WO2021200865A1 - Silicon nitride powder and method for producing silicon nitride sintered body - Google Patents

Silicon nitride powder and method for producing silicon nitride sintered body Download PDF

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WO2021200865A1
WO2021200865A1 PCT/JP2021/013391 JP2021013391W WO2021200865A1 WO 2021200865 A1 WO2021200865 A1 WO 2021200865A1 JP 2021013391 W JP2021013391 W JP 2021013391W WO 2021200865 A1 WO2021200865 A1 WO 2021200865A1
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silicon nitride
nitride powder
powder
less
sintered body
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PCT/JP2021/013391
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French (fr)
Japanese (ja)
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敏行 宮下
中村　祐三
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デンカ株式会社
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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

Definitions

  • the present disclosure relates to a method for producing silicon nitride powder and a silicon nitride sintered body.
  • silicon nitride is a material having excellent strength, hardness, toughness, heat resistance, corrosion resistance, heat impact resistance, etc., it is used for various industrial parts such as die casting machines and melting furnaces, and automobile parts. .. Further, since silicon nitride is excellent in mechanical properties at high temperatures, it is being studied to apply it to gas turbine parts that require high temperature strength and high temperature creep characteristics.
  • Patent Document 1 describes a silicon nitride sintered body characterized in that the thermal conductivity at room temperature is 100 to 300 W / (m ⁇ K) and the three-point bending strength at room temperature is 600 to 1500 MPa. Has been done.
  • An object of the present disclosure is to provide a silicon nitride powder capable of producing a sintered body having excellent bending strength. It is also an object of the present disclosure to provide a method for producing a silicon nitride sintered body having excellent bending strength.
  • the integrated value from the small particle size is 10% and 90% of the total in the volume-based particle size distribution curve measured by the laser diffraction / scattering method, which contains the primary particles of silicon nitride.
  • a silicon nitride powder in which the difference between D90 and D10 is 5.5 ⁇ m or less when the particle size at the time of reaching is D10 and D90, respectively.
  • a molded product (unfired product) having a narrow particle size distribution and a finer structure can be prepared. ..
  • the silicon nitride sintered body obtained by firing the molded body is excellent in bending strength because the generation of voids is suppressed.
  • the silicon nitride may have a D50 of 1.5 ⁇ m or less.
  • the silicon nitride powder has an appropriate particle size distribution, so that the packing density of the primary particles can be further improved.
  • the silicon nitride powder may have a D90 of 6.0 ⁇ m or less.
  • D90 6.0 ⁇ m or less.
  • the proportion of coarse particles can be sufficiently reduced, and the decrease in the density of the sintered body can be more sufficiently suppressed. In addition, it is superior in handleability.
  • the silicon nitride powder may have a BET specific surface area of less than 9.0 m 2 / g.
  • One aspect of the present disclosure provides a method for producing a silicon nitride sintered body, which comprises a step of molding and firing a sintered raw material containing the above-mentioned silicon nitride powder.
  • the method for producing the silicon nitride sintered body uses the sintered raw material containing the silicon nitride powder described above, the obtained silicon nitride sintered body can exhibit excellent bending strength.
  • a silicon nitride powder capable of producing a sintered body having excellent bending strength.
  • a method for producing a silicon nitride sintered body having excellent bending strength it is possible to provide a silicon nitride powder capable of producing a sintered body having excellent bending strength.
  • each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component in the composition are present, unless otherwise specified. ..
  • the "process" in the present specification may be a process independent of each other or a process performed at the same time.
  • silicon nitride powder contains primary particles of silicon nitride, and in the volume-based particle size distribution curve measured by the laser diffraction / scattering method, the integrated values from the small particle size are 10% and 90% of the total.
  • the difference between D90 and D10 is 5.5 ⁇ m or less when the particle diameters when the percentage reaches% are D10 and D90, respectively.
  • the upper limit of the difference between D90 and D10 is 5.5 ⁇ m or less, but for example, 5.4 ⁇ m or less, 5.2 ⁇ m or less, 5.0 ⁇ m or less, 4.8 ⁇ m or less, or 4.6 ⁇ m. It may be: When the upper limit of the above difference is within the above range, the molded product prepared by compression molding or the like of silicon nitride powder may have a finer structure, so that the generation of voids during sintering is further suppressed. can do. That is, the bending strength of the obtained silicon nitride sintered body can be further improved.
  • the lower limit of the difference between D90 and D10 may be, for example, 3.0 ⁇ m or more, 3.2 ⁇ m or more, or 3.4 ⁇ m or more.
  • the silicon nitride powder has an appropriate particle size distribution, so that the packing density of the primary particles can be further improved.
  • the above difference can be adjusted within the above range, and may be, for example, 3.0 to 5.5 ⁇ m, 3.2 to 5.4 ⁇ m, or 3.4 to 4.6 ⁇ m.
  • the above difference can be controlled by adjusting the pulverization conditions and the like at the time of producing the silicon nitride powder.
  • the upper limit of D90 of the silicon nitride powder may be, for example, 6.0 ⁇ m or less, 5.8 ⁇ m or less, 5.6 ⁇ m or less, 5.4 ⁇ m or less, or 5.2 ⁇ m or less.
  • the lower limit of D90 may be, for example, 3.5 ⁇ m or more, 3.7 ⁇ m or more, 3.9 ⁇ m or more, or 4.0 ⁇ m or more.
  • D90 can be adjusted within the above range and may be, for example, 3.5 to 6.0 ⁇ m or 4.0 to 5.2 ⁇ m.
  • the D90 of the silicon nitride powder can be controlled by, for example, adjusting the pulverization conditions at the time of producing the silicon nitride powder.
  • the upper limit of D50 of the silicon nitride powder may be, for example, 1.5 ⁇ m or less, or 1.4 ⁇ m or less. When the upper limit of D50 is within the above range, the strength of the silicon nitride sintered body can be further improved.
  • the lower limit of D50 of the silicon nitride powder may be, for example, 1.1 ⁇ m or more, or 1.2 ⁇ m or more.
  • the D50 of the silicon nitride powder can be adjusted within the above range, and may be, for example, 1.1 to 1.5 ⁇ m or 1.2 to 1.4 ⁇ m.
  • the integrated values from the small particle size of D10, D50, and D90 in the present specification are 10%, 50%, and 90% of the total, respectively.
  • the laser analysis scattering method can be measured according to the method described in JIS Z 8825: 2013 "Particle size analysis-laser diffraction / scattering method".
  • a laser diffraction / scattering method particle size distribution measuring device manufactured by Beckman Coulter, trade name: LS-13 320
  • D50 is also called a median diameter and means the average particle diameter of the silicon nitride powder.
  • the upper limit of the BET specific surface area of the silicon nitride powder may be, for example, less than 9.0 m 2 / g, 8.8 m 2 / g or less, 8.6 m 2 / g or less, or 8.5 m 2 / g or less. ..
  • the lower limit of the BET specific surface area of the silicon nitride powder is, for example, 5.0 m 2 / g or more, 5.1 m 2 / g or more, 5.2 m 2 / g or more, 5.3 m 2 / g or more, 5.4 m 2 It may be / g or more, 5.5 m 2 / g or more, 6.0 m 2 / g or more, or 7.0 m 2 / g or more.
  • the BET specific surface area of the silicon nitride powder can be adjusted within the above range, for example, 5.0 to 9.0 m 2 / g, 5.5 to 8.5 m 2 / g, or 7.0 to 8 It may be .5 m 2 / g.
  • the BET specific surface area of the silicon nitride powder can be controlled, for example, by adjusting the pulverization conditions during the production of the silicon nitride powder.
  • the BET specific surface area in the present specification is measured by the BET one-point method using nitrogen gas in accordance with the method described in JIS Z 8830: 2013 “Method for measuring the specific surface area of powder (solid) by gas adsorption”. The value.
  • the upper limit of the surface oxygen content of silicon nitride may be, for example, 2.0% by mass or less, 1.5% by mass or less, or 1.3% by mass or less.
  • the lower limit of the surface oxygen content of silicon nitride is, for example, 0.20% by mass or more, 0.30% by mass or more, 0.35% by mass or more, 0.40% by mass or more, 0.45% by mass or more, 0. It may be 60% by mass or more, 0.80% by mass or more, or 1.0% by mass or more.
  • the lower limit of the surface oxygen amount of silicon nitride is within the above range, grain growth at the time of firing silicon nitride can be promoted, and the bending strength of the silicon nitride sintered body can be further improved.
