JPS5891011A - Manufacture of silicon nitride powder with high alpha-phase content - Google Patents

Abstract

PURPOSE:To increase the alpha-phase content by granulating a powdered mixture of a compound contg. an Si-O component with C and silicon nitride, silicon carbide or the like to a prescribed grain size and by reacting the granules at a prescribed temp. in a nonoxidizing atmosphere contg. N2. CONSTITUTION:A powdered mixture as a starting material is prepared by adding >=1 kind of powder selected from silicon nitride powder, silicon carbide powder and silicon oxynitride powder to silica powder or powder of a compound contg. an Si-O component and carbon powder. The powdered mixture is granulated to form granules having <=30mm. minor axis size. The granules are treated at 1,300-1,550 deg.C in a nonoxidizing atmosphere contg. N2 to cause reduction and nitriding reactions. Thus, silicon nitride powder with a high alpha-phase content is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing silicon nitride powder with a high alpha phase content.

For example, silica-yttrium oxide or magnesium oxide (5i6N4-Y2O3 or 5t6N4-
MgO) sintered body Fi has high mechanical strength and excellent heat resistance, so it is being applied to high-temperature gas turbine parts and the like. The thermal and mechanical properties of a silicon nitride-based sintered body are greatly influenced by the properties of the starting materials, and it is desired that silicon nitride has as high an α-phase functionalization rate as possible.

Incidentally, conventionally, silicon nitride powder has been produced by various methods, but recently, as a method for obtaining island silicon nitride powder with α phase content, silicon nitride powder and silicon carbide powder are used in combination with silica powder and carbon powder. A method is adopted in which a mixed raw material powder is prepared by adding at least one of silicon oxynitride powder and silicon oxynitride powder, and then heat-treated in a nitrogen-containing non-oxidizing atmosphere to cause a reduction/nitriding reaction.

However, the above conventional method has the following drawbacks.

(1) Silicon nitride grows on the surface using the added powder such as silicon nitride in the mixed raw material powder as a core, so in order to obtain fine silicon nitride powder with good sinterability, it is necessary to use the added powder The amount of addition must be increased. When the amount added is increased in this way, the particle size of the silicon nitride powder produced becomes uniform, and the compacting density during compacting becomes low.

(2) In the reaction that generates 513N4 from 5ho2 and C, the rate-determining step is the same-same reaction between 5IO2 and C.
Good contact between silica powder and carbon powder is required. However, the starting materials are all fine powders, and the bulk specific gravity of the mixed raw material powder is extremely small (0.13~0
．． 20) It is difficult to obtain good contact between silica particles and carbine particles. In addition, since the amount of filling is small, production efficiency is poor.

(3) When the mixed raw material powder is filled with light into a container and subjected to the reduction/nitriding reaction, the starting raw material is fine even though the bulk specific gravity of the mixed raw material powder is small, so the gaps in the powder bed are very narrow. is in a state.

Therefore, the CO gas generated by the reaction is difficult to diffuse out from the powder bed, and the N2 gas necessary for the nitriding reaction is difficult to penetrate into the powder bed. In this case, if the powder bed is thick, the N2 concentration inside the powder bed will be low and the CO concentration will be high, so S
Since iC and Si2ON2 are produced as by-products and unreacted SiO2 remains, the generation of Si and N4 is not good. therefore,
The thickness of the powder bed is limited to about 15 mm. Furthermore, since the reaction rate inside the powder bed is slow, it takes time to complete the production of 5t3N4, resulting in poor production efficiency.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and after granulating mixed raw material powder, reduction and nitriding reactions are performed to improve production efficiency and produce fine α-phase particles that have good sinterability. It is an object of the present invention to provide a method for distributing silicon powder with a high content.

That is, in the present invention, at least one glaze of silicon nitride cumulative powder, silicon carbide cumulative powder, and silicon oxynitride powder is added to silica powder or compound powder and carbon powder that meet the 5i-0 component to obtain a mixed raw material powder. After adjusting this and granulating it so that the short axis is 30 mm or less, the granulated particles are 130 ()
It is treated in a nitrogen-containing non-oxidizing atmosphere at -1550°C to cause a reduction/nitriding reaction.

The mixing ratio of the three component powders used as starting materials in the present invention differs depending on the component powders, but for example, silica-carbon-hokasilicate (5i02-C-8
13N4) In the case of a mixed system, SiO: C: Sl
3N 4 = 1 20, 4~4:
It is desirable that the weight ratio is between 0.0005 and 1.0. This is because if C is less than 0.4 with respect to 5IO21, SiO□ remains unreacted and a large amount of 812ON2 is produced, but on the other hand, the amount of α-phase S i and N4 produced is small.

Moreover, if C exceeds 4, the formation of β-phase 513N4 is observed, resulting in a deterioration in the purity of α-phase S i 5N4, and in particular, a decrease in the air content is observed. On the other hand, S+02 1
If SI3N4 is less than 0.005, α phase SI
3N4 has little effect on increasing the yield, and conversely, if it exceeds 1, a powder with preferable powder characteristics cannot be obtained.

