JPS6272600A - Production of silicon carbide whisker - Google Patents

Abstract

PURPOSE:To obtain SiC whiskers having an acicular crystal of a high aspect ratio without having curving and branching at a high yield and high productivity by heating a mixed molding composed of SiO2 powder and metallic Si powder in an H2 atmosphere in the co-presence of powdery carbon. CONSTITUTION:The molding obtd. by mixing the SiO2 powder and metallic Si powder at a prescribed ratio, adding an org. binder thereto and molding the mixture to a prescribed shape is packed into a vessel of graphite or ceramics in the state of making the powdery carbon raw material exist around the molding, then the molding is heated while gaseous H2 is passed in the vessel. SiO is generated in the form of gas from the above-mentioned SiO2 and Si by the high-temp. heating in a reducing atmosphere and since this gas makes vapor reaction with the carbon raw material around the same, the SiC whiskers consisting of the acicular crystal of the large aspect ratio without curving and branching and having the high purity are easily obtd. at a high and high productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) This invention relates to a method for producing high-purity silicon carbide whiskers in high yield.

(Prior Art) Silicon carbide whiskers are fine whisker-like linear materials that have extremely excellent properties such as tensile strength 2 and bending strength, and have recently attracted particular attention. Various attempts have been made to use this type of whisker as a reinforcing material for metal, plastic, or ceramic base materials.
Heat resistance and wear resistance are significantly improved. In order to further enhance the effectiveness of such whiskers as a reinforcing material, in this field, we are trying to eliminate defects in the crystal structure as much as possible, have a long length in the fiber longitudinal direction compared to a thin fiber diameter, and have a shape with bends and branches. There is a need to provide silicon carbide whiskers that have needle-like crystals with a large aspect ratio and are free from oscillations.
It is also desired that the manufacturing cost be low. In response to such demands, many manufacturing methods have been proposed.

For example, (1) the method described in Japanese Patent Publication No. 50-18479, (2) the method described in Japanese Patent Publication No. 58-20799,
(3) The method described in JP-A-58-45196 is mentioned.

The above method (11) involves covering a mixed powder of metal silicon powder and silicon dioxide powder with graphite powder to which a predetermined catalyst has been added, or mixing it with the above mixed powder,
12 in a reducing gas atmosphere typically represented by H2 gas.
This method involves growing carbon-silicon whiskers between the graphite powders by heating at a temperature of 00° C. or higher.

In the method (2) above, a finely powdered silicon raw material containing silicon dioxide as a main component and a finely powdered carbon raw material are molded into granules together with an organic binder, and the whole is shaped to have sufficient voids for whisker growth. , this is loaded into a furnace, and while a non-oxidizing gas such as static gas is passed through the gap, 1
This method involves heating at 320 to 1450°C to grow whiskers in the voids.

The method (3) above uses rice husk ash as a silicon source, adds ultrafine powder silicon dioxide such as colloidal silica with a particle size of 7 to 40 μm, and further
A mixture raw material is prepared by mixing carbon black of This method suppresses the generation of granular SiC contaminants.

[Problem that the invention seeks to solve]

However, with all of the above conventional methods, it is difficult to produce silicon carbide whiskers with needle-like crystals with a large aspect ratio without bending or branching, which is necessary to make a desirable composite material. The silicon carbide whiskers produced contain silicon dioxide, and when used as reinforcing materials for certain types of composite materials, they are actively treated with hydrofluoric acid (hydrofluoric acid).
There is a problem in that an information processing process such as processing is required.

Furthermore, in any of the above methods, it is not easy to separate and extract the generated silicon carbide whiskers from the raw materials used, which poses a major practical problem.

This invention was made in view of these circumstances, and is a needle-like crystal with a large aspect ratio without bending or branching.
It is possible to produce highly pure silicon carbide whiskers with a low content of granular and powdery impurities and by-product silicon dioxide at a high yield, and the produced whiskers can be separated and taken out from the production system very easily. The purpose is to provide a manufacturing method that can be used.

