Silicon carbide powder and method for producing same

Abstract

Provided are: a silicon carbide powder which is not susceptible to thickening even when added to a liquid dissimilar material such as a liquid resin or a molten metal; and a method for producing the silicon carbide powder. The silicon carbide powder contains primary particles of silicon carbide having an alpha-type crystal system, the surface of the primary particles of silicon carbide contains at least one element selected from the group consisting of aluminum, yttrium and ytterbium elements, and the Hausner ratio of the silicon carbide powder is 2.1 or less.

Description

TECHNICAL FIELD

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

[0002] Silicon carbide (SiC) has various excellent properties such as high thermal conductivity, microwave heating properties, low specific gravity, low thermal expansion coefficient, high mechanical properties (hardness, rigidity), and the like, and is sometimes used in combination with a dissimilar material as a material for imparting the properties. For example, there are cases where silicon carbide is compounded in a dissimilar material such as a resin as a heat dissipation filler, a resin reinforcing material, and cases where silicon carbide is combined with a dissimilar material such as a metal to produce a heat generating material, a metal matrix composite (MMC).

[0003] In a case where silicon carbide powder is combined with a liquid dissimilar material (for example, a liquid resin, a molten metal) to produce a mixture, and a composite material is produced from the mixture, if the shape of the primary particles of silicon carbide contained in the powder is not a shape with high sphericity (a shape with a small number of corners present on the surface of the particles) but a shape with low sphericity (a shape with a large number of corners present on the surface of the particles), it is likely that thickening is caused by the addition of the silicon carbide powder, and the viscosity of the mixture is significantly higher than the viscosity of the liquid dissimilar material. Therefore, it is likely that problems such as difficulty in highly filling the silicon carbide powder in the liquid dissimilar material, and deterioration of the processability at the time of shaping the mixture occur.

[0004] Silicon carbide produced using an Acheson furnace is silicon carbide of the α-type (α-SiC), but is formed into a powder by a pulverization method, and therefore the shape of the primary particles of the silicon carbide obtained is a shape with low sphericity. As a method for forming a shape with high sphericity by removing corners from the surface of the primary particles of silicon carbide of a shape with low sphericity, a grinding method using a mortar and the like, a particle collision method using a jet mill and the like (for example, refer to Patent Document 1) are known.

[0005] However, silicon carbide has high hardness, and it is not easy to sufficiently remove corners from the surface of the primary particles of silicon carbide to form a shape with high sphericity, and therefore in a mechanical treatment method such as a grinding method, a particle collision method, thickening of a liquid dissimilar material is caused by the addition of the silicon carbide powder, and the viscosity of the mixture is likely to be significantly increased. In addition, in the mechanical treatment method as described above, it is likely that foreign matter is mixed into the silicon carbide powder from the device that performs the mechanical treatment, and it is likely that fine particles such as chippings produced when mechanical energy is applied to the primary particles of silicon carbide contribute to the thickening of the liquid dissimilar material caused by the addition of the silicon carbide powder.

[0006] As a method of making the primary particles of silicon carbide having a low sphericity into a shape having a high sphericity, granulation sintering is considered, but since silicon carbide is difficult to sinter, it is considered that it is difficult to make the primary particles of silicon carbide into a shape that is sufficiently dense and has a high sphericity in granulation sintering.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2013-245374 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] The present application has an object to provide a silicon carbide powder which is less likely to cause thickening even when added to a liquid-state heterogeneous material such as a liquid resin or a molten metal, and a method for producing the same.

[0012] SOLUTION TO PROBLEM

[0013] The silicon carbide powder of one embodiment of the present application is a silicon carbide powder including primary particles of silicon carbide of which crystal system is α-type, the primary particles of silicon carbide include at least one element among aluminum, yttrium, and ytterbium on the surface, and the Hausner ratio of the silicon carbide powder is 2.1 or less.

[0014] The method for producing a silicon carbide powder of another embodiment of the present application includes: mixing a metal-containing substance in a silicon carbide powder as a raw material; and performing heat treatment on the mixed silicon carbide powder as a raw material and the metal-containing substance, and the Hausner ratio of the silicon carbide powder after the heat treatment is 2.1 or less.

