JP2018062429A - SPHERICAL Si3N4 PARTICLES AND PROCESS FOR PRODUCING SPHERICAL Si3N4 PARTICLES - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide spherical SiNparticles that are higher in fillability and thermal conductivity than conventional ones and that are applicable in semiconductor fields, and also provide a process for producing the same.SOLUTION: There are provided spherical SiNparticles that contain 90 wt% or greater of SiNand have a circularity of 0.85-1.00. There is also provided a process for producing the spherical SiNparticles. The process comprises mixing 10-50 wt% of Si powder with 50-90 wt% of SiNpowder and nitriding powder granulated to be spherical in nitrogen-containing atmosphere at a heat treatment temperature of 1200-1700°C. The resultant spherical SiNparticles contain 90 wt% or greater of SiNand have a circularity of 0.85-1.00.SELECTED DRAWING: Figure 1

Description

The present invention relates to spherical Si ₃ N ₄ particles and a method for producing spherical Si ₃ N ₄ particles.

Si ₃ N ₄ (silicon nitride) is a material having high strength and high toughness among ceramics, and is used as various structural members. In recent years, practical application has been promoted as a substrate material for semiconductors as an application focusing on the high thermal conductivity of Si ₃ N ₄ . Since Si ₃ N ₄ is a material that is difficult to sinter, it is difficult to sinter with Si ₃ N ₄ alone. In general, oxides such as rare earth oxides, alumina, and silica are mainly used as sintering aids. It is used as an agent to obtain a dense sintered body.

Further, since Si ₃ N ₄ is oxidized at a high temperature, it is generally fired in a nitrogen gas atmosphere containing no oxygen during sintering. Furthermore, since Si ₃ N ₄ decomposes at a high temperature, N ₂ gas was used to suppress the decomposition reaction of Si ₃ N ₄ → 3Si + 2N ₂ when firing at a temperature exceeding 1800 ° C. A firing method using gas pressure sintering is used.

On the other hand, ceramic spherical particles are used for semiconductor sealing materials, insulating resin substrates, heat dissipation sheets, and the like. In these applications, spherical particles of oxides such as SiO ₂ (silica) and Al ₂ O ₃ (alumina) are mixed with resin, and those produced by thermal spraying are widely used. .

  In particular, alumina particles having a higher thermal conductivity than silica are also used for resin substrates, heat radiating sheets, heat radiating grease, etc. that require high thermal conductivity, but the thermal conductivity of alumina is about 30 W / mK in the sintered body. However, it is not necessarily high, and only a heat conductivity of a material of a few tens of W / mK can be obtained with a highly filled material.

  When applied to parts that require higher thermal conductivity, such as power devices, the spherical particles to be used also require higher thermal conductivity. In these uses, AlN and the like have been studied because high heat conduction and insulation are required. AlN is a material having a high thermal conductivity of 150 W / mK in a sintered body.

  However, since AlN is oxidized or decomposed at a high temperature, it is difficult to produce spherical particles by applying thermal spraying, which is a general mass production method of spherical particles. Further, AlN is easily oxidized and reacts with moisture to generate ammonia, so that it is chemically unstable. Therefore, there is a problem that it is inferior in reliability when used as a member by mixing with resin or the like. .

On the other hand, Si ₃ N _{4 is} also a material having a high thermal conductivity equivalent to that of AlN. In recent years, a sintered body having a thermal conductivity of 150 W / mK or more has been developed. Si ₃ N ₄ hardly reacts with moisture and the like, is a material excellent in chemical stability as compared with AlN, and can be expected to obtain a member having higher reliability than AlN.

However, since Si ₃ N _{4 is} also decomposed at a high temperature like AlN, it is difficult to obtain spherical Si ₃ N ₄ particles because it is not possible to use a spraying method that is a general method for producing spherical particles. Met.

Si ₃ N ₄ particles and powders can be produced by direct nitriding in which metal Si is heat-treated in a nitrogen gas or ammonia atmosphere, or in a nitrogen gas or ammonia atmosphere while mixing and reducing SiO ₂ and carbon. For example, a reduction nitriding method, an imide method in which silicon diimide is generated from SiCl ₄ and decomposed are used.

However, spherical Si ₃ N ₄ obtain particles techniques rarely disclosed method, to obtain Si ₃ N ₄ particles spherical has been difficult.

  In Patent Document 1, spherical particles in which particles containing silicon nitride as a main component are used as a core and the surface thereof is granulated and coated with metal silicon powder are used as raw materials, and this is used in a non-oxidizing gas atmosphere containing nitrogen or ammonia. A method for producing silicon nitride powder that is nitrided in a temperature range of ˜1500 ° C. is disclosed.

Although this technique uses granulated coated spherical particles, it is not intended to obtain spherical Si ₃ N ₄ grains, but by using Si ₃ N ₄ grains as a core, Si ₃ N ₄ powder with stable quality such as α and β phase ratios by suppressing heat generation due to nitriding reaction of metal silicon powder and effectively removing reaction heat generated in coating layer of metal silicon powder by heat conduction The purpose is to obtain.

  In Patent Document 2, particles obtained by granulating metal silicon powder are used as raw materials, and the above metal silicon powder is used in a non-oxidizing atmosphere containing nitrogen or ammonia in a temperature range of 1,000 to 1,400 ° C. A method for producing a silicon nitride powder is disclosed.

  This technique uses a granulated metal silicon powder to adjust the heat removal amount by the granulated particle diameter and fluid gas linear velocity in order to avoid adhesion of fine powder to the wall of the reaction tube and aggregation of the powders. Thus, the purpose is to make the nitriding reaction by the fluidized bed uniform.

Japanese Patent Laid-Open No. 9-25107 Japanese Patent Laid-Open No. 10-130006

With use in high-temperature environments such as power devices or higher heat generation, heat dissipation members are required to have higher thermal conductivity, especially as filler particles used for resin substrates, heat dissipation sheets, heat dissipation grease, etc. Spherical and dense Si ₃ N ₄ particles that can be filled and have high thermal conductivity are very useful.

Patent Document 1 proposes a method of nitriding a spherical granulated powder in which Si ₃ N ₄ particles are coated with metal Si. However, as shown in the examples, the nitriding rate of the obtained Si ₃ N ₄ powder is as low as about 70%. Moreover, since reaction occurs on the surface and Si ₃ N ₄ grows, the particles adhere to each other, or the surface of the granulated powder has irregularities and changes its shape, thus obtaining particles that remain spherical. Is difficult.

Patent Document 2 proposes a method of nitriding particles obtained by granulating metal Si powder. However, as shown in the examples, even with this method, the Si ₃ N ₄ powder obtained has a low nitridation rate of about 75%, and reaction occurs from the surface of the granulated powder to grow Si ₃ N ₄ . Similar to Document 1, it is difficult to obtain particles that maintain the spherical shape of the granulated powder.

Thus, particles having a high nitriding ratio cannot be obtained simply by granulating Si powder or coating Si powder around Si ₃ N ₄ core particles and nitriding. In these methods, since the nitriding rate is low and Si remains, particles having high thermal conductivity cannot be obtained.

Moreover, although neither patent document describes the shape of the particles after nitriding, as described above, when the granulated powder surface or the entire granulated powder is Si, Si ₃ N ₄ is generated and grown from the surface. Therefore, it is difficult to obtain particles that maintain the shape of the granulated powder.

The present invention has been made in view of the above-described problems of the prior art, and has an object to provide spherical Si ₃ N ₄ particles having high filling property and high thermal conductivity and applicable to the semiconductor field, and a method for producing the same. To do.

The following aspects are provided by the present invention.
[1]
Spherical Si ₃ N ₄ particles, characterized in that the content of Si ₃ N ₄ is 90 wt% or more and the circularity is 0.85 to 1.00.
[2]
Wherein the average particle diameter (D50) of 5 to 150 m, spherical _Si 3 _{N 4} particles according to Item [1].
[3]
Si powder is mixed at a ratio of 10 to 50 wt% and Si ₃ N ₄ powder is mixed at a ratio of 50 to 90 wt%, and the spherically granulated powder is nitrided at a heat treatment temperature of 1200 to 1700 ° C. in a nitrogen-containing atmosphere. ₃ the content of N ₄ is not less than 90 wt%, characterized in that to produce a spherical _Si 3 _{N 4} particle circularity is 0.85 to 1.00, the production method of spherical _Si 3 _{N 4} particles.
[4]
The method for producing spherical Si ₃ N ₄ particles according to item [3], wherein the spherical granulation method is a spray drying method.

