JPH01257117A - Production of silicon carbide fine powder - Google Patents

Abstract

PURPOSE:To obtain SiC fine powder having a narrow particle distribution suitable for sintering, in only one crushing process by setting the packing density above specified value when the mixed raw materials, of powdered silica, silicon metal and carbon, are packed in a refractory vessel and reacted at a high temp. CONSTITUTION:The three components, (A) powdered silica (<=400 mesh particle size), preferably silica colloid of 10-15% concn., (B) silicon metal (<=1mm particle size) and (C) carbon (<=1mum particle size) such as carbon black, coke, graphite, are mixed, preferably so as to have the compsn. (molar ratio) indicated in the range formed by connecting points f, g and h in the figure. The mixture is packed in the refractory vessel such as graphite crucible in >=0.45g/cm<3> packing density, preferably in >=0.5g/cm<3>, reacted usually at 1,400-1,900 deg.C for 1-6h and thereafter crushed with a ball mill, etc., to obtain siC fine powder having <=0.5mum particle size. The raw material granulated with a binder may be used, in this case, the packing density is preferably 0.4-1.2g/cm<3>, especially 0.5-0.9g/cm<3>.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing pulverized silicon carbide, and more specifically, a method for producing pulverized silicon carbide having a narrow particle size distribution without contamination with foreign objects in high yield. Regarding how it can be done.

[Problems to be Solved by the Prior Art and the Invention] Recently, materials having particle sizes on the submicron order have been used as raw materials for fine ceramics (particularly raw materials for materials having heat resistance and high strength at high temperatures).

Expectations are rising for pulverized silicon carbide.

Conventionally, as a method for producing finely divided silicon carbide, there is the Acheson method.

However, the Acheson method has a high degree of one reaction site;
Another disadvantage is that a complicated pulverization step is required after the reaction.

In addition, as a method for producing finely powdered silicon carbide, there is a method using a three-component system such as silica, metallic silicon, and carbon (Japanese Patent Publication No. 60-35283 and Japanese Patent Application Laid-open No. 50-75600).
(see publication).

The method described in Japanese Patent Publication No. 60-35283 allows the chain reaction to proceed instantaneously at a low reaction temperature (800 to 1450°C), but since it causes a spontaneous chain reaction to proceed, an oxidizing atmosphere is required; Moreover, since the composition range of the raw material composition is limited, reaction operations and preparation of raw materials are complicated. Furthermore, since it is a chain reaction, it is difficult to control the reaction.

In the method described in JP-A-50-75600, the composition range of the reaction raw materials is also limited; for example, the mixing molar ratio of granular carbon and silica is about 2:1 to 6:1, and metal Silicon is about 3.5-22% based on the total amount of the mixture. Therefore, the method described in the above publication has the same problems as the method described in Japanese Patent Publication No. 60-35283.

Moreover, since the method described in JP-A-50-75600 simply mixes and reacts granular carbon, silica, and metallic silicon, foreign substances such as whiskers are mixed in as impurities in the silicon carbide produced. However, it also has the disadvantage that the particle size distribution of silicon carbide is broad, making it impossible to obtain fine powder silicon carbide suitable for sintering.

The object of the present invention is to eliminate the contamination of foreign particles such as whiskers in the production of finely powdered silicon carbide using a three-component system of silica, metallic silicon, and carbon as raw materials, and to allow only one pulverization process without the need for multiple pulverization steps. The object of the present invention is to provide a method for producing finely divided silicon carbide having a narrow particle size distribution suitable for sintering through a process.

[Means and effects for solving the problem] In order to solve the above-mentioned problems, the present inventor conducted extensive research and found that a mixture obtained by mixing powdered raw materials was filled into a fireproof container and heated to a high temperature. The inventors have discovered that the above object can be achieved by setting the packing density of the mixture in the fireproof container to a predetermined value or more during the reaction, and have arrived at the present invention.

That is, the present invention to achieve the above object provides a method for producing finely divided silicon carbide by mixing silica, metallic silicon, and carbon as raw materials, filling the mixture in a fireproof container, and reacting at a high temperature. This method of producing finely divided silicon carbide is characterized in that the packing density of a mixture of raw materials filled in a plastic container is 0.45 g/cm' or more.

The method for producing pulverized silicon carbide according to the present invention generally includes a mixing step of mixing silica, metal silicon, and carbon as raw materials, and a step of filling the mixture obtained in the step into a fireproof container and reacting it at high temperature. It has at least two reaction steps.

Silica, metallic silicon, and carbon are used as raw materials in the mixing step.

