Silicon carbide powder and production method for same

Abstract

The present invention provides: a silicon carbide powder which is unlikely to cause thickening even when added to a different material that is liquid, such as a liquid resin or molten metal; and a production method for the same. Provided is a silicon carbide powder comprising primary particles of silicon carbide for which the crystal system is α-type, wherein at least one element selected from aluminum, yttrium, and ytterbium is contained on the surfaces of the primary particles of silicon carbide, and the Hausner ratio of the silicon carbide powder is not more than 2.1.

Description

Silicon carbide powder and its manufacturing method

[0001] The present invention relates to silicon carbide powder and a method for producing the same.

[0002] Silicon carbide (SiC) has many excellent properties, such as high thermal conductivity, microwave heating properties, low specific gravity, low thermal expansion coefficient, and high mechanical properties (hardness and rigidity), and is therefore sometimes used in combination with other materials to impart these properties. For example, silicon carbide may be blended with other materials such as resins as a heat-dissipating filler or resin reinforcement, or silicon carbide may be mixed with other materials such as metals to produce heat-generating materials or metal matrix composites (MMCs).

[0003] When silicon carbide powder is mixed with a liquid dissimilar material (e.g., liquid resin, molten metal) to form a mixture and a composite material is produced from this mixture, if the shape of the primary silicon carbide particles contained in the powder is low in sphericity (a shape with many corners on the particle surface) rather than high in sphericity (a shape with few corners on the particle surface), the addition of the silicon carbide powder can cause an increase in viscosity, which can result in the viscosity of the mixture being significantly higher than the viscosity of the liquid dissimilar material. This can lead to problems such as difficulty in densely filling the liquid dissimilar material with silicon carbide powder and poor processability when molding the mixture.

[0004] Silicon carbide produced using an Acheson furnace has an α-type silicon carbide crystal system (α-SiC), but because it is powdered by a pulverization method, the primary particles of the obtained silicon carbide have a low spherical shape. Methods for removing corners from the surfaces of primary particles of silicon carbide with a low spherical shape to give them a high spherical shape include a milling method using a millstone or the like and a particle collision method using a jet mill or the like (see, for example, Patent Document 1).

[0005] However, since silicon carbide has a high hardness and it is not easy to sufficiently remove the corners from the surface of the primary particles of silicon carbide to form a highly spherical shape, mechanical processing methods such as grinding and particle collision methods may cause the addition of silicon carbide powder to thicken the liquid heterogeneous material, resulting in a significant increase in the viscosity of the mixture. Furthermore, with the above-mentioned mechanical processing methods, there is a risk that foreign matter may be mixed into the silicon carbide powder from the mechanical processing device, and that fine particles such as chippings generated when mechanical energy is applied to the primary particles of silicon carbide may contribute to the thickening of the liquid heterogeneous material due to the addition of silicon carbide powder.

[0006] Granulation sintering is considered to be a method for converting primary particles of silicon carbide, which have a low sphericity, into a highly spherical shape. However, because silicon carbide is difficult to sinter, it is thought to be difficult to convert primary particles of silicon carbide into a shape that is sufficiently dense and has a high degree of sphericity using granulation sintering.

[0007] JP 2013-245374 A

[0008] An object of the present invention is to provide a silicon carbide powder that is less likely to cause thickening when added to a different liquid material such as a liquid resin or molten metal, and a method for producing the same.

[0009] The silicon carbide powder according to one embodiment of the present invention is a silicon carbide powder containing primary particles of silicon carbide having an α-type crystal system, wherein the primary particles of silicon carbide contain at least one element selected from the group consisting of aluminum, yttrium, and ytterbium on their surfaces, and the Hausner ratio of the silicon carbide powder is 2.1 or less.

[0010] Another aspect of the present invention provides a method for producing silicon carbide powder, which includes mixing a metal-containing substance with silicon carbide powder as a raw material, and subjecting the mixed raw material silicon carbide powder and metal-containing substance to heat treatment, wherein the silicon carbide powder after heat treatment has a Hausner ratio of 2.1 or less.

[0011] According to the present invention, it is possible to provide a silicon carbide powder that is unlikely to cause thickening when added to a different liquid material such as a liquid resin or molten metal.

