JPS599519B2 - Manufacturing method for high-grade SIC whiskers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high quality SiC whiskers free of particulate contaminants.

Rice husks, which are generated in large quantities as agricultural waste, remain as amorphous silicon dioxide after incineration and are therefore attracting attention as an inexpensive starting material for producing SiC whiskers.

As for the manufacturing method, rice husks are directly packed into a heat-resistant reaction container and heated at a temperature of around 1600°C in a non-oxidizing atmosphere, or the rice husks are first converted into ash and then mixed with an appropriate carbon material and placed in a reaction container. Methods are known in which the SiC whiskers are filled and heated in the same manner as described above, but the problem is that the SiC whiskers obtained by these methods contain a large amount of particulate SiC that is simultaneously produced.

Therefore, in order to use it as a high-performance composite reinforced material, it is required to separate the mixed granular SiC.

However, since the grains 8i C are entangled in the whisker fiber structure formed in the form of algae, an extremely complicated separation operation is required to separate the whisker fibers.

The present invention provides granular S without performing the above-mentioned secondary separation treatment.
This method provides a method for producing high-grade SiC whiskers that do not contain iC, and its structure consists of a reaction vessel filled with mixed raw materials of rice hull ash and carbon black in the lower part, and porous or fibrous carbon in the upper part. The material is charged to form a production zone, and an inert gas is introduced and diffused from the bottom of the container.
It is characterized by heating in a temperature range of 0 to 2000°C.

Rice husks, which serve as a starting material, are heated and incinerated at a temperature of 600° C. or higher to once convert them into ash, and the resulting rice husk ash is mixed with carbon material to form a raw material.

Carbon black is used as the carbonaceous material, but in order to provide appropriate air permeability during filling, it is preferable to use carbon plaque that has been granulated into pellets in advance.

Further, it is desirable that the blending ratio of carbon black carbonaceous material to rice hull ash is set in the range of 110 to 400% by weight.

For example, a heat-resistant cylindrical closed container made of graphite material and having an inert gas inlet and a porous diffusion plate at the bottom is useful as the reaction container, but piping that allows the inert gas to circulate through the heat treatment is useful. It is effective to design the structure in advance.

First, the lower layer of the reaction vessel is lightly filled with raw materials, and the upper layer is charged with a porous or fibrous carbonaceous material to form a production zone.

The porous or fibrous carbonaceous material packed into the area may be granular porous carbon, activated carbon, coke or carbon plaque, or carbon fiber felt, tow,
Selected from the cross.

The reaction vessel with a generation zone formed in the upper layer is placed in a suitable heating furnace such as an Acheson furnace or a Krybutol furnace, and the surrounding area is maintained in a non-oxidizing atmosphere.Then, the reaction vessel is heated at 1300 to 2000°C while inert gas is introduced from the bottom of the vessel. Heat to temperature.

Argon or helium is suitable as the inert gas flowing in, and the use of nitrogen partially converts Si3N due to high temperature reaction.
4 may be generated, which is not preferable.

In addition, the inert gas may be supplied at a flow rate that can smoothly transport the reaction component gas to the generation zone in the upper layer through the porous diffusion plate, and the space flow velocity may be in the range of 1 to 20 mm/sec. Enough.

Gas phase reaction components (SiO
and CO) rises along with the inert gas flowing in and diffusing from the bottom of the reaction vessel, reaches the production zone, and completes the reaction in a packed bed of porous or fibrous carbonaceous material with a large surface area.

The generated SiC whiskers adhere densely in a cotton-like manner to the surface or inside of the filled carbonaceous material.

After the reaction and production, the filled carbonaceous material in the production area is taken out from the container and the densely attached SiC whiskers are collected.

SiC whiskers are recovered by incinerating the filled carbonaceous material to remove the carbon content, or by washing the filled carbonaceous material with water and separating the adhering SiC whiskers. The latter water washing method is effectively applied when the filled carbonaceous material is a fibrous material with a relatively smooth surface such as cloth.

This water washing method requires various steps such as thoroughly separating the adhering SiC whiskers using means such as shaking or ultrasonic washing as necessary, and further performing a filtration treatment. This method is effective when using expensive filling materials because it has the advantage that the materials can be reused.

The SiC whiskers obtained in this way are of high quality and do not contain any impurities, and have a diameter of 0.2~
It is a single crystal with a good aspect ratio of 0.5 μm and a length of 500 to 1000 μm.

Therefore, it is extremely useful as a high-performance reinforcing material for ceramic-based or metal-based composites such as silicon nitride and aluminum.

Example 1 Pelletized IISAF-H was added to rice husk ash obtained by incinerating dry rice husk at a temperature of 600°C in an electric furnace.
e-class furnace carbon black [“SEAST 5
H "manufactured by Tokai Carbon Co., Ltd." was uniformly mixed at a blending ratio of 200% by weight.

The mixed raw materials were filled to a height of 70 mm into a reaction vessel made of high-purity graphite and having an inner diameter of 70 mm and a height of 150 mm, in which a gas introduction pipe was disposed at the bottom via a graphite porous diffusion plate.

The upper layer was then lightly charged with coconut shell activated carbon having an average particle size of 6×10 mm to form a generation zone.

A graphite lid was attached to the top of the container, and the container was transferred to a Kryptol furnace, and the temperature was raised while argon gas was introduced and diffused from the gas introduction tube at a flow rate of 5 h/sec, and the inside of the furnace was heated to a temperature of 1750° C. for 4 hours.

Inside the reaction vessel after heating, a pale greenish-white flocculent product was densely adhered to the entire area of the coconut shell activated carbon layer constituting the production zone.

Collect the coconut shell activated carbon layer from the reaction vessel and store it in the atmosphere for 700 minutes.
The carbon components were burned off by heat treatment at a temperature of °C.

The remaining product has a diameter of 0.2-0.5 μm and a length of 50 μm.
It is a pure SiC whisker with a β-type crystal form of 0 to 1000 μm, and its production yield is 3.6% (compared to the raw material rice husk).
weight).

Example 2 Using carbon fiber tow as the filler carbonaceous material in the production zone,
The heat treatment was carried out using the same equipment and conditions as in Example 1, except that the samples were loaded randomly.

Collect the carbon fiber layer from the reaction vessel and transfer it into a beaker;
After injecting pure water and shaking, S thickly adhered to the fiber surface.
The iC whiskers were thoroughly washed with water and separated.

The carbon fibers were then taken out and the contents of the beaker was filtered.

After drying, the residue was incinerated to burn off the remaining carbon components.

As in Example 1, the obtained SiC whiskers were pure β-type single crystals containing no impurities, and the production yield was 3% compared to the raw material rice husks.
．． It was 1% (weight).

Claims (1)

[Scope of Claims] 1. A production zone is formed by charging a porous or fibrous carbonaceous material into the upper layer of a reaction vessel whose lower layer is filled with mixed raw materials of rice husk ash and carbon black. A method for producing high-grade SiC whiskers, which comprises heating in a temperature range of 1300 to 2000'C while inflowing and diffusing active gas. 2. The porous or fibrous carbonaceous material forming the generation zone is selected from granular porous carbon, activated carbon, coke, carbon black, or carbon fiber felt, tow, or cloth. A method for manufacturing high-grade SiC whiskers. 3. The method for manufacturing high-quality SiC whiskers according to claim 1, wherein the inert gas flowing in and diffusing from the bottom of the container is argon, and is supplied through a diffusion plate at a spatial flow rate of 1 to 20 mm/fFJ.