JPH04209716A - Production of silicon carbide powder - Google Patents

Abstract

PURPOSE:To reduce an amount of whiskery material by heating mixed granules of SiO2 and C in a rotary furnace in a nonoxidizing atmosphere not containing N2 at a specific temperature. CONSTITUTION:100 pts.wt. SiO2 powder having <=50mum particle diameter and 60-180 pts.wt. carbon powder having <=5mum particle diameter are fed to a blending granulator, mixed with water having dissolved a small amount of polyethylene glycol, stirred at high speed, made into granules having 50mum to 5mm grain diameter, heated and dried to give mixed granules. Then the mixed granules are fed from a raw material hopper 1 of a continuous reducing carbonizing device through a blended granule feeder 2 to a shell 4 of a rotary furnace 3. The mixed granule is heated to 1,200-1,700 deg.C by a heater 5, reduced and carbonized in a nonoxidizing atmosphere not containing N2 while rocking, and SiC is taken out from a carbide recovery container 6. Carbon in the prepared SiC powder is heated and oxidized and removed to give B-SiC having a small amount of whiskery material.

Description

[Detailed description of the invention]

[00011

[Industrial Application Field] The present invention relates to a method for producing silicon carbide powder using a rotary furnace. [0O02] [Prior Art] Current methods for producing silicon carbide powder include:
There are the Acheson method using an Acheson furnace, the vertical continuous method in which raw materials are introduced from the top of a vertical furnace and the product is taken out from the bottom, and the Bushar furnace method in which raw materials are filled into a container and the container is continuously moved to take out the product. [0003]L However, in the above method, ■ Since the Acheson method involves reaction at a high temperature of 2000°C or higher, αS
icL is not produced, and the resulting silicon carbide particles become coarse, so pulverization is required as a post-process, and only a small portion of the atomized powder can be used as a raw material for fine ceramics, resulting in low efficiency. It's bad. [0004) ■ The vertical furnace method has the advantage that fine particles of β-3iC can be obtained and no subsequent pulverization step is required, but when the furnace becomes larger, there is a temperature difference between the vicinity of the furnace wall and the center of the furnace. The reaction tends to be non-uniform. [00051■ In the pusher furnace method, when the thickness of the layer filled with the raw material in the container is large, the reaction rate is slow, and whiskers are likely to be generated because the raw material powder is stationary. It has the following disadvantages. [0006N

[Problems to be Solved by the Invention] In view of the above circumstances, the present inventors have produced a silicon carbide powder that has finer particles and less whisker contamination than conventional methods, has a short industrial reaction time, and can be made into large scale. As a result of intensive study to find a method, the present invention was finally completed. [0007] [Means for Solving the Problems] That is, the present invention provides a process in which mixed grains of silicon oxide and carbon are shaken in a rotary furnace,
1200℃~170℃ under nitrogen-free non-oxidizing atmosphere
The present invention provides a method for producing silicon carbide powder, which is characterized by heating at 0°C. [0008] The method of the present invention will be explained in more detail below. When carrying out the method of the present invention, silicon oxide as a raw material is
This reaction is a gas phase reaction, and the particle size of the silicon carbide powder is not particularly limited because it does not depend on the particle size of the raw material silicon oxide, but from the viewpoint of ease of reaction, a particle size of 50 μm or less is usually used. . [00091 During the reaction, in order to obtain silicon carbide powder with finer particles and a sharp particle size distribution, ultrafine particles, e.g.
Hereinafter, it is also possible to mix silicon carbide powder, which preferably has a diameter of 0°571 m or less, as a seed in the silicon oxide powder used as the raw material for kneading. [00101 The carbon used as a raw material is usually carbon black, with a particle size of 511 m or less, preferably 3 gm or less. If the particle size is large, it is difficult to react. [001,11 In the reaction, silicon oxide and carbon are mixed and granulated in advance before use. During mixing, the ratio of silicon oxide and carbon used in step 2 is usually 60 to 180 parts, preferably 65 to 15 parts, of carbon per 100 parts of silicon oxide.
There is a cold in the 0th grade. If there is less carbon than silicon oxide, the conversion reaction to silicon carbide will not be sufficient, and if there is too much carbon, decarbonization will take a long time and the obtained silicon carbide may be reoxidized. [0012] Since the mixing time varies depending on the mixer used and the mixing area, it is sufficient to carry out mixing in advance under the mixing conditions used and set a time that enables uniform stirring of silicon oxide and carbon. [001,31 In the present invention, the mixed grains are 5011m to 5
It is used by granulating it into granules of mm or less. Mixed grains are 50I1.
If it is less than m, problems such as being easily scattered in the air current during reaction or easily adhering to the furnace wall may occur. [001,41 In the method of the present invention, it is essential that the mixed grains be subjected to reduction carbonization treatment while being shaken in a rotary furnace. The rotary furnace may be a known rotary furnace such as a kiln, and either a batch type or a continuous type can be used. The reduction carbonization treatment may be carried out normally in an argon atmosphere at a temperature of 1200 to 1700°C for 1 hour or more, usually 2 hours to 8 hours. [0015] FIG. 1 shows a schematic cross-sectional view of an embodiment of the apparatus used when performing continuous reduction carbonization treatment according to the method of the present invention, taken along a plane parallel to the longitudinal direction of the rotary furnace. In the figure, 1 is a raw material hopper, 2 is a mixed grain feeder, 3 is a rotary furnace, 4 is inside the shell, 5 is a heater, 6 is a carbide recovery container, 7
8 indicates a gas supply port, and 8 indicates a gas discharge port. [0016] In the figure, mixed grains consisting of silicon oxide and carbon in a raw material hopper 1 are fed into a shell 4 of a rotary furnace 3 by a feeder 2 such as a screw feeder. The rotary furnace is installed at an angle so that the inlet side of the mixed grains is higher, but in the case of a batch type, it is not necessarily necessary to be inclined. [00171 The mixed grains supplied into the rotary furnace from the supply device 2 are heated by a heater while moving within the shell, react with carbon, and become silicon carbide. The reduced and carbonized powder is collected in a carbide collection container 6. Argon-containing gas is forcibly supplied into the shell from the gas supply lower in order to perform the reduction carbonization process well. It is preferable to flow these gases in a countercurrent direction to the mixed grains because the efficiency of reduction carbonization is better and the efficiency is also better in terms of heat recovery. Although the rotation speed of the rotary furnace is not unique depending on the diameter of the rotary furnace used, etc., it is preferably 0.1 to 10 rotations/min in order to carry out the reaction uniformly. [00181 It is not clear why the silicon carbide powder obtained by the method of the present invention produces a small amount of whiskers, but because the mixed grains that are the raw material are constantly moving in the rotary furnace, crystal growth in a specific direction is inhibited. , Therefore, it is presumed that whiskers are less likely to occur. [0019]