[0012] An embodiment of the present invention will be described in detail. Note that the following embodiment shows an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications and improvements can be made to the following embodiment, and such modifications and improvements can also be included in the present invention.

[0013] The silicon carbide powder according to this embodiment is a silicon carbide powder containing primary particles of silicon carbide having an α-type crystal system, the primary particles of silicon carbide containing at least one element selected from the group consisting of aluminum, yttrium, and ytterbium on the surface, and the Hausner ratio of the silicon carbide powder being 2.1 or less.

[0014] The present inventors have found that silicon carbide powder containing at least one element selected from the group consisting of aluminum, yttrium, and ytterbium on the surfaces of silicon carbide primary particles and having a Hausner ratio of 2.1 or less tends to be less likely to cause thickening when added to a liquid dissimilar material (e.g., liquid resin, molten metal). Thus, the viscosity of a mixture of silicon carbide powder and a liquid dissimilar material according to this embodiment is approximately the same as the original viscosity of the liquid dissimilar material, or even if thickening occurs, it is unlikely to be significantly increased.

[0015] The silicon carbide powder according to this embodiment preferably does not contain granules or agglomerates, and more preferably consists of primary particles. Furthermore, the primary particles of silicon carbide contained in the silicon carbide powder according to this embodiment tend to have high thermal conductivity due to the presence of at least one element selected from aluminum, yttrium, and ytterbium on their surfaces. For example, when used as a filler for a heat dissipation sheet, high heat dissipation properties can be expected. The presence of at least one element selected from aluminum, yttrium, and ytterbium on the surface of the silicon carbide powder according to this embodiment can be determined by the presence or absence of peaks for each element obtained by performing elemental analysis on the surface of the primary particles of the silicon carbide powder using a scanning electron microscope and an energy dispersive X-ray analyzer. Here, the term "surface" refers to the portion extending from the outermost surface to a depth of about 5 μm.

[0016] The Hausner ratio of the silicon carbide powder according to this embodiment must be 2.1 or less, but may be 1.8 or less, or may be 1.0 or more, and is preferably 1.1 or more.

[0017] The Hausner ratio is the ratio of tapped density to loose bulk density (i.e., tapped density / loose bulk density). Here, loose bulk density is the bulk density when a powder is allowed to fall freely into a container of a fixed volume and filled to capacity, and the container volume is taken as the powder volume. Furthermore, tapped density is the bulk density when the powder is filled into a container and then mechanically tapped to crush the voids between the particles and densely pack the powder.

[0018] The silicon carbide powder according to this embodiment has a low Hausner ratio of 2.1 or less, and therefore can be highly filled into a liquid dissimilar material. Furthermore, the mixture of the silicon carbide powder according to this embodiment and a liquid dissimilar material has good processability when molding.

[0019] Therefore, by adding the silicon carbide powder according to this embodiment to a liquid dissimilar material, it is possible to impart to the liquid dissimilar material excellent properties such as high thermal conductivity, microwave heating properties, low specific gravity, low thermal expansion coefficient, high mechanical properties (hardness, rigidity), etc. Furthermore, a composite material having the above-mentioned excellent properties can be produced from a mixture of the silicon carbide powder according to this embodiment and a liquid dissimilar material.

[0020] The liquid dissimilar material to be mixed with the silicon carbide powder according to this embodiment is not particularly limited, but examples thereof include liquid resins and molten metals. Examples of liquid resins include silicone resins, epoxy resins, acrylic resins, and polyurethanes, and examples of molten metals include aluminum, silicon, copper, magnesium, and alloys containing these metals.

[0021] The loose bulk density and tap density of the silicon carbide powder according to this embodiment can be measured based on JIS R 1628. The loose bulk density is calculated by using a metal container as a measuring container, allowing the powder to fall naturally until the container is full, scraping off the powder that protrudes from the top of the container with a plate, measuring the powder mass, and dividing the powder mass by the powder volume.

