JP2663819B2 - Manufacturing method of silicon carbide fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing silicon carbide fibers. More specifically, the present invention relates to a method for producing a silicon carbide fiber useful as a reinforcing fiber of a composite material or a heat insulating material.

[0002]

2. Description of the Related Art Conventional methods for producing silicon carbide fibers include a method using an organic silicon compound as a precursor, and a method in which carbon fibers or tungsten wires having a diameter of several μm are coated with silicon carbide by CVD or vapor deposition. is there.

[0003] An example of the former method is disclosed in
As described in No. 3681, polydimethylsilane is synthesized from dimethyldichlorosilane using sodium metal by a dechlorination reaction, and polycarbosilane is synthesized by a thermal decomposition reaction. The obtained polymer is melt-spun and heated in air at 100 to 190 ° C. to perform a thermal oxidation infusibility treatment, and then in an inert gas stream at 1200 to 1500.
And a method of baking at ℃.

An example of the latter method is disclosed in
As described in Japanese Patent Publication No. 0-231820, there is a method of heating and reacting carbon fibers with silicon monoxide (SiO) gas. However, in this method, only the very surface of the carbon fibers is coated with silicon carbide. There is a problem that silicon carbide fibers completely siliconized to the inside cannot be obtained.

[0005]

Since the carbon fiber coated with silicon carbide has silicon carbide only on the very surface of the fiber, when the carbon fiber is treated at high temperature in an oxidizing atmosphere, the carbon inside the fiber is oxidized and becomes hollow. There was a problem that the weight was reduced and the strength was rapidly reduced. The present invention solves the above-mentioned problems, the fiber is not oxidized even when treated at a high temperature in an oxidizing atmosphere, so that the fiber does not become hollow, or the weight does not decrease or the strength does not decrease. An object of the present invention is to provide a method for producing silicon carbide fibers having excellent heat resistance and densely siliconized to the inside.

[0006]

SUMMARY OF THE INVENTION The first aspect of the present invention relates to a fiber diameter.
Is 5 to 100 μm and the specific surface area is 100 to 2500 m ² /
g of porous carbon fiber and silicon monoxide (SiO 2) gas at a temperature of 800 to 2000 ° C.
This is a method for producing silicon carbide fibers . The second aspect of the present invention is that
Porous carbon fiber having a fiber diameter of 5 to 20 μm and a specific surface area of 700
２０００2000 m ² / g activated carbon fiber
1 is a method for producing a silicon carbide fiber according to the first aspect of the present invention.

The type of the porous carbon fiber used in the present invention is as follows.
Although not particularly limited, carbon fibers having a large diameter of several angstrom to several hundred angstroms in a large amount inside the fiber, having a specific surface area of 100 to 2500 m ² / g, and having a fiber diameter of 5 to 100 μm. Can be advantageously used. Specific surface area of carbon fiber is 100 m ² /
If it is less than g, the inside is not completely siliconized and the surface is merely covered with silicon carbide.
If it exceeds ² / g, the strength of the obtained silicon carbide fiber becomes weak, and handling becomes difficult. Further, in order to obtain a silicon carbide fiber having high strength, the porous carbon fiber is linear,
In addition, it is desirable to use a fiber whose surface is smooth and free from defects, and if possible, a material free from defects inside the fiber.

Among the porous carbon fibers used in the present invention, activated carbon fibers obtained by activating the carbon fibers are particularly preferable . Examples of activated carbon fibers include cellulosic fibers, acrylonitrile fibers, petroleum pitch fibers, polyimide fibers and phenol fibers.
Raw material and the carbon fibers, while contacting the water vapor or the like, obtained by the known activation treatment of heating up to 450-1,000 ° C. higher than the dehydration carbonizing temperatures, the fiber diameter in order to obtain a dense silicon carbide fibers to the inside Unless the activated carbon fiber has a specific surface area of 5 to ²⁰ μm and a specific surface area of 700 to 2000 m ² / g.
No. If the specific surface area is less than 700 meters ² / g of activated carbon fibers, without being fully silicon carbide of the interior fibers, only the surface is coated with silicon carbide, whereas, 2000 m ²
/ G, the strength of the obtained silicon carbide becomes weak,
Handling becomes difficult.

