Aluminum nitride powder and manufacturing method

Abstract

[Problem] The present invention provides an aluminum nitride powder which is useful as a starting material for an aluminum nitride sintered body that is excellent as a highly heat conductive insulating member, especially in cases where the aluminum nitride sintered body is produced by press molding. [Solution] An aluminum nitride powder which is characterized by being composed of particles that have a sphericity of 0.8 or more, and which is also characterized in that: the median diameter D50 as determined by a laser diffraction method is from 0.5 to 1.5 μm; the ratio of the particle diameter D90 corresponding to 90% in the cumulative undersize distribution to the above-described D50, namely D90 / D50 is 2.2 or less; the BET specific surface area is from 2 to 4 m2 / g; and the total oxygen concentration is from 0.6% by mass to 1.2% by mass.

Description

[Technical Field]

[0001] The present invention relates to an aluminum nitride powder useful as a raw material for producing an aluminum nitride sintered body, which is excellent as an insulating and highly thermally conductive member, particularly when produced by press molding, and a production method thereof. [Background technology]

[0002] Aluminum nitride sintered bodies are widely used as heat dissipation materials and electrical insulating materials, taking advantage of the high thermal conductivity and high insulating properties of aluminum nitride, for applications such as heat dissipation substrates for electrical devices, electronic circuit boards, and components for semiconductor manufacturing equipment.

[0003] One method for producing the aluminum nitride sintered body is to form aluminum nitride powder into granules, press-molde them, and heat-sinter them (Patent No. 3479160).

[0004] The aluminum nitride powder granules are generally produced by mixing the powder with a solvent and, if necessary, a binder to prepare a slurry, and then granulating the slurry by spray drying (Patent No. 2525074).

[0005] However, when a sintered body is produced using granular aluminum nitride powder, the bulk density of the granules, and therefore the compact, is not high, and the sintered body obtained by firing the granules is not sufficiently densified, resulting in problems such as a decrease in the thermal conductivity and strength of the resulting sintered body.

[0006] A known raw aluminum nitride powder for such applications is produced by the so-called reduction-nitridation method, in which alumina powder is nitrided in a nitrogen gas atmosphere in the presence of carbon. This aluminum nitride powder produced by the reduction-nitridation method has spherical primary particles and good packing properties, but the heat generated during the reduction-nitridation process causes a large amount of lightly sintered agglomerates, preventing it from achieving a high bulk density. For this reason, pulverization has been performed to reduce the agglomerates.

[0007] For example, it is known to pulverize aluminum nitride powder containing carbon powder removed from a reduction-nitriding furnace (Japanese Patent Laid-Open Nos. 2-102109, 5-17109, 5-43209, and 4-265208).

[0008] Furthermore, as a method for crushing the aluminum nitride powder after nitriding, it is disclosed that a crusher such as a dry ball mill or pin mill is used (Japanese Patent Laid-Open Publication No. 2005-162555). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 3479160 [Patent Document 2] Patent No. 2525074 [Patent Document 3] Japanese Patent Application Publication No. 2-102109 [Patent Document 4] Japanese Patent Application Publication No. 5-17109 [Patent Document 5] Japanese Patent Application Publication No. 5-43209 [Patent Document 6] Japanese Patent Application Publication No. 4-265208 [Patent Document 7] Japanese Patent Application Laid-Open No. 2005-162555 Summary of the Invention [Problem to be solved by the invention]

[0010] However, when powerful milling is performed using media, such as in a ball mill, new problems have become apparent: partial milling of the aluminum nitride primary particles occurs, the specific surface area of ​​the aluminum nitride powder increases, reducing its storage stability, increasing the amount of impurities mixed in, and further increasing the amount of oxidation in the subsequent decarburization treatment, resulting in a decrease in the performance of the sintered body obtained using this powder. [Means for solving the problem]

[0011] Therefore, in order to solve the above problems, the present inventors conducted extensive research and discovered that, as a raw material for manufacturing aluminum nitride granules to be used for press molding, the bulk density of the granules can be increased by crushing (disintegrating) the aluminum nitride powder containing carbon powder removed from the reduction-nitriding furnace to the extent that large agglomerated particles are broken down, without having to be crushed forcefully.

[0012] Furthermore, it was found that the above-described crushing process does not increase the specific surface area of ​​the aluminum nitride powder excessively, suppresses an increase in the amount of oxidation in the subsequent oxidation treatment for decarburization (also called decarburization treatment), and is also effective in preventing a decrease in thermal conductivity.

