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• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
  • C01B21/068—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with silicon
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
  • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
  • C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
  • C04B35/587—Fine ceramics

Definitions

• the present disclosure relates to a silicon nitride powder and a method for producing the same, and a method for producing a silicon nitride sintered body.
• Silicon nitride is a material with excellent strength, hardness, toughness, heat resistance, corrosion resistance, heat impact resistance, etc. For this reason, it has been studied to use a silicon nitride sintered body as an insulating substrate for mechanical parts such as gas turbines, turbo rotors, and valves, and power modules for automobiles and machine tools.
• the silicon nitride sintered body used for these applications is required to have a dense and homogeneous structure.
• a technique for providing a high-purity and homogeneous silicon nitride powder has been studied.
• Examples of the method for synthesizing silicon nitride powder include a direct nitriding method (direct reaction method) in which metallic silicon powder is nitrided in a mixed atmosphere of hydrogen gas or ammonia gas and nitrogen gas, a reduction nitriding method for silica powder, and an imide decomposition method. It has been known.
• Patent Document 1 proposes a method for producing a silicon nitride powder having a high content of ⁇ -type Si 3 N 4 .
• Patent Document 2 proposes to produce a silicon nitride powder having few impurities by an imide decomposition method.
• the silicon nitride sintered body may be used even in a high temperature environment, it is required to have excellent strength under high temperature (high temperature strength). It is considered necessary to make the silicon nitride sintered body denser in order to improve the high temperature strength. As a factor that hinders the densification of the silicon nitride sintered body, the influence of impurities contained in the raw material, that is, the silicon nitride powder can be considered.
• the present disclosure provides a silicon nitride powder capable of producing a silicon nitride sintered body having excellent high-temperature strength by reducing impurities. Further, the present invention provides a method for producing a silicon nitride powder capable of producing a silicon nitride powder with sufficiently reduced impurities at a low production cost. Further, the present invention provides a method for producing a silicon nitride sintered body capable of producing a silicon nitride sintered body having excellent high temperature strength at a low production cost.
• the silicon nitride powder according to one aspect of the present disclosure has an oxygen content of 3.0% by mass or less and a total content of fluorine and chlorine of 25% by mass or less. Since such silicon nitride powder has a sufficiently low content of oxygen, fluorine, and chlorine that affect the high temperature strength, it is possible to produce a silicon nitride sintered body having excellent high temperature strength.
• the pregelatinization rate of the silicon nitride powder is preferably 92% by mass or more. By having a high pregelatinization rate, it is possible to promote grain growth during sintering of the silicon nitride powder. This makes it possible to produce a sufficiently densified silicon nitride sintered body. Therefore, a silicon nitride sintered body having more excellent high temperature strength can be obtained.
• the proportion of primary particles having a particle size of 2 ⁇ m or more is preferably 2% or less.
• the fine structure of the silicon nitride sintered body obtained by sintering the silicon nitride powder can be made more uniform. Therefore, a silicon nitride sintered body having more excellent high temperature strength can be obtained.
• a raw material powder containing silica powder, carbon powder and silicon nitride seed crystals is calcined in a nitrogen atmosphere at 1300 to 1550 ° C. for 50 hours or more to obtain silicon nitride. It has a firing step to obtain a powder.
• the raw material powder is calcined at 1300 to 1550 ° C. for a sufficiently long time in the calcining step, the reduction nitriding reaction of the silica powder proceeds sufficiently. Therefore, it is possible to produce a silicon nitride powder with sufficiently reduced impurities.
• This production method can reduce the production cost of the silicon nitride powder as compared with the imide method. Further, in the direct nitriding method, pulverization is usually required for pulverization, but acid treatment is required to reduce impurities derived from pulverization. In this case, the chemical component of the acid treatment remains and becomes an impurity. Therefore, according to the method for producing silicon nitride powder of the present disclosure, it is possible to produce silicon nitride powder with sufficiently reduced impurities at a low production cost.
• the oxygen content of the silicon nitride powder obtained in the above-mentioned firing step is 3.0% by mass or less, and the total content of fluorine and chlorine is 25% by mass or less.
• the silicon nitride powder obtained in the above-mentioned firing step preferably has a proportion of primary particles having a particle size of 2 ⁇ m or more of 2% or less.
• the proportion of the above-mentioned primary particles in the present disclosure is based on the number of particles.
• the method for producing a silicon nitride sintered body according to one aspect of the present disclosure is to obtain a silicon nitride sintered body by firing any of the above-mentioned silicon nitride powders or the silicon nitride powder obtained by any of the above-mentioned production methods. Has a sintering step to obtain.
