JPH0649565B2 - Method for producing α-type silicon nitride powder - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing α-type silicon nitride (α-type Si ₃ N ₄ ) powder, and provides high-quality α-type Si ₃ N ₄ powder at high yield. The obtained manufacturing method is related.

[Technical background of the invention and its problems] For example, a silicon nitride yttrium monoxide or magnesium oxide (Si ₃ N ₄ -Y ₂ O ₃ or Si ₃ N ₄ -MgO system) sintered body has high mechanical strength and heat resistance. Due to its excellent properties, application of high temperature to Starhin members has been attempted. However, when the above-mentioned Si ₃ N ₄ system sintered body is put to practical use as a high temperature and high stress material, physical and chemical stability and reliability at high temperature are strictly required. For this reason, strict process control and quality control are indispensable in the manufacturing process of the sintered body, but the raw material silicon nitride powder is particularly important as the starting point of the process. For example, the characteristics of the raw material powder are not simply high-purity and fine powders, but the characteristics that have an influence must be within a narrow proper range.

By the way, as a synthesis method of Si ₃ N ₄ powder, (1) a method of nitriding metallic silicon powder 3Si + 2N ₂ → Si ₃ N ₄ (2) a gas phase reaction method using silicon tetrachloride or silane and ammonia as a raw material 3SiCl ₄ + 4NH ₃ → Si ₃ N ₄ + 12HCl etc. (3) Method of nitriding SiO obtained by reducing silica (SiO ₂ ) with carbon (C) in a stoichiometric ratio 3 SiO ₂ + 6C + 2N ₂ → Si ₃ N ₄ + 6CO Has been.

However, in the case of (1), nitriding of Si is an exothermic reaction, and it is necessary to devise a process for controlling the exothermic. For example, Si having relatively coarse grains is selected and finely pulverized after nitriding. For this reason, the inclusion of impurities is unavoidable (crushing process), and it does not hinder the use as a general heat-resistant material such as bricks, but it is not suitable for high-temperature gas turbines.

In the case of (2), for example, it is suitable for surface coating of semiconductor elements, but it cannot be said to be mass-produced for inorganic heat-resistant materials and is not suitable for industrial production.

In the case of (3), it is necessary to use sufficiently purified SiO ₂ and C powders as a raw material, and in addition to Si ₃ N ₄ , silicon carbide, silicon oxynitride, etc. are often mixed in the generated powder. There is. However, there is an advantage that the reaction operation does not require complexity, and it is possible to improve and stabilize the quality by adding a small amount of "seed" Si ₃ N ₄ to the starting material in advance in order to accelerate the reaction and control the particles of the produced powder. Became. However, as described above, the raw material powder for a high-performance sintered body does not have to be a high-purity, fine powder, and the characteristics that greatly affect the production of the sintered body, for example, included in the raw material powder. The amount of oxygen supplied has a narrow proper range. Looking at silica-reduced Si ₃ N ₄ powder from this perspective, the synthetic reaction
Since the solid phase reaction of O ₂ and C particles is the starting point, excess C is indispensable for smoothing the reaction, and excess C must be removed after Si ₃ N _{4 is} produced. Usually, it is carried out by the method of oxidization removal (heat treatment at 700 ° C in air), but a slight amount of oxidation on the surface of the Si ₃ N ₄ particles generated in this step is unavoidable, and as a result, the oxygen content in the raw material powder increases. Inevitable. Si
Although sintering of ₃ N ₄ is believed to proceed in the liquid phase sintering through the glassy substance that in the reaction of the additive with the silica (containing oxygen) present in Si ₃ N _4, after completion of sintering Since mechanical properties at high temperatures cause deterioration, composition or crystallization treatment is being studied in order to reduce the amount of glassy substances.

[Object of the Invention]

The present invention is based on such knowledge, and a production method capable of obtaining a high yield of α-type Si ₃ N ₄ powder suitable for Si ₃ N ₄ high temperature and high stress material without requiring complicated operations or reaction devices. Is to provide.

