Silicon nitride powder, method for producing silicon nitride sintered body, and silicon nitride sintered body

Abstract

The main problem addressed by the present invention is the problem of providing a crystalline silicon nitride powder that makes it possible to obtain a silicon nitride sintered body having easy sinterability, sufficient mechanical strength characteristics, and excellent thermal conductivity.　The present invention provides a silicon nitride powder characterized in that the mass content of various metal impurities (Fe, Ti, Cr, Ni, Al, Ca, Mg, Na, and K) is controlled within a suitable range and the silicon nitride powder has powder characteristics suitable for obtaining a silicon nitride sintered body having both excellent mechanical characteristics and high thermal conductivity. Also provided are: a silicon nitride sintered body having both sufficient mechanical strength characteristics and excellent thermal conductivity as a result of molding and sintering a sintering raw material containing the silicon nitride powder and a sintering aid; and a method for producing the silicon nitride sintered body.

Description

Method for producing silicon nitride powder, silicon nitride sintered body, and silicon nitride sintered body

[0001] The present invention relates to crystalline silicon nitride powder suitable as a raw material for manufacturing silicon nitride sintered bodies useful as heat-resistant structural materials, wear-resistant materials, and circuit board materials, a method for manufacturing silicon nitride sintered bodies, and silicon nitride sintered bodies.

[0002] Silicon nitride sintered bodies are attracting attention as heat-resistant structural members for gas turbine components and automobile engine components, and as wear-resistant members for bearing components, due to their high strength, corrosion resistance, and excellent thermal shock resistance. Furthermore, silicon nitride sintered substrates are increasingly being used as insulating substrates in power modules for electric vehicles (EVs) and railway vehicles. Such silicon nitride sintered bodies are usually manufactured by mixing silicon nitride powder with a sintering aid, forming a molded body by press molding, injection molding, extrusion molding, sheet molding, etc., and then sintering this molded body under normal pressure, a pressurized atmosphere, or under a pressurized press. When manufacturing silicon nitride sintered bodies using these methods, it is known that the powder properties of the silicon nitride powder used as raw material, particularly the content and size of metal impurities, greatly affect the sinterability and properties of the sintered body. That is, it is known that depending on the type of metal impurity, some metal elements have a positive effect on the sinterability of silicon nitride powder, while others have a negative effect (i.e., inhibit sintering). Furthermore, it is known that if the metal impurities contained in the silicon nitride powder are coarse, they remain as coarse foreign matter in the resulting silicon nitride sintered body, becoming fracture initiation points and degrading the strength properties. It is also known that if metal impurities dissolve and remain in the grain boundary phase, they reduce the oxidation resistance of the silicon nitride sintered body, adversely affecting high-temperature strength and strength retention rate after oxidation treatment. Therefore, high-purity silicon nitride powder is required as the starting material. In particular, regarding the metal impurities that are inevitably included, it is necessary to investigate in detail how the type of metal element affects the silicon nitride sintering process and the properties of the resulting sintered body.

[0003] For example, Patent Document 1 is an invention relating to silicon nitride powder and a method for producing the same, which enables the production of silicon nitride sintered bodies with high thermal conductivity at a low manufacturing cost. The examples and comparative examples disclose silicon nitride powder in which the total amount of Fe, Al, and Ca is 400 to 1500 ppm by mass. However, there is no specific description of the content of metal impurities other than Fe, Al, and Ca. In particular, there is no mention at all of the presence of Group IVA metals in the periodic table.

[0004] Furthermore, Patent Document 2 is an invention aimed at eliminating color unevenness in sintered bodies obtained by sintering high-purity crystalline silicon nitride. The examples include a Fe content of 40 to 85 ppm, a Ca content of 10 to 20 ppm, a Cr content of less than 10 ppm, a Ni content of less than 10 ppm, an α-phase content of 98%, and a specific surface area of ​​10.5 to 12.8 m². ２ A silicon nitride powder with a concentration of 1 / g is disclosed. However, there is no mention of the presence of metal impurities other than Fe, Ca, Cr, and Ni.

[0005] Patent Document 3 relates to a silicon nitride powder with excellent sinterability and sufficiently reduced variation in quality, characterized by an α-conversion rate of 90.0% or more, a chromium content (Cr equivalent) of 50 to 250 μg / g (i.e., 50 to 250 ppm by mass), a nickel content (Ni equivalent) of 5 to 60 μg / g (i.e., 5 to 60 ppm by mass), and a BET specific surface area of ​​5 to 15 m². ２A silicon nitride powder with a content of 1 / g is disclosed. However, there is no mention of the presence of metal impurities other than Cr and Ni. Furthermore, the only physical property value that indicates that the variation in quality has been sufficiently reduced is the Weibull coefficient of the resulting silicon nitride sintered body. It is common technical knowledge to those skilled in the art that various factors influence the Weibull coefficient of a silicon nitride sintered body, and that the variation in the Weibull coefficient cannot be explained solely by the Cr and Ni content. Even if we assume that all factors other than the Cr and Ni content are the same, there is no basis for the Weibull coefficient to specifically decrease at a [Cr+Ni] content of 84 mass ppm or 301 mass ppm of the raw material powder (the Weibull coefficient is high even when the [Cr+Ni] content is 161-295 mass ppm or above 301 mass ppm (1105-1914 mass ppm), and there is no reason why the Weibull coefficient should decrease only at specific values ​​of [Cr+Ni] content). Therefore, it is thought that the effects of metal impurities other than Cr and Ni are being overlooked.

[0006] International Publication No. 2020 / 203697, Japanese Patent Publication No. 60-215575, International Publication No. 2024 / 195609

[0007] G. P. Gazzara and D. P. Messier, Am. Ceram. Soc. Bull. , 56 [9] pp. 777-80 (1977).

[0008] The object of the present invention is to solve the aforementioned problems and provide a crystalline silicon nitride powder that can produce a silicon nitride sintered body that is easily sintered and has excellent sintered body properties such as fracture strength. Furthermore, the object of the present invention is to provide a crystalline silicon nitride powder that enables the production of a silicon nitride sintered body that has sufficient mechanical strength and excellent thermal conductivity. In addition, the object of the present invention is to provide a silicon nitride sintered body that has both high bending strength and excellent thermal conductivity, and a method for producing the same.

[0009] The present inventors have conducted various studies on the effects of the BET specific surface area, oxygen content, and content of various metal impurities in silicon nitride powder on sinterability and sintered body properties, particularly hardness, mechanical strength, and thermal conductivity. As a result, they have found that silicon nitride powder capable of producing a silicon nitride sintered body that is easily sinterable and possesses excellent sintered body properties such as high strength and high thermal conductivity is silicon nitride powder in which the content of various metal impurities is controlled within an extremely narrow range. Specifically, the present invention provides silicon nitride powder having an iron (Fe) content (mass content) of 95 ppm or less, and a mass content of group IVA metals (Ti, Zr, Hf, etc.) of the periodic table of 0.5 ppm to 60 ppm.

[0010] In one embodiment of the present invention, silicon nitride powder is provided in which the aforementioned IVA group metal is titanium (Ti) and its mass content is 0.5 ppm or more and 50 ppm or less.

[0011] In one embodiment of the present invention, silicon nitride powder is provided, wherein the mass content of titanium (Ti) is 5 ppm or more and 40 ppm or less.

[0012] In one embodiment of the present invention, silicon nitride powder is provided having a chromium (Cr) mass content of 0.5 ppm or more and less than 48 ppm.

[0013] In one embodiment of the present invention, silicon nitride powder is provided having a nickel (Ni) mass content of 0.5 ppm or more and less than 25 ppm.

[0014] In one embodiment of the present invention, silicon nitride powder is provided, wherein the total mass content of chromium (Cr) and nickel (Ni) is 1.0 ppm or more and 50 ppm or less.

[0015] In one embodiment of the present invention, silicon nitride powder is provided having an aluminum (Al) mass content of 0.5 ppm or more and 100 ppm or less.

[0016] In one embodiment of the present invention, silicon nitride powder is provided, wherein the mass content of calcium (Ca) and magnesium (Mg) is 0.5 ppm to 100 ppm and 0.5 ppm to 40 ppm, respectively.

[0017] In one embodiment of the present invention, silicon nitride powder is provided having an alkali metal (Li, Na, K, etc.) mass content of 0.5 ppm or more and 85 ppm or less.

[0018] In one embodiment of the present invention, silicon nitride powder is provided in which the alkali metals are sodium (Na) and potassium (K), and the total mass content of these alkali metals is 1.0 ppm or more and 75 ppm or less.

[0019] In one embodiment of the present invention, silicon nitride powder is provided, which has a content (mass content) of metallic foreign matter larger than 20 μm of 0.17 ppm or less.

[0020] In one embodiment of the present invention, silicon nitride powder is provided, which has a content (mass content) of metallic foreign matter larger than 20 μm of 0.10 ppm or less.

[0021] In one embodiment of the present invention, silicon nitride powder is provided having an oxygen content (TO) of 0.7% by mass or more and 1.3% by mass or less.

[0022] In one embodiment of the present invention, the BET specific surface area (SA) is 7.0 m². ２ / g or more 15.0m ２ A silicon nitride powder with a concentration of less than / g is provided.

[0023] In one embodiment of the present invention, silicon nitride powder is provided in which the mass ratio α / (α+β) of the α phase to the total amount of the α phase and β phase is 90% by mass or more.

[0024] In one embodiment of the present invention, a method for producing a silicon nitride sintered body is provided, comprising the step of molding and sintering a sintering raw material containing the silicon nitride powder and a sintering aid.

[0025] In one embodiment of the present invention, a silicon nitride sintered body is provided, which is obtained by molding and sintering a sintering raw material containing the silicon nitride powder and a sintering aid, and having a titanium (Ti) mass content of 0.5 ppm or more and 50 ppm or less.

[0026] In one embodiment of the present invention, a silicon nitride sintered body is provided, which is obtained by molding and sintering a sintering raw material containing the silicon nitride powder and a sintering aid, and having a chromium (Cr) mass content of 0.5 ppm or more and less than 48 ppm.

[0027] In one embodiment of the present invention, a silicon nitride sintered body is provided, which is obtained by molding and sintering a sintering raw material containing the silicon nitride powder and a sintering aid, wherein the mass content of nickel (Ni) is 0.5 ppm or more and less than 25 ppm, and the total mass content of chromium (Cr) and nickel (Ni) is 1.0 ppm or more and 50 ppm or less.

[0028] In one embodiment of the present invention, a silicon nitride sintered body is provided, which is obtained by molding and sintering a sintering raw material containing the silicon nitride powder and a sintering aid, and having an aluminum (Al) mass content of 0.5 ppm or more and 100 ppm or less.

[0029] In one embodiment of the present invention, a silicon nitride sintered body is provided, obtained by molding and sintering a sintering raw material containing the silicon nitride powder and a sintering aid, wherein the mass content of calcium (Ca) and magnesium (Mg) is 0.5 ppm to 100 ppm and 0.5 ppm to 40 ppm, respectively.

[0030] In one embodiment of the present invention, a silicon nitride sintered body is provided, which is obtained by molding and sintering a sintering raw material containing the silicon nitride powder and a sintering aid, and having a total mass content of sodium (Na) and potassium (K) of 1.0 ppm or more and 75 ppm or less.

[0031] In one embodiment of the present invention, the above embodiments may be combined as appropriate, and typically the following embodiments are provided: [1] Silicon nitride powder having an iron (Fe) content (mass content) of 95 ppm or less, characterized in that the mass content of a group IVA metal (Ti, Zr, Hf, etc.) is 0.5 ppm or more and 60 ppm or less. [2] Silicon nitride powder according to [1], characterized in that the group IVA metal is titanium (Ti), and its mass content is 0.5 ppm or more and 50 ppm or less. [3] Silicon nitride powder according to [1] or [2], characterized in that the mass content of titanium (Ti) is 5 ppm or more and 40 ppm or less. [4] Silicon nitride powder according to any one of [1] to [3], characterized in that the mass content of chromium (Cr) is 0.5 ppm or more and less than 48 ppm. [5] A silicon nitride powder according to any one of [1] to [4], characterized in that the mass content of nickel (Ni) is 0.5 ppm or more and less than 25 ppm. [6] A silicon nitride powder according to any one of [1] to [5], characterized in that the total mass content of chromium (Cr) and nickel (Ni) is 1.0 ppm or more and 50 ppm or less. [7] A silicon nitride powder according to any one of [1] to [6], characterized in that the mass content of aluminum (Al) is 0.5 ppm or more and 100 ppm or less. [8] A silicon nitride powder according to any one of [1] to [7], characterized in that the mass content of calcium (Ca) and magnesium (Mg) is 0.5 ppm or more and 100 ppm or less, and 0.5 ppm or more and 40 ppm or less, respectively. [9] A silicon nitride powder according to any one of [1] to [8], characterized in that the mass content of alkali metals (Li, Na, K, etc.) is 0.5 ppm or more and 85 ppm or less.

[10] A silicon nitride powder according to any one of [1] to [9], characterized in that the alkali metals are sodium (Na) and potassium (K), and the total mass content thereof is 1.0 ppm or more and 75 ppm or less.

[11] A silicon nitride powder according to any one of [1] to

[10] , characterized in that the content (mass content) of metallic foreign matter larger than 20 μm is 0.17 ppm or less.

[12] A silicon nitride powder with a BET specific surface area of ​​7.0 m². ２ / g or more 15.0m ２[1] to

[11] 's silicon nitride powder, characterized in that it is less than or equal to [1] / g.

[13] Silicon nitride powder, characterized in that the mass ratio α / (α+β) of the α phase to the total amount of the α phase and β phase is 90% by mass or more, as described in any one of [1] to

[12] .

[14] A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing the silicon nitride powder and sintering aid described in any one of [1] to [3]'s silicon nitride powder and sintering aid.

[15] A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing the silicon nitride powder and sintering aid described in any one of [4] to [5]'s silicon nitride powder and sintering aid.

[16] A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing the silicon nitride powder and sintering aid described in [6]'s silicon nitride powder and sintering aid.

[17] A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing the silicon nitride powder and sintering aid described in [7]'s silicon nitride powder and sintering aid.

[18] A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in any one of [8] to

[13] .

[19] A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in any one of [1] to

[13] , characterized in that the mass content of titanium (Ti) obtained is 0.5 ppm or more and 50 ppm or less.

[20] A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in any one of [1] to

[13] , characterized in that the mass content of chromium (Cr) is 0.5 ppm or more and less than 48 ppm.

[21] A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in any one of items [1] to

[13] , characterized in that the mass content of nickel (Ni) is 0.5 ppm or more and less than 25 ppm, and the total mass content of chromium (Cr) and nickel (Ni) is 1.0 ppm or more and 50 ppm or less.

[22] A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in any one of [1] to

[13] , characterized in that the mass content of aluminum (Al) is 0.5 ppm or more and 100 ppm or less.

[23] A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in any one of [1] to

[13] , characterized in that the mass content of calcium (Ca) and magnesium (Mg) is 0.5 ppm or more and 100 ppm or less, and 0.5 ppm or more and 40 ppm or less, respectively.

[24] A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in any one of items [1] to

[13] , characterized in that the total mass content of sodium (Na) and potassium (K) is 1.0 ppm or more and 75 ppm or less.

[0032] According to the present invention, it is possible to provide silicon nitride powder and a method for producing the same, which can be used to obtain a silicon nitride sintered body that is easily sintered and possesses excellent mechanical properties and high thermal conductivity.

[0033] ≪Silicon Nitride Powder≫ (Mass Content of Metal Impurities) The silicon nitride powder in this invention has an iron (Fe) content (mass content) of 95 ppm or less, and a mass content of Group IVA metals of the periodic table (Ti, Zr, Hf, etc.) of 0.5 ppm or more and 60 ppm or less. Iron-containing components are one of the main metal impurities contained in silicon nitride powder and are known to adversely affect the thermal and mechanical properties of silicon nitride sintered bodies. For this reason, various measures have been considered to reduce the mass content of iron-containing components in terms of Fe (i.e., the mass content of Fe). As a result, it has become possible to expect that if the mass content of iron (Fe) is 95 ppm or less, the adverse effects on thermal and mechanical properties will be reduced. On the other hand, from the viewpoint of manufacturing costs, the mass content of iron (Fe) may be 1 ppm or more.

[0034] The titanium-containing component in the silicon nitride powder may be a titanium compound such as titanium oxide, titanium nitride, titanium carbide, etc., or may be elemental titanium (metallic titanium) or a titanium-containing alloy. The same applies to metal elements other than titanium, such as Fe, Zr, Hf, Al, Cr, Ni, Ca, Mg, etc. The titanium-containing component and the metal element-containing component other than titanium may be contained in the metal silicon particles, or may be intentionally added to the raw material powder before firing, or may be mixed in during the manufacturing process.

