JPS5845196A - Manufacture of silicon carbide whiskers - Google Patents

Abstract

PURPOSE:To reduce an amount of granular silicon carbide impurity, by substituting a specified range of amount of grain hull ashes for very fine powder of silica in manufacturing silicon carbide whiskers by mixing a specified amount of carbon black with hull ashes, filling a reaction vessel with the mixture, and heating it at a specified temp. in a nonoxidative atmosphere. CONSTITUTION:10-30wt% of hull ashes used for silicon source is substituted for very fine silica powder having 7-40mum primary particle diameter. With this mixture, 110-400wt% carbon black is mixed based on the ashes and silica, and filled into a graphite reaction vessel. The inside of the vessel is substituted by a nonoxidative gas, then, current is passed through the vessel to maintain it at 1,300-1,700 deg.C for at least 2hr, resulting in producing high quality silicon carbide whiskers containing very little granular silicon carbide impurity. Addition of 80-200wt% halogenides of alkali metals or alkali earth metals elevates efficiency based on the ashes and silica.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing 81C whiskers using a mixture of rice husk ash (silicon raw material) and carbon black as a basic raw material.

Rice husk, which is produced in large quantities as agricultural waste, becomes a considerable amount of amorphous 810. Therefore, it is suitable as an inexpensive and useful silica raw material for the production of 81C whiskers.

The applicant has focused on this point and has conducted extensive research, and has selected and blended carbon black as the most suitable carbon material for the use of the ashing residue of the fruit husks or stalks of gramineous plants, including rice husks, as a raw material. We have developed a method to produce 81C whiskers with a high level of formation rate with less 8iC particulate contaminants by using them as raw materials (%Grant No. 56-95086).
The present invention has been further improved to further suppress the inclusion of 81C particulate contaminants, which would be a hindrance to use as a composite reinforcing material.

That is, the prior art, which is the basis of the present invention, uses ashing residues such as rice husks (unique raw material) K110 to 400 by weight.
The requirement is to fill a raw material mixed with carbon black carbonaceous material (hereinafter referred to as "basic raw material") into a heat-resistant reaction vessel such as graphite and heat it to a temperature of 1500 to 1700 °C in a non-oxidizing atmosphere. shall be. According to this method, β-type 81 with a diameter of 0.2 to Q, an amount of 5 m, and a length of 50 to 80 μs
Cyh (scar) can be obtained with a high production yield exceeding 8% (relative to rice husk, weight -), and has the advantage of effectively reducing the content of contaminating particulate matter. It is still difficult to suppress the content to 5- or less, and while it is particularly effective in improving the yield of 3FiEliC whiskers when pelletized carbon black is used as the carbon material, large particles of 81C contaminants A phenomenon occurs in which the particles are unevenly generated around the periphery of the reaction vessel.

The present invention minimizes the mixing of 8jC granular debris by replacing a part of the rice husk ash, which is a raw material for silicon deposition, with ultrafine silicon dioxide and allowing it to coexist in the reaction vessel. .

As ultrafine silicon dioxide, the primary particle diameter is 7 to 40.
Colloidal silicic acid with a high specific surface area and dispersibility of mμ has been effectively used to reduce rice husk ash from 10 to 50911 (by weight).
Substitute and mix within a considerable amount.

This replacement blending ratio is limited; if it is less than 10% (by weight), the effect of inhibiting the production of 1000 particulate contaminants is poor;
If the weight exceeds 0-(weight), the production and growth of 81C whiskers will be significantly inhibited.

In order to make ultrafine silicon dioxide coexist in the reaction vessel, either the above-mentioned substitution blended silicon-based raw material is mixed with carbon black carbonaceous material and the whole is filled into the reaction vessel as a uniformly mixed raw material, or the mixture is filled in the center of the reaction vessel. A method is adopted in which the basic raw materials are charged and encapsulated, the above-mentioned substitution blending is carried out, and the nine-uniform mixed raw materials are concentrated only in the periphery. Among these methods, the latter method is effective when pellet-like granulated carbon black is used as the carbon material, and almost completely eliminates the phenomenon in which large grains of 81C contaminants are unevenly produced in the periphery of the reaction vessel.