[Outline of Invention]

To explain the invention in detail, a specific surface area of 50 m ² / g or more silica (SiO ₂₎ powder, 1 part by weight, a specific surface area of 50 m ² / g or more carbon (C) powder 0.39 to 0.41 parts by weight, and silicon nitride (Si
₃ N ₄ ) powder 0.005 to 1 part by weight of a mixed powder is heat-treated at 1350 to 1550 ° C. in an atmosphere containing nitrogen to carry out reduction and nitriding reactions.
₃ N ₄ ) This is a method for producing powder.

In the present invention, the weight mixing ratio of the SiO ₂ —C—Si ₃ N ₄ system is 1: 2.
The reason for choosing 0.39 to 0.41: 0.005 to 1.0 is as follows. That is, if C per 0.3 part by weight of SiO ₂ is less than 0.39, unreduced residual SiO ₂ increases and the formation of Si ₂ ON ₂ becomes remarkable, and the oxygen content in the synthetic powder is large, resulting in high temperature and high strength Si ₃ N ₄ firing. Not suitable for the production of ties. Also, when it exceeds 0.41, Si ₃ N _{4 formed}
Since the excess C is mixed as an impurity in the powder, it is not suitable as a raw material for a sintered body.

On the other hand, when the ratio of Si ₃ N ₄ to SiO ₂ is less than 0.005, α-type Si ₃ N
₄ is less effective in increasing the yield, and conversely, when it exceeds 1, the powder having the preferable powder characteristics obtained by the oxide reduction cannot be obtained, and the characteristics of the added Si ₃ N ₄ powder become remarkable and the original purpose can be achieved. Absent. However, it is preferable that the raw material composition of each of SiO ₂ , C and Si ₃ N ₄ is high purity of about 99% or more, and the average particle size of SiO ₂ and C is 1 μm.
The particle size is preferably m or less, and Si ₃ N ₄ is preferably as fine as possible, for example, 2 μm or less. The Si ₃ N ₄ used as a raw material is preferably of α type, but it may be one containing β type or other element such as Al or O in solid solution. Further, instead of Si ₃ N ₄ , silicon carbide SiC silicon oxynitride compound such as Si ₂ ON ₂ alone or a mixture thereof (including Si ₃ N ₄ ), or even if a part of these is placed with metallic Si You can get a great reaction promotion effect. However, SiC, S
When i ₂ ON ₂ is used, it tends to be slightly inferior in terms of purity. Hereinafter, the description will be focused on the addition of Si ₃ N ₄ .

In the present invention, when the SiO ₂ —C—Si ₃ N ₄ mixture is heated and calcined, the atmosphere is mainly N ₂ , NH ₃ , N ₂ -hydrogen (H ₂ ), N ₂ —inert gas or the like system. Reaction gas is N ₂ or NH ₃
Must. The reason is that high purity α type finally
This is because it was experimentally confirmed that the formation of Si ₃ N ₄ is greatly affected. On the other hand, the heating and firing temperature in the atmosphere containing N ₂ or NH ₃ as the main reaction gas is selected within the range of 1350 to 1550 ° C. The reason is that Si ₃ N ₄ is less likely to be generated below 1350 ° C, and that SiC is generated above 1550 ° C, so that the desired α-type Si ₃ N ₄ system powder suitable for high temperature and high stress materials is obtained. Because I can't.

As described above, while C acting as a reducing action in the reduction and nitriding reaction of SiO ₂ is used with a mixing ratio near the stoichiometric ratio,
According to the present invention in which Si ₃ N ₄ coexists, the reduction of SiO ₂ is greatly promoted, and the produced Si ₃ N ₄ grows smoothly with the previously added Si ₃ N ₄ as a nucleus, and α-type Si _{It is} possible to obtain a high-quality α-type Si ₃ N ₄ based powder having a high content of ₃ N ₄ in a high yield.

Therefore, according to the present invention, Si ₃ N that requires high temperature and high stress
_The reason why α-type Si ₃ N ₄ system powder suitable for manufacturing a ₄ system sintered body can be easily obtained is considered as follows.

