JPS6049121B2 - Silicon nitride manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing silicon nitride, particularly a method for producing silicon nitride with a low halogen content.

Silicon nitride has excellent heat resistance and corrosion resistance, and its sintered bodies are finding use in various turbine bundles, nozzles exposed to high temperatures, and the like.

Conventionally, silicon nitride has been produced by reacting gaseous silicon tetrachloride and ammonia at a high temperature of 590 to 1500'C in an oxygen-blocked atmosphere, followed by heat treatment. Are known.

(Refer to Ceramics Association Journal, 28, (1972)) According to this method, powdered silicon nitride (Si), which is partially α-crystallized, is produced.

Although ammonium chloride, a reaction by-product, can be removed in the post-reaction heat treatment step, chlorine that has partially reacted with this is incorporated into silicon nitride as an impurity, so using this, for example, When sintering into the desired shape using methods such as casting, the chlorine evaporates,
It is desirable to avoid such chlorine contamination as much as possible, as it may worsen the working environment and corrode the mold and surrounding equipment. In addition, in this case, if the silicon nitride is exposed to high temperatures for too long, even below the temperature at which sintering is originally performed for the purpose of dechlorination, sintering will occur due to the dislocation of silicon nitride from α crystal to β crystal, which will cause the silicon nitride to become unsuitable for subsequent use. I can't stand it anymore.

On the other hand, it is also conceivable to use a silicon source that does not contain chlorine, but such raw materials are generally expensive and are not industrially practical, especially when used in large quantities.

In view of these points, the present inventor has attempted to obtain silicon nitride that does not substantially contain chlorine in the powder as a raw material for the sintered body, while using silicon tetrachloride, which is available at a relatively low cost. As a result of various studies and examinations for the purpose of Removal is accompanied by considerable difficulty, but when such reactions are carried out under specific conditions! 5 is
It has been found that silicon nitride substantially free of chlorine can be easily obtained. Furthermore, when employing the method of the present invention, in addition to silicon tetrachloride, SlHCl3, SlBr4, S
It has also been found that similar results can be obtained using other halogen-containing inorganic silicon compounds such as iI4.

Thus, in the present invention, an inorganic silicon compound containing a halogen and ammonia are mixed under normal pressure with a molar ratio of ammonia to the inorganic silicon compound containing a halogen of 0.1 to 1.85.
00-1600° C1 reaction time 30-0.1 seconds, and then heated to 600-1700°C in a nitrogen and/or ammonia stream at 8-0.2110°C. An object of the present invention is to provide a method for producing silicon nitride substantially free of halogen by holding the nitride for a period of time.

Inorganic silicon compounds containing halogen used as raw materials in the present invention include SiCl4, SiHCl3, S
iH2Cl2, SiH3Cl. , SiBr4, SiHB
3, SiH2Br2, SiH3BrNSll4, SiH
I3, SiH2l2, SjH3l. ．． SiCl. Br2
, SiCl2l2, and some of these are gaseous at room temperature, while others are liquid or solid, and in order to quickly carry out a uniform reaction, they can be solubilized by means such as suitable indirect heating. It is appropriate to first gasify it and then subject it to the reaction with ammonia. 2. The amount of ammonia used in the first reaction must be in a molar ratio of 0.1 to 1.85 with respect to the halogen-containing inorganic silicon compound used as a raw material. be.

If the amount of ammonia used is less than the above range,
If the production rate of silicon nitride is low and not suitable for industrial use, and conversely exceeds the above range, silicon nitride as a raw material for a sintered body that does not contain halogens will substantially Both of these methods are inappropriate because they cannot be obtained.

Among the above ranges, when the molar ratio is from 0.5 to 1.8, silicon nitride that does not substantially contain halogen can be industrially advantageously produced, so it is particularly preferable! Delicious.

Further, the reaction temperature is required to be 400 to 1600°C.

If the reaction temperature is lower than 400°C, the by-product halogenated ammonia will precipitate as a solid, causing difficulties in reaction step 4 (processing); on the other hand, if the reaction temperature exceeds 1600°C, the final product will be Either method is unsuitable because halogen is incorporated into silicon nitride, making removal substantially difficult.

Further, it is necessary to adopt a reaction time of 30 to 0.1 seconds.

