Method for producing silicon nitride powder and silicon nitride sintered body

Abstract

One aspect of the present disclosure provides a silicon nitride powder which contains primary particles of silicon nitride, and wherein if D10 and D90 are particle diameters at which the integrated value from the smallest particle diameter reaches 10% and 90% of the total in the volume-based particle size distribution curve as determined by a laser diffraction / scattering method, the difference between D90 and D10 is 1.70 μm or less.

Description

Technical Field

[0001] The present disclosure relates to a method for producing silicon nitride powder and a silicon nitride sintered body.

Background Art

[0002] Silicon nitride is a material excellent in strength, hardness, toughness, heat resistance, corrosion resistance, thermal shock resistance, etc., and is therefore used in various industrial parts such as die casting machines and melting furnaces, and automotive parts. Further, since silicon nitride also has excellent mechanical properties at high temperatures, it has been studied for application to gas turbine parts that require high-temperature strength and high-temperature creep properties. For example, in Patent Document 1, as a method for improving the high-temperature properties of a silicon nitride sintered body, the total oxygen content of the silicon nitride powder is set to 1.5% by mass or less to reduce the grain boundary phase to be purified during sintering and maintain a high melting point to improve the high-temperature properties. has been studied.

[0003] Further improvement in thermal conductivity and mechanical properties is required for silicon nitride sintered bodies. For example, Patent Document 2 describes a silicon nitride-based sintered body characterized by having a thermal conductivity at room temperature of 100 to 300 W / (m·K) and a three-point bending strength at room temperature of 600 to 1500 MPa.

[0004] Further, Patent Document 3 discloses that the specific surface area is 4.0 to 9.0 m 2 / g, the ratio of the β phase is less than 40% by mass, the oxygen content is 0.20 to 0.95% by mass, the frequency distribution curve obtained by volume-based particle size distribution measurement by laser diffraction scattering method has two peaks, and the peak tops of the peaks are in the range of 0.4 to 0.7 μm and 1.5 to 3.0 μm, and the ratio of the frequencies of the peak tops (frequency of the peak top in the range of particle size 0.4 to 0.7 μm / frequency of the peak top in the range of particle size 1.5 to 3.0 μm) is 0.5 to 1.5, and the ratio D50 / DBET (μm / μm) of the median diameter D50 (μm) obtained by the particle size distribution measurement and the specific surface area equivalent diameter DBET (μm) calculated from the specific surface area is 3.5 or more. A silicon nitride powder characterized by being described.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present disclosure is to provide a silicon nitride powder capable of producing a sintered body excellent in thermal conductivity and bending strength. Another object of the present disclosure is to provide a method for producing a silicon nitride sintered body excellent in thermal conductivity and bending strength.

Means for Solving the Problems

[0007] One aspect of the present disclosure provides a silicon nitride powder containing primary particles of silicon nitride, wherein in the volume-based particle size distribution curve measured by the laser diffraction / scattering method, when the particle sizes at which the integrated values from the small particle sizes reach 10% and 90% of the whole are defined as D10 and D90, respectively, the difference between D90 and D10 is 1.70 μm or less.

[0008] Since the difference (D90 - D10) between D90 and D10 of the above silicon nitride powder is equal to or less than a predetermined value, a molded body (green body) having a narrow particle size distribution and a denser structure can be prepared. The silicon nitride sintered body obtained by firing the above molded body can suppress the generation of voids and the like, and exhibit excellent thermal conductivity and bending strength.

[0009] The silicon nitride powder may have a D90 of 2.00 μm or less. When the upper limit value of D90 is within the above range, the proportion of coarse particles can be sufficiently reduced, and the decrease in the density of the sintered body can be more sufficiently suppressed. In addition, such silicon nitride powder is excellent in handleability.

[0010] The silicon nitride powder may have a BET specific surface area of 8.0 to 15.0 m 2 / g.

