JPS63156098A - Production of silicon carbide whisker - Google Patents

Abstract

PURPOSE:To obtain the title silicon carbide whisker contg. a small amt. of remaining unreacted carbon and having an excellent acicular property, by separately heating the carbon compact contg. a catalyst along with carbon and an silicon-contg. raw material in the same H2-atmosphere reaction furnace. CONSTITUTION:The carbon-contg. compact contg. a metal or its compd. as the catalyst is prepared. The carbon-contg. compact and the silicon-contg. raw material are separately arranged in the reaction furnace. The compact and raw material are heated in an H2-atmosphere and allowed to react with each other, and the silicon carbide whisker is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing silicon carbide whiskers which are highly pure and substantially free of bent objects and particulate matter. In a method for producing silicon carbide whiskers by heating a silicon-containing raw material and a carbon-containing raw material in a hydrogen atmosphere, a carbon-containing molded body containing a catalyst together with carbon is used as a carbon-containing raw material, and the carbon-containing raw material is of high purity and substantially The present invention relates to a method for producing silicon carbide whiskers that are free of bends and particles.

The narrow-barrel silicon carbide whiskers have a perfect single-crystal structure and are lightweight, strong, and highly elastic, so they are expected to be used as reinforcing materials for metallic composite materials based on aluminum or its alloys. has been done.

Such silicon carbide whiskers are generally produced by reacting a silicon-containing raw material and a carbon-containing raw material, usually at a temperature of 1400° C. or higher. More specifically, gas phase synthesis method and solid phase synthesis method are conventionally known as typical methods for producing silicon carbide whiskers. Gas phase synthesis methods include thermally decomposing a mixed gas of silicon halides and hydrocarbons, or organosilicate metal gas containing carbon and halogen in a hydrogen stream, and carbonizing a silicon compound in a reactor. A method of generating silicon carbide whiskers in a reactor by circulating a gas such as hydrogen or hydrogen chloride (Japanese Patent Publication No. 52-28757), in which a crucible filled with silicon dioxide, carbon powder, sodium fluoride, etc. is inert. A method of precipitating and growing silicon carbide whiskers by heating in an atmosphere and reacting vaporized silicon monoxide and carbon monoxide in a low temperature range (Special Publication No. 54-15
555, Japanese Unexamined Patent Publication No. 56-100125), etc. are known.

These gas phase synthesis methods can produce acicular silicon carbide whiskers, so they are advantageous from this point of view, but on the other hand, the utilization rate of raw materials is low, and therefore the yield of silicon carbide whiskers is low. Therefore, it is not suitable as a method for mass production of silicon carbide whiskers. Furthermore, in this gas phase synthesis method, there is a problem that the feedstock decomposes in the furnace and contaminates the reactor and the generated whiskers.

On the other hand, as a solid phase synthesis method, for example, a method of mixing a powdered silicon-containing raw material and a carbon-containing raw material, molding the mixture, placing the molded body in a sagger pot, and heating it in a heating furnace equipped with a tray pusher (Unexamined Japanese Patent Publication No. Publication No. 58-20799, Japanese Unexamined Patent Publication No. 58-91
010, Japanese Patent Publication No. 50-25907), and this method is suitable for mass production of silicon carbide whiskers, but it produces a large amount of powdered or bent silicon carbide whiskers, and is difficult to obtain. The resulting silicon carbide whiskers contain a large amount of impurities.

Therefore, the present inventors are able to produce silicon carbide whiskers with improved shape and purity by forming a silicon-containing raw material into a predetermined shape in advance and heating this in a hydrogen atmosphere with a powdered carbon-containing raw material. Although a method has already been proposed, it is unavoidable that it contains small amounts of powder, tortuous materials, and impurities.

Problems to be Solved by the Invention As a result of intensive research in order to solve the above-mentioned problems in the production of silicon carbide whiskers, the present inventors have developed a carbon-containing molded body containing a catalyst such as an iron compound as a carbon-containing raw material. silicon carbide whiskers are selectively generated on the carbon-containing compact by heating this together with a powdered silicon-containing raw material in a hydrogen gas atmosphere to a high temperature,
Moreover, it was discovered that the silicon carbide whiskers obtained in this manner do not substantially contain any powder or tortuous material, and furthermore, have extremely high purity, leading to the present invention.

That is, the present invention uses a carbon-containing molded body containing a catalyst as a carbon-containing raw material and heats it to a high temperature together with a powdered silicon-containing raw material in a hydrogen gas atmosphere, thereby forming a carbon-containing molded body substantially free of bent objects and granular materials. The object of the present invention is to provide a method for producing silicon carbide whiskers with extremely high purity.

The present invention for solving the problem is a method for producing silicon carbide whiskers by heating and reacting a silicon-containing raw material and a carbon-containing raw material in a reactor, and a carbon-containing molded material containing an iron compound as a carbon-containing raw material. using a carbon-containing molded body and arranging the carbon-containing molded body separately from the silicon-containing raw material in a reactor,
It is characterized by heating under a hydrogen gas atmosphere.