[0035] The lower limit value of the mass content rate of the above Group IVA metals (Ti, Zr, Hf, etc.) may be, for example, 4.0 ppm or more, 5.0 ppm or more, 8.0 ppm or more, or 20 ppm or more. The above Group IVA metals have the effect of promoting the transition from α-Si ３ N ４ to β-Si ３ N ４ during the sintering process of silicon nitride. When the transition to the β phase is promoted, the α→β phase transition proceeds at a lower temperature, so the grain growth of β-Si ３ N ４ particles is suppressed, and a silicon nitride-based sintered body composed of finer β-columnar particles can be obtained. By refining the sintered body structure, the mechanical properties are improved. For example, not only does the fracture strength increase, but the hardness such as Vickers hardness also increases. The upper limit value of the mass content rate of the above Group IVA metals may be, for example, 50 ppm or less, 45 ppm or less, 40 ppm or less, or 30 ppm or less. If the upper limit value of the mass content rate of the above Group IVA metals exceeds the above range, the oxidation resistance of the obtained sintered body gradually deteriorates, and the high-temperature strength and the room-temperature strength after oxidation treatment tend to decrease, which is not preferable. It is more preferable that the mass content rate of the above Group IVA metals is 4.0 ppm or more and 40 ppm or less, further preferably 5.0 ppm or more and 40 ppm or less, and even more preferably 5.0 ppm or more and 36 ppm or less.

[0036] Since the majority of the Group IVA metals contained in silicon nitride powder is titanium (Ti), the mass content of titanium (Ti) is preferably 0.5 ppm or more and 50 ppm or less. The lower limit of the mass content of Ti may be, for example, 4.0 ppm or more, 5.0 ppm or more, 15 ppm or more, or 18 ppm or more. When the lower limit of the mass content of Ti is within the above range, the transition from the α phase to the β phase is promoted during the sintering process, and the α→β phase transition proceeds at a lower temperature, thus β-Si ３ N ４ Particle growth is suppressed, and a silicon nitride sintered body composed of finer β-columnar crystals is obtained. Refinement of the sintered body structure not only increases fracture strength but also hardness such as Vickers hardness. The upper limit of the Ti mass content may be, for example, 40 ppm or less, 36 ppm or less, 28 ppm or less, or 19 ppm or less. If the upper limit of the Ti mass content exceeds the above range, the oxidation resistance of the obtained sintered body gradually deteriorates, and the high-temperature strength and room-temperature strength after oxidation treatment tend to decrease, which is undesirable. The Ti mass content is more preferably 4.0 ppm or more and 40 ppm or less, even more preferably 5.0 ppm or more and 40 ppm or less, and even more preferably 5.0 ppm or more and 36 ppm or less.

[0037] In the present invention, the silicon nitride powder preferably has a chromium (Cr) mass content of 0.5 ppm or more and less than 48 ppm.

[0038] The lower limit of the mass content of Cr may be, for example, 1.0 ppm or more, 6 ppm or more, 8 ppm or more, or 13 ppm or more. When the lower limit of the mass content of Cr is within the above range, the oxidation resistance of the resulting sintered body is improved, and a silicon nitride sintered body with improved strength after oxidation treatment tends to be obtained (the effect is particularly noticeable when the mass content of Ti is 0.5 ppm or more and 50 ppm or less). The upper limit of the mass content of Cr may be, for example, 40 ppm or less, 30 ppm or less, 22 ppm or less, or 14 ppm or less. When the upper limit of the mass content of Cr exceeds the above range, β-Si ３ N４ This is undesirable because it can lead to variations in particle growth, resulting in greater non-uniformity of the resulting sintered body structure and a decrease in fracture strength. The mass content of Cr is more preferably 8 ppm to 40 ppm, and even more preferably 13 ppm to 22 ppm.

[0039] In the present invention, the silicon nitride powder preferably has a nickel (Ni) mass content of 0.5 ppm or more and less than 25 ppm. The lower limit of the Ni mass content may be, for example, 1.0 ppm or more, 2.0 ppm or more, 3.0 ppm or more, or 8 ppm or more. When the lower limit of the Ni mass content is within the above range, the molten silicate phase formed by the reaction of the sintering aid and the oxide layer on the surface of the silicon nitride particles during the sintering process becomes more easily wettable to the silicon nitride particles, promoting densification, and thus making it easier to obtain a high-density silicon nitride sintered body (the effect is particularly pronounced when the Ti mass content is 0.5 ppm or more and 50 ppm or less). The upper limit of the Ni mass content may be, for example, 19 ppm or less, 15 ppm or less, 13 ppm or less, or 10 ppm or less. If the upper limit of the Ni mass content exceeds the above range, voids may form between the particles of the resulting silicon nitride sintered body. Furthermore, the non-uniformity of the sintered body structure may increase, leading to a decrease in fracture strength, which is undesirable. The Ni mass content is more preferably 1.0 ppm to 19 ppm, and even more preferably 8 ppm to 13 ppm.

[0040] In the present invention, the silicon nitride powder preferably has a total mass content of chromium (Cr) and nickel (Ni) of 1.0 ppm or more and 50 ppm or less. The lower limit of the total mass content of Cr and Ni may be, for example, 2.0 ppm or more, 8.0 ppm or more, or 16 ppm or more. When the lower limit of the total mass content of Cr and Ni is within the above range, it is easier to obtain a high-density silicon nitride sintered body (the effect is particularly pronounced when the mass content of Ti is 0.5 ppm or more and 50 ppm or less). The upper limit of the total mass content of Cr and Ni may be, for example, 29 ppm or less, 25 ppm or less, or 20 ppm or less. If the upper limit of the total mass content of Cr and Ni exceeds the above range, the non-uniformity of the sintered body structure increases, which may reduce the fracture strength, so this is undesirable. The total mass content of Cr and Ni is more preferably 2.0 ppm or more and 29 ppm or less, and even more preferably 8.0 ppm or more and 25 ppm or less.

[0041] In the present invention, the silicon nitride powder preferably has an aluminum (Al) mass content of 0.5 ppm or more and 100 ppm or less. The lower limit of the Al mass content may be, for example, 2 ppm or more, 10 ppm or more, 20 ppm or more, or 30 ppm or more. When the lower limit of the Al mass content is within the above range, the densification of silicon nitride is promoted during the sintering process, and a high-density and high-strength silicon nitride sintered body can be obtained (the effect is particularly pronounced when the Ti mass content is 0.5 ppm or more and 50 ppm or less). The upper limit of the Al mass content may be, for example, 90 ppm or less, 70 ppm or less, 45 ppm or less, or 28 ppm or less. When the upper limit of the Al mass content exceeds the above range, β-Si ３ N ４ As the amount of Al dissolved in the particles increases, the thermal conductivity of the sintered body gradually deteriorates, and the thermal conductivity tends to decrease, which is undesirable. The mass content of Al is more preferably 2.0 ppm to 90 ppm, and even more preferably 20 ppm to 70 ppm.

[0042] In the present invention, the silicon nitride powder preferably has a mass content of calcium (Ca) and magnesium (Mg) of 0.5 ppm to 100 ppm and 0.5 ppm to 40 ppm, respectively.

[0043] The lower limit of the mass content of Ca may be, for example, 1.0 ppm or more, 3.0 ppm or more, 5.0 ppm or more, or 10 ppm or more. When the lower limit of the mass content of Ca is within the above range, the densification of silicon nitride is promoted during the sintering process, and a high-density and high-strength silicon nitride sintered body can be obtained (the effect is particularly pronounced when the mass content of Ti is 0.5 ppm or more and 50 ppm or less). The upper limit of the mass content of Ca may be, for example, 95 ppm or less, 80 ppm or less, 65 ppm or less, or 50 ppm or less. When the upper limit of the mass content of Ca exceeds the above range, the melting temperature of the grain boundary phase formed in the obtained silicon nitride sintered body decreases, and the strength deterioration at high temperatures becomes significant, which is undesirable. Furthermore, oxidation resistance deteriorates, and the strength after oxidation treatment decreases, which is undesirable (if the ratio of the room temperature strength after oxidation treatment to the room temperature strength before oxidation treatment is defined as the "strength retention rate," then the strength retention rate also decreases, which is undesirable). The mass content of Ca is more preferably 1.0 ppm or more and 80 ppm or less, and even more preferably 3.0 ppm or more and 65 ppm or less.

[0044] The lower limit of the mass content of Mg may be, for example, 2.0 ppm or more, 4.0 ppm or more, 6.0 ppm or more, or 8.0 ppm or more. When the lower limit of the mass content of Mg is within the above range, the densification of silicon nitride is promoted during the sintering process, and a high-density and high-strength silicon nitride sintered body can be obtained (the effect is particularly pronounced when the mass content of Ti is 0.5 ppm or more and 50 ppm or less). The upper limit of the mass content of Mg may be, for example, 35 ppm or less, 30 ppm or less, 21 ppm or less, or 15 ppm or less. When the upper limit of the mass content of Mg exceeds the above range, the melting temperature of the grain boundary phase formed in the obtained silicon nitride sintered body decreases, and the strength deterioration at high temperatures becomes significant, which is undesirable. Furthermore, oxidation resistance deteriorates, and the strength after oxidation treatment decreases, which is undesirable (if the ratio of the room temperature strength after oxidation treatment to the room temperature strength before oxidation treatment is defined as the "strength retention rate," then the strength retention rate also decreases, which is undesirable). The mass content of Mg is more preferably 2.0 ppm or more and 30 ppm or less, and even more preferably 4.0 ppm or more and 21 ppm or less.

[0045] In the present invention, the silicon nitride powder preferably has a mass content of alkali metals (such as Li, Na, and K) of 0.5 ppm or more and 85 ppm or less. The lower limit of the alkali metal mass content may be, for example, 2.0 ppm or more, 5.0 ppm or more, 10 ppm or more, or 15 ppm or more. When the lower limit of the alkali metal mass content is within the above range, the corrosion resistance of the resulting sintered body is improved, it is less likely to dissolve in aqueous solutions such as acids and alkalis, and strength deterioration due to corrosion tends to be suppressed (the effect is particularly pronounced when the Ti mass content is 0.5 ppm or more and 50 ppm or less). The upper limit of the alkali metal mass content may be, for example, 80 ppm or less, 60 ppm or less, 40 ppm or less, or 33 ppm or less. When the upper limit of the alkali metal mass content exceeds the above range, the corrosion resistance of the resulting sintered body deteriorates, it becomes more likely to dissolve in aqueous solutions such as acids and alkalis, and strength deterioration due to corrosion tends to progress, which is undesirable. The mass content of the alkali metal is more preferably 2.0 ppm or more and 60 ppm or less, and even more preferably 5.0 ppm or more and 33 ppm or less.

[0046] In the present invention, the silicon nitride powder preferably has a total mass content of sodium (Na) and potassium (K) of 1.0 ppm or more and 75 ppm or less. The lower limit of the total mass content of Na and K may be, for example, 2.0 ppm or more, 4.0 ppm or more, or 8.0 ppm or more. When the lower limit of the total mass content of Na and K is within the above range, the corrosion resistance of the resulting sintered body is improved, it is less likely to dissolve in aqueous solutions such as acids and alkalis, and strength deterioration due to corrosion tends to be suppressed (the effect is particularly noticeable when the mass content of Ti is 0.5 ppm or more and 50 ppm or less). The upper limit of the total mass content of Na and K may be, for example, 50 ppm or less, 32 ppm or less, or 24 ppm or less. If the upper limit of the total mass content of Na and K exceeds the above range, the corrosion resistance of the resulting sintered body deteriorates, it becomes more susceptible to leaching in aqueous solutions such as acids and alkalis, and the strength degradation due to corrosion tends to progress, which is undesirable. The total mass content of Na and K is more preferably 2.0 ppm or more and 50 ppm or less, and even more preferably 4.0 ppm or more and 32 ppm or less.

[0047] The mass content of metal impurities in the silicon nitride powder in this invention can be adjusted, for example, by controlling the concentration of metal impurities in the metal silicon powder used as a raw material for silicon nitride powder production. As metal silicon, it is possible to obtain silicon powder of various purities, from ultra-high purity metal silicon obtained as waste material from polycrystalline silicon production, to ordinary industrial silicon that has been crushed and refined. The amount of metal impurities mixed in during the crushing process to obtain metal silicon powder with a desired particle size can be determined empirically, so if the concentration of metal impurities in the metal silicon used as the starting material is determined, metal silicon powder with the desired amount of metal impurities and the desired particle size can be produced with good reproducibility. Furthermore, in order to obtain metal silicon powder having the mass content of metal impurities specified in this invention, it is also possible to adjust the mass content of metal impurities by mixing multiple metal silicon powders.

[0048] (Oxygen Content) In the present invention, the silicon nitride powder preferably has an oxygen content of 0.6% by mass or more and 1.3% by mass or less. During the sintering of silicon nitride, the sintering aid added during the preparation of the raw materials reacts with the oxide layer on the surface of the silicon nitride particles to form a molten phase consisting of silicate, and after the silicon nitride dissolves in this molten silicate phase, β-Si ３ N ４ The densification process proceeds through the precipitation of particles. Therefore, the higher the oxygen content of the silicon nitride powder, the greater the volume of the molten silicate phase, and the easier it is for densification to proceed. The lower limit of the oxygen content may be, for example, 0.7% by mass or more, 0.8% by mass or more, or 0.9% by mass or more. When the lower limit of the oxygen content is within the above range, there is a sufficient amount of molten silicate phase, the densification rate increases, and a high-density silicon nitride sintered body is obtained. On the other hand, if the oxygen content of the silicon nitride powder, which is the starting material, is high, the fracture toughness value of the obtained silicon nitride sintered body decreases, and mechanical properties such as bending strength deteriorate. In particular, the strength properties at high temperatures deteriorate. Therefore, the upper limit of the oxygen content may be, for example, 1.2% by mass or less, 1.1% by mass or less, or 1.0% by mass or less. When the upper limit of the oxygen content is within the above range, a high-density silicon nitride sintered body can be obtained, and since the oxygen content of the sintered body is not excessive and the amount of grain boundary phase is not large, it is easy to obtain a silicon nitride sintered body with high mechanical strength and high thermal conductivity. The oxygen content is more preferably 0.7% by mass or more and 1.2% by mass or less, and even more preferably 0.8% by mass or more and 1.1% by mass or less.

[0049] (BET specific surface area) The specific surface area of ​​silicon nitride powder in this invention, obtained by the BET method, is 7.0 m². ２ / g or more 15.0m ２ It is preferable that the amount is less than or equal to / g. Specific surface area is an important powder characteristic that governs densification through the dissolution and extraction process of silicon nitride particles during sintering, and a BET specific surface area of ​​7.0 m² is preferable. ２If the amount is less than / g, the driving force for sintering begins to decrease, and it may become impossible to obtain a high-density silicon nitride sintered body without adding a large amount of sintering aid. Adding a large amount of sintering aid deteriorates the properties of the silicon nitride sintered body. The lower limit of the BET specific surface area mentioned above is, for example, 8.0 m². ２ / g or more, 8.8m ２ / g or more, or 9.2m ２ It may be 1 / g or more. When the lower limit of the BET specific surface area is within the above range, densification proceeds easily, and a high-density silicon nitride sintered body can be obtained. On the other hand, if the BET specific surface area is 15.0 m² ２ If the BET specific surface area exceeds 1 / g, not only does the green density decrease with normal molding methods, making molding difficult, but microcracks, voids, etc. may occur after sintering. Furthermore, it not only negatively affects dimensional accuracy, but in the sintering of complex-shaped parts, it can cause cracks (aggregates of cracks) to form at the corners of the sintered body, which is undesirable. For this reason, the upper limit of the BET specific surface area should be, for example, 14.0 m². ２ / g or less, 12.8m ２ / g or less, or 12.0m ２ It may be less than or equal to / g. When the upper limit of the BET specific surface area is within the above range, a homogeneous molded body with appropriate green density can be obtained, and when this is sintered, a silicon nitride sintered body with high mechanical strength and high thermal conductivity can be easily obtained. The above BET specific surface area is 8.0 m². ２ / g or more 14.0m ２ Preferably less than / g, and 8.8m ２ / g or more 12.8m ２ It is more preferable to have less than / g, and 9.2m ２ / g or more 12.0m ２ It is even more preferable that the range be less than or equal to / g.

[0050] In this invention, the BET specific surface area is the value (BET specific surface area) measured by the BET single-point method using nitrogen gas, in accordance with the method described in JIS Z 8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption".