[0013] Furthermore, it was found that processing using an ejector is particularly effective as the above-mentioned crushing means. Based on the above findings, the inventors have found that it is possible to provide aluminum nitride powder having predetermined properties that have not been available before, and have thus completed the present invention.

[0014] The present invention is configured as follows. [1] It consists of primary particles with a sphericity of 0.8 or more, Median diameter D obtained by laser diffraction method 50 is 0.5 to 1.5 μm, and the particle diameter D corresponds to 90% of the cumulative undersize distribution 90 and the aforementioned D 50 Ratio D 90 / D 50 is less than or equal to 2.2, BET specific surface area is 2 to 4 m 2 / g, The total oxygen concentration is 0.6 to 1.2 mass% 1. An aluminum nitride powder characterized by:

[0015] [2] The median diameter D 50 and BET specific surface area according to the following formula, the degree of aggregation is in the range of 1.1 to 2.2. Cohesion = D 50 / D BET D BET = 6 / (ρ×S) S:BET specific surface area D BET : Primary particle size calculated from BET specific surface area D 50 : Average particle size obtained by laser diffraction method ρ: True specific gravity of AlN (3.26g / cm 3 )

[0016] [3] A method for producing aluminum nitride powder, comprising the steps of reducing and nitriding raw material powders of aluminum oxide powder and carbon powder under nitrogen to obtain a composite powder containing aluminum nitride agglomerated particles and carbon powder, followed by a media-free crushing treatment to remove excess carbon by oxidation.

[0017] [4] The method for producing aluminum nitride powder according to [3], wherein the crushing treatment is performed using an ejector. [Effects of the Invention]

[0018] The aluminum nitride powder of the present invention has a characteristic of high sphericity of its primary particles due to the use of a reduction nitridation method. Furthermore, the crushing treatment in the manufacturing method of the present invention allows for the production of aluminum nitride powder with a unique particle size distribution, in which the shoulder due to coarse particles disappears and the peak top portion increases in the particle size distribution curve, compared to the particle size distribution of aluminum nitride powder produced without the treatment. Furthermore, the increase in specific surface area before and after the treatment is kept low. Furthermore, aluminum nitride powder with these characteristics achieves a high pressed bulk density, and the granules obtained using this powder have a high bulk density, which allows the sintered body obtained by press-molding the powder to have high thermal conductivity and strength.

[0019] Furthermore, as described above, compared to aluminum nitride powder obtained by conventional pulverization processing, the aluminum nitride powder of the present invention has a lower oxygen content, and this, combined with the above particle size distribution, makes it possible to realize a sintered body having higher thermal conductivity. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of an apparatus for disintegrating aggregated particles. [Figure 2] 1 is a graph showing a change in particle size distribution due to a crushing treatment. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described. [Aluminum nitride powder] The aluminum nitride powder according to the present invention is composed of particles having a primary particle sphericity of 0.8 or more, preferably 0.9 or more. That is, the primary particles of the aluminum nitride powder according to the present invention have a uniform spherical particle shape. The shape of such aluminum nitride powder can be characterized by observation using an SEM photograph.

[0022] The aluminum nitride powder has a median diameter D obtained by laser diffraction. 50 is 0.5 to 1.5 μm, preferably 0.8 to 1.3 μm, and the particle diameter D corresponding to a cumulative undersize distribution of 90% 90 and the aforementioned D 50 Ratio D 90 / D 50 is 2.2 or less, preferably 2.0 or less. 90 / D 50 The aluminum nitride powder having the above formula (I) has a sharp particle size distribution and uniform particles, and therefore has a high pressed bulk density. The compacts made from this powder have a highly suppressed shrinkage rate after sintering, and therefore have excellent dimensional accuracy, and it is possible to obtain aluminum nitride sintered bodies with effectively reduced warpage and distortion.

[0023] The BET specific surface area of ​​aluminum nitride powder is 2 to 4 m 2 / g, preferably 2 to 3 m 2 / g, and the total oxygen concentration is 0.6 to 1.2 mass%. The total oxygen concentration increases due to the mechanochemical effect, but a concentration within the above range indicates that the powder has not been subjected to a large impact. Even at this total oxygen concentration, sintering proceeds sufficiently, and a sintered body with excellent physical properties such as thermal conductivity can be obtained.

