Silicon nitride-containing fine powder and method for producing silicon nitride-containing fine powder

Abstract

To provide a silicon nitride-containing fine powder production method that enables more efficient production of silicon nitride-containing fine powder than conventional methods, and to provide silicon nitride-containing fine powder produced by the method.SOLUTION: A method of producing silicon nitride-containing fine powder includes wet milling of a coarse powder containing silicon nitride by feeding it into a media agitation mill, the silicon nitride-containing fine powder having an average particle size of 1 μm or less, wherein the effective power consumption of the media agitation mill in the wet milling is 0.1 kWh / kg or more and 1 kWh / kg or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a fine powder comprising silicon nitride and a method for producing the fine powder comprising silicon nitride. [Background technology]

[0002] Silicon nitride sintered bodies are materials with excellent strength, hardness, toughness, heat resistance, corrosion resistance, thermal shock resistance, etc., and are therefore used in various industrial parts such as die-casting machines and melting furnaces, as well as insulating substrates for automotive parts, etc. As the silicon nitride powder that is the raw material for silicon nitride sintered bodies, silicon nitride powder with a high degree of alpha conversion is used in order to obtain high-quality sintered bodies.

[0003] Known methods for producing silicon nitride powder include the "direct nitridation method," in which metallic silicon is reacted at high temperature in a nitrogen or ammonia stream, the "silica reduction method," in which a mixed powder of silicon dioxide and carbon is reacted at high temperature in a nitrogen or ammonia stream, and the "vapor phase synthesis method," in which a silicon halide or monosilane is reacted with ammonia at high temperature. The direct nitridation method in particular is a production method that is widely used industrially.

[0004] To produce sintered silicon nitride, silicon nitride powder with a small particle size is required. Therefore, silicon nitride obtained by direct nitriding is then pulverized using a pulverizer. For example, Patent Document 1 discloses a method for producing silicon nitride fine powder with an average particle size of 0.28 μm by supplying silicon nitride coarse powder with an average particle size of 3 μm to a wet pulverizer (media agitation mill) and wet-pulverizing it. Pulverization is broadly divided into dry pulverization and wet pulverization, but it is generally known that wet pulverization is easier to produce fine particles. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 3-52653 Summary of the Invention [Problem to be solved by the invention]

[0006] Although wet milling produces silicon nitride micropowder with a small particle size, the metal media and components of the wet mill can wear during wet milling. This increases the frequency of maintenance of the wet mill, resulting in a problem of reduced operating rate. Furthermore, impurities (e.g., iron) derived from the metal media and components of the wet mill can be mixed into the silicon nitride micropowder. These impurities degrade the quality of the silicon nitride sintered body produced from the silicon nitride micropowder. Therefore, an acid treatment step is required in which the silicon nitride micropowder is immersed in an acidic solution to remove impurities. Subsequent washing and drying steps are also required to remove the acidic solution. Furthermore, because wet milling is carried out in water, some of the silicon nitride reacts with water to produce silica, which reduces the yield. Wet milling can also be carried out in an organic solvent, but this requires explosion-proofing of the equipment and complicates the subsequent acid treatment, washing, and drying processes.

[0007] An object of the present invention is to provide a method for producing a fine powder containing silicon nitride, which can produce a fine powder containing silicon nitride more efficiently than conventional production methods, and to provide a fine powder containing silicon nitride produced by the production method. [Means for solving the problem]

[0008] The present invention includes the following [1] to [5]. [1] A method for producing a fine powder containing silicon nitride, comprising supplying a coarse powder containing silicon nitride to a media-agitation mill and wet-pulverizing the coarse powder, wherein the average particle size of the fine powder containing silicon nitride is 1 μm or less, and the effective power consumption rate of the media-agitation mill in the wet-pulverization is 0.1 kWh / kg or more and 1 kWh / kg or less. [2] The method for producing a fine powder containing silicon nitride according to [1], wherein the peripheral speed of the media-agitation mill in the wet pulverization is 6 to 15 m / s. [3] The method for producing a fine powder containing silicon nitride according to [1] or [2], wherein the media diameter of the media agitation mill is less than 1.5 mm.

[0009] [4] A fine powder containing silicon nitride having an average particle size of 1 μm or less, the fine powder containing silicon nitride containing a compound containing oxygen, and the content of oxygen element relative to the total mass of the fine powder containing silicon nitride is 0.5 to 5 mass%. [5] The fine powder containing silicon nitride according to [4], wherein the fine powder containing silicon nitride contains iron or an iron compound, and the content of iron element relative to the total mass of the fine powder containing silicon nitride is 0.2 to 5 mass%. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for producing a fine powder containing silicon nitride, which can produce a fine powder containing silicon nitride more efficiently than conventional production methods, and a fine powder containing silicon nitride produced by the method. DETAILED DESCRIPTION OF THE INVENTION

[0011] The meanings and definitions of terms used in this specification are as follows: A numerical range expressed by "to" means a numerical range in which the numbers before and after "to" are the lower and upper limits. In this specification, the upper and lower limits can be combined in any way. By "coarse powder" is meant powder having an average particle size of more than 1 μm. "Fine powder" means a powder having an average particle size of 1 μm or less. "Average particle size" refers to the 50% cumulative volume particle size (hereinafter referred to as "D 50 The particle size distribution can be obtained in accordance with JIS R 1629:1997 "Method for measuring particle size distribution of fine ceramic raw materials by laser diffraction and scattering method." Hereinafter, the x% cumulative volume particle size will be referred to as "D x " Note that 0% is the minimum granularity and 100% is the maximum granularity. The "specific surface area" is a value measured by the BET single-point method using nitrogen gas in accordance with JIS R 1626:1996 "Method for measuring the specific surface area of ​​fine ceramic powders by the gas adsorption BET method."

