JP6941928B2 - Method for Producing Spherical Si3N4 Particles and Spherical Si3N4 Particles - Google Patents

Description

The present invention, spherical _Si 3 _{N 4} particles, and relates to 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. Further, 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 difficult-to-sinter material, _{it is difficult to sinter Si 3} N ₄ alone, and generally, rare earth oxides and oxides such as alumina and silica are mainly assisted in sintering. 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 at the time of 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 → 3 Si + 2 N ₂ when firing at a temperature exceeding 1800 ° C. A firing method by gas pressure sintering is used.

On the other hand, the spherical particles of ceramics are used as a sealing material for semiconductors, an insulating resin substrate, a heat radiating sheet, and the like. For these purposes, _{spherical particles of oxides such as SiO 2} (silica) and Al ₂ O ₃ (alumina) are mixed with a resin, and those manufactured by the thermal spraying method are widely used. ..

In particular, spherical particles of alumina, which have a higher thermal conductivity than silica, are also used for resin substrates, heat-dissipating sheets, heat-dissipating grease, etc., which require high thermal conductivity, but the thermal conductivity of alumina is about 30 W / mK for sintered bodies. Therefore, it is not always high, and the thermal conductivity of the material highly filled in the resin is only 10 W / mK.

When applied to parts such as power devices that require higher thermal conductivity, the spherical particles used also need to have higher thermal conductivity. In these applications, high thermal conductivity and insulating properties are required, so AlN and the like are being studied. 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 for spherical particles. Further, AlN is easily oxidized and is chemically unstable such that ammonia is generated by reacting with water, so that there is a problem that reliability is inferior when it is mixed with a resin or the like and used as a member. ..

On the other hand, Si ₃ N _{4 is} also a material having a high thermal conductivity equivalent to that of AlN, and in recent years, a sintered body having a thermal conductivity of 150 W / mK or more has been developed. Si ₃ N ₄ is a material having almost no reaction with water and having excellent chemical stability as compared with AlN, and it can be expected that a member having higher reliability than AlN can be obtained.

However, since Si _{3 N 4} also decomposes at a high temperature like Al N, it is not possible to use the thermal spraying method, which is a general method for producing spherical particles, and it is difficult to obtain _{spherical Si 3} N _{4 particles.} Met.

As _{a method for producing Si 3} N ₄ particles and powder, a direct nitriding method in which metallic Si is heat-treated in a nitrogen gas or ammonia atmosphere, and a nitriding method in a nitrogen gas or ammonia atmosphere while mixing _{SiO 2 and carbon and reducing them.} A reduction nitriding method is used, or an imide method in which silicon diimide is generated from _{SiCl 4 and decomposed.}

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, a particle containing silicon nitride as a main component is used as a core, and spherical particles obtained by granulating and coating metallic silicon powder on the surface thereof are used as a raw material in a non-oxidizing gas atmosphere containing nitrogen or ammonia. A method for producing a silicon nitride powder that is nitrided in a temperature range of about 1500 ° C. is disclosed.

Although this technique uses granulated coated spherical particles, it is not intended to obtain _{spherical Si 3} N _{4 particles, but by using Si 3} N ₄ particles as nuclei, at the center of the granulated particles. By suppressing the heat generated by the silicon nitride reaction of the metal silicon powder and effectively removing the reaction heat generated in the coating layer of the metal silicon powder by heat conduction, the Si ₃ N ₄ powder with stable quality such as α and β phase ratios. The purpose is to obtain.

Patent Document 2 describes the above-mentioned metallic silicon powder using particles obtained by granulating metallic silicon powder as a raw material and using a fluidized layer 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 by nitriding a silicon nitride powder is disclosed.

This technology uses granulated metal silicon powder in order to avoid adhesion of fine powder to the wall of the reaction tube and aggregation of powders, and adjusts the amount of heat removal by the granulated particle size and fluidized gas linear velocity. Therefore, the purpose is to make the nitrided reaction by the fluidized bed uniform.

