JP2610156B2 - Method for producing silicon nitride powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing silicon nitride powder using a reaction system of SiO ₂ -seed powder-NH ₃ -CmHn.

2. Description of the Related Art Japanese Patent Application No. 56-187762 discloses a method in which silicon nitride powder synthesized by a silica reduction method is mixed with silica powder as a seed powder, and the mixed powder is heated to produce a silicon nitride powder. .

According to this method, a relatively stable quality silicon nitride powder can be obtained in a high yield. In this case, silicon nitride powder synthesized by the silica reduction method is used as seed powder,
It is a stable source for the deposition and growth of silicon nitride.

Problems to be Solved by the Invention However, silicon nitride powder conventionally used as seed powder is synthesized by a SiO ₂ —CN ₂ silica reduction method. This silicon nitride powder contains 0.5 to 1.5% by weight of carbon in the grains.

Thus, when silicon nitride powder containing a relatively large amount (0.5 to 1.5% by weight) of carbon is used as a seed,
A portion having a relatively high carbon content is unevenly distributed also in the synthesized silicon nitride powder. Carbon in silicon nitride reacts with silicon nitride or silicon oxide during sintering to generate gas, which causes pores. Therefore, the density and strength of the sintered body are reduced.

The present applicant has proposed SiO ₂ proposed in Japanese Patent Application No. 61-308195.
- According to the seed powder -NH ₃ -CmHn synthetic method, it is possible to obtain a relatively small silicon nitride carbon content. However, when silicon nitride synthesized by a SiO ₂ —C—N ₂ -based silica reduction method is used as the seed powder, carbon is unevenly distributed in the obtained silicon nitride. Occurs.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a method for producing a silicon nitride powder having a low carbon content and excellent sinterability.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for producing a silicon nitride powder according to claim 1.

Means for Solving the Problems According to the method for producing silicon nitride powder of the present invention, mixed powder of silica powder and seed powder is mixed with NH ₃ and hydrocarbon gas (CmH
n), wherein the silica powder is heated in a second mixed gas composed of NH ₃ and hydrocarbon gas (CmHn) as the seed powder. The manufactured silicon nitride powder is used.

As the mixed powder, it is desirable to use a powder obtained by mixing silicon nitride powder at a ratio of 0.005 to 1 part by weight with respect to 1 part by weight of silica powder. Further, when the total carbon content of the silicon nitride powder is 0.3% by weight or less, the total carbon content of the synthesized silicon nitride powder can be kept low, and as a result, the uneven distribution of carbon can be advantageously eliminated.

In a mixture of silica powder and silicon nitride powder as seed powder, if the silicon nitride powder is less than 0.005 parts by weight per 1 part by weight of the silica powder, the effect of increasing the yield is small, and if it is more than 1 part by weight. In addition to the low yield, the characteristics of the added silicon nitride powder become remarkable and the original purpose cannot be achieved.

Referring to the optimum conditions in the manufacturing method of silicon nitride according to the present invention, the mixing ratio of the first and second mixed gas is, NH ₃ / CH ₄ in terms of CmHn to CH ₄ carbon reference = 0.5 to 20
00 (capacity ratio) is desirable. Here, the reason for mixing the CmHn gas is to remove H ₂ O generated by the reaction, thereby increasing the reaction speed and lowering the total oxygen content of the synthetic powder. Further so as to contain N ₂ or other inert gas as required. The amount of NH ₃ is NH ₃ /
When CH ₄ is less than 0.5, the reducing action of NH ₃ on silica is weakened, and the reaction does not proceed, and silicon nitride tends to be hardly generated. If the amount of NH ₃ in the opposite is more than NH ₃ / CH ₄ = 2000, the effect of the hydrocarbon gas removing H ₂ O formed during the reaction is reduced, the total oxygen content is increased tendency of the synthetic powder is there. The compositions of the first and second mixed gases may be the same or different. Further, the heating temperature is preferably set to 800 to 1600 ° C. If the heating temperature is lower than 800 ° C., the reaction may not substantially proceed. On the other hand, if the temperature is higher than 1600 ° C., the rate of thermal decomposition of NH ₃ itself may be too high to obtain a desired effect.

The present invention is based on Japanese Patent Application No. 61-308195 filed by the present applicant.
Various modifications within that range are possible based on.

Example Silica powder having an average particle size of 0.05 μm was NH ₃ : 300 l / hour, C ₃ H
The mixture was heated at 1400 ° C. for 4 hours in a second mixed gas stream of ₈ : 3 l / hour to obtain silicon nitride powder having a total carbon content of 0.12% by weight. The silicon nitride powder thus obtained was used as a seed powder, and silica having an average particle diameter of 0.05 μm was added to SiO ₂ : Si ₃ N ₄ = 1: 0.1.
(Weight ratio), NH ₃ = 300 l / h, C ₃ H ₈ =
The mixture was heated at 1400 ° C. for 1 hour in a first mixed gas flow of 15 l / hour to obtain α-type silicon nitride powder. (Example 1) Similarly, synthesis of α-type silicon nitride powder was attempted for Examples 2 and 3 under the conditions shown in Table 1 with the kind and blending ratio of seed powder.

On the other hand, as silicon nitride as seed powder, SiO ₂ -C
This was shown as Comparative Example 1 using a product produced by a —N ₂ -based silica reduction method. Comparative examples 3 and 4 show the case where silicon nitride produced by the silicon direct nitriding method and the gas phase method was used as seed powder. Note that Comparative Example 2 is similar to Examples 1 to
3 just as the silicon nitride produced by SiO ₂ -NH ₃ -CmHn synthetic methods as those used as seed powder.

Using the powders of Examples 1 to 3 and Comparative Examples 1 to 4 obtained by the above operation, Al ₂ O ₃ and Y ₂ O ₃ were used as sintering aids in an N ₂ atmosphere.
Sintered at 750 ° C for 2 hours. Thereafter, a test piece cut out to 3 × 4 × 40 mm was used as a test piece, and the bending strength was measured at room temperature according to JIS. The results are shown in the column of sintered body characteristics in Table 1.

From Table 1, it has been clarified that the sintered body using the α-type silicon nitride powder synthesized by the method for producing silicon nitride according to the present invention as a raw material has high strength, small standard deviation, and stable characteristics. In addition, the bending strength shows the average value of the results obtained for 10 test pieces. The composition ratio shown in the column of atmosphere in Table 1 is a value obtained by converting C ₃ H ₈ into CH _{4 based} on carbon.

Effect of the Invention According to the method for producing silicon nitride powder of the present invention, the method of synthesizing the seed powder and the silicon nitride powder using the same is the same method, and the generated silicon nitride is easily incorporated on the crystal nuclei of the seed powder. A stable and homogeneous powder can be obtained.

In addition, since silicon nitride powder having a low carbon content is used as seed powder, it is possible to eliminate uneven distribution of carbon contained in the generated silicon nitride.

Since the silicon nitride powder produced according to the present invention has excellent sintering properties, a homogeneous sintered body can be obtained, its strength is high, and its characteristics have little variation.

Claims (1)

(57) [Claims] 1. A mixed powder of silica powder and seed powder is mixed with NH ₃
A silicon mixed powder comprising NH ₃ and a hydrocarbon gas (CmHn) as the seed powder, wherein the silicon powder is heated in a first mixed gas composed of nitrogen and hydrocarbon gas (CmHn). A method for producing silicon nitride powder, comprising using silicon nitride powder produced by heating in a furnace.