JPH07121802B2 - Method for producing silicon carbide - Google Patents

Description

BACKGROUND OF THE INVENTION TECHNICAL FIELD The present invention is baked specific polyolefin containing a silyl group (Si _n H _{2n + 1} group) on the side chain (silicon-containing polymer compound) at a high temperature, The present invention relates to a method for producing silicon carbide.

[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.

Of these, the silicon carbide according to the present invention can be 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 (1400-26
00 ℃), which is reduced by coke and is inexpensive, but fine silica S to obtain fine crystal SiC with excellent sinterability.
It is difficult to control the reaction because iO ₂ is required and the reaction is exothermic. In the reduction carbonization method, SiO ₂ is reduced by coke, β-SiC is obtained by reacting in argon at 1500 to 2000 ° C., and α-SiC is obtained by the similar method, 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) or various organosilicon compounds such as tetramethylsilane, dimethyldichlorosilane, dodecamethylcyclohexasilane. Therefore, it has meltability and is soluble in an organic solvent such as benzene. As currently manufactured industrially by this pyrolysis method, SiC
There is a 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 having excellent 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 due to the use of metallic sodium 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 in 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) (Wherein m is 0 or 1 and a positive integer from 1 to 10), n is 2 or 3, R ₁ is hydrogen, an alkyl group or an aryl group, and R ₂ is an alkylene group or a phenylene group. A method for producing silicon carbide, which comprises firing a silicon-containing polymer compound containing units in a temperature range of 500 to 2500 ° C.

[Detailed Disclosure of the Invention]

 Hereinafter, the present invention will be described in detail.

The ceramic prepolymer for use in the present invention, there is provided a carbon-based polymer containing silyl group (Si _n H _{2n + 1} group) in the side chain, the general formula (1) Is a silicon-containing polymer compound containing a repeating structural unit represented by:

The weight degree l 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, m 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 (%)), the more preferable. It is preferably 0. Further, n is 2 or 3, and preferably 2. 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 , or —
[Phi (- [Phi] represents a phenyl group as already mentioned hereinafter the same..), - Φ-CH 3, raised like -CH ₂ - [Phi] is preferably higher with less number of carbon atoms, hydrogen being 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-
However, as with R ₁ , the smaller the carbon number, the more preferable. 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 composed of the repeating structural unit and another vinyl-based polymer structure containing no silicon, such as ethylene, propylene, styrene, vinyl chloride, butene, isibutene, 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.

As the silicon-containing polymer compound used in the present invention, those mentioned above are used, but the production method or polymerization method thereof is not particularly defined, and those produced by various methods can be preferably used.

For example, an α-olefin having a silyl group (Si _n H _{2n + 1} group) is coordinated with a Ziegler-Natta type catalyst (transition metal salt such as titanium halide, vanadium halide, zirconium halide and alkylaluminum) as a coordinating anion. Polymerization method: metal oxide (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 (B
_{F 3, AlCl 3, FeCl 3} , SnCl 4 and the like) method for cationic polymerization by 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; and the like. 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 silyl group-containing α-olefin serving as a polymerization monomer 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.

(The same applies to the case of Si ₃ H ₈ ) These methods use Si ₂ H ₆ or Si ₃ H ₈ as a raw material, and in particular, are hydrosilylation reactions using a Group VIII metal as a catalyst. The desired α-olefin can be easily obtained. In addition, these disilanes and trisilanes are new silicon raw materials that have been attracting attention as semiconductor gas in recent years. In view of the above, the demand for polysilicon and amorphous silicon has expanded, and it has come to be manufactured at low cost and in large quantities. It is a new silicon raw material that is expected to continue this trend in the future. Silicon-containing polymer compound containing a silyl group in the present invention is therefore the Si ₂ H ₆
Alternatively, it can be said that there is great significance in that it can be easily and inexpensively produced by polymerizing a monomer obtained from Si ₃ H ₈ and an olefin. Also this Si
_The silicon-containing polymer compound in the present invention in the case of using ₂ H ₆ or Si ₃ H ₈ 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 silicon-containing polymer compound of the present invention can be manufactured more inexpensively 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 silyl group present in the silicon-containing polymer of the present invention is extremely stable, and does not oxidize at room temperature even in air, but only at high temperatures near 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, the same method as in the case of using a prepolymer having a repeating structural unit can be used.