First, regarding the mixing ratio of C, the origin of the silica reduction reaction is considered to be a solid-state reaction at the interface of SiO ₂ particles as described above,
Reactions with many interfaces proceed smoothly. In this case, the degree (state) of the interface is also related to the average particle size of SiO ₂ and C, but in reality, it is greatly related to the specific surface areas of both. Here, in the present invention, the numerical value of the specific surface area of 50 m ² / g or more is an essential condition for the above reason. As a result, a sufficiently high-quality Si ₃ N ₄ powder is synthesized even if the amount of C required to reduce SiO ₂ is in the vicinity of the stoichiometric ratio, and the subsequent decarburization step becomes unnecessary.

On the other hand, premixing fine Si ₃ N ₄ powder into the SiO ₂ —C system is considered as follows.

That is, SiO ₂ + C → SiO + CO proceeds as a primary reaction.
This reaction is a solid-phase reaction, and is relatively fast when a raw material having a large specific surface area is used, and the produced SiO easily reacts with N ₂ or NH ₃ . In this reaction, with SiO
Since N ₂ and NH ₃ can exist in the vapor phase, it can be said that the proportion of carbon (C) vapor influences the reduction and nitriding reactions of SiO. However, in this case, it is considered that the α-type Si ₃ N ₄ is easily produced because the specific surface area of C is sufficiently large.

However, in the present invention, a predetermined amount of Si ₃ N ₄ powder is allowed to coexist in the reaction system. By the way, in the synthesis of Si ₃ N ₄ by the oxide reduction reaction, as SiO ₂ , N ₂ , NH ₃ etc. exist in the gas phase state as described above, when solid Si ₃ N ₄ is finally produced, The early stable deposition of Si ₃ N _{4 in} the as-deposited state and the subsequent growth greatly affect the reaction rate and yield. However, in the present invention, Si ₃ N ₄ powder is preliminarily made to coexist and acts as a nucleus for depositing and growing Si ₃ -N _{4 in the} vapor phase. This S
The deposition and growth effects of i ₃ N ₄ further prevent the generation of SiC, which greatly contributes to the improvement of the purity of Si ₃ N ₄ .

In addition, even if Fe-based compounds and the like are present in this reaction system,
The invention is, in principle, uncontrollable.

〔The invention's effect〕

Thus, according to the present invention, even if the decarburization treatment after the reaction is not required, the content of α-type Si ₃ N ₄ is high, and the content of impurities such as SiC is remarkably small, and the high-quality α-type Si ₃ N ₄ system is used. Since a powder is obtained, the method of the present invention requires Si ₃ N ₄ which requires high temperature and high stress.
It can be said that this is suitable for the production of the raw material Si ₃ N ₄ system powder for sintered type structural materials.

Example of Invention

 Next, examples of the present invention will be described.

SiO ₂ powder having a specific surface area of 200m ² / g, a C powder and the average particle systems from about 0.8 [mu] m Si ₃ N ₄ powder having a specific surface area of 100 m ² / g was adjusted composition ratio shown in Table 1 (weight ratio) ze mixed powder . These are N ₂ , N ₂ +
Heat treatment was performed at 1350 to 1550 ° C. for 2 to 10 hours in an atmosphere of H ₂ and NH ₃ for reduction and nitriding to obtain a synthetic powder. Table 1 shows the α-type Si ₃ N ₄ content, content of Si ₃ N ₄ , oxygen and oxygen obtained by analysis for each of the Si ₃ N ₄ powders thus obtained.

As is clear from the table, Si having a specific surface area of 50 m ² / g or more
By using O ₂ and C powder, a high-purity powder having a high α-Si ₃ N ₄ content can be synthesized.

Claims (1)

[Claims] 1. A specific surface area of 50 m ² / g or more silica (SiO ₂₎ powder 1 part by weight, the carbon the specific surface area is more than 50 m ² / g powder 0.39
~ 0.41 parts by weight of silicon nitride (Si ₃ N ₄ ), silicon oxynitride (Si
₂ ON ₂₎ and a mixed powder consisting of a proportion of at least one kind 0.005 part by weight of metallic silicon (Si) powder was heat treated at 1350-1550 ° C. in a non-oxidizing atmosphere containing nitrogen,
A method for producing an α-type silicon nitride powder, which comprises performing a reduction / nitriding reaction.