[Failure to solve the problem]

In order to achieve the above object, the method for producing silicon carbide whiskers of the present invention involves preparing a molded body obtained by mixing silicon dioxide powder and metal silicon powder in a predetermined ratio and molding the powdered carbon raw material, and preparing the powdered carbon raw material. The above-mentioned molded body is heated to a whisker generation reaction temperature in a hydrogen gas atmosphere in a state in which the above-mentioned molded body is coexisted with.

That is, the present inventors have conducted a series of studies in order to solve the above problems. As a result, metal silicon powder and silicon dioxide powder were mixed at a predetermined ratio, an organic binder was added thereto, and the mixture was molded into a predetermined shape. When this state is inserted into a graphite or ceramic container and heated while flowing hydrogen gas, the metal silicon and silicon dioxide generate silicon monoxide in gaseous form by heating at high temperature in a reducing atmosphere. It was discovered that by reacting in the gas phase with the surrounding carbon raw material, highly pure silicon carbide whiskers consisting of needle-like crystals with a large aspect ratio and no bending or branching can be obtained with high stock yield and productivity. , completed this invention.

Next, this invention will be explained in detail.

In general, in whisker synthesis, in order to obtain highly pure acicular crystals with undisturbed crystal planes and a large aspect ratio, it is necessary to 1) lower the concentration of the supplied raw material gas as much as possible, and 2) provide sufficient space for crystal growth. ■It is important to maintain the temperature at the minimum necessary level.

In other words, it is important to make the synthesis conditions as gentle as possible in order to obtain good whiskers.

However, this is completely contrary to the direction of increasing productivity.

The present invention is characterized in that it satisfies both quality improvement and productivity improvement, which are in an antinomic relationship, and cannot be achieved by the conventional methods described above. be.

That is, when a silicon raw material and a carbon raw material are mixed as powders and reacted while they are in contact with each other as in the conventional method, it is not possible to satisfy both quality and productivity as described above. To explain in more detail, the conventional (1)
When using a mixed powder raw material that is a mixture of metallic silicon powder and silicon dioxide powder, as in the method of happen. As a result, the amount of silicon monoxide gas generated, which is a starting material for producing silicon carbide whiskers, becomes temporarily significant and the gas concentration increases. As mentioned above, such an increase in gas concentration is the opposite of the conditions for good crystal formation, and therefore the whiskers that are formed have many bends and branches and a small aspect ratio. Become something. In addition, under the above-mentioned conditions of high gas concentration, powdered silicon carbide is produced as a by-product, which enters the resulting whiskers as impurities, reducing the purity of the whiskers. When taking out the powder, the powder used as the raw material is entrained, which requires time and effort for purification, and this becomes an impediment to productivity.

In the conventional method (2), a powdered mixture of silicon dioxide and carbon is molded into a predetermined shape using an organic binder. This means that there is no crystal growth space, which is one of the conditions for good crystal formation mentioned above. Therefore, the whiskers obtained are frequently bent and branched, and powdery substances are also generated, resulting in the same results as in the method (1) above.

The conventional method (3) is not much different from the methods (1) and (21) above in that it uses powdered raw materials, and the results are almost the same as the methods (11 and (2+) above. A slight effect is seen only in reducing the amount generated.

On the other hand, as mentioned above, the present invention does not use metal silicon powder and silicon dioxide powder as they are, but uses a molded product obtained by mixing both in a predetermined ratio, and this is mixed with powdered carbon and hydrogen gas. It is heated in an atmosphere to a whisker generation temperature. In this case, silicon monoxide gas is generated by a solid-phase reaction between metal silicon and silicon dioxide in the molded body, and it is mixed with powdered carbon and lower hydrocarbons (which include - (including carbon oxide) (gas phase/solid phase reaction or gas phase/vapor phase reaction or both reactions)
and generates silicon carbide in the form of whiskers. In this case, since the silicon-based raw material is in the form of a molded body and the carbon raw material is present around it, there is sufficient space for crystal growth between the two.

