JP7717680B2 - Method for producing silicon nitride powder and silicon nitride sintered body - Google Patents

Description

The present disclosure relates to a silicon nitride powder and a method for producing a silicon nitride sintered body.

Silicon nitride is a material with excellent strength, hardness, toughness, heat resistance, corrosion resistance, and thermal shock resistance, and is therefore used in various industrial parts such as die-casting machines and melting furnaces, as well as automotive parts. Furthermore, because silicon nitride also has excellent mechanical properties at high temperatures, its application to gas turbine parts, which require high-temperature strength and high-temperature creep properties, is being considered. For example, Patent Document 1 considers a method for improving the high-temperature properties of silicon nitride sintered bodies by reducing the total oxygen content of the silicon nitride powder to 1.5 mass% or less, thereby reducing the grain boundary phase refined during sintering and maintaining a high melting point, thereby improving high-temperature properties.

Further improvements in thermal conductivity and mechanical properties are required for silicon nitride sintered bodies. For example, Patent Document 2 describes a silicon nitride sintered body characterized by a thermal conductivity of 100 to 300 W/(m·K) at room temperature and a three-point bending strength of 600 to 1500 MPa at room temperature.

Patent Document 3 describes a silicon nitride powder characterized by having a specific surface area of 4.0 to 9.0 ^m2 /g, a β-phase ratio of less than 40 mass%, an oxygen content of 0.20 to 0.95 mass%, a frequency distribution curve obtained by volumetric particle size distribution measurement using a laser diffraction scattering method having two peaks with peak tops in the ranges of 0.4 to 0.7 μm and 1.5 to 3.0 μm, a frequency ratio of the peak tops (frequency of peak tops in the particle size range of 0.4 to 0.7 μm/frequency of peak tops in the particle size range of 1.5 to 3.0 μm) of 0.5 to 1.5, and a ratio D50/DBET (μm/μm) of the median diameter D50 (μm) obtained by the particle size distribution measurement to the specific surface area equivalent diameter DBET (μm) calculated from the specific surface area, of 3.5 or more.

Japanese Patent Application Publication No. 7-206409 Japanese Patent Application Laid-Open No. 2004-262756 International Publication No. 2015/194552

The present disclosure aims to provide a silicon nitride powder that can be used to produce sintered bodies with excellent thermal conductivity and bending strength. The present disclosure also aims to provide a method for producing silicon nitride sintered bodies with excellent thermal conductivity and bending strength.

One aspect of the present disclosure provides a silicon nitride powder containing primary particles of silicon nitride, in which, in a volume-based particle size distribution curve measured by laser diffraction/scattering, the difference between D90 and D10 is 1.70 μm or less, when D10 and D90 are the particle sizes at which the cumulative values from small particle sizes reach 10% and 90% of the total, respectively.

The above silicon nitride powder has a difference between D90 and D10 (D90 - D10) that is less than a specified value, making it possible to prepare a molded body (unsintered product) with a narrow particle size distribution and a denser structure. The silicon nitride sintered body obtained by sintering the above molded body has reduced void generation and can exhibit excellent thermal conductivity and bending strength.

The silicon nitride powder may have a D90 of 2.00 μm or less. When the upper limit of D90 is within the above range, the proportion of coarse particles can be sufficiently reduced, and the decrease in density of the sintered body can be more sufficiently suppressed. Furthermore, such silicon nitride powder has excellent handleability.

The silicon nitride powder may have a BET specific surface area of 8.0 to 15.0 ^{m 2} /g.

One aspect of the present disclosure provides a method for producing a silicon nitride sintered body, comprising the steps of molding and firing a sintering raw material containing the above-mentioned silicon nitride powder.

The above-mentioned method for manufacturing silicon nitride sintered bodies uses sintering raw materials containing the above-mentioned silicon nitride powder, and the resulting silicon nitride sintered bodies can exhibit excellent thermal conductivity and bending strength.

The present disclosure provides silicon nitride powder that can be used to produce sintered bodies with excellent thermal conductivity and bending strength.The present disclosure also provides a method for producing silicon nitride sintered bodies with excellent thermal conductivity and bending strength.

The following describes embodiments of the present disclosure. However, the following embodiments are examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content.

Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of those multiple substances present in the composition, unless otherwise specified. In this specification, the "steps" may be independent steps or steps performed simultaneously.