Japanese Unexamined Patent Publication No. 9-25107 Japanese Unexamined Patent Publication No. 10-130006

With the use in a high temperature environment such as a power device or the increase in heat generation, the heat radiation member is required to have higher heat conductivity. dense Si ₃ N ₄ particles spherical filler can high thermal conductivity can be obtained is very useful.

Patent Document 1 proposes a method of nitriding a spherical granulated powder having _{Si 3} N _{4 particles as a core and coated with metallic Si.} However, as shown in Examples, the obtained Si ₃ N ₄ powder has a low nitriding rate of about 70%. In addition, since a reaction occurs on the surface and Si ₃ N ₄ grows, the particles stick to each other or the surface of the granulated powder becomes uneven and the shape changes, so that the particles that maintain the spherical shape can be obtained. Is difficult.

Further, Patent Document 2 proposes a method of nitriding particles obtained by granulating metal Si powder. However, as shown in Examples, _{the nitriding rate of the obtained Si 3} N ₄ powder is as low as about 75% even with this method, and a 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 of the granulated powder while maintaining the spherical shape.

It is not possible to obtain particles having a high nitriding rate only by granulating the Si powder or _{coating the Si powder around the core particles of Si 3} N _{4 and nitriding the particles.} With these methods, the nitriding rate is low and the particles have Si remaining, so that particles with high thermal conductivity cannot be obtained.

Further, although there is no description about the shape of the particles after nitride in any of the patent documents, as described above, when the surface of the granulated powder or the entire granulated powder is Si, Si ₃ N ₄ is generated and grows from the surface. Therefore, it is difficult to obtain particles that maintain the shape of the granulated powder.

The present invention aims to provide more traditional view of the problems of the art, such as, high packing property, has a high thermal conductivity, also applicable spherical Si ₃ N ₄ particles and a manufacturing method thereof in the semiconductor field do.

The present invention provides the following aspects.
[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]
_{The spherical Si 3} N ₄ particles according to item [1], wherein the average particle size (D50) is 5 to 150 μm.
[3]
Si powder is mixed at a ratio of 10 to 50 wt% and Si ₃ N ₄ powder 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 to obtain Si. 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 method for granulating into spheres is a spray-drying method.

According to the present invention, high packing property, it has a high thermal conductivity, applicable spherical Si ₃ N ₄ particles and a method for producing the same in the semiconductor field.

3 is an SEM photograph _{of spherical Si 3} N ₄ particles of Invention Example 3 in Example 1. 6 is an SEM photograph _{of Si 3} N ₄ particles of Comparative Example 1 in Example 1.

As a result of diligent studies to solve the above problems, the inventor " _{is characterized in that the content of Si 3} N ₄ is 90 wt% or more and the circularity is 0.85 to 1.00. , Spherical Si ₃ N ₄ particles ”has been found to be able to realize _{spherical Si 3} N ₄ particles having high filling property and high thermal conductivity and applicable to the semiconductor field.

Conventionally, in order _{to produce Si 3} N ₄ particles, a method of directly nitriding Si or SiO ₂ or reducing nitride has been used, but these methods can only obtain _{amorphous Si 3} N _{4 particles.} could not. Further, it has not been practiced to produce _{Si 3} N ₄ particles from a material obtained by uniformly mixing Si or SiO ₂ powder with Si ₃ N _{4 powder.}

_{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 spherically granulated and dried granulated powder is nitrided.

When the granulated powder is produced only with Si powder, a reaction occurs from the surface of the granulated powder, and Si ₃ N ₄ generated by the reaction grows on the outer periphery of the granulated powder, so that the shape of the particles keeps the shape of the granulated powder. Without it, it becomes a distorted irregular shape.
In addition, since nitrogen in the atmospheric gas is required for the reaction, in order to nitrid the inside of the granulated powder to increase the nitriding ratio, it is necessary to treat the granulated powder for a long time or at a high temperature, and the granulated powders are separated from each other. It will be bonded and spherical particles cannot be obtained.