[0015] EFFECTS OF THE INVENTION

[0016] According to the present application, a silicon carbide powder which is less likely to cause thickening even when added to a liquid-state heterogeneous material such as a liquid resin or a molten metal can be provided. DETAILED DESCRIPTION

[0017] One embodiment of the present application will be described in detail. Note that the following embodiment represents one example of the present application, and the present application is not limited to the embodiment. In addition, various changes or modifications can be made to the following embodiment, and the embodiments to which such changes or modifications are made can also be included in the present application.

[0018] The silicon carbide powder of one embodiment of the present application is a silicon carbide powder including primary particles of silicon carbide of which crystal system is α-type, the primary particles of silicon carbide include at least one element among aluminum, yttrium, and ytterbium on the surface, and the Hausner ratio of the silicon carbide powder is 2.1 or less.

[0019] The present inventors have found that the silicon carbide powder in which the primary particles of silicon carbide contain at least one of aluminum, yttrium, and ytterbium on the surface and the Hausner ratio of the silicon carbide powder is 2.1 or less has a tendency not to easily cause thickening even when added to a liquid heterogeneous material such as a liquid resin or a molten metal. Thus, the viscosity of the mixture of the silicon carbide powder of the present embodiment and the liquid heterogeneous material is equivalent to the original viscosity of the liquid heterogeneous material, or even if thickening occurs, the thickening is not easily large.

[0020] The silicon carbide powder of the present embodiment preferably does not contain particles or agglomerated particles, and is further preferably composed of primary particles. Further, the primary particles of silicon carbide contained in the silicon carbide powder of the present embodiment have a high thermal conductivity by the presence of at least one of aluminum, yttrium, and ytterbium on the surface, and thus, for example, in the case of use as a filler for a heat sink, a high heat dissipation property can be expected. As to the presence of at least one of aluminum, yttrium, and ytterbium on the surface of the primary particles of the silicon carbide powder of the present embodiment, the presence or absence of a peak of each element can be determined by elemental analysis using a scanning electron microscope and an energy dispersive X-ray analyzer on the surface of the primary particles of the silicon carbide powder as an object. Here, the surface refers to a portion from the outermost surface to a depth of about 5 μm.

[0021] The Hausner ratio of the silicon carbide powder of the present embodiment needs to be 2.1 or less, can be 1.8 or less, and can be 1.0 or more, and is more preferably 1.1 or more.

[0022] The Hausner ratio refers to the ratio of the tap density to the loose bulk density (i.e., tap density / loose bulk density). Here, the loose bulk density refers to the bulk density when a powder is naturally dropped into a container of a certain volume and filled to the brim, and the volume of the container is taken as the volume of the powder. Further, the tap density refers to the bulk density when the powder is mechanically tapped after being filled in a container, and the voids between the particles are filled to be tightly packed.

[0023] The silicon carbide powder of the present embodiment can be highly filled with a liquid heterogeneous material because the Hausner ratio is as low as 2.1 or less. Further, the mixture of the silicon carbide powder of the present embodiment and the liquid heterogeneous material has good processability at the time of molding.

[0024] Thus, by adding the silicon carbide powder of the present embodiment to a liquid heterogeneous material, the liquid heterogeneous material can be endowed with excellent properties such as high thermal conductivity, microwave heating properties, low specific gravity, low thermal expansion coefficient, and high mechanical properties (hardness, rigidity). Further, a composite material having the above excellent properties can be produced from the mixture of the silicon carbide powder of the present embodiment and the liquid heterogeneous material.

[0025] The liquid foreign material mixed with the silicon carbide powder of the present embodiment is not particularly limited, and examples thereof include a liquid resin and a molten metal. Examples of the liquid resin include silicone resin, epoxy resin, acrylic resin, and polyurethane. Examples of the molten metal include aluminum, silicon, copper, and magnesium, and alloys containing these metals.

[0026] The bulk density and the tap density of the silicon carbide powder of the present embodiment can be measured based on JIS R 1628. The bulk density is calculated by measuring the mass of the powder after the powder is naturally dropped into a metal container as a measuring container until the container is filled, and the powder overflowing from the upper end of the container is scraped off with a plate, and dividing the mass of the powder by the volume of the powder.