Said silica can generally be represented by SiOx, for example quartz, silica, silica sand, cristobalite,
Tridymite etc. can be used. Furthermore, as the silica, silica colloid, ultrafine particulate anhydrous silica, zeolite, etc. can also be used.

When using silica colloid, there are no particular restrictions on its concentration, but from the viewpoint of easy availability,
Silica colloids with a concentration of 10-50% are preferred.
This is because when a silica colloid is used as a silica raw material, the yield of silicon carbide is improved compared to when other silica raw materials are used.

Natural silica stone and silica sand can also be used, but they can be difficult to crush, so for example, amorphous silicic acid fine powder or silicon tetrachloride, which is a by-product during the production of ferrosilicon or phosphate fertilizers, may be used. Silicic acid fine powder, generally called white carbon, such as Aerosil obtained by oxidative decomposition, is suitable.

When powdered silica is used, its particle size is usually 200 mesh or less, preferably 400 mesh or less.

The metallic silicon may have a fairly coarse particle size, but from the viewpoint of handling, it is preferable to use one that has been ground to a particle size of 11 or less.

Examples of the carbon include carbon black such as furnace black, channel black, and thermal black;
Although carbon sources such as coke and graphite can be used, it is preferable to use carbon as fine as possible, with a particle size of 1 μm or less.

The respective purity of silica, metallic silicon, and carbon used as raw materials in the mixing process may not have a particularly significant effect on the reaction, but may affect the purity and particle size of the product.

It is best to select it appropriately depending on the intended use of the product.

In addition, the proportions of silica, metallic silicon, and carbon during mixing are 1. Normally, the points a and b shown in Figure 1 are
and C, preferably the composition (mol%) within the range connecting points a, d, and e shown in FIG. 1, particularly preferably the point f shown in FIG. g and h
The composition (mol%) is determined as appropriate so that the composition (mol%) is within the range that connects the following. Note that the compositions indicated at each point a to h in Table 1 are as shown in Table 1.

Table 1 Mixing of the above three components can usually be carried out using a kneader, Eirich mixer, etc.

The above-mentioned three components are mixed while evaporating water under heating, and after sufficient mixing or kneading, hot air drying may be performed if necessary.

The mixture obtained in the above mixing step is provided to the next reaction step.

Although the mixture may be provided as it is to the reaction step, it is preferable to granulate the mixture and then provide the granulated and molded product to the next reaction step.

Granulation and molding can be carried out by rolling, extrusion, double roll, molding, etc.

For example, the mixture can be granulated and molded by adding a pv^ (polyvinyl alcohol) aqueous solution as a binder to the mixture to form an appropriate slurry, and applying the mixture to an extruder and a marmerizer. . In the operation step using a marmerizer, granulation and molding can be performed while adding the powder of the dry mixture obtained in the mixing step.

Also, put the raw materials into the Eirich mixer and mix thoroughly, then transfer the mixture to the pan-type granulator.

By rolling granulation while spraying PVA aqueous solution,
Can be granulated and molded.

In addition to the PVA, the binder includes dextrin, sodium alginate, CM(:(sodium carboxymethyl)), and PVP (polyvinylpyrrolidone).
, 5pp (sodium polyphosphate) and water glass can also be used.

The particle size of the granulated/molded product is usually 0.5 to 30 mm.

In particular, it is 2 to 15 mm.

In addition, the density of granulated and molded products is usually 0.4 to 1.2 g.
It is desirable to adjust it so that it is within the range of 0.5 to 0.9 g/cm'', particularly 0.5 to 0.9 g/cm''.

In the reaction step, the mixture of powdered raw materials obtained in the mixing step or preferably the granulated/molded product is filled into a fireproof container.

As the fireproof container, a graphite crucible or the like can be used.

What is important in the present invention is that when filling a fireproof container with a mixture that is a TX material, the packing density of the mixture is 0.4.
It should be 5 g/c-3 or more, preferably 0.50 g/c-coli.

Here, if the mixture is a non-granulated/formed product,
It is preferable that the mixture in the fireproof container is compressed to the above-mentioned packing density, and when the mixture is a granulated or molded product, the density of the granulated or molded product is set to 0.4. ~1.
2 g/cm', especially 0.5-0.9 g/cm
It is best to adjust it so that it falls within the range of ``.

If the density of the granulated/molded product is adjusted within the above range, the work of storing the powder mixture in a fireproof container and then compressing it can be omitted (simplification of operation). ), granulation/
The molded product is stored in a fire-resistant container, and the granulation and
The above-mentioned packing density can be achieved simply by bringing the molded product into a close-packed state.

