JPS58120599A - Production of beta-silicon carbide whisker - Google Patents

Abstract

PURPOSE:To obtain beta-silicon carbide whiskers with good efficiency and simple operation by disposing in close proximity a mixture of raw materials of siliceous materials and carbon and pulverized powder of carbonaceous raw materials and heating the same under specified conditions. CONSTITUTION:Pulverized powder of siliceous materials and carbon or carbonaceous materials are mixed in such a way that molar ratio of SiO2:C attains 1:1-1:2. A raw material mixture A thereof and a raw material B of pulverized powder of carbon or carbonaceous materials are disposed in close proximity in a reactor so as to make the ratio of the molar number of SiO2 in the mixture A: and the molar number of C in the raw material B 1:2-1:10. Both materials are heated to 1,300-1,600 deg.C in a non-oxidative atmosphere, to grow needle-like silicon carbide whiskers in the material B. If the resultant beta-silicon carbide whiskers are heated and are further treated with acids right after removal of the carbonaceous materials, the beta-silicon carbide whiskers having high purity are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for efficiently producing β-silicon carbide whiskers.

A conventional method for producing β-silicon carbide whiskers involves mixing a silicic acid substance and a carbonaceous substance at a molar ratio of about 0.8 to 2.6, forming the mixture into a nodule shape, and scorching it in a non-oxidizing atmosphere. The following method is being used. In this case, the generated S
IG whiskers are produced on the surface of or between the aggregates of the mixed raw materials, but the yield is poor, so this is not an economical method for producing whiskers.

The present inventors overcame this drawback and conducted various research on methods for producing whiskers economically, and found that a mixture A, which is a mixture of a finely divided silicic acid material and carbon or a carbon-containing material in a specific ratio, and a finely divided carbon or carbon-containing material are mixed together. Carbon material, raw material mixture A
Raw material B is made to have a specific ratio to SiO2 in the material, and both are placed close to each other.
When heated to ~1600°C, SiO produced by reaction in raw material mixture A is gasified and volatilized from raw material mixture A, reacts with carbon in raw material B, and acicular whiskers are generated in raw material B with good yield. I found out that.

Although the details of the formation mechanism of β-silicon carbide whiskers have not yet been completely elucidated, in the present invention, the raw material mixture A
In this step, SiO is generated by the reaction of Si 02 +C→SiO+GO (1). It is thought that this SiO gas reaches the raw material B placed close to the mixture A, and in the raw material B, SIC is generated by the reaction of St O+ 20 −+ Si C + CO, and gradually grows into whiskers.

The present invention is based on this knowledge, and 5i02:C
Raw material mixture A, which is a mixture of a finely divided silicic acid material and carbon or a carbon-containing material such that the molar ratio of Both raw materials are placed close to each other so that the ratio of SiO2 moles in raw material B to C moles in raw material B is 1:2 to 1:10, and both are heated in a temperature range of 1300 to 1600°C to make them non-oxidizing. This is a method for producing β-silicon carbide whiskers, which is characterized by heating in an atmosphere to generate silicon carbide whiskers in raw material B.

In the present invention, the silicic acid substance used may be either amorphous silicic acid or crystalline silicic acid, but in either case, it is preferably of good quality and preferably has a ζ particle size of about 10 μm or less. Further, as the carbon-containing substance, carbon-containing substances such as resin, resin carbide, cellulose, etc. are used. Since all of these carbon-containing substances are carbonized by heating at 1300° C. or higher in a non-oxidizing atmosphere, the number of moles of carbon in this case is calculated from the number of moles of carbide obtained after heating.

In the present invention, the mixing ratio of SiO2 and C in the raw material mixture A is such that when the molar ratio of SiO2:C is less than 1, unreacted 3i02 remains, and when the molar ratio exceeds 2, SiC powder is produced more than SiO2. Since the formation of
:2 is preferable.

In the present invention, the raw material mixture A and the raw material B may be in a powder state or molded into various shapes. Next, placing raw material mixture A and raw material B close to each other means, for example, when mixing molded raw material B into a molded raw material mixture as shown in Examples 1 and 2 below, or as shown in Example 3. In the vicinity of raw material mixture A, raw material B
When the raw material mixture A is arranged alternately in layers, the raw material mixture A
This means that the raw material B and the raw material B may be placed apart from each other by about several C-. In short, there must always be a portion consisting of a mixture of SiO2 and C and a portion consisting of C.

The reason why we divided the raw materials into two, A and B, is that Si
This is to prevent the decomposition reaction of SiC, ie, C+Si 02→2 Si o+c, and to increase the production efficiency of SiC.

The ratio of raw material B to raw material mixture is such that the number of moles of 5i02 in raw material mixture A and the number of moles of C in raw material B are the same in order to effectively collect 810 generated from raw material mixture A. Preferably, the ratio is 1:2 to 1:10. This is because if the molar ratio of C in raw material B to the number of moles of SiO2 in raw material mixture A is less than 2, raw material mixture A
Since the SiO produced from the raw material B becomes excessive with respect to the C of the raw material B, the SiO trapping effect decreases. Also, this molar ratio is 1
If it exceeds 0, the trapping effect will not increase even though the amount of residual C increases, which is not economical.