[0022] The tap density is calculated by measuring the powder mass and volume after placing a powder sample in a measuring container and mechanically tapping it until almost no change in the powder volume is observed, and then dividing the powder mass by the powder volume. Mechanical tapping is performed by lifting the container and dropping it a predetermined distance under its own weight. In order to minimize the separation of lumps that occurs during tapping, it is recommended to rotate the container during tapping.

[0023] The number of small corners among the corners on the surface of the primary particles of silicon carbide contained in the silicon carbide powder according to this embodiment may be 2.8 or less per primary particle. When the number of small corners among the corners on the surface of the primary particles of silicon carbide contained in the silicon carbide powder is 2.8 or less, the shape of the primary particles of silicon carbide has a high degree of sphericity, and therefore, even when added to a liquid heterogeneous material, it tends to be less likely to cause thickening. Here, a corner refers to a point where the outline of the primary particle in the projected image of the primary particle changes at an angle, and the angle is an interior angle facing inward toward the outline of the primary particle that is greater than 0° and less than 180°. Note that the outline forming the corner may be straight or rounded. Furthermore, a small corner is a corner present in the outline of the primary particle in the projected image of the primary particle, where twice the radius of curvature of the corner is less than 1 / 5 of the Heywood diameter of the projected image of the primary particle.

[0024] The Heywood diameter, also known as the diameter of a circle equivalent to the projected area of ​​a particle determined by image analysis, refers to the diameter of a circle having the same area as the projected area of ​​the particle. The silicon carbide powder according to this embodiment is primarily composed of primary particles of silicon carbide. A primary particle is a unit particle in terms of its geometric appearance, and refers to the smallest independent particle without agglomeration.

[0025] The number of small corners on the surface of the silicon carbide primary particles contained in silicon carbide powder can be measured, for example, as follows. The silicon carbide powder is observed using an electron microscope to obtain a secondary electron image of the silicon carbide primary particles, and the secondary electron image is analyzed using image analysis software. In the image analysis, a projection image of any one primary particle is obtained from the secondary electron image, and the radius of curvature of the corners present on the outline of the primary particle in the projection image (the radius of the largest circle that can touch the inside of the corner) is measured.

[0026] The shape of the projected image of the primary particle of silicon carbide is approximately polygonal, and each primary particle has multiple corners, but only the corners between the sides of the approximately polygon are the subject of analysis (measurement of the radius of curvature), and the minute irregularities formed along the sides are not the subject of analysis. The minute irregularities refer to corners that are so small that they cannot be distinguished from corners with the naked eye in the projected image of the primary particle obtained under the following measurement conditions.

[0027] The number of small corners among the corners on the surface of the primary particles of silicon carbide contained in the silicon carbide powder according to this embodiment is measured according to the following procedures <1> to <5>. [Measurement conditions] <1> The particle diameters D10%, D50%, and D90% of the silicon carbide powder to be measured (analyzed) are measured using a laser diffraction / scattering particle size distribution analyzer LA-300 manufactured by HORIBA, Ltd. Note that D10%, D50%, and D90% refer to particle diameters at which the cumulative particle volume from the small particle size side in the volume-based cumulative particle size distribution measured using the laser diffraction / scattering particle size distribution analyzer LA-300 manufactured by HORIBA, Ltd. is 10%, 50%, and 90%, respectively, of the total particle volume. Furthermore, when D50% measured using a laser diffraction / scattering particle size distribution analyzer LA-300 manufactured by Horiba, Ltd. is 150 nm or more, D10%, D50%, and D90% are measured using a laser diffraction / scattering particle size distribution analyzer Microtrac MT3300EXII manufactured by Microtrac Corporation.

[0028] <2> A secondary electron image of the silicon carbide primary particles is obtained using an electron microscope (Thermo Fisher Scientific, Phenom Pro-X tabletop scanning electron microscope, electron acceleration voltage 10 kV). The magnification is one of the following (i) to (iii): (i) For powders with a D50% of 100 μm or more, the magnification is 300x. (ii) For powders with a D50% of 40 μm or more but less than 100 μm, the magnification is 1000x. (iii) For powders with a D50% of less than 40 μm, the magnification is 2000x.