Raw materials include NaC4, MaF, KCI, etc. 7)
b Potassium metal halide t+ is MyCl, , CaF
When an alkaline earth metal halide such as , etc. is mixed in advance with rice husk ash in an amount of 80 to 200 weight - 0, it has the effect of promoting the production yield of 81C whiskers and the elongation of the crystals.

The reaction vessel filled with the raw materials is surrounded by a carbon backing material such as coke grains, and is maintained in a non-oxidizing atmosphere with a weight of 1,300 to 1,700 tons, preferably! 50
Heat to a temperature of 0-1600'C for at least 2 hours. During the heating process, the silicon component and carbon component in the raw material are converted into fine fibrous EliC through a gas phase reaction, and eventually flocculent whiskers are formed within the particle structure of the carbonaceous material carbon black or throughout the mutual space. However, the formation of 810 particulate contaminants is extremely effectively suppressed by the action of ultrafine silicon dioxide coexisting in the raw material.

Unreacted carbon black remaining in the product is
It can be easily removed by combustion treatment in air.

The products after the combustion treatment are all β-type 81C whiskers, which are pale greenish white except that they contain less than 5% of particulate 81C.

As described above, according to the present invention, high-quality OS1C whiskers with very little granular 81G contaminants can be produced, so there is an advantage that they can be used as 7Fx or composite reinforcing materials for metals without the need for separation and purification.

Example! The nine dried rice husks were incinerated into ashes in an electric furnace while retaining 600 tons of IIIL until they reached a constant weight. The resulting rice husk ash is a fine powder with a light gray color, and the ash residual rate is 20.5.
%<11 amount), 8101 was a91.9-(weight).

Several types of ultra-fine silicon dioxide (Japan Aerosil ■ II # M1RO8 Engineering I, $200) with a primary particle diameter of approximately t2 mμ (average) in the range of 5 to 4 o-(weight) were mixed with the above rice husk ash. Displaced sandy clay raw materials were prepared, and ungranulated carbon black carbonaceous material [manufactured by Tokai Car dln@,
Add '81A8'r, 51) at a blending ratio of t5o% (1 amount) and mix thoroughly and uniformly.

Each of the mixed raw materials, SO and O, was lightly filled into a high-purity graphite reaction vessel with an inner diameter of 700° and a height of 150 m, and a graphite lid was attached to the top of the reaction vessel. (Weight) of pellet-shaped granulated carbon black carbon material [manufactured by Tokai Carbon ■, '6111im 8T.

5H) and an amount equivalent to 20% (weight) of the rice husk ash from this basic raw material was mixed with ultrafine silicon dioxide [
Nippon Aerosil [1M, IhIBnos processing.

t of each raw material (replacement raw material)
The former basic raw material was put into the center of the reaction vessel and filled from the periphery so as to be covered with the latter replacement raw material, and then 81C whiskers were produced using the same processing conditions as in Example 1.

The condition after the heat treatment was the same as when the pelletized granulated carbon black material was used alone (only the basic raw material was filled). In this case, the 81C voice ker yield (relative to rice husks, weight %) was 8.7 mounds, the content of granular 81C impurities was 5%, and the whiskers had a diameter of 0.2 to 0.5 μm and a length of 3
It was 0 to 80/jff+.

519-

Claims (1)

[Claims] A method in which a basic raw material prepared by mixing rice husk ash with 110 to 400 weight of carbon silk carbon material is charged into a reaction vessel and heated to 1500 to 1700°C in a non-oxidizing atmosphere, A method for producing EliC whiskers, characterized in that ultrafine silicon dioxide having a primary particle diameter of 7 to 40 mμ is allowed to coexist in a reaction vessel by replacing and blending in an amount equivalent to the rice husk ash oxo-5ofk (weight). 2. Claim #: Mixing 80 to 2 oo weight of alkali metal or alkaline earth metal I-loginide to rice husk ash! 81C whisker manufacturing method according to item 1.