JPH07237971A - Production of silicon nitride reaction sintered compact - Google Patents

Abstract

PURPOSE:To obtain the sintered compact having high fired skin strength (mechanical strength in the case that a surface abrasion is not made after sintering) both at normal and elevated temperatures. CONSTITUTION:(a) A silicon powder mixture 5-300mum in average particle diameter, a mixture of at least two kinds of silicon powder virtually differing in particle size distribution from each other, is incorporated with a sintering auxiliary consisting of a combination of Y2O3 and at least one kind selected from MgO, CeO2, BeO, AIN, La2O3, ZrO2, Fe and Fe2O3, (b) using the resultant mixed powder, a molded form having a density standing at >=70% of the theoretical density is made, (c) this molded form is heated at a temperature of <1500 deg.C in a nitrogen-contg. atmosphere and nitrided, and then, (d) the nitrided molded form is sintered at 1500-2000 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon nitride reaction-sintered body, and particularly to a silicon nitride reaction-sintered body having good burn surface strength (strength when surface polishing is not performed after sintering) at room temperature and high temperature. The present invention relates to a method for producing a tie.

[0002]

2. Description of the Related Art A silicon nitride ceramic sintered body is a gas turbine member because of its high strength, high heat resistance, high thermal shock resistance, high wear resistance, oxidation resistance and the like. For example, it is expected to be used as a structural ceramic that is used under severe conditions at high temperatures.

As a method for producing a silicon nitride-based ceramic sintered body, there is a method in which a molded body having a desired shape is produced using silicon nitride powder and a sintering aid, and this is sintered. As another method, there is a so-called reactive sintering method in which a compact is produced using silicon powder and the compact is nitrided to obtain a silicon nitride sintered body. According to this latter method, the shrinkage seen during sintering can be suppressed to a low level, and a sintered body with relatively high dimensional accuracy can be obtained.
Further, since the raw material cost is low, various engineering ceramic members can be manufactured at low cost. Therefore, various proposals have been made regarding this reaction sintering method.

For example, JP-A-54-160410 discloses a silicon powder having a particle diameter of 0.1 to 44 μm, MgO, Y ₂ O ₃ and C.
eO ₂ , ZrO ₂ , BeO, Mg ₃ N ₂ , AlN, Mg
A compact having a density of 1.3 g / cm ^{3 was} prepared from a mixture with a sintering additive selected from Si, MgAl ₂ O ₄ , La ₂ O ₃ and Fe, and the compact was compacted under a nitrogen atmosphere at 1500 ° C. or lower. It discloses a method of nitriding a body and then sintering at 1500 ° C. in a nitrogen atmosphere. However, in this method, the density of the compact is increased by compression to obtain a high-strength, high-density sintered body, but since the particle size of the silicon powder and its distribution region are not taken into consideration, The density is about 67% of the theoretical value, which is not sufficiently large.

Further, JP-A-56-22678 discloses that the maximum particle size is 2
A method of molding a mixture of metal Si having a size of 5 μm or less and a sintering aid, subjecting the obtained molded body to reaction sintering in an atmosphere containing nitrogen, and then re-sintering at 1600 to 2200 ° C. in an atmosphere containing nitrogen. Is disclosed. However, in this method, although the decomposition and evaporation of silicon nitride on the surface are prevented by controlling the atmospheric pressure at the time of sintering, sufficient burn surface strength cannot be achieved.

However, in the case of a sintered product obtained by such a method, since silicon nitride on the surface is decomposed and evaporated during sintering, unevenness is formed on the surface (so-called rough skin phenomenon occurs), and strength is reduced. . Therefore, in order to remove the roughness of the surface, it is generally necessary to polish the surface of the sintered product.

Therefore, it is an object of the present invention to provide a method for producing a silicon nitride reaction sintered body having good strength at room temperature and high temperature without performing surface polishing after sintering.

[0008]

As a result of earnest research in view of the above objects, the present inventors have found that Y ₂ O can be added to a mixture of two or more kinds of silicon powders having substantially different particle size distribution regions.
₃ , MgO, CeO ₂ , BeO, AlN, La
_If reaction sintering is carried out by adding a sintering aid composed of at least one selected from ₂ O ₃ , ZrO ₂ , Fe and FeO ₃ , the dimensional accuracy and the strength are improved and the burnt surface strength is improved. It was discovered that a sintered body was obtained, and the present invention was completed.