If the reaction time exceeds 30 8, it becomes impossible to substantially remove halogen from the produced silicon nitride, and
If the reactor is unnecessarily large and the reaction time is less than 0.1 seconds, the reaction will not substantially proceed, which is inappropriate.

Of these reaction temperatures and times, the reaction temperature 50
It is particularly preferable to use a reaction time of 0 to 1550° C. and a reaction time of 10 to 0.5 seconds, since silicon nitride substantially free of halogen can be produced industrially advantageously.

Further, when carrying out this reaction, the presence of oxygen in the reaction system is not preferable since there is a risk that silica will be mixed in as an impurity. Regarding the relationship between reaction temperature and time, within each of the above ranges, as the reaction temperature becomes higher, the reaction time becomes shorter.

The reaction product thus obtained (generally a solid powder) is
This is then heated to 600-1700°C in a nitrogen and/or ammonia stream for 8-0. It is kept in a cloudy state.

If the holding temperature is lower than 600'C and for less than 0.2 hours, the halogen in silicon nitride cannot be substantially removed, whereas if the holding temperature is higher than 1700'C and for more than 8 hours, β Either way, a sintered body of silicon nitride, which is a crystal, is formed, which is inappropriate.

During these holding temperature and time ranges, temperature〕00
It is particularly preferable to use the temperature of 1600 DEG C. for 0.5 to 3 hours because the halogen in silicon nitride can be substantially completely removed while the formation of beta crystals is substantially suppressed.

Also, the amount of nitrogen and/or ammonia used in this reaction is determined by the reason that the amount of ammonia used in the previous and subsequent reactions is necessary to form silicon nitride. If the amount is less than the stoichiometric amount, it must be replenished2, and even if it is more than the stoichiometric amount, it is necessary to replace the halogen contained in silicon nitride with nitrogen after it has been removed. For these reasons, it is generally appropriate to use at least twice the theoretical amount required to form silicon nitride (Si3N4) from the halogenated inorganic silicon compound serving as source 1.

In fact, as a preferred specific example of carrying out the method of the present invention, gaseous halogenated inorganic silicon compounds and ammonia gas, which are raw materials, and nitrogen gas for dilution are transferred to an externally heated flow-through type sky column reaction tube. The resulting gas containing silicon nitride powder is introduced into a gas-solid separator such as a dust collector with oxygen cut off, and the resulting powder is separated and collected.

Next, using an externally heated rotary kiln or rocking furnace in which a nitrogen and/or ammonia gas stream can be passed while cutting off oxygen, the temperature is 8-0. Hold it for a full time. In such operations, diluting nitrogen may not necessarily be used. Next, the present invention will be specifically explained using examples.

Example The inner cylinder was a quartz reaction tube with an inner diameter of 36mm and a length of 900TmIn, and an inner diameter of 50W0fL. ．． Using an apparatus consisting of an externally heated flow-through reactor consisting of an alumina outer cylinder with a length of 100 mm and a reaction product collector attached to the bottom of the reaction tube, halogen is removed from the top of the reaction tube maintained at a predetermined temperature. Silicone (
Carrier gas (N2) and ammonia gas were blown into the reactor from separate introduction pipes to cause a reaction.

The powdered product collected in the collector (100° C.) was transferred to a silicon nitride crucible under a nitrogen atmosphere, and heat-treated in an electric furnace in a nitrogen-ammonia mixed gas flow.

The reaction conditions, heat treatment conditions, and analysis results of the obtained silicon nitride are as shown in the following table.

The halogen contained in silicon nitride was analyzed by fluorescent X-ray analysis.

Claims (1)

[Claims] 1 SiCl_4, SiHCl_3, SiH_2Cl_
2, SiH_3Cl, SiBr_4, SiHBr_3,
SiH_2Br_2, SiH_3Br, SiI_4, S
iHI_3, SiH_2I_2, SiH_3I, SiC
The molar ratio of ammonia to the halogen-containing inorganic silicon compound selected from l_2Br_2 and SiCl_2I_2 was set to 0.1 to 1.85, and the halogen-containing inorganic silicon compound and ammonia were mixed under normal pressure at 400 to 1600°C for a reaction time of 30 to 1.85. React for 0.1 seconds, then heat to 600-1700°C in a nitrogen and/or ammonia stream for 8-80 minutes.
A method for producing silicon nitride, characterized by holding the silicon nitride for 0.2 hours.