[0051] In the production of silicon nitride powder by imide pyrolysis, the BET specific surface area can be controlled, for example, by adjusting the BET specific surface area and oxygen content of the amorphous Si-N(-H) compound. In the production of silicon nitride powder by direct nitriding, the BET specific surface area can be controlled, for example, by adjusting the grinding conditions during production.

[0052] (Ratio of oxygen content (TO) to BET specific surface area (SA)) The preferred value of oxygen content (TO) in the silicon nitride powder of the present invention also changes with the specific surface area (SA). That is, the ratio of oxygen content (TO) to BET specific surface area (SA) (TO / SA) is 0.60 mg / m². ２ 1.40mg / m or more ２ Preferably the following (0.060% / m ２ g －１ 0.14% / m or more ２ g －１ (It can also be written as follows). TO / SA ratio is 0.60 mg / m². ２ The above conditions result in good densification rate and good mechanical strength. On the other hand, the TO / SA ratio is 1.40 mg / m². ２ The following conditions result in a desirable oxygen content in the sintered body, leading to good strength characteristics (room temperature strength, high-temperature strength, fracture toughness, etc.). In particular, a significant decrease in the thermal conductivity of the sintered body can be suppressed. The TO / SA ratio is 0.70 mg / m². ２ 1.30mg / m or more ２ The following is more preferable:

[0053] (Mass ratio of α phase α / (α+β)) In the silicon nitride powder of the present invention, the mass ratio of the α phase to the total amount of the α phase and β phase, α / (α+β), is preferably 90% by mass or more. In the sintering of silicon nitride, during the heating process, the sintering aid reacts with the oxide layer on the surface of the silicon nitride particles to form a molten phase consisting of silicate, and after the silicon nitride dissolves in this molten silicate phase, β-Si ３ N ４ The process proceeds through precipitation as particles. α-Si ３ N ４ The particles are β-Si ３ N ４Because it has a higher solubility in the molten silicate phase than particles, the higher the mass ratio of the α phase, the more columnar β-Si ３ N ４ As the particles grow, the mechanical properties (such as fracture toughness and flexural strength) of the resulting silicon nitride sintered body improve. The lower limit of the mass ratio α / (α+β) of the α phase may be 92% by mass or more, 94% by mass or more, or 96% by mass or more. If the lower limit of the mass ratio of the α phase is within the above range, columnar β-Si with a large aspect ratio will be formed. ３ N ４ The particles grow, and a good silicon nitride sintered body with excellent mechanical properties is obtained. A high mass ratio of the α phase in the silicon nitride powder is preferable, but if it becomes excessively high, β-Si precipitates. ３ N ４ The crystal nuclei decrease, and columnar β-Si ３ N ４ Abnormal particle growth may occur. For this reason, the upper limit of the α-phase mass ratio α / (α+β) may be 99% by mass or less, 98.5% by mass or less, or 98% by mass or less. If the upper limit of the α-phase mass ratio is within the above range, columnar β-Si ３ N ４ This is preferable because it suppresses abnormal particle growth and tends to eliminate non-uniformity in the microstructure of the resulting silicon nitride sintered body.

[0054] (Mass content of metallic foreign matter larger than 20 μm) In the present invention, it is preferable that the silicon nitride powder has a mass content of metallic foreign matter larger than 20 μm of 0.17 ppm or less. "Metallic foreign matter larger than 20 μm" contained in the starting material remains as molding defects in the silicon nitride powder molded body and abnormally grows β-Si even after sintering. ３ N ４ This can cause the formation of particles and coarse voids. As a result, the variability in the strength properties of the silicon nitride sintered body increases, which can be a major cause of property degradation. The mass content of metal foreign matter larger than 20 μm is preferably 0.16 ppm or less, 0.14 ppm or less, 0.10 ppm or less, or 0.02 ppm or less. If the upper limit of the mass content of "metal foreign matter larger than 20 μm" is within the above range, abnormal growth of β-Si after sintering may occur. ３ N４ The generation of particles and coarse voids is significantly reduced, the variation in the strength characteristics of the silicon nitride sintered body is reduced, and it is preferable that a good silicon nitride sintered body can be easily obtained.

[0055] (Method for measuring the amount of metallic foreign matter larger than 20 μm) A slurry of silicon nitride powder dispersed in distilled water is thoroughly stirred to obtain a dispersion. The obtained dispersion is passed through a stainless steel sieve (mesh size: 20 μm) to separate aggregates (including metallic foreign matter particles) larger than 20 μm onto the stainless steel sieve. The aggregates (including metallic foreign matter particles) larger than 20 μm on the stainless steel sieve are removed with distilled water and dispersed again in water. The obtained dispersion is introduced into a suction filtration device equipped with a Teflon® filter (mesh size: 1 μm) to recover the aggregates (including metallic foreign matter particles) larger than 20 μm onto the Teflon® filter. The Teflon® filter from which the aggregates (including metallic foreign matter particles) have been recovered is placed into a container containing an acidic solution of hydrofluoric acid and nitric acid, and after sealing, the container is heated and dissolved by irradiating it with microwaves. The resulting decomposition solution is then diluted to a fixed volume with ultrapure water to obtain the test solution. Using an ICP-MS instrument, the concentrations of various metals (Fe, Group IVA metals (Ti, Zr, Hf), Al, Cr, Ni, alkali metals (Li, Na, K), Ca, and Mg) in the sample solution were quantified from the detected wavelengths and their emission intensities. The total analytical values ​​of the detected metals were converted to their concentration per unit weight of the original silicon nitride powder to determine the amount of metal foreign matter larger than 20 μm.

[0056] (Carbon Content) The silicon nitride powder of the present invention preferably has a carbon content of 0.001% by mass or more and 0.2% by mass or less. During the heating process during sintering, the silicon oxide layer and silicon oxynitride layer present on the surface of the molded silicon nitride particles are reduced by carbon. A carbon content of 0.2% by mass or less is preferable because it ensures a sufficient amount of molten phase generated at high temperatures, allows for a high densification rate, and makes it easier to obtain a high-density sintered body. The upper limit of the carbon content may be, for example, 0.17% by mass or less, 0.14% by mass or less, 0.12% by mass or less, or 0.10% by mass or less. The lower limit of the carbon content may be, for example, 0.005% by mass or more, 0.008% by mass or more, 0.01% by mass or more, or 0.02% by mass or more. A carbon content of 0.02% by mass or more and 0.10% by mass or less is even more preferable. When the carbon content is within the above range, there is a sufficient amount of molten silicate phase, the densification rate increases, and a high-density silicon nitride sintered body is obtained.

[0057] ≪Method for Producing Silicon Nitride Powder≫ ≪Imide Thermal Decomposition Method≫ There are no particular limitations on the method for producing silicon nitride powder in the present invention. For example, in the imide thermal decomposition method, amorphous Si-N(-H) compounds are calcined to produce crystalline silicon nitride powder. In this method, nitrogen-containing silane compounds such as silicon diimide, silicon tetraamide, and silicon chlorimide are produced by known methods, for example, a method of reacting silicon halides with ammonia, specifically a method of reacting silicon halides such as silicon tetrafluoride, silicon tetrachloride, silicon tetrabromide, and silicon tetraiodide with ammonia in the gas phase, or a method of reacting liquid silicon halides with liquid ammonia.

[0058] Amorphous Si-N(-H) compounds are produced by known methods such as thermal decomposition of the obtained nitrogen-containing silane compound at a temperature of 1100°C or less under a nitrogen or ammonia gas atmosphere, or by reacting silicon halides such as silicon tetrafluoride, silicon tetrachloride, silicon tetrabromide, and silicon tetraiodide with ammonia at high temperatures.

[0059] The amorphous Si-N(-H) compound used in the present invention is an amorphous Si-N-H compound containing the elements Si, N, and H obtained by thermal decomposition of the nitrogen-containing silane compound, or amorphous silicon nitride containing Si and N, or amorphous Si-N-H compound containing the elements Si, N, and H obtained by a method of reacting silicon halide with ammonia at high temperature, or amorphous silicon nitride containing Si and N, and is represented by the following compositional formula (1). Si ６ N ２ｘ (NH) １２－３ｘ (However, x = 0 to 4 in the formula, and although not explicitly stated in the composition formula, it includes compounds containing halogens as impurities) ... (1)

[0060] The x-value is preferably between 1.3 and 3.6, and more preferably between 1.65 and 3.10. Note that Si is represented by x = 3. ６ N ６ (NH) ３ It is called silicon nitrogenimide.

[0061] (Carbon Content) The amount of carbon contained as an impurity in silicon nitride powder depends on the content of hydrocarbons such as toluene contained in the nitrogen-containing silane compound. For example, when the nitrogen-containing silane compound is silicon diimide, the carbon content of the silicon nitride powder after high-temperature firing can be set to 0.01% by mass or more and 0.20% by mass or less by controlling the toluene content of the silicon diimide to 0.01% by mass or more and 0.54% by mass or less. It is more preferable that the toluene content of the silicon diimide be 0.01% by mass or more and 0.35% by mass or less.

[0062] (BET specific surface area) The specific surface area of ​​the amorphous Si-N(-H) compound, which is an intermediate raw material for silicon nitride powder production according to the present invention, is 215 m². ２ / g or more 590m ２ It is preferable that the amount is less than or equal to / g. The BET specific surface area is 215 m². ２If the amount is greater than / g, rapid crystallization occurs in the temperature range of 1000 to 1400°C, preventing the formation of needle-shaped particles and aggregated particles. When a sintered body is made from such powder, a homogeneous structure is formed, and the strength and thermal conductivity of the resulting sintered body are good. On the other hand, if the BET specific surface area is 590 m² ２ When the concentration is less than / g, the degree of supersaturation near the particles increases during crystallization, resulting in a large number of nuclei, which prevents an excessive decrease in the BET specific surface area of ​​the crystalline silicon nitride powder. Therefore, it exhibits good sinterability, and the sintered body has good strength and thermal conductivity. The BET specific surface area of ​​amorphous Si-N(-H) compounds is 290 m². ２ / g or more 525m ２ It may be less than or equal to / g, and 340m ２ / g or more 500m ２ It is even more preferable that the amount is less than or equal to / g.

[0063] The BET specific surface area of ​​amorphous Si-N(-H) compounds can be adjusted by the maximum temperature at which the nitrogen-containing silane compound used as a raw material is thermally decomposed. The lower the maximum temperature during thermal decomposition, the larger the BET specific surface area of ​​the amorphous Si-N(-H) compound can be. When the nitrogen-containing silane compound is silicon diimide, the maximum temperature of thermal decomposition may be, for example, 480°C to 1060°C, and more preferably 580°C to 980°C.

[0064] (Oxygen Content) The oxygen content of amorphous Si-N(-H) compounds can be controlled by adjusting the amount of oxygen inevitably contained in nitrogen-containing silane compounds and the partial pressure of oxygen (oxygen concentration) in the atmosphere when the nitrogen-containing silane compounds are thermally decomposed. The lower the oxygen content of the nitrogen-containing silane compound, and the lower the partial pressure of oxygen in the atmosphere during thermal decomposition, the lower the oxygen content of the amorphous Si-N(-H) compounds can be. The oxygen concentration in the inert gas supplied to the thermal decomposition furnace may be, for example, 60 volume ppm or more and 1250 volume ppm or less, and more preferably 190 volume ppm or more and 530 volume ppm or less (hereinafter, volume ppm will be referred to as ppm(V)). The oxygen content of the amorphous Si-N(-H) compound may be, for example, 0.37% by mass or more and 1.5% by mass or less, 0.58% by mass or more and 1.0% by mass or less, and more preferably 0.62% by mass or more and 0.98% by mass or less.

[0065] As the metallic silicon to be blended into the amorphous Si-N(-H) compound, any metallic silicon powder with a 50% diameter (average particle size) of 5 μm or less in the volume-based cumulative particle size distribution may be used, and it is preferable to adjust the average particle size to 0.7 μm or more and 5.0 μm or less. The amount of metallic silicon powder to be blended is 0.5 to 40 parts by weight, preferably 1 to 20 parts by weight, per 100 parts by weight of amorphous silicon nitride powder.

[0066] There are no particular restrictions on the method of compounding amorphous Si-N(-H) compounds with metallic silicon powder. Methods using grinders such as ball mills, vibrating ball mills, attritor mills, and cutter mills, or mixers such as horizontal rotating cylindrical mixers, vertical double cone mixers, ribbon mixers, plow mixers, cubic mixers, V-shaped mixers, and screw mixers can be employed. By compounding with metallic silicon powder, the crystallization rate of silicon nitride during calcination can be increased, and the mass content of group IVA metals (Ti, Zr, Hf, etc.), iron group elements (Fe, Ni, etc.), aluminum (Al), chromium (Cr), alkali metals (Li, Na, K, etc.), and alkaline earth metals (Ca, Mg) in the resulting crystalline silicon nitride powder can be adjusted.

[0067] <Castration and Crystallization of Amorphous Si-N(-H) Compounds> In the present invention, an amorphous Si-N(-H) compound, or an amorphous Si-N(-H) compound containing metallic silicon, is ground using the aforementioned pulverizer, and then calcined in a nitrogen-containing inert gas atmosphere or a nitrogen-containing reducing gas atmosphere at a temperature of preferably 1400 to 1600°C to convert it into crystalline silicon nitride powder.

[0068] Conventional firing furnaces such as batch-type electric furnaces and pusher-type electric furnaces are used for heating amorphous Si-N(-H) compounds or amorphous Si-N(-H) compounds containing metallic silicon.

[0069] The aforementioned pusher furnace is a firing furnace equipped with a furnace chamber that allows for the firing of materials by sequentially pushing and transporting multiple base plates, on which crucibles containing ceramic raw materials and other materials to be fired, into the furnace using a pusher mechanism, and by controlling the temperature and atmospheric conditions.

[0070] (Nitrogen-containing inert gas atmosphere) A nitrogen-containing inert gas atmosphere refers to a nitrogen atmosphere, an inert gas atmosphere consisting of nitrogen and noble gases such as argon, etc. To obtain calcined powder with a low oxygen content, it is desirable to have no oxygen at all, but even if oxygen is present, the oxygen concentration may be 100 ppm(V) or less, and more preferably 50 ppm(V) or less. A nitrogen-containing reducing gas atmosphere is an atmosphere consisting of an inert gas such as nitrogen and a reducing gas such as hydrogen or ammonia.

[0071] (Firing temperature, heating rate) The BET specific surface area of ​​crystalline silicon nitride powder is affected by the BET specific surface area and oxygen content of amorphous Si-N(-H) compound, the grinding conditions of the Si-N(-H) compound before firing, the amount of the aforementioned metallic silicon powder added, and the heating rate and maximum holding temperature during firing. For this reason, it is preferable to set the heating rate to 53°C or more and 110°C or less, and the maximum holding temperature to 1430°C or more and 1595°C or less. Furthermore, since the α / (α+β) ratio in the crystalline phase is also affected by the heating rate and the maximum holding temperature, it is more preferable to set the heating rate to 59°C or more and 100°C or less, and the maximum holding temperature to 1480°C or more and 1570°C or less. The holding time at the maximum temperature may be, for example, 1 hour or more and 5 hours or less.

[0072] <Disintegration Treatment> The obtained crystalline silicon nitride powder is subjected to disintegration treatment under an inert gas atmosphere containing oxygen (for example, under air circulation) to adjust the surface oxygen content (FSO) and the ratio of surface oxygen content (FSO) to BET specific surface area (SA) (FSO / SA). Disintegration is carried out by milling, and general grinding equipment such as bead mills, vibratory mills, planetary ball mills, and jet mills can be used.

[0073] ≪Direct Nitriding Method≫ In the production of silicon nitride powder by the direct nitriding method, which involves heating metallic silicon powder in a non-oxidizing gas atmosphere containing nitrogen, the amount of metal impurities mixed in during the grinding process to obtain metallic silicon powder with the desired particle size can be determined empirically. Therefore, by controlling the concentration of metal impurities contained in the starting material metallic silicon, metallic silicon powder with the desired amount of metal impurities and the desired particle size can be produced with good reproducibility. Furthermore, it is also possible to adjust the mass content of metal impurities by mixing multiple metallic silicon powders to obtain metallic silicon powder with the desired mass content of metal impurities. The powder properties of the obtained silicon nitride powder (oxygen content, BET specific surface area, particle size distribution, etc.) can be obtained by controlling the average particle size and oxygen content of the raw material metallic silicon powder, as well as the moisture content in the atmosphere, to obtain the desired silicon nitride powder. Specifically, using metallic silicon powder in which the average particle size and oxygen content are adjusted to an appropriate range as a raw material, preferably nitrided in a nitrogen gas or nitrogen-containing non-oxidizing gas atmosphere with a moisture concentration of 600 ppm (V) or less, and then pulverized, silicon nitride powder having the BET specific surface area, oxygen content, and particle size distribution described above can be obtained.

