.7+%).

10 kg of the obtained adsorbed nickel acetate powder is fed into the dry classifier shown in Figure 1 every hour, and the supply dispersion pressure is set to 0.6 MPa to disperse the adsorbed nickel acetate powder and obtain the classified powder.

Next, the dispersed adsorbed nickel acetate powder (the powder to be classified) was introduced into the classification chamber, and the temperature inside the classifier was set to 25°C, the air volume was set to 8.5 ^m³ /min, and the suction pressure was set to -35 kPa, so as to produce inorganic micro powder by dry classification.

(Examples 2 to 5) Except that the carboxylic acid shown in Table 2 was used to replace acetic acid, the inorganic micro powder was produced in the same manner as in Example 1 above.

(Example 6) In this embodiment, the method described in the second embodiment above is used to obtain the fractionated powder by adsorbing carboxylic acid onto the inorganic raw material powder that is dispersed in the gas phase during generation, thereby producing inorganic micro powder. A more detailed explanation is as follows.

First, nickel acetate tetrahydrate (NAT) powder was prepared. This NAT powder was sprayed and heated to 1500°C to obtain nickel powder dispersed in the gas phase as an inorganic raw material powder. While the nickel powder was dispersed in the gas phase, the gas phase was cooled to 500°C. Under these conditions, adsorbed nickel acetate powder was obtained as a fractionated powder by supplying gaseous acetic acid into the gas phase. The amount of acetic acid added (used) was 120 mol per ^m³ of nickel raw material powder.

10 kg of the adsorbed nickel acetate powder obtained per hour is fed into the dry classifier shown in Figure 1. The temperature inside the classifier is set to 25°C, the air volume is set to 8.5 ^m³ /min, and the suction pressure is set to -35 kPa to produce inorganic micro powder through dry classification.

(Example 7) In this embodiment, the inorganic micro powder is produced by dispersing the inorganic raw material powder in an atmosphere containing a gaseous carboxylic acid as described in the third embodiment above, thereby obtaining a fractionated powder. A more detailed explanation is provided below.

First, as an inorganic raw material powder, nickel powder with a cumulative 50% particle size _D50 of 0.48 μm on a volume basis was prepared.

10 kg of this nickel powder is fed into the dry classifier shown in Figure 1 every hour. At the same time, acetic acid gas is supplied to the dispersion zone in such a way that the gas is 15 mol per 1 ^m3 of nickel powder. The supply and dispersion pressure is set to 0.6 MPa. Acetic acid is adsorbed onto the nickel powder while it is dispersed, and adsorbed nickel acetate powder is obtained as the powder to be classified.

Next, the powder to be classified is introduced into the classification chamber, and the temperature inside the classifier is set to 25°C, the air volume is set to 8.0 ^m³ /min, and the suction pressure is set to -25 kPa, so as to produce inorganic micro powder through dry classification.

(Examples 8 to 14) Except that the amount of acetic acid added is as shown in Table 4, the inorganic micro powder was produced in the same manner as in Example 7 above.

(Examples 15 to 18) Except that the particle size of the inorganic raw material powder is as shown in Table 4 and the conditions of the dry classification step are as shown in Table 4, the inorganic micro powder was manufactured in the same manner as in Example 10 above.

(Example 19) As an inorganic raw material powder, except that Cu powder with a cumulative particle size D ₅₀ of 2.45 μm based on volume is used, and the conditions of the dry fractionation step are as shown in Table 5, inorganic micro powder is manufactured in the same manner as in Example 1 above.

(Example 20) As an inorganic raw material powder, except that Ag-Pd alloy powder with a cumulative particle size _D50 of 1.30 μm based on volume (Ag:Pd = 7:3 (weight ratio)) was used, and the conditions of the dry fractionation step were set as shown in Table 5, the inorganic micro powder was manufactured in the same manner as in Example 1 above.

(Example 21) As an inorganic raw material powder, except that a BaO-SiO ₂ glass powder with a cumulative particle size D ₅₀ of 2.24 μm based on volume is used, and the conditions of the dry fractionation step are as shown in Table 5, the inorganic micro powder is manufactured in the same manner as in Example 1 above.

(Example 22) As an inorganic raw material powder, except that a silicon dioxide powder with a cumulative particle size D ₅₀ of 0.92 μm based on volume is used, and the conditions of the dry fractionation step are as shown in Table 5, the inorganic micro powder is manufactured in the same manner as in Example 1 above.

(Comparative Example 1) Except that carboxylic acid was not used, inorganic micro powder was produced in the same manner as in the aforementioned Example 1.

(Comparative Examples 2 and 3) Inorganic micro powders were produced in the same manner as in the aforementioned Example 1, except that the compounds shown in Table 2 were used to replace the carboxylic acid.

