JPS61242905A - Production of alpha-silicon nitride powder - Google Patents

Abstract

PURPOSE:To obtain alpha-Si3N4 powder of high quality in high yield, by specifying the ratios of the respective raw materials in the silica reduction method using SiO2-C system containing Si3N4, etc., added thereto. CONSTITUTION:Mixed powder consisting of 1pts.wt. SiO2 powder having >=50m<2>/g specific surface area, 0.39-0.41pts.wt. C powder having >=50m<2>/g specific surface area and 0.005-1pts.wt. one or more of silicon nitride (Si3N4), silicon nitride oxide (Si2ON2) and Si powder is prepared. The mixed powder is then heat-treated in a nonoxidizing atmosphere containing nitrogen at 1,350-1,550 deg.C and subjected to reducing and nitriding reaction. According to this method, the reduction of SiO2 is remarkably promoted, and the formed Si3N4 is smoothly grown using previously added Si3N4 as a nucleus to give the aimed alpha-Si3N4 based powder of high quality with a high alpha-Si3N4 content in high yield.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for producing α-fisi silicon (α-type 5laN4) powder, which is a manufacturing method that can obtain high-quality α-fisi, N, powder in high yield. Regarding.

[Technical background of the invention and its problems]

For example, silicon nitride-yttrium oxide or magnesium oxide (S-N4-Y, 0. or 8i, N,
-MfO type) sintered bodies have high mechanical strength and excellent heat resistance, so attempts have been made to apply them to high-temperature starching members. However, when the above-mentioned 5isN-based sintered body is put to practical use as a high-temperature, high-stress material, physical and chemical stability and reliability at high temperatures are strictly required. Therefore, strict process control and quality control are essential in the manufacturing process of sintered bodies, and silicon nitride powder, which is the raw material for sintering, is regarded as the starting point of the process. For example, the raw material powder characteristics are simply high purity.

It is not enough that it is a fine powder; it is necessary that the properties that influence it fall within a narrow appropriate range.

By the way, the general method for synthesizing 5isN powder is (1)
Method for nitriding metal silicon powder 3si + 2b → S
i,N.

(2) Gas phase reaction method using silicon tetrachloride, silane and ammonia as raw materials 3SiCJ4 + 4NH3→8 is N4 + 1
2HCJ, etc. (3) A method of nitriding 8i0 obtained by reducing silica (sift) with carbon 0 in a reaction stoichiometric ratio a8i0. + eC+ zNt→Si, N, -t−s
co is taken.

In the case of Shikaji (1), the nitriding of 8i is an exothermic reaction, and in order to control the heat generation, a process must be devised.For example, relatively coarse particles of Si are selected and pulverized after nitriding. For this reason, contamination with impurities is unavoidable (during the crushing process), and although there is no problem in using it as a general heat-resistant material such as refractory bricks, it is not suitable for high-temperature gas turbines.

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

In the case of (3), sufficiently purified sio as the raw material,
It is necessary to use C powder, and Si is added to the generated powder.
, N, such as silicon carbide, silicon oxynitride, etc., are often mixed together. However, it has the advantage of not requiring complicated reaction operations, and it is also possible to improve quality and stabilize by adding a small amount of one type of "St" or "N" to the starting materials in advance for the purpose of promoting the reaction and controlling the grains of the formed layer. However, as mentioned above, the raw material powder for high-performance sintered bodies does not just have to be a high-purity, fine powder. The amount of oxygen contained in the raw material powder has a narrow appropriate range.From this point of view, silica-reduced Si and N.

Looking at the powder, the first synthesis reaction starts from the solid phase reaction of sto,,c particles, so excess C is essential for smoothing the first reaction [,8i,N, the generation layer must remove excess C. There are many flowers. Usually, this is done by oxidation removal (heat treatment in air at 700°C), but the 81. N
However, a small amount of oxidation on the particle surface is unavoidable, and as a result, an increase in the oxygen content in the raw material powder is avoided. Sintering of 8i, N, is S! It is thought that liquid phase sintering occurs through a glassy substance generated by the reaction between silica (containing oxygen) present in sN+ and additives, but after sintering is completed, the mechanical properties at high temperatures deteriorate. Therefore, in order to reduce the amount of glassy material, single composition or crystallization treatment, etc. are being considered.