[0027] The tap density is calculated by measuring the mass and the volume of the powder after the powder sample is dropped into a measuring container and mechanically tapped until the volume of the powder is hardly confirmed to change, and dividing the mass of the powder by the volume of the powder. The mechanical tapping is performed by lifting the container and dropping it by its own weight over a predetermined distance. In order to minimize the separation of the lumps generated in the tapping, the container can be rotated during the tapping.

[0028] The number of small corners of the corners possessed by the primary particles of silicon carbide included in the silicon carbide powder of the present embodiment can be 2.8 or less per primary particle. In the case where the number of small corners of the corners possessed by the primary particles of silicon carbide included in the silicon carbide powder is 2.8 or less, the shape of the primary particles of silicon carbide becomes a shape with high sphericity, and thus even if added to a liquid foreign material, there is a tendency that thickening is difficult to occur. Here, the corner refers to a point at which the outline of the primary particle in a projection image of the primary particle changes at an angle, and the aforementioned angle is an internal angle toward the inside of the outline of the primary particle, and is more than 0° and less than 180°. Note that, for the corner, the outline forming the corner can have a straight line or a rounded corner. In addition, the small corner refers to a corner existing in the outline of the primary particle in the projection image of the primary particle, of which 2 times the radius of curvature is 1 / 5 or less of the Heywood diameter of the projection image of the primary particle.

[0029] The Heywood diameter is also referred to as the projected area circle equivalent diameter, and refers to the diameter of a circle having the same area as the projected area of the particle calculated by image analysis. In addition, in the silicon carbide powder of the present embodiment, the primary particles of silicon carbide are the main constituents. Furthermore, the primary particle is a unit particle observed from the geometry of the appearance, and refers to an independent smallest particle that is not agglomerated.

[0030] The number of small corners possessed by the primary particles of silicon carbide included in the silicon carbide powder on the surface can be determined, for example, as follows. The powder of silicon carbide is observed using an electron microscope to obtain a secondary electron image of the primary particles of silicon carbide, and image analysis of the secondary electron image is performed using image analysis software. In the image analysis, a projection image of an arbitrary one of the primary particles is obtained from the secondary electron image, and the radius of curvature of the corner present in the outline of the primary particle in the projection image (the radius of the largest circle that can be tangent to the inside of the corner) is determined.

[0031] The shape of the projection image of the primary particle of silicon carbide is a substantially polygonal shape, and a plurality of corners are present in one primary particle, but only the corners between the sides of the substantially polygonal shape are taken as the object of analysis (determination of the radius of curvature), and the slight concavities and convexities formed halfway along the sides are not taken as the object of analysis. The slight concavities and convexities refer to corners that are so small that they cannot be recognized as corners by visual observation in the projection image of the primary particle obtained by the following determination conditions.

[0032] The number of small corners among the corners possessed by the primary particles of silicon carbide included in the silicon carbide powder of the present embodiment on the surface is measured according to the following steps <1> to <5>.

[0033] [Measurement Conditions]

[0034] <1> The particle diameters D10%, D50%, and D90% of the silicon carbide powder that is the object of measurement (analysis) are measured using a laser diffraction / scattering type particle diameter distribution measuring device LA-300 manufactured by HORIBA, Ltd. Note that D10%, D50%, and D90% refer to the particle diameters at which the cumulative particle volume becomes 10%, 50%, and 90%, respectively, of the total particle volume from the small particle diameter side in the cumulative particle diameter distribution on a volume basis measured using a laser diffraction / scattering type particle diameter distribution measuring device LA-300 manufactured by HORIBA, Ltd.

[0035] In addition, in the case where D50% measured using a laser diffraction / scattering type particle diameter distribution measuring device LA-300 manufactured by HORIBA, Ltd. is 150 nm or more, D10%, D50%, and D90% are measured using a laser diffraction / scattering type particle diameter distribution measuring device Microtrac MT3300EXII manufactured by MicrotracBEL Corp.

[0036] <2> A secondary electron image of the primary particles of silicon carbide is obtained with an electron microscope (Phenom Pro-X desktop scanning electron microscope manufactured by Thermo Fisher Scientific, Inc., acceleration voltage of electrons 10 kV). Note that the magnification is set to any one of the following (i) to (iii).