  • the amount of surface oxygen of silicon nitride can be adjusted within the above range, for example, 0.20 to 2.0% by mass, 0.20 to 1.5% by mass, or 1.0 to 1.5% by mass. It may be there.
  • the amount of surface oxygen of silicon nitride can be controlled, for example, by adjusting the atmosphere component in the firing step in the production of silicon nitride powder, the firing temperature, the firing time, and the like.
  • “Surface oxygen amount” in this specification means a numerical value obtained by the following procedure.
  • the amount of oxygen and the amount of nitrogen in the silicon nitride powder are analyzed using an oxygen / nitrogen analyzer.
  • the sample for measurement is heated from 20 ° C. to 2000 ° C. at a heating rate of 8 ° C./sec in an atmosphere of helium gas.
  • Oxygen desorbed as the temperature rises is detected by the infrared absorption method.
  • oxygen bound to the surface of the silicon nitride powder is eliminated.
  • the silicon nitride begins to decompose.
  • the start of decomposition of silicon nitride can be grasped by the start of detection of nitrogen.
  • the oxygen inside the silicon nitride powder is eliminated. Therefore, since the oxygen desorbed at this stage corresponds to the amount of internal oxygen, the amount of oxygen detected and quantified before nitrogen is detected is defined as the amount of surface oxygen.
  • the above-mentioned silicon nitride powder can be produced, for example, by the following method.
  • One embodiment of the method for producing silicon nitride powder is a step of calcining the silicon powder in an atmosphere containing nitrogen and at least one selected from the group consisting of hydrogen and ammonia to obtain a calcined product (hereinafter, calcining step). It also has a step of dry-grinding the fired product to obtain a crushed product (hereinafter, also referred to as a crushing step), and a step of dry-classifying the crushed product (hereinafter, also referred to as a classification step).
  • a silicon powder having a low oxygen concentration may be used as the silicon powder.
  • the upper limit of the oxygen concentration of the silicon powder may be, for example, 0.40% by mass or less, 0.30% by mass or less, or 0.20% by mass or less.
  • the lower limit of the oxygen concentration of the silicon powder may be, for example, 0.10% by mass or more, or 0.15% by mass or more.
  • the oxygen concentration of the silicon powder can be adjusted in the above range, and may be, for example, 0.10 to 0.40% by mass.
  • the oxygen concentration of the silicon powder in the present specification means a value measured by an infrared absorption method.
  • the silicon powder As the silicon powder, a commercially available product may be used, or a separately prepared one may be used.
  • a pretreatment liquid containing hydrofluoric acid can be used to reduce the amount of oxygen bound to the silicon powder.
  • a pretreatment step of pretreating the silicon powder with a pretreatment liquid containing hydrofluoric acid to obtain a silicon powder having an oxygen concentration of 0.40% by mass or more is further added. You may have.
  • the pretreatment liquid contains hydrofluoric acid, but may be a mixed acid with an acid such as hydrochloric acid, or may consist only of hydrofluoric acid.
  • the temperature of the pretreatment liquid in the pretreatment step may be, for example, 40 to 80 ° C.
  • the time for contacting the pretreatment liquid with the silicon powder may be, for example, 1 to 10 hours.
  • the silicon powder is fired in a mixed atmosphere containing nitrogen and at least one selected from the group consisting of hydrogen and ammonia to obtain a fired product containing silicon nitride.
  • the total content of hydrogen and ammonia in the mixed atmosphere may be, for example, 10-40% by volume based on the entire mixed atmosphere.
  • the firing temperature may be, for example, 1100 to 1450 ° C, or 1200 to 1400 ° C.
  • the firing time may be, for example, 30 to 100 hours.
  • the crushing step the above-mentioned fired product obtained in the firing step is crushed by a dry method to obtain a crushed product.
  • the crushing step includes two steps, a ball mill crushing step and a vibration mill crushing step. By crushing the fired product and adjusting the particle size, control in the subsequent classification step becomes easy.
  • the fired product containing silicon nitride obtained in the firing step is in the form of a lump, an ingot, or the like, the effect of performing the crushing step is more remarkable.
  • Each crushing may be performed in a plurality of stages such as coarse crushing and fine crushing.
  • the crushing step is a dry crushing step.
  • the filling rate of balls in the container in the ball mill crushing step can be adjusted according to the particle size distribution of the target silicon nitride powder.
  • the lower limit of the filling rate of the balls in the container may be, for example, 40% by volume or more, 45% by volume or more, 50% by volume or more, or 60% by volume or more based on the volume of the container.
  • the upper limit of the filling rate of the balls in the container may be, for example, 70% by volume or less, or 65% by volume or less, based on the volume of the container.
  • the lower limit of the crushing treatment time (crushing time) in the ball mill crushing step may be, for example, 5 hours or more, 6 hours or more, 7 hours or more, or 8 hours or more.
  • the upper limit of the pulverization treatment time in the ball mill pulverization step may be, for example, 15 hours or less, 14 hours or less, 13 hours or less, or 12 hours or less.
  • the crushing time may be adjusted within the above range and may be, for example, 5 to 15 hours or 8 to 12 hours.
  • the above-mentioned fired product is further crushed by the vibration mill crushing step.
  • the filling rate of the balls in the container in the vibration mill crushing step can be adjusted according to the particle size distribution of the target silicon nitride powder.
  • the lower limit of the filling rate of the balls in the container may be, for example, 50% by volume or more, 55% by volume or more, or 60% by volume or more based on the volume of the container.
  • the upper limit of the filling rate of the balls in the container may be, for example, 80% by volume or less or 75% by volume or less based on the volume of the container.
  • the lower limit of the crushing treatment time (crushing time) in the vibration mill crushing step may be, for example, 8 hours or more, 9 hours or more, 10 hours or more, or 12 hours or more. By setting the lower limit of the crushing time within the above range, the crushed product can be sufficiently finely divided, and the processing efficiency of the classification step can be further improved.
  • the upper limit of the pulverization treatment time in the vibration mill pulverization step may be, for example, 20 hours or less, 19 hours or less, 18 hours or less, or 17 hours or less. By setting the upper limit of the crushing time within the above range, the fired product can be sufficiently crushed and excessive crushing can be prevented.
  • the crushing time may be adjusted within the above range and may be, for example, 8 to 20 hours or 12 to 17 hours.
  • the pulverized product prepared through the pulverization step is further classified by a dry method to prepare a silicon nitride powder having a desired particle size distribution.
  • the coarse powder can be removed to adjust the D90 of the silicon nitride powder.
  • the dry classification can be performed by, for example, airflow classification.
  • the air flow classifier can be classified by using, for example, a swirling air flow.
  • the primary air pressure (inlet pressure) may be, for example, 0.2 to 0.8 MPa or 0.3 to 0.7 MPa.
  • the silicon nitride powder obtained by the above-mentioned manufacturing method has excellent sinterability. That is, the above-mentioned silicon nitride powder can be suitably used as a raw material for a sintered body.
  • One embodiment of the method for producing a silicon nitride sintered body includes a step of molding and firing a sintered raw material containing the above-mentioned silicon nitride powder.
  • the sintering raw material may contain an oxide-based sintering aid in addition to the silicon nitride powder.
  • the oxide-based sintering aid for example, Y 2 O 3, MgO and Al 2 O 3 and the like.
  • the content of the oxide-based sintering aid in the sintering raw material may be, for example, 3 to 10% by mass.
  • the above-mentioned sintered raw material is pressed with a molding pressure of, for example, 3.0 to 30.0 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 molding 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 1.0 MPa.
  • the firing temperature may be 1860 to 2100 ° C. and may be 1880 to 2000 ° C.
  • the firing time at the firing temperature may be 6 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 obtained silicon nitride sintered body has a reduced grain boundary phase and has a dense structure, so that it can exhibit excellent bending strength.
  • the bending strength of the silicon nitride sintered body can be, for example, 550 MPa or more, 600 MPa or more, or 650 MPa or more at room temperature.
  • the bending strength of the silicon nitride sintered body in the present specification means a three-point bending strength measured at room temperature by preparing a test piece for strength measurement according to JIS R1601: 2008.
  • Example 1 ⁇ Preparation of silicon nitride powder>
  • Commercially available silicon powder (specific surface area: 3.0 m 2 / g) is immersed in a mixed acid containing hydrogen chloride and hydrogen fluoride whose temperature has been adjusted to 60 ° C., maintained at 60 ° C., and pretreated for 2 hours.
  • the mixed acid a commercially available hydrochloric acid (concentration: 35% by mass) and hydrofluoric acid (concentration: 55% by mass) were mixed at a mass ratio of 10: 1.
