JPH01226800A - Production of silicon carbide whisker - Google Patents

Abstract

PURPOSE:To obtain silicon carbide whisker in high yield by generating cluster of silicon carbide whisker having high purity and suitable for reinforcing use in a hollow part of a molded body inexpensively by mixing silica, carbon, alumina, fluoride flux, and a caking material in a specified proportion, molding the mixture to obtain a molded body, and heat-treating the molded body by shielding from outside atmosphere. CONSTITUTION:10-60wt.% silica, 10-60wt.% carbon (e.g., coke powder), and 10-60wt.% alumina are mixed so as to attain 100% in total. Then, adding 1-5wt.% fluoride flux (e.g., NaF), and 2-10wt.% caking material (e.g., phenolic caking material) to the above-described mixture, and a hollow molded body 1 is obtd. after kneading the mixture. The molded body 1 is charged to a graphite vessel 3, sealed with a graphite disc 4, wrapped with a ceramic fiber blanket 5, and heated at >=1,350 deg.C noncatalytically with a high frequency induction furnace 6 while shielding from outside atmosphere. Thus, clusters 2 of silicon carbide whisker are generated in the hollow parts of the molded body 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing silicon carbide whiskers at low cost using inexpensive raw materials and simple cleaving and manipulation.

BACKGROUND OF THE INVENTION It is known to heat silica, carbon and fluoride fluxes in a non-oxidizing atmosphere to obtain silicon carbide. Especially the patent application 1986-
In No. 188032, by covering the outside of a hollow molded body formed by adding a fluoride flux and a binder to coarse grained silica, carbon, and alumina with a melt of ceramics, glass, metal, etc. It is disclosed that silicon carbide whiskers are obtained in the hollow part of the molded body by heating.

This prior invention adds alumina to silica, carbon, and fluoride fluxes to prevent softening and deformation of the molded body, which is a raw material system, and uses the hollow part as a production system, and the production system is surrounded by the raw material system, but isolates the two. By doing so, it is possible to prevent a part of the raw material from being mixed into the generated silicon carbide whiskers, thereby eliminating the need for a subsequent purification step.

[Problems to be Solved by the Invention] In the above-mentioned prior invention, the outside of the molded body is covered with a fused body made of ceramics, glass, metal, etc. having a relatively large specific gravity, so that the molten body is heated while being isolated from the outside air. Since it is necessary for the molded body to have a strong structure so that it will not be crushed, a large amount of relatively coarse-grained raw materials are used. Therefore, there are problems in that raw material utilization efficiency and whisker production rate are low. Furthermore, molten material as a heating medium cannot be obtained anytime and anywhere, but can only be used in very limited places and times.

In addition, when the generated silicon carbide whiskers are mixed into metals, ceramics, plastics, etc. as a reinforcing material, the whiskers must be cut short to form a preform of the desired shape using a vacuum forming method etc. It is common practice to add binders or binders, but these have the problem of reducing the reinforcing effect.

The present invention has been made in view of the above points, and its purpose is to produce a carbonized material that can increase the production speed, has excellent raw material utilization efficiency, and can be produced in a desired shape as a reinforcing preform. An object of the present invention is to provide a method for manufacturing silicon whiskers.

[Means for solving the problem] The above purpose is to combine silica of 10 to 60% by weight and silica of 10 to 60% by weight.
A step of adding and kneading 1 to 5% of a fluoride flux and a 2 to 10% of a binder to a 100% by weight raw material consisting of 10 to 60% by weight of alumina; , a step of forming the kneaded raw material into a hollow molded body;
In order to generate agglomerates of silicon carbide whiskers in the hollow part of the molded body, the molded body was heated at 135°C in a non-contact manner with the molded body isolated from the outside air.
This is achieved by a method for producing silicon carbide whiskers, which comprises the step of heating to 0° C. or higher.

[Function] When the molded body (raw material system) isolated from the outside air is heated to 1350°C or higher, gas (Sin) for forming silicon carbide is released.
, Go, etc.) and fills the hollow part of the molded body.

This hollow part is a production system, and is a space surrounded by the raw material system but isolated from the raw material system, and silicon carbide whiskers are directed inside from all surfaces of the hollow part of the raw material system (i.e., the molded body). As the whiskers form and grow, the outer shape of the whisker agglomerate faithfully follows the shape of the hollow part of the molded body. Moreover, the growth rate is relatively fast, and a cylindrical silicon carbide whisker preform with a diameter of somm is formed in about 30 minutes after the temperature is raised to 1350° C. or higher.

By the above-described operation, agglomerates of white to light green silicon carbide whiskers having a diameter of about 1 μm and an extremely long length containing almost no impurities are formed in the hollow portion of the molded body. Each whisker is intertwined with each other and is partially spongy.

Although its bulk specific gravity is only o, oos or less, it is durable. The shape and dimensions faithfully follow the shape and dimensions of the hollow part of the molded article. Therefore, if the shape and dimensions of the hollow part of the molded body are set to the shape and dimensions desired for the whisker preform, a whisker preform with the desired shape and dimensions can be obtained without any post-processing. Since they are long and strongly intertwined, it is possible to obtain an excellent reinforcing effect.