[0011] One aspect of the present disclosure provides a method for manufacturing a silicon nitride sintered body, which includes a step of molding and firing a sintering raw material containing the above-described silicon nitride powder.

[0012] Since the method for manufacturing the silicon nitride sintered body uses a sintering raw material containing the above-described silicon nitride powder, the obtained silicon nitride sintered body can exhibit excellent thermal conductivity and flexural strength.

Advantages of the Invention

[0013] According to the present disclosure, it is possible to provide a silicon nitride powder capable of manufacturing a sintered body excellent in thermal conductivity and flexural strength. According to the present disclosure, it is also possible to provide a method for manufacturing a silicon nitride sintered body excellent in thermal conductivity and flexural strength.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following content.

[0015] Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition. The "steps" in this specification may be independent steps or steps performed simultaneously.

[0016] One embodiment of the silicon nitride powder includes primary particles of silicon nitride. In the volume-based particle size distribution curve measured by the laser diffraction / scattering method, when the cumulative values from the small particle sizes reach 10% and 90% of the total, the particle sizes at that time are defined as D10 and D90 respectively, and the difference between D90 and D10 is 1.70 μm or less.

[0017] The upper limit value of the difference (D90 - D10) between D90 and D10 is 1.70 μm or less. For example, it may be 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 value 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, so that the generation of voids during sintering can be more effectively suppressed. That is, the thermal conductivity and flexural strength of the obtained silicon nitride sintered body can be more highly balanced. The lower limit value 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 value of the difference is within the above range, since the silicon nitride powder has an appropriate particle size distribution, the packing density of the primary particles can be further improved. The difference can be adjusted within the above range, for example, it may be 0.50 - 1.70 μm, 0.80 - 1.65 μm, or 1.00 - 1.45 μm. The difference can be controlled by adjusting the grinding conditions during the production of the silicon nitride powder.

[0018] The upper limit value 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. When the upper limit value of D90 is within the above range, the proportion of coarse particles can be sufficiently reduced, and the density reduction of the sintered body can be more effectively suppressed. The lower limit value 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, it may be 1.40 - 2.00 μm, or 1.50 - 1.90 μm. The D90 of the silicon nitride powder can be controlled by adjusting the grinding conditions during the production of the silicon nitride powder.

[0019] The upper limit value 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 value of D50 is within the above range, the strength of the silicon nitride sintered body can be further improved. The lower limit value 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.

[0020] In this specification, D10, D50, and D90 respectively refer to the particle diameters when the cumulative values from small particle diameters reach 10%, 50%, and 90% of the whole in the volume-based particle diameter distribution curve measured by the laser diffraction / scattering method. The laser analysis scattering method can be measured in accordance with the method described in JIS Z 8825:2013 "Particle Size Analysis - Laser Diffraction / Scattering Method". For the measurement, a laser diffraction scattering method particle size distribution measuring device (manufactured by Beckman Coulter, trade name: LS-13 320), etc. can be used. Note that D50 is also called the median diameter and means the average particle diameter of the silicon nitride powder.

[0021] The lower limit value of the BET specific surface area of the silicon nitride powder is, 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 value of the BET specific surface area of the silicon nitride powder is, 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 range, and may be, for example, 8.0 to 15.0 m 2 / g, or 8.5 to 13.0 m 2It may be / 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.

[0022] 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 Specific Surface Area of Powder (Solid) by Gas Adsorption".