[0012] The "alpha phase ratio" refers to the ratio of alpha silicon nitride to the total silicon nitride, and is a value calculated by the following formula 1. αization rate (%)=[I α(102) +I α(210) ] / [I α(102) +I α(210) +I β(101) +I β(210) ]×100 formula 1 In the formula 1, I α(102) is the intensity of the diffraction peak of the (102) plane of the α-phase of silicon nitride, and I α(210) is the intensity of the diffraction peak of the (210) plane of the α-phase of silicon nitride, and I β(101) is the intensity of the diffraction peak of the (102) plane of the β phase of silicon nitride, and I β(210) is the intensity of the diffraction peak of the (210) plane of the β phase of silicon nitride. Each diffraction peak can be obtained from the XRD pattern obtained by powder X-ray diffraction measurement.

[0013] The oxygen and nitrogen contents in the powder are values ​​measured by infrared absorption method. The contents of elements other than oxygen and nitrogen (mainly metal elements) in the powder are values ​​measured by X-ray fluorescence (XRF) measurement.

[0014] The effective power unit is the value calculated using the following formula 2. P C =(P1-P0) / W Equation 2 When milling is performed continuously, in the above formula 2, Pc is the effective power consumption unit (kWh / kg), P1 is the input power (kW) when mixing with the raw materials and milling media packed, P0 is the no-load power (kW) of the mixer alone, and W is the feed rate of the powder to be processed (kg / h).When milling is performed batchwise, in the above formula 2, Pc is the effective power consumption unit (kWh / kg), P1 is the cumulative input power (kWh) when mixing with the raw materials and milling media packed, P0 is the cumulative no-load power (kWh) of the mixer alone, and W is the mass of the powder to be processed (kg).

[0015] When pulverization is performed under fixed conditions, it can also be calculated from the specific surface area as follows: 2 The raw material powder is used, pulverized under constant conditions, and the integral power consumption rate and the specific surface area of ​​the powder are measured over time. The integral power consumption rate is plotted on the x-axis and the specific surface area on the y-axis, and a and b in the following formula 2 are calculated. The specific surface area of ​​the raw material powder is, for example, 2 to 8 m 2 The number of plots is preferably 3 or more. y=ax b formula 3 In the above formula 3, y is the specific surface area, x is the integral power consumption unit, and a and b are constants in pulverization under fixed conditions.

[0016] The above formula 3 can be transformed into the following formula 4. x=(y / a) 1 / b formula 4

[0017] Based on the above formula 4, the specific surface area is S1m 2 / g powder S2m 2 The effective power consumption Δx when crushing to 1 / g can be calculated by the following formula 5. Δx=(S2 / a) 1 / b -(S1 / a) 1 / b formula 5

[0018] <Method for producing fine powder containing silicon nitride> The method for producing fine powder containing silicon nitride according to this embodiment includes supplying a coarse powder containing silicon nitride to a media stirring mill and performing wet grinding. The effective power per unit of the media stirring mill in wet grinding is 0.1 to 1 kWh / kg. The average particle size of the obtained fine powder containing silicon nitride is 1 μm or less. Hereinafter, the fine powder containing silicon nitride is also referred to as "Si3N₄ fine powder", and the coarse powder containing silicon nitride is also referred to as "Si3N₄ coarse powder". The manufacturing process of Si3N₄ coarse powder and the manufacturing process of Si3N₄ fine powder will be described.

[0019] <Manufacturing process of Si3N₄ coarse powder> The manufacturing process of Si3N₄ coarse powder includes a nitriding process of metallic silicon. If necessary, it may include a coarse grinding process of silicon nitride.

[0020] (Nitriding process of metallic silicon) As the metallic silicon powder, those obtained by grinding lumps or particles of metallic silicon can be used. Examples of the grinding device include a hammer mill, a pin mill, a ball mill, a vibration mill, a bead mill, and a jet mill.

[0021] The average particle size of the metallic silicon powder is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. When the average particle size of the metallic silicon powder is below the above upper limit value, nitriding in the nitriding process of metallic silicon proceeds easily. The average particle size of the metallic silicon powder is preferably 4 μm or more, more preferably 6 μm or more, and even more preferably 8 μm or more. When the average particle size of the metallic silicon powder is above the above lower limit value, excessive heat generation in the nitriding process can be suppressed.

