JPH03193611A - Production of combined silicon nitride powder - Google Patents

Abstract

PURPOSE:To improve the high-temp. strength of the powder by nitriding the compact of a mixture of the metallic Si powder and specified chromium carbide powder in a nitriding atmosphere contg. NH3 and/or H2 and with the prescribed O2 partial pressure or below and then crushing the resulting product. CONSTITUTION:A mixture consisting of 100 pts.wt. of metallic Si powder and 0.5-10 pts.wt. of chromium carbide powder having <=3.0mum average diameter and contg. >=20vol.% of the particles having <=1.0mum average diameter is compacted to obtain a compact having <=1.0g/cm<3> bulk density. The compact is nitrided at about 1150-1450 deg.C in a nitriding atmosphere contg. NH3 and/or H2 and with the O2 partial pressure controlled to <=10<-3>atm, and then crushed to obtain a combined Si3N4 powder having 7-15m<2>/g specific surface. Alternately, >=1 kind selected from alkali metal halide and alkaline-earth metal halide is charged to the nitriding atmosphere, and nitrided to obtain a low-oxygen contg. Si3N4 powder contg. <=0.6wt.% O2. Meanwhile, 1-5 pts.wt. of SiO2 can be added to 100 pts.wt. of metallic Si to accelerate the reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing an easily sinterable composite silicon nitride powder that can yield a sintered body with excellent high-temperature strength and fracture toughness.

[Conventional technology]

Silicon nitride sintered bodies have excellent heat resistance and corrosion resistance, so their use is expanding into various turbine blades, nozzles exposed to high temperatures, and the like. However, high-temperature strength and toughness were still insufficient, and there was a strong demand for improvement.

Therefore, attempts have been made to variously control the sintering conditions and variously change the sintering aids in order to compensate for the shortcomings in high-temperature strength, but no improvements have been made to a level that is fully satisfactory.

On the other hand, in order to improve the toughness, whisker strengthening by adding silicon carbide wicker or the like, particle dispersion strengthening by adding dispersed particles, etc. have been carried out. For example, JP-A-64-33076
In the publication, ceramic whiskers such as silicon carbide are mixed to improve the toughness of the sintered body. Also, JP-A-6
In JP 0-200812, a composite powder of silicon carbide and silicon nitride is synthesized by a vapor phase method. However, in the case of whisker reinforcement, there are problems such as dispersibility and orientation, making it difficult to produce large-sized sintered bodies, and also being disadvantageous in terms of cost. Moreover, the problem of carcinogenicity of silicon carbide whiskers has been pointed out in recent years. On the other hand, composite powders are mainly synthesized by gas phase methods and alkoxide methods, which are extremely expensive.

[Problem to be solved by the invention]

The present inventors investigated the structure of a sintered body manufactured by adding various dispersed particles as a second component in different amounts to silicon nitride powder and the composite morphology of the second component.
Chromium carbide is the best second component, and if the amount and method of compounding are controlled, the sinterability and properties of the sintered body can be significantly improved.In other words, silicon nitride has excellent high-temperature strength and fracture toughness. The present invention was completed by discovering that a sintered body can be obtained.

[Means to solve the problem]

That is, the present invention has the following gist.

1. The average particle size is 3.
A molded body comprising 0.5 to 10 parts by weight of chromium carbide powder in which the content of particles of 0 μm or less and 1.0 μm or less is 20% by volume or more, and has a bulk density of 1.0 g/c+fl or less, Contains NH3 and/or H2 02 partial pressure 1
A method for producing composite silicon nitride powder, which comprises nitriding in a nitriding atmosphere of 0-jatm or less and then pulverizing.

2. The nitriding atmosphere is one selected from the group consisting of alkali metal halides and alkaline earth metal halides.
The method for producing a composite silicon nitride powder according to claim 1, further comprising one or more species.

3. The molded body contains 1 to 100 parts by weight of metal silicon powder.
3. The method for producing a composite silicon nitride powder according to claim 1 or 2, further comprising 5 parts by weight of silicon dioxide powder.

These inventions will be explained in detail below.