• this production method since the silicon nitride powder with reduced impurities is sintered, a silicon nitride sintered body having excellent high temperature strength can be produced.
• a silicon nitride powder capable of producing a silicon nitride sintered body having excellent high temperature strength by reducing impurities. Further, it is possible to provide a method for producing silicon nitride powder capable of producing silicon nitride powder with sufficiently reduced impurities at a low production cost. Further, it is possible to provide a method for producing a silicon nitride sintered body, which can produce a silicon nitride sintered body having excellent high temperature strength at a low production cost.
• the silicon nitride powder has an oxygen content of 3.0% by mass or less, and a total content of fluorine and chlorine of 25% by mass or less.
• the oxygen content may be 2.5% by mass or less, may be 2.3% by mass or less, and may be 1.8 from the viewpoint of enabling the production of a silicon nitride sintered body having more excellent high-temperature strength. It may be less than% by mass.
• By reducing the oxygen content of the silicon nitride powder it is possible to reduce the internal defects of the silicon nitride sintered body obtained by sintering the silicon nitride powder. Thereby, a silicon nitride sintered body having a sufficiently high high temperature strength can be obtained.
• the oxygen content tends to depend on the firing time when producing the silicon nitride powder and the blending ratio of the carbon powder in the starting material used when producing the silicon nitride powder.
• the oxygen content of the silicon nitride powder may be 0.1% by mass or more, or 0.5% by mass or more, from the viewpoint of reducing the production cost of the silicon nitride powder.
• An example of the oxygen content of the silicon nitride powder may be 0.1 to 3.0% by mass, or 0.5 to 2.5% by mass.
• the oxygen content of the silicon nitride powder can be measured using a commercially available oxygen / nitrogen analyzer. The measurement is carried out by continuously raising the temperature from 20 ° C. to 3000 ° C. in an atmosphere of helium gas. Of the obtained measurement results, the oxygen content can be quantified from the area of the peak derived from the elimination of oxygen.
• the total content of fluorine and chlorine in the silicon nitride powder may be 22 mass ppm or less and 20 mass ppm or less from the viewpoint of enabling the production of a silicon nitride sintered body having more excellent high temperature strength. , 19 mass ppm or less.
• the total content of fluorine and chlorine is the purity of the starting material used in the production of silicon nitride powder, the blending ratio of silica powder and carbon powder (C / SiO 2 ), firing time, and post-treatment (cleaning) after firing. It tends to depend on the presence or absence of.
• the total content of fluorine and chlorine in the silicon nitride powder may be 1 mass ppm or more, or 5 mass ppm or more, from the viewpoint of reducing the production cost of the silicon nitride powder.
• An example of the total content of fluorine and chlorine in the silicon nitride powder may be 1 to 25 mass ppm, or 5 to 22 mass ppm.
• the total content of fluorine and chlorine in the silicon nitride powder can be measured by heating the silicon nitride powder and quantifying the fluorine and chlorine contained in the generated gas by ion chromatography.
• the pregelatinization rate of the silicon nitride powder may be 92% by mass or more, 95% by mass or more, or 96% by mass or more.
• the pregelatinization rate of the silicon nitride powder may be 92% by mass or more, 95% by mass or more, or 96% by mass or more.
• the pregelatinization rate of the silicon nitride powder may be 99% by mass or less, or 98% by mass or less, from the viewpoint of reducing the production cost of the silicon nitride powder.
• An example of the pregelatinization rate of the silicon nitride powder may be 92 to 99% by mass, 95 to 99% by mass, or 96 to 98% by mass.
• the pregelatinization rate of the silicon nitride powder can be determined based on the diffraction line intensity of X-ray diffraction.
• the proportion of primary particles having a particle size of 2 ⁇ m or more among the primary particles contained in the silicon nitride powder is preferably 2% or less.
• the ratio may be 1% or less, or 0.5% or less.
• the proportion of the primary particles having a particle size of 2 ⁇ m or more among the primary particles contained in the silicon nitride powder may be 0.1% or more, or 0.3%, from the viewpoint of reducing the production cost of the silicon nitride powder. It may be the above.
• An example of the above ratio may be 0.1 to 2% and may be 0.3 to 1%.
• the above ratio is a number-based ratio, and can be obtained based on the particle size distribution measured by incorporating the captured image of the scanning electron microscope into the image analysis type particle size distribution measurement software.
• the silicon nitride powder may contain carbon or carbide as a component other than silicon nitride.
• the total content of carbon and carbide in the silicon nitride powder is preferably 10% by mass or less, and more preferably 7% by mass or less in terms of carbon.