[0022] The purity of the metallic silicon powder is preferably 95% by mass or more, and more preferably 98% by mass or more. The metallic silicon powder may contain impurities derived from lumps or particles of metallic silicon and impurities derived from the grinding device.

[0023] The metallic silicon powder may be used as the raw material powder as it is, or may be blended with metallic silicon powder, fluorite, and other metal powders or metal compound powders to prepare the raw material powder. The content of the metallic silicon powder per 100 parts by mass of the raw material powder is preferably 92 parts by mass or more, more preferably 95 parts by mass or more, and even more preferably 97 parts by mass or more.

[0024] When the raw material powder contains fluorite, the content of fluorite per 100 parts by mass of metal silicon powder is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.8 parts by mass or more. If the content of fluorite is above the lower limit, nitridation of the metal silicon is likely to proceed. If the content of fluorite per 100 parts by mass of metal silicon powder is above the upper limit, the content of fluorite is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less. If the content of fluorite is below the upper limit, the contents of calcium and fluorine in the resulting Si3N4 fine powder can be reduced.

[0025] In the nitriding process for metal silicon, the raw material powder may be fired as is, or the raw material powder may be formed into a compact and then fired. Nitriding is performed by firing the raw material powder or a compact of the raw material powder (hereinafter also referred to as "raw material powder, etc.") in a firing furnace under a nitrogen-containing atmosphere. The firing furnace may be a continuous furnace or a batch furnace. Examples of batch furnaces include electric furnaces and rotary kilns. Examples of continuous furnaces include container-transporting tunnel-type pusher furnaces and roller hearth kilns. When firing the raw material powder as is, a continuous furnace is preferred. A continuous furnace allows the container containing the raw material powder to be continuously heated within the furnace. Since the raw material powder can be fired without being formed, the nitriding reaction proceeds efficiently. This allows silicon nitride to be obtained in a short period of time.

[0026] In the nitriding process for metal silicon, a raw material powder containing silicon powder and a fluoride, or a compact of the raw material powder, is fired in a mixed atmosphere containing nitrogen and either or both of hydrogen and ammonia to obtain a nitride. The total content of hydrogen and ammonia in the mixed atmosphere may be, for example, 10 to 40 volume % based on the total mixed atmosphere. The firing temperature may be, for example, 1100 to 1450°C, or 1200 to 1400°C. The firing time may be, for example, 30 to 100 hours.

[0027] The alpha phase ratio of the obtained silicon nitride is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. When the alpha phase ratio is equal to or greater than the lower limit, grain growth during sintering can be promoted when a sintered body is produced using the Si3N4 fine powder. As a result, a sufficiently densified silicon nitride sintered body can be produced. Therefore, a silicon nitride sintered body with even better high-temperature strength and high thermal conductivity can be obtained. Since the alpha silicon nitride rate is essentially determined by the nitriding process, the preferred ranges of alpha silicon nitride in the Si3N4 coarse powder, Si3N4 fine powder, and Si3N4 fine powder after acid treatment described below are also the same as above.

[0028] (coarse grinding process) In the coarse pulverization step, the molded or powdered silicon nitride obtained in the metal silicon nitriding step is coarsely pulverized. The pulverization may be carried out using, for example, a coarse pulverizer, a ball mill, a vibration mill, etc. The coarse pulverization is preferably carried out in a dry manner.

[0029] (Si3N4 coarse powder) The average particle size of the Si3N4 coarse powder is preferably 10 to 30 μm, more preferably 15 to 25 μm, and even more preferably 18 to 22 μm. When the average particle size of the Si3N4 coarse powder is equal to or less than the upper limit, the process for producing the Si3N4 fine powder can be carried out efficiently.

[0030] The specific surface area of ​​Si3N4 coarse powder is 1.5 to 4.5m 2 / g is preferred, and 2.0 to 4.0m 2 / g is more preferable, and 2.5 to 3.5m 2 When the specific surface area of ​​the Si3N4 coarse powder is equal to or less than the upper limit, the process for producing the Si3N4 fine powder can be carried out efficiently.

[0031] The iron content relative to the total mass of the Si3N4 coarse powder is preferably 0.4 mass% or less, more preferably 0.3 mass% or less, and even more preferably 0.25 mass% or less. The lower limit of the iron content relative to the total mass of the Si3N4 coarse powder is not particularly limited, but may be, for example, 0.01 mass% or more, 0.05 mass% or more, or 0.1 mass% or more. When the iron content relative to the total mass of the Si3N4 coarse powder is equal to or less than the upper limit, the iron content in the Si3N4 fine powder can be reduced.

[0032] The oxygen element content relative to the total mass of the Si3N4 coarse powder is preferably 2.0 mass% or less, more preferably 1.5 mass% or less, and even more preferably 1.0 mass% or less. The lower limit of the oxygen element content relative to the total mass of the Si3N4 coarse powder is not particularly limited, but may be, for example, 0.1 mass% or more, 0.2 mass% or more, or 0.4 mass% or more. When the oxygen element content relative to the total mass of the Si3N4 coarse powder is equal to or less than the upper limit, the oxygen element content in the Si3N4 fine powder can be reduced.