[0074] <Raw Material Metallic Silicon Powder> (50% Diameter (Average Particle Size)) The raw material metallic silicon powder should be one in which the 50% diameter (average particle size) in the volume-based cumulative particle size distribution is 10 μm or less, and it is preferable that the average particle size be between 0.7 μm and 10 μm. If the average particle size of the metallic silicon powder is 0.7 μm or more, the amount of internal oxygen in the silicon nitride powder obtained by nitriding and pulverization can be reduced. If the average particle size of the metallic silicon powder is 10 μm or less, the nitriding reaction time can be shortened, resulting in excellent productivity. It is also possible to prevent the residue of unreacted silicon. It is more preferable that the average particle size of the metallic silicon powder be between 1.0 μm and 5.0 μm.

[0075] (Oxygen Content) The oxygen content of metallic silicon powder can be adjusted by the grinding and pretreatment conditions. For example, metallic silicon powder with an average particle size of 3 μm has an oxygen content of about 0.50 mass%, metallic silicon powder with an average particle size of 6 μm has an oxygen content of about 0.30 mass%, and metallic silicon powder with an average particle size of 10 μm has an oxygen content of about 0.20 mass%. Since the oxygen content of metallic silicon powder affects the amount of internal oxygen in the resulting crystalline silicon nitride powder, the oxygen content of the metallic silicon powder used in the silicon nitride powder production of the present invention may be, for example, 0.4 mass% to 1.1 mass%. More preferably, the oxygen content is 0.5 mass% to 0.8 mass%.

[0076] (Additives) A ​​diluent, a nitriding accelerator, and an organic binder for molding are added to the above-mentioned metallic silicon powder to prepare the calcination raw material. As the diluent, crystalline silicon nitride powder with an average particle size of approximately 0.7 μm is used. As the nitriding accelerator, calcium fluoride powder is used. As the organic binder, polyvinyl alcohol, carboxymethylcellulose, wax-based emulsion, acrylic-based emulsion, etc., can be used.

[0077] (Diluent) Adding a diluent allows for the production of a calcined product (nitrided ingot) that is easy to pulverize. The amount of crystalline silicon nitride powder added may be, for example, 3% by mass or more and 22% by mass or less. Adding less than 3% by mass is undesirable because it not only requires a long time for the nitriding reaction but also makes the nitrided ingot extremely hard, increasing the load on the pulverization process. Adding more than 22% by mass has little effect on the high-temperature calcination conditions and the properties of the calcined product, but it is undesirable because it increases costs.

[0078] (Nitriding accelerator; calcium fluoride powder) The amount of calcium fluoride powder added may be, for example, 0.02% by mass or more and 0.09% by mass or less. If the amount added exceeds 0.09% by mass, the amount of internal fluorine in the resulting crystalline silicon nitride powder will increase, which is undesirable. If the residual calcium and fluorine in the nitrided ingot is a concern, calcium fluoride may be omitted.

[0079] (Organic Binder) In the case of polyvinyl alcohol, the amount of organic binder added may be, for example, 0.2% by mass or more and 2.0% by mass or less. If the amount added exceeds 2.0% by mass, the carbon content of the resulting crystalline silicon nitride powder will increase, which is undesirable. If it is not necessary to increase the amount of raw material to be filled into the firing container, the organic binder may not be added.

[0080] (Diluent, Nitriding Accelerator, and Organic Binder) The amount of crystalline silicon nitride powder added is preferably 6% by mass or more and 18% by mass or less. The amount of calcium fluoride powder added is preferably 0.02% by mass or more and 0.04% by mass or less. The amount of polyvinyl alcohol added is preferably 0.2% by mass or more and 1.4% by mass or less.

[0081] <Supply Gas> For nitriding the above-mentioned calcination raw material containing metallic silicon powder, nitrogen or a nitrogen-containing non-oxidizing gas is used as the supply gas. To obtain calcination powder with a low oxygen content, a supply gas that does not contain any oxygen is desirable, but even if oxygen is present, the oxygen concentration may be 140 ppm(V) or less, and more preferably 110 ppm(V) or less. The preferred lower limit of the oxygen concentration is 15 ppm(V) or more, or 25 ppm(V) or more. A nitrogen-containing reducing gas atmosphere is an atmosphere consisting of nitrogen, an inert gas containing nitrogen, and a reducing gas such as hydrogen or ammonia. Examples of mixed gases of hydrogen gas and nitrogen gas include nitrogen gas containing about 0.5 to 15% by volume of hydrogen gas, and examples of mixed gases of ammonia gas and nitrogen gas include nitrogen gas containing 0.1% to 4.4% by volume of ammonia gas. The mixing ratio of ammonia gas is preferably 0.6% to 3.4% by volume. In this case, it is even more preferable to set the moisture concentration in the gas atmosphere to 40 ppm(V) or more and 600 ppm(V) or less, and more preferably to set the moisture concentration to 80 ppm(V) or more and 300 ppm(V) or less.

[0082] <Nitriding Process; Sintering> (Nitriding Temperature, Time) When nitriding the above-mentioned sintering raw material containing metallic silicon powder in the above-mentioned gas atmosphere, the nitriding temperature may be, for example, 1150°C to 1450°C, or 1200°C to 1400°C. The nitriding time may be, for example, 15 to 40 hours, but the sintering time, including the heating process, will be, for example, 40 to 70 hours. It is preferable to raise the maximum temperature in the high-temperature sintering to around 1600°C, which also serves as heat treatment for the sintered product (nitrided ingot), in order to stabilize the properties of the resulting crystalline silicon nitride powder.

[0083] (Heating Rate) In the silicon nitride powder production of the present invention, it is preferable to investigate the nitriding reaction rate by preliminary studies and adjust the heating rate up to a nitriding rate of 50% to be between 5°C / h and 10°C / h. Setting the heating rate up to a nitriding rate of 5°C / h or higher is preferable because it shortens the firing time and does not increase costs. Setting the heating rate up to a nitriding rate of 50% to 10°C / h or lower is preferable because it prevents an excessive increase in the proportion of β-type silicon nitride particles in the fired product (nitrided ingot) and allows the α / (α+β) ratio to be raised to 90% by mass or higher. In the temperature range of a nitriding rate of 50% or higher, adjusting the heating rate to be between 20°C / h and 45°C / h increases the production rate and allows the nitriding time to be reduced to about 15 to 40 hours. Setting the heating rate up to a nitriding rate of 50% or higher to 20°C / h or higher is preferable because it shortens the firing time and does not increase costs. When the nitriding rate is 50% or higher, a heating rate of 45°C / h or less is preferable because the fired product (nitrided ingot) does not become too hard, and the load on the crushing process does not increase.

[0084] It is more preferable to adjust the heating rate up to a nitriding rate of 50% to be between 6°C / h and 9.5°C / h, and to adjust the heating rate at a nitriding rate of 50% or more to be between 25°C / h and 40°C / h.

[0085] (Maximum Temperature) The maximum temperature during high-temperature firing is, for example, between 1485°C and 1565°C. If the maximum temperature is 1485°C or higher, the quality of the fired product (nitrided ingot) will be stable, and in the grinding process after nitriding, there will be no variation in the degree of grinding, and the desired particle size distribution (especially the cumulative 10% diameter D) will be achieved. １０ and cumulative 90% diameter D ９０ This can be achieved. It is preferable that the maximum temperature be 1565°C or lower, as this suppresses the aggregation of the generated particles, prevents the calcined product from becoming hard, and prevents an increase in the load on the grinding process. It is also preferable that the β-type silicon nitride particles grow and the α / (α+β) ratio does not become too low. To obtain crystalline silicon nitride powder of stable quality with controlled particle size distribution, it is more preferable to set the maximum temperature to 1505°C or higher and 1555°C or lower.

[0086] <Grinding> After nitriding is complete, it is preferable to grind the calcined product (nitrided ingot) by methods such as dry grinding or wet grinding to adjust the particle size and obtain silicon nitride powder with an average particle diameter of 1.0 μm or less, more preferably 0.6 to 0.9 μm. The BET specific surface area of ​​the ground silicon nitride powder is, for example, 7 to 18 m². ２ The value is / g. In grinding using a vibratory mill, the grinding balls wear down and are mixed into the raw material, so the material must be selected considering the amount of contamination. In this invention, the powder contact parts such as the mill container are coated with a resin such as polyurethane, and a grinding medium made of a silicon nitride sintered body with a porosity of 2% or less and a Vickers hardness of 14 GPa or more is used, and fine grinding is performed by controlling the amount of metal impurities mixed in by grinding to the minimum value. A bead mill, attritor, etc. can also be used instead of a vibratory ball mill.

[0087] The grinding time may be, for example, 100 minutes or more and 270 minutes or less, but the required grinding time will vary depending on the type of grinding equipment. The grinding conditions need to be changed according to the high-temperature firing conditions, but as an example, when grinding an ingot nitrided under the above high-temperature firing conditions using a dry vibratory mill, it is preferable to adjust the mill amplitude to, for example, 7.0 mm or more and 10 mm or less, and the mill time to, for example, 120 minutes or more and 250 minutes or less. An average particle size of 1.0 μm or less is advantageous in terms of sinterability, such as ensuring a densification rate in the sintering process. The mill amplitude may be 7.3 mm or more and 9.0 mm or less, and the mill time may be 130 minutes or more and 230 minutes or less.

[0088] The oxygen content of the pulverized material is adjusted to, for example, 0.6% by mass or more and 1.3% by mass or less. The oxygen content of the pulverized material may be 0.7% by mass or more and 1.2% by mass or less.

[0089] <Acid treatment and washing> If the oxygen content of the pulverized material is excessively high, hydrofluoric acid (HF), hydrochloric acid (HCl), and sulfuric acid (H) may be used. ２ SO ４ ), nitric acid (HNO ３ The impurity oxygen in the pulverized material is reduced by using inorganic acids such as fluoride in combination. Specifically, acid treatment and washing are performed using a mixed acid of hydrofluoric acid and hydrochloric acid, a mixed acid of hydrofluoric acid and sulfuric acid, a mixed acid of hydrofluoric acid and nitric acid, etc. However, since purification by acid treatment is costly, it is preferable to reduce the oxygen concentration in the mill container to the absolute minimum to prevent oxidation of the material to be pulverized during the pulverization process.

[0090] ≪Direct Nitriding Method Using Self-Combustion Reaction≫ In the production of silicon nitride powder by combustion synthesis using a self-propagating combustion reaction in a nitrogen-containing atmosphere, similar to the above, the amount of metal impurities mixed in during the grinding process can be determined empirically. Therefore, by controlling the concentration of metal impurities contained in the starting material, metallic silicon powder with the desired amount of metal impurities and particle size can be obtained with good reproducibility. Since metallic silicon powder with a particle size of several μm can be used as the raw material, and conditions can be set so that the nitriding reaction is completed in a short time, it is suitable for the production of inexpensive silicon nitride powder.

[0091] <Raw material: Metallic silicon powder, etc.> In the production of silicon nitride powder by combustion synthesis, metallic silicon powder having a 50% diameter (average particle size) and oxygen content similar to that of the direct nitriding method described above can be used. A diluent and, if necessary, a nitriding accelerator and an organic binder for molding are added to the metallic silicon powder to prepare the calcined raw material.

[0092] <Diluent> As a diluent, crystalline silicon nitride powder with an average particle size of approximately 0.7 μm is used. Adding the diluent yields a calcined product (nitrided ingot) that is easy to pulverize. The mixing ratio of metallic silicon powder to diluent (silicon nitride powder) is calculated in terms of silicon nitride, and is usually 95:5 to 75:25 (i.e., the ratio of diluent (silicon nitride powder) is 5 to 25 mass%) as a calculated value after metallic silicon has been converted to silicon nitride). When the mixing ratio is converted back to the mixing ratio of metallic silicon powder to diluent (silicon nitride powder), the mass ratio of diluent (silicon nitride powder) is 8.1 to 35.7 mass%. If the amount of diluent (silicon nitride powder) added is less than 8.1 mass%, not only will the nitriding reaction take a long time, but the nitrided ingot will become extremely hard, increasing the load on the pulverization process, which is undesirable. Even if the amount added exceeds 35.7% by mass, the effect on the high-temperature firing conditions and the properties of the fired product is small, but it is undesirable because it increases costs. The amount of crystalline silicon nitride powder added may be 8.5% by mass or more and 30% by mass or less, and preferably 9% by mass or more and 25% by mass or less.

[0093] <Nitriding Process; Sintering> The metallic silicon powder and the silicon nitride powder used as a diluent are mixed, the resulting mixed powder is packed into a crucible, and the silicon powder is burned by a combustion synthesis method that utilizes the self-heating and propagation phenomena associated with the combustion reaction to produce a solidified mass composed of silicon nitride. The solidified mass is then crushed to produce silicon nitride powder.

[0094] The mixing ratio of the metallic silicon powder to the diluent in the aforementioned mixed powder is 92:8 to 65:35 by mass, and the bulk density of the powder layer formed from the aforementioned mixed powder filled in the firing container is 0.3 to 0.65 g / cm³. ３Preferably 0.34 to 0.55 g / cm³ ３ More preferably 0.36 to 0.48 g / cm³ ３ The process is controlled to achieve the desired result. By controlling the mixing ratio of metallic silicon powder and crystalline silicon nitride powder (which acts as a diluent), and the bulk density of the packed bed made up of these mixtures to predetermined values, high-purity silicon nitride powder with a low content of unreacted free silicon can be produced inexpensively.

[0095] <Method for measuring bulk density> In this invention, bulk density refers to the initial bulk density. The bulk density of a packed bed consisting of a mixture of metallic silicon powder and silicon nitride powder as a diluent was determined by a method in accordance with JIS R 1628:1997 "Method for measuring the bulk density of fine ceramic powders".

[0096] The rate of the combustion synthesis reaction also depends on the thickness of the powder layer, which consists of a mixture of metallic silicon powder and a diluent. For this reason, the mixture of metallic silicon powder and diluent is formed into a powder layer 20 to 70 mm thick, and the combustion synthesis reaction is initiated by igniting a specific part of the powder layer. If the thickness of the powder layer is less than 20 mm, the amount of heat generated by the combustion reaction decreases, and the self-propagation of combustion heat is hindered by heat dissipation to the firing container, etc., which can cause the combustion synthesis reaction to stop midway, leaving a large amount of unreacted silicon behind. If the thickness of the powder layer exceeds 70 mm, the combustion reaction becomes too vigorous due to heat accumulation within the powder layer, causing the silicon powder particles in the raw materials to fuse together, the gaps between the powders to be blocked by the fused silicon, some of the raw materials to remain as unreacted silicon, and the resulting silicon nitride powder to become larger in particle size, making it difficult to grind.

[0097] For the supply gas used to nitride the above-mentioned fired raw material containing metal silicon powder, nitrogen gas or a non-oxidizing gas containing nitrogen having the same purity as the above direct nitriding method is used. The higher the nitrogen gas pressure, the faster the progress rate of the combustion synthesis reaction. However, in the present invention, the nitriding reaction is allowed to proceed under a nitrogen gas pressure of 0.3 to 1.5 MPa. When the nitrogen gas pressure is less than 0.3 MPa, the rate of the nitriding reaction becomes slow, the self-propagation of the combustion heat is hindered, and the combustion synthesis reaction stops halfway. When the nitrogen gas pressure exceeds 1.5 MPa, the combustion reaction becomes too intense, fusion occurs between the silicon powders in the raw material, and the gaps between the powders that serve as introduction holes for nitrogen gas into the raw material are blocked by the fused silicon, and a part of the charged raw material may remain as unreacted silicon.

[0098] <Pulverization> The agglomerates of silicon nitride produced by the combustion synthesis method are roughly pulverized using a roll crusher equipped with silicon nitride rolls, thereby preventing the mixing of metal impurities and obtaining a roughly pulverized product of silicon nitride. After passing this roughly pulverized product through a sieve to remove particularly large particles, it is pulverized using a dry jet mill or a vibration mill. In vibration mill pulverization, the powder contact part such as the mill container is coated with a resin such as polyurethane, and a pulverization medium made of a silicon nitride sintered body having a porosity of 2% or less and a Vickers hardness of 14 GPa or more is used, and the pulverization is controlled so that the mixing of metal impurities due to pulverization becomes the minimum value, and fine pulverization is performed. Instead of a vibration ball mill, a bead mill, an attritor, etc. can also be used.

[0099] The silicon nitride powder obtained by the manufacturing method as described above has a β-phase ratio of 70% or more (α / (α + β) ratio of 30% or less) and a BET specific surface area of 3.0 to 13.0 m ２ / g.

