JPH07121801B2 - Method for producing silicon carbide - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silicon carbide by firing a specific polyolefin (silicon-containing polymer compound) having a SiH ₃ group in a side chain at high temperature.

[Background technology]

In recent years, the technological development of silicon-containing ceramics has been remarkable, and for example, silicon carbide (SiC), silicon nitride (Si ₃
N ₄ ), sialon, Si-Ti-C-O ceramics (Tyranno fiber, Ube Industries), SiC-B ₄ C ceramics, Si ₃ N
_4- SiC composite ceramics are drawing attention as so-called fine ceramics.

Among these, the silicon carbide according to the present invention is obtained in the form of powder, whiskers, fibers, etc., and has been conventionally produced by various methods. For example, a direct carbonization method, a reduction carbonization method, a vapor phase synthesis method, a thermal decomposition method of a silicon compound, and the like. The direct carbonization method uses metallic silicon at high temperature (1400 ~
2600 ℃), which is reduced by coke, but is cheap,
It is difficult to control the reaction because fine silica SiO ₂ is necessary to obtain fine crystal SiC with excellent sinterability and the reaction is exothermic. The reducing carbonization method is a method of reducing SiO ₂ with coke, and β-SiC is obtained by reacting in argon at 1500 to 2000 ° C., and α-SiC is obtained by a similar method, the Acheson method. This method is the mainstream of current industrial methods. The gas phase synthesis method is Si
It is a reaction of Cl ₄ , SiH _4, etc. with hydrocarbons at 1200 ° C. or higher. Although high purity and ultra fine powder can be obtained, the raw material is expensive and the productivity is low. The ceramics obtained by the above method are all in powder form, and in order to obtain a molded product from them, compression is performed under high temperature and high pressure in the presence of a sintering agent,
It needs to be processed. Therefore, not only a very large press machine is required for processing, but also molding processing is limited and it is difficult to manufacture a complicated shape.

On the other hand, the thermal decomposition method of a silicon compound is such that a chain-like or cyclic silicon-containing polymer compound having a repeating structural unit is thermally decomposed as a prepolymer for ceramics, as represented by the easily processable one described below. can get.

(A) Permethyl polysilane (B) Polysilastyrene (where X is 0.8 to 1.3,
Φ represents a phenyl group. same as below. ) (C) Polycarbosilane The polycarbosilane of (c) is obtained by thermal decomposition of permethylpolysilane of (a) and various organic silicon compounds such as tetramethylsilane, dimethyldichlorosilane, dodecamethylcyclohexasilane. It is meltable and soluble in organic solvents such as benzene. As currently industrially manufactured by this thermal decomposition method, Si
There is C fiber (Nippon Carbon Co., Ltd., trademark "Nicalon").
This fiber is produced according to the following formulas (I), (II) and (III) using dimethyldichlorosilane obtained by the direct method as a starting material, and is a resin as a high strength fiber excellent in heat resistance, It is expected that demand for metal and ceramics as a reinforcing material will grow in the future (Japanese Patent Publication No. 57-2652).
7, JP-B-57-53892, JP-B-57-38548).

The problem with this method is that the manufacturing process is complicated, and in particular in (I), the removal of unreacted sodium is complicated because metallic sodium is used in the solvent.
In addition, it is necessary to separate the polymer (separation and removal of low molecular weight polycarbosilane), and to perform the reaction of (II) under high temperature and high pressure (400 ° C, 100 atm). Free carbon and silica, which are low (particularly the steps (II) and (III)) and are contained in a large amount in the final product, adversely affect the physical properties of the product.

As described above, the inventors of the present invention are keen to develop a new high performance prepolymer for ceramics, which has a simple manufacturing method, is economical, and has a high ceramic yield as compared with the conventional prepolymers for ceramics. Through efforts, the inventors have found a specific silicon-containing polymer compound in the present invention and have reached the present invention.

[Summary of Invention]

That is, the present invention has the general formula (1) (However, n is 0 or a positive integer of 1 to 10, R ₁ is hydrogen,
A silicon-containing polymer compound containing a repeating structural unit represented by an alkyl group or an aryl group, and R ₂ represents an arylene group or a phenylene group) is fired in a temperature range of 500 to 2500 ° C. A method for producing silicon.