One embodiment of the silicon nitride powder contains primary particles of silicon nitride, and in a volume-based particle size distribution curve measured by laser diffraction/scattering, when the particle sizes at which the cumulative values from small particle sizes reach 10% and 90% of the total are defined as D10 and D90, respectively, the difference between D90 and D10 is 1.70 μm or less.

The upper limit of the difference between D90 and D10 (D90 - D10) is 1.70 μm or less, but may be, for example, 1.65 μm or less, 1.60 μm or less, 1.55 μm or less, 1.50 μm or less, or 1.45 μm or less. When the upper limit of the difference is within the above range, the molded body prepared by compression molding or the like of the silicon nitride powder can have a denser structure, thereby further suppressing the occurrence of voids during sintering. In other words, the resulting silicon nitride sintered body can achieve both high thermal conductivity and high bending strength. The lower limit of the difference between D90 and D10 may be, for example, 0.50 μm or more, 0.80 μm or more, or 1.00 μm or more. When the lower limit of the difference is within the above range, the silicon nitride powder has an appropriate particle size distribution, thereby further improving the packing density of the primary particles. The difference can be adjusted within the above range, for example, 0.50 to 1.70 μm, 0.80 to 1.65 μm, or 1.00 to 1.45 μm. The difference can be controlled by adjusting the grinding conditions during the production of the silicon nitride powder.

The upper limit of D90 of the silicon nitride powder may be, for example, 2.00 μm or less, 1.90 μm or less, 1.98 μm or less, 1.95 μm or less, or 1.90 μm or less. Keeping the upper limit of D90 within the above ranges allows for a sufficient reduction in the proportion of coarse particles, and more effectively suppresses a decrease in the density of the sintered body. The lower limit of D90 may be, for example, 1.40 μm or more, 1.50 μm or more, 1.52 μm or more, 1.55 μm or more, 1.60 μm or more, or 1.65 μm or more. D90 can be adjusted within the above range, for example, between 1.40 and 2.00 μm, or between 1.50 and 1.90 μm. The D90 of the silicon nitride powder can be controlled, for example, by adjusting the milling conditions during production of the silicon nitride powder.

The upper limit of D50 of the silicon nitride powder may be, for example, 0.75 μm or less, or 0.72 μm or less. When the upper limit of D50 is within the above range, the strength of the silicon nitride sintered body can be further improved. The lower limit of D50 of the silicon nitride powder may be, for example, 0.50 μm or more, or 0.55 μm or more. The D50 of the silicon nitride powder can be adjusted within the above range, and may be, for example, 0.50 to 0.75 μm, or 0.55 to 0.75 μm.

In this specification, D10, D50, and D90 refer to the particle sizes at which the cumulative value from the smallest particle size reaches 10%, 50%, and 90%, respectively, on the volume-based particle size distribution curve measured by laser diffraction/scattering. Laser diffraction/scattering measurements can be performed in accordance with the method described in JIS Z 8825:2013, "Particle Size Analysis - Laser Diffraction/Scattering Method." Measurements can be performed using a laser diffraction/scattering particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name: LS-13 320). D50, also known as the median diameter, refers to the average particle size of silicon nitride powder.

The lower limit of the BET specific surface area of the silicon nitride powder may be, for example, 8.0 ^{m 2} /g or more, 8.5 m ² /g or more, 8.7 ^{m 2} /g or more, or 9.0 ^{m 2} /g or more. The upper limit of the BET specific surface area of the silicon nitride powder may be, for example, 15.0 m ² /g or less, 13.0 ^{m 2} /g or less, 12.0 m ² /g or less, 11.0 m ² /g or less, 10.0 ^{m 2} /g or less, 9.5 ^{m 2} /g or less, or 9.2 ^m 2 /g or less. The BET specific surface area of the silicon nitride powder can be adjusted within the above-mentioned range and may be, for example, 8.0 to 15.0 ^{m 2} /g, or 8.5 to 13.0 m ² /g. The BET specific surface area of the silicon nitride powder can be controlled, for example, by adjusting the grinding conditions during the production of the silicon nitride powder.

The BET specific surface area in this specification is a value measured by the BET single-point method using nitrogen gas in accordance with the method described in JIS Z 8830:2013 "Method for measuring the specific surface area of powders (solids) by gas adsorption."