(Invention according to claim 1) The metal silicon powder used in the present invention may have a relatively large particle size of about 88 μm. The reason for this is that not all of the reactions between metallic silicon and the nitrogen source are solid/gas reactions, but after some solid/gas reactions on the surface, nitriding progresses through air/gas reactions. Even if silicon is used, if nitridation occurs on the surface due to a solid-gas reaction, a phenomenon of destruction of the metal silicon will occur due to the difference in density between the metal silicon and α-silicon nitride, resulting in fine metal silicon. However, if a material with a diameter significantly exceeding 88 μm is used, the same phenomenon occurs, but the temperature at which the solid-gas reaction occurs on the surface becomes high, and free metallic silicon tends to remain under normal nitriding conditions, which is not desirable.

There is no need to particularly limit the lower limit of the particle size of the metal silicon powder, and the smaller the average particle size of the metal silicon powder is, the more the gas-gas reaction is accelerated.

Regarding the particle size of the chromium carbide to be added, the average particle size is 3.
It is necessary that the thickness is 0 μm or less. If it exceeds 3.0 μm, it will act as a nucleus when silicon nitride is generated in the nitriding reaction described below, resulting in coarse crystals of the resulting silicon nitride ingot. This is because silicon nitride and chromium carbide are ground into individual particles.

In addition, in the present invention, 1.0 μm of chromium carbide powder
The amount of fine powder below must be 20% by volume or more. 2
If it is less than 0% by volume, the number of chromium carbides that act as nuclei during silicon nitride production decreases, making it impossible to obtain silicon nitride in which chromium carbide is sufficiently dispersed. In other words, even if the average particle size of the added chromium carbide is 3.0μ or less, 1.
If the amount of fine powder of 0 μm or less is less than 20% by volume, or even if the amount of fine powder of 1.0 μm or less is 20% by volume or more but the average particle size exceeds 3.0 μm, the composite with sufficiently dispersed chromium carbide Silicon nitride cannot be obtained, and sufficient improvement in sinterability and sintered body properties cannot be expected.

When mixing metal silicon powder and chromium carbide powder,
Mix using a ball mill, type mixer, etc., paying careful attention to the dispersibility and agglomeration of chromium carbide.

Next, the mixed powder is nitrided, at which time the bulk density is 1.0 g/an! It is formed into the following compact and then nitrided. The bulk density is determined by the uniform nitriding reaction, which will be explained in detail later.
Very important for qi reactions. Bulk density force cylinder, Og/cd
If it exceeds the nitriding temperature, sintering of the metal silicon powders will proceed before nitriding, and gas-gas reactions will not occur, and furthermore, the diffusion of the nitrogen source will not be sufficient, and unnitrided metal silicon may remain. There are no restrictions on the shape of the molded body. Because,
This is because the reaction of the present invention is a gas-gas reaction, and not a solid-gas reaction as conventionally thought.

Next, this molded body was heated with N at a partial pressure of 0
Nitriding is performed in a nitrogen atmosphere containing H3 and/or N2.

The reason why 02 is included in the atmosphere is that it is necessary to generate and concentrate SiO gas in the microcrystalline field generated by silicon nitride, and the reason why the upper limit is limited to 10-"atom is that This is because if it exceeds the oxidation of Si itself, the amount of oxygen contained in the resulting composite silicon nitride increases, and when it is made into a sintered body, deterioration in high temperature strength etc. is observed. On the other hand, there is no need to limit the lower limit of the 0□ partial pressure because 02 is circulated in the microscopic crystal field, as shown in equations (1) and (2), but if the equipment design is also taken into account. It is about 10-3 atm.

The reason for including NH and/or N2 in the atmosphere is that, similar to 0□, it was determined that the following reaction was occurring. In fact, when nitriding in an N2 atmosphere,
This is because the number of euhedral crystals that are thought to have been generated by the gas-gas reaction has become extremely small, and it is believed that NH3 is essential for promoting the gas-gas reaction described below. However, thermodynamically, this reaction occurs at around 1200°C, so
Even with N2, the same effect as with Nll3 was expected, and in fact, the same effect was observed in the 11□ atmosphere.

5i(s)+KOz(G) −5iO(G)
(1) 3SiO(G)+4Nfls
(G) →5i3N4(S) + 3/20□(G
) +6H2(G) (2) In addition, in the gas-gas reaction during the formation of silicon nitride in equation (2), the mixed and added chromium carbide powder becomes the core of silicon nitride generated in the gas-gas reaction, and nitridation occurs from there. It is thought that silicon grows. Therefore, as described above, the smaller the particle size of the chromium carbide powder used, the greater the effect as a seed.