DETAILED DISCLOSURE OF THE INVENTION Hereinafter, the present invention will be described in detail.

The prepolymer for ceramics used 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) Is a silicon-containing polymer compound containing a repeating structural unit represented by:

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. In addition, n is 0 or a positive integer of 1 to 10, and the smaller the ceramics yield (Si weight in the fired body / Si weight (%) in the silicon-containing polymer compound), the more preferable, and the most preferable. Is 0. R ₁ is hydrogen, an alkyl group or an aryl group, for example, —H, —CH ₃ , —C ₂ H ₅ , i-C ₃ H ₇ ,
Examples include -Φ (-Φ represents a phenyl group as described above. The same applies hereinafter), -Φ-CH ₃ , -CH ₂ -Φ, etc., and those having a smaller number of carbons are preferred, and hydrogen is most preferred. 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 . The R ₁ and R ₂ may contain a functional group such as —COOH, —NH ₂ , —OH.

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 terms of moldability and solubility in a solvent.

Further, a copolymer comprising the repeating structural unit and another vinyl-based polymer structure containing no silicon such as ethylene, propylene, styrene, vinyl chloride, butene, isobutene, and a repeating structural unit derived from vinyl such as MMA. Is also good. Such copolymerization may be random, alternating, block or graft. 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 generally 100 to 10,000,000, preferably about 200 to 1,000,000 is desirable in terms of moldability 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: 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-N
Coordination anion polymerization with atta-type catalysts (transition metal salts such as titanium halide, vanadium halide, zirconium halide and alkylaluminum); 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.), hydroxide (NaOH, KOH, etc.) catalyst for anionic polymerization; various methods such as 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 α-olefin containing a SiH ₃ group, which serves 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 recent years, SiH ₄ has become available at low cost and in large quantities due to the growing demand for polysilicon and amorphous silicon, and it is a new silicon raw material that is expected to continue this trend in the future. is there.
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,
The 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.

In the present invention, the silicon-containing polymer compound is made into ceramics by using a conventional silicon-based prepolymer, for example, Basically, it can be carried out by the same method as in the case of using a prepolymer having a repeating unit as a conceptual unit.

That is, by utilizing the fact that the silicon-containing polymer compound of the present invention is easily processable, a usual resin processing technique such as injection molding or extrusion molding in an inert gas like a normal thermoplastic polymer is applied. Then, after forming into the desired shape, firing at high temperature (500 to 2500 ° C); after mixing ceramic powder such as SiC powder or Si ₃ N ₄ powder to the extent that processability is not lost, injection or Method of extrusion molding and firing at high temperature (In this case, a function such as a binder of mixed SiC powder can be expected, and such a function can be achieved by a silicon-containing polymer compound containing a very small amount of Si. Expected); or after spinning into a fiber like SiC fiber and firing at high temperature to produce fibrous ceramics, any method can be adopted. After the SiC powder was fired under, it is of course possible to compression molding as in the existing method.

The features of the prepolymer in the present invention are that the yield of ceramics (SiC) is extremely high and the amount of free carbon in the ceramics after firing is extremely small, as described in the examples below.

That is, for example, a permethylpolysilane composed of the following repeating structural units, which is an infusible insoluble polymer conventionally used as a prepolymer: It is an inert gas, oligomerized by thermal decomposition when high temperature firing under normal pressure, which is very low ceramic yields to scatter out of the system, the reaction in an autoclave under high pressure and temperature (100 Kg / cm ² or so) A method such as adding a reaction accelerator such as polyborosiloxane or the like is used. Further, polycarbosilane composed of the following repeating structural units: Is currently used as a prepolymer for SiC fiber, but although the ceramic yield is reasonably good, it has a large amount of free carbon (about 10 wt%), and when it is used as a fiber, it is not used in the spinning process. It is said that SiO ₂ (about 20 wt%) is mixed in by the fusion treatment, and these adversely affect the fiber strength.