  • the silicon powder was taken out from the mixed acid, washed with water, and dried in a nitrogen atmosphere.
  • the oxygen concentration of the silicon powder after drying was 0.4% by mass. This oxygen concentration was measured by the infrared absorption method.
  • a molded product (bulk density: 1.4 g / cm 3 ) was prepared using the dried silicon powder.
  • the obtained molded product was allowed to stand in an electric furnace and fired at 1400 ° C. for 60 hours to prepare a fired product containing silicon nitride.
  • a mixed gas of nitrogen and hydrogen (a mixed gas in which N 2 and H 2 were mixed so that the volume ratio in the standard state was 80:20) was supplied.
  • the obtained fired body was roughly pulverized and then dry pulverized with a ball mill.
  • the filling rate of the balls in the container was set to 60% by volume, and the crushing time was set to 8 hours.
  • the filling rate of the balls to the container obtained by dry crushing with a vibration mill was set to 70% by volume, and the crushing time was set to 15 hours.
  • the silicon nitride powder obtained by dry pulverization was classified under the condition of a primary air pressure of 0.4 MPa to obtain a silicon nitride powder.
  • ⁇ Evaluation of silicon nitride powder Measurement of surface oxygen content> The amount of surface oxygen was measured using an oxygen / nitrogen simultaneous analyzer (manufactured by HORIBA, Ltd., device name: EMGA-920). Specifically, the silicon nitride powder was measured by heating it in a helium atmosphere at a heating rate of 8 ° C./sec from 20 ° C. to 2000 ° C. and quantifying the amount of oxygen before nitrogen was detected.
  • the obtained molded product was set in a carbon crucible together with a stuffing powder composed of a mixed powder of silicon nitride powder and BN powder, and fired in a nitrogen-pressurized atmosphere of 1 MPa at a temperature of 1900 ° C. for 12 hours to obtain a silicon nitride sintered body. Manufactured.
  • Example 2 A silicon nitride powder was prepared in the same manner as in Example 1 except that the vibration mill conditions for dry pulverization were changed to the conditions shown in Table 1. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
  • Example 3 A silicon nitride powder was prepared in the same manner as in Example 1 except that the ball mill pulverization conditions for dry pulverization were changed to the conditions shown in Table 1. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
  • Example 1 A silicon nitride powder was prepared in the same manner as in Example 1 except that the conditions for dry classification were changed to the conditions shown in Table 1. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
  • a silicon nitride powder capable of producing a sintered body having excellent bending strength.
  • a method for producing a silicon nitride sintered body having excellent bending strength it is possible to provide a silicon nitride powder capable of producing a sintered body having excellent bending strength.

Abstract

One aspect of the present disclosure provides a silicon nitride powder which contains primary particles of silicon nitride, and wherein if D10 and D90 are particle diameters at which the integrated value from the smallest particle diameter reaches 10% and 90% of the total in the volume-based particle size distribution curve as determined by a laser diffraction/scattering method, the difference between D90 and D10 is 5.5 μm or less.

Description

窒化ケイ素粉末、及び窒化ケイ素焼結体の製造方法Method for manufacturing silicon nitride powder and silicon nitride sintered body
　本開示は、窒化ケイ素粉末、及び窒化ケイ素焼結体の製造方法に関する。 The present disclosure relates to a method for producing silicon nitride powder and a silicon nitride sintered body.
　窒化ケイ素は、強度、硬度、靭性、耐熱性、耐食性、耐熱衝撃性等に優れた材料であることから、ダイカストマシン及び溶解炉等の各種産業用の部品、及び自動車部品等に利用されている。また、窒化ケイ素は、高温における機械的特性にも優れることから、高温強度、高温クリープ特性が求められるガスタービン部品に適用することが検討されている。 Since silicon nitride is a material having excellent strength, hardness, toughness, heat resistance, corrosion resistance, heat impact resistance, etc., it is used for various industrial parts such as die casting machines and melting furnaces, and automobile parts. .. Further, since silicon nitride is excellent in mechanical properties at high temperatures, it is being studied to apply it to gas turbine parts that require high temperature strength and high temperature creep characteristics.
　窒化ケイ素焼結体には、熱伝導率及び機械的特性の更なる向上が求められている。例えば、特許文献１では、常温における熱伝導率が１００～３００Ｗ／（ｍ・Ｋ）であり、常温における３点曲げ強度が６００～１５００ＭＰａであることを特徴とする窒化珪素質焼結体が記載されている。 The silicon nitride sintered body is required to further improve its thermal conductivity and mechanical properties. For example, Patent Document 1 describes a silicon nitride sintered body characterized in that the thermal conductivity at room temperature is 100 to 300 W / (m · K) and the three-point bending strength at room temperature is 600 to 1500 MPa. Has been done.
特開２００４－２６２７５６号公報Japanese Unexamined Patent Publication No. 2004-262756
　本開示は、曲げ強度に優れる焼結体を製造可能な窒化ケイ素粉末を提供することを目的とする。本開示はまた、曲げ強度に優れる窒化ケイ素焼結体の製造方法を提供することを目的とする。 An object of the present disclosure is to provide a silicon nitride powder capable of producing a sintered body having excellent bending strength. It is also an object of the present disclosure to provide a method for producing a silicon nitride sintered body having excellent bending strength.
　本開示の一側面は、窒化ケイ素の一次粒子を含み、レーザー回折・散乱法によって測定される体積基準の粒子径の分布曲線において、小粒径からの積算値が全体の１０％及び９０％に達した時の粒子径を、それぞれＤ１０及びＤ９０としたときに、Ｄ９０とＤ１０との差が５．５μｍ以下である、窒化ケイ素粉末を提供する。 One aspect of the present disclosure is that the integrated value from the small particle size is 10% and 90% of the total in the volume-based particle size distribution curve measured by the laser diffraction / scattering method, which contains the primary particles of silicon nitride. Provided is a silicon nitride powder in which the difference between D90 and D10 is 5.5 μm or less when the particle size at the time of reaching is D10 and D90, respectively.
　上記窒化ケイ素粉末は、Ｄ９０とＤ１０との差（Ｄ９０－Ｄ１０）が所定値以下となることから、粒度分布が狭く、より緻密な組織を有する成形体（未焼成物）を調製することができる。上記成形体を焼成して得られる窒化ケイ素焼結体は、ボイドの発生等が抑制され、曲げ強度に優れる。 Since the difference (D90-D10) between D90 and D10 is not more than a predetermined value in the silicon nitride powder, a molded product (unfired product) having a narrow particle size distribution and a finer structure can be prepared. .. The silicon nitride sintered body obtained by firing the molded body is excellent in bending strength because the generation of voids is suppressed.
　上記窒化ケイ素は、Ｄ５０が１．５μｍ以下であってよい。Ｄ５０の上限値が上記範囲内であると、窒化ケイ素粉末が適度な粒度分布を有するため、一次粒子のパッキング密度をより向上させることができる。 The silicon nitride may have a D50 of 1.5 μm or less. When the upper limit of D50 is within the above range, the silicon nitride powder has an appropriate particle size distribution, so that the packing density of the primary particles can be further improved.
　上記窒化ケイ素粉末は、Ｄ９０が６．０μｍ以下であってよい。Ｄ９０の上限値を上記範囲内であると、粗大粒子の割合を十分に低減でき、焼結体の密度低下をより十分に抑制することができる。また、取扱い性により優れる。 The silicon nitride powder may have a D90 of 6.0 μm or less. When the upper limit of D90 is within the above range, the proportion of coarse particles can be sufficiently reduced, and the decrease in the density of the sintered body can be more sufficiently suppressed. In addition, it is superior in handleability.
　上記窒化ケイ素粉末は、ＢＥＴ比表面積が９．０ｍ２／ｇ未満であってよい。 The silicon nitride powder may have a BET specific surface area of less than 9.0 m 2 / g.
　本開示の一側面は、上述の窒化ケイ素粉末を含む焼結原料を成形し焼成する工程を有する、窒化ケイ素焼結体の製造方法を提供する。 One aspect of the present disclosure provides a method for producing a silicon nitride sintered body, which comprises a step of molding and firing a sintered raw material containing the above-mentioned silicon nitride powder.
　上記窒化ケイ素焼結体の製造方法は、上述の窒化ケイ素粉末を含む焼結原料を用いることから、得られる窒化ケイ素焼結体は、優れた曲げ強度を発揮し得る。 Since the method for producing the silicon nitride sintered body uses the sintered raw material containing the silicon nitride powder described above, the obtained silicon nitride sintered body can exhibit excellent bending strength.