[0029] <3> The secondary electron image is analyzed using image analysis software Mac-View manufactured by Mountech Co., Ltd., to obtain projection images of 100 or more random primary particles of silicon carbide in the secondary electron image.

[0030] <4> Further, image analysis is performed to calculate the Heywood diameter R for the projected image of the primary particles whose corner curvature radius has been measured. That is, the diameter of a circle having the same area as the area of ​​the projected image of the primary particles is calculated. Then, for the projected image of the primary particles, the number of corners whose twice the curvature radius is one-fifth or less of the Heywood diameter R (hereinafter referred to as "small corners") is counted.

[0031] <5> The same analysis as above is performed on each of the projection images of a plurality of primary particles (for example, 50 particles) in the secondary electron image, the radius of curvature of the corners is measured, the Heywood diameter R is calculated, and the number of small corners is counted. Then, the average value of the number of small corners for the plurality of primary particles is calculated, and the number of small corners per primary particle is calculated.

[0032] The silicon carbide powder according to this embodiment has a particle diameter D50%, where the cumulative particle volume from the small particle side in the volume-based cumulative particle diameter distribution is 50% of the total particle volume, of 1 μm or more, 10 μm or more, or 15 μm or more. Furthermore, the particle diameter D50% may be 300 μm or less, or 250 μm or less. When the particle diameter D50% is 1 μm or more, the silicon carbide powder according to this embodiment tends to be less likely to cause thickening when added to a liquid heterogeneous material such as a liquid resin or molten metal. The method for measuring the particle diameter D50% of the silicon carbide powder according to this embodiment is not particularly limited, but can be measured, for example, by laser diffraction / scattering.

[0033] The thickening property of the silicon carbide powder according to this embodiment can be evaluated by measuring and comparing the viscosity of the resin composition obtained by mixing it with a liquid resin and the viscosity of the liquid resin before mixing. For example, the viscosity of a resin composition obtained by mixing 73 parts by mass of the silicon carbide powder according to this embodiment with 27 parts by mass of a silicone resin and the viscosity of the silicone resin alone were measured at a measurement temperature of 25°C and a shear rate of 1 s －１The thickening property of the silicon carbide powder according to this embodiment can be evaluated by measuring the viscosity of the silicon carbide powder with a rheometer at 1000 kJ / cm2 and comparing the viscosity of the silicon carbide powder with the rheometer. When the silicon carbide powder contains at least one element selected from aluminum, yttrium, and ytterbium on its surface and has a Hausner ratio of 2.1 or less, the silicon carbide powder is unlikely to cause thickening even when added to a liquid dissimilar material such as a liquid resin or molten metal.

[0034] The shear properties of the silicon carbide powder according to this embodiment can be evaluated by measuring kinetic friction. For example, for the silicon carbide powder according to this embodiment, a powder bed shear force measuring device manufactured by Nano Seeds Co., Ltd. is used to apply shear to a stationary powder bed while applying a predetermined normal stress to the powder bed, and the critical state line (CSL) at which the powder bed collapses is measured. The kinetic friction angle between the powder beds is defined as the angle between the obtained CSL and the normal stress axis. Here, the CSL is a line passing through the origin with the shear stress and normal stress as its axes.

[0035] The silicon carbide powder according to this embodiment is mainly composed of silicon carbide containing at least one element selected from the group consisting of aluminum, yttrium, and ytterbium on the particle surface, but may contain elements other than silicon, carbon, aluminum, yttrium, and ytterbium, such as beryllium, magnesium, and boron.

[0036] The silicon carbide powder of this embodiment can be produced by the following method, which includes mixing a metal-containing substance with silicon carbide powder as a raw material and heat treating the mixed silicon carbide powder and metal-containing substance as raw materials, such that the Hausner ratio of the silicon carbide powder after heat treatment is 2.1 or less.

[0037] According to the method for producing silicon carbide powder of this embodiment, even if silicon carbide has high hardness, the silicon carbide powder of this embodiment can be easily produced. In the method for producing silicon carbide powder of this embodiment, silicon carbide powder that does not easily cause thickening even when added to a liquid heterogeneous material can be produced simply by mixing the raw material silicon carbide powder and a metal-containing substance and heat-treating the mixture. Therefore, the silicon carbide powder of this embodiment can be produced more easily than the above-mentioned mechanical processing method, which requires sufficient removal of corners from the surfaces of the silicon carbide primary particles to give them a highly spherical shape.