[0024] Furthermore, the aluminum nitride powder according to the present invention has a median diameter D 50 and the BET specific surface area, the degree of agglomeration calculated by the following formula is preferably in the range of 1.1 to 2.2, and more preferably 1.3 to 2.0. The aluminum nitride powder of the present invention has a low degree of agglomeration, and therefore has high dispersibility in resins, solvents, etc., and can produce granules that are easily dispersible.

[0025] Cohesion = D 50 / D BET D BET = 6 / (ρ×S) S:BET specific surface area D BET : Particle size calculated from BET specific surface area D 50 : Average particle size obtained by laser diffraction method ρ: True specific gravity of AlN (3.26g / cm 3 ) The method for producing such aluminum nitride powder according to the present invention is not particularly limited, but it can be produced, for example, by the following production method.

[0026] [Method for producing aluminum nitride powder] A composite powder containing aluminum nitride agglomerated particles and carbon powder obtained by reducing and nitriding raw material powders of aluminum oxide powder and carbon powder under nitrogen is subjected to a crushing treatment without using media, and then excess carbon is removed by oxidation.

[0027] In the present invention, first, aluminum nitride powder is synthesized by a reduction-nitridation method in which a mixed powder of alumina powder and carbon powder is reacted in a nitrogen-containing atmosphere at 1400 to 1700° C. for 2 to 10 hours.

[0028] The average particle size of the alumina powder used in the present invention may be any size used in known reduction-nitridation methods, and is generally, for example, from 0.15 μm to 1.5 μm, preferably from 0.5 μm to 1.2 μm.

[0029] The raw carbon powder is not particularly limited, but examples thereof include acetylene black, channel black, furnace black, graphite powder, etc. Among these, acetylene black is preferred in terms of higher purity. The specific surface area of ​​the carbon powder is not particularly limited, but is preferably 0.01 to 500 m 2 / g is preferred.

[0030] The method for mixing and dispersing the alumina powder and the carbon powder may be any known method, and is not particularly limited, but various mixers such as a ball mill can be used. The raw material powder is nitrided in a nitrogen atmosphere at 1400°C to 1700°C. Nitriding is carried out using a conventional method until complete nitriding. To facilitate completion of the reduction-nitridation reaction, a reaction equivalent or greater amount of carbon powder is usually used relative to the alumina powder. The mixing ratio of alumina powder to carbon powder, expressed as a carbon / alumina molar ratio, is preferably in the range of 3.5 to 5.0. If the molar ratio is less than 3.5, unreacted alumina will remain, while if it is too high, the cost of removing the carbon will increase and become uneconomical.

[0031] In the synthetic powder obtained by the reduction-nitridation reaction, generally, about 5 to 30 mass %, particularly about 10 to 20 mass %, of carbon remains. By carrying out the crushing treatment while the carbon remains, it is possible to prevent the generation of coarse particles due to re-aggregation of the crushed particles.

[0032] In the present invention, the crushing treatment of the synthetic powder needs to employ a crushing means that does not use media such as balls or beads, specifically, a treatment using an ejector, a treatment using a Laval nozzle, a treatment using a jet mill, or the like.

[0033] As a means for crushing the synthetic powder, a process using an ejector, which can crush the powder by utilizing the acceleration of the air flow and the shear flow, is particularly preferably adopted, since it can be effective with a simple device and minimizes the generation of fine powder during crushing, thereby stabilizing the quality.

[0034] To explain in detail the preferred processing conditions using the ejector, the pressure of the compressed gas (generally air) supplied to the ejector is 0.1 to 1 MPa, preferably 0.2 to 0.7 MPa, and the concentration of the synthetic powder in the gas stream to be processed is 1.00 kg / m at normal pressure. 3 Preferably, 0.02 to 0.60 kg / m or less 3 is.

[0035] Furthermore, the specific surface area of ​​the synthesized powder and the specific surface area of ​​the aluminum nitride powder finally obtained by decarburizing the synthesized powder are hardly changed before and after the crushing treatment, with the change rate being 10% or less. From this, it is presumed that the crushing treatment does not cause pulverization of small diameter particles, particularly primary particles. Furthermore, the D of the aluminum nitride powder finally obtained by the crushing treatment is 50 And the particle diameter D corresponding to 10% of the cumulative undersize distribution 10 Although there is little difference between treated and untreated, D 90 is reduced by the treatment and satisfies the specified particle size ratio of the present invention.

