TWI657043B - Method for manufacturing silicon nitride powder and silicon nitride sintered body - Google Patents

Abstract

The object of the present invention is to provide a silicon nitride powder which does not increase the environmental pressure during sintering and can produce nitrogen having both high thermal conductivity and high mechanical strength even without heat treatment after sintering Sintered silicon body. The present invention provides a silicon nitride powder having a specific surface area of 5 m ² / g or more and 20 m ² / g or less, a ratio of β-type silicon nitride of 70% by mass or more, D50 of 0.5 μm or more and 3 μm or less, and D90 of 3 μm or more and 6μm or less, the content of Fe is 200ppm or less, the Al content of 200ppm or less of metallic impurities other than Fe, and Al ratio of a total amount of 200ppm or less of, the beta] type silicon nitride crystallite size D _C of 60nm or more, and _{a BET} specific surface area ratio equivalent diameter D and D _C D _BET of / D _C (nm / nm) is 3 or less, a crystalline β-type silicon nitride strain of 1.5 × 10 ^-4 or less.

Description

   Method for manufacturing silicon nitride powder and silicon nitride sintered body   

The present invention relates to a method for producing silicon nitride powder having a silicon nitride sintered body having both high thermal conductivity and high mechanical strength, and a silicon nitride sintered body using it as a raw material.

The silicon nitride sintered body obtained by molding and sintering silicon nitride powder is excellent in mechanical strength, corrosion resistance, thermal shock resistance, thermal conductivity, electrical insulation, etc., so it is used as abrasion resistance for cutting blades or ball bearings Consumable components, automotive engine parts and other high-temperature structural components, circuit boards, etc. In addition, in applications such as circuit boards, silicon nitride sintered bodies with high thermal conductivity and high mechanical strength are required to be at an extremely high level.

For example, Patent Document 1 describes a silicon nitride powder that provides a sintered body with excellent sheet formability, high strength, high toughness, and excellent heat dissipation properties. The silicon nitride powders D10, D50, and D90 have 0.5 ~ 0.8μm, 2.5 ~ 4.5μm and 7.5 ~ 10.0μm particle size distribution, with oxygen content of 0.01 ~ 0.5wt%, and the proportion of β-type silicon nitride particles present in particles with an average particle size (D50) or more 1 to 50%.

In addition, Patent Document 2 describes the following silicon nitride powder, which can provide a silicon nitride sintered body having high thermal conductivity and high strength without high-temperature, high-pressure baking and other high-cost baking methods. The β fraction of silicon powder is 30-100%, the oxygen content is less than 0.5wt%, the average particle size is 0.2-10μm, and the aspect ratio is 10 or less. It includes columnar particles with grooves formed on the long axis of the particles , And the Fe content and Al content are each 100 ppm or less.

    [Prior Technical Literature]         [Patent Literature]    

[Patent Document 1] Japanese Unexamined Patent Publication No. 2002-265276

[Patent Document 2] Japanese Patent Laid-Open No. 2004-262756

However, in Patent Documents 1 and 2, since the ambient pressure during sintering is close to 10 atmospheres, a sintering furnace with high pressure resistance is required and heat treatment after sintering, etc., resulting in the increased production cost of the silicon nitride sintered body . Therefore, there is a need for a silicon nitride powder that can further reduce the environmental pressure during sintering and can produce a silicon nitride sintered body that combines high thermal conductivity and high mechanical strength even without heat treatment after sintering.

Therefore, the object of the present invention is to provide a silicon nitride powder that does not increase the environmental pressure during sintering, and can produce silicon nitride with high thermal conductivity and high mechanical strength even without heat treatment after sintering Sintered body.

The present inventors have conducted intensive research on obtaining silicon nitride powder that can obtain a silicon nitride sintered body having both high thermal conductivity and high mechanical strength, and as a result, found a silicon nitride powder having the following characteristics, that is, having a specific Specific surface area, higher ratio of β-type silicon nitride, specific particle size distribution and specific metal impurity content ratio, in addition to specific crystallite size and ratio of crystallite size to specific surface area equivalent particle size, Furthermore, β-type silicon nitride has a specific crystal strain of silicon nitride powder, and it has been found that if the silicon nitride powder is used as a raw material, the environmental pressure during sintering will not be increased, and even if the heat treatment is not performed after sintering, The silicon nitride sintered body having both high thermal conductivity and high mechanical strength can also be manufactured, thereby completing the present invention. That is, the present invention relates to the following matters.

(1) A silicon nitride powder characterized in that the specific surface area measured by the BET method is 5 m ² / g or more and 20 m ² / g or less, and the ratio of β-type silicon nitride is 70% by mass or more. The volume-based 50% particle size measured by the laser diffraction scattering method is D50, and when the 90% particle size is D90, D50 is 0.5 μm or more and 3 μm or less, D90 is 3 μm or more and 6 μm or less, Fe The content ratio is 200 ppm or less, the content ratio of Al is 200 ppm or less, and the total content ratio of metal impurities other than Fe and Al is 200 ppm or less. In accordance with the powder X-ray diffraction pattern of β-type silicon nitride, Williamson- when the calculated Hall type crystallite diameter of the β-type silicon nitride to D _C, D _C is 60nm or more, will be set to the equivalent diameter D _BET specific surface area was calculated according to the ratio of the surface area, D _BET / D _C (nm / nm) is 3 or less, and the crystal strain of β-type silicon nitride calculated from the powder X-ray diffraction pattern of β-type silicon nitride using the Williamson-Hall formula is 1.5 × 10 ^-4 or less.

(2) The silicon nitride powder as described in (1) above, characterized in that D50 is 2 μm or less.

(3) The silicon nitride powder according to (1) or (2) above, characterized in that D90 is 5 μm or less.

(4) The silicon nitride powder according to any one of (1) to (3) above, characterized in that the ratio of β-type silicon nitride is greater than 80% by mass.