Therefore, whiskers are not formed in close contact with the inside and side surfaces of the molded body, but are formed entirely outside the molded body in the field of powdered carbon, and are generated in a space sufficient for crystal growth. Therefore, the resulting whiskers are
It has an excellent shape and aspect ratio, and is of good quality. In addition, the above reaction does not occur on the contact surfaces between the powders as in the conventional method, but in principle proceeds as a gas phase reaction, and unlike in the conventional method, the rapid reaction at the contact surfaces does not occur. No powdery silicon carbide is produced because the raw material gas concentration does not become too high. Furthermore, since the generation of whiskers occurs in a field separate from the starting material, the compact, there are no contaminants, and as a result, there is almost no need for a purification process, making it possible to improve productivity. become.

This invention uses the above metal silicon powder (preferably particle size is 100 mesh or less) as one of the essential ingredients as a raw material for a silicon-based molded body, and uses silicon dioxide powder as another essential ingredient and mixes them in a predetermined ratio. After that, it is made into a molded body.

Typical examples of the above-mentioned silicon dioxide powder include quartz powder, silica powder, powdered silica gel, various amorphous silicas, precipitated silicas, clays, etc. whose main component is silicon dioxide, and these can be used alone or in combination. be done. In addition, as a carbon raw material,
Powdered carbon is used. Carbon black and powdered activated carbon are typical examples, but it is preferable to use carbon black because the finer and bulkier the powder, the higher the reactivity. Several types of these carbon raw materials may be used in combination.

In particular, of the above two raw materials, for silicon dioxide powder,
It is preferable to choose one containing 50% by weight (hereinafter abbreviated as "%") or more of silicon dioxide. As described above, the silicon dioxide powder used in this invention includes not only those with extremely high purity, but also those containing a considerable amount of impurities.
This applies not only to silicon dioxide powder but also to metallic silicon powder.

The usage ratio of the above two powders is SiO□ in those powders,
Based on Si, the molar ratio of 5iOz/Si is 0.5/
It is preferable to mix them in a ratio of 1 to 10/1. The most preferred range is 2/1 to 8/1. If this ratio is less than 0.5/1 and the amount of SiO□ component is small, the molded material of the raw material will soften under the temperature conditions during the reaction and lose its initial shape, making it difficult to maintain the shape of the molded product. In addition, because the amount of Si component with a fast reaction rate is relatively large, the amount of silicon oxide generated temporarily increases, the concentration of the raw material gas increases, and the shape of the generated whiskers changes. There is a tendency for disorder, bending, and branching to occur frequently.On the contrary, when the above ratio exceeds 10/1 and the amount of SiO□ component increases, the amount of SiO□ component, which has a slow reaction rate, becomes relatively large. Therefore, the amount of -silicon oxide generated becomes minute, and the amount of whiskers produced under the same reaction conditions, that is, the productivity tends to decrease.

Therefore, both of the above raw materials have a SiO□/Si molar ratio of
It is desirable to use the mixture in a range of 0.5/1 to 10/l.

In this invention, both of the above raw materials are mixed in powder form and molded into a predetermined shape. During this molding, both raw materials may be molded as they are, but good results can be obtained by adding an organic binder to the molding.

A typical example of the organic binder is PVA.

Examples include water-soluble polymers and organic solvent-soluble polymers such as CMC, HEC, methyl cellulose, hydroxypropyl cellulose, and PEG, which may be used alone or in combination.

To explain the above molding in more detail, for example, one of the above organic binders is injected as an aqueous or organic solution into a powder mixture of the two raw materials so that the solid content concentration in the total volume is 5% or less, and water, After the organic solvent is vaporized and dried, it is molded into a desired shape by pressure or extrusion. Typical shapes are temporary, rod, tube, cylinder, one sphere, and linear. These molded bodies are placed in a reaction vessel together with powdered carbon and subjected to a heating reaction. In some cases, the two raw materials mentioned above are formed into a 9-tubular box shape, and this is used as a reaction vessel. Powdered carbon is filled inside the box, and the reaction vessel is directly heated by perspiration or placed in an electric furnace and heated to produce whiskers. What is done is done. In this case, there is an advantage that the molded body itself can be used as a reaction vessel and handling becomes simple. It should be noted that it is difficult to specify the ratio of powdered carbon to the above-mentioned compact from a weight perspective.This is because - a compact of any shape, i.e., any weight, can be filled into a given reaction vessel. This is due to the fact that when powdered carbon with a low bulk density is used, it may not be possible to use the amount necessary to convert all of the silicon raw material used into carbide.