That is, according to the method for producing a silicon nitride sintered body of the present invention, (a) an average particle diameter of 5 to 300 is obtained by mixing two or more kinds of silicon powders having substantially different particle diameter distribution regions.
Y ₂ O ₃ , MgO, and CeO were added to the silicon powder mixture of μm.
₂ , a BeO, AlN, La ₂ O ₃ , ZrO ₂ , Fe and a sintering additive consisting of a combination with at least one selected from FeO ₃ is added, and (b) the theoretical density of the obtained powder mixture is calculated. A molded body having a density of at least 70% is produced, and (c) the molded body is subjected to a nitrogen-containing atmosphere for 15 minutes.
Nitriding is performed by heating at a temperature of less than 00 ° C, and (d) the nitriding formed body is then heated to 1500 ° C to 2 ° C.
It is characterized by being sintered at 000 ° C.

The present invention will be described in detail below. [1] Starting Material (a) Two or more kinds of silicon powders having substantially different particle size distribution regions of silicon powder are mixed and used. For example, silicon powder having a particle size distribution as shown in FIGS. 1 (a) and 1 (b) is used. In FIG. 1 (a), it is preferable that the distribution 1 has a large particle diameter and the distribution 2 having a small particle diameter, and the tails of the curves of the distribution 1 and the distribution 2 do not substantially overlap. When the distribution 1 and the distribution 2 largely overlap each other (when a large amount of particles exist in the region V in the figure), the green density decreases. In a preferred embodiment, the particle size of distribution 1 is in the range of 10-80 μm, the average particle size is 20-50 μm, and the particle size of distribution 2 is 1-20.
Within the range of μm, the average particle size is 2-5 μm.

When the silicon powder having such two distribution regions is used, the weight ratio of the silicon powder of distribution 1 having a large particle diameter to the silicon powder of distribution 2 having a small particle diameter is 5: 5 to 9: 1.
Is preferable, and more preferably 7: 3 to 8: 2. In a preferred embodiment, it is about 7: 3.

Further, in FIG. 1B, there are three distributions 1, 2, and 3. Even in this case, it is preferable that the distributions do not substantially overlap. In a preferred embodiment, the particle size of distribution 1 is in the range of 20-80 μm and the average particle size is 30.
˜50 μm, the particle size of distribution 2 is in the range of 5 to 20 μm, the average particle size is 10 to 15 μm, the particle size of distribution 3 is in the range of 0.5 to 5 μm, and the average particle size is 1 ~ 2 μm. The powder mixing ratio is 100%, and the distribution is 1
60 to 80% of the silicon powder of 10 to 10% of the silicon powder of distribution 2
It is preferable that the silicon powder of 30% and the distribution 3 is 5 to 20%. More preferably, the silicon powder of distribution 1 is 65-75.
%, The silicon powder of distribution 2 is 15 to 25%, and the silicon powder of distribution 3 is 5 to 15%.

The average particle size of the above silicon powder mixture is 5 to 30.
It must be 0 μm. If the average particle size is less than 5 μm, the density of the molded product is reduced and the shrinkage rate due to sintering is increased, so that good dimensional accuracy cannot be obtained. Further, the strength and toughness of the obtained sintered body are also reduced. On the other hand, the average particle size is 300
If a silicon powder having a particle size of more than μm is used, it takes a long time for nitriding and the moldability is deteriorated. Preferably, the silicon powder has an average particle size of 5 to 50 μm.

The maximum particle size of the silicon powder mixture is 50 to 50.
It is preferably in the range of 600 μm. Maximum particle size is 50
If a silicon powder having a particle size of less than μm is used, the density of the compact tends to decrease, and shrinkage due to sintering tends to increase. On the other hand, if a silicon powder having a maximum particle size of more than 600 μm is used, nitriding is difficult and moldability is poor, which is not preferable. The more preferable range of the maximum particle size of the silicon powder is 50 to 100 μm.
Is.

In order to improve the moldability of the silicon powder mixture, 0.1 to 1 μm, preferably 0.2 to 0.5 μm.
α-Si ₃ N ₄ powder having an average particle size of m may be added. The amount of α-Si ₃ N ₄ added is 100
The amount of α-Si ₃ N ₄ is preferably 10 to 30 parts by weight, more preferably 15 to 20 parts by weight, based on parts by weight.