The carbon-containing molded body used in the method of the present invention contains carbon and a catalyst, and is preferably a porous molded body. Such a molded body is made of, for example, a carbon precursor that can be carbonized by heating and firing, such as a thermosetting resin or various pitches, a catalyst, and optionally various additives, such as
After kneading it with a binder and molding it into the desired shape,
It can be obtained by heating and firing to carbonize the carbon precursor. As described above, the method itself for firing a molded body of a carbon precursor into a porous body is already known. In order to adjust the porosity of the resulting molded body, an organic substance that decomposes and volatilizes during carbonization firing may be added to the kneaded material containing the carbon precursor, if necessary.

Although the shape of the carbon-containing molded body is not particularly limited, a thin plate shape with a thickness of approximately 0.1 to 1 mm is suitable, for example.

However, in the present invention, the shaping means and the shape of the carbon-containing molded body are not limited at all, and as the shaping means,
For example, means such as extrusion molding, press molding, and granulation can be used, and the molded object can also have a shape of a plate, rod, tube, tube, sphere, line, or a combination thereof.

In the method of the invention, the carbon-containing molded body contains a reaction catalyst. Such catalysts are already known, and in the process of the invention, for example, iron, nickel, cobalt, or compounds thereof, such as oxides, nitrates, chlorides, sulfates, carbonates, etc., are preferably used. can. Particularly suitable are iron oxide and iron chloride, for example.

In the method of the present invention, silicon carbide whiskers are obtained by heating the carbon-containing molded body and the silicon-containing raw material to a predetermined reaction temperature in a hydrogen gas atmosphere. Here, the hydrogen gas atmosphere includes not only hydrogen gas but also an atmosphere containing 20% by volume or more of hydrogen, with the remainder being a non-oxidizing inert gas.

As the silicon-containing raw material, for example, silicon dioxide powder can be used, but in the present invention, a mixed powder of simple silicon and silicon dioxide is preferably used. In particular, it is preferable to use a mixed powder containing 1 to 6 moles of silicon dioxide per mole of silicon alone. The reason will be explained later.

In the method of the invention, the reaction temperature is at least 1400
℃ or higher, usually preferably 1500 to 1700℃
is within the range of When the reaction temperature is lower than 1400°C, silicon carbide whiskers are insufficiently produced. on the other hand,
If the temperature is too high, the effects of improving the yield and reducing impurities will be saturated and the production cost will increase, so the upper limit of the reaction temperature is usually preferably about 1700°C. Although the heating means is arbitrary, electric heating is easy to use.

The reaction time is 30 minutes to 10 hours, and usually about 2 to 6 hours is sufficient. 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 increase only slightly. , there is no advantage.

In the method of the present invention, when heating the above-described carbon-containing molded body and silicon-containing raw material to a predetermined temperature in a hydrogen atmosphere to generate silicon carbide whiskers, the carbon-containing molded body is The body and the silicon-containing raw material are placed separately. As described later, according to the method of the present invention, silicon carbide whiskers are selectively generated on the carbon-containing molded body, so by separating the carbon-containing molded body from the silicon-containing raw material in this way, silicon carbide whiskers can be obtained. There is no possibility that unreacted silicon dioxide or the like will be mixed into the silicon carbide whiskers as impurities.

In the solid phase synthesis method according to the present invention using a carbon-containing molded body and a silicon-containing raw material, ideally, C (solid) +
2To (air) - CH# (air) (1) Si (solid) + S
iO□ (solid) → 2SiO (air) (2) SiO□ (solid) +
CHt (Ki) → 5in (Ki) + GO + 2) 1g (
3) Sin (Ki) + 2C (Hard) → 5iC (Hard”)
+ CO (gas) (4) reaction occurs, and in particular, by using a mixed powder of simple silicon and silicon dioxide as the silicon-containing raw material, silicon monoxide contributes to the generation of silicon carbide whiskers according to formula (2). , the yield of silicon carbide whiskers increases, and furthermore,
Silicon carbide whiskers grow on a carbon-containing molded body using the catalyst contained in the carbon-containing molded body as a formation nucleus, so they can be easily separated from the molded body, and therefore, they can be easily separated from the molded body, and therefore contain substantially no unreacted carbon. It has excellent acicular properties and contains virtually no powder or bent substances.

After producing silicon carbide whiskers at a predetermined temperature in this way, the heating is stopped, the reaction product is taken out from the reactor, and then, if necessary, the reaction product is placed in a Matsufuru furnace for 600 min. Heating to a temperature of ~1100℃,
By thermally incinerating a small amount of unreacted carbon material that may be contained, extremely pure, acicular silicon carbide whiskers can be obtained in high yield.

Effects of the Invention According to the method of the present invention, as described above, silicon carbide whiskers are produced on a carbon-containing molded body using a porous body containing carbon and a catalyst as a carbon-containing raw material.
Not only is it easy to separate silicon carbide whiskers, but also
There is significantly less unreacted carbon remaining in the resulting silicon carbide whiskers.