The filled refractory container is loaded into a general industrial furnace for firing refractories, such as a vertical high-temperature reactor, an open electric furnace, or a gas furnace, and the refractory container is heated inside the industrial furnace. The reaction of said mixture within is carried out.

Moreover, a high temperature variable atmosphere furnace can also be used for one reaction.

The reaction atmosphere may be an oxidizing atmosphere, but 1
It is usually a non-oxidizing atmosphere.

The reaction temperature is usually 1400 to 1900°C, preferably 1.500 to 1,700°C, and the reaction time is 1 to 6 hours, preferably 2 to 3 hours, so the reaction can be carried out in a very short time. . At this time, the reaction pressure is not particularly limited, but is generally normal pressure.

The reaction is thought to occur according to the following formula.

Reaction: 5iOz+ Si+ 4C= zsic+ z
c.

The product obtained through the mixing and reaction steps contains almost no foreign substances such as whiskers.

In addition, the product has a property of being easily crushed due to its low degree of agglomeration, and can be made into a fine powder through only one crushing process without requiring a multi-stage crushing process. be able to.

The product can be very easily ground using a grinding machine such as a conventional ball mill or vibratory mill.

The powder obtained by pulverization, that is, the fine powder of silicon carbide, is 1
It has a fine particle size of 0.5 μm or less and a narrow particle size distribution.

The purity of the finely divided silicon carbide obtained through the whole process is 9.
0-99%, and the yield of pulverized silicon carbide is 80-95% based on the silicon source.

[Example] (Example 1) Silica colloid aqueous solution (silica content 30% by weight) 3 g, metal silicon (pulverized to 74 IL- or less) 420 g
g and 720 g of carbon black were sufficiently mixed with S using a kneader. At this time, water was evaporated by heating, and the dry powder with a water content of 34% by weight was
I got g.

1.7 kg of dry powder was added to 430 g of aqueous O, S% PVA solution, and the slurry was made into an appropriate slurry. After extruding through a plate with a hole size of 5 mm, granulation was performed using a marmerizer. . In this step, when the above dry powder is further added with 980 g of hot air-dried powder (water content 4% by weight),
Granules with well-uniform particle sizes were obtained.

The particle size of the obtained granules was 2-1 to 5.71, and the density was 0.6 to 0.8 g/cm'.

Next, 53 g of this granulated material was filled into a graphite crucible. The packing density at this time was 0.55 g/c3. The filled crucible is placed in a vertical high-temperature reactor and the reaction begins.
The temperature was 1600°C for 3 hours.

The product obtained by the reaction was analyzed by X-ray diffraction and was found to be silicon carbide. Furthermore, as shown in the electron micrograph of FIG. 2, the product had a low degree of aggregation and was easily crushed. In addition, there were almost no whisker-like abnormalities. By grinding the product in a ball mill for 24 hours,
A fine powder with an average particle size of 0.24 p, m and a narrow particle size distribution was selectively obtained. A particle size distribution diagram of this fine powder is shown in FIG.

(Example 2) 1500 g of silica fine powder (average particle size 1.5 g), 700 g of metal silicon (pulverized to 74 gm or less), and 1200 g of carbon black were thoroughly mixed using an Eirich mixer. , to this mixture 1.0 g
Transfer to a pan-type granulator and add 0.5% PVA aqueous solution 58
Transfer granulation of the mixture was carried out while sprinkling 0 g, and the particle size was 2I.
Granules having a size of 1 m to 15 mm and a density of 0.6 to 0.8 g/cm'3 were obtained.

56 g of dried granules obtained by further drying this granulate with hot air
was filled into a graphite crucible. The packing density at this time is
0.57 g/am''.One reaction was carried out at 1600°C in a crucible-like vertical high-temperature reactor that had already been filled.

I went for 3 hours.

When the product obtained by the above reaction was analyzed by X-ray diffraction, it was found to be silicon carbide. Moreover, as shown in the electron micrograph of FIG. 4, the raw material obtained by the reaction is
As in Example 1, the degree of aggregation was apparently low and it was easily crushed, and furthermore, it contained almost no whisker-like irregularities. By milling the product in a ball mill for 24 hours, the average particle size was reduced to 0.2S.
A fine powder with a narrow particle size distribution in ILm was selectively obtained. A particle size distribution diagram of this fine powder is shown in FIG.

(Example 3) Silica colloid aqueous solution (silica content 15.5% by weight)
968 kg, 70 g of metallic silicon (pulverized to 741 Ls or less), and 120 g of carbon black were thoroughly mixed and kneaded using a kneader. At this time, water was evaporated by heating to obtain a dry powder.