According to the present invention, spherical Si ₃ N ₄ particles having a high filling property and high thermal conductivity and applicable to the semiconductor field and a method for producing the same are provided.

_{4 is} a SEM photograph of spherical Si ₃ N ₄ particles of Invention Example 3 in Example 1. _{4 is} a SEM photograph of Si ₃ N ₄ particles of Comparative Example 1 in Example 1.

The inventor has conducted extensive studies to solve the above problems, and as a result, “the content of Si ₃ N ₄ is 90 wt% or more, and the circularity is 0.85 to 1.00,” The spherical Si ₃ N ₄ particles ”have found that spherical Si ₃ N ₄ particles having high filling properties and high thermal conductivity and applicable to the semiconductor field can be realized.

Conventionally, to produce particles the Si ₃ N ₄ is, Si or SiO ₂ to direct nitridation, or a method of reduction and nitridation has been used, that these methods give only irregular the Si ₃ N ₄ particles could not. Further, production of Si ₃ N ₄ particles using a raw material obtained by uniformly mixing Si or SiO ₂ powder with Si ₃ N ₄ powder has not been performed.

The spherical Si ₃ N ₄ particles according to the present invention can be produced by a method in which Si powder and Si ₃ N ₄ powder are mixed, and granulated powder that is granulated and dried in a spherical shape is nitrided.

When granulated powder is produced using only Si powder, reaction occurs from the surface of the granulated powder, and Si ₃ N ₄ produced by reaction grows on the outer periphery of the granulated powder, so that the shape of the particles maintains the shape of the granulated powder. Instead, it becomes an irregular, irregular shape.
In addition, since nitrogen in the atmosphere gas is required for the reaction, in order to increase the nitriding rate by nitriding to the inside of the granulated powder, it is necessary to process for a long time or at a high temperature. They are bound together and spherical particles cannot be obtained.

In addition, when the granulated powder is produced only with the Si ₃ N ₄ powder, the sintering of the Si ₃ N ₄ powder does not occur unless a sintering aid is added, and high-strength spherical particles cannot be obtained. It cannot be used as a spherical particle because it is easily broken when mixed with the like.
In this case, by adding a sintering aid and heat-treating at a high temperature of 1700 ° C. or higher, the Si ₃ N ₄ particles can be densified to increase the strength of the particles. Since the fixation proceeds, spherical particles cannot be obtained.

When a granulated powder in which Si powder and Si ₃ N ₄ powder are mixed is used, the amount of nitrogen required for the reaction is less than when the entire granulated powder is composed of Si. The nitriding reaction is likely to occur, and the reaction occurs in the entire granulated powder, so that the temperature non-uniformity due to the exothermic reaction is reduced, and uniform spherical Si ₃ N ₄ particles can be obtained.

Further, when a granulated powder in which Si powder and Si ₃ N ₄ powder are mixed is used, not only Si but also Si ₃ N ₄ is present on the surface of the granulated powder, so that Si ₃ N ₄ due to nitriding of Si is present. Formation of surface irregularities due to the generation of Si ₃ N ₄ and the adhering to the adjacent granulated powder due to the generation of Si ₃ N ₄ are less likely to occur, so that spherical Si ₃ N ₄ having a high circularity of 0.85 to 1.00 It becomes possible to obtain particles.

Further, by using fine Si powder as a raw material, nitriding reaction is likely to occur, and powder in the granulated powder is bonded to each other by Si ₃ N ₄ generated by nitriding to obtain dense spherical Si ₃ N ₄ particles. be able to.

By these effects, it becomes possible to obtain spherical Si ₃ N ₄ particles characterized in that the content of Si ₃ N ₄ is 90 wt% or more and the circularity is 0.85 to 1.00. .

