WO2021200814A1 - 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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WO2021200814A1
WO2021200814A1 PCT/JP2021/013267 JP2021013267W WO2021200814A1 WO 2021200814 A1 WO2021200814 A1 WO 2021200814A1 JP 2021013267 W JP2021013267 W JP 2021013267W WO 2021200814 A1 WO2021200814 A1 WO 2021200814A1
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silicon nitride
nitride powder
powder
sintered body
mass
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PCT/JP2021/013267
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French (fr)
Japanese (ja)
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中村　祐三
敏行 宮下
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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 as a method for improving the high temperature characteristics of the silicon nitride sintered body, the total oxygen content of the silicon nitride powder is set to 1.5% by mass or less to reduce the grain boundary phase to be purified at the time of sintering. It has been studied to maintain a high melting point to improve high temperature characteristics.
  • Patent Document 2 proposes using a silicon nitride substrate as an aluminum-ceramic bonding substrate. In such applications, it is required to have high insulation and heat dissipation.
  • An object of the present disclosure is to provide a silicon nitride powder capable of producing a sintered body having sufficient bending strength and excellent thermal conductivity. It is also an object of the present disclosure to provide a method for producing a silicon nitride sintered body capable of exhibiting sufficient bending strength and excellent thermal conductivity.
  • One aspect of the present disclosure provides a silicon nitride powder having a ratio of total oxygen content to specific surface area of 0.05 to 0.14% / m 2 g -1.
  • the ratio of the total amount of oxygen to the specific surface area of the silicon nitride powder indicates how thick the total amount of oxygen of the primary particles of silicon nitride is distributed on the surface of the primary particles, and the primary particles of silicon nitride. It can be an index for evaluating the degree of thickness of the oxide film on the surface of.
  • the silicon nitride powder is a sintered body having an oxide film of an appropriate thickness on the surface of the primary particles, having sufficient bending strength, and having excellent thermal conductivity when the above ratio is within a predetermined range. It can be manufactured. The reason why such an effect can be obtained is considered as follows.
  • the oxide film portion on the surface of the primary particles is preferentially melted to form a liquid phase. Then, silicon nitride is dissolved in the liquid phase, and then a dense structure is formed in the process of reprecipitation.
  • the action is the same as that of the sintering aid, but in the case of the silicon nitride powder, by having an oxide film capable of exerting the same function on the surface of each primary particle, the silicon nitride is melted and re-melted more uniformly. Precipitation can be caused, excellent sinterability can be exhibited, and the obtained sintered body can exhibit excellent bending strength.
  • the liquid phase portion forms a grain boundary phase in the sintered body, but in the silicon nitride powder, the ratio of the total oxygen amount to the specific surface area is within a predetermined range, so that the formation ratio of the grain boundary phase It is also possible to provide a sintered body having better thermal conductivity than the conventional silicon nitride powder.
  • the silicon nitride powder may have a specific surface area of 8.0 m 2 / g or more.
  • 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 sintered raw material has excellent sinterability, and the obtained sintered body has sufficient bending strength. Moreover, it can exhibit excellent thermal conductivity.
  • a silicon nitride powder capable of producing a sintered body having sufficient bending strength and excellent thermal conductivity.
  • 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 comprises silicon nitride primary particles.
  • the silicon nitride powder has a ratio of total oxygen content to specific surface area of 0.05 to 0.14% / m 2 g -1 .
  • the ratio of the total oxygen amount to the specific surface area means a value represented by [total oxygen amount] / [specific surface area].
  • the above-mentioned ratio indicates how the total oxygen amount of the silicon nitride primary particles is distributed on the surface of the primary particles, and evaluates the degree of the thickness of the oxide film on the surface of the silicon nitride primary particles. It can be an indicator.
  • the oxide film contains, for example, silicon dioxide.
  • the lower limit of the ratio of the total oxygen content to the specific surface area is, for example, 0.05% / m 2 g -1 or more, 0.06% / m 2 g -1 or more, or 0.07% / m 2 g -1 or more. That may be the above.
  • the lower limit of the ratio is within the above range, the sinterability can be further improved.
  • the lower limit of the ratio is within the above range, the grain growth at the time of firing the silicon nitride can be promoted, and the bending strength of the silicon nitride sintered body can be further improved.
  • the upper limit of the ratio of the total oxygen content to the specific surface area is, for example, 0.14% / m 2 g -1 or less, 0.13% / m 2 g -1 or less, or 0.12% / m 2 g -1. It may be: When the upper limit of the ratio is within the above range, the grain boundary phase at the time of producing the sintered body can be more sufficiently reduced, and the thermal conductivity can be further improved.
  • the ratio can be adjusted within the above range, for example 0.05 to 0.14% / m 2 g -1 , 0.06 to 0.13% / m 2 g -1 , or 0.07. It may be ⁇ 0.12% / m 2 g -1.
  • the above ratio can be controlled, for example, by adjusting the acid treatment conditions during the production of the silicon nitride powder.
  • the lower limit of the specific surface area of the silicon nitride powder may be, for example, 8.0 m 2 / g or more, 8.5 m 2 / g or more, or 8.7 m 2 / g or more.
  • the upper limit of the specific surface area of the silicon nitride powder is, for example, 15.0 m 2 / g or less, 13.0 m 2 / g or less, 12.0 m 2 / g or less, 11.0 m 2 / g or less, 10.0 m 2 / or less. It may be g or less, 9.5 m 2 / g or less, or 9.2 m 2 / g or less.
  • the specific surface area of the silicon nitride powder can be adjusted within the above range, and may be, for example, 8.0 to 15.0 m 2 / g or 8.5 to 9.2 m 2 / g.
  • the 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 specific surface area in the present specification is a value 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”. (BET specific surface area).
  • the total oxygen content of the silicon nitride powder means the amount of oxygen contained in the primary particles of the silicon nitride powder.
  • the upper limit of the total oxygen content of silicon nitride may be, for example, 1.5% by mass or less, 1.4% by mass or less, or 1.3% by mass or less.
  • the lower limit of the total oxygen content of silicon nitride may be, for example, 0.6% by mass or more, 0.7% by mass or more, or 0.8% by mass or more.
  • the total oxygen content of silicon nitride can be adjusted within the above range, and may be, for example, 0.6 to 1.5% by mass or 0.7 to 1.4% by mass.
  • the total oxygen content of the silicon nitride can be controlled, for example, by adjusting the atmosphere component in the firing step in the production of the silicon nitride powder, the hydrofluoric acid concentration of the acid treatment, and the like.
  • the upper limit of the 90% cumulative diameter in the volume-based cumulative particle size distribution may be, for example, 2.00 ⁇ m or less, 1.98 ⁇ m or less, 1.95 ⁇ m or less, or 1.90 ⁇ m or less.