As a reaction vessel for storing the above molded body together with powdered carbon, a short tube made of a magnetic material such as mullite or alumina or a graphite material is used when manufacturing silicon carbide whiskers on a small scale. When conducting on a large scale, a box-shaped container made of the above material is preferably used. In addition, as already mentioned, if the molded object itself is in the shape of a container,
Since this molded body serves both as a reaction raw material and a container, the effect of simplifying the reaction operation can be obtained.

The reaction temperature in the reaction vessel is generally 1400°C.
The temperature is preferably within the range of 1500 to 1700°C. When the reaction temperature is lower than 1400° C., silicon carbide whiskers tend to be insufficiently produced, and a large amount of unreacted molded body raw material remains. On the other hand, if the temperature is too high, the effects of improving yield and reducing impurities tend to be saturated, and production costs tend to increase. From this point of view, the upper limit of the reaction temperature is usually set at about 1700°C. Although any heating means can be used to reach the above reaction temperature, electric heating is advantageous in terms of operability.

A carrier gas containing hydrogen gas is introduced into the reaction vessel in order to set the interior to a hydrogen atmosphere.
The amount introduced is determined by the gas flow unit cross-sectional area (cIa) of the reaction vessel.
) 0.5 to 50 m1/min, preferably 1 to 20 m1
A rate of 1 minute is suitable.

The reaction time is 30 minutes to 10 hours, usually 2 to 6 hours.
About an hour is enough. If the reaction time is too short, a large amount of unreacted raw materials will remain; on the other hand, if the reaction is too long, the yield of silicon carbide whiskers will only increase slightly, so there is little advantage from the viewpoint of productivity and thermal energy cost. .

In the present invention, iron is usually used as a reaction catalyst when a molded body formed by mixing metal silicon powder and silicon dioxide powder in a predetermined ratio is subjected to a reaction with powdered carbon.

Nickel, cobalt or their compounds are used alone or in combination. Examples of the compound include powders of oxides, hydroxides, chlorides, sulfates, nitrates, and carbonates. These catalysts are usually added to powdered carbon, but when a salt of the compound is used, it is also possible to dissolve it in water or an organic solvent and then sprinkle it on the powdered carbon to make it adhere. It can also be used by mixing it into a silicon-based molding raw material. The amount of the catalyst used is usually 5 x 10-h to 5
X 10-'g, preferably lXl0-' to 1 x 10
It is used in the range of -3g. When the amount of the catalyst is less than 5xlO-6g per unit surface area (cIa) of the molded body, the catalytic action becomes insufficient and the formation of silicon carbide whiskers becomes insufficient, resulting in a reaction under the specified conditions. There is also a tendency for unreacted molded body raw materials to remain. On the other hand, when the amount is more than 5xlO-'g, the catalyst powder remains in the generated whiskers, complicating the purification process of the generated silicon carbide whiskers, and increases the aspect ratio by increasing the cross-sectional diameter of the generated whiskers. There is a tendency to lower the ratio, which is not desirable.

Further, in this invention, a reaction accelerator can be used. This is effective in aligning the whisker shapes and increasing the aspect ratio. As the reaction accelerator, halides of alkali metals and alkaline earth metals, particularly chlorides and fluorides, are preferable, and silicofluorides of alkali metals are also useful. Specific examples include lithium chloride, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, lithium fluoride, sodium fluoride, potassium fluoride, sodium silicofluoride, potassium silicofluoride, and the like. Among these, typical reaction accelerators include sodium chloride, lithium fluoride, sodium fluoride, and potassium fluoride. The above accelerators may be used alone or in combination. For any of these reaction accelerators, good results can be obtained by mixing the powder with powdered carbon used as a raw material.