By setting the content ratio of the Si ₃ N _{4 in} the spherical Si ₃ N ₄ particles to 90 wt% or more, a high thermal conductivity can be obtained when mixed with a resin or the like.
If the content ratio the Si ₃ N ₄ is less than 90 wt%, the thermal conductivity of unreacted Si is low, since the thermal conductivity when mixed with the resin is lowered, spherical _Si 3 _{N 4} particles _Si 3 N The content ratio of ₄ needs to be 90 wt% or more.

The content ratio of Si ₃ N _{4 in} the spherical Si ₃ N ₄ particles is measured by analysis of X-ray diffraction. When measuring by X-ray diffraction, the content ratio of Si ₃ N ₄ can be calculated by calculating the integrated area ratio of peaks of Si ₃ N ₄ , Si and other compounds.

By setting the circularity of the spherical Si ₃ N ₄ particles to a range of 0.85 to 1.00, high fluidity can be obtained and the filler can be used as a filler with good filling properties.
When the circularity is lower than 0.85, since many irregular particles are contained, it is difficult to increase the filling rate when mixed with the resin, which is not desirable.
The circularity can be measured by a commercially available flow type particle image analyzer. Moreover, it can obtain | require as follows using image analysis processing software from micrographs, such as a scanning electron microscope (SEM). A photograph of a sample of spherical Si ₃ N ₄ particles is taken, and the area and circumference length of the silica particles (two-dimensional projection view) are measured. Assuming that the spherical Si ₃ N ₄ particle is a perfect circle, the circumference of the perfect circle having the measured area is calculated. The degree of circularity is obtained by the formula of circularity = circumference / perimeter length. When the circularity = 1, it is a perfect circle. That is, the closer the circularity is to 1, the closer to a perfect circle.

The spherical Si ₃ N ₄ particles preferably have an average particle size (D50) of 5 to 150 μm. When the average particle diameter exceeds 150 μm, nitrogen necessary for nitriding Si to the inside of the particles may be difficult to enter, and there may be particles in which a large amount of Si remains in the center of the particles. Further, in the case of particles smaller than 5 μm, Si is easily sintered and aggregated with other particles in the process of nitriding Si ₃ N ₄ (compared to particles having a particle size larger than 5 μm), and the circularity May be reduced.
In addition, it is preferable to obtain | require the average particle diameter here by the particle size distribution measurement by a laser diffraction method.
The average particle diameter referred to here is called the median diameter. The particle diameter distribution is measured by a method such as laser diffraction, and the particle diameter at which the cumulative frequency of the particle diameter is 50% is determined as the average particle diameter ( D50).

As described above, the spherical Si ₃ N ₄ particles according to the present invention can be produced by a method in which Si powder and Si ₃ N ₄ powder are mixed and granulated powder that has been granulated and dried into a spherical shape is nitrided. Hereinafter, the production of the spherical Si ₃ N ₄ particles of the present invention will be described in the order of steps.

(material)
The spherical Si ₃ N ₄ particles of the present invention promote the nitriding of Si by mixing and granulating Si raw material 10 to 50 wt% and Si ₃ N ₄ powder 50 to 90 wt%. An effect is obtained.
When the Si powder is less than 10 wt%, the amount of Si ₃ N ₄ generated by the nitriding reaction is small, so that the effect of combining the particles of the granulated powder with the generated Si ₃ N ₄ is small, and the high-strength spherical Si ₃ N ₄ particles It becomes difficult to get.
Further, when the amount of Si powder is more than 50 wt%, Si nitriding reaction is difficult to occur (the Si ₃ N ₄ content in the obtained Si ₃ N ₄ particles is small), so 50 wt% or less is preferable. When the nitriding reaction is liable to occur by increasing the heat treatment temperature during nitriding to over 1700 ° C. or by keeping the holding time extremely long, the surface unevenness due to nitriding becomes large, and it is difficult to obtain spherical particles. is there. Further, when the ratio of the Si powder is large, the granulated powders adhere to each other due to the generation of Si ₃ N ₄ by nitriding, so that only a lump-like one can be obtained.