Next, the raw materials used in the present invention will be explained.

The silica raw material is foundry sand, river sand, or a natural mineral whose main component is silica, and the carbon is electrode scrap, coke powder, carbon black, etc.

The alumina is preferably tabular alumina or fused alumina, but high alumina refractory materials can also be used.

Regarding the particle size of the raw materials, in the case of the earlier invention, coarse particles of 150 mesh or more were required for silica, carbon, and alumina, but in the present invention, they do not necessarily need to be coarse particles, and the particle size is 10.
The amount can be less than 100 ml, and the presence of fine powder is not a problem.

When fine powder is used, it also has the effect of accelerating the reaction rate. Further, unlike the previous application, there is no need to receive the load of a heating medium and it is only necessary to maintain its own shape, so only the suspension necessary for the reaction is required. Alumina also has a kind of catalytic action,
If it is less than 0%, the amount of silicon carbide whiskers produced decreases.

Fluorides are NaF, Na2 Si F6, Na 3A
fl F 6, etc., and at the same time CaF2, M Q F
2. Addition of AI F3 may increase the amount of whiskers produced. As the caking agent, organic caking agents that are normally used in castings are suitable, and among them, those that harden with time are easy to use.

The graphite container may be of a size that allows the molded body to be inserted therein, that can be sealed tightly, and of a size that can be accommodated in the external heating device to be used.

In addition, when a refractory mortar or the like is used to isolate it from the outside air, it is preferable that the mortar has a high degree of fire resistance, and for example, HMS cement made by Toshiba Monoflux Co., Ltd. with water is suitable.

As the external heating device, a high frequency induction furnace, Tammann type, Super Kanthal type, etc. are used.

EXAMPLES] The present invention will be described in more detail below using preferred examples with reference to the drawings. FIG. 1 is a conceptual diagram for explaining this embodiment.

40% flattery sand-like silica at fffffi ratio
Cryolite 3 is added to the raw material powder consisting of 40% tabular alumina and 20% carbon electrode powder (both 100 mesh or less).
Weight σ%, phenolic self-hardening binder Type 5 I% and its hardening agent 2% are added, kneaded, and molded using a wooden mold into a cylinder with an outer diameter of 120 nm, an inner diameter of 80 IIIR, and a height of 200 n+n+. A molded body 1 having a porosity of 1.6 h/d and a porosity of 31% is obtained.

This molded body 1 is cured in about 45 minutes after molding. The cured molded body is inserted into a crucible-shaped graphite container 3 having an inner diameter of 125IIIll, and the portion ) is sealed with a graphite disc 4.

Next, the main container 3 is covered with a ceramic fiber blanket 5.
Wrapped with outer wall 7, coil diameter 2501! Heating was performed using a high frequency induction furnace 6 having a high frequency induction coil 8 and an exhaust pipe 9 at a heating rate of 35°C/1n, and after the outside of the container 3 reached 1350°C, heating was continued for an additional 30 minutes. After that, apply positive electricity and cool it down. After cooling, the hollow part of the molded body 1 contains a spongy white silicon carbide whisker agglomerate (preform) with a diameter of 801111 and a height of 20011 m and a uniform density.
4 is generated.

The whisker agglomerate 4 thus generated is the molded body 1
It can be easily removed from the residue without losing its shape. The diameter of each whisker constituting this whisker agglomerate 4 is approximately 1 μ. Moreover, the total weight of the whiskers produced is about 5 g.

[Effects of the Invention] According to the present invention, it is possible to obtain silicon carbide whiskers in the form of agglomerates that are filled in the hollow part of a molded body with uniform density, are highly pure, and are each long and tightly intertwined with each other. can. Moreover, the shape of this silicon carbide whisker agglomerate is the same as the shape of the hollow part of the molded body, and it can be easily taken out from the residue of the molded body without breaking, so it can be used as a reinforcing preform in that form. It can be used as

Furthermore, the raw materials, silica, carbon, and alumina, can be made of fine powder, which has the advantage of being quick to the skin and requiring less use.

[Brief explanation of the drawing]

- FIG. 1 is a conceptual diagram for explaining a preferred embodiment of the present invention. 1... Molded body, 2... Silicon carbide whisker agglomerate, 3... Graphite container, 4...
Graphite disc, 5...Ceramic fiber blanket, 6...High frequency induction furnace, 7...
・Outer wall, 8... High frequency induction coil, 9...
··Exhaust pipe. Figure 1

Claims (2)

[Claims] (1) 10-60% by weight silica and 10-60% by weight
of carbon and 10 to 60% by weight of alumina.
0 wt% raw material with 1-5 wt% fluoride flux and 2-1
A stage of adding and kneading 0% by weight of a binder, a stage of molding the kneaded raw materials into a hollow molded body, and a stage of molding the molded body in order to generate agglomerates of silicon carbide whiskers in the hollow part of the molded body. A method for producing silicon carbide whiskers, which comprises the step of heating to 1350° C. or higher in a non-contact manner while being isolated from outside air. (2) The method according to claim 1, characterized in that the shape and dimensions of the hollow portion of the molded body are made to match the shape and dimensions of a desired silicon carbide whisker preform.