[0100] ≪Method for Manufacturing Silicon Nitride Sintered Bodies for Structural Members≫ A silicon nitride sintered body according to one aspect of the present invention is manufactured by the following method. By mixing the silicon nitride powder of the present invention with a sintering aid, molding the resulting mixed powder (sintering raw material), and then sintering the resulting molded body, a silicon nitride sintered body for high-temperature structural members according to one aspect of the present invention can be manufactured. Alternatively, a silicon nitride sintered body for high-temperature structural members according to one aspect of the present invention can be manufactured by performing molding and sintering simultaneously.

[0101] (Sintering aids) In order to increase the mechanical strength of silicon nitride sintered bodies, it is desirable to make the structure of the silicon nitride sintered body a fine structure with a high aspect ratio of β-type columnar crystals. In this case, magnesium oxide (MgO) and aluminum oxide (Al) are generally used as sintering aids. ２ O ３ ) and yttrium oxide (Y ２ O ３ A combination of these as appropriate is used. The amount of oxide-based sintering aid added to the sintered body manufacturing raw material may be, for example, 5% by mass or more and 12% by mass or less.

[0102] The present invention allows for any method of mixing silicon nitride powder and sintering aid, whether wet or dry, as long as they can be mixed uniformly. Known methods such as rotary mills, barrel mills, and vibratory mills can be used. For example, a method can be employed in which silicon nitride powder, sintering aid, molding binder, and dispersant are ball-milled with water or the like as a dispersion medium, and then spray-dried to obtain a granular mixture.

[0103] (Method for molding mixed powder) Various known methods can be used for molding mixed powder. For example, CIP (cold isohydrostatic pressing) molding can be used, in which the obtained granular mixed powder is filled into a rubber mold and pressure is applied to obtain a molded body. Alternatively, sheet molding methods such as the doctor blade method can also be used.

[0104] (Sintering method of the molded body) As the sintering method of the molded body, any method may be used as long as the obtained sintered body is densified. Preferably, for sintering, nitrogen gas or a nitrogen-containing inert gas is used. In the case of atmospheric pressure sintering, it is carried out at about 1700 to 1800 ° C, and in the case of pressure atmosphere sintering in which the atmospheric gas pressure is increased to about 0.2 to 10 MPa, it is carried out in a temperature range of about 1800 to 2000 ° C. The heating rate from 1400 ° C to the maximum temperature may be, for example, 40 ° C / h or more and 150 ° C / h or less, and the holding time at the maximum temperature may be, for example, 2 hours or more and 20 hours or less.

[0105] <<Manufacturing method of silicon nitride-based sintered body for circuit board>> The silicon nitride-based sintered body for circuit board according to one aspect of the present invention is manufactured by the following method. To the silicon nitride powder according to the present invention, a sintering aid, an organic binder, etc. are added to prepare a raw material mixture (sintering raw material). Next, the obtained raw material mixture is formed into a molded body (green sheet) by a sheet forming method such as the doctor blade method. Then, after removing the organic binder by degreasing treatment, the obtained degreased molded body is sintered in a nitrogen-containing inert atmosphere under the above sintering conditions (heating rate, maximum temperature, and holding time at the maximum temperature) to manufacture a silicon nitride-based sintered body for circuit board according to one aspect of the present invention. When evaluating the thermal conductivity and mechanical properties of the silicon nitride-based sintered body for circuit board, the thermal and mechanical properties of the sintered body obtained by the above CIP (cold isostatic pressing) molding may be measured.

[0106] (Sintering aid) In one aspect of the present invention, sintering aids such as yttrium oxide, lanthanoid-based rare earth oxides, magnesium oxide, magnesium silicon nitride (MgSiN ２ , MgSi ４ N ６ ), rare earth-silicon composite nitrides (Y ２ Si ３ N ６ ) can be used alone or in appropriate combinations. In this case, the addition amount of the sintering aid in the raw material for manufacturing the sintered body may be, for example, 3% by mass or more and 8% by mass or less.

[0107] To increase the thermal conductivity of a silicon nitride sintered body, it is effective to increase the purity of the β-type crystals and increase their size. However, there is often a trade-off between such crystalline morphology (large crystal grain size) and mechanical strength of a silicon nitride sintered body. Therefore, a sintering aid that can form a complex structure of β-type crystals with an appropriate grain size and densify with a minimum amount of grain boundary phase is appropriately selected from the aforementioned sintering aids in an appropriate amount.

[0108] <<Mechanical Properties of High-Strength Silicon Nitride Sintered Bodies for Structural Components>> The high-strength silicon nitride sintered bodies for structural components manufactured in this manner have excellent mechanical properties. For example, the three-point bending strength at room temperature may be 800 MPa or more, or 900 MPa or more. Also, the three-point bending strength at high temperature (1200°C) may be 510 MPa or more, or 540 MPa or more.

[0109] <<Mechanical Properties and Heat Dissipation of High Thermal Conductivity Silicon Nitride Sintered Bodies for Circuit Boards>> Furthermore, high thermal conductivity silicon nitride sintered bodies for circuit boards possess excellent mechanical properties and heat dissipation. For example, the three-point bending strength at room temperature may be 710 MPa or higher, and may be 800 MPa or higher. Also, the thermal conductivity at room temperature may be 100 W / (m·K) or higher, and may be 108 W / (m·K) or higher.

[0110] (Method for measuring toluene content) Nitrogen-containing silane compounds such as silicon diimide were immersed and dispersed in hexane, and toluene from the nitrogen-containing silane compounds was extracted into the hexane. The toluene concentration in the hexane was then quantified by gas chromatography to determine the toluene content of the nitrogen-containing silane compounds.

[0111] (Method for compositional analysis of amorphous Si-N(-H) compounds) The silicon (Si) content of amorphous Si-N(-H) compounds was measured by a total silicon quantification method using dehydrated gravimetric ICP emission spectroscopy in accordance with JIS R 1603:2007 "Chemical analysis method for silicon nitride fine powder for fine ceramics". The nitrogen (N) content was measured by a total nitrogen quantification method using steam distillation separation and neutralization titration in accordance with JIS R 1603:2007. The oxygen (O) content was measured using an oxygen / nitrogen simultaneous analyzer by a quantification method using inert gas fusion-carbon dioxide infrared absorption in accordance with JIS R 1603:2007. In this process, to suppress oxidation of amorphous Si-N(-H) compounds, the samples were handled in a nitrogen-purged glove box. For example, in the case of measuring silicon and nitrogen content by ICP emission spectrometry or steam distillation separation and neutralization titration, the atmosphere during sample storage up to immediately before sample pretreatment for measurement was a nitrogen atmosphere. In the case of measuring oxygen content by infrared absorption spectrometry, the atmosphere during sample storage up to immediately before measurement and during capsule insertion was a nitrogen atmosphere. The hydrogen (H) content of amorphous Si-N(-H) compounds was calculated based on the stoichiometric composition as the residue after subtracting the silicon (Si), nitrogen (N), and oxygen (O) content from the total amount of amorphous Si-N(-H) compounds.

[0112] Based on the above, the ratios of Si, N, and H were determined, and the compositional formula of the amorphous Si-N(-H) compound was determined.

[0113] (Method for measuring oxygen content) For measuring the oxygen content (TO), an oxygen-nitrogen simultaneous analyzer (LECO TCH600 model) was used, and the oxygen content of silicon nitride powder was measured according to the following procedure, in accordance with the method for determining oxygen by inert gas fusion-carbon dioxide infrared absorption method specified in "10 Method for determining oxygen" of JIS R 1603:2007 "Chemical analysis method for silicon nitride fine powder for fine ceramics". Specifically, the silicon nitride powder was weighed and the sample for measurement was set in the oxygen-nitrogen simultaneous analyzer. In a helium gas atmosphere, the temperature was raised from 20°C to 2000°C at a desired heating rate, and the oxygen and nitrogen that desorbed with the temperature increase were detected to obtain analytical values ​​for oxygen (by non-dispersive infrared absorption method) and nitrogen (by thermal conductivity method).

[0114] (Method for measuring carbon content) The carbon content of silicon nitride powder was measured using a carbon analyzer (LECO C844) and the carbon quantification method of combustion-infrared absorption in accordance with JIS R 1603:2007 "Chemical analysis method for silicon nitride fine powder for fine ceramics".

[0115] (Method for measuring metallic silicon content) The metallic silicon content of silicon nitride powder was measured by the hydrogen gas generation-gas volume method in accordance with JIS R 1616:2007, "9. Method for determining free silicon," which applies to free silicon content of 0.01% by mass or more and 1% by mass or less.

[0116] (Method for measuring BET specific surface area) The BET specific surface area of ​​silicon nitride powder and amorphous Si-N(-H) compounds was determined by the BET single-point method using nitrogen gas adsorption with a BET specific surface area analyzer (Macsorb) manufactured by Mountech.

[0117] (Measurement method for α-phase, β-phase, and α / (α+β) ratio) A RIGAK RINT-TTRIII wide-angle X-ray diffractometer was used to measure the X-ray diffraction pattern of silicon nitride powder. Powder X-ray diffraction measurements using CuKα rays were performed, and the crystalline phases (α-phase and β-phase) of the generated silicon nitride powder were identified and the α / (α+β) ratio was calculated using the Gazzara & Messier method described in Non-Patent Literature 1.

[0118] (Method for measuring the mass content of Fe, Ti, Al, Cr, Ni, Na, K, Ca, and Mg, and the mass content of metal impurities other than Fe, Ti, Al, Cr, Ni, Na, K, Ca, and Mg) The mass content of iron (Fe), titanium (Ti), aluminum (Al), chromium (Cr), nickel (Ni), sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) in the silicon nitride powder of the present invention, the silicon powder used as a raw material, and the raw material mixed powder, as well as the mass content of metal impurities other than Fe, Ti, Al, Cr, Ni, Na, K, Ca, and Mg, were measured as follows.

[0119] The sample was weighed into a resin pressurized decomposition vessel, mixed acid (nitric acid and hydrofluoric acid solution) was added, and the sample was microwaved and subjected to pressurized acid decomposition to completely dissolve the impurities. The mass content of iron, chromium, aluminum, and other metal impurities was determined by adjusting the volume of the decomposition solution with ultrapure water to prepare a test solution. Using an ICP-AES (SPS5100) analyzer manufactured by SII Nanotechnology, the mass content of Fe, Ti, Al, Cr, Ni, Na, K, Ca, and Mg in the test solution, as well as the mass content of metal impurities other than Fe, Ti, Al, Cr, Ni, Na, K, Ca, and Mg, was quantified from the detected wavelength and emission intensity, and the mass content of the aforementioned metal impurities in the sample was calculated.

[0120] (Method for measuring the amount of metallic foreign matter larger than 20 μm) A slurry was prepared by adding 250 g of silicon nitride powder and 750 g of distilled water to a 1000 ml beaker. If the sample to be measured was strongly aggregated, dispersion treatment was performed in an ultrasonic bath of about 300 W for about 20 minutes. The obtained dispersion was passed through a stainless steel sieve (mesh size: 20 μm) to separate aggregates larger than 20 μm (including metallic foreign matter particles) on the stainless steel sieve. The aggregates larger than 20 μm (including metallic foreign matter particles) on the stainless steel sieve were removed with distilled water over an empty beaker and dispersed again in water. The obtained dispersion was put into a suction filtration device equipped with a Teflon® filter (mesh size: 1 μm) to recover the aggregates larger than 20 μm (including metallic foreign matter particles) on the Teflon® filter. The Teflon® filter from which the aggregates (including metallic foreign particles) were collected was placed in a resin pressurized container containing a mixture of hydrofluoric acid and nitric acid. After sealing the container, it was heated and dissolved by irradiating it with microwaves, and the resulting decomposition solution was diluted to a fixed volume with ultrapure water to obtain the test solution. Using an ICP-MS analyzer, the mass content of various metallic impurities in the test solution (mass content of Fe, Ti, Al, Cr, Ni, Na, K, Ca, and Mg, as well as metals other than Fe, Ti, Al, Cr, Ni, Na, K, Ca, and Mg) was quantified from the detected wavelength and its emission intensity. The total amount of the analytical values ​​of the various metals detected was converted to a concentration per the initial weight of silicon nitride powder (250 g) to determine the amount (mass content) of metallic foreign matter larger than 20 μm.

[0121] <Evaluation Method for High-Strength Sintered Bodies for Structural Members> The sintered bodies obtained by the above-described method for manufacturing silicon nitride sintered bodies for structural members were cut, machined, and polished to produce 3 mm x 4 mm x 40 mm bending test specimens in accordance with JIS R 1601:2008.

[0122] (Method for measuring the bulk density of sintered bodies) The bulk density of sintered bodies was measured using the Archimedes method in accordance with JIS R 1634:1998. Assuming that all silicon nitride particles are converted to β-type silicon nitride, the relative density (%) was calculated from the calculated density obtained from the raw material composition and the bulk density of the sintered body.

[0123] (Method for measuring Vickers hardness of sintered body) The surface of the obtained sintered body was mirror-polished, and the Vickers hardness was measured with a load of 1 kg using a method in accordance with JIS R 1610:2003 "Hardness test method for fine ceramics".

[0124] (Method for measuring the three-point bending strength of sintered bodies) The three-point bending strength at room temperature and 1200°C was measured using an Instron universal material testing machine in accordance with JIS R 1601:2008 (room temperature bending strength) and JIS R 1604:2008 (high temperature bending strength). The crosshead speed was set to 0.5 mm / min. The bending strength at room temperature is the average value of 40 specimens. For the high-temperature bending test, the specimens were held at 1200°C in an air atmosphere for 10 minutes, and then the strength was measured for 8 or more specimens, and the average value was calculated. In addition, 3 mm × 4 mm × 40 mm specimens were heat-treated in air at 1250°C for 100 hours, and the three-point bending strength at room temperature after oxidation treatment was measured for 10 specimens of each type, and the average value was calculated.

[0125] (Analysis method for the Weibull coefficient of the three-point bending strength of sintered bodies) Based on the above-mentioned measurement data of the three-point bending strength at room temperature, Weibull statistical analysis was performed in accordance with JIS R 1625:2010 (Weibull statistical analysis method for strength data of fine ceramics). Forty strength data σi (i = 1 to 40) were sorted in ascending order of strength, and the cumulative fracture probability F was calculated for each rank of data using the median rank method. ｉ The following was calculated. The intensity data σ was plotted on a graph with ln[ln{1 / (1-F(σ))}] on the vertical axis and lnσ on the horizontal axis. By drawing a regression line of the Weibull plot using the most likely method, the estimated value m of the shape parameter and the estimated value β of the scale parameter were obtained. The estimated value m of the shape parameter is the Weibull coefficient.

[0126] (Solution Corrosion Test) A 3 mm x 4 mm x 40 mm test specimen prepared for the bending test was polished to a surface roughness of 0.02 μm Ra or less across the entire surface, as specified in JIS B 0601:2013. This test specimen was subjected to a corrosion test in accordance with JIS R 1614:2002 (Test Methods for Acid and Alkali Corrosion of Fine Ceramics). The test solution was a 3 mol / L (6N) sulfuric acid solution. 0.5 L of the test solution was heated to a gentle boil, and the test specimen was gently immersed in it for a continuous boiling test for 24 hours. After the corrosion test, the test specimen was removed from the test container, thoroughly washed, and dried at 105-120°C. After cooling to room temperature, the mass of each specimen was measured, and the mass loss was calculated. Ten test specimens were used, and the average value was calculated.

[0127] <Evaluation Method for High Thermal Conductivity Sintered Bodies for Circuit Boards> The sintered body obtained by the above-described method for manufacturing silicon nitride sintered bodies for circuit boards was cut, machined, and polished to produce a 3 mm × 4 mm × 40 mm bending test specimen in accordance with JIS R 1601:2008. In addition, a disc-shaped test specimen with a diameter of 10 mmφ and a thickness of 1 mmt for measuring thermal conductivity was produced in accordance with JIS R 1611:2010. The bulk density (relative density (%)) and three-point bending strength at room temperature of the sintered body were measured in the same manner as the evaluation method for high-strength sintered bodies for structural members described above. Furthermore, the thermal conductivity was measured at room temperature using the flash method in accordance with JIS R 1611:2010. The thermal conductivity is the average value of three disc-shaped test specimens.