　本開示によれば、曲げ強度に優れる焼結体を製造可能な窒化ケイ素粉末を提供できる。本開示によればまた、曲げ強度に優れる窒化ケイ素焼結体の製造方法を提供できる。 According to the present disclosure, it is possible to provide a silicon nitride powder capable of producing a sintered body having excellent bending strength. According to the present disclosure, it is also possible to provide a method for producing a silicon nitride sintered body having excellent bending strength.
　以下、本開示の実施形態について説明する。ただし、以下の実施形態は、本開示を説明するための例示であり、本開示を以下の内容に限定する趣旨ではない。 Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents.
　本明細書において例示する材料は特に断らない限り、１種を単独で又は２種以上を組み合わせて用いることができる。組成物中の各成分の含有量は、組成物中の各成分に該当する物質が複数存在する場合には、特に断らない限り、組成物中に存在する当該複数の物質の合計量を意味する。本明細書における「工程」とは、互いに独立した工程であってもよく、同時に行われる工程であってもよい。 Unless otherwise specified, the materials exemplified in this specification may be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component in the composition are present, unless otherwise specified. .. The "process" in the present specification may be a process independent of each other or a process performed at the same time.
　窒化ケイ素粉末の一実施形態は、窒化ケイ素の一次粒子を含み、レーザー回折・散乱法によって測定される体積基準の粒子径の分布曲線において、小粒径からの積算値が全体の１０％及び９０％に達した時の粒子径を、それぞれＤ１０及びＤ９０としたときに、Ｄ９０とＤ１０との差が５．５μｍ以下である。 One embodiment of the silicon nitride powder contains primary particles of silicon nitride, and in the volume-based particle size distribution curve measured by the laser diffraction / scattering method, the integrated values from the small particle size are 10% and 90% of the total. The difference between D90 and D10 is 5.5 μm or less when the particle diameters when the percentage reaches% are D10 and D90, respectively.
　上記Ｄ９０とＤ１０との差（Ｄ９０－Ｄ１０）の上限値は５．５μｍ以下であるが、例えば、５．４μｍ以下、５．２μｍ以下、５．０μｍ以下、４．８μｍ以下、又は４．６μｍ以下であってよい。上記差の上限値が上記範囲内であると、窒化ケイ素粉末を圧縮成形等して調製される成形体がより緻密な組織を有し得るため、焼結した際のボイドの発生等をより抑制することができる。つまり、得られる窒化ケイ素焼結体の曲げ強度をより向上させることができる。上記Ｄ９０とＤ１０との差の下限値は、例えば、３．０μｍ以上、３．２μｍ以上、又は３．４μｍ以上であってよい。上記差の下限値が上記範囲内であると、窒化ケイ素粉末が適度な粒度分布を有するため、一次粒子のパッキング密度をより向上させることができる。上記差は上述の範囲内で調整することができ、例えば、３．０～５．５μｍ、３．２～５．４μｍ、又は３．４～４．６μｍであってよい。上記差は、窒化ケイ素粉末の製造時の粉砕条件等を調整することで制御できる。 The upper limit of the difference between D90 and D10 (D90-D10) is 5.5 μm or less, but for example, 5.4 μm or less, 5.2 μm or less, 5.0 μm or less, 4.8 μm or less, or 4.6 μm. It may be: When the upper limit of the above difference is within the above range, the molded product prepared by compression molding or the like of silicon nitride powder may have a finer structure, so that the generation of voids during sintering is further suppressed. can do. That is, the bending strength of the obtained silicon nitride sintered body can be further improved. The lower limit of the difference between D90 and D10 may be, for example, 3.0 μm or more, 3.2 μm or more, or 3.4 μm or more. When the lower limit of the difference is within the above range, the silicon nitride powder has an appropriate particle size distribution, so that the packing density of the primary particles can be further improved. The above difference can be adjusted within the above range, and may be, for example, 3.0 to 5.5 μm, 3.2 to 5.4 μm, or 3.4 to 4.6 μm. The above difference can be controlled by adjusting the pulverization conditions and the like at the time of producing the silicon nitride powder.
　窒化ケイ素粉末のＤ９０の上限値は、例えば、６．０μｍ以下、５．８μｍ以下、５．６μｍ以下、５．４μｍ以下、又は５．２μｍ以下であってよい。Ｄ９０の上限値を上記範囲内であると、粗大粒子の割合を十分に低減でき、焼結体の密度低下をより十分に抑制することができる。Ｄ９０の下限値は、例えば、３．５μｍ以上、３．７μｍ以上、３．９μｍ以上、又は４．０μｍ以上であってよい。Ｄ９０は上述の範囲内で調整でき、例えば、３．５～６．０μｍ、又は４．０～５．２μｍであってよい。窒化ケイ素粉末のＤ９０は、例えば、窒化ケイ素粉末の製造時における粉砕条件等を調整することで制御できる。 The upper limit of D90 of the silicon nitride powder may be, for example, 6.0 μm or less, 5.8 μm or less, 5.6 μm or less, 5.4 μm or less, or 5.2 μm or less. When the upper limit of D90 is within the above range, the proportion of coarse particles can be sufficiently reduced, and the decrease in the density of the sintered body can be more sufficiently suppressed. The lower limit of D90 may be, for example, 3.5 μm or more, 3.7 μm or more, 3.9 μm or more, or 4.0 μm or more. D90 can be adjusted within the above range and may be, for example, 3.5 to 6.0 μm or 4.0 to 5.2 μm. The D90 of the silicon nitride powder can be controlled by, for example, adjusting the pulverization conditions at the time of producing the silicon nitride powder.
　窒化ケイ素粉末のＤ５０の上限値は、例えば、１．５μｍ以下、又は１．４μｍ以下であってよい。Ｄ５０の上限値が上記範囲内であると、窒化ケイ素焼結体の強度をより向上させることができる。窒化ケイ素粉末のＤ５０の下限値は、例えば、１．１μｍ以上、又は１．２μｍ以上であってよい。窒化ケイ素粉末のＤ５０は上述の範囲内で調整することができ、例えば、１．１～１．５μｍ、又は１．２～１．４μｍであってよい。 The upper limit of D50 of the silicon nitride powder may be, for example, 1.5 μm or less, or 1.4 μm or less. When the upper limit of D50 is within the above range, the strength of the silicon nitride sintered body can be further improved. The lower limit of D50 of the silicon nitride powder may be, for example, 1.1 μm or more, or 1.2 μm or more. The D50 of the silicon nitride powder can be adjusted within the above range, and may be, for example, 1.1 to 1.5 μm or 1.2 to 1.4 μm.
　本明細書におけるＤ１０、Ｄ５０、及びＤ９０はそれぞれ、レーザー回折・散乱法によって測定される体積基準の粒子径の分布曲線において、小粒径からの積算値が全体の１０％、５０％及び９０％に達した時の粒子径をいう。レーザー解析散乱法は、ＪＩＳ　Ｚ　８８２５：２０１３「粒子径解析－レーザー回折・散乱法」に記載の方法に準拠して測定できる。測定には、レーザー回折散乱法粒度分布測定装置（ベックマンコールター社製、商品名：ＬＳ－１３　３２０）等を使用することができる。なお、Ｄ５０は、メディアン径とも呼ばれ、窒化ケイ素粉末の平均粒径を意味する。 In the volume-based particle size distribution curves measured by the laser diffraction / scattering method, the integrated values from the small particle size of D10, D50, and D90 in the present specification are 10%, 50%, and 90% of the total, respectively. The particle size when it reaches. The laser analysis scattering method can be measured according to the method described in JIS Z 8825: 2013 "Particle size analysis-laser diffraction / scattering method". For the measurement, a laser diffraction / scattering method particle size distribution measuring device (manufactured by Beckman Coulter, trade name: LS-13 320) or the like can be used. In addition, D50 is also called a median diameter and means the average particle diameter of the silicon nitride powder.