Next, to explain the temperature increase rate and NZ partial pressure during nitriding, considering the α fraction of the composite silicon nitride obtained, 1150
In the temperature range from °C to 1450 °C, the heating rate is 1
It is desirable to carry out the process at 0°C/h or less and at a N2 partial pressure of 0.8 atm or less. Regarding the relationship between temperature increase rate, N2 partial pressure, and α fraction of the obtained silicon nitride powder, see Japanese Patent Application No. 63-1.
It was described in the specification of No. 98987. That is, it is preferable that the α fraction of the composite silicon nitride powder obtained by the present invention is 80% or more, and if it is less than 80%, there is a risk that the high temperature strength etc. will decrease.

As the nitriding furnace, either a batch furnace or a continuous pusher type can be used.

The composite silicon nitride ingot of the present invention obtained as described above is prepared by a conventional method, for example, after rough crushing or medium crushing, dry or wet crushing with a ball mill, vibration mill, jet mill, attritor mill, etc. The composite silicon nitride powder has a surface area of 7 to 15 n(/g).

The amount of enzyme in the composite silicon nitride powder is desirably 1.5% by weight or less from the viewpoint of improving the properties of the sintered body.

In the present invention, since chromium carbide is added as a seed during nitriding, the dispersibility of chromium carbide in the obtained composite silicon nitride powder is very excellent compared to composite powders produced by conventional mixing methods. Therefore, the properties of the sintered body such as sinterability at high temperature strength and fracture toughness are significantly improved. This will be explained in more detail below with consideration.

If chromium carbide is simply mixed with silicon nitride powder, the dispersibility of chromium carbide can be improved no matter how the conditions are controlled, but there is no chemical bond between chromium carbide and silicon nitride, so sintering Sometimes, first, chromium carbide reacts with the sintering aid, and then silicon nitride melts and precipitates in this liquid phase, causing segregation of chromium carbide and making it impossible to obtain a sintered body structure in which chromium carbide is uniformly dispersed. . On the contrary,
The composite silicon nitride powder obtained by the present invention is a product in which chromium carbide and silicon nitride are evenly and chemically composited by adding chromium carbide powder as seeds and compounding it during nitriding. During sintering, chromium carbide and silicon nitride are melted out simultaneously and uniformly, and chromium carbide is uniformly and uniformly dissolved.
It is possible to obtain a sintered body structure in which the particles are dispersed. And “,
The composite silicon nitride powder obtained by the method of the present invention is
Compared to conventional mixed powders, the amount of chromium carbide dissolved into the liquid phase during sintering is uniform, and the simultaneous dissolution of silicon nitride into the liquid phase and the form of precipitated silicon nitride can be uniformly controlled. It is possible to obtain a sintered body in which sufficiently grown β-columnar crystals with a high aspect ratio and fine β-columnar crystals are evenly mixed in the crystal structure. We believe that these factors significantly contribute to the improvement of high-temperature strength and fracture toughness.

The relationship between the properties of the sintered body and the high temperature strength as described above is described in Japanese Patent Application No. 64-43079.

(Invention of Claim 2) Next, the invention of Claim 2 will be explained. This invention is
The invention according to claim 1, characterized in that the nitriding atmosphere further contains one or more halides selected from the group consisting of alkali metal halides and alkaline earth metal halides. , the purpose is to reduce the oxygen content of composite silicon nitride powder.

To explain in more detail below, in the present invention, the reaction formula for producing silicon nitride is considered to be formula (3) rather than formula (2).

3Si(G)+4Nlb(G)→Si:+N4(S)
+6Hz (G) (3) Taking CaPz (G) as an example of a halide further included in the nitriding atmosphere, the estimated reaction until 5i (G) is generated and its circulation reaction in the microscopic crystal field are expressed by equation (4). ~(7)
Shown below.

5i(S)+%0z(G)-3iO(G)
(4) SiO(G)+CaFz(G
)+Hz(G)-5i (G) +CaO(S) +2
)IF (G) (513Si(G)+4NH
+(G)→5iJ4(S)+6Hz(G)
(6) (CaO(S) +28F (G) -Ca
Fz (G) + lIz (G) + 'A Oz (
G) ) (7) As is clear from this, it is also possible that halide gas circulates in the microscopic crystal field.