[0033] The total content of silicon element and nitrogen element relative to the total mass of the Si3N4 coarse powder (ie, the content of silicon nitride) is preferably 96 mass % or more, more preferably 98 mass % or more, and even more preferably 99 mass % or more.

[0034] The Si3N4 coarse powder may contain elements other than silicon, nitrogen, iron, and oxygen. Examples of the other elements include calcium and halogen elements derived from fluorite, and metal elements other than iron and silicon derived from the metal powder and the metal compound powder. The content of the other elements relative to the total mass of the Si3N4 coarse powder is preferably 4% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less.

[0035] <Manufacturing Process of Si3N4 Fine Powder> The manufacturing process of Si3N4 fine powder includes supplying Si3N4 coarse powder to a media stirring type mill and performing wet grinding.

[0036] Wet grinding means grinding in a state where Si3N4 coarse powder and a solvent are mixed, that is, in a slurried state. As the solvent, for example, water can be used.

[0037] The effective power per unit of the media stirring type mill is 0.1 - 1 kWh / kg, preferably 0.15 - 0.95 kWh / kg, and more preferably 0.2 - 0.9 kWh / kg. When the effective power per unit is at or above the lower limit value, the Si3N4 coarse powder can be sufficiently pulverized into fine powder. When the effective power per unit is at or below the upper limit value, the Si3N4 coarse powder can be pulverized into fine powder more efficiently. As a result, the wear of the media and the members of the media stirring type mill is suppressed, and the decrease in the operating rate of the media stirring type mill is suppressed. Also, the incorporation of impurities (e.g., iron) derived from the metal media and the members of the media stirring type mill into the silicon nitride fine powder is suppressed. Furthermore, since the processing time can be shortened, the amount of silica generated by the reaction of silicon nitride and water is suppressed, and the yield is improved.

[0038] The effective power per unit can be adjusted by changing any one of the input power, no-load power, and powder supply amount in the above formula 2. For example, when changing the amount of media, the mass of media, the stirring peripheral speed, the processing time, etc., the effective power per unit is also changed.

[0039] The stirring peripheral speed is preferably 6 - 15 m / s, more preferably 7 - 14 m / s, and even more preferably 8 - 12 m / s. The stirring peripheral speed means the tip peripheral speed of the agitator of the media stirring type mill. When the stirring peripheral speed is at or above the lower limit value, the Si3N4 coarse powder can be sufficiently pulverized into fine powder. When the stirring peripheral speed is at or below the upper limit value, the Si3N4 coarse powder can be pulverized into fine powder more efficiently.

[0040] The media in the media agitation mill may be either metallic or ceramic. From the viewpoint of sufficiently pulverizing the Si3N4 coarse powder, metallic media are preferred. As the metal, iron and steel containing iron as the main component are preferred. Only one type of media may be used, or two or more types may be used in combination.

[0041] The media diameter of the media agitation mill is preferably less than 1.5 mm, more preferably 1.2 mm or less, and even more preferably 1.0 mm or less. The media diameter is preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.5 mm or more. The media diameter refers to the average diameter of all the media packed in the media agitation mill. When the media diameter is equal to or greater than the lower limit, the media can be stirred well and pulverization can proceed.When the media diameter is equal to or less than the upper limit, the Si3N4 coarse powder can be pulverized more efficiently.

[0042] The media filling rate relative to the volume of the media-agitation mill is preferably 60 to 95 volume %, more preferably 70 to 90 volume %, and even more preferably 80 to 85 volume %. The media filling rate is a value calculated by "bulk volume of media / effective volume of mill x 100", and the effective volume of the mill is a value calculated by "total volume of mill - volume of shaft etc." When the media packing ratio is equal to or greater than the lower limit, the pulverization of the Si3N4 coarse powder is easily promoted. When the media packing ratio is equal to or less than the upper limit, the amount of Si3N4 coarse powder that can be processed per batch can be increased, which is efficient.

[0043] The solid concentration of the slurry of coarse Si3N4 powder and solvent in the media agitation mill (ie, the concentration of coarse Si3N4 powder) is preferably 30 to 75 mass %, more preferably 50 to 70 mass %, and even more preferably 55 to 65 mass %. When the solids concentration of the slurry is equal to or higher than the lower limit, the amount of Si3N4 coarse powder that can be processed per batch can be increased, which is efficient.When the solids concentration of the slurry is equal to or lower than the upper limit, the pulverization of the Si3N4 coarse powder is easily promoted.

[0044] The Si3N4 coarse powder and the solvent may be directly fed to the media agitation mill, or a slurry may be prepared in advance and fed to the media agitation mill. When the total volume of the Si3N4 coarse powder and the solvent is equal to or greater than the lower limit, the amount of Si3N4 coarse powder that can be processed per batch can be increased, which is efficient.When the total volume of the Si3N4 coarse powder and the solvent is equal to or less than the upper limit, the pulverization of the Si3N4 coarse powder is easily promoted.