(5) The silicon nitride powder according to any one of (1) to (4) above, characterized in that the content ratio of Fe is 100 ppm or less, the content ratio of Al is 100 ppm or less, and metal impurities other than Fe and Al The total content ratio is 100 ppm or less.

(6) The silicon nitride powder according to any one of (1) to (5) above, characterized in that when the volume-based 10% particle diameter measured by the laser diffraction scattering method is D10, D10 is 0.3 μm or more and 0.6 μm or less.

(7) A method for manufacturing a silicon nitride sintered body, characterized by sintering the silicon nitride powder as described in any one of (1) to (6) above.

(8) The method for producing a silicon nitride sintered body as described in (7) above, characterized in that magnesium oxide and yttrium oxide are used as sintering aids.

According to the silicon nitride powder of the present invention, it does not increase the environmental pressure during sintering, and even without heat treatment after sintering, a silicon nitride sintered body having both high thermal conductivity and high mechanical strength can be manufactured.

1‧‧‧Combustion synthesis reaction device

2‧‧‧mixed raw material powder

3‧‧‧Graphite container

4‧‧‧Ignition agent

5‧‧‧Carbon heater

6‧‧‧Pressure resistant container

7‧‧‧Vacuum pump

8‧‧‧ Nitrogen bottle

9‧‧‧window

FIG. 1 is a schematic view of a combustion synthesis reaction device used to manufacture silicon nitride powders of Examples 1-9 and Comparative Examples 1-11.

The embodiment of the silicon nitride powder of the present invention will be described in detail.

(Silicon nitride powder)

The silicon nitride powder of the present invention is characterized in that the specific surface area measured by the BET method is 5 m ² / g or more and 20 m ² / g or less, and the ratio of β-type silicon nitride is 70% by mass or more. The volume-based 50% particle diameter measured by the laser diffraction scattering method is D50, and when the 90% particle diameter is D90, D50 is 0.5 μm or more and 3 μm or less, D90 is 3 μm or more and 6 μm or less, and Fe contains The ratio is 200 ppm or less, the content ratio of Al is 200 ppm or less, the total content ratio of metal impurities other than Fe and Al is 200 ppm or less, the Williamson-Hall formula is used according to the powder X-ray diffraction pattern of β-type silicon nitride when the crystallite diameter is calculated β type silicon nitride of the set D _C, D _C is 60nm or more, according to the above specific surface area is calculated from the equivalent grain diameter D _BET specific surface area, D _BET / D _C (nm / nm) is 3 or less, and the crystal strain of β-type silicon nitride calculated from the powder X-ray diffraction pattern of β-type silicon nitride using the Williamson-Hall formula is 1.5 × 10 ^-4 or less.

The silicon nitride powder of the present invention has a specific surface area measured by the BET method of 5 m ² / g or more and 20 m ² / g or less. If the specific surface area is within this range, a dense sintered body structure can be obtained, so that a silicon nitride sintered body having both high thermal conductivity and high mechanical strength can be obtained. The specific surface area measured by the BET method may be 6 m ² / g or more, 8 m ² / g or more, or 15 m ² / g or less, 13 m ² / g or less, or 12 m ² / g or less.

The proportion of β-type silicon nitride of the silicon nitride powder of the present invention is 70% by mass or more. If the ratio of β-type silicon nitride is within this range, a homogeneous sintered body structure can be obtained, thereby obtaining a silicon nitride sintered body having both high thermal conductivity and high mechanical strength. From this viewpoint, the ratio of β-type silicon nitride is preferably more than 80% by mass. The ratio of β-type silicon nitride may be 90% by mass or more, 95% by mass or more, or 100% by mass.

The components other than silicon nitride are preferably less than 3% by mass, more preferably less than 1% by mass, and particularly preferably less than 0.1% by mass. If a component other than silicon nitride is present, a silicon nitride sintered body with high thermal conductivity and high mechanical strength that does not increase the environmental pressure during sintering and does not undergo heat treatment after sintering as in the present invention cannot be obtained .

In the silicon nitride powder of the present invention, when the volume-based 50% particle size measured by the laser diffraction scattering method is D50, D50 is 0.5 μm or more and 3 μm or less. If D50 is in this range, a sufficient density of the molded body can be obtained, so a dense sintered body structure can be obtained, and a silicon nitride sintered body having both high thermal conductivity and high mechanical strength can be obtained. From this viewpoint, D50 is more preferably 2 μm or less. In addition, when the 90% particle size is D90, D90 is 3 μm or more and 6 μm or less. If D90 is within this range, a homogeneous sintered body structure can be obtained, thereby obtaining a silicon nitride sintered body having both high thermal conductivity and high mechanical strength. From this viewpoint, D90 is more preferably 5 μm or less. D50 may be 0.6 μm or more, 0.7 μm or more, and 0.8 μm or more, and may also be 2.5 μm or less, 2.0 μm or less, 1.5 μm or less, and 1.3 μm or less. D90 may be 3.5 μm or more, and may also be 4.5 μm or less and 4.0 μm or less.

In the silicon nitride powder of the present invention, when the volume-based 10% particle size measured by the laser diffraction scattering method is D10, D10 is preferably 0.3 μm or more and 0.6 μm or less. If D10 is in this range, the density of the molded body is increased, so a denser sintered body structure can be obtained, and thus a silicon nitride sintered body having higher thermal conductivity and higher mechanical strength can be obtained. D10 may be 0.35 μm or more, or 0.55 μm or less, 0.50 μm or less, 0.45 μm or less, or 0.40 μm or less.

