JPH07116642B2 - Method for producing silicon carbide fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a silicon carbide fiber obtained by spinning a specific polyolefin (silicon-containing polymer compound) having a SiH ₃ group in its side chain and then firing it at a high temperature. To a method of manufacturing.

[Background technology]

In recent years, the technical development of highly functional fibers, especially inorganic fibers, has been remarkable, for example, silicon carbide fibers and Si-Ti-C.
-O fiber, silicon nitride fiber, carbonized fiber, glass fiber,
SiO ₂ -TiO ₂ fibers, etc. have been developed, and some of them have already been marketed as a high-strength fiber with excellent heat resistance, especially as a reinforcing material for basic materials such as resins, metals, and ceramics. Demand growth is expected.

Among these, the silicon carbide fiber, which is the object of the present invention, is particularly expected as an advanced composite material due to its high-temperature characteristics, and as currently manufactured industrially, for example, Nippon Carbon Co., Ltd. , Manufactured under the trademark "Nicalon" (Japanese Patent Publication No. 57-26527, Japanese Patent Publication No.
57-53892, JP-B-57-38548). This is produced according to the following formulas (I), (II) and (III) using dimethyldichlorosilane obtained by the direct method as a starting material.

The step (I) is usually carried out in a state where metal sodium is melted in xylene and then dispersed (to 100 ° C.), but the treatment of unreacted residual sodium is complicated. In addition, the process of (II) is performed under high temperature and high pressure (about 500 ° C, 1
(00 atm) or a reaction accelerator such as polyborosiloxane (350 ° C, normal pressure) is used, but low molecular weight compounds cannot be used and the yield is low (50% or less). (III)
In the process of, the infusibilization treatment is performed in air after melt or dry spinning, and thereafter 1200 to 1200 in nitrogen or vacuum.
The target SiC fiber is obtained by firing at 1300 ℃, but the SiC fiber thus obtained is free carbon (10 to 20w
t%) or silica (about 20 wt%),
It is said that these adversely affect the physical properties of the product and the strength at high temperature.

The inventors of the present invention have the above-mentioned problems of the conventional method (that is, (1) the manufacturing process is complicated, (2) the yield is low, (3)
Free carbon is contained in the final SiC fiber),
The present invention has been achieved as a result of earnest efforts to develop a manufacturing method for producing a SiC fiber that is more economical and has excellent physical properties.

[Summary of Invention]

That is, the present invention is (However, n is 0 or a positive integer of 1 to 10, R ₁ is hydrogen,
An alkyl group or an aryl group, and R ₂ represents an alkylene group or a phenylene group) is formed into a fiber by spinning a silicon-containing polymer compound containing a repeating structural unit represented by: b. And 50.degree.-300.degree. C. for infusibilizing treatment, and c. Furthermore, the infusibilized fiber is heated at 800-2000.degree. C. in vacuum or in an inert gas for producing a silicon carbide fiber, Is.

[Detailed Disclosure of the Invention]

 Hereinafter, the present invention will be described in detail.

The polymer used as a starting material in the present invention is a carbon-based polymer having a silyl group (SiH ₃ group) in its side chain, and has the general formula (1) It is a silicon-containing polymer compound containing a repeating structural unit represented by, and this is the greatest feature of the present invention.

The degree of polymerization m of the polymer compound represented by the formula (1) is 3 or more,
It is preferably 10 or more, more preferably 50 or more. Further, n is 0 or a positive integer of 1 to 10, and the smaller the ceramic yield (Si weight in the fired body / Si weight (%) in the silicon-containing polymer compound), the more preferable, and the most preferable. 0. R ₁ is hydrogen, an alkyl group or an aryl group such as —H, —CH ₃ , —C ₂ H ₅ , iC ₃ H ₇ , or —Φ.
(-Φ indicates a phenyl group. The same applies hereinafter), -Φ-C
H ₃ and —CH ₂ —Φ are listed, and those having a smaller number of carbon atoms are preferable, and hydrogen is most preferable. R ₂ is an alkylene group or a phenylene group, for example, —CH ₂ —, (—CH ₂ ) ₂ ,
(-CH ₂ ) ₄ , -Φ-, -CH ₂ -Φ-, etc., but the smaller the carbon number is, the more preferable it is as in R ₁ . Note that R ₁ and R ₂ above are -COO
It may contain functional groups such as H, —NH ₂ , and —OH. It may be chain-like or cyclic, and in the case of chain-like, the end thereof is hydrogen, an alkyl group or the like.