(B) Sintering aid Y ₂ O ₃ as a sintering aid, MgO, CeO ₂ , Be
O, AlN, La ₂ O ₃ , ZrO ₂ , Fe and FeO ₃
Or a combination with at least one selected from
A combination of these and Al ₂ O ₃ is added. By using this sintering aid, sufficient high temperature strength can be achieved even if sintering is performed at a low temperature. In addition, since decomposition and evaporation of silicon nitride on the surface of the sintered body that occurs when sintering at high temperature due to low-temperature sintering can be prevented, surface roughness is prevented, and burnt surface strength (strength in a state where it is not polished as it is sintered) ) Is improved. The average particle size of these sintering aids is preferably about 0.1 to 5 μm. Further, as a preferable sintering aid, Y ₂ O is used.
₃ and MgO, or a combination of Y ₂ O ₃ , Al ₂ O ₃ and MgO may be mentioned.

3% to 10% by weight of Y ₂ O ₃ with the total of silicon powder (weight converted to Si ₃ N ₄ ), sintering aid and Si ₃ N ₄ powder (when added) as 100% by weight. Is preferable, and more preferably 5 to 7% by weight. In addition, MgO, CeO ₂ , BeO, AlN, La ₂ O ₃ ,
Is preferably at least one of a 1-7% by weight selected from ZrO _2, Fe and Fe ₂ O _3, more preferably 3 to 6 wt%. The total amount of the sintering aid is 5 to 1
It is preferably 5% by weight, more preferably 8 to 13
Weight% If the amount of each sintering aid is less than the lower limit value of the above range, the sinterability is poor. On the other hand, it is not preferable to add a sintering additive in an amount exceeding the upper limit of the above range, because the high temperature strength of the sintered body will decrease.

[2] Method for manufacturing silicon nitride sintered body (a) Preparation of molded body First, the components (a) and (b) are mixed so as to have the above-mentioned mixing ratio. This mixture can contain various organic binders in addition to the above-mentioned ceramic components. Examples of such an organic binder include ethyl silicate, polyethylene glycol, polyvinyl alcohol (PVA), acrylic emulsion, polyurethane emulsion and the like. Also, an inorganic binder can be added.

The components (a), (b), the binder (if necessary) and the like can be mixed by a known method such as a ball mill or a kneader. In addition, in the mixing by the ball mill, a wet method in which a dispersion medium such as water, ethanol or butanol is added to the powder mixture may be used in addition to the dry method.

Each of the conventionally known methods such as die molding, cold isostatic pressing (CIP), slip casting, and injection molding can be used for producing the molded body, but molding of a complicated shape is possible. Slip casting and injection molding are preferred for producing the body.

(B) Nitriding treatment Next, the compact is heated in a nitrogen-containing atmosphere, preferably in a nitrogen gas atmosphere, to nitride the silicon powder in the compact.

In the nitriding treatment, the treatment temperature, the pressure of the nitrogen-containing atmosphere and the treatment time are set so that 90% or more, and more preferably 95% or more of the silicon in the compact is nitrided into silicon nitride. . In the present specification, the degree of nitriding is expressed as a percentage, which is calculated from the weight change of the molded body (the weight change associated with the change of Si in the molded body to Si ₃ N ₄ ).

The various conditions of the nitriding treatment need to be changed to some extent depending on the thickness of the molded body and the like, but the treatment temperature should be 1250 ° C. or higher and less than 1500 ° C. The pressure of the nitrogen-containing atmosphere is preferably 1 kg / cm ² or more. Temperature is 1250
If the temperature is lower than 0 ° C or the pressure of the nitrogen-containing atmosphere is lower than 1 kg / cm ² , nitriding of the silicon powder in the molded body does not proceed well. On the other hand, if the heating temperature is 1500 ° C. or higher, Si is eluted and vaporization of Si occurs, which is not preferable.
The nitriding time varies depending on the thickness of the compact, the nitriding temperature, etc., but is generally about 1 to 10 hours. More preferably, the temperature of the nitriding treatment is 1350 to 1450 ° C.
And the pressure of the nitrogen-containing atmosphere is 5 to 2000 kg / cm ²
Is.

When the nitriding treatment is performed under the above conditions, the silicon particles in the compact are nitrided to produce Si ₃ N ₄ containing α-Si ₃ N ₄ . When the silicon particles are nitrided and silicon nitride is generated, the particles in the compact expand, and the pores (voids between the powder particles) existing in the compact are greatly reduced.