The content ratio of Fe in the silicon nitride powder of the present invention is 200 ppm or less. If the content ratio of Fe is within this range, Fe does not significantly dissolve in the sintered body structure, so a homogeneous sintered body structure can be obtained, thereby obtaining a silicon nitride sintered body having both high thermal conductivity and high mechanical strength. From this viewpoint, the content ratio of Fe is more preferably 100 ppm or less, 70 ppm or less, 50 ppm or less, 30 ppm or less, and 10 ppm or less. In addition, the content ratio of Al in the silicon nitride powder of the present invention is 200 ppm or less. If the content ratio of Al is within this range, Al will not significantly solid-dissolve in the sintered body structure, so a homogeneous sintered body structure can be obtained, and a silicon nitride sintered body having both high thermal conductivity and high mechanical strength can be obtained. From this viewpoint, the content ratio of Al is more preferably 100 ppm or less, 70 ppm or less, 50 ppm or less, 30 ppm or less, and 10 ppm or less. The total content of metal impurities other than Fe and Al is 200 ppm or less. If the total content ratio of metal impurities other than Fe and Al is within this range, the metal impurities other than Fe and Al will not significantly solid-dissolve in the sintered body structure, so a homogeneous sintered body structure can be obtained, thereby achieving both Silicon nitride sintered body with high thermal conductivity and high mechanical strength. From this viewpoint, the total content ratio of metal impurities other than Fe and Al is more preferably 100 ppm or less, 70 ppm or less, 50 ppm or less, 30 ppm or less, and 10 ppm or less.

When according to the β-type silicon nitride powder X-ray diffraction patterns and calculated using the Williamson-Hall type of β-type silicon nitride crystallite size D _C of the set, a silicon nitride powder of the present invention D _C Above 60nm. If D _C within this range, the obtained sintered body of homogeneous tissue, thereby silicon nitride having both high thermal conductivity and a high mechanical strength of the sintered body. D _C may also be more than 70nm, 100nm or more, 120nm or more.

When silicon nitride powder of the present invention to be set to the equivalent diameter D _BET specific surface area was calculated according to the ratio of the surface _{area, D BET / D C (nm} / nm) is 3 or less. If D _BET / D _C (nm / nm) is in this range, there are few grain boundaries in the particles, so the heterogeneous grain growth is suppressed during the sintering process, and it becomes a dense sintered body structure, which can achieve both Silicon nitride sintered body with high thermal conductivity and high mechanical strength. _{D BET / D C (nm /} nm) may also be 2 or less, 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less.

According to the powder X-ray diffraction pattern of the β-type silicon nitride and the Williamson-Hall formula, the crystal strain of the silicon nitride powder of the present invention has a crystal strain of 1.5 × 10 ^-4 or less. If the crystal strain of the β-type silicon nitride is within this range, a homogeneous sintered body structure composed of β particles with good crystallinity can be obtained, so that a silicon nitride sintered body having both high thermal conductivity and high mechanical strength can be obtained. The crystal strain of β-type silicon nitride can also be 1.4 × 10 ^-4 or less.

(Manufacturing method of silicon nitride powder)

Hereinafter, an example of the method for producing silicon nitride powder of the present invention will be described. The silicon nitride powder of the present invention uses specific manufacturing conditions, for example, in the combustion synthesis process of silicon nitride that synthesizes silicon nitride by the "combustion synthesis method using self-heating and propagation phenomena accompanying the combustion reaction of silicon", Specifically, mixing the silicon nitride powder as a diluent in the silicon powder of the raw material in a specific ratio to reduce the content of metal impurities in the silicon powder of the raw material and the silicon nitride powder as the diluent, reducing the The filling density of the mixture of silicon nitride powder and the combustion reaction to produce a combustion product with a lower compressive strength, using a method with less crushing energy and difficulty in mixing metal impurities to crush the combustion product with a lower compressive strength, This can be used to produce features with a small content of metal impurities, a large content of β-type silicon nitride, a specific surface area and particle size distribution specified by the present invention, a large crystallite size, and a small crystal strain. Silicon nitride powder. Hereinafter, an example of the manufacturing method will be specifically described.

<Preparation steps of mixed raw material powder>

First, the silicon powder and the silicon nitride powder of the diluent are mixed to prepare a mixed raw material powder. Since the combustion synthesis reaction becomes a high temperature above 1800 ° C, there is a case of melting and fusing of silicon in the part where the combustion reaction is performed. In order to suppress this, it is preferable to add silicon nitride powder as a diluent to the raw material powder within a range that does not hinder the self-propagation of the combustion reaction. The addition rate of the diluent is usually 10-50% by mass (the mass ratio of silicon: silicon nitride is 90: 10-50: 50), and then 15-40% by mass. In addition, in terms of adjusting the ratio of the β-type silicon nitride of the combustion product obtained in the combustion synthesis reaction, NH ₄ Cl or NaCl may also be added. These additives have the effect of lowering the reaction temperature through sensible, latent and endothermic reactions. Here, the content ratio of Fe in the obtained mixed raw material powder, the content ratio of Al, and the content ratio of metal impurities other than Fe and Al are preferably 100 ppm or less, more preferably 50 ppm or less, 10 ppm the following. Therefore, both the silicon powder and the silicon nitride powder of the diluent are preferably high-purity powders containing a relatively small amount of metal impurities. In addition, the inner surface of the mixing container used for mixing the raw material powder and the mixing medium, that is, the portion in contact with the raw material powder are preferably non-metallic materials having a small content of Al, Fe, and the like. The mixing method of the raw material powder is not particularly limited. For example, when mixing with a ball mill, the inner surface of the mixing container is preferably made of resin, and the outer surface of the mixing medium is preferably made of silicon nitride. In addition, it is preferable to set the bulk density of the mixed raw material powder to less than 0.5 g / cm ³ . In order to make the bulk density of the mixed raw material powder less than 0.5 g / cm ³ , it is preferable to use silicon powder with a bulk density of 0.45 g / cm ³ or less as the raw material powder. If the bulk density of the mixed raw material powder does not reach 0.5 g / cm ³ , it is easy to set the crushing strength of the bulk combustion product obtained in the following <combustion synthesis reaction step> to 4 MPa or less.