This dry powder is molded into a mold molding machine (pressure 100 kg/c 3).
It was molded into a square shape and filled into a graphite crucible. The packing density at this time was 0.55 g/cm. One reaction is carried out in a vertical high-temperature reactor with a filled crucible.
The temperature was 600°C for 3 hours.

The product obtained by the reaction was analyzed by X-ray diffraction and was found to be silicon carbide. Moreover, as shown in the electron micrograph of FIG. 6, the product obtained by the above reaction is
Similar to Example 1, it is apparent.

It had a low degree of aggregation, was easily crushed, and contained almost no whisker-like irregularities.

By milling the product in a ball mill for 24 hours, a fine powder with an average particle size of 0.28 #Lm and a narrow particle size distribution was selectively obtained. A particle size distribution diagram of this fine powder is shown in FIG.

(Comparative Example 1) The same procedure as in Example 3 was carried out except that the dry powder in Example 3 was directly filled into a graphite crucible (packing density: 0.40 g/cs3).

The product obtained by the reaction was analyzed by X-ray diffraction and was found to be silicon carbide.

However, as shown in the electron micrograph in Figure 8, the silicon carbide obtained contained many whisker-like irregularities, and had a wide particle size distribution as shown in Figure 9. .

(Comparative Example 2) The same procedure as in Example 3 was carried out, except that the dry powder in Example 3 was directly filled into a graphite crucible (packing density: 0.38 g).

The product obtained by the reaction was analyzed by X-ray diffraction and was found to be silicon carbide.

However, as shown in the electron micrograph in Figure 10, the obtained silicon carbide contained many whisker-like irregularities, and had a wide particle size distribution as shown in Figure 11. .

Table 2 shows the raw material packing density and other matters in Example 1.2.3 and Comparative Example 1.2.

(Hereinafter referred to as margins) The numbers listed in Table 2 (Note) Morphological observation and particle size distribution indicate the numbers of each drawing.

[Effects of Application] According to the present invention, in the production of finely powdered silicon carbide using a three-component system of shisoka, metallic silicon, and carbon as raw materials, there is no contamination of foreign objects such as whiskers, and the distribution width is suitable for sintering. It was possible to provide a method that can produce finely divided silicon carbide having a narrow particle size distribution without requiring a multi-stage pulverization process.

[Brief explanation of the drawing]

FIG. 1 is a raw material composition diagram showing the blended amounts (mol%) of silica, metallic silicon, and carbon in the present invention, and FIG. 2 is a photograph substituted for a drawing, showing silicon carbide obtained in Example 1 of the present invention. FIG. 3 is a particle size distribution diagram showing the particle size distribution of silicon carbide obtained in Example 1, and FIG. 4 is a photograph substituted for a drawing. An electron micrograph showing the morphology of the obtained silicon carbide, FIG. 5 is a particle size distribution diagram showing the particle size distribution of the silicon carbide obtained in Example 2, and FIG. 6 is a photograph substituted for a drawing. An electron micrograph showing the morphology of silicon carbide obtained in Example 3, FIG. 7 is a particle size distribution diagram showing the particle size distribution of silicon carbide obtained in Example 3, and FIG. 8 is a photograph substituted for a drawing. , an electron micrograph showing the morphology of silicon carbide obtained in Comparative Example 1, FIG. 9 is a particle size distribution diagram showing the particle size distribution obtained in Comparative Example 1, and No. 1O is a photograph substituted for a drawing, showing the shape of the silicon carbide obtained in Comparative Example 1. Electron micrograph showing the morphology of silicon carbide obtained in 2 and 1
FIG. 1 is a particle size distribution diagram showing the particle size distribution obtained in Comparative Example 2. Fig. 1 Si Sin> (mol%) Fig. 1 Fig. 2 Fig. 3 Fig. 5 Fig. 7 Fig. 1, Fig. 9... Fig. 6 Fig. 10 Fig. 11 1: (Method) 198610 Jl 2 daro

Claims (3)

[Claims] (1) In a method for producing pulverized silicon carbide by mixing silica, metallic silicon and carbon as raw materials, filling the mixture in a fire-resistant container and reacting at high temperature, the mixture of raw materials filled in the fire-resistant container is Packing density 0.45g/
A method for producing finely powdered silicon carbide, characterized in that it has a particle size of cm^3 or more. (2) Claim 1, wherein the silica is a silica colloid.
The method for producing finely divided silicon carbide as described in . (3) Production of finely divided silicon carbide according to claim 1, wherein the mixture of raw materials filled in the fireproof container is a granulated product obtained by mixing the silica, metal silicon, and carbon and then granulating the mixture. Method.