(C) Sintering In the present invention, the molded body after the above nitriding treatment is further sintered at a temperature of 1500 ° C. or higher, preferably 1500 to 2000 ° C., more preferably 1700 to 2000 ° C. To do. If the sintering temperature is less than 1500 ° C, the strength and toughness of the sintered body will decrease. Sintering is performed in a non-oxidizing atmosphere, preferably a nitrogen gas atmosphere. At this time, the atmospheric gas pressure is preferably about 5 to 2000 kg / cm ² . Further, the sintering time (time kept at 1500 ° C. or higher) is preferably about 1 to 5 hours.

By performing the sintering within the above temperature range, the α-Si ₃ N ₄ particles produced by the above nitriding treatment are changed into acicular β-Si ₃ N ₄ crystal particles. When the acicular β-Si ₃ N ₄ crystal particles are densely formed in this manner, the strength and toughness of the sintered body are significantly improved.

In the present invention, sintering may be performed in a state in which the above-mentioned nitriding-formed compact is buried in the rough skin preventing powder. It is preferable to use a mixture of silicon nitride powder and silicon powder as the powder for preventing roughening of the sintered body.
Further, a sintering aid and an additive such as boron nitride may be mixed. The average particle size of these powders is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm. In addition, the mixing ratio of the rough skin preventing powder is such that the total amount of the rough skin preventing powder is 100% by weight, and the silicon nitride powder is 70% by weight.
˜99 wt% and silicon powder is preferably 1 to 30 wt%. More preferably, the silicon nitride powder is 90 to 99% by weight and the silicon powder is 1 to 10% by weight. When a sintering aid, boron nitride and the like are mixed, the entire surface roughening prevention powder is set to 100% by weight and the silicon nitride powder is added in an amount of 40 to 8%.
9% by weight, 1 to 30% by weight of silicon powder, additives 10 to 3
It is preferably 0% by weight. More preferably, the silicon nitride powder is 65 to 84% by weight, the silicon powder is 1 to 10% by weight, and the additive is 15 to 25% by weight. In a preferred embodiment, the weight ratio of silicon nitride powder to silicon powder is 9: 1. By sintering in the powder for preventing skin roughening, decomposition and evaporation of silicon nitride on the surface of the molded body can be prevented, so that the formation of irregularities on the surface of the sintered product is prevented and the burnt surface strength is improved. . In this case, other sintering conditions may be the same as the above-mentioned sintering.

[0028]

EXAMPLES The present invention will now be described in more detail with reference to specific examples, but the present invention is not limited thereto. Example 1 Silicon powder having an average particle size of 33.6 μm and a particle size range of 20 to 80 μm, and an average particle size of 3.5 μm and a particle size range of 1 to 2
A mixture with 0 μm of silicon powder has an average particle size of 0.4-
0.5 μm α-Si ₃ N ₄ powder, Y ₂ O ₃ powder having an average particle size of 1.4 μm as a sintering aid, and an average particle size of 0.
3 to 0.5 μm of MgO powder was blended in the ratio shown in Table 1 below.

Table 1 Component ratio (wt% ) Silicon and silicon nitride powder Large particle size powder (Average particle size 33.6 μm) 55.4 ⁽¹⁾ Small particle size powder (Average particle size 3.5 μm) 23.8 ⁽¹⁾ α-Si ₃ N ₄ powder 8.8 Sintering aid Y ₂ O ₃ powder 7 MgO powder 5 Note (1): The weight% of silicon powder is the Si ₃ N ₄ conversion value.

80 parts by weight of ethanol was added to 100 parts by weight of this powder mixture, and ball mill mixing was carried out at 170 rpm for 18 hours using a ball mill in which one mill ball was placed in a polyethylene pot.

The obtained mixture was dried by a rotary evaporator, and was pressed by a mold and CIP (3000 kg / cm).
² ), and molded into a size of 30 mm × 50 mm × 5 mm.

After drying the obtained molded body, 9 kg /
Nitriding was performed at 1450 ° C. for 4 hours in a nitrogen atmosphere of cm ² .

After the nitriding treatment, it was cooled, the molded body was embedded in powder for preventing rough skin, the temperature was raised to 1700 ° C. and kept for 4 hours, and sintering was carried out in a nitrogen atmosphere of 9 kg / cm ² . The powder for preventing rough skin has an average particle size of 26.2 μm.
Silicon powder and α-S having an average particle size of 0.4 to 0.5 μm
A mixture of i ₃ N ₄ powder and a weight ratio of 1: 9 was used.