The form of solid produced by such a gas-gas reaction is greatly influenced by the degree of supersaturation of the reaction, that is, logkp. In other words, 1ogk at 1300℃ in equation (2)
Whereas p is about 1.6, it is about 46 in equation 3). Therefore, the form of silicon nitride produced by the formula (3) is easy to grind, perhaps because it has a granular shape, so oxygen is not taken in or very little oxygen is taken in during grinding, so a low-oxygen composite silicon nitride powder is used. It has the advantage of being easily obtainable. Moreover, since the reaction of formula (3) itself does not contain oxygen during the reaction, the amount of oxygen in the resulting composite silicon nitride ingot is also small.

As for the concentration of alkali metal and alkaline earth metal halides, for example, as can be seen from the estimated reaction formula mentioned above, if the gas is an alkaline earth metal halide, the concentration is 1 mol or more for 1 mol of Si (S). ,
Further, if it is an alkali metal halide, 2 mo1 or more is sufficient. In reality, since nitriding is not performed all at once, it may be less than that. Regarding the method of including these halides in a nitriding atmosphere, that is, the supply method, for example, halides of alkali metals and alkaline earth metals are charged into a separate furnace, heated and sublimated, and metal silicon powder is charged. This can be done by feeding the solution into the furnace while adjusting the concentration. As the carrier gas in this case, for example, nitrogen or argon is used. Alternatively, a halide may be placed near the metal silicon powder in a furnace in which the metal silicon powder is charged, and the metal silicon powder may be nitrided and the halide sublimated at the same time. can. The supply method is not limited to these. Furthermore, when two or more types of halides are used, they may be introduced separately or as a mixture.

The halide is supplied continuously, intermittently, or occasionally at the temperature at which nitriding is being performed, that is, in the temperature range of 1150°C to 1450°C.

This temporary supply can be achieved, for example, by opening and closing the introduction piping to the sublimation furnace and the nitriding furnace as described above.

The reason for this temporal supply is understood to be that in the microcrystal field, the introduced gaseous halide is circulated within the system, as described above. In fact, even if the halide is introduced up to a temperature of 1350°C and the supply is then stopped, the form of silicon nitride produced is 145°C.
It was no different from the case where the introduction was continued until 0°C.

Examples of halides of alkali metals and alkaline earth metals include Li, Na, K, Mg, Ca
, Sr.

Examples include fluoride, chloride, and bromide of Ba element. Among these, fluorides of Ca, Mg, and Li are particularly preferred. The reason for this is that Si has a stronger affinity for oxygen than Si in the relationship between standard energy of formation and temperature for oxide formation, and as a result, the above-mentioned granulation is further promoted. These halides may be used alone or in combination of two or more.

The composite silicon nitride of the present invention having small granular crystals obtained as described above has a low oxygen content because it is difficult to produce fine powder when pulverized. As for oxygen content, 0
．． It is preferably 6% by weight or less. Normally, such low-oxygen powders are difficult to sinter, but the composite silicon nitride powder according to the present invention has improved sinterability and sufficient high-temperature strength because it is uniformly composited with chromium carbide. The result is a sintered body with improved fracture toughness.

(Invention of Claim 3) Next, the invention of Claim 3 will be explained. In the invention of claim 1 or claim 2, the present invention further comprises adding silicon dioxide powder to the molded body in an amount of 1 part by weight per 100 parts by weight of metal silicon powder.
It is characterized by containing ~5 parts by weight, and its purpose is to promote the above-mentioned gas-chip reaction.

To explain in more detail, since the reaction of formula (1) is difficult to occur in the early stage of nitriding when the metal silicon particles are large, the present invention attempts to promote the gas-gas reaction by causing the reaction of formula (8) below. It is something.

SiO□(S)+H2(G) →5iO(G)+l1
zO(G) (8) In the present invention, if the amount of silicon dioxide used is less than 1 part by weight based on 100 parts by weight of metal silicon powder, it is not possible to produce an easily pulverizable composite silicon nitride; If it is exceeded, there is a risk that 5izON2 will be generated or a large amount of oxygen will be taken in. Regarding the particle size of silicon dioxide, those with a large specific surface area, such as Aerosil, tend to be more effective. The relationship between the addition of silicon dioxide and the morphology and crushability of the resulting silicon nitride is described in detail in Japanese Patent Application No. 198979/1983. The present invention lies in the application of this reaction mechanism.

