JPS5950006A - Manufacture of alpha-type silicon nitride powder - Google Patents

Abstract

PURPOSE:To manufacture fine alpha-type Si3N4 powder in a high yield by reacting a powdered mixture consisting of SiO, C and Si in an atmosphere contg. N and by heat-treating the resulting Si3N4 in an oxidizing atmosphere. CONSTITUTION:A powdered mixture is prepared by mixing SiO powder having >=99% purity and <=1mum average grain size with C powder having >=99% purity and <=1mum average grain size and Si powder having >=99% purity and <=10mum average grain size in 1: (0.2-2.0):(0.01-1.0) weight ratio. The mixture is heated to 1,350-1,480 deg.C in an atmosphere contg. N such as an NH3 atmosphere to form alpha-type Si3N4 by reduction and nitriding. The residual carbon is removed from the alpha-type Si3N4 by heating to 600-700 deg.C in an oxidizing atmosphere to obtain alpha-type Si3N4 powder suitable for use in the manufacture of a material resistant to high stress at high temp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a method for producing α-type silicon nitride (Si3N4) powder.

[Technical background of the invention and its problems]

For example, silicon nitride-yttrium oxide (813N4-Y2
O2), silicon nitride single layer magnesium (Si3N4-M
Since gO2)-based sintered bodies have high mechanical strength and excellent heat resistance, attempts have been made to apply them to high-temperature gas turbine components. When such a 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. Thermal and mechanical properties, which are especially important factors, are greatly influenced by the type and impurity content of the starting raw material, and for silicon nitride, it is desirable to use a raw material containing a large amount of α-type powder.

By the way, conventional methods for synthesizing 5ixN4 powder include: ■ nitriding metal silicon (St) powder, and 3S.
l+2N2→S! 5N4 ■ Gas phase reaction method using silicon chloride (or silane) and ammonia as raw materials, 3SIC14+ 4NH3-+ Si 3N4+ 12
HCt■ Silica (5SO2) @Method of nitriding SiO obtained by reduction with cardene (C) at reaction stoichiometric ratio, 3
SiO2+ 60 +2N2-+ 813N4+ 6C
O is known.

However, in method (2) above, the nitriding of Si is an exothermic reaction, so it is necessary to devise a process to control the exothermic reaction. ing. As a result, the contamination of impurities during this pulverization process is unavoidable, and although it is not a problem for use as a raw material for general refractories such as refractory materials, it is not suitable for use in high-temperature gas turbines. Further, the method (2) above is suitable for, for example, coating the surface of semiconductor elements, but cannot be said to be mass-produced for inorganic heat-resistant materials, and is not suitable for industrial manufacturing. Furthermore, while the above method (2) has the advantage that it does not require complicated reaction operations, it does not require complicated reaction operations;
Silicon oxynitride Si2ON2. and SiC
There is a drawback that the yield of α-type 513N4 is low in mixed systems such as.

[Purpose of the invention]

The present invention aims to provide a method for producing fine α-type 5t3N4 powder with good yield.

[Summary of the invention]

The present invention uses StO powder in a weight ratio of 1. C powder 0.2-2.
0 and St powder at a ratio of 0.01 to 1.0 is heated in an atmosphere containing nitrogen to cause a reduction and nitriding reaction.
This method is characterized in that after i3N4Th is generated, it is heat-treated in an oxidizing atmosphere.

The reason why the blending ratio of the mixed powder, which is the starting material, is limited as described above in the present invention is as follows. That is, if C per 5iO is less than 0.2, 5l
Although the production of o2N2 increases, the amount of α-type Si3N4 produced is small. However, when C exceeds 2.0, car? Not only was there no effect on increasing the amount of
Formation of type silicon carbide (SiC) was observed, and α type Si, N
This results in a decrease in the purity and yield of 4. On the other hand, if the ratio of Si to 5lo1 is less than 0.01, α-type Si 3
The high yield effect of N4 is small, but the sl is 1.0.
If the particle size exceeds 1 μm, fine α-type Si 3N
4 powder is difficult to obtain, and a final pulverization step is required, which leads to the contamination of other impurities. These SiO,C.

Preferably, Si has a high purity of about 99% or more, and regarding the particle size, Slo and C preferably have an average particle size of 1 μm or less, and 81 preferably has an average particle size of 10 μm or less.