[0038] According to the method for producing silicon carbide powder of this embodiment, foreign matter is less likely to be mixed into the silicon carbide powder during processing compared to the mechanical processing method described above. Furthermore, according to the method for producing silicon carbide powder of this embodiment, chipping or other fine particles are less likely to occur in the primary particles of silicon carbide during processing. In addition, the method for producing silicon carbide powder of this embodiment can produce the silicon carbide powder of this embodiment in a method easier than granulation sintering.

[0039] The conditions for the heat treatment are not particularly limited, but the temperature condition may be 1700°C or higher and 2300°C or lower, 1750°C or higher and 2250°C or lower, or 1800°C or higher and 2200°C or lower. The atmosphere during the heat treatment is preferably an inert gas atmosphere. The type of inert gas is not particularly limited, but examples include nitrogen gas, helium, argon, neon, xenon, and krypton.

[0040] When producing the silicon carbide powder according to this embodiment, a liquid phase forming additive may be mixed as a metal-containing substance into the silicon carbide powder as a raw material and then subjected to a heat treatment step. When the liquid phase forming additive is mixed into the silicon carbide powder, the liquid phase forming additive adheres to the surfaces of the silicon carbide primary particles. When heat treatment is performed in a state in which the liquid phase forming additive is adhered, the liquid phase forming additive reacts with the silicon dioxide present on the surfaces of the silicon carbide primary particles at a high temperature to form a molten liquid (liquid phase) of the mixture, and this molten liquid covers the surfaces of the silicon carbide primary particles.

[0041] The surfaces of the silicon carbide primary particles are covered with the molten liquid, which promotes atomic diffusion and mass transfer, causing the silicon carbide to dissolve in the molten liquid. The surface tension of the molten liquid with the silicon carbide dissolved in it causes the outer shape of the silicon carbide primary particles to become highly spherical, and as the molten liquid solidifies, a thin film is formed, resulting in primary particles with a highly spherical shape.

[0042] The types of the metal-containing substance and the liquid phase forming assistant used as the metal-containing substance are not particularly limited, but examples thereof include aluminum-containing substances, yttrium-containing substances, and ytterbium-containing substances. Examples of the aluminum-containing substance, yttrium-containing substance, and ytterbium-containing substance include aluminum salts, yttrium salts, ytterbium salts, aluminum oxide, yttrium oxide, and ytterbium oxide. Specific examples of aluminum salts include aluminum nitrate (Al(NO ３ ) ３ ), aluminum chloride, aluminum sulfate, aluminum acetate, aluminum lactate, and hydrates of these aluminum salts.

[0043] Since the silicon carbide powder that has undergone the heat treatment step may have agglomerated primary particles, after the heat treatment step, the silicon carbide powder may be crushed using a centrifugal crusher or classified using a sieve.

[0044] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples.

[0045] Example 1 A mixed powder was obtained by dry-mixing 100 parts by mass of silicon carbide powder having an α-type crystal system and a particle size D50% of 12 μm with 0.22 parts by mass of aluminum oxide, and then heat-treating the mixed powder at 1830° C. for 4 hours in an argon atmosphere.

[0046] Since the mixed powder after the heat treatment had agglomerated primary particles in some places, it was crushed using a centrifugal crusher and classified (removed agglomerates) using a sieve with 32 μm openings to obtain the silicon carbide powder of Example 1. The rotation speed of the centrifugal crusher was 18,000 rpm.

[0047] (Example 2) Silicon carbide powder of Example 2 was obtained in the same manner as in Example 1, except that silicon carbide powder having an α-type crystal system and a particle size D50% of 15 μm was used as the raw material, the heat treatment temperature was 1920 ° C, and the mesh size of the sieve used for classification was 45 μm.

[0048] (Examples 3 and 4) Silicon carbide powders having different particle diameters D50% were used as raw materials, the rotation speed of the centrifugal crusher was 12000 rpm, and the mesh size of the sieve during classification was 53 μm. Silicon carbide powders of Examples 3 and 4 were produced in the same manner as in Example 2.