  • the lower limit of the 90% cumulative diameter in the volume-based cumulative particle size distribution is, for example, 1.40 ⁇ m or more, 1.50 ⁇ m or more, 1.52 ⁇ m or more, 1.55 ⁇ m or more, 1.60 ⁇ m or more, or 1.65 ⁇ m or more. You can.
  • the 90% cumulative diameter in the volume-based cumulative particle size distribution can be adjusted within the above range and may be, for example, 1.40 to 2.00 ⁇ m or 1.50 to 1.90 ⁇ m.
  • the 90% cumulative diameter in the volume-based cumulative particle size distribution of the silicon nitride powder can be controlled, for example, by adjusting the crushing conditions and the classification conditions at the time of producing the silicon nitride powder.
  • the 90% cumulative diameter in the volume-based cumulative particle size distribution in the present specification is when the cumulative value in the volume-based cumulative particle size distribution when the particle size distribution is measured by the laser diffraction / scattering method for silicon nitride powder is 90%. It means the particle size (D90).
  • 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
  • the above-mentioned silicon nitride powder can be produced, for example, by the following method.
  • One embodiment of the method for producing a 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 crushing the fired product to obtain a crushed product (hereinafter, also referred to as a crushing step), and a step of treating the crushed product with an acid (hereinafter, also referred to as an acid treatment step).
  • the silicon powder use a silicon powder having an oxygen content of 0.40% by mass or less.
  • the upper limit of the oxygen content of the silicon powder may be, for example, 0.30% by mass or less, or 0.20% by mass or less.
  • the lower limit of the oxygen content of the silicon powder may be, for example, 0.10% by mass or more, or 0.15% by mass or more.
  • the amount of oxygen in the silicon powder can be adjusted in the above range, and may be, for example, 0.10 to 0.40% by mass.
  • the amount of oxygen in 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. That is, the above-mentioned method for producing silicon nitride powder further includes a pretreatment step of pretreating the silicon powder with a pretreatment liquid containing hydrofluoric acid to obtain a silicon powder having an oxygen content of 0.40% by mass or less. 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 above-mentioned fired product obtained in the firing step is crushed to obtain a crushed product.
  • the fired product and adjusting the particle size it becomes easy to control the surface treatment in the subsequent acid treatment step, and it becomes easy to control the ratio of the total oxygen amount to the specific surface area of the silicon nitride powder.
  • 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.
  • the lower limit of the crushing treatment time (crushing time) in the 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 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 crushing may be performed in a plurality of stages such as coarse crushing and fine crushing.
  • the pulverization may be either wet pulverization or dry pulverization.
  • the pulverization is preferably wet pulverization from the viewpoint of facilitating the adjustment of the particle size.
  • the medium used for wet grinding may be, for example, water or the like.
  • the filling rate of the balls in the container can be adjusted according to the particle size of the silicon nitride powder of interest.
  • 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, or 50% 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, 65% by volume or less, or 60% by volume or less based on the volume of the container.
  • the upper limit of the oxygen content of the pulverized product may be, for example, 7.5% by mass or less, 7.0% by mass or less, 6.5% by mass or less, or 6.0% by mass or less.
  • the lower limit of the oxygen content of the pulverized product may be, for example, 1.5% by mass or more, 2.0% by mass or more, 2.5% by mass or more, or 3.0% by mass or more.
  • the amount of oxygen in the pulverized product can be adjusted in the above range, and may be, for example, 1.5 to 7.5% by mass or 2.0 to 7.0% by mass.
  • the amount of oxygen in the crushed product can be controlled by, for example, adjusting the amount of oxygen in the silicon powder, the components of the atmosphere in the firing step, the crushing time, and the like.
  • the oxygen amount of the silicon nitride powder in the present specification means the "total oxygen amount" of the silicon nitride powder.
  • the “total oxygen amount” can be 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. Detects oxygen desorbed as the temperature rises. At the beginning of the temperature rise, oxygen bound to the surface of the silicon nitride powder is eliminated. The "surface oxygen amount” can be obtained by quantifying the amount of oxygen desorbed.
  • 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.
  • the "internal oxygen amount” can be obtained.
  • the total value of the "surface oxygen amount” and the “internal oxygen amount” obtained in this way is the “total oxygen amount”.
  • the crushed product is treated by contacting it with an acid.
  • the acid include hydrogen fluoride and hydrogen chloride.
  • the acid may be a mixed acid of hydrogen fluoride and hydrogen chloride, or may be either hydrogen fluoride or hydrogen chloride alone, but preferably contains hydrogen fluoride.
  • the acid may be an aqueous solution (eg, hydrofluoric acid or hydrochloric acid).
  • an acid for example, hydrofluoric acid having a concentration of 10 to 40% by mass.
  • the upper limit of the acid concentration may be, for example, 38% by mass or less, 35% by mass or less, or 30% by mass or less.
  • the lower limit of the acid concentration may be, for example, 12% by mass or more, or 15% by mass or more. By setting the lower limit of the acid concentration within the above range, the thickness of the oxide film can be easily and sufficiently reduced.
  • the acid concentration may be adjusted within the above range and may be, for example, 12-38% by mass or 15-35% by mass.
  • the means of contact between the pulverized product and the acid may be, for example, a method of dispersing the pulverized product in the acid.
  • the temperature of the acid (for example, an aqueous solution) in the acid treatment step is set to 40 to 80 ° C.
  • the lower limit of the acid temperature in the acid treatment step may be, for example, 45 ° C. or higher, 50 ° C. or higher, or 60 ° C. or higher.
  • the upper limit of the acid temperature in the acid treatment step may be 75 ° C. or lower, or 70 ° C. or lower.
  • the temperature of the acid in the acid treatment step may be adjusted within the above range, for example, 45 to 75 ° C. or 50 to 70 ° C.
  • the time for contacting the fired product or the ground product obtained by crushing the fired product with the acid is set to 1.0 to 10.0 hours.
  • the lower limit of the acid treatment time may be, for example, 1.2 hours or more, 1.5 hours or more, or 2.0 hours or more.
  • the acid treatment time may be, for example, 9.7 hours or less, 9.5 hours or less, 9.0 hours or less, 8.5 hours or less, or 8.0 hours or less.
  • the acid treatment time may be adjusted within the above range, and may be, for example, 1.2 to 9.7 hours or 2.0 to 8.0 hours.
  • 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 and thermal conductivity.
  • the bending strength of the silicon nitride sintered body can be, for example, 550 MPa or more, 570 MPa or more, 590 MPa or more, or 610 MPa or more.
  • 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 R 1601: 2008.
  • the thermal conductivity of the silicon nitride sintered body is, for example, 90 W / (m ⁇ K) or more, 95 W / (m ⁇ K) or more, 100 W / (m ⁇ K) or more, or 105 W / (m ⁇ K) or more. can do.