　窒化ケイ素粉末のＢＥＴ比表面積の上限値は、例えば、９．０ｍ２／ｇ未満、８．８ｍ２／ｇ以下、８．６ｍ２／ｇ以下、又は８．５ｍ２／ｇ以下であってよい。窒化ケイ素粉末のＢＥＴ比表面積の下限値は、例えば、５．０ｍ２／ｇ以上、５．１ｍ２／ｇ以上、５．２ｍ２／ｇ以上、５．３ｍ２／ｇ以上、５．４ｍ２／ｇ以上、５．５ｍ２／ｇ以上、６．０ｍ２／ｇ以上、又は７．０ｍ２／ｇ以上、であってよい。窒化ケイ素粉末のＢＥＴ比表面積は上述の範囲内で調整することができ、例えば、５．０～９．０ｍ２／ｇ、又は５．５～８．５ｍ２／ｇ、又は７．０～８．５ｍ２／ｇであってよい。窒化ケイ素粉末のＢＥＴ比表面積は、例えば、窒化ケイ素粉末の製造時における粉砕条件等を調整することで制御できる。 The upper limit of the BET specific surface area of the silicon nitride powder may be, for example, less than 9.0 m 2 / g, 8.8 m 2 / g or less, 8.6 m 2 / g or less, or 8.5 m 2 / g or less. .. The lower limit of the BET specific surface area of the silicon nitride powder is, for example, 5.0 m 2 / g or more, 5.1 m 2 / g or more, 5.2 m 2 / g or more, 5.3 m 2 / g or more, 5.4 m 2 It may be / g or more, 5.5 m 2 / g or more, 6.0 m 2 / g or more, or 7.0 m 2 / g or more. The BET specific surface area of the silicon nitride powder can be adjusted within the above range, for example, 5.0 to 9.0 m 2 / g, 5.5 to 8.5 m 2 / g, or 7.0 to 8 It may be .5 m 2 / g. The BET specific surface area of the silicon nitride powder can be controlled, for example, by adjusting the pulverization conditions during the production of the silicon nitride powder.
　本明細書におけるＢＥＴ比表面積は、ＪＩＳ　Ｚ　８８３０：２０１３「ガス吸着による粉体（固体）の比表面積測定方法」に記載の方法に準拠し、窒素ガスを使用してＢＥＴ一点法によって測定される値である。 The BET specific surface area in the present specification is measured by the BET one-point method using nitrogen gas in accordance with the method described in JIS Z 8830: 2013 “Method for measuring the specific surface area of powder (solid) by gas adsorption”. The value.
　窒化ケイ素の表面酸素量の上限値は、例えば、２．０質量％以下、１．５質量％以下、又は１．３質量％以下であってよい。窒化ケイ素の表面酸素量の上限値が上記範囲内であると、窒化ケイ素焼結体を製造した際の粒界相をより十分に低減することができる。窒化ケイ素の表面酸素量の下限値は、例えば、０．２０質量％以上、０．３０質量％以上、０．３５質量％以上、０．４０質量％以上、０．４５質量％以上、０．６０質量％以上、０．８０質量％以上、又は１．０質量％以上であってよい。窒化ケイ素の表面酸素量の下限値が上記範囲内であると、窒化ケイ素を焼成させる際の粒成長を促進させることができ、窒化ケイ素焼結体の曲げ強度をより向上させることができる。窒化ケイ素の表面酸素量は上述の範囲で調整することができ、例えば、０．２０～２．０質量％、０．２０～１．５質量％、又は１．０～１．５質量％であってよい。窒化ケイ素の表面酸素量は、例えば、窒化ケイ素粉末の製造における焼成工程における雰囲気の成分、並びに、焼成温度及び焼成時間等の調整によって制御できる。 The upper limit of the surface oxygen content of silicon nitride may be, for example, 2.0% by mass or less, 1.5% by mass or less, or 1.3% by mass or less. When the upper limit of the surface oxygen amount of silicon nitride is within the above range, the grain boundary phase at the time of producing the silicon nitride sintered body can be more sufficiently reduced. The lower limit of the surface oxygen content of silicon nitride is, for example, 0.20% by mass or more, 0.30% by mass or more, 0.35% by mass or more, 0.40% by mass or more, 0.45% by mass or more, 0. It may be 60% by mass or more, 0.80% by mass or more, or 1.0% by mass or more. When the lower limit of the surface oxygen amount of silicon nitride is within the above range, grain growth at the time of firing silicon nitride can be promoted, and the bending strength of the silicon nitride sintered body can be further improved. The amount of surface oxygen of silicon nitride can be adjusted within the above range, for example, 0.20 to 2.0% by mass, 0.20 to 1.5% by mass, or 1.0 to 1.5% by mass. It may be there. The amount of surface oxygen of silicon nitride can be controlled, for example, by adjusting the atmosphere component in the firing step in the production of silicon nitride powder, the firing temperature, the firing time, and the like.
　本明細書における「表面酸素量」は以下の手順で求められる数値を意味する。窒化ケイ素粉末の酸素量及び窒素量は、酸素・窒素分析装置を用いて分析する。測定用の試料を、ヘリウムガスの雰囲気中、８℃／秒の昇温速度で２０℃から２０００℃まで昇温する。昇温に伴って脱離する酸素を赤外吸収法によって検知する。昇温当初は、窒化ケイ素粉末の表面に結合している酸素が脱離する。更に加熱し、温度が１４００℃近傍に到達すると、窒化ケイ素が分解をし始める。窒化ケイ素の分解開始は、窒素が検出され始めることによって把握することができる。窒化ケイ素が分解をし始めると、窒化ケイ素粉末の内部にある酸素が脱離する。したがって、この段階で脱離する酸素は、内部酸素量に相当するため、窒素が検出される前までに検出され、定量された酸素量を表面酸素量とする。 "Surface oxygen amount" in this specification means a numerical value obtained by the following procedure. The amount of oxygen and the amount of nitrogen in the silicon nitride powder are analyzed using an oxygen / nitrogen analyzer. The sample for measurement is heated from 20 ° C. to 2000 ° C. at a heating rate of 8 ° C./sec in an atmosphere of helium gas. Oxygen desorbed as the temperature rises is detected by the infrared absorption method. At the beginning of the temperature rise, oxygen bound to the surface of the silicon nitride powder is eliminated. When the temperature reaches around 1400 ° C. after further heating, the silicon nitride begins to decompose. The start of decomposition of silicon nitride can be grasped by the start of detection of nitrogen. When the silicon nitride begins to decompose, the oxygen inside the silicon nitride powder is eliminated. Therefore, since the oxygen desorbed at this stage corresponds to the amount of internal oxygen, the amount of oxygen detected and quantified before nitrogen is detected is defined as the amount of surface oxygen.
　上述の窒化ケイ素粉末は、例えば、以下のような方法で製造することができる。窒化ケイ素粉末の製造方法の一実施形態は、ケイ素粉末を、窒素と、水素及びアンモニアからなる群より選択される少なくとも一種とを含む雰囲気下で焼成して焼成物を得る工程（以下、焼成工程ともいう）と、上記焼成物を乾式粉砕して粉砕物を得る工程（以下、粉砕工程ともいう）と、上記粉砕物を乾式分級する工程（以下、分級工程ともいう）と、を有する。 The above-mentioned silicon nitride powder can be produced, for example, by the following method. One embodiment of the method for producing silicon nitride powder is a step of calcining the silicon powder in an atmosphere containing nitrogen and at least one selected from the group consisting of hydrogen and ammonia to obtain a calcined product (hereinafter, calcining step). It also has a step of dry-grinding the fired product to obtain a crushed product (hereinafter, also referred to as a crushing step), and a step of dry-classifying the crushed product (hereinafter, also referred to as a classification step).
　ケイ素粉末としては、酸素濃度の低いケイ素粉末を用いてもよい。ケイ素粉末の酸素濃度の上限値は、例えば、０．４０質量％以下、０．３０質量％以下、又は０．２０質量％以下であってよい。ケイ素粉末の酸素濃度を上記範囲内とすることで、得られる窒化ケイ素粉末の内部における酸素量をより低減できる。ケイ素粉末の酸素濃度の下限値は、例えば、０．１０質量％以上、又は０．１５質量％以上であってよい。ケイ素粉末の酸素濃度は上述の範囲で調整することができ、例えば、０．１０～０．４０質量％であってよい。 As the silicon powder, a silicon powder having a low oxygen concentration may be used. The upper limit of the oxygen concentration of the silicon powder may be, for example, 0.40% by mass or less, 0.30% by mass or less, or 0.20% by mass or less. By setting the oxygen concentration of the silicon powder within the above range, the amount of oxygen inside the obtained silicon nitride powder can be further reduced. The lower limit of the oxygen concentration of the silicon powder may be, for example, 0.10% by mass or more, or 0.15% by mass or more. The oxygen concentration of the silicon powder can be adjusted in the above range, and may be, for example, 0.10 to 0.40% by mass.
　本明細書におけるケイ素粉末の酸素濃度は、赤外線吸収法によって測定される値を意味する。 The oxygen concentration of the silicon powder in the present specification means a value measured by an infrared absorption method.
