JPS60131899A - Manufacture of silicon carbide whisker - Google Patents

Abstract

PURPOSE:To manufacture safely a titled silicon carbide whisker at low cost and in high yield by allowing Si3N4 to react with C by heating in a nonoxidizing atmosphere. CONSTITUTION:An Si3N powder and powdery C are charged into a tubular vessel made of graphite. A nonoxidizing gas contg. 0.1-90vol% CO is introduced into the vessel, and the vessel is heated at 1,400-1,900 deg.C to carry out the reaction. A silicon carbide whisker is manufactured in this way. The reaction pressure is not specifically limited and the reaction proceeds even under ordinary pressure.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing silicon carbide whiskers.

[Prior art]

Conventionally, various methods have been proposed as methods for producing silicon carbide whiskers. Focusing on silicon sources as raw materials, chlorides and oxides (5102) such as 5tcz4
, or a mixture of a simple substance (Si) and an oxide (Sin2), and silicon nitride (5ij) is used as the raw material.
There are few examples using N4). Methods using chlorides such as 5lC24 as raw materials have a long Qi and can be heat-treated at low temperatures, but the raw materials are easily hydrolyzed and are difficult to handle, making them difficult to use industrially. It cannot be said to be an ideal method. In addition, in the method of using oxide (5h02) or simple substance (Si) and oxide (5102) as raw materials, & family Sin is produced in the SiC whiskers! Since B4 distillation is carried out, tree cutting is necessary, and the yield is low, so even though inexpensive raw materials are used, the manufacturing cost is high. In addition, Tokkosho, to
Japanese Patent Application No. 17200 discloses a method of using nitride as a silicon source. In this method, silicon nitride powder and carbonaceous powder are mixed in an aqueous system at /3θθ℃~/S00
The reaction is carried out by heating at ℃ for 7 hours or more. However, this method requires sufficient consideration to prevent explosions because it is carried out in a hydrogen atmosphere, and the yield is also extremely low, making it difficult to achieve industrial advantages. It cannot be called a method.

[Purpose of the invention]

Therefore, it is an object of the present invention to provide a method for producing silicon carbide whiskers at low cost, pot yield and safety.

[Structure of the invention]

The present inventors have conducted intensive research on a method for preparing silicon carbide whiskers used as a silicon nitride (5lsN4) t-silicon source. They found that the purpose of the invention was to be repeated, and the present invention was completed.

That is, the present invention is a method for preparing silicon carbide whiskers, which is characterized by carrying out a heating reaction in a non-oxidizing atmosphere containing silicon nitride, carbon, and carbon oxide.

Using silicon nitride and carbon as raw materials, heat treatment in a hydrogen atmosphere produces silicon carbide! In the method described in Japanese Patent Publication No. 30'-17200, silicon carbide whiskers are thought to be produced by a direct reaction between silicon nitride and carbon as shown in Formula I.

Si, N4+3C→, J'SIG +-2N2↑ In contrast, the method of the present invention is characterized in that -carbon oxide gas is present in the reaction system containing silicon nitride and carbon. Although not bound by the following theory, in the present invention, as the first step, silicon silica reacts with carbon monoxide to form an intermediate product Fy (formula 510), and then this SiO is Reacts with carbon to form silicon carbide whiskers
Cf is generated (Formula III), and the carbon monoxide simultaneously generated by the reaction of 2) is recycled and used again for the reaction of the formula... In other words, carbon monoxide acts as a kind of catalyst in this reaction thread. it is conceivable that.

313N4,0003C0→, 7510 +3C+JN2↑knock, 7SiO+ l, C→3SiC+ 3COuI11 In the present invention, the carbon monoxide concentration in the reaction system atmosphere is 0.
/body Mt% or more is preferable.

At a concentration lower than this, granular silicon carbide is produced, and the visibility of whisker-like silicon carbide becomes extremely small.

- Although there is no particular upper limit for the carbon oxide concentration, since V-synthesis gas is generated by decomposition of the raw material silicon nitride, - the carbon oxide lam degree usually does not become higher than about 1A% of 7θ body.

In the present invention, the reaction atmosphere may contain a non-oxidizing gas other than carbon monoxide, such as nitrogen, argon, or a mixture thereof.In the present invention, the reaction atmosphere may contain a non-oxidizing gas other than carbon monoxide. carbon monoxide, preferably 0. /It is good to include more than that in the past, but it is not necessarily necessary to actively flow, stir, or circulate a non-oxidizing atmospheric gas into the reaction system. Therefore, - while feeding a non-oxidizing gas, such as nitrogen or argon, containing carbon oxide into the reaction system, - or - creating an atmosphere in the reaction vessel with a non-oxidizing gas containing carbon oxide, or - carbon oxide gas. After the substitution, a heating reaction may be performed. In addition, since the reaction yarn contains raw material carbon, even if the initial atmosphere in the reaction vessel is an oxidizing atmosphere, it can be converted into a non-oxidizing atmosphere containing carbon monoxide by heating.