[0045] The wet-pulverized slurry may be fed back to the media-agitation mill for multiple wet-pulverization cycles. The pulverized slurry is subjected to solid-liquid separation, and the resulting solid is dried to obtain a fine powder containing silicon nitride. The resulting fine powder containing silicon nitride may be classified as needed.

[0046] (Si3N4 fine powder) Si3N4 fine powder D 10 The diameter of the Si3N4 fine powder is preferably 0.7 μm or less, more preferably 0.6 μm or less, and even more preferably 0.5 μm or less. 10 The lower limit of is not particularly limited, but may be, for example, 0.15 μm or more, 0.2 μm or more, or 0.25 μm or more. Si3N4 fine powder D 10 When the value is equal to or less than the upper limit, it becomes easier to produce a silicon nitride sintered body.

[0047] Si3N4 fine powder D 50 The diameter of the Si3N4 fine powder is 1 μm or less, preferably 0.9 μm or less, and more preferably 0.8 μm or less. 50 The lower limit of the thickness is not particularly limited, but may be, for example, 0.4 μm or more, 0.5 μm or more, or 0.6 μm or more. Si3N4 fine powder D50 When the value is equal to or less than the upper limit, it becomes easier to produce a silicon nitride sintered body.

[0048] Si3N4 fine powder D 90 The diameter of the Si3N4 fine powder is preferably 5.5 μm or less, more preferably 5 μm or less, and even more preferably 4.5 μm or less. 90 The lower limit of the thickness is not particularly limited, but may be, for example, 1 μm or more, 1.5 μm or more, or 2 μm or more. Si3N4 fine powder D 90 When the value is equal to or less than the upper limit, it becomes easier to produce a silicon nitride sintered body.

[0049] Si3N4 fine powder D 100 The diameter of the Si3N4 fine powder is preferably 90 μm or less, more preferably 80 μm or less, and even more preferably 75 μm or less. 100 The lower limit of the thickness is not particularly limited, but may be, for example, 5 μm or more, 6 μm or more, or 7 μm or more. Si3N4 fine powder D 100 When D is equal to or less than the upper limit, it becomes easier to produce a silicon nitride sintered body. 100 is the particle size of particles formed by agglomeration of impurities mainly originating from media and components of the wet mill, and therefore may exceed the upper limit.

[0050] The specific surface area of ​​Si3N4 fine powder is 30m 2 / g or more is preferable, and 40m 2 / g or more is more preferable, and 50m 2 / g or more is more preferable. The specific surface area of ​​Si3N4 fine powder is 65m 2 / g or less is preferable, and 62m 2 / g or less is more preferable, and 60m 2 / g or less is more preferable.

[0051] The Si3N4 fine powder may contain iron or an iron compound. The content of iron element relative to the total mass of the Si3N4 fine powder is preferably 5 mass% or less, more preferably 4.5 mass% or less, even more preferably 4.2 mass% or less, and particularly preferably 4 mass% or less. The lower limit of the content of iron element relative to the total mass of the Si3N4 fine powder is not particularly limited, but may be, for example, 0.2 mass% or more, 0.5 mass% or more, or 1 mass% or more. When the content of iron element relative to the total mass of the Si3N4 fine powder is not more than the above upper limit, the strength, fracture toughness, thermal conductivity, and electrical insulation of the silicon nitride sintered body produced using the Si3N4 fine powder are likely to be improved.

[0052] The oxygen content relative to the total mass of the Si3N4 fine powder is preferably 5.5 mass% or less, more preferably 5.2 mass% or less, and even more preferably 5 mass% or less. The lower limit of the oxygen content relative to the total mass of the Si3N4 fine powder is not particularly limited, but may be, for example, 0.5 mass% or more, 1 mass% or more, or 2 mass% or more. The oxygen element relative to the total mass of the Si3N4 fine powder is mainly oxygen element derived from silica. Therefore, when the content of oxygen element relative to the total mass of the Si3N4 fine powder is equal to or less than the upper limit, it can be determined that the yield is improved. In addition, oxygen element derived from Fe2O3 and FeOOH may also be present.

[0053] The total content of silicon element and nitrogen element relative to the total mass of the Si3N4 fine powder (ie, the content of silicon nitride) is preferably 90 mass % or more, more preferably 93 mass % or more, and even more preferably 95 mass % or more.

[0054] The Si3N4 fine powder may contain elements other than silicon, nitrogen, iron, and oxygen. Examples of the other elements include calcium and halogen elements derived from fluorite, and metal elements other than iron and silicon derived from the metal powder and the metal compound powder. The content of the other elements relative to the total mass of the Si3N4 fine powder is preferably 1% by mass or less, more preferably 0.8% by mass or less, and even more preferably 0.5% by mass or less.

[0055] <Acid treatment process> An acid treatment step may be further carried out in which the Si3N4 fine powder obtained in the Si3N4 fine powder production process is immersed in an acidic solution. By immersing the Si3N4 fine powder in an acidic solution, impurities such as iron and silica contained in the Si3N4 fine powder can be dissolved and removed. As will be shown in the examples below, the method for producing a silicon nitride-containing fine powder of this embodiment results in a lower iron content and oxygen content (silica content) in the Si3N4 fine powder after wet milling than conventional methods for producing a silicon nitride-containing fine powder. Therefore, the Si3N4 fine powder of this embodiment may be used to produce a silicon nitride sintered body without the acid treatment step.