[0037] (i) For powders with a D50% of 100 μm or more, the magnification is set to 300x.

[0038] (ii) For powders with a D50% of 40 μm or more but less than 100 μm, the magnification is set to 1000 times.

[0039] (iii) For powders with D50% less than 40μm, the magnification is set to 2000 times.

[0040] <3> Image analysis of the secondary electron image was performed using Mac-View image analysis software manufactured by Mountech Co., Ltd., to obtain projection images of any 100 or more primary silicon carbide particles in the secondary electron image.

[0041] <4> Then, image analysis is performed. For the projection image of a primary particle whose corner radius of curvature has been measured, the Heywood diameter R is calculated. That is, the diameter of a circle with an area equal to the area of ​​the projection image of the primary particle is calculated. Then, for the projection image of the primary particle, the number of corners (hereinafter referred to as "small corners") whose radius of curvature is less than or equal to twice the Heywood diameter R is measured.

[0042] <5> The same analysis as described above is performed on the projected images of multiple (e.g., 50) primary particles in the secondary electron image, determining the radius of curvature of the corners and calculating the Heywood diameter R, and measuring the number of small corners. Then, the average number of small corners is calculated for multiple primary particles, and the number of small corners for each primary particle is calculated.

[0043] In this embodiment, the particle size D50% of the silicon carbide powder, where the cumulative particle volume from the smallest particle size side constitutes 50% of the total particle volume in the volume-based cumulative particle size distribution, can be 1 μm or more, 10 μm or more, or 15 μm or more. Furthermore, the particle size D50% can be 300 μm or less, or 250 μm or less. If the particle size D50% is 1 μm or more, there is a tendency to prevent thickening when the silicon carbide powder of this embodiment is added to liquid dissimilar materials such as liquid resins or molten metals. The method for measuring the particle size D50% of the silicon carbide powder of this embodiment is not particularly limited; for example, it can be measured using laser diffraction / scattering.

[0044] The thickening properties of the silicon carbide powder in this embodiment can be evaluated by measuring and comparing the viscosity of the resin composition obtained by mixing it in a liquid resin with the viscosity of the liquid resin before mixing. For example, the viscosity of the resin composition obtained by mixing 73 parts by mass of the silicon carbide powder of this embodiment with 27 parts by mass of the organosilicon resin, and the viscosity of the organosilicon resin alone, were measured at a measurement temperature of 25°C and 1 second.-1 The thickening properties of the silicon carbide powder of this embodiment can be evaluated by measuring and comparing the shear rate at which the thickening properties are measured using a rheometer. The silicon carbide powder contains at least one element selected from aluminum, yttrium, and ytterbium on its surface. If the Haussner ratio of the silicon carbide powder is 2.1 or less, it is not easy to cause thickening even when added to liquid dissimilar materials such as liquid resins or molten metals.

[0045] The shear characteristics of the silicon carbide powder in this embodiment can be evaluated by measuring the kinetic friction force. For example, for the silicon carbide powder in this embodiment, a powder layer shear force measuring device manufactured by Nano Seeds Corporation can be used to apply shear force to a stationary powder layer under a specified vertical stress, measure the critical state line (CSL) of powder layer disintegration, and calculate the kinetic friction angle between the powder layers, defined as the angle between the obtained CSL and the vertical stress axis. Here, the CSL is a straight line passing through the origin with the shear stress and vertical stress as axes.

[0046] The silicon carbide powder of this embodiment has silicon carbide containing at least one of aluminum, yttrium, and ytterbium as the main component on the particle surface, but it may also contain elements other than silicon, carbon, aluminum, yttrium, and ytterbium. Examples of elements other than those mentioned above include beryllium, magnesium, and boron.

[0047] The silicon carbide powder of this embodiment can be manufactured by the following method. That is, a method for manufacturing silicon carbide powder includes: mixing a metal-containing substance into silicon carbide powder as a raw material; and subjecting the mixed silicon carbide powder as a raw material and the metal-containing substance to heat treatment, wherein the haussna ratio of the heat-treated silicon carbide powder is 2.1 or less.

[0048] According to the silicon carbide powder manufacturing method of this embodiment, even silicon carbide with high hardness can be easily manufactured into silicon carbide powder of this embodiment.