• the method for producing silicon nitride powder includes a blending step of blending silica powder, carbon powder, and silicon nitride seed crystals to prepare a raw material powder, and the raw material powder in a nitrogen atmosphere at 1300 to 1550 ° C. It has a firing step of firing for 50 hours or more to obtain silicon nitride powder.
• the firing time may be, for example, 200 hours or less from the viewpoint of production efficiency.
• the silica powder include fused silica powder, crystalline silica powder and silicate compounds.
• Examples of the carbon powder include acetylene black, furnace black, channel black, and graphite.
• the silicon nitride used as the seed crystal preferably has a high pregelatinization rate (for example, a pregelatinization rate of 90% or more) from the viewpoint of improving sinterability.
• the compounding ratio of the carbon powder to the silica powder in the compounding step is based on the molar standard (C / SiO 2 ) from the viewpoint of obtaining the silicon nitride powder in which the total content of fluorine and chlorine and the oxygen content are sufficiently reduced. It may be 0 to 3.8, and may be 3.0 to 3.7.
• the blending amount of the silicon nitride seed crystal with respect to 100 parts by mass of the silica powder may be 10 to 20 parts by mass and 11 to 18 parts by mass from the viewpoint of obtaining a silicon nitride powder having sufficiently high purity while reducing the production cost. It may be.
• the total content of fluorine and chlorine in the raw material powder is preferably 50 mass ppm or less, more preferably 40 mass ppm, from the viewpoint of sufficiently reducing the total content of fluorine and chlorine in the silicon nitride powder produced. It is as follows. On the other hand, the total content of fluorine and chlorine in the raw material powder may be 10 mass ppm or more, or 20 mass ppm or more, from the viewpoint of reducing the production cost of the silicon nitride powder.
• the following reaction formula (1) proceeds by firing the raw material powder using an electric furnace.
• the firing temperature may be 1450 to 1550 ° C. from the viewpoint of sufficiently proceeding the reaction of the reaction formula (1).
• the firing time may be 150 hours or more, or 200 hours or more, from the viewpoint of sufficiently advancing the reduction nitriding reaction of the silica powder.
• the firing time may be 500 hours or less, or 400 hours or less, from the viewpoint of reducing the production cost of the silicon nitride powder.
• the firing process is performed in a nitrogen atmosphere.
• the oxygen concentration in the nitrogen atmosphere may be 100 volume ppm or less, or 20 volume ppm or less. By sufficiently lowering the oxygen concentration in the nitrogen atmosphere, the oxygen content of the produced silicon nitride powder can be further reduced.
• a decarburization step may be performed. The decarburization step can be performed, for example, by heating the silicon nitride powder to 650 to 900 ° C. in the air. This makes it possible to reduce the total content of carbon and carbide in the silicon nitride powder.
• the silicon nitride powder according to the above-described embodiment can be obtained.
• properties such as the oxygen content of the silicon nitride powder, the total content of fluorine and chlorine, the pregelatinization rate and the particle size are as described above.
• silicon nitride powder is produced by a reduction nitriding reaction of silica powder. Therefore, the production cost of the silicon nitride powder can be reduced as compared with the imide method.
• pulverization is usually required for pulverization, but acid treatment is required to reduce impurities derived from pulverization.
• the chemical component of the acid treatment remains and becomes an impurity. Therefore, according to the method for producing silicon nitride powder of the present disclosure, it is possible to produce silicon nitride powder with sufficiently reduced impurities at a low production cost.
• the method for producing a silicon nitride sintered body according to one embodiment includes a sintering step of firing the silicon nitride powder according to the above embodiment to obtain a silicon nitride sintered body.
• silicon nitride powder is pressed with a molding pressure of, for example, 3.0 to 10.0 MPa to obtain a molded product.
• the molded product may be produced by uniaxial pressure or by CIP. Alternatively, it may be fired while being molded by hot pressing.
• the molded product may be fired in an atmosphere of an inert gas such as nitrogen gas or argon gas.
• the pressure at the time of firing may be 0.7 to 0.9 MPa.
• the firing temperature may be 1700 to 1900 ° C.
• the firing time at the firing temperature may be 4 to 20 hours and may be 8 to 16 hours.
• the rate of temperature rise to the firing temperature may be, for example, 1.0 to 10.0 ° C./hour.