The upper limit of the surface oxygen content of silicon nitride may be, for example, 0.70% by mass or less, 0.60% by mass or less, or 0.50% by mass or less. When the upper limit of the surface oxygen content of silicon nitride is within the above range, the grain boundary phase can be more sufficiently reduced when producing a silicon nitride sintered body, thereby further improving thermal conductivity. When the upper limit of the surface oxygen content of silicon nitride is within the above range, the acid treatment time in the subsequent acid treatment step can also be reduced. The lower limit of the surface oxygen content of silicon nitride may be, for example, 0.20% by mass or more, 0.30% by mass or more, 0.35% by mass or more, 0.40% by mass or more, or 0.45% by mass or more. When the lower limit of the surface oxygen content of silicon nitride is within the above range, grain growth can be promoted during sintering of the silicon nitride, thereby further improving the bending strength of the silicon nitride sintered body. The surface oxygen content of silicon nitride can be adjusted within the above range, for example, 0.20 to 0.70% by mass or 0.20 to 0.50% by mass. The surface oxygen content of silicon nitride can be controlled, for example, by adjusting the composition of the atmosphere in the firing step in the production of silicon nitride powder, as well as the firing temperature, firing time, and the like.

In this specification, "surface oxygen content" refers to a value determined by the following procedure. The oxygen and nitrogen content of silicon nitride powder is analyzed using an oxygen/nitrogen analyzer. The measurement sample is heated from 20°C to 2000°C at a heating rate of 8°C/sec in a helium gas atmosphere. The oxygen released as the temperature rises is detected using infrared absorption. Initially, oxygen bonded to the surface of the silicon nitride powder is released. With further heating, when the temperature reaches approximately 1400°C, the silicon nitride begins to decompose. The start of silicon nitride decomposition can be determined by the start of nitrogen detection. When silicon nitride begins to decompose, oxygen inside the silicon nitride powder is released. Therefore, the oxygen released at this stage corresponds to the internal oxygen content, and the amount of oxygen detected and quantified before nitrogen is detected is considered to be the surface oxygen content.

The silicon nitride powder described above can be produced, for example, by the following method. One embodiment of a method for producing silicon nitride powder includes the steps of: calcining silicon powder in an atmosphere containing nitrogen and at least one gas selected from the group consisting of hydrogen and ammonia to obtain a calcined product (hereinafter also referred to as the calcining step); wet-pulverizing the calcined product to obtain a pulverized product (hereinafter also referred to as the pulverization step); treating the pulverized product with acid to obtain an acid-treated product (hereinafter also referred to as the acid-treatment step); and wet-classifying the acid-treated product (hereinafter also referred to as the classification step).

Silicon powder with a low oxygen concentration may be used. The upper limit of the oxygen concentration of the silicon powder may be, for example, 0.40% by mass or less, 0.30% by mass or less, or 0.20% by mass or less. By keeping the oxygen concentration of the silicon powder within the above range, the amount of oxygen inside the resulting silicon nitride powder can be further reduced. The lower limit of the oxygen concentration of the silicon powder may be, for example, 0.10% by mass or more, or 0.15% by mass or more. The oxygen concentration of the silicon powder can be adjusted within the above range and may be, for example, 0.10 to 0.40% by mass.

The oxygen concentration of silicon powder in this specification refers to the value measured by infrared absorption method.

Commercially available silicon powder can be used, or separately prepared silicon powder can be used. If the silicon powder has a high oxygen concentration, the amount of oxygen bound to the silicon powder can be reduced, for example, by using a pretreatment liquid containing hydrofluoric acid. For example, the above-mentioned method for producing silicon nitride powder may further include a pretreatment step in which silicon powder is pretreated with a pretreatment liquid containing hydrofluoric acid to obtain silicon powder with an oxygen concentration of 0.40% by mass or more.

The pretreatment liquid contains hydrofluoric acid, but may be a mixed acid with an acid such as hydrochloric acid, or may consist solely of hydrofluoric acid. The temperature of the pretreatment liquid in the pretreatment step may be, for example, 40 to 80°C. The time for which the pretreatment liquid is in contact with the silicon powder may be, for example, 1 to 10 hours.

In the firing step, the silicon powder is fired in a mixed atmosphere containing nitrogen and at least one gas selected from the group consisting of hydrogen and ammonia to obtain a fired product containing silicon nitride. The total content of hydrogen and ammonia in the mixed atmosphere may be, for example, 10 to 40 volume % based on the entire 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.

In the pulverization process, the sintered product obtained in the sintering process is wet-pulverized to obtain a pulverized product. By pulverizing the sintered product and adjusting the particle size, it becomes easier to control the surface treatment with acid in the subsequent acid treatment process, and it becomes easier to control the amount of surface oxygen in the primary particles of silicon nitride. The effect of performing the pulverization process is more pronounced when the sintered product containing silicon nitride obtained in the sintering process is in the form of a block, ingot, etc.

The grinding process may be carried out in multiple stages, such as coarse grinding and fine grinding. The grinding process may include, for example, a dry grinding process. In this case, the grinding process may be a process in which wet grinding is carried out after dry grinding. The medium used for wet grinding may be, for example, water.

For example, a ball mill or the like can be used for pulverization. When using a ball mill, the ball filling rate in the container can be adjusted to match the particle size distribution of the desired silicon nitride powder. The lower limit of the ball filling rate in the container, based on the volume of the container, may be, for example, 40 vol.% or more, 45 vol.% or more, 50 vol.% or more, or 60 vol.% or more. The upper limit of the ball filling rate in the container, based on the volume of the container, may be, for example, 70 vol.% or less, or 65 vol.% or less.

The lower limit of the grinding time (grinding time) in the grinding step may be, for example, 5 hours or more, 6 hours or more, 7 hours or more, or 8 hours or more. By setting the lower limit of the grinding time within the above range, the ground material can be sufficiently finely ground, and the acid treatment efficiency in the acid treatment step can be further improved. The upper limit of the grinding time may be, for example, 15 hours or less, 14 hours or less, 13 hours or less, or 12 hours or less. By setting the upper limit of the grinding time within the above range, the fired material can be sufficiently ground and excessive grinding can be prevented. The grinding time may be adjusted within the above range, and may be, for example, 5 to 15 hours or 8 to 12 hours.

In the acid treatment step, the ground material is brought into contact with an acid to obtain an acid-treated product. Examples of acids include hydrogen fluoride and hydrogen chloride. The acid may be a mixed acid of hydrogen fluoride and hydrogen chloride, or may be either hydrogen fluoride or hydrogen chloride alone, but preferably contains hydrogen fluoride. The acid may be an aqueous solution (e.g., hydrofluoric acid or hydrochloric acid).

The upper limit of the acid (e.g., hydrofluoric acid) concentration may be, for example, 55% by mass or less, 40% by mass or less, 38% by mass or less, 35% by mass or less, or 30% by mass or less. The lower limit of the acid concentration may be, for example, 10% by mass or more, 11% by mass or more, or 12% by mass or more. By setting the lower limit of the acid concentration within the above range, insufficient acid treatment can be prevented. The acid concentration may be adjusted within the above range, and may be, for example, 10 to 55% by mass, 11 to 38% by mass, or 12 to 30% by mass.

The means for contacting the ground material with the acid may be, for example, a method of dispersing the ground material in the acid.

The lower limit of the temperature of the acid (e.g., aqueous solution) in the acid treatment step may be, for example, 40°C or higher, 45°C or higher, 50°C or higher, or 60°C or higher. The upper limit of the temperature of the acid in the acid treatment step may be 80°C or lower, 75°C or lower, or 70°C or lower. The temperature of the acid in the acid treatment step may be adjusted within the above-mentioned range, and may be, for example, 40 to 80°C, 45 to 75°C, or 50 to 70°C.

In the acid treatment step, the lower limit of the time (acid treatment time) for contacting the calcined product or the pulverized product obtained by pulverizing the calcined product with acid may be, for example, 1.0 hour or more, 1.2 hours or more, 1.5 hours or more, or 2.0 hours or more. By setting the lower limit of the acid treatment time within the above range, insufficient acid treatment can be prevented. The acid treatment time may be, for example, 10.0 hours or less, 9.7 hours or less, 9.5 hours or less, 9.0 hours or less, 8.5 hours or less, or 8.0 hours or less. The acid treatment time may be adjusted within the above range, and may be, for example, 1.0 to 10.0 hours, 1.2 to 9.7 hours, or 2.0 to 8.0 hours.

In the classification process, the acid-treated product prepared through the pulverization and acid treatment processes is further wet-classified to produce silicon nitride powder with the desired particle size distribution. For example, coarse particles can be removed to adjust the D90 of the silicon nitride powder. Wet classification can be performed, for example, by centrifugation. The centrifuge can be, for example, a liquid cyclone (manufactured by Murata Manufacturing Co., Ltd., product name: Three-liquid Classifying Cyclone TR-10). The pressure applied to the inlet (inlet pressure) can be, for example, 0.2 to 1.0 MPa, or 0.3 to 0.7 MPa.

The silicon nitride powder obtained by the above-mentioned manufacturing method has excellent sinterability. In other words, the above-mentioned silicon nitride powder can be suitably used as a raw material for sintered bodies.