[Purpose of the invention]

Based on this knowledge, the present invention aims to provide a manufacturing method that can obtain αW 81s N4 powder suitable for 1C8i, N, high-temperature, high-stress materials in high yield without requiring complicated operations or reaction equipment. It is something to do.

[Summary of the invention]

To explain the present invention in detail, 1 part of silica (StO) powder with a specific surface area of 50 m"79 or more, 0.39 to 0.41 parts by weight of carbon (C) powder with a specific surface area of 50 m" or more,
and silicon nitride (Sin N4) powder 0.005-1
A mixed powder consisting of 1 part by weight in an atmosphere containing nitrogen
α-type silicon nitride (α・8i, N,) characterized by heat treatment at 350 to 1550°C to undergo reduction and nitridation reactions.
This is a method for producing powder.

In the present invention, the weight mixing ratio of Sin, -〇-Si, N, system is 1: 0.39 to 0.41: 0.005.
The reason why the ratio is selected to be 1.0 is as follows. That is, 8i0
! If 1 part by weight C is less than 0.39, unreduced residual St
813 The oxygen content in the synthetic powder is high, and as a result, the high temperature and high strength 813
It is suitable for manufacturing N4 sintered bodies.

Moreover, if it exceeds 0.41, 7'1H8i, N, and residual C are mixed in the powder as impurities, making it unsuitable as a raw material for a sintered body.

On the other hand, 84. for 8i0,1. If the ratio of N is less than 0.005, it is α type 81. The effect of increasing the yield of N4 is small, and on the contrary, 1
If it exceeds this, a powder with preferable powder characteristics obtained by oxide reduction cannot be obtained, and the characteristics of the added 8i, N, and powder become noticeable, and the original purpose cannot be achieved. However, these S
Each raw material composition of iO, C, Sl, and N preferably has a high purity of about 99ζ or more.

The particle size is 810. , C both have an average particle size of 1μIn
8-N is preferably as fine as possible, for example, 2 μm or less. In addition, 81. used as a raw material. N is preferably in the α-type, but it may also be in the β-type or in solid solution with other elements such as AJ and 0. Furthermore, in place of Si, N, silicon carbide, SIC, silicon oxynitride compounds such as S1, ON, etc. alone or a mixture thereof (including N4) 1 or a part thereof may be placed on the metal St. A similar reaction promoting effect can be obtained.However, SIC, 8i!ON.

There is a tendency for purity to be slightly inferior when using . The following explanation will focus on 8isN and its addition.

In the present invention, 810. -C-8i, N, When the mixture is heated and fired, the atmosphere is N, , NH,, N, -hydrogen (H,).

Systems such as N, -inert gas can be mentioned, but the main reaction gas is N! or NH. The reason for this is that it has been experimentally confirmed that it greatly influences the final production of high-purity α-type 5i8N. On the other hand, the firing temperature in the atmosphere containing N1 or NH as the main reaction gas is selected within the range of 1350 to 1550°C. The reason for this is that below 1350°C, 84N is difficult to generate, and 15N is difficult to generate.
When the temperature exceeds 50°C, formation of SiC is observed.

Finally, the desired α-type 5isN4 suitable for high-temperature and high-stress materials
This is because it is not possible to obtain powder based on this method.

As described above (reduction of 8tO, in the nitriding reaction, a mixing ratio near the stoichiometric ratio of C is used, while a predetermined amount of 8i and N coexist. According to the present invention, the reduction of Sin is achieved. The S-N that is generated is greatly promoted and grows smoothly using the 8-N added in advance as a nucleus.
High-grade αfi Si with high content of N,
N, system powder can be obtained in high yield.