  • the thermal conductivity of the silicon nitride sintered body in the present specification is the product of the thermal diffusivity, the thermal diffusivity and the specific heat capacity obtained by measuring the thermal diffusivity and the specific heat capacity by a laser flash method (based on JIS R 1611). Means the value obtained by calculating.
  • Example 1 ⁇ Preparation of silicon nitride powder> A commercially available silicon powder (specific surface area: 3.0 m 2 / g) was immersed in a mixed acid containing hydrogen chloride and hydrogen fluoride whose temperature was adjusted to 60 ° C., and pretreated at 60 ° C. for 2 hours. ..
  • 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.
  • 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 wet pulverized with a ball mill. In the wet pulverization, the filling rate of the balls in the container was 60% by volume, water was used as a solvent, and the pulverization time was 9 hours.
  • the amount of oxygen in the obtained pulverized product was 5.0% by mass.
  • the pulverized product obtained by wet pulverization was immersed in hydrofluoric acid (hydrofluoric acid concentration: 30% by mass) and treated with acid. Then, the pulverized product was taken out from hydrofluoric acid, washed with water, and dried in a nitrogen atmosphere. In this way, a silicon nitride powder was obtained.
  • ⁇ Evaluation of silicon nitride powder total oxygen content> The total oxygen content 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 detected.
  • ⁇ Evaluation of silicon nitride powder Measurement of D90>
  • the 90% cumulative diameter (D90) of the silicon nitride powder in the volume-based cumulative particle size distribution is measured by the laser analysis scattering method in accordance with the method described in JIS Z 8825: 2013 “Particle size analysis-laser diffraction / scattering method”. bottom.
  • a laser diffraction / scattering method particle size distribution measuring device manufactured by Beckman Coulter, trade name: LS-13 320 was used for the measurement.
  • an aqueous solution prepared by mixing 2 mL of a 20% aqueous solution of sodium hexametaphosphate with 200 cc of pure water was prepared, 60 mg of silicon nitride powder was added to the aqueous solution, and an ultrasonic homogenizer (manufactured by Nissei Tokyo Office, trade name: It was prepared by dispersing in US-300) for 3 minutes, and the obtained measurement sample was measured.
  • Table 1 The results are shown in Table 1.
  • 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 10 hours to obtain a silicon nitride sintered body. Manufactured.
  • thermal conductivity> The silicon nitride sintered body was ground to prepare a 10 mm ⁇ ⁇ 3 mm disk body for measuring thermal conductivity.
  • the thermal diffusivity and the specific heat capacity were measured by the laser flash method (based on JIS R 1611), and the product of the density, the thermal diffusivity and the specific heat capacity of the sintered body was calculated and used as the thermal conductivity at room temperature. The results are shown in Table 1. In Table 1, the measurement results of the thermal conductivity are shown as relative values based on the thermal conductivity of the silicon nitride sintered body prepared in Comparative Example 1 described later.
  • Example 2 A silicon nitride powder was prepared in the same manner as in Example 1 except that the acid treatment conditions were changed as shown in Table 1. The prepared 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 acid treatment conditions were changed as shown in Table 1. The prepared 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 acid treatment conditions were changed as shown in Table 1. The prepared silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
  • Example 2 A silicon nitride powder was prepared in the same manner as in Example 1 except that the acid treatment conditions were changed as shown in Table 1. The prepared silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
  • the silicon nitride sintered body prepared by using the silicon nitride powder obtained in the example is a silicon nitride sintered body prepared by using the silicon nitride powder obtained in the comparative example.
  • both bending strength and thermal conductivity can be achieved at a higher level.
  • a silicon nitride powder capable of producing a sintered body having sufficient bending strength and excellent thermal conductivity.

Abstract

One aspect of the present disclosure provides silicon nitride powder having a ratio of the total oxygen content to the specific surface area of 0.05-0.14%/m2g-1.

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。例えば、特許文献１では、窒化ケイ素焼結体の高温特性を向上させる方法として、窒化ケイ素粉末の全酸素量を１．５質量％以下にして、焼結時に精製する粒界相を低減し、融点を高く維持して高温特性を向上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. For example, in Patent Document 1, as a method for improving the high temperature characteristics of the silicon nitride sintered body, the total oxygen content of the silicon nitride powder is set to 1.5% by mass or less to reduce the grain boundary phase to be purified at the time of sintering. It has been studied to maintain a high melting point to improve high temperature characteristics.
　窒化ケイ素基板は、自動車及び工作機械等のパワーモジュール等の絶縁基板としての利用も検討されている。例えば、特許文献２では、アルミニウム－セラミックス接合基板に窒化ケイ素基板を用いることが提案されている。このような用途では、高い絶縁性及び放熱性を有することが求められる。 The use of the silicon nitride substrate as an insulating substrate for power modules of automobiles and machine tools is also being considered. For example, Patent Document 2 proposes using a silicon nitride substrate as an aluminum-ceramic bonding substrate. In such applications, it is required to have high insulation and heat dissipation.
特開平７－２０６４０９号公報Japanese Unexamined Patent Publication No. 7-206409 特開２０１１－０７７５４６号公報Japanese Unexamined Patent Publication No. 2011-077456
　本開示は、十分な曲げ強さを有し且つ熱伝導性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、十分な曲げ強さ、且つ優れた熱伝導性を発揮し得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 sufficient bending strength and excellent thermal conductivity. It is also an object of the present disclosure to provide a method for producing a silicon nitride sintered body capable of exhibiting sufficient bending strength and excellent thermal conductivity.
　本開示の一側面は、比表面積に対する全酸素量の比が０．０５～０．１４％／ｍ２ｇ－１である、窒化ケイ素粉末を提供する。 One aspect of the present disclosure provides a silicon nitride powder having a ratio of total oxygen content to specific surface area of 0.05 to 0.14% / m 2 g -1.