[0128] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to these examples. (Metallic Silicon Powder) Prior to the production of silicon nitride powder, metallic silicon powder to be used as a raw material was prepared and ground using a silicon nitride grinding medium until the desired average particle size was achieved. Note that silicon powder B is silicon powder C with a trace amount of chromium oxide (Cr ２ O ３ Silicon powder G is prepared by adding and mixing ), calcium oxide (CaO) and magnesium oxide (MgO). Silicon powder G is silicon powder F with a trace amount of titanium oxide (TiO). ２), aluminum oxide (Al ２ O ３ ), chromium oxide (Cr ２ O ３ Silicon powder I is prepared by adding and mixing silicon powder H with a small amount of aluminum oxide (Al ２ O ３ ), chromium oxide (Cr ２ O ３ It is prepared by adding and mixing ), nickel oxide (NiO), calcium oxide (CaO), and magnesium oxide (MgO). Silicon powder J is silicon powder H with a trace amount of aluminum oxide (Al ２ O ３ ), chromium oxide (Cr ２ O ３ Silicon powder M is prepared by adding and mixing silica glass containing nickel oxide (NiO) and alkali metals (Li, Na, and K) to silicon powder L. Silicon powder R is prepared by adding and mixing silicon powder Q with trace amounts of silica glass containing alkali metals (Li, Na, and K), calcium oxide (CaO), and magnesium oxide (MgO). Silicon powder R is prepared by adding and mixing silicon powder Q with trace amounts of titanium oxide (TiO) ２ ), chromium oxide (Cr ２ O ３ It was prepared by adding and mixing ) and nickel oxide (NiO). The average particle size and mass content of metal impurities after grinding treatment of the 20 types of metallic silicon powders prepared are shown in [Table 1]. The average particle size of the metallic silicon powder was 0.7 to 4.6 μm, the mass content of iron (Fe) was 70 to 550 ppm, the mass content of group IVA metals of the periodic table (Ti, Zr, Hf, etc.) was 13 to 975 ppm, the mass content of titanium (Ti) was 8 to 850 ppm, the mass content of aluminum (Al) was 12 to 500 ppm, the mass content of chromium (Cr) was 9 to 295 ppm, and the mass content of nickel (Ni) was 5 to 85 ppm. The average particle size refers to the particle size at 50% of the integrated particle size distribution measured by laser diffraction and scattering.

[0129] (Example 1) Silicon nitride powder was produced by the following manufacturing method (imide thermal decomposition method). The manufacturing conditions for silicon nitride powder by imide thermal decomposition are shown in Table 2 below. Furthermore, the powder properties of the obtained crystalline silicon nitride powder are shown in Tables 2 and 3 below.

[0130] [Method for producing silicon nitride powder by imide pyrolysis] After replacing the air in a vertical pressure-resistant reaction vessel with a diameter of 40 cm and a height of 60 cm, cooled to 0°C, with nitrogen gas, 40 liters of liquid ammonia and 5 liters of toluene were charged into the reaction vessel. In the reaction vessel, the liquid ammonia and toluene were slowly stirred, separating the liquid ammonia to the upper layer and the toluene to the lower layer. A pre-prepared solution (reaction solution) consisting of 2 liters of silicon tetrachloride and 6 liters of toluene was supplied through a conduit to the lower layer in the slowly stirred reaction vessel. As the solution was supplied, a white reaction product precipitated near the interface between the upper and lower layers. In the initial stages of the reaction, there was a large excess of liquid ammonia, but as the reaction progressed, the ammonia was consumed, so ammonia was continuously supplied to the reaction vessel. In a steady state, the volume ratio of silicon tetrachloride supplied to the reaction vessel to the liquid ammonia in the reaction vessel was 4 / 100. After the reaction is complete, the reaction products and residual liquid in the reaction vessel are transferred to a filtration tank. The reaction products are then washed in batches five times with approximately 22 liters of liquid ammonia (totaling 110 liters), filtered, and dried to obtain a BET specific surface area of ​​780 m². ２ Approximately 1 kg of purified silicon diimide with a toluene content of 0.30% by mass was obtained.

[0131] As shown in [Table 2], using a rotary kiln furnace, the obtained silicon diimide was thermally decomposed at 700°C while circulating nitrogen gas containing 85 ppm (V) of oxygen, resulting in a composition formula Si ６ N ９．８７ H ５．６１ It is represented as, that is, Si ６ N ２ｘ (NH) １２－３ｘ An amorphous Si-N(-H) compound was obtained in which x in the formula was 2.13. The BET specific surface area of ​​the obtained amorphous Si-N(-H) compound was 435 m². ２The oxygen content was 0.84% ​​by mass per gram.

[0132] Next, the obtained amorphous Si-N(-H) compound was ground using a vibratory mill, and then molded into an almond shape with a thickness of 6 mm, a short axis diameter of 8 mm, and a long axis diameter of 12 mm using a briquette machine. The almond-shaped molded product, which contained some burr-like fragments, was filled into a carbon container coated with silicon carbide (SiC) on its surface, supplied to a pusher furnace, and fired at high temperature under the conditions described in [Table 2] in a nitrogen gas flow atmosphere to produce grayish-white silicon nitride powder. Specifically, heating and firing were performed at a heating rate of 35°C / hr and a maximum temperature of 1520°C, with a holding time at the maximum temperature of 1.5 hours. This crystalline silicon nitride powder was put into a vibratory mill and post-milled for 30 minutes at an amplitude of 7.5 mm in an air atmosphere with a moisture concentration of 100 ppm (V). The production conditions for silicon nitride powder by imide pyrolysis are shown in [Table 2].

[0133] Table 2 shows the production conditions for silicon nitride powder by imide pyrolysis, as well as the BET specific surface area, oxygen content, the ratio of oxygen content to BET specific surface area, and the mass ratio of the α phase (α / (α+β) ratio) of the obtained crystalline silicon nitride powder. Table 3 shows the mass content of various metal impurities contained in the obtained crystalline silicon nitride powder and the amount (mass content) of metal foreign matter larger than 20 μm.

[0134] (Examples 2-6 and Comparative Example 1) The purified silicon diimide obtained in Example 1 was decomposed by heating at 700°C under a flow of nitrogen gas at the oxygen concentration shown in [Table 2] to obtain a silicon diimide with the composition formula Si ６ N ２ｘ (NH) １２－３ｘAn amorphous Si-N(-H) compound represented by the formula was obtained. The values ​​of x in the formula were all close to those of Example 1. A predetermined amount of metallic silicon powder A, B, C, D, or N (as listed in Table 2) was added to the obtained amorphous Si-N(-H) compound, and the mixture was mixed and ground in a vibratory mill. Then, using a briquette machine, it was molded into an almond shape with a thickness of 6 mm, a short axis diameter of 8 mm, and a long axis diameter of 12 mm. The almond-shaped molded product, which contained some burr-like fragments, was heated and fired in a pusher furnace in the same manner as in Example 1, except for the high-temperature firing conditions listed in Table 2, to produce grayish-white silicon nitride powder. This crystalline silicon nitride powder was put into a vibratory mill and crushed with the same amplitude and mill time as in Example 1 and as listed in Table 2.

[0135] Table 2 shows the production conditions for silicon nitride powder by imide pyrolysis, along with the BET specific surface area, oxygen content, the ratio of oxygen content to BET specific surface area, and the mass ratio of the α phase (α / (α+β) ratio) of the obtained crystalline silicon nitride powder. Table 3 shows the mass content of various metal impurities contained in the obtained crystalline silicon nitride powder and the amount (mass content) of metal foreign matter larger than 20 μm.

[0136] Example 1 has a BET specific surface area (SA) of 7.5 m². ２ The oxygen content (TO) is 0.8% by mass, and the BET specific surface area (SA) of Examples 2 to 6 is 9.4 to 11.3 m². ２ The oxygen content (TO) was 0.9 to 1.1% by mass per gram. The TO / SA ratio for Examples 1 to 5 was 0.92 to 1.09 mg / m³. ２ The mass ratio of the α phase (α / (α+β)) was 93-98% by mass. The BET specific surface area (SA) of Comparative Example 1 was 12.0 m². ２ The oxygen content (TO) was 1.1% by mass, and the mass ratio of the α phase (α / (α+β)) was 90% by mass.

[0137] In Examples 1 to 6, the mass content of Fe was 6 to 11 ppm, and the amount of metallic foreign matter (mass content) larger than 20 μm was 0.006 to 0.018 ppm. In Examples 2 to 6, the mass content of Ti was 5 to 40 ppm, the mass content of Al was 4 to 36 ppm, the mass content of Cr was 2 to 18 ppm, the mass content of Ni was 1.5 to 7 ppm, and the total mass content of Na and K was 3 to 18 ppm. The mass content of Ca and Mg was both 2 to 5 ppm. In Comparative Example 1, the mass content of the Group IVA metals (Ti, Zr, Hf, etc.) was 69 ppm, the mass content of Ti was 60 ppm, the mass content of Cr was 20 ppm, and the mass content of Ni was 8 ppm.

[0138] The carbon content of Examples 1 to 6 and Comparative Example 1 was all between 0.01 and 0.10% by mass.

[0139] In Examples 1 to 6 and Comparative Example 1, no metallic silicon was detected in the obtained silicon nitride powder. That is, the metallic silicon content of the obtained silicon nitride powder was less than 0.01% by mass.

[0140]

[0141]

[0142]

[0143] (Example 7) Silicon nitride powder was produced by the following manufacturing method (direct nitriding method). The manufacturing conditions for silicon nitride powder by direct nitriding are shown in Table 4 below. Furthermore, the powder properties of the obtained crystalline silicon nitride powder are shown in Tables 4 and 5 below.

[0144] [Method for producing silicon nitride powder by direct nitriding] Metallic silicon powder E (average particle size D) shown in Table 1 ５０ The particles are 2.9 μm in size and have an oxygen content of 0.51% by mass. The mixture contains crystalline silicon nitride powder (average particle size D ５０A mixture of 5.6% by mass of silicon dioxide (0.7 μm, oxygen content 0.9% by mass, α / (α+β) = 94.0% by mass) and 0.02% by mass of calcium fluoride was prepared (i.e., metallic silicon powder E was 94.38% by mass). Furthermore, an organic binder (polyvinyl alcohol) was added to the mixture in a slurry state at a ratio of 1.5 parts by mass per 100 parts by mass of the mixture, and then dried to prepare the raw material powder. Using this raw material powder, almond-shaped molded products with a thickness of 4 mm, a short axis diameter of 5 mm, and a long axis diameter of 8 mm were produced using a briquette machine and filled into a silicon nitride firing container. The packing density was 1.0 g / cm³. ３ That was the case.

[0145] This almond-shaped molded material was heated to 1545°C in an electric furnace and fired to produce a silicon nitride ingot. The heating program was set so that the heating rate from 1100°C to the temperature at which the nitriding rate reached 50% was 8.0°C / h as shown in [Table 4], and the heating rate from the temperature at which the nitriding rate reached 50% to 1545°C was 42°C / h. After holding at the maximum temperature (1545°C) for 1 hour, the temperature was lowered.

[0146] The atmosphere during firing is a mixed atmosphere of nitrogen and ammonia (N ２ : NH ３ The ratio was set to 97.0:3.0 (by volume). The water content of the supplied gas was 80 ppm (V), and the oxygen content was 16 ppm (V).

[0147] After nitriding was complete, the ingot was cooled and removed. It was then coarsely and mediumly ground using a jaw crusher and a roll crusher equipped with rollers made of silicon nitride sintered body. Furthermore, the material to be ground was placed in a resin pot in which the powder contact parts of the mill container, etc., were coated with a resin such as polyurethane. The aforementioned silicon nitride balls for grinding (sintered silicon nitride with a porosity of 2% or less and a Vickers hardness of 14 GPa or higher) were loaded, a grinding aid (methyl ethyl ketone) was added, and dry grinding was performed using a vibrating mill to produce silicon nitride powder. As shown in Table 4, the mill amplitude was set to 7.3 mm and the milling time to 130 minutes. In this way, the crystalline silicon nitride powder of Example 7 was obtained.

[0148] (Examples 8-13) Using the metallic silicon powders F-K shown in Table 1 as raw materials, silicon nitride ingots were produced by direct nitriding in the same manner as in Example 7, except for the firing conditions shown in Table 4 (heating rate A from 1100°C to a temperature at which the nitriding rate reaches 50% and heating rate B at a nitriding rate of 50% or more). The obtained silicon nitride ingots were subjected to dry grinding in the same manner as in Example 7, except for the grinding conditions (mill amplitude and mill time) shown in Table 4, to produce silicon nitride powder.

[0149] The production conditions for silicon nitride powder by direct nitriding are shown in [Table 4]. Furthermore, the BET specific surface area, oxygen content, the ratio of oxygen content to BET specific surface area, and the mass ratio of the α phase (α / (α+β)) of the obtained crystalline silicon nitride powder are shown in [Table 4]. In addition, the mass content of various metal impurities contained in the obtained crystalline silicon nitride powder and the amount (mass content) of metal foreign matter larger than 20 μm are shown in [Table 5].

[0150] Examples 7-13 have a BET specific surface area (SA) of 7.8-13.0 m². ２ The oxygen content (TO) is 0.8–1.2% by mass, and the TO / SA ratio is 0.92–1.08 mg / m³. ２ The mass ratio of the α-phase in Examples 7 to 10 (α / (α+β)) was 90 to 93% by mass, while the mass ratio of the α-phase in Examples 11 to 13 and Comparative Examples 2 to 7 (α / (α+β)) was 80 to 89% by mass.

[0151] Comparative Examples 3 to 6 have a BET specific surface area (SA) of 8.5 to 12.0 m². ２ The oxygen content (TO) is 0.9–1.1% by mass, and the TO / SA ratio is 0.94–1.06 mg / m³. ２ Comparative Examples 2 and 7 had a BET specific surface area (SA) of 6.8 or 16.0 m². ２ The concentration is per g, the oxygen content (TO) is 0.9 or 1.4% by mass, and the TO / SA ratio is 1.25 or 0.88 mg / m³. ２ That was the case.

[0152] In Examples 7-13, the Fe mass content was 85 ppm, the Ti mass content was 5-40 ppm, and the amount of metallic foreign matter (mass content) larger than 20 μm was 0.12-0.17 ppm. In Examples 7-11, the Al mass content was 15-90 ppm, the Cr mass content was 12-25 ppm, the Ni mass content was 4-14 ppm, and the total mass content of Na and K was 9-28 ppm. In Examples 7-10, 12, and 13, the Ca mass content was 50-90 ppm, and the Mg mass content was 12-34 ppm. In Example 11, the Ca mass content was 110 ppm and the Mg mass content was 39 ppm, indicating high mass content of both Ca and Mg. In Example 12, the mass content of Al was 88 ppm, the mass content of Cr was 25 ppm, and the mass content of Ni was 13 ppm. The total mass content of Na and K was 77 ppm, indicating a high total mass content of Na and K. In Example 13, the mass content of Al was 200 ppm, the mass content of Cr was 50 ppm, the mass content of Ni was 30 ppm, and the total mass content of Na and K was 34 ppm, indicating high mass content of Al, Cr, and Ni.

[0153] In Comparative Example 2, the mass content of Fe was 45 ppm, the mass content of Ti was 60 ppm, the mass content of Al was 50 ppm, the mass content of Cr was 18 ppm, the mass content of Ni was 10 ppm, the total mass content of Na and K was 28 ppm, the mass content of Ca was 25 ppm, and the mass content of Mg was 20 ppm, indicating a high mass content of Ti. In addition, the amount (mass content) of metallic foreign matter larger than 20 μm in Comparative Example 2 was 0.18 ppm. In Comparative Examples 3 and 4, the mass content of Fe was 45 ppm, the mass content of Ti was 245 or 355 ppm, the mass content of Al was 240 or 115 ppm, the mass content of Cr was 120 or 55 ppm, the mass content of Ni was 40 or 26 ppm, the total mass content of Na and K was 107 or 51 ppm, the mass content of Ca was 31 or 40 ppm, and the mass content of Mg was 28 or 36 ppm. The mass content of Ti, Al, Cr, and Ni was high. In Comparative Example 3, the total mass content of Na and K was 107 ppm, which was high. In addition, the amount (mass content) of metallic foreign matter larger than 20 μm in size in Comparative Examples 3 and 4 was 0.21 to 0.26 ppm. In Comparative Example 7, the mass content of Fe was 340 ppm, the mass content of Ti was 530 ppm, the mass content of Al was 310 ppm, the mass content of Cr was 180 ppm, the mass content of Ni was 55 ppm, the total mass content of Na and K was 160 ppm, the mass content of Ca was 220 ppm, and the mass content of Mg was 70 ppm, indicating that the mass content of all metal impurities was high. In addition, the amount (mass content) of metal foreign matter larger than 20 μm was 0.42 ppm. In Comparative Examples 5 and 6, the mass content of Fe was 90 ppm, the mass content of Ti was 55 ppm, the mass content of Al was 200 ppm, the mass content of Cr was 60 ppm, and the mass content of Ni was 30 ppm, indicating that the mass content of Ti, Al, Cr, and Ni was high. Furthermore, Comparative Example 6 also had high total mass content of Na and K (81 ppm), mass content of Ca (200 ppm), and mass content of Mg (69 ppm). In addition, the amount (mass content) of metallic foreign matter larger than 20 μm in Comparative Examples 5 and 6 was 0.24 to 0.34 ppm.