However, according to the present invention, Si, which is required to have high temperature and high stress properties,
, N, α type 81. suitable for manufacturing sintered bodies. The reason why N-based powder can be easily obtained is thought to be as follows.

First, regarding the mixing ratio of C, the silica reduction reaction starts with Sin and is considered to be a solid phase reaction at the particle interface, as described above, and the reaction proceeds more smoothly as there are more interfaces. In this case, the size (state) of the interface is also related to the average grain size of SiO, C, but in reality it is largely related to the specific surface area of both. Here, in the present invention, the reason why the specific surface area is set as an essential condition of 50WL''7p or more is due to the above reason.As a result, Sin
Even if the amount of C required to reduce , is close to the stoichiometric ratio, a sufficiently high quality 8i, N, powder can be synthesized, and the subsequent decarburization step is also unnecessary.

On the other hand, 8i0. The reason why fine Si, N, and powder are mixed in advance into the -C system can be considered as follows.

That is, as a first reaction, SiO! 10-+SiO+CO progresses. This reaction is an in-phase reaction, and using raw materials with a large specific surface area makes it relatively faster, and the generated 5
Easily reacts with iOdN or NH. In this reaction, 8i0 and N! , NH, can exist in a gaseous state, so reduction where the proportion of carbon (C) vapor is 8i0,
It can be said that it influences the nitriding reaction. However, in this case, C
It is thought that since the O specific surface area is sufficiently large, α-type Si and N are easily generated.

However, in the present invention, a predetermined amount of 8i,N is further added.

Powder is allowed to coexist in the reaction system. By the way, 8isN4 synthesis by oxide reduction reaction is Sin, as mentioned above.

Since N, , NHs, etc. exist in the gas phase, when solid Si3N4 is finally produced, 5is in the gas phase
The early stable deposition of N4 and the subsequent growth greatly influence the reaction rate and yield. However, in the present invention, 5iaN4
Si in the gas phase above is prepared by coexisting the powder in advance, -
Serves as a nucleus for N4 deposition and growth. This S-N
The deposition and growth effect of , further prevents the production of 8iC, which greatly contributes to improving the purity of 5isN.

Incidentally, even if an Fe-based compound or the like is present in this reaction system, the present invention is not hindered in principle.

〔Effect of the invention〕

Thus, according to the present invention, high-quality α-type 5isN, which has a high content rate of α-type 5isN and has a significantly low content of impurities such as SiC, can be produced without requiring decarburization treatment after the reaction.
Since it is possible to obtain Si, N, powders, the method of the present invention can be said to be suitable for producing 8i, N, raw material Si, N, powders for sintered structural materials that require high temperatures and high stress.

[Embodiments of the invention]

Next, examples of the present invention will be described.

Specific surface area 200 dlF OS t O! Powder, C powder with a specific surface area of 100 m7'p and an average particle size of about 0.8 μm
081. A mixed powder was prepared using the composition ratio (weight ratio) shown in Table 1.

kot'L rat Nz -N2 + Hz, NH-
A heat treatment was performed in an atmosphere of 1350 to 1550'O''t' for 2 to 10 hours to reduce and nitridate to obtain a synthetic powder.

α for each Si, N, powder obtained in this way
Table 1 shows the results of Si+N, oxygen, and carbon determined by type St, N, content ratio 9 analysis.

As is clear from the table, by using sio, C powder having a specific surface area of 50m"71 or more, α-8i,
N.

High purity powder with high content can be synthesized.

Claims (1)

[Claims] Silica (SiO_2) with a specific surface area of 50m^2/g or more
1 part by weight of powder, 0.39 to 0.41 part by weight of carbon powder with a specific surface area of 50 m^2/g or more, and silicon nitride (S
i_3N_4), silicon oxynitride (Si_2ON_2), and metal silicon (Si) powder.
Production of α-type silicon nitride powder, characterized in that a mixed powder consisting of 0.005 to 1 part by weight of seeds is heat-treated at 1350 to 1550°C in a non-oxidizing atmosphere containing nitrogen to cause a reduction and nitriding reaction. Method.