　上記窒化ケイ素粉末における比表面積に対する全酸素量の比は、窒化ケイ素の一次粒子の全酸素量が該一次粒子の表面にどの程度の厚みを持って分布しているかを示し、窒化ケイ素の一次粒子の表面における酸化膜の厚みの程度を評価する指標となり得る。上記窒化ケイ素粉末は、上述の比が所定範囲であることによって、一次粒子の表面に適度な厚みの酸化膜を有し、十分な曲げ強さを有し且つ熱伝導性に優れる焼結体を製造可能である。このような効果が得られる理由は以下のように考えられる。まず、窒化ケイ素粉末の焼結体を製造する際には、一次粒子の表面における酸化膜部分が優先的に溶融し液相を形成する。そして当該液相に窒化ケイ素が溶解し、その後再析出する過程で緻密な組織が形成される。当該作用は焼結助剤と同様であるが、上記窒化ケイ素粉末の場合、各一次粒子の表面に同様の機能を発揮し得る酸化膜を有することで、より一層均一に窒化ケイ素の溶融及び再析出を生じさせることができ、優れた焼結性を発揮し、得られる焼結体は優れた曲げ強さを発揮し得る。また、上記液相部分は焼結体においては粒界相を形成するが、上記窒化ケイ素粉末においては、比表面積に対する全酸素量の比が所定範囲内であることによって、粒界相の形成割合も低減され、従来の窒化ケイ素粉末よりも熱伝導性に優れた焼結体を提供し得る。 The ratio of the total amount of oxygen to the specific surface area of the silicon nitride powder indicates how thick the total amount of oxygen of the primary particles of silicon nitride is distributed on the surface of the primary particles, and the primary particles of silicon nitride. It can be an index for evaluating the degree of thickness of the oxide film on the surface of. The silicon nitride powder is a sintered body having an oxide film of an appropriate thickness on the surface of the primary particles, having sufficient bending strength, and having excellent thermal conductivity when the above ratio is within a predetermined range. It can be manufactured. The reason why such an effect can be obtained is considered as follows. First, when producing a sintered body of silicon nitride powder, the oxide film portion on the surface of the primary particles is preferentially melted to form a liquid phase. Then, silicon nitride is dissolved in the liquid phase, and then a dense structure is formed in the process of reprecipitation. The action is the same as that of the sintering aid, but in the case of the silicon nitride powder, by having an oxide film capable of exerting the same function on the surface of each primary particle, the silicon nitride is melted and re-melted more uniformly. Precipitation can be caused, excellent sinterability can be exhibited, and the obtained sintered body can exhibit excellent bending strength. Further, the liquid phase portion forms a grain boundary phase in the sintered body, but in the silicon nitride powder, the ratio of the total oxygen amount to the specific surface area is within a predetermined range, so that the formation ratio of the grain boundary phase It is also possible to provide a sintered body having better thermal conductivity than the conventional silicon nitride powder.
　上記窒化ケイ素粉末は、比表面積が８．０ｍ２／ｇ以上であってよい。 The silicon nitride powder may have a specific surface area of 8.0 m 2 / g or more.
　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、焼結原料は焼結性に優れ、得られる焼結体は十分な曲げ強さを有し且つ優れた熱伝導性を発揮し得る。 Since the method for producing the silicon nitride sintered body uses the sintered raw material containing the silicon nitride powder described above, the sintered raw material has excellent sinterability, and the obtained sintered body has sufficient bending strength. Moreover, it can exhibit excellent thermal conductivity.
　本開示によれば、十分な曲げ強さを有し且つ熱伝導性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、十分な曲げ強さ、且つ優れた熱伝導性を発揮し得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 sufficient bending strength and excellent thermal conductivity. According to the present disclosure, it is also possible to provide a method for producing a silicon nitride sintered body capable of exhibiting sufficient bending strength and excellent thermal conductivity.
　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む。上記窒化ケイ素粉末は、比表面積に対する全酸素量の比が０．０５～０．１４％／ｍ２ｇ－１である。ここで、比表面積に対する全酸素量の比とは、［全酸素量］／［比表面積］で表される値を意味する。そして、上述の比は、窒化ケイ素の一次粒子の全酸素量が該一次粒子の表面にどのように分布しているかを示し、窒化ケイ素の一次粒子の表面における酸化膜の厚みの程度を評価する指標となり得る。酸化膜は、例えば、二酸化ケイ素を含む。 One embodiment of silicon nitride powder comprises silicon nitride primary particles. The silicon nitride powder has a ratio of total oxygen content to specific surface area of 0.05 to 0.14% / m 2 g -1 . Here, the ratio of the total oxygen amount to the specific surface area means a value represented by [total oxygen amount] / [specific surface area]. Then, the above-mentioned ratio indicates how the total oxygen amount of the silicon nitride primary particles is distributed on the surface of the primary particles, and evaluates the degree of the thickness of the oxide film on the surface of the silicon nitride primary particles. It can be an indicator. The oxide film contains, for example, silicon dioxide.
　比表面積に対する全酸素量の比の下限値は、例えば、０．０５％／ｍ２ｇ－１以上、０．０６％／ｍ２ｇ－１以上、又は０．０７％／ｍ２ｇ－１以上であってよい。上記比の下限値が上記範囲内であると、焼結性をより向上させることができる。上記比の下限値が上記範囲内であるとまた、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さをより向上させることができる。比表面積に対する全酸素量の比の上限値は、例えば、０．１４％／ｍ２ｇ－１以下、０．１３％／ｍ２ｇ－１以下、又は０．１２％／ｍ２ｇ－１以下であってよい。上記比の上限値が上記範囲内であると、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、熱伝導率をより向上させることができる。上記比は上述の範囲内で調整することができ、例えば、０．０５～０．１４％／ｍ２ｇ－１、０．０６～０．１３％／ｍ２ｇ－１、又は０．０７～０．１２％／ｍ２ｇ－１であってよい。上記比は、例えば、窒化ケイ素粉末の製造時における酸処理条件等を調整することで制御できる。 The lower limit of the ratio of the total oxygen content to the specific surface area is, for example, 0.05% / m 2 g -1 or more, 0.06% / m 2 g -1 or more, or 0.07% / m 2 g -1 or more. That may be the above. When the lower limit of the ratio is within the above range, the sinterability can be further improved. When the lower limit of the ratio is within the above range, the grain growth at the time of firing the silicon nitride can be promoted, and the bending strength of the silicon nitride sintered body can be further improved. The upper limit of the ratio of the total oxygen content to the specific surface area is, for example, 0.14% / m 2 g -1 or less, 0.13% / m 2 g -1 or less, or 0.12% / m 2 g -1. It may be: When the upper limit of the ratio is within the above range, the grain boundary phase at the time of producing the sintered body can be more sufficiently reduced, and the thermal conductivity can be further improved. The ratio can be adjusted within the above range, for example 0.05 to 0.14% / m 2 g -1 , 0.06 to 0.13% / m 2 g -1 , or 0.07. It may be ~ 0.12% / m 2 g -1. The above ratio can be controlled, for example, by adjusting the acid treatment conditions during the production of the silicon nitride powder.