One embodiment of a method for producing a silicon nitride sintered body includes molding and firing a sintering raw material containing the above-mentioned silicon nitride powder.

The sintering raw material may contain an oxide-based sintering aid in addition to the silicon nitride powder. Examples of the oxide-based sintering aid include Y ₂ O _3, MgO, and Al ₂ O _3. The content of the oxide-based sintering aid in the sintering raw material may be, for example, 3 to 10 mass %.

In the above process, the above-mentioned sintering raw materials are pressed at a molding pressure of, for example, 3.0 to 30.0 MPa to obtain a molded body. The molded body may be produced by uniaxial pressing or by CIP. It may also be fired while being molded by hot pressing. The molded body may be fired in an inert gas atmosphere such as nitrogen gas or argon gas. The pressure during firing may be 0.7 to 1.0 MPa. The firing temperature may be 1860 to 2100°C, or 1880 to 2000°C. The firing time at this firing temperature may be 6 to 20 hours, or 8 to 16 hours. The rate of temperature rise to the firing temperature may be, for example, 1.0 to 10.0°C/hour.

The resulting silicon nitride sintered body has a reduced grain boundary phase and a dense structure, which allows it to exhibit excellent thermal conductivity and bending strength.

The thermal conductivity of silicon nitride sintered bodies can be, for example, 90 W/(m·K) or more, 95 W/(m·K) or more, 100 W/(m·K) or more, 105 W/(m·K) or more, or 110 W/(m·K) or more in an environment of 25°C. The thermal conductivity of silicon nitride sintered bodies in this specification refers to the value obtained by measuring the thermal diffusivity and specific heat capacity using the laser flash method (in accordance with JIS R1611) and calculating the product of the density, thermal diffusivity, and specific heat capacity of the sintered body.

The bending strength of the silicon nitride sintered body can be, for example, 550 MPa or more, 600 MPa or more, or 650 MPa or more at room temperature. In this specification, the bending strength of the silicon nitride sintered body refers to the three-point bending strength measured at room temperature using a test piece for strength measurement prepared in accordance with JIS R1601:2008.

Although several embodiments have been described above, the present disclosure is in no way limited to the above-described embodiments. Furthermore, the descriptions of the above-described embodiments can be applied to each other.

The present disclosure will be explained in more detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples.

Example 1
<Preparation of silicon nitride powder>
Commercially available silicon powder (specific surface area: 3.0 m ² /g) was immersed in a mixed acid containing hydrogen chloride and hydrogen fluoride, the temperature of which was adjusted to 60°C, and the mixture was maintained at 60°C for 2 hours for pretreatment. The mixed acid used was a mixture of commercially available hydrochloric acid (concentration: 35% by mass) and hydrofluoric acid (concentration: 55% by mass) in a mass ratio of 10:1. The silicon powder was then removed from the mixed acid, washed with water, and dried under a nitrogen atmosphere. The oxygen concentration of the dried silicon powder was 0.4% by mass. This oxygen concentration was measured by infrared absorption.

A molded body (bulk density: 1.4 g/cm ³ ) was produced using the dried silicon powder. The obtained molded body was placed in an electric furnace and fired at 1400°C for 60 hours to produce a fired body containing silicon nitride. A mixed gas of nitrogen and hydrogen (a mixed gas in which N ₂ and H ₂ were mixed at a volume ratio of 80:20 under standard conditions) was supplied as the firing atmosphere. The obtained fired body was coarsely crushed and then wet-pulverized in a ball mill. For the wet crushing, the ball filling rate to the container was 60% by volume, water was used as the solvent, and the crushing time was 8 hours.

The silicon nitride powder obtained by wet milling was immersed in hydrofluoric acid (hydrofluoric acid concentration: 15% by mass) at 60°C for 2 hours for acid treatment. The silicon nitride powder was then removed from the hydrofluoric acid and washed with water. Water was then added to the silicon nitride powder, and the mixture was wet classified at 0.5 MPa. The supernatant was removed and dried under a nitrogen atmosphere. This yielded silicon nitride powder.

<Evaluation of Silicon Nitride Powder: Measurement of D10, D50, and D90>
The D10, D50, and D90 of the silicon nitride powder were measured by a laser diffraction scattering method in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - laser diffraction and scattering method." For the measurements, a laser diffraction scattering particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name: LS-13 320) was used.