<Combustion synthesis reaction step>

Then, the obtained mixed raw material powder is combusted in a nitrogen-containing environment to produce a massive combustion product composed of silicon nitride. For example, the mixed raw material powder and the igniting agent are contained in a container made of graphite, etc., the igniting agent is ignited in the combustion synthesis reaction device, and the nitriding reaction of the silicon in the mixed raw material powder is caused by the igniting heat of igniting At the beginning, the reaction is propagated through the whole silicon, and the combustion synthesis reaction is ended, and a massive combustion product composed of silicon nitride is obtained.

Here, the obtained combustion product preferably has a compressive strength of 4 MPa or less. If the compressive strength of the combustion product is 4 MPa or less, the specific surface area or particle size distribution (D50) specified by the present invention can be easily obtained even without crushing with a large crushing energy in the following <combustion product crushing and classification step> , D90 or D10) silicon nitride powder, the above crushing energy is greater means: such as the increase in the mixing of metal impurities, or the reduction of the crystallinity of silicon nitride powder.

<Steps of crushing and classifying combustion products>

Then, the obtained block-shaped combustion products are coarsely pulverized. The pulverization means for coarse pulverization is not particularly limited, and as the pulverization medium, it is preferable to use hard non-metallic materials containing Al and Fe with a small content ratio, and more preferably a pulverization medium made of silicon nitride. Because the combustion products are massive, the crushing by the roller crusher is very efficient. As the roller crusher used for pulverization, the roller is preferably a hard non-metallic material containing a small proportion of Al, Fe, etc., and it is preferable to provide a ceramic roller such as silicon nitride.

It is preferable to remove the particularly coarse particles and the like by sieving the obtained silicon nitride powder by coarse grinding as described above. The sieve used for sieving is preferably made of non-metal having a small content of Al, Fe, etc., and is preferably made of resin.

Then, the silicon nitride powder obtained by coarse grinding is finely pulverized. The means for finely pulverizing is not particularly limited, and it is preferably pulverized by a vibratory mill. In the case of pulverization by a vibratory mill, the inner surface of the tank for the vibratory mill and the mixed medium, that is, the portion in contact with the raw material powder is preferably a non-metallic material containing a small amount of Al, Fe, and the like. The inner surface of the tank is preferably made of resin, and the outer surface of the mixed medium is preferably made of silicon nitride. By appropriately adjusting the conditions of the vibratory mill (amplitude, number of vibrations, crushing time), the silicon nitride powder of the present invention with a desired specific surface area or particle size distribution (D50, D90 or D10) can be obtained. For example, when the pulverization time is short, the specific surface area may become small and D50 and D90 may become large. If the pulverization time is long, the specific surface area may become large and D50 and D90 may become small. Further, when pulverization time is longer, or the smaller D _{C D BET / D C (nm /} nm) or large crystal strain of the present.

As described above, with respect to the silicon nitride powder of the present invention, the silicon powder and the silicon nitride powder of the diluent are mixed, the obtained mixed raw material powder is filled into a container, and by “using combustion reaction "Combustion synthesis method of heat generation and propagation phenomenon", in the production method of silicon nitride powder that burns the above silicon powder and pulverizes the obtained combustion product, the mixed raw material powder preferably has a content ratio of Fe, Al the content ratio of compression, and metal impurities other than the content ratio of Fe and Al, respectively, and a bulk density of less than 0.5g / cm ³ of silicon nitride powder manufacturing method of manufacturing of 100ppm or less, and further preferably of the combustion products The strength is below 4MPa, and it is particularly preferred to use a silicon nitride crushing medium for the crushing of the above combustion products.

(Manufacturing method of silicon nitride sintered body)

The method for manufacturing the silicon nitride sintered body of the present invention is characterized by sintering the silicon nitride powder of the present invention. An example of the method for manufacturing the silicon nitride sintered body of the present invention will be described below. If the silicon nitride powder of the present invention is used, for example, by mixing with a sintering aid, the obtained mixed powder can be shaped and the obtained molded body can be sintered to produce both high thermal conductivity and high mechanical strength The silicon nitride sintered body.

In the present invention, as the sintering aid, yttrium oxide, lanthanide-based rare earth oxides, magnesium oxide, etc. can be used alone or in appropriate combination according to the purpose. In addition, magnesium compounds such as MgSiN ₂ and Mg ₂ Si, titanium oxide, zirconium oxide, lithium oxide, boron oxide, calcium oxide, etc. may be used alone or in combination with yttrium oxide, lanthanide-based rare earth oxides, and magnesium oxide At least one of them is suitably used in combination. As the method for producing the silicon nitride sintered body of the present invention, it is preferable to use magnesium oxide and yttrium oxide as a sintering aid. The reason is that high thermal conductivity and high mechanical strength can be taken into account at a particularly high level.

As the mixing method of the silicon nitride powder and the sintering aid of the present invention, any method can be used regardless of the wet type or dry type as long as the method can uniformly mix these, and a roller mill, a barrel grinder, Vibration mills and other known methods. For example, a method of mixing silicon nitride powder, sintering aid, molding binder, and dispersing agent with a ball mill using water or the like as a dispersion medium, and spray-drying the granulated powder may be used. As the molding method of the mixed powder, known methods such as press molding, casting molding, extrusion molding, injection molding, sludge molding, and cold pressure forming can be used. For example, CIP (cold pressure equalization) molding in which a molded body is obtained by filling the obtained granular mixed powder into a rubber mold and applying pressure to obtain a molded body.

As the sintering method of the molded body, any method may be used as long as it can densify the obtained sintered body, and atmospheric pressure sintering under an inert gas environment or atmospheric pressure sintering to increase the ambient pressure to about 0.2 to 10 MPa . The greater the environmental pressure during sintering, the easier the mechanical strength and thermal conductivity of the obtained silicon nitride sintered body are to increase, but in the present invention, even if sintering is performed at a relatively low environmental pressure, both Silicon nitride sintered body with high thermal conductivity and high mechanical strength. Nitrogen is usually used for sintering. Atmospheric pressure sintering is carried out in the temperature range of 1700 ~ 1800 ℃, and air pressure sintering system is in the range of 1800 ~ 2000 ℃.