The surface of the obtained sintered body was not polished,
Ceramics 3 for burnt surface strength at room temperature and 1300 ° C
The point bending was measured according to the JIS method. Table 6 shows the measurement results of the density of the molded body, the nitriding degree of the calcined body (molded body after nitriding treatment), and the burn surface strength of the sintered body together with the sintering conditions.

Example 2 The same silicon powder mixture as in Example 1 was used, but with an average particle size of 0.4 to
0.5 μm α-Si ₃ N ₄ powder and Y as a sintering aid
₂ O ₃ powder and MgO powder were mixed in the proportions shown in Table 2 below, and ball mill mixing, drying, molding, nitriding and sintering were carried out in the same manner as in Example 1 to obtain a silicon nitride reaction sintered body.

With respect to the obtained sintered body, burnt strength at room temperature and 1300 ° C. was measured in the same manner as in Example 1. Table 6 shows the measurement results of the density of the molded body, the nitriding degree of the calcined body, and the burnt surface strength of the sintered body together with the sintering conditions.

Table 2 Component ratio (wt%) Silicon and silicon nitride powder Large particle size powder (Average particle size 33.6 μm) 56.7 ⁽¹⁾ Small particle size powder (Average particle size 3.5 μm) 24.3 ⁽¹⁾ α-Si ₃ N ₄ powder 9 Sintering aid Y ₂ O ₃ powder 5 MgO powder 5 Note (1): The weight% of silicon powder is a Si ₃ N ₄ conversion value.

Comparative Example 1 In the same manner as in Example 1, silicon powder having an average particle size of 26.2 μm was added to α-Si ₃ N ₄ having an average particle size of 0.4 to 0.5 μm.
As a powder and a sintering aid, Y ₂ O ₃ powder and Al ₂ O ₃ powder were blended in a ratio shown in Table 3 below. Example 1 using this mixture
Ball mill mixing, molding, and nitriding were performed in the same manner as in. Then, at 1900 ° C. in a nitrogen atmosphere (nitrogen gas pressure:
Sintering was performed for 4 hours at 9 kg / cm ² ) to obtain a silicon nitride sintered body.

With respect to the obtained sintered body, burnt strength at room temperature and 1300 ° C. was measured in the same manner as in Example 1. Table 6 shows the measurement results of the density of the molded body, the nitriding degree of the calcined body, and the burnt surface strength of the sintered body together with the sintering conditions. Table 3 Component ratio (wt%) Silicon and silicon nitride powder Silicon powder (average particle size 26.2 μm) 86.8 ⁽¹⁾ α-Si ₃ N ₄ powder 9.7 Sintering aid Y ₂ O ₃ powder 2 .5 Al ₂ O ₃ powder 1.0 Note (1): The weight% of silicon powder is the Si ₃ N ₄ conversion value.

Comparative Example 2 In the same manner as in Example 1, silicon powder having an average particle diameter of 5.9 μm, α-Si ₃ N ₄ powder having an average particle diameter of 0.4 to 0.5 μm and a sintering aid were used. Y ₂ O ₃ powder and Al ₂ O ₃ powder were blended in the proportions shown in Table 4 below. Using this mixture, ball mill mixing, molding and nitriding were performed in the same manner as in Example 1. Then, at 1900 ° C. in a nitrogen atmosphere (nitrogen gas pressure:
Sintering was performed for 4 hours at 9 kg / cm ² ) to obtain a silicon nitride sintered body.

With respect to the obtained sintered body, burnt strength at room temperature and 1300 ° C. was measured in the same manner as in Example 1. Table 6 shows the measurement results of the density of the molded body, the nitriding degree of the calcined body, and the burnt surface strength of the sintered body together with the sintering conditions.

Table 4 Component ratio (wt%) Silicon and silicon nitride powder Silicon powder (average particle size 5.9 μm) 86.8 ⁽¹⁾ α-Si ₃ N ₄ powder 9.7 Sintering aid Y ₂ O ₃ Powder 2.5 Al ₂ O ₃ powder 1.0 Note (1): The weight% of silicon powder is the Si ₃ N ₄ conversion value.