　ケイ素粉末は、市販の物を用いることもでき、別途調製したものを用いてもよい。ケイ素粉末の酸素濃度が高い場合には、例えば、フッ化水素酸を含む前処理液を用いて、ケイ素粉末に結合する酸素量を低減することができる。例えば、上記窒化ケイ素粉末の製造方法は、フッ化水素酸を含む前処理液を用いてケイ素粉末を前処理し、酸素濃度が０．４０質量％以上であるケイ素粉末を得る前処理工程を更に有していてもよい。 As the silicon powder, a commercially available product may be used, or a separately prepared one may be used. When the oxygen concentration of the silicon powder is high, for example, a pretreatment liquid containing hydrofluoric acid can be used to reduce the amount of oxygen bound to the silicon powder. For example, in the above method for producing silicon nitride powder, a pretreatment step of pretreating the silicon powder with a pretreatment liquid containing hydrofluoric acid to obtain a silicon powder having an oxygen concentration of 0.40% by mass or more is further added. You may have.
　前処理液は、フッ化水素酸を含むが、例えば、塩酸等の酸との混酸であってもよく、フッ化水素酸のみからなってもよい。前処理工程における前処理液の温度は、例えば、４０～８０℃であってよい。また、前処理液とケイ素粉末とを接触させる時間は、例えば、１～１０時間であってよい。 The pretreatment liquid contains hydrofluoric acid, but may be a mixed acid with an acid such as hydrochloric acid, or may consist only of hydrofluoric acid. The temperature of the pretreatment liquid in the pretreatment step may be, for example, 40 to 80 ° C. The time for contacting the pretreatment liquid with the silicon powder may be, for example, 1 to 10 hours.
　焼成工程では、ケイ素粉末を、窒素と、水素及びアンモニアからなる群より選択される少なくも一種と、を含む混合雰囲気下で焼成して窒化ケイ素を含む焼成物を得る。混合雰囲気における水素及びアンモニアの合計の含有量は、混合雰囲気全体を基準として、例えば、１０～４０体積％であってよい。焼成温度は、例えば、１１００～１４５０℃、又は１２００～１４００℃であってよい。焼成時間は、例えば、３０～１００時間であってよい。 In the firing step, the silicon powder is fired in a mixed atmosphere containing nitrogen and at least one selected from the group consisting of hydrogen and ammonia to obtain a fired product containing silicon nitride. The total content of hydrogen and ammonia in the mixed atmosphere may be, for example, 10-40% by volume based on the entire mixed atmosphere. The firing temperature may be, for example, 1100 to 1450 ° C, or 1200 to 1400 ° C. The firing time may be, for example, 30 to 100 hours.
　粉砕工程では、焼成工程で得られた上記焼成物を乾式で粉砕して粉砕物を得る。本実施形態に係る窒化ケイ素粉末の製造方法において、粉砕工程は、ボールミル粉砕工程及び振動ミル粉砕工程の２つの工程を含む。焼成物を粉砕し、粒度を調整することによって、後の分級工程での制御が容易となる。焼成工程で得られる窒化ケイ素を含む焼成物が、塊状、インゴット状等になっている場合、粉砕工程を行う効果がより顕著である。 In the crushing step, the above-mentioned fired product obtained in the firing step is crushed by a dry method to obtain a crushed product. In the method for producing silicon nitride powder according to the present embodiment, the crushing step includes two steps, a ball mill crushing step and a vibration mill crushing step. By crushing the fired product and adjusting the particle size, control in the subsequent classification step becomes easy. When the fired product containing silicon nitride obtained in the firing step is in the form of a lump, an ingot, or the like, the effect of performing the crushing step is more remarkable.
　各粉砕は、粗粉砕と微粉砕というように複数段階に分けて行ってもよい。粉砕工程は、乾式粉砕工程で行われる。 Each crushing may be performed in a plurality of stages such as coarse crushing and fine crushing. The crushing step is a dry crushing step.
　ボールミル粉砕工程における容器へのボールの充填率は、目的とする窒化ケイ素粉末の粒度分布に合わせて調整することができる。容器へのボールの充填率の下限値は、容器の容積を基準として、例えば、４０体積％以上、４５体積％以上、５０体積％以上、又は６０体積％以上であってよい。容器へのボールの充填率の上限値は、容器の容積を基準として、例えば、７０体積％以下、又は６５体積％以下であってよい。 The filling rate of balls in the container in the ball mill crushing step can be adjusted according to the particle size distribution of the target silicon nitride powder. The lower limit of the filling rate of the balls in the container may be, for example, 40% by volume or more, 45% by volume or more, 50% by volume or more, or 60% by volume or more based on the volume of the container. The upper limit of the filling rate of the balls in the container may be, for example, 70% by volume or less, or 65% by volume or less, based on the volume of the container.
　ボールミル粉砕工程における粉砕処理の時間（粉砕時間）の下限値は、例えば、５時間以上、６時間以上、７時間以上、又は８時間以上であってよい。粉砕時間の下限値を上記範囲内とすることで、粉砕物を十分に細かくすることができ、乾式での更なる粉砕時の粉砕効率をより向上させることができる。ボールミル粉砕工程における粉砕処理の時間の上限値は、例えば、１５時間以下、１４時間以下、１３時間以下、又は１２時間以下であってよい。粉砕時間の上限値を上記範囲内とすることで、焼成物を十分に粉砕することができ、過剰な粉砕を防ぐこともできる。粉砕時間は上述の範囲内で調整してよく、例えば、５～１５時間、又は８～１２時間であってよい。 The lower limit of the crushing treatment time (crushing time) in the ball mill crushing step may be, for example, 5 hours or more, 6 hours or more, 7 hours or more, or 8 hours or more. By setting the lower limit of the pulverization time within the above range, the pulverized product can be sufficiently finely divided, and the pulverization efficiency at the time of further pulverization in the dry method can be further improved. The upper limit of the pulverization treatment time in the ball mill pulverization step may be, for example, 15 hours or less, 14 hours or less, 13 hours or less, or 12 hours or less. By setting the upper limit of the crushing time within the above range, the fired product can be sufficiently crushed and excessive crushing can be prevented. The crushing time may be adjusted within the above range and may be, for example, 5 to 15 hours or 8 to 12 hours.
　粉砕工程はボールミル粉砕工程の後に、振動ミル粉砕工程によって上述の焼成物を更に粉砕する。振動ミル粉砕工程における容器へのボールの充填率は、目的とする窒化ケイ素粉末の粒度分布に合わせて調整することができる。容器へのボールの充填率の下限値は、容器の容積を基準として、例えば、５０体積％以上、５５体積％以上、又は６０体積％以上であってよい。容器へのボールの充填率の上限値は、容器の容積を基準として、例えば、８０体積％以下、又は７５体積％以下であってよい。 In the crushing step, after the ball mill crushing step, the above-mentioned fired product is further crushed by the vibration mill crushing step. The filling rate of the balls in the container in the vibration mill crushing step can be adjusted according to the particle size distribution of the target silicon nitride powder. The lower limit of the filling rate of the balls in the container may be, for example, 50% by volume or more, 55% by volume or more, or 60% by volume or more based on the volume of the container. The upper limit of the filling rate of the balls in the container may be, for example, 80% by volume or less or 75% by volume or less based on the volume of the container.
　振動ミル粉砕工程における粉砕処理の時間（粉砕時間）の下限値は、例えば、８時間以上、９時間以上、１０時間以上、又は１２時間以上であってよい。粉砕時間の下限値を上記範囲内とすることで、粉砕物を十分に細かくすることができ、分級工程の処理効率をより向上させることができる。振動ミル粉砕工程における粉砕処理の時間の上限値は、例えば、２０時間以下、１９時間以下、１８時間以下、又は１７時間以下であってよい。粉砕時間の上限値を上記範囲内とすることで、焼成物を十分に粉砕することができ、過剰な粉砕を防ぐこともできる。粉砕時間は上述の範囲内で調整してよく、例えば、８～２０時間、又は１２～１７時間であってよい。 The lower limit of the crushing treatment time (crushing time) in the vibration mill crushing step may be, for example, 8 hours or more, 9 hours or more, 10 hours or more, or 12 hours or more. By setting the lower limit of the crushing time within the above range, the crushed product can be sufficiently finely divided, and the processing efficiency of the classification step can be further improved. The upper limit of the pulverization treatment time in the vibration mill pulverization step may be, for example, 20 hours or less, 19 hours or less, 18 hours or less, or 17 hours or less. By setting the upper limit of the crushing time within the above range, the fired product can be sufficiently crushed and excessive crushing can be prevented. The crushing time may be adjusted within the above range and may be, for example, 8 to 20 hours or 12 to 17 hours.