[0049] In the silicon carbide powder manufacturing method of this embodiment, silicon carbide powder that does not easily thicken even when added to a liquid dissimilar material can be manufactured simply by mixing silicon carbide powder as a raw material with a metal-containing substance and performing heat treatment. Therefore, compared with the aforementioned mechanical processing method that requires sufficient removal of the corners from the surface of primary silicon carbide particles to form a shape with high sphericity, silicon carbide powder of this embodiment can be manufactured more easily.

[0050] According to the silicon carbide powder manufacturing method of this embodiment, compared with the aforementioned mechanical processing method, foreign matter is less likely to be mixed into the silicon carbide powder during processing. Furthermore, according to the silicon carbide powder manufacturing method of this embodiment, fine particles such as debris are less likely to be generated in the primary silicon carbide particles during processing. Moreover, the silicon carbide powder manufacturing method of this embodiment can produce the silicon carbide powder of this embodiment using a method easier than granulation and sintering.

[0051] There are no particular limitations on the conditions for heat treatment. The temperature conditions can be above 1700℃ and below 2300℃, above 1750℃ and below 2250℃, or above 1800℃ and below 2200℃.

[0052] The atmosphere used during heat treatment is preferably a non-reactive gas atmosphere. There are no particular limitations on the types of non-reactive gases, but examples include nitrogen, helium, argon, neon, xenon, and krypton.

[0053] When manufacturing the silicon carbide powder of this embodiment, a liquid phase forming aid, which is a metal-containing substance, can be mixed into the silicon carbide powder used as a raw material for heat treatment. If a liquid phase forming aid is mixed into the silicon carbide powder, the liquid phase forming aid adheres to the surface of the primary silicon carbide particles. If heat treatment is performed with the liquid phase forming aid attached, the liquid phase forming aid reacts with the silicon dioxide present on the surface of the primary silicon carbide particles at high temperature to form a molten liquid mixture (liquid phase), which covers the surface of the primary silicon carbide particles.

[0054] The surface of the primary silicon carbide particles is covered by the molten liquid, which promotes atomic diffusion and material movement, allowing the silicon carbide to dissolve into the molten liquid. Due to the surface tension of the molten liquid containing dissolved silicon carbide, the primary silicon carbide particles become highly spherical in shape. Through the solidification of the molten liquid, a thin film is formed, resulting in primary particles with highly spherical shapes.

[0055] There are no particular limitations on the types of metallic substances and liquid-phase forming aids used as metallic substances. For example, aluminum-containing substances, yttrium-containing substances, and ytterbium-containing substances can be listed. Examples of aluminum-containing, yttrium-containing, and ytterbium-containing substances include aluminum salts, yttrium salts, ytterbium salts, aluminum oxide, yttrium oxide, and ytterbium oxide. Specific examples of aluminum salts include aluminum nitrate (Al(NO3)3), aluminum chloride, aluminum sulfate, aluminum acetate, aluminum lactate, and the hydrates of these aluminum salts.

[0056] Silicon carbide powder that has undergone heat treatment sometimes experiences particle agglomeration. Therefore, after the heat treatment process, silicon carbide powder can be crushed using centrifugal pulverizers or classified using sieves.

[0057] [Example]

[0058] The following examples and comparative examples further illustrate the present invention.

[0059] (Example 1)

[0060] 100 parts by mass of silicon carbide powder with an α-type crystal system and a particle size D50% of 12 μm and 0.22 parts by mass of alumina were dry-mixed to obtain a mixed powder. The obtained mixed powder was then heat-treated at a temperature of 1830 °C for 4 hours in an argon atmosphere.

[0061] The heat-treated mixed powder underwent primary particle agglomeration in some parts, so it was crushed using a centrifugal pulverizer and classified using a 32μm sieve (to remove the agglomerates), thereby obtaining the silicon carbide powder of Example 1. The centrifugal pulverizer rotated at 18000 rpm.

[0062] (Example 2)

[0063] Using silicon carbide powder with an α-type crystal system and a particle size D50% of 15 μm as raw material, the heat treatment temperature was set to 1920 °C, and the sieve aperture during grading was 45 μm. Otherwise, the silicon carbide powder of Example 2 was obtained in the same manner as in Example 1.