The composite silicon nitride obtained by the present invention has a diameter of 0.5
It contains whiskers or needle-like crystals as thin as micrometers or less.Those containing such whiskers or needle-like crystals have extremely good crushability, so the specific surface area is 1.
Composite silicon nitride powder of 5 rrr/g or more can be easily produced. Therefore, compared to conventional silicon nitride powders, the material obtained by the present invention is able to obtain a sufficiently dense sintered body even at a lower sintering temperature, or is it possible to obtain a sufficiently dense sintered body at the same sintering temperature? Even if the sintering agent is reduced, a sufficiently densified sintered body can be obtained, and the sintered body has excellent properties such as high-temperature strength and fracture toughness.

〔Example〕

The present invention will be explained in more detail below by giving Examples and Comparative Examples.

= 11-12. 1 to 8 100 parts by weight of metallic silicon powder with a Si purity of 99.9% by weight and a predetermined amount of chromium carbide Cr=Cz powder shown in Table 1 were mixed for 1 hour in a ■ type mixer with an internal volume of 201, and then 0.
150 having the bulk density shown in Table 1 using 5 kg
A compact having a size of about 150 x 30 was formed, loaded into an electric furnace, and nitrided under the conditions shown in Table 1.

The obtained composite silicon nitride ingot was coarsely crushed/medium crushed (show crusher and top grinder) to a size of 0.2 m.
m, and then placed in a ball mill with an internal volume of 21 mm.
Add 100 g of pulverized product under 2 mm, 1 r of 4φ Fe balls, and 200 g of water, and after pulverizing for 20 hours, acid treatment with hydrochloric acid and hydrofluoric acid, filtering, drying, and crushing to obtain composite silicon nitride powder for sintering raw material. was manufactured. The oxygen content, specific surface area, α fraction, and residual Sii of the obtained composite silicon nitride powder were measured. The results are shown in Table 2.

Further, a diagram of the dispersion shape of chromium contained in the composite silicon nitride powder obtained in Example 1 is shown in FIG.

Next, in order to evaluate the sinterability and sintered compact properties of this composite silicon nitride powder, 93 parts by weight of composite silicon nitride powder, 5 parts by weight of YzOa having an average particle size of 1.3 μm, and 5 parts by weight of YzOa having an average particle size of 1.3 μm were added.
Add 2 parts by weight of 4 μm A#zOt, and further 1.1.
1-) Lichloroethane was added and wet mixed in a ball mill for 4 hours, and after drying, it was mixed at a molding pressure of 100 kg/cIA for 6 hours.
After molding into a shape of X10X60m, it weighs 2700 kg.
CIP molding was performed at a molding pressure of /cIa. These molded bodies were placed in a carbon crucible and heated for 1 hour in a N2 gas atmosphere.
A sintered body was obtained by firing at a temperature of 750° C. for 4 hours.

After grinding, the obtained sintered body was measured for relative density, fracture toughness, and three-point bending strength at room temperature and 1200°C. The results are shown in Table 2.

This example is an example in which a simple mixed powder of silicon nitride powder and chromium carbide powder was used instead of the composite silicon nitride powder produced as in the present invention.

Various chromium carbide powders shown in Table 3 were mixed with 100 parts by weight of the silicon nitride powder of Comparative Example 1, and 100 g of the mixed powder and 1 15φ 5iJ4 ball were placed in a ball mill with an internal volume of 21.
1 and dry-mixed for 2 hours to obtain a mixed powder of silicon nitride and chromium carbide, and the sintering thereof was evaluated in the same manner as in Example 1. The results are shown in Table 3.

Further, FIG. 2 shows a diagram of the dispersion shape of chromium contained in the mixed powder of silicon nitride and chromium carbide obtained in Comparative Example 1O.

13-17. '14 100 parts by weight of metallic silicon powder with a Si purity of 99.9% by weight and the predetermined amount of chromium carbide powder shown in Table 4 were mixed into an inner volume of 20 parts by weight.
Mix for 1 hour with an ffi V-type mixer, then add 0.5
150 x 150 with a bulk density of 0.8g/- using
A molded body having a size of approximately 30 mm was formed, and the molded body was loaded into an electric furnace and nitrided. The nitriding conditions are shown in Table 4. At that time, CaFz(G) was heated at 201/h from another electric furnace filled with solid CaF and maintained at 1200°C.
(25°C) while entraining with nitrogen gas.