In addition, hot pressing as a method of simultaneously forming and sintering may be used. Sintering by hot pressing is usually carried out in a nitrogen atmosphere at a pressure of 0.2 to 10 MPa and a sintering temperature of 1950 to 2050C.

By subjecting the obtained silicon nitride sintered body to HIP (Hot Pressing), the strength can be further improved. HIP treatment is usually carried out under a nitrogen atmosphere at a pressure of 30 to 200 MPa and a sintering temperature of 2100 to 2200 ° C.

    [Example]    

Hereinafter, the present invention will be described in more detail with specific examples. The physical properties of the silicon nitride powder of the present invention, the silicon powder used as the raw material powder, the raw material mixed powder, and the combustion product, and the production and evaluation of the silicon nitride sintered body of the present invention are performed by the following methods.

(Measurement method of specific surface area of silicon nitride powder and calculation method of specific surface area equivalent particle diameter D _BET )

The specific surface area of the silicon nitride powder of the present invention is determined by using Macsorb manufactured by Mountech Corporation and measuring by BET 1 point method based on nitrogen adsorption.

In addition, the specific surface area equivalent particle diameter D _BET is calculated based on the following formula (1), assuming that all particles constituting the powder are balls of the same diameter.

D _BET = 6 / (ρ _S × S) (1)

Here, ρ _S is the true density of silicon nitride (by the true density of α-Si ₃ N ₄ 3186kg / m ³ , the true density of β-Si ₃ N ₄ 3192kg / m ³ , and the relationship between α phase and β phase The ratio calculates the average true density and sets it as the true density), and S is the specific surface area (m ² / g).

(Measurement method of the ratio of β-type silicon nitride of silicon nitride powder)

The ratio of the β-type silicon nitride powder of the silicon nitride powder of the present invention is calculated as follows. Regarding the silicon nitride powder of the present invention, a target composed of a copper bulb and a graphite monochromator are used, and the diffraction angle (2θ) is within the range of 15 to 80 ° with a scale of 0.02 °, making the X-ray detector use step The X-ray diffraction measurement is carried out by the progressive stepping scanning method. When the silicon nitride powder contains components other than silicon nitride, the ratio of these components can be obtained by comparing the peaks of these components with the peaks corresponding to the standard samples of these components. In all the following examples and comparative examples, it was confirmed from the obtained powder X-ray diffraction pattern that the silicon nitride powder of the present invention is composed of only α-type silicon nitride and β-type silicon nitride. Furthermore, the ratio of β-type silicon nitride of the silicon nitride powder of the present invention can be determined by GPGazzara and DPMessier, “Determination of Phase content of Si ₃ N ₄ by X-ray Diffraction Analysis”, Am. Ceram.Soc.Bull. , 56 [9] 777-80 (1977) described in the method of Gazzara & Messier.

(crystallite size D _C and the method of measuring crystal strain of β-type silicon nitride)

Crystallite size and crystal strain D _C based β-type silicon nitride of the silicon nitride powder of the present invention is measured in the following manner. Regarding the silicon nitride powder of the present invention, a target composed of a copper bulb and a graphite monochromator are used, and the diffraction angle (2θ) is within the range of 15 to 80 ° with a scale of 0.02 °, making the X-ray detector use step The X-ray diffraction measurement is carried out by the progressive stepping scanning method. Based on the obtained X-ray diffraction pattern of the silicon nitride powder of the present invention, the integral widths of the (101), (110), (200), (201), and (210) planes of the β-type silicon nitride are calculated, The above-mentioned integral width is substituted into the Williamson-Hall formula of the following formula (2). Plot the "2sinθ / λ" in the following formula (2) as the x-axis and the "βcosθ / λ" as the y-axis, and use the least square method to obtain the intercept and slope of the straight line obtained by the Williamson-Hall formula . Then the calculated intercept of the β-type silicon nitride crystallite size D _C in accordance with, and, the β-type crystalline silicon nitride above the slope of the strain was calculated.

βcosθ / λ = η × (2sinθ / λ) + (1 / D _C ) (2)

(β: integral width (rad); θ: Bragg angle (rad); η: crystal strain; λ: wavelength of the X-ray source (nm); DC: crystallite size (nm))

(Determination of D10, D50 and D90 of silicon nitride powder)

The particle size distribution of the silicon nitride powder of the present invention and the silicon powder used as a raw material in the present invention are measured as follows. The above powder was put into a 0.2% by mass aqueous solution of sodium hexametaphosphate, and a dilute solution was prepared using an ultrasonic homogenizer equipped with a stainless steel center cone with a diameter of 26 mm at an output of 300 W for 6 minutes to prepare a dilute solution. Sample. A laser diffraction / scattering particle size distribution measuring device (Microtrac MT3000 manufactured by Nikkiso Co., Ltd.) was used to measure and measure the particle size distribution of the sample to obtain a volume-based particle size distribution curve and its data. According to the obtained particle size distribution curve and its data, D10, D50 and D90 of the silicon nitride powder of the present invention and D50 of the silicon powder used as the raw material in the present invention are calculated.

(Measurement method for the content ratio of metal impurities other than Fe, Al, Fe and Al in silicon nitride powder, silicon powder and raw material mixed powder)

The content ratios of the silicon nitride powder of the present invention, the silicon powder used as the raw material in the present invention, and the raw material mixed powder of Fe and Al, and metal impurities other than Fe and Al are measured as follows. Put the above powder into a container containing a solution of mixed hydrofluoric acid and nitric acid and stopper tightly, irradiate the container with microwave and heat to completely decompose silicon nitride or silicon, and use ultrapure water to decompose the obtained The solution is made constant volume to make a test solution. Use ICP-AES (SPS5100 type) manufactured by SII Nano Technology Inc., and quantify the metal impurities other than Fe, Al, Fe, and Al in the test solution according to the detected wavelength and the luminous intensity, and calculate Fe, Al, The content ratio of metal impurities other than Fe and Al.