[0154] The carbon content of Examples 7-13 and Comparative Examples 2-7 was all between 0.01 and 0.10% by mass.

[0155] In Examples 7 to 13 and Comparative Examples 2 to 7, the metallic silicon content of the obtained silicon nitride powder was less than 0.05% by mass.

[0156]

[0157]

[0158] (Example 14) Silicon nitride powder was produced by the following manufacturing method (direct nitriding method using autocombustion reaction). The powder properties of the obtained crystalline silicon nitride powder are shown in Tables 6 and 7 below.

[0159] [Method for producing silicon nitride powder by direct nitriding using autocombustion reaction] Metallic silicon powder O (average particle size D) shown in Table 1 ５０ The particles are 4.6 μm in size and have an oxygen content of 0.37% by mass. As a diluent, crystalline silicon nitride powder (average particle size D ５０ The synthesis raw materials were prepared by blending silicon with a particle size of 0.7 μm, an oxygen content of 0.9 mass%, and an α / (α+β) ratio of 94.0 (mass%), so that the mixing ratio of metallic silicon to diluent (silicon nitride) was 8.0:2.0 when converted to silicon nitride (i.e., the proportion of diluent (silicon nitride) after the metallic silicon has been converted to silicon nitride is 20 mass%). Note that silicon nitride is Si ３ N ４ As can be seen from the chemical reaction equation (2) below, 3 moles of silicon produce 1 mole of silicon nitride. Therefore, 3 moles of silicon (mass: 28.086 × 3 = 84.26 g) are considered to be equivalent to 1 mole of silicon nitride (mass: 140.28 g) after conversion to silicon nitride, so 140.28 g is adopted as the mass of silicon nitride converted from silicon (84.26 g). In other words, the value of silicon converted to silicon nitride means, for example, that when there are 3 moles of silicon and 1 mole of silicon nitride, the weight ratio is 1:1. 3Si + 2N ２ → Si ３ N ４ ... (2)

[0160] Next, using a combustion synthesis apparatus equipped with a pressure-resistant container, a mass of silicon nitride powder was synthesized from the raw material by a self-combustion reaction according to the following procedure.

[0161] The above-mentioned raw materials (total weight 4.0 kg) were filled into a graphite crucible with a base of 770 mm x 320 mm. The thickness of the powder layer was 40 mm, and the bulk density was 0.59 g / cm³. ３ That was the case.

[0162] A small amount of aluminum molded material was placed as an ignition agent at a designated location on the upper edge of the filled powder layer. This was then placed inside a pressure-resistant container, and under a nitrogen atmosphere, the necessary voltage-current was applied via a carbon heater for 10 seconds to induce combustion. The heat generated by the combustion of the aluminum was used to induce the self-combustion reaction of the silicon powder. The mixed powder of silicon and diluent (silicon nitride), which was the raw material, burned stably. The nitrogen gas pressure inside the pressure-resistant container was 0.9 MPa, and the reaction time was approximately 25 minutes. After cooling, the resulting mass of silicon nitride powder was removed from the pressure-resistant container. Note that the area around the location where the ignition agent (small amount of aluminum molded material) was placed was 10 cm. ３ The igniter was removed from the product to a certain extent. No diffusion of the igniter to other parts was detected.

[0163] After crushing a lump of silicon nitride powder with a plastic hammer, the material was passed through a roll crusher equipped with a silicon nitride sintered roll for coarse grinding. The material was then sieved using an 80 μm mesh sieve to obtain coarsely ground silicon nitride. The BET specific surface area of ​​the coarsely ground material was 0.5 m². ２ It was / g.

[0164] Furthermore, silicon nitride powder was produced by placing coarsely ground material into a resin pot in which the powder contact parts of the mill container, etc., were coated with a resin such as polyurethane, loading silicon nitride balls for grinding, adding a grinding aid (methyl ethyl ketone), and performing dry grinding in a vibrating mill. As shown in Table 6, the mill amplitude was set to 7.3 mm and the milling time to 130 minutes. In this way, crystalline silicon nitride powder of Example 14 was obtained.

[0165] (Examples 15-19) Using the metallic silicon powders P to T shown in Table 1 as raw materials, silicon nitride powder lumps were produced by direct nitriding using a self-combustion reaction, in the same manner as in Example 14, except for the firing conditions (thickness and bulk density of the powder layer) shown in Table 6. The obtained silicon nitride powder lumps were subjected to dry grinding in the same manner as in Example 14, except for the grinding conditions (mill amplitude and mill time) shown in Table 6, to produce silicon nitride powder.

[0166] The production conditions for silicon nitride powder by direct nitridation using a self-combustion reaction are shown in [Table 6]. Furthermore, the BET specific surface area, oxygen content, the ratio of oxygen content to BET specific surface area, and the mass ratio of the α phase (α / (α+β)) of the obtained crystalline silicon nitride powder are shown in [Table 6]. In addition, the mass content of various metal impurities contained in the obtained crystalline silicon nitride powder and the amount of metal foreign matter larger than 20 μm (mass content) are shown in [Table 7].

[0167] Examples 14-19 have a BET specific surface area (SA) of 7.9-10.2 m². ２ The oxygen content (TO) is 0.8–1.0% by mass, and the TO / SA ratio is 0.96–1.07 mg / m³. ２ The mass ratio (α / (α+β)) of the α phase in Examples 14-19 was 0-5% by mass.

[0168] Comparative Example 8 has a BET specific surface area (SA) of 10.0 m². ２ The oxygen content (TO) is 1.0% by mass, and the TO / SA ratio is 1.00 mg / m³. ２ That was the case.

[0169] The Fe mass content in Examples 14-18 was 45 ppm, and the Fe mass content in Example 19 was 85 ppm. The Ti mass content in Examples 14-19 was 2-40 ppm, the Al mass content was 9-95 ppm, the Cr mass content was 6-28 ppm, the Ni mass content was 3-14 ppm, the combined Na and K mass content was 3-27 ppm, the Ca mass content was 5-55 ppm, and the Mg mass content was 3-32 ppm. In addition, the amount (mass content) of metallic foreign matter larger than 20 μm in Examples 14-19 was 0.09-0.16 ppm.

[0170] In Comparative Example 8, the mass content of Fe was 94 ppm, Ti was 56 ppm, Al was 230 ppm, Cr was 64 ppm, Ni was 32 ppm, the combined mass content of Na and K was 77 ppm, Ca was 185 ppm, and Mg was 65 ppm. All metal impurities had high mass content. In addition, the amount (mass content) of metal foreign matter larger than 20 μm was 0.36 ppm.

[0171] The carbon content of Examples 14-19 and Comparative Example 8 was all between 0.01 and 0.10% by mass.

[0172] In Examples 14-19 and Comparative Example 8, the metallic silicon content of the obtained silicon nitride powder was less than 0.05% by mass.

[0173]

[0174]

[0175] <Example of Use Test> (Method for Manufacturing and Evaluating High-Strength Sintered Bodies for Structural Components) 92 parts by mass of silicon nitride powder, with yttrium oxide (specific surface area 3 m²) as a sintering aid. ２ (Shin-Etsu Chemical Co., Ltd.) 5 parts by mass and aluminum oxide (specific surface area 7.4 m²) ２ A compound powder containing 3 parts by mass of (sodium ethanol, manufactured by Sumitomo Chemical Co., Ltd.) was wet-mixed in a ball mill for 36 hours using ethanol as a medium, and then dried under reduced pressure. The resulting mixture was molded into a 6 × 45 × 75 mm shape at a molding pressure of 50 MPa, and then CIP molded at a molding pressure of 150 MPa. The resulting molded body was placed in a silicon nitride crucible and sintered at 1780°C for 2 hours under a nitrogen gas atmosphere to produce a silicon nitride sintered body for structural members. The strength properties of the obtained silicon nitride sintered body were evaluated according to the method described in (Evaluation method for high-strength sintered body for structural members) above.

[0176] (Method for fabricating and evaluating high thermal conductivity sintered bodies for circuit boards) 94.5 parts by mass of silicon nitride powder, with yttrium oxide (specific surface area 3 m²) as a sintering aid. ２ / g, manufactured by Shin-Etsu Chemical Co., Ltd.) 3.5 parts by mass and magnesium oxide (specific surface area 3 m²) ２A compound powder containing 2 parts by mass of (manufactured by Kojun Chemical Laboratory) was wet-mixed in a ball mill for 24 hours using ethanol as a medium, and then dried under reduced pressure. The resulting mixture was molded into 6 × 45 × 75 mm and 12.3 mmφ × 1.6 mmt shapes at a molding pressure of 50 MPa, and then CIP molded at a molding pressure of 150 MPa. The resulting molded bodies were placed in a boron nitride crucible and sintered at 1900°C for 10 hours under a pressurized atmosphere of 0.8 MPa using nitrogen gas to produce silicon nitride sintered bodies for circuit boards. Silicon nitride sintered bodies for circuit boards were produced according to the method described in (Method for producing and evaluating high thermal conductivity sintered bodies for circuit boards) above. The strength characteristics and thermal conductivity of the obtained silicon nitride sintered bodies were evaluated according to the method described in (Method for evaluating high thermal conductivity sintered bodies for circuit boards) above.

[0177] [Sintering Test of Silicon Nitride Powder Produced by Imide Pyrolysis Method] Using the silicon nitride powders obtained in Examples 1 to 6 and Comparative Example 1 by imide pyrolysis method as raw materials, high-strength sintered bodies for structural members and high-thermal-conductivity sintered bodies for circuit boards were fabricated and evaluated. The measurement results of the ultimate density (relative density), Vickers hardness, flexural strength (room temperature strength and its Weibull coefficient, high-temperature strength, and strength after oxidation treatment), and mass loss due to solution corrosion of the obtained silicon nitride sintered bodies for structural members are shown in Table 8 below. Similarly, the measurement results of the ultimate density (relative density), flexural strength (room temperature), and thermal conductivity (room temperature) of the obtained silicon nitride sintered bodies for circuit boards are also shown in Table 8 below.

[0178] Since the mass content of the group IVA metals in the silicon nitride powders of Examples 2 to 6 is 7 to 43 ppm (in particular, the mass content of Ti is 5 to 40 ppm), Y ２ O ３ - Al ２ O ３ The Vickers hardness (15.3–17.0 GPa) of the sintered body increased with increasing Ti mass content, and the three-point bending strength (1195–1230 MPa) was also high. Furthermore, the Weibull coefficient (18–20) was also high.

[0179] The Al mass content of the silicon nitride powders in Examples 2 to 6 is 4 to 36 ppm, and Y ２ O３ - The MgO-based sintered body exhibited high three-point bending strength (975-1005 MPa) and high thermal conductivity (108-118 W / (m·K)). The thermal conductivity tended to decrease as the mass content of Al increased. The Cr mass content of the silicon nitride powder in Examples 2-6 was 2-18 ppm, and Y ２ O ３ - Al ２ O ３ The oxidation resistance of the sintered body was improved, resulting in higher three-point bending strength at high temperatures (1200°C) (780-915 MPa) and room temperature three-point bending strength after strength oxidation treatment (835-865 MPa). The Weibull coefficient (18-20) was also high. In Examples 2-6, the mass content of silicon nitride powder in Ni was 1.5-7 ppm, and the mass content of Ca and Mg was 2-5 ppm each. ２ O ３ - Al ２ O ３ The sintered body has a high attainable density (relative density 98.8-99.5%), Y ２ O ３ - The attainable density (relative density 99.0-99.6%) of the MgO-based sintered body was also high. ２ O ３ - Al ２ O ３ Sintered body (1195-1230 MPa at room temperature, 780-915 MPa at 1200°C) and Y ２ O ３ - The MgO-based sintered bodies (975-1005 MPa) both showed high pressure.

[0180] The total mass content of Na and K in the silicon nitride powders of Examples 2 to 6 was 3 to 18 ppm, and the lower the mass content of (Na + K), the lower the Y content. ２ O ３ - Al ２ O ３ The corrosion resistance of the sintered body is improved, and the mass loss due to corrosion in an aqueous sulfuric acid solution is reduced (3.6-5.9 g / m²). ２ ) was small.

[0181] Since the mass content of the IVA group metals in the silicon nitride powder of Comparative Example 1 is 69 ppm (in particular, the mass content of Ti is 60 ppm), Y ２ O３ - Al ２ O ３ The Vickers hardness of the sintered body decreased to 15.0 GPa, and the three-point bending strength decreased to 940 MPa. Furthermore, the oxidation resistance gradually deteriorated with increasing Ti mass content, and the three-point bending strength at high temperature (1200°C) decreased to 560 MPa, and the three-point bending strength at room temperature after oxidation treatment decreased to 615 MPa. The Al mass content of the silicon nitride powder in Comparative Example 1 was 40 ppm, which is a higher concentration than in Examples 2 to 6, and therefore Y ２ O ３ - The three-point bending strength of the MgO-based sintered body decreased to 890 MPa, and the thermal conductivity decreased to 98 W / (m·K). The mass content of Cr in the silicon nitride powder of Comparative Example 1 was 20 ppm, the mass content of Ni was 8 ppm, and the mass contents of Ca and Mg were 25 ppm and 10 ppm, respectively. Since these concentrations are higher than those of Examples 2 to 6, Y ２ O ３ - Al ２ O ３ The room-temperature three-point bending strength of the sintered body decreased to 940 MPa, and the Weibull coefficient also decreased to 14. The three-point bending strength after oxidation treatment also decreased to 615 MPa, and the strength retention rate (ratio of room-temperature strength after oxidation treatment to room-temperature strength before oxidation treatment) also decreased to 0.65. ２ O ３ - The room-temperature three-point bending strength of the MgO-based sintered body also decreased to 890 MPa.

[0182] The total mass content of Na and K in the silicon nitride powder of Comparative Example 1 is 26 ppm, which is a higher concentration than in Examples 2 to 6, therefore Y ２ O ３ - Al ２ O ３ The corrosion resistance of the sintered body deteriorated, and the mass decreased due to corrosion in an aqueous sulfuric acid solution (7.3 g / m²). ２ The mass content of Ti had a significant effect on the strength characteristics, but the effects of the mass content of Cr, Ni, Ca, Mg, etc. were also observed.

[0183] Furthermore, the metal impurity content of the high-strength sintered bodies for structural members obtained in Examples 1 to 6 and Comparative Example 1 was in the range of 0.92 to 1.05 times the mass content of metal impurities in the silicon nitride powder raw material used in the sintering test, excluding Al. In addition, the metal impurity content of the high thermal conductivity sintered bodies for circuit boards obtained in Examples 1 to 6 and Comparative Example 1 was in the range of 0.94 to 1.05 times the mass content of metal impurities in the silicon nitride powder raw material used in the sintering test, excluding Mg.

[0184]

[0185] [Sintering Test of Silicon Nitride Powder Produced by Direct Nitriding] Using the silicon nitride powders obtained in Examples 7 to 13 and Comparative Examples 2 to 7 by direct nitriding as raw materials, silicon nitride sintered bodies for structural members were prepared according to the method described in (Method for Produce and Evaluate High-Strength Sintered Bodies for Structural Members) above, and their strength characteristics were evaluated. The measurement results of the attainable density (relative density), Vickers hardness, and flexural strength (room temperature strength and its Weibull coefficient, high-temperature strength, and strength after oxidation treatment) of the sintered bodies are shown in Table 9 below.

[0186] Similarly, silicon nitride sintered bodies for circuit boards were prepared using the silicon nitride powders obtained in Examples 7 to 13 and Comparative Examples 2 to 7 as raw materials, according to the method described in (Method for Manufacturing and Evaluating High Thermal Conductivity Sintered Bodies for Circuit Boards) above, and their strength characteristics and thermal conductivity were evaluated. The measurement results for the attainable density (relative density), bending strength (room temperature), and thermal conductivity (room temperature) of the sintered bodies are also shown in Table 9 below.

[0187] The mass content of the group IVA metals in the silicon nitride powders of Examples 7 to 13 is 8 to 43 ppm (in particular, the mass content of Ti is 5 to 40 ppm), therefore Y ２ O ３ - Al ２ O ３ The Vickers hardness (14.3–16.1 GPa) of the sintered body increased with increasing Ti mass content, and the room-temperature three-point bending strength (825–940 MPa) was also higher than that of Comparative Examples 2–7. Furthermore, the Weibull coefficient (12–16) was also higher than that of the comparative examples.