[0056] Examples of acidic substances contained in the acidic solution include inorganic acids such as hydrogen fluoride, hydrogen chloride, nitric acid, and sulfuric acid. To dissolve metals contained in the Si3N4 fine powder after wet milling, it is preferable to use hydrochloric acid (aqueous hydrogen chloride solution). To dissolve silica contained in the Si3N4 fine powder after wet milling, it is preferable to use hydrofluoric acid (aqueous hydrogen fluoride solution). That is, it is preferable to carry out the acid treatment step using a mixed solution of hydrofluoric acid and hydrochloric acid. The acid treatment step may be carried out with stirring, or may be carried out by leaving it to stand without stirring.

[0057] The temperature of the acidic solution is preferably 5 to 90°C, more preferably 10 to 85°C, and even more preferably 20 to 80°C. When the temperature of the acidic solution is equal to or higher than the lower limit, the reaction rate is improved and dissolution of impurities is promoted. When the temperature of the acidic solution is equal to or lower than the upper limit, it is advantageous in terms of energy.

[0058] The total concentration of acidic substances such as hydrogen fluoride and hydrogen chloride relative to the total mass of the acidic solution is preferably from 2 to 60 mass %, more preferably from 5 to 50 mass %, and even more preferably from 10 to 30 mass %. When the concentration of the acidic substance is equal to or higher than the lower limit, dissolution of impurities such as iron and silica contained in the Si3N4 fine powder is promoted.When the concentration of the acidic substance is equal to or lower than the upper limit, the acidic substance can be easily removed by washing.

[0059] The amount of the acidic solution used relative to 100 parts by mass of the Si3N4 fine powder is preferably 10 to 300 parts by mass, more preferably 50 to 250 parts by mass, and even more preferably 100 to 150 parts by mass.

[0060] The immersion time is preferably 1 to 15 hours, more preferably 2 to 10 hours, and even more preferably 3 to 8 hours.

[0061] After the immersion, the Si3N4 fine powder and the acidic solution are subjected to solid-liquid separation, for example, by known methods such as decantation, centrifugation, and filtration.

[0062] The Si3N4 fine powder after solid-liquid separation is preferably washed. Examples of washing liquids include water and alkaline solutions, with ammonia water being preferred as the alkaline solution. The washed Si3N4 fine powder can be dried to obtain acid-treated Si3N4 fine powder.

[0063] (Si3N4 fine powder after acid treatment) D of Si3N4 fine powder after acid treatment 10 , D 50 The preferred range of is the D of the Si3N4 fine powder before the acid treatment. 10 , D 50 The preferred range is the same as that of

[0064] D of Si3N4 fine powder after acid treatment 90 The diameter of the Si3N4 fine powder after the acid treatment is preferably 3 μm or less, more preferably 2.5 μm or less, and even more preferably 2 μm or less. 90The lower limit of the thickness is not particularly limited, but may be, for example, 0.8 μm or more, 1 μm or more, or 1.2 μm or more. D of Si3N4 fine powder after acid treatment 90 When the content is equal to or less than the upper limit, a dense silicon nitride sintered body having high strength and high thermal conductivity is easily obtained.

[0065] D of Si3N4 fine powder after acid treatment 100 The diameter of the Si3N4 fine powder after the acid treatment is preferably 8 μm or less, more preferably 6 μm or less, and even more preferably 4 μm or less. 100 The lower limit of the thickness is not particularly limited, but may be, for example, 1.5 μm or more, 2 μm or more, or 2.5 μm or more. D of Si3N4 fine powder after acid treatment 100 When the content is equal to or less than the upper limit, a dense silicon nitride sintered body having high strength and high thermal conductivity is easily obtained.

[0066] The specific surface area of ​​the Si3N4 fine powder after acid treatment is 8m 2 / g or more is preferable, and 9m 2 / g or more is more preferable, and 10m 2 The specific surface area of ​​the Si3N4 fine powder after acid treatment is 15m / g or more. 2 / g or less is preferable, and 14m 2 / g or less is more preferable, and 13m 2 / g or less is more preferable.

[0067] The content of iron element relative to the total mass of the Si3N4 fine powder after the acid treatment is preferably 300 mass ppm or less, more preferably 280 mass ppm or less, and even more preferably 250 mass ppm or less. The lower limit of the content of iron element relative to the total mass of the Si3N4 fine powder after the acid treatment is not particularly limited, but may be, for example, 1 mass ppm or more, 10 mass ppm or more, or 50 mass ppm or more. When the content of iron element relative to the total mass of Si3N4 fine powder after acid treatment is not more than the above upper limit, the strength, fracture toughness, thermal conductivity, and electrical insulation of the silicon nitride sintered body produced using the Si3N4 fine powder are likely to be improved.