As the Si powder used for the raw material, it is desirable to use one having an average particle diameter (D50) of 0.1 to 5 μm. When Si powder having an average particle size (D50) of less than 0.1 μm is used, the filling rate in the granulated powder obtained by granulation and drying tends to be low (the fine powder is not uniform in the granulated powder). Aggregates and easily encloses voids), and voids tend to remain in the obtained spherical Si ₃ N ₄ particles. In addition, when Si powder having an average particle size (D50) larger than 5 μm is used (if the particle size increases, the number of contact points (contact area) between the powders per unit volume decreases, and the bonding strength between the particles decreases). because) granulated powder strength is lowered, and broken spherical granulated powder was granulated, there is a case where the degree of circularity of the resulting Si ₃ N ₄ particles is decreased, also, Si ₃ Si powder by nitriding When N ₄ is used, the surface irregularities increase and the circularity decreases, so it may be difficult to increase the filling rate when mixed with the resin.
The average particle diameter of the Si powder is measured by the median diameter (D50), for example, by measuring the particle size distribution by a laser diffraction method or measuring the particle size observed by SEM.

Further, _Si 3 _{N 4} powder used as the raw material, average particle size (D50) of it is desirable to use those 0.1 to 5 [mu] m. When Si ₃ N ₄ powder having an average particle size (D50) smaller than 0.1 μm is used, the filling rate in the granulated powder obtained by granulation and drying tends to be low (in the case of fine powder, Therefore, voids are likely to remain in the resulting spherical Si ₃ N ₄ particles. In addition, when Si ₃ N ₄ powder having an average particle size (D50) larger than 5 μm is used (the number of contact points (contact area) between powders per unit volume decreases as the particle size increases), and the bonding strength between the particles Since the strength of the granulated powder is reduced, the granulated powder granulated in a spherical shape may be broken, and the circularity of the resulting Si ₃ N ₄ particles may be reduced. It may be difficult to increase the filling rate.
The average particle diameter of the Si ₃ N ₄ powder is measured by the median diameter (D50), for example, by measuring the particle size distribution by a laser diffraction method or measuring the particle size observed by SEM.

(Mixing and granulation)
For mixing the raw material Si powder and the Si ₃ N ₄ powder, any method may be used as long as it is a uniformly mixed method. It can be mixed by dry mixing or wet mixing using a solvent such as water, alcohol, acetone or the like.

As a method of granulating the mixed powder into a spherical shape, methods such as spray drying, rolling granulation, stirring granulation, and fluid granulation can be used.
In particular, when the spray drying method is used, a large amount of raw material powder can be efficiently granulated into a spherical shape. When performing granulation by spray drying, by using an additive such as a dispersant or a binder in a solvent such as water, the raw material can be uniformly dispersed and a granulated powder having high strength can be obtained.
Further, since the spherical Si ₃ N ₄ particles obtained by nitriding are almost the same as or slightly smaller than the particle size of the granulated powder, the spherical Si ₃ N particles having a desired particle size can be controlled by controlling the particle size of the granulated powder. _Four particles can be obtained.
Here, the granulated powder is not excessively dense, and appropriately contains voids, so that a nitrogen-containing gas is supplied to the inside, and the nitriding reaction reacts not only on the surface of the granulated powder but also inside the granulated powder. As a result, spherical Si ₃ N ₄ particles having a Si ₃ N ₄ content of 90 wt% or more can be obtained.
The voids to be included are desirably 30 to 70% by volume (with the bulk volume of the granulated powder (including the voids included) being 100% by volume). When the voids are less than 30% by volume, the nitrogen-containing gas is not sufficiently supplied to the inside of the granulated powder, and the nitriding reaction is not easily caused, and the spherical Si ₃ N ₄ particles having a high Si ₃ N ₄ content Therefore, the voids are preferably 30% by volume or more. When there are more voids than 70% by volume, the strength of the granulated powder is weakened, and there is a possibility that the granulated powder is destroyed in the process before nitriding, or a lot of voids remain in the nitrided granulated powder. Therefore, since it may be difficult to obtain spherical Si ₃ N ₄ particles having high thermal conductivity, the voids are preferably 70% by volume or less.
The porosity can be measured with a mercury porosimeter (manufactured by MICROMERITICS, AutoPore IV).