　分級工程では、粉砕工程を経て調製された上記粉砕物を更に乾式で分級して、所望の粒度分布を有する窒化ケイ素粉末を調製する。例えば、粗粉を除去して窒化ケイ素粉末のＤ９０を調整する等することができる。乾式分級は、例えば、気流分級等によって行うことができる。気流分級機は、例えば、旋回気流等を用いて分級することができる。一次エアー圧力（入口圧力）は、例えば、０．２～０．８ＭＰａ、又は０．３～０．７ＭＰａであってよい。 In the classification step, the pulverized product prepared through the pulverization step is further classified by a dry method to prepare a silicon nitride powder having a desired particle size distribution. For example, the coarse powder can be removed to adjust the D90 of the silicon nitride powder. The dry classification can be performed by, for example, airflow classification. The air flow classifier can be classified by using, for example, a swirling air flow. The primary air pressure (inlet pressure) may be, for example, 0.2 to 0.8 MPa or 0.3 to 0.7 MPa.
　上述の製造方法によって得られる窒化ケイ素粉末は焼結性に優れる。すなわち、上述の窒化ケイ素粉末は焼結体原料に好適に用いることができる。 The silicon nitride powder obtained by the above-mentioned manufacturing method has excellent sinterability. That is, the above-mentioned silicon nitride powder can be suitably used as a raw material for a sintered body.
　窒化ケイ素焼結体の製造方法の一実施形態は、上述の窒化ケイ素粉末を含む焼結原料を成形し焼成する工程を有する。 One embodiment of the method for producing a silicon nitride sintered body includes a step of molding and firing a sintered raw material containing the above-mentioned silicon nitride powder.
　焼結原料は窒化ケイ素粉末の他に、酸化物系焼結助剤を含んでいてもよい。酸化物系焼結助剤としては、例えば、Ｙ２Ｏ３、ＭｇＯ及びＡｌ２Ｏ３等が挙げられる。焼結原料における酸化物系焼結助剤の含有量は、例えば、３～１０質量％であってよい。 The sintering raw material may contain an oxide-based sintering aid in addition to the silicon nitride powder. The oxide-based sintering aid, for example, Y 2 O 3, MgO and Al 2 O 3 and the like. The content of the oxide-based sintering aid in the sintering raw material may be, for example, 3 to 10% by mass.
　上記工程では、上述の焼結原料を例えば３．０～３０．０ＭＰａの成形圧力で加圧して成形体を得る。成形体は一軸加圧して作製してもよいし、ＣＩＰによって作製してもよい。また、ホットプレスによって成形しながら焼成してもよい。成形体の焼成は、窒素ガス又はアルゴンガス等の不活性ガス雰囲気中で行ってよい。焼成時の圧力は、０．７～１．０ＭＰａであってよい。焼成温度は１８６０～２１００℃であってよく、１８８０～２０００℃であってもよい。当該焼成温度における焼成時間は６～２０時間であってよく、８～１６時間であってよい。焼成温度までの昇温速度は、例えば１．０～１０．０℃／時間であってよい。 In the above step, the above-mentioned sintered raw material is pressed with a molding pressure of, for example, 3.0 to 30.0 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 molding 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 1.0 MPa. The firing temperature may be 1860 to 2100 ° C. and may be 1880 to 2000 ° C. The firing time at the firing temperature may be 6 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.
　得られる窒化ケイ素焼結体は、粒界相が低減されており、緻密な組織を有することから、優れた曲げ強度を発揮し得る。 The obtained silicon nitride sintered body has a reduced grain boundary phase and has a dense structure, so that it can exhibit excellent bending strength.
　窒化ケイ素焼結体の曲げ強度は、室温で、例えば、５５０ＭＰａ以上、６００ＭＰａ以上、又は６５０ＭＰａ以上とすることができる。本明細書における窒化ケイ素焼結体の曲げ強度は、ＪＩＳ　Ｒ１６０１：２００８に準じて強度測定用の試験片を作製し、室温において測定される３点曲げ強さを意味する。 The bending strength of the silicon nitride sintered body can be, for example, 550 MPa or more, 600 MPa or more, or 650 MPa or more at room temperature. The bending strength of the silicon nitride sintered body in the present specification means a three-point bending strength measured at room temperature by preparing a test piece for strength measurement according to JIS R1601: 2008.
　以上、幾つかの実施形態について説明したが、本開示は上記実施形態に何ら限定されるものではない。また、上述した実施形態についての説明内容は、互いに適用することができる。 Although some embodiments have been described above, the present disclosure is not limited to the above embodiments. In addition, the contents of the description of the above-described embodiments can be applied to each other.
　以下、実施例及び比較例を参照して本開示の内容をより詳細に説明する。ただし、本開示は、下記の実施例に限定されるものではない。 Hereinafter, the contents of the present disclosure will be described in more detail with reference to Examples and Comparative Examples. However, the present disclosure is not limited to the following examples.
（実施例１）
＜窒化ケイ素粉末の調製＞
　市販のケイ素粉末（比表面積：３．０ｍ２／ｇ）を、６０℃に温度調整した、塩化水素及びフッ化水素を含む混酸中に浸漬して、６０℃に維持し、２時間、前処理を施した。上記混酸は、市販の塩酸（濃度：３５質量％）とフッ化水素酸（濃度：５５質量％）とを、１０：１の質量比で混合したものを用いた。その後、混酸からケイ素粉末を取り出して水で洗浄し、窒素雰囲気下で乾燥した。乾燥後のケイ素粉末の酸素濃度は、０．４質量％であった。この酸素濃度は、赤外線吸収法によって測定した。 (Example 1)
<Preparation of silicon nitride powder>
Commercially available silicon powder (specific surface area: 3.0 m 2 / g) is immersed in a mixed acid containing hydrogen chloride and hydrogen fluoride whose temperature has been adjusted to 60 ° C., maintained at 60 ° C., and pretreated for 2 hours. Was given. As the mixed acid, a commercially available hydrochloric acid (concentration: 35% by mass) and hydrofluoric acid (concentration: 55% by mass) were mixed at a mass ratio of 10: 1. Then, the silicon powder was taken out from the mixed acid, washed with water, and dried in a nitrogen atmosphere. The oxygen concentration of the silicon powder after drying was 0.4% by mass. This oxygen concentration was measured by the infrared absorption method.
　乾燥後のケイ素粉末を用いて成形体（嵩密度：１．４ｇ／ｃｍ３）を作製した。得られた成形体を電気炉内に静置し、１４００℃で６０時間かけて焼成し窒化ケイ素を含む焼成体を作製した。焼成時の雰囲気として、窒素と水素との混合ガス（Ｎ２とＨ２とを標準状態における体積比で８０：２０となるように混合した混合ガス）を供給した。得られた焼成体を粗粉砕した後、ボールミルで乾式粉砕した。ボールミル粉砕は、容器に対するボールの充填率を６０体積％とし、粉砕時間を８時間とした。更に振動ミルにて乾式粉砕した、容器に対するボールの充填率を７０体積％とし、粉砕時間を１５時間とした。 A molded product (bulk density: 1.4 g / cm 3 ) was prepared using the dried silicon powder. The obtained molded product was allowed to stand in an electric furnace and fired at 1400 ° C. for 60 hours to prepare a fired product containing silicon nitride. As an atmosphere at the time of firing, a mixed gas of nitrogen and hydrogen (a mixed gas in which N 2 and H 2 were mixed so that the volume ratio in the standard state was 80:20) was supplied. The obtained fired body was roughly pulverized and then dry pulverized with a ball mill. In the ball mill crushing, the filling rate of the balls in the container was set to 60% by volume, and the crushing time was set to 8 hours. Further, the filling rate of the balls to the container obtained by dry crushing with a vibration mill was set to 70% by volume, and the crushing time was set to 15 hours.
　乾式粉砕して得られた窒化ケイ素粉末を、一次エアー圧力を０．４ＭＰａの条件で分級し、窒化ケイ素粉末を得た。 The silicon nitride powder obtained by dry pulverization was classified under the condition of a primary air pressure of 0.4 MPa to obtain a silicon nitride powder.