The action of the reaction accelerator is to promote the generation of a volatile silicon compound during reaction from a molded product obtained by mixing metal silicon powder and silicon dioxide powder. decomposes in the presence of hydrogen halides and contributes to the above-mentioned promoting effect.

In this invention, the use of a reaction accelerator is not essential, but when used, the unit surface area of the molded article (usually 5 x 10-' to 5 x l O-'g per cd, preferably lXl0- ' to lXl0-'g gives good results.In other words, if the amount is less than 5x10-4g, almost no effect will be seen; The amount of hydrogen halide generated becomes locally concentrated, and there is a greater tendency for volatile silicon compounds to be released outside the system as they are.
This is because the amount of whisker production tends to decrease.

In this invention, as described above, the molded body and powdered carbon are placed in a reaction vessel and subjected to reaction, and after silicon carbide whiskers are generated at a predetermined temperature, heating is stopped and the reaction product is removed from the reaction vessel. Then, the obtained reaction product is heated in a Matsufuru furnace to a temperature of 600 to 800°C, and the unreacted carbon raw material is oxidized and incinerated to obtain the desired silicon carbide whiskers.

According to the method of the present invention, silicon carbide whiskers can be obtained with a high yield of 90% or more based on silicon vaporized from the generally solid molded body, and the obtained silicon carbide whiskers can be bent and It is needle-like with no branches, has long fibers, and a high aspect ratio. Moreover, since the silicon carbide whisker has a content of silicon dioxide as an impurity of usually 7% or less, it can be used without any particular purification.
It can be used for normal purposes. However, if necessary, after immersion in hydrofluoric acid, it may be kept at room temperature or heated to 70 to 80°C to dissolve silicon compounds other than silicon carbide, and purified by washing with water. .

The silicon carbide whiskers produced by the method of the present invention contain almost no powdery impurities, and generally have a fiber diameter of
Fiber length and aspect ratio are 0.1 to 0.7 μm, respectively.
, 50 to 800 μm, and 500 to 1000 μm, and has a smaller diameter and higher aspect ratio than those manufactured by conventional methods.

(Effect of the invention) As described above, the present invention provides silicon dioxide powder.

Rather than simply putting the metal silicon powder and powdered carbon into a reaction container and allowing them to react, silicon dioxide powder and metal silicon powder are mixed in advance in a predetermined ratio and then molded, and this molded body is formed in the presence of powdered carbon. Because silicon carbide whiskers are produced by heating in a hydrogen atmosphere, the raw material powders do not come into direct contact with each other and react rapidly as in conventional methods, and the whiskers are generated in sufficient crystal space. do. Therefore, good needle-shaped crystals with a high aspect ratio without bending or branching can be obtained with extremely little powdery impurities, and since no raw materials are involved, the effort of purification is reduced. It becomes unnecessary and can be separated and extracted from the production system very easily. As a result, significant improvements in manufacturing efficiency can be seen. That is, according to the present invention, it is possible to simultaneously achieve improvements in quality and productivity that could not be achieved with conventional methods, and is extremely useful in practice.

Next, examples will be described together with comparative examples.

[Example 1] Quartz powder with an average particle size of 5 to 10 μm and an average particle size of 10 to 20 μm
Using μm metal silicon powder as a starting material, SiO□/Si
Weigh both powders so that the molar ratio is 4/1? I had a H match. On the other hand, prepare a viscous liquid by dissolving hydroxypropylcellulose in dichloromethane, and pour an amount of the solution to make the solid content 5% of the total solid content used for molding into the above mixed powder to form a paste. , and then air-dried to remove the solvent. After this, the mixed powder with the binder attached was filled into a 7X15X70 dragon mold, and the powder was 0.57/cnt.
Pressure molding was carried out at room temperature at a pressure of 200 mL to obtain a prismatic solid molded body. Note that this prismatic molded body contained 20 g of the above raw material as a silicon raw material. The bending strength of this product at room temperature was 15 kg/cal.