Further, when the granulated powder is prepared only from _{Si 3} N _{4 powder, sintering of Si 3} N ₄ powder does not occur unless a sintering aid is added, and high-strength spherical particles cannot be obtained. Since it is easily destroyed when mixed with the like, it cannot be used as spherical particles.
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, but at the same time, by sintering the granulated powders with each other. Spherical particles cannot be obtained due to the progress of fixation.

When a granulated powder obtained by mixing Si powder and Si ₃ N ₄ powder is used, the amount of nitrogen required for the reaction is smaller than that when the entire granulated powder is composed of Si. Therefore, Si inside the granulated powder is required. likely to occur nitriding reaction of, by which the reaction takes place in the entire granulated powder, unevenness in temperature due to the exothermic reaction is reduced, it is possible to obtain a uniform spherical the Si ₃ N ₄ particles.

In the case of using the granulated powder obtained by mixing Si powder and _Si 3 _{N 4} powder, due to the presence of _Si 3 _{N 4} but also Si on the surface of the granulated powder, _Si 3 _{N 4} by nitridation of Si Since the formation of surface irregularities due to the formation of Si ₃ N _{4 is suppressed and the adhesion to the adjacent granulated powder due to the formation of Si 3 N 4 is less likely to occur, a spherical Si 3} N ₄ having a high circularity of 0.85 to 1.00 is less likely to occur. It becomes possible to obtain particles.

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

Due to 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 Si ₃ N ₄ of the spherical Si ₃ N ₄ particles to 90 wt% or more, 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.

Content ratio the _Si 3 _{N 4} of 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 the peaks of _{Si 3} N _{4, Si and other compounds.}

By setting the circularity of the spherical Si ₃ N ₄ particles in the range of 0.85 to 1.00, high fluidity can be obtained and the spherical Si 3 N 4 particles can be used as a filler having good filling property.
When the circularity is lower than 0.85, it is not desirable because it contains many particles having a distorted shape and it becomes difficult to increase the filling rate when mixed with the resin.
The circularity can be measured by a commercially available flow-type particle image analyzer. Further, it can be obtained from a micrograph such as a scanning electron microscope (SEM) by using image analysis processing software as follows. A photograph of a sample of spherical Si ₃ N ₄ particles is taken, and the area and peripheral length of the silica particles (two-dimensional projection drawing) are measured. Assuming that the spherical Si ₃ N ₄ particles are a perfect circle, the circumference of the perfect circle having the measured area is calculated. The circularity is calculated by the formula of circularity = circumference / circumference length. A perfect circle is when the circularity is 1. That is, the closer the circularity is to 1, the closer to a perfect circle.

It is desirable that the spherical Si ₃ N ₄ particles have an average particle size (D50) of 5 to 150 μm. If the average particle size exceeds 150 μm, it may be difficult for nitrogen required for Si to nitriding into the inside of the particles, and the particles may have a large amount of Si remaining in the center of the particles. Further, in the case of particles smaller than 5 μm, in the _{process of silicon nitride to Si 3} N ₄ , they are likely to be sintered and aggregated with other particles (compared to particles having a particle size larger than 5 μm), and have a circularity. May be reduced.
The average particle size here is preferably obtained by measuring the particle size distribution by a laser diffraction method.
Further, the average particle size referred to here is called a median diameter, and the particle size is measured by a method such as a laser diffraction method, and the particle size at which the cumulative frequency of particle sizes is 50% is the average particle size (the average particle size). D50).

As described above, the spherical Si ₃ N ₄ particles according to the present invention can be produced by a method of mixing Si powder and Si ₃ N ₄ powder, and granulating and drying the granulated powder into a spherical shape by a method of nitriding. Hereinafter, the production of the spherical Si ₃ N ₄ particles of the present invention will be described in order of steps.