(Comparative Example 4) Except that carboxylic acid was not used, inorganic micro powder was produced in the same manner as in the aforementioned Example 7.

(Comparative Example 5) Except that the compounds shown in Table 4 were used to replace the carboxylic acid, the inorganic micro powder was produced in the same manner as in the aforementioned Example 10.

(Comparative Example 6) Except that carboxylic acid was not used, inorganic micro powder was produced in the same manner as in the aforementioned Example 15.

(Comparative Example 7) Except that carboxylic acid was not used, the inorganic micro powder was produced in the same manner as in the aforementioned Example 19.

(Comparative Example 8) Except that carboxylic acid was not used, the inorganic micro powder was manufactured in the same manner as in the aforementioned Example 20.

(Comparative Example 9) Except that carboxylic acid was not used, the inorganic micro powder was produced in the same manner as in the aforementioned Example 21.

(Comparative Example 10) Except that carboxylic acid was not used, inorganic micro powder was produced in the same manner as in the aforementioned Example 22.

[2] Evaluation [2-1] Yield For the aforementioned embodiments and comparative examples, the weight of the powder before grading (i.e., the weight of the powder to be graded) and the weight of the powder after grading (i.e., the weight of the inorganic micro powder) were measured, and the yield was calculated using the following formula: Yield (%) = (Weight of powder after grading / Weight of powder before grading) × 100

Furthermore, the inorganic micro powders of the aforementioned embodiments and comparative examples were further dry-classified in the same manner as described above, that is, a total of two dry-classifications were performed, and the yield at that time was also obtained.

[2-2] The particle size distribution was evaluated using a laser diffraction/scattering type particle size distribution measuring device LA-960 (manufactured by HORIBA). For the aforementioned embodiments and comparative examples, the particle size distribution of the inorganic raw material powder and the obtained inorganic micro powder was obtained, and the volume fraction values of the particle size distribution at 10% (D ₁₀ ) [μm], 50% (D ₅₀ ) [μm], and 90% (D ₉₀ ) [μm] were obtained respectively.

Then, using the values of _D10 [μm], _D50 [μm], and _D90 [μm] obtained in the above manner, calculate ( _D90 - _D10 )/ _D50 .

[2-3] Evaluation of coarse particle number: For the aforementioned embodiments and comparative examples, 20 mL of ethanol as the dispersion medium was mixed with 1.0 g of the secondary fractionated powder, and the mixture was treated with an ultrasonic cleaner (Honda Electric Co., Ltd., W-113) for 1 minute to prepare a dispersion. 30 μL of the prepared dispersion was weighed and dropped onto an aluminum sample stage, and then dried to remove the dispersion medium, thereby preparing a sample for determination. The sample was observed using a scanning electron microscope (Hitachi High-Tech Corporation, SU-1510) at magnification up to 10,000x, with 50 fields of view. Using the particle size obtained by the above method [2-2], particles with a D ₅₀ greater than 2.0 times that of the inorganic micro powder of the object are considered as coarse particles, and the number of coarse particles is obtained.

These results, along with the manufacturing conditions of the inorganic micropowders, are summarized in Tables 2 to 5. In these tables, acetic acid is represented as "AA", propionic acid as "PA", butyric acid as "BA", isobutyric acid as "IBA", oleic acid as "OA", ethanol as "EtOH", and isopropanol as "IPA". The units for suction volume are [ ^m³ /min] and suction pressure is [kPa]. In Tables 3 and 4, the units for the amount of carboxylic acid added are [mol/ ^1m³ Ni]. Furthermore, when determining the number of particles with a particle size more than 3.0 times the cumulative particle size D ₅₀ of the volume 50% of the inorganic micro powder obtained in the aforementioned embodiments using the method shown in [2-3] above, no such particles were found in any of the embodiments.

[Table 2]

[Table 3]

[Table 4]

[Table 5]

As clearly shown in Tables 2 to 5, the aforementioned embodiments can successfully produce metal micropowders with a _D50 range of 0.01 μm to 5.0 μm and a very low number of coarse particles with high yield. [Industrial Applicability]