　窒化ケイ素粉末の比表面積の下限値は、例えば、８．０ｍ２／ｇ以上、８．５ｍ２／ｇ以上、又は８．７ｍ２／ｇ以上であってよい。窒化ケイ素粉末の比表面積の上限値は、例えば、１５．０ｍ２／ｇ以下、１３．０ｍ２／ｇ以下、１２．０ｍ２／ｇ以下、１１．０ｍ２／ｇ以下、１０．０ｍ２／ｇ以下、９．５ｍ２／ｇ以下、又は９．２ｍ２／ｇ以下であってよい。窒化ケイ素粉末の比表面積は上述の範囲内で調整することができ、例えば、８．０～１５．０ｍ２／ｇ、又は８．５～９．２ｍ２／ｇであってよい。窒化ケイ素粉末の比表面積は、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 lower limit of the specific surface area of the silicon nitride powder may be, for example, 8.0 m 2 / g or more, 8.5 m 2 / g or more, or 8.7 m 2 / g or more. The upper limit of the specific surface area of the silicon nitride powder is, for example, 15.0 m 2 / g or less, 13.0 m 2 / g or less, 12.0 m 2 / g or less, 11.0 m 2 / g or less, 10.0 m 2 / or less. It may be g or less, 9.5 m 2 / g or less, or 9.2 m 2 / g or less. The specific surface area of the silicon nitride powder can be adjusted within the above range, and may be, for example, 8.0 to 15.0 m 2 / g or 8.5 to 9.2 m 2 / g. The 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一点法により測定される値（ＢＥＴ比表面積）である。 The specific surface area in the present specification is a value 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". (BET specific surface area).
　窒化ケイ素粉末の全酸素量は、窒化ケイ素粉末の一次粒子が含有する酸素量を意味する。窒化ケイ素の全酸素量の上限値は、例えば、１．５質量％以下、１．４質量％以下、又は１．３質量％以下であってよい。窒化ケイ素の全酸素量の下限値は、例えば、０．６質量％以上、０．７質量％以上、又は０．８質量％以上であってよい。窒化ケイ素の全酸素量は上述の範囲で調整することができ、例えば、０．６～１．５質量％、又は０．７～１．４質量％であってよい。窒化ケイ素の全酸素量は、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、酸処理のフッ化水素酸濃度等の調整によって制御できる。 The total oxygen content of the silicon nitride powder means the amount of oxygen contained in the primary particles of the silicon nitride powder. The upper limit of the total oxygen content of silicon nitride may be, for example, 1.5% by mass or less, 1.4% by mass or less, or 1.3% by mass or less. The lower limit of the total oxygen content of silicon nitride may be, for example, 0.6% by mass or more, 0.7% by mass or more, or 0.8% by mass or more. The total oxygen content of silicon nitride can be adjusted within the above range, and may be, for example, 0.6 to 1.5% by mass or 0.7 to 1.4% by mass. The total oxygen content of the silicon nitride can be controlled, for example, by adjusting the atmosphere component in the firing step in the production of the silicon nitride powder, the hydrofluoric acid concentration of the acid treatment, and the like.
　窒化ケイ素粉末において、体積基準の累積粒度分布における９０％累積径の上限値は、例えば、２．００μｍ以下、１．９８μｍ以下、１．９５μｍ以下、又は１．９０μｍ以下であってよい。体積基準の累積粒度分布における９０％累積径の下限値は、例えば、１．４０μｍ以上、１．５０μｍ以上、１．５２μｍ以上、１．５５μｍ以上、１．６０μｍ以上、又は１．６５μｍ以上であってよい。体積基準の累積粒度分布における９０％累積径は上述の範囲内で調整でき、例えば、１．４０～２．００μｍ、又は１．５０～１．９０μｍであってよい。窒化ケイ素粉末の体積基準の累積粒度分布における９０％累積径は、例えば、窒化ケイ素粉末の製造時における粉砕条件及び分級条件等を調整することで制御できる。 In the silicon nitride powder, the upper limit of the 90% cumulative diameter in the volume-based cumulative particle size distribution may be, for example, 2.00 μm or less, 1.98 μm or less, 1.95 μm or less, or 1.90 μm or less. The lower limit of the 90% cumulative diameter in the volume-based cumulative particle size distribution is, for example, 1.40 μm or more, 1.50 μm or more, 1.52 μm or more, 1.55 μm or more, 1.60 μm or more, or 1.65 μm or more. You can. The 90% cumulative diameter in the volume-based cumulative particle size distribution can be adjusted within the above range and may be, for example, 1.40 to 2.00 μm or 1.50 to 1.90 μm. The 90% cumulative diameter in the volume-based cumulative particle size distribution of the silicon nitride powder can be controlled, for example, by adjusting the crushing conditions and the classification conditions at the time of producing the silicon nitride powder.
　本明細書における体積基準の累積粒度分布における９０％累積径は、窒化ケイ素粉末に対するレーザー回折散乱法で粒度分布を測定したときの体積基準の累積粒度分布における累積値が９０％となったときの粒子径（Ｄ９０）を意味する。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。 The 90% cumulative diameter in the volume-based cumulative particle size distribution in the present specification is when the cumulative value in the volume-based cumulative particle size distribution when the particle size distribution is measured by the laser diffraction / scattering method for silicon nitride powder is 90%. It means the particle size (D90). 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.
　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、上記粉砕物を酸で処理する工程（以下、酸処理工程ともいう）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 a 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 crushing the fired product to obtain a crushed product (hereinafter, also referred to as a crushing step), and a step of treating the crushed product with an acid (hereinafter, also referred to as an acid treatment step).
　ケイ素粉末は、酸素量が０．４０質量％以下であるケイ素粉末を用いる。ケイ素粉末の酸素量の上限値は、例えば、０．３０質量％以下、又は０．２０質量％以下であってよい。ケイ素粉末の酸素量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。ケイ素粉末の酸素量の下限値は、例えば、０．１０質量％以上、又は０．１５質量％以上であってよい。ケイ素粉末の酸素量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, use a silicon powder having an oxygen content of 0.40% by mass or less. The upper limit of the oxygen content of the silicon powder may be, for example, 0.30% by mass or less, or 0.20% by mass or less. By setting the amount of oxygen in 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 content of the silicon powder may be, for example, 0.10% by mass or more, or 0.15% by mass or more. The amount of oxygen in 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量は、赤外線吸収法によって測定される値を意味する。 The amount of oxygen in 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。ケイ素粉末の酸素量が高い場合には、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。つまり、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、酸素量が０．４０質量％以下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 amount of oxygen in 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. That is, the above-mentioned method for producing silicon nitride powder further includes a pretreatment step of pretreating the silicon powder with a pretreatment liquid containing hydrofluoric acid to obtain a silicon powder having an oxygen content of 0.40% by mass or less. 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粉砕して粉砕物を得る。焼成物を粉砕し、粒度を調整することによって、後の酸処理工程における表面処理の制御が容易となり、窒化ケイ素粉末の比表面積に対する全酸素量の比の制御が容易なものとなる。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 to obtain a crushed product. By crushing the fired product and adjusting the particle size, it becomes easy to control the surface treatment in the subsequent acid treatment step, and it becomes easy to control the ratio of the total oxygen amount to the specific surface area of the silicon nitride powder. 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.