The method for producing silicon carbide by firing the silicon-containing polymer compound in the present invention has a high ceramic yield and a small amount of free carbon is not clear,
It is presumed that the Si—H bond of the SiH ₃ group is first broken during the thermal decomposition process, crosslinks and becomes less likely to fly out of the system as an oligomer, and this 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 reacted at 450 ° C. to produce vinylsilane (CH ₂ ═CHSiH ₃ ) (Journal of America Chemical Society).
Chemical Society), 76, 3897 (1954)). Next, in a nitrogen atmosphere, 36.7 g of this vinylsilane, 1 g of a titanium trichloride type catalyst for olefin polymerization (manufactured by Toho Titanium Co., Ltd.), Al (i-C ₄
H ₉ ) ₃ 3.3 ml and n-heptane 150 ml were charged into an autoclave having a volume of 200 ml and reacted at 70 ° C. for 4 hours. After the completion of the reaction, the reaction solution 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).

Next, 0.5 g of the above polymer was put into a quartz baking tube having an inner diameter of 15 mm, and the temperature was raised in an argon stream (flow rate 50 ml / min) at a rate of 5 ° C./min.
The temperature was raised to 1400 ° C. Ceramics yield is 55wt
% (79% on Si basis), the calcined product was further calcined to 2000 ° C. and examined by X-ray diffraction, but no diffraction peak due to free carbon was observed.

Example 2 In Example 1, titanium trichloride type catalyst, Al (iC)
₄ H ₉ ) ₃ , n-heptane instead of Cp ₂ Zr (C
H ₃ ) ₂ 0.5 g, methylalumoxane ([Al (CH ₃ ) 0]
_16-20 ) 9g, toluene 150ml, reaction temperature 20 ℃ 10
An experiment was conducted in the same manner as in Example 1 except that the reaction was carried out for a time. A polymer having a repeating structural unit of was obtained.

The results of polymer evaluation 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.

The results of polymer evaluation are shown in Table 1.

Comparative Examples 1 and 2 As the polymer, And a repeating structural unit of permethylpolysilane (produced by Shin Nisso Kako Co., Ltd., average molecular weight about 2000), and Polymer evaluation was carried out in the same manner as in Example 1 except that polycarboxysilane having the following repeating structural unit was used (obtained by heating and calcining permethylpolysilane in an autoclave at 400 ° C. and 100 atm for an hour). .

The 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 ceramics (silicon carbide). The prepolymer used in the present invention is not only excellent in plasticity and solvent solubility and easy to process, but also conventional prepolymers (polysilane, polycarbosilane, etc.).
Compare to The ceramic yield is high. Moreover, it has excellent characteristics such as low free carbon in the ceramics obtained by firing. The prepolymer is, for example, α-containing a silyl group from industrially easily available monosilane.
It can be easily produced by producing an olefin and polymerizing the α-olefin.

Further, in the present invention, unlike the conventional pressure molding method of ceramic powder that requires a large-scale facility, the specific easily processable silicon-containing polymer compound defined in the present invention is used as a prepolymer, Needless to say, a silicon carbide ceramic molded body having an arbitrary shape can be obtained by molding and firing this.

Claims (8)

[Claims] 1. A general formula (However, n is 0 or a positive integer of 1 to 10, R ₁ is hydrogen,
An alkyl group or an aryl group, R ₂ represents an alkylene group or a phenylene group), and a silicon-containing polymer compound containing a repeating structural unit represented by the formula (1) is fired in a temperature range of 500 to 2500 ° C. Manufacturing method. 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 allylsilane. 4. The method according to claim 1, wherein the silicon-containing polymer compound is a polymer of butenylsilane. 5. The method according to claim 1, wherein the silicon-containing polymer compound is molded and then fired. 6. The method according to claim 1, wherein the ceramic powder prepared in advance is added to and mixed with the silicon-containing polymer compound, followed by molding and then firing. 7. The method according to claim 4, wherein the silicon-containing polymer compound is spun into a fibrous state and then fired. 8. The method according to claim 6, wherein the ceramic powder is silicon carbide or silicon nitride.