The supply source of the silicon monoxide (SiO) gas used in the present invention is not particularly limited, but silicon monoxide, silicon dioxide lump or powder, or silicon and silicon monoxide, or silicon and silicon dioxide fine particles are well mixed. ^10-6 to 1
Si generated by heating to 500 ° C. or more under reduced pressure of 0 Pa
It is particularly preferable to use O gas.

For the heating, a vertical or horizontal heating furnace capable of sintering a sample under reduced pressure of an internal heating type, an external heating type or an induction heating type, or in a gas atmosphere or an air stream is used. It is preferable to use a tubular or box furnace made of a material such as alumina, magnesia, zirconia, mullite or carbon.

[0011] Further, silicon carbide is generated when SiO gas enters the pores of the porous carbon fiber and reacts with carbon on the pore walls, so that the surrounding SiO gas is diffused so that the gas is easily diffused into the pores. The higher the concentration, the better. A particularly preferable gas concentration is 10 ⁻³ to 10 ² Pa in terms of vacuum. In order to generate more SiO gas as described above, a fine particle having a particle size of 0.1 to 5000 μm is used as a source material. It is desirable to use powder or granular ones,
Fine particles of 100 μm are preferable, and 10 μm
Vacuum degree as high as Pa or higher, 500-170
It is particularly desirable to heat to 0 ° C, especially 1000 to 1400 ° C.

In order for the SiO gas diffused into the pores to react with the carbon on the pore walls, it is necessary to apply energy from the outside. If the temperature is low, silicon carbide is not generated. Therefore, in order to generate silicon carbide, it is necessary to heat the porous carbon fiber and the SiO gas inside the pores after the SiO gas diffuses into the pores.

As a heating method, a tube made of a material such as alumina, magnesia, zirconia, mullite, or carbon, which can sinter a sample under reduced pressure of an internal heating type, an external heating type, or an induction heating type, or in a gas atmosphere or a gas stream. Alternatively, using a box-shaped vertical or horizontal heating furnace, in a vacuum or in an atmosphere of an inert gas such as argon or nitrogen, 800 to
It is desirable to heat to 2000 ° C. Heating temperature is 800
If the temperature is lower than ℃, the reaction is insufficient and silicon carbide is not completely converted into the interior. On the other hand, if the temperature is higher than 2,000 ° C, the generated silicon carbide fine particles grow, break easily, and the strength is lowered. In particular, the heating temperature is preferably from 1000 to 1400 ° C. in order to generate silicon carbide that is completely dense inside, and it is desirable to carry out the reaction under a vacuum of 10 Pa or less to suppress the generation of whiskers.

The heating rate during the heat treatment is not particularly limited, but is preferably from 50 to 1500 ° C./hr. Further, the holding time in the heat treatment is preferably 1 minute to 2 hours, particularly 3 hours.
0 minutes to 1 hour 30 minutes is optimal. If the heat treatment is performed for less than 1 minute, the reaction is insufficient and silicon carbide is not completely converted into the interior. On the other hand, if the heat treatment is performed for more than 2 hours, the generated fine particles of silicon carbide grow, the strength decreases, and the silicon carbide is easily broken.

As a method of bringing the porous carbon fiber into contact with the SiO gas, the SiO gas-generating substance is heated in a heating furnace in accordance with the above-described method to generate a SiO gas, which is introduced into a reaction furnace to react with the fiber. Alternatively, the gas generation and the silicon carbide generation may be performed simultaneously by placing the SiO gas generating material and the fiber in the same furnace and heating both at the same time.