[0023] The upper limit of the surface oxygen amount of silicon nitride may be, for example, 0.70 mass% or less, 0.60 mass% or less, or 0.50 mass% or less. When the upper limit of the surface oxygen amount of silicon nitride is within the above range, the grain boundary phase when manufacturing a silicon nitride sintered body can be more sufficiently reduced, and the thermal conductivity can be further improved. When the upper limit of the surface oxygen amount 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 amount of silicon nitride may be, for example, 0.20 mass% or more, 0.30 mass% or more, 0.35 mass% or more, 0.40 mass% or more, or 0.45 mass% or more. When the lower limit of the surface oxygen amount of silicon nitride is within the above range, the grain growth during firing of silicon nitride can be promoted, and the bending strength of the silicon nitride sintered body can be further improved. The surface oxygen amount of silicon nitride can be adjusted within the above range, and may be, for example, 0.20 - 0.70 mass%, or 0.20 - 0.50 mass%. The surface oxygen amount of silicon nitride can be controlled, for example, by adjusting the components of the atmosphere in the firing step during the production of the silicon nitride powder, as well as the firing temperature and firing time.

[0024] The "surface oxygen amount" in this specification means a numerical value obtained by the following procedure. The oxygen amount and nitrogen amount of silicon nitride powder are analyzed using an oxygen-nitrogen analyzer. A sample for measurement is heated from 20°C to 2000°C at a heating rate of 8°C / second in an atmosphere of helium gas. Oxygen desorbing with the heating is detected by the infrared absorption method. At the beginning of the heating, oxygen bonded to the surface of the silicon nitride powder desorbs. When further heated and the temperature reaches near 1400°C, silicon nitride begins to decompose. The start of decomposition of silicon nitride can be grasped by the fact that nitrogen begins to be detected. When silicon nitride begins to decompose, oxygen inside the silicon nitride powder desorbs. Therefore, since the oxygen desorbing at this stage corresponds to the internal oxygen amount, the oxygen amount detected and quantified before nitrogen is detected is defined as the surface oxygen amount.

[0025] The above-mentioned silicon nitride powder can be produced, for example, by the following method. One embodiment of the method for producing silicon nitride powder includes a step of firing silicon powder in an atmosphere containing nitrogen and at least one selected from the group consisting of hydrogen and ammonia to obtain a fired product (hereinafter, also referred to as the firing step), a step of wet-grinding the above-mentioned fired product to obtain a ground product (hereinafter, also referred to as the grinding step), a step of treating the above-mentioned ground product with an acid to obtain an acid-treated product (hereinafter, also referred to as the acid treatment step), and a step of wet-classifying the above-mentioned acid-treated product (hereinafter, also referred to as the classification step).

[0026] As the silicon powder, silicon powder with a low oxygen concentration may be used. The upper limit value of the oxygen concentration of the silicon powder may be, for example, 0.40 mass% or less, 0.30 mass% or less, or 0.20 mass% or less. By setting the oxygen concentration of the silicon powder within the above range, the oxygen amount inside the obtained silicon nitride powder can be further reduced. The lower limit value of the oxygen concentration of the silicon powder may be, for example, 0.10 mass% or more, or 0.15 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 mass%.

[0027] The oxygen concentration of the silicon powder in this specification means a value measured by the infrared absorption method.

[0028] Commercially available silicon powder can be used, or silicon powder prepared separately may also be used. When the oxygen concentration of the silicon powder is high, for example, a pretreatment liquid containing hydrofluoric acid can be used to reduce the amount of oxygen bonded to the silicon powder. For example, the method for producing the silicon nitride powder may further include a pretreatment step of pretreating the silicon powder with a pretreatment liquid containing hydrofluoric acid to obtain silicon powder having an oxygen concentration of 0.40% by mass or more.

[0029] The pretreatment liquid contains hydrofluoric acid, but may be, for example, a mixed acid with an acid such as hydrochloric acid, or may consist only of hydrofluoric acid. The temperature of the pretreatment liquid in the pretreatment step may be, for example, 40 to 80°C. Also, the time for contacting the pretreatment liquid with the silicon powder may be, for example, 1 to 10 hours.

[0030] In the firing step, the silicon powder is fired in a mixed atmosphere containing nitrogen and at least one 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% by 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.