[0036] In the present invention, since the synthesized powder after the crushing treatment contains excess carbon powder as described above, it is subjected to a decarburization treatment to obtain aluminum nitride powder. The decarburization treatment may be carried out by any known method, without particular limitation, in which excess carbon powder is burned at high temperature using an oxidizing gas.

[0037] For example, the oxidizing gas used in the decarburization treatment can be any gas capable of oxidizing carbon, such as air or oxygen, but air is preferred in consideration of economic efficiency and the oxygen concentration in the resulting aluminum nitride. Furthermore, when the decarburization treatment is performed in an air atmosphere at normal pressure, rapid oxidation of aluminum nitride occurs at temperatures around 1200°C, so the treatment temperature is preferably 500 to 1100°C, and more preferably 600 to 900°C in consideration of the efficiency of decarburization and excessive oxidation of the aluminum nitride surface.

[0038] The time for decarburization treatment may be set appropriately depending on the degree of carbon reduction, but if it is carried out at 600 to 900°C, for example, it can be completed in 1 to 6 hours.

[0039] In the method for producing aluminum nitride powder according to the present invention, for example, the following production apparatus can be used. That is, an apparatus is used which comprises a transfer device (also called a hopper) for transferring the synthesized powder after nitriding to a crushing means, a crushing means provided below the hopper, and a collecting means for recovering the crushed powder, as shown in FIG.

[0040] Any known hopper can be used without any particular restrictions, and those having a conical or inverted pyramidal container shape are preferably used because the powder is less likely to remain at the bottom. The outlet of the hopper is connected to a crusher so that the synthetic powder can be fed into the crusher. As the crusher, a crushing means that does not use media, such as the ejector described above, is preferably used. The crushed synthetic powder is collected in a collection means, such as a bag filter, via a pipe and then sent to the oxidation step.

[0041] According to an embodiment employing the treatment device used in the synthetic powder transport pipe such as the ejector, crushing can be carried out simultaneously with the transport of the synthetic powder, and the crushing treatment can be carried out industrially in an extremely advantageous manner.

[0042] The aluminum nitride powder obtained by the present invention can be suitably used, for example, as a raw material for producing a sintered body. Specifically, when the aluminum nitride powder is processed by a known method into aluminum nitride granules to be used as a raw material for press molding, a sheet molded body, or the like, a sintered body can be obtained that has a highly suppressed shrinkage rate, excellent dimensional accuracy, and effectively reduced warpage and distortion.

[0043] To give a specific example of a method for producing the above-mentioned aluminum nitride granules, the aluminum nitride powder obtained by the present invention is mixed with a known sintering aid that can be used for sintering aluminum nitride, for example, alkaline earth metal oxides such as calcium oxide and strontium oxide; rare earth oxides such as yttrium oxide and lanthanum oxide; or composite oxides such as calcium aluminate, in such an amount that the proportion of the additive in the total amount with the aluminum nitride powder is 0.1 to 10 mass %, and the mixture is formed into granules.

[0044] In addition to the above components, the aluminum nitride granules may contain, if necessary, surfactants, binders, lubricants, plasticizers, etc., which are composed of organic components.

[0045] The surfactant is generally used to improve the dispersibility of the ceramic powder in the slurry. Any known surfactant may be used as the surfactant of the present invention without any particular limitations. However, surfactants having a hydrophilic-lipophilic balance (hereinafter abbreviated as HLB) of 4.5 to 18 are particularly preferred. If the HLB is lower than 4.5, the aluminum nitride powder is not sufficiently dispersed in the slurry, and the thermal conductivity of the resulting aluminum nitride sintered body tends to decrease. Furthermore, if the HLB is higher than 18, the strength of the molded body tends to decrease.

[0046] The HLB value is calculated by Davis's formula. Specific examples of surfactants that can be suitably used include carboxylated trioxyethylene tridecyl ether, diglycerol monooleate, diglycerol monostearate, carboxylated heptaoxyethylene tridecyl ether, tetraglycerol monooleate, hexaglycerol monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, etc. Two or more surfactants may be mixed and used.