In the case of the method of placing in the same furnace, in order to increase the concentration of SiO gas around the fiber, it is desirable that the SiO generating substance is in the form of fine powder or granules as described above, and its weight is A method of placing fibers on a powder or granular SiO generating substance in order to make the distance between them as small as possible with an excess of 2 to 30 times the mass of the porous carbon fibers, Embed,
Make the inside of the heating furnace as high as possible 10 Pa or more,
800 to 1700 ° C, more preferably 1000 to 140
A method of heating to 0 ° C. is desirable. In this case, in order to bring the SiO gas into contact with the porous carbon fiber at a high concentration for a long time, it is desirable that the rate of temperature rise at the SiO gas generation temperature be as low as possible, but 50 to 1500 ° C./hr, more preferably 200 to 1000 ° C. ° C / hr, and the holding time in the heat treatment is also 1 minute to 2 hours, more preferably 30 minutes to 2 hours.
1 hour and 30 minutes.

In order to produce silicon carbide fibers having high strength, it is desirable that the fibers be kept in tension when the porous carbon fibers are brought into contact with SiO gas to generate silicon carbide. For example, it is desirable to take a method of fixing both ends of the long fiber with an adhesive or a weight while keeping the long fiber in tension, or fixing one end of the long fiber and attaching a weight to the other end and lowering it in the vertical direction.

The silicon carbide fiber thus obtained is
Since the surface is smooth and hard and silicon carbide is completely and densely formed to the inside, 800 to 150 in an oxidizing atmosphere.
No loss in weight and strength is observed when treated at a high temperature of 0 ° C.

[0019]

The present invention will be described in more detail with reference to the following examples.

Example 1 Activated carbon fiber (fiber diameter 10 μm, specific surface area 1500 m ² / g) obtained by activating phenolic carbon fiber on 2 g of silicon monoxide fine powder (particle size 5 to 50 μm)
g, fiber length 100 mm), and 0.1 g of a long fiber bundle was placed thereon, and both ends of the fiber were fixed by placing weights. The fixed fiber and the silicon monoxide powder are put into an internally heated tubular carbon furnace, the pressure is reduced to 1 Pa, the temperature is raised to 1000 ° C. at a rate of 3000 ° C./hr, and then the temperature is increased to 1200 ° C.
After the temperature was raised at a rate of 0 ° C./hr, the temperature was maintained for 1 hour, and the firing was performed, and then 1000 ° C. again at a rate of 200 ° C./hr.
After cooling to room temperature, the mixture was naturally cooled to room temperature.

When the infrared absorption spectrum of the obtained fiber was examined by the potassium bromide tablet method, it was 900 cm ^-1.
The absorption of silicon carbide was observed in the vicinity, and the diffraction angle of the crystal was examined using an X-ray diffractometer. CuKα2θ = 3
Since a gentle peak was observed at around 5.7 degrees, this fiber was found to be a microcrystalline silicon carbide fiber. Further, the obtained fiber was put in an oxidizing atmosphere at 1000
After heating at 1 ° C. for 1 hour, no weight loss was observed, indicating that the fibers contained no carbon and were completely siliconized to the inside. This bundle of fibers is about 100 ~
300 pieces were subjected to a tensile test at a tensile speed of 2 mm / min using a tensile tester, and an average of 10 times was obtained.
Tensile strength is 1100 MPa and elastic modulus is 120 GPa
Met.

Example 2 In an external heating furnace, silicon monoxide fine powder (particle size: 5 to 5) was used.
0 μm) under high vacuum at a degree of vacuum of 10 ⁻¹ Pa.
Heating to 00 ° C at a heating rate of 3000 ° C / hr, and further heating to 1500 ° C at a heating rate of 1000 ° C / hr,
An SiO gas was generated. Separately, activated carbon fibers obtained by activating phenolic carbon fibers (fiber diameter 10 μm, specific surface area 1500 m ² / g, length 5
A bundle of 0.5 g (00 mm) is fixed at one end, and the other end is attached to a weight and tensioned in the vertical direction, placed in an externally heated tubular furnace, reduced in pressure to 10 ^-2 Pa, and heated to 1000 ° C. Then, the SiO gas generated as described above is introduced into the
The temperature was raised to 1200 ° C. at a temperature rising rate of 0 ° C./hr, held for 1 hour and calcined, and then fired at a rate of 200 ° C./hr.
The temperature was lowered to 00 ° C., and then naturally cooled to room temperature. The heating of silicon monoxide was continued to supply gas into the heating furnace until the silicon carbide generation reaction was completed in the heating furnace, and after the reaction was completed, the silicon monoxide was naturally cooled.

When the infrared absorption spectrum of the obtained fiber was examined by the potassium bromide tablet method, it was found to be 900 cm ^-1.
The absorption of silicon carbide was observed in the vicinity, and the diffraction angle of the crystal was examined using an X-ray diffractometer. CuKα2θ = 3
Since a gentle peak was observed at around 5.7 degrees, this fiber was found to be a microcrystalline silicon carbide fiber. Further, the obtained fiber was put in an oxidizing atmosphere at 1000
After heating at ℃ for 1 hour, a weight loss of about 10% was observed. Approximately 100 to 300 bundles of the fibers were subjected to a tensile test at a tensile speed of 2 mm / min using a tensile tester.
When the average of 0 times was determined, the tensile strength was 1400MP.
a, and the elastic modulus was 150 GPa.

Comparative Example 1 Firing was carried out in the same manner as in Example 1 except that phenol-based carbon fibers not activated were used instead of activated carbon fibers of the phenol-based carbon fibers.

When the infrared absorption spectrum of the obtained fiber was examined by the potassium bromide tablet method, it was found to be 900 cm ^-1.
Absorption was observed in the vicinity, and the presence of silicon carbide was confirmed. However, when heated at 1000 ° C. for one hour in an oxidizing atmosphere, 95%
% And a cross section was observed by SEM. As a result, it was found that only the very surface of the fiber was coated with silicon carbide, and the inside was not carbonized at all but remained carbon.

As is clear from the results of Comparative Example 1 and Examples 1 and 2, when the SiO gas is reacted with the carbon fiber, the porous carbon fiber is used to make the inside of the fiber dense and completely silicon carbide. Fibers can be obtained.

Comparative Example 2 In the same manner as in Example 1, except that the firing temperature was 600
C. and 2100.degree. C. for baking.

The obtained fiber was examined for infrared absorption spectrum by potassium bromide tablet method.
At 0 ° C., no absorption was observed at around 900 cm ⁻¹ , and the presence of silicon carbide was not confirmed. On the other hand, firing temperature 21
In the case of 00 ° C., absorption was observed at around 900 cm ⁻¹ and the presence of silicon carbide was confirmed. However, when the diffraction angle of the crystal was examined using an X-ray diffractometer, CuKα2θ = 35.7.
Since a sharp peak was observed in the vicinity of the degree, it was found that this fiber was a crystalline silicon carbide fiber in which crystals had grown considerably. Further, the obtained fiber is oxidized in an oxidizing atmosphere for 10 minutes.
After heating at 00 ° C for 1 hour, none of those with a sintering temperature of 600 ° C remained, but those with a sintering temperature of 2100 ° C did not show any weight loss. It turns out that it is becoming. Furthermore, a bundle of fibers obtained at a firing temperature of 2100 ° C.
When 300 pieces were subjected to a tensile test at a tensile speed of 2 mm / min using a tensile tester, the strength was weak and measurement was impossible.

[0029]

According to the present invention, it is possible to obtain a silicon carbide fiber which is dense and completely siliconized up to the center of the fiber, has excellent heat resistance and high strength.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location D01F 11/12 C04B 35/56 101U D06M 11/77 D06M 11/00 B

Claims (2)

(57) [Claims] 1. A fiber having a fiber diameter of 5 to 100 μm and a specific surface area of 1
A method for producing a silicon carbide fiber, comprising reacting a porous carbon fiber of 00 to 2500 m ² / g with a silicon monoxide (SiO 2) gas at 800 to 2000 ° C. 2. The porous carbon fiber has a fiber diameter of 5 to 20 μm.
m and activated carbon fiber having a specific surface area of 700 to 2000 m ² / g
The silicon carbide fiber according to claim 1,
Manufacturing method .