The method for manufacturing inorganic micro powder of the present invention is a method for manufacturing inorganic micro powder with a cumulative particle size _D50 of 50% in the range of 0.01 μm to 5.0 μm based on a volume metric. It includes a step of generating fractionated powder by dispersing inorganic raw material powder containing adsorbed carboxylic acid in an inorganic raw material powder with _D50 of less than 10 μm in a gas phase to obtain fractionated powder, and a step of dry fractionation by performing dry fractionation on the aforementioned fractionated powder. Furthermore, the method for manufacturing inorganic micro powder of the present invention is a method for manufacturing inorganic micro powder with a cumulative particle size _D50 of 0.01 μm to 5.0 μm in the volumetric 50% range. It includes a step of generating a fractionated powder by dispersing inorganic raw material powder with a _D50 of 10 μm or less in the gas phase, allowing carboxylic acid to be adsorbed onto the inorganic raw material powder to obtain fractionated powder, and a step of dry fractionation of the fractionated powder. Furthermore, the method for manufacturing inorganic micro powders of the present invention is a method for manufacturing inorganic micro powders with a cumulative particle size _D50 of 0.01 μm to 5.0 μm in volumetric 50% of the powder. It includes a step of generating fractionated powder by dispersing inorganic raw material powder with D50 of 10 _μm or less to obtain fractionated powder, and a dry fractionation step of dry fractionation of the fractionated powder. The fractionated powder generation step is carried out in an atmosphere containing carboxylic acid in gaseous state. Therefore, this invention provides a method for manufacturing inorganic micropowders that can produce with high productivity a very small number of coarse particles, with the cumulative 50% particle size _D50 in the volumetric dimension ranging from 0.01 μm to 5.0 μm. Thus, the method for manufacturing inorganic micropowders of this invention is industrially feasible.

1: Classifier 3: Shell 4: Inlet 5: Air nozzle 6: Guide vane 7: Micro powder outlet 8: Coarse powder outlet 10: Classification chamber (classification area) 11: Dispersion area

[Figure 1] Figure 1 is a diagram showing an example of the structure of one of the classifiers used in the method for manufacturing inorganic micro powders of the present invention.

1: Classifier

3: Shell

4:Inlet

5: Air nozzle

6: Guide vane

7: Micronized powder discharge port

8: Coarse powder discharge outlet

10: Classification Room (Classification Area)

11: Dispersed Areas

Claims (8)

A method for manufacturing inorganic micro powder, wherein the cumulative 50% particle size _D50 on a volume basis is in the range of 0.01 μm to 5.0 μm, comprises: a step of generating a fractionated powder, wherein a carboxylic acid with a boiling point of 100°C to 400°C is adsorbed in a gaseous state onto an inorganic raw material powder with a _D50 of less than 10 μm, and the adsorbed carboxylic acid inorganic raw material powder is dispersed in a gas phase to obtain fractionated powder; and a dry fractionation step, wherein the aforementioned fractionated powder is dry-fractionated. A method for manufacturing inorganic micropowder, comprising: a method for manufacturing inorganic micropowder with a cumulative particle size _D50 of 0.01 μm to 5.0 μm in a volumetric 50% range, comprising: a step for generating a fractionated powder, wherein an inorganic raw material powder with a _D50 of 10 μm or less, which is dispersed in the gas phase during generation, is subjected to adsorption of a carboxylic acid with a boiling point of 100°C to 400°C in a gaseous state onto the inorganic raw material powder to obtain fractionated powder; and a dry fractionation step, wherein the fractionated powder is subjected to dry fractionation. The method for manufacturing inorganic micropowder as described in claim 2 includes, between the aforementioned powder generation step and the aforementioned dry classification step, a: recovery step, which recovers the aforementioned powder; and dispersion step, which disperses the aforementioned powder obtained in the aforementioned recovery step in the gas phase. A method for manufacturing inorganic micropowder, comprising: a method for manufacturing inorganic micropowder with a cumulative 50% particle size _D50 of 0.01 μm to 5.0 μm on a volume basis; and a method for manufacturing inorganic micropowder with a D50 of 10 μm or less, comprising: a powder generation step, wherein inorganic raw material powder with a _D50 of 10 μm or less is dispersed to obtain the powder to be classified; and a dry classification step, wherein the powder to be classified is subjected to dry classification; wherein the powder generation step is carried out in an atmosphere containing a carboxylic acid in a gaseous state, wherein the boiling point of the carboxylic acid is 100°C to 400°C. The method for manufacturing inorganic micro powder as described in any of claims 2 to 4, wherein the proportion of the aforementioned carboxylic acid used is between 30 mol and 960 mol per ^m³ of the aforementioned inorganic raw material powder. The method for manufacturing inorganic micro powder as described in any of claims 1 to 4, wherein the aforementioned carboxylic acid is selected from at least one of acetic acid, propionic acid, butyric acid, and oleic acid. The method for manufacturing inorganic micropowder as described in any of claims 1 to 4, wherein the aforementioned dry classification step is carried out in a gas phase at a temperature of 60°C to 300°C. The method for manufacturing inorganic micro powder as described in any one of claims 1 to 4, wherein the inorganic component of the aforementioned inorganic raw material powder is selected from at least one of the group consisting of metals, metal oxides, glass, ceramics, and semiconductors.