[Effects] According to the method of the present invention detailed above, the time required for reduction carbonization can be reduced to less than half compared to the conventional standing method, and it is also possible to obtain powder with a small amount of whisker formation. Its industrial value is enormous. [00201] [Examples] The method of the present invention will be explained in more detail by Examples below, but the method of the present invention is not limited by these Examples. In the present invention, a Sedigraph was used to measure the particle size of 40 μm or less, and a sieving method was used to measure the particle size of more than 40 μm. The amount of whiskers is 10μm by wet method after decarbonization.
I screened it out and found it. In the examples, parts are parts by weight unless otherwise specified. [00213 Example 1 Silicon oxide powder 1 with an average particle size of 10 μm and a purity of 99.8%
00 parts, average particle size 1.5 μm, ash content 0. 100 parts of 1% carbon black was put into a mixing granulator, and a slurry in which 1 part of silicon nitride seed with an average particle size of 0.5 μm was dispersed was added to 545 parts of water in which 1 part of polyethylene glycol was dissolved. The mixture was stirred at high speed and mixed, granulated into mixed granules, and then dried at 150° C. in a hot air dryer. The particle size of the obtained mixed grains was 0. It was 1 to 3 mm. [0022] This mixture was charged into the hopper shown in FIG. 1, rotated at 1 revolution/min, the furnace temperature was set at 1600°C, and argon with a purity of 99.99% or more was pumped at 1ONm3/min.
At 3K, the mixed grains are introduced into a rotary furnace in a countercurrent flow with Hr.
g/H and subjected to reduction carbonization treatment. [0023] Residual carbon in the silicon carbide powder thus obtained was removed by oxidation at 750° C. using a conventional method. The average particle size of the obtained silicon carbide powder was 0.6μ, its crystal structure was β-8iC, and the amount of whiskers produced was 0.
It was less than 5%. [0024] Comparative Example 1 Approximately 600 g of mixed grains prepared in the same manner as in Example 1 was filled into a 25 cm square carbon container, and such containers were stacked in five stages. (The filling height of the filling material is 1.5 cm.) [0025] The 5-tiered container is inserted into a pusher-type tunnel furnace at a rate of 1 unit/Hr, and the furnace temperature is 153 cm.
A reduction and carbonization reaction was carried out at 0°C. (The residence time in the furnace was 8 hours.) [0026] The gap between the filling and the bottom of the upper container was 1.5 cm, and argon with a purity of 99.99% or more was introduced through the gap. did. Argon used is 25Nm3/H
r, and if it was less than this, the reaction would not be completed within 8 hours. [0027] Residual carbon in the obtained silicon carbide powder was oxidized at 750°C. The average particle size of the obtained powder was 0.6
μ, its crystal structure was β-3iC, and the amount of whiskers produced was 1.8%. [0028]

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an apparatus used for continuous reduction carbonization treatment in the method of the present invention.

[Explanation of symbols]

In the figure, 1 is a raw material hopper, 2 is a mixed grain feeder, 3 is a rotary furnace, 4 is inside the shell, 5 is a heater, 6 is a carbide recovery container,
7 indicates a gas supply port, and 8 indicates a gas discharge port.

Claims (2)

[Claims] Claim 1: Mixed grains of silicon oxide and carbon are heated in a non-oxidizing atmosphere without nitrogen while being rocked in a rotary furnace.
A method for producing silicon carbide powder, the method comprising heating at 200°C to 1700°C. 2. The method for producing silicon carbide powder according to claim 1, wherein the mixed grains are granules of silicon oxide of 50 μm or less and carbon black of 5 μm or less and having a particle size of 50 μm to 5 mm.