[0047] These surfactants are usually selected and used in an amount ranging from 0.01 to 10 parts by mass, preferably from 0.02 to 3.0 parts by mass, relative to 100 parts by mass of aluminum nitride powder. If the amount of surfactant is less than 0.01 part by mass, the dispersion of the slurry will be insufficient, and if it is more than 10 parts by mass, the strength of the molded body will decrease, which is not preferable.

[0048] The binder may be any binder commonly used in ceramic powder molding. Examples include oxygen-containing organic polymers such as polyvinyl butyral, polymethyl methacrylate, polyethyl methacrylate, poly(2-ethylhexyl methacrylate), polybutyl methacrylate, polyacrylate, cellulose acetate butyrate, nitrocellulose, methyl cellulose, hydroxymethyl cellulose, polyvinyl alcohol, polyoxyethylene oxide, and polypropylene oxide; hydrocarbon-based synthetic resins such as petroleum resin, polyethylene, polypropylene, and polystyrene; polyvinyl chloride; and organic polymers such as wax and its emulsions. While the molecular weight of the organic polymer used as the binder is not particularly limited, it is generally 3,000 to 1,000,000, preferably 5,000 to 300,000, which increases the density of the aluminum nitride powder compact obtained by press molding.

[0049] In the aluminum nitride granules, the mixing ratio of aluminum nitride powder to binder is preferably 0.1 to 30 parts by mass of binder per 100 parts by mass of aluminum nitride. If the binder is less than this range, it is difficult to form a good molded body due to insufficient strength, and if the binder is more than this range, the physical properties of the aluminum nitride sintered body obtained by press-molding the aluminum nitride granules and firing them tend to deteriorate.

[0050] Furthermore, if necessary, a lubricant for increasing pressure transmission during press molding, a plasticizer for increasing the crushability of granules, etc. may be used in a proportion of 5 parts by mass or less per 100 parts by mass of aluminum nitride powder.

[0051] Examples of organic solvents preferably used in the production of granules include ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; alcohols such as ethanol, propanol, and butanol; aromatic hydrocarbons such as benzene, toluene, and xylene; esters such as ethyl acetate and butyl acetate; and halogenated hydrocarbons such as trichloroethylene, tetrachloroethylene, and bromochloromethane, or a mixture of two or more of these. The amount of organic solvent used is selected from the range of 20 to 200 parts by mass per 100 parts by mass of aluminum nitride.

[0052] The above-mentioned components are mixed to form a slurry, which is then made into aluminum nitride granules by a known granulation method such as a spray dryer method. The aluminum nitride granules are packed into a predetermined mold and pressed with a press molding machine, that is, by a so-called dry pressing method, to form a pressed body.

[0053] When the aluminum nitride powder obtained by the product of the present invention is used as a raw material, the pressed bulk density can be increased by selectively crushing and reducing the large agglomerated particles of the aluminum nitride powder, which makes it possible to improve the packing properties during press molding.This allows the bulk density of the press-molded body and, ultimately, the sintered density of the resulting sintered body to be sufficiently increased, and an aluminum nitride sintered body with further improved thermal conductivity can be obtained. [Example]

[0054] Specific examples of the present invention will be described below using examples, but the present invention is not limited to these examples in any way. (1) Cumulative undersize distribution on a volume basis: 10%, 50% (median diameter), and 90% particle diameter (D 10 , D 50 and D 90 ) Each particle size was measured by dispersing aluminum nitride powder in an aqueous solution of sodium pyrophosphate using a homogenizer and then using a laser diffraction method with a Microtrac HRA manufactured by Microtrac Bell. (2) Specific surface area The specific surface area of ​​the aluminum nitride powder was measured by the BET method using a flow-type automatic surface area measuring device, Flowsorb 2300, manufactured by Shimadzu Corporation. (3) Total oxygen concentration The total oxygen concentration in the aluminum nitride powder was measured using a ceramic oxygen and nitrogen analyzer EMGA-620W manufactured by Horiba, Ltd. (4) Pressurized bulk density The pressed bulk density of aluminum nitride powder is 200 kg / cm 2 A pellet having a diameter of 20 mm and a thickness of 2.0 mm was prepared using a pressure of 1000 kJ / cm2, and the size and mass of the pellet were measured. (5) Sphericity The sphericity of the aluminum nitride powder was determined by randomly selecting 100 particles from an electron microscope photograph, measuring the major and minor axes of the particle image using a scale, and averaging the ratio (minor axis) / (major axis).