　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、酸処理工程での酸処理効率をより向上させることができる。上記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、また過剰な粉砕を防ぐことで製造コストを抑えることができる。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 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 crushing time within the above range, the crushed product can be sufficiently finely divided, and the acid treatment efficiency in the acid treatment step can be further improved. The upper limit of the pulverization treatment time may be, for example, 15 hours or less, 14 hours or less, 13 hours or less, or 12 hours or less. By setting the upper limit of the crushing time within the above range, the fired product can be sufficiently crushed, and the production cost can be suppressed by preventing excessive crushing. 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。粉砕は、湿式粉砕及び乾式粉砕のいずれでもよい。粉砕は、粒度の調整を容易とする観点から、好ましくは湿式粉砕である。湿式粉砕に使用される媒体は、例えば、水等であってよい。 The crushing may be performed in a plurality of stages such as coarse crushing and fine crushing. The pulverization may be either wet pulverization or dry pulverization. The pulverization is preferably wet pulverization from the viewpoint of facilitating the adjustment of the particle size. The medium used for wet grinding may be, for example, water or the like.
　粉砕には、例えば、ボールミル等を用いることができる。ボールミルを使用する場合、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、又は５０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、６５体積％以下、又は６０体積％以下であってよい。 For crushing, for example, a ball mill or the like can be used. When using a ball mill, the filling rate of the balls in the container can be adjusted according to the particle size of the silicon nitride powder of interest. 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, or 50% 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, 65% by volume or less, or 60% by volume or less based on the volume of the container.
　粉砕物の酸素量は、１．０～８．０質量％に調整する。粉砕物の酸素量の上限値は、例えば、７．５質量％以下、７．０質量％以下、６．５質量％以下、又は６．０質量％以下であってよい。粉砕物の酸素量の上限値を上記範囲内とすることで、続く酸処理工程における酸処理時間を低減することができる。粉砕物の酸素量の下限値は、例えば、１．５質量％以上、２．０質量％以上、２．５質量％以上、又は３．０質量％以上であってよい。粉砕物の酸素量の下限値を上記範囲内とすることで、酸処理後の窒化ケイ素粉末における酸化膜の厚みの調整が容易となり得る。粉砕物の酸素量は上述の範囲で調整することができ、例えば、１．５～７．５質量％、又は２．０～７．０質量％であってよい。粉砕物の酸素量は、例えば、ケイ素粉末の酸素量、焼成工程における雰囲気の成分、並びに、粉砕時間等の調整によって制御できる。 Adjust the oxygen content of the crushed product to 1.0 to 8.0% by mass. The upper limit of the oxygen content of the pulverized product may be, for example, 7.5% by mass or less, 7.0% by mass or less, 6.5% by mass or less, or 6.0% by mass or less. By setting the upper limit of the oxygen content of the pulverized product within the above range, the acid treatment time in the subsequent acid treatment step can be reduced. The lower limit of the oxygen content of the pulverized product may be, for example, 1.5% by mass or more, 2.0% by mass or more, 2.5% by mass or more, or 3.0% by mass or more. By setting the lower limit of the oxygen content of the pulverized product within the above range, it is possible to easily adjust the thickness of the oxide film in the silicon nitride powder after the acid treatment. The amount of oxygen in the pulverized product can be adjusted in the above range, and may be, for example, 1.5 to 7.5% by mass or 2.0 to 7.0% by mass. The amount of oxygen in the crushed product can be controlled by, for example, adjusting the amount of oxygen in the silicon powder, the components of the atmosphere in the firing step, the crushing time, and the like.
　本明細書における窒化ケイ素粉末の酸素量とは、窒化ケイ素粉末の「全酸素量」を意味する。「全酸素量」は以下の手順で求めることができる。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。脱離する酸素を定量することで「表面酸素量」が求められる。その後、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。この段階で脱離する酸を定量することで、「内部酸素量」が求められる。このようにして得られた「表面酸素量」と、「内部酸素量」との合計値が「全酸素量」である。 The oxygen amount of the silicon nitride powder in the present specification means the "total oxygen amount" of the silicon nitride powder. The "total oxygen amount" can be 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. Detects oxygen desorbed as the temperature rises. At the beginning of the temperature rise, oxygen bound to the surface of the silicon nitride powder is eliminated. The "surface oxygen amount" can be obtained by quantifying the amount of oxygen desorbed. After that, when the temperature reaches around 1400 ° C., 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. By quantifying the acid desorbed at this stage, the "internal oxygen amount" can be obtained. The total value of the "surface oxygen amount" and the "internal oxygen amount" obtained in this way is the "total oxygen amount".
　酸処理工程では、粉砕物を酸と接触させて処理する。酸としては、例えば、フッ化水素、及び塩化水素等が挙げられる。酸は、フッ化水素と塩化水素との混酸であってもよく、フッ化水素又は塩化水素のいずれか単独であってもよいが、好ましくはフッ化水素を含む。酸は、水溶液（例えば、フッ化水素酸又は塩酸）であってよい。 In the acid treatment process, the crushed product is treated by contacting it with an acid. Examples of the acid include hydrogen fluoride and hydrogen chloride. The acid may be a mixed acid of hydrogen fluoride and hydrogen chloride, or may be either hydrogen fluoride or hydrogen chloride alone, but preferably contains hydrogen fluoride. The acid may be an aqueous solution (eg, hydrofluoric acid or hydrochloric acid).
　酸（例えば、フッ化水素酸）は、１０～４０質量％の濃度であるものを用いる。酸の濃度の上限値は、例えば、３８質量％以下、３５質量％以下、又は３０質量％以下であってよい。酸の濃度の上限値を上記範囲内とすることで、窒化ケイ素粉末における酸化膜の厚みの調整が容易となり得る。酸の濃度の下限値は、例えば、１２質量％以上、又は１５質量％以上であってよい。酸の濃度の下限値を上記範囲内とすることで、酸化膜の厚みを容易且つ十分に低減させることができる。酸の濃度は上述の範囲内で調整してよく、例えば、１２～３８質量％、又は１５～３５質量％であってよい。 Use an acid (for example, hydrofluoric acid) having a concentration of 10 to 40% by mass. The upper limit of the acid concentration may be, for example, 38% by mass or less, 35% by mass or less, or 30% by mass or less. By setting the upper limit of the acid concentration within the above range, it is possible to easily adjust the thickness of the oxide film in the silicon nitride powder. The lower limit of the acid concentration may be, for example, 12% by mass or more, or 15% by mass or more. By setting the lower limit of the acid concentration within the above range, the thickness of the oxide film can be easily and sufficiently reduced. The acid concentration may be adjusted within the above range and may be, for example, 12-38% by mass or 15-35% by mass.
　粉砕物と酸との接触の手段は、例えば、酸中に粉砕物を分散させる方法であってよい。 The means of contact between the pulverized product and the acid may be, for example, a method of dispersing the pulverized product in the acid.