[0031] In the pulverization step, the fired product obtained in the firing step is wet-pulverized to obtain a pulverized product. By pulverizing the fired product and adjusting the particle size, it becomes easy to control the surface treatment with acid in the subsequent acid treatment step, and it becomes easy to control the amount of surface oxygen in the primary particles of silicon nitride. When the fired product containing silicon nitride obtained in the firing step is in the form of a lump, an ingot, etc., the effect of performing the pulverization step is more remarkable.

[0032] The pulverization may be carried out in multiple stages such as coarse pulverization and fine pulverization. The pulverization step may include, for example, a dry pulverization step. In that case, the pulverization step may be a step of performing wet pulverization after dry pulverization. The medium used for wet pulverization may be, for example, water or the like.

[0033] For pulverization, for example, a ball mill or the like can be used. When using a ball mill, the filling rate of the balls in the container can be adjusted according to the desired particle size distribution of the silicon nitride powder. The lower limit value of the filling rate of the balls in the container may be, for example, 40% by volume or more, 45% by volume or more, 50% by volume or more, or 60% by volume or more based on the volume of the container. The upper limit value of the filling rate of the balls in the container may be, for example, 70% by volume or less, or 65% by volume or less based on the volume of the container.

[0034] The lower limit value of the pulverization treatment time (pulverization time) in the pulverization process 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 value of the pulverization time within the above range, the pulverized product can be made sufficiently fine, and the acid treatment efficiency in the acid treatment step can be further improved. The upper limit value of the pulverization treatment 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 value of the pulverization time within the above range, the fired product can be sufficiently pulverized, and excessive pulverization can also be prevented. The pulverization time can be adjusted within the above range, for example, 5 to 15 hours, or 8 to 12 hours.

[0035] In the acid treatment step, the pulverized product is brought into contact with an acid for treatment to obtain an acid-treated product. Examples of the acid include hydrogen fluoride and hydrogen chloride. The acid may be a mixed acid of hydrogen fluoride and hydrogen chloride, or either hydrogen fluoride or hydrogen chloride alone, but preferably contains hydrogen fluoride. The acid may be an aqueous solution (for example, hydrofluoric acid or hydrochloric acid).

[0036] The upper limit of the concentration of the acid (e.g., hydrofluoric acid) 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 concentration of the acid 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 concentration of the acid within the above range, insufficient acid treatment can be prevented. The concentration of the acid may be adjusted within the above range, for example, 10 - 55% by mass, 11 - 38% by mass, or 12 - 30% by mass.

[0037] The means of contact between the pulverized material and the acid may be, for example, a method of dispersing the pulverized material in the acid.

[0038] 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 range, for example, 40 - 80°C, 45 - 75°C, or 50 - 70°C.

[0039] In the acid treatment step, the lower limit of the time (acid treatment time) for contacting the fired product or the pulverized material obtained by pulverizing the fired product with the 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 above 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 above acid treatment time may be adjusted within the above range, for example, 1.0 - 10.0 hours, 1.2 - 9.7 hours, or 2.0 - 8.0 hours.

[0040] In the classification step, the acid-treated product prepared through the pulverization step and the acid treatment step is further classified wet to prepare silicon nitride powder having a desired particle size distribution. For example, coarse powder can be removed to adjust the D90 of the silicon nitride powder. Wet classification can be performed, for example, by centrifugation or the like. As the centrifuge, for example, a liquid cyclone (manufactured by Murata Manufacturing Co., Ltd., product name: 3-liquid classification cyclone TR-10 type) or the like can be used. 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.

[0041] The silicon nitride powder obtained by the above manufacturing method is excellent in sinterability. That is, the above silicon nitride powder can be suitably used as a sintered body raw material.

[0042] One embodiment of the method for manufacturing a silicon nitride sintered body has a step of molding and firing a sintering raw material containing the above silicon nitride powder.

[0043] In addition to the silicon nitride powder, the sintering raw material may contain an oxide-based sintering aid. Examples of the oxide-based sintering aid include Y2O 3、 MgO, Al2O3, and the like. The content of the oxide-based sintering aid in the sintering raw material can be, for example, 3 to 10 mass%.