[0068] The oxygen content of the Si3N4 fine powder after acid treatment is preferably 1.2 mass% or less, more preferably 1.0 mass% or less, and even more preferably 0.9 mass% or less, relative to the total mass of the Si3N4 fine powder. The lower limit of the oxygen content relative to the total mass of the Si3N4 fine powder is not particularly limited, but may be, for example, 0.4 mass% or more, 0.5 mass% or more, or 0.6 mass% or more.

[0069] The total content of silicon and nitrogen elements (ie, silicon nitride content) relative to the total mass of the Si3N4 fine powder after acid treatment is preferably 99.0 mass % or more, more preferably 99.2 mass % or more, and even more preferably 99.4 mass % or more.

[0070] The Si3N4 fine powder after acid treatment may contain elements other than silicon, nitrogen, iron, and oxygen. Examples of other elements include calcium and halogen elements derived from fluorite, and metal elements other than iron and silicon derived from the metal powder and metal compound powder. The content of other elements relative to the total mass of the Si3N4 coarse powder is preferably 0.3 mass% or less, more preferably 0.25 mass% or less, and even more preferably 0.2 mass% or less.

[0071] <Application> The silicon nitride fine powder of this embodiment has a small average particle size and therefore has excellent sinterability, and can therefore be used as a sintering material for silicon nitride sintered bodies.

[0072] The sintering raw material may contain an oxide-based sintering aid in addition to the silicon nitride fine powder. Examples of the oxide-based sintering aid include yttrium oxide, magnesia, and alumina. The content of the oxide-based sintering aid in the sintering raw material is, for example, 3 to 10 mass %.

[0073] The silicon nitride sintered body is produced by a process of producing a molded body and a process of firing. In the process of producing a molded body, for example, a molding pressure of 3.0 to 30 MPa is applied to obtain a molded body. The molded body may be produced by uniaxial pressing or by CIP molding. Furthermore, the molded body may be fired while being molded by hot pressing. The molded body may be fired in an inert gas atmosphere such as nitrogen or argon. The pressure during firing may be 0.7 to 1 MPa. The firing temperature is preferably 1860 to 2100°C, more preferably 1880 to 2000°C. The firing time at the firing temperature is preferably 6 to 20 hours, more preferably 8 to 16 hours. The rate of temperature rise to the firing temperature is preferably, for example, 1.0 to 10.0°C / hour.

[0074] The silicon nitride fine powder of this embodiment has a small average particle size and a low content of impurities such as iron, and therefore the resulting silicon nitride sintered body has excellent thermal conductivity and mechanical properties. [Example]

[0075] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0076] <Measurement method> (D 10 , D 50 , D 90 , D 100 ) D 10 , D 50 , D 90 , D 100 was measured using the method described above. Specifically, it was performed in accordance with the method described in JIS R 1629:1997 "Method for measuring particle size distribution of fine ceramic raw materials by laser diffraction and scattering." To measure the particle size distribution, 60 mg of the powder to be measured was weighed into a 500 mL container. This was mixed with a 20% aqueous solution of sodium hexametaphosphate (2 mL) and water (200 g) as dispersants. This container was placed in an ultrasonic disperser manufactured by Sharp Corporation so that the entire portion containing the dispersion was immersed, and ultrasonic dispersion was performed for 1 minute. The particle size distribution measurement described above was performed using the sample after ultrasonic dispersion.

[0077] (specific surface area) The specific surface area was measured by the method described above. Specifically, the BET specific surface area of ​​the powder was measured by the BET single-point method using nitrogen gas in accordance with JIS R 1626:1996 "Method for measuring the specific surface area of ​​fine ceramic powders by the gas adsorption BET method."

[0078] (oxygen element content) The oxygen content of the measured powder was determined as the total oxygen content. The oxygen content was measured using an oxygen / nitrogen analyzer (Horiba, Ltd., model EMGA-920). Specifically, the measured powder was heated from 20°C to 2000°C at a rate of 8°C / s in a helium atmosphere, and the amount of oxygen released was quantified to determine the oxygen content (mass%) of the entire measured powder.

[0079] (Iron element content) The iron element content of the powder to be measured was measured using an X-ray fluorescence analyzer (manufactured by Rigaku Corporation, device name: Primas II).

[0080] (gelatinization rate) The alpha phase ratio was measured by the method described above. XRD patterns were obtained by measurement using CuKα radiation using an X-ray diffractometer (Rigaku, model Ultima IV). The alpha phase ratio was calculated using Equation 1 above from the diffraction peak intensity of the (102) plane of the alpha phase of silicon nitride, the diffraction peak intensity of the (210) plane of the alpha phase of silicon nitride, the diffraction peak intensity of the (102) plane of the β phase of silicon nitride, and the diffraction peak intensity of the (210) plane of the β phase of silicon nitride in the XRD patterns.