[0049] (Example 5) Silicon carbide powder having a particle diameter D50% of 51 μm was used as a raw material, the heat treatment temperature was 2000 ° C., the rotation speed of the centrifugal crusher was 6000 rpm, the mesh size of the sieve used for classification was 90 μm, and the silicon carbide powder of Example 5 was produced in the same manner as in Example 1, except that classification (removal of fine particles) was performed using a sieve with a mesh size of 32 μm.

[0050] (Example 6) Silicon carbide powder of Example 6 was produced in the same manner as in Example 5, except that silicon carbide powder having a particle diameter D50% of 62 μm was used as the raw material and the heat treatment temperature was 2040 ° C.

[0051] (Example 7) Silicon carbide powder of Example 7 was produced in the same manner as in Example 4, except that silicon carbide powder having a particle diameter D50% of 124 μm was used as the raw material, the heat treatment temperature was 2110 ° C, the rotation speed of the centrifugal crusher was 6000 rpm, and the mesh size of the sieve during classification was 180 μm.

[0052] (Example 8) Silicon carbide powder of Example 8 was produced in the same manner as in Example 7, except that silicon carbide powder having a particle diameter D50% of 240 μm was used as the raw material, the rotation speed of the centrifugal crusher was 8000 rpm, and classification by sieve was not performed.

[0053] Comparative Example 1 Silicon carbide powder having an α-type crystal system and a particle size D50% of 15 μm was prepared and used as the silicon carbide powder of Comparative Example 1.

[0054] (Presence or absence of aluminum element on silicon carbide particle surface) Elemental analysis was performed on the primary particle surfaces of the silicon carbide powders obtained in Examples 1 to 8 and Comparative Example 1 using a scanning electron microscope SU8000 manufactured by Hitachi High-Tech Corporation and an energy dispersive X-ray analyzer X-Max 80 manufactured by Oxford Instruments Ltd. If a peak attributable to aluminum element was present in the obtained spectrum, it was determined that aluminum element was present on the primary particle surface of the silicon carbide powder. These results are shown in Table 1.

[0055]

[0056] (Hausner Ratio) For the silicon carbide powders obtained in Examples 1 to 8 and Comparative Example 1, the loose bulk density and tapped density were measured using a 30 mL metal container according to JIS R 1628. The Hausner ratio (= tapped density / loose bulk density) was calculated from these measured values. The results are shown in Table 1.

[0057] (Particle size) The particle sizes D10%, D50%, and D90% of the silicon carbide powders obtained in Examples 1 to 8 and Comparative Example 1 were measured using a laser diffraction / scattering particle size distribution analyzer LA-300 manufactured by Horiba, Ltd. In addition, when D50% measured using the laser diffraction / scattering particle size distribution analyzer LA-300 manufactured by Horiba, Ltd. was 150 nm or more, D10%, D50%, and D90% were measured using a laser diffraction / scattering particle size distribution analyzer Microtrac MT3300EXII manufactured by Microtrac Corporation. These results are shown in Table 1.

[0058] (Number of small corners per primary particle of silicon carbide powder) The number of small corners among the corners on the surface of the primary particles of silicon carbide contained in the silicon carbide powders obtained in Examples 1 to 8 and Comparative Example 1 was calculated by image analysis of the secondary electron images of the primary particles of silicon carbide. This is explained in detail below.

[0059] In the image analysis, a projection image of any one primary particle was obtained from the secondary electron image, and the radius of curvature of the corners present on the outline of the primary particle in the projection image (the radius of the largest circle that can touch the inside of the corners) was measured. The shape of the projection image of a silicon carbide primary particle is approximately polygonal, and one primary particle has multiple corners, but only the corners between the sides of the approximately polygon were analyzed (measurement of the radius of curvature), and minute irregularities formed along the sides were not analyzed.