[0064] (Examples 3 and 4)

[0065] Silicon carbide powders with different particle sizes (D50%) were used as raw materials. The centrifugal pulverizer rotated at 12,000 rpm, and the sieve used for grading had a mesh size of 53 μm. Otherwise, the silicon carbide powders of Examples 3 and 4 were manufactured in the same manner as in Example 2.

[0066] (Example 5)

[0067] Using silicon carbide powder with a particle size D50% of 51 μm as raw material, the heat treatment temperature was set to 2000°C, the speed of the centrifugal pulverizer was 6000 rpm, the sieve aperture during classification was 90 μm, and then a sieve with an aperture of 32 μm was used for classification (removal of particles). Otherwise, the silicon carbide powder of Example 5 was manufactured in the same manner as in Example 1.

[0068] (Example 6)

[0069] Using silicon carbide powder with a particle size D50% of 62 μm as raw material, the heat treatment temperature was set to 2040 °C. Otherwise, the silicon carbide powder of Example 6 was manufactured in the same manner as in Example 5.

[0070] (Example 7)

[0071] Using silicon carbide powder with a particle size D50% of 124 μm as raw material, the heat treatment temperature was set to 2110°C, the speed of the centrifugal pulverizer was 6000 rpm, and the sieve aperture during grading was 180 μm. Otherwise, the silicon carbide powder of Example 7 was manufactured in the same manner as in Example 4.

[0072] (Example 8)

[0073] Silicon carbide powder with a particle size D50% of 240 μm was used as raw material. The centrifugal pulverizer was operated at a speed of 8000 rpm. No grading was performed using a sieve. Otherwise, the silicon carbide powder of Example 8 was produced in the same manner as in Example 7.

[0074] (Comparative Example 1)

[0075] A silicon carbide powder with 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.

[0076] (Presence or absence of aluminum on the surface of silicon carbide particles)

[0077] Elemental analysis was performed on the primary particle surfaces of the silicon carbide powders obtained in Examples 1-8 and Comparative Example 1 using a Hitachi High-Tech Corporation scanning electron microscope SU8000 and an Oxford Instruments KK energy-dispersive X-ray analyzer X-Max80. When peaks attributable to aluminum were found in the obtained spectra, it was determined that aluminum was present on the primary particle surfaces of the silicon carbide powders. These results are shown in Table 1.

[0078] [Table 1]

[0079]

[0080] (Hausnaby)

[0081] For the silicon carbide powders obtained in Examples 1-8 and Comparative Example 1, the loose bulk density and tapped density were measured using a 30 mL metal container based on JIS R 1628. Furthermore, the Hausner ratio (= tapped density / loose bulk density) was calculated from these measurements. These results are shown in Table 1.

[0082] (particle size)

[0083] The particle sizes D10%, D50%, and D90% of the silicon carbide powders obtained in Examples 1-8 and Comparative Example 1 were determined using a laser diffraction / scattering particle size distribution measuring device LA-300 manufactured by Horiba Corporation.

[0084] In addition, when the D50% measured using the LA-300 laser diffraction / scattering particle size distribution measuring device manufactured by Horiba Corporation was 150 nm or higher, the D10%, D50%, and D90% were measured using the Microtrac MT3300EXII laser diffraction / scattering particle size distribution measuring device manufactured by Microtrac Corporation. These results are shown in Table 1.

[0085] (Number of small corners in each primary particle of silicon carbide powder)

[0086] The number of small corners among the corners of the primary silicon carbide particles on the surface of the silicon carbide powders obtained in Examples 1-8 and Comparative Example 1 was calculated by image analysis of secondary electron images of the primary silicon carbide particles. Detailed explanation follows.

[0087] In image analysis, a projection image of any primary particle is acquired from a secondary electron image, and the radius of curvature (the radius of the largest circle that can connect to the inside of the corner) of the primary particle's outline in the projection image is measured. The projection image of a silicon carbide primary particle is roughly polygonal in shape, with multiple corners in a single primary particle. However, only the corners between the edges of the roughly polygonal shape are analyzed (the radius of curvature is measured), and minute irregularities formed in the middle of the edges are not considered in the analysis.