(Measurement method of bulk density of mixed raw material powder)

The bulk density of the mixed raw material powder obtained in the present invention is obtained by a method according to JIS R1628 "Measurement method of bulk density of precision ceramic powder".

(Measurement method of compressive strength of combustion products)

The compressive strength of the combustion products obtained in the present invention is measured in the following manner. Five cubes with a side of 10 mm were cut out from the combustion products and set as measurement samples. The compressive strength of the measurement sample was measured using a manual compressive strength measuring device (manufactured by Aikoh Engineering Co., Ltd., MODEL-1334). Apply a load to the measurement sample placed on the pedestal to perform a compression test, and calculate the compressive strength based on the maximum load measured. The compressive strength of the combustion products obtained in the present invention was set as the average value of the compressive strengths of five measured samples.

(Method of making and evaluating silicon nitride sintered body)

In the embodiment of the present invention, using ethanol as a medium and using a ball mill, "a blended powder containing 3.5 parts by mass of yttrium oxide and 2 parts by mass of magnesium oxide added to 94.5 parts by mass of silicon nitride powder" was carried out 24 After hourly wet mixing, it was dried under reduced pressure. After molding the obtained mixture into a shape of 62 mm × 62 mm × 7.3 mm thickness and a shape of 12.3 mm φ × 3.2 mm thickness at a molding pressure of 50 MPa, CIP molding was performed at a molding pressure of 150 MPa. The obtained shaped body was put in a crucible made of boron nitride, heated to 1900 ° C under a nitrogen atmosphere of 0.8 MPa, and held at 1900 ° C for 22 hours to be sintered. The obtained silicon nitride sintered body was cut to prepare a 3 mm × 4 mm × 40 mm bending test piece according to JIS R1601, and a 10 mm × 2 mm test piece for measuring thermal conductivity according to JIS R1611. The Archimedes method was used to determine the relative density of the sintered body. A universal material testing machine manufactured by Instron was used and the room temperature 4-point bending strength was measured by the method according to JIS R1601, and the thermal conductivity at room temperature was measured by the flash measurement method according to JIS R1611.

(Example 1)

To silicon powder with D50 of 4.0 μm, bulk density of 0.40 g / cm ³ , Fe content of 3 ppm, Al content of 4 ppm, and metal impurities other than Fe and Al of 3 ppm, silicon nitride The addition rate becomes 20% by mass (the mass ratio of silicon: silicon nitride is 80:20) by adding silicon nitride powder (manufactured by Ube Kosei Co., Ltd., product name "SN-E10" (Fe The content ratio: 9 ppm; the content ratio of Al: 2 ppm; the content ratio of metal impurities other than Fe and Al: 4 ppm)) to make raw material powder. The above-mentioned raw material powder was contained in a nylon tank filled with silicon nitride balls and the inner wall surface was lined with urethane. Using a batch-type vibrating mill, the mixture was mixed at a vibration number of 1200 cpm and an amplitude of 8 mm for 0.5 hours to obtain a mixed raw material powder.

FIG. 1 shows a combustion synthesis reaction device 1 used for the combustion synthesis reaction of silicon in this embodiment. The mixed raw material powder 2 obtained by mixing the raw material powders was housed in a sheath-like graphite container 3 having a bottom surface of 200 × 400 mm, a depth of 30 mm, and a thickness of 10 mm. At this time, the bulk density of the mixed raw material powder was 0.45 g / cm ³ . The titanium powder and the carbon powder are mixed and shaped in a titanium: carbon mass ratio of 4: 1, and an igniter 4 for combustion synthesis reaction is prepared, and the igniter 4 is placed on the mixed raw material powder 2. Then, the graphite container 3 containing the mixed raw material powder 2 and the igniter 4 is housed in the pressure-resistant container 6 provided with the carbon heater 5 for igniter heating so that the carbon heater 5 is positioned directly above the igniter 4 Inside.

After degassing the pressure-resistant container 6 using the vacuum pump 7, nitrogen gas was introduced into the reaction container from the nitrogen bottle 8 to set the ambient pressure to 0.6 MPa. Then, the carbon heater 5 is energized to heat the igniter 4 to ignite the mixed raw material powder, and the combustion synthesis reaction starts. In the combustion synthesis reaction, the nitrogen ambient pressure of the pressure-resistant container 6 is 0.6 MPa and is approximately fixed. Observation of the inside of the pressure-resistant container 6 from the window 9 revealed that the combustion synthesis reaction ended after approximately 20 minutes. After the reaction is completed, the graphite container 3 is taken out of the pressure-resistant container 6 and the massive combustion products are recovered.

From the combustion products obtained, the igniting agent was partially removed, and the remaining part was coarsely pulverized by a roller crusher coated with urethane on the inner surface and equipped with a silicon nitride roller, and a nylon sieve with a mesh of 100 μm was used. Perform sieving and recover the powder under the sieve. The obtained powder was contained in an aluminum oxide tank filled with silicon nitride balls and the inner wall surface was lined with urethane, and was pulverized for 1 hour using a batch-type vibratory mill with a vibration number of 1280 cpm and an amplitude of 8 mm to obtain The silicon nitride powder of Example 1. When pulverizing with a batch-type vibratory mill, 1% by mass of ethanol relative to the powder is added as a pulverizing aid.

The physical property values of the silicon powder and diluent used in the raw material powder in Example 1-1, the physical property values of the mixed raw material powder, and the compressive strength of the combustion product are shown in Table 1, and the physical properties of the silicon nitride powder值 示 于 表 2。 Values are shown in Table 2.

The silicon nitride sintered body of Example 1 was produced by the method described in (Method of Making and Evaluating Silicon Nitride Sintered Body), the relative density of the obtained sintered body, the bending strength at room temperature, and the Thermal conductivity. The results are shown in Table 3.