Comparative Example 3 The same silicon powder mixture as in Example 1 was used, but with an average particle size of 0.4 to
0.5 μm α-Si ₃ N ₄ powder and Y ₂ as a sintering aid
O ₃ powder and Al ₂ O ₃ powder were blended in the proportions shown in Table 5 below. Thereafter, in the same manner as in Example 1, ball mill mixing, molding, and nitriding treatment were performed. Then, sintering is performed at 1900 ° C. in a nitrogen atmosphere (nitrogen gas pressure: 9 kg / cm ² ) for 4 hours,
A silicon nitride sintered body was obtained.

With respect to the obtained sintered body, burnt strength at room temperature and 1300 ° C. was measured in the same manner as in Example 1. Table 6 shows the measurement results of the density of the molded body, the nitriding degree of the calcined body, and the burnt surface strength of the sintered body together with the sintering conditions.

Table 5 Component ratio (wt%) Silicon and silicon nitride powder Large particle size powder (average particle size 33.6 μm) 60.8 ⁽¹⁾ Small particle size powder (average particle size 3.5 μm) 26.0 ⁽¹⁾ α-Si ₃ N ₄ powder 9.7 Sintering aid Y ₂ O ₃ powder 2.5 Al ₂ O ₃ powder 1.0 Note (1): The weight% of silicon powder is the Si ₃ N ₄ conversion value.

Table 6 Calcined Surface Burning Strength ⁽³⁾ Sintering Conditions Compact Density ⁽¹⁾ Nitriding Degree ⁽²⁾ Room Temperature 1300 ° C Temperature Time Example NO. (%) (%) (MPa) (MPa) (° C ) (HR) example 1 70.7 96 610 405 1700 4 example 2 71.3 98 590 415 1700 4 Comparative example 1 66.0 95 420 287 1900 4 Comparative example 2 65.2 98 436 - 1900 4 Comparative example 3 70. 4 95 492 350 1900 4 Note (1): Theoretical density (2): Measured by weight change of molded body (3): Strength measured without sintering surface after sintering 3 points of ceramics Bending Measured according to JIS method

As is clear from Table 6, a mixture of a silicon powder having a large particle diameter and a silicon powder having a small particle diameter is used as a raw material silicon powder, and a sintering aid composed of Y ₂ O ₃ and MgO is used. As a result, the burnt surface strength of the sintered body was significantly improved.

[0048]

As described above in detail, according to the method of the present invention, decomposition and evaporation of silicon nitride on the surface due to sintering can be prevented, and the smoothness of the surface can be improved. It is possible to obtain a silicon nitride sintered body having burnt surface strength. The silicon nitride reaction-sintered body produced by the method of the present invention has a small shrinkage due to sintering and can be formed into a near-net shape, so that it is particularly suitable for a ceramic member having a complicated shape.

[Brief description of drawings]

FIG. 1 is a graph schematically showing a particle size distribution of a silicon powder mixture used for producing a molded body of the present invention, (a) showing a two-peak distribution and (b) showing a three-peak distribution.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location 102 H

Claims (5)

[Claims] 1. (a) An average particle size obtained by mixing two or more kinds of silicon powders having substantially different particle size distribution regions is 5 to 5.
In a 300 μm silicon powder mixture, Y ₂ O ₃ , MgO,
CeO ₂ , BeO, AlN, La ₂ O ₃ , ZrO ₂ , F
e and a sintering aid consisting of a combination with at least one selected from FeO ₃ are added, and (b) a molded body having a density of at least 70% of the theoretical density is produced from the obtained powder mixture, c) Nitriding treatment is performed by heating the molded body under a nitrogen-containing atmosphere at a temperature of less than 1500 ° C., and (d) Next, the nitrided molded body is heated to 1500 ° C.
A method of manufacturing a silicon nitride reaction sintered body, which comprises sintering at 2000 ° C. 2. The method for producing a silicon nitride reaction sintered body according to claim 1, wherein the sintering aid is Y ₂ O ₃ and MgO.
A method for producing a silicon nitride sintered body, comprising: 3. The method for manufacturing a silicon nitride reaction sintered body according to claim 1, wherein the sintering aid is Al.
_A method for producing a silicon nitride sintered body, which comprises ₂ O ₃ . 4. The method for producing a silicon nitride reaction sintered body according to any one of claims 1 to 3, wherein in the step (d), the silicon nitride is sintered by being buried in a rough skin preventing powder. Manufacturing method of sintered body. 5. The method for manufacturing a silicon nitride reaction sintered body according to claim 4, wherein the rough skin preventing powder is a mixture of silicon powder and silicon nitride powder. Manufacturing method.