[0081] [Manufacturing Example 1] <Preparation of coarse powder containing silicon nitride> A compact was produced using a mixture of metal silicon powder and an organic binder aqueous solution, which had been mixed and kneaded. The resulting compact was dried, then placed in an electric furnace and fired at 1000-1450°C in nitrogen gas for 60 hours to obtain a fired body containing silicon nitride. The fired body was crushed using a dry jaw crusher and then crushed in a dry ball mill to obtain a coarse powder containing silicon nitride. In the dry ball mill crushing, the ball filling rate relative to the volume of the dry ball mill was set to 60% by volume, and the crushing time was 8 hours. The D of the resulting coarse powder containing silicon nitride was 50 , D 90 , D 100 Table 1 shows the specific surface area, oxygen element content (represented as "O" in Table 1), iron element content (represented as "Fe" in Table 1), and gelatinization rate.

[0082] [Example 1] The silicon nitride-containing coarse powder obtained in Production Example 1 was fed to a media-agitation mill (commercially available) and wet-pulverized to obtain a silicon nitride-containing fine powder. Spherical high-carbon chromium steel (SUJ-2) with a diameter of 1 mm was used as the media. The type of media, media diameter, media packing rate, effective power consumption, and agitation peripheral speed are shown in Table 2 (the same applies to Examples 2 to 10 and Comparative Example 1 below). The D of the obtained silicon nitride-containing fine powder was 10 , D 50 , D 90 , D 100 The specific surface area, oxygen element content (represented as "O" in Table 2), iron element content (represented as "Fe" in Table 2), and gelatinization rate are also shown in Table 2 (the same applies to Examples 2 to 10 and Comparative Example 1 below).

[0083] [Examples 2 to 10, Comparative Example 1] The silicon nitride-containing coarse powder obtained in Production Example 1 was supplied to a media-agitation mill and wet-pulverized to obtain a silicon nitride-containing fine powder in the same manner as in Example 1, except that one or more of the type of media, media diameter, effective power consumption unit, agitation peripheral speed, and media packing rate were changed as shown in Table 2. In Examples 2 to 10, a media-agitation mill (commercially available) was used, and in Comparative Example 1, a media-agitation mill (manufactured by Nippon Coke and Engineering Co., Ltd., product name: Attritor) was used.

[0084] [Acid treatment] To 1000 g of the silicon nitride-containing fine powder obtained in Examples 3 and 6 and Comparative Example 1, 1313 g of a mixed solution of 220 g of hydrofluoric acid and 1093 g of hydrochloric acid was added, and the mixture was stirred at room temperature for 2 hours. The hydrogen fluoride concentration in the mixed solution was 2.7 mass %, and the hydrogen chloride concentration was 8.6 mass %. Thereafter, the silicon nitride-containing fine powder and the mixed solution were separated by decantation, and the silicon nitride-containing fine powder was washed and then dried to obtain the silicon nitride-containing fine powder after acid treatment. The D of the obtained silicon nitride-containing fine powder after acid treatment 10 , D 50 , D 90 , D 100 The specific surface area, oxygen element content, iron element content, and alpha conversion rate are shown in Table 2.

[0085] [Table 1]

[0086] [Table 2]

[0087] The iron content in the silicon nitride-containing fine powders obtained in Examples 1 to 10 was 1.7 to 3.5 mass%, which was extremely low compared to the 9.6 mass% iron content in the silicon nitride-containing fine powder obtained in Comparative Example 1. Furthermore, the oxygen content in the silicon nitride-containing fine powders obtained in Examples 1 to 10 was 3.1 to 4.8 mass%, which was low compared to the 5.8 mass% oxygen content in the silicon nitride-containing fine powder obtained in Comparative Example 1. This confirms that wear of the media and the components of the media-agitation mill was suppressed in Examples 1 to 10. Furthermore, it is believed that the silicon nitride-containing fine powders of Examples 1 to 10 can be used to produce silicon nitride sintered bodies without acid treatment. Furthermore, it was confirmed that the amount of silica produced by the reaction of silicon nitride with water was suppressed, improving yield.

Claims

1. A method for producing a fine powder containing silicon nitride, comprising supplying a coarse powder containing silicon nitride to a media-agitation mill and wet-pulverizing the coarse powder, the average particle size of the fine powder containing silicon nitride is 1 μm or less; The method for producing a fine powder containing silicon nitride, wherein the effective power consumption unit of the media agitation mill in the wet grinding is 0.1 kWh / kg or more and 1 kWh / kg or less.

2. 2. The method for producing a fine powder containing silicon nitride according to claim 1, wherein the peripheral speed of the media-agitation mill in the wet pulverization is 6 to 15 m / s.

3. 3. The method for producing a fine powder containing silicon nitride according to claim 1, wherein the diameter of the media in the media-agitation mill is less than 1.5 mm.

4. A fine powder containing silicon nitride having an average particle size of 1 μm or less, the fine powder containing silicon nitride containing a compound containing oxygen, and the content of oxygen element relative to the total mass of the fine powder containing silicon nitride is 0.5 to 5 mass %.

5. 5. The silicon nitride-containing fine powder according to claim 4, wherein the silicon nitride-containing fine powder contains iron or an iron compound, and the content of iron element relative to the total mass of the silicon nitride-containing fine powder is 0.2 to 5 mass%.

Images