(Examples 2 to 5)

The time for the fine pulverization of Examples 2 to 5 was set to 1.25 hours, 1.50 hours, 3.00 hours, and 4.00 hours in order from Example 2 except that Examples 2 to 5 were obtained in the same manner as Example 1. Of silicon nitride powder. Then, using the silicon nitride powders of Examples 2 to 5, a silicon nitride sintered body was produced in the same manner as in Example 1. Furthermore, the relative density of these sintered bodies, the bending strength at room temperature, and the thermal conductivity at room temperature were measured in the same manner as in Example 1.

(Example 6)

To the raw material powder, ammonium chloride (made by Wako Pure Chemicals, purity 99.9%) was added as an additive 5.3% by mass (in a way that the mass ratio of the mixed powder of silicon and silicon nitride to ammonium chloride becomes 94.7: 5.3), Except for this, a combustion product was produced in the same manner as in Example 1, and the obtained combustion product was coarsely pulverized and sieved. The time of the subsequent fine pulverization was set to 1.42 hours, except that the obtained silicon nitride powder was finely pulverized in the same manner as in Example 1 to obtain the silicon nitride powder of Example 6. Then, using the silicon nitride powder of Example 6, a silicon nitride sintered body was produced in the same manner as in Example 1. Furthermore, the relative density of these sintered bodies, the bending strength at room temperature, and the thermal conductivity at room temperature were measured in the same manner as in Example 1.

(Example 7)

An example was obtained in the same manner as Example 6 except that the additive ratio of ammonium chloride was 9.2% by mass (the mass ratio of the mixed powder of silicon and silicon nitride to ammonium chloride was 90.8: 9.2). 7 silicon nitride powder. Then, using the obtained silicon nitride powder of Example 7, a silicon nitride sintered body was produced in the same manner as in Example 1. Furthermore, the relative density of these sintered bodies, the bending strength at room temperature, and the thermal conductivity at room temperature were measured in the same manner as in Example 1.

(Examples 8, 9)

Except for using the powder shown in Table 1 as the raw material silicon powder, a combustion product was produced in the same manner as in Example 1, and the obtained combustion product was coarsely pulverized and sieved. The time of subsequent fine pulverization was set to 1.42 hours in Example 8 and 1.50 hours in Example 9, except that the silicon nitride powder was obtained in the same manner as in Example 1, and the obtained The silicon nitride powder was finely pulverized to obtain the silicon nitride powder of Example 6. Then, using the obtained silicon nitride powder of each example, a silicon nitride sintered body was produced in the same manner as in Example 1. Furthermore, the relative density of these sintered bodies, the bending strength at room temperature, and the thermal conductivity at room temperature were measured in the same manner as in Example 1.

(Comparative examples 1 to 6)

The time for the fine grinding of Comparative Examples 1 to 6 was set to 0.75 hours, 5.50 hours, 0.83 hours, 0.92 hours, 4.17 hours, and 4.00 hours in order from Comparative Example 1, except that it was the same as in Example 1. The silicon nitride powders of Comparative Examples 1 to 6 were obtained. As shown in Table 2, the silicon nitride powder of Comparative Example 1 is a powder with a small specific surface area and large D50 and D90; the silicon nitride powder of Comparative Example 2 is a powder with a large specific surface area; the nitrogen of Comparative Example 3 The siliconized silicon powder is a powder with a larger D50; the silicon nitride powder of Comparative Example 4 is a powder with a larger D90; the silicon nitride powder of Comparative Example 5 is a powder with a smaller D50; the silicon nitride powder of Comparative Example 6 is a D90 Smaller powder. Then, using the silicon nitride powder of each comparative example, a silicon nitride sintered body was produced in the same manner as in Example 1. Furthermore, the relative density of these sintered bodies, the bending strength at room temperature, and the thermal conductivity at room temperature were measured in the same manner as in Example 1.

(Comparative example 7)

Except for using the powder shown in Table 1 as the raw material silicon powder, a combustion product was produced in the same manner as in Example 1, and the obtained combustion product was coarsely pulverized and sieved. The time of subsequent fine pulverization was set to 6.33 hours, except that the silicon nitride powder was obtained in the same manner as in Example 1, and the obtained silicon nitride powder was finely pulverized to obtain the nitride of Comparative Example 7. Silicon powder. Comparative Example 7 The silicon nitride-based powder crystallite size D _C is small, a large strain of the crystalline powder. Then, using the obtained silicon nitride powder of Comparative Example 7, a silicon nitride sintered body was produced in the same manner as in Example 1. Furthermore, the relative density of these sintered bodies, the bending strength at room temperature, and the thermal conductivity at room temperature were measured in the same manner as in Example 1.

(Comparative Example 8)

The addition ratio of ammonium chloride of the additive was set to 11.6% by mass (the mass ratio of the mixed powder of silicon and silicon nitride to the mass ratio of ammonium chloride was 88.4: 11.6), except that the combustion was produced in the same manner as in Example 6. The product is coarsely crushed and sieved. The silicon nitride powder obtained in Comparative Example 8 was obtained by finely pulverizing in the same manner as in Example 1 except that the time for finely pulverizing the obtained silicon nitride powder was 1.83 hours. As shown in Table 2, the silicon nitride powder of Comparative Example 8 is a powder with a small proportion of β-type silicon nitride. Then, using the obtained silicon nitride powder of Comparative Example 8, a silicon nitride sintered body was produced in the same manner as in Example 1. Furthermore, the relative density of these sintered bodies, the bending strength at room temperature, and the thermal conductivity at room temperature were measured in the same manner as in Example 1.