Further, the silicon-containing polymer compound in the present invention may be a polymer composed only of the same kind of repeating structural unit represented by the general formula (1), or may be the same as each other represented by the general formula (1). It may be a polymer composed of different types of repeating structural units. Of course, the stereoregularity of these polymers is not limited, and may have any stereostructure such as isotactic, syndiotactic, and atactic. The molecular weight is not particularly limited, but is usually 100 to 1
0,000,000, preferably about 200 to 1,000,000, is desirable in view of easy processability and solubility in a solvent.

Further, a copolymer comprising the repeating structural unit and another vinyl-based polymer structure containing no silicon, for example, a repeating structural unit derived from vinyl such as ethylene, propylene, styrene, vinyl chloride, butene, isibutene, and MMA. Is also good. Such copolymerization may be random, alternating, block or draft. In this case, at least 0.1% by weight of the structural unit of the invention
It is desirable to have more than one. The molecular weight of these copolymers is not particularly limited, but usually 100 to 10,000,000, preferably about 200 to 1,000,000 is desirable in view of easy processability and solubility in a solvent.

Needless to say, it is particularly desirable that the silicon-containing polymer compound used in the present invention is easily processable and has a high ceramic yield, for the purpose of the present invention.
From these ceramics yields, the ease of obtaining monomers, the ease of producing polymers, the meltability, and the solvent solubility (workability), as a particularly preferred specific example, a repeating structural unit is: Or Examples thereof include silicon-containing polymer compounds containing one kind or two or more kinds and copolymers thereof.

The above-mentioned compounds are used as the silicon-containing polymer compound used in the present invention, but the manufacturing method or polymerization method thereof is not particularly limited, and those manufactured by various methods can be preferably used.

For example, an α-olefin having a SiH ₃ group is treated with Ziegler-Na
Coordination anion polymerization with tta type catalysts (transition metal salts such as titanium halide, vanadium halide, zirconium halide and alkylaluminium); metal oxides (CrO ₃ , SiO ₂ , Al ₂ O ₃ etc.) , Hydrogen acid (H ₂ SO ₄ , H ₃
PO ₄ , HClO ₄ , HCl, etc.), Lewis acid (BF ₃ , AlCl ₃ , FeCl ₃ ,
(SnCl ₄ etc.) Cationic polymerization with a catalyst; alkali metal (Li, Na, K etc.), alkyl alkali (C ₂ H ₅ Na,
(C ₂ H ₅ ) ₃ Al, C ₆ H ₅ Li, etc.), a method of anionic polymerization using a hydroxide (NaOH, KOH, etc.) catalyst; a method of radical polymerization using a peroxide as an initiator; Method can be adopted. As a matter of course, the polymerization can be carried out in either a gas phase or a liquid phase, or in a solvent or without a solvent (bulk polymerization). Further, in these polymerizations, the molecular weight of the polymer can be easily adjusted by coexisting hydrogen and the like.

The SiH ₃ group-containing α-olefin serving as a monomer for polymerization can be produced by various methods and is not particularly limited in the present invention. For example, the method represented by the following formula can be adopted.

Among these, SiH ₄ is used as a raw material, and particularly, is a hydrosilylation reaction using a Group VIII metal as a catalyst, and the desired α-olefin can be easily obtained. In addition, SiH ₄ has become popular in recent years as demand for polysilicon and amorphous silicon has expanded, and it is now manufactured at low cost and in large quantities. Is. Therefore, the silicon-containing polymer compound containing the SiH ₃ group in the present invention is of great significance in that it can be easily and inexpensively produced by polymerizing a monomer obtained from this SiH ₄ and an olefin. Can be said. Further, the polymer of the present invention when using this SiH ₄ is, for example, a polymer having the following repeating structural unit from a conventional alkylchlorosilane as a raw material as described in the section of the background art, for example, In comparison, the production can be carried out in a non-chlorine system, and there is no fear of corrosion, and the process is extremely simple. From the above, it seems that the polymer according to the present invention can be manufactured at a lower cost in the future.