[0044] In the above step, the above sintering raw material is pressurized 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. Also, it may be fired while being molded by hot pressing. The firing of the molded body may be performed in an inert gas atmosphere such as nitrogen gas or argon gas. The pressure during firing can be 0.7 to 1.0 MPa. The firing temperature can be 1860 to 2100 °C, or may be 1880 to 2000 °C. The firing time at the firing temperature can be 6 to 20 hours, or may be 8 to 16 hours. The heating rate to the firing temperature can be, for example, 1.0 to 10.0 °C / hour.

[0045] The obtained silicon nitride sintered body has a reduced grain boundary phase and a dense structure, and thus can exhibit excellent thermal conductivity and flexural strength.

[0046] The thermal conductivity of the silicon nitride sintered body 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 at 25°C. The thermal conductivity of the silicon nitride sintered body in this specification means a value obtained by measuring the thermal diffusivity and specific heat capacity by 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.

[0047] The flexural 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. The flexural strength of the silicon nitride sintered body in this specification means the three-point flexural strength measured at room temperature after preparing a test piece for strength measurement in accordance with JIS R1601:2008.

[0048] As described above, several embodiments have been described, but the present disclosure is not limited to the above embodiments at all. Also, the description contents of the above-described embodiments can be applied to each other.

Examples

[0049] Hereinafter, the content of the present disclosure will be described in more detail with reference to Examples and Comparative Examples. However, the present disclosure is not limited to the following Examples.

[0050] (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 whose temperature was adjusted to 60°C, maintained at 60°C, and pretreated for 2 hours. As the above mixed acid, a mixture of commercially available hydrochloric acid (concentration: 35% by mass) and hydrofluoric acid (concentration: 55% by mass) at a mass ratio of 10:1 was used. Then, the silicon powder was taken out 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 the infrared absorption method.

[0051] Using the dried silicon powder, a molded body (bulk density: 1.4 g / cm 3 ) was produced. The obtained molded body was placed still in an electric furnace and fired at 1400°C for 60 hours to produce a fired body containing silicon nitride. As the atmosphere during firing, a mixed gas of nitrogen and hydrogen (a mixed gas in which N2 and H2 were mixed so that the volume ratio in the standard state was 80:20) was supplied. After the obtained fired body was coarsely pulverized, it was wet pulverized with a ball mill. For the wet pulverization, the filling rate of the balls with respect to the container was 60% by volume, water was used as the solvent, and the pulverization time was 8 hours.

[0052] The silicon nitride powder obtained by wet pulverization was immersed in hydrofluoric acid (hydrofluoric acid concentration: 15% by mass) at a temperature of 60°C for 2 hours for acid treatment. Then, the silicon nitride powder was taken out from the hydrofluoric acid and washed with water. Further, water was added to the silicon nitride powder, and wet classification was performed under the condition of 0.5 MPa, and the supernatant was removed and dried under a nitrogen atmosphere. Thus, silicon nitride powder was obtained.

[0053] <Evaluation of silicon nitride powder: Measurement of D10, D50, and D90> The D10, D50, and D90 of the silicon nitride powder were measured by the laser diffraction scattering method in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - Laser diffraction / scattering method". For the measurement, a laser diffraction scattering method particle size distribution measuring device (manufactured by Beckman Coulter, trade name: LS-13 320) was used.

[0054] <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.

[0055] <Evaluation of Silicon Nitride Powder: Measurement of Surface Oxygen Content> The surface oxygen content was measured using an oxygen / nitrogen simultaneous analyzer (manufactured by Horiba, Ltd., model name: EMGA-920). Specifically, the silicon nitride powder was heated from 20°C to 2000°C at a heating rate of 8°C / second in a helium atmosphere, and the oxygen content before nitrogen was detected was quantified for measurement.