This molded body raw material was prepared with an inner diameter of 40 mm and a wall thickness of 5.1 mm. length 1
It is inserted into a 00 dragon graphite cylinder, one opening is closed with a graphite lid, and 1 g of CoC 6H20 is added as a catalyst into the internal space.
．． 7.5 g of carbon black (U-XC-72R manufactured by Cabot), which had been added and mixed in the form of 093 g powder, was inserted and filled, and the opening on the insertion side was covered with carbon fiber felt.

The reaction vessel thus prepared was inserted into the center of an alumina furnace core tube with an outer diameter of 65 em, an inner diameter of 60 mm, and a length of 1000 mm, and then inserted into a siliconite electric furnace.

Next, add nitrogen gas to 5 m per unit cross-sectional area (cd) of the furnace core tube.
After introducing the nitrogen gas at a flow rate of 11 minutes for 1 hour, the temperature was raised at a rate of 5° C./minute, and after the temperature at the center of the furnace reached 1000° C., the introduction of nitrogen gas into the electric furnace was stopped. Next, while hydrogen gas was introduced into the furnace core tube at a flow rate of 5 ml/min/cd (core tube cross-sectional area), the temperature at the center of the tube was raised to 1530° C. and maintained at this temperature for 4 hours. Thereafter, the introduction of hydrogen gas was stopped while the temperature inside the furnace was gradually lowered, the atmosphere inside the furnace was changed to nitrogen gas, and then the contents were taken out.

The contents taken out from the graphite cylinder are dark green mossy lumps, and in the lower center of the lumps, the solid molded body used as the raw material remains after sintering and shrinking, with a gap between the lumps and the lumps. Ta. In order to remove residual carbon from this reaction product, it was fired for 4 hours in a Matsufuru furnace with an internal temperature of 700°C to obtain 6.6 g of silicon carbide whiskers. In this case, the weight loss of the solid molded body was 9.03 g. Therefore, the yield of silicon carbide whiskers based on the silicon vaporized from the solid moldings is 90.5%, and the silicon dioxide as an impurity is 5%.
%Met. In addition, the obtained silicon carbide whiskers are
The g-diffraction diagram shows a pattern of only β-5iC, and it has an acicular shape without bending or branching, and the fiber diameter, fiber length, and aspect ratio are 0.1 to 0°5 μm and 50 to 400 μm, respectively.
m, 500-800. The presence of powdered silicon carbide and other impurities was not observed at all.

[Comparative example]

Using the same quartz powder and metal silicon powder as in Example 1,
A total of 20 g of the mixed powder was weighed so that the molar ratio of 5iOz/Si was 4/1 and was inserted into the same graphite cylinder used in Example 1. Next, 7.5 g of carbon black containing the same amount of catalyst as used in Example 1 was covered on the above-mentioned mixed powder, and all other reaction conditions were the same as in Example 1. The reaction was allowed to proceed, and after cooling, the contents were taken out.

The contents were black-rimmed mossy lumps, but since they were integrated with the mixed powder used as the raw material at the bottom, most of the raw powder was separated by tapping. However, it was not possible to completely separate the whiskers, and some of them accompanied the whisker lumps, and some of the fine pseudo-whiskers, which were almost powder-like, fell together with the separated powder. Next, the above-mentioned contents from which the raw material powder had been separated were subjected to a firing treatment to remove residual carbon using a Matsufuru furnace in the same manner as in Example 1, and silicon carbide whiskers 5.2
I got g. The content of silicon dioxide as an impurity is 12%
The yield of silicon carbide whiskers was 35% based on 20 g of the raw material used.

The obtained silicon carbide whiskers contained extremely bent and branched materials, lacked a simple needle-like shape, and contained a large amount of powdery impurities. When the fiber diameter, fiber length, and aspect ratio of the nearly acicular whiskers were measured, they were 1 to 3 μm, 10 to 30 μm, and 10 to 50, respectively.

The prismatic molded body used in Example 1 and the mixed powder used in Comparative Example (20 g of both were used as raw materials) were each separately inserted into the graphite cylinder used in Example 1. , Heat treated in a hydrogen atmosphere in the same manner as in Example 1 except that the catalyst and carbon black were removed, and the weight loss was measured after holding at 1530°C for 30 minutes, 1 hour, 2 hours, and 4 hours. did. The results are shown in Table 1.