(Nitriding treatment)
Further, by nitriding the granulated powder of Si and _Si 3 _{N 4} was granulated into spherical high temperature, it can be content ratio the _Si 3 _{N 4} to obtain a high spherical _Si 3 _{N 4} particles.

When nitriding Si in the granulated powder by heat treatment, NH ₃ gas or N ₂ gas can be used, but even if cheap and safe N ₂ gas is used as a nitrogen source, spherical Si ₃ N ₄ particles can be obtained. it can.
Spherical Si ₃ N ₄ particles can be obtained by heat-treating the spherical granulated powder in a nitrogen-containing atmosphere, for example, at a temperature of 1200 to 1700 ° C.
At temperatures lower than 1200 ° C., Si nitridation is unlikely to occur, and particles with a low Si ₃ N ₄ content ratio are undesirable. When heat treatment is carried out at a temperature higher than 1700 ° C., the nitriding reaction occurs abruptly, so that it is not desirable because the particles are combined or the granulated powder is broken and it is difficult to obtain spherical particles. At a temperature higher than 1700 ° C., Si ₃ N ₄ starts to decompose into Si and N ₂ . For these reasons, it is desirable to perform heat treatment at a temperature of 1700 ° C. or lower.
In addition, it is possible to obtain the desired spherical Si ₃ N ₄ particles by changing the temperature depending on the conditions such as the temperature of the heat treatment depending on the ratio of Si powder and Si ₃ N ₄ powder contained in the granulated powder. It becomes. For example, the heat treatment temperature is set higher in order to ensure a Si ₃ N ₄ content of 90 wt% or more as the proportion of Si in the granulated powder increases. For example, when the raw material Si powder is granulated by mixing 40-50 wt% and Si ₃ N ₄ powder at a ratio of 50-60 wt%, the heat treatment temperature is preferably 1300 ° C. or higher.

As described above, the spherical Si ₃ N ₄ particles according to the present invention have 10 to 50 wt% of Si powder having an average particle size of 0.1 to 5 μm and Si ₃ N ₄ having an average particle size of 0.1 to 5 μm. The powder can be produced by mixing powder at a rate of 50 to 90 wt% and nitriding a spherical granulated powder at a heat treatment temperature of 1100 to 1500 ° C. in a nitrogen-containing atmosphere.

The spherical Si ₃ N ₄ particles according to the present invention have a Si ₃ N ₄ content of 90 wt% or more and a circularity of 0.85 to 1.00. According to the particle size and composition of the Si powder and Si ₃ N ₄ powder, the temperature and holding time, which are nitriding conditions, are appropriately adjusted to adjust the content and circularity of the target Si ₃ N _4. It becomes possible.

The spherical Si ₃ N ₄ particles according to the present invention preferably have an average particle size (D50) of 5 to 150 μm, but the obtained spherical Si ₃ N ₄ particles have a particle size of the granulated powder. Therefore, it is possible to obtain spherical Si ₃ N ₄ particles having a target particle size by adjusting the granulation method and granulation conditions and changing the particle size of the granulated powder.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not construed as being limited to the following examples.

Example 1
Spray-dried a mixture of Si powder with a particle size of 2 μm and Si ₃ N ₄ powder with a particle size of 1.5 μm, mixed in a ball mill after adding a PVA binder, polycarboxylic acid dispersant and water, as shown in Table 1. Was granulated. The obtained granulated powder was heat-treated at 1300 ° C. (held for 8 hours) in a nitrogen atmosphere to obtain Si ₃ N ₄ particles.