In the method of the present invention, the reaction temperature is /'700 to /900
C is preferred. If the V is lower than /lI0θC, the yield of whiskers will be low, and if the V is higher than /900C, the whiskers will be destroyed by β→α transition of silicon carbide, which is not preferable. When argon is used as the carrier gas, whiskers can be obtained at /4t00°C, but when nitrogen is used, the whisker production yield will not be sufficient unless the temperature is 7500°C or higher.

The reaction pressure of the present invention is not particularly limited. Generally, the reaction proceeds satisfactorily at normal pressure.

According to the present invention, the shape of the generated whiskers can be arbitrarily changed by adjusting the presence or absence of carbon oxide gas, carrier gas, type of carrier gas, and heating temperature.

For example, to produce long whiskers, typically
-The lower the carbon oxide concentration, the better, and the lower the heating temperature. When a carrier gas is used, longer whiskers are more likely to be obtained when a carrier gas is used than when argon is used. Furthermore, long whiskers are often obtained when a carbon source with low crystallinity is used, and furthermore, when a mixture of silicon nitride and carbon powder is used, the lower the packing density, the longer the whiskers. Whiskers can now be obtained. Thus, according to the invention, length 2θ-j 00 #=% diameter 0.1-20 μmn
whiskers can be obtained in optionally high yields.

The shapes of the raw material silica and carbon used in the present invention 1J4 are not particularly limited. It is best to completely mix the powders of both powders, or to have them present in the reaction system without mixing them. Also,
Even if it is used in bulk form without powdering, the reaction proceeds and silicon carbide whiskers are obtained. Furthermore, it is also possible to cause the reaction to take place in an FC reactor made of one material, with the powder or lumps of bare shaving of the other material present in its entirety.

〔Effect of the invention〕

According to the present invention, high-quality silicon carbide whiskers with few impurities can be produced at low cost, high yield, and low cost. Explain. Note that in the Examples and Comparative Examples, the "yield" of whiskers was calculated using the following formula.

Example/Silicon nitride powder containing ~3θ α and β/A mixture of 4tK2 and powdered carbon θ, 6 and 9 was placed in a graphite tube container (/,
33. Fill the circle with graphite resistance heating element (22g1 x15.2.g'X
The tube container was heated and fired in a continuous horizontal enclosed air furnace using a 210θL) at a predetermined temperature, a predetermined atmosphere, and a feed rate of 23 wm/min as shown in the table. Atmosphere gas was supplied from the outlet side of the tube at a flow rate of SQL/mn in the opposite direction to the feeding direction of the Thug container.

When the atmosphere consists of nitrogen and -carbon oxide, the CO gas concentration produced by whiskers ranges from 0.7 to 4 it%
The range was up to However, 00=/θ0 in Example D
% was diluted to around 90% in commercial practice due to the generation of nitrogen gas through thermal decomposition of silicon as a raw material. In the other Examples, almost no difference was observed in the gas composition between the inflow time and the reaction time.

As is clear from Examples D to G, Ca2
As for the degree, S-G0 body punch is more preferable.

When the atmosphere consists of argon and -carbon oxide, the CO concentration is
~30 bodies N*chi is more desirable.

The length and shape of the whisker (the aspect ratio, that is, the length/diameter ratio is preferably larger) are as described above.
It can be controlled by changing the type a of carbon in the raw material, the filling degree, etc. In order to obtain whiskers with a length of about 500 μm in good yield, it is preferable to use a type of carbon having low crystallinity, such as furnace graccharide (FEF) (Examples 7 and 4).

In addition, the silicon carbide conversion ratio, that is, the ratio of silicon nitride converted to silicon carbide, h1 is 99% in Example 6, 39% in Example IO, and 1% in the comparative example /, which will be described later.
ctt was all 700%.

The method described in Japanese Patent Publication No. 30-17200, in which the atmosphere consists of hydrogen or hydrogen and nitrogen, is shown in Comparative Examples. In this case as well, whiskers d are produced, but the yield is less than 60% even in the most daring method (Comparative Example 3), indicating that this is an extremely inefficient method. However, with the method of the present invention in which carbon monoxide coexists in the atmospheric gas, the yield of silicon carbide iscar is comparable to that of hydrogen, and the yield of silicon carbide is still over 90%. It can be said that this is an extremely excellent method for economically mass producing multi-layered whiskers.

Until now, the production cost of silicon carbide whiskers was high and it was considered difficult to mass-produce them, but our company's method allows 00 sulfur to coexist in the atmosphere under various temperature IgL conditions. By doing so ~ good whisker yield! ＃Can be done in parallel. Moreover, it has become possible to control the shape arbitrarily, and it has become possible to provide shapes that suit the purpose.

Claims (1)

[Scope of Claims] (1) A method for producing silicon carbide whiskers, which features a heating reaction between silicon nitride and carbon in a non-oxidizing atmosphere containing -carbon oxide. The method according to claim (1), wherein the carbon concentration is 0./~wo θ volume. (3) The method according to claim 1, wherein the reaction temperature is /'700~/9θθC. Range No. (method described in item 11).