• the silicon nitride sintered body thus obtained has a sufficiently reduced oxygen content and a total content of fluorine and chlorine. Since the oxygen content is sufficiently reduced, defects generated inside the silicon nitride sintered body can be suppressed. Therefore, it is excellent not only in high temperature strength but also in insulating property and thermal conductivity. As the defects contained in the silicon nitride sintered body, lattice defects such as dislocations and pores can be considered. Further, since the total content of fluorine and chlorine is sufficiently reduced, it is possible to suppress the softening of the grain boundary phase of the silicon nitride sintered body at a high temperature. Therefore, a silicon nitride sintered body having a sufficiently high high temperature strength can be obtained.
• the high temperature strength in the present disclosure means the strength at 1300 ° C.
• Silicon nitride sintered bodies having high strength in such a temperature range can be particularly suitably used for applications such as gas turbines, power modules for automobiles, and bearings.
• the bending strength of the silicon nitride sintered body according to the embodiment at a temperature of 1300 ° C. may be, for example, 700 MPa or more, or 750 MPa or more. This strength is a 4-point bending strength (1300 ° C.) measured using a commercially available measuring device.
• the silicon nitride powder may be used for applications other than the production of a silicon nitride sintered body.
• the raw material powder was calcined at 1500 ° C. for 60 hours in a nitrogen atmosphere at atmospheric pressure using an electric furnace to obtain a massive nitride.
• This nitride was crushed in a silicon nitride mortar to obtain a nitride powder.
• This was placed in an alumina crucible and heated in an electric furnace at 800 ° C. for 3 hours to decarburize.
• the decarburized powder obtained by decarburization was filled in an alumina pot together with a silicon nitride ball and pulverized with a vibration mill for 3 hours to obtain a silicon nitride powder.
• Example 2 A silicon nitride powder was obtained in the same manner as in Example 1 except that the time for firing the raw material powder at 1500 ° C. was changed from 60 hours to 110 hours.
• Example 1 A silicon nitride powder was obtained in the same manner as in Example 1 except that the time for firing the raw material powder at 1500 ° C. was changed from 60 hours to 10 hours.
• Example 3 A silicon nitride powder was obtained in the same manner as in Example 1 except that the time for firing the raw material powder at 1500 ° C. was changed from 60 hours to 5 hours.
• the total content of fluorine and chlorine contained in the silicon nitride powder was measured by the following procedure.
• the silicon nitride powder was heated using an automatic sample combustion device (manufactured by Mitsubishi Chemical Corporation, device name: AQF-2100H type), and the generated gas was dissolved in water. Fluorine and chlorine dissolved in water were measured using an ion chromatograph (manufactured by Thermo Fisher Scientific Co., Ltd., device name: ICS-2100) according to JIS R 1603: 2007. Based on this measured value, fluorine and chlorine contained in the silicon nitride powder were quantified. The measurement results are as shown in Table 1. In Table 1, the "halogen content" is the total content of fluorine and chlorine.
• the pregelatinization rate of the prepared silicon nitride powder was measured by the following procedure.
• An X-ray diffractometer manufactured by Rigaku, device name: Ultima IV
• the pregelatinization rate was calculated by the following formula. The results are as shown in Table 1.
• Pregelatinization rate (mass%) (I a102 + I a210 ) / (I a102 + I a210 + I b101 + I b210 ) ⁇ 100
• the proportion of particles having a particle size of 2 ⁇ m or more contained in the prepared silicon nitride powder was measured by the following procedure. Using a scanning electron microscope (manufactured by JEOL Ltd., device name: JSM-6301F), the silicon nitride powder was observed at a magnification of 5000 times, and an image was taken (field of view: 16 ⁇ m ⁇ 23 ⁇ m). The image taken by the image analysis type particle size distribution measurement software (manufactured by Mountech Co., Ltd., product name: Mac View version 4.0) was captured and the particle size distribution was measured. From the measurement results, the proportion of primary particles having a particle size of 2 ⁇ m or more was calculated. The results are as shown in Table 1.
• Comparative Examples 1 and 3 having a higher oxygen content than Examples 1 and 2 had lower high-temperature intensities than Examples 1 and 2.
• Comparative Example 2 in which the total content of fluorine and chlorine was higher than in Examples 1 and 2, also had a lower high temperature intensity than in Examples 1 and 2.
• Table 1 it was confirmed that a silicon nitride sintered body having excellent high temperature strength can be obtained by using silicon nitride powder having a low oxygen content and a low total content of fluorine and chlorine.
• a silicon nitride powder capable of producing a silicon nitride sintered body having excellent high temperature strength by reducing impurities. Further, it is possible to provide a method for producing a silicon nitride powder capable of producing a silicon nitride powder with sufficiently reduced impurities at a low production cost. Further, it is possible to provide a method for producing a silicon nitride sintered body, which can produce a silicon nitride sintered body having excellent high temperature strength at a low production cost.

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