In the present invention, a method for preparing a mixed powder raw material by mixing starting materials includes, for example, a wet or dry beer mill method.

In the present invention, the mixed raw material powder is granulated using water, alcohol,
It may be granulated by a wet method using acetone, etc., and then dried, or it may be granulated using vinyl alcohol.

Granulation and drying may be performed using an organic binder such as phenol resin or wheat flour (5-) or an inorganic binder such as ethyl silicate or colloidal silica.In addition, as a granulation method, one rotation of wet or dry extrusion may be used. method, pressure compression method, fluidized bed granulation method.

Examples include centrifugal flow method, agitation granulation method, spray dryer method, and combination methods thereof. By granulating the mixed raw material powder, the contact state between 5102 and C is good, and the bulk specific gravity of the granulated particles filled in the reaction container becomes 0.35 to 0.6, so The same-same reaction between SiO□ and C, which is the rate-determining step in the 813N4 production reaction, becomes more likely to occur. Inside the granulated particles, SiO gas and CO gas generated by the reaction between SIO□ and C cause cracks in the particles. CQ gas diffuses to the outside through these cracks, and N2 gas permeates inside, making it easier for reactions to occur and improving Si3N4 production efficiency. The reason why the short axis of the granulated particles is set to 30 mm or less is because if it exceeds 30 tan, it becomes difficult for CO gas to diffuse from inside the granulated particles and for N2 gas to penetrate into the inside of the granulated particles. Further, in order to widen the gap between the granulated particles, it is desirable that the short axis of each granulated particle is 0.2 tab or more and 80 inches or more.

In the present invention, the nitrogen-containing southern non-oxidizing atmosphere includes N2
．． NH3, N2- N2. Examples include N2-inert gas.

In the present invention, the temperature range of the non-oxidizing atmosphere containing
The reason for setting the temperature to 300 to 1550℃ is that S is lower than 1300℃.
l 3N4 is difficult to generate, and if the temperature exceeds 1550℃, Si
This is because the formation of C is observed.

The present invention will be explained in detail below.

Example: 1 part by weight of silica powder and oil absorption: 250 mVloo, i/
Runno bra 1. A mixed raw material powder was prepared by adding 01 parts by weight of silicon nitride powder having an average particle size of 1.0 μm to 05 parts by weight. Next, this mixed raw material powder was extruded and granulated to produce granulated particles having a width of 0.5 mm and a length of 3.0 mm, as shown in the table below. Subsequently, these granulated particles were filled into a graphite container with various particle bed thicknesses shown in the table below, and 14
A reduction/nitridation reaction was performed under a nitrogen atmosphere at 50° C. for 5 hours. Examples of this heating means include a method of high-frequency induction heating of the container itself or a conductor on the outer periphery of the container, or a method of heating by resistance heating. After that, 7
The mixture was treated in air at 00° C. for 8 hours to burn off residual carbon and obtain silicon nitride powder.

When the obtained silicon nitride powder was observed with a scanning electron microscope, it was found that it had a granular shape.

Also, the particle size range and average particle size of silicon nitride powder.

The nitrogen content, alpha phase content, and by-product formation were investigated. The results are also listed in the same table.

In the table below, as Comparative Examples 1 and 2, the mixed raw material powder is granulated and is granulated, and as a reference example, the mixed raw material powder is granulated with a short diameter of 35 mm.
The granules in the shell are shown in each case.

9- As is clear from the above diagram, the particle size range of the silicon nitride powder in Examples 1 to 6 is wider than that in Comparative Example 1.2,
Small average particle size. That is, the silicon nitride powders of Examples 1 to 6 have good sinterability. In addition, in Comparative Example 2, when the particle bed thickness was 20 mm, SiC was produced as a by-product and the properties of the silicon nitride powder deteriorated, but in Example 4.6, the particle bed thickness was 80 mm.
Even with ++1+++, 5iCU does not occur as a side effect. That is, in the example, the thickness of the particle bed can be increased to about 80 mm, and production efficiency can be improved. On the other hand, as in the reference example, when the breadth of the granulated particles is 35mm, which exceeds the range of the breadth of the granulated particles of the present invention (30mm or less), the α phase content is low and SiC is produced as a by-product. The properties of silicon nitride powder change.

As described in detail above, according to the present invention, it is possible to provide a method for producing fine silicon nitride powder with a high content of α phase, which can improve production efficiency and has good sinterability.

Applicant's agent: Patent attorney Suzue Takehiko = 10-

Claims (1)

[Claims] A mixed raw material powder is prepared by adding at least one of silicon nitride powder, silicon carbide powder, and silicon oxynitride powder to silica powder or compound powder containing the 5i-0 component and carbon powder, and the mixed raw material powder is prepared with a short axis of 30 m. Silicon nitride powder with a high α phase content, which is characterized by being granulated as follows, and the granulated particles are treated in a nitrogen-containing non-oxidizing atmosphere at 1300 to 1550°C to undergo a reduction and nitriding reaction. manufacturing method.