<Evaluation of Silicon Nitride Powder: Measurement of BET Specific Surface Area>
The BET specific surface area was measured by the BET single-point method using nitrogen gas in accordance with JIS Z 8803:2013. The results are shown in Table 1.

<Evaluation of Silicon Nitride Powder: Measurement of Surface Oxygen Amount>
The surface oxygen content was measured using an oxygen/nitrogen simultaneous analyzer (manufactured by Horiba, Ltd., model EMGA-920). Specifically, the silicon nitride powder was heated in a helium atmosphere from 20°C to 2000°C at a temperature increase rate of 8°C/sec, and the amount of oxygen was measured before nitrogen was detected.

[Production of silicon nitride sintered body]
90 parts by mass of the prepared silicon nitride powder, 5 parts by mass of _{Y2O3 powder} with an average particle size of 1.5 μm, and 5 parts by mass of _{Yb2O3 powder} with an average particle size of 1.2 μm were weighed into a container, and methanol was added and wet-mixed for 4 hours. The dried mixed powder (sintered raw material) was then molded in a mold at a pressure of 10 MPa and then cold isostatically pressed (CIP) at a pressure of 25 MPa. The resulting molded body was placed in a carbon crucible together with a packed powder consisting of a mixed powder of silicon nitride powder and BN powder, and sintered at a temperature of 1900 °C for 12 hours under a nitrogen pressure of 1 MPa to produce a silicon nitride sintered body.

<Measurement of thermal conductivity of sintered silicon nitride>
The silicon nitride sintered body was ground to prepare a 10 mm diameter x 3 mm disk for measuring thermal conductivity. Thermal diffusivity and specific heat capacity were measured using the laser flash method (based on JIS R1611), and the product of the density, thermal diffusivity, and specific heat capacity of the sintered body was calculated to determine the thermal conductivity at room temperature. The results are shown in Table 1. The thermal conductivity measurement results in Table 1 are shown as relative values based on the silicon nitride sintered body prepared in Comparative Example 1, which will be described later.

<Measurement of bending strength of sintered silicon nitride>
Test pieces for strength measurement were prepared from the silicon nitride sintered body in accordance with JIS R1601:2008, and the three-point bending strength was measured at room temperature. The results are shown in Table 1. Note that the bending strength measurement results in Table 1 are shown as relative values based on the silicon nitride sintered body prepared in Comparative Example 1, which will be described later.

<Evaluation of silicon nitride sintered body>
The silicon nitride sintered body was evaluated according to the following criteria.
A: Thermal conductivity (relative value) is 1.20 or more, and bending strength (relative value) is 1.10 or more.
B: Thermal conductivity (relative value) is 1.20 or more, and bending strength (relative value) is 1.05 or more and less than 1.10, or thermal conductivity (relative value) is 1.10 or more and less than 1.20, and bending strength (relative value) is 1.10 or more.
C: Thermal conductivity (relative value) is 1.10 or more and less than 1.20, and bending strength (relative value) is 1.05 or more and less than 1.10.
D: Thermal conductivity (relative value) is less than 1.10, or bending strength (relative value) is less than 1.05.

Example 2
Silicon nitride powder was prepared in the same manner as in Example 1, except that the wet classification conditions were as shown in Table 1. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 3
Silicon nitride powder was prepared in the same manner as in Example 1, except that the wet-pulverization conditions were as shown in Table 1. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
Silicon nitride powder was prepared in the same manner as in Example 1, except that the wet classification conditions were as shown in Table 1. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.

The present disclosure provides silicon nitride powder that can be used to produce sintered bodies with excellent thermal conductivity and bending strength.The present disclosure also provides a method for producing silicon nitride sintered bodies with excellent thermal conductivity and bending strength.

Claims (3)

Contains primary particles of silicon nitride,
The BET specific surface area is 8.0 to 15.0 ^{m 2} /g;
The surface oxygen content is 0.30 to 0.70 mass %,
A silicon nitride powder for use as a raw material for sintered bodies, in which, in a volume-based particle size distribution curve measured by a laser diffraction /scattering method, the particle sizes at which the integrated values from small particle sizes reach 10% and 90% of the total are defined as D10 and D90, respectively, and the difference between D90 and D10 is 1.52 μm or more and 1.70 μm or less. 2. The silicon nitride powder for use as a raw material for a sintered body according to claim 1, wherein D90 is 2.00 μm or less. A method for producing a silicon nitride sintered body, comprising the steps of molding and firing a sintering raw material containing the silicon nitride powder for a sintered body raw material according to claim 1 or 2.