Furthermore, since silicon carbide whiskers grow using the catalyst contained in the carbon-containing molded body as a generation nucleus, they have excellent acicular properties and substantially do not contain powder or bent objects.

Further, according to the method of the present invention, by arranging the carbon-containing molded body separately from the silicon-containing raw material in the reactor, unreacted silicon components are not mixed into the silicon carbide whiskers produced.

Therefore, according to the method of the present invention, it is possible to obtain acicular silicon carbide whiskers of extremely high purity and substantially free of powder or bent materials at a high yield.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way.

Porous carbon plate containing 4% by weight of iron oxide (length 100
R1 width 5011, thickness 1) were vertically attached at 1 fl intervals to a container made of isotropic graphite, and at the same time, at the bottom of the container, at 5 fl intervals from the lower end of the molded body, as a silicon-containing raw material. , a homogeneous mixture of 2 g of silicon powder and 17.1 g of silicon oxide powder was laid down.

This container was loaded into a reactor and heated to 1530°C under a hydrogen stream.
After holding at a temperature of 4 hours, the product was taken out of the furnace, and β-silicon carbide whiskers were obtained as a white mold-like substance growing densely on the carbon-containing molded product. This fungal substance is
It could be easily peeled off from the carbon-containing molded body. still,
The amount of unreacted carbon contained in this silicon carbide whisker was small.

After the silicon carbide whiskers were immersed in hydrofluoric acid overnight, the weight loss was 2%, and it was confirmed that the silicon carbide whiskers had extremely high purity.

Further, when this silicon carbide whisker was examined using a scanning electron microscope, substantially no powdery or bent material was observed.

Comparative Example An NC Tammann tube containing 49% by weight of silicon dioxide and having an outer diameter of 25 nm, an inner diameter of 201 m, and a length of 100 fl was used as a silicon-containing molded body that also served as a reaction vessel.

50 parts of carbon black powder, 0.2 parts of finely powdered iron oxide as a reaction catalyst, and 17 parts of sodium chloride powder (grade 1 reagent) as a reaction promoter were stirred in a ball mill for 1 hour to form a homogeneous mixture. 2 g of the mixture was filled into the Tammann tube, and the tube was inserted into an electric furnace.

After introducing nitrogen gas into this electric furnace at a flow rate of 5 ml/min per unit cross-sectional area (cd) of the furnace core tube for 1 hour, the temperature at the center of the furnace reached 1530°C at a temperature increase rate of 5°C/min. It was heated until it was. In this temperature raising process, after the indoor hot water reaches 1000°C, the introduction of nitrogen gas to the electric furnace is stopped, and then,
While hydrogen gas was introduced into the electric furnace at a flow rate of 5 ml/min, the temperature inside the furnace was raised to 1550° C. and maintained at this temperature for 2 hours. After this, the introduction of hydrogen gas was stopped while gradually lowering the temperature inside the furnace, and then the atmosphere inside the furnace was changed to nitrogen gas, and the contents were taken out and the black-rimmed, lightweight, bulky mass was reacted. Obtained as product. The amount of unreacted carbon in this reaction product was about 50%.

In order to remove excess carbon from this reaction product, it was fired for 4 hours in a Matsufuru furnace with an inner hot water of 800°C to obtain silicon carbide whiskers. The silicon dioxide as an impurity in this silicon carbide whisker was 12%. Also,
The obtained silicon carbide whiskers had branches and bends.

Patent applicant: Kobe Steel, Ltd. Kanebo Co., Ltd.

Claims (7)

[Claims] (1) In a method of manufacturing silicon carbide whiskers by heating and reacting a silicon-containing raw material and a carbon-containing raw material in a reactor, a carbon-containing molded body containing a metal or its compound as a catalyst is used as the carbon-containing raw material. With,
A method for producing silicon carbide whiskers, which comprises arranging this carbon-containing molded body separately from a silicon-containing raw material in a reactor and heating it in a hydrogen gas atmosphere. (2) The method for producing silicon carbide whiskers according to claim 1, wherein the carbon-containing molded body is a porous body formed by molding a thermosetting resin containing a catalyst and carbonizing and firing the molded body. . (3) The method for producing silicon carbide whiskers according to claim 1 or 2, wherein the catalyst is selected from the group consisting of iron, nickel, cobalt, and compounds thereof. (4) The method for producing silicon carbide whiskers according to claim 3, wherein the catalyst is an oxide, nitrate, chloride, sulfate or carbonate of iron, nickel or cobalt. (5) The method for producing silicon carbide whiskers according to claim 1, characterized in that a mixed powder of simple silicon and silicon dioxide is used as the silicon-containing raw material. (6) The method for producing silicon carbide whiskers according to claim 5, wherein the mixed powder contains 1 to 6 mol of silicon dioxide per 1 mol of silicon. (7) The method for producing silicon carbide whiskers according to claim 1, wherein the reaction temperature is 1400°C or higher.