　酸処理工程における酸（例えば、水溶液）の温度は、４０～８０℃に設定する。酸処理工程における酸の温度の下限値は、例えば、４５℃以上、５０℃以上、又は６０℃以上であってよい。酸処理工程における酸の温度の上限値は、７５℃以下、又は７０℃以下であってよい。酸処理工程における酸の温度は上述の範囲内で調整してよく、例えば、４５～７５℃、又は５０～７０℃であってよい。 The temperature of the acid (for example, an aqueous solution) in the acid treatment step is set to 40 to 80 ° C. The lower limit of the acid temperature in the acid treatment step may be, for example, 45 ° C. or higher, 50 ° C. or higher, or 60 ° C. or higher. The upper limit of the acid temperature in the acid treatment step may be 75 ° C. or lower, or 70 ° C. or lower. The temperature of the acid in the acid treatment step may be adjusted within the above range, for example, 45 to 75 ° C. or 50 to 70 ° C.
　酸処理工程において、焼成物又は焼成物を粉砕して得られる粉砕物と酸と接触させる時間（酸処理時間）は、１．０～１０．０時間に設定する。上記酸処理時間の下限値は、例えば、１．２時間以上、１．５時間以上、又は２．０時間以上であってよい。酸処理時間の下限値を上記範囲内とすることで、酸化膜の厚みを容易且つ十分に低減させることができる。上記酸処理時間は、例えば、９．７時間以下、９．５時間以下、９．０時間以下、８．５時間以下、又は８．０時間以下であってよい。酸処理時間の上限値を上記範囲内とすることで、窒化ケイ素粉末における酸化膜の厚みの調整が容易となり得る。上記酸処理時間は上述の範囲内で調整してよく、例えば、１．２～９．７時間、又は２．０～８．０時間であってよい。 In the acid treatment step, the time for contacting the fired product or the ground product obtained by crushing the fired product with the acid (acid treatment time) is set to 1.0 to 10.0 hours. The lower limit of the acid treatment time may be, for example, 1.2 hours or more, 1.5 hours or more, or 2.0 hours or more. By setting the lower limit of the acid treatment time within the above range, the thickness of the oxide film can be easily and sufficiently reduced. The acid treatment time may be, for example, 9.7 hours or less, 9.5 hours or less, 9.0 hours or less, 8.5 hours or less, or 8.0 hours or less. By setting the upper limit of the acid treatment time within the above range, it is possible to easily adjust the thickness of the oxide film in the silicon nitride powder. The acid treatment time may be adjusted within the above range, and may be, for example, 1.2 to 9.7 hours or 2.0 to 8.0 hours.
　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、優れた曲げ強さ及び熱伝導率を発揮し得る。 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 and thermal conductivity.
　窒化ケイ素焼結体の曲げ強さは、例えば、５５０ＭＰａ以上、５７０ＭＰａ以上、５９０ＭＰａ以上、又は６１０ＭＰａ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さは、ＪＩＳ　Ｒ　１６０１：２００８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, 570 MPa or more, 590 MPa or more, or 610 MPa or more. 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 R 1601: 2008.
　窒化ケイ素焼結体の熱伝導率は、例えば、９０Ｗ／（ｍ・Ｋ）以上、９５Ｗ／（ｍ・Ｋ）以上、１００Ｗ／（ｍ・Ｋ）以上、又は１０５Ｗ／（ｍ・Ｋ）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熱伝導率は、レーザーフラッシュ法（ＪＩＳ　Ｒ　１６１１に準拠）によって熱拡散率と比熱容量を測定し、焼結体の密度、熱拡散率及び比熱容量の積を算出して得られる値を意味する。 The thermal conductivity of the silicon nitride sintered body is, for example, 90 W / (m · K) or more, 95 W / (m · K) or more, 100 W / (m · K) or more, or 105 W / (m · K) or more. can do. The thermal conductivity of the silicon nitride sintered body in the present specification is the product of the thermal diffusivity, the thermal diffusivity and the specific heat capacity obtained by measuring the thermal diffusivity and the specific heat capacity by a laser flash method (based on JIS R 1611). Means the value obtained by calculating.
　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℃で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。 (Example 1)
<Preparation of silicon nitride powder>
A commercially available silicon powder (specific surface area: 3.0 m 2 / g) was immersed in a mixed acid containing hydrogen chloride and hydrogen fluoride whose temperature was adjusted to 60 ° C., and pretreated at 60 ° C. for 2 hours. .. 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.
　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、ボールミルで湿式粉砕した。湿式粉砕は、容器に対するボールの充填率を６０体積％とし、溶媒として水を用い、粉砕時間を９時間とした。得られた粉砕物の酸素量は５．０質量％であった。 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 wet pulverized with a ball mill. In the wet pulverization, the filling rate of the balls in the container was 60% by volume, water was used as a solvent, and the pulverization time was 9 hours. The amount of oxygen in the obtained pulverized product was 5.0% by mass.
　湿式粉砕して得られた粉砕物を、フッ化水素酸（フッ化水素酸濃度：３０質量％）中に浸漬して酸処理した。その後、フッ化水素酸から粉砕物を取り出して水で洗浄し、窒素雰囲気下で乾燥した。こうして窒化ケイ素粉末を得た。 The pulverized product obtained by wet pulverization was immersed in hydrofluoric acid (hydrofluoric acid concentration: 30% by mass) and treated with acid. Then, the pulverized product was taken out from hydrofluoric acid, washed with water, and dried in a nitrogen atmosphere. In this way, a silicon nitride powder was obtained.
＜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一点法によって測定した。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：全酸素量＞
　全酸素量は、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、検出される酸素量を定量することで測定した。 <Evaluation of silicon nitride powder: total oxygen content>
The total oxygen content 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 detected.
＜窒化ケイ素粉末の評価：Ｄ９０の測定＞
　窒化ケイ素粉末の体積基準の累積粒度分布における９０％累積径（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。また、測定サンプルは、純水２００ｃｃに、ヘキサメタリン酸ナトリウムの２０％水溶液２ｍＬを混ぜた水溶液を用意し、当該水溶液に窒化ケイ素粉末６０ｍｇを投入し、超音波ホモジナイザー（日本精機製作所製、商品名：ＵＳ－３００）で３分間分散させて調製し、得られた測定サンプルを対象として測定を行った。結果を表１に示す。 <Evaluation of silicon nitride powder: Measurement of D90>
The 90% cumulative diameter (D90) of the silicon nitride powder in the volume-based cumulative particle size distribution is measured by the laser analysis scattering method in accordance with the method described in JIS Z 8825: 2013 “Particle size analysis-laser diffraction / scattering method”. bottom. A laser diffraction / scattering method particle size distribution measuring device (manufactured by Beckman Coulter, trade name: LS-13 320) was used for the measurement. As a measurement sample, an aqueous solution prepared by mixing 2 mL of a 20% aqueous solution of sodium hexametaphosphate with 200 cc of pure water was prepared, 60 mg of silicon nitride powder was added to the aqueous solution, and an ultrasonic homogenizer (manufactured by Nissei Tokyo Office, trade name: It was prepared by dispersing in US-300) for 3 minutes, and the obtained measurement sample was measured. The results are shown in Table 1.