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. However, it is possible to employ any method such as producing a fibrous ceramic by spinning at a high temperature after spinning into a fiber like SiC fiber. It is of course possible to perform compression molding as in the existing method after firing the prepolymer at a high temperature to obtain SiC powder.

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 mainly 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 used as a fiber, the spinning 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 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,
In the thermal decomposition process, the Si-H engagement of the silyl group is first broken,
Cross-linking to prevent it from scattering as an oligomer outside the system,
It is also presumed that this decomposed hydrogen prevents carbonization of the polymer.

Further, for example, the silicon-containing polymer compound in the present invention is In the case of, the ratio of carbon atoms to silicon atoms in the polymer compound is the same as that of the final ceramic (SiC), which is 1: 1.
Therefore, it is presumed that the amount of scattered carbon is small and the ceramic yield is improved.

〔Example〕

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

Example 1 Si ₂ H ₆ and acetylene were used in the literature (Journal of American Chemical Society).
Chemical Society), 76, 3897 (1954)) to produce vinyldisilane (CH ₂ = CHSi ₂ H ₅ ). Next, in a nitrogen atmosphere, 38.4 g of this vinyldisilane, 1 g of titanium trichloride type catalyst for olefin polymerization (manufactured by Toho Titanium Co., Ltd.), Al
3.3 ml of (i-C ₄ H ₉ ) ₃ and 150 ml of n-heptane were placed in 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 to be a silicon-containing polymer compound having a repeating structural unit of The polymer was stable in air at room temperature, and the silyl group rapidly disappeared at about 150 ° C to form a siloxane bond. The crystallinity was about 40% and the melting point was 170 to 180 ° C. The average molecular weight was about 70,000 (by the viscosity method, the same as the following).

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 57wt
% (72% based on Si), 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, memorial moxane ([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 silicon-containing polymer compound having a repeating structural unit of was obtained.

The evaluation results of this polymer are shown in Table 1.

Examples 3 and 4 Experiments were carried out in the same manner as in Example 1 except that vinyltrisilane, propyldisilane and butenyldisilane were used instead of vinyldisilane as the polymerization monomer, A silicon-containing polymer compound having a repeating structural unit of was obtained.

The evaluation results of this polymer 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 Except that polycarbosilane having a repeating structural unit (which was obtained by heating and firing permethylpolysilane in an autoclave at 400 ° C. and 100 atm for an hour) was used.
Polymer evaluation was performed in the same manner as in Example 1.

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.)
The ceramic yield is higher than that of. Moreover, it has excellent characteristics such as low free carbon in the ceramics obtained by firing. In addition, this prepolymer is produced, for example, by producing an α-olefin containing a silyl group from monosilane or disilane which is industrially readily available,
It can be easily produced by polymerizing an 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 (7)

[Claims] 1. A general formula (Provided that m is 0 or a positive integer of 1 to 10, n is 2 or 3, R ₁ is hydrogen, an alkyl group or an aryl group, and R ₂ is an alkylene group or a phenylene group). 1. A method for producing silicon carbide, which comprises firing a silicon-containing polymer compound containing C in a temperature range of 500 to 2500 ° C. 2. The manufacturing method according to claim 1, wherein n is 2. 3. The method according to claim 1, wherein the silicon-containing polymer compound is a polymer of vinyldisilane. 4. The method according to claim 1, wherein the silicon-containing polymer compound is a polymer of butenyldisilane. 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 5, wherein the silicon-containing polymer compound is spun into a fibrous state and then fired.