Further, the silicon-containing polymer compound in the present invention is not only easy to polymerize, but also its processability (flowability of the melt,
Solvent solubility) can be easily changed by controlling its molecular weight and stereoregularity. Furthermore, the SiH ₃ group present in the silicon-containing polymer of the present invention is extremely stable, does not oxidize at room temperature even in air, and finally oxidizes at a high temperature around 150 ° C.

The silicon-containing polymer compound in the present invention can be formed into fibers by conventional polycarbosilane, etc., for example, Basically, the same method as in the case of using a prepolymer having a repeating structural unit can be used.

That is, taking advantage of the fact that the silicon-containing polymer compound of the present invention is easily processable, it is spun by a melt, wet or dry spinning method in an inert gas, particularly preferably by a melt or dry spinning method.

Next, the obtained fiber is placed in an oxygen-containing gas at 50-30
Surface oxidization, that is, infusibilization treatment is performed in the range of about 0 ° C. to prevent fiber adhesion. The treatment time may vary depending on the temperature and the oxygen concentration, but is appropriately selected within the range of several seconds to several hours. The oxygen concentration is in the range of 10 ppm to 100%. However, depending on the properties of the fibers, it is of course possible to omit this treatment as shown in the examples below.

Subsequently, the infusibilized fiber was placed under vacuum or nitrogen,
Several minutes to several tens of minutes at 800 to 2000 ° C in an inert gas atmosphere such as helium, neon, argon, and krypton.
The desired silicon carbide fiber is obtained by heating within the range of time.

As a feature of the method for producing a silicon carbide fiber in the present invention,
As described in Examples below, ceramics (Si
C) The yield is extremely high, and the amount of free carbon in the fiber after firing is extremely low.

For example, polycarbosilane consisting of the following repeating structural units: Is currently used as a prepolymer for SiC fiber, but although the ceramic yield when converted to fiber is reasonably good, it has a large amount of free carbon (about 10 wt%), and when it is used as fiber, it is a preventive process. It is said that SiO ₂ (about 20 wt%) is mixed in the infusibilizing treatment performed in the above, and these adversely affect the fiber strength.

The method for producing a silicon carbide fiber by firing the silicon-containing polymer compound in the present invention is a silyl group (SiH ₃ group) in which the silicon-containing polymer compound is highly reactive with oxygen.
Therefore, by controlling the amount of oxygen (oxygen concentration) infusibilizing temperature in the oxygen-containing gas atmosphere gas to be infusibilized in an appropriate range, only the surface of the spun polymer is suitably oxidized, Can be infusibilized. That is, in the method of the present invention, a part of the surface silyl group (SiH ₃ group) SiH bond is oxidized and crosslinked by the siloxane bond.
Compared with the case of using conventional polycarbosilane,
It is possible to obtain a fiber having high physical properties, which has a low oxygen uptake and a small amount of silica contained in the fiber.

The silicon carbide fiber according to the present invention is far superior in high temperature strength to the fiber obtained by the conventional method, as shown in the following examples, reflecting the low carbon and silica contents.

In the method of the present invention, the reason why the ceramic yield is high and the amount of free carbon in the fiber is small is not clear, but in the thermal decomposition process, the Si--H bond of the SiH ₃ group is first broken and crosslinked. It is presumed that it is difficult for the oligomer to scatter out of the system, and that the decomposed hydrogen prevents carbonization of the polymer.

〔Example〕

 Hereinafter, the present invention will be described with reference to examples.