＜窒化ケイ素粉末の評価：Ｄ１０、Ｄ５０、及びＤ９０の測定＞
　窒化ケイ素粉末のＤ１０、Ｄ５０、及びＤ９０を、ＪＩＳ　Ｚ　８８２５：２０１３「粒子径解析－レーザー回折・散乱法」に記載の方法に準拠してレーザー解析散乱法で測定した。測定には、レーザー回折散乱法粒度分布測定装置（ベックマンコールター社製、商品名：ＬＳ－１３　３２０）を用いた。 <Evaluation of Silicon Nitride Powder: Measurement of D10, D50, and D90>
The silicon nitride powders D10, D50, and D90 were measured by a laser analysis scattering method according to the method described in JIS Z 8825: 2013 “Particle size analysis-laser diffraction / scattering method”. A laser diffraction / scattering method particle size distribution measuring device (manufactured by Beckman Coulter, trade name: LS-13 320) was used for the measurement.
＜窒化ケイ素粉末の評価：ＢＥＴ比表面積の測定＞
　ＢＥＴ比表面積は、ＪＩＳ　Ｚ　８８０３：２０１３に準拠し、窒素ガスを使用してＢＥＴ一点法により測定した。結果を表１に示す。 <Evaluation of silicon nitride powder: Measurement of BET specific surface area>
The BET specific surface area was measured by the BET one-point method using nitrogen gas in accordance with JIS Z 8803: 2013. The results are shown in Table 1.
＜窒化ケイ素粉末の評価：表面酸素量の測定＞
　表面酸素量は、酸素／窒素同時分析装置（堀場製作所社製、装置名：ＥＭＧＡ－９２０）を用いて測定した。具体的には、窒化ケイ素粉末を、ヘリウム雰囲気中、昇温速度８℃／秒で２０℃から２０００℃まで加熱し、窒素が検出される前までの酸素量を定量することで測定した。 <Evaluation of silicon nitride powder: Measurement of surface oxygen content>
The amount of surface oxygen was measured using an oxygen / nitrogen simultaneous analyzer (manufactured by HORIBA, Ltd., device name: EMGA-920). Specifically, the silicon nitride powder was measured by heating it in a helium atmosphere at a heating rate of 8 ° C./sec from 20 ° C. to 2000 ° C. and quantifying the amount of oxygen before nitrogen was detected.
［窒化ケイ素焼結体の製造］
　容器に、調製した窒化ケイ素粉末を９０質量部、平均粒径が１．５μｍであるＹ２Ｏ３粉末を５質量部、及び、平均粒径が１．２μｍであるＹｂ２Ｏ３粉末を５質量部、測り取り、メタノールを加えて、４時間湿式混合した。その後、乾燥して得た混合粉末（焼成原料）を１０ＭＰａの圧力で金型成形し、その後、更に２５ＭＰａの圧力で冷間等方圧加圧（ＣＩＰ）成形した。得られた成形体を、窒化ケイ素粉末及びＢＮ粉末の混合粉末からなる詰め粉とともにカーボン製坩堝にセットし、１ＭＰａの窒素加圧雰囲気下、温度１９００℃で１２時間焼成して窒化ケイ素焼結体を製造した。 [Manufacturing of silicon nitride sintered body]
The container, 90 parts by weight of silicon nitride powder prepared, Y 2 O 3 powder 5 parts by weight average particle size of 1.5 [mu] m, and the Yb 2 O 3 powder with an average particle size of 1.2 [mu] m 5 By weight, weighed, methanol was added and wet mixed for 4 hours. Then, the mixed powder (baking raw material) obtained by drying was mold-molded at a pressure of 10 MPa, and then cold isotropic pressurization (CIP) molding was further performed at a pressure of 25 MPa. The obtained molded product was set in a carbon crucible together with a stuffing powder composed of a mixed powder of silicon nitride powder and BN powder, and fired in a nitrogen-pressurized atmosphere of 1 MPa at a temperature of 1900 ° C. for 12 hours to obtain a silicon nitride sintered body. Manufactured.
＜窒化ケイ素焼結体の曲げ強度測定、及び評価＞
　窒化ケイ素焼結体から、ＪＩＳ　Ｒ１６０１：２００８に準じて強度測定用の試験片を作製し、室温における３点曲げ強さを測定した。測定結果から基準で評価した。結果を表１に示す。なお、表１において曲げ強度の測定結果は、後述する比較例１で調製した窒化ケイ素焼結体を基準とした相対値で示した。
Ａ：曲げ強度（相対値）が１．１０以上である。 
Ｂ：曲げ強度（相対値）が１．０５以上１．１０未満である。
Ｃ：曲げ強度（相対値）が１．０５未満である。 <Measurement and evaluation of bending strength of silicon nitride sintered body>
A test piece for strength measurement was prepared from the silicon nitride sintered body according to JIS R1601: 2008, and the three-point bending strength at room temperature was measured. Evaluation was made based on the measurement results. The results are shown in Table 1. In Table 1, the measurement results of the bending strength are shown as relative values based on the silicon nitride sintered body prepared in Comparative Example 1 described later.
A: The bending strength (relative value) is 1.10 or more.
B: Bending strength (relative value) is 1.05 or more and less than 1.10.
C: Bending strength (relative value) is less than 1.05.
（実施例２）
　乾式粉砕の振動ミル条件を表１に記載した条件に変更したこと以外は、実施例１と同様にして、窒化ケイ素粉末を調製した。得られた窒化ケイ素粉末について、実施例１と同様に評価を行った。結果を表１に示す。 (Example 2)
A silicon nitride powder was prepared in the same manner as in Example 1 except that the vibration mill conditions for dry pulverization were changed to the conditions shown in Table 1. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
（実施例３）
　乾式粉砕のボールミル粉砕条件を表１に記載した条件に変更したこと以外は、実施例１と同様にして、窒化ケイ素粉末を調製した。得られた窒化ケイ素粉末について、実施例１と同様に評価を行った。結果を表１に示す。 (Example 3)
A silicon nitride powder was prepared in the same manner as in Example 1 except that the ball mill pulverization conditions for dry pulverization were changed to the conditions shown in Table 1. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
（比較例１）
　乾式分級の条件を表１に記載した条件に変更したこと以外は、実施例１と同様にして、窒化ケイ素粉末を調製した。得られた窒化ケイ素粉末について、実施例１と同様に評価を行った。結果を表１に示す。 (Comparative Example 1)
A silicon nitride powder was prepared in the same manner as in Example 1 except that the conditions for dry classification were changed to the conditions shown in Table 1. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　本開示によれば、曲げ強度に優れる焼結体を製造可能な窒化ケイ素粉末を提供できる。本開示によればまた、曲げ強度に優れる窒化ケイ素焼結体の製造方法を提供できる。 According to the present disclosure, it is possible to provide a silicon nitride powder capable of producing a sintered body having excellent bending strength. According to the present disclosure, it is also possible to provide a method for producing a silicon nitride sintered body having excellent bending strength.

Claims (5)

  1. 　窒化ケイ素の一次粒子を含み、
    　レーザー回折・散乱法によって測定される体積基準の粒子径の分布曲線において、小粒径からの積算値が全体の１０％及び９０％に達した時の粒子径を、それぞれＤ１０及びＤ９０としたときに、Ｄ９０とＤ１０との差が５．５μｍ以下である、窒化ケイ素粉末。     Contains primary particles of silicon nitride,
    When the particle size when the integrated value from the small particle size reaches 10% and 90% of the whole in the volume-based particle size distribution curve measured by the laser diffraction / scattering method is D10 and D90, respectively. In addition, a silicon nitride powder having a difference of 5.5 μm or less between D90 and D10.
  2. 　Ｄ５０が１．５μｍ以下である、請求項１に記載の窒化ケイ素粉末。 The silicon nitride powder according to claim 1, wherein D50 is 1.5 μm or less.
  3. 　Ｄ９０が６．０μｍ以下である、請求項１又は２に記載の窒化ケイ素粉末。 The silicon nitride powder according to claim 1 or 2, wherein D90 is 6.0 μm or less.
  4. 　ＢＥＴ比表面積が９．０ｍ２／ｇ未満である、請求項１～３のいずれか一項に記載の窒化ケイ素粉末。 The silicon nitride powder according to any one of claims 1 to 3, wherein the BET specific surface area is less than 9.0 m 2 / g.
  5. 　請求項１～４のいずれか一項に記載の窒化ケイ素粉末を含む焼結原料を成形し焼成する工程を有する、窒化ケイ素焼結体の製造方法。 A method for producing a silicon nitride sintered body, which comprises a step of molding and firing a sintered raw material containing the silicon nitride powder according to any one of claims 1 to 4.
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