(material)
The spherical Si ₃ N ₄ particles of the present invention promote the silicon nitride of Si by mixing and granulating Si powder as a raw material at a _{ratio of 10 to 50 wt% and Si 3} N ₄ powder at a ratio of 50 to 90 wt%. The effect is obtained.
When the amount of Si powder is less than 10 wt%, the amount of Si ₃ N ₄ produced by the silicon nitride reaction is small, so that the effect of binding the particles of the granulated powder to each other by the generated Si ₃ N ₄ is small, and the spherical Si ₃ N ₄ particles having high strength are small. It becomes difficult to obtain.
Further, when the amount of Si powder is more than 50 wt%, the nitriding reaction of Si is less likely to occur (the content of Si ₃ N _{4 in the obtained Si 3} N ₄ particles is small), so 50 wt% or less is preferable. When the heat treatment temperature at the time of nitriding is higher than 1700 ° C. or the holding time is made extremely long to facilitate the nitriding reaction, the surface irregularities due to nitriding become large and it is difficult to obtain spherical particles. be. Further, if the ratio of the Si powder is large, the granulated powders are fixed to each other due to the formation of _{Si 3} N _{4 by nitriding, so that only a lumpy powder can be obtained.}

It is desirable that the Si powder used as a raw material has an average particle size (D50) of 0.1 to 5 μm. When Si 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 (fine powder is non-uniform in the granulated powder). (It tends to aggregate and excessively enclose voids), so that pores tend to remain in _{the obtained spherical Si 3} N _{4 particles.} Further, when Si powder having an average particle size (D50) larger than 5 μm is used (as the particles become larger, the number of contact points (contact areas) between the powders per unit volume decreases, and the bonding strength between the particles decreases. Therefore, the strength of the granulated powder may be lowered, the spherically granulated granulated powder may be broken, and _{the circularity of the obtained Si 3} N ₄ particles may be reduced, and the Si powder may be nitrided to Si ₃ When it becomes N ₄ , the unevenness of the surface becomes large and the circularity becomes low, so that it may be difficult to increase the filling rate when mixing with the resin.
The average particle size 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, it is desirable that the Si 3} N ₄ powder used as a raw material has an average particle size (D50) of 0.1 to 5 μm. _{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 / drying tends to be low (in the fine powder, in the granulated powder). It tends to aggregate non-uniformly and excessively enclose voids), so that pores tend to remain in _{the obtained spherical Si 3} N _{4 particles. Further, when Si 3} N ₄ powder having an average particle size (D50) larger than 5 μm is used (as the particles become larger, the number of contact points (contact areas) between the powders per unit volume decreases, and the bonding strength between the particles decreases. The strength of the granulated powder is reduced, and the spherically granulated granulated powder may be broken, resulting in a decrease in the circularity of _{the obtained Si 3} N _{4 particles.} It may be difficult to increase the filling rate.
The average particle size 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 / Granulation)
Mixing Si powder and Si ₃ N ₄ powder as a raw material, may be used, especially any method as long as the mixing method which is uniformly mixed. It can be mixed by dry mixing or wet mixing using a solvent such as water, alcohol or acetone.