Example 1 SiH ₄ and acetylene were added to the Journal of American
Chemical Society (Journal of American Chemic
al Society), 76, 3897 (1954)) to produce vinylsilane (CH ₂ = CHSiH ₃ ). Next, under nitrogen atmosphere, 36.7 g of this vinylsilane, 1 g of titanium trichloride type catalyst for olefin polymerization (manufactured by Toho Titanium Co., Ltd.), Al (iC ₄ H ₉ ) ₃ 3.3 m
150 ml of l, n-heptane was charged into an autoclave having a volume of 200 ml and reacted at 70 ° C. for 4 hours. After completion of the reaction, the reaction mixture was charged into methanol to remove the catalyst residue in the polymer and at the same time to precipitate the produced polymer. The obtained polymer weighs 19 g, and the results of IR, elemental analysis, etc. It was confirmed that the polymer had a repeating structural unit of This polymer is stable in air at room temperature, around 150 ° C.
At this point, the SiH ₃ group disappeared rapidly and a siloxane bond was formed. The crystallinity was about 60% and the melting point was 170 to 180 ° C. The average molecular weight was about 100,000 (according to the viscosity method.
same as below).

This polymer was spun by a melt spinning method to obtain an organosilicon polymer compound fiber having a diameter of 10 μm. This fiber is heated in vacuum (1 × 10 ³ mmHg) to 1000 ° C. for 10 hours, preheated, further heated to 1200 ° C. in an argon gas atmosphere, and baked at that temperature for 2 hours to obtain SiC fiber. Got The ceramic yield in this fiber production was 48%, the fiber tensile strength was 750 kg / mm ² , and the calcined material was further calcined at 2000 ° C. and examined by X-ray diffraction, but a diffraction peak due to free carbon was observed. I couldn't do it.

Example 2 In Example 1, titanium trichloride type catalyst, Al (iC
₄ H _{9) 3,} respectively in place of n- heptane _{Cp 2 Zr (CH 3) 2} 0.
An experiment was conducted in the same manner as in Example 1 except that 5 g, methylalumoxane ([Al (CH ₃ ) O] _16-20 ) 9 g, and toluene 150 ml were used, and the reaction was performed at a reaction temperature of 20 ° C. for 10 hours. A polymer having the following repeating structural unit was obtained.

This polymer was dissolved in toluene and spun by a dry spinning method to obtain an organosilicon polymer compound fiber having a diameter of 10 μm. This fiber was treated in the same manner as in Example 1 to obtain a silicon carbide fiber.

The evaluation results are shown in Table 1.

Examples 3 and 4 Experiments were carried out in the same manner as in Example 1 except that propylsilane and butenylsilane were used in place of vinylsilane as the polymerization monomer, and the experiments were carried out respectively. A polymer having a repeating structural unit of was obtained.

Using this polymer, a silicon carbide fiber was obtained in the same manner as in Example 2.

The evaluation results are shown in Table 1.

Comparative Example 1 400 in an autoclave of permethylpolysilane with a repeating structural unit
℃, obtained by heating at 100 atm for time Polymer evaluation was carried out in the same manner as in Example 1 except that polycarbosilane having the following repeating structural unit was used.

The evaluation results are shown in Table 1.

〔The invention's effect〕

The present invention provides a method for producing silicon carbide ceramics using a novel silicon-containing polymer compound as a prepolymer for silicon carbide fibers. The silicon-containing polymer compound used in the present invention has excellent plasticity, solvent solubility, etc., and is not only easy to spin, but a method for obtaining a fiber from this is to use a conventional silicon carbide fiber made of polycarbosilane as a raw material. In comparison, it has excellent characteristics such as high ceramic yield, low oxygen uptake in the infusibilization process after spinning, and low free carbon and silica contained in the fiber. . For this reason,
A fiber having a significantly improved tensile strength as compared with the conventional fiber can be obtained.

The fiber prepolymer used in the present invention can be easily produced, for example, by producing an α-olefin containing a silyl group from industrially easily obtainable monosilane, and polymerizing the α-olefin. It is possible to

Claims (3)

[Claims] 1. (However, n is 0 or a positive integer of 1 to 10, R ₁ is hydrogen,
An alkyl group or an aryl group, and R ₂ represents an alkylene group or a phenylene group) is formed into a fiber by spinning a silicon-containing polymer compound containing a repeating structural unit represented by: b. And 50.degree.-300.degree. C. for infusibilizing treatment, and c. The infusibilized fiber for heating at 800-2000.degree. C. in vacuum or in an inert gas. 2. The method according to claim 1, wherein the silicon-containing polymer compound is a vinylsilane polymer. 3. The method according to claim 1, wherein the silicon-containing polymer compound is a polymer of butenylsilane.