(Comparative examples 9 to 11)

Except for using the powder shown in Table 1 as the raw material silicon powder, a combustion product was produced in the same manner as in Example 1, and the obtained combustion product was coarsely pulverized and sieved. The time of subsequent fine pulverization was set to 1.42 hours, 1.67 hours, and 1.42 hours in order from Comparative Example 9, except that the silicon nitride powders of Comparative Examples 9 to 11 were obtained in the same manner as in Example 1. As shown in Table 2, the silicon nitride powders of Comparative Examples 9 to 11 are powders with a large Fe content, Al content, and / or metal impurity content other than Fe and Al. Then, using the silicon nitride powder of each comparative example, a silicon nitride sintered body was produced in the same manner as in Example 1. Furthermore, the relative density of these sintered bodies, the bending strength at room temperature, and the thermal conductivity at room temperature were measured in the same manner as in Example 1.

(Comparative examples 12, 13)

A silicon powder with a D50 of 2.5 μ, bulk density of 0.26 g / ml, Fe content of 2 ppm, Al content of 3 ppm, and metal impurities other than Fe and Al of 3 ppm is filled into a mold with an inner diameter of 30 mm In this process, uniaxial molding is performed at a pressure of 1500 kg / cm ^{2 to} obtain a uniaxial molded body of silicon powder. The above molded body was filled in a graphite container and contained in a batch-type nitriding furnace. After the furnace was replaced with a nitrogen atmosphere, the temperature was raised to 1450 ° C under a nitrogen atmosphere and held for 3 hours. After allowing to cool to room temperature, the nitrided product was taken out. Using a roller crusher coated with urethane on the inner surface and equipped with a roller made of silicon nitride, the obtained nitrided product was coarsely pulverized and sieved using a nylon sieve with a mesh of 100 μm to recover the powder under the sieve . Next, the powder was contained in an aluminum oxide can filled with silicon nitride balls and urethane-lined inner surface, and finely pulverized using a batch-type vibratory mill at a vibration number of 1780 cpm and an amplitude of 5 mm. The time of fine pulverization was set to 0.42 hours in Comparative Example 12 and 1.25 hours in Comparative Example 13 to obtain silicon nitride powder of each Comparative Example. As shown in Table 2, the silicon nitride powders of Comparative Examples 12 and 13 which are a direct nitridation method but not a combustion synthesis method have a small crystallite diameter D _C , a large crystal strain, and a large D _BET / D _C In addition, the silicon nitride powder of Comparative Example 13 is a powder with a small proportion of β-type silicon nitride and a small D90. Then, using the silicon nitride powder of each comparative example, a silicon nitride sintered body was produced in the same manner as in Example 1. Furthermore, the relative density of these sintered bodies, the bending strength at room temperature, and the thermal conductivity at room temperature were measured in the same manner as in Example 1.

The physical property values of the silicon powder and the diluent used in the raw material powders of Examples 2 to 9 and Comparative Examples 1 to 13, the physical property values of the mixed raw material powders, and the compressive strength of the combustion products are shown in Table 1. The physical property values of the silicon nitride powders of Examples 2 to 9 and Comparative Examples 1 to 13 are shown in Table 2. In addition, the relative density of the silicon nitride sintered body produced by sintering the silicon nitride powders of Examples 2 to 9 and Comparative Examples 1 to 13, the bending strength at room temperature, and the thermal conductivity at room temperature are shown in table 3. It is understood that if the silicon nitride powder of the present invention is used as a raw material, a silicon nitride sintered body having both high thermal conductivity and high mechanical strength can be obtained.

    [Industry availability]    

If the silicon nitride powder of the present invention is used as a raw material, a silicon nitride sintered body having both high thermal conductivity and high mechanical strength can be manufactured. Therefore, the silicon nitride powder of the present invention is used as a silicon nitride sinter for circuit boards The raw materials are particularly useful. In addition, the silicon nitride powder of the present invention does not require a large environmental pressure during sintering and a heat treatment after sintering, so it is possible to manufacture a silicon nitride sintered body for a circuit board without high cost.

Claims (8)

A silicon nitride powder with a specific surface area measured by the BET method of 5 m ² / g or more and 20 m ² / g or less, and the ratio of β-type silicon nitride is 70% by mass or more, which will be diffracted by laser The volume-based 50% particle size measured by the scattering method is D50, and when the 90% particle size is D90, D50 is 0.5 μm or more and 3 μm or less, D90 is 3 μm or more and 6 μm or less, and the Fe content ratio is 200 ppm or less , The content ratio of Al is 200 ppm or less, and the total content ratio of metal impurities other than Fe and Al is 200 ppm or less, based on the β-type silicon nitride powder X-ray diffraction pattern calculated using the Williamson-Hall formula when the crystallite size of the silicon nitride type when set D _C, D _C is 60nm or more, will be set to the equivalent diameter D _BET specific surface area was calculated according to the ratio of the surface _{area, D BET / D C (nm} / nm ) Is 3 or less, and the crystal strain of β-type silicon nitride calculated from the powder X-ray diffraction pattern of β-type silicon nitride using the Williamson-Hall formula is 1.5 × 10 ^-4 or less. For example, the silicon nitride powder in the first item of the patent application, where D50 is 2 μm or less. For example, the silicon nitride powder of the first or second patent application, where D90 is less than 5μm. For example, the silicon nitride powder according to item 1 or 2 of the patent application, wherein the proportion of β-type silicon nitride is greater than 80% by mass. For example, in the silicon nitride powder of claim 1 or 2, the content of Fe is 100 ppm or less, the content of Al is 100 ppm or less, and the total content of metal impurities other than Fe and Al is 100 ppm or less. For example, the silicon nitride powder according to item 1 or 2 of the patent application, in which, when the volume-based 10% particle size measured by the laser diffraction scattering method is D10, D10 is 0.3 μm or more and 0.6 μm the following. A method for manufacturing a silicon nitride sintered body is to sinter the silicon nitride powder according to any one of items 1 to 6 of the patent application. For example, the method for manufacturing a silicon nitride sintered body according to item 7 of the patent scope uses magnesium oxide and yttrium oxide as sintering aids.