[0188] The mass content of Al in the silicon nitride powder of Examples 7 to 12 is 15 to 90 ppm, and Y ２ O ３ - The MgO-based sintered body had high room temperature three-point bending strength (765-850 MPa) and higher thermal conductivity (88-107 W / (m·K)) compared to Comparative Examples 3-7. In Example 13, the thermal conductivity (70 W / (m·K)) decreased due to an increase in the Al mass content to 200 ppm. The Cr mass content of the silicon nitride powder in Examples 7-12 was 12-25 ppm, and Y ２ O ３ - Al ２ O ３ The oxidation resistance of the sintered body was improved, and the three-point bending strength at high temperature (1200°C) (520-575 MPa) and the three-point bending strength at room temperature after oxidation treatment (580-650 MPa) were slightly higher. The Weibull coefficient (13-16) was also slightly higher. The Ni mass content of the silicon nitride powder in Examples 7-12 was 4-14 ppm, and Y ２ O ３ - Al ２ O ３ The attainable density of the sintered body (relative density 97.1-98.0%) is slightly high, Y ２ O ３ - The attainable density (relative density 97.3-98.6%) of the MgO-based sintered body was also slightly higher. Furthermore, the three-point bending strength was also Y ２ O ３ - Al ２ O ３ System sintered body (890-940 MPa) and Y ２ O ３ - The MgO-based sintered bodies (765-850 MPa) both showed slightly higher readings.

[0189] The mass content of Ca and Mg in the silicon nitride powder of Examples 7 to 10 is 50 to 90 ppm and 12 to 34 ppm, respectively, Y ２ O ３ - Al ２ O ３ The sintered body of the system has a slightly higher attainable density (relative density 97.1-98.6%), Y ２ O ３ - The attainable density (relative density 97.3-97.9%) of the MgO-based sintered body was also high. ２ O３ - Al ２ O ３ Sintered body (895-940 MPa) and Y ２ O ３ - The MgO-based sintered bodies (765-850 MPa) were both slightly higher. Furthermore, the thermal conductivity (90-107 W / (m·K)) was also higher than that of Examples 12 and 13. In Example 13, the mass content of Cr in the silicon nitride powder was 50 ppm and the mass content of Ni was 30 ppm, therefore, Y ２ O ３ - Al ２ O ３ The three-point bending strength at room temperature of the sintered body decreased to 825 MPa, and after oxidation treatment, it decreased to 585 MPa. The Weibull coefficient also decreased to 12.

[0190] The total mass content of Na and K in the silicon nitride powders of Examples 7-11 and 13 was 9-34 ppm, and the lower the total mass content of Na and K, the lower the Y content. ２ O ３ - Al ２ O ３ The corrosion resistance of the sintered body is improved, and the mass loss due to corrosion in an aqueous sulfuric acid solution is reduced (3.9-7.9 g / m²). ２ ) was small. In the silicon nitride powder of Example 12, the total mass content of Na and K was high (77 ppm), so Y ２ O ３ - Al ２ O ３ The corrosion resistance of the sintered body deteriorated, and the mass loss due to corrosion in an aqueous sulfuric acid solution was 11.4 g / m². ２ It rose to [a certain level].

[0191] The mass content of group IVA metals in the silicon nitride powders of Comparative Examples 2 to 7 was 85 to 610 ppm (in particular, the mass content of Ti was 55 to 530 ppm), and the mass content of group IVA metals (especially Ti) was high. Therefore, Y ２ O ３ - Al ２ O ３The Vickers hardness of the sintered body decreased to 12.6–14.0 GPa, and the three-point bending strength at room temperature decreased to 665–710 MPa. Furthermore, oxidation resistance gradually deteriorated, with the three-point bending strength at high temperature (1200°C) decreasing to 420–440 MPa, and the three-point bending strength at room temperature after oxidation treatment decreasing to 450–470 MPa.

[0192] The mass content of Al in the silicon nitride powders of Comparative Examples 3 to 7 was 115 to 310 ppm, and Y ２ O ３ - The room temperature three-point bending strength of the MgO-based sintered body decreased to 610-630 MPa, and the thermal conductivity decreased to 63-87 W / (m·K). On the other hand, since the mass content of Al in Comparative Example 2 was 50 ppm, the thermal conductivity was 98 W / (m·K). The mass content of Cr in the silicon nitride powder of Comparative Examples 3-7 was 55-180 ppm, and the mass content of Ni was 26-55 ppm, and Y ２ O ３ - Al ２ O ３ The three-point bending strength of the sintered body decreased to 665-690 MPa, and the Weibull coefficient also decreased to 7-10. ２ O ３ - The three-point bending strength of the MgO-based sintered body decreased to 610-630 MPa.

[0193] The mass content of Ca and Mg in the silicon nitride powders of Comparative Examples 6 and 7 was 200-220 ppm and 69-70 ppm, respectively. ２ O ３ - Al ２ O ３ The three-point bending strength of the sintered body decreased to 665-685 MPa at room temperature and to 420-430 MPa at high temperatures (1200°C). Furthermore, oxidation resistance began to deteriorate, with the room-temperature three-point bending strength after oxidation treatment decreasing to 450-470 MPa, and the strength retention rate (ratio of room-temperature strength after oxidation treatment to room-temperature strength before oxidation treatment) also decreasing to 0.68. ２ O ３ The room-temperature three-point bending strength of the MgO-based sintered body also decreased to 610-630 MPa.

[0194] The total mass content of Na and K in the silicon nitride powders of Comparative Examples 3, 6, and 7 was 81 to 160 ppm, and Y ２ O３ - Al ２ O ３ The corrosion resistance of the sintered body deteriorates, and the mass loss due to corrosion in an aqueous sulfuric acid solution is 12.0 to 14.9 g / m². ２ ) grew bigger.

[0195] Furthermore, the metal impurity content of the high-strength sintered bodies for structural members obtained in Examples 7-13 and Comparative Examples 2-7, excluding Al, was in the range of 0.92 to 1.05 times the mass content of metal impurities in the silicon nitride powder raw material used in the sintering test. In addition, the metal impurity content of the high-thermal-conductivity sintered bodies for circuit boards obtained in Examples 7-13 and Comparative Examples 2-7, excluding Mg, was in the range of 0.94 to 1.05 times the mass content of metal impurities in the silicon nitride powder raw material used in the sintering test.

[0196]

[0197] [Sintering Test of Silicon Nitride Powder Produced by Direct Nitriding Method Using Self-Combustion Reaction] Using the silicon nitride powders obtained in Examples 14 to 19 and Comparative Example 8 by direct nitriding using self-combustion reaction as raw materials, silicon nitride sintered bodies for structural members were produced according to the method described in (Method for Production and Evaluation of High-Strength Sintered Bodies for Structural Members) above, and their strength characteristics were evaluated. The measurement results of the attainable density (relative density), Vickers hardness, and flexural strength (room temperature strength and its Weibull coefficient, high-temperature strength, and strength after oxidation treatment) of the sintered bodies are shown in Table 10 below.

[0198] Similarly, silicon nitride sintered bodies for circuit boards were prepared using the silicon nitride powders obtained in Examples 14-19 and Comparative Example 8 as raw materials, according to the method described in (Method for Manufacturing and Evaluating High Thermal Conductivity Sintered Bodies for Circuit Boards) above, and their strength characteristics and thermal conductivity were evaluated. The measurement results for the attainable density (relative density), bending strength (room temperature), and thermal conductivity (room temperature) of the sintered bodies are also shown in Table 10 below.

[0199] The mass content of the IVA group metals in Examples 14 to 19 is 4 to 43 ppm (in particular, the mass content of Ti is 2 to 40 ppm), and Y ２ O ３ - Al ２ O ３The Vickers hardness (13.8–15.8 GPa) of the sintered bodies increased with increasing Ti mass content. Examples 14–18 (Ti mass content 5–40 ppm) showed high three-point bending strength (860–915 MPa at room temperature, 510–580 MPa at 1200°C) and slightly higher Weibull coefficients (13–16). In contrast, Example 19 had a low Ti mass content (2 ppm), resulting in a smaller improvement in strength characteristics.

[0200] The mass content of Al in Examples 14 to 19 is 9 to 95 ppm, and Y ２ O ３ - The MgO-based sintered body had high room temperature three-point bending strength (715-840 MPa) and high thermal conductivity (95-113 W / (m·K)). In Example 18, the thermal conductivity (95 W / (m·K)) was slightly lower due to an increase in the Al mass content to 95 ppm. The Cr mass content of Examples 14-19 was 6-28 ppm, and Y ２ O ３ - Al ２ O ３ The oxidation resistance of the sintered body was improved, and the three-point bending strength at high temperature (1200°C) (510-580 MPa) and the three-point bending strength at room temperature after oxidation treatment (560-625 MPa) were slightly higher. The Weibull coefficient (13-16) was also slightly higher. The mass content of Ni in Examples 14-19 was 3-14 ppm, and the mass content of Ca and Mg was 5-55 ppm and 3-32 ppm, respectively. ２ O ３ - Al ２ O ３ The attainable density of the sintered body (relative density 97.0-97.8%) is slightly high, Y ２ O ３ - The attainable density (relative density 97.4-98.9%) of the MgO-based sintered body was also slightly higher. In addition, the three-point bending strength at room temperature was also Y ２ O ３ - Al ２ O ３ System sintered body (860-915 MPa) and Y ２ O ３ - The MgO-based sintered bodies (715-840 MPa) both showed higher pressures compared to the comparative examples.

[0201] Y in Examples 14-19２ O ３ The thermal conductivity (95-113 W / (m·K)) of the MgO-based sintered body was also higher than that of Examples 12 and 13.

[0202] In Example 18, the mass content of Cr is 28 ppm and the mass content of Ni is 14 ppm, therefore, Y ２ O ３ - Al ２ O ３ The three-point bending strength at room temperature of the sintered body was 915 MPa, and the three-point bending strength at room temperature after oxidation treatment was 625 MPa, but the Weibull coefficient decreased to 13.

[0203] The total mass content of Na and K in Examples 14 to 19 was 3 to 27 ppm, and the lower the total mass content of Na and K, the lower the Y content. ２ O ３ - Al ２ O ３ The corrosion resistance of the sintered body is improved, and the mass loss due to corrosion in an aqueous sulfuric acid solution is reduced (3.4-7.5 g / m²). ２ ) was small.

[0204] In Comparative Example 8, the mass content of the IVA group metals was 83 ppm (in particular, the mass content of Ti was 56 ppm), indicating a high mass content of the IVA group metals (especially Ti). Therefore, Y ２ O ３ - Al ２ O ３ The Vickers hardness of the sintered body decreased to 13.9 GPa, and the three-point bending strength at room temperature decreased to 680 MPa. The three-point bending strength at high temperature (1200°C) decreased to 430 MPa, and the three-point bending strength at room temperature after oxidation treatment decreased to 485 MPa.

[0205] The mass content of Al in Comparative Example 8 was 230 ppm, Y ２ O ３ - The room-temperature three-point bending strength of the MgO-based sintered body decreased to 660 MPa, and the thermal conductivity decreased to 69 W / (m·K). In Comparative Example 8, the mass content of Cr was 64 ppm, the mass content of Ni was 32 ppm, and the mass contents of Ca and Mg were 185 ppm and 65 ppm, respectively. ２ O ３ - Al ２ O ３The three-point bending strength of the sintered body decreased to 680 MPa at room temperature and to 430 MPa at high temperature (1200°C), and the Weibull coefficient also decreased to 9. ２ O ３ - The room-temperature three-point bending strength of the MgO-based sintered body decreased to 660 MPa.

[0206] The total mass content of Na and K in Comparative Example 8 was 77 ppm, Y ２ O ３ - Al ２ O ３ The corrosion resistance of the sintered body deteriorated, and the mass decreased due to corrosion in an aqueous sulfuric acid solution (10.4 g / m²). ２ The mass content of Ti had a significant effect on the strength characteristics, but the effects of the mass content of Cr, Ni, Ca, Mg, etc. were also observed.

[0207] Furthermore, the metal impurity content of the high-strength sintered bodies for structural members obtained in Examples 14-19 and Comparative Example 8, excluding Al, was in the range of 0.92 to 1.05 times the mass content of metal impurities in the silicon nitride powder raw material used in the sintering test. In addition, the metal impurity content of the high-thermal-conductivity sintered bodies for circuit boards obtained in Examples 14-19 and Comparative Example 8, excluding Mg, was in the range of 0.94 to 1.05 times the mass content of metal impurities in the silicon nitride powder raw material used in the sintering test.

[0208]

[0209] As described above, the present invention provides silicon nitride powder and a method for producing the same, which can be obtained by controlling the mass content of various metal impurities (Fe, Ti, Cr, Ni, Al, Ca, Mg, Na, and K) to an appropriate range, thereby producing a silicon nitride sintered body that combines excellent mechanical properties and high thermal conductivity. Furthermore, in addition to the inherent high strength of the silicon nitride sintered body (high strength at room temperature, high temperature, and room temperature after oxidation treatment), it also possesses high thermal conductivity, thus providing a silicon nitride sintered body and a method for producing the same that combine excellent mechanical properties and high thermal conductivity.

Claims

1. A silicon nitride powder having an iron (Fe) content (mass content) of 95 ppm or less, characterized in that the mass content of a group IVA metal (Ti, Zr, Hf, etc.) is 0.5 ppm or more and 60 ppm or less.

2. The silicon nitride powder according to claim 1, characterized in that the group IVA metal is titanium (Ti), and its mass content is 0.5 ppm or more and 50 ppm or less.

3. The silicon nitride powder according to claim 2, characterized in that the mass content of titanium (Ti) is 5 ppm or more and 40 ppm or less.

4. Silicon nitride powder according to any one of claims 1 to 3, characterized in that the mass content of chromium (Cr) is 0.5 ppm or more and less than 48 ppm.

5. The silicon nitride powder according to claim 4, characterized in that the mass content of nickel (Ni) is 0.5 ppm or more and less than 25 ppm.

6. The silicon nitride powder according to claim 5, characterized in that the total mass content of chromium (Cr) and nickel (Ni) is 1.0 ppm or more and 50 ppm or less.

7. The silicon nitride powder according to claim 6, characterized in that the mass content of aluminum (Al) is 0.5 ppm or more and 100 ppm or less.

8. The silicon nitride powder according to claim 7, characterized in that the mass content of calcium (Ca) and magnesium (Mg) is 0.5 ppm or more and 100 ppm or less, and 0.5 ppm or more and 40 ppm or less, respectively.

9. The silicon nitride powder according to claim 8, characterized in that the mass content of alkali metals (Li, Na, K, etc.) is 0.5 ppm or more and 85 ppm or less.

10. The silicon nitride powder according to claim 9, characterized in that the alkali metals are sodium (Na) and potassium (K), and the total mass content of these alkali metals is 1.0 ppm or more and 75 ppm or less.

11. Silicon nitride powder according to any one of claims 2 to 10, characterized in that the content (mass content) of metallic foreign matter larger than 20 μm is 0.17 ppm or less.

12. BET specific surface area is 7.0 m² ２ / g or more 15.0m ２ The silicon nitride powder according to any one of claims 2 to 11, characterized in that it is less than or equal to / g.

13. The silicon nitride powder according to any one of claims 2 to 12, characterized in that the mass ratio of the α phase to the total amount of the α phase and the β phase, α / (α+β), is 90% by mass or more.

14. A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in any one of claims 1 to 3.

15. A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in claim 4.

16. A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in claim 6.

17. A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in claim 7.

18. A method for producing a silicon nitride sintered body, characterized by comprising the step of molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in claim 8.

19. A silicon nitride sintered body characterized in that the mass content of titanium (Ti) obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in any one of claims 1 to 3 is 0.5 ppm or more and 50 ppm or less.

20. A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in claim 4, characterized in that the mass content of chromium (Cr) is 0.5 ppm or more and less than 48 ppm.

21. A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in claim 6, characterized in that the mass content of nickel (Ni) is 0.5 ppm or more and less than 25 ppm, and the total mass content of chromium (Cr) and nickel (Ni) is 1.0 ppm or more and 50 ppm or less.

22. A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in claim 7, characterized in that the mass content of aluminum (Al) is 0.5 ppm or more and 100 ppm or less.

23. A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in claim 8, characterized in that the mass content of calcium (Ca) and magnesium (Mg) is 0.5 ppm or more and 100 ppm or less, and 0.5 ppm or more and 40 ppm or less, respectively.

24. A silicon nitride sintered body obtained by molding and sintering a sintering raw material containing silicon nitride powder and a sintering aid as described in claim 10, characterized in that the total mass content of sodium (Na) and potassium (K) is 1.0 ppm or more and 75 ppm or less.

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