(The following is a blank space) Table 1 From Table 1, it can be seen that according to the method of the present invention, volatile compounds are gradually generated and the whisker-forming raw material components are not temporarily concentrated.

[Example 2] Colloidal silica with an average particle size of 9 μm (Nipple Seal LP, manufactured by Nippon Silikani Gyo Co., Ltd.) and reagent silicon (purity 98%, 1
00mesh passing particles), weighed both powders so that the Sing/Si molar ratio was 2/1, and 30g of mixed powder.
0.1 g of Fe2O2 powder was added and mixed. Then, an acetone solution of methylcellulose is used as an organic binder, and this is injected into the above mixed powder in an amount equivalent to 3% of the total solid content, kneaded into a paste, and then air-dried to volatilize the acetone and form a plate. Molded body (raw material mixed powder 30g
(used) was created.

This starting material has an outer diameter of 25 mm, an inner diameter of 'lQ*s, and a length of 1
00 Tsuru was inserted into the alumina Tamman tube, and 10 g of carbon black (manufactured by Lion Oil Co., Ltd., Ketjen Black EC) mixed with 112.5 g of NaC was placed in the internal gap between the tube and the plate-shaped molded body. The shaped body was covered, and the opening of the Tamman tube was covered with felt made of carbon fiber. From this point on, the reaction was carried out under the same conditions as in Example 1, and the obtained product was taken out.

Next, residual carbon was removed from the obtained product to obtain 13.5 g of silicon carbide whiskers. The weight loss of the plate-shaped compact is 15.8 g, and therefore the yield of silicon carbide whiskers based on the silicon vaporized from the plate-shaped compact is 9.
It was 1%. Silicon dioxide content as an impurity is 6%
Met.

The whiskers thus obtained contain almost no powdered silicon carbide, are composed of acicular crystals with little bending and branching, and have fiber diameters, fiber lengths, and aspect ratios of 0.2 to 0.2, respectively.
0.7 μm, 100-800 pm, 500
It was ~l 000.

2 Patent applicant Kanebo Co., Ltd.

Claims (9)

[Claims] (1) A molded body made by mixing silicon dioxide powder and metal silicon powder in a predetermined ratio and a powdered carbon raw material are prepared, and the molded body is heated in a hydrogen gas atmosphere with the powdery carbon raw material coexisting with the molded body. 1. A method for producing silicon carbide whiskers, which comprises heating the silicon carbide whiskers to a whisker-forming reaction temperature. (2) A mixed molded body of silicon dioxide powder and metal silicon powder,
The method for producing silicon carbide whiskers according to claim 1, wherein the molar ratio of silicon dioxide to metal silicon is set in the range of 0.5:1 to 10:1. (3) A mixed molded body of silicon dioxide powder and metal silicon powder,
A method for producing silicon carbide whiskers according to claim 1 or 2, which comprises an organic binder for bonding both powders. (4) The method for producing silicon carbide whiskers according to any one of claims 1 to 3, wherein the powdered carbon raw material is at least one of carbon black and powdered activated carbon. (5) The method for producing silicon carbide whiskers according to any one of claims 1 to 4, wherein at least one of silicon dioxide powder, metal silicon powder, and powdered carbon raw material contains a catalyst. (6) The method for producing silicon carbide whiskers according to claim 5, wherein the catalyst is at least one selected from the group consisting of iron, nickel, cobalt, and compounds thereof. (7) The powdered carbon raw material contains a reaction accelerator consisting of at least one of an alkali metal halide and an alkaline earth metal halide. Method for manufacturing silicon carbide whiskers. (8) The method for producing silicon carbide whiskers according to any one of claims 1 to 7, wherein the whisker generation reaction temperature is 1400°C or higher. (9) The method for producing silicon carbide whiskers according to any one of claims 1 to 8, wherein the molded body itself is formed to serve as a reaction vessel.