[0055] [Example 1 and Comparative Example 1] Average particle size 1.0μm, specific surface area 6m 2 / g and 280g of α-alumina with a specific surface area of ​​110m 2 140 g of carbon black with a carbon content of 1 / g was mixed in a dry vibration ball mill for 2 hours, and then nitrided in a nitrogen atmosphere at a firing temperature of 1600°C for 10 hours to obtain a synthetic powder.

[0056] The obtained synthetic powder was ejected from the hopper of the equipment shown in Figure 1 using an ejector using compressed air at 0.3 MPa until the concentration of the synthetic powder at normal pressure was 0.3 kg / Nm 3 The aluminum nitride powder thus treated was sent to a bag filter via a pipe, collected, and then decarburized in an air atmosphere at 650°C for 3 hours in a container equipped with a heater and a stirring function, to obtain aluminum nitride powder.

[0057] As Comparative Example 1, the synthetic powder of Example 1, which had not been subjected to the crushing treatment, was subjected to a decarburization treatment under the same conditions. The aluminum nitride powder of Example 1, which was subjected to decarburization after crushing, and the aluminum nitride powder of Comparative Example 1, which was obtained by decarburizing synthetic powder that was not crushed, were measured for specific surface area, pressed bulk density, and D 10 , D 50 and D 90 The total oxygen concentration and particle size distribution were measured. The results are shown in Table 1 and Figure 2. The sphericity was 0.9 or more.

[0058] Comparative Example 2 Average particle size 1.0μm, specific surface area 6m 2 / g and 280g of α-alumina with a specific surface area of ​​110m 2 140 g of carbon black with a carbon content of 1 / g was mixed in a dry vibration ball mill for 2 hours, and then nitrided in a nitrogen atmosphere at a firing temperature of 1700°C for 10 hours to obtain a synthetic powder.

[0059] The above-mentioned synthesized powder, which had not been subjected to the crushing treatment, was subjected to a decarburization treatment to obtain aluminum nitride powder. The specific surface area, D 10 , D 50 and D 90 The total oxygen concentration and the pressed bulk density were measured, and the results are shown in Table 1.

[0060] [Examples 2 and 3] Aluminum nitride powder was obtained in the same manner as in Example 1, except that the conditions for disintegrating the synthesized powder using an ejector were changed as shown in Table 1. The specific surface area, D 10 , D 50 and D 90 The total oxygen concentration and the pressed bulk density were measured, and the results are shown in Table 1.

[0061] Example 4 The synthesized powder obtained in Comparative Example 2 was subjected to the same crushing treatment as in Example 1, and then to the same decarburization treatment to obtain aluminum nitride powder. The specific surface area, D 10 , D 50 and D 90 The total oxygen concentration and the pressed bulk density were measured, and the results are shown in Table 1.

[0062] [Sintered body shrinkage rate] Using the aluminum nitride powder obtained in each example and comparative example, granules with a particle size of about 80 μm were produced under the same conditions, and then the granules were mixed at 1.92 t / cm 3 The compact was press-molded at a pressure of 1000 psi to form a rectangular solid body. The dimension (L0) of the longest direction of this compact was measured. This compact was then sintered at 1800°C to produce a sintered body. The dimension (L) of the longest direction of the obtained sintered body was measured in the same manner as the compact. s ) was measured, and the shrinkage rate (%) was calculated using the following formula, and is also shown in Table 1.

[0063] The shrinkage percentages shown in Table 1 are calculated by preparing 10 sintered bodies for each aluminum nitride powder, and the average shrinkage percentages are shown. Shrinkage rate (%) = (L0 - L s )×100 / L0

[0064] [Table 1] By crushing the aluminum nitride powder, the D 902, which shows the particle size distribution of the obtained aluminum nitride powder, shows that the shoulder portion that existed on the large particle side in Comparative Example 1 disappeared due to the crushing treatment, and the rising angle of the particle size distribution curve became sharper. 90 / D 50 The D of the aluminum nitride powder of Example 1 obtained by the crushing treatment of the present invention was 2.4. 90 / D 50 was 1.8.

Claims

[Claim 1] A method for producing aluminum nitride powder, comprising the steps of reducing and nitriding raw material powders of aluminum oxide powder and carbon powder under nitrogen to obtain a composite powder containing aluminum nitride agglomerated particles and carbon powder, and then treating the composite powder with an ejector, after which excess carbon is removed by oxidation.

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