[0056] [Manufacture 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, methanol was added, and wet mixing was carried out for 4 hours. Then, the mixed powder (firing raw material) obtained by drying was die-molded at a pressure of 10 MPa, and then cold isostatic pressing (CIP) was carried out at a pressure of 25 MPa. The obtained molded body was set in a carbon crucible together with a packing powder composed of a mixed powder of silicon nitride powder and BN powder, and fired at a temperature of 1900°C for 12 hours in a nitrogen pressurized atmosphere of 1 MPa to manufacture a silicon nitride sintered body.

[0057] <Measurement of Thermal Conductivity of Silicon Nitride Sintered Body> The silicon nitride sintered body was ground to produce a 10 mmφ × 3 mm disk for measuring thermal conductivity. The thermal diffusivity and specific heat capacity were measured by the laser flash method (in accordance with JIS R1611), and the product of the density, thermal diffusivity, and specific heat capacity of the sintered body was calculated to obtain the thermal conductivity at room temperature. The results are shown in Table 1. In Table 1, the measurement results of the thermal conductivity are shown as relative values based on the silicon nitride sintered body prepared in Comparative Example 1 described later.

[0058] <Measurement of Bending Strength of Silicon Nitride Sintered Body> A silicon nitride sintered body was used to prepare test pieces for strength measurement in accordance with JIS R1601:2008, and the three-point bending strength at room temperature was measured. The results are shown in Table 1. In Table 1, the measurement results of the bending strength are shown as relative values based on the silicon nitride sintered body prepared in Comparative Example 1 described below.

[0059] <Evaluation of Silicon Nitride Sintered Body> The silicon nitride sintered body was evaluated according to the following criteria. A: The thermal conductivity (relative value) is 1.20 or more, and the bending strength (relative value) is 1.10 or more. B: The thermal conductivity (relative value) is 1.20 or more, and the bending strength (relative value) is 1.05 or more and less than 1.10, or the thermal conductivity (relative value) is 1.10 or more and less than 1.20, and the bending strength (relative value) is 1.10 or more. C: The thermal conductivity (relative value) is 1.10 or more and less than 1.20, and the bending strength (relative value) is 1.05 or more and less than 1.10. D: The thermal conductivity (relative value) is less than 1.10, or the bending strength (relative value) is less than 1.05.

[0060] (Example 2) Silicon nitride powder was prepared in the same manner as in Example 1, except that the conditions of wet classification were changed to those described 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.

[0061] (Example 3) Silicon nitride powder was prepared in the same manner as in Example 1, except that the conditions of wet grinding were changed to those described 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.

[0062] (Comparative Example 1) Silicon nitride powder was prepared in the same manner as in Example 1, except that the conditions of wet classification were changed to those described 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.

[0063]

Table 1

Industrial Applicability

[0064] According to the present disclosure, it is possible to provide a silicon nitride powder capable of manufacturing a sintered body excellent in thermal conductivity and bending strength. According to the present disclosure, it is also possible to provide a method for manufacturing a silicon nitride sintered body excellent in thermal conductivity and bending strength.

Claims

1. comprising primary particles of silicon nitride, The BET specific surface area is 8.0 to 15.0 m ２ / g, and having an oxygen content on the surface of 0.30 to 0.70 mass%, in the particle size distribution curve of volume basis measured by the laser diffraction / scattering method, when the particle sizes at which the cumulative values from the small particle size reach 10% and 90% of the whole are defined as D10 and D90, respectively, the difference between D90 and D10 is 1.52 μm or more and 1.70 μm or less, silicon nitride powder for sintered body raw material.

2. The silicon nitride powder for sintered body raw material according to claim 1, wherein D90 is 2.00 μm or less.

3. A method for manufacturing a silicon nitride sintered body, comprising a step of molding and firing a sintered raw material containing the silicon nitride powder for sintered body raw material according to claim 1 or 2.

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