Examples of the atmosphere for the reduction and nitridation reactions in the present invention include NH, N2-N2, or N2-inert gas systems. The heating temperature during such reduction and nitriding reactions is preferably in the range of 1350 to 1480°C. The reason for this is that sufficient reduction and nitriding reactions do not proceed at temperatures below 1350°C, and on the other hand, at temperatures exceeding 14801°C, the formation of SiC is observed. This is because it becomes difficult to obtain i3N4 powder.

The purpose of the heat treatment in an oxidizing atmosphere after the nitriding reaction in the present invention is to remove residual carbon. The temperature of such heat treatment is preferably in the range of 600 to 700°C. The reason for this is that if the temperature is less than 600°C, the effect of removing residual carbon is low, whereas if it exceeds 7001:'i, oxidation of α-type S i and N4 will occur.

According to the method of the present invention, the reduction of SiO is promoted by adding C to SiO in an amount that far exceeds the reaction stoichiometric ratio during the reduction and nitriding reactions, and by coexisting with a predetermined amount of St. In addition, the nitridation of Si progresses smoothly, and the yield of high-grade α-type Si3N4-based powder, which has a high content of α-type Si3N4 and is suitable for manufacturing Si3N4-based sintered bodies that require high temperature and high stress properties, is achieved. You can get a good deal. The reason why such α-type 513N4 powder is obtained is considered to be due to the following mechanism.

That is, the reaction is relatively faster as the sto ratio is higher, and S10 easily reacts with N2 or NH3. In this reaction, SIO and N2#NH3 can exist in the gas phase, so The presence of C vapor influences the reduction and nitriding reactions of StO.However, in this case, when the amount of C is around the reaction stoichiometric ratio or slightly higher, 512ON2 is generated.
The transition from Si2ON2 to α-type S l 3N4 is extremely difficult, but since the amount of C is in natural excess compared to the reaction stoichiometric ratio as described in 1, the generation of 512ON2 is suppressed and it is easily converted to α-type S i , N4 is generated. The excessive presence of C facilitates the production of α-type 5t3N4, but on the other hand, it leads to the co-production of slc6- and other impurities, resulting in a relative decrease in the content of α-type 513N4. Therefore, the present invention further allows a predetermined amount of 3t'l to coexist. As a result, the gi powder itself is nitrided, but rather the oxide film (810 □) on the surface of the sio powder is made easier to generate StO vapor by the reaction of 5so2 + si → 2810, and the subsequent SiO + C + N
It is thought that the production of α-type St and N4 by 2 can be easily progressed, dramatically improving the production yield of the desired fine α-type Si3N4, and preventing the generation of SIC and the contamination of other impurities. .

[Embodiments of the invention]

Examples 1 to 14 Sio powder with an average particle size of 15 μm, C with an average particle size of 30 μm
The powder and St powder having an average particle size of 2.0 μm were mixed in the proportions shown in the table below to prepare 20 kg of 14 types of mixed powder.

Next, these mixed powders were heated under the conditions shown in the same table to cause reduction and nitriding reactions, and then heat treated in air at a temperature of 700° C. for 8 hours to obtain 14 types of 513N4 powders.

The average particle size of the obtained Si3N4 powder, α-type Si
The 3N4 content (wt%), the SiC content, and the metal impurity content were examined. The results are also listed in the same table. In addition, Comparative Examples 1 to 6 are also listed in the table.

〔Effect of the invention〕

As detailed above, according to the present invention, 513N, which requires high temperature and high stress properties, can be used without the need for complicated operations or complicated equipment.
It has remarkable effects such as being able to obtain fine α-type Si3N4 powder in high yield, which is suitable for producing 4-series sintered bodies.

Applicant's agent: Patent attorney Suzue Takehiko 10- 32-

Claims (1)

[Claims] Silicon monoxide powder 1, carden powder 0.2-2 in weight ratio
．． 0 and metal silicon powder at a ratio of 0.01 to 1.0 is heated in an atmosphere containing nitrogen to cause a reduction and nitridation reaction to produce silicon nitride, and then heat treatment is performed in an oxidizing atmosphere. A method for producing α-type silicon nitride powder, characterized by: