JPS6262188B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing silicon carbide-coated carbon fibers in which the surfaces of carbon fibers are coated with β-type silicon carbide. Carbon fiber is rayon, polyacrylonitrile,
It is already well known that lignin, lignin, etc. can be made by thermal decomposition in an inert gas, and due to its high strength and heat resistance, it has recently attracted attention as an industrial material. Applications to composite materials with plastics and metals are also being attempted. However, this carbon fiber has a limited oxidation resistance at high temperatures, has poor wettability with plastics and metals, and reacts with metals at high temperatures, so it requires various complex surface treatments. is being carried out. On the other hand, silicon carbide fibers, which have been developed in recent years as this type of heat-resistant fiber, have strong oxidation resistance at high temperatures, good wettability with plastics and metals, and do not react with metals. The raw material for its production is a special organosilicon polymer, and its production requires a complicated process of synthesizing such a polymer, then spinning it, making it infusible, and firing it. , which has the disadvantage of being very expensive. To this end, this heat-resistant fiber is produced by thermally decomposing silicon compounds such as SiCl ₄ and HSiCl ₃ on the surface of pre-manufactured carbon fibers to precipitate metallic silicon on the surface of the fiber. A method of producing silicon carbide fiber by firing this at high temperature
38700) has been proposed, but it has not yet been put into practical use because the process is complicated and requires high temperatures. The present invention relates to a method for producing silicon carbide-coated carbon fibers that solves these disadvantages, and is a method for producing carbon fibers coated with silicon carbide, which does not contain SiX (X represents a halogen atom or an oxygen atom) bond on the carbon fibers and has at least one carbon fiber in the molecule. An organosilicon compound having one hydrogen-silicon bond is thermally decomposed in the gas phase at a temperature of 700 to 1400°C.
It is characterized by forming a film mainly composed of β-type silicon carbide on the surface of carbon fibers. To explain this, the present inventors previously found that silicon carbide fibers can be obtained by subjecting the above-mentioned organosilicon compound that does not contain SiX bonds to vapor phase pyrolysis using metal or metal compound fine particles as a seed catalyst. We found that
When this organosilicon compound was subjected to vapor phase pyrolysis on carbon fibers prepared in advance, a film mainly composed of β-type silicon carbide was formed on the carbon fibers, and the resulting fibers showed no decrease in strength. The present invention was completed after confirming that it has almost no oxidation resistance, excellent wettability with plastic metals, and no reactivity with metals, and is useful as a material for heat-resistant materials, FRM, FRP, etc. . The carbon fibers used in the method of the present invention include not only organic carbon fibers obtained by firing polyacrylonitrile, rayon, pitch, lignin, etc., but also fibrous carbon obtained by vapor phase pyrolysis. Often, the method of the present invention involves, following the carbonization or graphitization step of the starting material in the firing furnace used in the carbon fiber manufacturing process, introducing the organosilicon compound described later into the same firing furnace, and Since it is sufficient to perform phase thermal decomposition, this method has the advantage that coated carbon fibers mainly composed of silicon carbide can be obtained very easily. On the other hand, if the organosilicon compound used in the method of the present invention contains SiX bonds in its molecules, sufficient thermal decomposition will not occur unless it is at a high temperature of 1500°C or higher; The silicon carbide obtained by this method does not form a uniform coating, and a trace amount of SiX remains, causing strength deterioration of the resulting coated fiber. It is necessary to do so. This organosilicon compound has, for example, the general formula R ₂ n+ ₂ (Si)n [where R is a hydrogen atom, or a monovalent hydrocarbon group selected from a methyl group, an ethyl group, a propyl group, a phenyl group, a vinyl group, etc. , n is a positive number of 1 to 4], and the general formula

[Formula] [where R is the same as above, R' is a methylene group or a phenylene group, m is 1-
Examples include silalkylene compounds or silphenylene compounds represented by the positive number 2, or compounds having the main skeletons of both in the same molecule.
If it contains a silicon bond, it can be thermally decomposed at a relatively low temperature, so this ≡
It is required to contain a SiH group. The organic silicon compounds have the following formula: CH ₃ SiH ₃ , (CH ₃ ) ₂ SiH ₂ , (CH ₃ ) ₃ SiH,
_{( C2H5 ) 2SiH2 , C3H6SIH3 , CH2 = CHCH3SiH2 , C6H5SiH3 ,} Examples include silals and polysilanes represented by the formula: Methylhydrodienepolysilanes obtained by thermally decomposing dimethylpolysilane represented by (where X is a positive number) at a temperature of 350° C. or higher are preferred. In the method of the present invention, the above-mentioned organosilicon compound is introduced into a reaction zone containing carbon fibers heated to a predetermined temperature and subjected to gas phase thermal decomposition. Thermal decomposition is slow, and at temperatures above 1400°C, this thermal decomposition becomes faster, making it difficult to form a β-type silicon carbide coating on the carbon fibers uniformly, and the physical properties of the fibers deteriorate.
This is required to be in the range of 700-1400°C, preferably in the range of 900-1300°C. The organosilicon compound may be introduced into the reaction zone using hydrogen gas or an inert gas such as nitrogen or helium as a carrier gas. If the thickness of the β-type carbon silicon film produced by thermal decomposition of this organosilicon compound is less than 0.01 μm, it will not exhibit sufficient oxidation resistance, and if it exceeds 3 μm, the fiber diameter will increase. When carrying out this process, it is necessary to adjust the amount of the organosilicon compound introduced, the reaction temperature, and the reaction time so that the β-type silicon carbide film has a thickness in the range of 0.01 to 3 μm. good. The method of the present invention involves mixing a thermally decomposable hydrocarbon compound with the above-mentioned organosilicon compound and simultaneously thermally decomposing them to form a mixed coating of β-type silicon carbide and carbon on the carbon fiber. You can do it like this. The hydrocarbon compound in this case may be either saturated or unsaturated as long as the boiling point is 250°C or less, and examples include methane, ethane, propane, acetylene, benzene, and toluene, but the amount of carbon The molar ratio of carbon/silicon carbide in the mixed coating of β-type silicon carbide and carbon formed on the fiber is often set to a range of 1 or less, and within this range, the coating with this Carbon fiber does not impair the object of the present invention in terms of oxidation resistance or reactivity with metals. Next, examples of the present invention will be given. Example 1 A quartz core tube with an inner diameter of 50 mm and a length of 1000 mm was held horizontally in a tubular electric furnace, and inside the core tube was a polyacrylonitrile-based high-strength carbon long fiber trading card T-300A with an average diameter of 10 μm and a specific gravity of 1.75. [Manufactured by Toray Industries, Inc.]
Product name: Filled with 0.213g and heated to 1030℃ in nitrogen gas.
heated to. Next, 100 c.c. of hydrogen gas containing 10% by volume of dimethylsilane [(CH ₃ ) ₂ SiH ₂ ] was added to this furnace tube.
After 30 minutes of hydrogen gas, heating was stopped and only hydrogen gas was introduced into the furnace, and the fibers were taken out after cooling. This fiber had a rather matte black color, and when it was observed using an electron microscope and examined by X-ray diffraction, it was found that this fiber had a β-SiC coating of approximately 0.4 μm on its surface. When the physical properties of this material were measured, the tensile strength of this material was 265 kg/mm ²
It is 263Kg/mm ² , which is almost the same as that at 800℃.
Even after heating for 24 hours, it still showed a value of 258 Kg/mm ² , indicating excellent oxidation resistance. Example 2 Using the same reactor as in Example 1, approximately 0.2 g of pitch-based high-elastic long carbon fiber KCF-200 (manufactured by Kureha Chemical Co., Ltd., trade name) was filled into the core tube. was heated to 980°C. Next, add tetramethyldisilane to this core tube. Hydrogen gas containing 5% by volume at a rate of 100 c.c./min 40
After being introduced for a minute, the heating was stopped and only hydrogen gas was introduced into the furnace, and the fibers were taken out after cooling. When this fiber was examined using an electron microscope and X-ray diffraction, it was found that approximately 0.3 μm of β was formed on the surface of the carbon fiber.
- It has a SiC coating, which has a tensile strength of 210 kg/ ^mm2 compared to the initial tensile strength of carbon fiber of 280 kg/mm2.
Kg/mm ² tensile strength, which also
The tensile strength after heating at 800℃ for 24 hours is also 198Kg/
mm ² and had excellent oxidation resistance. In addition, this treated fiber is immersed for 30 minutes in a metal aluminum bath heated and melted at 680℃.
After cooling, the fractured surface was observed using a scanning electron microscope, and no abnormalities were observed on the fiber surface, confirming that it did not react with aluminum. For comparison, similar equipment and raw materials were used, but when the reaction temperature was set to 680°C, almost no silicon carbide coating was obtained on the carbon fiber surface.
Although this product does not deteriorate in strength, it has a resistance of 800% in the air
When heated to ℃, it was violently oxidized and lost its fibrous shape. In addition, the reaction temperature was increased to 1450℃ using the same method.
In this case, a carbon fiber coated with β-type silicon carbide was obtained, but its strength was significantly reduced to 130 kg/ ^mm2 , and the surface of this fiber was examined using an electron microscope. When observed, it was found to be non-uniformly coated with silicon carbide. Example 3 Using the same reactor as in Example 1, an alumina substrate with a width of 30 mm x length of 200 mm x thickness of 3 mm with iron powder as a seed catalyst uniformly sprinkled on its surface was installed in the core tube. This was then heated to 1080°C, and 700 volumes of hydrogen gas containing 10 volumes of benzene was added to it.
When the catalyst was introduced at a rate of cc/min for 1 hour, it was observed that carbon fibers were produced on this type of catalyst. Next, the temperature of this reaction zone was increased to 1210℃,
Here, hydrogen gas containing 5% by volume of dimethylsilane is added.
After introducing hydrogen gas at a rate of 200c.c./min for 1 hour, heating was stopped and only hydrogen gas was introduced and cooled, the obtained fibrous material was taken out and its physical properties were examined. Fiber diameter 14μm, average length 10.5μm
m, tensile strength 248Kg/ ^mm2 , and as a result of X-ray diffraction analysis, approximately 1μm of β-
It was coated with a SiC layer. In addition, the tensile strength of this fiber after heating in air at 800℃ for 24 hours was 242Kg/mm ² , which was almost unchanged from before heating, and this was also the same in a molten aluminum bath maintained at 680℃. There were no abnormalities after immersion in water for 30 minutes, and the material did not react with aluminum. Example 4 Using the same reactor as in Example 1, about 2.5 g of polyacrylonitrile high-strength carbon long fibers (mentioned above) were filled into the furnace tube, heated to 1170°C, and then Here, hydrogen gas containing 5 volumes each of methylsilane (CH ₃ SiH ₃ ) and methane is added.
After introducing the fibers at a rate of 200c.c./min for 30 minutes, the heating was stopped and only hydrogen gas was introduced to cool the fibers.The fibers were then taken out and examined using an electron microscope and X-ray diffraction. It was confirmed that the surface of the carbon fiber was coated with a mixture of silicon carbide and carbon having a molar ratio of about 0.3 μm to β-SiC and C to 2/1. Next, I investigated this physical property and found that it is
It exhibits a tensile strength of 270Kg/ ^mm2 , which is also 800
Even after heating in air at ℃ for 24 hours, its tensile strength was 262 Kg/mm ² and it had excellent oxidation resistance. For comparison, when the above reaction gas was hydrogen gas containing 5% by volume of each of dimethylsilane and benzene at 200 c.c./min, the resulting fibers had β-SiC and C on the surface of the carbon fibers. It is coated with a silicon carbide-carbon mixture with a high carbon content, with a molar ratio of 1/3.5.
℃, after heating in air for 24 hours, it was thermally oxidized and deteriorated significantly, and although the fiber shape was maintained, it lost all strength. When immersed in a molten aluminum bath, it reacted violently with aluminum, causing the fiber shape to deteriorate. I lost.

Claims (1)

[Claims] 1. An organosilicon compound having at least one hydrogen-silicon bond in its molecule, which does not contain SiX (X represents a halogen atom or an oxygen atom) bond, on carbon fibers and has 700 to 1400 A method for producing silicon carbide-coated carbon fibers, characterized by forming a film mainly composed of β-type silicon carbide on the surface of carbon fibers by vapor-phase pyrolysis at a temperature of °C. 2. Claim 1, characterized in that a hydrocarbon compound is added to the organosilicon compound in such a range that the molar ratio of carbon to silicon carbide produced by their vapor phase thermal decomposition is 1 or less. A method for producing silicon carbide-coated carbon fiber.