[0060] The projection images of the primary particles for which the radius of curvature of the corners had been measured were further analyzed to calculate the Heywood diameter R, and the number of small corners where twice the radius of curvature was one-fifth or less of the Heywood diameter R was counted. The same analysis as above was performed on each of the projection images of 50 randomly selected primary particles in the secondary electron image to measure the radius of curvature of the corners, calculate the Heywood diameter R, and count the number of small corners. The average number of small corners for the 50 primary particles was then calculated, and the number of small corners per primary particle was calculated. These results are shown in Table 1.

[0061] (Viscosity of Resin Composition) For each of Examples 1 to 8 and Comparative Example 1, 73 parts by mass of silicon carbide powder and 27 parts by mass of a liquid silicone resin were mixed using a planetary centrifugal mixer at a rotational speed of 2000 rpm for 2 minutes to prepare a slurry resin composition. As the silicone resin, silicone oil (dimethyl silicone oil, product name Element 14 PDMS series) manufactured by Momentive Corporation was used.

[0062] The viscosity of the prepared resin composition was measured using a rheometer MCR302 manufactured by Anton Paar. Parallel plates with a diameter of 49.974 mm were used as the measurement jig for the rheometer. The measurement conditions were a measurement temperature of 25°C, a shear rate of 1 s －１ The gap between the parallel plates was set to 1 mm. The results are shown in Table 1.

[0063] The viscosity of the silicone oil used in the resin composition at 25° C. was measured in the same manner as for the resin composition and was found to be 1.1 Pa·s.

[0064] (Dynamic Friction Angle) For the silicon carbide powders of Examples 1 to 8 and Comparative Example 1, the kinetic friction angle was measured using a powder bed shear force measuring device NS-S500 manufactured by Nano Seeds Co., Ltd. Specifically, shear was applied to a stationary powder bed while a predetermined normal stress was applied, the critical state line (CSL) at which the powder bed collapsed was measured, and the kinetic friction angle between the powder layers, defined as the angle between the CSL and the normal stress axis, was calculated. These results are shown in Table 1.

[0065] (Evaluation) As shown in Table 1, compared to Comparative Example 1 in which aluminum element was not introduced onto the particle surface, Examples 1 to 8 in which aluminum element was introduced onto the particle surface all showed a small increase in viscosity due to the addition of silicon carbide powder, and the viscosity of the resin composition was also low. In particular, in Examples 2 to 8 in which the Hausner ratio was 1.8 or less, the increase in viscosity due to the addition of silicon carbide powder was even smaller, and the viscosity of the resin composition was 55 Pa s or less, which was significantly lower than that of Comparative Example 1 in which aluminum element was not introduced onto the particle surface. Therefore, it is considered that the silicon carbide powders of Examples 1 to 8 are easily highly filled into liquid heterogeneous materials. Furthermore, it is considered that the mixtures of silicon carbide powder and liquid heterogeneous materials of Examples 1 to 8 have good processability during molding.

Claims

1. A silicon carbide powder comprising primary particles of silicon carbide having an α-type crystal system, the primary particles of silicon carbide containing at least one element selected from the group consisting of aluminum, yttrium, and ytterbium on the surface thereof, and the Hausner ratio of the silicon carbide powder being 2.1 or less.

2. The silicon carbide powder according to claim 1, wherein the primary particles of silicon carbide contained in the silicon carbide powder have corners, the number of small corners among the corners is 2.8 or less per primary particle, and the small corners are corners present in the outline of the primary particles in a projected image of the primary particles, and have twice the radius of curvature of 1 / 5 or less of the Heywood diameter of the projected image of the primary particles.

3. A silicon carbide powder according to claim 1 or 2, wherein in a volume-based cumulative particle size distribution, a particle size D50% at which the cumulative particle volume from the small particle size side of the silicon carbide powder is 50% of the total particle volume is 1 μm or more.

4. A method for producing silicon carbide powder, comprising: mixing a metal-containing substance with a raw material silicon carbide powder; and subjecting the mixed raw material silicon carbide powder and the metal-containing substance to a heat treatment, wherein the silicon carbide powder after the heat treatment has a Hausner ratio of 2.1 or less.

5. The method of producing silicon carbide powder according to claim 4, wherein the metal-containing material contains at least one of the elements aluminum, yttrium, and ytterbium.

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