＜窒化ケイ素粉末の評価：焼結性＞
［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１０時間焼成して窒化ケイ素焼結体を製造した。 <Evaluation of silicon nitride powder: Sinterability>
[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 10 hours to obtain a silicon nitride sintered body. Manufactured.
＜窒化ケイ素焼結体の評価：曲げ強さ＞
　窒化ケイ素焼結体から、ＪＩＳ　Ｒ　１６０１：２００８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。結果を表１に示す。なお、表１において曲げ強さの測定結果は、後述する比較例１で調製した窒化ケイ素焼結体の曲げ強さを基準とした相対値で示した。 <Evaluation of silicon nitride sintered body: flexural strength>
A test piece for strength measurement was prepared from the silicon nitride sintered body according to JIS R 1601: 2008, and the three-point bending strength at room temperature was measured. The results are shown in Table 1. In Table 1, the measurement results of the bending strength are shown as relative values based on the bending strength of the silicon nitride sintered body prepared in Comparative Example 1 described later.
＜窒化ケイ素焼結体の評価：熱伝導率＞
　窒化ケイ素焼結体を研削加工して、熱伝導率測定用の１０ｍｍφ×３ｍｍの円盤体を作製した。レーザーフラッシュ法（ＪＩＳ　Ｒ　１６１１に準拠）により熱拡散率と比熱容量を測定し、焼結体の密度、熱拡散率及び比熱容量の積を算出して、室温における熱伝導率とした。結果を表１に示す。なお、表１において熱伝導率の測定結果は、後述する比較例１で調製した窒化ケイ素焼結体の熱伝導率を基準とした相対値で示した。 <Evaluation of silicon nitride sintered body: thermal conductivity>
The silicon nitride sintered body was ground to prepare a 10 mmφ × 3 mm disk body for measuring thermal conductivity. The thermal diffusivity and the specific heat capacity were measured by the laser flash method (based on JIS R 1611), and the product of the density, the thermal diffusivity and the specific heat capacity of the sintered body was calculated and used as the thermal conductivity at room temperature. The results are shown in Table 1. In Table 1, the measurement results of the thermal conductivity are shown as relative values based on the thermal conductivity of the silicon nitride sintered body prepared in Comparative Example 1 described later.
（実施例２）
　酸処理条件を表１に示すとおり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。調製し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 acid treatment conditions were changed as shown in Table 1. The prepared silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
（実施例３）
　酸処理条件を表１に示すとおり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。調製し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 acid treatment conditions were changed as shown in Table 1. The prepared silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
（比較例１）
　酸処理条件を表１に示すとおり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。調製し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 acid treatment conditions were changed as shown in Table 1. The prepared silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
（比較例２）
　酸処理条件を表１に示すとおり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。調製し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 2)
A silicon nitride powder was prepared in the same manner as in Example 1 except that the acid treatment conditions were changed as shown in Table 1. The prepared 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
　表１に示されるとおり、実施例で得られた窒化ケイ素粉末を用いて調製された窒化ケイ素焼結体は、比較例で得られた窒化ケイ素粉末を用いて調製された窒化ケイ素焼結体に比べて、曲げ強さと熱伝導率とをより高水準で両立できることが確認された。 As shown in Table 1, the silicon nitride sintered body prepared by using the silicon nitride powder obtained in the example is a silicon nitride sintered body prepared by using the silicon nitride powder obtained in the comparative example. In comparison, it was confirmed that both bending strength and thermal conductivity can be achieved at a higher level.
　本開示によれば、十分な曲げ強さを有し且つ熱伝導性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、十分な曲げ強さ、且つ優れた熱伝導性を発揮し得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 sufficient bending strength and excellent thermal conductivity. According to the present disclosure, it is also possible to provide a method for producing a silicon nitride sintered body capable of exhibiting sufficient bending strength and excellent thermal conductivity.

Claims (3)

  1. 　比表面積に対する全酸素量の比が０．０５～０．１４％／ｍ２ｇ－１である、窒化ケイ素粉末。 A silicon nitride powder having a ratio of total oxygen content to specific surface area of 0.05 to 0.14% / m 2 g -1.
  2. 　比表面積が８．０ｍ２／ｇ以上である、請求項１に記載の窒化ケイ素粉末。 The silicon nitride powder according to claim 1, wherein the specific surface area is 8.0 m 2 / g or more.
  3. 　請求項１又は２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 claim 1 or 2.
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JPH02107509A (en) * 1988-08-31 1990-04-19 Bayer Ag Silicon nitride powder improved in its surface characteristics and production thereof
JPH04295005A (en) * 1991-03-26 1992-10-20 Denki Kagaku Kogyo Kk Production of silicon nitride
JPH07267614A (en) * 1994-03-29 1995-10-17 Ngk Insulators Ltd Production of silicon nitride powder, sintered compact of silicon nitride and its production
JPH0812306A (en) * 1994-07-01 1996-01-16 Ube Ind Ltd Silicon nitride powder
JPH11292522A (en) * 1998-04-13 1999-10-26 Ube Ind Ltd Silicon nitride powder
WO2013146713A1 (en) * 2012-03-28 2013-10-03 宇部興産株式会社 Silicon nitride powder production method, silicon nitride powder, silicon nitride sintered body and circuit substrate using same
WO2019235593A1 (en) * 2018-06-07 2019-12-12 宇部興産株式会社 Plate-like silicon nitride sintered body and production method thereof

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH02107509A (en) * 1988-08-31 1990-04-19 Bayer Ag Silicon nitride powder improved in its surface characteristics and production thereof
JPH04295005A (en) * 1991-03-26 1992-10-20 Denki Kagaku Kogyo Kk Production of silicon nitride
JPH07267614A (en) * 1994-03-29 1995-10-17 Ngk Insulators Ltd Production of silicon nitride powder, sintered compact of silicon nitride and its production
JPH0812306A (en) * 1994-07-01 1996-01-16 Ube Ind Ltd Silicon nitride powder
JPH11292522A (en) * 1998-04-13 1999-10-26 Ube Ind Ltd Silicon nitride powder
WO2013146713A1 (en) * 2012-03-28 2013-10-03 宇部興産株式会社 Silicon nitride powder production method, silicon nitride powder, silicon nitride sintered body and circuit substrate using same
WO2019235593A1 (en) * 2018-06-07 2019-12-12 宇部興産株式会社 Plate-like silicon nitride sintered body and production method thereof

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