As a method for granulating the mixed powder into a spherical shape, a method such as spray-drying, rolling granulation, stirring granulation, or 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 spheres. When granulation is performed by spray-drying, by using an additive such as a dispersant or a binder in a solvent such as water, the raw materials are uniformly dispersed and a highly strong granulated powder can be obtained.
Further, spherical Si ₃ N ₄ particles obtained by nitriding, since substantially the same or slightly smaller and the particle size of the granulated powder, by controlling the particle size of the granulated powder, spherical Si ₃ N of the desired particle size ₄ particles can be obtained.
Here, the granulated powder is not excessively dense, and by appropriately containing voids, the 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 included voids are preferably 30 to 70% by volume (assuming 100% by volume of the bulk volume of the granulated powder (including the included voids)). If the gap is less than 30 vol%, the nitrogen-containing gas is not supplied to the inside of the well granulated powder, nitriding reaction is hard to occur sufficiently, Si ₃ N ₄ content of high spherical Si ₃ N ₄ particles The void is preferably 30% by volume or more because it may not be possible to obtain. If there are more voids than 70% by volume, the strength of the granulated powder will be weakened, and there is a possibility that the granulated powder will be destroyed by the process before nitridement, or many voids will remain in the nitrided granulated powder. _{Therefore, it may be difficult to obtain spherical Si 3} N ₄ particles having high thermal conductivity, so the voids are preferably 70% by volume or less.
The porosity can be measured with a mercury porosity meter (AutoPore IV, manufactured by MICROMERITICS).

(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 Si in the granulated powder is nitrided by heat treatment, NH ₃ gas or N _{2 gas can be used, but spherical Si 3} N ₄ particles can be obtained even if an inexpensive and safe N ₂ gas is used as a nitrogen source. can.
_{Spherical Si 3} N ₄ particles can be obtained by heat-treating the spherical granulated powder in a nitrogen-containing atmosphere at a temperature of, for example, 1200 to 1700 ° C.
At a temperature lower than 1200 ° C., nitriding of Si is unlikely to occur, and the particles have a low content ratio of _{Si 3} N _{4, which is not desirable.} When the heat treatment is performed at a temperature higher than 1700 ° C., the nitriding reaction occurs rapidly, so that the particles are bonded or the granulated powder is destroyed, and it is difficult to obtain spherical particles, which is not desirable. Further, at a temperature higher than 1700 ° C., Si ₃ N ₄ begins to decompose into Si and N _2. For these reasons, it is desirable to heat treat at a temperature of 1700 ° C. or lower.
Further, as for the conditions such as the temperature of the heat treatment, it is possible to obtain the _{desired spherical Si 3} N ₄ particles by changing the temperature or the like depending on the ratio of the _{Si powder and the Si 3} N _{4 powder contained in the granulated powder.} It becomes. For example, as the proportion of Si in the granulated powder increases, the heat treatment temperature is set higher in order to secure a _{Si 3} N _{4 content of 90 wt% or more.} For example, a Si powder as a raw material 40~50wt%, _Si 3 _{N 4} if the powder was granulated by mixing in a ratio of 50～60Wt%, it is preferable that the heat treatment temperature 1300 ° C. or higher.

As described above, the spherical Si ₃ N ₄ particles according to the present invention contain 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 the powder at a ratio of 50 to 90 wt% and nitriding the spherically 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. By appropriately adjusting the temperature and holding time, which are the conditions for nitriding, according to the particle size and composition of the Si powder and Si ₃ N ₄ powder, the content rate and circularity _{of the target Si 3} N _{4 can be adjusted.} 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, by adjusting the granulation method and the granulation conditions and changing the particle size of the granulated powder, it is possible to obtain _{spherical Si 3} N _{4 particles having a target particle size.}

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

(Example 1)
The Si ₃ N ₄ powder Si powder and the particle size 1.5μm particle size 2μm to the formulation shown in Table 1, spray drying a mixture in PVA binder, a ball mill with the addition of a polycarboxylic acid dispersant and water Granulated by. The obtained granulated powder was heat-treated at 1300 ° C. (holding for 8 hours) in a nitrogen atmosphere to obtain _{Si 3} N _{4 particles.}

The average particle size (D50) of the obtained Si ₃ N ₄ particles was measured by a laser diffraction / scattering type particle size distribution measuring device “CILAS 920” manufactured by CILAS. The circularity was measured using a flow-type particle image analyzer "FPIA-2100" manufactured by Sysmex Corporation.
The content of Si ₃ N ₄ was measured by measuring the X-ray diffraction pattern with the 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. 01-082-0697), Si (PDF card No. 01-082-0697). The integrated intensity of the peak of card No. 00-05-0565) was measured, and the Si ₃ N ₄ content was calculated as a percentage from the ratio of the total values of the integrated intensity.
_{The Si nitriding rate was calculated from the conversion ratio of Si 3} N ₄ of Si in the raw material from the contents of _{Si and Si 3} N ₄ obtained by X-ray diffraction.