In the present invention, the heating may be performed rapidly or slowly, but the heating temperature is about 1300 to 1600°C, and the heating time is, for example, about several tens of minutes when the heating temperature is 1500°C. Further, the heating is performed in a non-oxidizing atmosphere such as argon or hydrogen 2 to prevent oxidation of the carbon material.

According to the present invention, after the reaction is completed, the raw material mixture, A contains Si
Almost no C is produced, and β-8iC whiskers are produced only in raw material B. β-8i obtained by the present invention
Since C whiskers are obtained in the coexistence of carbon substances and usually contain impurities, the obtained β
-8iC whiskers can be heated in air to remove carbon substances and then further treated with an acid to obtain higher purity whiskers.

According to the present invention, β-8t with a purity of 99% or more can be obtained by simple operation.
C whiskers can be obtained with a yield of more than 50%.

Example 1 Amorphous silica (purity 99%) and carbon black powder (purity 99%, particle size 10μ or less) were mixed in a pot mill at a molar ratio of 1:1 for 30 minutes, and the mixture was mixed with a particle size of 3.
- to produce raw material mixture A. Separately, carbon black was granulated to produce raw material B having a particle size of approximately 3-1.

The granules thus obtained were charged into a reaction vessel at a weight ratio of 1.5 of the raw material mixture A to 1 of the raw material B, as shown in Figure 1', and heated at 1500°C for 1 hour under an argon atmosphere. However, β-8IC whiskers were produced only in raw material B. The obtained β-8iC whiskers were heated at 100°C in air.
After heating for 30 minutes to eliminate carbon, treatment with hydrochloric acid resulted in β-8iC whiskers with a purity of about 99%.
Obtained with a yield of 5%.

Comparative Example A mixture of raw material mixture A granules prepared in Example 1 and raw material B granules at a weight ratio of 1.5:1 was ground in a bot mill for 1 hour to form a homogeneous mixture of 5 iOz and C. A powder consisting of was obtained. This powder was heated to 1500℃ under an argon atmosphere.
The reaction product obtained by heat treatment for 1 hour at
After heating at ℃ for 30 minutes, the product obtained by treatment with hydrochloric acid is β-3i.
It was mainly composed of β-8iC fine powder containing about 10% of C' strength, and the overall yield of SiC was 52%, and the yield of only whiskers was about 5%.

Example 2 Amorphous silica (purity 99%) and carbon black powder (purity 99%, particle size 10μ or less) were mixed in a bot mill at a molar ratio of 1:1.2 for 1 hour, and the mixture was mixed with a particle size of 5.
- granulation to produce raw material mixture A. Separately, carbon black was granulated to produce a raw material B having a particle size of 5-1.

The granules produced in this way are added to 5IC of raw material mixture A.
)+ and the number of moles of C in raw material B were 1=4, and the same nucleus as in Example 1 was charged into a reaction vessel and heated at 1480°C for 100 minutes in a hydrogen atmosphere. Raw material B
β-8iC whiskers were generated only in the inside. The obtained β
-8iC whiskers were heated in air at 750° C. for 40 minutes to eliminate carbon, and then treated with hydrochloric acid to obtain β-8iC whiskers with a purity of 98% or higher at a yield of 68%.

Example 3 Amorphous silica (purity 99%) and carbon black powder (purity 98.5%, particle size 10μ or less) were mixed in a molar ratio of 1
= 1 and mixed in a bot mill for 30 minutes to produce a powder of raw material mixture A. Apart from this, amorphous carbon (
Raw material B was prepared as a powder (particle size of 10 μm or less) with a purity of 98.5%.

The thus prepared raw material mixture A and raw material B were placed in the same reaction vessel as in Example 1 so that the ratio of the number of moles of 8102 in raw material mixture A to the number of moles of C in raw material B was 1:5. When the materials were arranged alternately in layers as shown in FIG. 2 and heated at 1550 DEG C. for 40 minutes in an argon atmosphere, β-8IC whiskers were formed only in raw material B. Obtained β-8i
When C whiskers were heated in air at 800°C for 1 hour to eliminate carbon, the yield of β-8iC whiskers was 6.
The purity was 98% at 1%. Next, when this SiC whisker was treated with hydrofluoric acid, β-8iC whisker with a purity of 99.5% was obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the charged state of raw material mixture A and raw material B in the reaction vessels in Examples 1 and 2;
The figure shows raw material mixture A and raw material B in the reaction vessel in Example 3.
FIG. In the figure, 1... Raw material mixture A, 2...
...Raw material B.

Claims (1)

[Claims] Raw material B consisting of finely powdered carbon or carbon-containing material is added to a raw material mixture in which finely powdered silicic acid material and carbon or carbon-containing material are mixed so that the molar ratio of SiO2:C is 1:1 to 1:2. , are placed close together so that the ratio of 8102 moles in raw material mixture A to C moles in raw material B is 1:2 to 1:10, and both are non-oxidizing in the temperature range of 1300 to 1600°C. A method for producing β-silicon carbide whiskers, which comprises heating in an atmosphere to generate silicon carbide whiskers in raw material B.