The obtained composite silicon nitride ingot was pulverized under the conditions of Example 1 to obtain composite silicon nitride powder.

The powder properties of the powder were measured, and the same sintering evaluation as in Example 1 was performed. The results are shown in Table 5.

100 parts by weight of metallic silicon powder with a purity of 99.9% by weight and a specified amount of chromium carbide powder shown in Table 6 and a specific surface area of 30
A predetermined amount of silicon dioxide powder of about rd/g and an internal volume of 2
0I! Mix for 1 hour in a V-type mixer, then mix at 0.5 k
150 x 15 with a bulk density of 0.8 g/cd using
A molded body having a size of 0x30 mm was molded, loaded into an electric furnace, and nitrided under the conditions shown in Table 6.

The obtained composite silicon nitride ingot was pulverized under the conditions of Example 1 to obtain composite silicon nitride powder.

Its powder properties are shown in Table 7.

Table 7 Next, for the obtained powder, the sintering temperature was set to 1700°C.
The sintering evaluation was performed in the same manner as in Example 1 except for the following. The results are shown in Table 8. Also, 94.7 parts by weight of composite silicon nitride powder, 33.8 parts by weight of '1t0, A
Sintering evaluation was performed in the same manner as in Example 1 except that the weight was 1.5. The results are shown in Table 9.

As can be seen from Table 8, the composite silicon nitride powder obtained by further adding silicon dioxide powder has a higher sintering rate than the composite silicon nitride powder obtained by adding silicon dioxide powder at the same amount of sintering aid. The temperature can be lowered from 1750°C to 1700°C. Further, as shown in Table 9, the amount of sintering aid can be reduced from 7 parts by weight to 5.3 parts by weight at the same sintering temperature.

The measured values shown on each side were determined by the following method.

(11 Average particle diameter (μm): Based on particle size distribution meter (laser diffraction method, Microtrac 5PA manufactured by NIL).

(2) 1.0 μm below (volume): Same as above (3) Oxygen amount (
Weight %): Based on TC-136 model 0/N simultaneous analyzer manufactured by LECO.

(4) Specific surface area (n?/g): Based on Cantersoap, Ir BET, manufactured by Yuasa Ionics, one point method.

(5) α fraction (χ): Based on X-ray diffraction using Geiger-Franks RAD-IIB model manufactured by Rigaku Denki Co., Ltd.

(6) Residual Si amount (weight%): Same as above (7) Relative density (χ): Based on Archimedes method.

(8) Three-point bending strength (MPa): Based on Autograph AG-2000A model manufactured by Shimadzu Corporation.

(9) Fracture toughness value (Mpa-m"") s Based on IF method.

〔Effect of the invention〕

The composite silicon nitride powder produced according to the present invention is easily sinterable, and a sintered body having excellent high-temperature strength and fracture toughness can be easily obtained. This is famous because chromium carbide is uniformly dispersed in the structure of the sintered body, and the powder properties related to the generation and growth of β-columnar crystals of silicon nitride are controlled.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the dispersion shape of chromium contained in the composite silicon nitride powder obtained in Example 1, and FIG. 2 is a diagram showing the mixture of silicon nitride and chromium carbide obtained in Comparative Example 10. It is a figure showing the dispersion shape of chromium contained in powder. Both FIGS. 1 and 2 are X-ray images of chromium taken with an analytical electron microscope at a magnification of 1000 times.

Claims (3)

[Claims] 1. The average particle size for 100 parts by weight of metal silicon powder is 3.
A molded article comprising 0.5 to 10 parts by weight of chromium carbide powder in which the content of particles of 0 μm or less and 1.0 μm or less is 20% by volume or more, and the bulk density is 1.0 g/cm^3 or less , containing NH_3 and/or H_2 O_2
A method for producing composite silicon nitride powder, which comprises nitriding in a nitriding atmosphere with a partial pressure of 10^-^3 atm or less, and then pulverizing. 2. The nitriding atmosphere is one selected from the group consisting of alkali metal halides and alkaline earth metal halides.
The method for producing a composite silicon nitride powder according to claim 1, further comprising one or more species. 3. The molded body contains 1 to 100 parts by weight of metal silicon powder.
3. The method for producing a composite silicon nitride powder according to claim 1 or 2, further comprising 5 parts by weight of silicon dioxide powder.