The average particle diameter (D50) of the obtained Si ₃ N ₄ particles was measured by a laser diffraction scattering type particle size distribution analyzer “CILAS 920” manufactured by Cirrus. The circularity was measured using a flow type particle image analyzer “FPIA-2100” manufactured by Sysmex.
As for the content of Si ₃ N _4, an X-ray diffraction pattern was measured with a Rigaku X-ray diffractometer “RINT-2500 TTR”. The calculation of the content ratio of Si ₃ N ₄ is α-Si ₃ N ₄ (PDF card No. 01-076-1407), β-Si ₃ N ₄ (PDF card No. 01-072-0697), Si (PDF Card No. 00-005-0565) peak integrated intensity was measured, and the Si ₃ N ₄ content was calculated as a percentage from the ratio of the total integrated intensity.
The Si nitridation rate was calculated from the Si and Si ₃ N ₄ content obtained by X-ray diffraction as the conversion ratio of Si ₃ N _{4 in} the raw material.

As shown in Table 1, spherical Si ₃ N ₄ particles according to the present invention (Invention Examples 1 to 5) have a high circularity of 0.93 to 0.96, and FIG. 1 (for example, Si: 30 wt%, Si ₃ N ₄ : Spherical particles were obtained as shown in the SEM photograph of Invention Example 3) of a sample obtained by heat-treating 70% of the granulated powder at 1300 ° C. Further, _Si 3 _{N 4} content was obtained as high as 90.6~100wt%.
In contrast, in a comparative example (Comparative Examples 1 to 3) that is outside the scope of the present invention, for example, a granulated product of only Si (Comparative Example 1), as shown in the SEM photograph of FIG. It was fixed and particles having a circular shape before nitriding could not be obtained. On the other hand, the particles according to the present invention obtained spherical particles having a circularity of 0.93 to 0.96 for the other particles according to the present invention.

On the other hand, in the case of granulating only Si ₃ N ₄ (Comparative Example 3), the strength after heat treatment is low, the shape collapses only by dispersing in water to measure the particle size distribution, and the spherical shape cannot be maintained. It was in a state.

(Example 2)
Using the same raw material as in Example 1, granulated powder similarly produced was heat-treated at 1350 to 1400 ° C. (held for 8 hours) in a nitrogen atmosphere to produce silicon nitride particles.
The particles according to the present invention (Invention Examples 6 to 9) have a high degree of circularity of 0.92 to 0.94 and spherical Si ₃ N ₄ particles having a Si ₃ N ₄ content of 97.5 wt% or more. was gotten.
On the other hand, in the case of outside the scope of the present invention (Comparative Examples 4 to 7), for example, in which only Si is granulated (Comparative Example 4), Si ₃ N ₄ is generated on the surface of the granulated powder. Particles adhered to each other, and particles with high circularity could not be obtained.

(Example 3)
Using the same raw material as in Example 1, granulated powder similarly produced was heat-treated at 1100 to 1800 ° C. in a nitrogen atmosphere to produce silicon nitride particles.
The particles according to the present invention (Invention Examples 10 to 13) have high circularity of 0.91 to 0.94, and spherical Si ₃ N ₄ particles having a Si ₃ N ₄ content of 90.7 wt% or more. was gotten.
On the other hand, in the case of heat treatment at 1100 ° C. × 72 h, which is outside the scope of the present invention (Comparative Example 8), nitriding reaction hardly occurred and only particles having a low Si ₃ N ₄ content could be obtained. In addition, in the case of heat treatment at 1800 ° C. (Comparative Example 9), the decomposition of Si ₃ N ₄ occurred, and a sample could not be obtained in the state of particles.

Claims (4)

Spherical Si ₃ N ₄ particles, characterized in that the content of Si ₃ N ₄ is 90 wt% or more and the circularity is 0.85 to 1.00.
2. The spherical Si ₃ N ₄ particles according to claim 1, wherein an average particle diameter (D50) is 5 to 150 μm.
Si powder is mixed at a ratio of 10 to 50 wt% and Si ₃ N ₄ powder is mixed at a ratio of 50 to 90 wt%, and the spherically granulated powder is nitrided at a heat treatment temperature of 1200 to 1700 ° C. in a nitrogen-containing atmosphere. ₃ the content of N ₄ is not less than 90 wt%, characterized in that to produce a spherical _Si 3 _{N 4} particle circularity is 0.85 to 1.00, the production method of spherical _Si 3 _{N 4} particles.
4. The method for producing spherical Si ₃ N ₄ particles according to claim 3, wherein the method of granulating into a spherical shape is a spray drying method.