_{The spherical Si 3} N ₄ particles according to the present invention (Invention Examples 1 to 5) show a high circularity of 0.93 to 0.96 as shown in Table 1, 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 the sample obtained by heat-treating 70% of the granulated powder at 1300 ° C. Further, a high Si ₃ N ₄ content of 90.6 to 100 wt% was obtained.
On the other hand, in the case of the comparative example (Comparative Examples 1 to 3) outside the scope of the present invention, for example, the one in which only Si is granulated (Comparative Example 1), the particles are separated from each other as shown in the SEM photograph of FIG. It was stuck and it was not possible to obtain particles that maintained the circular shape before nitriding. On the other hand, as for the particles according to the present invention, spherical particles having a circularity of 0.93 to 0.96 were obtained as other particles according to the present invention.

On the other hand, _{in the case where only Si 3} N ₄ is granulated (Comparative Example 3), the strength after the heat treatment is low, and the shape collapses only by being dispersed 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 materials as in Example 1, the similarly prepared granulated powder was heat-treated in a nitrogen atmosphere at 1350 to 1400 ° C. (holding for 8 hours) to prepare silicon nitride particles.
Particles according to the present invention (Invention Examples 6-9), the degree of circularity has high circularity and 0.92~0.94, _Si 3 _{N 4} content of 97.5 wt% or more of spherical _Si 3 _{N 4} particles was gotten.
On the other hand, in the case of those outside the scope of the present invention (Comparative Examples 4 to 7), for example, those in which only Si is granulated (Comparative Example 4), Si ₃ N ₄ is generated on the surface of the granulated powder. The granules were stuck to each other, and it was not possible to obtain particles with a high degree of circularity.

(Example 3)
Using the same raw materials as in Example 1, the similarly prepared granulated powder was heat-treated at 1100 to 1800 ° C. in a nitrogen atmosphere to prepare silicon nitride particles.
Particles according to the present invention (Invention Examples 10 to 13), the degree of circularity has high circularity and 0.91~0.94, _Si 3 _{N 4} content of 90.7wt% or more spherical _Si 3 _{N 4} particles was gotten.
On the other hand, in the case of heat treatment at 1100 ° C. × 72 h, which is outside the range of the present invention (Comparative Example 8), almost no nitriding reaction occurred and only particles having a low _{Si 3} N _{4 content could be obtained.} Further, in the case of heat treatment at 1800 ° C. (Comparative Example 9), _{decomposition of Si 3} N ₄ occurred, and a sample could not be obtained in the state of particles.

Claims (2)

Si is ₃ content of N ₄ or more 90 wt%, degree of circularity is 0.85 to 1.00, average particle size (D50) Ri 5~150μm der,
Here, the content of the _{Si 3} N _{4 is α-Si 3} N ₄ (PDF card No. 01-076-1407), β-Si ₃ N ₄ (PDF card No. 01-082-0697), Si. measuring the integrated intensity of the X-ray diffraction peaks of (PDF card Nanba00-005-0565), characterized that you percentages calculated from the ratio of the sum of the integrated intensity, spherical _Si 3 _{N 4} particles. Si powder is mixed at a ratio of 10 to 50 wt% and Si ₃ N ₄ powder 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 to obtain Si. _{To produce spherical Si 3} N ₄ particles having a ₃ N ₄ content of 90 wt% or more and a circularity of 0.85 to 1.00 , and
A method for producing spherical Si ₃ N ₄ particles, wherein the method for granulating into spheres is a spray-drying method.

Images