[0088] For a single particle projection image from which the radius of curvature of the corners was measured, further image analysis was performed to calculate the Heywood diameter R, and the number of small corners whose radius of curvature is twice that of one-fifth of the Heywood diameter R was measured.

[0089] The same analysis as above was performed on the projected images of any 50 primary particles in the secondary electron image, measuring the radius of curvature of the corners and calculating the Heywood diameter R, and measuring the number of small corners. Then, the average number of small corners was calculated for the 50 primary particles, and the number of small corners for each primary particle was calculated. These results are shown in Table 1.

[0090] (Viscosity of the resin composition)

[0091] For Examples 1-8 and Comparative Example 1, 73 parts by weight of silicon carbide powder and 27 parts by weight of silicone resin as liquid resin were mixed using a rotary mixer at 2000 rpm for 2 minutes to prepare a slurry-like resin composition. As the silicone resin, silicone oil (dimethyl silicone oil, trade name Element 14 PDMS series) manufactured by Momentive Performance Materials Inc. was used.

[0092] The viscosity of the prepared resin composition was determined using an Anton Parr MCR302 rheometer. A parallel plate with a diameter of 49.974 mm was used as the measuring fixture for the rheometer. The measurement conditions were: a temperature of 25°C and a shear rate of 1 s⁻¹. -1 The gap between the parallel plates is 1 mm. These results are shown in Table 1.

[0093] The viscosity of the silicone oil used in the resin composition at 25°C was measured in the same manner as that of the resin composition, and the result was 1.1 Pa·s.

[0094] (Angle of kinetic friction)

[0095] For the silicon carbide powders of Examples 1-8 and Comparative Example 1, the dynamic friction angle was measured using a Nano Seeds Corporation NS-S500 powder layer shear force measuring device. Specifically, shear was applied to a stationary powder layer under a specified vertical stress, the critical state line (CSL) for powder layer disintegration was measured, and the dynamic friction angle between powder layers, defined as the angle between the CSL and the vertical stress axis, was calculated. These results are shown in Table 1.

[0096] (evaluate)

[0097] As shown in Table 1, compared to Comparative Example 1 where aluminum was not introduced onto the particle surface, in Examples 1-8 where aluminum was introduced onto the particle surface, the thickening caused by the addition of silicon carbide powder was minimal, and the viscosity of the resin composition was also low. In particular, in Examples 2-8 where the Hausner ratio was 1.8 or less, the thickening caused by the addition of silicon carbide powder was even less, and the viscosity of the resin composition was 55 Pa·s or less, which was significantly lower than that of Comparative Example 1 where aluminum was not introduced onto the particle surface.

[0098] Therefore, it is believed that the silicon carbide powder of Examples 1-8 can be easily filled into liquid dissimilar materials. In addition, it is believed that the mixture of silicon carbide powder and liquid dissimilar materials of Examples 1-8 has good processability during molding.

Claims

1. A silicon carbide powder comprising primary silicon carbide particles of the α-type crystal system, wherein the primary silicon carbide particles contain at least one element selected from aluminum, yttrium, and ytterbium on their surface, and the silicon carbide powder has a Hausner ratio of 2.1 or less.

2. The silicon carbide powder according to claim 1, wherein, The silicon carbide powder contains primary silicon carbide particles with corners. The number of small corners in the corner portion is less than 2.8 per primary particle. The small corner is a corner in the outline of the primary particle in the projected image of the primary particle, whose radius of curvature is less than 1 / 5 of the Heywood diameter of the projected image of the primary particle, which is twice the radius of curvature of the corner.

3. The silicon carbide powder according to claim 1 or 2, wherein, In the cumulative particle size distribution based on volume, the particle size D50% of the cumulative particle volume of the silicon carbide powder, which is 50% of the total particle volume from the smallest particle size side, is 1 μm or larger.

4. A method for manufacturing silicon carbide powder, comprising: Metallic substances are mixed into silicon carbide powder, which is used as a raw material. as well as The mixed silicon carbide powder and the metal-containing substance are subjected to heat treatment. The hauschnab ratio of the heat-treated silicon carbide powder is below 2.

1.

5. The method for manufacturing silicon carbide powder according to claim 4, wherein, The metallic substance contains at least one element selected from aluminum, yttrium, and ytterbium.

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